Decrease of Compound Layer Thickness Obtained in Plasma Nitriding of Alloyed Steels by Diffusion Stage (original) (raw)
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FORMATION OF LAYERS BY PLASMA NITRIDING IMPOSED TO 32CrMoV13 LOW ALLOY STEEL
The aim of the study is to optimise the application of heat treatments by modifying the nitriding conditions in high temperature process. The influence of gas mixture (composed of N2, H2 and CH4) and time of nitriding on the mechanical and structural properties of 32CrMoV13 low alloy steel samples was studied. The composition and structure of the nitrided layers was determined by EDS and XRD respectively. Vickers micro hardness profiles were also performed to study the influence of the gas mixture and time of nitriding. The morphology of the nitrided layers was observed by optical microscopy. EDS analyses permitted to verify the composition of the layers while their structure was determined by XRD. The time of nitriding was influent on the diffusion layer's thickness and properties. Furthermore, it was obvious that increasing the nitrogen contents from 20 to 80 % in the nitriding gas mixture N2+H2 or adding 5% of methane permits to increase the nitrided layer's thickness a...
Study Concerning the Effects of Plasma Nitriding on the Characteristics of Structural Alloy Steels
Due to the many technical-economical advantages it offers in comparison to the classical heat treatment processes, plasma nitriding has in recent years considerably enlarged its range of industrial applications. The main purpose of plasma nitriding is to provide advantageous conditions of the parts' machinability and reliability, by modifying their chemical composition, the structure and reducing any internal stresses. Nitrogen diffusion in the base material's crystal lattice creates in the parts' superficial layer compounds that determine an increase in wear and corrosion strength and an improvement of the general tribological properties. In the current paper, the authors focus on the kinetics of forming and on the hardness of layers obtained after plasma nitriding in structural steels such as 39CrAlMo6-9-2, 42CrMo4, 18CrMn4-4 and 40Cr4.
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Materials Characterization, 2002
AISI 5140 steel was plasma nitrided at various gas mixtures of nitrogen, hydrogen, and argon to investigate the actions of hydrogen and argon on plasma nitriding. The structural and mechanical properties of ion-nitrided AISI 5140 steel have been assessed by evaluating composition of phases, surface hardness, compound layer thickness, and case depth by using X-ray diffraction (XRD), microhardness tests, and scanning electron microscopy (SEM). It was found that the growth of compound layer can be controlled and the diffusion improved when the gas mixture includes H 2 gas. Additionally, it was determined that the amount of Ar in dual gas mixture must be at 20% minimum to obtain distinctive surface hardness and compound layer thickness. D
Residual stress-affected diffusion during plasma nitriding of tool steels
Metallurgical and Materials Transactions A, 2004
Plasma nitriding of tool materials is common practice to improve the wear resistance and lifetime of tools. Machining-induced compressive residual stresses in shallow layers of some tenths of microns are observed accompanied by other characteristic properties of machined surfaces in these high-strength materials. After plasma nitriding of M2 high-speed steel, previously induced compressive residual stresses remain stable and the depth of diffusion layers decreases with increasing compressive residual stresses. This article reports investigations of plasma nitrided samples with different levels of residual stresses induced prior to the nitriding process. For comparison, experiments with bending load stresses during plasma nitriding have also been carried out. The plasma nitriding treatment was performed at constant temperature of 500 °C with a gas mixture of 5 vol pct N 2 in hydrogen. Nitriding time was varied from 30 to 120 minutes. All samples were characterized before and after plasma nitriding concerning microstructure, roughness, microhardness, chemical composition, and residual stress states. Experimental results are compared with analytical calculations on (residual) stress effects in diffusion and show a clear effect of residual and load stresses in the diffusion of nitrogen in a high-strength M2 tool steel.
Metallurgical response of an AISI 4140 steel to different plasma nitriding gas mixtures
Materials Research, 2013
Plasma nitriding is a surface modification process that uses glow discharge to diffuse nitrogen atoms into the metallic matrix of different materials. Among the many possible parameters of the process, the gas mixture composition plays an important role, as it impacts directly the formed layer's microstructure. In this work an AISI 4140 steel was plasma nitrided under five different gas compositions. The plasma nitriding samples were characterized using optical and scanning electron microscopy, microhardness test, X-ray diffraction and GDOES. The results showed that there are significant microstructural and morphological differences on the formed layers depending on the quantity of nitrogen and methane added to the plasma nitriding atmosphere. Thicknesses of 10, 5 and 2.5 µm were obtained when the nitrogen content of the gas mixtures were varied. The possibility to obtain a compound layer formed mainly by γ '-Fe 4 N nitrides was also shown. For all studied plasma nitriding conditions, the presence of a compound layer was recognized as being the responsible to hinder the decarburization on the steel surface. The highest value of surface hardness-1277HV-were measured in the sample which were nitrided with 3vol.% of CH 4 .
Materials Research
For the first time, the influence of gas mixture on first damage resistance of a plasma nitrided DIN 18MnCrSiMo6-4 bainitic steel was investigated. Samples were nitrided at 500 °C with three different N 2-H 2 gas mixtures, containing 5, 24, and 76 vol.% N 2. Samples were characterized concerning the resulting roughness, microstructure, compound layer's phase composition, residual stresses in the diffusion zone, and surface hardness. Tribological ball-on-flat tests were carried out in reciprocal mode using zirconia as ball material for friction coefficient and the compound layer resistance until the first damage. The test results were evaluated statistically by analysis of variance (ANOVA). As the amount of nitrogen in the gas mixture decreases, the ε-Fe 2-3 (C)N content in the compound layer decreases. A γ'-Fe 4 N monophasic compound layer was achieved at 5 vol.% N 2 gas mixture. The diffusion zone as expected presented compressive residual stresses with the highest values near the surface. In the tribological tests, better results were obtained for 5 and 24 vol.% N 2 in the gas mixture as higher amounts of γ'-Fe 4 N were formed. The 76 vol.% N 2 gas mixture led to a brittle behavior, due to the biphasic compound layer (γ'-Fe 4 N and ε-Fe 2-3 (C)N) with a predominant content of ε-Fe 2-3 (C)N.
Materials Research, 2010
This work aims to characterize the phases, thickness, hardness and hardness profiles of the nitride layers formed on the CA-6NM martensitic stainless steel which was plasma nitrided in gas mixtures containing different nitrogen amounts. Nitriding was performed at 500 °C temperature, and 532 Pa (4 Torr) pressure, for gas mixtures of 5% N 2 + 95% H 2 , 10% N 2 + 90% H 2 , and 20% N 2 + 80% H 2 , and 2 hours nitriding time. A 6 hours nitriding time condition for gas mixture of 5% N 2 + 95% H 2 was also studied. Nitrided samples results were compared with non-nitrided condition. Thickness and microstructure of the nitrided layers were characterized by optical microscopy (OM), using Villela and Nital etchants, and the phases were identified by X-ray diffraction. Hardness profiles and hardness measured on surface steel were determined using Vickers hardness and nanoindentation tester, respectively. It was verified that nitrided layer produced in CA-6NM martensitc stainless steel is constituted of compound layer, being that formation of the diffusion zone was not observed for the studied conditions. The higher the nitrogen amounts in gas mixture the higher is the thickness of the nitrided layer and the probability to form different nitride phases, in the case γ'-Fe 4 N, ε-Fe 2-3 N and CrN phases. Intrinsic hardness of the nitrided layers produced in the CA-6NM stainless steel is about 12-14 GPa (~1200-1400 HV).
Change of Selected Parameters of Steel Surface after Plasma Nitriding
Manufacturing Technology, 2019
This article deals with the evaluation of the change of selected 2D structure parameters of the grinded surfaces before and after application of plasma nitridation. Changes in parameters were analyzed on 30CrMoV9 steel samples which were ground to Ra ≈ 0.03 and then plasma nitrided in a standard nitriding atmosphere. An absolute method was used to evaluate the surfaces. Measurements were performed on a profilometer CLI 1000. The parameters comprehensively describing the surface structure were subjected by analyzes, namely the height, length, shape parameters and parameters of the material ratio. After plasma nitriding, almost all selected surface structure parameters have been increased. Higher values of the monitored parameters have an influence on the increase of friction and wear and negatively affect the running-up properties of nitrided components.
Journal of the Brazilian Society of Mechanical Sciences and Engineering
In this study, the effect of the controlled injection of air as a source of contamination, corresponding to 10%, 20% and 30% of total renewal flow, on the microstructural characteristics and microhardness of plasma-nitrided plain carbon steels was investigated. Samples were submitted to microstructural, mechanical and chemical characterization by optical and scanning electron microscopy, energy-dispersive X-ray spectroscopy, X-ray diffraction and microhardness measurements. It was found that all percentages of air addition promoted a reduction in surface hardness of all samples treated due to the formation of a thinner compound layer, with a more dramatic drop observed at 30% of air addition. The formation of Fe 3 O 4 iron oxide in the surface was detected in the X-ray diffraction analysis of SAE 1005 samples processed under this condition. Also, SEM and EDS analysis showed that a thin layer of iron oxide was formed in the treatment with the same atmosphere.
The influence of process gas characteristics on the properties of plasma nitrided steel
Surface and Coatings Technology, 1995
This study attempts to elucidate some of the effects of adding argon, neon and hydrogen to Iow pressure thermionically supported discharges used for plasma nitriding AISI M2 steel substrates. Four runs were performed at the same substrate temperature (550 °C) and bias voltage (500 V), using the following gas mixtures: 8% N2 in Ar, 8% N2 in Ne, N2 + H2 in equal proportions, and N2 only. By careful control of the discharge parameters, most of the bombardment energy was transported to the substrates by 500 eV ions in all cases; these were mainly Ar + ions in the N2 + Ar run and N2 + ions in the other runs, notably by the action of Penning ionization in the N2 + Ne run. We found that the surface hardness was not significantly influenced by the type of ion delivering the bombardment energy, although we suggest that ions would need sufficient mass to cause (for example) sputtering, if the substrate is susceptible to contamination during nitriding. Furthermore, the results showed that there was a strong dependence on the availability of nitrogen thermal neutral molecules during processing; we suggest that there may be a critical value of nitrogen gas density or range of values for effective plasma nitriding, so that a process may be inadequately supplied (resulting in reduced case hardness) or over-supplied (increasing the significance of white layer formation).