材料期刊网

计算得到低碳马氏体形成时使残余奥氏体富碳所需扩散的时间约为7×10~(-3)—3×10~(-4)s。与条状马氏体形成的时间——10~(-3)—10~(-6)s比较,可见碳的扩散跟得上或稍落后于马氏体条的形成。残余奥氏体均匀富碳的时间落后于马氏体条的形成至少达1个数量级。这些表明低碳马氏体形成时可能存在碳的扩散,但后者不是马氏体相变的主要或必需过程。若低碳马氏体按上贝氏体形式长大,则计算所得其长大速率仅3×10~(-4)cm/s,比现有实验数据至少低2个数量级。本文工作再次证明低碳马氏体的形成机制和上贝氏体的不同。

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.