Electron microscopy study of solution kinetics for M23C6 type carbide in austenitic steels

Using electron microscopy and X-ray diffraction analysis,s the studied wa kinetics of the dissolution of carbide particles in 30Kh13N8G8 and 40Kh13N8G8M steels at temperatures of 900 and 1000 deg C. The variation of the identity period of austenite and of the M23C6 particle size distribution histograms indicated that the dissolution of carbides is a multi-stage process. It was found that the first stage is a classical variant of a diffusion-controlled dissolution. The second stage consists of the simultaneous dissolution of fine (up to 500 A) carbides and the diffusion growth of coarse (larger than 800 A) carbides. The third stage is the precipitation of the carbide M23C6 with a decrease of the austenite lattice. The fourth stage is a diffusion coagulation of the precipitated carbide particles