Recent progress on primary carbides in AISI H13 hot work mold steel

This paper reviewed the recent development of primary carbides in H13 steel from the aspects of solidification segregation theory, solidification method, production process, and alloy design. The relationship between the production process of H13 steel and the characteristics of primary carbides was clarified. During the solidification of H13 steel, primary carbides can be easily generated by dendritic segregation. The primary carbides in H13 steel can be divided into polygonal, stripy, blocky, and eutectic structures according to the different shapes and can be divided into MC, M₂C, M₇C₃, and M₂₃C₆ according to the different structures. The primary carbides can also be classified as Mo-rich, V-rich, and Ti/Nb-rich carbides according to the different compositions. Primary carbides are detrimental to the performance of H13 steel because cracks can easily form around primary carbides during service of the materials. The widely used methods of controlling the primary carbides in H13 steel under industrial production conditions, including solidification control, modification treatment, high-temperature diffusion of the ingot, and alloy composition optimization, were introduced. Modification treatment and solidification control are able to control the size and quantity of primary carbides but are unable to avoid the precipitation of primary carbides entirely. The stability of primary carbides can be relieved by composition optimization. High-temperature homogenization treatment of ingot is the most important means of controlling primary carbides in H13 steel. However, the heating temperature and holding time need further investigation.