Response of Modified 9Cr-1Mo Steel Under Asymmetrical Stress Loading at 600 °C

Abstract

Response of materials under cyclic loading depends on loading type (symmetrical and asymmetrical). Modified 9 Cr-1 Mo steel is an important material used as tube or pipe in steam generator, superheater and reheater components in thermal/nuclear power plants. This investigation deals with cyclic stress–strain behaviour of this steel in asymmetric loading under different combinations of the mean stress (σm), stress amplitude (σa), stress rate (σ˙ ) at 600 °C. Fatigue tests under asymmetrical loading were performed with various combinations of σm (80–100 MPa), σa (215–255 MPa) and σ˙ (50–450 MPa/s) at 600 °C. Cyclic hardening and softening behaviour were studied from hysteresis loops in forms of loop width, area and plastic strain energy. There was cyclic softening with rise in σm and σa, whereas with rise in σ˙ there was cyclic hardening. The fractrographs revealed striation like marks on the cylindrical surface and dimples on the fracture surface. © 2022, The Author(s), under exclusive license to Springer Nature Singapore Pte Ltd.