ZG06Cr13Ni4Mo马氏体不锈钢中TRIP效应的同步辐射高能X射线原位研究

INVESTIGATION OF TRIP EFFECT IN ZG06Cr13Ni4Mo MARTENSITIC STAINLESS STEEL BY IN SITU SYNCHROTRON HIGH ENERGY X-RAY DIFFRACTION

利用自制的小型拉伸装置对淬火+回火热处理后的ZG06Cr13Ni4Mo马氏体不锈钢试样进行单轴拉伸变形,使用同步辐射高能X射线衍射技术对钢中逆变奥氏体力学稳定性和相变诱导塑性(transformation induced plastic,TRIP)进行原位研究.结果表明,随着拉伸应力的增加,逆变奥氏体衍射峰积分强度逐渐减弱,逆变奥氏体在变形过程中逐步发生了形变诱导马氏体相变.利用Rietveld全谱精修拟合方法对不同应力状态下的逆变奥氏体相分数进行定量分析,发现逆变奥氏体的形变诱导马氏体相变开始于材料的宏观弹性阶段,并持续至整个塑性变形阶段.通过比较分析不同热处理工艺下逆变奥氏体的形变诱导相变过程和材料的加工硬化行为发现,逆变奥氏体的形变诱导相变的出现增加了马氏体基体的位错密度,导致材料加工硬化指数的提高,有效提高了材料的塑性.

After quenching and proper intercritical tempering, ZG06Crl3Ni4Mo martensitic stainless steel is composed of tempered martensite matrix and reversed austenite. The deformation induced martensitic transforma- tion of reversed austenite occurring during the deformation results in the transformation induced plasticity （TRIP） effect, which is beneficial to the mechanical properties of this steel. However, studies on the TRIP effect of re- versed austenite are limited to description of phenomenon and mechanism behind is not clear. In order to reveal the mechanical stability and transformation induced plasticity of the reversed austenite during tension test in tempered ZG06Crl3Ni4Mo steel, a custom-built mini tensile instrument has been designed and installed on Shanghai Syn- chrotron Radiation Facility to conduct the in situ synchrotron high energy X-ray diffraction （SHXRD） experiment during the uniaxial tension. Three samples, which were tempered at 620 ℃ with different holding times and cool- ing rates in order to obtain different volume fraction of reversed austenite, were used to investigate the relationship between the deformation induced martensitic transformation and work hardening behavior. The integral intensity and the full width at half maximum of diffraction peaks of the reversed austenite and tempered martensitic matrix under different engineering stress were recorded. The gradual decrease in the integral diffraction intensity of re- versed austenite with increase in tensile stress indicates that the reversed austenite has been induced to transform in- to martensite during the tension deformation. Furthermore, the volume fraction of reversed austenite during tension was quantitatively calculated by fitting the whole diffraction spectra of reversed austenite and tempered martensitic matrix with the Rietveld refinement method. The evolution of the reversed austenite fraCtion indicates that the de- formation induced martensitic transformation initiates at the macro-elastic stage and through the whole deforma- tion, which is different to the retained austenite in TRIP steel. Meanwhile, the work hardening exponents of three samples with different volume fraction of reversed austenite have been compared. It is found that the deformation induced martensitic transformation of reversed austenite increases the dislocation density of martensitic matrix and results in the increase in the work-hardening exponent during the plastic deformation, which enhances the ductility of ZG06Cr13Ni4Mo martensitic stainless steel.