Development of Roll Formable Ultra High Strength Steels for Energy Efficient Manufacture of Lightweight Crash Resistant Automotive Structures

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This project is concerned with the development of Ultra High Strength Steels (UHSS - steels with a ultimate tensile strength greater than 1000 MPa) specifically designed to be formed by a novel low energy and flexible manufacturing process, known as 3D roll forming, to produce lightweight crash resistant structures for the automotive industry. The roll forming process is an incremental bending process that turns a flat sheet into a structural profile as compared to traditional stamping processes that involves severe stretching of the sheet to create the required part geometry. The 3D roll forming process is extremely flexible - leading developers of the technology claim a single set of tooling can be used to manufacture up to a quarter of the automotive structure, whereas the stamping process requires an expensive set of tools to be manufactured for each individual part. Furthermore a roll forming line only take 10 to 16 weeks to setup as compared to 18 months for a stamping line. Today ultra high strength automotive steels are usually formed using the energy intensive hot stamping as it is very difficult, and costly, to design steels that achieve the required high room temperature uniform ductility in combination with an ultimate tensile strength in excess of 1000 MPa. As roll forming only requires the material to be bendable, it is proposed that steels with low work hardening rates and a high yield ratio (yield strength /ultimate tensile strength) could be suitable for shaping using this process. The development of UHSS for roll forming allows simpler compositions that are leaner and have a lower alloy cost which reduces exposure to raw materials supply issues (scarcity), have better compatibility with existing capabilities and are more consistent (higher yield/lower scrap). This is potentially a disruptive technology that could revolutionise the manufacture of automotive structural members. It will: eliminate the need for energy intensive hot stamping currently used for shaping UHSS; dramatically reduce tooling requirements and the energy associated in their manufacture; increase material utilisation; avoid the need to use energy intensive materials for lightweighting such as Al, Mg and CFRP; all whilst producing a product that will yield significant CO2 savings during use. It is estimated that if roll formed steel replaced 50 kg of hot stamped components in a vehicle, then 40,000 tonnes of CO2 could be saved in the UK automotive manufacturing industry per annum.