New Prediction Model of Tempered Martensite Hardnesses for Quenched and Tempered Low-Alloy Steel

Several experimental formulas have been proposed by many researchers to estimate the tempered martensite hardness of high-strength low-alloy (HSLA) steel under different tempering conditions. The objective of the present study was to develop a new mathematical model to estimate the tempered martensite hardness and the tensile strength for low-alloy steels under different tempering conditions with enhanced accuracy. The experimental results of previous research were relied on to develop the new mathematical models. A best fit for the tempered martensite hardness model has been developed by adding a factor of correlation obtained from the difference (error) between the hardness values measured by literature and the calculated hardness values from the tempered martensite hardness model. Moreover, the best equation that feature the value of this difference was presented as a function of the tempering temperature. The new model considered the combined parameters, which are tempering conditions (temperature and time) and the parameters of alloy elements. The proposed model has been examined and compared with the experimental results of a previous research and was shown to provide a good reasonable approximation with mean percentage error between the measured and calculated of hardness values was 0.89% and 0.79% for holding time of 2 and 48 h, respectively. Furthermore, it was concluded that the hardness feature is affected significantly by tempering parameters and the parameters of alloy elements. The hardness showed also decreasing in values with increasing the tempering temperature and holding. Also, the proposed equation for the tensile strength and area reduction have been written as a function of the tempering temperature.