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Oxide formation and pickling performance of duplex stainless steel 2205
Swerea KIMAB, Stockholm.
Outokumpu Stainless AB, Avesta Research Centre, Avesta, Sweden.
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.

Place, publisher, year, edition, pages
2009.
National Category
Metallurgy and Metallic Materials
Identifiers
URN: urn:nbn:se:kth:diva-27729OAI: oai:DiVA.org:kth-27729DiVA: diva2:380317
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
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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