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Measures for the preventing of decarburization on the surface of steel products

更新日期:2013-06-24  浏览:1959

The service life of many steel products is related with the surface decarburization degree of steel products. For example, the service life of steel rope mainly depends on its fatigue strength and resistance. If wire rope surface decarburization exceeds the standard, it will reduce carbon as the reinforcing phase and wear-resistant phases in the surface layer, which will directly affect the two performances. In addition, if don’t clean the surface decarburized layer of tool steel and bearing steel, it will make the tool steel and bearing steel surface layer hardness and wear resistance decrease and when quenching, the outer layer of different volume change and make the surface crack formation. Therefore, how to prevent the surface decarburization of steel products is a problem that should be paid attention to in the production process. Decarburization layer of imported wire rod surface is 0.02~0.04 mm; Kobe can do no decarburization and the average depth of decarburized layer of gas pipeline similar domestic products exceeds 0.05mm. It should take measures to change this situation.

To solve the problem of surface decarburization, the key factor is in the heat treatment process. Due to oxidation and decarburization of steel wire are carried out at the same time, therefore, in the process of heat treatment, only to make the wire contact less with air can reach the purpose of improving decarburization. For example, American Spring Wire Corp adopts double lead groove oil quenching and tempering treatment valve spring steel wire, which has obtained ideal results. The production process is: Structral Steel Pipes first the molten lead groove steel play the role of austenitizing and first the lead liquid is heated to 871 ℃, wire in molten lead through to realize the austenitizing, then enters the quench tank and enters the second molten lead bath tempering (482 ℃). Because the steel wire in molten lead not contact with air, it effectively avoids decarburization. With this process the main problems to be solved is how to prevent lead dust pollution.

Surface decarburization is mainly caused by the oxidizing gas, such as oxygen, water vapor and carbon dioxide. When the oxidizing gas contact the heated wire surface, oxidation and decarburization occurred at the same time; because the iron in these gases dissolved carbon and affinity is relatively large, so the surface of the carbon take off. These gases are generally from the furnace to go into the surface of steel products; iron oxide scale, rust and cold-drawn steel wire surface residue, into the furnace after will decomposition, reaction to generate some oxidizing gases. We can have the purpose of controlling the furnace atmosphere, so that in reductive state, can effectively avoid surface decarburization. For example, the control of carbon dioxide and carbon monoxide in the furnace of proportion, in the equilibrium point, neither oxidation nor decarburization; more than the balance point in the carbon dioxide concentration, oxidation and decarburization; SSAW steel pipe below the equilibrium point is not from oxidation and decarburization. The specific numerical balance should be calculated according to the carbon content and temperature of iron.

In addition, it is also a kind of effective measure to blow protect neutral nitrogen into furnace. Nitrogen enters into furnace can disperse the oxidizing atmosphere in some regions, while maintaining the furnace pressure and preventing air infiltration and reducing or avoiding steel decarburization.
 

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