In this study, the hot deformation behaviour of niobium stabilized ferritic stainless steel [0.013 – 0.017% C, 17 – 17.4% Cr, 0.9 - 1% Mo and 0.4 - 0.5% Nb] was investigated in order to establish the differences in morphology, as well as the distribution of the carbides formed during the hot rolling of some Transfer Bar (TB) and Hot Band (HB) sample strips. The hot deformation process was simulated following an industrial hot rolling process of a roughing mill (TB samples) and a Steckel mill (HB samples), in which continuous reverse rolling was achieved in 7 passes at each stage. Samples obtained from these two hot rolling processes were then mechanically prepared to a fine polished stage using colloidal silica (OPS) for both the optical microscopic (OM) and scanning electron microscope (SEM) analysis. The Jeol JSM-IT300LV SEM was used in this work. The microstructural results obtained illustrated very clearly the disparities between the roughing mill samples (TB) and the Steckel mill (HB) samples, with the latter clearly showing some very distinct grain structures (equiaxed grains) as opposed to large sub-grains in the roughing mill samples with very little recrystallized grain structures. A detailed analysis of the carbides formed in the TB samples revealed the distinct directional alignment of the carbides formed along the rolling direction, while the HB samples showed a more homogeneous distribution of the carbides. In both rolling stages however, there is clear evidence of heterogeneous nucleation (preferential formation) of carbides on inclusions.

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