Three heat treatment process of gray cast iron casting
Views: 46 Author: Site Editor Publish Time: 2016-09-26 Origin: Site
Gray cast iron casting mainly refers to a flake graphite cast iron, the more thin than cast steel can be obtained and complex casting, cooling speed sensitivity is very big, and gray cast iron after heat treatment process, mainly in the following three ways.
1, the stress relieving
Castings in the casting cooling process, due to the different cooling rate of each part, easy to produce stress, may result in warping and casting cracks, in order to ensure the dimensional stability, prevent deformation, for some complex shape of castings, such as bed, cylinder block, cylinder head, etc., need to eliminate internal stress annealing.Its specification is commonly: heating temperature of 500 ~ 550 ℃, the heating speed of 60 ~ 120 ℃ / h, furnace cooling after heat preservation time to 150 ~ 220 ℃ from air cooling.
Grey cast iron surface and some thin section, in the process of condensing cooling speed faster, easier to produce white tissue, increase the hardness and brittleness of casting, machining difficulties, require annealing treatment.Will cast iron heating to 850 ~ 890 ℃, the heat preservation of 2 ~ 5 h make Fe 3 C decomposition, and then with the slow cooling furnace 400 ~ 500 ℃, then empty out cold.
3, surface quenching
Some castings, such as machine tool guideway surface and the inner wall of the cylinder need to improve the surface hardness and wear resistance, used for surface hardening treatment, such as high frequency induction heating surface quenching, contact resistance heating surface hardening.
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