Microstructure and mechanical properties of Cr14 ultra-high-strength steel at different tempering temperatures around 773Â K

This study investigated the effect of tempering temperature on the microstructure and mechanical properties of Cr14 ultra-high-strength steel. The steel was first normalized at 1223 K for 1 h, cold treated at 200 K for 1 h, and then tempered at five different temperatures between 723 K and 833 K for 4 h. The microstructures of the Cr14 steel were characterized by X-ray diffraction, optical microscopy, field emission scanning electron microscopy, and transmission electron microscopy. The tensile strength, impact toughness, and fracture toughness properties of Cr14 steel at different tempering temperatures were evaluated. Results show that inclusions in the steel mainly comprise MgO-Al2O3-SiO2 and a (Mo, W)C precipitated phase. With increasing tempering temperature, carbides became increasingly segregated and exhibited a chain-like distribution. In addition, the tensile strength increased and the yield strength, elongation, impact toughness, and fracture toughness decreased with increasing tempering temperature. For tempering temperatures in the range 753-773 K, the volume fraction of austenite decreased rapidly from 20% to approximately 12% while the mechanical properties changed rapidly as well.