Abstract
Using a 100 mm thick continuously cast slab with a chemical composition of 0.10C-0.16Si-0.58Mn-0.01P-0.003S (mass%), we have clarified the effect of the manganese segregation on the transformed ferrite structure when the slab was reheated to make austenite grains equi-axed and smaller and followed by the Grain Refinement Process (GRP) of heavy compression and subsequent controlled cooling. Samples from which the Mn segregation was eliminated were also prepared for comparison. The resultant microstructure was examined for compressive strains between 0.7 and 2.1. When the austenite grain size is 160 or 120μm prior to GRP, the ferrite grain size of the samples with the Mn segregation is smaller at the given strain than that of the samples from which the Mn segregation was eliminated. The Mn band formed by the heavy compression is thought to act as a barrier in the form of a relatively stable austenite against the ferrite growth. Moreover, we found a unique equation to predict the transformed ferrite grain size in the samples with the Mn segregation. Namely, the ferrite grain size can be accounted for according to a parameter, ES (effective spacing): a mean spacing that considers both the pancake austenite grain boundary and the Mn band. We also suggest that the smaller Mn band spacing may make the ferrite structure finer even when the austenite grain size is large.
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