Effect of graphite morphology and distribution on properties of nodular cast iron

In recent years, with the development of mechanical equipment towards portability, low energy consumption and high efficiency, new requirements are put forward for the properties of nodular cast iron, especially low temperature impact toughness. The conventional methods to improve the properties of nodular cast iron mainly include alloying and self microstructure optimization. The effect of Alloying on the properties of nodular cast iron has always been the focus of research, and a series of studies have been carried out at home and abroad.

Yu Guangyuan and lekakh studied the effects of Si element and content on the properties of nodular cast iron. The results show that Si can improve the strength and hardness of nodular cast iron, but the increase of Si element can increase the ductile brittle transition temperature and significantly reduce its low temperature impact toughness. Lacaze et al. And sun et al. Studied the effect of Ni on the properties of nodular cast iron. The results showed that Ni could significantly improve the tensile strength and hardness, but had no obvious effect on the low temperature impact toughness. Wang Wenhui et al. Studied the effect of Ni and Si element composition on the low-temperature impact toughness of nodular cast iron. The results show that with the increase of Ni and Si content in the material, the low-temperature impact energy of low-temperature and High Toughness Nodular Cast Iron continues to decrease and the brittle fracture characteristics are intensified. Omran et al. Studied the effect of Mn on the properties of nodular cast iron. The results show that Mn can significantly improve the yield strength, but has no obvious effect on the tensile strength, and the increase of Mn content can significantly deteriorate its impact toughness.

(1) the diameter distribution of the three spheroidizing processes is nearly normal, and the diameter of qt-cwm graphite is the smallest, the largest number and the smallest diameter fluctuation; Qt-cfm graphite has the largest diameter, the least quantity and the largest diameter fluctuation.

(2) the hardness, yield strength and tensile strength are gradually reduced according to qt-cfm, qt-tcm and qt-cwm, with a reduction range of 10% ~ 20%, but the impact toughness is significantly improved, with a range of about 200%.

(3) the interpretation of spheroidization rate by neural network model is the most important, followed by the standard deviation of graphite ball diameter and the number of graphite balls, and then the average diameter of graphite balls.

In conclusion, the addition of alloy elements can not take into account all aspects of mechanical properties, especially low-temperature impact toughness, and even worsen the low-temperature impact toughness, and the cost of alloy elements is high.

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