purpose: generally to obtain a ferrite matrix, improve its plasticity and toughness, improve machinability, and eliminate casting stress.
1. High-temperature annealing: The high-temperature annealing process is to heat the casting to above the eutectoid temperature range, that is, 900-950℃, hold for 2-4 hours, so that the casting will undergo the first stage of graphitization, and then slowly cool to 600℃ with the furnace to make the casting happen. Graphitization in the middle and second stages, and then air cooling.
2. Low temperature annealing: The low temperature annealing process is to heat the casting to near the eutectoid temperature range, that is, 720-760℃, hold for 2-8 hours, so that the casting will undergo the second stage of graphitization, and then slowly cool to 600℃ with the furnace, and then air-cooled. .
purpose: to make the mixed structure of the matrix in the as-cast state into a pearlite matrix, thereby improving its strength and wear resistance.
1. High temperature normalizing: heating the casting to above the eutectoid temperature range, generally 880-920℃, holding it for 1-3 hours, so that the matrix structure is completely austenitized, and then air-cooled out of the furnace to make it within the eutectoid temperature range. Quickly cool to obtain a pearlite matrix.
2. Low-temperature normalizing: heating the casting to the eutectoid temperature range, that is, 840-860℃, holding it for 1-4 hours, so that the matrix structure is partially austenitized, and then air-cooled out of the furnace. Improve the toughness and plasticity of the casting, but the strength is lower.
three. Although the normalizing treatment of austempered ductile iron is widely used, when the shape of the casting is complex and high comprehensive mechanical properties are required, the normalizing treatment has been difficult to meet the technical requirements, and austempering is often used.
The process is to heat the casting to 860-920°C, hold it for a certain period of time (about twice that of steel), and then quickly put it in an isothermal salt bath at a temperature of 250-350°C for half an hour to one and a half hours of isothermal treatment. Then take out the air cooling. four. Quenching and tempering treatment For castings with complex forces, large cross-sectional dimensions, and high comprehensive mechanical performance requirements, normalizing or austempering cannot meet the above requirements, so quenching and tempering (quenching + high temperature tempering) is often used.