DIFFUSION OF CARBON DURING FORMATION OF LOW-CARBON MARTENSITE (Continued)

The time required for carbon diffusion to enrich the retained austenite is 7×10~(-3) —3×10~(-4) s as calculated. In comparison with the time of formation of a martensite lath——10~(-3)—10~(-6) s, the result of calculation implies that the diffusion of carbon can keep pace with or slightly lags behind the formation of lath martensite. The time required for equalizing the carbon concentration enriched in the retained austenite is at least one order of magnitude lower than that for the formation of lath martensite. These results show that there may exist the carbon diffusion in the course of formation of low-carbon martensite, however, the carbon diffusion is not a main or required process in the martensitie transformation. Supposing that the growth of low-carbon martensite is analogous to that of upper bainite, we obtain the growth rate is only 3×10~(-4)cm/s, at least two orders of magnitude lower than the available experimental data at present. The present work proves once more the formation mechanism of low-carbon martensite differs from that of upper hainite.