Abstract

A high-ductility TRIP steel sheet has been developed to achieve weight savings in automotive bodies. When TRIP steel is deformed by pressing, etc., the transformation of the retained austenite distributed in its matrix structure into martensite controls the strain concentration. This gives the material higher formability than other steels. However, TRIP steel sheets contain a higher amount of Si than standard steel sheets, and this can cause the platability of the material during hot-dip galvanealing and the ability of cold rolled sheets to accept coatings to decline. A TRIP steel displaying the required strength and formability while possessing identical platability and coatibility to standard steels has therefore been developed by optimizing the amount of C, Si and Mn, the main constituent elements of the steel, adding an element which controls Si concentration to sheets for hot-dip galvannealed (GA steel sheet) and removing the concentrated Si surface layer of non-galvanealed sheets for cold rolling (CR steel sheet). As a result, it has been possible to achieve an identical level of formability in 590MPa and 780MPa grade steel sheets when compared to 440MPa and 590MPa grade standard high strength steel sheets (HSS) respectively. In addition, the new steel possesses identical energy absorption characteristics to existing high-tensile steel but is 10% lighter, enabling weight per vehicle to be reduced by more than 10kg when the new sheets are employed.

References

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Author (organization or company)

• Takahiro TANAE（Tochigi R&D Center）
• Katsuyoshi KANEKO（Honda R&D Europe (UK)）

Publication Information

Article of Honda R&D Technical Review Vol.16 No.2 (183 - 190)

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Citation Information