Comparative study on microstructure evolution upon unidirectional and multidirectional cold working in an Fe-15%Cr ferritic alloy

Deformation microstructures of an Fe-15%Cr ferritic stainless steel during cold working to strains above 7 were studied. Two processing methods, unidirectional working consisting of bar rolling followed by swaging and multidirectional working involving multiple forging through three orthogonal axes, were used. The unidirectional deformation resulted in the evolution of a ribbon-like microstructure consisting of highly elongated grains. The mean grain size gradually decreased to about 0.4 μm during rolling/swaging to strains above 7. In contrast, the multiple forging resulted in the development of almost equiaxed fine grains with an average grain size of 0.45 μm at relatively small strains of about 4 followed by a slight grain refinement during further processing. On the other hand, both processing methods were characterised by almost the same strain dependence for the transverse grain and subgrain sizes, which were measured crosswise to the metal flow direction.