Endothermic Atmosphere Research Articles

Study on the High-temperature Properties of High-titania Slags produced with Cr-bearing Vanadia-titania Magnetite Smelting in Blast Furnace

The high-temperature metallurgical property of high-titania slag is one of the most significant indicators to measure the production status of Cr-bearing vanadia-titania magnetite blast furnace (CVTM-BF). Due to the continuous high temperature in the furnace, titania is over-reduced to titanium carbonitride with a high melting point (over 3000°C), which causes the viscosity of the slag to be too high to separate the molten iron and molten slag well. However, a high proportion of N2 in the air blasted into the furnace participates in the generation of TiN, and the large required air volume causes a high coke ratio and excessively high furnace temperature, which is not conducive to suppressing the over-reduction of titania. Here we show that TiN was significantly reduced and the metallurgical properties of high-titania slag were improved by injecting abandoned basic oxygen furnace gas (ABOFG), which is a kind of by-product gas containing CO, CO2, lower N2 and high physical heat. The experimental results demonstrated that the ABOFG was likely to function in suppressing TiN from 2.46% to 1.06%, dropping the melting temperature down from 1478.8°C to 1290.3°C, pushing the slag-iron interface tension from 0.641 N/m to 0.882 N/m as well as bring the viscosity down from 0.353 Pa⋅s to 0.341 Pa⋅s. Overall, ABOFG as a kind of endothermic atmosphere compared to O2-enriched air is beneficial to restrain the over-deduction of titania to TiN upon the slag-coke interface with lower N2. It also helps CVTM-BF to be recovered from the continued deterioration as soon as possible.

Simulation modeling of the automated endothermic atmosphere quality management system for chemical and terminological processing of metals

In the article the simulation model of the automated system of quality management of endothermic atmosphere for chemical and thermal treatment of metals is developed. A step-by-step description of the algorithm implementation is given and an example of the proposed method application is given. The results of the development can be used in the design of automated control systems.

Low-temperature cementation – perspective technology of hardening of toothed parts

The structure, properties and geometrical accuracy of gear wheels after chemical heat treatment which cementation was carried out at 930°C and 870°C are investigated. Advantage of low-temperature cementation of toothed parts in size of a radial runout, fluctuation of a side clearance, ovality of an internal opening and the area of a spot of contact between teeths of the strengthened gear wheels is shown. Influence of structure of the endothermic atmosphere on mechanical properties and intensity of saturation by carbon steel 15HGN2TA and 20HGNMTA is investigated. It is established that increase in content of hydrogen from 20% to 40% in the endoatmosphere increases saturation speed carbon steel by 10 – 34%, excludes their hydrogen saturation and keeps indicators of mechanical properties of the cemented parts. The technology of chemical heat treatment of toothed parts including cementation at 870°C in the endothermic atmosphere containing 40% of hydrogen in the structure is developed and recommended for application.

Features of Technological Materials Application in Thermal Manufacturing

Widely used in thermal production quenching surroundings, gas atmospheres and working mixtures for shot peening are considered. Features of materials at their use are presented and recommendations for more effective application are given. The change of quenching surroundings cooling capacity on the water-soluble polymer basis after an annual operation is shown. Hardening oils during operation are exposed to oxidation and viscosity index change, what affects on the quenched products properties. For endothermic atmospheres that are used in the parts chemical-thermal treatment the composition improvements are required. Working mixtures for shot peening must have a certain composition, properties and sizes, depending on the tasks to be solved.

Low-temperature gas carburizing of austenitic X5CrNi18-10 steel activated with a thin iron coating

The study investigated the effectiveness of X5CrNi18-10 stainless steel activation by means of a thin iron coating for low temperature carburizing and the usefulness of the generator endothermic atmosphere for this process. In order to activate the steel surface an iron coating with a thickness of 1–2 µm was applied on it electrolytically electroless. Carburizing was carried out at the temperatures of 450–500oC in the atmospheres based on the generator endothermic atmosphere with the addition of nitrogen or hydrogen. Coating modification by adding a few per cent of sulphur to iron resulted in a reduction of the dispersion of hardness on the surface, and the appearing soot showed a loose connection with the coating. Alternative activation by means of the short-term oxy-nitriding and the following diffusion annealing promoted an increase of hardness on the surface and a reduction of its dispersion after carburizing. After carburizing in endogas of X5CrNi18-10 steel at 470oC during 30 h, a carburized layer with a thickness of approx. 35 μm and the surface hardness of approx. 1150 HV0,05 were obtained. Lowering the carburizing temperature by 20oC resulted in a decrease of the layer thickness by 20% after 24 hours of carburizing. The changes in the thickness of the layer carburized in endogas and the hardness on the surface since the carburization were determined.

Quality-cost analysis of modern carburising technology implementation in the production cycle of cog elements for the aviation industry

Purpose: The aim of the study was to analyse the possibility of introducing vacuum carburising technology with pre-nitriding in the aviation industry. Design/methodology/approach: The samples have been tested with new technology and the planet gear requirements for aviation applications were determined. The effect of pre-nitriding technology used before vacuum carburising was also investigated for antidiffusional surface protection. A cost analysis of replacing the conventional technology with a new low-pressure carburising technology has also been introduced. Findings: Structural characteristics of the obtained layers were determined in terms of carbon concentration distribution, effective and total thicknesses, hardness of the surface and core, structure, grain size, residual austenite content and lack of decarburization and internal oxidation. The degree of degradation of various forms of anti-diffusion protections in the form of pastes and coppering and their effect on the surface layer have also been investigated. The comparative economic analysis of the use of conventional and vacuum technologies, namely the carburization in a function of the required thickness of the hardened layer and temperatures of processes, has also been made. Research limitations/implications: Basing on the studies and analyses carried out in this work, it can be concluded that the introduction of pre-nitriding carburising technology instead of conventional carburising technology in endothermic atmosphere is justified qualitatively and economically alike. Practical implications: The analysis of the test results confirms that it is possible to meet the requirements of the aviation industry through high temperature pre-nitriding vacuum carburising. The results of anti-diffusion protection tests confirm that it is possible to use anti-fouling pastes instead of electrolytic copper. Cost analysis confirms the economic benefits of implementing a new technology. The implication of the above is the willingness of the proposed technology to allow testing in the aviation industry. Originality/value: The research confirming the fulfilment of quality requirements set for hardened layers in aviation applications which also have an economic advantage.

Optimization of processing conditions in plasma activated nitrogen–hydrocarbon carburizing

Problems with intergranular oxidation, energy efficiency and carbon footprint of the conventional endothermic atmosphere (CO–H2–N2) carburizing are forcing heat treating and manufacturing companies to move toward increasingly capital- and operating-cost expensive, low-pressure/vacuum carburizing methods. To offer a less-expensive alternative, a new activated carburizing method has recently been developed, bridging the endothermic atmosphere and vacuum processes, where a plasma-activated, oxygen-free, non-equilibrium nitrogen–hydrocarbons gas blend is utilized. The optimization of activated carburizing for industrial application presented here involved improvement of multi-dimensional case uniformity. As a part of this optimization, a computational fluid dynamics study was conducted for examination of gas flow field inside heat treating furnace and trays holding steel parts treated. To maximize carburizing rate and mitigate soot in non-equilibrium nitrogen–hydrocarbon atmospheres, effects of different gas mixture combinations were investigated. A mixture of N2–0.4% C3H8–1% CH4 mixture has been found to provide a well carburized case with minimized soot in the atmosphere and reduced coke deposition on the metal surface. The soot formation mechanisms for non-equilibrium carburizing atmospheres were also discussed.

Development of Nitrogen-Hydrocarbon Atmospheric Carburizing and Process Control Methods

Atmospheric pressure carburizing and neutral carbon potential annealing in nitrogen containing small additions of hydrocarbon gases can offer cost and steel surface quality alternatives to the comparable, endothermic atmosphere, or vacuum operations. An experimental program was conducted for refining real-time process control methods in carburizing of AISI 8620 steel under N2-CH4, N2-C3H8 blends containing <5 vol.% of hydrocarbon gas at 900 and 930 °C. Multiple types of gas analyzers were used to monitor residual concentrations of H2, CO, CO2, H2O, O2, CH4, C3H8, and other hydrocarbons inside furnace. A modified shim stock technique was additionally evaluated for correlation with gas analysis and diffusional modeling using measured carbon mass flux values (g/cm2/s). Results of this evaluation work are presented.

MPPA-SSI12 automated module facility for “liquid” carburizing

An automated module facility of model MPPA-SSi12 for making controlled endothermic furnace atmospheres based on carbon-containing liquids is described. The facility is used for batching and feeding process liquids into carburizing shaft electric furnaces with automatic control of the carbon potential by changing the flow of added air.

Equilibration of plain carbon and alloy steels with endothermic carburizing atmospheres: Part I. Activity of carbon in plain carbon steels

Experimental data on the activity of carbon in commercial plain carbon steel, AISI type 1010, common shim-stock material, at 871 °C, 927 °C, 1000 °C, and 1038 °C, equilibrated with common endothermic carburizing atmospheres, were found to be generally in agreement at relatively high carbon concentrations with previously published data on pure iron equilibrated with CO-CO2 mixtures. However, noticeable differences were found at low carbon concentrations. The carbon contents of type 1010 steel were generally higher compared to those of previously published data regarding pure iron except at very high activities of carbon. The carbon contents of type 1010 steel foil specimens by weight gain were generally higher than or equal to those chemically analyzed; however, they corresponded with each other within 0.02 wt.% except at very low carbon potentials.

Multi-objective optimisation of gas carburising process in batch furnaces with endothermic carburising atmosphere

A methodology for multi-objective optimisation of gas carburising heat treatment has been developed in terms of cost, cycle time and quality of carburised parts. The optimisation strategy is based on: modelling the effect of process parameters (carbon potential, temperature and time) on the mass transfer coefficient and carbon diffusivity in austenite, correlating the observed variations in the process parameters on the carburising kinetics, and developing a robust multiobjective optimisation technique to achieve the desired case depth with minimum cost and minimum case depth variation. The tradeoff between these two objective functions corresponded to carburising at 938·5°C and carbon potential of 1·14 wt-%C. This combination produced the target case depth of 0·6 mm with corresponding ±0·05 mm case depth variation and minimum total cycle cost. Overall, application of this multi-objective optimisation will result in significant energy reduction by shortening cycle time and thereby enhancing furnace capacity.

05/00617 Synthesis gas production via dielectric barrier discharge over Ni/γ [sbnd]Al 2O 3 catalyst

Problems with intergranular oxidation, energy efficiency and carbon footprint of the conventional endothermic atmosphere (CO–H2–N2) carburizing are forcing heat treating and manufacturing companies to move toward increasingly capital- and operating-cost expensive, low-pressure/vacuum carburizing methods. To offer a less-expensive alternative, a new activated carburizing method has recently been developed, bridging the endothermic atmosphere and vacuum processes, where a plasma-activated, oxygen-free, non-equilibrium nitrogen–hydrocarbons gas blend is utilized. The optimization of activated carburizing for industrial application presented here involved improvement of multi-dimensional case uniformity. As a part of this optimization, a computational fluid dynamics study was conducted for examination of gas flow field inside heat treating furnace and trays holding steel parts treated. To maximize carburizing rate and mitigate soot in non-equilibrium nitrogen–hydrocarbon atmospheres, effects of different gas mixture combinations were investigated. A mixture of N2–0.4% C3H8–1% CH4 mixture has been found to provide a well carburized case with minimized soot in the atmosphere and reduced coke deposition on the metal surface. The soot formation mechanisms for non-equilibrium carburizing atmospheres were also discussed.

Properties of internal heat supply with carbon dioxide reforming of methane over a Ni/Al2O3catalyst.

An addition of 6%-oxygen into a reactant of CH4/CO2(1/1) gave lower operating temperature of carbon dioxide reforming of methane by 130 K in obtaining 0.029 MPa of H2, accompanied by a more endothermic atmosphere in the catalyst bed than in the absence of oxygen.

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.

Thermochemical Treatment of Steel 20Kh with Cyclic Changes of Temperature

Results of a study of saturation of steel 20Kh with carbon in an endothermic atmosphere with an additive of natural gas and ammonia under the conditions of cyclic temperature changes within 900 ⇄ 650°C are presented. It is shown experimentally that it is possible to form martensite and martensite-carbide structures in the diffusion layer depending on the process parameters. The distribution of carbon over the thickness of the diffusion layer is calculated.

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.

Super-carburization of low alloy steel and low carbon steel by fluidized-bed furnaces

The present work is concerned with super-carburization treatment on low alloy steel AISI 4135 and plain carbon steel AISI 1020 by fluidized-bed furnaces. Super-carburization is a repetition of carburization and precipitation heat treatment processes to produce a dense spheroidized carbide layer near to the steel surface. Carburization was conducted at 930°C and 800°C in an endothermic atmosphere with a carbon potential higher than 1.3% generated by the direct boosting of propane and air into the bed. The precipitation of carbides in steels was conducted at 600°C in a nitrogen-fluidized bed. The rapid cooling rate associated with the great undercooling of the fluidized bed effectively suppressed the formation of network cementite when carburized steels were cooled from the austenitizing temperature to the precipitation temperature. This phenomenon has made it possible for even a plain carbon steel to be super-carburized without difficulty.

Feasibility assessment of an endothermic gas generator-built-in fluidized bed furnace

Advantages of the fluidized bed furnace are claimed to be the rapid heating rate, fast atmosphere purging speed and good temperature uniformity. However, it consumes enormous amounts of fuel gas and the atmosphere composition in the bed is unstable because of direct boosting of fuel gas and air from the bottom of the bed. As a result, the effective treating zone of the bed is too narrow for applying the fluidized bed to high-quality carburization or bright heat treatment of steel. An endothermic gas generator-built-in fluidized bed furnace constructed with a catalytic zone in the lower part of the furnace was studied in this research. The fuel gas and air were stoichiometrically mixed and endothermically reacted in the catalytic zone before the product gases were guided upwards into the bed so as to acquire a stable endothermic atmosphere. The results showed that it substantially enlarged the effective working zone of the furnace, which made the precise carburization and/or bright heat treatment of steels possible in the fluidizing bed furnace. In order to simulate the high humidity season of the year in subtropical settings, the incoming air for reforming the endothermic atmosphere was further moistened according to the humidity of the rainy season and the results were compared with those of the theoretical computer calculations.

Using a catalyst in natural-gas conversion for preparing endothermic gas in the volzhskii automonile plant

Special catalysts are used to accelerate the conversion of natural gas in the converter of the generator for preparing protective endothermic atmospheres. VAZ has tested and introduced a catalyst of protective atmospheres (KZA) produced by the Novomoskovsk Branch of the State Institute of the Nitrogen Industry (GIAP) instead of the GIAP-25 catalyst used previously. The KZA catalyst is a promoted lower nickel oxide deposited on a large-pore carrier (cubic particles 17 mm in size) made of a chamotte-pearlite lightweight refractory of grade ShL-04 produced by the Vnukovskii Refractory Plant. During the eight years of employing this catalyst in VAZ its stability decreased from 1.5 years to 1.5 -4 weeks. The operating capacity of a catalyst usually decreases due to its break up into a dust-like state, which markedly decreases the penetrability of the process gases through the converter. The present paper is devoted to the causes of the low stability of the KZA catalyst and suggests ways to improve it.

Optimum schedules for carburizing articles of steel 16Kh3NVMFB in endogas

1. It is recommended to perform carburizing of structural alloy steel 16Kh3NVMFB in a controlled atmosphere with regulation of the carbon potential. 2. An endothermic atmosphere with addition of propane-butane as a carburizing gas is the preferred impregnating medium for carburizing. 3. Optimum impregnation with carbon for components of steel 16Kh3NVMFB with the aim of preparing high mechanical properties of the hardened case is achieved with carburizing by two-stage addition of propane-butane, leading after quenching to preparation of a martensitic structure with uniformly distributed carbides. The production process of gas carburizing in an endothermic atmosphere for steel 16Kh3NVMFB has been introduced in the Kazan Engine Building Production Association.