Microstructural characterisation of thermally degraded 2·25Cr–1Mo steel using ultrasonic measurement and its correlation with mechanical properties

Abstract

Ultrasonic testing is a sensitive tool not only for defect detection and evaluation of components and structures but also to characterise microstructural features which affect mechanical properties. In this study, four different thermally degraded specimens of 2·25Cr–1Mo steel have been prepared by aging at 873 K for 10 h, 923 K for 20 h, 973 K for 40 h and 973K for 80 h to obtain variation in microstructural features. Mechanical properties of each specimen having different microstructures were investigated using tensile and hardness tests. Ultrasonic parameters of each specimen having different microstructural features were studied by pulse echo technique using 5 MHz longitudinal probe. It has been observed that ultrasonic velocity and attenuation both increased with increase in the size of carbide precipitates obtained due to increased time and temperature of aging. Our results indicated that these ultrasonic parameters could be used as a tool to assess the degraded microstructure of operating components in service.

Keywords:

• 2·25Cr–1Mo steel
• Thermal degradation
• Pulse-echo ultrasonic testing
• Mechanical properties