1. Features: The surface of the product is oily and shiny, and the cross-section has small graphite points or nest-shaped spots. In severe cases, the product has a lubricating feeling and black marks when touched by hand.
2. Reason: because the total carbon content in the mixture is too high, or the carbon content of the filler is too high, or the hydrocarbon concentration in the gas phase in the low temperature zone is too high, or the carbon in the graphite boat diffuses into the sintered body, or is dehydrated. When removing the forming agent, the heating rate is too fast and the time is short, and the forming agent cracks to generate free graphite, which causes alloy carburization.
3. Source of free carbon ⑴ cracking of forming agent in dewaxing (degumming) process ⑵ carbon diffusion in graphite boat ⑶ control of sintering atmosphere in vacuum furnace
4. Judgment: Carburizing of products will generally affect the performance, and should be judged according to the requirements of each brand and use, and the unqualified products will be returned to the production unit for processing.
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