Five measures to prevent the surface decarbonization of galvanized pipes

The service life of many galvanized pipes is related to the degree of surface decarburization. If the decarbonized layer on the surface is not cleaned in time, the hardness and wear resistance of the surface layer will be reduced. And when the galvanized pipe is quenched, cracks are formed on the surface of the workpiece due to the different volume changes in the outer layer. Therefore, how to prevent the surface decarbonization of galvanized pipes is a problem that should be paid attention to in the production process. Today, we will introduce five measures to prevent the decarbonization of the surface of galvanized pipes:

(1) The atmosphere that causes surface decarbonization is mainly oxidizing gases such as oxygen, water vapor and carbon dioxide. When these oxidizing gases are in contact with the surface of the hot-dip galvanized pipe, oxidation and decarburization occur simultaneously. Since the solid carbon in iron has a relatively large affinity with these gases, the carbon on the surface is removed first;

(2) To control the ratio of carbon dioxide and carbon monoxide in the furnace, at the balance point neither oxidation nor decarbonization. When the carbon dioxide ratio exceeds the equilibrium point, oxidation and decarbonization occur. Below the equilibrium point, oxidation and decarbonization do not occur. The specific value of the equilibrium point should be calculated according to the carbon content and temperature of iron;

(3) Because the decarbonization and the oxidation of galvanized pipes are carried out at the same time, the purpose of improving decarbonization can be achieved as long as the heat treatment process is as little as possible in contact with the air;

(4) Spraying neutral protective nitrogen into the furnace is also an effective measure. Nitrogen into the furnace can disperse the oxidizing atmosphere in some sections, while maintaining the positive pressure in the furnace, preventing air infiltration, reducing or avoiding the decarburization of galvanized pipes;

(5) The oxidized iron sheet, rust on the surface of the galvanized pipe and the residue on the surface after cold drawing will also decompose after heating in the furnace and react to produce some oxidizing gases. The atmosphere in the furnace can be purposefully controlled to make it in a reducible state, which can effectively avoid surface decarbonization.