Method for regulating and controlling ferrite grain size of nodular cast iron

The invention discloses a method for regulating and controlling the grain size of spheroidal graphite cast iron ferrite, and provides a novel method for regulating and controlling the grain size of spheroidal graphite cast iron ferrite through heat treatment on the basis of the mechanism that the thicker the spheroidal graphite cast iron ferrite grains are, the higher the low-temperature impact energy is. According to the method, as-cast nodular cast iron is heated to a secondary graphitization temperature range, and ferrite grains are promoted to grow while a matrix is ferritized in the heat preservation process. In the heat preservation process, a pulse type temperature control mode is adopted, so that the highest temperature exceeds the transformation temperature from ferrite to austenite in a small amount and in a short time, and then the temperature is reduced to the secondary graphitization temperature range, so that rapid growth of ferrite grains is stimulated. According to the method, the problem that