Bruchverhalten von Fe-Si-Al Stählen

Translated title of the contribution: Fracture behaviour of Fe-Si-Al steels

Andreas Umgeher

Research output: ThesisDoctoral Thesis

Abstract

The Fe-Si alloyed steel, generally called electrical steel, has excellent magnetic and electrical properties, which makes it used as a core material in electric motors and transformers. In order to reduce heating of the soft magnets due to losses in the hysteresis, an increase in the alloying content of Si is needed. However, an increase in Si-content reduces the workability and spontaneous cleavage cracks occur. To get a better understanding of this transcrystalline cleavage fracture, fracture mechanic tests of two different Fe-Si-Al alloys under various test conditions are performed . The materials under investigation are Fe - 2 wt% Si - 2 wt% Al and Fe-3 wt% Si - 2 wt% Al. Both alloys have polycrystalline microstructure. XRD measurements close to the surface and in the middle of the specimen show different orientations because grains close to the surface are recrystallized and grains in the middle of the sample are recovered. By performing fracture mechanic test at various temperature it is pointed out, that critical fracture toughness decreases with decreasing temperature. Different rates at fracture mechanic tests represent only a weak velocity dependence in critical fracture toughness. In fatigue experiments at various frequencies show that in higher frequencies transcrystalline cleavage cracks occur at lower critical fracture toughness. Compare to lower frequencies transcrystalline cleavage cracks in the fatigue tests take place at higher critical fracture toughness. A simple strain rate estimation from the results of fatigue and fracture mechanic tests is worked out. Strain rate sensitivity of both materials are represented. Stereophotogrammetry and EBSD measurements are used to indicate fracture plains on the fracture surface. The results should help to get a better understanding of the mechanisms of transcrystalline cleavage fracture in Fe-Si-Al alloys.
Translated title of the contributionFracture behaviour of Fe-Si-Al steels
Original languageGerman
QualificationDr.mont.
Supervisors/Advisors
  • Ebner, Reinhold, Assessor B (internal)
  • Kolednik, Otmar, Assessor A (internal)
Publication statusPublished - 2016

Bibliographical note

no embargo

Keywords

  • cleavage fracture
  • Fe-Si alloys
  • fracture mechanic tests
  • transcrystalline cleavage fracture
  • fatigue tests
  • strain rate
  • fracture toughness
  • Kc

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