Carbonitriding is an important industrial process applied for the improvement of the mechanical characteristics of the component of many steels employed in several machines parts like cam shafts, crank shafts and gears to enhance fatigue strength and wear resistance. In this study, the influence of the gaseous carbonitriding on the enhancement of surface characteristics and mechanical properties was investigated using different parameters for low alloy steel. The analysis and characterization of the treated material were carried out employing optical microscopy (OM) and scanning electron microscopy (SEM) and X-ray diffraction methods (retained austenite and residual stresses). Microhardness and tensile tests were performed and the fracture mechanisms of the various materials were ultimately examined and discussed. The main contribution of this research work is to show and optimize the selection of the appropriate parameters for this kind of steel in industrial field. Diffusion mechanism and microstructure proved that the process of high temperature gas carbonitriding allowed enhancing the mechanical properties of material. This process resulted in a rise of the yield strengths and a loss in a pronounced ductility associated with the brittle intergranular fracture surface caused by the nitride precipitation in the grain boundaries.

In this paper, the time of gas-carbonitriding effects on fatigue limit improvement of low alloy steel specimens was 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 improved remarkably the components fatigue resistance. The fatigue life of carbonitrided specimens was prolonged between 16%, for CN11, and 32%, for CN21, compared to the untreated state. It is obvious, from the fractography analysis, utilizing (SEM), that fatigue cracks appeared first at the carbonitrided specimens surface.

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The present paper investigates the friction and wear resistance of carbonitrided AISI 4130 steels using single and multi-pass scratch techniques. The influence of carbon concentration in high-temperature gas carbonitriding on friction, wear, and corrosion behavior was studied. The microstructure and morphological properties of carbonitrided layers were investigated employing optical microscope and XRD. The corrosion performance of carbonitrided layers was also evaluated using potentiodynamic polarization in 3.5 wt.% aqueous solution of NaCl. The results of microstructure showed the formation of an arrangement of carbonitrides, chromium nitride, retained austenite, and [Formula: see text] carbides phases in the carbonitrided layers. The carbonitrided layer microhardness increased as a function of increasing carbon concentration to attain a maximum value of about 980 HV0.1 at a carbon content between 1 and 1.2%. The microhardness value was more than 3 times than those of the untreated AISI 4130 steels. Moreover, carbon content has a significant influence on the scratch resistance. For single pass, a critical load (LC1) of about 3.5 N was found. The use of multi-pass scratching allowed to examine friction coefficient, wear volume, and damage mechanism. Carbonitrided layers revealed a low friction coefficient (0.06) and a low wear volume that does not exceed [Formula: see text]. Moreover, the multi-pass scratch technique can extract valuable information about the wear behavior of the carbonitrided layers. The results of corrosion test showed that the formation of [Formula: see text], [Formula: see text] and chromium nitride phases in carbonitrided layers were at the origin of high electrochemical resistance.