What are the heat treatment of ductile iron way? - Nodular cast iron

by:XEX     2020-12-19
Ductile cast iron is through get spheroidal graphite spheroidization and inoculation, effectively improve the mechanical properties of cast iron, especially improve the plasticity and toughness, and the strength is higher than carbon steel. Small make up today to tell you something about what of nodular cast iron heat treatment. A, annealing purpose: usually, in order to obtain a ferritic matrix to improve the plasticity and toughness, improve the cutting processability, and eliminate the internal stress of casting. 1, high temperature annealing: high temperature annealing process is the eutectoid temperature range above the casting heat, which is 900 - 2-950 ℃, the heat preservation 4 hours, the first stage graphitization in the casting, and then slowly with furnace cooling to 600 ℃, occur in the middle and the second stage graphitization, castings from empty cold again. 2, low temperature annealing: low temperature annealing process is heated to the casting near the eutectoid temperature range, which is 720 - 2-760 ℃, the heat preservation 8 hours, the second stage graphitization in the casting, and then with the slow cooling furnace to 600 ℃, then empty out cold. Normalizing purpose: matrix of hybrid organization under as-cast pearlite becomes matrix, thus improve the strength and abrasion resistance. 1, high temperature normalizing: above the eutectoid temperature range is the casting heat, usually is 880 - 1-920 ℃, the heat preservation 3 hours, the matrix was all austenitizing, then came empty cold, in the eutectoid temperature range due to the fast cooling and pearlite matrix. 2, low temperature normalizing: it is heated to the casting eutectoid temperature range, which is 840 - 1-860 ℃, the heat preservation 4 hours, make the matrix was part of the austenitizing, then empty out cold. Improve the casting toughness and plasticity, but lower strength. Three, isothermal quenching nodular cast iron to normalizing treatment while the application is very wide, but when the casting shape is complex, and requires high comprehensive mechanical properties, the normalizing treatment has been difficult to meet the technical requirements, and often adopt the isothermal quenching. Its craft is heated to 860 - the casting 920 ℃, the heat preservation time, About the steel double) And then quickly into the temperature is 250 - In 350 ℃ isothermal salt-bath isothermal treatment for half an hour to an hour and a half, and then take out the air cooling. Tempering treatment for complex loading, section size, high comprehensive mechanical performance requirements of large castings, such as adopting normalizing and isothermal quenching can not meet the above requirements, therefore often use conditioning treatment ( Quenching and high temperature tempering) Tempering treatment of quenching and heat preservation time, basically the same as the isothermal quenching, the heating temperature is 860 - Generated when the 920 ℃, in order to avoid the quenching crack, besides shape simple casting using water, generally USES the oil cooling. Organization for fine lamellar martensite after quenching and spheroidal graphite. And then heated to 550 - 600 ℃ and tempering 2 - 6 hours. Nodular cast iron can be a variety of heat treatment such as QT400 annealing, QT700 normalizing and tempering, but before the induction heating surface quenching, it's best to start normalizing treatment. That is about of nodular cast iron heat treatment is introduced, hope can help to you. Today small make up to you at this point, let's see you next time.
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