In terms of heat treatment process, Kadir Kocatepe et al. Studied the effect of high temperature annealing heat treatment process on the mechanical properties of nodular cast iron. In order to obtain the best mechanical properties, through several groups of comparative experiments, it is found that the best composition of nodular cast iron is WC = 3.5%, WSI = 1.9%, WMN = 0.32%. After high temperature annealing heat treatment, the matrix structure is ferrite and a small amount of austenite. At this time, it not only has high tensile strength, but also has good impact toughness. Susil et al. Studied the effect of isothermal quenching heat treatment on the microstructure and mechanical properties of nodular cast iron. The experiment was conducted by austenitizing at 950 ℃ for 1 hour, then cooling to 860 ℃ for 0.5 hours, and finally isothermal quenching. The experimental results show that the nodular cast iron after two-stage isothermal quenching has higher strength and impact toughness, which is suitable for lightweight automobile industry.
In terms of matrix structure, the effects of pearlite and ferrite content on the mechanical properties of nodular cast iron were studied. With the increase of pearlite content, the tensile strength increases. When the pearlite content is, the tensile strength is 91-98% higher than that of all ferrite, while the impact toughness is reduced by 75%. With the increase of ferrite content, toughness and plasticity increase and hardness decrease. J. Baeal et al. Studied the matrix structure and mechanical properties of low carbon nodular cast iron. The metallographic observation shows that the low temperature impact toughness of nodular cast iron can be improved when there is a small amount of residual austenite in the matrix structure. If austenite is transformed into martensite by heat treatment, microcracks will occur around it. In the low-temperature impact test, the microcrack expands rapidly and finally brittle fracture occurs. At this time, the low-temperature impact toughness will be significantly reduced.
In addition to studying the chemical composition, heat treatment process and matrix structure of nodular cast iron, G. toktas et al. Also studied the effect of different temperatures on the impact toughness of nodular cast iron. The results show that ferrite has the highest impact toughness, while austenite ferrite has the best comprehensive properties. M. Cavallini et al. Studied the fracture mechanism of nodular cast iron by scanning electron microscope, and described in detail the interaction between ferrite, pearlite, bainite and propagating crack during fracture The essential reason for the fracture of nodular cast iron was revealed.