预变形对Q&P钢微观组织及烘烤硬化性能的影响

Effect of pre-strain on microstructure and bake hardening properties of Q&P steel

分析了Q&P钢在不同预变形(0%、3%、6%和9%)条件下的烘烤硬化行为。采用扫描电镜、X射线衍射仪(XRD)和电子背散射衍射(EBSD)等表征了试验钢在预变形和烘烤过程中的微观组织演变。结果表明:随着预变形量的增加,试验Q&P钢的烘烤硬化(BH)值先增加后减小,预变形量为6%时,BH值最大,为144 MPa。此外,在预变形较小时,晶粒尺寸是影响残留奥氏体稳定性的主要因素,马氏体转变优先发生在尺寸较大的残留奥氏体当中;随着预变形量的增加,大尺寸残留奥氏体消耗殆尽,在剩余残留奥氏体尺寸相差不大的情况下,其所在位置及其周围组织分布决定了残留奥氏体的稳定性。最后,烘烤过程中,会造成残留奥氏体数量的少量减少,这也会影响后续变形过程中相变诱导塑性效应的发生,不利于材料的整体塑性。

The bake hardening behavior of Q&P steel under different pre-strains(0%,3%,6%and 9%)was analyzed.Microstructure evolution of the experimental steel during pre-strain and baking was characterized by means of scanning electron microscopy,X-ray diffraction(XRD)and electron backscatter diffraction(EBSD)technique.The results show that with the increase of pre-strain,the bake hardening(BH)value of the experimental Q&P steel first increases and then decreases.When the pre-strain is 6%,the BH value is the highest,which is 144 MPa.In addition,when the pre-strain is small,grain size is the main factor affecting the stability of retained austenite,and martensitic transformation preferentially occurs in larger retained austenite.With the increase of pre-strain,large-sized retained austenite is consumed completely.In the case where the size of remaining retained austenite is not significantly different,its location and surrounding microstructure distribution determine the stability of retained austenite.Finally,during the baking,there will be a slight decrease in the amount of retained austenite,which will also affect the occurrence of phase transformation-induced plasticity effects in subsequent deformation processes,which is not conducive to the overall plasticity of the material.