Kundu, Amrita
(2011).
Grain structure development during casting, reheating and deformation of Nb-microalloyed steel.
University of Birmingham.
Ph.D.
Abstract
This thesis looks at the effect of micro segregation of Nb, generated from the continuous casting on grain structure development during reheating and deformation. The amount of segregated material present in the microstructure has been quantified in the as-cast condition and that has been used to model grain size distribution after reheating and deformation which is required for subsequent toughness prediction in 0.045 wt % Nb steel. The limits of validity of the original Dutta-Sellars model for predicting the amount of recrystallisation; investigating the influence of the variables such as starting grain size distribution, strain and Nb content has been examined. A modified Dutta-Sellars model considering the starting grain size distribution has been found to be more accurate in quantifying the amount of recrystallisation. This approach has been used to model grain size distribution after deformation both in the homogenised and in presence of Nb segregation. The effect of AlN, to replace Nb(C,N), on pinning the austenite grain boundaries during reheating has been investigated, as the segregation tendency of Al is much less compared with Nb.
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