Fatigue Life Optimization of Steel by Thermomechanical Treatment with the Use of Physical Thermomechanical Simulator

Abstract

The investigated 34CrNiMo steel is traditionally used for highly loaded components with very high hardenability, fatigue strength and toughness. There were obtained very good experiences with this material, therefore there is no demand for change of the material, but for the material full potential utilization. This goal could be attained by application of thermo-mechanical treatment to the material of interest. There are compared several materials states obtained by conventional thermal treatment with new thermo-mechanically processed states in the current study. Conventionally treated materials exhibit about half tensile strength of the material after the thermomechanical treatment. The material fatigue life is related to tensile strength of the material. Therefore for representative comparison it is useful to compare materials with similar tensile properties, if the advantage of thermomechanical over heat treatment is to be evaluated. Samples of material of similar tensile strength to thermomechanically treated state were prepared by heat treatment. Fatigue tests were performed for traditionally treated samples with thermomechanically treated state and heat treated state. Thermo-mechanically treated state exhibits superior strength and fatigue life in comparison to all other states investigated. There was also performed metallographical investigation of microstructures of compared states providing information on what sort of microstructures were obtained by which treatment, that could be related to mechanical properties. The study presented here shows potential of thermo-mechanical treatment of traditionally used steels.