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Ductile casting annealing? Exactly what causes? - Ductile casting

by:XEX     2021-04-02
Ductile casting is a casting process, are made from rare earth magnesium nodulizing agent, cupola and grey are the same. In order to guarantee good spheroidizing, to control the content of sulfur and phosphorus lower. Considering the temperature loss, the temperature of the molten iron should be higher than grey. Small make up today to tell you something about ductile casting annealing is what reason. 1, eliminate chilling annealing: ordinary grey cast iron or ductile casting surface or thin walled in casting process for cooling speed too quickly appear white, iron can not machining. To eliminate chilling lower hardness often will this kind of castings to heating above the eutectoid temperature ( Usually 880 ~ 900 ℃) And insulation (1 ~ 2 h If cast iron Si content is high, the time is short) Annealing, cementite is decomposed into graphite, then iron slowly cooled to 400 ℃ 500 ℃ from air cooling. In 700 - temperature 780 ℃, or near the eutectoid temperature should not be cold speed too slow, so that cementite too much into graphite, reduces the strength of cast iron parts. 2, improve the toughness of ductile iron annealing, spheroidal graphite cast iron in the process of casting chilling tendency of the ordinary gray iron, internal stress is bigger also, cast iron or hard to get pure ferrite pearlite matrix, in order to improve the ductility or toughness of cast iron parts, it will cast iron often heated to 900 - again 950 ℃ high temperature annealing and heat preservation time, furnace cooling to 600 ℃ after getting cold again. Cementite decomposition of matrix in the process of the graphite, the precipitation in the austenite, graphite, graphite gathered in the original around the nodular graphite, matrix into ferrite. If the as-cast organization by ( Ferrite + pearlite) Matrix, and the composition of spheroidal graphite, to improve the toughness, just put the pearlite into ferrite and cementite decomposition of spheroidal graphite, so it will soon be iron heated to 700 - again After 760 ℃ the eutectoid temperature fluctuation by holding furnace cooling to 600 ℃ from getting cold. 3 and improving their strength of ductile cast iron is fire: ductile cast iron is the purpose of normalizing the matrix was converted into fine pearlitic structure. Process is the substrate of ferrite and pearlite ductile cast iron is heated to 850 - again Temperature of 900 ℃, the original ferrite and pearlite transformation to austenite, and a portion of the spheroidal graphite dissolves in austenite, air cooling after heat preservation austenite transformed into fine pearlite, thus the strength of the castings. 4, quenching and tempering treatment of nodular cast iron, ductile castings as bearing need higher hardness, often will cast iron pieces of quenching and tempering treatment at low temperature. Process is: heating to 860 - casting All the temperature of 900 ℃, insulation to the original matrix again after austenitizing cooling achieve quenching in oil or molten salt, after 250 - 350 ℃ heat insulating tempering, the original matrix into tempered martensite and retained austenite, the original spheroidal graphite morphology is constant. After processing of castings with high hardness and a certain toughness, retained the lubrication performance of the graphite, wear-resisting performance is improved. Nodular cast iron as the axial parts, such as diesel engine crankshaft, connecting rod, high strength and toughness good comprehensive mechanical machinery performance, conditioning treatment was carried out on the cast iron pieces. The process is: cast iron heating to 860 - 900 ℃ of austenitizing temperature thermal insulation for matrix, and then cooling achieve quenching in oil or molten salt, after 500 - 600 ℃ high temperature tempering, obtain tempered sorbite structure ( Generally there are a few populist blocky ferrite) , the original spheroidal graphite morphology is constant. After processing strength, toughness good match, adapted to the working conditions of shaft parts. 5, isothermal quenching process of ductile iron, nodular cast iron of the isothermal quenching process aims to let the iron matrix was converted to the toughness of bainite, ultimate strength can be more than 1100 mpa, impact toughness AK≥ 32J。 Process is: will ductile cast iron is heated to 830 - 870 ℃ after austenitizing temperature insulation matrix, 280 - 350 ℃ heat preservation in the molten salt for austenitic part into the bainite, the original spheroidal graphite remains the same. To obtain high strength ductile iron. Above is the reason why the ductile casting annealing, the hope can help you. Today small make up to you at this point, let's see you next time.
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