Effect of inclusions on internal fracture in skew rolling

Abstract

This paper discusses the effect of inclusions on internal fracture in skew rolling. The prediction of internal fractures is crucial given that internal fractures cause loss of product strength and are difficult to detect. Our previous report, published in 2019, proposed a new ductile fracture criterion that considers the effect of shear stress on void coalescence in a cylindrical coordinate system. This paper covers the following three points: (1) the evaluation of the hot workability of materials with different inclusions in tensile testing, (2) the relationship between the hot workability and the damage value determined using the proposed criterion, and (3) the effect of inclusions on void evolution in skew rolling. Given that the critical damage value decreased with decreasing hot workability, internal fractures are more likely to occur in a material that contains numerous large inclusions. The experimental results led to the hypotheses that the plastic strain nucleates the voids originating from inclusions and that shear stress allows the voids to coalesce. This study has demonstrated that decreasing the diameter and number density of inclusions is effective toward suppressing internal fractures.