Strength of AISI 316L in torsion at high temperature

Hot torsion flow behaviour of 30 mu m grained AISI 316L stainless steel was investigated in the range of temperatures 850-1100 degrees C with equivalent strain rates 0.0001-0.006s(-1). For temperatures higher than 900 degrees C the material presented an unusual linear relationship at low strains between equivalent stress, sigma(Eq), and equivalent strain, epsilon(Eq), whilst at 850 degrees C a parabolic sigma(Eq)-epsilon(Eq) relationship was observed. The flow behaviour of 100 mu m grained AISI 316L stainless steel torsionally deformed at 1000 degrees C with equivalent strain rate of 0.006s(-1) was reported to follow the expected parabolic sigma(Eq)-epsilon(Eq) relationship and produced a significantly higher flow stress than the 30 mu m grained material (about 40% higher at 0.5 equivalent strain). In both materials an unusual grain shape evolution from pre-deformation equiaxed to rhomboidal was observed during torsion, which was rationalised [G. Angella, B.P. Wynne, W.M. Rainforth, J.H. Beynon, Acta Mater. 53 (2005) 1263] in terms of strain induced grain boundary migration (SIGBM) combined with the torsion stress field. A qualitative model is proposed to describe the flow behaviour of the AISI 316L stainless steel based on the unusual grain structure evolution and, in turn, on SIGBM.