Holger Surm

Publications (2)3.09 Total impact

• Article: Interdependence of Distortion and Residual Stress Relaxation of Cold-Rolled Bearing Rings During Heating

  Jérémy Epp, Holger Surm, Julien Kovac, Thomas Hirsch, Franz Hoffmann
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  ABSTRACT: This article discusses the distortion behavior during heating of bearing rings produced by cold rolling. The residual stress relaxation was characterized intensively and correlated to the distortion behavior. In the initial state, the rings show compressive residual stresses in tangential and axial direction with almost no variations along the circumference. Because of the cold-rolling process, the entire cross section is affected by residual stresses. The rings present a characteristic size change between the soaking temperatures 773K and 823K (500°C and 550°C), which can be correlated with the macroresidual stress relaxation in the core of the rings. Changes in roundness deviation were found, but the amplitude of oval and triangular shape increases continuously until austenitizing temperature is reached. As the macrostress relaxation is already completed at 873K (600°C), another mechanism should be responsible for these distortions. A correlation between amplitude of the oval shape and decrease of full width at half maximum seems to be present. This may indicate that inhomogeneous recrystallization happens along the circumference of the rings. A triangular shape may result from the influence of the loading tool used as rings are positioned on three contact points during the stress relief treatment.
  Metallurgical and Materials Transactions A 05/2012; 42(5):1205-1214. · 1.54 Impact Factor
• Article: In-Situ X-Ray Investigations and Computer Simulation during Continuous Heating of a Ball Bearing Steel

  Jérémy Epp, Holger Surm, Olaf Kessler, Thomas Hirsch
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  ABSTRACT: This article presents a comparison between transformation kinetics obtained by in-situ X-ray diffraction during continuous heating of a ball bearing steel AISI52100 to austenitizing temperature and computer simulation. In order to have acquisition times short enough for good time resolution, X-ray diffraction experiments were done with special equipment such as a rotating anode producing intense X-ray radiation and an area detector. Computer simulations of austenitizing were performed with a Johnson–Mehl–Avrami equation. Besides transformation kinetics, the lattice parameters of ferrite and austenite were also studied. Lattice parameters measured by in-situ X-ray diffraction match calculations from models. Good agreement between phase contents obtained by simulation and by X-ray diffraction was obtained.
  Metallurgical and Materials Transactions A 09/2007; 38(10):2371-2378. · 1.54 Impact Factor