Carburized Depth Research Articles

Studying the Depth of Carbonifying Castings Obtained by the Lost Foam Casting Method with a Complex Polystyrene Composition

At present, lost foam casting method is an updated, long-term and the most economically feasible method in the foundry industry. Despite the fact that the casting technique is relatively simple, high demands are placed on the model materials. Carburization of the surfaces of steel castings obtained by the lost foam casting method is one of the main and the most significant problems in the use of this casting method. One solution is to use a complex composition of the material: a combination of cast and construction polystyrene. It was determined that the complex composition of the cast and construction polystyrene model in the ratio of 60 to 40% helps to reduce the depth of carburization and the percentage of internal defects. In addition, the cost of 1 kg of the complex composition models is 25% lower than the cost of 1 kg of models made of cast polystyrene.

Low-frequency incremental permeability for the evaluation of deep carburization treatments: Theoretical understanding

Precise evaluation of deep carburization treatments is essential to prevent degradation of high-performance mechanical components. A nondestructive magnetic method called low-frequency incremental permeability testing appears to be particularly suitable for this purpose. This method consists of slowly magnetizing the specimen to be controlled and then superimposing a relatively low-frequency eddy current testing process on the specimen (<2 kHz). The sensor’s coil impedance is monitored along with the magnetization cycle. When plotted versus the magnetic excitation, the impedance produced butterfly-shaped curves that were dependent on the carburization depth. Operating at low frequency increases the scanned layer thickness up to the untreated inner part of the specimen and induces characteristic variations in the butterfly-shaped curves. A model to solve for the indirect relationship between the magnetic properties and the carburization treatment properties is presented in this manuscript. This model combines the Dodd and Deeds analytical expression for a flat sensor coil above a two-layer conductor with Jiles-Atherton theory for consideration of the hysteresis. The magnetic and electromagnetic responses are well considered, providing accurate reconstructions of experimental data. The model predictions reveal magnetic indicators that are highly correlated with the carburization depth and provide optimal conditions for nondestructive testing observation.

Carburization depth evaluation from magnetic nondestructive testing

Precise estimation of carburization depth is mandatory to avoid failure and critical degradation of high-performance mechanical parts. In this work, we studied magnetic methods as an indirect way to obtain this information. Usual techniques consisting of complex combinations of unrelated indicators have been left aside and replaced by a theoretical approach based on the magnetization mechanisms.A series of rod specimens were pre-characterized using destructive hardness tests and classified into four categories from virgin to very deep carburization depth. Then, rods from each batch were tested with different magnetic testing techniques. Identical experimental conditions were kept to limit the degrees of freedom and ensure the viability of the conclusions. The Magnetic Incremental Permeability (MIP) maximal amplitude ΔZ which is associated with the domain wall bulging mechanism showed the highest linear correlation with the carburization depth.Based on these first observations, new experimental conditions were proposed: MIP AC component frequency was reduced to 1 kHz, leading to a magnetic penetration large enough to reach the specimen core. A sudden change in slope was observed on the MIP signature of the treated specimens when the excitation field was close to the core coercivity (of similar magnetic behavior as untreated specimens). The corresponding local slope obtained a very high 0.987 linear correlation coefficient vs. carburization depth and revealed low-frequency MIP as an effective magnetic nondestructive technique for thick carburization evaluation.

Proposal of simultaneous measurement of carburization depth and lift-off of heating furnace steel tube

In recent years, the necessity for inspection of the deteriorated oil-refining plant is increased. In the steel tube to be used in a heating furnace has carburizing phenomenon is the cause of the accident. As these carburizing depths increase, so does the steel tube. Therefore, inspection of these depths is important. Therefore, studies are being conducted to determine the life of steel tube by applying electromagnetic non-destructive inspection electromagnetic. However, it is difficult to put it to practical use in the field because measurement error occurs due to the effect of lift-off. In this paper, we proposed an inspection method that can measure carburizing depth and lift-off at the same time. This method uses two types of search coil. One is the magnetic flux testing and the other is the eddy current testing.

Effect of Carburizing Helium Environment on Corrosion Behavior of the High-Temperature Alloys for High-Temperature Gas-Cooled Reactor

The primary coolant of High-Temperature Gas-cooled Reactor (HTGR) is expected to contain impurities that can make corrosion to structural metallic materials at elevated temperatures. According to the chemical thermodynamics and kinetics, the carbon activity of helium can be calculated, and it is indicated that a high “CH4/H2O” ratio may lead to severe carburizing of the alloys. On this basis, corrosion tests were conducted on the three heat-resistance alloys Inconel 617, Hastelloy X, and Incoloy 800H at 950°C using helium environment with impurities, and mainly the effect of carburization was investigated. The corrosion samples were observed by Scanning Electron Microscopy (SEM) with Energy Disperse Spectroscopy (EDS), Electron Probe Microanalyzer (EPMA), and Carbon-sulfur Analyzer. These all alloys showed the oxidation and carburizing behavior, in which the carburized depth of Hastelloy X was shallow due to the dense oxide scale.

Effect of surface finishing on the oxidation characteristics of a Fe-21Cr-32Ni alloy in supercritical carbon dioxide

The effect of surface finishing on the oxidation behavior of a Fe-21Cr-32Ni alloy in supercritical carbon dioxide (650 ºC for 1000 h) was studied. After exposure, the cross-section of the specimen showed a typical inner-outer oxide layers structure with subsurface carburization. Reduced oxidation and carburization rates were identified for the ground surface, where a much thinner Cr-rich oxide scale and a shallower carburization depth were observed. Grinding introduced an ultra-fine grained layer and a highly deformed layer on the metal surface, where Cr diffusion rate was significantly enhanced. The high Cr diffusion led to the transition from internal to external oxidation by favoring the formation of a thin/protective Cr-rich oxide layer. This continuous Cr-rich oxide layer not only protected the substrate matrix from further oxidation, but also reduced the permeability of carbon into the oxides, thus improving the oxidation and carburization resistance of the ground specimen.

Factors Affecting the Hardness Characteristics of Microstructures in Gas Carburized Chromium Alloy Steels

We analyzed the factors affecting the gas carburizing microstructure of parts for constant velocity joints. Gas carburizing 0.15-0.20C1.13-1.14Cr chromium alloy steel used in automobile drive units is characterized by changing the properties of the carburizing layer in the depth direction.&#x0D; The experimental conditions were set to enable field application. The components of the specimen to be used for gas carburization were analyzed by X-ray fluorescence. Changes in the mechanical properties of the carburized layer were analyzed by micro-hardness, microstructure, and carburizing content. The gas carburization cycle was selected based on the simulation results. The characteristics change before and after carburization of two samples with different carbon and chromium content were analyzed.&#x0D; The carburization temperature that can be used for manufacturing automobile parts was 930°C, the carbon potential required for carburization was 0.90wt%, and the carbon potential required for diffusion was 0.75wt%. The inner and outer hardness values of the carburized layer satisfying the effective hardening depth of 550Hv were 400Hv-740Hv. In the case of 0.20C alloy steel, the effective hardening depth with a carburizing amount of 0.36wt% and a hardness of 550Hv was 1.467 mm. also in the case of 0.15C steel, its effective hardening depth was 0.746 mm. The simulation results for selecting the carburizing heat treatment conditions and the carbon change in the carburizing layer showed a similar trend. The carburizing structure related to hardness change was martensite. As a result of EPMA, SEM, and XRD analysis, the amount of carburized and the amount of martensite structure correlated, and the martensite increased as the amount of carburized increasing. As a result of EPMA analysis, the smaller the carburizing content the greater the depth of carburization.&#x0D; We intend to proceed with optimization conditions for mass production in connection with wear resistance and fatigue. It is expected that these results will contribute to the improvement of durability of automobile driving parts.

Electromagnetic inspection method of carburization depth inside and outside of heating furnace steel tube

Electromagnetic inspection method of carburization depth inside and outside of heating furnace steel tube

Distribution of Magnetic Field Parameters in the Surface Layer of the Material of Reaction Furnace Coils after Operation Period

One of the main reasons for the limited service life period of the reaction furnace coils is the carburization of the surface layers, which leads to a decrease in the performance characteristics of the pipe material, decrease in plasticity, generation of internal stresses, change in the metal structure. Therefore, monitoring the state of coils surface in order to detect critical parameters of the carburized layer thickness, using non-destructive methods of control is relevant. The results of the distribution of magnetic parameters over the depth of the carburized layer in the fragments of pipes made of steel 20Х25Н20C2, operated under furnace conditions at high temperatures, for 1300, 6000, 8000, 10000 hours are presented in the article. Analysis of the results showed that the magnetic properties are manifested only in the surface layers of the reaction furnace tubes. At the same time, the longer the service life period, the deeper is the layer exercising the magnetic properties and the higher in this layer the values ​of the constant magnetic field intensity. Analysis of magnetic properties distribution in all studied pipe fragments, both from the inner and from the outer side, showed the non-uniformity of the constant magnetic field intensity distribution, while zones of extremely high values ​are observed. The layer-by-layer surface removal in these zones with the determination of the resultant constant magnetic field intensity showed that there are critical values of the carburization depth, after which a sharp increase of this parameter is registered. These results can be used as a method for carburization depth determination, and also used to develop criterion for rejecting coils of reaction furnaces.

Corrosion Behavior and Mechanism of Heat-Resistant Steel T91 in High-Temperature Carbon Dioxide Environment

Corrosion behavior of martensitic heat resisting steel T91 in high-temperature carbon dioxide environment at 500-700 °C was investigated. X-ray diffraction, scanning electron microscopy and glow-discharge optical emission spectrometry were employed to characterize the corrosion products. The results showed that the corrosion kinetics of T91 followed a parabolic law with experimental time. The oxide scale thickness of T91 followed an exponential growth law from 500 °C to 700 °C. Internal carburization was detected underneath the corrosion scale. What’s more, the carburization depth was larger than the corrosion scale. The variations of Cr and C elements distribution were discussed.

Multi-step Simulation of Vacuum-carburizing Reactor based on Kinetics Approach

A novel and efficient simulation technique for the purpose of optimization of vacuum-carburizing process was proposed. This method consists of three steps: calculation of gas convection and diffusion, calculation of only gas diffusion, and calculation of carbon diffusion in steel. The first step provides the gas convection velocity that is employed in the second step. Adsorption rate of carbon on the steel surface is obtained in the second step, and carbon concentration in the steel is calculated in the third step based on the adsorption rate of carbon. Experiments were conducted to verify the proposed method in both laboratory- and industrial-scale reactors. Comparison of the computational predictions to the experimental data revealed that the proposed technique enabled accurate prediction of the adsorption rate of carbon on the steel surface at various temperature conditions, the amount of carburized carbon at each operating time, and the profile of carbon concentration in the steel; in other words, the carburized depth. In addition, the calculation of the industrial-scale reactor, whose simulation model consisted of approximately seven million computational meshes, was completed within about two days. Therefore, the proposed simulation technique could be used to control and optimize the process in industrial vacuum-carburizing reactors.

Modeling and Analysis of Effective Case Depth on Meshing Strength of Internal Gear Transmissions

The effective case depth (ECD) plays an important role in the meshing strength of internal gear transmissions. Carburizing quenching heat treatment is commonly used to enhance gear strength and wear resistance. However, the different ECDs in internal and external gears caused by heat treatment significantly affect the meshing strength, causing vibration, reducing gear service life, and hastening malfunction in internal gear transmission. In this study, we conducted an investigation of different ECDs by the heat treatment of carburized gear pairs by numerical simulation with the finite element method (FEM) and experiment tests. We analyzed three different carburized layer models, with the ECD in the internal gear being greater than, less than, and equal to the ECD in the external gear. In addition, we investigated the ability to distinguish between hardness gradients in gear teeth by dividing the carburized depth into seven layers to improve modeling accuracy. Results revealed that the meshing strength of internal gear transmission could be significantly enhanced by adopting the model with the ECD in the internal gear being less than the ECD in the external gear, and moreover, the shear stress of carburized gears initially increased and then decreased along with depth direction, and the maximum value appeared in the middle of the lower surface.

Carburization of Heat-Exchanger Pipes of 09Kh18N9 Grade Steel in Contact with Sodium Coolant

The carburization process of heat-exchanger piping of 09Kh18N9 grade steel in contact with sodium coolant under conditions of long-term service at 515°С has been investigated. An effective diffusion coefficient has been determined on the basis of the experimental data on carbon concentration in the metal surface layer; the carburization depth within the temperature range 450–515°С has been calculated.

Fault Analysis on Bevel Gear Teeth Surface Damage of Aeroengine

Aiming at the trouble phenomenon for bevel gear teeth surface damage of Aero-engine, Fault Tree of bevel gear teeth surface damage was drawing by logical relations, the possible cause of trouble was analyzed, scanning electron-microscope, energy spectrum analysis, Metallographic examination, hardness measurement and other analysis means were adopted to investigate the spall gear tooth. The results showed that Material composition, Metallographic structure, Micro-hardness, Carburization depth of the fault bevel gear accord with technical requirements. Contact fatigue spall defect caused bevel gear teeth surface damage. The small magnitude of Interference of accessory gearbox install hole and driving bevel gear bearing seat was mainly caused. Improved measures were proposed, after proof, Thermoelement measures are effective.

Damage Analysis of Planetary Gear Train in Wind Turbine Gearbox

Wind turbine industry is meaningful for the energy safety, but there are still some bottlenecks with the development of the wind turbine technology. How to improve the fatigue life and reliability of wind turbines has become a major problem. In this paper, the 1.5MW wind turbine gearbox was used as an example to study the damage mechanism of the planetary gear train. First, the chemical compositions, tensile properties, Rockwell hardness, impact energy and carburized depth of the gear and bearing material were measured, and the result shows that all the above-mentioned parameters can meet the design requirements, which means they are not the reasons causing the damage of the gear. Second, based on the actual patterns of the damaged components, the main source of damage is deduced to be the inner-hole surface of the planet gear. Further, the curves of the maximum sliding distance with respect to load under different fit tolerances (P6 & R6) were compared. As a result, P6 is found not a rational fit tolerance for the planetary gear train, and it is the main reason causing the damage of the gearbox. Therefore, fit tolerance R6 should be chosen for the design.

Proposal of Electromagnetic Inspection of Both Front Side and Rear Side Carburization Depth in Heating Furnace Steel Tubes

Proposal of Electromagnetic Inspection of Both Front Side and Rear Side Carburization Depth in Heating Furnace Steel Tubes

Changes in Microstructural and Mechanical Properties of AISI Type 316LN Stainless Steel and Modified 9Cr-1Mo Steel on Long-Term Exposure to Flowing Sodium in a Bi-Metallic Sodium Loop

AISI Type 316LN stainless steel (SS) and modified 9Cr-1Mo steel were exposed to flowing sodium at 798 K (525 °C) for 30000 hours in a bi-metallic sodium loop. The changes in microchemical, microstructural, and mechanical properties were evaluated and compared with the as-received and thermally aged specimens. Effective carbon diffusion coefficient $$ {\left( {D_{\text{C}}^{\text{eff}} } \right)} $$ was calculated to be 6.8 × 10−19 m2/s. Depth of carburization analyzed by secondary ion mass spectroscopy technique was around 100 µm for sodium-exposed 316LN SS. Selective leaching of nickel occurred across depth from the surface of sodium-exposed 316LN SS with the formation of 10 µm ferrite layer, and it showed an increase in yield strength by 15 pct, reduction in ductility by 60 pct, and a decrease in impact energy by 15 pct vis-a-vis the as-received and thermally aged specimens. This reduction in ductility occurred due to extensive precipitation of sigma phase as a result of long-term thermal aging. No significant changes were observed in the sodium/modified 9Cr-1Mo steel interfacial microstructure as well as tensile properties of sodium-exposed modified 9Cr-1Mo steel. Although modified 9Cr-1Mo neither showed carburization nor decarburization on sodium exposure, it showed a drastic reduction in the impact strength, which was attributed to the presence of Laves phase, observed in X-ray diffraction patterns.

The Effect of Ce Added to Carburizing Paste on Phase Composition of Carburized Surface Layers

Investigations on carburized layers phase composition are usually made ​​by optical microscopy, electron microscopy and X-ray diffraction. A microstructure consisting in different proportions of superior bainite, inferior bainite, martensite and retained austenite was found after carburizing in paste of the 21NiCrMo2 steel which has appropriate bainitic hardenability. The investigations carried out on 21NiCrMo2 steel samples, carburized in paste with additions of about 10% Ce, highlighted a significant change of phase proportions ratio in the carburized layer resulting in an important increasing of the lower bainite ratio. It was also observed, that the carburized layer case depth obtained in the carburizing paste with Ce additions does not significantly differ in relation to that attained in the carburizing paste without Ce additions but the microhardness increases considerably. The reason is connected also to the presence of Ce carbide identified by X-ray diffraction in the carburized layer. The Ce hard affinity towards oxygen and its influence on bainitic hardenability increasing is well known and adopted, however neither Ce transfer mechanism from carburizing paste to the carburizing layer and nor the effects of its high affinity to oxygen (for example) are not addressed in this particular case. The present study proposes a possible transfer mechanism of Ce in the carburized layer and an explanation of the consequences of Ce hard affinity towards oxygen on the phase composition of the carburized layer. Nanoscale iron oxides such as wüstite, magnetite and maghemite were identified in the surface of the carburized layer by Mössbauer spectrometry.

침탄 두께에 따른 피로강도 영향 특성 평가

Carburizing treatments are the important way to developing fatigue strength and wear resistance. It is well known that the case depth is one of the most significant parameters determining fatigue strength. In this study, 3-point bending fatigue test was conducted to evaluate fatigue strength for the carburized depth with 18CrNiMo7-6 steel. As a result, fatigue strength increased with effective case depth decreased. It is shown that hardness in case hardened layer played principal role in the fatigue strength.

Analysis of Electromagnetic Inspection Method of Opposite Side Carburization Depth in Steel Plate Taking Account of Minor Loop

There is a need to inspect the opposite side of carburized layer in a heating furnace steel tube in an oil-refining plant. The conductivity of the layer with carburization is larger than the layer without carburization in the steel, and its permeability is smaller than the layer without carburization. Then, the estimation of the opposite side carburized depth in the steel is possible by using the differences of these electromagnetic properties. In this paper, the electromagnetic inspection method using a dc magnetic field and a minute ac magnetic field is proposed. The behavior of flux in steel is examined using 3-D nonlinear FEM taking account of minor loops and eddy current. It is shown that the inspection of opposite side of carburized depth in the steel is possible using the differential permeability of minor loop of which the position on the hysteresis loop is affected by the depth of carburized layer.