The effect of tempering temperature on the mechanical properties and fracture morphology of a NiCrMoV steel

The present study focuses on the mechanical properties and the fracture morphology of a NiCrMoV steel with a specific composition. All specimens were austenitized at 870 °C for 1 h, followed by oil quenching, and then tempered at temperatures in the range of 200–600 °C. The results of tensile testing indicated that the yield strength (YS) and ultimate tensile strength (UTS) decreased with increased tempering temperature. However, UTS decreased at a higher rate compared with that for the YS. Fractography of the Charpy impact specimens did not show cleavage and/or quasi-cleavage. The presence of dimples was obvious at the fracture surface of these specimens, indicating a ductile fracture mechanism. The Charpy V-Notch (CVN) impact energy was improved by increasing the tempering temperature without any evidence of tempered martensite embrittlement (TME). The lack of TME was attributed to the chemical composition, namely the Mn, Si and Mo content of the steel investigated.