Abstract: Effect of quenching temperature on microstructure and mechanical properties of NM450 corrosion-wear resistant steel was studied by means of scanning electron microscope (SEM), electron backscatter diffraction (EBSD) and mechanical property testing. The results show that the tempered lath martensite microstructure is obtained by quenching at 840-960 ℃ and low temperature tempering. When the quenching temperature is at or lower than 870 ℃, the dispersed second phase appears in the microstructure, and the Cr content is obviously higher than that of the matrix. When the quenching temperature is higher than 900 ℃, the second phase disappears and the austenite grains begin to grow obviously. With the increase of quenching temperature, the strength and hardness of the tested steel tend to decrease, and the impact absorbed energy reaches the highest at 900 ℃. According to the orientation distribution and grain boundary distribution, it can be found that when quenched at 960 ℃, the effective grain size is the largest, the proportion of large angle grain boundary is the lowest and the impact property is the worst. When quenched at 900 ℃, the effective grain size is close to that at 840 ℃, but the microstructure is more uniform, and the proportion of large angle grain boundary increases, which is the main reason for the high impact property when quenched at 900 ℃.

Key words: NM450 corrosion-wear resistant steel, quenching temperature, second phase, hardness, impact property, large angle grain boundary