Papers by Keyword: Plasma Nitriding

Abstract: A fine blanking (FB) has grown up as a manufacturing means to fabricate the precise automotive parts from the thick sheet metals. During this net-shaping process, each part product had fully burnished surfaces through a single stroke. The punch for this FB, were highly loaded enough to distort the punch edge and to deteriorate the cost competitiveness and sustainability. A chamfered SKH51 tool steel punch was designed by controlling the chamfer widths and angles. A massively nitrogen supersaturated SKH51 punch was also prepared to investigate its effect on the suppression of punch edge distortion. AISI304 stainless steel work was used to describe the variation of punch distortion and blank qualities with increasing the number of strokes.

Abstract: Austenitic stainless steels are characterised by excellent corrosion resistance and good formability, but their low hardness and fatigue life are limitations in demanding applications. The aim of this study was to analyze the effect of solution annealing and plasma nitriding on the microstructure, hardness and fatigue properties of AISI 304 steel. The experimental material was examined in three states: initial, after solution annealing and after plasma nitriding. Solution annealing resulted in the removal of deformation martensite, giving a homogeneous austenitic structure with a decrease in hardness. On the contrary, plasma nitriding produced a hard nitride layer (1291 HV0.01), while no martensite retransformation took place. The results of the fatigue tests showed that the specimens after plasma nitriding reached the highest fatigue limit (878 MPa), while the specimens in the initial condition had the highest number of cycles to fracture. Fractographic analysis revealed typical fatigue failure characteristics in all conditions. The study highlights the possibility of optimising the fatigue properties of austenitic steels through an appropriate combination of thermal and chemical-heat treatments.

Abstract: Conventional plasma nitriding can induce defects due to direct plasma formation on the surface of the treated material. To address this issue, the screen-assisted direct current plasma nitriding (S-DCPN) method was developed, which generates plasma on both the sample and a surrounding screen, thereby reducing such defects. In this study, S-DCPN was applied to ferritic stainless steel (SUS430) using austenitic stainless steel (SUS304) as the screen material. Treatments were performed at 633 K for 15 hours under gas pressures of 200 and 600 Pa, with varying gas compositions of 75 % N₂ – 25 % H₂, 50 % N₂ – 50 % H₂, and 25 % N₂ – 75 % H₂. To evaluate the effects of gas composition and pressure, a range of analyses was conducted, including X-ray diffraction (XRD), cross-sectional microstructural observations, glow discharge optical emission spectrometry (GD-OES), hardness testing, and corrosion testing. The results revealed the formation of the α_N phase, a supersaturated solid solution of nitrogen in ferrite, under all conditions. Nitrogen diffusion and surface hardness increased with higher hydrogen content, and corrosion resistance was notably enhanced under the 25 % N₂ – 75 % H₂ condition. These findings demonstrate the effectiveness of S-DCPN in improving the surface properties of ferritic stainless steel while maintaining or enhancing corrosion resistance.

Abstract: The paper presents the use of integral methods of surface texture evaluation of structural steel samples used in armaments production for the analysis of the functional behaviour of gear surfaces. The aim of the paper is to evaluate the relationship between the quality of the ground surface and the surface after the plasma nitriding process and the functional properties of the surface using unconventional characteristics. These characteristics include Amplitude Distribution and Material Ratio, Autocorrelation Function (ACF), Frequency Spectrum (FS) and Power Spectral Density (PSD). These characteristics can, for example, reveal small changes in surface texture caused by both the cutting tool and surface treatments, such as diffusion nitriding technology, which show only slight changes in standard parameters. Thus, these characteristics can be used as a suitable diagnostic tool for evaluating changes in the functional properties of surfaces. These changes can usually be characterized by wavelength profile inequalities and statistical and spectral properties. In this paper, the surfaces of C45, 15NiCr13, 18CrNiMo7-6 and 16MnCr5 steels after the finishing operation of grinding and further after plasma nitriding are evaluated. Measurement of the standard parameter, i.e. the arithmetic mean height Ra, of ground and nitrided surfaces resulted in the same or slightly higher values after diffusion technology. Using integral characteristics, changes in surface texture were found to be directly related to the functional behaviour of surfaces in interaction and can predict, for example, noise levels, wear and lubrication properties.

Abstract: Plasma nitriding (ion nitriding) is a plasma-supported thermochemical cementation of steel, during which the hardness of the surface and resistance to wear and fatigue of the material increases due to the formation of a hard layer. The process of plasma nitriding is very variable, which makes it possible to nitride all types of steel, but the result depends primarily on the chemical composition and process tech-nique. In this way, for example, cement, construction, tool steels, high-strength and stainless steels, as well as cast iron, are nitrided. Structural steel belongs to a group of very important and diverse materi-als, it has versatile use in many areas of industry such as machines, vehicles, buildings, bridges, etc. Corrosion of materials is a common phenomenon that cannot be completely eliminated. This degrada-tion is often classified as one of the main reasons for material loss. The article presents the benefit of plasma nitriding on the corrosion resistance of structural steels. Experiments were carried out for select-ed three types of structural steels, on which plasma nitriding was performed and then a corrosion test in a mist of neutral sodium chloride solution. The achieved results confirmed that plasma nitriding has a significant effect on increasing the corrosion resistance of structural steels.

Abstract: Shot peening mechanical treatment surface, commonly used to improve material surface mechanical properties, as fatigue and wear resistance increase, induces deformations in the material crystal lattice, characterized by the presence of stress. Additionally, plasma nitriding, another surface treatment used to minimize failures in austenitic stainless steels, can produce resistant surface layers, composed of the interstitial nitrogen atoms accommodated in austenitic structure, increasing the layer hardness. Thus, the present work aims to study the residual stress and layer formation on austenitic stainless steel F138 surface, after different treatment conditions. Plasma nitriding treatment after shot peening differences were analyzed. Residual stress was investigated by X-ray diffraction, using sin²ψ method. Samples of surface morphology and formed layer were analyzed by scanning electron microscopy (SEM) and X-ray diffraction. Previous shot peening treatment to plasma nitriding promotes the formation of a less homogeneous layer, with microcracks and induced residual stress increase. It was observed the formation of iron nitrides and expanded austenite after plasma nitriding treatment. Surface residual stress induction after shot peening and plasma nitriding treatments can be efficient methods to improve material mechanical properties.

Abstract: The acidic environment and polarization in proton exchange membrane fuel cells (PEMFC) result in severe electrochemical corrosion issues for the bipolar plates of metal-based fuel cells. AISI 304 stainless steel is studied in this paper as the bipolar substrate and treated with plasma nitriding to improve its corrosion resistance performance. The influence of process parameters on the growth pattern of nitrided layers was discussed, and the microstructure and properties of modified layers were systematically studied. Results show that an expanded austenite nitride layer is obtained when the nitriding temperature is under 450°C, which has good corrosion resistance. When CrN precipitates at higher nitriding temperatures, the corrosion resistance of the nitride layer sharply decreases. The presence of valence states of N and Cr atoms in the nitrided layer determines the corrosion resistance of nitrided stainless steel samples.

Abstract: The article is focused on the analysis of fracture mechanisms of specimens made of austenitic steel, which have been subjected to dynamic tests. Austenitic stainless steels are characterized as high corrosion resistant materials with high bio-tolerance and relatively high strength. They are made by cold working, where plastic deformation occurs and they are deformed especially by slipping and twinning. Deformed regions are characterized by deformation twins and slip deformation. Specimens were used in two states, in the initial state and after chemical-thermal treatment. Dynamic tests to which specimens were subjected were the impact test and the three-point bending test. Fracture areas were evaluated by scanning electron microscope.

Abstract: The plasma nitriding conditions and processing parameters were controlled to attain the high-density nitrogen ion and NH-radical populations and to form the nitrogen supersaturated layer into AISI420 type martensitic stainless steel mold substrate at 673 K for 14.4 ks and 28.8 ks. Thicker nitrided layer than 80 mm was attained for fine machining of the optical diffraction elements onto this nitrided AISI420 mold surface. The average hardness in this nitrogen supersaturated layer reached 1400 HV. After this hardness testing and microstructure analysis, the machinability test was performed to describe the ductile mode cutting behavior of nitrogen-supersaturated work by using the PCD (Poly-Crystalline Diamond)-chip tool. Higher average nitrogen solute content than 4 mass% was responsible for fine turning by PCD-chip and CVD (Chemical Vapor Deposition)-diamond coated cutting tools without any damages and for precisely finishing the mold surface with the lower maximum surface roughness than 10 nm on the machined mold surface. The low roughness and homogeneous machined surface profile proved that the nitrogen supersaturated AISI420 series stainless steel was adaptive as a stamping mold of chalcogenide glasses with high dimensional accuracy and demolding capacity.

Abstract: The nitriding process is a well-known technology for increasing of wear resistance of steel. The conventional gas nitriding process of stainless steel is difficult in the case of surface passivation and formation of Cr₂O₃. The using of plasma enables to form hard surface area during the nitriding process. The plasma nitriding process was developed using Ionit Metaplas device. The kinetic growth was analysed in 2, 4, 6 and 8 h processes. The plasma gasses composition was selected for formation only diffusion layer without “white area” of nitrides. The microstructure, chemical and phase composition were analysed. As a result, the diffusion layer was formed. The iron nitrides formed the precipitations in the diffusion layer. The obtained results showed that 4h process enables to form nitride layer with required composition and hardness. The relationship between process time and nitride layer thickness and its hardness was observed.