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Characterisation and pickling behaviour of oxides formed during production annealing of stainless steel
Swerea KIMAB, Stockholm.
2010 (English)Licentiate thesis, comprehensive summary (Other academic)
Place, publisher, year, edition, pages
Stockholm: E-print , 2010. , 49 p.
Series
TRITA-CHE-Report, ISSN 1654-1081 ; 2010:42
Keyword [en]
stainless steel, oxidation, annealing, hot rolling, cold rolling, water vapour and mixed acid pickling
National Category
Other Chemistry Topics
Identifiers
URN: urn:nbn:se:kth:diva-27737ISBN: 978-91-7415-754-3 (print)OAI: oai:DiVA.org:kth-27737DiVA: diva2:380417
Presentation
2010-11-04, KTH, Stockholm, 13:00 (English)
Opponent
Supervisors
Note

QC 20101221

Available from: 2010-12-21 Created: 2010-12-21 Last updated: 2015-06-23Bibliographically approved
List of papers
1. Pickling of Process-Oxidised Austenitic Stainless Steels in HNO3-HF Mixed Acid
Open this publication in new window or tab >>Pickling of Process-Oxidised Austenitic Stainless Steels in HNO3-HF Mixed Acid
2010 (English)In: STEEL RES INT, ISSN 1611-3683, Vol. 81, no 7, 542-551 p.Article in journal (Refereed) Published
Abstract [en]

Oxide formation during production annealing and the subsequent pickling response in mixed acid have been studied. The aims were to characterise the oxides formed and to understand how the pickling mechanism and kinetics are affected by the nature of the oxide. Totally, eight different versions of the austenitic stainless steel grades AISI 301, 304L and 309L were studied, all annealed in production lines. Cold rolled oxides (formed during annealing) are thin (< 1 mu m), dense and formed in a multilayered manner. Hot rolled oxides (formed during reheating, hot rolling and annealing) are thicker (>1 mu m) and more heterogeneous in thickness and composition. The dissolution rate of the chromium depleted layer (CDL) under the oxide is the most important factor for the overall pickling rate. The permeability of acid through the oxide and the tendency of the oxide to spall are also important factors affecting the pickling kinetics. The dense oxide formed on cold rolled materials can to some extent hinder the acid to reach the CDL. The oxides on hot rolled materials are porous and do not provide such a barrier but they are thicker and thereby more difficult to remove. Shot-blasting prior to pickling of the hot rolled materials improves the pickling performance because it thins the oxide, improves the permeability and increases the tendency of the oxide to spall during the pickling step.

Keyword
pickling, oxidation, stainless steel
National Category
Metallurgy and Metallic Materials
Identifiers
urn:nbn:se:kth:diva-27718 (URN)10.1002/srin.201000011 (DOI)000280782000006 ()2-s2.0-77956584717 (Scopus ID)
Note

QC 20101220

Available from: 2010-12-20 Created: 2010-12-20 Last updated: 2015-01-21Bibliographically approved
2. Oxide formation and pickling performance of duplex stainless steel 2205
Open this publication in new window or tab >>Oxide formation and pickling performance of duplex stainless steel 2205
2009 (English)In: Proceeding of the International Stainless Steel Word Conference, 10-12th Nov 2009, Maastricht, Netherlands, 2009Conference paper, Published paper (Refereed)
Abstract [en]

Duplex stainless steels have gained popularity due to their high corrosion resistance and higher strength for a lower/more stable raw material cost compared to the austenitic grades. However, processing of the duplex grades may be more difficult, partly because of their relatively high corrosion resistance. The materials used for this study were cold and hot rolled variants of the duplex stainless steel grade 2205. Annealing was done in industrial production lines using either induction or conventional gas-fired furnaces. The specimens were laboratory pickled in mixed acid (HNO3 + HF) and analyzed after different pickling times. The techniques employed were scanning electron microscopy (SEM), electron backscatter diffraction (EBSD), glow discharge optical emission spectroscopy (GDOES), X-ray diffraction (XRD) and wet-chemical techniques. The aim was to understand the oxidation behaviour during production annealing and to elucidate the pickling mechanism in mixed acid. Comparison was made to the pickling behaviour of the standard austenitic grades 304L and 309L.

The oxide formed on cold and hot rolled 2205 comprised an inner á-Cr2O3 and outer mixture of iron rich M3O4 spinel (M = Fe, Cr, Mn) and á-Fe2O3. The oxide thickness was 0.5-1 and 2-10 μm for the cold and hot rolled materials respectively. Manganese enrichment in the spinel was primary observed for the cold rolled variants.

Chromium enrichment in the oxide alters the phase balance of the material under the oxide towards a higher austenite/ferrite ratio. Pickling duplex stainless steels has many similarities with pickling of austenitic grades in that electrochemical dissolution of this chromium depleted and austenitic enriched layer is the most important process. The oxides formed affect the pickling kinetics to a large extent. Thick oxides formed in scratches or pores require up to three times longer pickling time until clean.

National Category
Metallurgy and Metallic Materials
Identifiers
urn:nbn:se:kth:diva-27729 (URN)
Conference
International Stainless Steel Word Conference, 10-12th Nov 2009, Maastricht, Netherlands
Note

QC 20101220

Available from: 2010-12-21 Created: 2010-12-21 Last updated: 2015-01-21Bibliographically approved
3. Fast and Efficient Annealing of Stainless Steel Strip Using Oxyfuel Burners
Open this publication in new window or tab >>Fast and Efficient Annealing of Stainless Steel Strip Using Oxyfuel Burners
2015 (English)In: Steel Research International, ISSN 1611-3683, E-ISSN 1869-344X, Vol. 86, no 5, 557-566 p.Article in journal (Refereed) Published
Abstract [en]

Pilot plant and annealing experiments have been conducted to study the effect of the higher water content in oxyfuel annealing on oxidation and pickling of cold rolled stainless steel. The experiments were conducted on the austenitic grade AISI 304 in a propane-fired furnace using air and pure oxygen as oxidizers. The experiments were conducted at 1050-1200 degrees C for typically less than 60 s, in order to simulate industrial annealing of thin strip. Supplementary laboratory annealing trials were made to study the evolution of the microstructure during fast heating rates and short hold times. Increasing the water content from 15 to 50 mol% did not alter the oxidation kinetics or the chemistry of the oxide. Since the oxidation is not altered significantly, the pickling performance of the material remains unchanged. The presence of spalled areas increased the pickling efficiency significantly but this was only seen for material annealed at higher temperature compared to industrial practice. Oxyfuel combustion allows higher heat input and therefore faster heating. The 304 grade recrystallizes readily even at moderate cold rolling reductions so the total annealing time can be reduced substantially if the heating rate can be increased. The present work suggests that this can be done without any downstream effects.

Keyword
oxyfuel, cold rolled stainless steel, annealing, oxide formation, mixed acid pickling
National Category
Metallurgy and Metallic Materials
Identifiers
urn:nbn:se:kth:diva-159022 (URN)10.1002/srin.201400168 (DOI)000354202500012 ()2-s2.0-84928882243 (Scopus ID)
Note

QC 20150120. Updated from e-pub ahead of print to published.

Available from: 2015-01-20 Created: 2015-01-20 Last updated: 2017-12-05Bibliographically approved

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