Effect of Different Austenitizing Temperatures on the Microstructure and Mechanical Properties of Austempering Gray Cast Iron

To meet the mechanical property requirements of gray cast iron for the shells of coal mine explosion-proof equipment and investigate the effect of austenitizing temperature on the microstructure and mechanical properties of gray cast iron, isothermal quenching was conducted at four austenitizing temperatures (890 °C, 910 °C, 930 °C, and 950 °C), with cast samples as the control group. The microstructure was using a scanning electron microscope, and the mechanical properties were tested using a universal tensile testing machine, a drop-weight impact testing machine and a hardness tester. The results show that the matrix microstructure of gray cast iron transforms from ferrite + pearlite to ausferrite after isothermal quenching, and the proportion of ausferrite increases gradually with the rise of austenitizing temperature. At an austenitizing temperature of 930 °C, the hardness of the sample reaches a maximum value of 247.6 HBW, which is 31.9% higher than that of the cast sample. At 910 °C, the impact energy and tensile strength achieve the optimal values of 9.59 J and 219 MPa, respectively, with an increase of 6.43 J and 51 MPa compared with the cast sample. Comprehensive analysis indicates that the austenitizing temperature of 910 °C can improve the strength while maintaining good toughness, which makes it more suitable for application scenarios requiring both strength and toughness such as coal mine explosion-proof equipment.