Nitrocarburized Specimens Research Articles

On the effect of salt bath nitrocarburizing on the cavitation erosion behavior of AISI 304L stainless steel

In this study, salt bath nitrocarburizing was applied on austenitic stainless steel AISI 304L to stabilize austenite at the surface exposed to cavitation attack. Samples were treated at 470 °C and 500 °C for 6 h, giving an average thickness of the nitrocarburized layer of 6 µm and 26 µm, respectively. The thickness of the nitrocarburized layer is found to influence the formation of deformation-induced martensite (DIM) in the material and, thereby, the cavitation erosion resistance. The mass loss vs. time plot shows that the nitrocarburized specimens performed significantly better than the base material under ultrasonic vibratory cavitation erosion test (ASTM G32). Cross-sectional micrographs show that the phenomenon responsible for the failure in the base material is the formation of DIM. The specimen, nitrocarburized at 470 °C, showed a reduction of about 90 % in mass loss when compared to the base material (AISI 304L SS), owing to a higher yield strength (/resilience) after the formation of more stable austenite.

Effect of the roughness produced by plasma nitrocarburizing on corrosion resistance of AISI 304 austenitic stainless steel

In this work, we studied the influence of surface roughness produced by sputtering during plasma nitrocarburizing treatments on corrosion resistance of AISI 304 austenitic stainless steel in an aqueous solution of sodium chloride. Plasma nitrocarburizing treatments were carried out in a gaseous atmosphere containing 80% N2+2% CH4+18% H2, at 400Pa, for 2h and at temperatures of 375°C, 430°C and 475°C. Surface roughness after plasma nitrocarburizing was characterized using 3D confocal microscopy. Corrosion susceptibility of the plasma nitrocarburized surfaces was investigated by electrochemical impedance spectroscopy, potentiodynamic polarization, and scanning electron microscopy. The results showed that when increasing the temperature of the plasma nitrocarburizing treatment, both thickness and amount of precipitates increased, as expected. Analyses by 3D confocal microscopy also showed increased surface roughness with increasing plasma nitrocarburizing temperature. When comparing two plasma nitrocarburized specimens with similar precipitate-free structure, it was found that thinner thickness of the expanded austenite layer and lower surface roughness resulted in higher corrosion resistance.

Microstructure, adhesion and tribological properties of CrN/CrTiAlSiN/WCrTiAlN multilayer coatings deposited on nitrocarburized AISI 4140 steel

In this study, the CrN/CrTiAlSiN/WCrAlTiN multilayer coatings have been deposited on polished AISI 4140 steel substrates (named only-coating specimens) and plasma nitrocarburized specimens (named duplex specimens) by cathodic multi-arc evaporation. The microstructure and composition of the specimens were studied using X-ray diffraction (XRD), scanning electron microscopy (SEM) with Energy dispersive X-ray analysis (EDX), and transmission electron microscope (TEM) techniques. The micro-hardness and nano-hardness were measured by Vickers hardness tester and nanoindentation, respectively. The adhesion and tribological behavior were evaluated using the Rockwell-C indentation and micro-tribometer, respectively. The results showed that plasma nitrocarburizing gives rise to a modified layer due to diffusion of nitrogen/carbon, leading to surface hardness, H, of 13.0 GPa, compared to H = 6.8 GPa for the untreated steel. Notably, it shows that the super-hardness (H = 47.9 GPa) multilayer coating consists of a bottom CrN layer, a middle CrTiAlSiN layer, and an outmost superlattice WCrTiAlN layer. The nitrocarburizing pretreatment considerably improves adhesion strength of the duplex specimen compared with the only-coating one. The improved mechanical and tribological properties of the duplex specimen are mainly related to the gradient in the hardness profile of the diffusion nitrocarburized layer.

Effect of the deformation on nitrocarburizing microstructure of the cold deformed Ti-6Al-4V alloy

In this paper, the combined modification of deformation-led low-temperature plasma nitrocarburizing was carried out to improve low hardness and poor surface wear resistance of Ti6Al4V. The composite process of solid solution + cold rolling and low-temperature plasma nitrocarburizing simultaneous aging is proposed to modify Ti6Al4V alloy. As indicated by the experiment results, with the increase of deformation, the refinement degree of microstructure increases and the thickness of nitrocarburized layer increases. The nitrocarburized specimen's surface consists of titanium nitrides and carbide. After modification, the overall hardness and wear resistance of Ti6Al4V is significantly improved and the continuity of cross-sectional hardness of specimen is continuously improved. This research is aimed to solve the quality problem of plasma nitriding/carburizing, such as hydrogen embrittlement and oxidation of high temperature, which existed in the industrial field.

Development of highly hard and corrosion resistant A286 stainless steel through plasma nitrocarburizing process

A286 (AISI 660), an austenitic precipitation hardening stainless steel has good strength and corrosion resistance, but its low hardness restricts their use in applications involving abrasive wear. In order to improve the hardness without loss of corrosion resistance properties of A286 stainless steel, plasma nitrocarburizing process was carried out at temperatures ranging from 350°C to 500°C for 4 and 8h. The gas mixture composition employed during the process was 78% nitrogen, 20% hydrogen and 2% acetylene gas. Plasma was generated using a pulse DC power supply having a frequency of 30kHz.After plasma nitrocarburizing, a dual layer was formed consisting of nitrogen and carbon in the top layer followed by carbon in the bottom layer. Compared with the untreated A286 stainless steel specimens, the microhardness values measured from the plasma nitrocarburized specimens treated at 400 and 450°C increased by a factor of two and three respectively. The electrochemical corrosion behavior of the plasma nitrocarburized A286 specimens has been studied in 3.5wt.% NaCl solution. The results show that specimens treated at 400°C for 4h has better pitting corrosion resistance and higher surface hardness compared with that of the untreated A286 stainless steel. This is mainly attributed to the presence of carbon and nitrogen in the modified layer existing as a solid solution.

Microstructure and mechanical properties of M50NiL steel plasma nitrocarburized with and without rare earths addition

M50NiL steel was plasma nitrocarburized at 500°C with and without rare earth (RE) addition. The nitrocarburized layers were characterized by optical microscope, scanning electron microscope equipped with an energy dispersive X-ray analyzer, X-ray diffraction, hardness tests and pin-on-disc tribometer. The results show that the RE atoms can diffuse into M50NiL steel surface and change the surface morphology of the nitrocarburized layer. The incorporation of RE atoms increases the surface hardness of the nitrocarburized layer (approximately 130HV0.1 higher), layer thickness (about 14% thicker) and carbon content of the modified layer, respectively. The wear rates of the nitrocarburized specimens are significantly lower than that of the un-nitrocarburized one. The wear mechanisms of the specimens plasma nitrocarburized with and without RE addition are different mainly due to the differences in the surface morphology, the phase proportion and the hardness of the modified layer.

Grain and grain boundary characters in surface layer of untreated and plasma nitrocarburized 18Ni maraging steel with nanocrystalline structure

The nanocrystallized 18Ni maraging steel was plasma nitrocarburized at 460°C for 4h in a mixture gas of N2, H2 and C2H5OH. The surface phase compositions of the specimens were analyzed using X-ray diffractometer. The grain shape and size, and grain boundaries in the subsurface layers of the samples were characterized by electron backscattering diffraction and transmission electron microscopy. The results show that the nitrocarburized layers are composed of α-Fe, γ′-Fe4N and FeN0.049 phases. Most α-Fe and γ′-Fe4N grains show in columnar shape. The major and minor axes of some α-Fe grains are elongated and shortened after nitrocarburizing, respectively. In the subsurface layers of the untreated and nitrocarburized specimens, the average areas of γ′-Fe4N and α-Fe grains both with a dimension of nanometer are 0.395μm2 and 0.397μm2, respectively. The γ′-Fe4N grain boundaries are mainly high angle boundaries with a very small fraction of low angle boundaries. Coincidence site lattice boundaries in the subsurface layer of the untreated specimen are composed mainly of Σ3, Σ11 and Σ13b, and their fraction decreases after nitrocarburizing.

Influence of Vacuum Heat Treatment and Salt-Bath Nitrocarburization on the Corrosion Behavior of JIS SKD61 and DH31S Hot Work Steels

The corrosion behavior of the nitrocarburized JIS SKD61 and DH31S hot work steels has been investigated. The as received JIS SKD61 and DH31S steel was quenched and tempered to obtain the tempered martensitic microstructure. The nitrocarburizing treatment was conducted in a 570°C salt bath for 40, 80, and 120 minutes, respectively. Treated specimens were characterized by means of microstructural analysis, microhardness measurements, X-ray diffraction analysis, glow discharge spectrometer analysis and electrochemical tests in a 3.5wt% NaCl aerated solution. The thickness of compound layer of nitrocarburized specimens was about 1-3μm, and the microhardness is in the range between 790 – 820 HV0.05. The compound layer of the nitrided specimen was consisted of ε-phase (Fe2-3N) and the γ’-phase (Fe4N). The highest corrosion potential (Ecorr) in this study reached to -0.3 V for NC-S80 and NC-H80 specimen, it’s about 1.5 times higher than that of ferrite substrate. There is no evident difference on corrosion current density (Icorr) with prolonging nitrocarburizing treatment for both steels. Nevertheless, the corrosion properties were improved by nitrocarburizing process.

Martensitic stainless steel modified by plasma nitrocarburizing at conventional temperature with and without rare earths addition

17-4PH Martensitic stainless steel was plasma nitrocarburized at conventional temperature (560 °C) with and without rare earths (RE) addition. The surface treated layers were characterized by optical microscope, scanning electron microscope equipped with an energy dispersive X-ray analyzer, X-ray diffraction and microhardness test. The wear and corrosion behavior of the modified specimens was studied respectively using pin-on-disc tribometer and anodic polarization tests. The results show that rare earths atoms can diffuse into the surface of the stainless steel. The microstructures of all modified layers are characterized by a compound layer containing three distinct zones but without an evident diffusion zone. The phases on all modified surface layers are mainly of θ-Fe 3C and CrN. It is exciting that the hardness profile of the modified layer is decreased gradually, which is rarely found in plasma nitriding of the stainless steel. The friction coefficient of a specimen can be dramatically decreased by plasma RE nitrocarburizing, whereas the corrosion resistance is deteriorated. In contrast, the corrosion resistance of a plasma nitrocarburized specimen is enhanced but the friction coefficient is not improved as much as that of a plasma RE nitrocarburized one.

Microstructure and mechanical properties of 17-4PH steel plasma nitrocarburized with and without rare earths addition

17-4PH stainless steel was plasma nitrocarburized at 500 °C with and without rare earths (RE) addition. The nitrocarburized layers were characterized by optical microscope, scanning electron microscope equipped with an energy dispersive X-ray analyzer, X-ray diffraction, hardness tests and pin-on-disc tribometer. The results show that rare earths atoms can diffuse into 17-4PH steel surface and change the microstructure of the nitrocarburized layer. The incorporation of RE elements increases the layer thickness and the hardness of the nitrocarburized layer up to 29% and 70–120 HV, respectively. The friction coefficients and wear rates of the nitrocarburized specimens are apparently lower than that of un-nitrocarburized one. The wear mechanisms of steel specimen plasma nitrocarburized with and without RE addition are different mainly due to the differences in the microstructure, the phase proportion and the hardness of the modified layer.

Erosion and wear behavior of nitrocarburized DC53 tool steel

The influence of nitrocarburizing holding time on the slurry erosion and wear behavior of DC53 tool steel has been studied. DC53 tool steel was nitrocarburized at 570°C for 2, 4, and 6h. The microstructures and hardnesses of the nitrocarburized coatings were analyzed. The erosion-behavior test was conducted using a slurry jet at different impinging angles. Wear behavior was examined on a block-on-roller wear tester under unlubricated conditions. The surface roughness was also measured.The results show that white compound layers are composed mainly of ɛ-nitride (Fe3N) and a small amount of γ′-nitride (Fe4N). The nitrocarburizing treatment not only increases the hardness but also decreases the friction coefficient of the specimen. Furthermore, the erosion rate and the wear loss of the nitrocarburized specimen decrease. The anti-wear property of the nitrocarburized specimen is found to relate to the increase in the depth of the diffusion zone. The maximum erosion rate appears at an impinging angle of 30° for all specimens. In this condition, plough grooves and cutting lips appear in the eroded surface; however, the traces of erosion on the untreated specimen are wider and deeper. After nitrocarburizing, the severe adhesive wear is replaced by a much milder abrasive wear. As the nitrocarburizing holding time increases the erosion rate decrease, but the wear properties including the wear loss, friction coefficient, wear mechanism and the width of the abrasion grooves do not change significantly.

Improving the mechanical properties of 17-4PH stainless steel by low temperature plasma surface treatment

17-4PH stainless steel was plasma nitrocarburized at low temperature for improving its mechanical properties. The results show that the modified layer thicknesses increase with increasing treatment time and the layers growth approximately conforms to the parabolic law. The phases in the modified layers are mainly of incipient γ′-Fe 4N and α′-Fe with amorphous characterization, and then changed into γ′-Fe 4N, α′ N and traces of CrN with the treatment time increasing. The hardness of the nitrocarburized specimen is more than 1280 HV, which is about 3.5 times as hard as the untreated one. Meanwhile, the wear resistance of the steel specimen can be dramatically improved by plasma nitrocarburizing. The surface hardness and the wear resistance of the nitrocarburized specimens slightly decrease with an increase in treatment time for the surface hardness as well as microstructure changing.

Microstructure and properties of 17-4PH steel plasma nitrocarburized with a carrier gas containing rare earth elements

The effect of rare earth addition in the carrier gas on plasma nitrocarburizing of 17-4PH steel was studied. The microstructure and crystallographically of the phases in the surface layer as well as surface morphology of the nitrocarburized specimens were characterized by optical microscope, X-ray diffraction and scanning tunneling microscope, respectively. The hardness of the surface layer was measured by using a Vickers hardness test. The results show that the incorporation of rare earth elements in the carrier gas can increase the nitrocarburized layer thickness up to 55%, change the phase proportion in the nitrocarburized layer, refine the nitrides in surface layer, and increase the layer hardness above 100HV. The higher surface hardening effect after rare earth addition is caused by improvement in microstructure and change in the phase proportion of the nitrocarburized layer.

Effect of Nitrocarburizing Time on the Microstructures and Erosion Behavior of Cold-work Tool Steel

In this study we examined the influence of nitrocarburizing holding time on the surface microstructures and erosion behavior of JIS SKD11 modified cold-work tool steel (DC11 tool steel). The steel was nitrocarburized at 570°C for varying durations of 1, 3, and 5 h. The microstructures and hardness of the nitrocarburized coatings were then analyzed. Particle erosion was examined at different impinging angles (15–90°) and impact speeds (20.2–45.6 m/s).The results show that a single diffusion zone is formed on the specimens at 1 h nitrocarburizing while a compound layer together with diffusion zone are formed on the specimens for the nitrocarburizing time beyond 3 h. In addition, the compound layer formed on the specimens exhibits a higher erosion resistance. The nitrocarburizing treatment not only increases the surface hardness but also improves the erosion resistance of the experimental steel. This improvement in erosion rates is more obvious at higher impact speeds and lower impinging angles. The maximum erosion rate appears at an impinging angle of 30° for all specimens. In this condition, plough grooves and cutting lips appear in the eroded surface; however, the erosion tracks are more superficial for nitrocarburized specimens than untreated specimen. The exponent in the power law Ė=kVn varied between 1.9–2.3 for impinging angles between 15° and 90°.

熱間ダイス鋼における軟窒化拡散層のＴＥＭ組織観察

Nitriding, which includes nitrocarburizing, is the most popular surface treatment in order to prolong durability of hot working die steels. However, it has not been elucidated that either precipitation hardening or solid solution hardening caused the hardening mechanism of the nitriding. In this work, the morphology of nitrogen in a diffusion layer of Fe-C-Si-Mn-Cr in a practical nitrocarburizing condition was investigated by transmission electron microscopy and X-ray diffraction in order to elucidate the influence of Cr on the hardening mechanism in the nitrocarburizing. In the diffusion layer of the nitrocarburized specimens, precipitation of CrN was identified regardless of the amount of Cr contents. The crystal structure of CrN was confirmed as a cubic B1 type and has Baker-Nutting orientation relationship with martensite. Besides, the lattice constant of martensite in the diffusion layer measured by X-ray diffraction was still similar to that of the unnitrided zone. Those results show that the major contribution of nitrogen to the hardening in the diffusion layer is precipitation hardening as CrN, and the contribution to the solid solution hardening is small. And increasing Cr contents enhanced the CrN precipitation and the hardness of the diffusion layer, although the diffusion layer shrank.

Frictional behaviour of oxide films produced on S45C steel by plasma nitrocarburizing and post plasma oxidation treatment

The frictional behavior of oxide films on top of the plasma nitrocarburized compound layers was investigated in terms of post-oxidation treatment temperatures. The post-oxidation treatment at both temperatures(<TEX>$400^{\circ}C,\;500^{\circ}C$</TEX>) produced magnetite(<TEX>$Fe_3O_4$</TEX>) films which led to a significant enhancement in corrosion resistance. However, this process did not result in any improvement in frictional behavior of the nitrocarburized surface. The wear mechanisms were governed predominantly by the abrasive action of the slider on the surface irrespective of the counterface material(SiC and Bearing steel). When the specimen was sliding against a SiC counterface, the oxide films were destroyed during the early stage of the sliding process and the wear debris of the oxide film at the sliding track had a great influence on the friction coefficient. On the other hand, when sliding against a bearing steel counterface, the slider was mainly worn out due to the much higher hardness of the surface hardened layer. The fluctuation of the friction coefficient of <TEX>$400^{\circ}C$</TEX>-oxidized/ nitrocarburized specimen is much severer than that of <TEX>$500^{\circ}C$</TEX> specimen, due to the less amount of wear debris.

Influencia del acabado superficial sobre el comportamiento tribológico de capas nitrocarburadas en acero X40CrMoV5 1

In this work the surface roughness behaviour in the forming of gaseous nitrocarburized layers has been analyzed. Ra values from 0.02 to 1.50 μm. has been considered. Obtained results prove a minor influence on layer thickness. A little increase of Ra has been observed. The abrasive wear resistance of nitrocarburized specimens was researched. The carbonitride e is the only constituent in the about 6 μm thickness layers that have been carried out in this work. The tests revealed a minor wear resistance of the external part in the layers. This way, the external zone is less effective to wear phenomena than the internal. The specimens with small roughness parameters values show a higher poor wear resistance zone.

Effect of CH 4 addition on plasma nitrocarburizing of austenitic stainless steel

This article evaluates the influence of the plasma atmosphere composed of different ratios of N 2/H 2/CH 4 on the micro-structures, wear resistance and corrosion resistance of 304L and 316L austenitic stainless steels. DC power with a bias voltage in the range of 250–350 V was applied between the vessel (anode) and the work (cathode). The results show that the thickness of the hardened layers decreased with increasing methane addition and dramatically decreased when methane addition reached 5%. The wear resistance behavior was significantly improved, especially in the nitrocarburized specimens. The corrosion resistance of nitrided and nitrocarburized layers, in general, as inferior to that of the bare materials when they were tested in an imitation gastric juice. However, the specimen of 304L nitrocarburized with 5% addition of CH 4 exhibited excellent improvement to corrosion resistance, even better than the bare material. This excellent corrosion resistance is attributed to the formation of chromium nitrides and chromium carbides, such as CrN, Cr 7C 3 and Cr 2N instead of Fe 4N.

Wear behavior of nitrocarburized JIS SKD61 tool steel

The surface wear characteristics of the nitrocarburized JIS SKD61 tool steel were investigated. The ferritic substrate (FS) JIS SKD61 tool steel as received was pretreated in quenching and tempering processes to obtain the tempered martensitic microstructure. Specimens were then nitrocarburized for 1, 3, and 5 h. The chemistry, microstructure, and hardness of the nitrocarburized coatings were analyzed. Wear behavior was examined on a block-on-roller wear tester under unlubricated conditions. The results have shown that white layers were predominantly composed of the ϵ-phase iron nitrides dispersed with γ′-phase, and a large amount of nitrogen and carbon trapped in the ferrite phase was observed in the diffusion layer for FS. The nitrocarburizing treatment increased the surface roughness, hardness and the friction coefficients of the specimens. Wear contact pressures and nitrocarburized holding time also affected the friction coefficients of the nitrocarburized specimens. In this study, both the FS and the tempered martensitic substrate (TMS) specimens treated with subsequent nitrocarburizing process have shown significant improvement of the wear resistance. Wear behaviors of the specimens nitrocarburized for 1, 3, and 5 h did not vary significantly.

Microstructure and tribological properties of complex nitrocarburized steel

Two kinds of tribological apparatus were employed to investigate the friction and wear performance of steel 1045 treated by quenching plus tempering and complex nitrocarburizing processes. The microstructures, phase identification, surface hardness and hardness profiles of the specimens were analyzed by optical metallography, microhardness tests and X-ray diffraction; at the same time the surface roughness of specimen surfaces was tested using a profilometer. The experimental results show that: the ε-phase formed on the specimen surface has a significant effect on reducing the friction coefficient and improving wear resistance; the oxidation after nitrocarburizing rarely changes the friction coefficient but decreases the wear resistance; and with oxidation plus polishing and secondary oxidation complex treatments being performed, the wear resistance of nitrocarburized specimens is improved even further.