The Influence of Shortened Low- and High-Temperature Tempering on the Crack Growth Resistance of Differently Alloyed Tool and Structural Steels

Present study investigates the effect of low-temperature tempering duration (۲۰۰ °C, ۱ – ۱۴ h) and short-duration low- and high-temperature tempering regimes on crack resistance development in various alloyed tool and structural steels: ۵Kh۲SMF, KhVG, ۱۲KhNVA and ۳۸KhN۳MFA. The experiments revealed that the dependence of crack resistance on tempering duration for each steel grade mentioned above exhibits a non-monotonic character. For KhVG steel, maximum crack resistance is achieved after tempering for ۵ h; for ۵Kh۲SMF steel – after ۳ and ۵ h; for ۱۲KhNVA – after ۳, ۵, and ۷ h; for ۳۸KhN۳MFA – after ۳ h. Application of short (minute-scale) tempering regimes enables achieving equal or greater crack resistance values at a comparable hardness level in comparison to standard (hour-long) tempering. For ۵Kh۲SMF steel, short-term low-temperature tempering (۲۶۵ °C, ۱۰ min and ۶۶۰ °C, ۱۵ min) improves resistance to brittle fracture compared to standard tempering regimes at ۲۰۰ and ۶۰۰ °C for ۲ h. For KhVG steel, the optimal short tempering regime of ۲۵۵ °C, ۶ min ensures enhanced crack resistance with only a minor reduction in hardness, which is probably due to the preservation of a higher amount of retained austenite. For ۱۲KhNVA steel, short tempering at ۲۵۵ °C, ۶ min and ۲۷۰ °C, ۷ min results in a substantial increase in crack resistance – ۵۰۰ and ۳۴۰ kgf, respectively, compared to brief standard tempering, with only insignificant loss of hardness. For ۳۸KhN۳MFA steel, short tempering regimes allow achieving similar or higher crack resistance values without any decrease in hardness.

کلیدواژه ها:

Steel ، quenching ، Tempering ، Hardness ، crack resistance ، austenite