热时效对含硅铁素体/马氏体钢力学性能的影响

Four kinds of 9Cr-ferritic/martensitic (F/M) steels with different Si contents were heat aged at 550°C (the longest time was 5000 h), and their mechanical properties such as yield strength (R_p0.2), tensile strength (R_m) and elongation (A) were tested. The relationship between microstructure and mechanical properties was studied by means of scanning electron microscope/energy dispersive spectrometer (SEM/EDS) and transmission electron microscope (TEM). The results show that the strength of 9Cr-F/M steel can be improved by adding a small amount of Si, and when the Si content (mass fraction) is 0.7%, R_p0.2 and R_m reach the maximum, but the addition of Si will promote Laves phase precipitation. Aging time (t) has a significant effect on the plasticity of 9Cr-F/M steel. When t < 2500 h, the plasticity of 9Cr-F/M steel has little change, but when the Si content is increased to 1.0%, the plasticity decreases greatly after aging for 5000 h, which is attributed to the precipitation and growth of Laves phase at the grain boundary.