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Pickling of Process-Oxidised Austenitic Stainless Steels in HNO3-HF Mixed Acid
Swerea KIMAB, Stockholm.
Outokumpu Stainless, Avsesta Research Centre, Avesta, Sweden.
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.

Place, publisher, year, edition, pages
2010. Vol. 81, no 7, 542-551 p.
Keyword [en]
pickling, oxidation, stainless steel
National Category
Metallurgy and Metallic Materials
Identifiers
URN: urn:nbn:se:kth:diva-27718DOI: 10.1002/srin.201000011ISI: 000280782000006Scopus ID: 2-s2.0-77956584717OAI: oai:DiVA.org:kth-27718DiVA: diva2:380035
Note

QC 20101220

Available from: 2010-12-20 Created: 2010-12-20 Last updated: 2015-01-21Bibliographically approved
In thesis
1. 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
2. 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

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