Tribology properties of composite layer of CrMoCu alloy cast iron by combined treatment of ion nitrocarburizing and sulphurizing

Composite layer with nitrocarbonide and sulfide was made on the surface of CrMoCu alloy cast iron by combined treatment of ion nitrocarburizing and sulphurizing. The composite layer is composed of sulfide layer, nitrocarbonide hypo-surface layer and its diffusing layer, the size of sulfide globular grains distributing equably on the surface is in nano-micron-scale, and the phase structure of the composite layer is composed of FeS, FeS1-x, Fe2C and Fe3N. Under oil lubrication, sulphurized surface shows good scuffing-resistance only under low velocity, and nitrocarburized and sulphurized surface greatly improves the scuffing-resistance and wear-resistance of CrMoCu alloy cast iron, its integrated friction and wear properties are better than those of the plain and sulphurized surfaces under all the velocities.

Effect of Rare Earth Elements on the Impact Wear Resistance of Nitrocarburizing Layers

In this paper the effect of rare earth elements on the toughness and impact wear resistance of nitrocarburiz- ing layers is studied.The experimental results show that the toughness and impact wear resistance of RE-nitrocarburizing layers are increased significantly compared with that of conventional nitrocarburizing lay- ers.The service life of hot die for manufacturing bicycle bolts increased more than 100%.The impact wear mechanism of RE-nitrocarburizing layers is investigated by SEM as well.

Effects of lanthanum and cerium on low temperature plasma nitrocarburizing of nanocrystallized 3J33 steel

Plasma nitrocarburizing of nanocrystallized （NC） 3J33 steel were carried out at 400 and 430 ℃ for 4 h in a mixed gas of N2：3H2 and different flow rates of rare earths （RE） La and Ce reagents in this paper. Effects of temperature, rare earth addition and its addition amount on the microstructure and hardness of the nitrocarburized layer of NC 3J33 steel were also investigated. Surface phase composition of the nitrocarburized samples was analyzed by X-ray diffraction. Metallurgical structure, La and Ce concentration and microhardness profiles of cross-sectional nitrocarburized samples were studied using an optical microscope, a scanning electron microscope equipped with an energy dispersive X-ray analyzer and Vickers microhardness tester, respectively. The results showed that the surfaces of the nitrocarburized samples were mainly composed of γ＇-Fe4N and α＇-Fe （α-Fe dissolved with N and C） when the NC 3J33 steel was nitrocarburized at 400 ℃. As the temperature was enhanced up to 430 ℃, the surfaces consisted of γ＇-Fe4N, α＇-Fe and low nitrogen compound FeNx （x=0.0324–0.0989）, and simple substance La was presented when RE flow rate was 0.1 L/min. The addition of La and Ce into nitrocarburized gas increased the thickness and hardness of the nitrocarburized layers. The samples nitrocarburized at 400 ℃ with RE flow rate of 0.025 L/min and 430 ℃ of 0.05 L/min possessed the thickest nitrocarburized layer, highest proportion of nitrides and hardness profile. RE elements could diffuse into the nitrocarburized layer and their concentration increased with temperature. The excess RE impeded the permeation of N, C elements and led to thinner compound layer as well as the diffusion layer.

Effect of Rare Earth Elements on Erosion Resistance of Nitrocarburized Layers of 38CrMoAl Steel

Effect of rare earth elements (RE) on erosion resistance of nitrocarburized layer of 38CrMoAl steel was investigated. The results indicate that significant improvement occurs in erosion resistance of nitrocarburized 38CrMoAl steel by introducing RE during nitrocarburizing processing as compared with conventional nitrocarburizing processing. Results of mechanical testing show that both hardness and impact toughness of RE-nitrocarburizing layer of 38CrMoAl steel increase as compared with the conventional one. Optical microscopy reveals that there is improvement in the nitrocarburized layer attributed to the introduction of RE, which results in improvement in erosion resistance. Surface morphology observation of tested samples reveals that predominantly furrow-like peelings from plastic deformation are observed for RE nitrocarburizied 38CrMoAl steel, while the furrow-like peeling with initial cross crack and large grinding peelings were observed for conventionally nitrocarburized samples.

Effect of rare earths on mechanical properties of plasma nitrocarburized surface layer of 17-4PH steel

The aim of this investigation is to reveal the influence of rare earths(RE) addition on mechanical properties of plasma nitrocarburized 17-4PH steel.The nitrocarburized layers were characterized by optical microscope,scanning electron microscope equipped with energy dispersive X-ray analyzer,X-ray diffractometer,microhardness tester and pin-on-disc tribometer.The results showed that RE atoms could diffuse into the surface layer of 17-4PH steel plasma nitrocarburized at 500 °C for 4 h and did not change the ...

COMBINATION STRENTHENING PROCESS OF Ni-W-Ti-SiC COMPOSITE COATING AND NITROCARBURIZATION

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Plasma Post Oxidation of Plasma Nitrocarburized SKD 61 Steel

Plasma nitrocarburizing and plasma oxidizing treatments were performed to improve the wear and corrosion resistance of SKD 61 steel.Plasma nitrocarburizing was conducted for 12 h at 540℃in the nitrogen, hydrogen and methane atmosphere to produce theε-Fe-（2-3）（N,C） phase.The compound layer produced by plasma nitrocarburising was predominantly composed ofε-phase,with a small proportion ofγ′-Fe-4 （N,C） phase. The thickness of the compound layer and the diffusion layer are about 10μm and about 200μm,respectively. Plasma post oxidation was performed on the nitrocarburized samples with various oxygen/hydrogen ratio at constant temperature of 500℃for 1 h.The very thin magnetite （Fe-3O-4） layer of 1-2μm in thickness on top of the compound layer was obtained.Anodic polarization test revealed that plasma nitrocarburizing process contributed a significant improvement of corrosion resistance of SKD 61 steel.However,the corrosion characteristics of the nitrocarburized compound layer was deteriorated by oxidation treatment.

Effect of processing temperatures on characteristics of surface layers of low temperature plasma nitrocarburized AISI 204Cu austenitic stainless steel

The influence of processing temperatures on the surface characteristics of AISI 204Cu austenitic stainless steel was investigated during a low temperature plasma nitrocarburizing.The resultant layer was a dual-layer structure,which comprises a N-enriched layer on the top of C-enriched layer.The surface hardness and the layer thickness increase up to about HV 0.05 1000 and 20μm with increasing temperature.The specimen treated at 400°C shows a much enhanced corrosion resistance compared to the untreated steel.A loss in corrosion resistance was observed for specimens treated at temperatures above 430°C due to the formation of Cr2N.

ANALYSIS ON MECHANISM OF FRACTURE FOR THE SURFACE-HARDENING STEEL

The tensile characteristic of nitrocarburized 45 steel treated by different cooling rates was studied in this work. We had observed a new kind zigzig tensile curve and it showed that the tensile curve and the characterastics of the failure surface related to the cooling rate.

Study on composite surface treatment of 38CrMoAl steel

In this paper, a new composite surface treatment technology of electric brush plating Ni W alloy and nitrocarburizing composite process of 38CrMoAl steel has been studied .The properties, microstructure and phase composition of the surface layer of 38CrMoAl steel are examined by optical microscopy , scanning electron microscope (SEM) and X ray diffraction . The experiment on the wear resistance of surface layer is carried out . The effect of the thickness of electric brush plating of Ni W alloy and the holding time of nitrocarburizing on the properties and the microstructure of surface layer are studied .The results show that good metallurgical bonding is transformed from mechanical bonding in electric brush plating deposits with 38CrMoAl steel; the components of surface deposit microstructure are Ni base phase with less disperse WC,WN particles . The wear resistance of surface layer of 38CrMoAl steel treated by the composite process has increased 8 times compared with that by nitrocarburizing .The optimum electric brush plating thickness is 20 μm , and the optimum holding time of nitrocarburizing is 80 min at 540 ℃ .

Plasma post oxidation of nitrocarburized AISI 4140 steel

Plasma nitrocarburizing and plasma oxidizing treatments were performed to improve the wear and corrosion resistance of AISI 4140 steel. Plasma nitrocarburizing was conducted for 3 h at 570 ℃ in the nitrogen, hydrogen and methane atmosphere to produce the ε-Fe2-3(N,C) phase. It was found that the compound layer produced by plasma nitrocarburising was predominantly composed of ε-phase, with a small proportion of γ′-Fe4(N,C) phase. The thickness of the compound layer was about 10 μm and the diffusion layer was about 300 μm in thickness, respectively. Plasma post oxidation was performed on the nitrocarburized samples with various oxygen/hydrogen ratio at a constant temperature of 500 ℃ for 1 h. The very thin magnetite (Fe3O4) layer 1-2 μm in thickness on top of the compound layer was obtained by plasma post oxidation. It was confirmed that the corrosion characteristics of the nitrocarburized compound layer can be further improved by the application of the superficial magnetite layer.

Influence of Medium Used during Ferritic Nitro-Carburizing of AISI H-13 Hot Work Tool Steel

Ferritic nitro-carburizing is one of the most popular surface hardening methods used to improve lifespan of hot work tool steels.Different types of mediums like gas,liquid,plasma and fluidized bed are generally used during ferritic nitro-carburizing process.In this paper,various ferritic nitro-carburizing methods were compared where gas,salt bath and fluidized are used as mediums.AISI H-13 hot work tool steel specimens were treated by using these different methods of nitro-carburizing and their performance was evaluated by using micro-structural and mechanical analysis.Optical microscopy,micro-hardness testing and X-ray stress analyzer were used for specimen characterization.Moreover,pin on disk dry sliding wear tests were performed to compare wear performance of specimens treated with different nitro-carburizing methods.It is perceived that,medium used during nitro-carburizing has significant influence on the final surface properties that can be achieved by ferritic nitro-carburizing.

STUDY ON STRUCTURE AND PROPERTIES OF Ni-W-SiC COMPOSITE COATING

The effects of electroplating conditions on the composition of N-W-SiC composite coating were studied; the znfiuence of heat-treatment and nitrocarburization on the microstructure, hardness and wear resistance of the coating were discussed. The results showed that an amorphous composite coating, containing(wt%) 50-55Ni, 42-45.IW and 3.0-7.6SiC, could be electroplated on the matrix. Afier heat-treatment or nitrocarburization the coating crystallized to form some new phases, and the haordness and wear resistance of the composite coating were enhanced retmarkably.

Effect of rare earth addition on microstructure and corrosion behavior of plasma nitrocarburized M50NiL steel

M50NiL steel was plasma nitrocarburized at 480 °C with and without rare earth （RE） addition. The microstructures of the surface layer were characterized by optical microscopy, X-ray diffraction and scanning electron microscopy. The mechanical proper-ties and corrosion resistances of the surface layer were studied by Vickers microhardness measurements and polarization tests in 3.5% NaCl solution. The results showed that RE atoms could diffuse into the surface layer of the steel and inhabit the formation ofε-Fe2–3（N,C） phase. As compared to the treatment without RE addition, RE addition further increased the surface hardness by 143 HV0.1, and further increased the thickness of the nitrocarburized layer by 39μm. Compared with the quenched bearing steel, the cor-rosion resistance of the samples nitrocarburized with and without RE addition could be significantly improved. Especially, the sample plasma nitrocarburized with RE addition exhibited the highest corrosion resistance.

Effects of Rare Earth Elements on the Characteristics of Low Temperature Plasma Nitrocarburized Martensitic Stainless Steel

Low temperature plasma nitrocarburizing of 17-4PH martensitic stainless steel was conducted at 430 ℃ with and without rare earth （RE） addition. The microstructure, kinetics, microhardness, wear behavior as well as corrosion resistance of the modified layer were studied by optical microscopy, X-ray diffraction, Vickers microhardness tester, pin-on-disc tribometer and potentiodynamic polarization tests. The results show that the thickness of plasma RE nitrocarburized layer is much thicker than that formed by nitrocarburizing without RE addition. The incorporation of RE does not change the kind of the phases and the nitrocarburized layer consists mainly of nitrogen and carbon expanded martensite （aN）, γ-Fe4N and a-Fe with a trace of CrN phases. The surface microhardness of plasma nitrocarburized layer can be increased by 100 HV after RE addition. Wear resistance of the specimen can be apparently improved by low temperature plasma nitrocarburizing with and without RE addition and without sacrificing its corrosion resistance. Wear reduction effect of low temperature plasma nitrocarburizing with RE addition is better than that of the conventional one.

Microstructure and mechanical properties of surface layers of 30CrMnSiA steel plasma nitrocarburized with rare earth addition

The pulse plasma nitrocarburizing for 30CrMnSiA steel was conducted at 560 ℃ for 8 h in mixed gases of N2：3H2 and different flow rates of rare earths （RE） addition. Effects of rare earths （RE） addition in the carrier gas on the surface morphology, phase structure and mechanical properties of the nitrocarburized layer were characterized by optical microscopy （OM）, X-ray diffraction （XRD）, scanning electron microscopy （SEM）, microhardness testing and wear testing, respectively. The results showed that the surface phase structures changed from dual phases ε-Fe2.3N（C） and γ′-Fe4N（C） to phase Fe3C and incipient nitrides, and the nitrocarburized surface hardness value decreased slightly from 756 to 681 HV0.1 with the RE addition increasing in the cartier gas, and the corresponding morphology of the nitrocarburized surface was granular nitride group （diameter 0.8-1.5 μm） and compact-fine Fe3C stick and patch （mean size 100-300 nm）, respectively. The wear resistance of the experimental steel could be improved remarkably by plasma RE nitrocarburizing. The nitrocarburized layer with Fe3C phase formed in the mixed gases of N2：3H2 and flow rate of 0.5 L/min RE addition showed the lowest friction coefficient and the narrowest wear track.

Mechanical and corrosion resistant properties of martensitic stainless steel plasma nitrocarburized with rare earths addition

In order to improve surface hardness and corrosion resistant property of 17-4PH martensitic stainless steel, the steel was plasma nitrocarburized at 560 ℃ for 2-4 h in a gas mixture of nitrogen, hydrogenand ethanol with rare earths （RE） addition. The experimental results showed that the modified layer was characterized by a compound layer containing two distinct zones （i.e. out ~dark zone＇ and inner ＇white zone＇）. The inner ＇white zone＇ was almost a precipitation free zone and had high hardness as well as good corrosion resistance. An- odic polarization test results showed that the specimens plasma nitrocarburized with RE addition had good corrosion resistance resulted mainly from their higher corrosion potentials, lower corrosion current densities and larger passive regions as compared with those of the un- treated one.

An Electron Microscopy Study of Vein-like Grain Boundary Microstructure in Nitrocarburized Low Carbon Steels

The coarsened grain boundaries （GBs） with vein-like morphology frequently appear in the nitrogen diffusion layer of nitrocarburized carbon steels. The electron probe X-ray microanalysis shows that such vein-like GBs are rich in nitrogen and carbon atoms. Transmission electron microscopy and scanning electron microscopy further reveal that the coarsened GBs consist of γ＇-nitrocarbide （Fe4（C,N）） and ε-nitrocarbide lamellas that are formed during nitrocarburizing due to high nitrogen concentration at GBs. It is shown that many of {111}〈112〉 micro twins exist in the γ＇-phase lamellas and thin ε-phase slices prefer to nucleate at their twin boundaries with the orientation relationship of {0001}ε//{111}γ＇. Upon growing large γ＇-Iamellas may become faceted and thin ε-Iamellas may grow thicker and become the main portions in the vein-like GBs. The microstructure evolution occurring in the vein-like GBs can be depicted as： α ＋ [N]/[C] → ＋ [C,N] →ε-nitrocarbides.