Microstructure, tensile and toughness properties after quenching and partitioning treatments of a medium-carbon steel

The effect of different microstructures on the tensile and toughness properties of a low alloy medium carbon steel (0.28C–1.4Si–0.67Mn–1.49Cr–0.56Mo wt%) was investigated, comparing the properties obtained after the application of selected quenching and partitioning (Q&P) and quenching and tempering (Q&T) treatments. After Q&T the strength–toughness combination was the lowest, whereas the best combination was achieved by Q&P, as a result of the carbon depletion of the martensite and the high stabilization of the austenite. Nonetheless, the presence of islands of martensite/austenite (MA) constituents after Q&P treatments prevented the achievement of toughness levels comparable to the ones currently obtainable with other steels and heat treatments.