Domestic research on low temperature impact toughness of nodular cast iron started late, but it has developed rapidly in recent years. Before, the domestic wind power generation technology was not perfect, and the operation cost of wind power was high. Although it was widely valued, there were few substantive studies. The low-temperature impact toughness of nodular cast iron has not attracted much attention, and there is no nodular cast iron brand used to produce wind power accessories in the current nodular cast iron standard GB / T1348-1988. Since, with the continuous development and improvement of wind power generation technology, the cost of wind power has been reduced, and the wind power industry has gradually sprung up. Some large foundry enterprises, foundry research institutes and colleges and universities have successively begun to study the low-temperature impact toughness of nodular cast iron. After research and development in recent years, China has made great progress in the development and application of low-temperature ductile nodular cast iron and achieved many results.
Different from foreign research, domestic research focuses more on the actual production, aiming at producing qualified casting products, and pays more attention to its practical application while paying attention to theoretical research. Li Peng of China first heavy machinery group and others studied the production technology of nodular iron castings for large wind turbines by taking the wheel hub as an example. By selecting appropriate chemical composition, optimizing spheroidizing treatment and inoculation treatment process, and selecting low-temperature graphitization annealing process, qualified wind power castings are produced, which provides practical experience for the production of wind power castings.
Huang Yongchang of Harbin University of technology and others studied the effects of carbon, silicon, manganese and copper on the microstructure and mechanical properties of nodular cast iron by orthogonal method. The results show that the factors affecting hardness are copper, silicon, manganese and carbon from primary to secondary, the factors affecting impact toughness are silicon, carbon, copper and manganese from primary to secondary, and the factors affecting wear resistance are carbon, copper, manganese and silicon from primary to secondary.
Shen Hongjie of Qingdao Sifang locomotive and rolling stock Casting Co., Ltd. and Wang Zehua of Hehai University jointly developed the low temperature toughness ductile cast iron. The results show that the content of silicon, manganese and phosphorus has a significant effect on the low-temperature impact toughness of nodular cast iron. The amount of silicon should be controlled below, and the lower the content of manganese and phosphorus, the better.
Lu Zhong of Inner Mongolia University of technology studied the effect of nickel content on the low temperature impact toughness of QT400-18L. Different contents of nickel were added to one and two-stage graphitization annealing heat treatment process was selected. The experimental results show that when the amount of nickel is 0.3%, the grain of the sample is refined after heat treatment, and the typical graphite ball and ferrite structure can be obtained, which has the best impact toughness.
Wang Qiang of Jilin University and others studied the chemical composition, spheroidization and inoculation process and heat treatment process through the development of ferritic nodular cast iron for low temperature. The experimental results show that adding an appropriate amount of nickel can significantly improve the low-temperature impact toughness, and two-stage graphitization annealing heat treatment is an important way to obtain low-temperature ferritic nodular cast iron.
Yang Qiyu of Beijing University of science and technology studied the effect of heat treatment process on the impact toughness of nodular cast iron. Through the study of three different annealing heat treatment processes of nodular cast iron, the results show that after two-stage graphitization annealing at 920 ℃, the impact absorption energy at – 40 ℃ can be reached and the impact toughness is high.
Gong wenbang of Huazhong University of science and technology studied the production process and mechanical properties of high toughness isothermal quenched nodular cast iron. The results show that the mechanical properties of the samples are obviously better than the EU standard value, and the mechanical properties of alloyed high toughness ADI castings do not follow the variation law among tensile strength, elongation, impact energy, yield strength and Brinell hardness in en1564 standard.
The effect of Hebei Jinhai University on the microstructure of cast iron ball was studied. It is found that the spheroidization rate has little effect on the tensile strength of ferrite
, which has a great influence on elongation. Pearlite and mixed matrix are just the opposite, with little effect on elongation and great effect on tensile strength. The impact toughness of graphite cast iron increases linearly with the increase of spheroidization rate.