Improving the bending toughness of Al-Si coated press-hardened steel by tailoring coating thickness

A ferrite layer is formed between the outer intermetallics layers and the martensite substrate during the hot stamping process of Al-Si coated press-hardened steel (PHS). Unexpectedly, it is found here that the ferrite layer does not effectively prevent brittle cracks propagating continuously from the intermetallics to the martensite substrate. This leads to a high stress intensity factor (SIF) at the crack tip, therefore initiating highly localized shear deformation in the martensite substrate, degrading the bendability of the steel. A thinner Al-Si coating produces thinner brittle intermetallics and ferrite layers, and therefore shorter coating cracks and smaller SIF at the crack tip, thus improving the bendability. In addition, a thinner Al-Si coating also has a lower material cost while keeping similar paintability and corrosion resistance. The thin Al-Si coating could potentially change the current practice of Al-Si coating, impacting the global automotive industry. (C) 2020 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.

Automated summary

During the hot stamping process of Al-Si coated press-hardened steel, the ferrite layer formed does not effectively prevent brittle cracks from propagating, leading to decreased bendability of the steel. Thinner Al-Si coating reduces coating cracks and SIF at the crack tip, improving bendability and lowering material cost.