Influence of process-related microstructural and geometrical inhomogeneities on the fatigue behavior of two steel types considering the influence of chemical composition

• Applicant: Professorin Dr.-Ing. Martina Zimmermann, since 7/2023
• Subject Area: Mechanical Properties of Metallic Materials and their Microstructural Origins
• Term: from 2018 to 2023
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 413507401

• Final Report Year: 2024

Final Report Abstract

In the industrial practice of laser cutting, the quality of the cut edges in terms of roughness and freedom from burrs must be assessed. This applies in particular to sheet metal parts to be formed, as notches on the cut edge are often the starting point for fatigue cracks. For two steels, the corrosion-resistant Cr-Ni steel 1.4301 and the unalloyed steel 1.0335, the influence of pre-deformation, the laser cutting parameters, the microstructural changes due to cutting and batch influences on the fatigue strength of the steels could be shown. One of the key insights is that suitable pre-deformation can result in a detachment of the burr adhesions, which brings about an increase in fatigue strength compared to the pure laser-cut variant. Additional strength-increasing effects for 1.4301 can be achieved by using the lowest possible temperatures during preforming and thus increasing the α'-martensite volume fraction as well as with relatively high sulphur contents in the batch. For steel 1.0335, the parameters for laser cutting should be selected so that the burrs are not too large and the hardening is moderate (approx. 1/10 mm burr height at approx. 300 HV). In principle, the quality of laser cutting must continue to be assessed on the basis of roughness and burr formation; due to the high variability and a potential deformation-related detachment of burr adhesions, a significant improvement in fatigue strength can be achieved by adjusting the process parameters. However, the derivation of a generalized Wöhler curve, which would be generally applicable to laser-cut sheets, seems impossible at the present time.

Publications

• Influence of preforming and laser cutting on VHCF behavior of AISI 304. 8th International Conference on Very High Cylce Fatigue (VHCF8), Edts: Takashi Nakamura & Tatsuo Sakai (2021)
  T. Zeuner, T. Wanski, S. Schettler, R. Kühne & M. Zimmermann
  
• Deformation-Induced Martensitic Transformation in Laser Cladded 304 Stainless Steel Coatings. Materials, 15(18), 6392.
  Zeuner, André T.; Gerdt, Leonid; Ostwald, Andrea; Grün, Peter; Barbosa, Maria; Kaspar, Jörg & Zimmermann, Martina
  
• Investigation of the influence of a two-step process chain consisting of laser cutting and subsequent forming on the fatigue behavior of AISI 304. International Journal of Fatigue, 159, 106779.
  Wanski, Thomas; Zeuner, André T.; Schöne, Sebastian; Herwig, Patrick; Mahrle, Achim; Wetzig, Andreas & Zimmermann, Martina
  
• The Influence of Heat Treatment on the Microstructure, Surface Roughness and Shear Tensile Strength of AISI 304 Clinch Joints. Metals, 12(9), 1514.
  Zeuner, André Till; Ewenz, Lars; Kalich, Jan; Schöne, Sebastian; Füssel, Uwe & Zimmermann, Martina
  
• Influence of a Pronounced Pre-Deformation on the Attachment of Melt Droplets and the Fatigue Behavior of Laser-Cut AISI 304. Metals, 13(2), 201.
  Zeuner, André T.; Wanski, Thomas; Schettler, Sebastian; Fell, Jonas; Wetzig, Andreas; Kühne, Robert; Fischer, Sarah C. L. & Zimmermann, Martina
  
• Influence of the Dross Formation of the Laser-Cut Edge on the Fatigue Strength of AISI 304. Metals, 13(3), 624.
  Bach, Julia; Zeuner, André T.; Wanski, Thomas; Fischer, Sarah C. L.; Herwig, Patrick & Zimmermann, Martina
  
• Investigations on dross formation susceptibility in laser fusion cutting of different stainless steel compositions with emphasis on minor element effects. Journal of Laser Applications, 35(3).
  Mahrle, A.; Wanski, T.; Zeuner, A. T.; Herwig, P. & Zimmermann, M.