Gas Carburizing Research Articles

Modern Concept of Nitrogen Potential

Considering the problems of gas nitriding and low-temperature thermochemical treatment the authors treat gas carburizing at 900 – 950°C and gas nitriding at 500 – 600°C as similar processes. This approach is considered from the standpoint of chemical, heterophase, and solid-solution diffusion. The use of specially developed equipment allows the authors to suggest new concepts of nitrogen potential and structure of the gas nitriding process.

Carburization behaviour of Haynes 556 exposed to CH4/H2 gas mixtures

The carburization behaviour of Haynes 556 has been studied after cyclic and isothermal exposures to CH4/H2 carburizing gas mixtures at high temperatures for 500h exposures. A thermodynamic analysis indicated that 1000°C was an approximate critical temperature, below which the environment should result in mixed oxidizing/carburizing behaviour, while above this temperature reducing carburizing behaviour should occur. The experimental results agree with the thermodynamic analysis. Below 1000°C Haynes 556 suffered external carburization and oxidation, typically at 800°C in 2%CH4/H2 where the external reaction products comprised Cr7C3 and Co3W3C (major phases), and (Co,Mn)(Mn,Co)2O4 and TaOx (minor phases). At temperatures in excess of 1000°C exclusive external carburization occurred, typically at 1100°C in 10%CH4/H2 resulting in the formation of Cr7C3 (major phase) and (Cr,Fe)7C3 (minor phase). Metal dusting was not experienced under highly carburizing conditions (ac >1) in this study. The morphology of an outer carbide layer is both temperature- and time-dependent, while its continuity is more temperature-dependent rather than time-dependent.

Fe-base alloys in CH4/H2 carburizing gas mixtures

This study involved cyclic carburization exposures of three Fe-base alloys (310SS, 800HT, and 556) at 800°C in 2% CH4/H2 and at 1,100°C in 10% CH4/H2 carburizing gas mixtures for 500h. Carburization thermodynamics, kinetics, and carburization behavior are discussed. The exposure at 800°C in 2% CH4/H2 was mixed oxidizing/carburizing, but reducing carburizing at 1,100°C in 10% CH4/H2. At 800°C Fe-base alloys suffered external carburization and oxidation, and the external Cr-rich scale layers were continuous consisting of oxides and carbides. Carburization resistance primarily depends on the protection afforded by external continuous layers rather than Ni content. At 1,100°C, extensive external carburization occurred, and external layers became discontinuous consisting of Cr/Fe-carbides or metallic CrFe phases. Carburization resistance depends greatly on Ni (Co) content.

Carburization Behavior of 310 Stainless Steel in CH4/H2Gas Mixture with Trace Amount of Oxygen

The carburization behavior of 310 stainless steel has been studied after cyclic exposures to carburizing gas mixtures at elevated temperatures for 500 hr exposures. A thermodynamic analysis indicated that 1000 °C was an approximate critical temperature, below which the environment should result in mixed oxidizing/carburizing behavior while above this temperature, reducing-carburizing behavior should occur. The experimental results agree well with the thermodynamic analysis, at 800 °C in 2% CH4/H2 for 310SS which suffers both external oxidation, carburization, and internal carburization. At 1100 °C in 10% CH4/H2 external carburization occurs and internal carburization becomes less pronounced. Schematics are illustrated to show corrosion mechanisms in various exposure environments.

Surface Modification of Dilute Mo-Ti Alloys by Gas Carburization

Surface Modification of Dilute Mo-Ti Alloys by Gas Carburization

Runner-up Simulation of Gas Carburising: Development of Computer Program with Systematic Analyses of Process Variables Involved

Numerous process parameters involved in different stages of gas carburising make the process difficult to control, which in turn makes predictions of properties difficult. In the present work, a computer program was developed to simulate the entire gas carburising process, focusing on the thermodynamics of the gas phase and thermochemical reaction kinetics at the gas/solid interface in endothermic atmospheres. By combining gas phase kinetics and carbon activities in gas and steel with the alloy dependent diffusivity of carbon in austenite, the program can predict accurate carbon diffusion profiles for both batch and continuous furnaces. The program has been designed to account for all the major process variables that affect resultant carbon diffusion such as steel alloy composition, part geometry, gas composition and basic treatment parameters with their possible variations during the process. It is also able to predict other important properties such as transformation temperatures and the as quenched and tempered hardness of carburised parts. Comparison with the results of the experiments performed in industrial carburising furnaces provided validation of the model predictions.

天然ガスを有効利用した鋼の表面熱処理

The gas carburizing atmosphere for surface treatment of steel can be regulated using the carbon potential, which is obtained by measuring the dew point, oxygen concentration or carbon dioxide concentration. The carbon potential which is calculated with carbon dioxide concentration is consistent with the carbon content of carburized steel foil. However, since a zirconium oxide oxygen sensor is easier to handle and its response is better than others, it is generally used for controlling the carbon potential, Methane is the main component of natural gas and it is stable at high temperature, so that the majority of tends to remain in the furnace. Since the retained methane decomposes on the oxygen sensor tip, the oxygen concentration around it decreases. Therefore the measurement of carbon potential with an oxygen sensor has been considered to be difficult when natural gas is used as the enriched gas. In this study, the carbon potential is regulated by taking account of the difference of the carbon potentials which are calculated with carbon dioxide concentration and with oxygen concentration; therefore the carbon potential can be controlled by the oxygen sensor, using natural gas for enriched gas. Target surface hardness and effective case depth are obtained when gas carburizing is carried out using this method, In addition, when the carrier gas is generated with natural gas and air, the carbon oxide concentration is 20.5 volume%, and the hydrogen concentration is 39.0 volume%; therefore the carburizing speed is higher than that when the carrier gas is generated with propane or butane.

Effect of Abnormal Surface Layer on Tooth Surface Strength Increase of Gas Carburized Gears

Gas carburizing has been widely applied to power transmission gears in mass production. Gas carburized gears have so called abnormal surface layers on their surfaces that are generated during the carburizing process. Although the influence of the abnormal surface layer on the bending strength of the gear tooth has already been reported (Lyu et al., 1994), that on the tooth surface strength has not been clarified. The authors have carried out experiments to study the influence of the layer on the tooth surface strength. As a result of the experiments, it was found that the layer on the tooth surface has an effect to increase the tooth surface strength and that the effect of the layer greatly depends on its characteristics. By examining the layer microscopically five characteristics were given, and their suitable conditions that increase the tooth surface strength were discussed. Furthermore, experiments were carried out to examine whether the tooth surface strength of Cr-Mo alloy steel (JIS SCM420H) can be increased by improving the characteristics of the abnormal surface layer. A trial material was prepared by modifying the chemical composition of the Cr-Mo alloy steel. From the experiments with the gears made of the modified Cr-Mo alloy steel, it is demonstrated that the tooth surface strength of the gas carburized gears can be increased by improving the characteristics of the layer. Presented at the 57th Annual Meeting Houston, Texas May 19–23, 2002

ステンレス鋼の低温ガス窒化と低温ガス浸炭

ステンレス鋼の低温ガス窒化と低温ガス浸炭

Thermal diffusion coatings for protection from gas corrosion, coke deposition, and carburization

Thermal diffusion coatings for protection from gas corrosion, coke deposition, and carburization

Surface hardening for austenitic stainless steels based on carbon solid solution

A novel low temperature carburising approach for austenitic stainless steels, the NV Pionite process, is described. The formation of a metal fluoride layer on the surface before carburising allows carbon to be introduced into the workpiece by gas carburising at 450-500° C. Laboratory trials using 316 have been conducted. A single phase expanded austenite diffusion layer with surface microhardness of 810 HV0.05 and good corrosion properties is produced.

Modelling, simulation, and graphical user interface for industrial gas carburising process

A mathematical model has been developed for the gas carburising (diffusion) process using finite volume method. The computer simulation has been carried out for an industrial gas carburising process. The model's predictions are in good agreement with industrial experimental data and with data collected from the literature. A study of various mass transfer and diffusion coefficients has been carried out in order to suggest which correlations should be used for the gas carburising process. The model has been interfaced in a Windows environment using a graphical user interface. In this way, the model is extremely user friendly. The sensitivity analysis of various parameters such as initial carbon concentration in the specimen, carbon potential of the atmosphere, temperature of the process, etc. has been carried out using the model.

607 天然ガスをエンリッチガスに用いたガス浸炭における鋼の高機能化

607 天然ガスをエンリッチガスに用いたガス浸炭における鋼の高機能化

Fatigue Properties of Plasma Carburized Low Carbon Cr-Mo Steel.

Low carbon Cr-Mo steel (0.176C, 0.119Si, 1.014Cr, 0.387Mo) has been plasma carburized and its fatigue properties have been investigated. The effective case depth in plasma carburized steel at a lower temperature for a shorter time increased up to 50% in comparison to that of gas carburizing. In case of boost-diffuse carburizing, which cycles the carburization and diffusion period, the number of cycle times had more effect than carburizing time on the surface carbon content. High cycle fatigue properties of plasma carburized steel were assessed by comparing with those of gas carburized steel in reference to microstructure, effective case depth, amount of retained austenite and compressive residual stress near the surface. The fatigue limit of the plasma carburized steel was higher than that of gas carburized steel in the same effective case depth because the former had a higher compressive residual stress and had no internal oxidation layer. Transgranular fracture was in plasma carburized steel due to the fact that it had no grain boundary internal oxidation layer that initiated the crack.

Study on absorption and transport of carbon in steel during gas carburizing with rare-earth addition

Abstract The effect of rare-earth (RE) as a catalyst adding to carburizing atmosphere on absorption and transport of carbon is presented in this paper. The processing were carried out at 900°C for different time in a decomposition atmosphere of kerosene and methanol with and without RE addition. The compositions of carburizing atmosphere such as CO, CH4, etc. and the average carbon concentrations in 75 μm thick 08F steel foil were measured by infrared and chemical analysis, respectively. The surface activity and boundary transfer coefficient of carbon have been calculated based on the measured data. The results show that introducing RE into carburizing atmosphere increases the volume fraction of CO, CH4, etc. degree of dissociation of kerosene, carbon potential, surface activity and boundary transfer coefficient of carbon.

The effect of rare earth catalyst on carburizing kinetics in a sealed quench furnace with endothermic atmosphere

We study the effect of a rare earth (RE) catalyst on the kinetics of gas carburizing of 08F and 8620 steels. Carburizing was conducted in a sealed-quench furnace employing an endothermic atmosphere with and without RE addition at 900°C for different times. These experimental results show that compared with conventional gas carburizing the incorporation of RE leads to an obvious increase in layer depth and carbon (C) concentration profile under the same carburizing condition. Cerium (Ce) existing in the carburizing atmosphere and diffusing into the surface layer does not change the kinetics law of carburized layer growth. In addition, the calculated results show that the reaction constant and the diffusion coefficient of carbon between the gas–solid interface can also be increased during RE carburizing.

天然ガスをエンリッチガスに使用した際の酸素センサおよび二酸化炭素センサによる鋼の浸炭雰囲気制御

天然ガスをエンリッチガスに使用した際の酸素センサおよび二酸化炭素センサによる鋼の浸炭雰囲気制御

Plasma carburizing process for the low distortion of automobile gears

In a plasma carburizing process, the effect of the process gases such as propane (C 3H 8) and methane (CH 4) on the uniformity of the carburized layer has been investigated using a newly designed plasma carburizing system which is equipped with an in situ quenching chamber. The uniformity of the carburized layer has been improved up to ∼23% using C 3H 8 at 930°C in comparison to the process using a conventional CH 4 gas in the plasma carburizing. The distortion of the gears has been estimated by the measurement of the profile and lead errors at the teeth of the gear. The profile error has been decreased with the use of C 3H 8 up to ∼57% of the error which was obtained from the process using CH 4 gas and the lead error has also been improved up to ∼50% using a masking block for a gear with a small module of ∼2 mm. In addition the effective case depth of plasma carburizing process has been increased up to ∼35% as compared with the case depth of a conventional gas carburizing process.

Die Beeinflussung der Kohlenstoffübertragung bei der Unterdruckaufkohlung

The low pressure carburizing technology developed in the last few years, which uses propane gas in the pressure range up to roughly 20 mbar, does not satisfy all requirements of users with respect to high furnace productivity and low maintenance because of problems with carburizing uniformity, soot and tar formation in the furnace as well as control of the process. Therefore, a research program was initiated to develop a new and more suitable low pressure carburizing technology. In the frame of this work, several different types of hydrocarbon gases like methane, propane, ethene and ethine have been examined with respect to their capability to transfer carbon. From the results it can be concluded that with the hvdrocarbon gas ethine an almost perfect carburizing gas exists, which is capable of uniformly carburizing the most complicated part geometries and loads of high densities.

Effect of Abnormal Surface Layer on Tooth Surface Strength of Gas Carburized Gears.

The effect of abnormal surface layer produced by gas carburizing on the bending strength of gear tooth has already been reported, although the effect on the tooth surface strength has not been clarified. The authors carried out experiments to study the effect of abnormal surface layer on the tooth surface strength. The test gears with various conditions of abnormal surface layer used in this experiments were prepared by changing the machining process and the material of gears. As a result of experiments, the tooth surface strength of gas carburized gears is affected by the existence of abnormal surface layer. With in the limits of this experiments, it showed that the tooth surface strength of gears with abnormal surface layer is higher than that of gears without abnormal surface layer. Furthermore, it was observed that the quantitative effect of abnormal surface layer on the tooth surface strength is different from the coilditions of abnormal surface layer, i. e. the uniformity and the hardness of slack quenching layer, and the production shape of intergranular oxidation. We concluded from the experiments that the suitable conditions of abnormal surface layer improve thye tooth surface strength of gas carburized gears.