Effect of Tempering on Mechanical Properties and Microstructure of a 9 Cr Heat Resistant Steel

摘要

Effect of tempering temperature ranged from 400 to 720℃ on mechanical properties and microstructure of a P92-type creep resistant steel was investigated. The hardness value of 400 HB, which was obtained after solution treatment, increased to 430 HB with increasing the tempering temperature to 525℃. Further increase in the tempering temperature resulted in gradual decrease in hardness, which approached a level of about 220 HB after tempering at 720℃. The equiaxed particles of MX-type carbonitrides with a size of about 30 nm were precipitated randomly after tempering under all conditions. At temperatures below 525℃, the tempered martensite lath structure (TMLS) was characterized by a random distribution of fine M_3C-type carbides and MX-type carbonitrides. The precipitation of M_(23)C_6 was observed after tempering at T ≥ 525℃. At 525℃, the M_(23)C_6 carbides appeared as thin films on high-angle boundaries (HAB), while M_(23)C_6 particles having almost equiaxed shape and located on various boundaries including low-angle lath boundaries precipitate at higher temperatures.