Development of Door Beam ERW Tubing Made of 1470N/mm2 Cold Rolled High Strength Steel Sheet

To develop ultra high strength ERW tubing for the door beams of passenger cars using cold rolled steel sheet, an FEM analysis was performed using a tubing deformation model which simulated door beam testing.

In the elastic and plastic FEM analysis, the effects of the yield strength and tensile strength of the steel sheet on tubing properties were investigated. The results showed that the tubing peak load in three-point bending increases 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 1470N/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 2mm 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 1470N/mm² and a yield ratio of 0.82 showed, in actual door beam testing, as high a peak load and absorbed 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.