Effect of different tempering processes on fatigue behavior and mechanical propertiesof CK45 steel

Fatigue behavior and mechanical properties of CK45 mildcarbon steel has been investigated under combined heattreatments processes. The 80 standard samples weremachined, quenched and tempered at various temperaturesfor 20 min, then subjected to several tests. The resultsshows that the fatigues limit of treated samples are morethan non-treated samples significantly. The fatigue strengthof treated samples at 450 °C is approximately 2 times morethan non-treated samples. In addition, the fatigue limit doesnot increase with temperature and it has pick point, in otherwords further heating above 450 °C does not increase thefatigue strength significantly. This increasing in fatiguestrength is due to the dual phase microstructure which ischanged by treatment processes. Configuration of the dualphasemicrostructure can delay crack initiation andpropagation processes.