Development of door beam ERW tubing made of 1470N mm<sup>2</sup> cold rolled high strength steel sheet

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Development of door beam ERW tubing made of 1470N mm² cold rolled high strength steel sheet

Kashima, T. / Tanaka, Y. / Watanabe, K. / Shirasawa, H. / Miyahara, M. / Sawaki, S.

To develop ultra high strength ERW tubing for the door beams of passenger cars using cold rolled steel sheet, an FFM analysis was performed using a tubing deformation model which simulated door beam testing. In the elastic and plastic FEM analysis, the effets of the yield strength and tensile strength of the steel sheet of tubing properties were investigated. The results showed that the tubing peak load in three-point bending increasing with an increase in tensile strength. An increase in yield strength enhances the endurance load in the early stages of deflection while it slightly accelerates buckling. The analysis resulted in the production of TS 1470 N/mm² grade cold rolled sheet to be manufactured into ERW tubing. A 0.22 % C - 0.4 % Si - 2.4 % Mn - 0.03 % Nb cold rolled steel with a thickness of 2 mm was processed in a continuous annealing line which employed water quenching. An ultra high tensile strength along with a relatively high yield ratio was obtained by the introduction of large amounts of tempered martensite into the microstructure. ERW tubing made from cold rolled sheet with a tensile strength of 1470 N/mm² and a yield ratio of 0.82 showed, in actual door beam testing, as high a peak load and adsorbed energy as conventional induction heated and quenched ERW tubing made from hot rolled steel. These results show the potential for a more economical manufacturing process.