Influence of Pre-Ratcheting Fatigue on Tensile Behavior of Modified 9Cr-1Mo Steel at Ambient Temperature

Abstract

Modified 9 Cr-1Mo steel is a material of prime significance in power plants used for components of steam generation units. The phenomenon of ratcheting involves aggregation of plastic strain in each cycle during asymmetric cyclic stressing. In the present study, the role of prior ratcheting has been studied on tensile behavior of this steel at ambient temperature. Cyclic tests were performed under uniaxial stress under the three parameters namely mean stress (σm), stress amplitude (σa) and stress rate (σ˙) for 200 cycles. Tensile behavior of the pre-ratcheted samples was evaluated at ambient temperature at a strain rate of 10−4 s−1. It was found that pre-ratcheting enhanced the yield strength (SYS) and tensile strength (SUTS) but reduced the ductility. The results are discussed in terms of cyclic hardening resulting from the pre-ratcheting under different variables, and the internal microstructural changes are revealed by transmission electron microscopy. © 2021, The Indian Institute of Metals - IIM.