A Study of Void Closure in Hot Rolling Bars of Stainless Steel

Casting metal products are characterized by porosity due to shrinkage occurring during solidification of the molten material. However, final products such as bars must comply with internal soundness requirements, usually assessed by ultrasonic testing. In this view hot metal forming processes such as rolling or forging could mechanically ensure void closure and therefore the desired product soundness. Based on literature and previous experience, a study of the void closure during hot rolling of austenitic stainless-steel bars coming from ingot has been carried out. The effects of hot rolling main parameters on void closure have been first investigated by FE analysis and then experimental trails on rolling mill have been designed. Material coming from experimental tests was then analyzed both with destructive and non destructive tests (i.e., ultrasonic analysis, micro and macro etches) so to validate process design and optimization. Experimental results allowed the validation of FE analysis and also showed an effective improvement in terms of void closure.