Types, causes and prevention of defects in quenching

- Sep 11, 2017 -

The flaw in the quenching such as oxidation and decarburization, deformation, cracks, overheating, burnt, insufficient hardness, soft, soft spot, etc., the oxidation and decarbonization, overheating, deformation and cracking is most serious.

The heating medium is contained in the oxidizing substances, such as oxygen, carbon dioxide and water vapor,  they react with iron or carbon on the surface of the parts, to generate iron oxide or the surface of carbon burning into poverty by carbon when heating. All that result in Oxidation and decarburization phenomenon.

How to prevent from oxidation and decarburization?In electric box furnace and electric pit type furnace, inject the protective gas, also have access to drip into the kerosene, alcohol, or ammonia, nitrogen and other gases to protect it; a simple way is to put some wood and produce gases such as co to protected.At present, in the form of a coating on the surface parts are coated with a protective agent, oxidation and decarburization can effectively prevent the same parts.General in the salt bath furnace deoxidization with silica gel to also can get good effect.

Insufficient hardness is often because of short heat preservation time or the slow cooling speed, high carbon steel heating temperature is too high to make the hardness. So using reasonable heating specification with the correct operating methods (such as when heated.

Leave some space between the parts, stir on cooling, etc.), you can prevent this kind of defect.

Deformation and cracking are the most serious defects of heat treatment. The root cause of this defect is excessive internal stress.When the internal stress is greater than the yield limit of material, parts will produce plastic deformation;Internal stress exceeds ultimate strength, parts cracking.Specifically, part shape asymmetry, cross section thickness, the original organization improper adverse, heating, cooling, such as the shape of the sharp Angle can cause the deformation and cracking of parts.Measures only, especially choose reasonable technological parameters, can effectively prevent the formation of such defects.

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