Oxide-scale structures formed on commercial hot-rolled steel strip and their formation mechanisms

Citation
Ry. Chen et Wyd. Yuen, Oxide-scale structures formed on commercial hot-rolled steel strip and their formation mechanisms, OXID METAL, 56(1-2), 2001, pp. 89-118
Citations number
22
Language
INGLESE
art.tipo
Article
Categorie Soggetti
Metallurgy
Journal title
OXIDATION OF METALS
ISSN journal
0030-770X → ACNP
Volume
56
Issue
1-2
Year of publication
2001
Pages
89 - 118
Database
ISI
SICI code
0030-770X(200108)56:1-2<89:OSFOCH>2.0.ZU;2-Y
Abstract
The oxide-scale structure developed on commercial hot-rolled steel str ip a t the mid-coil position was examined. The initial oxide scale after rolling and cooling on the run-out table had a three-layer (hematite, magnetite, a nd wustite) structure; the thickness was found to be a function of the fini shing temperature. From this initial structure, various final scale structu res developed after coiling, depending on the coiling temperature, oxygen a vailability, and cooling rate. For relatively low coiling temperatures (e.g ., at 520 degreesC), the final scale structure comprised an inner magnetite /iron mixture layer, an outer magnetite layer, and at regions away from the center, a very thin outermost hematite layer. For higher coiling temperatu res (e.g., in the range of 610 to 720 degreesC), a two-layer hematite/magne tite structure was observed at the edge regions, whereas at the center regi ons, these two layers were absent and the entire scale layer comprised a mi xture of the wustite-transformation products, i.e., a mixture of proeutecto id magnetite, magnetite + ir on eutectoid, and a certain amount of retained wustite. At regions between the edges and the center, the oxide structures were similar to those developed at low coiling temperatures (<570<degrees> C), i.e., an inner layer comprising a mixture of the wustite-transformation products, an inter mediate magnetite layer and at regions near the edges, an outermost hematite layer. In addition, two distinct structures were obse rved on strips with a coiling temperature of 720 degreesC. One structure co mprised a very thick hematite layer (3-5 mum) formed near the edges (within 20-20 mm from the edges), while the other structure comprised a substantia l amount of retained wustite formed at the center regions. The formation me chanisms of various oxide scale structures are discussed.