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Fast and Efficient Annealing of Stainless Steel Strip Using Oxyfuel Burners
Swerea Kimab AB, Sweden.
Jernkontoret, Sweden.ORCID iD: 0000-0002-0980-0560
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.

Place, publisher, year, edition, pages
2015. Vol. 86, no 5, 557-566 p.
Keyword [en]
oxyfuel, cold rolled stainless steel, annealing, oxide formation, mixed acid pickling
National Category
Metallurgy and Metallic Materials
Identifiers
URN: urn:nbn:se:kth:diva-159022DOI: 10.1002/srin.201400168ISI: 000354202500012Scopus ID: 2-s2.0-84928882243OAI: oai:DiVA.org:kth-159022DiVA: diva2:782227
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
In thesis
1. Process-microstructure-corrosion interrelations for stainless steel
Open this publication in new window or tab >>Process-microstructure-corrosion interrelations for stainless steel
2015 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Stainless steels were first developed in the early 20th century and have since then emerged as a very diverse class of engineering materials. Along with steels having new combinations of properties, there is a continuous development of new technologies allowing the material to be produced in a faster and more energy effcient manner. A prerequisite for new technologies to be adapted quicklyis a fundamental understanding of the microstructure evolution throughout theprocess chain. The first part of this thesis has been dedicated to the annealing and pickling processes from a process-microstructure perspective. In the second part the concept of utilising crystallographic texture as a way to attain microstructures with new combinations of properties has been evaluated.

In the first part, annealing can be regarded as a high temperature oxidation process, resulting in chromium depletion that necessitate subsequent chemical pickling. Chemical pickling, on the other hand, is basically a wet-corrosion process and hence more difficult for highly corrosion-resistant grades. The chromium depleted layer was found to be enriched in austenite in case of duplex stainless steel UNS S32205 (Paper I) and this may inuence the pickling process. Proper pretreatment like shot-blasting dramatically increases the pickling rate because it provides the pickling acid with access to the chromium depleted layer (Paper II). Oxidation kinetics for S30400 in conditions relevant to strip annealing do not seem to be affected by the choice of air/oxygen as oxidiser even though the latter results in substantially higher water content (Paper III). This gives new possibilities regarding both cost savings and increased throughput.

In the second part, the effect of crystallographic texture on resistance towards corrosion of S31603 in a solution of FeCl3 and AlCl3 in ethanol/glycerol and in 30 vol% H2SO4 is investigated. In the former, high density surfaces {1111} and {100} are less prone for pit nucleation, however the effect is relativelysmall. In H2SO4 pronounced crystallographic anisotropy is observed inwhich the corrosion rate increase in the order {111} < {110} ≤ {100} (Paper IV).For corrosion at high temperatures, chromium diffusion is governed by randomhigh angle boundaries with ~20—55° misorientation. The possibilities to alter the texture in austenitic stainless steels by means of warm-rolling and annealing has been evaluated for S30403 and S31603. During warm-rolling, both steels develop the copper-type texture in contrast to the brass-type texture observedat room temperature. However only S30403 is prone to recrytallise cube texture during subsequent annealing (Paper V).

Place, publisher, year, edition, pages
Stockholm: KTH Royal Institute of Technology, 2015. xii, 75 p.
Series
TRITA-CHE-Report, ISSN 1654-1081 ; 2015:3
Keyword
stainless steel, processing, annealing, pickling, microstructure, corrosion, anisotropy, oxyfuel
National Category
Metallurgy and Metallic Materials
Research subject
Chemistry
Identifiers
urn:nbn:se:kth:diva-159072 (URN)978-91-7595-425-7 (ISBN)
Public defence
2015-02-16, F3, Lindstedtsvägen 26, KTH, Stockholm, 10:00 (English)
Opponent
Supervisors
Note

QC 20150121

Available from: 2015-01-21 Created: 2015-01-20 Last updated: 2015-01-21Bibliographically approved
2. Characterisation and pickling behaviour of oxides formed during production annealing of stainless steel
Open this publication in new window or tab >>Characterisation and pickling behaviour of oxides formed during production annealing of stainless steel
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
stainless steel, oxidation, annealing, hot rolling, cold rolling, water vapour and mixed acid pickling
National Category
Other Chemistry Topics
Identifiers
urn:nbn:se:kth:diva-27737 (URN)978-91-7415-754-3 (ISBN)
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

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