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Abstract

Final report on Contract No 7210-PR/118, 1 July 1998 to 30 June 2001.

Strips for automotive applications are becoming thinner and thinner to lighten the weight of cars. This requires the production of higher-strength steels. New steel grades are now appearing on the market, such as rephosphorised steels or other qualities alloyed more with manganese and silicon, and also microalloyed steels with manganese additions. These steels are renowned for presenting galvanizing problems:
- wettability and adhesion problems during hot dipping for steel grades alloyed with silicon and/or manganese;
- reactivity problems during galvannealing of rephosphorised steels.

In this study, an improvement in the galvanization and/or galvannealing was obtained by strip pre-oxidation in the heating section followed by a reduction during soaking. The oxidation is obtained by increasing the air/gas ratio of the burners of the direct fired furnace in a range between 1.15 and 1.25 depending on the steel chemistry and the hydrogen content in the radian tube furnace. Such heating conditions allow the building of an iron oxide of around 0.2µm, which can be reduced completely in the soaking section with the formation of a pure and porous metallic iron layer. That new surface allows the galvanizing of all dual-phase steel chemistries without any bare spots or coating adhesion problems. If TRIP steels alloyed with aluminium are also galvanized with such a process, the wetting improvement for silicon steels is not sufficient to suppress the occurrence of bare spots.

Additional information

Authors: BORDIGNON L, CRM, Liège (BE);VANDEN EYNDE X, CRM, Liège (BE);PAAVILAINEN J, Rautaruukki, Oulu (FI);BOLT H, Corus NL, IJmuiden (NL);HEKKENS R, Corus NL, IJmuiden (NL);DEINHAMMER, VASL, Linz (AT);MASCHECK W, VASL, Linz (AT);ANGELI G, VASL, Linz (AT)
Bibliographic Reference: EUR 20566 EN (2002), pp.177. Euro: 26.50
Availability: EUR-OP reference: KI-NA-20566-EN-S Available from EUR-OP sales agents URL: http://publications.eu/general/en/publications_en.htm
ISBN: ISBN: 92-894-4535-1
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