Precipitation and Transformation of Carbides during Tempering of 7Cr14 Martensitic Stainless Steel

The precipitation and transformation of carbides in steel are gaining more interest since they are closely related to the properties of steel. Herein, the precipitation and transformation of carbides during tempering of the 7Cr14 martensitic stainless steel subjected to high‐temperature solution treatment (HTST) are investigated. The results indicate that the precipitation of M 3 C (300–333 °C) and M 23 C 6 (612–645 °C) carbides occurs during tempering of the HTST steel. The effective precipitation activation energies of M 3 C and M 23 C 6 carbides are 120 ± 7 and 272 ± 13 kJ mol −1 , respectively. The precipitation processes of M 3 C and M 23 C 6 carbides are dominated by C and Cr atomic diffusion, respectively. Moreover, it is found that two transformation processes occur during tempering with increasing temperature, namely, M 3 C carbides dissolve in the matrix and then M 23 C 6 carbides precipitate along the boundaries of martensitic laths, and the plate‐like M 3 C carbides decompose into several globular or rod‐like M 23 C 6 carbides that arrange in a chain‐like morphology.