Influence of a thermomechanical treatment on the lifetime of a high strength steel in very high cycle fatigue.

The fatigue failure beyond the traditional fatigue limit of 107 cycles, the so called very high cycle fatigue (VHCF) is constantly gaining attention due to the demand for long service life of highly stressed components to reach a better sustainability. While the underlying characteristic VHCF mechanism still needs to be fully understood, it is beneficial to investigate measures to improve the fatigue lifetime even in the VHCF range. For this purpose, a thermomechanical treatment (TMT) in the temperature range of maximum dynamic strain aging, for which an increase in fatigue strength in the high cycle fatigue (HCF) range was already shown for the steel SAE 52100, was applied to the steel SAE 4140H. The positive influence of TMT on fatigue results were found for HCF as well as VHCF-regime. The aim of this publication is to analyze as well as to substantiate the influence of TMT on the stress intensity factors (SIF) of failure-causing inclusions and on the forming characteristic of fine granular area (FGA) in the VHCF-regime. [ABSTRACT FROM AUTHOR]