The influence of cyclic straining on the work hardening behavior of AISI 304 stainless steel bars in multiple-pass drawing

The occurrence of strain softening in drawn low carbon steel bars, as a consequence of cyclic torsion, was previously observed in terms of changes in the mechanical properties of the bars and in the drawing stress, bringing out the possibility of employing cyclic straining in order to improve multiple-stage forming operations. In the present paper, the influence of the structural features of the drawn material on the strain softening phenomenon was analyzed. A commercial AISI 304 stainless steel was used in the experiments. Drawing was carried out in five passes. Cyclic torsion was conducted between the last two stages of drawing and between every drawing pass. In addition to the evaluation of the drawing stress, microstructural and X-ray diffraction analyses were performed, allowing the examination and the calculation of the amount of martensite formed during plastic deformation. Contrasting with the low carbon steel investigation, torsion did not lead to changes in the drawing stress of the AISI 304 stainless steel, for both experimental procedures. The quantitative phase analysis revealed that, even though a considerable deformation value was applied to the material, the amount of martensite formed in cyclic torsion was very low.