The Effect of Stress Ratios on the Very High Cycle Fatigue Behavior of 9%Cr Turbine Steel at 630 °C

Quanyi Wang; Yao Chen; Yongjie Liu; Chong Wang; Lang Li; Chao He; Xiufang Gong; Tianjian Wang; Wei Zhang; Qingyuan Wang; Hong Zhang

doi:10.3390/ma13163444

The Effect of Stress Ratios on the Very High Cycle Fatigue Behavior of 9%Cr Turbine Steel at 630 °C

Materials (Basel). 2020 Aug 5;13(16):3444. doi: 10.3390/ma13163444.

Authors

Quanyi Wang^{1

2

3}, Yao Chen^{2

3}, Yongjie Liu^{2

3}, Chong Wang^{2

3}, Lang Li^{2

3}, Chao He^{2

3}, Xiufang Gong⁴, Tianjian Wang⁴, Wei Zhang⁵, Qingyuan Wang^{1

2

3

6}, Hong Zhang^{2

3}

Affiliations

¹ School of Aeronautics and Astronautics, Sichuan University, Chengdu 610065, China.
² Failure Mechanics and Engineering Disaster Prevention and Mitigation Key Laboratory of Sichuan Province, College of Architecture and Environment, Sichuan University, Chengdu 610065, China.
³ Key Laboratory of Deep Underground Science and Engineering, Ministry of Education, Sichuan University, Chengdu 610065, China.
⁴ State Key Laboratory of Long-Life High Temperature Materials, DongFang Turbine Co., Ltd., Deyang 618000, China.
⁵ DongFang Boiler Group Co., Ltd., ZiGong 643001, China.
⁶ School of Architecture and Civil Engineering, Chengdu University, Chengdu 610106, China.

Abstract

Effects of the stress ratio on the very high cycle fatigue behaviors of 9%Cr turbine steel have been investigated at 630 °C. The experimental results show that the S-N curve has a continuous downward trend and has no fatigue limit with the increasing in the cycles at 630 °C. Meanwhile, according to the analysis of microstructure, there are two failure modes that were observed at different stress ratios (R = -1 and 0.1), including surface crack failure and internal crack failure, respectively. Besides, the theoretical threshold value of the crack growth is compared with the calculated value of the fracture surface. To decrease the difference between the threshold value of internal crack initiation and the corresponding theoretical value, a new model for the crack growth threshold of the interior-induced fracture at different stress ratios is proposed and discussed.

Keywords: 9%Cr turbine steel; high temperature; stress intensity factor; stress ratio; very high cycle fatigue.