| The diffusivity of carbon in austenite steel containing 3 percent nickel, 0.8 percent chronium and 0.3 percent molybdenium has been determined using diffusion couples at the temperatures from 900℃ to 1,100℃. Carbon isotope C^(14) was added to the higher carbon side of the couple. After cast into steel moulds and forged, the specimens were homogenized in the purified argon atmosphere for 24 hrs. at 1400℃ or 1280℃ and then friction welded to make the diffusion couples. After the couples were annealed, the surface counting technique and the microphotography-autoradiograph technique were used to obtain the concentration-penetration curves, and then the diffusion coefficient, D, was computed by the Boltzman-Matano method. The experimental results lead to the following conclusions. 1) The computed diffusivities obtained by the both methods were agreed well within 3 percent error. Therefore the microphotography method can be effectively used to determine the diffusion coefficient. 2) The rate of diffusion of carbon was slightly accelerated at 1100℃ and the diffusion coefficient was proportional to the carbon concentration. 3) The diffusion coefficient could be expressed by D=D_0 exp (-36,000㎈/RT), where D ranged from 0.53 to 0.70 in the carbon concentration ranged from 0.2 to 0.8 percent. These values are in fairly good agreement with those obtained by the chemical analysis technique. |
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