Surface Defect on Hot Rolled Steel Sheet with Cu Content

Abstract:

Structural steel grades S235JRCCu+N and S355JRCCu+N with 0.25 – 0.35% copper content are intended for products with increased corrosion resistance. They are used for railcar and container bodies. The low copper alloying strongly increases the material life-time in the conditions of atmospheric corrosion. Sheets with fine sharp needle-type bodies on both sheet surfaces were delivered for the analysis. As per the customer information, they were present on almost whole length of on cast strips. Considering the steel copper content, it was assumed that the improper steel alloying was the reason of imperfection. Chemical composition results didn’t confirm this expectation. Metallographic analysis should determine the imperfection origin and decide if copper presence was the primary factor of it. The analyses using SEM coupled with EDS analyzer have shown that the sliver-type defects, few millimeters long bands of ductile iron oxides, were present in very small material depth of about 50 – 150 μm in the analyzed material The bands were formed in more layers parallel to the sheet surface; their thickness was similar to the thickness of surface scales. Oxidic material under the sliver had the same micro-morphology and chemical composition like the scales on the sheet surface. Very fine globular copper particles were randomly and very sporadically present in the layer of ductile oxides in slivers and also in surface scale. Besides this, the material in defect area was chemically homogeneous and no particles were found in the layer boundaries. Copper particles were not detected in the steel basic material; the copper was dissolved in the matrix. The nature of imperfection was typical for V-shaped slivers, caused by overheating sheet surface in reheat furnace. After revising technical conditions of reheat furnace operation, this imperfection type was suppressed.

• Periodical: Materials Science Forum (Volume 782)
• Pages: 239-242
• DOI: https://doi.org/10.4028/www.scientific.net/MSF.782.239
• Online since: April 2014
• Authors: Lucia Hrabčáková*, Jaroslav Duška, Alicia Mašlejová
• Keywords: Corrosion Resistance, Cu Alloying, S235JRCCu+N Steel, Slivers, Surface Overheating

References

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[2] EN 10025-2/04 Hot rolled products of structural steel.

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[4] Kizu T., Nagataki Y., Inazumi T. and Hosoya Y., ISIJ International, Vol. 42 (2002), No. 2, p.206–214.

DOI: 10.2355/isijinternational.42.206