Effects of thermal aging on 12Cr-1Mo steel

Abstract

A study of the microstructural evolution during thermal aging was made on two heats of 12Cr-1Mo steel (HT-9) at various temperatures from 500 to 800°C for times of 30–10,000 h. Optical microscopy examination showed that for increasing temperature, the time of aging dictates changes in microstructure. Generally, an aging temperature of 650°C with times of greater than 600 h was required before precipitation reactions became noticeable. Aging at 800°C for times greater than 3,000 h produced an austenitic transformation product. This signifies that the lower temperature boundary of the austenitic region was exceeded. The slower aging rate of one heat is attributed to the presence of delta ferrite in the as-received material.