In the production process of nodular iron castings, in order to ensure the product quality, the tensile strength, yield strength, elongation after fracture and spheroidization rate of the test block attached to the same furnace must be within the range of the material grade requirements. This requirement must be strictly controlled in the physical and chemical inspection specifications. Especially, if the nodularity rate of the test block is unqualified, we should look at the metallography of the casting body If the metallographic spheroidization rate is less than 90%, the castings must be scrapped, which will cause certain economic losses.
In the middle of February 2020, the physical and chemical laboratory found that the tensile strength, yield strength and elongation after fracture of nodular cast iron test block were unqualified, and the spheroidization rate of metallographic block cut from the sample was only 65% – 80%, which was unqualified. We immediately tested the body metallography, and found that the spheroidization rate of some castings was only 70% – 85%, so the performance was not qualified The casting of lattice must be scrapped.
There are many factors that cause bad spheroidization, such as technical problems, operation problems and management problems. Therefore, in order to obtain high-quality nodular cast iron, we should strictly control and eliminate the causes of poor spheroidization in production.