Repassivierungskinetik von austenitischen Stählen

Translated title of the contribution: Repassivation kinetics of austenitic steels

Andreas Umgeher

Research output: ThesisDiploma Thesis

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Abstract

In this diploma thesis three different austenitic stainless steels (Bohler grades A220, A975, P560) and one ferritic 13% chromium steels (1.4000) have been investigated regarding their repassivation behaviour in chloride solutions. The austenites were in solution annealed and 27% cold worked condition. One low 3wt% CaCl2 solution and one high 43wt% CaCl2 solution were used. The influence of the temperature was also of interest. In the 3wt% CaCl2 solution experiments at 25°C, 40°C and 70°C were conducted, in the high concentrated solution at 25°C, 40°C and 120°C. All experiments regarding repassivation were performed on a specially designed test rig. During the test a scratch with a diamond tip was created on the passivated surface of the specimen. Time and current were recorded during the experiment from which significant graphs were generated. These graphs made a comparison of the different repassivation behaviours possible. The CrNiMo (A220, A975) alloys did not show any influence of cold working on the repassivation behaviour in any of the used media. The CrMnN (P560) steel on the other hand exhibited little influence of cold working on the repassivation behaviour in the 3wt% CaCl2 solution, but a significant influence in the high concentrated 43wt% CaCl2 solution. The influence of the chloride concentration on the repassivation, which is meant to get worse with increasing degree of Cl- ions, was obvious at the A975 and the P560. At the A220 the different solutions did not show a significant influence on the repassivation behaviour. The ferritic 1.4000 steel did exhibit an even worse repassivation behaviour with increasing Cl- ion concentration and increasing temperature. With increasing temperature worse repassivation behaviour was observed at the austenitic P560 and the ferritic 1.4000. The austenite A220 indicated a slight influence of the temperature of the test solution, whereas the highly alloyed A975 showed the same repassivation behaviour regardless of temperature. Concluding it can be said, that the highest alloyed CrNiMo material (A975) exhibits the best repassivation behaviour in all tested environments. It is followed by the lower alloyed A220. The repassivation behaviour of the CrMnN steel is not good in 43wt% CaCl2 solution regardless of temperature. In 3wt% CaCl2 solution no distinct repassivation was observed at 25°C and 40°C, at 70°C however, the steel repassivates shows a good repassivation behaviour. The ferritic 1.4000 did not repassivate in any of the investigated media.
Translated title of the contributionRepassivation kinetics of austenitic steels
Original languageGerman
QualificationDipl.-Ing.
Supervisors/Advisors
  • Mori, Gregor Karl, Supervisor (internal)
Award date16 Dec 2011
Publication statusPublished - 2011

Bibliographical note

embargoed until 15-11-2016

Keywords

  • repassivation
  • repassivation kinetics

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