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  • Investigation of the formation, constitution and properties of scale formed during the finishing, rolling, cooling and coiling of thin hot strips

Abstract

The properties of tertiary scale on hot-rolled steel are receiving increasing attention, because customers of hot-strip mills place increasingly stringent requirements on the properties of unpickled hot-rolled steel strip, e.g. easy-to-pickle, minimised powdering during formation, or minimised oxide dust formation during laser cutting. On the other hand, the possibilities to influence the tertiary scale characteristics have increased over the years, due to the continuous improvement of hot-rolling technology.
for a group of unalloyed ULC, ELC LC and HSLA steels as well as DP steels, the relationship between scale adherence, scale characteristics and hot-rolling process parameters was investigated. Suitable scale adherence tests had been modified. Several microscopical and analytical investigation techniques were used to to evaluate the scale layer and the interface steel/scale in terms of morphology, phase and chemical composition.
From the shop trials and laboratory experiments including laboratory hot rolling, guidelines were defined to get a well-adherent or easy to pickle scale. Scale composition, however, was found to be more important for scale integrity in terms of adherence and coherence than scale thickness. Completely decomposed wustite within the scale gives the best results. Partially retained wustite or layers of magnetite and hermatide lead to poor scale integrity. The influence of enrichments of chemical elements (e.g. silicon) at the interface steel/scale is much less than assumed.
There seems to be a broad optimal coiling temperature for wustite decomposing around 600 degree Celsius. Although low finishing temperatures, particularly in the ferritic range, result in a thin oxide scale, they do not guarantee a good scale integrity. High levels of elements like Mn, Si, V, Nb in HSLA grades decrease the scale adherence.

Additional information

Authors: FRIEDEL F, Thyssen Krupp Stahl AG, Duisburg (DE);BOLT H, CORUS NL, IJmuiden (NL);CORNET X, CRM - Centre de recherches metallurgiques, Liege (BE);BOURDON G, CRM - Centre de recherches metallurgiques, Liege (BE);VANDEN EYNDE X, CRM - Centre de recherches metallurgiques, Liege (BE);ZEIMETZ E, CRM - Centre de recherches metallurgiques, Liege (BE);EHLERS S, Stahlwerke Bremen, Bremen (DE);STEINERT F, TU Bergakademie, Institut fur Eisen- und Stahltechnologie, Freiberg (DE)
Bibliographic Reference: EUR 21128 EN (2004), 407 pp. Euro: 45
Availability: EUR-OP reference: KI-NA-21128-EN-S Available from EUR-OP sales agents URL: http://publications.eu/general/en/publications_en.htm
ISBN: ISBN: 92-894-7957-4
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