Cyclic responses and microstructure sensitivity of Cr-based turbine steel under different strain ratios in low cycle fatigue regime

Materials & Design

Qingyuan Wang¹  Quanyi Wang²  Hong Zhang²  Wei Zhang³  Yongjie Liu³  Xiufang Gong⁴  Tianjian Wang⁴  Qingsong Li⁴ 

[1] Corresponding author at: Failure Mechanics and Engineering Disaster Prevention and Mitigation Key Laboratory of Sichuan Province, College of Architecture and Environment, Sichuan University, Chengdu 610065, China.;Key Laboratory of Deep Underground Science and Engineering, Ministry of Education, Sichuan University, Chengdu 610065, China;Failure Mechanics and Engineering Disaster Prevention and Mitigation Key Laboratory of Sichuan Province, College of Architecture and Environment, Sichuan University, Chengdu 610065, China;State Key Laboratory of Long-Life High Temperature Materials, DongFang Turbine Co., Ltd, Deyang 618000, China;

关键词: Cyclic response;    Microstructure-sensitive;    9% Cr turbine steel;    Low cycle fatigue;    Strain ratio;   

DOI  :  

来源: DOAJ

【 摘 要 】

When turbine steel services, i.e., startup and shutdown processes, the cyclic mechanical stress caused by the asymmetry loading conditions is introduced. To study the effect of mean strain on the cycle response and microstructure-sensitive at room temperature, the low cycle fatigue under two strain ratios was used. Experimental results indicate that significant cyclic softening was observed for both modes. The cyclic strain ratio is independent of strain amplitude and strain ratio. The plastic strain, plastic strain energy density, and cumulative strain energy density at strain ratio of 0.1 are higher than that at strain ratio of −1. Therefore, applied stress amplitude and fatigue life fitted by Manson-Coffin formula under strain ratio of 0.1 is lower than that at strain ratio of −1. According to the evaluation of the internal stress variables, i.e., back stress, isotropic stress and viscous stress under both modes, the back stress is a critical part of the cyclic stress, which can directly control the cycle softening behavior. Besides, the fatigue life prediction model considering the strain ratio is constituted through hysteresis energy method. Finally, the mechanical results are linked to the microstructure observed by transmission electron microscopy. The microstructure sensitive was evaluated and deduced.

【 授权许可】

Unknown