The Joint Effects of Nitriding and Parameters Related to the Destabilisation of Austenite on Wear Resistance in White Cast Iron with 25% Cr

In this article, the effects of an ionic nitriding treatment are analysed, together with deliberate variation of different thermal parameters associated with the destabilisation of austenite, on erosive wear resistance of white cast irons with 25% Cr. The methodology followed in this research was an experimental design, where six factors were analyzed by performing eight experiments. The thickness of the nitrided layer is much smaller than in white cast iron with lower percentages in Cr, never reaching 20 microns. The nitriding treatment entails considerable softening of the material underneath the nitriding layer. This softening behaviour becomes partially inhibited when the destabilisation temperature of austenite is 1100 °C and dwell times at such temperature are prolonged. This temperature seems to play a significant role in the solubilization of non-equilibrium eutectic carbides, formed during industrial solidification. The nitriding treatment leads to additional hardening, which, in these cases, favours a second destabilisation of austenite, with additional precipitation of secondary carbides and the transformation of retained austenite into martensite. Despite softening of the material, the nitriding treatment, together with air-cooling after destabilisation of the austenite, allows a noticeable increase in resistance to erosive wear.

Ionic Nitriding of Certain Parts Protected on Nonfunctional Surfaces With Special Paints. Electric Energy Consumed

The experimental researches on the promotion of new technologies for the local protection of metallic parts against plasma nitriding, led to two types of special paints for protection in ionic nitriding, paints elaborated on the basis of copper lamellar powder in combination with magnesium oxide and carbon tetrachloride. In the created context, it was considered that the elaborated paints could be used not only for preventing the hardening during ionic nitriding of certain technological surfaces of the parts on which they are applied, but also for coating certain nonfunctional surfaces, their degasification taking such a long time. These nonfunctional areas could be: surfaces resulted from casting, fragments with macroirregularities, surfaces that contain slag, residues, soot, other oxides, impurities, etc. and are the cause for a very large number of transitions of the glow discharges in electric arcs. The use of special protecting paints for the plasma nitriding of the parts that present nonfunctional surfaces leads to a major reduction in the energy consumption. This paper presents the ways of determining the consumed electric energy on the basis of absorbed power in the case of ionic nitriding of certain parts protected on nonfunctional surfaces with special paints.

Optimization, by Means of a Design of Experiments, of Heat Processes to Increase the Erosive Wear Resistance of White Hypoeutectic Cast Irons Alloyed with Cr and Mo.

To identify the design parameters in heat treatments that have a significant effect on the erosive wear resistance of hypoeutectic high chromium white cast irons, a design of experiment was applied to a white cast iron with 18wt.% Cr and 2wt.% Mo. The analyzed factors were the destabilization heat treatment of austenite (1000 or 1100 °C, for 4 or 8 h), different quench cooling media (in air or oil), different tempering treatments (200 or 500 °C, for 3 or 6 h), and the application of an ionic nitriding treatment. Despite what was expected, the nitriding treatment was not found to have a significant effect on said wear resistance. However, it is concluded that the highest wear resistance is obtained with the shortest dwell time at the destabilization temperature (4 h), quenching in oil, and with the shortest tempering times (3 h). Among the nitrided samples, the highest nitrided layer thicknesses were obtained when the destabilization temperature of the austenite was 1000 °C and the tempering temperature was 200 °C.

Metallographical Aspects of the Application of Special Paint Layers for the Protection of Machine Part Sections against the Effect of lonitriding

The paper presents aspects concerning the appreciation of the protection through special paints based on copper powders used against plasma nitriding. First of all the choice of copper is motivated as an important metallic component of protecting paints, with the characteristics that the copper presents in the context of the physical and chemical phenomena (from the cathode and from gas volume) specific for the ionic nitriding process. The paper contains comparatively some characteristics (the duration of drying on the coat, the compatibility of the components, the capacity of extension and of avoiding the leakage, the power of covering, the capacity of joining, and the emitting of gases, the resistance in friction before and after the ionic nitriding, the way of obtaining the copper powder and its quality, the capacity of removing after ionic nitriding etc.) of the mixtures, for the protection against ionic nitriding. Following the researches on making more efficient technologies of local protection of metal pieces on certain areas with isolated layers against plasma nitride, the authors realized 2 different kinds of special original paints noted V-1 and V-2 used for this purpose. These paints are made having a basis of copper powder combined with magnesium oxide and polystiren dissolved in carbon chloride.

Energy and gas dynamic characteristics of ionization nitrogen installations of industrial type

The work provides the analysis of power characteristics of the industrial equipment – ionic nitriding applications – with different types of vacuum chambers – with hot and cold walls. The calculations results and experimental researches of thermal balance of the system “melt-wall chamber” at the process of plasma nitration for industrial applications are given. The work examines the influence of heat-shielding screens quantity in the applications with cold walls on the internal screen temperature and power of thermal losses at warming up parts melt and at its isothermal endurance. It has been displayed the significant influence of the discharge chamber geometry on the discharge power value which is necessary for the melt warming up and its exposition at the certain temperature – the less are geometrical sizes of the chamber (diameter and height), the smaller is the power of the smoldering discharge which is required for ensuring necessary melt temperature. It is shown that at sufficient melt parts distance from the chamber walls, the voltage drop on the skeleton of the smoldering discharge can be tens volts that causes the decrease of cathodic falling potential and, respectively, the increase of the electric power which is required to maintain necessary melt temperature in comparison to melt which is as close as possible to chamber walls. It leads to the fact that at more dense loading, smaller specific consumption of the electric power to ensure the necessary depth of the nitrated layer is required; at the same time the specific energy consumptions by the melt temperature of 525–530 °C are 0.6–1.6 kW∙h/kg, depending on the loading extent of the chamber. It has been displayed that at ionic nitration, the value of working gas pressure must provide the deviance of the smoldering discharge i. e. the whole area the cathode –melt must be captured by the discharge luminescence.

Options for Forming of Nanostructured Surface Coatings

The possible technologies of formation of nanostructured surface layers: a method of thermal mass transfer in a high temperature gradient; the combined method, comprising plasma nitriding a cathode in a low pressure and deposition of titanium nitride in a single process cycle; combined method comprising an ionic nitriding and high frequency deposition of chromium carbide by pyrolysis of organic chromium compounds in a glow discharge plasma are considered. The possibility of formation of nanostructured layers is shown. Examples of the practical use of these technologies are given. The tests found that the use of the combined coating nitriding + TiN increases cyclic durability of machinery parts in contact loading conditions and corrosive environments on the two orders, providing a specified level of reliability and combined nitriding + CrC coating on steel С1050 allowed to reach values ​​of the fatigue limit under Impact NaCl 400 MPa.

Cathodic Cage Plasma Nitriding: An Innovative Technique

Cylindrical samples of AISI 1020, AISI 316, and AISI 420 steels, with different heights, were simultaneously treated by a new technique of ionic nitriding, entitled cathodic cage plasma nitriding (CCPN), in order to evaluate the efficiency of this technique to produce nitrided layers with better properties compared with those obtained using conventional ionic nitriding technique. This method is able to eliminate the edge effect in the samples, promoting a better uniformity of temperature, and consequently, a smaller variation of the thickness/height relation can be obtained. The compound layers were characterized by X-ray diffraction, optical microscopy, and microhardness test profile. The results were compared with the properties of samples obtained with the conventional nitriding, for the three steel types. It was verified that samples treated by CCPN process presented, at the same temperature, a better uniformity in the thickness and absence of the edge effect.