Abstract: A reduced activation steel produced by vacuum induction melting and electroslag remelting was used as the research object and the effects of normalizing temperature and tempering temperature on microstructure and mechanical properties of the steel were investigated. The phase transformation temperature of the steel was measured and calculated by thermodilatometry and Thermo-Calc software. The microstructure and precipitates of the steel normalized and tempered were observed by means of optical microscope, scanning electron microscope and transmission electron microscope. The hardness, tensile and impact property were tested by microhardness tester, electronic universal material testing machine and pendulum impact testing machine. The results show that the lower normalizing temperature cannot eliminate the rolling banded structure, and the higher normalizing temperature result in grain coarsening. When tempered at different temperatures, the microstructure of the steel is tempered martensite. The precipitation of Laves phase can be avoided by tempering at 755 ℃ and 790 ℃. With the increase of tempering temperature, the precipitation of M₂₃C₆ and MX in the steel coarsens, and the precipitation of carbide reduces the solution strengthening effect of carbon. The microhardness, yield strength and tensile strength decrease with the tempering temperature increasing. When the tempering temperature ranged from 690 ℃ to 755 ℃, the elongation and impact absorbed energy at room temperature increase with the tempering temperature, and the ductile to brittle transition temperature decreases with the tempering temperature. The elongation and impact absorbed energy of the steel tempered at 790 ℃ decrease, and the ductile to brittle transition temperature increases. The best comprehensive mechanical properties can be obtained by normalizing at 1050 ℃×30 min+tempering at 755 ℃×90 min. Fine grain size and dispersed nanometer carbides are the key factors for the excellent mechanical properties of the steel.

Key words: reduced activation steel, normalizing, tempering, precipitated phase, tensile properties, impact property