Characterization of the Bendability of Press-Hardened 22MnB5 Steel

Abstract

The bendability of press-hardened 22MnB5 steel was used as evaluation criterion to assess the ability of a press-hardened part to deform plastically in side impact crash conditions. The initiation sites of crack initiating shear bands during the bending operation of press-hardened 22MnB5 steel were found to be formed by surface roughening. Uncoated press-hardened 22MnB5 steel is subject to decarburization and oxidation phenomena occurring during austenitization. These surface processes were found to have a pronounced influence on the bendability of the steel, but their influence on the tensile properties was negligible. Decarburization has a positive influence on bendability by softening the outer sheet surface. Austenitization times prior to press forming in excess of 10min, resulted in the formation of a surface oxide layer which suppressed the continuation of the decarburization and resulted in the re-homogenization of the carbon concentration profile in the subsurface region. As a result, the decarburization layer was gradually removed, and the bendability of the press-hardened 22MnB5 steel was reduced.