低温强变形奥氏体的马氏体相变

Martensite Phase Transformation Behavior of Severe Plastic Deformed Austentite at Low Temperature

研究了Fe-32%Ni合金在形变温度550℃、形变速率2×10-2s-1的实验条件下,经过多道多向锻压变形后奥氏体的马氏体相变过程。采用电阻法、XRD分别研究了累积应变量对Ms点以及马氏体生成量的影响;采用TEM对形变位错密度以及马氏体组织进行了分析。结果表明:随着累积应变量的增大,奥氏体组织不断细化,深冷处理后马氏体生成量逐渐减少,Ms点逐渐降低,最终趋于恒定。原因是奥氏体的细晶强化以及形变位错的引入导致母相加工硬化抑制了马氏体形核,随着形变的累积,奥氏体的晶粒细化效果逐渐减弱,使得马氏体生成量减少的趋势也逐渐减弱,最终趋于恒定。

The martensite phase transformation behavior of multiaxial forged Fe-32%N alloy at the temperature of 550℃ and a strain rate of 2×10^-2 s^-1 was studied. The effect of cumulative strain on the Ms temperature and volume fraction of martensite was investigated by measurement of electrical resistance and X-ray diffraction. The deformat-ion dislocation density and martensite microstructure were also analysed by TEM. The results show that the austentite grains were obviously refined, and the volume fraction of martensite and martensite transformation starting （Ms） temperature decrease with the increase of culmulative strain, and reach an stable value at last. The reason is that the austentite grain refinement and deformation dislocation suppress the nucleation of martensite. The austentite grain refinement effect weakens with the increase of culmulative strain, and leads to the decrease of martensite volume fraction, which reaches a fixed value at last.