Analyzing the Effect of CeB₆ on Microstructure and Mechanical Properties of High-Speed Steel Consolidated by Powder Metallurgy

By adding various amounts of CeB₆, high-speed steel (M3:2) was consolidated by powder metallurgy in the form of sintering. The addition of CeB₆ improved the density of the sintered steel and the formation of M₆C phase in microstructure. It is speculated that CeB₆ was decomposed into boron and cerium. Boron atoms were enriched in M₆C carbide phases, but cerium atoms were mainly clustered on grain boundary while they were converted to oxides, whereby the mechanical properties were improved. For example, upon the sintering at 1210 °C, relative density ~ 98.5% and average grain size ~ 18 μm were obtained with CeB₆ content at 0.3 wt.%. Excellent mechanical properties, e.g., the Rockwell hardness ~ 52 HRC, flexural strength ~ 3.05 GPa, and fracture toughness ~ 40.92 MPa m^1/2, were achieved in the sample containing 0.3 wt.% CeB₆, which implies accordingly remarkable increases by 23.5, 38.1, and 23.7%, of the properties compared with those in the sample free of CeB₆.