The influence of carbon potential after gas-carbonitriding on the microstructure and fatigue behavior of low alloyed steel

In this paper, the effects of gas-carbonitriding time on fatigue limit improvement of low alloy steel specimens were investigated by experimental tests of three points fatigue flexion. Besides, metallurgical evaluations and micro-Vickers hardness tests were performed employing metallographic techniques, optical, scanning electron microscopy and x-ray diffraction techniques. Test findings showed that this amount remarkably improved the components fatigue resistance. The fatigue life of carbonitrided specimens was prolonged between 16%, for CN11 (i.e. austenization-870°/7 h, atmosphere with 1% carbon potential, quenching-oil medium and tempering-200 °C/1 h), and 32%, for CN21(i.e. austenization-870°/8 h, atmosphere with 1, 2% carbon potential, quenching-oil medium and tempering-200 °C/1 h), compared to the untreated state. It is obvious, from the fractography analysis, utilizing (SEM), that fatigue cracks appeared first at the carbonitrided specimens surface.