Both graphite ball and matrix will affect the mechanical properties of nodular cast iron.
It is found that with the increase of spheroidization grade and graphite size grade of nodular cast iron, the tensile strength and elongation are slightly improved, the hardness changes little, and the low-temperature impact toughness is greatly improved. Therefore, in order to ensure the low-temperature impact toughness of nodular cast iron, the spheroidization level should not be lower than grade 2 and the graphite size level should be higher than grade 6.
The figure shows the relationship between pearlite content and mechanical properties of nodular cast iron.
It can be seen from the figure that with the increase of pearlite content of nodular cast iron, the tensile strength and hardness gradually increase, while the elongation and low-temperature impact toughness obviously decrease. When the pearlite content is less than 25%, the tensile strength is about 400MPa, the elongation is more than 18%, the Brinell hardness is about 150, and the low-temperature impact toughness is more than 12j. When the content increases again, the tensile strength increases obviously, the hardness increases gradually, and the elongation and low-temperature impact toughness decrease obviously. Therefore, it can be seen that the pearlite content of nodular cast iron for wind power fittings can not exceed 25% at most under the as cast condition.