C型环试样淬火及深冷处理应力演变的数值研究

Numerical simulation of stress evolution in C-ring specimen during quenching and deep cryogenic treatment

基于金属-热-力耦合理论,建立了C型环试样淬火和深冷处理的多物理场耦合数值模型,探讨了淬火和深冷处理过程中试样冷却行为和组织转变对其应力演变和分布的影响。研究表明:淬火和深冷处理过程中,由于C型环试样不同部位的冷却行为差异,导致温度变化和组织转变呈现非同时性。淬火和深冷处理后,试样残留奥氏体的含量分别为15.5%和2%左右,与实验测试结果吻合。在淬火过程中,试样等效应力变化曲线先后出现两个峰值,其中第一个应力峰值是由于试样心表温差引起的热应力所致,第二个应力峰值与试样心表组织转变的非同时性引起的组织应力密切相关;在深冷处理过程,试样心表温差和心表奥氏体体积分数差峰值出现的时间基本保持一致,且比淬火过程小两个数量级,导致试样的等效应力变化相比淬火过程要平缓得多。相比于淬火过程,深冷处理后试样残余应力的分布状态未发生明显改变,但试样的整体应力值有所下降,尤其是在缺口和最大壁厚附近残余应力得到释放。

Based on the metallo-thermo-mechanical coupled theory,multi-field coupled numerical models of the quenching and deep cryogenic treatment( DCT) processes were established to evaluate the influence of cooling behavior and phase transformation on the stress evolution and distribution of C-ring specimen during quenching and DCT. The results indicate that,due to the difference in cooling behavior at different locations of the C-ring specimen,both the temperature change and phase transformation present the non-simultaneity during quenching and DCT.After quenching and DCT,the amounts of retained austenite in C-ring specimen are about 15. 5% and 2%,respectively,which are in good agreement with the experimental data. During the quenching process,there are two stress peak values on the effective stress curves at different tracking points on the C-ring specimen,the one can be attributed to the thermal stress caused by the temperature difference between the core and surface of specimen,and the other is closely related to the phase transformation stress induced by the non-simultaneity of austenite transformation between the core and surface of specimen. During DCT,both the peak values of temperature difference and the austenite volume fraction difference between the core and surface of C-ring specimen appear nearly simultaneously and their values are about two orders of magnitude lower than that of the quenching process,which leads to the effective stress evolution in the specimen during DCT is more slowly and gently. Compared with the quenching process,although there are no significant changes for the residual stress distribution of specimen after DCT,the residual stress level in the whole specimen has declined to some extent,especially in the gap and the vicinity of the maximum wall thickness of specimen where the relaxation of residual stress is more obvious.