Carbon Pickup Research Articles

Arc heating in the tundish with a graphite electrode in comparison to a metallic plasma torch

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Power increase of plasma heating systems by CO2addition into the furnace atmosphere: Investigations in view of the plasma ladle furnace

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Analysis of porous silicon silicon-on-insulator materials

Silicon-on-insulator materials are being used in the development of radiation hard VLSI electronic circuits and one promising route is the use of porous silicon. Porous silicon is produced by electrochemically etching selected regions of silicon wafers to produce volumes of highly reactive porous silicon which can be converted to dielectric oxide or conducting metal or suicide. Results are presented of accelerator-based nuclear reaction measurements of the behaviour of porous silicon under a range of conditions. Oxidation behaviour as a function of temperature and different annealing conditions is reported together with evidence of the pick-up and removal of carbon. Fluorine, which has been reported to improve radiation hardness, has been implanted into porous silicon and is found to be very mobile at 1090 ° C. Preliminary results are also reported on the distribution of chemical vapour deposited tungsten in masked porous silicon structures.

射出成形した高速度鋼ＳＫＨ５３の焼結挙動と機械的性質

Sintering behavior and mechanical properties of the injection molded SKH53 high speed steel were investigated. Water atomized fine powder mixed with organic binder was molded by injection into transverse rupture specimen. After thermal debinding, specimens were sintered in vacuum at the temperatures between 1215 and 1246°C for 1 hour. On the sintered specimens, transverse rupture strength was estimated and microstructures were examined in detail.The debound specimen exhibited very rapid densification at the tempreature between 1220 and 1225°C, which is characteristic to liquid phase sintering. Above 1225°C, nearly full density was attained and the specimens showed high transverse rupture strength more than 200kg/mm2. When the sintering temperature of 1240°C was exceeded, however, transverse rupture strength sharply decreased with the formation of continuous grain boundary carbides.For the binder and the debirding method used in this study, the amount of carbon picked up from binder was inferred about 0.17wt% from the chemical analyses of the powder and the sintered specimen.In conclusion, excellent mechanical properties can be obtained by applying powder injection molding to SKH53 high speed steel if sintering temperature is strictly controlled. But pick-up of carbon from binder should be taken into consideration to control carbon content of sintered parts.

A Dual Stream Model of Carbon Pickup based on Carbon Activity

An improved model of carbon pickup (CPU) in cupolas was derived from a previous model. The improved model assumes that, upon melting, (1) the liquid iron and steel descend the cupola without interm...

P. F.

The effect of pulse duration and electrode type (copper or graphite) on the pick-up of carbon in the surface of a die steel shaped using electrodischarge machining and on surface microcracks has been studied. The present work suggests that the number and the size of surface microcracks increase with pulse duration when machining with a copper electrode, but there is some evidence to suggest that, when using a graphite electrode, the number and the length of microcracks and the average thickness of the recast layer may be greatest at intermediate (75–150μs) pulse durations. Although no definite conclusion can be drawn from the results, it is suggested that this may be because the manner of decay of the temperature field after each pulse is determined by both electrode material and pulse duration. At high current densities and long pulse durations, the length and frequency of microcracks is increased greatly at the corners of specimens machined using a graphite electrode, but this occurred to a much lesser extent when using a copper electrode – a difference that would seem to reinforce the suggestion that the characteristics of the temperature field after each pulse depend on the electrode material. It was concluded that carbon was absorbed from the dielectric (paraffin) rather than from the electrode. The amount of copper absorbed did not depend on pulse duration.MST/1040

Use of Tribocor 532N for a carbon-free induction furnace for vacuum-induction melting and casting of uranium and its alloys

Vacuum-induction melting (VIM) of uranium and its alloys commonly utilizes graphite crucibles and components that are typically coated with crucible/mould washes [1, 2] of yttria, zirconia or erbia. Carbon/ carbide contamination of the uranium and/or alloys arises from several mechanisms [3-5] that are enumerated in Table I along with the level of pick-up observed in large castings produced from feedstock containing 33 + 15w.p.p.m. carbon. The carbon/ carbide contamination has very undesirable effects on metallurgical properties, and many efforts have been made to reduce or eliminate this contamination. Because the carbon contamination all results from the use of graphite components in the VIM operation, the most obvious method of eliminating carbon/ carbide contamination in uranium systems is to replace the graphite components with carbon-free (or noncarbon) components. This letter summarizes the results of our effort to develop a carbon-free induction furnace at the Oak Ridge Y-12 Plant. Initially, the carbon-free furnace utilized oxidebased ceramics (alumina-silica or alumina-zirconiasilica) along with a plasma-sprayed tungsten susceptor [6]. Recently, however, a new material (Tribocor 532N, an alloy produced by Fansteel, Inc., of 50 wt % niobium, 30 wt % titanium, 20 wt % tungsten nitrided at > 1800°C [7-13]) has been shown to be relatively inert with uranium and its alloys [14] and, thus, to be an ideal candidate material for a noncarbon crucible/ susceptor. The Tribocor 532N material is a heavily nitrided metal (1.6ram (0.063in.) nitride-affected depth, with 0.25 mm (0.010 in.) of mostly nitride) and thus has a very hard outer layer (microhardness ~2300kgmm -2 at 100g load) consisting mostly of titanium nitride. The hard, abrasion-resistant (Ti, Nb)N surface of Tribocor 532N prevents gouging and puncturing upon loading heavy uranium parts, a main source of the uranium graphite reaction as a contribution to carbon pick-up (see Table I). The uranium-carbon monoxide reaction [3] in standard graphite-component VIM furnaces occurs primarily from in-leakage of air followed by an oxygen reaction with the graphite crucible to generate the carbon monoxide which is readily gettered by the molten uranium. This carbon monoxide source is virtually eliminated with Tribocor 532N: although some oxidation of Tribocor 532N can occur at production-level vacuum levels (6.7 to 33.4 Pa or 50 to 250#m), the surface appears to remain inert and intact. Conventional crucible/mould coatings [1, 2] do not react with Tribocor 532N as they do with graphite; thus the coating-graphite reation is eliminated. Coating outgassing could contribute a low level carbon pick-up (estimated below l w.p.p.m.), which could be eliminated by using an inorganic-binderbased coating. Zirconia coatings are quite effective with Tribocor 532N and can be used instead of yttria. Yttria is preferable to zirconia for coating graphite only because of its greater stability with graphite. Zirconia and Yttria are equally good with uranium [15, 161. In addition to eliminating sources of carbon con-

高純度フェライト系ステンレスクラッド鋼の溶接に関する研究 ＩＩ 肉盛溶接部の脆化機構

A study on the mechanism of the embrittlement in the low interstitial ferritic stainless overlay welds has been undertaken using 26Cr-1Mo steels with carbon content ranging 20 to 490 ppm. Tensile test was performed on 26Cr-1Mo steels with various carbon contents and grain diameters in order to obtain the fracture stress, friction stress and Hall-Petch slope of the steels. Various mechanisms proposed in the literatures for brittle fracture were evaluated with comparison the experimental results and the calculated fracture stresses through each models. It was elucidated that the embrittlement of 26Cr-1Mo steel examined could best be explained by Almond's model involving the embrittler effect of grain boundary carbides to give lower crack initiation energy, and it was suggested that the increase in the thickness of grain boundary carbide due to pick-up of carbon from the base metal during welding might be the main cause of the overlay weld embrittlement in the low interstitial ferritic stainless steels.

An X-ray Diffraction Method for the Determination of Temperatures in Coke Reactions

Information about the conditions and reactions in a foundry cupola is essential to understand the thermochemistry of a cupola and thus improve its efficiency. A potential source of such information is coke taken from inside an operating cupola. In the region of the cupola that extends from the melt zone to the taphole, coke is directly involved in important chemical processes such as combustion, gasification, slag formation, iron sulfurization, carbon pickup, and oxide reduction. Coke is also suspected of being involved in the transport of silicon to the liquid iron. Each of these processes produces characteristic physical and/or chemical changes in the coke, making it possible to extract information about the processes from an examination of coke pieces taken from within an operating cupola. A program to study such coke samples is in progress. To effectively interpret these data it is necessary to know the temperature history of the coke being examined, especially the maximum temperature attained by the coke piece in the cupola.

Inconel 617の高温ガス炉近似ヘリウム中における腐食挙動

Corrosion tests of Inconel 617 were carried out in a temperature range from 900°C to 1040°C in helium environment with small amounts of impurity gases, which was the simulated primary coolant of High Temperature Gas cooled Reactor (HTGR), and the carburization, decarburization, and oxidation were investigated in terms of temperature.(1) The alloy was carburized in the temperature range from 900°C to 970°C, but was decarburized above 990°C. The transition temperature from carburization to decarburization was estimated to be 975°C. In the temperature range, where carburization occurred, the largest carbon pickup was observed at 940°C, however, in the temperature range of decarburization, the degree of decarburization increased with the increase of temperature.(2) In the temperature range of carburization, the carburized layer was observed at near-surface region, and Cr-Mo carbides precipitated along the grain boundaries and twin boundaries. In the temperature range of decarburization, the carbides along the grain boundaries disappeared, and this led to the formation of altered layer, the depth of the layer reaching to about 2000μ after 500h corrosion at 1040°C.(3) In contrast to the results that the oxide films formed at high temperature in air were dense and protective, the films formed in the helium environment were very porous and less protective. Further, the chromium content in the oxide films along the grain boundaries beneath the surface decreased with the increase of test temperature. This could lead to make the films much less protective.

Influence of sodium in calculating the strength of reactor unit elements

Basis of the Calculation Method. The effect of the action of liquid sodium on constructional materials may be caused by a variety of elementary processes [i]. However, in calculating the strength of heat-exchanger reactor equipment parts it is normally limited to a study of the influence on the material of only certain of them such as thermal mass transport, the influence of oxygen in the sodium on corrosion, the reduction in stress-rupture strength of metals, the increase in creep rate of metals, decarburization of pearlitic steels, and carbon pick-up of austenitic sneels. In liquid sodium the rate of thermal mass transport is low. However~since heat-exchange equipment is designed for a long service life (10-20 years) a substantial decrease in part thickness as a result of the occurrence of even such a slow process is not impossible. Because of the linear character of thermal mass transport kinetics [i, 2] its influence on the strength of parts may be calculated by calculating the decrease in their thickness by multiplying the corrosion rate by the proposed service time of the part. At present it is impossible to give the corrosion rate of each type of steel and alloy individually both as a result of insufficient study of the thermal mass transport processes of constructional materials and for the reason of a significant spread in corrosion data. Therefore, in Strength calculations it is rational to group them by three types of materials characterized by close values of the thermal mass transport rate -- pearlitic steels, chromiumnickel austenitic steels with a nickel content up to 15%, and nickel base alloys -- and to represent them in the form of a log v vs I/T curve similar to that shown in Fig. 1 for austenitic chromiunr-nickel steels and drawn on the basis of the maximum thermal mass transport rates [3-7 et al.]. The mass transport rate of austenitic chromiunr-nickel steels and alloys containing from 15 to 50% nickel (an element capable of mass transport to a known degree) may be determined from Fig. 1 by multiplying by the coefficient ~ = v,/v (in accordance with Fig. 2), which is the ratio of the corrosion rate of steels and alloys with an increased nickel content to the corrosion rate of 12KhI8NIOT steel. The corrosion data presented refers to pure sodium, i.e., that containing up to i0-3~ 02. The higher values of corrosion rates in sodium containing oxygen may be calculated by using the coefficient K = vo/v (Fig. 3), i.e., the ratio of the corrosion rate of the material in sodium contaminated with oxygen to the rate in pure sodium [3]. If the part is at all times under the action of static stresses and at the same time experiences thermal mass transport the reduction in its life is more correctly determined from the results of laboratory investigations of the stress-rupture strength and creep of samples in liquid sodium. In this case the influence of the active medium is far more than that related to a simple decrease in cross section [i, 8]. However, such tests are complex, and the amount of the corresponding information is small. Therefore, until now the primary method of alloying for the reduction in stress-rupture strength and the acceleration of creep of materials is the introduction of safety factors to the values of stress-rupture strength and creep determined in air. Summarizing of experimental data makes it possible to propose a number of safety factors for the stress-rupture strengths (105 h) and creep (i0-5%/h) (Table I). As experience in the use of sodium loops has shown, one of the most intense corrosion processes is decarburization of pearlitic steels, which is especially intense if austenitic steels are in contact with the sodium at the same time. This process leads to the formation oN the surfade of the parts of a layer with lower short-term and stress-rupture strengths than the original. In view of the fact that in decarburization the carbon content decreases gradually in the direction of the steel surface, in calculating the depth of the decurburized layer it is necessary to select a conditional maximum relative value of the carbon content in it. This may be selected as 0.7, i.e. , the layer in which the carbon content drops

Effects of Silicon Content and Oxidation Potential on the Carburization of Centrifugally Cast HK-40

Abstract The influence of oxidation potential on the gas carburization resistance of cast HK-40 tube sections was evaluated in equilibrated hydrogen-ethane-steam mixtures or equivalents at 1366 K. Below an oxidation potential roughly corresponding to the stability limit of SiO2 as a surface species, carburization was pronounced in all alloys, with only a slight reduction in the extent of carbon pickup with high alloy silicon contents. At higher oxygen contents in the gas, resistance was proportional to both alloy silicon content and to oxidation potential. The results are interpreted in terms of silica stability and the kinetics of silica formation. It is suggested that more realistic assessments of materials performance in carburizing environments will require the oxidation potential to be taken into account.

Preparation of in-situ Nb<inf>3</inf>Sn-Cu wire by consumable arc melting

Procedures have been developed for casting 10 cm diameter Cu-Nb ingots and for fabricating these castings into Nb <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</inf> Sn-Cu in-situ wire. Operating conditions which produce consumable arc cast ingots homogeneous to 1.5 wt % Nb are presented along with analyses of macro-segregation, carbon pickup and Nb dendrite size. Carbon impurity level is found to be an important parameter which controls the critical current.

A physical and chemical examination of an ethylene steam cracker coke and of the underlying pyrolysis tube

The physical properties, chemical composition and structure of a carbonaceous deposit formed on a radiantly heated HK40 steel tube at 920 to 930° C after ~ 50 days cracking operations in naphtha-steam have been examined. The deposit consisted of two layers. The innermost (i.e. adjacent to the tube) varied in thickness from 20μm to 1.5 mm, and was formed by heterogeneous reactions catalysed by iron and nickel. Enhanced deposition was characterized by a higher concentration of entrapped chromium rich oxide particles, a principal source of catalytic species. The outer deposit layer was of uniform thickness, had a columnar radial and an axial layered structure, which together with the absence of any significant inorganic constituents, suggested an autocatalytic growth mechanism. The corrosion of the inner (pyrolysis) and the outer (hot box) surfaces of the underlying HK40 steel tube had similar features. The chromium rich outer scales were of variable thickness, due to the attack of certain grains, underlying which were zones denuded in carbon precipitates and intergranular silica formation. The major difference was carburization from beneath the decarburized zone at the inner surface. The processes of decarburization, carburization and of intergranular corrosion were interconnected. Carbon pick-up probably resulted from a crevice corrosion mechanism. A general reduction in the nitrogen level through the cracker tube, with enhanced denitriding at both surfaces, originated from a similar mechanism to that responsible for decarburization. The more severe denitriding at the inner surface was derived from chromium nitride conversion to the more stable chromium carbide.

The use of in the x-ray photo-electron spectroscopy analyses of passive layers on stainless steel

The repassivation of a commercial grade 18% Cr 8% Ni austenitic stainless steel in low temperature, neutral, de-oxygenated water was studied by XPS, obtaining composition profiles by argon ion milling. Evaluation of the technique revealed negligible effect of sample transfer through air from the spectrometer to the corrosion cell, but photo-electron attenuation and reduction in peak definition resulted from organic carbon pick-up both from water and spectrometer vacuum. The passive layers contained chromium-rich and iron-rich areas. The Cr 3+, Fe 2+ and Fe 3+ cations are incorporated in layers containing both OH − and O 2− ions. The unreacted nickel of the alloy showed an attenuation of the 2p 3 2 signal with exposure which presented a unique opportunity to calculate film thickness. Increases in refreshment rate (1, 3 and 6 ml/h) at 313 K and 353 K respectively increased the film thickness (1.5–3.0 nm); possibly due to increased carbon accreation, incorporating hydrogen-bonded water into the film. The outer 33% of the film revealed (Fe 2+ + Fe 3+)/(Cr 3+) corresponding to alloy proportions, suggesting no overall selective oxidation or dissolution.

Evaluation of Solid Metal Specimens Produced for Spectrographic Analysis by the Inert-Gas dc-Arc Fusion of Wire and Chips

A study has been made of the chemical composition of solid-metal buttons of low-alloy steel, stainless steel, high-temperature alloys, and copper-base and aluminum-base alloys produced by the dc-arc fusion of wire and chips under argon shielding. The effect of fusion on 22 elements commonly encountered in these alloys has been determined quantitatively. A correlation has been shown between boiling points and element losses. With the exception of zirconium, no significant changes in the composition of metallic elements having boiling points greater than manganese (2150° C) were noted while using the recommended procedures for button preparation. Steels showed consistent, slight losses of manganese and occasional loss of zirconium. Losses of lead in copper-base alloys and of magnesium, lead and manganese in aluminum-base alloys, which occur with high currents, may be eliminated by first briquetting the chips, then fusing at relatively low amperage. Consistent and significant losses of zinc were noted. Carbon pickup from the graphite electrode is slight, but inconsequential. Copper pickup from the water-cooled copper cup is usually negligible.

On cracking and carbon pickup in the oxide formed on uranium in carbon dioxide at 650°C

On cracking and carbon pickup in the oxide formed on uranium in carbon dioxide at 650°C

Investigation of high-temperature carburizing of steel in solid carburizer with high-frequency heating

1. An increase in the carburizing temperature of steel using high frequency heating and solid carburizer, increased the productivity by a factor of 3–4 at 1000° C and by 5–8 at 1150° C compared with ordinary heating. 2. Successful high-temperature carburizing in a solid carburizer depended basically on prevention of local carbon pick-up by the steel at its contact points with carburizer particles; this was achieved by precoating the steel with chalk. 3. The results of high-temperature carburizing depend on temperature, duration of treatment and the content of carbonates in the carburizer. The greatest influence is shown by temperature and with its increase, the depth of the case increases rapidly while its saturation with carbon falls off. The optimum content of BaCO3 in the carburizer is 8–10%. 4. Upon holding at high carburizing temperatures, the austenite grain grew violently in the case and less so in the core. After a single quench, the impregnated layer was coarse-grained and had a strong tendency to retain austenite; this resulted into low brittle strength. 5. A double heat treatment was required after high-temperature carburizing to secure high mechanical properties of case and core in the investigated steels. Protection from carbon saturation (stop-off action) could be secured by copper coatings up to 1000° C and by chromium coatings above this temperature.

Brittle failure of steel parts heated in salt baths deoxidized with potassium ferrocyanide

1. Steel components heated in baths deoxidized with potassium ferrocyanide have a thin,hard and brittle surface layer causing premature failure. 2. With increase of the time of holding and the ferrocyanide content, the surface layer becomes more brittle and therefore more dangerous. With about 2% ferrocyanide, only 8 minutes in the bath produce a surface layer about 100μ deep. 3. When specimens are heated in a salt bath deoxidized with ferrocyanide, a network is formed at the austenite grain boundaries, either at the surface, or a little distance below it. 4. There is comparatively little carbon pickup during the first 7–8 minutes' holding of specimens in the salt bath; and carbon depletion occurs after three hours. Nitrogen is absorbed to an extent which increases with the amount of ferrocyanide in the bath and the time of holding. 5. Deoxidizing of a salt bath with ferrocyanide is unacceptable for pre-quench heating of stressed components of constructional steel.

Use of resistance pickup units for recording gastrointestinal movements

Carbon pickup units for registration of motor activity from different portions of the digestive tract and of the gall-bladder under different conditions of series experimentation are described. Units are implanted in the areas under study, and output terminals are soldered to the pairs of a plastic coil which is fastened in the abdominal wall.