Low Temperature Plasma Carburizing Research Articles

Slurry and liquid impingement erosion behavior of low-temperature plasma carburized AISI 420 martensitic stainless steel

The impact of plasma carburizing treatment on the erosion wear resistance of AISI 420 martensitic stainless steel (MSS) was studied. Experiments were carried out varying a broad spectrum of erosion parameters, including impact velocity, impact angle, and exposure duration. Both slurry and liquid impingement erosion were employed in the experiments, with testing conducted using both distilled water and saline solutions to assess the combined effects of corrosion and erosion wear. Compared to untreated samples, a significant improvement in the erosion wear resistance of AISI 420 MSS due to low-temperature plasma carburizing treatment was observed for all tested conditions. The observed performance enhancement can be attributed to the formation of the carburized layer, constituted of the α'C and Fe3C phases. Results also highlighted that the severity of the tribosystem was significantly influenced by the test solution characteristics. A marginal increase in severity was observed upon introducing the saline solution, while a more substantial severity increase occurred with the addition of solid particles in the test fluid. The specimens' mass loss was increased by increasing impact velocity, following a simple potential relationship, and with impact angle, following a first-degree linear equation. In the case of the exposure time, the mass loss curves depended on the test environment. For solutions containing quartz particles, an additional final stabilization stage was observed in addition to the acceleration stage observed in the absence of abrasive component. This phenomenon was attributed to surface work hardening induced by the impact of solid particles. Regarding wear mechanisms, samples tested only with distilled water displayed erosion flow marks. Those containing distilled water and NaCl exhibited not only flow marks but also pits. Lastly, solutions containing solid particles additionally presented features of plastic deformation, lip formation, craters, indentations, and extruded material.

Effect of frictional treatment and low temperature plasma carburizing on the microhardness and electromagnetic characteristics of metastable austenitic steel

Microhardness and electromagnetic characteristics of corrosion-resistant chromium-nickel (wt. %: 16.80 Cr; 8.44 Ni) austenitic steel subjected to electron beam plasma carburizing at temperatures of 350 and 500°C, frictional treatment with a sliding indenter and combined treatments, including frictional treatment and plasma carburizing have been investigated. It has been found that plasma carburizing increases the microhardness of the steel surface from 200 to 1100 HV0.025. The total hardening depth was 25 microns after carburizing at T = 350°C and 300 microns after carburizing at T = 500°C. Frictional treatment increases the microhardness of the steel to 600 HV0.025 with a total hardening depth of 500 microns. It has been shown that the diffusion-active layer with a dispersed structure formed during preliminary frictional treatment contributes to additional hardening of the steel (up to 1275 HV0.025) during subsequent low-temperature (350°C) carburizing. Combined treatment with carburizing at a temperature of 500 °C increases the microhardness of the steel to 820 HV0.025, and the total hardening depth is 500 microns for both combined treatments. It has also been found that plasma carburizing of the steel leads to a decrease in the eddy-current readings compared to the quenched steel and their growth compared to the steel subjected to frictional treatment, which can be used to develop quality control techniques for such treatments.

The Influence of Frictional Treatment and Low-Temperature Plasma Carburizing on the Microhardness and Electromagnetic Properties of Metastable Austenitic Steel

The Influence of Frictional Treatment and Low-Temperature Plasma Carburizing on the Microhardness and Electromagnetic Properties of Metastable Austenitic Steel

Effects of Solid-Solution Carbon and Eutectic Carbides in AISI 316L Steel-Based Tungsten Carbide Composites on Plasma Carburizing and Nitriding

AISI 316L stainless-steel-based tungsten carbide composite layers fabricated via laser metal deposition are used for additive manufacturing. Heat treatment practices such as low-temperature plasma carburizing and nitriding improve the hardness and corrosion resistance of austenitic stainless steels via the formation of expanded austenite, known as the S phase. In the present study, practices to enhance the hardness and corrosion resistances of the stainless-steel parts in the composite layers have been investigated, including single plasma carburizing for 4 h and continuous plasma nitriding for 3.5 h following carburizing for 0.5 h at 400 and 450 °C. The as-deposited composite layers contain solid-solution carbon and eutectic carbides owing to the thermal decomposition of tungsten carbide during the laser metal deposition. The eutectic carbides inhibit carbon diffusion, whereas the original solid-solution carbon contributes to the formation of the S phase, resulting in a thick S phase layer. Both the single carburizing and continuous processes are effective in improving the Vickers surface hardness and corrosion resistance of the composite layers despite containing the solid-solution carbon and eutectic carbides.

Growth of Fe3C-VACNT surfaces by metal dusting under plasma carburizing: Fractional factorial study and correlation with morphological and structural aspects

This study investigates the development of surfaces that combine wear-resistance and solid lubrication properties using single low-temperature plasma carburizing treatments associated with the metal dusting phenomenon. The surfaces consisted of a regular cementite (Fe3C) layer and a film composed by vertically aligned carbon nanotubes (VACNT) grown over the carburized layer. For that, specimens of AISI 1005 steel were used as a substrate. A fractional factorial design of experiments was conducted to identify the best processing conditions to achieve the required Fe3C-VACNT surfaces. Morphological and structural aspects of the surfaces were assessed by scanning and transmission electron microscopy, X-ray diffraction, and Raman spectroscopy. The results show that the carburizing performed between 600 and 700 °C and with plasma power densities ≥0.30 W/cm2 were effective for developing the bilayer surfaces. A signature of that process was a temporal increase of the plasma current. According to a created statistical model, the most influential experimental parameters in the average power plasma density were output voltage, %CH4 in the gas mixture, and duty cycle. The surfaces were able to reduce the friction coefficient to values down to 0.08 and decrease the wear rate by 25 to 70 %, depending on their characteristics.

The Influence of Frictional Treatment and Low-Temperature Plasma Carburizing on the Structure and Phase Composition of Metastable Austenitic Steel

The features of the structure and phase composition of corrosion-resistant austenitic chromium–nickel steel (16.80 wt % Cr, 8.44 wt % Ni) subjected to carburizing in electron beam plasma at temperatures of 350 and 500°C, frictional treatment with a sliding indenter, and a combination of frictional treatment and plasma carburizing have been considered. It has been established that plasma carburizing results in the formation of a modified surface layer consisting of carbon-saturated austenite and carbides (Cr23C6, Fe3C); in this case, the formation of γC-phase occurs only at a temperature of 350°C. The depth of a modified layer increases with an increase in the carburizing temperature. It has been shown that it is useful to perform combined frictional treatment and plasma carburizing at a carburizing temperature of 350°C, since in this case the deformation-induced structure formed as a result of frictional treatment is preserved, and the precipitated carbides remain highly dispersed. In this case, frictional treatment should provide the formation of the deepest possible diffusion-active layer with a dispersed structure.

Galling-Free Fine Blanking of Titanium Plates Using Carbon-Supersaturated High-Speed Steel Punch

A carbon-supersaturated (CS-) high-speed steel punch was prepared using low-temperature plasma carburizing for fine blanking of pure titanium plates. The bare high-speed steel punch was also prepared as a reference to describe the adhesion and abrasive galling in the fine blanking of the titanium plates, even in a single shot. The CS-punch was free from severe chemical galling, even after repeatedly fine-blanking the pure titanium plates. A microstructure analysis, element mapping and a chemical composition analysis demonstrated that titanium debris fragments slightly deposited at the CS-punch edges in the presence of agglomerated free-carbon film due to the CS-punch. This galling-free fine-blanking behavior came from the in situ formation of free carbon tribofilms. This in situ lubrication resulted in the completely burnished surfaces of pure titanium blanks.

Effect of low-temperature plasma carburizing on surface topography, mechanical and tribological properties of sintered iron and nitrided sintered iron

This study investigated the effect of a low-temperature carburized layer on the topography, mechanical and tribological properties of sintered and nitrided sintered iron. Two nitride layers (γ’-Fe4N and ε-Fe2–3N) were produced by plasma nitriding. Subsequently, low-temperature plasma carburizing was used to develop a cementite layer over the samples. The carburized layer increased H/E* and H3/E*2 of the sintered iron more effectively than the nitride layers. The cementite layer improved the wear resistance of the iron by 45%, statistically similar to the γ ´ nitride layer. Postcarburizing enhanced the mechanical properties of the nitrided iron due to the formation of a duplex layer. However, the presence of pores at the interfacial region of the duplex layers induced a brittle wear mechanism.

Formation and Properties of Nitrocarburizing S-Phase on AISI 316L Stainless Steel-Based WC Composite Layers by Low-Temperature Plasma Nitriding

Stainless steel-based WC composite layers fabricated by a laser cladding technique, have strong mechanical strength. However, the wear resistance of WC composite layers is not sufficient for use in severe friction and wear environments, and the corrosion resistance is significantly reduced by the formation of secondary carbides. Low-temperature plasma nitriding and carburizing of austenitic stainless steels, treated at temperatures of less than 450 °C, can produce a supersaturated solid solution of nitrogen or carbon, known as the S-phase. The combined treatment of nitriding and carburizing can form a nitrocarburizing S-phase, which is characterized by a thick layer and superior cross-sectional hardness distribution. During the laser cladding process, free carbon was produced by the decomposition of WC particles. To achieve excellent wear and corrosion resistance, we attempted to use this free carbon to form a nitrocarburizing S-phase on AISI 316 L stainless steel-based WC composite layers by plasma nitriding alone. As a result, the thick nitrocarburizing S-phase was formed. The Vickers hardness of the S-phase ranged from 1200 to 1400 HV, and the hardness depth distribution became smoother. The corrosion resistance was also improved through increasing the pitting resistance equivalent numbers due to the nitrogen that dissolved in the AISI 316 L steel matrix.

Low-pressure hollow cathode plasma source carburizing technique at low temperature

A low-pressure hollow cathode plasma source carburizing was developed as a novel surface treatment technique based on the active screen plasma carburizing combined with hollow cathode sources. The cylindric cathodic cage with array holes was made of pure graphite, where the hollow cathode graphite tubes were inlaid on. A pulsed high voltage power with a peak voltage of 800 V and a pulse frequency of 30 kHz was supplied to ignite the hollow cathode discharge inside graphite tubes at a low pressure less than about 300 Pa using a gas mixture of CH 4 + 90%H 2 . The hollow cathode plasma source together with the pulsed high voltage power realized a high biasing current on the carburized samples at low pressure, and produced an enhanced heating except the thermal radiation by the cathodic cage. The graphite cathode as a carbon source besides the gas precursor provided an additional carbon potential. The AISI 304L austenitic stainless steel was carburized at a low temperature of 450 °C for a treatment time of 6 h with a bias of 200 V under the carburizing pressure of 50 Pa and 300 Pa, respectively. It was observed that the carburizing case at 50 Pa was about 13 μm with a higher surface carbon concentration of about 6.5 at.% and a higher hardness of about HV 0.25 N 8.5 GPa compared with that at 300 Pa. The carbon-expanded austenite (γ C ) phase was observed by the x-ray diffraction of both the carburizing cases. The metastable high carbon carbide Fe 5 C 2 only appeared at 50 Pa, which was attributed to high carbon potential at the lower pressure. Therefore, an increased carburizing efficiency at the low temperature was obtained by the low-pressure hollow cathode plasma source carburizing technique using a pulsed high voltage power. • Hollow cathode plasma source is utilized in low temperature plasma carburizing. • Pulsed high voltage is used in graphite hollow cathode discharge at low pressure. • High sample biasing current with enhanced heating is realized by plasma source. • Graphite cathode provides additional carbon potential besides the gas precursor. • Thick carburizing case with metastable carbide and high hardness is obtained.

Sequential low-temperature plasma-assisted thermochemical treatments of the AISI 420 martensitic stainless steel

The application of low-temperature plasma carburizing (C), nitriding (N) and nitrocarburizing (NC) treatments in sequential steps on AISI 420 martensitic stainless steel was investigated through nine different treatments. Experiments were performed at 400 °C, being divided in three (8 h)-single treatments, namely C, N and NC, and six distinct (4 h + 4 h)-sequential treatments, namely C + N, N + C, C + NC, N + NC, NC + N, and NC + C, using appropriate gas mixtures for each treatment step. Sequential treatments promoted the formation of treated layers constituted of iron carbides/nitrides, chromium nitrides, and nitrogen/carbon-expanded martensite phases. Interesting results were obtained for both C + N and C + NC sequential treatments, whose application results in greater hardening depths (~20% thicker) and leads to ~40% increase on the surface hardness, when compared to the obtained for the single C treatment keeping a smooth hardness profile. From the microstructural characterization, no significant sensitization was evidenced in the outer layers obtained for all treatments comprising the carburizing step, an indicative result that the interstitial carbon retards the chromium-rich particles precipitation kinetics. The combination of N + NC treatments produced thicker and harder treated cases compared to those produced by the respective single treatments. In brief, results showed that the appropriate selection of thermochemical treatments' sequence can promote increased treatments efficiency concerning the treated layers thickness or effective surface hardness. This work also contributes to the validation of the presented processing approach, proving its advantages over single thermochemical treatments.

Effects of mould wear on hydrophobic polymer surfaces replicated using plasma-treated and laser-textured stainless steel inserts

ABSTRACT The mass production of polymeric parts with functional surfaces requires economically viable manufacturing routes. Injection moulding is a very attractive option, however, wear and surface damage can be detrimental to the lifespan of replication masters. In this research, austenitic stainless steel inserts were hardened by low temperature plasma carburising and then different micro and nano scale surface textures, inspired by Lotus leaves and Springtail skins, were laser fabricated. A commonly available talc-loaded polypropylene was used to produce 5000 replicas and thus to investigate the evolution of surface textures both on inserts and replicas together with their functional response. The progressive wear or surface damage on the inserts during the injection moulding process had a clear impact on surface roughness and peak-to-peak topographies of the replicas. In general, polymer replicas produced with the carburised inserts retained wetting properties for longer periods compared with those produced with the untreated replication masters.

Improvement of mechanical properties and corrosion resistance of 316L and 304 stainless steel by low temperature plasma cementation

Low temperature plasma carburizing treatment of austenitic stainless steels is a carbon surface diffusion process for a surface hardness and corrosion and wear resistance. The process is carried out by introducing a mixture of carbon-containing gases and through the use of low temperatures the resulting cemented layer usually contains a single phase of supersaturated austenite with carbon – S-phase. For the present investigation, austenitic stainless steels AISI 316L and 304 were plasma cemented for 8 hours in the gas mixture containing 7.5% CH4 in H2, with a pressure of 500 Pa, at temperatures of 375 oC and 450 oC. The phases formed were determined by X-ray diffraction. The corrosion resistance was evaluated through immersion tests over time and cyclic voltammetry. The results indicate that there was no formation of compounds (carbides) in the cemented layer for both steels at any of the temperatures and there was a corrosion resistance improvement. Keywords: plasma carburizing, AISI 304, AISI 316L, corrosion.

AISI 420 martensitic stainless steel corrosion resistance enhancement by low-temperature plasma carburizing

Corrosion resistance of plasma carburized AISI 420 martensitic stainless steel was evaluated by cyclic polarization test in 3.5% NaCl solution. Two distinct treatment groups were studied with the purpose of evaluating the influence of the carburizing temperature and time on the corrosion behavior of treated material (one at 350–500 °C temperature range for 8, and 12 h times; and other one at 400 °C for 12–48 h time range, and at 450 °C for 4–16 h time range). To support the discussions on electrochemical test results, microstructural characterization was carried out using metallographic analysis and XRD techniques. Microstructural characterization results show that low temperature and short time treatments produce outer layer composed by α′C and Fe3C phases. High temperature and/or long time treatments promote outer layer Cr7C3 and Cr23C6 phases precipitation. Corrosion test results show improved carburized samples resistance, which is related to chromium-carbides precipitation-free outer layer formation. The Cr-carbides formation promotes a reduction on carburized samples corrosion resistance due to depletion of Cr in the solid solution of carburized layer. Finally, by confronting the behavior of untreated and carburized samples, it is verified the potentialities of the low-temperature plasma carburizing to enhance the corrosion resistance of AISI 420 MSS.

Effects of Thermochemical Surface Treatments on the Industrially Important Properties of X2CrNiMo 17-12-2 Austenitic Stainless Steel

Austenitic stainless steels have low corrosion resistance in applications where strong acids and vapors attack the surface, typically in food and chemical industries. This drawback can be improved by surface treatments. Salt bath, gaseous or plasma-based surface treatments are a diffusion process for improving the hardness of the surface layer of stainless steels without significantly affecting their corrosion resistance. Low temperature nitriding and carburizing process can form a diffusion zone or/and compound phase. The corrosion-wear resistance of austenitic stainless steels can also improve with low temperature plasma nitriding and carburizing. The effect of these treatments on hardness and corrosion resistance was investigated in this research. Optical microscopy and Vickers hardness test were used for the characterization of the surface and potentiodynamic tests were performed to determine the corrosion rate. The results show that the hardness of the kolsterised sample is higher compared to the plasma nitride one. Beside this property, the corrosion rate is similar, but pitting corrosion was observed on the surface, due to the Cr2N formation.

Cavitation erosion resistance enhancement of martensitic stainless steel via low-temperature plasma carburizing

This work presents the potential of low-temperature plasma carburizing treatments for improving the cavitation erosion resistance of martensitic stainless steel (MSS). As-hardened AISI 420 MSS samples were treated via dc plasma carburizing at 450 °C for 12 h. The cavitation erosion behaviors were compared with that of an untreated steel sample tempered at 220 °C for 1 h. Cavitation erosion tests were performed with an ultrasonic vibratory apparatus in accordance with the ASTM G32-10 standard. The nominal incubation period of the carburized samples was approximately three times higher than that of the untreated sample (23 h versus 7.8 h, respectively). The cavitation erosion behavior was discussed in terms of mechanical surface properties (hardness (H) and elastic modulus (E)) obtained via the nanoindentation technique and respective H/E, H2/E, and H3/E2 ratios.

Characteristics of AISI 420 Stainless Steel Modified by Low-Temperature Plasma Carburizing with Gaseous Acetone

In this research work, low-temperature carburizing of AISI 420 martensitic stainless steel was conducted at 460 °C for different amounts of time using an acetone source. The microstructure and phase structure of the carburized layers were characterized by optical microscope and X-ray diffraction. The properties of the carburized layers were tested with a microhardness tester and an electrochemical workstation. The results indicate uniform layers are formed on martensitic stainless steel surfaces, and the carburized layers are mainly composed of carbon “expanded” α (αC) and Fe3C phases. The property tests indicated that after plasma–carburizing, the hardness of the stainless steel surface can reach up to 850 HV0.1. However, the corrosion resistance of stainless steel decreased slightly, and the corrosion characteristic of stainless steel was altered from pitting to general corrosion. The semiconductor characteristic of the passivation film on stainless steel was transformed from the p-type for untreated specimens to the n-type for carburized specimens.

Expanded Austenite Phase Formed by Low-Temperature Plasma Carburizing of Austenite Stainless Steel and Its Sliding Characteristics

Expanded Austenite Phase Formed by Low-Temperature Plasma Carburizing of Austenite Stainless Steel and Its Sliding Characteristics

Martensite coarsening in low-temperature plasma carburizing

This work shows microstructural evidences of morphological transformation from as-hardened martensite to C-expanded martensite as a result of the low-temperature plasma carburizing treatment carried out in AISI 420 martensitic stainless steel. Treatments were carried out at different treatment temperatures (350, 400, 450, and 500 °C, for a 12 h fixed time) and times (12, 24, 36, and 48 h, at 400 °C fixed temperature). Confocal laser scanning microscopy and SEM results show martensite coarsening in the treated surfaces regarding the respective substrate bulks, which is related to the surface C-alloying, thus being dependent on the treatment time and temperature. Hardness measurement and XRD results strongly suggest that the martensite coarsening is related to the transformation from lath- to plate-type martensite due to the enhancement of the martensite C content, in accordance with the Zener ordering theory. For samples carburized at relatively low temperatures (namely 350, and 400 °C), as C diffuses in paraequilibrium, strain-induced transformation mechanism would govern the changes in the initial martensite morphology as a result of its C content increase. On the other hand, as the chromium carbide precipitation occurs for samples treated at relatively high temperatures (higher than 450 °C for 12 h), and long times (longer than 36 h at 400 °C), C atoms would leave the supersaturated (expanded) martensite phase solid solution, leading the plate martensite to transform back to lath martensite.

A Methodology for Fabrication of Highly Pitting Corrosion-Resistant Type 304 Stainless Steel by Plasma Carburizing and Post-Pickling Treatment

Low temperature plasma carburizing was performed to improve the pitting corrosion resistance of Type 304 stainless steel. The optimal composition of the plasma gas and post-treatment were then examined. Carburizing was carried out for 18 ks at 470°C in H2-CH4, Ar-H2-CH4 or Ar-CH4 plasma, and carburized layers ca. 9 μm in thickness with an average ca. 1.3 mass% carbon concentration were obtained. However, it was found that Cr23C6 was precipitated in the carburized layer and intergranular corrosion occurred under anodic polarization in 0.1 M NaCl. The precipitation behavior of Cr23C6 differed according to the plasma gas composition: H2 gas was found to suppress the size of Cr23C6. No Cr23C6 was precipitated in the inner part of the carburized layer formed in the H2-CH4 plasma, and no stable pit was initiated on the inner parts of the carburized layer under anodic polarization in 0.1 M NaCl. Pickling treatment using HF-HNO3 was applied to remove the Cr-depleted zones in the outer part of the plasma carburized layer. The Type 304 stainless steel after the plasma carburizing in the H2-CH4 atmosphere and subsequent the HF-HNO3 pickling exhibited no pitting corrosion under anodic polarization even in 3 M NaCl at 25°C.