Effects of tempering on microstructure, hardness, wear resistance, and fracture toughness of Cr3C2/steel surface composites fabricated by high-energy electron-beam irradiation

Abstract

This study aimed at improving hardness, wear resistance, and fracture toughness by tempering chromium carbide (Cr3C2)/carbon steel surface composites fabricated by high-energy electron-beam irradiation. The mixture of Cr3C2 powders and MgF2 flux was placed on a plain carbon steel substrate, and then electron beam was irradiated on this mixture using an electron-beam accelerator. In the specimens fabricated with flux powders, the surface composite layer of 1.9 mm in thickness was successfully formed without defects, and contained about 3 vol pct of Cr7C3 carbides in the matrix composed of plate-type martensite and austenite. When the Cr3C2/steel surface composite was tempered, the martensite was resolved, and Cr7C3 carbides were coarsely precipitated along cell boundaries while the austenite disappeared, thereby leading to the increase in hardness and wear resistance. Observation of the microfracture process of the 500 C-tempered surface composite revealed that cracks initiated and propagated along intercellular Cr7C3 carbides and stopped propagating when they met the relatively ductile tempered martensite matrix. Accordingly, this composite showed improved fracture toughness and presented good application possibilities as hard and tough wear-resistant materials.