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Dynamic softening and substructural changes during hot deformation of a ferritic Fe-26Cr stainless steel were studied. The flow stress increased to reach a steady state in all the cases and the steadystate stress decreased with decreasing Z, the Zener-Hollomon parameter. A constant subgrain size was observed to correspond to the steady-state flow and the steady-state subgrain size increased with decreasing Z. Substructure examinations revealed that elongated, pancake-shaped subgrains formed in the early stage of deformation. Straight sub-boundaries and equiaxed subgrains developed progressively with strain, leading eventually to a stable substructure at strains greater than 0.7. During deformation at 1100 ЊC, dynamic recrystallization occurred by the migration and coalescence of subboundaries. Dynamic recovery dominated during deformation at 900 ЊC, resulting in the formation of fine equiaxed subgrains. Based on microstructural observations, the process of substructural changes during hot deformation was described by a schematic diagram.

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Characterization of prior austenite grain size is important for understanding the microstructure-property relationships in steels. The prior austenite grain size plays an important role in defining the microstructural scale of low-temperature phases and the mechanical properties (e.g., strength, ductility, fracture toughness, etc.) of steels in the final product form. Moreover, in several failure analyses, the cracks are observed to propagate along the prior austenite grain boundaries (PAGBs). The delineation of PAGBs in steels of new composition can be quite challenging, as the response to a particular etching protocol is very sensitive to the chemical composition of steel. The objective of this study was to establish a methodology to delineate PAGBs in AF9628, a newly developed low-alloy high-performance steel. Several different etchants and etching techniques from the literature were evaluated. These methods were unsuccessful or had limited success in revealing PAGBs in AF9628. However, swab etching with a solution of 100 ml saturated aqueous picric acid and 0.5 g sodium dodecyl benzene sulfonate worked remarkably well for delineating the PAGBs in this steel. This etchant was found to have high selectivity, revealing PAGBs preferentially over packet, block, and sub-block boundaries.

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