The processed castings have high hardness and certain toughness, retain the lubricating properties of graphite, and improve wear resistance. As shaft parts, ball milled iron castings, such as crankshafts and connecting rods of diesel engines, require comprehensive mechanical properties with high strength and good toughness. The iron castings are quenched and tempered.
The process is to heat the cast iron to a temperature of 860-900℃ to keep the matrix austenitized, then cool in oil or molten salt to quench it, and then temper at 500-600℃ to obtain a tempered sorbite structure , The original spherical graphite shape remains unchanged. After treatment, the strength and toughness match well, which is suitable for the working conditions of shaft parts.
Due to the high tendency of spheroidizing cast iron in the casting process of this ordinary gray cast iron, the internal stress is also large, it is difficult to obtain pure ferrite or pearlite matrix for iron castings, so in order to improve the ductility or toughness of iron castings, often Reheat the cast iron to 900-950°C and keep it for sufficient time for high-temperature annealing, and then cool it to 600°C and let it cool.
The purpose of normalizing ball milled cast iron is to convert the matrix structure to fine pearlite structure. Only the ball milled cast iron with the matrix of ferrite and pearlite must be reheated to a temperature of 850-900℃. The original ferrite and pearlite The spheroidal graphite is converted into austenite, and part of the spherical graphite is dissolved in the austenite. After heat preservation, the air-cooled austenite is transformed into fine pearlite, so the strength of the ductile casting is improved.