Influence of Tempering Temperature on the Mechanical Properties of CrMnNiMo Steel

The mechanical properties of a new-invented CrMnNiMo steel tempered at 200°C~650°C were studied. The results show that mechanical properties are affected by tempering temperature severely. Strengths drop rapidly with increasing tempering temperature, concomitant with gradually rise of elongation and reduction in area. Yet impact energy decreases stepwisely, reaching minimum value at around 450°C and then ascends fast. Comparatively, optimum mechanical properties are reached at about 550°C. Fracture surface of impact specimen, dominated by dimples with different sizes, shows failure by microvoid coalenscence. Large amounts of complex inclusions, mainly Rare Earth-oxysulfides and aluminum oxides, sphericity or ellipsoid with dimension less than 10μm, are observed, which have little influence on mechanical properties.