Role of Heat Treatment on Grain Refinement and Microhardness of 9Cr�1Mo�V�Nb Steel

Abstract

Effect of �double austenitizing� (DN) on microstructure evolution and mechanical properties of martensitic 9Cr�1Mo�V�Nb (P91) steel were studied and compared with the �conventional normalizing� (CN) process. In CN treatment, P91 steel is normalized at 1050��C for 1�h, finally air cooled. In DN treatment, the first stage of normalizing was performed at 1050��C/1�h/air cool. The second stage of normalizing was performed in the temperature range of 950�1150��C for 1�h (950��C-DN1, 1050��C-DN2, 1150��C-DN3), followed by water quenching. The grain size was measured 42 and 35��m for CN and DN1 treatment, respectively. The double normalizing (DN) produced complete martensitic microstructure as a result of complete dissolution of precipitates. In DN-based heat treatment, optimized microstructure and mechanical properties were obtained for the sample that normalized at 950��C, followed by water quenching. � 2019, ASM International.