Most advanced-high-strength steels (AHSS) materials comprise specific chemical compositions and microstructures, with a number of strengthening mechanisms used to boost strength, ductility, toughness and fatigue properties. While such characteristics are good news for designers, the challenge for manufacturing engineers is forming these materials, whether that be cold-stamping door beams, seat components or crash boxes; roll-forming bumpers, rocker panels or seat tracks; or hot-forming complex impact-resistant parts.

“Spring-back, for example, has often been considered as a major roadblock for stamping AHSS, but the hot-stamping process eliminates this risk,” explains Jean-Luc Thirion, general manager at ArcelorMittal Global R&D. “When they were first released, AHSS materials were quickly recognised by OEMs as a major opportunity to save weight thanks to their very high tensile strength combined with robustness during processing. This trend has been reinforced by laser-welded blank [LWB] technology, which can combine several hot-stamping grades to optimise crash management.”

The roll forming of ultra-high-strength steels (UHSS) is another way to control spring-back through progressive bending, and the sections that can be obtained are becoming increasingly complex. ArcelorMittal’s MartINsite product range currently has a maximum UTS (ultimate tensile strength) of 1,700 MPa, although this is likely to be extended. One of the drivers in the success of these materials is their lower overall cost, as the roll-forming process is significantly less expensive than stamping parts that feature a constant section in their length, such as side sills or door beams.