Tensile and bending properties are two critical attributes of press hardened steels (PHSs) for automotive body structural components. However, the research on these properties of PHSs with retained austenite (RA), which is introduced to improve the mechanical properties, has not been well reported. In this study, the effect of RA on the quasi-static uniaxial tensile and three-point bending behaviors has been systematically investigated for a newly developed Cr and Si alloyed PHS. RA with various degrees of mechanical stabilities was obtained by tuning the auto-tempering of martensite through the control of the die contact pressure during the press hardening process. Mechanically stable RA provides the optimal combination of tensile and bending performance, while the PHS with RA of poor mechanical stability has a deteriorated bending toughness as manifested by a reduction of bending angle from approximately 61.6° to 56.8°. However, its tensile properties, in contrast, are the best in terms of the product of ultimate tensile strength and total elongation (15.9 GPa %). This is mainly attributed to the unstable RA on the outermost surface of the bending sample. The unstable RA can easily transform into brittle martensite under local plane strain and strain gradient conditions in the bending test compared with uniaxial stress in the tensile test, promoting crack initiation and propagation. Furthermore, the effect of martensitic auto-tempering or contact pressure on the quantity and stability of RA are also discussed. This study would provide a useful reference to guide hot stamping process optimization for the newly developed Cr and Si-containing press-hardened steel.

拉伸和弯曲性能是用于汽车车身结构部件的压制硬化钢 (PHS) 的两个关键属性。然而，为了改善机械性能而引入的具有残余奥氏体（RA）的PHS的这些性能的研究尚未得到很好的报道。在本研究中，系统研究了 RA 对新开发的 Cr 和 Si 合金 PHS 的准静态单轴拉伸和三点弯曲行为的影响。通过在压制硬化过程中控制模具接触压力来调整马氏体的自动回火，获得了具有不同程度机械稳定性的 RA。机械稳定的 RA 提供了拉伸和弯曲性能的最佳组合，而具有较差机械稳定性的 RA 的 PHS 具有恶化的弯曲韧性，表现为弯曲角度从大约 61.6° 减小到 56.8°。然而，相比之下，它的拉伸性能在极限拉伸强度和总伸长率的乘积（15.9 GPa %）方面是最好的。这主要归因于弯曲样品最外表面的不稳定RA。与拉伸试验中的单轴应力相比，在弯曲试验中的局部平面应变和应变梯度条件下，不稳定的RA很容易转变为脆性马氏体，促进裂纹的萌生和扩展。此外，还讨论了马氏体自回火或接触压力对 RA 数量和稳定性的影响。