Effect of heat treatment variables on microstructure and mechanical properties of 15Cr-4Ni-0.08C martensitic stainless steel

In order to understand the best regime of heat treatment for 15Cr-4Ni-0.08C martensitic stainless steel, different heat treatment procedures involving solution treatment and tempering were investigated. The solution treatment was performed at temperatures of 900-1100 degrees C for different soaking times of 30, 60 and 120 min followed by air cooling. Optical and scanning electron microscopy observations revealed that grain growth commenced by dissolution of pre-existing chromium carbides at similar to 1000 degrees C after 60 min soaking. Therefore, this regime was considered as the best solution treatment procedure. The tempering treatment was performed on the solution treated samples at temperatures of 250-600 degrees C for 2 h followed by air cooling. Standard tensile test and Charpy impact tests were performed on the tempered specimens and showed that two secondary hardening steps at 450 and 550 degrees C contribute in ductility loss and increment of strength and hardness. The fractography observations corroborated the mechanical testing results.