How the skin-pass rolling reduction ratio affects the strain aging behaviour of low-carbon steel sheets

Abstract

When producing cold-rolled steel sheets, the penultimate annealing process is followed by a final skin-pass rolling (or temper rolling) whose purpose is to eliminate any discontinuous yielding which creates stretcher-strain markings when the steel sheets are formed. To find out the critical reduction ratio eliminating the discontinuous yield phenomenon, the samples were annealed at 820°C for 3 min and then subjected to the temper rolling at various thickness reductions at room temperature. Results showed that the discontinuous yield phenomenon could not be eliminated in the case of a thickness reduction less than 0.5%, that a certain reduction ratio should be exceeded to eliminate the discontinuous yielding, and that the aging time varied depending on the reduction ratio. In addition, while the low-carbon steels did not undergo strain aging in three months with a 1% thickness reduction, they underwent strain aging in at least four months with higher thickness reductions.