超高强度钢喷丸表面残余应力在疲劳过程中的松弛规律

Shot-peened surface residual stress relaxationduring fatigue for ultra-high strength steel

对超高强度钢23Co14Ni12Cr3MoE进行了喷丸强化,采用X射线衍射应力分析方法研究了旋转弯曲疲劳过程中喷丸表面残余应力的松弛变化规律。结果表明,在疲劳循环过程中,残余应力的松弛主要发生在疲劳的初始循环100周次内,疲劳循环100周次后残余应力基本稳定在某一个应力水平上,而且其中的大幅度松弛发生在疲劳的初始循环10周次内。对比不同应力水平下的松弛行为,在疲劳极限以上的应力水平下,残余应力松弛的幅度和速率都较大。对喷丸后的试样在疲劳试验前先进行200℃/2h的保温提前应力松弛处理,然后再进行疲劳试验,200℃/2h的保温处理可降低残余应力松弛的幅度和速率甚至在低于疲劳极限的应力水平时只发生小的松弛或不发生松弛。但由于喷丸强化试样疲劳裂纹往往从次表层萌生,表面残余应力的松弛只能作为评价材料疲劳性能的一个参考数值,在工程应用时不能只依据表面残余应力来判定材料的疲劳性能。

Ultra-high strength 23Co14Ni12Cr3MoE steel was shot peened and the surface residual stress of shot-peened specimens was determined during rotating bending fatigue by X-ray diffraction method. The surface residual stress decreases greatly in the first 10 cycles and it is steady after 100 cycles. With higher stress, the value and rate of stress relaxation are greater. This investigations also show a remarkable stability of the surface residual stress during fatigue for shot peened and following 200℃/2h treated specimens. Surface residual stress is only a referenced parameter to evaluate fatigue performance because of the fact that fatigue crack often initiates at subsurface.