Forming and quenching behaviours in hot stamping of thin quenchable sheets

Abstract

A thin aluminium-coated quenchable steel sheet was hot-stamped to investigate the effect of the thickness. The sheets having 0.6, 1.0 and 1.6 mm in thickness were heated at 900 °C by a furnace and formed after 7 s from the furnace. The cooling rates of 0.6 mm and 1.0 mm in thickness from 900 °C to 400 °C under air cooling were 20.9 °C/s and 13.6 °C/s, respectively. The hardness of the air-cooled sheets having 1.0 mm in thickness was 300 HV1, whereas that of the sheet having 0.6 mm in thickness was 380 HV1 because of the high cooling rate. The Vickers hardness of the U-bent sheets of 0.6 and 1.0 mm after 7 s from the furnace without the holding time at the bottom dead centre were 500 and 430 HV1, respectively.