Superior mechanical properties of M35 high-speed steel obtained by controlling carbide precipitation and distribution via electropulsing treatment

Abstract

Carbide precipitation and distribution always significantly affect the mechanical properties of High-speed Steel (HSS). Thus, the effect of electropulsing treatment (EPT) on the microstructure and mechanical properties of M35 HSS was investigated in this paper. The results show that the electropulsing austenitising then quenched, followed by electropulsing tempered (EQ + ET) samples, showed a 2.3% increase in Rockwell hardness, a 9.7% increase in the bending strength, and the impact toughness increased by 10.3% compared with the conventional heat treatment (CQ + CT) samples. The superior mechanical properties were attributed to the reduction of retained austenite (RA), the uniform distribution of the carbide, and the refinement of the prior austenite grains. Under the action of the current, Ms increased in response to various combinations of alloying elements, thereby reducing the content of RA. Compared to conventional heat treatments, the electropulsing treatment provides additional Gibbs free energy, as well as a large number of dislocations generated by the thermo-compressive stresses, which increase the carbide nucleation sites, resulting in a large number of small-sized carbides precipitating and uniformly distributed in the matrix. The fracture morphology indicates that micro-cracks arise between the carbide and martensite, and the larger carbide provides a preferential path for crack initiation.