Abstract
The authors previously reported single carbide layers of VC, NbC or Cr7C3+Cr23C6 were formed on the surface of steels immersed in molten borax baths containing Fe-V, Fe-Nb or metallic Cr powder
When steels, carbide-coated by immersing in the first bath containing V, Nb or Cr element, were immersed in the second bath containing element different from that in the first bath, tow carbide layers were formed on the surface of steels
The inner carbide layer was formed in the first bath and the outer carbide layer was formed in the second bath. Both carbide layers had similar composition and crystal structure to those of the carbide layers formed by the single immersion method, and no diffusion of elements into each layer were observed
The thickness of the outer layer increased linearly with square root of the immersion time, and the growth rate of the layer was controlled by the diffusion speed of the carbon in the carbide layer, as the case by the single immersion method
