ZG06Cr13Ni4Mo馬氏體不銹鋼中TRIP效應(yīng)的同步輻射高能X射線原位研究INVESTIGATION OF TRIP EFFECT IN ZG06Cr13Ni4Mo MARTENSITIC STAINLESS STEEL BY IN SITU SYCHROTRON HIGH ENERGY X-RAY DIFFRACTION

利用自制的小型拉伸裝置對(duì)淬火+回火熱處理后的 ZG06Cr13Ni4Mo 馬氏體不銹鋼試樣進(jìn)行單軸拉伸變形, 使用同步輻射高能 X 射線衍射技術(shù)對(duì)鋼中逆變奧氏體力學(xué)穩(wěn)定性和相變誘導(dǎo)塑性(transformation induced plastic, TRIP)進(jìn)行原位研究. 結(jié)果表明, 隨著拉伸應(yīng)力的增加, 逆變奧氏體衍射峰積分強(qiáng)度逐漸減弱, 逆變奧氏體在變形過(guò)程中逐步發(fā)生了形變誘導(dǎo)馬氏體相變. 利用Rietveld全譜精修擬合方法對(duì)不同應(yīng)力狀態(tài)下的逆變奧氏體相分?jǐn)?shù)進(jìn)行定量分析, 發(fā)現(xiàn)逆變奧氏體的形變誘導(dǎo)馬氏體相變開(kāi)始于材料的宏觀彈性階段, 并持續(xù)至整個(gè)塑性變形階段. 通過(guò)比較分析不同熱處理工藝下逆變奧氏體的形變誘導(dǎo)相變過(guò)程和材料的加工硬化行為發(fā)現(xiàn), 逆變奧氏體的形變誘導(dǎo)相變的出現(xiàn)增加了馬氏體基體的位錯(cuò)密度, 導(dǎo)致材料加工硬化指數(shù)的提高, 有效提高了材料的塑性.

After quenching and proper intercritical tempering, ZG06Cr13Ni4Mo martensitic stainless steel is composed of tempered martensite matrix and reversed austenite. The deformation induced martensitic transformation 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, the studies on the TRIP effect of reversed austenite are limited to the description of phenomenon and the mechanism behind is not clear. In order to reveal the mechanical stability and the transformation induced plasticity of the reversed austenite during the tension test in the tempered ZG06Cr13Ni4Mo steel, a custom-built mini tensile instrument has been designed and installed on Shanghai Synchrotron 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 cooling 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 reversed austenite with increase in tensile stress indicates that the reversed austenite has been induced to transform into 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 deformation induced martensitic transformation initiates at the macro-elastic stage and through the whole deformation, 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.
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