Characterization of high temperature long-term fatigue properties for advanced ferritic heat-resisting steels

Abstract

Axial strain-controlled fatigue tests of a 9 mass% chromium (Cr)-2 mass% tungsten (W) and a 12Cr-2W ferritic heat-resisting steels were performed to obtain fatigue life curves (S-N curve) over a wide from 10 2 to 10 6 cycles at room tem- perature (RT), 400, 600, 650 and 700 ◦ C, respectively. As the results, Manson-Coffin relationships between plastic strain range and fatigue life for the both the steels appear linear at RT and 400 ◦ C, however the relationships have inflection around 10 4 cy- cles beyond 600 ◦ C. Moreover, it is cleared that subgrains became coarse uniformly in the low-cycle regions, while subgrains did coarse locally near grain boundaries in the high-cycle regions. Therefore it is suggested that differences in the mechanical factors and change in subgrain structure cause the inflection of Manson-Coffin relations at the elevated temperatures. Then, a modified universal slope method is proposed for S-N curves that considered to inflection in Manson-Coffin relations.