相续室温蠕变中屈服强度附近的应力应变行为

STRESS-STRAIN BEHAVIORS AROUND THE YIELD STRENGTH IN SEQUENTIAL ROOM TEMPERATURE CREEP TESTS

研究了正火态X70管线钢的相续室温蠕变现象及其对随后变形的影响,结果表明,在屈服点上、下的数种应力水平下X70钢均存在室温蠕变现象,且通常呈现为速率递减的α型蠕变.屈服点后的室温蠕变提高了随后的流变应力.利用应变速率-应力曲线判断室温蠕变对随后应力应变行为的影响:经历低于屈服强度的室温蠕变过程后,应变速率突变点明显低于普通拉伸实验的比例极限;而在较高应力水平下的室温蠕变使随后的应变速率-应力曲线出现明显峰值.利用局部可动位错密度模型解释了室温蠕变的影响.

The deformation of metallic materials at low homologous temperature （the ratio of experimental temperature and melting point T/Tm 〈0.2） used to be described by time independent models. With the development of measuring technique and the improvement of required accuracy, the time dependence of deformation has been concerned about. So far, room temperature creep （RTC） has been observed in many metals and alloys, and some experiments have been performed to investigate the fundamental deformation mechanism and influencing factors. A previous paper reported that RTC increased the subsequent flow stress of an X70 pipeline steel. However, the evolution of deformation following RTC is not thoroughly understood. In this paper, sequential RTC tests and their effects on the subsequent deformation have been investigated in the X70 pipeline steel. The steel exhibits time dependent deformation at various stress levels around yield strength, and RTC is generally primary α- type. Moreover, the post yield RTC markedly enhances the subsequent flow stress. The influence of RTC on subsequence stress strain behavior can be evaluated using strain rate stress curve： the burst point of strain rate, due to pre yield RTC process, is lower than elastic limit, while a distinct peak is observed after RTC has been performed at higher stress level. Local mobile dislocation model has been applied to analyze the behavior.