Gleitstufenuntersuchungen an austenitischen Stahlproben mittels Rasterkraftmikroskopie

Translated title of the contribution: Slip step analysis of austenitic steel samples using atomic force microscopy

Nurdogan Gürkan

Research output: ThesisDiploma Thesis

Abstract

Using differing alloying approaches, two different austenitic stainless steels were cast. These were in particular a CrNiMoN (A975) and a CrMnN (P556) steel. For the experiments, the effects of three different hardening states were investigated on the austenitic steels. The tensile tests were performed with a servohydraulic universal testing unit, each at a constant maximum stress of 500 MPa in the tensile swell area. Furthermore, the samples were tested at a constant relative load (ratio of the upper stress (σw) to tensile strength (Rm) (σw / Rm = const. = 0.6)). The herein investigated materials are often applied at high temperatures and under aggressive environments, therefore good mechanical properties and sufficient corrosion resistance is of importance. Under mechanical stress these materials can form local slips, which can notably influence the mechanical and corrosive properties, through the formation of extrusions and intrusions. The pairs of extrusions and intrusions form slip steps and micro-notches on the material's surface. These newly created surface areas are highly susceptible to corrosion, when exposed to aggressive environmental conditions. Modern scanning probe microscopy with nanometer resolution offers the possibility to quantify these surface areas. In this master thesis, plastically deformed zones near the failure area were analyzed using atomic-force microscopy (AFM) to investigate the dislocation slip behavior of austenitic stainless steels. The individual height and width values of the slip steps were determined by cross-sectional analysis of the AFM images. At the end of this work, a comparison of P556 and A975 steels in relation to height and width of the slip steps for these is presented in diagrams. The determined values for the slip step heights and widths were lower for the solution hardened state than for the cold-worked state. Furthermore, the Wenzel ratio, which is the ratio of true length to projected length, was determined. The Wenzel ratio of the investigated steels decreased continuously with increasing degree of hardening. For constant relative loads, the Wenzel ratio for P556 was larger than for A975.
Translated title of the contributionSlip step analysis of austenitic steel samples using atomic force microscopy
Original languageGerman
QualificationDipl.-Ing.
Supervisors/Advisors
  • Teichert, Christian, Supervisor (internal)
Award date17 Dec 2010
Publication statusPublished - 2010

Bibliographical note

embargoed until null

Keywords

  • Austenitic steels
  • corrosion fatigue
  • atomic-force microscopy
  • slip steps

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