To evaluate the performance characteristics of various surfaces, a detailed and precise description of the surface's micro-geometry properties is required. In this context, roughness is a reliable indicator of the possible behavior of mechanical piece performance, since distortions on the surface can form a direct cause for cracks or corrosion. As a result, characterization of surface roughness is very important for zero-defect fabrication. This paper investigates the 2D roughness parameters of a 42CrMo4 steel surface before and after nitrocarburizing treatment. The latter was accomplished at 580 °C for 10 hours in a salt bath containing sodium cyanates and potassium carbonates. A surface profilometer was used to analyze the influence of nitrocarburizing treatment on the material's surface roughness parameters behavior. The parameters that comprehensively describes the surface structure, namely the amplitude, spacing, hybrid parameters, and material ratio parameters were highlighted. The results of the experiments indicated that the nitrocarburizing treatment was effective in increasing almost all the 2D roughness parameters of the 42CrMo4 steel surface.

The aim of this paper is to study and analyze the effects of a surface controlled salt bath nitriding on the microhardness of AISI 1045 steel. The nitriding process was implemented in the salt bath component at ten different times (from 1 h to 10 h) when the temperature was constant at (520ºC). The nitriding process repeated of other specimens at the same times, but the temperature was (580ºC).The microstructure of the surface layers was investigated by scanning electron microscopy (SEM) and optical microscopy. Hardness profiles were measured with lowload hardness testing to determine the growth of the case depth after nitriding. Microhardness testing was carried out on samples to investigate the hardness profile at the transition from the compound to the diffusion layer. The microhardness of the surface of the nitrided sample at 520ºC and 580ºC was observed in the range of 318-430 HV0.3 and 329-421 HV0.3, respectively. Experimental results showed that the nitrides ε-Fe2-3(N, C) and γ'-Fe4(N,C) present in the compound layer increase the microhardness , It also showed that the Increasing the salt bath nitriding parameters (treatment time and temperature) increases the surface hardness and hardness profile.

In the present research, AISI 4140 steel was nitrided in salt bath to study and analyze the behaviour of the surface roughness. The structural surface characterization behaviour of the nitrided steel was compared to the behaviour of the same steel which was untreated. The nitriding process was implemented in the salt bath component at ten different times (from 1 h to 10 h) when the temperature was constant at (580ºC). The influence of nitriding treatment on structural properties of the material was studied by scanning electron microscopy (SEM), microhardness tester and surface profilometer. It was found that salt bath nitriding was effective in improving the surface properties behaviour of this steel. Experimental results showed that the nitrides ε-Fe2-3(N,C) and γ'-Fe4(N,C) present in the compound layer increase the microhardness (406-502 HV0.3), the initial surface roughness values of nitrided samples were higher than those of unnitrided specimens, it also observed that the increasing the nitriding time increases the surface roughness parameters (Ra, Rq and Rz).Keywords: salt bath nitriding, AISI 4140 steel, microhardness, surface roughness IntroductionSurface topography is an important characteristic that determines, among other things, catalytic activity, electrochemical potential, adhesion, friction coefficient, susceptibility to wear and scuffing failure and aesthetic appearance [1][2]. Salt bath nitriding [3,4,5] is one of the most widely used thermo-chemical methods [6,7,8], which produces strong and shallow case with high compressive residual stresses on the surface of steel components such as gears, crankshafts, dies and tools [9,10,11]. Surface roughness of industrial components strongly affects their performance, i.e, many surface properties such as friction [12][13], surface wear [14], fluid flow in rough pipes [15] and the functioning of vacuum seals [16] are strictly dependent on surface roughness. In addition, surface roughness seems to be important in bioengineering for example in the joints of the bones [17]. Quite often small roughness is desired since small roughness reduces wear and energy loss, but when high friction is needed also the roughness should be larger. Hence, the inspection of surface roughness of the work piece is very important to assess the quality of a component. The quality of surface roughness is an important requirement for coated parts [18]. There are at least five different mechanisms by using the surface modification methods to increase the fretting resistance: (1) to induce a residual compressive stress; (2) to decrease the coefficient of friction; (3) to increase the surface hardness; (4) to alter the surface chemistry; (5) to increase the surface roughness [19].

In this work,we tented to study the mixed mode of failure with two angles of inclination, of a treated steel, for that we tried to determine the parameters of failure as the stress intensity factor, tenacity and the critical energy in mixed mode of a rupture and see the criterion of rupture and seeing the effect of the angles evolution applied for all parameters. of in our close there is a fragile and less ductile rupture.