Journal articles: 'Bainite, steel, hot rolling, retained austenite'

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Lv, Wei, Di Wu, and Zhuang Li. "Development of Laminar Flow Cooling of Ultra-High Strength Ferrite-Bainite Dual Phase Steel." Applied Mechanics and Materials 184-185 (June 2012): 940–43. http://dx.doi.org/10.4028/www.scientific.net/amm.184-185.940.

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In the present paper, controlled cooling in different ways was performed using a laboratory hot rolling mill in ultra-high strength hot rolled ferrite-bainite dual phase (DP) steel. The results have shown that the final microstructures of DP steel comprise ferrite, bainite and a small amount of retained austenite and martensite. DP steel has a tensile strength ranging from 1010 to 1130MPa and yet retains considerable total elongation in the range of 14–17%. The addition of Mn and Nb to DP steel leads to the maximum ultimate tensile strength, yield strength and the product of ultimate tensile strength and total elongation due to the formation of retained austenite and granular bainite structure. Laminar flow cooling after hot rolling results in a significant increase in the quantity of ferrite and bainite due to the suppression of pearlite transformation, and as a result, the present steel possesses high strengths and good toughness.

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Li, Zhuang, Di Wu, Wei Lv, and Ming Fu Shao. "Phase Transformation Behavior during Continuous Cooling of Fe-C-Mn-Si Multiphase Steels." Applied Mechanics and Materials 377 (August 2013): 123–27. http://dx.doi.org/10.4028/www.scientific.net/amm.377.123.

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In the present paper, controlled cooling of Fe-C-Mn-Si multiphase steel was conducted by a laboratory hot rolling mill. The results show that polygonal ferrite, granular bainite and the stable retained austenite can be obtained through hot deformation and subsequent two steps cooling pattern. The amount of ferrite increased with the duration of intermediate air cooling during controlled cooling. The formation of the bainitic ferrite resulted in the carbon concentration enrichment in austenite further during the simulated coiling. This increases the stability of the remaining austenite. Satisfactory mechanical properties can be obtained through hot rolling process and two steps cooling pattern in this work due to the TRIP effect of the stable retained austenite.

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Li, Zhuang, Di Wu, and Ming Fu Shao. "Controlled Rolling and Controlled Cooling Technology of Fe-C-Mn-Si Multiphase Steel." Applied Mechanics and Materials 377 (August 2013): 107–11. http://dx.doi.org/10.4028/www.scientific.net/amm.377.107.

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In the present paper, controlled rolling and controlled cooling of Fe-C-Mn-Si multiphase steel was conducted by a laboratory hot rolling mill. The results show that ferrite (grey), granular bainite (black) and retained austenite (white) and/or MA islands (white) are observed in a color etched LOM micrograph. The presence of the retained austenite is confirmed by SEM observation. Controlled rolling and controlled cooling technology contributes to the improvement of the microstructure. Excellent mechanical properties for Fe-C-Mn-Si multiphase steel are attributed to the TRIP effect of the stable retained austenite.

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Kliber, Jiří, Gabriela Plestilova, Ondrej Zacek, and Mahesh C. Somani. "Effects of Thermomechanical Processing on Microstructure and Mechanical Properties Multiphase Steels Exhibiting a TRIP Effect." Materials Science Forum 539-543 (March 2007): 4357–62. http://dx.doi.org/10.4028/www.scientific.net/msf.539-543.4357.

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Effects of hot-rolling conditions on these steels are much less studied than their importance for practice would suggest. It should be emphasized that bainite transformation is the key reaction to enrich non-transformed austenite with carbon. This study was carried out in order to gain understanding of the effect of thermomechanical hot rolling on final microstructure and mechanical properties of C-Mn-Si TRIP steel. Fundamental of the transformation induced plasticity effect – TRIP is the stabilization of substantial amount of retained austenite down to the ambient temperature by thermomechanical processing and its subsequent transformation into strain induced martensite as a consequence of applied plastic deformation. The special prepared stepped specimens were rolled on laboratory tandem mill. The effects of finish rolling temperature, strain and isothermal bainite transformation temperature on mechanical properties of mentioned TRIP steel were evaluated (mechanical properties were examined with tension test). Major deformation, higher finishing rolling temperature and higher temperature of bainite hold result in drop in strength. Proportionately to the drop in strength, the ductility grows in the TRIP steel. Microstructures were examined with X-ray diffraction (retained austenite). Image analysis software was used to process SEM micrographs of structure (ferrite, bainite assessment). Plastometric testing was conducted on GLEEBLE 3800 thermo-mechanical simulator. First stage of experiment yielded stress-strain curves for various temperatures and strain rates. Gleeble 1500 was used for the remaining plastometric simulation. Specimens were reheated to austenitization temperature of 1100°C and soaked. Then they were cooled to the temperature of deformation and subsequently cooled at higher rate down to the bainitic transformation temperature (400 – 550 °C). Specimens were held at the bainitic transformation temperature and then air-cooled. Final microstructures were evaluated with respect to transformation diagrams and optical microscopy findings. Higher bainite volume fraction was found in the specimens cooled at higher cooling rate as compared with more slowly cooled specimens.

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Skowronek, Adam, Dariusz Woźniak, and Adam Grajcar. "Effect of Mn Addition on Hot-Working Behavior and Microstructure of Hot-Rolled Medium-Mn Steels." Metals 11, no. 2 (February 19, 2021): 354. http://dx.doi.org/10.3390/met11020354.

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Hot plastic working behavior and microstructure evolution were investigated during a production process of four medium-Mn steels, which differed in Mn (3 and 5%) and Nb contents. The production process started with casting, followed by hot forging, rough hot-rolling and concluded with final thermomechanical processing, which was performed to obtain multiphase bainite-based alloys with some fractions of retained austenite. The rough rolling was composed of four passes with total true strain of 0.99 and finishing rolling temperature of 850 °C, whereas thermomechanical processing contained five passes and total true strain of 0.95 at a finishing rolling temperature of 750 °C. During the process, the force parameters were recorded, which showed that the rolling forces for steels containing 3% Mn are higher compared to the 5% Mn alloys. There was no significant influence of Nb on the rolling parameters. The produced as-cast microstructures were composed of dendritic bainitic-martensitic phases. A positive effect of Nb micro-addition on a refinement of the as-cast structure was noticed. The thermomechanical processed steels showed fine multiphase microstructures with some fractions of retained austenite, the fraction of which depended on the Mn content in steel. The steels containing 3% Mn generated higher forces both during rough and thermomechanical rolling, which is related to slower recrystallization softening in these alloys compared to the steels containing 5% Mn.

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Kuziak, Roman, Zofia Kania, Valeriy Pidvysots'kyy, Hans Roelofs, Monika Pernach, and Maciej Pietrzyk. "Through Process Modelling of Rolling and Controlled Cooling of TRIP Assisted Bainitic Steel Rods and Prediction of the Retained Austenite in Products." Materials Science Forum 892 (March 2017): 23–33. http://dx.doi.org/10.4028/www.scientific.net/msf.892.23.

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Simulation of the rolling and controlled cooling sequence for bainitic steel rods was the general objective of the paper. The main focus was put on exploring possibility of prediction of the retained austenite occurrence in TRIP assisted bainitic steels. Existing discrete phase transformation models require long computing times and their application to optimization of industrial processes is limited. Therefore, a model based on the modified JMAK equation was proposed. The occurrence of the retained austenite was predicted by carbon distribution calculations in the austenite during bainite transformation. This model was implemented into the FE software for simulation of cooling of rods. The model was verified by comparison of results with the physical simulations during rolling in the pilot mill and during cooling. The first part of the paper contains thermal-mechanical-microstructural simulations of rod hot rolling process. The objective of this part was to determine temperature and grain size distribution at the rod cross section at the beginning of phase transformations. FE simulations of the cooling were performed next. Correlation between cooling parameters and the volume fraction of the retained austenite in rod was determined.

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Lee, Hak Cheol, Xiao Dan Wu, Young Min Kim, and Nack J. Kim. "Effect of Second Phase on Mechanical Properties of Bainite-Base Steels." Advanced Materials Research 15-17 (February 2006): 780–85. http://dx.doi.org/10.4028/www.scientific.net/amr.15-17.780.

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Effects of acicular ferrite and retained austenite on the mechanical properties of bainite-base steels were investigated. Various morphology and volume fraction of constituent phases have been obtained by control of hot rolling conditions and alloy compositions. It has been shown that the steels containing retained austenite have better combinations of strength and ductility than the ones with no retained austenite. However, there is no noticeable change in DBTT by the incorporation of retained austenite in the microstructure since retained austenite exists as fine particles. On the other hand, DBTT of the steels are largely affected by the presence of acicular ferrite in the microstructure. EBSD analyses of fractured Charpy specimens show that cracks are deflected within the morphological packet of acicular ferrite, indicating its role in reducing the effective grain size of the steels.

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Tian, Yu, Zhunli Tan, Ji Li, Bo Gao, Min Zhang, and Bingzhe Bai. "Low Temperature Deformation Induced Microstructure Refinement and Consequent Ultrahigh Toughness of a 20Mn2SiCrNi Bainitic Steel." Metals 10, no. 1 (December 21, 2019): 19. http://dx.doi.org/10.3390/met10010019.

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In this paper, we have studied the influence of deformation on the microstructure and mechanical properties of 20Mn2SiCrNi bainitic high strength steel processed through a hot rolling route. Simulation of different temperatures and degrees of deformation was carried out via Gleeble-1500. The study suggested that grain size is refined when the deformation is carried out at lower temperature (> Ac3). When the degree of deformation was increased from 20% to 60%, grain size and microstructure were both refined and the size of retained austenite was reduced. The tensile strength increased from 1345 MPa to 1432 MPa. The impact toughness increased from 115 J/cm2 to 210 J/cm2 at room temperature, from 63 J/cm2 to 142 J/cm2 at −40 °C. Furthermore, it was observed that the microstructure after air cooling was composed of granular bainite (GB), lath bainite (LB) and martensite/austenite (MA) island for different deformation conditions. The study reveals that the impact toughness of 20Mn2SiCrNi bainitic high strength steel can be increased by increasing the degree of deformation.

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Rana, R., S. Chen, A. Haldar, and S. Das. "Mechanical Properties of a Bainitic Steel Producible by Hot Rolling." Archives of Metallurgy and Materials 62, no. 4 (December 1, 2017): 2331–38. http://dx.doi.org/10.1515/amm-2017-0342.

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AbstractA carbide-free bainitic microstructure is suitable for achieving a combination of ultra high strength and high ductility. In this work, a steel containing nominally 0.34C-2Mn-1.5Si-1Cr (wt.%) was produced via industrial hot rolling and laboratory heat treatments. The austenitization (900°C, 30 min.) and austempering (300-400°C, 3 h) treatments were done in salt bath furnaces. The austempering treatments were designed to approximately simulate the coiling step, following hot rolling and run-out-table cooling, when the bainitic transformation would take place and certain amount of austenite would be stabilized due to suppression of carbide precipitation. The microstructures and various mechanical properties (tensile properties, bendability, flangeability, and room and subzero temperature impact toughness) relevant for applications were characterized. It was found that the mechanical properties were highly dependent on the stability of the retained austenite, presence of martensite in the microstructure and the size of the microstructural constituents. The highest amount of retained austenite (~ 27 wt.%) was obtained in the sample austempered at 375°C but due to lower austenite stability and coarser overall microstructure, the sample exhibited lower tensile ductility, bendability, flangeability and impact toughness. The sample austempered at 400°C also showed poor properties due to the presence of initial martensite and coarse microstructure. The best combination of mechanical properties was achieved for the samples austempered at 325-350°C with a lower amount of retained austenite but with the highest mechanical stability.

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10

Kliber, Jiří, Bohuslav Mašek, Ondrej Zacek, and H. Staňková. "Transformation Induced Plasticity (TRIP) Effect Used in Forming of Carbon CMnSi Steel." Materials Science Forum 500-501 (November 2005): 461–70. http://dx.doi.org/10.4028/www.scientific.net/msf.500-501.461.

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Transformation induced plasticity (TRIP) steel combines high strength and high ductility that makes it particularly suitable for forming. Martensite within a ferrite matrix is usually obtained either by continuous casting of slabs followed by hot rolling (which is the fastest method, hence the most economical one, producing, however, relatively thick products) or by the continuous casting of slabs followed by hot rolling, cold rolling and annealing (the method used for thin products). High cooling rates, low coiling temperatures and low reduction during hot deformation were generally found to suppress the formation of polygonal ferrite and promote the presence of retained austenite. This paper focuses on development and modifications of two CMnSi-based TRIP steels with 0,23 % C;1,4 % Mn; 1,9 % Si; ( 0,08 % Nb) by means of laboratory thermomechanical processing. Description of experimental devices for the analysis of transformation plasticity under tensioncompression loading is given. Experiments were carried out on the simulator for thermaldeformation cycles SMITWELD and TANDEM was used for thermomechanical processing on the laboratory rolling mill. The maximum volume fraction of retained austenite and the resulting optimum combination of tensile strength and ductility were achieved in testing heats. Special attention was paid to volume fraction changes of single phases and to changes in morphology of phases. The results suggest that rather short isothermal bainite transformation times are sufficient to obtain TRIP microstructure. The influence of parameters of thermomechanical processing such as the amount of strain, forming temperature and austenitization time and temperature on microstructures of TRIP steels were evaluated.

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Janakiram, S., J. Prakash Gautam, A. Miroux, J. Moerman, and Leo Kestens. "Microstructure and Texture Control in Cold Rolled High Strength Steels." Diffusion Foundations 22 (May 2019): 84–93. http://dx.doi.org/10.4028/www.scientific.net/df.22.84.

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Formability had been important property of metals which is attributed to the texture development during thermomechanical processing particularly during hot rolling and cold rolling. In the present paper, the high strength steels with different carbon and manganese composition have been hot rolled above and below of austenite recrystallization temperature and followed by fast cooling up to different coiling temperature to get hot bands with different texture and two phase microstructure consisting ferrite with pearlite, bainite and martensite. Subsequently, these hot bands were cold rolled with 80 percent under plain strain condition. The microstructure of cold rolled sheets samples were analyzed using scanning electron microscope and showed the cold rolled microstructure with strong pancaked of two phase which was carried from the hot rolling. Cold rolled texture in ferrite pearlite microstructure is completely replaced by new texture components from hot rolled condition without the effect of Tnr. Hot rolled texture was retained in ferrite-bainite and martensite microstructure with the effect of Tnr. Increase in alloy chemistry weakens the texture intensity in ferrite pearlite/bainite microstructure. Whereas increase in alloy chemistry strengthens the texture intensity in ferrite martensite microstructure.

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12

Li, Zhuang, Di Wu, Wei Lv, Shao Pu Kang, and Zhen Zheng. "The Effects of Thermomechanical Processing on the Microstructure and Mechanical Properties of Ultra-High Strength Dual Phase Steel." Advanced Materials Research 631-632 (January 2013): 666–69. http://dx.doi.org/10.4028/www.scientific.net/amr.631-632.666.

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In this paper, ultra-high strength dual phase steel was investigated. Thermomechanical processing was conducted by using a laboratory hot rolling mill. The results have shown that the main transformation products at three different kinds of thermomechanical processing were ferrite, bainite, and small amounts of martensite. Laminar cooling led to ferrite grain refinement. The mechanical properties of specimen 1 which was controlled cooling after a relative lower temperature rolling are much higher than that of specimen 2. The presence of martensite islands and precipitates contributed to the enhancement of strength of the present steel. And the presence of retained austenite resulted in higher toughness. As a result, these specimens exhibited satisfactory mechanical properties.

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Olina, Anna, Miroslav Píška, Martin Petrenec, Charles Hervoches, Přemysl Beran, Jiří Pechoušek, and Petr Král. "Assessment of Retained Austenite in Fine Grained Inductive Heat Treated Spring Steel." Materials 12, no. 24 (December 5, 2019): 4063. http://dx.doi.org/10.3390/ma12244063.

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Advanced thermomechanical hot rolling is becoming a widely used technology for the production of fine-grained spring steel. Different rapid phase transformations during the inductive heat treatment of such steel causes the inhomogeneous mixture of martensitic, bainitic, and austenitic phases that affects the service properties of the steel. An important task is to assess the amount of retained austenite and its distribution over the cross-section of the inductive quenched and tempered wire in order to evaluate the mechanical properties of the material. Three different analytical methods were used for the comparative quantitative assessment of the amount of retained austenite in both the core and rim areas of the sample cross-section: neutron diffraction—for the bulk of the material, Mössbauer spectroscopy—for measurement in a surface layer, and the metallographic investigations carried by the EBSD. The methods confirmed the excessive amount of retained austenite in the core area that could negatively affect the plasticity of the material.

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Hou, Xiao Ying, Yun Bo Xu, and Di Wu. "Microstructure and Mechanical Properties of High Strength Hot-Rolled TRIP Steel Containing Vanadium." Advanced Materials Research 160-162 (November 2010): 324–29. http://dx.doi.org/10.4028/www.scientific.net/amr.160-162.324.

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Laboratory hot rolling experiments on a low-carbon TRIP steel containing vanadium have been carried out to study the microstructure characteristics and mechanical properties. The results showed that the multiphase microstructure with ferrite, granular bainite and retained austenite could be obtained if the finish rolling initial temperature was properly decreased and the finishing temperature was controlled in the range of Ae3~ Ar3, and the tensile strength achieved 930 MPa or above. The average ferrite grain size was about 4.5 μm in this experiment, the vanadium nitrides and vanadium carbides precipitated dispersedly within ferritic grains or at grain boundaries, and the higher dislocation density existed in ferrite matrix. EBSD analyses revealed that the high angle boundaries accounted for a large proportion and the misorientation angles were within the interval between 29° and 60° mostly. When the finishing temperature was 800°C and the final air cooling temperature was 630°C, the steel had excellent mechanical properties, which was characterized by combination of high strength(about 930MPa), high elongation(21.7%), low yield/strength ratio(0.49) and as well as high work-hardening exponent(0.23).

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Tan, Xiao Dong, Yun Bo Xu, Xiao Long Yang, Zhi Ping Hu, Fei Peng, Xiao Wei Ju, Yong Mei Yu, and Di Wu. "Microstructure and Tensile Deformation Behavior of a Hot-Rolled Directly Quenched and Dynamically Partitioned Steel Containing Proeutectoid Ferrite." Materials Science Forum 817 (April 2015): 246–51. http://dx.doi.org/10.4028/www.scientific.net/msf.817.246.

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Hot-rolling direct quenching and dynamical partitioning (HDQ&DP) processes were applied to a low-carbon steel containing silicon and manganese based on thermo-mechanical control process (TMCP) technology and ultra-fast cooling (UFC) technology. The microstructures and phase compositions were characterized and analyzed using SEM, EBSD, TEM and XRD. The mechanical properties and tensile deformation behaviors were investigated by means of uniaxial tensile test. The microstructures and tensile deformation behaviors of both HDQ&DP steel with and without proeutectoid ferrite were comprehensively expounded by comparing with each other. Results show that the amount of retained austenite in the HDQ&DP steel with proeutectoid ferrite can reach up to 17.3%, which is higher than that in the HDQ&DP steel without proeutectoid ferrite (15.7%). The HDQ&DP steel without proeutectoid ferrite possesses extremely high ultimate tensile strength (UTS) up to 1700 MPa with yield ratio about 0.73 and elongation about 11.5%. The introduction of proeutectoid ferrite can result in a moderate decrease of UTS to 1240-1400 MPa, a drastic decrease of yield ratio to 0.51-0.69 and a certain increase of elongation to 13.0-13.7%. The existence of the proeutectoid ferrite can partly enhance the work hardening ability of the steel and may improve its formability. It is concluded that the HDQ&DP steel with relatively large amount of proeutectoid ferrite and certain amount of bainite has extensive application prospects.

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Korpała, Grzegorz, Frank Hisker, Brigitte Hammer, Thomas Heller, Rudolf Kawalla, and Ulrich Prahl. "The Influence of Hot‐Rolling Conditions on the Content and Morphology of Retained Austenite in Ultra‐High Strength Bainitic Steel and Its Mechanical Properties." steel research international 90, no. 6 (March 7, 2019): 1800386. http://dx.doi.org/10.1002/srin.201800386.

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Zhao, Yina, Yinli Chen, He Wei, Jiquan Sun, and Wei Yu. "The Role of Elements Partition and Austenite Grain Size in the Ferrite-Bainite Banding Formation during Hot Rolling." Materials 14, no. 9 (May 1, 2021): 2356. http://dx.doi.org/10.3390/ma14092356.

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The partitioning and diffusion of solute elements in hot rolling and the effect of the partitioning and diffusion on the ferrite-bainite banding formation after hot rolling in the 20CrMnTi steel were experimentally examined by EPMA (electron probe microanalysis) technology and simulated by DICTRTA and MATLAB software. The austenite grain size related to the hot rolling process and the effect of austenite grain size on the ferrite-bainite banding formation were studied. The results show that experimental steel without banding has the most uniform hardness distribution, which is taken from the edge of the cast slab and 1/4 diameter position of the cast slab, heating at 1100 °C for 2 h and above 1200 °C for 2–4 h during the hot rolling, respectively. Cr, Mn, and Si diffuse and inhomogeneously concentrate in austenite during hot rolling, while C homogeneously concentrates in austenite. After the same hot rolling process, ΔAe3 increases and ferrite-bainite banding intensifies with increasing initial segregation width and segregation coefficient K of solute elements. Under the same initial segregation of solute elements, ΔAe3 drops and ferrite-bainite banding reduces with increasing heating temperature and extension heating time. When ΔAe3 drops below 14 °C, ferrite-bainite banding even disappears. What is more, the austenite grain size increases with increasing heating temperature and extension heating time. When the austenite grain size is above 21 μm, the experimental steel will not appear to have a banded structure after hot rolling.

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Grajcar, Adam, and Mateusz Morawiec. "Microstructure-Property Relationships in Medium-Mn Steels with Metastable Retained Austenite." Materials Science Forum 879 (November 2016): 619–24. http://dx.doi.org/10.4028/www.scientific.net/msf.879.619.

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The study addresses relationships between the microstructure and mechanical properties of thermomechanically processed carbide-free bainitic steels containing 3% and 5% Mn. A simulated thermomechanical processing using Gleeble equipment and thermomechanical hot strip rolling were applied to produce fine-grained mixtures of blocky-type and interlath metastable retained austenite embeded between bainitic ferrite laths. To monitor the transformation behaviour of retained austenite into strain-induced martensite interrupted tensile tests were applied. The identification of morphological features of retained austenite and strain-induced martensite was carried out using scanning electron microscopy (SEM) equipped with EBSD (Electron Backscatter Diffraction). The amount of retained austenite was determined by the EBSD technique. It was found that manganese content strongly affects mechanical stability of retained austenite resulting in a different degree of TRIP effect in the investigated alloys and subsequent mechanical properties of produced sheets.

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Yin, Yun Yang, Fang Fang, Wei Chen, and Yong Tao Fu. "Effect of Thermomechanical Parameters on the Microstructure and Retained Austenite Characteristics in a Hot-Rolled TRIP Steel." Advanced Materials Research 295-297 (July 2011): 1294–99. http://dx.doi.org/10.4028/www.scientific.net/amr.295-297.1294.

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The influence of thermomechanical parameters on the microstructure and retained austenite characteristics in a hot rolled Al-Si-Mn transformation induced plasticity (TRIP) steel based on dynamic transformation of undercooled austenite was investigated, in an effort to produce a desired microstructure and better control retained content. The results show that strain rate had a minor effect on the microstructure, but the volume fraction of retained austenite decreased with increasing strain rate. Decreasing coiling temperature caused a decrease in volume fraction of retained austenite and decrease in the size of bainitic ferrite platelets. Increasing the isothermal holding time during bainite treatment, the volume fraction of retained austenite first gradually increased then decreased. Moreover, The deformation of undercooled austenite not only can influenc the transformation of bainite, but also can refine the grain size of bainite, increase the chemical and mechanical stabilization of retained austenite.

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El-Shenawy, Eman, Hoda Refaiy, and Hoda Nasr El-Din. "Thermal Stability of Retained Austenite in Advanced TRIP Steel with Bainitic Ferrite Matrix for Automotive Industries." Materials Science Forum 1016 (January 2021): 429–34. http://dx.doi.org/10.4028/www.scientific.net/msf.1016.429.

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Multiphase steels consisting of retained austenite and martensite/bainite microstructures such as TRIP, low-temperature-bainite, and Q&P steels are attractive candidates for the new-generation of AHSS. These steels exhibit a remarkable combination of strength and toughness which is essential to meet the objective of weight reduction of engineering-components, while maintaining the compromise of tough-safety requirements. Such good mechanical properties are due to the enhanced work hardening rate caused by austenite-to-martensite transformation during deformation and the strengthening contribution of martensite/bainite. The retained austenite can thermally decompose into more thermodynamically stable phases as a consequence of temperature changes, which is referred to as the thermal stability of retained austenite. TRIP-aided steel is an effective candidate for automotive parts because of safety and weight reduction requirements. The strength–ductility balance of high strength steel sheets can be remarkably improved by using transformation induced plasticity behavior of retained austenite. In manufacturing hot rolled TRIP-aided sheet steels, austenite transforms into bainite during the coiling process. Because black hot coils cool slowly after the coiling process, they are exposed at about 350–450°C for a few hours or days. Therefore, the metastable residual austenite can be decomposed into other phases. This decomposition of residual austenite can produce serious deteriorate of mechanical properties in hot rolled TRIP-aided sheet steels. The present work identified the decomposition behavior and study the thermal stability of retained austenite in the TRIP-aided steel with bainitic/ferrite matrix depending on coiling temperatures and holding times by means of DSC and XRD analysis.

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Emadoddin, E., A. Akbarzadeh, R. Petrov, L. Kestens, and H. Pirgazi. "Influence of cold-rolling reduction on retained austenite texture in cold-rolled and intercritically annealed TRIP-assisted steel." Journal of Applied Crystallography 44, no. 6 (November 12, 2011): 1190–97. http://dx.doi.org/10.1107/s0021889811041069.

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The newly developed multiphase transformation-induced plasticity (TRIP) steels are of interest for industrial applications because of their excellent combination of high strength and ductility. Their performance can be successfully controlled by designing an optimum balance in the volume fractions of ferrite, bainite and retained austenite. The characteristics of the retained austenite are considered to be the main key to achieving the desired final properties. Against this background, the effects of retained austenite characteristics, such as volume fraction, carbon concentration, size and shape, on the behaviour of TRIP steels have been studied. The crystallographic orientation of the retained austenite was measured by electron backscattered diffraction (EBSD). The effect of initial cold-rolling reduction on the microtexture development of the retained austenite was studied on an aluminium-containing TRIP steel. The results show that, by increasing the cold-rolling reduction before the final austempering, the main components of the face-centred cubic phase,i.e.copper, brass and Goss, dominate the texture of the retained austenite. In contrast, the copper and Goss components of the retained austenite are absent in the texture of lightly deformed sheets. The features of the preferred orientation of the retained austenite are discussed and explained in terms of the annealing texture of the recrystallized ferrite and bainite.

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Kobayashi, Junya, Hiroto Sawayama, Naoya Kakefuda, Goroh Itoh, Shigeru Kuraoto, and Tomohiko Hojo. "Microstructure and Tensile Properties of TRIP-Aided Steel Sheet Subjected to Hot-Rolling and Austempering." Materials Science Forum 1016 (January 2021): 732–37. http://dx.doi.org/10.4028/www.scientific.net/msf.1016.732.

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Various high strength steel sheets for weight reduction and safety improvement of vehicles have been developed. TRIP-aided steel with transformation induced plasticity of the retained austenite has high strength and ductility. Conventional TRIP-aided steels are subjected to austempering process after austenitizing. Generally, elongation and formability of TRIP-aided steel are improved by finely dispersed retained austenite in BCC phase matrix. The finely dispersed retained austenite and grain refinement of TRIP-aided steel can be achieved by hot rolling with heat treatment. Therefore, the improvement of mechanical properties of TRIP-aided steel is expected from the manufacturing process with hot rolling and then isothermal transformation process. In this study, thermomechanical heat treatment is performed by combining hot rolling and isothermal holding as the manufacturing process of TRIP-aided steel sheets. The complex phase matrix is obtained by hot rolling and then isothermal holding. Although the hardness of the hot rolled and isothermal held TRIP-aided steel is decreased, the volume fraction of retained austenite is increased.

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Godet, S., J. C. Glez, Y. He, J. J. Jonas, and P. J. Jacques. "Grain-scale characterization of transformation textures." Journal of Applied Crystallography 37, no. 3 (May 11, 2004): 417–25. http://dx.doi.org/10.1107/s0021889804007320.

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Orientation relationships during the austenite-to-ferrite (γ-to-α) phase transformation were investigated using electron back-scattered diffraction (EBSD) on a bainitic steel containing retained austenite. The steel was hot rolled within the austenite phase field, but below the `no-recrystallization' temperature, to two different strains. The observed orientation relationships between the bainite and retained austenite are expressed in Rodrigues–Frank space. The exact Kurdjumov–Sachs relation was never found. The local spread of orientation in the parent austenite (owing to deformation) is seen to be inherited by the bainite. This is attributed to the displacive mode of transformation to bainite. The influence of austenite prior deformation on the occurrence of variant selection was also studied. It is shown that a critical strain is necessary in order to observe a significant amount of variant selection.

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Park, Seong Jun, Dong Woo Suh, Chang Seok Oh, and Sung Joon Kim. "Crystallographic Texture in Low Alloy TRIP Steel." Materials Science Forum 558-559 (October 2007): 1423–28. http://dx.doi.org/10.4028/www.scientific.net/msf.558-559.1423.

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Low alloy transformation induced plasticity (TRIP) steels have a complex microstructure consisting of ferrite, bainite and retained austenite. Their excellent mechanical properties are ascribed to the martensitic transformation of retained austenite during plastic deformation. In the present contribution, the crystallographic texture of fcc and bcc phases in TRIP steels was measured by means of orientation mapping. The austenite texture was close to a typical rolling texture of fcc metals. For bcc phase, the effects of orientation and grain size on the distribution of pattern quality were investigated. The texture of transformation product phase was separated by grain size. The transformation texture showed stronger α fiber including {113}<110> component than the recrystallization texture. It showed a good agreement with a transformation texture predicted by Kurdjmov-Sachs (KS) relationship without any variant selection.

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25

Dembiczak, Tomasz, and Marcin Knapiński. "Shaping Microstructure and Mechanical Properties of High-Carbon Bainitic Steel in Hot-Rolling and Long-Term Low-Temperature Annealing." Materials 14, no. 2 (January 14, 2021): 384. http://dx.doi.org/10.3390/ma14020384.

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Based on the research results, coefficients in constitutive equations, describing the kinetics of dynamic, meta-dynamic, and static recrystallization in high-carbon bainitic steel during hot deformation were determined. The developed mathematical model takes into account the dependence of the changing kinetics in the structural size of the preliminary austenite grains, the value of strain, strain rate, temperature, and time. Physical simulations were carried out on rectangular specimens. Compression tests with a flat state of deformation were carried out using a Gleeble 3800. Based on dilatometric studies, coefficients were determined in constitutive equations, describing the grain growth of the austenite of high-carbon bainite steel under isothermal annealing conditions. The aim of the research was to verify the developed mathematical models in semi-industrial conditions during the hot-rolling process of high-carbon bainite steel. Analysis of the semi-industrial studies of the hot-rolling and long-term annealing process confirmed the correctness of the predicted mathematical models describing the microstructure evolution.

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26

Chen, Xi, Fuming Wang, Changrong Li, and Jing Zhang. "Dynamic continuous cooling transformation, microstructure and mechanical properties of medium-carbon carbide-free bainitic steel." High Temperature Materials and Processes 39, no. 1 (July 18, 2020): 304–16. http://dx.doi.org/10.1515/htmp-2020-0051.

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AbstractThe effects of the cooling rate after hot deformation on phase transformation, the microstructure of the designed nonquenched and tempered medium-carbon carbide-free bainitic steel have been investigated during the dynamic continuous cooling process. The results show that with the increase of the cooling rate, the morphology of the carbide-free bainite of the experimental steel evolves from granular bainite to lath bainite. Meanwhile, the hardness increases, and the amount of the retained austenite decreases with the increase of the cooling rate. Besides, the morphology evolution of the retained austenite from block to film is revealed by EBSD. Moreover, 0.5°C/s is considered to be the favorable cooling rate to obtain the best strength–toughness matching. Furthermore, the semi-industrial experimental results proved that the tensile strength, yield strength and Charpy impact energy were 1,298 MPa, 847 MPa and 38 J, respectively.

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27

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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28

Wei, Zhan Shan, Zhuang Li, Wei Lv, and Zhen Yao Shao. "The Influence of the Substitution of Si by Al on the Properties of Hot Rolled C-Mn-Si TRIP Steel." Materials Science Forum 896 (March 2017): 198–201. http://dx.doi.org/10.4028/www.scientific.net/msf.896.198.

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The influence of the substitution of Si by Al on the properties of hot rolled C-Mn-Si TRIP steel was investigated by TMCP. The results have shown that the microstructures of the present steels consist of polygonal ferrite, granular bainite and retained austenite. The Al substitution of Si in a conventional C-Mn-Si TRIP steel leads to excellent mechanical properties (UTS>714MPa, A50>31%). TMCP led to the stability of the remaining austenite and a satisfactory TRIP effect. Excellent mechanical properties were obtained through tmcp for the hot rolled TRIP steel.

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29

Dutta, R. K., R. M. Huizenga, M. Amirthalingam, H. Gao, A. King, M. J. M. Hermans, and I. M. Richardson. "In Situ Synchrotron Diffraction Studies on Hot Deformation of Austenite in a High Strength Quenched and Tempered Structural Steel." Advanced Materials Research 922 (May 2014): 126–31. http://dx.doi.org/10.4028/www.scientific.net/amr.922.126.

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The effect of plastic deformation of austenite at elevated temperatures on the kinetics ofphase transformations during continuous cooling was studied in a high strength quenched and tem-pered structural steel S690QL1 (Fe-0.16C-0.2Si-0.87Mn-0.33Cr-0.21Mo (wt.%)) by means of in-situsynchrotron diffraction. The steel was heated to 900 C (above Ac3) in the austenite region and elon-gated by 6% followed by quenching to room temperature. Time-temperature-load resolved 2D syn-chrotron diffraction patterns were recorded and used to calculate the local d-spacings between latticeplanes. The plane specific diffraction elastic constants of austenite at 900 C in the steel were deter-mined from the local d-spacings. The effect of the deformation of austenite on the phase transforma-tion kinetics was studied. The evolution of lattice parameters and the phase fraction of the bcc phasesduring the quenching process were calculated.The calculated plane specific elastic constants of austenite at 900 C varied between 32 GPa to140 GPa for the different fhklg reflections of austenite. The deformation of austenite at 900 C re-sulted in the formation of a mixture of 38 % bainite, 59 % martensite and 3 % retained austenite afterquenching to room temperature. Without hot deformation, austenite transformed to 9 % bainite and88 % martensite with 3 % retained austenite. The presence of the bainitic and the martensitic phaseswas observed fromthe change in the slopes of the lattice parameters of the bcc phase during quenchingand confirmed by microscopy.

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30

Morawiec, Mateusz, Adam Grajcar, Władysław Zalecki, Carlos Garcia-Mateo, and Marek Opiela. "Dilatometric Study of Phase Transformations in 5 Mn Steel Subjected to Different Heat Treatments." Materials 13, no. 4 (February 21, 2020): 958. http://dx.doi.org/10.3390/ma13040958.

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The work presents results of phase transformation kinetics of hot-rolled 5% Mn steel subjected to different heat treatments. Three different schedules were introduced: isothermal holding in a bainite region, coiling simulation and intercritical annealing. The evolution of microstructure components was investigated using dilatometric and metallographic analyses. According to obtained results, the medium-Mn steel exhibits high resistance for γ/α transformation during the bainite transformation and coiling simulation (upon cooling from the austenite region). During 5 h isothermal holding, no bainite and/or ferrite formation was detected. This results in the formation of martensite upon cooling to room temperature. Differently, when the steel was subjected to the intercritical annealing at 720 and 700 °C (upon heating from room temperature), a final microstructure consisted of ferrite, martensite and retained austenite. At 700 °C, no fresh martensite formation was detected upon cooling to room temperature. This means that the austenite was enriched in carbon during the intercritical annealing step enough to keep its thermal stability.

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31

Yin, Yun Yang, Fang Fang, and Zhi Jin Fan. "Microstructure and Mechanical Properties of Hot Rolled TRIP Steel Based on Dynamic Transformation of Undercooled Austenite." Advanced Materials Research 152-153 (October 2010): 1038–43. http://dx.doi.org/10.4028/www.scientific.net/amr.152-153.1038.

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The microstructure characteristics and tensile properties in a 0.2C-1.5Mn-1.0Al-0.50Si, high strength hot rolled TRIP steel obtained by a new processing based on dynamic transformation of undercooled austenite(DTUA) were investigated. The results show that the main feature of the new technology is that the ferrite was produced by the applied strain during DTUA. Characterization by means of optical and scanning electron microscopy, transmission electron microscopy and X-ray diffraction has shown that the microstructure of the investigated steel contained a ferrite matrix with fine grain size, bainite with small bainitic packets, and high volume fraction of retained austenite with a large number of granular retained austenite. Tensile testing indicates the steels produced by this processing have higher strength (790MPa) and total elongation (35%) as well as low yield ratio..

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32

Schindler, I., R. Kawulok, Y. Seillier, P. Kawulok, P. Opěla, S. Rusz, V. Vodárek, and R. Turoň. "Continuous cooling transformation diagrams of HSLA steel for seamless tubes production." Journal of Mining and Metallurgy, Section B: Metallurgy 55, no. 3 (2019): 413–26. http://dx.doi.org/10.2298/jmmb181217031s.

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The CCT and two DCCT diagrams were constructed for the HSLA steel containing Cr, V, Nb, and N microadditions, taking into account industrial processing parameters of this material in a seamless tubes rolling mill. The typical finish hot rolling temperature of 1173 K was used for the construction of the standard CCT diagram and the effect of previous austenite deformation at this temperature was evaluated in the DCCT diagram. Another DCCT diagram was developed after heating at 1553 K, followed by plastic deformation at 1173 K. The prior austenite grain size in the hot rolled material after heating at 1173 K was approx. 10 ?m, the heating of the as-cast material at 1553 K resulted in the prior austenite grain size over 200 ?m. The effect of the previous austenite deformation after low-temperature heating on the CCT diagram was negligible. The high-temperature heating showed a great influence on the austenite decomposition processes. The Ferrite-start temperature was significantly reduced at high cooling rates and the preferred decomposition of coarse grained austenite to acicular ferrite suppressed the bainite transformation at medium cooling rates. The developed DCCT diagrams can be used for the prediction of austenite decomposition products during the cooling of the seamless tubes from the finish rolling temperature. The CCT diagram can be utilized for the quality heat treatment of tubes.

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33

Kabanov, Alexander, Grzegorz Korpala, Rudolf Kawalla, and Sergey Ionov. "Effect of Hot Rolling and Thermal Treatment on the Microstructure Evolution of Microalloyed Bainitic Steels for Pipeline." Key Engineering Materials 746 (July 2017): 176–83. http://dx.doi.org/10.4028/www.scientific.net/kem.746.176.

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Heavy plate for pipelines, which are used in earthquake-prone areas, must have among other a good ductility. The ductility is needed to prevent cracking in the case of local plastic deformation. The bainitic steels with retained austenite or martensite meet these requirements. The aim of this investigation is the determination of the thermo-mechanical treatment parameters with which such microstructures can be generated during the heavy plate production or an additional heat treatment. Experimental modelling of the production process for heavy plate was realized on a Gleeble HDS-V40 thermo-mechanical simulator. Moreover, the microstructure evolution processes during cooling on the round out table were investigated by dilatometry. The investigations on the formation of the microstructure during following accelerated cooling and heat treatment combination were carried out. All investigations were realized with two high-strength micro-alloyed steels, one of which was additionally alloyed with molybdenum. Results revealed that the decreasing of the temperature and duration of the heat treatment as well as addition of molybdenum reduce the size of grains and promotes the nucleation of the bainitic microstructure.

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34

Kawulok, Petr, Ivo Schindler, Jaroslav Sojka, Stanislav Rusz, Rostislav Kawulok, Vladimír Šíma, Pavel Hanus, Rostislav Turoň, and Petra Turoňová. "Defects and Particles in Laboratory Hot Rolled Steel of C-Mn-Cr-Nb Type." Materials Science Forum 782 (April 2014): 221–26. http://dx.doi.org/10.4028/www.scientific.net/msf.782.221.

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Susceptibility to cracking of the as-cast C-Mn-Cr-Nb steel was studied by laboratory rolling. The variable parameters were the heating temperature (1150 - 1340 °C) as well as the rolling temperature (950 - 1150 °C). Final microstructure of the free-cooled samples was constituted by bainite, pearlite and ferrite with different morphology and various contribution. Deformation temperature below 1000 °C yielded in the incomplete recrystallization of austenite. Surface cracks originated preferentially on the austenite grains boundaries. Size of the present particles (inclusions and precipitates) varied from 101 nm to 101 μm. SEM and EDS analysis revealed that the inclusions ware mostly of the MnS type. TEM analysis confirmed that the grain boundaries were not enriched by any particles. In addition to the Fe3C particles, the discoid niobium carbide particles with approximately 40 nm diameter and 10 nm thickness were detected. These small particles were not connected by any notable pinning of dislocations.

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35

Morawiec, Mateusz, and Adam Grajcar. "Strain Rate Dependent Mechanical Stability of Retained Austenite in Hot-Rolled Medium-Mn Sheet Steels." Materials Science Forum 1016 (January 2021): 946–51. http://dx.doi.org/10.4028/www.scientific.net/msf.1016.946.

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The paper presents microstructural and mechanical results of medium manganese steel deformed under high strain rates. The rotary hammer tests at strain rates of 250, 500 and 1000 s-1 were applied. Mechanical properties under dynamic tensile loads were determined. According to the obtained results, when strain rate increased the yield point of the steel increased. An opposite trend was present regarding total elongation. In case of tensile strength, its level is similar for all analyzed deformation rates. The microstructure of the steel after the dynamic tensile test is composed of bainite, martensite and martensitic-austenitic islands. The strain-induced martensitic transformation was identified in microscopic investigations.

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36

Wu, Teng, Run Wu, Bin Liu, Wen Liang, and Deqing Ke. "Enhancing the Mechanical Properties of a Hot Rolled High-Strength Steel Produced by Ultra-Fast Cooling and Q&P Process." Metals 9, no. 9 (August 31, 2019): 958. http://dx.doi.org/10.3390/met9090958.

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The quenching and partitioning (Q&P) process of advanced high strength steels results in a significant enhancement in their strength and ductility. The development of controlled rolling and cooling technology provides an efficient tool for microstructural design in steels. This approach allows to control phase transformations in order to generate the desired microstructure in steel and, thus, to achieve the required properties. To refine grain structure in a Fe-Si-Mn-Nb steel and to generate the microstructure consisting of martensitic matrix with embedded retained austenite grains, hot rolling and pressing combined with ultrafast cooling and Q&P process is employed. The slender martensite in hot rolled Q&P steel improves the strength of test steel and the flake retained austenite improves the plasticity and work hardening ability through the Transformation Induced Plasticity (TRIP) effect.

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37

Tan, Xiao Dong, Zi Quan Liu, Yun Bo Xu, Xiao Long Yang, and Di Wu. "TRIP Effect in a Hot-Rolled Low-Carbon High Strength Complex Phase Steel." Materials Science Forum 788 (April 2014): 267–71. http://dx.doi.org/10.4028/www.scientific.net/msf.788.267.

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In the present work, a study has been made of the hot-rolling process for a transformation induced plasticity (TRIP) steel Fe-0.12C-0.5Si-1.4Mn-0.5Cr (wt%). The volume fractions of retained austenite before and after a deformation were determined by X-ray diffraction (XRD). The microstructure was characterized by optical microscope, scanning electron microscope (SEM) equipped with electron backscattered diffraction (EBSD) and transmission electron microscope (TEM). A uniaxial tension text indicated that the steel possesses ultimate tensile strength of 748 MPa with yield ratio of 0.7 and elongation of 20%. The steel with the volume fraction of retained austenite of 12.5 % exhibits significant TRIP effect.

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38

Grajcar, Adam, and Roman Kuziak. "Softening Kinetics in Nb-Microalloyed TRIP Steels with Increased Mn Content." Advanced Materials Research 314-316 (August 2011): 119–22. http://dx.doi.org/10.4028/www.scientific.net/amr.314-316.119.

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Two 5Mn-1.5Al TRIP steels with and without Nb microaddition were developed in the present study. The steels contain bainite, martensite, interlath retained austenite and martensite- austenite islands. The paper presents the results of the compression tests carried out at various temperatures using the Gleeble simulator. To analyze the kinetics of static recrystallization in these steels, a softening kinetics were determined in a double-hit compression test. It was found that the dynamic recovery is a main thermally activated process occurring during hot deformation. The Nb microalloyed steel has higher flow stresses and peak strains than the Nb-free steel. A solute drag effect of Nb results in a slower softening kinetics of Nb containing steel. The effects of Mn on the retardation of Nb(C,N) precipitation and hot deformation characteristics are also discussed.

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39

Suwanpinij, Piyada, Xiaoxiao Li, Ulrich Prahl, and Wolfgang Bleck. "Modeling Bainite Transformation and Retained Austenite in Hot Rolled TRIP Steel by Instantaneous Carbon Enrichment." steel research international 88, no. 12 (September 4, 2017): 1700122. http://dx.doi.org/10.1002/srin.201700122.

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40

da Cruz, José Alberto, Thiara Francis Mateus Rodrigues, Virgínia Dutra Costa Viana, and Dagoberto Brandão Santos. "Bainite Formation at Low Temperatures in High C-Si Steel and its Mechanical Behavior." Materials Science Forum 706-709 (January 2012): 173–80. http://dx.doi.org/10.4028/www.scientific.net/msf.706-709.173.

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A significant amout of stabilized austenite can be obtained in high carbon steel containing high amounts of manganese and silicon (1.5-2 %). At relatively low temperatures the bainite plates formed are extremely thin, making the material very strong. In this study, the influence of the thermal cycle of austempering on the mechanical behavior of a spring steel 0.56C-1.43Si-0.58Mn-0.47Cr (wt. %), with TRIP effect was investigated. The thermal cycle consisted of heating three groups of hot-rolled wire steel at austenite field of 900°C for 300 s, and quickly transferring those to a metallic bath maintained at 200, 220 or 270°C, respectively, for different heat treatment times. The samples were then tested in tension and their microstructures were examined by scanning and transmission electron microscopy. The samples treated at 220°C showed higher elongation, yield strength and tensile strength than those maintained at 200 or 270°C. The high level of strength and ductility is due to a mixture of martensite and very fine bainitic ferrite with interlath film of retained austenite. The temperature has shown a strong influence on bainite formation kinetics. The fracture behavior of the steel was also evaluated using SEM fractography.

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41

Zhou, Le Yu, Tian Hao Cui, Bo Jiang, Chao Lei Zhang, Jian Zhong He, and Ya Zheng Liu. "Effect of Mo on Transformation, Microstructure and Property of Hot-Rolled DP600 Steel." Materials Science Forum 817 (April 2015): 560–64. http://dx.doi.org/10.4028/www.scientific.net/msf.817.560.

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In according with the transformation rules of C-Si-Mn-Cr and C-Si-Mn-Cr-Mo tested steels, rolling experiment was carried out in lab. to analyze the effect of Mo on transformation, microstructure and property of high strength hot rolled dual phase steels. The results showed that the addition of element Mo decreased start temperature of ferrite transformation and restrains pearlite transformation. There was a metastable austenite zone between ferrite and bainite transformation zone of No.2 steel with 0.35% of Mo. After controlled rolling and step cooling process, dual phase microstructures in which fine martensite islands dispersed in soft ferrite matrix were obtained by two kinds of tested steel. With the addition of Mo, yield strength and tensile strength increased by 80MPa and 60MPa respectively, meanwhile, elongation increased slightly.

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42

Zhou, Guanghua, Wenting Wei, and Qinglong Liu. "Effect of Hot Rolling on Microstructural Evolution and Wear Behaviors of G20CrNi2MoA Bearing Steel." Metals 11, no. 6 (June 13, 2021): 957. http://dx.doi.org/10.3390/met11060957.

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Hot rolling can improve the mechanical properties after heat treatment by improving the microstructure. The effect of hot rolling (HR) deformation on the microstructural transformation of G20CrNi2MoA bearing steel in the subsequent CQT (carburizing-quenching and tempering) and RQT (reheating-quenching and tempering) processes was studied. The results indicate that the austenite grain size decreased by 20% after 45% hot rolling reduction, and the number of large-angle grain boundaries increased due to the recovery and recrystallization induced by hot deformation. The refinement effect of hot deformation on austenite grains was retained after dual austenitizing, and the large-angle grain boundaries and massive dislocation in the grains caused by hot deformation promoted the diffusion of carbon atoms during carburization, resulting in a higher surface carbon concentration. The refined grains and higher carbon concentration affected the volume fraction and size of undissolved carbides in RQT specimens. When the initial hot rolling reduction reached 45%, the average particle size of carbides decreased by 40%, and the area volume fraction increased by 37%. The Vickers hardness increased, but the friction coefficient and wear rate were significantly reduced with the increase in the initial hot rolling reduction. The main reasons for the improved wear resistance were fine grains, superior carbide distribution and high hardness.

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43

Pohjonen, Aarne, Mahesh Somani, Juha Pyykkönen, Joni Paananen, and David Porter. "The Onset of the Austenite to Bainite Phase Transformation for Different Cooling Paths and Steel Compositions." Key Engineering Materials 716 (October 2016): 368–75. http://dx.doi.org/10.4028/www.scientific.net/kem.716.368.

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We present calculations of austenite to bainite phase transformation start for different cooling paths and for different steel compositions and a method to estimate the cooling water required to cool a steel strip to desired temperatures during water cooling line after industrial hot rolling. We also quantitatively compare how different alloying elements affect the phase transformation activation energy and the time required for the transformation to start and proceed to the extent that it can be detected with dilatometer. This analysis can be used for aid when designing suitable cooling paths for hot rolled steel products. The calculations of the activation energy can be used as input in more detailed microstructure models.

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44

Graux, Alexis, Sophie Cazottes, David De Castro, David San-Martín, Carlos Capdevila, Jose Maria Cabrera, Sílvia Molas, et al. "Design and Development of Complex Phase Steels with Improved Combination of Strength and Stretch-Flangeability." Metals 10, no. 6 (June 20, 2020): 824. http://dx.doi.org/10.3390/met10060824.

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This study presents the design and development of a hot-rolled bainitic steel, presenting a good combination of strength and stretch-flangeability, for automotive applications. Ti, Nb, and Mo were added in the steel composition in order to control austenite grain sizes, enhance precipitation hardening, and promote the formation of bainite. This study focuses on the effect of process parameters on final microstructures and mechanical properties. These parameters are the finishing rolling temperature, which conditions the austenite microstructure before its decomposition, and the coiling temperature, which conditions the nature and morphology of the ferritic phases transformed. A preliminary study allowed to determine the austenite grain growth behavior during reheating, the recrystallization kinetics, and the continuous cooling transformation curves of the studied steel. Then, a first set of parameters was tested at a semi-industrial scale, which confirmed that the best elongation properties were obtained for homogeneous bainitic lath/granular microstructures, that can be produced by choosing a coiling temperature of 500 ∘ C . When choosing those parameters for the final industrial trial, the microstructure obtained consisted of a homogeneous lath/granular bainite mixture that presented a Ultimate Tensile Strength of 830 MPa and a Hole Expansion Ratio exceeding 70%.

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45

Al Jabr, Haytham M., John G. Speer, David K. Matlock, Peng Zhang, and Sang Hyun Cho. "Anisotropy of Mechanical Properties of API-X70 Spiral Welded Pipe Steels." Materials Science Forum 753 (March 2013): 538–41. http://dx.doi.org/10.4028/www.scientific.net/msf.753.538.

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The effects of microstructure and texture on the toughness anisotropy of two API-X70 pipeline steels were investigated. One steel contained no nickel (0Ni) and the other contained 0.3 wt pct nickel (0.3Ni). Charpy V-notch impact testing was conducted on plate samples for both steels in three directions: longitudinal (L), transverse (T), and diagonal (D) with respect to the rolling direction. The microstructures of both steels were mixed and consisted of acicular ferrite, granular bainite, and small amounts of polygonal ferrite, with martensite-austenite and retained austenite islands as secondary phases. The ductile to brittle transition temperatures (DBTT) for the Charpy impact test were higher in the D direction for both plates, with a pronounced increase in the 0Ni steel. The anisotropy in toughness was mainly attributed to the crystallographic texture.

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Yang, Wang Yue, Long Fei Li, Yun Yang Yin, Zu Qing Sun, and Xi Tao Wang. "Hot-Rolled TRIP Steels Based on Dynamic Transformation of Undercooled Austenite." Materials Science Forum 654-656 (June 2010): 250–53. http://dx.doi.org/10.4028/www.scientific.net/msf.654-656.250.

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A novel thermomechanical process to manufacture hot-rolled transformation-induced plasticity (TRIP) steels was developed based on dynamic transformation of undercooled austenite (DTUA). Between DTUA and the isothermal bainitic treatment, only one-step controlled-cooling was required. The microstructure evolution of hot-rolled C-Mn-Si and C-Mn-Al-Si TRIP steels based on DTUA was investigated by hot uniaxial compression tests using a Gleeble1500 simulation test machine. The results indicated that during DTUA, the kinetics of ferrite formation was fast, the volume fraction of ferrite formed was determined by applied strain. In comparison with the process based on static transformation of austenite, a more uniform multiphase microstructure with fine ferrite grains was formed, the bainite packets were small and had relatively random orientations, the retained austenite distributed uniformly and had relatively high volume fraction. Hot-rolled TRIP steels based on DTUA demonstrated better mechanical properties, especially for C-Mn-Al-Si TRIP steel.

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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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Xu, Yun Bo, Tian Yong Deng, Yong Mei Yu, Xiao Ying Hou, Xiang Hua Liu, and Guo Dong Wang. "Modeling and Optimization of Cross-Sectional Microstructure Distribution during Hot Rolling of HSLA Steel Plates." Materials Science Forum 638-642 (January 2010): 2736–42. http://dx.doi.org/10.4028/www.scientific.net/msf.638-642.2736.

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The metallurgical equations have been implemented into the finite difference model to predict the microstructure evolution at different locations in the plate cross-section. Recrystallization kinetics and grain size distributions instead of average grain size values were computed for different rolling schedules. For 20mm plate, the austenite grain sizes at the surface are smaller than at the center, with the exception of the conner where there are the largest grain sizes in throughout cross-section, and the smallest grain sizes can be found near the end of the horizontal central line. The fine austenite grain size and relatively high retained strain could be obtained by modifying rolling practice, such as changing the temperature and thickness at the entrance of finishing rolling and adopting intermediate water cooling. The ferrite grain size and its distribution have a good agreement with the measurements.

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Miettunen, Ilkka Herman, Sumit Ghosh, Mahesh Chandra Somani, Sakari Pallaspuro, David Porter, and Jukka Kömi. "Effect of Silicon Content on the Decomposition of Austenite in 0.4C Steel during Quenching and Partitioning Treatment." Materials Science Forum 1016 (January 2021): 1361–67. http://dx.doi.org/10.4028/www.scientific.net/msf.1016.1361.

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Although quenched and partitioned (Q&P) steels are traditionally alloyed with Si, its precise role on microstructural mechanisms occurring during the partitioning process is not thoroughly investigated. In this study, a systematic investigation has been carried out to reveal the influence of Si on austenite decomposition, phase transformation and carbide precipitation during Q&P treatment. Using a Gleeble thermomechanical simulator, three medium carbon steels with varying Si contents (0.25, 0.70 and 1.5 wt.%) were hot-rolled, reaustenitized, quenched into the Ms -Mf range, retaining about 20% austenite at the quench-stop temperature (TQ), and held for 1000 seconds above TQ in the temperature range of 200-300°C in order to better understand the mechanisms operating during partitioning. Dilatometric measurements combined with microstructural characterization using SEM-EBSD, TEM, and XRD clearly revealed the occurrence of various mechanisms. The effect of partitioning temperature/time on the hardness of the Q&P samples was correlated with the microstructural features. Steel containing low Si content (0.25%) was incapable of promoting carbon enrichment of austenite during partitioning, leading to its continuous decomposition into isothermal martensite and/or bainite without any detectable austenite retained even holding at 300°C. In comparison, 1.5% Si content promoted retention of about 19% austenite under similar Q&P conditions. Small fractions of bainite and high-carbon martensite formed during final cooling in both steels after partitioning at 200°C. Moreover, carbide precipitation was strongly retarded by high Si content.

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Zisman, A. A., N. Yu Zolotorevsky, S. N. Petrov, E. I. Khlusova, and E. A. Yashina. "Local texture analysis of structure non-uniformity in low carbon high-strength steel after direct quenching." Voprosy Materialovedeniya, no. 3(103) (November 30, 2020): 9–16. http://dx.doi.org/10.22349/1994-6716-2020-103-3-09-16.

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The direct quenching of high-strength steels after hot rolling, which enables discard of the reheating operation, is economically efficient but necessitates a careful analysis of corresponding structural features. In particular, this treatment sometimes results in extended domains of coarse bainite decreasing the fracture toughness of steel. To reveal dependence of such effects on ausforming conditions, local textures of the parent γ-phase have been reconstructed from EBSD orientation data with allowance for the inter-phase orientation relationship. According to the obtained results, the unfavorable structural non-uniformity appears in the direct quenching due to excessive work hardening of austenite at the finish rolling stage; however, the structure and properties of steel can be improved by the reheating and subsequent quenching.

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Journal articles on the topic 'Bainite, steel, hot rolling, retained austenite'

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