The lightweighting of heavy-duty vehicles (HDVs) is an effective strategy to reduce fuel consumption and lower CO₂ emissions in the transport sector. The widespread application of ultra-high-strength steels (UHSSs) in HDV construction offers a viable solution, particularly for thick-walled chassis components. This study aimed to support the lightweighting of heavy vehicles by developing a methodology capturing the entire warm-forming process in the range of 430–580 °C for thick-walled UHSSs—from material characterisation, including elastoplastic and fracture properties, to downstream forming process simulations. A novel 7 mm thick UHSS grade, WARMLIGHT-980 (ultimate tensile strength (UTS) of 980 MPa), intended for warm forming was investigated at 430, 505, and 580 °C using samples of reduced thickness. The results showed that thickness reduction had minimal influence on mechanical response at elevated temperatures, enabling flexible specimen design. The thermal uniformity improved in thinner samples, enhancing testing reliability. The calibrated hardening and fracture models demonstrated strong agreement with experimental data. Validated simulations of thick-walled components confirmed the accuracy of the modelling approach. The findings support the development of reliable, temperature-dependent models for warm-forming applications and contribute to the design of lighter, more sustainable HDV components without compromising structural integrity.

The automotive industry is currently in a paradigm shift transferring the fleet over from internal combustion vehicles to battery electric vehicles (BEV). This introduces new challenges when designing the body-in-white (BIW) due to the sensitive and energy-dense battery that needs to be protected in a crash scenario. Press-hardening steels (PHS) have emerged as an excellent choice when designing crash safety parts due to their ability to be manufactured to complex parts with ultra-high strength. It is, however, crucial to evaluate the crash performance of the selected materials before producing parts. Component testing is cumbersome and expensive, often geometry dependent, and it is difficult to separate the bulk material behaviour from other influences such as spot welds. Fracture toughness measured using the essential work of fracture method is a material property which has shown to be able to rationalise crash resistance of advanced high-strength steel (AHSS) grades and is thereby an interesting parameter in classifying steel grades for automotive applications. However, most of the published studies have been performed at quasi-static loading rates, which are vastly different from the strain rates involved in a crash. These higher strain rates may also lead to adiabatic self-heating which might influence the fracture toughness of the material. In this work, two PHS grades, high strength and very high strength, intended for automotive applications were investigated at lower and higher strain rates to determine the rate-dependence on the conventional tensile properties as well as the fracture toughness. Both PHS grades showed a small increase in conventional mechanical properties with increasing strain rate, while only the high-strength PHS grade showed a significant increase in fracture toughness with increasing loading rate. The adiabatic heating in the fracture process zone was estimated with a high-speed thermal camera showing a significant temperature increase up to 300 °C.