Microstructure evolution of an ultra-high strength metal alloy with tempering temperature

Optical microscopy (OM) and transmission electron microscopy (TEM) were used to investigate the effect of tempering temperature on the experimental extra-high carbon steels. It is found that tempering reaction can reduce austenite content and influence the stability of the austenite. As-normalized microstructure is a mixture of twinned martensite and retained austenite. Tempered at 250 °C for 2 h, lath martensite can occasionally be found nearby the diffusionally decomposed austenite area. It also is found that tempering at 650 °C for 2 h, nanoparticles of carbides precipitate in the martensite and decomposed austenite.