Development of a Methodology for the Quality Management of Duplex Stainless Steels

Abstract

The use of traditional materials leads to failures and breakdowns of expensive equipment, so advanced materials are needed that can provide reliable and durable solutions. The ability to control the quality of duplex stainless steels (DSSs) can greatly help with the development of new compositions or choosing existing DSSs. In this case, it is necessary to consider the final consumer properties—corrosion resistance and mechanical properties, which depend on the phase composition, contamination with non-metallic inclusions (NMIs), and the presence of undesirable secondary phases. In this research, specimens of cast DSSs of different grades, produced at laboratory and industrial scales, were studied. A technique for quantifying the microstructure of DSSs was developed. A thermodynamic database was chosen that adequately describes the processes of phase formation in DSSs. The effects of heat treatment on the microstructure and corrosion properties of cast DSSs were studied. The effects of the structural state on the changes in consumer properties of the final product are shown. It is shown that using various deoxidation technologies, it is possible to obtain both NMIs that are dangerous in terms of corrosive activity and ones that are relatively safe.

Stress Corrosion Cracking Mechanisms of UNS S32205 Duplex Stainless Steel in Carbonated Solution Induced by Chlorides

“…This inclusion was found inside a cleavage facet, which showed higher chromium and lower nickel content, suggesting α-phase (ferrite cleavage facet) [49]. Performing an EDX analysis on the inclusion, it was confirmed that it was a TiN nonmetallic inclusion (NMI) (see Figure 10b) [61,62]. This type of TiN NMI has been seen to promote higher corrosion susceptibility in duplex stainless steel, leading in some cases to the promotion of TG-SCC [63,64].…”

Control of the Composition and Morphology of Non-Metallic Inclusions in Superduplex Stainless Steel

“…In an earlier work by the authors, three steels deoxidized with titanium, aluminum, and rare earth metals were studied and the effect of deoxidizers on resistance to pitting and crevice corrosion was shown [2]. However, the nature of NMIs was not sufficiently studied.…”

“…These steels are used to produce various castings: fittings, casings and the moving parts of pumps. Such local corrosion damage occurs even if the chemical composition and heat treatment provide the required quality of the structure [2,3]. Localization of pitting occurs near non-metallic inclusions (NMIs) [4][5][6][7][8], formed during the melting, casting and solidification of these steels [4,5,[9][10][11][12].…”

“…The influence of NMI types on pitting formation has been studied in detail [2,[4][5][6][13][14][15]. The most critical inclusions are oxides [4,5] and sulfides [13][14][15].…”

“…The final concentration of sulfur in induction melting depends only on the quality of the raw materials, so rare earth metals are also added to remove it. There are many works that show the positive effect of REM on the properties of DSS [2,5,9,12,17].…”