In the production of low temperature ductile nodular cast iron, the common method is to add nickel, which can improve the impact toughness of nodular cast iron to a level of 40 ℃. As China’s nickel resources are very limited, the current domestic market price of nickel is about 200000 yuan / ton. Based on the addition of 0.3%, the production cost will increase by 600 yuan / ton.
For the bismuth addition method used in the experiment, the highest impact toughness at 40 ℃ is 17J. The domestic market price of bismuth is about 130000 yuan / ton. Calculated by adding 0.006%, the production cost is increased by 8 yuan / ton, which is only about 1 / 7 of that of nickel addition method.
(1) Bismuth is an element that interferes with the graphite spheroidization of nodular cast iron. Although fine fossil graphite can improve the low-temperature impact toughness of nodular cast iron, it will also deteriorate the morphology of graphite ball and reduce the properties of nodular cast iron due to excess. The experiment only studied the addition of 0.006% bismuth, but did not study the effect of excessive bismuth on Microstructure and properties.
(2) In order to maintain the impact toughness and improve the tensile strength, copper was added in the experiment. When copper and bismuth are added at the same time, the stability of mechanical properties is poor, which is reflected in the good low-temperature impact toughness of single cast samples, while the mechanical properties of attached cast samples are not ideal. How to improve the stability of mechanical properties after the addition of copper and bismuth is a problem that needs to be further solved.