Einfluss der Herstellparameter auf die Korrosionseigenschaften ausgewählter Auflagewerkstoffe walzplattierter Bleche

Translated title of the contribution: Impact of production parameters on corrosion properties of different highly-alloyed cladding materials

Manuel Prohaska

Research output: ThesisDoctoral Thesis

Abstract

Five different corrosion - resistant iron- and nickel-based alloys have been investigated regarding their corrosion properties after application of a thermo-mechanical rolling process during production of cladded sheets. The impact of important rolling process parameters like end rolling temperature and cooling rate was evaluated with conventional corrosion tests (Streicher - test, CPT) as well as with electrochemical methods (DL-EPR). Furthermore, several isothermal heat treatments between 640 and 900 °C were performed and used as reference conditions. With an exception of superaustenitic stainless steel Alloy 926 no material was susceptible to end rolling temperature or cooling rate variation in the investigated range (850 and 950 °C; water and air cooling). In case of materials 316L, Alloy 825 and Alloy 625 the highest intergranular corrosion resistance was found after end rolling at 850 °C with subsequent water cooling. Contrarily, stainless steels 904L and Alloy 926 exhibited the lowest degrees of sensitization (DOS) after end rolling at 950 °C with subsequent water cooling. Susceptibility to process parameter variation of Alloy 926 during thermo-mechanical processing was referred to the precipitation of chromium- and molybdenum - rich phases, which were identified by electron diffraction as intermetallic chi phases (χ). High DOS were obtained especially at lower end rolling temperatures and low cooling rates due to sensitization processes at grain boundaries during chi phase precipitation. Moreover, the influence of two quenching and tempering processes after thermo-mechanical rolling was studied (Alloy 926). It was found that a quenching temperature of at least 1000 °C is necessary to avoid further sensitization due to particle growth of chi phases. DOS of Alloy 926 after isothermal annealing and thermo-mechanical rolling was obtained quantitatively by means of EDX - linescans in a transmission electron microscope. Morphology and extent of elemental depletion zones adjacent to grain boundary precipitates were in good agreement with corrosion test results. A local PREN was calculated to evaluate the local DOS. The influences of deformation degree and required wait time after rolling were investigated by means of deformation dilatometer simulation and the DL-EPR method (Alloy 926). Dynamic recrystallization processes, which took place at high deformation degrees and high temperatures lead to pronounced chi phase precipitation and high DOS. The longer the wait time the higher the amount of precipitated phases. Thus, sensitization increases considerably after long wait times.
Translated title of the contributionImpact of production parameters on corrosion properties of different highly-alloyed cladding materials
Original languageGerman
QualificationDr.mont.
Supervisors/Advisors
  • Hofstätter, Herbert, Assessor B (internal)
  • Mori, Gregor Karl, Assessor A (internal)
Publication statusPublished - 2011

Bibliographical note

embargoed until null

Keywords

  • Roll Cladding
  • Intergranular Corrosion
  • Oil- and Gas Production
  • DL-EPR
  • Test
  • Microstructural Evaluation

Cite this