Microstructure and Mechanical Properties of Modified M2 High‐Speed Steel by Adding La2O3 in the Electroslag Casting Process

Abstract

An electroslag casting method is used to add rare‐earth La to M2 high‐speed steels by adding La2O3 into the molten slag. The effects of the La content on the microstructure and mechanical properties of M2 high‐speed steel are studied. The results show that rare‐earth La is effectively added to steel by taking advantage of the decomposition of La2O3. The rare‐earth La partially modifies the pre‐existing oxide and sulfide inclusions into small and spherical rare‐earth oxysulfide inclusions. By adding an appropriate amount of La, the as‐cast iron dendrite matrix and coarse eutectic carbides can be refined, the carbide content is reduced, the carbide network is broken, and the decomposition of M2C into M6C and MC is promoted. After heat treatment, the network breaking and spheroidalization of the carbides are further facilitated, and the carbide content is reduced. The impact toughness and bending strength of the studied samples are improved by modifying the inclusions and optimizing the microstructure.