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Microstructure Evolution and Tempering Transformation Kinetics in a Secondary Hardened M50 Steel Subjected to Cold Ring Rolling
The microstructure evolution and tempering transformation kinetics of the M50 steel subjected to cold ring rolling (CRR) have been investigated. The results indicate that the brass R{110} texture is weakened with the enhancement of the //ND texture during CRR. Due to the increased low angle boundaries by CRR, the A _(c1) temperature decreases while the carbon content and volume fraction of RA increase. During tempering, the activation energy of carbon atoms segregation and transition carbide precipitation decrease, while the activation energy of retained austenite (RA) decomposition increases after CRR. The kinetic analysis shows that the CRR is beneficial to the carbon atoms segregation during the beginning of tempering. Then, the CRR leads to the delay of the onset of transition carbide precipitation, but decreases the whole reaction time, which has been verified by the transmission electron microscopy (TEM) and hardness results. The lagging of transition carbide precipitation in the early stage is caused by the increased segregation trapping of carbon atoms, while the higher nucleation rate is responsible for the enhanced precipitation of transition carbide during the later stage. For the cementite formation, there are no significant changes in the predictive kinetics after the applied CRR. However, the kinetic transformation of RA decomposition is inhibited by the CRR, which is attributed to the higher carbon content and smaller grain size of RA. Additionally, the alloy carbides precipitation is also enhanced by the CRR process during secondary hardening.
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机译：研究了对冷环轧制（CRR）进行了M50钢的微观结构演化和回火转化动力学。结果表明，在CRR期间的增强// ND纹理的增强，黄铜R {110}纹理削弱。由于CRR的低角度边界增加， A _（C1）温度降低，而RA的碳含量和体积分数增加。在回火期间，碳原子偏析的激活能量和过渡碳化物沉淀降低，而保留奥氏体（Ra）分解的活化能在CRR之后增加。动力学分析表明，CRR在回火开始期间有利于碳原子间隔。然后，CRR导致过渡碳化物沉淀的发作的延迟，但是降低了通过透射电子显微镜（TEM）和硬度结果验证的整个反应时间。早期阶段过渡碳化物沉淀的滞后是由碳原子的增加俘获引起的，而较高的成核速率是在后期阶段增强过渡碳化物的增强沉淀。对于渗碳石形成，应用CRR后预测动力学没有显着变化。然而，CRR抑制了Ra分解的动力学转化，其归因于碳含量较高和Ra的较小晶粒尺寸。另外，在二次硬化期间CRR工艺也增强了合金碳化物沉淀。
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