Effect of Microstructural Variation on Hardness Degradation of 2.25Cr-1Mo Steel and Its Impact on Residual Life Assessment

Abstract

Hardness measurement for assessing the remaining life of high temperature components undergoing microstructure degradation has become a popular method. This paper examines the variation in hardness of different phases of 2.25Cr-1Mo steel as a result of thermal ageing. The severity of thermal ageing has been expressed in terms of a Larson-Miller parameter (LMP). Microstructural examinations were carried out using Optical and Scanning Electron Microscopy (SEM) techniques. Transmission Electron Microscope (TEM) and Electron Probe Micro Analyzer (EPMA) have been used to identify different phases besides analysis of their shape, size and distribution. Hardness degradation of both phases (bainite and ferrite) has been examined in terms of microstructural degradation due to thermal ageing. Finally, a modified approach has been suggested for accurate prediction of residual life of components made up of 2.25Cr-1Mo steel and operating at high temperatures.