关键词: 高Cr, 马氏体, 正火, 析出强化, 力学性能

Abstract: Effect of normalizing heat treatment on microstructure， mechanical properties and fracture mechanism of high Cr martensitic heat resistant steel was investigated by optical microscopy， transmission electron microscopy (TEM) and scanning electron microscope (SEM) analysis. The results show that after normalizing at 900~970℃， grain size is very small which is less than 10μm. After normalizing at 1060~1200℃， grain size increases rapidly which is about 33μm at 1060℃. After normalizing at 1060℃ for 2h and tempering at 760℃ for 3h， the excellent mechanical property can be achieved where the tensile yield strength at room temperature and high temperature at 600℃ is about 535MPa and 380MPa， respectively; while a longer normalizing time at 1060℃ has no obvious effect on mechanical property. Moreover， after normalizing at 1060℃ for 2h and tempering at 760℃ for 3h， mechanical properties can also be improved effectively by the fine grains of the tempered martensite， the precipitate of M₂₃C₆with its size of 200 ~ 300nm at the grain boundaries and the MX dispersion with its size of 5~50nm inside grains.

Key words: high Cr, martensite, normalizing, precipitation strengthening, mechanical property