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A new type of bake-hardenable high strength hot-rolled sheet steel was developed, which shows a remarkable increase in tensile strength as well as yield strength after strain age hardening without addition of special elements. The new sheet possesses excellent crashworthiness and high fatigue strength, and also shows good formability, equal to that of conventional high strength sheets. This unique combination of properties makes it possible to reduce the weight of the car body by using thinner gauge material when the new sheet is applied to crash-resistant parts and underbody parts.

The effects of strain rate on the deformation behavior of several steels were investigated to find the most appropriate material for anti-crash parts of automobiles, such as front-side-members. Dual phase steel, TRIP steel, and work hardened steel showed higher dynamic to static yield strength ratios than solid-solution hardened steel. The dual phase steel absorbed a higher amount of energy during dynamic deformation than other steels with the same static yield strength due to its high strain rate sensitivity and high work hardening coefficient during dynamic deformation.

Improved formability and higher heat-resistance are increasingly demanded to materials used for hot end parts of automotive exhaust gas system in order to meet stricter emission regulations. A heat-resistant ferritic stainless steel and pipe with high formability was developed by refining the microstructure of hot rolled and annealed sheets. The newly developed steel showed a remarkable improvement in various forming properties such as limit drawing ratio, limit expansion ratio of pipe, and thickness reduction ratio of pipe after bending in comparison with conventional steels.

The goal of this study was to identify a pre-coated steel sheet that will satisfy press formability, seam weldability, spot weldability, brazing property, external corrosion resistance and internal fuel resistance. We established an experimental method for anti-fuel resistance measurement by applying synthetic spoiled gasoline by investigating the composition of spoiled gasoline and corrosion products in the fuel tank, which was collected in North America after 160,000 kilometers' running. Newly developed lead-free pre-coated steel sheet shows excellent anti-fuel corrosion resistance in comparison with that of usual terne coated steel sheet according to this method.