Preparation And Properties Research Of High Temperature Oxidation And Decarbonization -resistant Coating For Spring Steel

Oxidation and decarburization are the main reasons for losses of steel at high temperature, which bring great harm to the steel including low producing efficiency, high energy consumption and high producing cost. So it is necessary to reduce the oxidation and decarburization of steel at high temperature. Comparing with other technologies, the protective coating possesses more advantages, such as more simple preparative technological process, better protective effect, lower cost, and more suitable for applying in large work-piece. Therefore, it is exigent to research the high-temperature protective coating of steel.The silicate glass protective coating was successfully prepared by solid phase reaction method for spring steel 55SiCr on the basis of characteristics of the substrate, protective mechanism and design rules of coatings. The major components of the coating were 40%⁶0% SiO2, 2%¹5% Al₂O₃, 10%³0% B₂O₃, 0%¹5% MgO, 10%³0% Na₂O+K₂O. The coating was brushed on the surface of the sample. Spring steel samples and samples with coatings were heated at 960℃for 40 minute. Micrograph, micro-hardness, scanning electron microscopy (SEM) were applied to analyze the protective effects of the coating. Protective mechanism of the coating was also researched combined with differential thermal analysis (DTA) and scanning electron microscopy (SEM).The results indicated that the oxidative weight loss of spring steel 55SiCr increased with increasing temperature, and the total decarburized depth was a parabola-shape function of temperature, with the maximum appearing at 800℃. Results also showed that the coating could effectively protect the spring steel 55SiCr from oxidation and decarbonization between 700℃and 1087℃. The rate of oxidative weight loss dropped from 2.39% to 0.80%, reducing nearly 70%. The depth of decarburized layer dropped from 119μm to 7μm, reducing more than 90%. In addition, the coating could be easily removed from the substrate, removing the process of steel descaling. The coating had a broad applying prospect for its low cost, good qualities, simple using method and less demanding on the surface of the sample.