The process is: the iron casting is heated to a temperature of 860-900℃ to keep the matrix austenitized, then cooled in oil or molten salt to achieve quenching, and then tempered at 500-600℃ to obtain tempered sorbite structure ( Generally there is still a small amount of lumpy ferrite ) , the shape of the original spherical graphite remains unchanged. After treatment, the strength and toughness match well, which is suitable for the working conditions of shaft parts. Nodular graphite castings now use rare earth magnesium alloys as spheroidizing agents , which are produced by professional production plants . The iron furnace is the same as gray iron. In order to ensure good spheroidization, the content of sulfur and phosphorus should be lower. Considering the temperature loss during incubation, the temperature of molten iron should be higher than that of gray iron. Non-ferrous alloys. The development of China's machinery industry has moved the casting market in China. As the main castings, the quality of ductile castings has a great impact on the casting market. One of the main reasons affecting the quality of ductile castings is the heat treatment of ductile castings. .