| The diffusivity of carbon in austenite containing 3%-Ni, 0.8%-Cr and 0.45%-Mo has been determined using diffusion couples for the temperature range 1,000℃ to 1,200℃. The diffusion coefficient of carbon increases approximately 50% as the carbon concentration is increased from 0.1 to 0.5 Wt. percent. The rate of diffusion of carbon is not appreciably affected by the presence of alloying elements at about 1,000℃ but slightly accelerated at higher temperature and slightly retarded at lower temperature. This retardation can explain only a amall part of the effect of these alloying elements on hardenability of Ni-Cr-Mo steel. The diffusion equation is D=D_o exp(-36.6 ㎉/RT), where D_o varies from 0.53 to 0.74 between 0.1 and 0.5 weight percent carbon. |
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