Structural characterization of plasma nitrided interstitial-free steel at different temperatures by SEM, XRD and Rietveld method (original) (raw)
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Metallurgical and Materials Transactions, 2019
The effect of prior cold deformation and nitriding parameters on the kinetics and mechanism of plasma nitriding and the resultant hardness, wear and corrosion properties of automotive-grade interstitial-free (IF) steel has been investigated. Following controlled prior cold deformation (uniaxial rolling), plasma nitriding was carried out in pulsed direct current glow discharge mode with applied voltage, current, temperature and time varied in the range 540 to 710 V, 3 to 6 A, 350 to 480°C and 1 to 4 hours, respectively. The phases formed after nitriding were found to be mostly c-Fe 4 N with a small volume fraction of Fe 3 N embedded in a ferrite matrix. Prior cold deformation increases the kinetics of the nitride formation. The volume fraction of nitride phases increased with an increase in nitriding temperature and time. Detailed characterization suggested that 80 pct cold deformation followed by plasma nitriding led to significant improvement in hardness and wear resistance of IF steel, particularly when nitrided at 480°C for 4 hours. Moreover, plasma nitriding also enhanced the corrosion resistance of IF steel, enhancement being directly related to the nitride volume fraction at the surface. Hence, it was concluded that prior cold deformation was effective in enhancing the kinetics of plasma nitriding and in turn surface hardness and resistance to wear and corrosion of IF steel, which otherwise possess a fairly poor bulk strength and does not respond to usual bulk/surface-hardening treatments.
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...
Surface hardening of IF steel by plasma nitriding: Effect of a shot peening pre-treatment
Surface and Coatings Technology, 2014
Shot peening and plasma processes are widely used to improve surface properties of several alloys. In this work, triode plasma nitriding (TPN) was applied to Ti-stabilized interstitial free (IF) steels in an attempt to increase their hardness without compromising their excellent conformability. Shot peening was also trialed before triode plasma nitriding in an attempt to enhance nitriding kinetics and achieve deeper case depths. Triode plasma nitriding was performed at 450°C, 475°C and 500°C for 4 h on Ti-stabilized IF steel. Scanning electron microscopy (SEM) and X-ray diffraction (XRD) were used to characterize the steel structure. Instrumented indentation hardness-depth profiles indicated that a significant hardening effect was achieved after plasma nitriding at 500°C for 4 h. These nitriding conditions doubled the near-surface hardness of the parent IF steel and led to a case depth of 500 μm. Instrumented indentation hardness-profile data also indicated that the shot peening pre-treatment did not have any beneficial effect on nitriding kinetics as a reduction in case depth occurred after this mechanical pretreatment. Increased surface roughening promoted by shot peening reduced the nitrogen uptake during nitriding. Dry sliding wear tests also corroborated the benefits of plasma nitriding on Ti-stabilized IF steels, as significantly lower wear volumes resulted after this surface hardening treatment. Although oxidative wear was found to occur in all IF steel samples, wear performance was found to be influenced by load support provided by underlying steel substrates and thickness of compound layers. The best wear performance of solely plasma nitrided samples could be attributed to thicker compound layers and deeper hardened cases compared to shot-peened + plasma nitrided samples, which exhibited shallower case depths and thinner compound layers.
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.
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 .
Effect of plasma nitriding time on the structural and mechanical properties of AISI‐O1 steel
Engineering Reports, 2020
In this paper, the effect of plasma nitriding time on the improvement of surface microhardness of AISI O1 steel as a strategy to increase its wear resistance was addressed. The plasma nitriding was carried out in a controlled atmosphere (80% H2(g) and 20% N2(g)), temperature (500°C), and pressure (6 mbar), during the different amount of time (4, 5, and 6 hours). The material was characterized by X‐ray diffraction (XRD), scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), and microhardness measurements. Moreover, microhardness measurements were carried out to investigate the mechanical properties. From the results, it was verified that the XRD patterns, SEM images, and EDS spectra confirmed the formation of a layer with ε‐Fe3N and γ′‐Fe4N phases in all nitrided samples. The sample AISI‐O1 steel, which was nitrided for 6 hours, exhibited a hardness about 46% higher than the one measured for the untreated sample. This sample also showed the thicker layer, with a m...
Structural surface characterization of ion nitrided AISI 4340 steel
Materials & Design (1980-2015), 2012
In this work,AISI 4340 steel samples were plasma nitrided in a mixture of 50%N 2-50%H 2 process gas at 470°C temperatures for different nitriding times of 1, 4 and 8 h. Prior to nitriding, the specimens were normalized at 850°C for 30 min. Nitrided samples were characterized using optical microscopy (OM), scanning electron microscopy (SEM), X-Ray diffraction (XRD) and microhardness testing. The thickness of diffusion and compound layers was determined by using cross-sectional OM & SEM micrographs and microhardness profiles. Residual stresses in diffusion layers were determined using XRD g-method. The results showed that compound layers of 4.5-7 m thick consisting of Fe 4 N (γ) and Fe 2-3 N (ε) phases are formed on samples surface. The thickness of the diffusion layer increases from 90m to 240 m with increasing plasma nitriding time. The surface and cross-sectional hardness are also increased with increasing nitriding time and the maximum surface hardness of 750 HV obtained after 8 h plasma nitriding. All samples contain compressive residual stress and the highest compressive residual stress of 260 MPa is obtained for sample nitrided.
Effects of various gas mixtures on plasma nitriding behavior of AISI 5140 steel
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
Plasma nitriding of AISI 52100 ball bearing steel and effect of heat treatment on nitrided layer
Bulletin of Materials Science, 2011
In this paper an effort has been made to plasma nitride the ball bearing steel AISI 52100. The difficulty with this specific steel is that its tempering temperature (∼170-200 • C) is much lower than the standard processing temperature (∼460-580 • C) needed for the plasma nitriding treatment. To understand the mechanism, effect of heat treatment on the nitrided layer steel is investigated. Experiments are performed on three different types of ball bearing races i.e. annealed, quenched and quench-tempered samples. Different gas compositions and process temperatures are maintained while nitriding these samples. In the quenched and quench-tempered samples, the surface hardness has decreased after plasma nitriding process. Plasma nitriding of annealed sample with argon and nitrogen gas mixture gives higher hardness in comparison to the hydrogen-nitrogen gas mixture. It is reported that the later heat treatment of the plasma nitrided annealed sample has shown improvement in the hardness of this steel.
Journal of ASTM International, 2012
High chromium content is responsible for the formation of a protective passive surface layer on austenitic stainless steels (ASS). Due to their larger amounts of chromium, superaustenitic stainless steels (SASS) can be chosen for applications with higher corrosion resistance requirements. However, both of them present low hardness and wear resistance that has limited their use for mechanical parts fabrication. Plasma nitriding is a very effective surface treatment for producing harder and wear resistant surface layers on these steel grades, without harming their corrosion resistance if low processing temperatures are employed. In this work UNS S31600 and UNS S31254 SASS samples were plasma nitrided in temperatures from 400 C to 500 C for 5 h with 80 % H 2 -20 % N 2 atmosphere at 600 Pa. Nitrided layers were analyzed by optical (OM) and transmission electron microscopy (TEM), x-ray diffraction (XRD), and Vickers microhardness testing. Observations made by optical microscopy showed that N-rich layers were uniform but their thicknesses increased with higher nitriding temperatures. XRD analyses showed that lower temperature layers are mainly composed by expanded austenite, a metastable nitrogen supersaturated phase with excellent corrosion and tribological properties. Samples nitrided at 400 C produced a 5 lm thick expanded austenite layer. The nitrided layer reached 25 lm in specimens treated at 500 C. There are indications that other phases are formed during higher temperature nitriding but XRD analysis was not able to determine that phases are iron and/or chromium nitrides, which are responsible for increasing hardness from 850 up to 1100 HV. In fact, observations made by TEM have indicated that formation of fine nitrides, virtually not identified by XRD technique, can begin at lower temperatures and their growth is affected by both thermodynamical and kinetics reasons.