Body-in-white design demands affordability and improved crash performance, combined with low weight and good formability. This is pushing the limits of high-strength, low-alloy (HSLA) steels. Carmakers are increasing their material-strength requirements to enable lightweighting, which can give rise to forming issues. Dual-phase (DP) 600 has become a conventional grade for front longitudinals. Transformation Induced Plasticity (TRIP) steels offer higher strength and good formability, but are rarely used due to coating and joining reasons.
Tata Steel has developed an innovative generation of high-strength steels called HyperForm, which combine the best features of both. HyperForm demonstrates the formability of TRIP steels, while at the same time featuring the good post-processing characteristics of DP steels.
Tata Steel analysed the benefits of HyperForm use in body-in-white design on front longitudinal beams and the lower A-pillar as they are major contributors to meeting the demands of front-crash performance. In addition the study evaluated the influence that HyperForm has on sustainability and total cost of ownership – the balance between costs, lightweight design potential and performance.
Potential for weight reduction
The study began by analysing the lightweight design potential offered by the front-crash structure, while maintaining the necessary strength and safety characteristics. The longitudinal beam is made of a tailored blank of three different material gauges. The starting point was to assess the crash performance of the longitudinal beams and lower A-pillar sections from a series production compact-class car. These components were made from the HSLA steels HX260LAD and HX300LAD.
The crash test applied was the Euro NCAP frontal-impact test. This base material combination was then compared with HX340LAD and HX420LAD, as well as DP600 and DP800 HyperForm. The strains and thickness changes caused by the forming process were calculated in one-step forming simulations, and incorporated into the crash model. The aim of applying the forming effects was to demonstrate the benefits of increased work hardening in the DP steels.
Carmakers can use HyperForm to replace HSLA steels and DP600 in body-in-white components, achieving lightweight design benefits
Under comparable vehicle deceleration g-forces and passenger-compartment intrusion levels, DP800 HyperForm demonstrated considerably greater lightweight design benefits. Compared with HX260LAD, the weight of the longitudinal and lower A-pillar could be reduced by 23% due to lower material thickness. The weight reduction compared with HX340LAD is 14%, with HX420LAD, 5.5%, and with DP600, 8%.
|tags:||Lightweighting Body-in-white Safety|