不锈钢中亚稳奥氏体-马氏体相变行为的原位分析

In-situ analysis of phase transformation behavior of metastable austenite-martensite in stainless steel

采用原位EBSD分析方法,系统研究铁素体不锈钢淬火配分(quenching and partitioning,Q&P)工艺后残余奥氏体特征对其相变行为的影响。结果表明:变形过程中残余奥氏体的相变行为与其晶粒尺寸、分布和形貌有关,其影响程度按降序排列。与马氏体间奥氏体和马氏体与铁素体间奥氏体相比,三叉晶界处的奥氏体和孪晶奥氏体在变形早期更容易发生马氏体相变,这与变形过程中不同分布残余奥氏体所受不同的应变或应力密切相关。与大尺寸奥氏体相比,小尺寸奥氏体在变形后期开始转变,有助于延长均匀伸长率。这可能是由于小尺寸奥氏体具有较高的界面能和平均C含量,并且由于细晶强化效应需要较大的宏观应力/应变来诱导马氏体相变。拉长/等轴残余奥氏体在变形早期容易转变,而薄膜状残余奥氏体的转变主要集中在变形后期,有助于进一步提高塑性。不同的转变行为是由于C和N含量的差异以及层错、位错和滑移等缺陷的存在。

The in-situ EBSD analysis method was used to systematically study the effect of retained austenite characteristics on the phase transformation behavior of ferritic stainless steel after the quenching and partitioning(Q&P)process.The results show that the phase transformation behavior of retained austenite during deformation is related to its grain size,distribution,and morphology,and its influence degree is arranged in descending order.Compared with inter-martensitic austenite and inter-martensite-ferrite austenite,the trigeminal and twin austenite are more prone to martensitic transformation in the early stage of deformation.This is closely related to the different strains or stresses applied to different distributed retained austenites during deformation.Compared with large-sized austenite,small-sized austenite begins to transform in the later stage of deformation,which is helpful to prolong the uniform elongation.This may be due to the higher interfacial energy and average C content of small-sized austenite,and the need for larger macroscopic stress/strain to induce martensitic transformation due to the strengthening effect of fine grains.The elongated/equiaxed austenite is easy to transform in the early stage of deformation,while the transformation of thin film-retained austenite is mainly concentrated in the later stage of deformation,which is helpful to further improve plasticity.The different transformation behaviors are due to the differences in C and N content,as well as the presence of defects such as stacking faults,dislocations,and slip.