退火马氏体基体TRIP钢拉伸过程中的残余奥氏体转变

Retained Austenite Transformation in Tensile Process for Annealed Martenite Matrix TRIP Steel

研究了冷轧退火马氏体基体TRIP钢在不同预拉伸过程中残余奥氏体向马氏体的转变。为了使残余奥氏体转变充分,试验拉伸速度设定为1mm/min。对不同变形条件下的试样进行分析,通过XRD分析残余奥氏体转变的体积分数及残余奥氏体中的碳浓度,通过SEM观察拉伸断裂后的断口形貌。分析发现:残余奥氏体转变过程与应力-应变有十分密切的关系,在变形的初始阶段和试样断裂之前,残余奥氏体的转变率较均匀变形阶段要小很多;在均匀变形阶段,即在出现颈缩之前,残余奥氏体发生稳定的马氏体相变,其转变率达到最大值,此时可以有效地提高均匀伸长率;在出现颈缩之后,残余奥氏体继续发生马氏体转变,但其转变率要较均匀转变时稍低。在整个变形过程中,残余奥氏体中的碳浓度呈线性增加。在变形的始末,虽然是应力-应变的最大梯度,但奥氏体的转变率并不是最高,反而为最低。

The transformation of retained austenite （RA） to martenite of cold roiled annealed martenite （AM） matrix TRIP steel in different pre-tensions was investigated. The lmm/min tensile rate was adopted for fully transformation. The transformation volume fractions of RA and carbon concentration in RA were calculated quantitatively by X-ray diffractometer （XRD） analysis, the fracture morphology was also analyzed by scanning electron microscope （SEM）. The results indicate that, the RA transformation and strains have close relationship. The transformation rates of initial stage and just before fracture are much lower than that of uniform deformation stage. From 5 % elongation to necking stage, RA transforms into martenite stably and the transformation rate reaches to its maximum. The uniform elongation could be enhanced in this stage. When necking occurred, RA transforms into martenite con- tinuously, but the transformation rate is slightly lower than uniform transformation stage. In the whole deformation process, carbon concentration in RA increases linearly. Although they are the maximum gradients of stress and strain, the transformation rates of initial and last stages are not maximum, but minimum.