Effect of small additions of ruthenium on pitting corrosion resistance of LDX2101 duplex stainless steel

Abstract

Four stainless steel alloys with ruthenium compositions of 0·16, 0·24, 0·32 and 0·64 wt-% were produced from pieces cut from commercial LDX2101 duplex stainless steel plate with the manufacturer's composition of 0·03C–21·5Cr–1·5Ni–0·3Mo–5·0Mn plus pressed ruthenium powder with purity of 99·8%. After solution annealing the samples, the actual chemical composition was analysed using X-ray fluorescence analysis, and then, ASTM A923 (01·03) test method A – sodium hydroxide etch test for classification of etch structures of duplex stainless steel was used to analyse their microstructure. Corrosion potential and pitting potential of these samples were evaluated using a potentiodynamic polarisation technique, and the results were compared to corrosion and pitting potentials of the control alloy LDX2101. The tests for both produced and control alloys were performed in naturally aerated 3·56%NaCl aqueous solution at 25±2°C. The results indicated that small additions of ruthenium significantly improved the pitting potentials of the resulting alloys. The results also indicated that ruthenium additions have no detrimental effect to the microstructure of the resulting alloys. In addition, if such small additions of ruthenium will not improve the general corrosion of the resulting alloy, it will at least not have any detrimental effect on the resulting alloy. Ruthenium will also lower the current required to maintain the passive state of LDX2101 stainless steel. In addition to reduced current to maintain the passivity of LDX2101 stainless steel, ruthenium also increased the passive range of LDX2101 stainless steel.

Keywords

Corrosion potential Control alloys Passivity Pitting potential Potentiodynamic test Produced alloys Ruthenium Sodium chloride Sodium hydroxide etch test

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References

Outokumpu: ‘Steel grades, properties and global standards’ 2008. http://www.outokumpu.com/applications/upload/pubs_102110190.pdf (accessed 7 April 2010).

Potgieter

J. H.

Heyns

A. M.

and Skinner

: ‘Cathodic modification as a means of improving the corrosion resistance of alloy’ J. Appl. Electrochem. 1990 20 711–715.

Higginson

: ‘Passivation of cathodically modified alloys’ Br. Corros. J. 1989 24 (4) 297–302.

Mcgill

I. R.

: ‘Platinum metals in stainless steels: a review of corrosion and mechanical properties’ Platinum Met. Rev. 1990 34 (2) 85–97.

Streicher

M. A.

: ‘Alloying stainless steels with the platinum metals: increased resistance to corrosion in acids’ Platinum Met. Rev. 1977 21 (2) 51–55.

Wolff

I. M.

: ‘New applications for ruthenium: platinum in South Africa’ S. Afr. J. Sci. 1999 95 (11/12) 539–542.

El-Sayed

Sherif

E. M.

Potgieter

J. H.

Comins

J. D.

Cornish

Olubambi

P. A.

and Machio

C. N.

: ‘Effects of minor additions of ruthenium on the passivation of duplex stainless-steel corrosion in concentrated hydrochloric acid solutions’ J. Appl. Electrochem. 2009 39 (8), 1385-1392.

Outokumpu: ‘LDX2101- duplex stainless steel’ 2004. http://www.outokumpu.de/29143.epibrw (accessed 10 May 2011).

Schmuki

Hildebrand

Friedrich

and Virtanen

: ‘The composition of the boundary region of MnS inclusions in stainless steel and its relevance in triggering pitting corrosion’ Corros. Sci. 2004 47 (2005), 1239-1250.

10.

ASTM: ‘Standard test methods for detecting detrimental intermetallic phase in duplex austenic/ferritic stainless steels’ ASTM Standard A923, ASTM International, West Conshohocken, PA, USA 2008.

11.

ASTM: ‘Conducting cyclic potentiodynamic polarisation measurements for localised corrosion susceptibility of iron-, nickel-, or cobalt-based alloys’ Standard G61 1986 ASTM International, West Conshohocken, PA, USA, 1998.

12.

Loubser

and Verryn

: ‘Reference for preparation of samples and sample analyses: combining XRF and XRD analyses and sample preparation to solve mineralogical problems’ S. Afr. J. Geol. 2008 111 229–238.

13.

Takeno

: ‘Intercomparison of thermodynamic databases’419; 2005

Japan

Geological Survey of Japan. typhoon.jaea.go.jp (accessed 5 December 2011).

14.

Metrohm Autolab

B.V.

: ‘Autolab Application Note COR02: corrosion. Part 2 – Measurement of corrosion rates’ Metrohm Autolab B.V., Utrecht, The Netherlands 2011. www.ecochemie.nl/Applications/ (accessed 5 December 2011).

15.

ASTM: ‘Standard practice for calculation of corrosion rates and related information from electrochemical measurements’ ASTM Standard G102-89, ASTM International, West Conshohocken, PA, USA 1989.