Experimental characterization and prediction of forming limit diagrams of PHS1800 during hot stamping

Abstract

The use of press-hardening steels (PHSs) in automotive bodies creates the opportunity of producing thinner, higher-strength components. PHS1800, an Al-Si coated PHS grade with ultimate tensile strength of around 1.8 GPa after hot stamping, is a candidate material for vehicle anti-intrusion applications. The current study aims to investigate the formability of this steel during the hot-stamping process. A custom Marciniak punch test and in situ digital image correlation (DIC) techniques were used to determine the in-plane forming limits of this steel during quenching from an austenitic temperature. The carrier blank thickness and geometry were exploited to quench the surrounding material of the specimens while promoting localization in their central regions. Approximately linear strain paths ranging from uniaxial to biaxial stretching were obtained in the tests while avoiding friction and out-of-plane bending. The forming limit curves (FLCs) of the material under various hot-stamping conditions were then predicted using the Marciniak-Kuczyński (MK) model, taking into account the temperature and strain-rate histories. The predicted limit strains were in good accord with the measured data.