Gas carburizing process

The purpose of gas carburizing: gas carburizing is to increase the carbon content and a certain carbon concentration gradient of the steel surface. The chemical heat treatment process of heating and holding the steel in the carburizing medium to make carbon atoms penetrate into the steel surface is called carburizing. Generally, ordinary carbon steel, high-quality carbon structural steel, low-carbon alloy structural steel and Q235 steel are used for carburizing.

Preparation before opening:

(1) The surface of carburized workpiece shall be free of rust, dirt, crack, scar and other defects.

(2) The surface of the workpiece without carburizing can be copper plated or coated with anti carburizing coating to prevent carburizing, or after carburizing, the part without carburizing can be cut to remove the carburizing layer. The thickness of copper plating layer shall generally be greater than 0.03mm; the thickness of anti carburizing coating shall generally be greater than 0.3mm, and the coating shall be dense.

(3) When drip carburizing is adopted, the carburizing agent is usually methanol (to form carrier gas); kerosene or acetone, ethyl acetate (to form rich gas), and other controlled atmosphere carburizing can be adopted when conditions permit. In order to obtain high quality carburizing and reduce carbon black, aviation kerosene is the best choice.

(4) Prepare the sample and the intermediate sample. The sample should be taken from the same batch of parts, and the surface of the sample should not be rusted or greasy. The middle sample is generally Φ 10 mm × 10 steel test bar.

Carburizing operation:

1. Inspection equipment before opening (refer to the operation specification of well type gas carburizing furnace)

2. Carburizing shall be carried out according to the time of furnace shutdown and the situation of furnace and tank and the regulations of process documents. The carburizing time of furnace is generally 6-12h for new furnace and about 2-4h for old furnace.

3. charging:

① The workpieces with the same material, the same carburizing layer technical requirements and the same post carburizing heat treatment method shall be put in the same furnace for production. The sample is placed in the representative position of the basket. The loading capacity and loading height of each furnace shall be less than the maximum loading capacity and loading height specified by the equipment.

② . in order to ensure smooth circulation of carburizing atmosphere in the furnace and uniform carburizing layer, a gap of more than 5mm in vertical and horizontal shall be left between workpieces.

③ . when the baskets are put into the furnace, they shall be placed vertically, and the baskets of each layer shall be neat without any gap, and the intermediate sample bar shall be suspended at the same time.

④ . after the workpiece is put into the furnace, the furnace cover shall be tightly closed and no air leakage is allowed. After the carburizing agent is dripped, the furnace pressure shall be maintained at 196-490pa. Ignite the waste gas with a flame height of 200-300mm.

4. Carburizing process curve: according to the requirements of material and microstructure of carburizing layer, the carburizing process curve is specified by relevant process documents. Generally, for low alloy steel workpiece requiring strict control of carbide, refer to the process curve. For low carbon steel and low alloy steel workpieces that do not require strict control of carbide.

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