Kurzzeitkriechverhalten von Warmarbeitsstählen

Translated title of the contribution: Short-term creep of hot-work tool steels

Harald Wurmbauer

Research output: ThesisDoctoral Thesis

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Abstract

Hot-work tool steels represent a group of tool steels which are often used for metal forming operations, e.g. die casting, extrusion molding and drop forging. The advanced microstructure of these steels permits operations at elevated temperatures and high stresses. Elevated temperatures in combination with stress causes creep effects. Therefore, in this work short-term creep tests of three different Cr Mo V-hot-work tool steels from the Böhler-Uddeholm AG were performed. Two of these investigated hot-work tool steels represent novel alloys. Short-term creep tests were performed at temperatures in the range of 400 - 600 °C and at stress levels between 300 - 900 MPa. These creep investigations showed that due to the high stress levels dislocation creep is the dominating creep mechanism. Furthermore it was shown that a secondary, so called steady-state, creep range does not emerge. Due to the fact that all investigated hot-work tool steels possessed a different chemical composition, it was possible to show, that a high content of the alloying elements vanadium and molybdenum as well as a moderate content of chromium and carbon improves the short-term creep behavior. A further creep experiment dealing with martensitic and bainitic microstructures resulted in better short-term creep behavior of the martensitic compared to the bainitic microstructure. Microstructural investigations were performed by light microscopy, scanning electron microscopy, transmission electron microscopy as well as X-ray diffraction to clarify the influence of the microstructure on the short-term creep behavior. These investigations revealed that exceeding a creep temperature of 500 °C results in an unstable mircostructure, which explains the absence of a steady-state creep range. As a consequence of a permanently coarsening microstructure a minimum creep rate forms. Furthermore it was shown that short-term creep resistance of hot-work tool steels is closely connected to temperature-stable secondary hardening carbides. A comparison of the investigated hot-work tool steels showed, that a high content of vanadium and molybdenum rich MC and M2C secondary hardening carbides results in an improved short-term creep behavior.
Translated title of the contributionShort-term creep of hot-work tool steels
Original languageGerman
QualificationDr.mont.
Supervisors/Advisors
  • Dehm, Gerhard, Assessor B (internal)
  • Clemens, Helmut, Assessor A (internal)
Publication statusPublished - 2010

Bibliographical note

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Keywords

  • creep
  • short-term creep
  • Cr Mo V hot-work tool steel
  • hot-work tool steels
  • TEM

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