Control of the oxidation/reduction process for strip galvanisation
New steel grades appear now on the market like more alloyed with manganese and silicon. These steels are renowned to present zinc wetting and coating adhesion problems. Previous research has clearly shown that the oxidation/reduction process can improve the zinc wettability on high strength steels. However, the oxide thickness needed during the oxidation step has to be controlled to avoid the segregation of the selective oxidation to the top surface during soaking, without living residual iron oxide layer. Therefore, the aim of this work was to supply technical solutions to the problem of oxide thickness measurement. Moreover, as the strip emissivity changes drastically after oxidation, the control of the strip temperature was also an important item. Laboratory and industrial trials have shown that a sensor, based on reflectance spectroscopy, can very well measure an iron oxide thickness in the range 70-250 nm and give at the same time the correct strip temperature. The influence of the steel grade is also of minor importance with such technology. After oxidation made during heating, the iron oxide, produced on HSS can be reduced by the alloying elements during soaking. In the case of an IF Ti steel treatment, without alloying elements, the iron oxide can be fully reduced during 5s in a reactive section put at the end of the soaking section containing 40% H2 and 1.2% H2O. After such strip preparation, DP steels and rephosphorised IF steels can be galvanised without any zinc wetting problems or coating adhesion failures.
Bibliographic Reference: EUR 22014 EN (2006), 90 pp. Euro: 15
Availability: Katalogue Number: KI-NA- 22014-EN-S The paper version can be ordered online and the PDF version downloaded at: http://bookshop.europa.eu
ISBN: ISBN: 92-79-01675-X
Record Number: 200618661 / Last updated on: 2006-07-20
Original language: en
Available languages: en