Journal articles: 'Bainitic steel'

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Timokhina, Ilana, Hossein Beladi, Xiang Yuan Xiong, Yoshitaka Adachi, and Peter D. Hodgson. "Application of Advanced Experimental Techniques for the Microstructural Characterization of Nanobainitic Steels." Solid State Phenomena 172-174 (June 2011): 1249–54. http://dx.doi.org/10.4028/www.scientific.net/ssp.172-174.1249.

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A 0.79C-1.5Si-1.98Mn-0.98Cr-0.24Mo-1.06Al-1.58Co (wt%) steel was isothermally heat treated at 350°C bainitic transformation temperature for 1 day to form fully bainitic structure with nano-layers of bainitic ferrite and retained austenite, while a 0.26C-1.96Si-2Mn-0.31Mo (wt%) steel was subjected to a successive isothermal heat treatment at 700°C for 300 min followed by 350°C for 120 min to form a hybrid microstructure consisting of ductile ferrite and fine scale bainite. The dislocation density and morphology of bainitic ferrite, and retained austenite characteristics such as size, and volume fraction were studied using Transmission Electron Microscopy. It was found that bainitic ferrite has high dislocation density for both steels. The retained austenite characteristics and bainite morphology were affected by composition of steels. Atom Probe Tomography (APT) has the high spatial resolution required for accurate determination of the carbon content of the bainitic ferrite and retained austenite, the solute distribution between these phases and calculation of the local composition of fine clusters and particles that allows to provide detailed insight into the bainite transformation of the steels. The carbon content of bainitic ferrite in both steels was found to be higher compared to the para-equilibrium level of carbon in ferrite. APT also revealed the presence of fine C-rich clusters and Fe-C carbides in bainitic ferrite of both steels.

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Liu, Miao, Yusong Fan, Xiaolu Gui, Jie Hu, Xi Wang, and Guhui Gao. "Relationship between Microstructure and Properties of 1380 MPa Grade Bainitic Rail Steel Treated by Online Bainite-Based Quenching and Partitioning Concept." Metals 12, no. 2 (February 13, 2022): 330. http://dx.doi.org/10.3390/met12020330.

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According to the concept of the bainite-based quenching and partitioning (BQ&P) process, we designed the online heat treatment routes of bainitic rail steel for heavy haul railway. The new heat treatment process reduced the fraction and size of the blocky martensite/austenite (M/A) islands formed during the conventional air-cooling process. The M/A islands are coarse and undesirable for mechanical properties. A new kind of 1380 MPa grade bainitic rail steel with more uniform microstructure and better mechanical properties was produced by the online BQ&P process. We characterized the multiphase microstructures containing bainite, martensite, and retained austenite of 1380 MPa grade bainitic rail steels via optical microscope, scanning electron microscopy, transmission electron microscopy, and X-ray diffractometer. We investigated in-depth the relationship between the microstructure, retained austenite stability, and mechanical properties, particularly the resistance to wear and rolling contact fatigue, of the new 1380 MPa grade bainitic rail steels. Meanwhile, the conventional air-cooling bainitic rail steel was studied as a comparison.

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Pei, Wei, Wei Liu, Yue Zhang, Rongjian Qie, and Aimin Zhao. "Study on Kinetics of Transformation in Medium Carbon Steel Bainite at Different Isothermal Temperatures." Materials 14, no. 11 (May 21, 2021): 2721. http://dx.doi.org/10.3390/ma14112721.

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Ultra-fine carbide-free bainitic (UCFB) steel, also known as nano-bainite (NB) steel, is composed of bainitic ferrite laths with nanoscale thickness and carbon-rich film-like retained austenite located between laths. The bainite transformation kinetic model can accurately describe the bainite transformation kinetics in conventional austempering (CA) processes based on the shear mechanism combined with the dilatometer test. UCFB steels with medium and high carbon composition are designed in this work to systematically study the transformation kinetics of bainite, and the evolution of its microstructure and properties, and reveal the influence of heat treatment processes on the microstructure and properties the UCFB steels. The results show that the activation energy for BF nucleation decreases during the CA process and isothermal transformation temperature decreases. The bainite transformation is first nucleated at the grain boundaries, and then nucleated at the newly formed bainitic ferrite/austenite interface.

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Fang, Hong Sheng, Gu Hui Gao, Yan Kang Zheng, Zhi Gang Yang, and Bing Zhe Bai. "The Development of Mn-Series Air-Cooled and Water-Quenched Bainitic Steels in China." Materials Science Forum 654-656 (June 2010): 57–61. http://dx.doi.org/10.4028/www.scientific.net/msf.654-656.57.

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The origin and development of air-cooled Mn-series bainite steels are introduced. The invented idea, strengthening-toughening mechanism, mechanical performances, development and application of this kind of steel including granular bainitic steels, FGBA / BG duplex steels, CFB/M duplex steels, medium carbon bainite/martensite steels, cast bainitic steels are presented. The invented idea mechanical performances, development and application of second generation of Mn-series bainitic steels, i.e. water-quenched Mn-series bainitic steels invented by the authors newly are introduced. The water quenched Mn-series bainitic steels can meet the performance requirements of most steels used in engineering structure, reduce the amount of alloying content, increase harden capability and improve weldability. It should be pointed out that the application of both air-cold and water- quenched Mn-series bainitic steels are complementary and mutually reinforcing. Some newest technology of Mn-series bainitic steels in China are discussed in this paper. It is suggested that the significance of the development of the Mn-series bainitic steels can be summarized as: significantly reducing costs of both raw materials and production; good combination of strength and toughness; excellent weldability; simple procedure; large savings in energy resources and environmental pollution is reduced.

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Wang, Pengfei, Peng Chen, Dapeng Yang, Tao Wang, and Hongliang Yi. "980 MPa Grade Low-Alloy Carbide-Free Bainitic Steel Obtained by Dynamic Continuous Cooling Transformation." Crystals 13, no. 2 (January 24, 2023): 213. http://dx.doi.org/10.3390/cryst13020213.

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The addition of high-content alloying elements and the unbefitting process make carbide-free bainite steel difficult in industrial production. Thus, we adopted a dynamic continuous cooling process for developing the high-strength cold-rolled low-alloy carbide-free bainitic steels in this study. The influence of cooling rates on the microstructure and mechanical properties was investigated by dilatometry, scanning electron microscopy (SEM), X-ray diffraction (XRD), electron backscatter diffraction (EBSD), and tensile tests. The results show that the bainitic ferrite plates were refined by decreasing the cooling rate, and more austenite was retained in the steel with a medium cooling rate. Both the TRIP effect and the refined bainitic ferrite plate contribute to the good strength–ductility match. Consequently, the propitious microstructure adjustment is critical for developing 980 MPa carbide-free bainitic steel.

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Cui, Wen Fang, Chang Jing Shao, and Chun Ming Liu. "Corrosion Behavior of New Weathering Steel in the Environment Simulating Coastal Industrial Atmosphere." Advanced Materials Research 479-481 (February 2012): 322–26. http://dx.doi.org/10.4028/www.scientific.net/amr.479-481.322.

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The corrosion behavior of low carbon bainitic steel with Cu-P alloying in the environment simulating coastal industrial atmosphere was investigated by using dry-wet cycling corrosion test. 09CuPCrNi steel and low carbon bainitic steel without Cu-P alloying were used as comparative steels. The corrosion kinetics and electrochemical impedance spectra of the steels were measured, respectively. The morphologies of rust layers were observed by SEM and the phase constitutes of the rust layers were analyzed by XRD. Low carbon bainitic steel with Cu-P alloying behaves the lowest corrosion rate and the highest resistance of rust layer. Bainite microstructure is responsible for the uniform corrosion and the formation of dense rust layer. Cu-P alloying accelerates the transformation of gamma-FeOOH and Fe3O4 to thermodynamic stable phase alpha-FeOOH, which improves the protective effect of the rust layer.

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Ansari, M. H. Sheikh, and M. Aghaie-Khafri. "Investigation of Microstructure and Mechanical Properties of Ultra High Strength Bainitic Steel." Applied Mechanics and Materials 313-314 (March 2013): 77–81. http://dx.doi.org/10.4028/www.scientific.net/amm.313-314.77.

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In this study, medium carbon low alloy steel was used to obtain bainitic structures. The lower bainite and tempered martensite-lower bainite structures were achieved by isothermal austempering and up quenching treatment, respectively. Based on the results obtained these structures showed a very good combination of strength and toughness. Furthermore, it has been shown that austenitization time and temperature, as well as austempering time and temperature play a major role in achieving ultra-high strength bainitic steels.

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Wang, Ke Lu, Xin Li, and Xian Juan Dong. "Effect of Tempering Temperature on Mechanical Properties and Microstructures of 800MPa Microalloy Low Carbon Bainitic Steel." Advanced Materials Research 893 (February 2014): 406–9. http://dx.doi.org/10.4028/www.scientific.net/amr.893.406.

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The effect of tempering temperature on the microstructures and mechanical properties of a microalloy low carbon bainitic steel was investigated by microscopic analysis and testing of mechanical properties. The results show that the microstructures of the tested steel primarily consists of lath bainite, granular bainite, quasipolygonal ferrite and little acicular ferrite at different tempering temperatures. With the tempering temperature increasing, the proportion of lath bainitie decreases, while the volume of granular bainite and quasipolygonal ferrite increases. At the tempering temperatures of 550-650°C and tempering time of 1 hour, the steel was mostly composed of granular bainite, quasipolygonal ferrite and a little lath bainite, which a good combination of strength and toughness can be obtained.

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Guo, Hui, Xianying Feng, Aimin Zhao, Qiang Li, and Jun Ma. "Influence of Prior Martensite on Bainite Transformation, Microstructures, and Mechanical Properties in Ultra-Fine Bainitic Steel." Materials 12, no. 3 (February 12, 2019): 527. http://dx.doi.org/10.3390/ma12030527.

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A multiphase microstructure comprising of different volume fractions of prior martensite and ultra-fine bainite (bainitic ferrite and retained austenite) was obtained by quenching to certain temperatures, followed by isothermal bainitic transformation. The effect of the prior martensite transformation on the bainitic transformation behavior, microstructures, and mechanical properties were discussed. The results showed that the prior martensite accelerated the subsequent low-temperature bainite transformation, and the incubation period and completion time of the bainite reaction were significantly shortened. This phenomenon was attributed to the enhanced nucleation ratio caused by the introduced strain in austenite, due to the formation of prior martensite and a carbon partitioning between the prior martensite and retained austenite. Moreover, the prior martensite could influence the crystal growth direction of bainite ferrite, refine bainitic ferrite plates, and reduce the dimension of blocky retained austenite, all of which were responsible for improving the mechanical properties of the ultra-fine bainitic steel. When the content of the prior martensite reached 15%, the investigated steels had the best performance, which were 1800 MPa and 21% for the tensile strength and elongation, respectively. Unfortunately, the increased content of the prior martensite could lead to a worsening of the impact toughness.

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10

Wang, Zhi Fen, Yun Guan, Li Xin Wu, Yi Qiang Sun, and Rong Dong Han. "Influence of Cooling Rate on the Microstructure of Bainitic Steel." Advanced Materials Research 311-313 (August 2011): 886–90. http://dx.doi.org/10.4028/www.scientific.net/amr.311-313.886.

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The microstructure of a bainitic steel after different cooling rates has been investigated by transmission electron microscopy (TEM) and electron backscattered diffraction (EBSD). The effect of cooling rate on the intermediate transformation microstructure was studied. The results showed that the final microstructure contained complex mixture of bainitic ferrite, granular bainite and polygonal ferrite. There was mainly lath-like bainitic ferrite at fast cooling rate (20Ks-1), while microstructure in samples cooled with intermediate rates (8~15 Ks-1) contained bainitic ferrite and granular bainite. When cooling rate decreased to less than 5Ks-1, polygonal ferrite occurred.

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Deineko, L. M., A. Yu Borysenko, A. О. Taranenko, T. O. Zaitseva, and N. S. Romanova. "Features of the ferrite-bainite structure low-alloy low-carbon steel after heat hardening and subsequent tempering." Physical Metallurgy and Heat Treatment of Metals, no. 2 (93) (June 9, 2021): 33–47. http://dx.doi.org/10.30838/j.pmhtm.2413.270421.33.739.

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Problem statement. In recent decades, there has been a tendency to increase the mechanical properties of low-carbon, low-alloyed steel plate iron by using controlled rolling or hardening heat treatment of finished steel parts. At the same time, for welded parts, the most suitable is a metal having a ferrite-bainite (or bainite) structure. The work investigated the features of the ferrite-bainite structure of low-carbon and low-alloyed steel 15ХСНД for the production of connecting pipeline parts. Purpose of the article. To establish the laws of formation of a ferritic-bainitic structure in low-carbon low-alloy steels depending on the parameters of heat treatment. Determine the effect of heat treatment parameters on the properties of the connecting parts of pipelines made of these steels. Conclusion. The regularities of the influence of heat treatment parameters on the structure, mechanical properties and topography of fractures of impact samples of 15ХСНД steel with a ferrite-bainitic structure are established. Keywords: stamped-welded connecting parts of man pipelines; heat treatment; microstructure; bainite;mechanical properties; fractography

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Illescas, Silvia, Javier Fernández, Juan Asensio, and Josep Maria Guilemany. "TEM Study of Bainitic Low-Carbon HSLA Steel: The Orientation Relationships of Cementite." Practical Metallography 44, no. 7 (July 1, 2007): 334–46. http://dx.doi.org/10.1515/pm-2007-0073.

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Abstract Two different bainitic structures can be present in steel depending on the heat treatment to which the samples are subjected. The two different types of bainitic structures exhibit a different orientation relationship between the cementite and the ferrite matrix. The Pitsch orientation relationship is observed in upper bainite while the Bagaryatski orientation relationship is observed in lower bainite [1]. Different heat treatment samples of low-carbon High Strength Low Alloy (HSLA) steel were studied using TEM observations in order to ascertain the orientation relationship between ferrite and carbide in the different bainitic structures and to determine whether this relationship may indicate the type of bainitic structure.

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da Cruz, José Alberto, Jefferson José Vilela, Berenice Mendonça Gonzalez, and Dagoberto Brandão Santos. "Effect of Retained Austenite on Impact Toughness of the Multi-Phase Bainitic-Martensitic Steel." Advanced Materials Research 922 (May 2014): 298–303. http://dx.doi.org/10.4028/www.scientific.net/amr.922.298.

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The new class of bainitic steels can present toughness at room temperature greater than traditional quenched and tempered martensitic steel. This is because the microstructure of steel with high Si content (≈1.5wt%) submitted to bainitic transformation is compose of fine plates of bainitic ferrite separated by retained austenite. The inhibition of cementite precipitation leads to the improvement of toughness. The presence of cementite facilitates the nucleation of cracks. Moreover, the blocks of retained austenite are undesirable. This morphology is rather unstable and tends to transform into hard and brittle untempered martensite under the influence of small stress, contributing to a low toughness. However, it was observed in this work that the greater the volume fraction of retained austenite, the greater is the toughness (10-24 J) for multi-phase steel. The values of toughness were independent whether the retained austenite is present on film or block forms. The decrease of toughness values was observed by the tempered samples after the bainitic transformation (10-14 J). This occurred because the blocks of retained austenite decomposed into carbides, martensite and/or bainite.

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Szymański, Michał. "Rails with Bainitic Microstructure." Problemy Kolejnictwa - Railway Reports 65, no. 193 (December 2021): 115–19. http://dx.doi.org/10.36137/1936e.

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The review article describes bainite as an example of a steel microstructure that can be successfully used in the production of railway rails. A comparison has been made between the key parameters to be met by railway rails: resistance to abrasive wear, resistance to flaking and presence of white etching layer for bainitic and pearlitic steel. The important role of residual austenite and the tempering process in shaping the mechanical properties of rails with bainitic microstructure has been discussed. Keywords: bainite, railway rails, white etching layer, abrasive wear, residual austenite, tempering

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Rojhirunsakool, Tanaporn, Thammaporn Thublaor, Mohammad Hassan Shirani Bidabadi, Somrerk Chandra-ambhorn, Zhigang Yang, and Guhui Gao. "Corrosion Behavior of Multiphase Bainitic Rail Steels." Metals 12, no. 4 (April 18, 2022): 694. http://dx.doi.org/10.3390/met12040694.

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Pearlitic steel experiences excessive corrosion in a hot and humid atmosphere. The multiphase bainitic/martensitic structure was developed for a better combination of strength and ductility, especially rolling contact fatigue, but little attention to corrosion has been investigated. Corrosion behaviors of multiphase steels obtained from bainitic-austempering (BAT) and bainitic-quenching and -partitioning (BQ&P) processes were investigated via immersion and electrochemical tests in 3.5 wt.% NaCl solution. The corroded surface and rust after immersion and electrochemical tests were analyzed via electron microscopy, Fourier transform infrared spectra, and x-ray diffraction. The multiphase bainite + martensite/retained austenite island showed higher corrosion resistance than that of the pearlitic one. The acicular bainite obtained from the BQ&P process showed slightly higher corrosion resistance than the granular bainite + martensite structure obtained from the BAT process.

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Xu, Guang, Tao Xiong, Yu Long Zhang, Ming Xing Zhou, and Yi Zhang. "The Effects of High Temperature Deformation on Bainite Transformation." Applied Mechanics and Materials 513-517 (February 2014): 206–9. http://dx.doi.org/10.4028/www.scientific.net/amm.513-517.206.

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The effects of high temperature deformation on transformed microstructure and transformation amount in a high strength bainitic steel were investigated. It indicates that isothermal bainitic transformation is promoted by high temperature deformation. The transformed bainite microstructure is also affected by high temperature deformation, i.e. deformation retards the growth of bainite sheaves, leading to shorter banitie plates. The present study is useful to further understand the effects of ausforming on bainitic transformation.

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Soliman, Mohamed, Mehdi Asadi, and Heinz Palkowski. "Role of Dilatometer in Designing New Bainitic Steels." Advanced Materials Research 89-91 (January 2010): 35–40. http://dx.doi.org/10.4028/www.scientific.net/amr.89-91.35.

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Dilatometric measurements were used to design the processing parameters of two types of bainitic steels. The first type is a hypoeutectoid ultra fine bainite steel, for which the dilatometer was used to locate the temperature at which cementite is completely dissolved during intercritical annealing (TC). The intercritical annealing temperatures are then selected will above TC. To obtain the martensite start temperatures (MS), the steel is quenched to the room temperature (RT) from these selected temperatures and then the bainite transformation temperatures were selected to be well above MS. The dilatometer was then used to monitor the bainite transformation kinetics from which the required time frames for cessation of the bainitic reactions were estimated. In the second type, bimodal bainite had been produced in thermo-mechanically processed TRIP-steel. A deformation dilatometer is used to perform three deformation-steps before slow cooling to form approx. 30% polygonal ferrite. The material was then rapidly cooled to the first bainite formation temperature. During this step, the dilatometer was used to monitor the bainite reaction from which the required time for 50% decomposition of austenite is estimated. The martensite start of the undecomposed austenite was located by quenching to RT. The second bainite transformation step was then performed well above the new MSII to form a second generation of finer bainite.

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Fu, Lihua, Meng Zhou, Yanlin Wang, Yuanan Gao, Yongzhen Zhang, Sanming Du, Yi Zhang, and Yanshan Mao. "The Microstructure Transformations and Wear Properties of Nanostructured Bainite Steel with Different Si Content." Materials 15, no. 18 (September 8, 2022): 6252. http://dx.doi.org/10.3390/ma15186252.

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Nanostructured bainite (NB) bearing steel has excellent strength and ductility combinations, which can improve the fatigue life and wear resistance of bearing steel in harsh conditions. However, the phase transformations and the correlation between the microstructure and wear properties of NB bearing steel are still unclear. In this study, bearing steels with different Si contents (GCr15SiMo and GCr15Si1Mo) were prepared to have nano-bainitic structures, and their microstructure transformations and wear mechanisms were investigated. The results show that the Si element can inhibit the precipitation of carbides and can then promote the block-like retained austenite formation and refine the bainitic ferrite lamellar structure. The impact energy of GCr15Si1Mo is larger than that of GCr15SiMo because the nanostructured bainite and retained austenite are the main toughness phase in these steels. The wear results indicate that the steels which possess appropriate strength and toughness are helpful for improving wear resistance properties. Finally, the wear resistance performance of the GCr15Si1Mo austempered at 210 °C and GCr15SiMo austempered at 230 °C was good in this work.

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Jezierska, E., J. Dworecka, and K. Rozniatowski. "Nanobainitic Structure Recognition and Characterization Using Transmission Electron Microscopy/ Rozpoznawanie I Charakteryzacja Struktury Nanobainitycznej Za Pomocą Transmisyjnej Mikroskopii Elektronowej." Archives of Metallurgy and Materials 59, no. 4 (December 1, 2014): 1633–36. http://dx.doi.org/10.2478/amm-2014-0277.

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Abstract Various transmission electron microscopy techniques were used for recognition of different kinds of bainitic structures in 100CrMnSi6-4 bearing steel. Upper and lower bainite are morphologically different, so it is possible to distinguish between them without problem. For new nanobainitic structure, there is still controversy. In studied bearing steel the bainitic ferrite surrounding the retained austenite ribbon has a high density of dislocations. Significant fragmentations of these phases occur, bainitic ferrite is divided to subgrains and austenitic ribbons are curved due to stress accommodation.

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Arabaci, Uğur, and Şafhak Turan. "Weldability of austempered rail steel using the flash-butt process." Materials Testing 63, no. 7 (July 1, 2021): 662–67. http://dx.doi.org/10.1515/mt-2020-0105.

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Abstract In this study, bainitic microstructure was formed via heat treatmenton R260 rail steel, which is generally used in railways. Bainitic steel, which is considered more advantageous than current rail steel, waswelded by flash butt welding, which is often used for joining rails andthe mechanical and microstructure of the samples were thenexamined and compared. Bainitic structural steel obtained by austempering heattreatment with normal rail steel was welded by flash butt welding. Flash-butt welding parameters were kept constant during the experiment. The welding capabilities of the joints were compared and the results wereevaluated. It was determined that the bainite structure obtained as a result of austempering heat treatment changes the microstructuralproperties of the samples and affects the mechanical values of the joints.

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Luo, Ping, Gu Hui Gao, Xiao Lu Gui, Bai Feng An, Zhun Li Tan, and Bing Zhe Bai. "Charpy Impact Properties of Grain Boundary Allotriomorphic Ferrite and Granular Bainite Duplex Microstructure." Advanced Materials Research 1004-1005 (August 2014): 1236–44. http://dx.doi.org/10.4028/www.scientific.net/amr.1004-1005.1236.

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A new type of high strength and low cost bainitic steel with ultra-low carbon content and high Si content has been developed on the basis of Mn-series air-cooling bainitic steels. The tensile properties of YS>690MPa and the impact toughness of AKV>60J at-40°C were obtained by controlling the processing parameters. This was attributed to the formation of the grain boundary allotriomorphic ferrite (FGBA) and the granular bainite (GB) with different shape of M/A islands. The high strength due to the inter-lath lamellar M/A islands or retained austenite companying with high dislocated bainitic ferrite laths of average 300nm width. The effect of microstructure on the impact crack initiation and propagation was studied. The results showed that crack initiation occurred in two different types of sites: at interphase boundaries of bainite ferrite (BF) and M/A islands, at grain boundaries. The FGBA and bainite ferrite (BF) both had blunting effect on microcrack tip to reduce the crack propagation path. Because of the presence of FGBA, the unit crack path was short, at less than 5μm. The blunting effect of BF could be enhanced by the M/A islands, which force the cracks change the propagation path and reduce the unit crack path to less than the size of bainite packets. The mechanism of low temperature microcrack origin of the ultra-low carbon bainitic (ULCB) steel with the microstructure of the FGBA and GB was also discussed.

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Wang, Zhi Fen, Shao Kang Pu, Y. Guan, Ping He Li, Li Xin Wu, and Qing Feng Chen. "A Study on the Microstructure of Ultra Low Carbon Bainitic Steels by RPC Technique." Materials Science Forum 561-565 (October 2007): 2107–10. http://dx.doi.org/10.4028/www.scientific.net/msf.561-565.2107.

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The effect of tempering process on the microstructure of ultra low carbon bainitic (ULCB) steel produced by relaxation precipitation controlled phase transformation (RPC) has been investigated by transmission electron microscopy (TEM) and electron backscattered diffraction (EBSD). The results showed that the final microstructure mainly contained lath-like bainitic ferrite, granular bainite and martensite-austenite (MA) constituent in ULCB steels. On tempering at 650°C a slight increase was detected in the effective grain size as the strain-induced precipitates pinned up the dislocation walls and subgrains. After tempering at 700°C, bainitic ferrite laths started to coarsen and polygonal ferrite occurred. The effective grain size of ULCB steels in as-rolled condition was 1.5 μm at the tolerance of 10o~15o measured by EBSD technique.

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Huo, Xiang Dong, Zhang Guo Lin, Yu Tao Zhao, and Yu Qian Li. "Development of Low Carbon Bainitic Cr-B Steel with High Strength and Good Toughness." Advanced Materials Research 146-147 (October 2010): 937–40. http://dx.doi.org/10.4028/www.scientific.net/amr.146-147.937.

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In order to develop low carbon bainitic Cr-B steel, experimental procedures including melting, thermal simulation study and laboratory hot rolling were adopted. The dynamic CCT diagram was established, microstructure and properties of experimental steel were also analyzed. The transformation temperature of experimental steel lies between 650～400°C and final microstructure changes fromquasi-polygonal ferrite, granular bainite to lath bainite as cooling rate increases from 0.2 to 50°C.s-1. The microstructure of steel plates, air cooled or water cooled to 530°C then air cooled, is mainly composed of granular bainite and quasi-polygonal ferrite, and the large size islands in granular bainite are responsible for the low strength and poor toughness. However, steel plate with lath bainite, water cooled to roomtemperature, boasts high yield strength (672MPa) and superior impact toughness (127J at -20°C). Therefore, it is feasible to produce low carbon bainitic Cr-B steel with high strength and good toughness through controlling cooling parameters.

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Yang, Xiao Long, Yun Bo Xu, Xiao Dong Tan, Yong Mei Yu, and Di Wu. "Microstructures and Mechanical Properties of High Strength Low Carbon Bainitic Steel." Materials Science Forum 817 (April 2015): 257–62. http://dx.doi.org/10.4028/www.scientific.net/msf.817.257.

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Based on TMCP and UFC technology, the microstructures and mechanical properties of 0.05% C bainitic steel were studied in this paper. The bainite morphology and precipitation within bainite lath were observed by SEM and TEM, and the mechanical properties of bainitic steel were measured by tensile and impact test. The results showed that the yield and tensile strengths of steel were 713 MPa and 891 MPa respectively, and the elongation was 15.8% with impact energy of 95J at the temperature of-20°C as the final cooling temperature in hot rolling of 550°C. For comparison, the steel obtained the yield strength of 725 MPa, tensile strength of 930 MPa and elongation of 18% as the final cooling temperature of 450°C. However, the impact energy of steel was 195J at the temperature of-20°C. While at the same final cooling temperature of 450°C, the fast cooling-holding temperature-fast cooling was applied to experimental steel with a faster cooling rate of 50°C/s, hence the steel acquired the yield strength of 845 MPa, tensile strength of 1037 MPa, and elongation of 15.5% with impact energy of 168J at the temperature of-20°C. The strength and toughness of 0.05%C bainitic steel is related to the bainite morphology and precipitation distribution. Hence, the strength and toughness can be improved by control the different cooling processes for adjusting the content of lath bainite, distribution of granular bainite and precipitation.

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Wang, Yanhui, Baisong Liu, Qiang Pan, Jing Zhao, Xiaojia Zhao, Huaqiang Sun, Dong Xu, and Zhinan Yang. "Effect of Austempering on Mechanical Properties of Nb/V Microalloyed Bainitic Bearing Steel." Crystals 12, no. 7 (July 19, 2022): 1001. http://dx.doi.org/10.3390/cryst12071001.

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In this study, a multi-element microalloyed GCr15Si1MoNbV bainitic bearing steel was designed by adding trace amounts of Nb and V. The bainite/martensite/retained austenite/undissolved carbide multiphase bearing steel with a short heat-treated cycle and remarkable comprehensive mechanical properties was prepared via low-temperature austempering, which was compared with a traditional quenched and tempered martensitic microstructure. The results showed that the comprehensive mechanical properties of the low-temperature bainitic microstructure of the Nb/V microalloyed bearing steel were better than those of a traditional tempered martensitic microstructure. In addition, as the isothermal temperature increased, the impact toughness of experimental steel was significantly improved, and the hardness decreased slightly. The tensile strength was improved with the increase in isothermal time. As the isothermal temperature increased, the bainite content of the experimental steel rose, and the stability of the retained austenite enhanced due to more carbon atoms being partitioned into it. The research work in this paper made a preliminary exploration for the application of Nb/V microalloyed bainitic bearing steel in the bearing field and provided some basic data for reference.

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Tressia, Gustavo, Luis H. D. Alves, Amilton Sinatora, Helio Goldenstein, and Mohammad Masoumi. "Effect of bainitic transformation on the microstructure and wear resistance of pearlitic rail steel." Industrial Lubrication and Tribology 72, no. 9 (October 20, 2020): 1095–102. http://dx.doi.org/10.1108/ilt-07-2019-0282.

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Purpose The purpose of this study is to develop a lower bainite structure consists of a dispersion of fine carbide inside plates of bainitic ferrite from chemical composition unmodified conventional pearlitic steel under bainitic transformation and to investigate its effect on tensile properties and wear resistance. Design/methodology/approach A commercial hypereutectoid pearlitic rail steel was subjected to three different bainitic transformation treatments followed by tempering to develop a desirable microstructure with a DIL805 BÄHR dilatometer. A comprehensive microstructural study was performed by scanning electron microscopy and energy dispersive x-ray spectroscopy. Finally, the mechanical properties and wear resistance were evaluated by tensile, microhardness, and pin-on-disc tests. Findings The results showed that the best combination of mechanical properties and sliding wear resistance was obtained in the sample subjected to bainitic transformation at 300°C for 600 s followed by tempering at 400°C for 300 s. This sample, which contained a bainitic ferrite structure, exhibited approximately 20% higher hardness and approximately 53% less mass loss than the as-received pearlitic sample due to the mechanically induced transformation in the contact surface. Originality/value Although pearlitic steel is widely used in the construction of railways, recent studies have revealed that bainitic transformation at the same rail steels exhibited higher wear resistance and fatigue strengths than conventional pearlitic rail at the same hardness values. Such a bainitic microstructure can improve the mechanical properties and wear resistance, which is a great interest in the railway industry. Peer review The peer review history for this article is available at: https://publons.com/publon/10.1108/ILT-07-2019-0282/

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Feng, Chun, Bing Zhe Bai, and Yan Kang Zheng. "Effect of 0.06%Nb on the Microstructure and Mechanical Properties of Mn-Series Low Carbon Air-Cooling Bainitic Steels." Advanced Materials Research 284-286 (July 2011): 1191–95. http://dx.doi.org/10.4028/www.scientific.net/amr.284-286.1191.

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The effect of 0.06%Nb on the microstructure and mechanical properties of grain boundary allotriomorphic ferrite (FGBA) / granular bainite (Bg) air-cooling bainitic steels has been investigated in this paper. The results indicate that the steel acquires superior mechanical properties by adding 0.06%Nb. Compared with Non-Nb steel, the addition of 0.06%Nb increases the tensile strength and yield strength about 37.1% (From 780MPa to 1070MPa)and 26.6%(From 557MPa to 705MPa) respectively, remaining 18.3% elongation and 97J toughness. The addition of 0.06%Nb not only promotes the nucleation of intragranular ferrite but also refines the allotriomorphic ferrite grain , both of which in turn contribute to the refinement of granular bainite cluster including its ferrite platelets and M-A islands. Under the synthetic roles of the microstructure refinement and precipitation strengthening, 148MPa yield strength improvement has been acquired in the low carbon air-cooling bainitic steel by the adding of 0.06%Nb.

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Das, Sourav, Saurabh Kundu, and Arunansu Haldar. "Development of Continuously Cooled High Strength Bainitic Steel through Microstructural Engineering at Tata Steel." Materials Science Forum 702-703 (December 2011): 939–42. http://dx.doi.org/10.4028/www.scientific.net/msf.702-703.939.

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Bainitic steels, which are transformed at very low temperatures, offer an excellent combination of strength and ductility where the strength comes from the nano-structured bainitic plates and thin-film of austenite sandwiched between two bainite sheaves offers the ductility. The main drawback of this structure is the long transformation time which is not ideal for industrial application. Through the microstructural engineering, the extent and kinetics of transformation can be manipulated by judicious selection of alloy composition and process variables. The main challenge is to delay the transformation till the coiling stage and allow the formation of bainite only during the cooling of the coil. In the current work, an approach will be shown, starting from the alloy design based on thermodynamics till the cooling after coiling, which can satisfy the requirements to develop such steel with 1300 MPa UTS combined with 20% elongation (min).

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Santacruz-Londoño, Andrés Felipe, Oscar Rios-Diez, José A. Jiménez, Carlos Garcia-Mateo, and Ricardo Aristizábal-Sierra. "Microstructural and Mechanical Characterization of a Nanostructured Bainitic Cast Steel." Metals 10, no. 5 (May 8, 2020): 612. http://dx.doi.org/10.3390/met10050612.

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Nanoscale bainite is a remarkable microstructure that exhibits a very promising combination of high strength with good ductility and toughness. The development of these types of microstructures has been focused on wrought materials, and very little information is available for steel castings. In this work, a specially designed cast steel with 0.76 wt % C was fabricated, and the heat treatment cycles to develop bainitic nanostructures were determined by studying the kinetics of the bainitic transformation using high-resolution dilatometry. The effects of isothermal holding temperature and time on the final microstructure and mechanical properties were thoroughly characterized in order to evaluate a future industrial implementation of the process in an effort to contribute to enhance and widen the potential applications for cast steels.

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Liang, Xiao Jun, Ming Jian Hua, and Anthony J. DeArdo. "The Mechanism of Martensite-Austenite Microconstituents Formation during Thermomechanical Controlling Processing in Low Carbon Bainitic Steel." Materials Science Forum 783-786 (May 2014): 704–12. http://dx.doi.org/10.4028/www.scientific.net/msf.783-786.704.

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Bainite or the mixture of bainite and martensite is required to reach high strength levels in low carbon high strength steel. However, the bainite reaction rarely goes to completion, resulting in mixed structures of predominately bainitic ferrite and minor amounts of retained austenite, cementite or martensite mainly located at the ferrite grain boundaries. The exact nature of this minor transformation product depends on several factors including bulk composition, segregation and cooling rate. When the minor phase is largely martensite, the non-bainitic microstructure is called martensite-austenite microconstituent or MA. Interestingly, MA is believed to be one of the main factors causing the deterioration of toughness of steels. MA is also often associated with hydrogen-related cracking. In this current study, the formation of martensite-austenite constituents was studied experimentally and the results analyzed theoretically.

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31

Timokhina, I. B., K. D. Liss, D. Raabe, K. Rakha, H. Beladi, X. Y. Xiong, and P. D. Hodgson. "Growth of bainitic ferrite and carbon partitioning during the early stages of bainite transformation in a 2 mass% silicon steel studied by in situ neutron diffraction, TEM and APT." Journal of Applied Crystallography 49, no. 2 (February 16, 2016): 399–414. http://dx.doi.org/10.1107/s1600576716000418.

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In situ neutron diffraction, transmission electron microscopy (TEM) and atom probe tomography (APT) have been used to study the early stages of bainite transformation in a 2 mass% Si nano-bainitic steel. It was observed that carbon redistribution between the bainitic ferrite and retained austenite at the early stages of the bainite transformation at low isothermal holding occurred in the following sequence: (i) formation of bainitic ferrite nuclei within carbon-depleted regions immediately after the beginning of isothermal treatment; (ii) carbon partitioning immediately after the formation of bainitic ferrite nuclei but substantial carbon diffusion only after 33 min of bainite isothermal holding; (iii) formation of the carbon-enriched remaining austenite in the vicinity of bainitic laths at the beginning of the transformation; (iv) segregation of carbon to the dislocations near the austenite/ferrite interface; and (v) homogeneous redistribution of carbon within the remaining austenite with the progress of the transformation and with the formation of bainitic ferrite colonies. Bainitic ferrite nucleated at internal defects or bainite/austenite interfaces as well as at the prior austenite grain boundary. Bainitic ferrite has been observed in the form of an individual layer, a colony of layers and a layer with sideplates at the early stages of transformation.

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Yuan, Lian Jie, Qing Suo Liu, and Bin Gao. "Effect of Austenitization Temperature on Formation of Low Temperature Bainite." Advanced Materials Research 912-914 (April 2014): 103–6. http://dx.doi.org/10.4028/www.scientific.net/amr.912-914.103.

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The influence of austenitization temperature on the incubation period and bainitic transformation behaviours of the high-carbon silicon steel has been investigated. It was found that the nose temperature of bainite transformation and incubation period decreases with increasing austenitization temperature. The microstructure characteristics of the bainitic transformation products have been also observed. After isothermal heat treatment at 230°C for 20 mins, all samples austenitized at different temperatures produced a bainitic structure, which consists of packets of parallel ferrite laths. The major difference lies in the edge boundary morphology. Bainitic laths formed in low-temperature austenitization conditions has sharp saw-tooth edge boundaries, whereas bainite transformed from high-temperature austenitization conditions, have smooth wedge boundaries. Key Words: austenitization temperature; low-temperature bainite; incubation period;edge boundary

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33

Zhou, Peng, Hui Guo, Ai Min Zhao, Zhu Kai Yin, and Jia Xing Wang. "Effect of Pre-Existing Martensite on Bainitic Transformation in Low-Temperature Bainite Steel." Materials Science Forum 898 (June 2017): 803–9. http://dx.doi.org/10.4028/www.scientific.net/msf.898.803.

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The effect of different volume fractions of pre-existing martensite on the low-temperature bainitic transformation and microstructures was quantitatively analyzed by dilatometer, optical microscope and scanning electron microscope. The results showed that pre-existing martensitic transformation accelerated the subsequent low-temperature bainitic transformation, and the incubation period and completion time of bainitic reaction were significantly shortened. This phenomenon was attributed to the increasing nucleation sites caused by the introduced dislocations in austenite due to the formation of pre-existing martensite. However, it was noteworthy that, because of the increased bainitic plates adjacent to the pre-existing martensitic plates, the probability of the impingement of bainitic plates during growth was increased, which resulted in a decrease in the maximum attainable volume fraction of bainite.

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Wang, Xue Min, Xin Lai He, Shan Wu Yang, and Cheng Jia Shang. "The Ultra-Fine Bainitic Steels and Refinement Technology." Materials Science Forum 539-543 (March 2007): 4566–71. http://dx.doi.org/10.4028/www.scientific.net/msf.539-543.4566.

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By employing the new developed relaxation-precipitation-controlling phase transformation (RPC) technique in large scale production the bainitic steels with ultra fine bainite has been obtained. These bainitic steels have good synergistic properties. With the aid of thermal simulation the refinement mechanism of RPC technique has also been investigated. The optical microscope, scanning electron microscope, transmission electron microscope and Electron back scattering diffraction technique were employed to study the features of microstructure produced by RPC technique, precipitation and the evolution of dislocation configuration during the relaxation. The results show that when produced by RPC technique the microstructure of the steel is mainly ultra-fine lath bainite packets, and these bainite packets block each other. It is also found that during the relaxation the dislocation cells form and strain induced precipitation occurs, the dislocation cell pinned by the precipitates can confine the bainite transformation. After the relaxation during the cooling the acicular ferrite forms at first and in succeeding the bainite transformation is blocked by the acicular ferrite and the bainite is refined effectively.

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Zhu, Jiaqi, Zhunli Tan, Yu Tian, Bo Gao, Min Zhang, Junxiang Wang, and Yuqing Weng. "Effect of Tempering Temperature on Microstructure and Mechanical Properties of Bainitic Railway Wheel Steel with Thermal Damage Resistance by Alloy Design." Metals 10, no. 9 (September 10, 2020): 1221. http://dx.doi.org/10.3390/met10091221.

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Thermal damage is one of the principle modes of wagon railway wheels. A new bainitic railway wheel steel with high thermal damage resistance and good combination of strength, plasticity, and toughness was developed. Microstructure and mechanical properties of the new steels in a tempered condition at different temperatures were examined. Microstructures were observed using scanning electron microscope and transmission electron microscope. Mechanical properties were evaluated by tensile, hardness, and Charpy impact tests with a simultaneous comparison to pearlitic railway wheel steel. The characteristic of retain austenite and V(C,N) were measured through X-ray diffractometry and energy disperse spectroscopy. The results indicate that this new bainitic wheel steel presents a submicron-sized carbide-free bainite morphology and preferable integrated mechanical properties when tempered at 280–360 °C. Precipitation strengthening plays an important role for the high strength, since a two-time-strengthening mechanism of the yield strength led by precipitation has been found at 280–360 and 480–560 °C, respectively. Compared with a pearlitic railway wheel steel, bainitic wheel steel tempered at 320 °C has a 10% higher yield strength, five times higher impact toughness, and much better thermal damage resistance, which is a promising railway wheel material for higher speed or heavier axle-load service conditions.

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Fourlaris, G., and G. Papadimitriou. "TEM Microscopical Examination of the Stepped Bainite Reaction in Silicon Steels." Microscopy and Microanalysis 3, S2 (August 1997): 689–90. http://dx.doi.org/10.1017/s1431927600010333.

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The bainitic reaction in steels has been extensively studied, however it is still controversial whether it proceeds by a diffusional or a shear mechanism. In a previous investigation of the bainite reaction in a Fe-3.9Si-0.9C steel the transformation was considered to be the result of two competing elementary mechanisms, i.e., the shear transformation of the α-iron lattice and the diffusion of interstitial carbon away from the transformation interface.In this paper, the microstructural and crystallographic characteristics of the bainite products obtained through the step quenching experiments are examined, using TEM and Electron diffraction. The results are compared to those obtained by the corresponding bainitic transformation in a single step. The results obtained here support the proposed model in and the shear character of the bainitic transformation.The same steel as in, an alloy with 3.9 w.t.% silicon and 0.9 w.t.% carbon, was used. After austenitizing at 1130°C for 30 minutes a number of samples were transformed at 420°C for 30 minutes and subsequently quenched in a second bath where they were kept for times increasing from one to thirty days at temperatures of either 360,340 or 290°C.

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Zuo, Long Fei, Zhan Lei Wei, Ri Ni, Ben Ma, and Zi Dong Wang. "Effect of Aging Temperature on the Microstructure and Mechanical Properties of 1000MPa Grade Low Carbon Bainitic Steel." Applied Mechanics and Materials 152-154 (January 2012): 376–80. http://dx.doi.org/10.4028/www.scientific.net/amm.152-154.376.

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A kind of 1000MPa low carbon bainitic steel belonged to the Fe-Cu-Nb series was hot rolled and aged, the influence of aging temperatures on the microstructure and mechanical properties of the steel were investigated by using Scanning electron microscopy (SEM) and transmission electron microscopy(TEM). The results show that the microstructure of the low carbon bainitic steel consisted of lath-shaped bainite(LB), granular bainite(GB) and quasi-polygonal ferrite(QF), and the proportion of each kind of microstructure changed with the aging temperatures. The strength of steel with the increase of aging temperature first increased, then decreased, Aging temperatures had distinct effect on yield strength of the tested steel, and less effect on the ultimate tensile strength, we can get the best comprehensive properties yield strength 1011.87 MPa and elongation rate 16.38% of good tough match aged at 450°C. Through analysis it is concluded that the strength of the tested steels aged at 450°C reaches the maximum value, which is attributed to the precipitation of a large amount of fine ε-Cu particles(5~10nm) and a small number of(Nb,Ti)(C,N) precipitates.

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Liu, Zhi Xue, and Ju Qiang Cheng. "Microstructure and Mechanical Properties of New Type Bainitic Carburized Steel for Gear." Advanced Materials Research 602-604 (December 2012): 300–304. http://dx.doi.org/10.4028/www.scientific.net/amr.602-604.300.

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This paper presents the microstructure, mechanical properties and carburized behavior of new type bainitic carburized steel. The results show that after new carburized steel is normalized at 920°C and tempered at 300°C, its microstructure consists of bainitic ferrite and residual austenite, and belongs to the carbide-free bainite or atypical bainite. Large or small cross-section size new carburized steel bar all have reached the performance requirements of Cr-Ni carbonized steel. The microstructure of new carburized steel surface consists of high carbon martensite and residual austenite after carburized and air-cooled, It retains austenite fraction of the new carburized steel and 18Cr2Ni4WA steel are about 18% and 38%, respectively. Carbon concentration gradient of new carburized steel changes smoothly and have ideal carbon concentration distribution. Effective carburizing surface depth of new carburized steel is about 0.6mm and is smaller than 18Cr2Ni4WA steel. The gear entities made of new carburized steel meet the technical requirements of heavy duty carburized gear.

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Wada, Kentaro, Soma Yoshimura, Tomoko Yamamoto, Yoshihiro Ohkomori, and Hisao Matsunaga. "Shear-mode Crack Initiation Behavior in the Martensitic and Bainitic Microstructures." MATEC Web of Conferences 165 (2018): 04009. http://dx.doi.org/10.1051/matecconf/201816504009.

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Fully reversed torsional fatigue tests were conducted to elucidate the behaviour of shear-mode crack initiation and propagation in one martensitic and two bainitic steels. The relationship between the crack initiation site and microstructure was investigated by means of an electron backscatter diffraction (EBSD) technique. From the S-N diagram, two notable results were obtained: (i) the shear-mode crack was initiated on the prior austenitic grain boundary in martensitic steel, while in bainitic steels, the crack was initiated along the {110} plane; one of the slip planes of bcc metals, and (ii) the torsional fatigue limit of lower bainitic steel with finer grains was 60 MPa higher than that of upper bainitic steel with coarser grains even though the hardnesses were nearly equivalent. The mechanism determining the torsional fatigue strength in these steels is discussed from the viewpoint of microstructure morphology.

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Wang, Zhi Fen, Yi Qiang Sun, Rong Dong Han, and Li Xin Wu. "Investigation of the Corrosion Resistance of Bainitic Steel." Advanced Materials Research 295-297 (July 2011): 896–99. http://dx.doi.org/10.4028/www.scientific.net/amr.295-297.896.

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The corrosion resistance of bainitic steel was compared with a weathering steel 09CuPCrNi through accelerated corrosion tests. The results indicated that the corrosion resistance was better for bainitic steel than 09CuPCrNi based on the weight loss. The characteristics of the rust layers indicated the rust layers on two steels are composed of two parts: the loose outer rust layer and the dense inner rust layer. The rust layers are mainly composed of goethite (α-FeOOH) with a few of lepidocrocite (γ-FeOOH). The factors including homogeneous microstructure and lower carbon content played important roles in enhancing the corrosion resistance of bainitic steel.

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Hu, Fang Zhong, Wei Jun Hui, and Qi Long Yong. "High-Cycle Fatigue Fracture Behavior of Microalloyed Bainitic Steels for Hot Forging." Advanced Materials Research 634-638 (January 2013): 1746–51. http://dx.doi.org/10.4028/www.scientific.net/amr.634-638.1746.

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High-cycle fatigue fracture behavior of microalloyed bainitic steels with three different carbon and vanadium contents were studied using rotating-bending fatigue test and compared with the ferrite-pearlite type microalloyed steel F38MnVS. The results indicated that the fatigue properties of the microaIloyed bainitic steels had a significant relation to the microstructures in forging condition. Compared with the ferrite-pearlite type microalloyed steel F38MnVS, the bainitic steels possessed higher fatigue strength and lower fatigue limit ratio σ-1/Rm. It was found that the bainitic transformation temperature was decreased and the hardness of the bainitic ferrite was enhanced, at the same time, the fatigue strength was increased, however, the fatigue limit ratio was lower. Furthermore, according to the SEM images of the fracture surface of fatigue specimens, it was revealed that the fatigue cracks mainly initiated along the bainitic ferrite laths in the specimen surface and preferred to propagate along the length direction of laths.

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Kumnorkaew, Theerawat, Junhe Lian, Vitoon Uthaisangsuk, and Wolfgang Bleck. "Kinetic Model of Isothermal Bainitic Transformation of Low Carbon Steels under Ausforming Conditions." Alloys 1, no. 1 (June 13, 2022): 93–115. http://dx.doi.org/10.3390/alloys1010007.

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Carbide-free bainitic steels show attractive mechanical properties but are difficult to process because of the sluggish phase transformation kinetics. A macroscopic model based on the classical nucleation theory in conjunction with the modified Koistinen–Marburger relationship is proposed in this study to simulate the kinetics of incomplete bainitic and martensitic phase transformations with and without austenite deformation. A 0.26C-1Si-1.5Mn-1Cr-1Ni-0.003B-0.03Ti steel and a 0.18C-1Si-2.5Mn-0.2Cr-0.2Ni-0.02B-0.03Ti steel were investigated with different levels of ausforming. The concept of ausforming is expected to accelerate the onset of the bainitic transformation and to enhance the thermodynamic stability of austenite by increased dislocation density. The phase transformation kinetics of both steels is quantitatively analyzed in the study by dilatometry and X-ray diffraction so that the carbon concentration in the retained austenite and bainitic ferrite, as well as their volume fractions, is determined. A critical comparison of the numerical and experimental data demonstrates that the isothermal kinetics of bainite formation and the variation of driving energy can be satisfactorily described by the developed model. This model captures the incompleteness of the bainite phase transformation and the carbon enrichment in the austenite well. A fitting parameter can be used to elucidate the initial energy barrier caused by the ausforming. An increase in austenite stability can be described by the nucleation reaction and the thermodynamic energies associated with the change of dislocation density. The proposed model provides an in-depth understanding of the effect of ausforming on the transformation kinetics under different low-carbon steels and is a potential tool for the future design of heat treatment processes and alloys.

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Ji, Feng Qin, and Guo Dong Wang. "Effects of Cooling Processes on Microstructure Evolution of X80 Pipeline Steel." Materials Science Forum 788 (April 2014): 378–83. http://dx.doi.org/10.4028/www.scientific.net/msf.788.378.

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With the development of pipeline industry, the pipeline steels with higher strength and plasticity, better low-temperature toughness and weldability are the main development trend. For bainitic pipeline steels, M/A constituent is the main hard phase. Although the M/A constituent can enhance the strength, the larger block-form M/A constituent can deteriorate low-temperature toughness. Therefore, it is essential to further investigate how to refine the M/A constituent. In the present paper, X80 pipeline steel was cooled to room temperature with various cooling paths after hot compression deformation at the temperature of 800oC. The evolution of microstructure of X80 pipeline steel has been analyzed by optical microscope (OM) and scanning electron microscope (SEM). The experimental results show that increasing the cooling rate can significantly refine M/A constituent and promote the formation of granular bainite, and the bainitic ferrite can be also greatly refined. In addition, the effects of five final temperatures of fast cooling were also investigated.

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Lin, Sen, Ulrika Borggren, Andreas Stark, Annika Borgenstam, Wangzhong Mu, and Peter Hedström. "In-Situ High-Energy X-ray Diffraction Study of Austenite Decomposition During Rapid Cooling and Isothermal Holding in Two HSLA Steels." Metallurgical and Materials Transactions A 52, no. 5 (March 10, 2021): 1812–25. http://dx.doi.org/10.1007/s11661-021-06192-x.

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AbstractIn-situ high-energy X-ray diffraction experiments with high temporal resolution during rapid cooling (280 °C s−1) and isothermal heat treatments (at 450 °C, 500 °C, and 550 °C for 30 minutes) were performed to study austenite decomposition in two commercial high-strength low-alloy steels. The rapid phase transformations occurring in these types of steels are investigated for the first time in-situ, aiding a detailed analysis of the austenite decomposition kinetics. For the low hardenability steel with main composition Fe-0.08C-1.7Mn-0.403Si-0.303Cr in weight percent, austenite decomposition to polygonal ferrite and bainite occurs already during the initial cooling. However, for the high hardenability steel with main composition Fe-0.08C-1.79Mn-0.182Si-0.757Cr-0.094Mo in weight percent, the austenite decomposition kinetics is retarded, chiefly by the Mo addition, and therefore mainly bainitic transformation occurs during isothermal holding; the bainitic transformation rate at the isothermal holding is clearly enhanced by lowered temperature from 550 °C to 500 °C and 450 °C. During prolonged isothermal holding, carbide formation leads to decreased austenite carbon content and promotes continued bainitic ferrite formation. Moreover, at prolonged isothermal holding at higher temperatures some degenerate pearlite form.

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45

Li, Jianhua, Peng Chen, Dapeng Yang, Hongshuang Di, and Hongliang Yi. "Improving Strength-Ductility via Short Austenitization in a Low-Carbon Carbide-Free Bainitic Steel." Crystals 12, no. 11 (November 14, 2022): 1636. http://dx.doi.org/10.3390/cryst12111636.

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The strength and ductility of low-carbon carbide-free bainitic (CFB) automotive steel are not good enough. In this study, a short austenitization (SA) process in conjunction with isothermal bainitic transformation was adopted to refine the bainitic ferrite lath, thus improving the mechanical properties of low-carbon CFB steel. The microstructure evolution was traced by dilatometric measurements and microstructure characterization, which revealed the refined microstructure by SA process. Besides, the deformation behaviors of the studied steels were analyzed, indicating that the improved work hardening capability by refined bainitic ferrite lath and more stable austenite were responsible for the better strength-ductility match. The CFB steel treated by SA process exhibits a high tensile strength of ~1180 MPa, and its elongation of 22.6% is comparable with commercial QP980 steel.

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Morawiec, M., V. Ruiz-Jimenez, C. Garcia-Mateo, and A. Grajcar. "Thermodynamic analysis and isothermal bainitic transformation kinetics in lean medium-Mn steels." Journal of Thermal Analysis and Calorimetry 142, no. 5 (October 9, 2020): 1709–19. http://dx.doi.org/10.1007/s10973-020-10259-z.

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AbstractThe work presents the results of thermodynamic analysis of two medium manganese steels with different Mn contents. The steels containing 3.1 and 3.6% of manganese were subjected to theoretical thermodynamic calculations using MUCG83 software and dilatometric experiments. The steels were heat-treated in two different isothermal holding temperatures of 400 and 350 °C for 15 min. The bainite transformation kinetics at different temperatures for different manganese contents was investigated. In the steel including 3.1% Mn, a complete transformation was obtained. The results indicated a strong influence of the holding temperature on the kinetics of bainitic transformation. It was related to the driving force of this process. When the manganese content was increased by 0.5%, an incomplete bainite transformation occurred. The microstructure investigations after heat treatment were performed using light and scanning electron microscopy. The XRD analysis to determine retained austenite amount and its carbon enrichment was performed. The microstructure of 3MnNb steel consisted of bainite and retained austenite with filmlike and blocky morphologies. The steel with the higher Mn content contained also fresh martensite for both isothermal holding temperatures.

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47

Regier, R. W., A. Reguly, David K. Matlock, J. K. Choi, and John G. Speer. "Effects of Austenite Conditioning and Transformation Temperature on the Bainitic Microstructure in Linepipe Steels." Materials Science Forum 783-786 (May 2014): 85–90. http://dx.doi.org/10.4028/www.scientific.net/msf.783-786.85.

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Low carbon bainitic steels are important in applications such as linepipe, and the details of the bainite microstructure control strength and toughness. The transformation of austenite to bainitic ferrite has been widely researched over the years, although recent use of electron backscatter diffraction techniques has provided opportunity to advance the characterization of various crystallographic aspects. In recent work, microstructures were characterized in a base steel containing 0.04 C and 1.7 Mn (wt. pct.) and two additional steels having modest carbon and manganese variations to influence the transformation behavior, with an interest in the MA (martensite-austenite) constituent and characteristics of the bainite developed at different transformation temperatures. Effects of austenite conditioning were also examined, as these steels contained an addition of 0.04 wt. pct. Nb. Microstructural details including crystallographic characteristics assessed using EBSD are presented, along with comments related to the implications of the results.

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48

Feng, Chun, Bing Zhe Bai, Y. K. Zheng, and Hong Sheng Fang. "Mn-Series Low Carbon Air Cooling Bainitic Steels Containg Niobium." Advanced Materials Research 89-91 (January 2010): 112–17. http://dx.doi.org/10.4028/www.scientific.net/amr.89-91.112.

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Abstract:

The effect of four different niobium(From 0-0.1%) addition on the mechanical properties of allotriomorphic ferrite (FGBA)/ granular bainite (BG) air cooling bainitic steels has been investigated in this paper. The results show that (1) The 0.06%Nb steel acquired superior strength and toughness combination by applying 1250°C×60min solution treated, finish rolling at 850°C, and air cooling. The corresponding mechanical properties of the thick plate(30mm) is: σb>1050MPa, σ0.2>700MPa,δ5>17%,Akv>90J. (2) The addition of niobium refine the grain size of FGBA, and promoted the transformation of bainite structure. With the increase of niobium content, the refinement of ferrite grain and bainitic cluster is improved. (3) More refined M-A island is acquired by the small addition of niobium. According to M-A Analysis tools and transversal methods, with the rise of niobium content, the volume fraction of M-A island increase from 21% to 35%, and the average size of M-A island decrease from 1.1μm to 0.7um. (4)It is suggested that 0.02-0.06% niobium can improve the mechanical properties of the steel obviously. However, excess addition of Nb (0.1%) deteriorates the impact toughness obviously. (5)Under the synthetic roles of the microstructure refinement and precipitation strengthen, 60-160MPa yield strength improvement has been acquired in the low carbon air cooling bainitic steel by the small addition of niobium. (6)This steel is with low production cost since the alloying element Mn is cheap.

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49

Feng, Chun, Bing Zhe Bai, Y. K. Zheng, and Hong Sheng Fang. "Mn-Series Low Carbon Air Cooling Bainitic Steels Containing Niobium." Materials Science Forum 638-642 (January 2010): 3038–43. http://dx.doi.org/10.4028/www.scientific.net/msf.638-642.3038.

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Abstract:

The effect of four different niobium(From 0-0.1%) addition on the mechanical properties of allotriomorphic ferrite (FGBA)/ granular bainite (BG) air cooling bainitic steels has been investigated in this paper. The results show that (1) The 0.06%Nb steel acquired superior strength and toughness combination by applying 1250°C×60min solution treated, finish rolling at 850°C, and air cooling. The corresponding mechanical property of the thick plate (30mm) is: σb>1050MPa, σ0.2>700MPa, δ5>17%, Akv>90J. (2) The addition of niobium refine the grain size of FGBA, and promoted the transformation of bainite structure. With the increase of niobium content, the refinement of ferrite grain and bainitic cluster is improved. (3) More refined M-A island is acquired by the small addition of niobium. According to M-A Analysis tools and transversal methods, with the rise of niobium content, the volume fraction of M-A island increase from 21% to 35%, and the average size of M-A island decrease from 1.1μm to 0.7um. (4) It is suggested that 0.02-0.06% niobium can improve the mechanical properties of the steel obviously. However, excess addition of Nb (0.1%) deteriorates the impact toughness obviously. (5) Under the synthetic roles of the microstructure refinement and precipitation strengthen, 60-160MPa yield strength improvement has been acquired in the low carbon air cooling bainitic steel by the small addition of niobium. (6) This steel is with low production cost since the alloying element Mn is cheap.

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50

Xie, Hui, Lin Xiu Du, and Jun Hu. "Effect of Cooling Procedure on Tensile and Charpy Impact Properties of Cr-Mo Ultra-High Strength Steel." Materials Science Forum 816 (April 2015): 761–68. http://dx.doi.org/10.4028/www.scientific.net/msf.816.761.

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Abstract:

The effect of cooling procedure on the transformation behavior of low-carbon Cr-Mo microalloyed steel was investigated by using microstructural observations, mechanical properties and impact fractographs. Three steel plates were adopted under three different cooling rates, and their microstructure, tensile and impact properties were evaluated. The results indicated that the strength of experimental steels was increased and the impact toughness was decreased with decreasing the coiling temperature. Steel A consisted of granular bainite, coarse bainitic ferrite lath and M/A constituent subjected to a coiling temperature of 560 oC. The yield strength, tensile strength and impact energy of 1/2-size Charpy impact at-20 oC were 740MPa, 1020MPa, and 33.5J, respectively, which were imperfect in strength. The effects of coiling temperature were potent on the refinement of microstructure and the size of M/A constituents. Steel B consisted of a small amount of lath bainite, fine M/A constituents and bainitic ferrite lath subjected to a lower coiling temperature of 520 oC. The yield strength, tensile strength and impact energy of 1/2-size Charpy impact at-20°C were 840MPa, 1030MPa, and 30.7J, respectively. However, steel C was composed of lath bainite and lath martensite subjected to the lowest coiling temperature of 380 oC (slightly above Ms point). The yield strength, tensile strength and impact energy of 1/2-size Charpy impact at-20 oC were 985MPa, 1200MPa and 22.5J, respectively, which could meet the demand of ultra high strength structural steel applications.

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Journal articles on the topic 'Bainitic steel'

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