Evaluation of porosity closure during hot compression of steel by synchrotron X-ray laminography and FEM analysis

The shape change due to hot compression of the porosities formed in center of the steel ingot of carbon steel S25C and stainless steel SUS316L was sequentially, nondestructively and three-dimensionally observed by synchrotron X-ray laminography. As a result, it was revealed that closure of porosities was easier in SUS316L than in S25C. In addition, when the compression ratio increased, originally high aspect ratio porosities (length/width ratio, ℓ /w > 2.5) became decoupled. Larger porosities were more readily closed with smaller compression ratio. As a result of verifying the difference in closure behavior between S25C and SUS316L by Finite Element Method (FEM), it was demonstrated that the hydrostatic integration was larger for SUS 316L of which work hardening coefficient was smaller. This result was consistent with the experiment as results that porosities of SUS 316L tended to close easily.