During the casting process, the iron castings have different cooling rates from the surface to the inside, forming the casting internal stress. If it is not eliminated, it will deform or even crack the parts during the cutting process and use it. To relieve stress, artificial aging and natural aging are often used. The casting is heated to about 500~560℃ for a certain period of time, and then the casting is taken out with the furnace to cool down. This kind of aging is artificial aging; natural aging is to store the cast iron outdoors for 6 to 18 months to let the stress release naturally. Aging can partially relieve the stress, but because of the long time and low efficiency, it has not been adopted.
2. Heat treatment can improve the overall performance of iron castings
In order to improve the overall performance of Ductile iron casting, there are often nodular cast iron annealing to eliminate white-mouth annealing, to improve toughness, normalizing, and quenching to increase the strength of ductile iron.
3. Surface heat treatment of cast iron
The purpose of surface heat treatment of iron castings is to improve the wear resistance of iron castings. Induction heating quenching, laser heating quenching, soft nitriding, and other processes in steel are all suitable for cast iron. At present, the cylinder liners of diesel engines and internal combustion engines often adopt laser heating quenching or soft nitriding treatment. The laser heating cast iron parts have a very fast heating speed. After air cooling, the workpiece can form a hardened layer of high-carbon martensite structure, so the wear resistance is greatly enhanced. After the iron casting is soft nitriding treatment, a compound (Fe2-3N) high hardening layer is formed on the surface, which not only has high hardness but also has a small friction coefficient, so the wear resistance of ductile casting is greatly improved.
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