Effects of silicon carbide contents on the microstructure of sintered steels

Abstract

Silicon and carbon are common alloying elements in wrought steel production. A judicious content of silicon can prevent carbide precipitation. So silicon is commonly used in the production of carbide-free bainitic steel, which is one of advanced high strength steels. It was found previously that both silicon and carbon elements from silicon carbide additives can be alloyed to form iron-based powder compacts via sintering process. In this study, sintered steels were produced from mixtures of pre-alloyed Fe-0.50Mo-0.15Mn powder and various silicon carbide contents (1.0, 2.0, 3.0, and 4.0 wt.%) using 'press and sinter' process. Microstructures of sintered steels changed in accordance with added silicon carbide content. The microstructure consisting of ferrite plate and martensite/austenite constituent in the low silicon carbide-added steel was changed to the microstructure with martensite matrix in high silicon carbide-added steel. Surprisingly, diffusional phase transformations resulting in the formations of pearlite and inverse bainite were occurred prior to diffusionless martensitic transformation in high silicon carbide-added steel. The ultimate tensile strength and hardness of the studied sintered steels increased with increasing martensite volume fraction but dropped with the presence of grain boundary carbide networks.