Effect of rare earth on primary carbides in H13 die steel and their addition method: a review

Abstract

Larger-sized primary carbides lead to stress concentration during the application of H13 hot-work die steel, resulting in microcracks and fatigue failure. Rare earth was usually added to modify the carbides and inclusions. The existing literature is reviewed on the effect of rare earth on primary carbides in H13 steel. A comprehensive review on the effect of rare earth on the characteristics of primary carbides, i.e., number, size, morphology, and thermal stability in H13 steel, was done. The precipitation mechanism and nucleation of primary carbides with rare earth were summarized. The position and form of rare earth in steel and their effects on alloying elements segregation were reviewed. The addition techniques of rare earth in H13 steel were compared, and the prospects for other uncommon rare earth and emerging technology were present. Based on the current references, it can be known that adding rare earth facilitated refined and dispersed primary carbides. The size of primary carbides would be reduced, and their morphology would be improved because the rare earth inclusions formed in H13 steel can act as nucleation cores for γ-Fe or δ-Fe, refining the dendritic structure. Besides, the number of primary carbides at grain boundaries would be significantly reduced. However, rare earth had little impact on thermal stability. The nucleation of primary carbides tended to be inhibited due to the modification of inclusions by rare earth which were likely to be nucleation cores for primary carbides. Rare earth had been reported to affect the mechanism and process of primary carbide precipitation. Additionally, the addition of rare earth can inhibit the segregation of alloying elements and carbon diffusion by calculation. Thus, laboratory experiments and theoretical calculations need to be conducted to study the states and evolution of rare earth steels.