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Han Dong - One of the best experts on this subject based on the ideXlab platform.
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A Comparative Study on Formability of the Third-Generation Automotive Medium-Mn Steel and 22MnB5 Steel
Journal of Materials Engineering and Performance, 2018Co-Authors: Guojun Zheng, Ying Chang, Cunyu Wang, Han DongAbstract:Third-generation advanced automotive medium-Mn Steel, which can replace 22MnB5 Steel, was newly developed to improve the lightweight and crashworthiness of automobile. Studies on the formability and simulation method of medium-Mn Steel have just been initiated. In this study, finite element simulation models of square-cup deep drawing were established based on various material property experiments and validated by experiments. The effects of blank holder force (BHF), fillet radii of tools (die and punch) on the maximum drawing depth (MDD), thickness distribution of the formed products, and the microstructure before and after forming were investigated and compared with those on 22MnB5 Steel. Results show that the MDD of the two Steels decreased with increased BHF but increased with the fillet radius of punch; however, the fillet radius of die showed no significant effect on the MDD for both Steels. Compared with hot-formed 22MnB5 Steel, the martensitic transformation of the hot-formed medium-Mn Steel is rarely influenced by the process parameters; thus, it holds the complete, fine-grained, and uniform martensitic microstructure. Moreover, the medium-Mn has better formability, lower initial blank temperature, and smaller impact of BHF and fillet radius of tools on the hot-formed product. Thus, a theoretical basis for the replacement of 22MnB5 Steel by medium-Mn Steel in hot forming process is provided.
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Formability study of the third generation automotive medium-Mn Steel
2018 IEEE International Conference on Mechatronics and Automation (ICMA), 2018Co-Authors: Guojun Zheng, Ying Chang, Xiaodong Li, Cunyu Wang, Han DongAbstract:Third-generation advanced automotive medium-Mn Steel, which can replace 22MnB5 Steel, was newly developed to improve the lightweight and crashworthiness of automotive. Studies on the formability and simulation method of medium-Mn Steel have just been initiated. This study elucidated the effects of initial forming temperature (IFT) on formability, thickness distribution, macro mechanical property and micro performance of medium-Mn Steel hot-formed products. Results show that the IFT intensely affects the formability and the thickness distribution of the deep drawing zone on the medium-Mn Steel hot-formed part, and the recommended IFT range is between 400 °C and 500 °C.
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Study of thermal forming limit of medium-Mn Steel based on finite element analysis and experiments
The International Journal of Advanced Manufacturing Technology, 2017Co-Authors: Guojun Zheng, Ying Chang, Cunyu Wang, Zhiyuan Fan, Han DongAbstract:The medium-Mn Steel, which is an outstanding representative of third-generation advanced automotive Steel, is newly developed. Thus, studies on the thermal forming of this Steel have just been initiated. This study was performed primarily on the thermal formability of medium-Mn Steel. The uniaxial tensile simulation model was established in LSDYNA based on various material property experiments, and the ductile fracture critical values were obtained by simulated and experimental force–deformation curves. Results show that the medium-Mn Steel is an isotropic material, and the strain rate has no significant effect on its flow stress at elevated temperature. The predicted thermal forming limit diagram (TFLD) was achieved from the numerical simulation results and was verified by the TFLD experiments based on the Nakazima test. Results show that the formability of medium-Mn Steel increases rapidly at the beginning and then decreases gradually as the temperature increase. The theoretical optimal temperature for the formability was approximately 400 °C, and the recommended initial forming temperature is approximately 450 °C in actual industrial application of the thermal forming medium-Mn Steel by considering the influence of contact heat transfer and heat radiation.
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Comparison of the hot-stamped boron-alloyed Steel and the warm-stamped medium-Mn Steel on microstructure and mechanical properties
Materials Science and Engineering: A, 2017Co-Authors: Ying Chang, Cunyu Wang, Han DongAbstract:Abstract The application of high strength Steels (HSS) for automotive structural parts is an effective way to realize lightweight and enhance safety. Therefore, improvements in mechanical properties of HSS are needed. In the present study, the warm stamping process of the third generation automotive medium-Mn Steel was discussed, the characteristics of martensitic transformation were investigated, as well as the microstructure and mechanical properties were analyzed, compared to the popular hot-stamped 22MnB5 Steel in the automotive industry. The results are indicated as follows. Firstly, the quenching rate of the medium-Mn Steel can be selected in a wide range based on its CCT curves, which is beneficial to the control of forming process. Secondly, the influence of stamping temperature and pressure on the Ms temperature of the medium-Mn Steel is not obvious and can be neglected, which is favorable to the even distribution of martensitic microstructure and mechanical properties. Thirdly, the phenomenon of decarbonization is hardly found on the surface of the warm-stamped medium-Mn Steel, and the ultra-fine-grained microstructure is found inside the medium-Mn Steel after warm stamping. Besides, the warm-stamped medium-Mn Steel holds the better comprehensive properties, such as a lower yield ratio, higher total elongation and higher tear toughness than the hot-stamped 22MnB5 Steel. Furthermore, an actual warm-stamped B-pillar of medium-Mn Steel is stamped and ultra-fine-grained martensitic microstructure is obtained. The mechanical properties are evenly distributed. As a result, this paper proves that the warm-stamped medium-Mn Steel part can meet the requirements of lightweight and crash safety, and is promising for the industrial production of automotive structural parts.
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a novel observation on cementite formed during intercritical annealing of medium Mn Steel
Metallurgical and Materials Transactions A-physical Metallurgy and Materials Science, 2016Co-Authors: Haiwen Luo, Jianhui Liu, Han DongAbstract:A medium Mn Steel with the martensitic microstructure was rapidly heated at a high rate of 300 K/s to the intercritical temperature of 923 K (650 °C) and then isothermally hold for 5 minutes. Although cementite should dissolve above the Ae1 temperature due to the constraint of thermodynamics, it is surprising to find cementite particles after such intercritical annealing (IA), whose Mn contents and sizes are even up to 30 wt pct and 60 nm, respectively. Numerical simulations have been performed to reveal the mechanism responsible for this new observation. They indicate that a small nucleus of cementite in martensite could rapidly grow to the observed size before austenitization takes place during IA. Such a rapid growth is driven by the rapid partition of C from martensite into cementite. It is then concluded that the precipitation of cementite during the IA of martensitic Mn-alloyed Steel appears inevitable no matter how high the heating rate is. Moreover, the growth kinetics of cementite depend on the composition and size of its neighboring martensitic phase, rather than those of cementite nucleus.
Dagoberto Brandao Santos - One of the best experts on this subject based on the ideXlab platform.
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Effect of ultrafine grain structure on strain hardening of C–Mn Steel warm rolled and subjected to intercritical annealing
Materials Science and Technology, 2008Co-Authors: Dagoberto Brandao Santos, E. G. Neves, B. M. GonzalezAbstract:AbstractThe behaviour during the work hardening of low carbon–manganese (0·15%C–1·39%Mn) Steel with an ultrafine ferritic grain structure was investigated using Jaoul–Crussard analysis. This microstructure was produced through out quenching, warm rolling and intercritical annealing at 800°C. The Steel exhibited a high strain hardening exponent and tensile strength.
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formation of ultra fine ferrite microstructure in warm rolled and annealed c Mn Steel
Materials Science and Engineering A-structural Materials Properties Microstructure and Processing, 2003Co-Authors: Dagoberto Brandao Santos, Rodrigo K Bruzszek, P C M Rodrigues, Elena V PerelomaAbstract:Abstract Laboratory simulations of warm rolling followed by intercritical annealing of a low carbon 0.15%C–1.39%Mn Steel have been performed. The effects of austenitising temperature, amount of deformation and annealing time on microstructure and mechanical properties have been investigated. The results have shown that the homogeneous ultra-fine ferrite grain microstructure (∼1.1–1.2 μm average grain size) has been achieved after austenitising at 900 °C, warm rolling with 3 passes of 20% reduction each at 700 °C and annealing at 800 °C for 60 min. This correlates to the 20% improvement in mechanical properties compared to traditional industrial hot rolled Steel.
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Formation of ultra-fine ferrite microstructure in warm rolled and annealed C–Mn Steel
Materials Science and Engineering A-structural Materials Properties Microstructure and Processing, 2003Co-Authors: Dagoberto Brandao Santos, Rodrigo K Bruzszek, P C M Rodrigues, Elena V PerelomaAbstract:Abstract Laboratory simulations of warm rolling followed by intercritical annealing of a low carbon 0.15%C–1.39%Mn Steel have been performed. The effects of austenitising temperature, amount of deformation and annealing time on microstructure and mechanical properties have been investigated. The results have shown that the homogeneous ultra-fine ferrite grain microstructure (∼1.1–1.2 μm average grain size) has been achieved after austenitising at 900 °C, warm rolling with 3 passes of 20% reduction each at 700 °C and annealing at 800 °C for 60 min. This correlates to the 20% improvement in mechanical properties compared to traditional industrial hot rolled Steel.
Elena V Pereloma - One of the best experts on this subject based on the ideXlab platform.
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formation of ultra fine ferrite microstructure in warm rolled and annealed c Mn Steel
Materials Science and Engineering A-structural Materials Properties Microstructure and Processing, 2003Co-Authors: Dagoberto Brandao Santos, Rodrigo K Bruzszek, P C M Rodrigues, Elena V PerelomaAbstract:Abstract Laboratory simulations of warm rolling followed by intercritical annealing of a low carbon 0.15%C–1.39%Mn Steel have been performed. The effects of austenitising temperature, amount of deformation and annealing time on microstructure and mechanical properties have been investigated. The results have shown that the homogeneous ultra-fine ferrite grain microstructure (∼1.1–1.2 μm average grain size) has been achieved after austenitising at 900 °C, warm rolling with 3 passes of 20% reduction each at 700 °C and annealing at 800 °C for 60 min. This correlates to the 20% improvement in mechanical properties compared to traditional industrial hot rolled Steel.
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Formation of ultra-fine ferrite microstructure in warm rolled and annealed C–Mn Steel
Materials Science and Engineering A-structural Materials Properties Microstructure and Processing, 2003Co-Authors: Dagoberto Brandao Santos, Rodrigo K Bruzszek, P C M Rodrigues, Elena V PerelomaAbstract:Abstract Laboratory simulations of warm rolling followed by intercritical annealing of a low carbon 0.15%C–1.39%Mn Steel have been performed. The effects of austenitising temperature, amount of deformation and annealing time on microstructure and mechanical properties have been investigated. The results have shown that the homogeneous ultra-fine ferrite grain microstructure (∼1.1–1.2 μm average grain size) has been achieved after austenitising at 900 °C, warm rolling with 3 passes of 20% reduction each at 700 °C and annealing at 800 °C for 60 min. This correlates to the 20% improvement in mechanical properties compared to traditional industrial hot rolled Steel.
Bruno C. Cooman - One of the best experts on this subject based on the ideXlab platform.
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Surface Selective Oxide Reduction During the Intercritical Annealing of Medium Mn Steel
Metallurgical and Materials Transactions A, 2017Co-Authors: Kyoung Rae Jo, Lawrence Cho, Jong Han Oh, Myoung Soo Kim, Ki Cheol Kang, Bruno C. CoomanAbstract:Third generation advanced high-strength Steels achieve an excellent strength–ductility balance using a cost-effective alloy composition. During the continuous annealing of medium Mn Steel, the formation of an external selective oxide layer of MnO has a negative impact on the coating quality after galvanizing. A procedure to reduce the selective oxide was therefore developed. It involves annealing in the temperature range of 1073 K to 1323 K (800 °C to 1050 °C) in a HN_x gas atmosphere. Annealing at higher temperatures and the use of larger H_2 volume fractions are shown to make the gas atmosphere reducing with respect to MnO. The reduction of the surface MnO layer was observed by SEM, GDOES, and cross-sectional TEM analysis.
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Tensile Properties of Medium Mn Steel with a Bimodal UFG α + γ and Coarse δ-Ferrite Microstructure
Metallurgical and Materials Transactions A, 2017Co-Authors: Sunmi Shin, Minhyeok Kwon, Bruno C. CoomanAbstract:While the tensile strength and elongation obtained for medium Mn Steel would appear to make it a candidate material in applications which require formable ultra-high strength materials, many secondary aspects of the microstructure–properties relationships have not yet been given enough attention. In this contribution, the microstructural and tensile properties of medium Mn Steel with a bimodal microstructure consisting of an ultra-fine grained ferrite + austenite constituent and coarse-grained delta-ferrite are therefore reviewed in detail. The tensile properties of ultra-fine-grained intercritically annealed medium Mn Steel reveal a complex dependence on the intercritical annealing temperature. This dependence is related to the influence of the intercritical annealing temperature on the activation of the plasticity-enhancing mechanisms in the microstructure. The kinetics of deformation twinning and strain-induced transformation in the ultra-fine grained austenite play a prominent role in determining the strain hardening of medium Mn Steel. While excellent strength–ductility combinations are obtained when deformation twinning and strain-induced transformation occur gradually and in sequence, large elongations are also observed when strain-induced transformation plasticity is not activated. In addition, the localization of plastic flow is observed to occur in samples after intercritical annealing at intermediate temperatures, suggesting that both strain hardening and strain rate sensitivity are influenced by the properties of the ultra-fine-grained austenite.
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Tensile Properties of Medium Mn Steel with a Bimodal UFG α + γ and Coarse δ-Ferrite Microstructure
Metallurgical and Materials Transactions A, 2017Co-Authors: Seonjong Lee, Sunmi Shin, Minhyeok Kwon, Kyoo-young Lee, Bruno C. CoomanAbstract:While the tensile strength and elongation obtained for medium Mn Steel would appear to make it a candidate material in applications which require formable ultra-high strength materials, many secondary aspects of the microstructure–properties relationships have not yet been given enough attention. In this contribution, the microstructural and tensile properties of medium Mn Steel with a bimodal microstructure consisting of an ultra-fine grained ferrite + austenite constituent and coarse-grained delta-ferrite are therefore reviewed in detail. The tensile properties of ultra-fine-grained intercritically annealed medium Mn Steel reveal a complex dependence on the intercritical annealing temperature. This dependence is related to the influence of the intercritical annealing temperature on the activation of the plasticity-enhancing mechanisms in the microstructure. The kinetics of deformation twinning and strain-induced transformation in the ultra-fine grained austenite play a prominent role in determining the strain hardening of medium Mn Steel. While excellent strength–ductility combinations are obtained when deformation twinning and strain-induced transformation occur gradually and in sequence, large elongations are also observed when strain-induced transformation plasticity is not activated. In addition, the localization of plastic flow is observed to occur in samples after intercritical annealing at intermediate temperatures, suggesting that both strain hardening and strain rate sensitivity are influenced by the properties of the ultra-fine-grained austenite.
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Characterization of fracture in medium Mn Steel
Materials Science and Engineering: A, 2017Co-Authors: Hongki Choi, Seonjong Lee, Jaewook Lee, Frédéric Barlat, Bruno C. CoomanAbstract:Abstract In the present study, the damage mechanisms operating during the tensile deformation of intercritically annealed Fe-0.3%C-6.0%Mn-3%Al-1.5%Si medium Mn Steel were investigated. The Steel was annealed at different temperatures to obtain a range of strain hardening properties in uniaxial tension by activating the twinning-induced plasticity and transformation-induced plasticity effects. The initial microstructure consisted of coarse δ-ferrite grains and an ultra-fine grained (UFG) constituent containing ferrite (α) and austenite (γ). However, the volume fraction of martensite (α′) increased significantly by phase transformation from austenite as the material deformed plastically. The internal damage and the fracture appearance after monotonic standard uniaxial tension tests and in-situ interrupted tensile experiments were characterized at macro- and micro-scale. The fracture features were analyzed as a function of the intercritical annealing temperature, which is the most important processing parameter for medium Mn Steel. Three mechanisms contributed to the damage that developed in these materials. First, nucleation and growth of voids occurred at non-metallic inclusions. Second, debonding of the α-α′ and α′-α′ interfaces due to a local loss of interfacial strength was observed in the UFG constituent. While the voids initiated at non-metallic inclusions were in the order of several microns, the size of those initiated at the α-α′ and α′-α′ interfaces in the UFG constituent was limited by the initial grain size, with little or no growth. Finally, in addition to void damage, longitudinal cleavage-like cracks formed along the δ-ferrite layers, and parallel to the sheet plane, were observed in the fractured specimens. These longitudinal cleavage-like cracks were the consequence, but not the cause, of a fracture process triggered by plastic flow localization during uniaxial tension testing.
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Combined Intercritical Annealing and Q&P Processing of Medium Mn Steel
Metallurgical and Materials Transactions A, 2017Co-Authors: Bruno C. Cooman, Sunmi Shin, John G. SpeerAbstract:The microstructure and mechanical properties of intercritically annealed medium Mn Steel are dependent on the selection of the intercritical annealing (IA) temperature. While the yield strength (YS) decreases with increasing IA temperature, the ultimate tensile strength increases with increasing IA temperature. Strain aging phenomena, both static and dynamic, are also often observed. The present contribution shows that, by combining IA with the quench and partitioning processing of the intercritical austenite, it is possible to obtain non-aging mechanical properties which combine a high YS with an ultra-high tensile strength. These properties are particularly suitable for automotive parts related to passenger safety.
Ying Chang - One of the best experts on this subject based on the ideXlab platform.
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A Comparative Study on Formability of the Third-Generation Automotive Medium-Mn Steel and 22MnB5 Steel
Journal of Materials Engineering and Performance, 2018Co-Authors: Guojun Zheng, Ying Chang, Cunyu Wang, Han DongAbstract:Third-generation advanced automotive medium-Mn Steel, which can replace 22MnB5 Steel, was newly developed to improve the lightweight and crashworthiness of automobile. Studies on the formability and simulation method of medium-Mn Steel have just been initiated. In this study, finite element simulation models of square-cup deep drawing were established based on various material property experiments and validated by experiments. The effects of blank holder force (BHF), fillet radii of tools (die and punch) on the maximum drawing depth (MDD), thickness distribution of the formed products, and the microstructure before and after forming were investigated and compared with those on 22MnB5 Steel. Results show that the MDD of the two Steels decreased with increased BHF but increased with the fillet radius of punch; however, the fillet radius of die showed no significant effect on the MDD for both Steels. Compared with hot-formed 22MnB5 Steel, the martensitic transformation of the hot-formed medium-Mn Steel is rarely influenced by the process parameters; thus, it holds the complete, fine-grained, and uniform martensitic microstructure. Moreover, the medium-Mn has better formability, lower initial blank temperature, and smaller impact of BHF and fillet radius of tools on the hot-formed product. Thus, a theoretical basis for the replacement of 22MnB5 Steel by medium-Mn Steel in hot forming process is provided.
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Formability study of the third generation automotive medium-Mn Steel
2018 IEEE International Conference on Mechatronics and Automation (ICMA), 2018Co-Authors: Guojun Zheng, Ying Chang, Xiaodong Li, Cunyu Wang, Han DongAbstract:Third-generation advanced automotive medium-Mn Steel, which can replace 22MnB5 Steel, was newly developed to improve the lightweight and crashworthiness of automotive. Studies on the formability and simulation method of medium-Mn Steel have just been initiated. This study elucidated the effects of initial forming temperature (IFT) on formability, thickness distribution, macro mechanical property and micro performance of medium-Mn Steel hot-formed products. Results show that the IFT intensely affects the formability and the thickness distribution of the deep drawing zone on the medium-Mn Steel hot-formed part, and the recommended IFT range is between 400 °C and 500 °C.
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Study of thermal forming limit of medium-Mn Steel based on finite element analysis and experiments
The International Journal of Advanced Manufacturing Technology, 2017Co-Authors: Guojun Zheng, Ying Chang, Cunyu Wang, Zhiyuan Fan, Han DongAbstract:The medium-Mn Steel, which is an outstanding representative of third-generation advanced automotive Steel, is newly developed. Thus, studies on the thermal forming of this Steel have just been initiated. This study was performed primarily on the thermal formability of medium-Mn Steel. The uniaxial tensile simulation model was established in LSDYNA based on various material property experiments, and the ductile fracture critical values were obtained by simulated and experimental force–deformation curves. Results show that the medium-Mn Steel is an isotropic material, and the strain rate has no significant effect on its flow stress at elevated temperature. The predicted thermal forming limit diagram (TFLD) was achieved from the numerical simulation results and was verified by the TFLD experiments based on the Nakazima test. Results show that the formability of medium-Mn Steel increases rapidly at the beginning and then decreases gradually as the temperature increase. The theoretical optimal temperature for the formability was approximately 400 °C, and the recommended initial forming temperature is approximately 450 °C in actual industrial application of the thermal forming medium-Mn Steel by considering the influence of contact heat transfer and heat radiation.
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Comparison of the hot-stamped boron-alloyed Steel and the warm-stamped medium-Mn Steel on microstructure and mechanical properties
Materials Science and Engineering: A, 2017Co-Authors: Ying Chang, Cunyu Wang, Han DongAbstract:Abstract The application of high strength Steels (HSS) for automotive structural parts is an effective way to realize lightweight and enhance safety. Therefore, improvements in mechanical properties of HSS are needed. In the present study, the warm stamping process of the third generation automotive medium-Mn Steel was discussed, the characteristics of martensitic transformation were investigated, as well as the microstructure and mechanical properties were analyzed, compared to the popular hot-stamped 22MnB5 Steel in the automotive industry. The results are indicated as follows. Firstly, the quenching rate of the medium-Mn Steel can be selected in a wide range based on its CCT curves, which is beneficial to the control of forming process. Secondly, the influence of stamping temperature and pressure on the Ms temperature of the medium-Mn Steel is not obvious and can be neglected, which is favorable to the even distribution of martensitic microstructure and mechanical properties. Thirdly, the phenomenon of decarbonization is hardly found on the surface of the warm-stamped medium-Mn Steel, and the ultra-fine-grained microstructure is found inside the medium-Mn Steel after warm stamping. Besides, the warm-stamped medium-Mn Steel holds the better comprehensive properties, such as a lower yield ratio, higher total elongation and higher tear toughness than the hot-stamped 22MnB5 Steel. Furthermore, an actual warm-stamped B-pillar of medium-Mn Steel is stamped and ultra-fine-grained martensitic microstructure is obtained. The mechanical properties are evenly distributed. As a result, this paper proves that the warm-stamped medium-Mn Steel part can meet the requirements of lightweight and crash safety, and is promising for the industrial production of automotive structural parts.
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an introduction to medium Mn Steel metallurgy mechanical properties and warm stamping process
Materials & Design, 2016Co-Authors: Ying Chang, Chongyu Wang, Kangning Zhao, Han DongAbstract:Abstract The medium-Mn Steel with M3 characteristics (multi-phase, multi-scale, meta-stable) is a promising third-generation automotive Steel. Its chemical composition, microstructure, thermal and mechanical properties are introduced and a warm stamping process for the medium-Mn Steel is proposed. The optimal process parameters are identified through mechanical testing and microscopic analysis to achieve balanced properties of hardenability, hardness, strength, elongation and fracture behavior. The optimal forming process consists of an austenitization temperature of 790–840 °C, a soaking time of 4–7 min, an initial stamping temperature of 450–500 °C, and a cooling rate of 10–60 °C/s. A typical automotive structural part B-pillar was stamped using the proposed process and the final part exhibits ultrafine martensite-lath microstructure and desired mechanical properties for intrusion prevention and energy absorption.