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 (Refereed)
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
Metallurgy and Metallic Materials
IdentifiersURN: urn:nbn:se:kth:diva-27729OAI: oai:DiVA.org:kth-27729DiVA: diva2:380317
International Stainless Steel Word Conference, 10-12th Nov 2009, Maastricht, Netherlands
QC 201012202010-12-212010-12-212015-01-21Bibliographically approved