Kinetic Transition During Ferrite Growth Induced by Interfacial Solute Segregation in an Fe-C-Mn-Si Alloy

The kinetic transition of partitionless proeutectoid ferrite transformation from austenite, experimentally reported earlier in an Fe-C-Mn-Si alloy, is simulated incorporating interfacial segregation of carbon and alloy elements. The time-dependent diffusion equations of solutes are solved within the alpha/gamma interface to evaluate the transient effects of solute accumulation on the migration of interface. The carbon concentration at the interface in the matrix decreased faster and the interface migration ceased, or the so-called stasis occurred, when the carbon concentration gradient in the immediate front of the interface turned to null or reversed. This can happen earlier than the partitionless-to-partitioned growth transition predicted from conventional theory in the absence of interfacial segregation, depending upon austenite grain size, i.e., the extent of soft impingement of carbon diffusion fields in the matrix in which a large carbon supersaturation remained. The subsequent transformation may be resumed accompanying the bulk partitioning of Mn (and probably Si) and/or nucleation of new ferrite crystals.

Automated summary

This study investigated the kinetic transition of partitionless proeutectoid ferrite transformation from austenite in an Fe-C-Mn-Si alloy. By incorporating interfacial segregation of carbon and alloy elements, the time-dependent diffusion equations of solutes were solved to evaluate the transient effects of solute accumulation on the migration of interface. It was found that the migration of interface ceased and stasis occurred when the carbon concentration gradient in the immediate front of the interface turned to null or reversed, leading to earlier transformation than predicted by conventional theory.