Community Research and Development Information Service - CORDIS


Final report on Contract no. 7210-PR/062, 1 July 1997 to 31 December 2000

The main parameter responsible for poor coating wettability is identified as carbon segregation before hot dipping. During the hot-rolling process, carbon segregation at the steel/scale interface induces the formation of pearlite. During reheating at low temperature, that pearlite can reject carbon to form an homogeneous graphite layer, which significantly reduces zinc wettability on the steel surface. An increase of the annealing temperature promotes decarburising and significantly improves the zinc wettability. The easiest way to improve zinc wettability on industrial lines is, however, the increase of the bath and/or the strip-dipping temperature. That practice, however, increases the steel/bath reactivity and induces the formation of brittle Fe-Zn compounds at the strip/coating interface with probably the formation of a higher amount of drosses in the bath.

These results indicate that the hot-rolling conditions are more important for the zinc wettability than the steels. That is mainly explained by the weak selective oxidation amount induced by the low reheating temperature (550 °C). That low temperature is, however, sufficient to reduce completely the iron oxide left on the surface after pickling. A thin iron oxide, produced during cooling, can be admitted on the surface before hot dipping without lowering the zinc wettability or the coating adhesion. Finally, H(2) blistering is due to the zinc de-cohesion at the Fe(2)Al(5) interface. The amount of H(2) in the annealing atmosphere plays a key role in the h(2) blistering problem.

Additional information

Authors: BORDIGNON L, CRM, Liège (BE);LE JEUNE D, Corus UK Ltd, Port Talbot (GB);SCHUHMACHER B, TKS, Dortmund (DE);MEURER M, TKS, Dortmund (DE);URAN K, TKS, Dortmund (DE);GRAPKE H J, MPI, Düsseldorf (DE);SCHLUTER T, MPI, Düsseldorf (DE)
Bibliographic Reference: EUR 20345 EN (2002), pp.103. Euro: 16.00
Availability: EUR-OP reference: KI-NA-20345-EN-S Available from EUR-OP sales agents. URL:
ISBN: ISBN: 92-894-3694-8
Record Number: 200214995 / Last updated on: 2002-07-16
Original language: en
Available languages: en