Research on the influence of heat treatment parameter on the mechanical property of austempered ductile iron

DI materials were quenched at the temperature of 250°C, 300°C, 350°C and with the isothermal time of 1h, 2h and 3h respectively. So there were nine different ADI materials, which owned different mechanical properties. Through analyzing the changes of their metallographic structures, curves of the relationships between quenching temperatures, isothermal time and materials intensity, hardness could be built respectively. A model that shows the relationships between parameters of heat treatment and hardness was built in the base of fuzzy subtractive clustering method, and the correlation coefficient between predicted and real values was calculated, with which the rules of isothermal temperatures affecting the mechanical properties of ADI could be further studied. Test results show a significant improvement in metallographic structure and mechanical properties of the material as a result of different heat treatment process. From the curves and fuzzy model, we knew that the effect of austempering temperature on the mechanical properties of ADI was predominant, whereas austempering time was inferior. As the temperature increased, the tensile strength and hardness increased, and as the time increased, tensile strength increased at first, and then decreased, hardness decreased at first, and then increased.