Prediction Model and Control Strategy of Hardenability of Gear Steel Based on Production Data

The hardenability of a carburized Mn-Cr gear steel was calculated and compared by linear model, nonlinear model, analytical function, partial approximation method, 1stOpt, and JMatPro software. Jominy hardness curve and chemical composition data were obtained from a steel plant. An appropriate model was optimized and chosen in accordance with the calculation results. Furthermore, the causes of hardenability fluctuations were clarified. The fluctuation of practical chemical composition was statistically analyzed and calculated by the selected model. The main unstable alloying element was Mn, which had the biggest influence on J15. More significantly, the fluctuations of residual elements Ni and Cu were the root cause of large bandwidth of hardness curve. On this basis, the hardenability bandwidth was controlled to within 4 HRC by composition adjustment. Finally, the shortcomings of the various models were discussed, especially the effect of boron and the micro-alloying element. The result showed that the hardenability was slightly improved after adding 0.02% Nb. The hardenability was reduced when Nb content increased to 0.06%. Boron greatly improved the hardenability, but its effect was unstable.