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Abstract

This work deals with the problem of intermetallic phases in cast standard duplex steel ASTM A890 Gr 4A (generally known as 2205). The investigated steel was subjected to isothermal heat treatment in the range from 595 °C to 900 °C and in the duration from 15 minutes to 245 hours, and was also investigated in terms of anisothermal (natural) cooling after casting into the mould. The precipitation starts at grain boundaries with a consistent ferrite transformation. The work is focused on the precipitation of the sigma phase (σ) and the chi phase (χ). Examination of the microstructure was conducted using light and scanning electron microscopy. Their statistical analysis was carried out using the results of the investigations of precipitation processes in the microstructure, both within the grains and at the grain boundaries. To illustrate this impact, the surface area of precipitates was evaluated. The percentage of these intermetallic phases was calculated by measuring their area using a computer image analysis system. Based on their observations, a combined time-temperature transformation (TTT) diagram with continuous cooling transformation (CCT) curves was created.
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Authors and Affiliations

M. Myška
1
ORCID: ORCID
P. Bořil
1
ORCID: ORCID
V. Krutiš
1
ORCID: ORCID
V. Kaňa
1
ORCID: ORCID
A. Zádĕra
1
ORCID: ORCID

  1. Brno University of Technology, Czech Republic
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Abstract

The paper discusses possible applications of the percolation theory in analysis of the microstructure images of polycrystalline materials.

Until now, practical use of this theory in metallographic studies has been an almost unprecedented practice. Observation of structures so

intricate with the help of this tool is far from the current field of its application. Due to the complexity of the problem itself, modern

computer programmes related with the image processing and analysis have been used. To enable practical implementation of the task

previously established, an original software has been created. Based on cluster analysis, it is used for the determination of percolation

phenomena in the examined materials. For comparative testing, two two-phase materials composed of phases of the same type (ADI

matrix and duplex stainless steel) were chosen. Both materials have an austenitic - ferritic structure. The result of metallographic image

analysis using a proprietary PERKOLACJA.EXE computer programme was the determination of the content of individual phases within

the examined area and of the number of clusters formed by these phases. The outcome of the study is statistical information, which

explains and helps in better understanding of the planar images and real spatial arrangement of the examined material structure. The results

obtained are expected to assist future determination of the effect that the internal structure of two-phase materials may have on a

relationship between the spatial structure and mechanical properties.

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Authors and Affiliations

W. Trzaskowski
S. Świłło
W. Sobaszek
D. Myszka
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Abstract

The aim of this work is to investigate the resistance of cast duplex (austenitic-ferritic) steels to pitting corrosion with respect to the value of PREN (Pitting Resistance Equivalent Number). Pitting corrosion is one of the most common types of corrosion of stainless steels. In most cases, it is caused by the penetration of aggressive anions through the protective passive layer of the steel, and after its disruption, it leads to subsurface propagation of corrosion. The motivation for the research was a severe pitting corrosion attack on the blades of the gypsum-calcium water mixer in a thermal power plant operation.
In order to examine the corrosion resistance, 4 samples of 1.4517 steel with different concentrations of alloying elements (within the interval indicated by the steel grade) and thus with a different PREN value were cast. The corrosion resistance of the samples was evaluated by the ASTM G48 – 11 corrosion test in a 6% aqueous FeCl3 solution at room and elevated solution temperatures. To verify the possible effect of different alloying element concentrations on the mechanical properties, the research was supplemented by tensile and Charpy impact tests. Based on the results, it was found that a significant factor in the resistance of duplex steels to pitting corrosion is the temperature of the solution. For the components in operation, it is therefore necessary to take this effect into account and thoroughly control and manage the temperature of the environment in which the components operate.
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Bibliography

[1] Reardon, A. (2011). 12.5 Duplex Stainless Steels. In metallurgy for the non-metallurgist (2nd Edition). Ohio: ASM International, ISBN 978-1-61503-821-3, Retrieved from https://app.knovel.com/hotlink/pdf/id:kt009JBTT4/metallurgy-non-metallurgist/duplex-stainless-steels
[2] McGuire, M.F. (2008). Duplex stainless steels. in stainless steels for design engineers (91–108) [online]. Materials Park, Ohio 44073-000: ASM International, [cit. 2020-05-19]. ISBN 978-1-61503-059-0., Retrieved from: https://app.knovel.com/hotlink/pdf/id:kt008GRPY2/stainless-steels-design/duplex-stainless-introduction
[3] O'Brien, A. ed. (2011) Stainless and Heat-Resistant Steels. In Welding Handbook, Volume 4 - Materials and Applications, Part 1 [online]. 9th Edition. Miami: American Welding Society (AWS), p. 351 [cit. 2020-05-27]. ISBN 978-1-61344-537-2. Retrieved from https://app.knovel.com/hotlink/pdf/id:kt0095SGE2/welding-handbook-volume/duplex-sta-composition
[4] Revie, R.W. ed. (2011). In Uhlig’s Corrosion Handbook [online]. Third edition. Duplex stainless steels. (695–705). Hoboken, New Jersey: John Wiley & Sons, 2011 [cit. 2020-06-14]. ISBN 978-1-61344-161-9. Retrieved from https://app.knovel.com/hotlink/pdf/id:kt008TZY32/uhlig-s-corrosion-handbook/duplex-sta-history
[5] Prošek, T. & Šefl, V. (2018). Corrosion resistance of stainless steel in drinking water treatment plants and water storage units. Koroze a ochrana materialu. 62(4), 141-147. DOI: 10.2478/kom-2018-0020.
[6] Cicek, V. (2014). Corrosion engineering. Hoboken, New Jersey: Scrivener Publishing/Wiley. ISBN 978-1-118-72089-9. Retrieved from https://app.knovel.com/hotlink/toc/id:kpCE00004B/corrosion-engineering/corrosion-engineering.
[7] Marcus, P. ed. (2012). Corrosion mechanisms in theory and practice. Third edition. Boca Raton: CRC Press, Corrosion technology (Boca Raton, Fla.). ISBN 978-1-4200-9463-3.
[8] G48 - 11(2015). Standard test methods for pitting and crevice corrosion resistance of stainless steels and related alloys by use of ferric chloride solution. West Conshohocken: ASTM International, 2015.
[9] Jargelius-Pettersson, R.F.A. (1998). Application of the pitting resistance equivalent concept to some highly alloyed austenitic stainless steels. Corrosion. 54(2), 162-168. DOI: 10.5006/1.3284840.
[10] (2015). Austenitic-ferritic (duplex) casting materials [online]. Otto Junker, 2015 [cit. 2020-06-25]. Retrieved from: https://www.otto-junker.com/cache/dl-Austenitic-Ferritic-DUPLEX-Casting-Materials-aa4d1dd1db00d37343728c6ba0598a75.pdf

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Authors and Affiliations

P. Müller
1
ORCID: ORCID
V. Pernica
1
ORCID: ORCID
V. Kaňa
1
ORCID: ORCID

  1. Brno University of Technology, Czech Republic

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