Neue Einsatz- und Vergütungsstähle für die Herstellung über eine Kaltbandroute

Translated title of the contribution: New case hardening and heat treatable steels for the production on a cold rolling mill

Sarah Ploberger

Research output: ThesisDiploma Thesis

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Abstract

Case hardening and heat treatable steels with a defined chemical composition are able to cure even at cooling in air and are therefore so-called air-hardening steels. Due to their good ductility and the improved formability in the cold rolled state they gain a high potential as low alloyed steels. A subsequent heat treatment and cooling in air leads to the final strength of the parts. In the course of this diploma thesis, new fields of hardening and heat treatable steels with reduced costs of alloying elements were characterized during the whole production process. Furthermore the necessary process parameters and the phase transformations occurring during cooling were determined. For that purpose the influence of alloying elements which delay the phase transformation, e.g. carbon, chromium, manganese, molybdenum and vanadium has been considered. Metallographic examinations and the mechanical properties were both carried out for the hot-rolled material as the cold rollability. The phase characterization was carried out on LePera etched specimen by light microscope- and SEM- investigations. To illustrate the influence of alloying elements on the recrystallization, combinations of annealing temperature and time were performed. Further, the ratio of bound nitrogen after annealing was determined by wet chemical analysis. To describe the transformation kinetics, dilatometer measurements with continuous cooling rates were performed and the phase transformations were represented in TTT diagrams. The present study demonstrated that a soft annealing process is necessary before cold rolling and that the combination of 10 h and 650°C for recrystallization process afterwards is most suitable. Due to the transformation diagrams the critical cooling rate was determined as a function of the alloying elements. The increasing content of chromium and manganese showed a stronger reduction of the critical cooling rate than molybdenum and vanadium.
Translated title of the contributionNew case hardening and heat treatable steels for the production on a cold rolling mill
Original languageGerman
QualificationDipl.-Ing.
Supervisors/Advisors
  • Clemens, Helmut, Co-Supervisor (internal)
  • Leitner, Harald, Supervisor (internal)
  • Pichler, Andreas, Supervisor (external)
Award date29 Jun 2012
Publication statusPublished - 2012

Bibliographical note

embargoed until 26-06-2017

Keywords

  • case hardening steel
  • heat treatable steel
  • air hardening steel
  • hardenability
  • delay of transformation
  • critical cooling rate
  • TTT
  • nitrogen fixation

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