Carbon Content Distribution Research Articles

Surface modification of pure titanium treated with B 4C at high temperature

A solid diffusion method was employed to modify the surface of commercial pure titanium in this paper. The thermodynamics and the reactive process were analyzed. And the performance of the modified surface was also examined. The modified surface of pure titanium was covered with a compound layer of TiC, TiB and TiB 2. The thickness of the compound layer was about 400 μm. The formation of the compounds is thermodynamically and kinetically feasible at the temperature of 1000 °C. The surface corrosion resistance in a 2% HF solution was improved greatly. The Vickers microhardness of the modified surface reached 820HV, which was much higher compared with the hardness of the original titanium substrate of 180HV. The surface shows a hardness gradient according to the concentration distribution of carbon and boron atoms.

Carbon concentration tracked by numerical simulation in vacuum tank degasser during decarburisation treatment

Two-phase flows in gas stirred steel bath and their effects on the carbon concentration distribution in the ladle during a decarburisation vacuum treatment are analysed. For this purpose, a numerical tool based on the coupling between the CFD Fluent software and kinetic model developed at IRSID has been used. The CFD Fluent software, equipped with a Lagrangian approach, provides a local description of the ladle hydrodynamics (molten steel flow and turbulence). The kinetic model is based on the physical description of the different reaction sites in the vacuum tank degasser. It is used to determine the evolution of the global carbon concentration in ladle. The coupling gives a complete mapping of the carbon concentration in the ladle according to time treatment. Numerical results applied to a water model configuration reveal good agreement in terms of velocity and turbulence profiles with experimental data provided from laser devices. In industrial configuration, the effect of the bath surface pressure and of the gas flow rate is analysed in terms of generated hydrodynamics and carbon distribution in the ladle.

Modelling of spatial controls on denitrification at the landscape scale

AbstractA simple model for estimating likely spatial patterns in landscape‐scale denitrification rates is described. In the absence of limiting nitrate concentration, denitrification is assumed to be controlled principally by the soil water regime and the amount of available soil carbon. A formulation of TOPMODEL is used to estimate the spatial distribution of water table depths. Soil carbon concentration is assumed to decrease exponentially with depth. The spatial distribution of carbon concentrations at the soil surface is assumed to be imperfectly correlated with the topographic index used in TOPMODEL. Monte Carlo simulation techniques were used to introduce a stochastic element to the spatial distribution of soil carbon. This allowed estimates of the uncertainty in model outputs, resulting from uncertainties in the distribution and variability of soil carbon to be made. The model predicted spatial and temporal patterns of nitrate‐non‐limiting denitrification for a 15 year period in the Slapton Wood catchment in southwest England. Predicted denitrification followed a slight seasonal pattern with a winter maximum. Total annual denitrification losses tended to be positively correlated with total annual precipitation in the catchment. Highest rates tended to be predicted near to the stream. The modelling approach provides a means of assessing the proximity of local‐scale field measurements to probable landscape‐scale denitrification fluxes. Combining a deterministic model core with a stochastic generation of model parameters or state variables provides an attractive way of embracing variability and uncertainty whilst maintaining a conceptual description of the system dynamics. Copyright © 2002 John Wiley & Sons, Ltd.

Effects of Gear-Side Case-Hardening on Residual Stress of Case-Hardened Gears.

This paper presents a study on effects of gear-side case-hardening on residual stresses of case-hardened gears. The carbon content of each element of the FEM models due to carburizing was computed on the basis of the relation between carburizing condition and carbon content distribution. A heat conduction analysis and an elastic-plastic stress analysis during the case-hardening process of spur gears were carried out for various case-hardening conditions by the three-dimensional finite-element method (3D-FEM), considering changes of the thermal expansion coefficient and the yield stress with the temperature and the carbon content distribution, and then residual stresses were obtained. The effects of the case depth, the case-hardened part (tooth surface, gear-side and bore), the face width, the rim thickness and the standard pressure angle on the residual stress were determined.

GM-20 CARBURIZING OF BIG MODULE AND LARGE DIAMETER GEARS(GEAR MANUFACTURING)

The carburizing gears have higher strength and better life-time compared with induction-hardening or quench-tempered gears, but in big-module gears, the carburizing heat-treatment becomes time-consuming, cost-expensive and sometimes cannot achieved good hardness due to the big mass-effect, and it is not easy to reduce the distortion of gears during heat treatment. In order to achieve good surface hardness of carburizing layer, it is necessary to precisely control the carbon content distribution. Since the carburizing time is much longer for big module gears due to deeper case-depth requirement, after carburizing it is necessary to have intermediate cooling under 650℃ to get finer grain size and better mechanical properties. By using a carburizing furnace equipped with fast cooling function, the work-pieces can proceeding intermediate cooling and heat up again to quench temperature inside the same furnace. This can reduce the total heat-treatment time as well as costs remarkably. The distortion comes from heat treatment is not avoidable, by improving the arrangement of load we can reduce the distortion and then reduce the manufacturing costs.

Vertical distribution of Microcystis population in the regulated Nakdong River, Korea

The vertical distribution of a bloom-forming Microcystis population was studied based on the relevant limnological parameters obtained from the lower Nakdong River (Mulgum) during the summer of 1994. Over three months (late June to late September), a high abundance of Microcystis population (mean ± SD, 2.9 ± 8.4 × 105 cells ml−1, n = 40) and algal biomass (mean ± SD, chlorophyll a, 131 ± 346 μg l−1, n = 31) was persistent throughout the entire water column (0–5 m, n = 11). The vertical distribution of carbon content was uneven, with a high concentration near the surface zone (mean ± SD, total, 7.9 ± 7.8; Microcystis, 5.2 ± 8.3 μg C ml−1, n = 15). Incorporating limnological and meteorological factors, a diel study of the vertical distribution of Microcystis showed that the chlorophyll a concentration was highest near the surface zone on a calm night (wind velocity, 4 m s−1, 1100–1900). Among many possible factors, wind velocity may have played an important role in controlling the vertical distribution of Microcystis in the lower Nakdong River.

Modeling and countermeasures of combustion characteristics of char particles in CFBC

A mathematical model of single char particle combustion in circulating fluidized bed combustor (CFBC) is developed in this paper. Its numerical solution in operating conditions of CFBC verifies the nature of a phenomenon that the distribution of carbon content of char particles has a peak value versus their diameters. The results show that the temperature of smaller char particle is close to the bed temperature, and there also exits a peak value for the burn-out time of char particles versus their diameters. The countermeasures are presented to improve combustion of fine particles, such as use of the fly-ash recirculation, the hot cyclone, and so on.

Study of the carbon concentration distribution in iron and titanium after low-temperature carbon ion implantation

Carbon ion distribution profiles after implantation in iron and titanium were extensively investigated using Rutherford Backscattering Spectrometry (RBS) and Elastic Recoil Detection Analysis (ERDA). Ion energy and fluence were varied over large ranges using target temperatures of less than −70°C. In both systems a retention of a gaussian-like implantation profile was found up to very high fluences. Unexpected high values of local carbon concentration were obtained for high fluences. Results were compared to Monte Carlo simulations using the dynamical code TRIDYN. Additionally the influence of subsequent annealing on the carbon distribution was studied. The diffusive behaviour was found to be very different in both systems. The iron–carbon system shows strong rearrangement of carbon atoms and tries to achieve local concentrations of 25 at.% upon thermal treatment. In the corresponding temperature regime no significant carbon diffusion in titanium takes place.

Formation of titanium carbide by high-fluence carbon ion implantation

Titanium carbide has been prepared by high fluence carbon ion implantation in titanium at temperatures between −70°C and 450°C. The carbon ion dose has been varied between 1.2 and 36 × 10 17 C +-ions/cm 2 and the ion energy between 30 and 180 keV. The carbon concentration distribution, the structure, the morphology and the microhardness have been examined with Rutherford backscattering, transmission electron microscopy, X-ray diffraction and nanoindentation, respectively. The concentration distribution of carbon is characterized by a symmetric Gaussian profile for doses up to 12×10 17C +-ions/cm 2 and a more and more asymmetrical profile for higher fluences. The evolution of the concentration distribution is discussed on basis of swelling and sputtering. Precipitates of the titanium carbide phase can be observed after implantation at −70°C with doses ⩾3×10 17C +-ions/cm 2. The average diameter of the TiC precipitates is a function of ion dose, temperature and duration of annealing. A significant increase of the hardness in the near surface region of implanted samples can be detected. The measured hardness values depend strongly on ion dose, annealing conditions and the hardness of the unimplanted titanium.

Mechanistic Simulation of Vertical Distribution of Carbon Concentrations and Residence Times in Soils

AbstractWe developed a numerical simulation model of the decay and vertical transport of soil organic matter. Soil organic matter is divided into a number of compartments each with different decay rates but with similar migration parameters. Decay has been represented with first‐order processes. Two elementary forms of migration were explored: diffusive equations represent transport through soil mixing whereas translational convection simulates movement within the liquid phase. Coefficients of decay, diffusion, and convection were taken to be uniform with depth. Carbon input is both through the surface in the form of litter fall and directly underground from roots. Profiles of total C content and 14C content were measured for a temperate forest silt loam soil. Similar data for other forest soils, available in the literature, were also assembled. Statistical adjustment, through nonlinear regression, of decay, migration, compartment configuration, and plant production parameters, accurately simulated profiles of C and 14C. The rapidly decaying compartment was successfully likened to the 50‐ to 2000‐µm particle‐size fraction. Convection rates of ≈0.3 mm yr−1 and diffusion rates ranging from 1 to 15 cm2 yr−1 were obtained. Diffusive processes appear to be preponderant relative to convection. The model has proven sensitive to differences between temperate and tropical soils as well as textural variations.

Vertical variations of organic matter content in Guayuta Group (upper Cretaceous), Interior Mountain Belt, Eastern Venezuela

A geochemical study of the vertical variations of organic matter in the Guayuta Group (Querecual and San Antonio Formations) has been conducted on a series of samples taken from a sedimentary sequence outcropping in the Interior Mountain Belt. The results indicate that despite very high thermal maturity, the organic matter content in the samples is still very high and shows geochemical characteristics related to anoxic paleoenvironmental conditions of sedimentation. Based on micropaleontological data, mineralogical data, and trace metal (V/Ni) ratio of kerogen, the analysis of the sequence shows stronger anoxic depositional conditions toward the base of the section and an increase of clastic sediments toward the top. The total organic carbon of the sediments increases toward the base of the sequence. In addition, there are pseudocyclic patterns and heterogeneities of the organic carbon content distribution at the meter-scale. The results indicate that the lower part of this sedimentary sequence represents a major anoxic event, that can be correlated with other sequences of middle and upper Cretaceous age.

Fluid Flow in Ladle and Its Effect on Decarburization Rate in RH Degasser.

Theoretical and experimental studies were carried out to quantitatively understand the effect of fluid flow on the decarburization reaction rate in an RH degasser. Hydrodynamic calculations on fluid flow in the ladle were proved reasonable by a cold model experiment. The decarburization model in conjunction with the fluid flow by hydrodynamic calculations in the ladle made it clear that the decarburization rate obtained from this model was faster than that for perfectly mixed flow, and slower than that for plug flow when the same parameters were used for the calculations. The decarburization model enabled us to predict the concentration distribution of carbon in the ladle during an RH treatment. The maximum carbon content, which was found in the recirculating zone in the ladle, reached about twice the minimum value obtained in the region just below the down-leg. No dead zone existed which would disturb the decarburization rate in the process, and it was also made clear that the shape of ladle had little effect on the decarburization rate.

Transport restriction effect for gaseous components on the carbon content of LEC GaAs

Gas convection above B 2O 3 was restricted using a quartz cap over the crucible to examine the gas transport effect on the carbon content of LEC GaAs crystals. It has been found that the carbon content of crystals grown with a cap closing the crucible is much larger than that of crystals grown without a cap. Also, a BN cylinder was introduced in a puller to reduce the interface area between GaAs melt and B 2O 3, and between B 2O 3 and the ambient gas. Estimates of carbon extraction rate from the melt were made by gas analysis in the puller which was operated in a hypothetical pulling process with different cylinder diameters. In addition, the dependence of the carbon concentration in polycrystalline GaAs remaining in the crucible on the pass time from the start of heating was investigated. The results suggest not only that the rate of carbon extraction is faster than incorporation, but also that the initial carbon content of the starting charge affects the carbon content of the grown crystal. It has been concluded that the extraction rate of carbon from the melt as well as the initial carbon content of the starting charge are significant factors in estimating the actual distribution of carbon concentration along the growth direction of LEC GaAs.

RH真空脱ガス装置の取鍋内溶鋼流動と脱炭反応

Theoretical and experimental studies were carried out to quantitatively understand the effect of fluid flow on the decarburization reaction rate in an RH degasser. Hydrodynamic calculations on fluid flow in the ladle were proved reasonable by a cold model experiment. The decarburization model in conjunction with the fluid flow by hydrodynamic calculations in the ladle made it clear that the decarburization rate obtained from this model was faster than that for perfectly mixed flow, and slower than that for plug flow when the same parameters were used for the calculations. The decarburization model enabled us to predict the concentration distribution of carbon in the ladle during an RH treatment. The maximum carbon content, which was found in the recirculating zone in the ladle, reached about twice the minimum value obtained in the region just below the down-leg. No dead zone existed which would disturb the decarburization rate in the process, and it was also made clear that the shape of ladle had little effect on the decarburization rate.

Calculation of the kinetics of steel austenization in laser heating

We examine both the kinetic features and the present the formulation of the problem dealing with the distribution of carbon concentrations in an austenite, as well as the motion of the phase separation boundaries in the case of laser heating of pre-, post-, and eutectoid steels. We also obtain results from calculations carried out on a number of laser treatment regimes on eutectoid steel.

Microstructure of hypo-eutectoid steel in laser hardening process.

The heat-affected-zone microstructure was analyzed both theoretically on S45C carbon steel as an example of hypo-eutectoid steel irradiated with CO2 laser beams. The affected zone was examined with the Nomarski microscope, SEM, EPMA and micro-hardness tester. The micro-hardness in the hardened layer varies remarkably, depending on carbon contents of the regions. The distribution of carbon contents is subject to the diffusion process of carbon atoms from the prior-pearlite colonies to ferrite phase after Ac1 transformation. Final microstructure is formed below the Ms point in the rapid cooling period. Experimental results could be explained well with the theoretical thermal history at each part of hardened layers. Microstructural change can be estimated by theoretical analysis on hardening process as well as the shape and size of transverse cross-section of the hardened layers.

歯車の浸炭焼入過程における炭素濃度依存性を考慮した温度，組織および応力の解析

The paper deals with the simulation of carburized-quenching process as a coupling problem among temperature, metallic structure and stress with consideration of their dependence on carbon content. The distribution of carbon content was determined by using the diffusion equation. A set of coupled fundamental equations of heat conduction, transformation kinetics and elastic-plastic constitutive modelling were formulated to obtain temperature, metallic structure and stress.The carburized-quenching process of a gear of nickel-chromium steel (SNC 815) was analyzed using the finite element technique. Also, the normal-quenching process was analyzed for comparison. The calculated results were compared with the experimental data of the distribution of residual stress, Vicker's hardness and micrographs showing metallic structures as well as carbon content.

Restoration carburizing of steel ShKh15 in endothermal atmosphere

1. It was shown that it is possible to program the distribution of carbon concentrations in high-temperature restoration of ShKh15 in a controlled endothermal atmosphere. 2. In designing the restoration process one must take into consideration the change in the surface layer that occurs during decarburizing (grain growth and internal oxidation of alloying elements).

Use of photoelectric method of spectral analysis for studying the distribution of carbon concentration in diffusion coatings

Use of photoelectric method of spectral analysis for studying the distribution of carbon concentration in diffusion coatings

高周波加熱による高温ガス浸炭

For the purpose of rapid carburizing of steel, we studied induction high temperature carburizing for Ni-Cr-Mo case hardening steel SNCM 23, in the atmosphere of propane-butane gas (JIS LPG No. 3) only or in the atmosphere diluted by nitrogen, and examined the influence of heating temperature (950°∼1300°C), holding time (below 90 min), gas flow (0.5∼1.51/min), dilute ratio of gas (propane-butane gas: nitrogen gas……1:4, 1:8, 1:16) on the rate of carburizing and microstructure. The results were as follows: (1) When the atmosphere was propane-butane gas only, the soot deposited at the surface of the specimen, and with prolongation in carburizing time, carburizing was injured. Under this condition, the rate of carburizing was a little larger than that obtained by the conventional gas carburizing at the same temperature.(2) When the atmosphere was diluted by nitrogen gas, the soot did not deposit and for the dilute ratio adopted in this experiment, the rate of carburizing was about 1.4 times larger than that obtained in the propane-butane gas only at the same temperature. Under this condition, the depth of the carburized layer was 2.0 mm at 1200°C for 30 min or 1.8 mm at 1300°C for 10 min. (3) The surface of the carburized layer had a carbon content which was rich enough to obtain the hardness above Hv 700, and the carbon content distribution curve became more gentle with increase in heating temperature. (4) The flow rate or the dilute ratio of gas did not affect the rate of carburizing so far as this experiment was concerned. (5) No grain growth was observed at the core of the specimen carburized at temperatures 1000°∼1300°C for only 30 min. For the carburized layer and core of the specimen, a normal microstructure and gentle hardness distribution curve were obtained by quenching and tempering.