When the carbon steel castings are heated, the castings are directly loaded into the box heat treatment furnace. After the heat treatment is completed, a thick layer of oxide skin appears on the surface of the casting, and it is very difficult to clean the shot blasting. For the castings with strict size requirements, there will be size out of tolerance. The results show that the surface of carbon steel castings to be treated with heat treatment is coated with mullite powder coating, and after being fully dried, the effect of oxidation prevention and decarbonization is good.

      Mullite powder is a kind of aluminum silicate refractory, the main composition is AL2O3 and SiO2, and the formula of refractory components have similarities, there are a small number of other components, such as Fe2O3, Na2O, K2O, CaO, MgO2, TiO2, but does not contain Cr2O3, with 1700℃ high refractoriness, low cost, It is generally used in the back layer of the shell making process of investment mold precision casting. The coating made of silica sol has good fluidity and coating performance, and can be sintered well at the temperature of 1000 ~ 1200℃. It should be used as protective coating for heat treatment.