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Increasing the fatigue limit of high-strength steels (100Cr6 and 42CrMo4) by thermomechanical treatments

M.Sc. Amin Khayatzadeh

Motivation

  • It has already been shown that a suitable thermomechanical treatment (TMT) in the temperature range of maximum dynamic strain aging (DSA) can increase the fatigue strength of high-strength steels for high-cycle fatigue (HCF).

  • In the field of Very High Cycle Fatigue (VHCF), the failure of high-strength steels typically starts from critical inclusions in the material volume.

  • It might be possible for these materials, to strengthen the microstructure of critical inclusions by finding an appropriate thermomechanical treatment at maximum DSA range.

Objective

  • It should be understood how a TMT affects the microstructure as well as the lifetime for very high cycle fatigue.

  • A suitable TMT should be found to optimize fatigue strength in the VHCF range.

  • A model should be developed to explain the relation between the microstructure and HCF and VHCF lifetime

Methods

  • For the materials 42CrMo4 and 100Cr6, the temperature with the maximum DSA is identified for a given stress amplitude.

  • At the temperature of maximum DSA, some load cycles with increasing stress amplitude are applied to strengthen the microstructure.

  • HCF (Nf 107) and VHCF (Nf 107) experiments need to be performed on the samples.

  • Fractography using SEM and TEM analysis of the microstructure to identify failure mechanisms and microstructure around crack initiation sites: Does TMT treatment affect microstructure and failure mechanisms?

Project partner

Technical University of Kaiserslautern

Funding