Effects of grain size on the sheared surface in micropiercing of austenitic stainless steel SUS304

Abstract

Over the last decade, development of fine-grained materials and investigation into the effect of different grain sizes on metal forming at the micro-scale have been seen worldwide. There were several technical reports and scientific papers dealing with the quality improvements with use of the ultra-fine grained steel due to the different grain deformations. However, there were few studies concerning effect of the grain size on the sheared surface in micropiercing. In this study, we investigated stability of the sheared surface length of the cross section in micro-pierced holes. The inner diameter of the holes and maximum piercing forces were measured in order to evaluate the effect of the grain size in the micropiercing process. As reducing the material grain size, ratio of the fractured surface and maximum piercing force increased with tendency to tensile strength. However, the ratio of the burnished surface to the fractured surface as well as inner diameter of the pierced holes varied, depending on the grain size of the material. As a result, a suitable grain size should be considered for a micropiercing process.