Effect of wire diameter and grain size on tensile properties of austenitic stainless steel wire

Tensile tests were carried out for fine austenitic stainless steel wires with different grain sizes and wire diameters, and then the effect of wire diameter on the grain size dependence of tensile properties was discussed in terms of the behavior of dislocation slip near the material surface. 0.2% proof stress and total elongation of fine wires depended on not only grain size but also its diameter: these properties were strongly influenced by the ratio of wire diameter (D) to grain size (d), Did, which represents the number of grains existing along a diameter direction. It was found that the tensile properties of fine wires were markedly deteriorated when the Did became smaller than 5. This was due to the occurrence of local necking which is just like the deformation of single crystal. In the grains facing the wire surface, dislocations can easily pass out from the material surface and this leads to easier deformation in comparison with the grains within the wire where the dislocation movement is interrupted by grain boundaries. In the case when Did is sufficiently large, because the volume fraction of the grains facing the surface is very small: thus, the whole deformation of wire is not affected by the wire diameter.