Steam oxidation resistance of new 12%Cr steels:Comparison withsome other ferritic steelsV.Lepingle a,*,G.Louis a ,D.Allue´b ,B.Lefebvre c ,B.Vandenberghe c aEcole des Mines de Douai,BP 10838,F-59508Douai,FrancebCentre de Recherche Vallourec,BP 17,F-59620Aulnoye Aymeries,France cVallourec and Mannesmann Tubes,BP 2,F-59880St.Saulve,FranceReceived 8February 2007;accepted 17November 2007Available online 28January 2008AbstractThe oxidation resistance in pure steam at the 600–650°C temperature range of a newly developed 12%Cr steel has been investigated for long-term exposures (224days =5,376h).The laboratory and industrial heats were tested in comparison with other ferritic 9–13%chromium steels.Corrosion rates were determined by direct measurements of mass losses obtained after a reducing descaling process.Weight loss and metallographic results confirm the good corrosion resistance in steam of the new steel and allow classing the tested steels in 2families:one classical with average oxidation behaviour,‘‘T91-type ”and another one with low mass losses,varying very slightly with the temperature and the exposure time increasing.To have a better understanding of the observed phenomena,the possible influences of the main alloying elements (Cr,Si,Mn,Mo,W)of steels mentioned by different authors were reviewed and compared to the results obtained for the ten 9–13%Cr studied steels.It appears that the alloying elements cannot be considered separately:as a matter of fact they have not only a specific influence but also a joint influence on the steam corrosion behaviour of the 9–13%Cr ferritic steels.Ó2007Elsevier Ltd.All rights reserved.Keywords:A.Steel;B.Weight loss;C.High temperature corrosion;C.Steam;C.Alloying elements1.IntroductionThe need for an improved ferritic steel has evolved worldwide over these past ten years due to the conditions in the advanced power stations.The development goal of such a steel is to jointly meet a lot of criteria concerning:low corrosion,good welding,fabricability,mechanical properties,engineering code requirements,costs ...Several studies indicate that the basic requirement is a 9–12%chromium content to withstand high temperature corrosion in steam [1–3].Various alloying elements are added mainly to increase the creep strength.A new 12%Cr ferritic steel which is able to fulfil the given aims [4]has been developed.The first step was the production and characterisation of seven laboratory heats with various but close chemical compositions.The mini-mum Cr-content was 11%and variations on C,Si,Mo,W,Co and Mn were made to obtain the best combination of the above-mentioned properties.Some of the heats were eliminated on metallurgical results.The second step was the production of small diameter tubes (OD 60.3Â8.8mm)and big diameter pipes (OD 406.4Â35mm)from industrial heats of 20tons based on the chemical composi-tion of the two selected lab heats,F and G.The first aim of this study was to determine the oxida-tion resistance in steam of these new steels as close as pos-sible to real service conditions.The second aim was to make a comparison with the oxidation resistance of some other steels used in the same field of application.0010-938X/$-see front matter Ó2007Elsevier Ltd.All rights reserved.doi:10.1016/j.corsci.2007.11.033*Corresponding author.Tel.:+330327712314;fax:+330327712916.E-mail address:lepingle@ensm-douai.fr (V.Lepingle).www.elsevier.com/locate/corsciAvailable online at www.sciencedirect.comCorrosion Science 50(2008)1011–1019
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