LAUSR

Inclusions are inevitably present in molten steel during the smelting process. The morphology, size, number and distribution of inclusions determine the cleanliness level of molten steel, which will affect the impact toughness, fatigue properties, fracture toughness of steel ingots. Especially large-sized hard inclusions are usually crack sources, which directly cause quality defects in steel ingots.1–5) H13 steel (4Cr5MoSiV1) is the most widely used and most representative hot work die steel, widely used in hammer forging dies, hot extrusion dies and die casting dies. H13 steel generally works under harsh conditions. It needs to withstand high temperature and high pressure and sometimes suffer large impact. Thus the thermal fatigue performance is required to be high. For the die steel whose main failure mode is fatigue damage, brittle inclusions that tend to cause intense stress concentration in the steel matrix are one of the important reasons for service life.6–8) Therefore, improving the cleanliness level of molten steel can significantly improve the product quality and service life of the die steel. Due to strong thermodynamic affinity with O and S,9–11) the application of rare earth metals in steel has received extensive attention. Some scholars showed that rare earth metals could reduce the contents of impurity elements such as O and S and effectively modify inclusions in steel and Ni-base alloy.12,13) However, some other scholars put forward different opinions.14–17) Evolution Mechanism of Inclusions in H13 Steel with Rare Earth Magnesium Alloy Addition