Effect Of Carburization Research Articles

Effect of the promoters on oxidation behavior of Fe-based Fischer-Tropsch catalyst: Deciphering the role of H2O

The effect of carburization and reduction degree on H2O oxidation behaviour for the iron carbides in Fe-based FTS catalyst were firstly investigated using a combination method including X-ray diffraction (XRD), Raman and temperature-programmed-hydrogenation (TPH). The relationship between carbon species transformation and H2O oxidation behaviour of iron carbides was investigated simultaneously. Based on these observations, the influence of typical promoters like K and SiO2 on the structure and H2O oxidation behaviour of Fe-based FTS catalysts was further studied. The results indicated that, for the iron catalyst, the stability of iron carbides against H2O oxidation was increased with the increase of iron carbides content, and the H2O oxidation process led to the formation of more graphitic carbon. The carburization ability was effectively enhanced when certain amount of K promoter was incorporated. Addition of K into Fe-based FTS catalyst increased the number of graphitic carbons, which increased the stability of iron carbides toward H2O oxidation ultimately. It was also found that promotion of SiO2 greatly degraded the carburization degree of the catalyst, while their tendency to be oxidized to form Fe3O4 in the H2O atmosphere was obviously hindered.

Effect of vacuum carburizing on surface properties and microstructure of a tungsten heavy alloy

Vacuum carburizing of the R2M tungsten alloy was carried out to obtain a carburized layer that improves the surface properties. The effects of various carburizing temperatures and times on the structure and hardness were studied by Optical microscopy(OM), x-ray Diffraction(XRD) and Scanning electron microscope(SEM). In this work, the microstructure of the carburized layer, the relative content of the surface layer, the depth of the layer and the microhardness of the carburized sample were studied. The results show that the microstructure exhibited three layers from the surface to the bulk of the sample after carburizing. The outside layer comprised a 40 ∼ 60 μm deep WC carburized layer. The hardness of the surface layer (396 HV) was significantly higher than that of the substrate (282 HV). As the carburizing temperature and time increased, the WC and W content of the surface layer of the sample gradually increased, and the depth of the carburized outer layer increased.

Structure and Surface Properties of Metastable Austenitic Steel Subjected to Liquid Carburizing at a Reduced Temperature

This work investigates the effect of liquid carburizing at 780°C on the structure, chemical and phase composition, microhardness, and surface roughness of corrosion-resistant austenitic chromium-nickel steel. The depth of the carburized layer has been determined to be about 2 mm. The steel structure at a distance of 0.15 mm from the surface consists of carbon-saturated austenite γC, α' martensite, and fine Cr23C6 chromium carbides located along austenitic grain boundaries. No carbides are observed in the grain body. There are austenite γC and chromium Cr23C6 carbides in the structure at a depth from 0.15 to 2 mm. The number and the size of carbides decrease with distance from the steel surface. Carburizing increased the microhardness of the steel surface by a factor of four (from 200 to 800 HV0.025) and the roughness parameter Ra to 1.35 μm.

Влияние низкотемпературной цементации в плазме электронного пучка на упрочнение и шероховатость поверхности метастабильной аустенитной стали

Влияние низкотемпературной цементации в плазме электронного пучка на упрочнение и шероховатость поверхности метастабильной аустенитной стали

The Effects of Carburization on the Fatigue Crack Growth Behaviors of Local Surface Cracks in Cylindrical Bars

In this study, a series of fatigue tests were conducted on C45 steel specimens with local surface cracks. The effects of carburizing treatment with different case depths were discussed under cyclic tensile and torsional loading. Moreover, the surface crack extension paths and crack propagation rates were discussed. In addition, the effects of additional static torsion under cyclic tensile loading and additional static tension under cyclic torsional loading were analyzed, and comparisons were made between the results of the carburized materials and those of the uncarburized materials. Some conclusions show that carburization can effectively retard crack extension and improve fatigue life. However, the improvement provided by the case depth on the fatigue life is limited to a certain range, and extensive case depths might decrease the fatigue strengths of materials. For the studied material, carburization had a more direct influence on the crack growth under cyclic tensile loading than cyclic torsional loading.

Влияние науглероживания вольфрама на активацию газа при синтезе алмазных структур

In order to develop a gas-jet method of diamond structures deposition, the flow of hydrogen and methane mixture through heated tungsten coaxial cylindrical channels with a built-in tungsten spiral is studied. The main attention is paid to the study of the carburization of tungsten surfaces during gas-jet deposition and the effect of carburization on the deposition rate and the morphology of the deposited coatings. A series of experiments to study the carburization of tungsten surfaces under different conditions for feeding a mixture of hydrogen and methane is performed. The flow parameters are investigated by the direct simulation Monte Carlo method. The possible ways of delivering methane and its fragments onto the surface of the spiral are determined.

Effect of end chills, reinforcement content and carburization on the hardness of LM25-borosilicate glass particulate composite

Aluminium metal matrix composites (AMCs) are widely employed in aerospace and automobile applications. Thus, they are required to operate reliably under a severe corrosive, high temperature and carbonaceous environments, without undergoing any deterioration in their mechanical properties. The paper is the compilation of the experimental results and analysis carried out to investigate the effect of different end chills, reinforcement content and carburization on the LM25 aluminium alloy reinforced with borosilicate glass powder. The composites are prepared via stir casting route by varying the weight percent (wt.%) of the reinforcement starting from 3 wt.% and going up till 12 wt.% with an increment of 3wt.% in every step. To obtain quality castings, end chills are placed within the sand mould. The specimens drawn from the chill-end of the castings are pack carburized in a muffle furnace for a set duration of time. The hardness of the specimens before and after carburization is recorded. The analysis of the results illustrates that the hardness increases linearly with the increase in the reinforcement content within the matrix from 3 wt.% up to 9 wt.%. It is also evident that the Volumetric Heat Capacities (VHC) of the chill material bears a strong effect not only on the quality of the castings produced but also on the hardness of the AMCs. Carburization leads to carbon deposition on the surface causing a change in the hardness of the specimens.

Effect of Substrate Pre-carburizing on Properties of TiN (Ti) Hard Coatings Deposited on Ti-6Al-4V Alloy

Interface fracture often occurs in systems of soft substrate and hard coatings during the service process, which is related to the weak interface strength and the unstable expansion of cracks along the interface induced by the residual thermal stress. The residual thermal stress mainly comes from the mismatch of thermal physical properties between matrix and hard coatings. In this study, a gradient carburized layer was prepared on TC4 substrate before the deposition of TiN(Ti) coatings using double glow plasma carburization. And then the mono- and multilayer TiN(Ti) coatings were synthesized on the carburized layer, forming composite hard coatings. The effect of substrate carburizing on properties of coatings was studied. The results show that the composite coatings' hardness can be increased nearly 2 times and the bonding strength is enhanced to over 80 N, compared with that of mono-and multilayer TiN(Ti) coatings. Also the interface brittle fracture tendency is restrained obviously by the hardened substrate, and the coordinative deformation ability of the coating at extra load is optimized. The composite coating composed of pre-carburized layer and TiN hard coating shows a higher strength and toughness.

Pollutant reduction and catalytic upgrading of a Venezuelan extra-heavy crude oil with Al2O3-supported NiW catalysts: Effect of carburization, nitridation and sulfurization

Alumina-supported Ni-promoted W oxides, carbides and nitrides were presulfided and employed for reducing pollutants and increasing the quality of an extra-heavy crude oil during catalytic upgrading reactions. These materials were prepared by temperature programmed reaction using reactive gases and varying the (Ni/(Ni + W)) atomic ratio from 0.00 to 1.00. Catalysts were characterized by XRD, SEM, HRTEM and N2 physisorption. In order to study the effect of the atomic ratio in the conversion of the model molecule thiophene, room pressure HDS tests were used. The catalysts with best performances during thiophene HDS were tested in the upgrading of a Venezuelan extra-heavy crude oil characterized by having high asphaltenes, S and N contents, affecting competitiveness in the global market. These results were compared with a commercial NiMo catalyst. API gravity of crude oil, CHNS elemental analysis, 13C- and 1H NMR of crude oil and asphaltenic fraction, in addition to flocculation threshold of asphaltenes, were studied in order to verify variations in physicochemical properties of oil due to catalytic upgrading and to seek evidence of pollutants reduction and improvement of quality during this process. NiW catalysts with atomic ratio (Ni/(Ni + W) = 0.50 showed remarkable performance during thiophene HDS and heavy oil hydrotreatment, improving API gravity and reducing S content, modifying chemical nature of crude oil and asphaltenes, as it was revealed by results of elemental analysis, H/C ratio, flocculation threshold, Caro/Cali and Haro/Hali ratios. However, no significant variations were found in N contents of crudes and asphaltenes revealing poor HDN performance, apparently due to Na traces from the W precursor remaining in the final NiW catalysts.

Methodology for the analysis of astm a335 p92 steel exposed to real atmospheres of refinery combustion

This work proposes a methodology for the study of the physical and chemical effects of the materials used in the petrochemical industry, specifically ASTM A335 P92 steel. This methodology includes stages such as: selection of atmospheres and determining variables, experiment design, preliminary tests and experiment calibrations, manufacture of corrosion coupons, experimentation of the material with the different environments, kinetic study, characterization of the material by means metallographic analysis, of hardness and micro-hardness, scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDS), X-ray diffraction analysis (XRD), X-ray photoelectron spectroscopy (XPS) and finally discussion of results. This paper studies four corrosion phenomena at high temperatures: oxidation, nitridation, carburization and water vapor effect. Within the working conditions, five exposure times (1, 20, 50, 100 and 200 h) and four service temperatures (450, 550, 650 and 750 °C) were selected.

Study of continuous corrosion on astm a335 p91 steel in an environment of co2-o2-n2-h2o derived from the theoretical combustion products of a mixture of refining gases at high temperatures

The current energy production processes go hand in hand with corrosive phenomena; which is the case of combustion process in a refinery, where the presence of compounds such as CO2 and H2O, result in alloys catastrophic carburization and oxidation respectively. In this research work was evaluated the corrosive effect that can be generated in a real combustion environment, for which, it was necessary to select a model mixture of refinery gases and to simulate its theoretical combustions products. The main results showed the formation of a semi-protective duplex oxide layer; whose inner layer was composed mainly of chromium, while the outer layer was much richer in iron. On the other hand, the carburizing effect of CO2 was suppressed by the high oxygen potential in the combustion environment; leading to the conclusion that in real conditions, at 750 oC and after 200 h of testing, steels such as ferritic alloy ASTM A335 P91, could not present appreciable damages during their operation in refinery boilers and furnaces.

Effect of solid carburization on the surface microstructure and mechanical properties of the equiatomic CoCrFeNi high-entropy alloy

The surface modification of the equiatomic CoCrFeNi high-entropy alloy has been studied via solid carburization at 920 °C for 10 h. Microstructure, hardness and wear resistance were investigated by X-ray diffraction (XRD), scanning electron microscope (SEM), transmission electron microscope (TEM), microhardness and nanoindentation tester. Microstructure and phase analysis indicated that two types of nano-size carbide precipitates (M7C3 and M23C6) formed in the surface. The orientation relationship between the M7C3 precipitate and FCC matrix were (1(_)100)C1//(11(_)1)M and [0001]C1//[1(_)12]M. The M23C6 precipitate possessed a cube-cube orientation relationship with the FCC matrix. Vickers hardness and nanoindentation testing results indicated that the carburized surface performed significant improvement of about 100% in hardness compared with the matrix. The strengthening mechanisms including solid-solution strengthening and precipitate strengthening were studied. Moreover, nano-scratch experiments have been conducted on the cross section of the carburized sample under a constant load mode to investigate the friction and wear behavior. The surface profile and depth of scratched tracks were examined using scanning probe microscopy (SPM) technology. The wear and deformation mechanisms at different distances from the surface have been discussed. The calculated values of the wear volume, wear rate, and wear resistance coefficient reveal that the carbide precipitates can improve the wear resistance of the carburized surface.

Carburization effects on the corrosion of Cr, Fe, Ni, W, and Mo in fluoride-salt cooled high temperature reactor (FHR) coolant

Corrosion of structural alloys in fluoride salt cooled high temperature reactors (FHRs) is affected by the presence of carbon. The stability of the carbides of alloying elements augments their corrosion, however the same property can be useful if these stable carbides are used to protect materials. Exposure tests of pure elements Cr, Fe, Ni, W, and Mo in graphite crucibles at 700 °C were conducted in molten FLiNaK salt for 100 h. Carbide particles were detected on the surfaces of Cr, Mo, and W samples after exposure. The ranking of these elements, from least to greatest corrosion resistance by mass loss per unit area was Cr < Fe < W < Mo < Ni. The stability of chromium carbides was further investigated using chromium samples which were pre-carburized in a reducing hydrocarbon environment at 800 °C prior to exposure tests in molten FLiNaK. The chromium carbide layer produced by pre-carburization was resistant to attack by molten fluoride and slowed corrosion of the underlying chromium metal.

THE EFFECTS OF PACK CARBURIZING USING CHARCOAL ON PROPERTIES OF MILD STEEL

The aim of this research is to study the effects of pack carburizing using charcoal on properties of mild steel. The properties are represented by the results of microstructure, hardness test and tensile test. The carburizing process was conducted in the temperature of 930oC which is the austenite temperature of the mild steel. The source of carbon was charcoal. The specimens were held for 2, 3 and 4 hours at the carburizing temperature. The carbon content of the raw amterial was 0.17%. The raw material was hypoeutectoid steel with ferrite and pearlite phases in its microstructure. After the carburizing process, the microstructure can be divided into two zones e.i. case zone and core zone. The case zone consists of hypereutectoid, eutectoid, and hypoeutectoid sub-zone. The core zone is the same as raw material. The longer the holding time will result in the deeper the case zone and the stronger the material.

Sustainable Steel Carburization by Using Snack Packaging Plastic Waste as Carbon Resources

In recent years, the research regarding waste conversion to resources technology has attracted growing attention with the continued increase of waste accumulation issues and rapid depletion of natural resources. However, the study, with respect to utilizing plastics waste as carbon resources in the metals industry, is still limited. In this work, an environmentally friendly approach to utilize snack packaging plastic waste as a valuable carbon resources for steel carburization is investigated. At high temperature, plastic waste could be subject to pyrolytic gasification and decompose into small molecular hydrocarbon gaseous products which have the potential to be used as carburization agents for steel. When heating some snack packaging plastic waste and a steel sample together at the carburization temperature, a considerable amount of carbon-rich reducing gases, like methane, could be liberated from the plastic waste and absorbed by the steel sample as a carbon precursor for carburization. The resulting carburization effect on steel was investigated by optical microscopy, scanning electron microscopy, electron probe microanalyzer, and X-ray photoelectron spectrometer techniques. These investigation results all showed that snack packaging plastic waste could work effectively as a valuable carbon resource for steel carburization leading to a significant increase of surface carbon content and the corresponding microstructure evolution in steel.

Effect of Vacuum Carburizing on the Structure and the Properties of Aluminide Coatings on Nickel Superalloys

The processes that occur during vacuum carburizing of turbine blades made of carbon-free nickel superalloys are considered. Disperse alloying-element carbide particles are found to form in the surface layer of the VZhM5 alloy. These particles increase the fatigue life of the alloy during high-temperature oxidation. The disperse carbide particles are shown to hinder the formation of coarse γ′-Ni3Al grains and topologically close-packed phases under a coating; hence, they prevent premature fracture of the alloy.

Effect of Solid Carburization on the Tribological Behaviors of Ti13Nb13Zr Alloy

Due to its high mechanical strength, exceptional biocompatibility, low elastic modulus, and superior corrosion resistance, Ti13Nb13Zr alloy is one of the potential candidates for implanted joints. However, the poor tribological property of Ti13Nb13Zr alloy has greatly limited its wide usage in artificial joints. The elevated temperature solid carburizing technology was used to improve tribological property of Ti13Nb13Zr alloy. It was found that the surface hardness of Ti13Nb13Zr alloy was increased to 812 HV after the carburization at 1523 K due to the formation of titanium carbide on the surface. With the increase in experimental temperature, the thickness of the carburized layer increased to 120 μm. In addition, the wear rate of Ti13Nb13Zr alloy decreased by 63.9% under serum lubrication condition after the carburization at 1473 K due to the formation of hard TiC on the surface of Ti13Nb13Zr.

Degradation of Alloy 800H Used in Ethylene Furnace Tube Application by the Combined Effects of Carburization and Thermal Fatigue

An ethylene furnace tube made of the wrought alloy 800H has developed through the thickness crack. The cracking has been correlated with massive precipitation of embrittling carbide phases due to carburization attack and the thermally induced stresses during decoking cycles. Changes in microstructure and state of stress are reflected on the crack propagation mode, which is observed to change from fatigue near the outer surface to intergranular near the inner surface. It is concluded that the tube has been subjected to an environment of low oxygen potential and high carbon activity precluding the formation of protective oxide by the Cr2O3-forming alloy 800H. Process modification to reduce the decoking frequency and/or replacing the tube material with one capable of developing more protective oxide such as the Al2O3-forming alloy 214 may be considered to combat the problem.

Effect of carburizing and annealing processes in improving the Ni/WC–Co adhesion strength

Heat treatment processes have a positive impact in improving the adhesion strength of different interlayer/substrate materials. However, information regarding the effect of these processes in enhancing the adhesion strength of an electroplated nickel interlayer on tungsten carbide substrate for diamond deposition is lacking. In this study, the effect of carburizing and annealing process conditions in enhancing the adhesion strength of the electroplated nickel interlayer was investigated. The heat treatment processes were designed and modeled by the design of experiments technique. The heat-treated specimens were characterized by the field-emission electron microscopy, energy-dispersive X-ray spectroscopy, and X-ray diffraction techniques. The adhesion of the interlayer before and after the heat treatment was assessed by the scratch test. The results show that the adhesion of the electroplated nickel interlayer was remarkably improved by both processes. The mathematical models for predicting the adhesion strength of the carburized and annealed nickel interlayer within the specified ranges were developed. The maximum adhesion strength of 30 N was obtained from the nickel interlayer annealed at the highest process condition of temperature and time.

Effects of Carburization with Palm Kernel Shell/Coconut Shell Mixture on the Tensile Properties and Case Hardness of Low Carbon Steel

The effect of using mixtures of palm kernel shell and coconut shell as carburizers for low carbon steel at 950oC on the tensile properties and case hardness was studied. The carburizers were washed, dried, milled and sieved to 150µm particle size. They were mixed in various compositions to serve as carburizers. In each composition, 20wt% of calcium carbonate (CaCO3) was added as energizer. Tensile and hardness specimens were machined from low carbon steel. Seven tensile and seven hardness specimens were subjected to pack carburization process with different compositions of the carburizers, and thereafter quenched and tempered at 450oC for forty five minutes in a heat treatment furnace. The tensile and hardness properties show that better properties were obtained with mixtures of the carburizers compared to the use of single carburizing agent.