Journal articles: 'Bainite ; Bainitic steel'

1

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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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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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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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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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, 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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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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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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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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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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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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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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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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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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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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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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Takayama, Naoki, Goro Miyamoto, and Tadashi Furuhara. "Effects of Transformation Temperature on Variant Grouping of Bainitic Ferrite in Low Carbon Steel." Solid State Phenomena 172-174 (June 2011): 155–60. http://dx.doi.org/10.4028/www.scientific.net/ssp.172-174.155.

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Effects of transformation temperature on variant grouping tendency of bainitic ferrite in a low carbon low alloy steel transformed isothermally are investigated by means of electron backscatter diffraction analysis. Baintic variants of Kurdjumov-Sachs (K-S) orientation relationship belonging to the same Bain correspondence tend to form adjacently in the bainite structure formed at 823K, while the K-S variants sharing the same close-packed plane parallel relation form adjacently in the bainite structure formed at 723K and lath martensite formed by quenching.

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Yudin, Yu V., A. A. Kuklina, M. V. Maisuradze, and M. S. Karabanalov. "Visualization of the Bainite Fine Structure Using EBSD and Euler Angles." KnE Engineering 1, no. 1 (April 15, 2019): 11. http://dx.doi.org/10.18502/keg.v1i1.4385.

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The electron backscatter diffraction method (EBSD) is widely used to studycrystallographic orientational relationships of the steel microstructure constituentsincluding bainite. Nevertheless the fine structure of bainite (subunits, plates) is notinvestigated by this method. In this paper we propose a technique for visualizing ofthe structure of a bainitic steel near-surface layer using the values of Euler anglesobtained by EBSD method. A three-dimensional picture of the bainite fine structure ofthe HY-TUF steel obtained by the proposed technique is in

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Beladi, Hossein, Ilana B. Timokhina, and Peter D. Hodgson. "The Formation of Ultrafine Ferrite and Low Temperature Bainite through Thermomechanical Processing." Materials Science Forum 706-709 (January 2012): 2047–52. http://dx.doi.org/10.4028/www.scientific.net/msf.706-709.2047.

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In the current study, a novel approach was employed to produce a unique combination of ultrafine ferrite grains and low temperature bainite in a low carbon steel with a high hardenability. The thermomechanical route included warm deformation of supercooled austenite followed by reheating in the ferrite region and then cooling to bainitic transformation regime (i.e. 400-250°C). The resultant microstructure was ultrafine ferrite grains (i.e. <4μm) and very fine bainite consisting of bainitic ferrite laths with high dislocation density and retained austenite films. This microstructure offers a unique combination of ultimate tensile strength and elongation due to the presence of ductile fine ferrite grains and hard low temperature bainitic ferrite laths with retained austenite films. The microstructural characteristics of bainite were studied using optical microscopy in conjunction with scanning and transmission electron microscopy techniques.

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Ławrynowicz, Z. "Rationalisation of Austenite Transformation to Upper or Lower Bainite in Steels." Advances in Materials Science 14, no. 2 (June 1, 2014): 14–23. http://dx.doi.org/10.2478/adms-2014-0006.

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Abstract The paper presents an analytical evaluation of transition temperature from upper to lower bainite in Fe-C-Cr steel. The calculations was based on the model constructed by Matas and Hehemann which involves a comparison between the times needed to precipitate cementite within the bainitic ferrite plates (tθ), with the time required to decarburise supersaturated ferrite plates (td). The transition between upper and lower bainite is found to occur over a narrow range of temperatures (350-410°C) and depends on the thickness of bainitic ferrite laths and the volume fraction of precipitated cementite. On comparing the td and tθ times it was found that the transition temperature from upper to lower bainite reaction (LS) of about 350oC could be predicted if the thickness of bainitic ferrite laths is set as wo = 0.1 μm and volume fraction of cementite is set as ξ = 0.01

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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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Zhu, Jian G., Xichen Sun, Gary C. Barber, Xue Han, and Hao Qin. "Bainite Transformation-Kinetics-Microstructure Characterization of Austempered 4140 Steel." Metals 10, no. 2 (February 10, 2020): 236. http://dx.doi.org/10.3390/met10020236.

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Bainite transformation is a kinetic process that involves complex solid diffusion and phase structure evolution. This research systematically studies the bainite transformation of austempered 4140 steel in a wide range of isothermal temperatures, in which four bainite phases structures were generated: upper bainite; mixed upper bainite and lower bainite; lower bainite and mixed lower bainite and martensite. The kinetics of bainite transformation has been described with a linear trend using an Avrami n-value. It was found that the bainitic ferrite sheaves grow with widthwise preference. The sheaves are stable when half-grown and are variable in length, due to austenite size limit or soft/hard impingement, or autocatalytic nucleation, or these conditions combined. The full-grown upper/lower bainite sheaves were found to be 1.9 μm/1.2 μm in width under the conditions of this study. Each individual bainite sheave is lath-like instead of wedge-like. The upper bainite sheaves mostly appear as broad-short-coarse lath, while the lower bainite sheaves appear as narrow-long-fine lath. The overall bainite transformation activation energy ranges from 50–167 kJ/mol.

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Morri, A., L. Ceschini, M. Pellizzari, C. Menapace, F. Vettore, and E. Veneri. "Effect of the Austempering Process on the Microstructure and Mechanical Properties of 27MnCrB5-2 Steel." Archives of Metallurgy and Materials 62, no. 2 (June 1, 2017): 643–51. http://dx.doi.org/10.1515/amm-2017-0094.

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AbstractThe effect of austempering parameters on the microstructure and mechanical properties of 27MnCrB5-2 steel has been investigated by means of: dilatometric, microstructural and fractographic analyses; tensile and Charpy V-notch (CVN) impact tests at room temperature and a low temperature.Microstructural analyses showed that upper bainite developed at a higher austempering temperature, while a mixed bainitic-martensitic microstructure formed at lower temperatures, with a different amount of bainite and martensite and a different size of bainite sheaf depending on the temperature. Tensile tests highlighted superior yield and tensile strengths (≈30%) for the mixed microstructure, with respect to both fully bainitic and Q&T microstructures, with only a low reduction in elongation to failure (≈10%). Impact tests confirmed that mixed microstructures have higher impact properties, at both room temperature and a low temperature.

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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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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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26

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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27

Sun, Chao, Shan Wu Yang, Ming Xuan Lin, and Xian Wang. "Microstructure Evolution in Low-Carbon Bainitic Steel during Tempering." Advanced Materials Research 399-401 (November 2011): 160–65. http://dx.doi.org/10.4028/www.scientific.net/amr.399-401.160.

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Microstructure evolution in low-carbon bainitic steel during tempering is investigated by hardness measurements and metallographical examinations. It is found that the microstructure evolution and the hardness variation can be divided into four stages when samples were tempered at 600°C and 700°C, and the evolution of bainte is similar to recovery and recrystallization of deformed metals. It is also found that the newly formed ferrite during recrystallization grows more rapidly along the long axis of bainite laths, and there is evidence of composition changing during recrystallization.

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28

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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29

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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30

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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31

Liang, Xiao Jun, Ming Jian Hua, and Anthony J. DeArdo. "The Influence of Thermomechanical Controlled Processing on Bainite Formation in Low Carbon High Strength Steel." Materials Science Forum 783-786 (May 2014): 21–26. http://dx.doi.org/10.4028/www.scientific.net/msf.783-786.21.

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Thermomechanical controlled processing is a very important way to control the microstructure and mechanical properties in low carbon, high strength steel. This is especially true in the case of bainite formation, where the complexity of the austenite-bainite transformation makes the control of the processing important. In this study, a low carbon, high manganese steel containing niobium was investigated to better understand the roles of austenite conditioning and cooling rates on the bainitic phase transformation. Specimens were compared with and without deformation, and followed by seven different cooling rates ranging between 0.5°C/s and 40°C/s. The CCT curves showed that the transformation behaviors and temperatures are very different. The different bainitic microstructures which varied with austenite deformation and cooling rates will be discussed.

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32

Woźniak, Tadeusz Z., Jerzy Jelenkowski, Krzysztof Rozniatowski, and Zbigniew Ranachowski. "Effect of Microstructure on Rolling Contact Fatigue of Bearings." Materials Science Forum 726 (August 2012): 55–62. http://dx.doi.org/10.4028/www.scientific.net/msf.726.55.

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There has been proposed an innovative thermal treatment of bearing steel 100CrMnSi6-4, where the existing standard heat treatment has been replaced by austempering. The structure of low-temperature tempered martensite has been replaced by a microstructure composed of martensite and lower bainite with midrib. The kinetics of bainitic transformation and isothermal martensitic transition at selected austempering temperatures was controlled by acoustic emission. The research on contact strength was made under the conditions of rolling-sliding friction. The microstructure was revealed with the use of a light microscope and the forms of pitting wear were displayed by a scanning electron microscope. It was found that the optimum microstructure providing the best used contact strength of the tested steel is conditioned by the formation of a lower bainite with midrib at the temperatures near MS. A plausible cause of the increased resistance to pitting is bifurcation of fatigue cracks on dispersion bainitic carbides in combination with primary carbides, in bainitic-martensitic matrix.

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33

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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34

Han, Xue, Gary Barber, Zhenpu Zhang, Bingxu Wang, Jian Zhu, Jing Shi, and Xichen Sun. "Austenite-Bainite Transformation Kinetics in Austempered AISI 5160 Steel." European Scientific Journal, ESJ 14, no. 12 (April 30, 2018): 1. http://dx.doi.org/10.19044/esj.2018.v14n12p1.

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This research investigates the process of the formation of bainite in austempered 5160 steel. Steel bar samples were austenitized at 1128 K for 20 minutes followed by holding at various times from 10 seconds to 2 hours and isothermal temperatures from 561K to 728K to obtain a multi-phase matrix. Micro-hardness analysis and metallurgical optical microscopy were used to analyze the experimental results. Hardness results indicated that at the 561K, 589K, and 566K isothermal temperatures for 5160 steel, lower bainite transformation occurred. However, from 644K to 728K, upper bainite transformation was found from the steel. The formation of the bainitic phase in SAE 5160 steel was characterized using thermodynamic and kinetic theories.

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35

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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36

Kučerová, Ludmila, Martin Bystrianský, and Josef Káňa. "The Effect of Isothermal Hold Temperature on Microstructure and Mechanical Properties of TRIP Steel." Solid State Phenomena 270 (November 2017): 253–57. http://dx.doi.org/10.4028/www.scientific.net/ssp.270.253.

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TRIP (transformation induced plasticity) steels are low alloyed low carbon steels with complex microstructures consisting of ferrite, bainite and retained austenite. This complex microstructure provides them with excellent strength to ductility balance, making them a member of advanced high strength steels (AHSS) group. Suitable microstructure can be obtained by either heat or thermo-mechanical treatment. A hold in bainite transformation region is an integral part of any form of commercial TRIP steel processing route, as it enables formation of sufficient volume fraction of bainite and also stabilization of retained austenite in the final microstructure. Various bainitic hold temperatures ranging from 350 °C to 500 °C were tested within thermo-mechanical treatment of 0.2C-1.5Mn-0.6S-1.5Al steel and the final microstructures were evaluated with regard to the suitability to TRIP effect and achieved mechanical properties. The microstructures were analyzed by scanning electron microscopy and mechanical properties measured by tensile test.

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37

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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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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38

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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39

Polevoi, E. V., Yu N. Simonov, N. A. Kozyrev, R. A. Shevchenko, and L. P. Bashchenko. "Phase and structural transformations when forming a welded joint from rail steel. Report 2. Isothermal diagram of decomposition of supercooled austenite of R350LHT rail steel." Izvestiya. Ferrous Metallurgy 64, no. 4 (June 4, 2021): 266–72. http://dx.doi.org/10.17073/0368-0797-2021-4-266-272.

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An isothermal diagram of decomposition of supercooled austenite of R350LHT steel was constructed based on the results of dilatometric, metallographic and hardness analysis of this decomposition during continuous cooling and under isothermal conditions. When comparing the thermokinetic and isothermal diagrams, it was found that the thermokinetic diagram plotted during continuous cooling shifts downward and to the right in comparison with the isothermal diagram. This result is fully consistent with the known regularities. During the research, the critical points of R350LHT steel were determined: Ас1 = 711 °С; Мn = 196 °С. This isothermal diagram was used to determine the temperature of the minimum stability of overcooled austenite, which was 500 °C. Under isothermal conditions, pearlite-type structures appear in the temperature range from 700 to 600 °C. At 550 °C, a mixture of pearlitic and bainitic structures is formed. In the temperature range from 500 to 250 °C, bainitic structures are formed: at 500 – 400 °C – upper bainite; at 350 ° C – a mixture of upper and lower bainite; at 300 – 250 °С – lower bainite. Almost in the entire studied temperature range of overcooled austenite isothermal decomposition, an increase in the hardness of the transformation products is observed with a decrease in the holding temperature from 246 HV (at 700 °C) to 689 HV (at 250 °C). However, at a temperature of 500 °C, a slight drop in hardness occurs, which is apparently caused by the appearance of retained austenite during the development of bainitic transformation.

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40

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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41

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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42

Zhang, Zhan Ling, Ke Ke Zhang, Yun Yue, Ning Ma, and Zhi Wei Xu. "Microstructure and Mechanical Properties of Austempered Ultrahigh Carbon Steel 1.4%C." Materials Science Forum 682 (March 2011): 97–101. http://dx.doi.org/10.4028/www.scientific.net/msf.682.97.

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An ultrahigh carbon steel alloy containing 1.4 wt pct carbon (UHCS-1.4C) was studied. The steel was processed into ultrafine grain and fully spheroidized microstructure through a controlled rolling and controlled-cooling divorced eutectoid transformation, and was then given austempering treatment to form bainite. The mechanical properties of the heat-treated steel were evaluated by tension tests at room temperature. After austenitized at 850 °C and then austempered at 300 - 350 °C, the microstructure was ultrafine upper bainite, retained austenite, and unsolvable cementite. It was shown that the ultimate tensile strengths of UHCS-1.4C ranged from 1420 to 1830 MPa, elongations to failure from 6 to 14%; the ultimate tensile strength increases with decreasing austempering temperature, while the tensile ductility decreases. The fracture surface of bainitic UHCS-1.4C consists mainly of dimples and voids, which reveal a ductile fracture. The present results indicate that ultrahigh carbon steel can be easily processed to achieve bainitic microstructures and unique properties.

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43

Caballero, Francisca García, Michael K. Miller, and Carlos García-Mateo. "Slow Bainite: an Opportunity to Determine the Carbon Content of the Bainitic Ferrite during Growth." Solid State Phenomena 172-174 (June 2011): 111–16. http://dx.doi.org/10.4028/www.scientific.net/ssp.172-174.111.

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The amount of carbon in solid solution in bainitic ferrite at the early stage of transformation has been directly determined by atom probe tomography at 200 °C, taking advantage of the extremely slow transformation kinetics of a novel nanocrystalline steel. Results demonstrated that the original bainitic ferrite retains much of the carbon content of the parent austenite providing strong evidence that bainite transformation is essentially displacive in nature.

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44

Tao, Xue Li, Kai Ming Wu, and Xiang Liang Wan. "Effect of Nb on Microstructure Evolution of Coarse-Grained Heat-Affected Zone with Large Heat Input Welding." Advanced Materials Research 284-286 (July 2011): 1174–79. http://dx.doi.org/10.4028/www.scientific.net/amr.284-286.1174.

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The effect of Nb microalloying on microstructure transformation of coarse-grained heat-affected zone of high strength low alloy steels were investigated utilizing different heat input welding simulation. For the low-Nb steel, the microstructures of coarse-grained heat-affected zone mainly consisted of acicular ferrite, bainite and grain boundary ferrite for small heat input welding; the amount of acicular ferrite decreased whereas grain boundary ferrite, polygonal ferrite and pearlite increased with increasing heat input. In constrast, for the high-Nb steel, granular bainite was the dominant microstructure. The formation of granular bainitic microstructure was associated with the solid solution of Nb, which suppressed ferrite transformation and promoted the formation of granular bainite. The hardness of coarse-grained heat-affected zone increased with increasing Nb content, and decreased with decreasing heat input, which was attributed to the microstructural change.

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45

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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46

Lan, Hui Fang, Xiang Hua Liu, and Lin Xiu Du. "Ultra-Hard Bainitic Steels Processed through Low Temperature Heat Treatment." Advanced Materials Research 156-157 (October 2010): 1708–12. http://dx.doi.org/10.4028/www.scientific.net/amr.156-157.1708.

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Relative high carbon steel bearing Cr and Mo with microstructure consisting of nanoscaled bainitic laths and certain amount of retained austenite was produced through the combination of rolling and isothermal/multi-step heat treatment at low temperatures. The effect of the heat treatment temperature, time and path on the volume fraction of retained austenite and the width of bainitic lath was investigated. Nanoindentation was applied to inspect the separate hardness of the tiny bainite and retained austenite for different heat treatment parameters. The results showed that bainitic lath treatedt at 250°C was much thinner than that at 300°C and the volume fraction of retained austenite changed with different heat treatment temperatures, time and paths. The nanohardness of the baintic lath and retained austenite also changed with the processing of both carbon partitioning and displacive transformation for different heat treatment paths.

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47

Yang, Shan Wu, Hui Bin Wu, S. Q. Yuan, Cheng Jia Shang, Xue Min Wang, and Xin Lai He. "Dislocation-Precipitate Interaction and Its Effect on Thermostability of Bainite in a Nb-Bearing Steel." Materials Science Forum 475-479 (January 2005): 125–28. http://dx.doi.org/10.4028/www.scientific.net/msf.475-479.125.

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After bainitic transformation, the dislocations formed in deformed austenite remained to be pinned by the precipitates so that thermostability of the bainitic ferrite was improved. Coarsening of the precipitates accompanied by their distribution density change occurred during reheating. After long reheating, further precipitates nucleated in bainite. Dislocations inside laths getting rid of pinning of precipitates and their polygonization play the precursor to the evolution of microstructures, in which lath boundaries disappeared gradually.

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48

Lis, Andrzej Kazimierz, and Jadwiga Lis. "Effect of Hot Deformation and Cooling Rate on Phase Transformations in Low Carbon HN5MVNb Bainitic Steel." Materials Science Forum 539-543 (March 2007): 4620–25. http://dx.doi.org/10.4028/www.scientific.net/msf.539-543.4620.

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Deformations at temperatures 900 °C, 860 °C, 810 °C and 780 °C in the consecutive amounts 24%, 20%, 19% and 18.5% were applied to low carbon HN5MVNb bainitic steel using hot compression testing in dilatometer Bähr 805 followed by continuous cooling. The results show clearly that the kinetics of the austenite decomposition were depended on local equilibrium conditions between recovery, recrystallization and phase transformation processes for a given cooling rate. Bainite transformation was accelerated when sample was cooled after deformation at cooling rate 60 °C/s. At lower cooling rates than 5 °C/s down to 0.5 °C/s, bainite transformation was postpone when comparing its kinetics with those for non deformed steel. The bainitic transformation cannot be fitted to a single transformation mechanism owing to the formation of carbides. Different behavior was observed for austenite to ferrite transformation. Usually it was accelerated with consecutive deformations of the steel for all cooling rates used in experiments.

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49

Hodgson, Peter D., Ilana Timokhina, Xiang Yuan Xiong, Yoshitaka Adachi, and Hossein Beladi. "Understanding of the Bainite Transformation in a Nano-Structured Bainitic Steel." Solid State Phenomena 172-174 (June 2011): 123–28. http://dx.doi.org/10.4028/www.scientific.net/ssp.172-174.123.

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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 200°C for 10 days to form a nano-scale bainitic microstructure consisting of nanobainitic ferrite laths with high dislocation density and retained austenite films. The crystallographic analysis using TEM and EBSD revealed that the bainitic ferrite laths are close to the Nishiyama-Wassermann orientation relationship with the parent austenite. There was only one type of packet identified in a given transformed austenite grain. Each packet consisted of two different blocks having variants with the same habit plane, but different crystallographic orientations. The presence of fine C-rich clusters and Fe-C carbides with a wide range of compositions in bainitic ferrite was revealed by Three-dimensional Atom Probe Tomography (APT). The high carbon content of bainitic ferrite compared to the para-equilibrium level of carbon in ferrite, absence of segregation of carbon to the austenite/bainitic ferrite interface and absence of partitioning of substitutional elements between the retained austenite and bainitic ferrite were also found using APT.

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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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Journal articles on the topic 'Bainite ; Bainitic steel'

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