Internal oxidation and formation of Si/Al-enriched oxide bands in the scale of electrical steel grades

Thomas Höfler,Bernhard Linder,Gerhard Angeli,Christian Gierl-Mayer,Herbert Danninger,Michael Auinger

doi:10.1016/j.corsci.2021.109502

Thomas Höfler, Bernhard Linder + Show 4 more

Open Access

https://doi.org/10.1016/j.corsci.2021.109502

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Abstract

Oxidation during steel hot rolling is responsible for various surface defects. Local enrichments of oxygen-affine alloying elements such as silicon or aluminium can cause such defects by complicating oxide scale removal. In this paper, correlations between the temperature profile during oxidation and enrichment formation in electrical steels are investigated. Diffusion and reaction simulations using the numerical Crank-Nicolson-scheme are evaluated by comparing them to laboratory-scale oxidized samples. Furthermore, analytical approximations (spectral methods) are investigated as an alternative approach, focusing on trade-offs between accuracy and calculation times. A link between heating periods during oxidation and Si/Al-rich bands in the scale was established.

Highlights

During the production of flat steel products, the material is exposed to a series of subsequent rolling steps at high temperatures in air
One of the first observations was that the majority of the enrichments was not located directly at the steel-scale-interface, but rather near the original metal surface, suggesting that most of the Si- and Al-oxides were formed during the initial stages of oxidation
Oxidation of the 2.4 wt.% Si and 1.1 wt.% Al steel using a water vapour containing atmosphere (H2O/O2/CO2/N2 (20/3/7, v/v/v)) mimicking the conditions found during slab reheating led to the for mation of a finely porous scale with distinct exterior and interior parts separated by the original metal surface

Summary

Introduction

During the production of flat steel products, the material is exposed to a series of subsequent rolling steps at high temperatures in air. During hot rolling, the material suffers significantly from the formation of oxides which have to be removed in order to achieve the required excellent surface finish of the final product. Certain (electrical) steel grades are known to form strongly adherent scales, resulting in the re sidual scale being rolled into the metal during the subsequent hot rolling step. One of these critical scale constituents is silicon [1,2,3], the effect of which on descaling motivates the present study. Even more in the presence of aluminium, a ternary eutectic with hercynite (FeAl2O4) may form at a melting temperature as low as 1148 ◦C [6]

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