Gas Carburizing Process
The purpose of gas carburizing is:
Gas carburizing is to increase the carbon content and a certain carbon concentration gradient on the surface of steel parts. The chemical heat treatment process of heating and holding steel parts in carburizing medium so that carbon atoms penetrate into the surface of steel parts is called carburizing. Carburizing steel generally adopts ordinary carbon steel, high quality carbon structural steel and low carbon alloy structural steel, and Q235 steel can also be used.
Preparations before start-up:
1. There should be no rust, dirt, crack and scar on the surface of carburized workpiece.
2. Copper plating or Anti-carburizing coating can be used to prevent Carburization on the surface of workpiece without carburizing, or carburizing layer can be cut on the part without carburizing after carburizing. The thickness of copper plating layer should generally be greater than 0.03mm; the thickness of Anti-carburizing coating should generally be greater than 0.3mm, requiring compact coating.
3. When drip carburizing is used, the carburizing agent is generally methanol (to form carrier gas); kerosene or acetone, ethyl acetate (to form enriched gas); other controlled atmosphere carburizing can be used when conditions permit. In order to obtain high quality carburization and reduce carbon black, it is better to use aviation kerosene drip injection.
4. Prepare samples and intermediate samples. Samples should be taken from the same batch of parts. No rust or oil stain is allowed on the surface of the samples. The intermediate sample is usually 10mm * 10 steel bar.
1. Inspection equipment before start-up (refer to operation rules of well-type gas carburizing furnace)
2. Carburizing the furnace pot according to the stopping time and the condition of the furnace pot and the technical documents. The carburizing time of furnace pot is 6-12 hours for new furnace pot and 2-4 hours for old furnace pot.
A. Workpieces with the same material, the same technical requirements for carburizing layer and the same heat treatment after carburizing shall be produced in the same furnace. The sample is placed in a representative position in the basket. The loading capacity and height of each furnace shall be less than the maximum loading capacity and height specified by the equipment.
B. In order to ensure smooth circulation of carburizing atmosphere in furnace and uniform carburizing layer, clearance greater than 5 mm in length and width should be left between workpieces.
C. When the baskets are loaded into the furnace, they should be placed vertically. The baskets of all layers should be neat, with no gap, and suspended into the intermediate sample bar.
D. After the workpiece is put into the furnace, the cover of the furnace is tightened and no leakage is allowed. After dripping carburizing agent, the pressure in the furnace should be maintained at 196-490Pa. The exhaust gas is ignited and the flame height is 200-300 mm.
4. Carburizing a. Carburizing process curve: According to the requirements of material quality and microstructure of carburizing layer, the carburizing process curve is stipulated by relevant process documents. Generally, for low alloy steel workpieces requiring strict control of carbides, the process curve diagram can be referred to as (1-4). For low carbon steel and low alloy steel workpieces which do not require strict control of carbides, refer to the process chart.