To eliminate the white mouth annealing ordinary gray cast iron plate, cast iron platform surface or thin wall in the casting process due to the cooling too fast white, cast iron pieces can not be cut. To eliminate the white mouth to reduce the hardness often cast iron pieces of this type of reheating to eutectoid temperature above (usually 880 ~ 900 ℃), and heat 1 ~ 2h (if the Si content of cast iron, time can be short) for annealing, cementite decomposition For graphite, and then cast iron parts slowly cooled to 400 ℃ -500 ℃ baked air cooling. In the temperature of 700-780 ℃, the eutectic temperature near the cold should not be too slow, so that too much cementite into graphite, reducing the strength of cast iron. Ductile iron ductile iron ductile iron ductile iron ductile iron ductile iron ductile iron ductile iron ductile iron ductile iron ductile iron ductile iron ductile iron ductile iron cast ductile iron ductile iron ductile iron ductile iron Or toughness, often cast iron pieces reheated to 900-950 ℃ and heat enough time for high temperature annealing, and then cooled to 600 ℃ furnace cooled. During the process, the cementite in the matrix decomposes graphite, and graphite is precipitated from the austenite. These graphite accumulate around the original spherical graphite, and the matrix is ​​completely converted into ferrite. If the as-cast microstructure consists of (ferrite + pearlite) matrix, as well as spherical graphite, in order to improve the toughness, only the cementite in the pearlite is decomposed into ferrite and spherical graphite, and the cast iron is reheated To 700-760 ℃ eutectoid temperature up and down after the furnace cooled to 600 ℃ baked cold. The purpose of normalizing nodular cast iron to increase the ductile iron strength is to convert the matrix into fine pearlite. The process is to re-ferrite and pearlite matrix ductile iron reheated to 850-900 ℃ temperature, the original ferrite and pearlite into austenite, and some spherical graphite dissolved in austenite, the After cooling air-cooled austenite into fine pearlite, casting strength increased. Ductile iron quenching and tempering ductile iron castings as shaft parts, such as the diesel engine crankshaft, connecting rod, requiring high strength and good toughness of the comprehensive mechanical properties, the cast iron pieces for quenching and tempering. Process is: cast iron heating to a temperature of 860-900 ℃ so that the substrate soaking austenitic, and then cooled in oil or molten salt to achieve quenching, after tempering at 500-600 ℃ tempering, get tempered sorbite (There is usually a small amount of massive massive ferrite), the original spherical graphite morphology unchanged. After treatment, the strength and toughness are well matched to the working conditions of shaft parts.