Mechanical properties and microstructure of Mg-treated and Ca-treated industrial H13 steel after quenching and tempering

The effect of magnesium treatment and calcium treatment on the microstructure and mechanical properties of industrial H13 steel after quenching and tempering was investigated. The impact toughness and tensile tests were mainly carried out, and the microstructure was observed by scanning electron microscopy, electron backscattered diffraction, and X-ray diffraction. The results show that magnesium treatment is still feasible in industrial trials. It is mainly manifested in the refinement of lath martensite and carbides. Compared with calcium treatment, the prior austenite grains and carbides size of industrial H13 steel treated with magnesium decreased by 3.17 μm after quenching. After quenching and tempering, the carbides (especially V-rich carbides) in Mg treatment obviously spheroidized and distributed uniformly and increased in quantity significantly. The lath martensite size is reduced from 2.45 to 2.31 μm. This suggests that magnesium treatment was able to yield smaller grains and more evenly distributed carbides. Moreover, the impact toughness, yield strength, and ultimate tensile strength of industrial H13 steel with magnesium treatment increased by 28%, 65.5 MPa and 123.7 MPa, respectively. The increment of strength mainly comes from dislocation strengthening, grain refinement strengthening, and precipitation strengthening, among which precipitation strengthening accounts for the largest proportion.