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By Maria José Santos Lima

Neste trabalho a estrutura cristalina do carbeto de tântalo (TaC), que é um material extremamente duro, com elevado ponto de fusão e elevada estabilidade química, foi analisada por difração de raios- X e pelo método Rietiveld.Para isto, o carbeto de tântalo foi obtido a partir do precursor tris(oxalato)oxitantalato de amônio hidratado, através de reação gás-sólido e sólido-sólido a baixa temperatura (1000°C) e curto tempo de reação, e foi caracterizado através de Difração de Raios-X (DRX), Refinamento Rietveld e Micróscopia Eletronica de Varredura (MEV). Através das analises de DRX e do refinamento Reitiveld para o TaC com S= 1,1584, observou-se a formação do carbeto de tântalo puro com estrutura cúbica e tamanho médio de cristalitos na ordem de 12,9 nanômetros.

Aug 16, 2017

By Denise Weber, Jürgen Kateloe, Marku Papst, Laurenz Preusse, Axel Preusse

"The angle of draw (in Germany, referred to as Limit Angle) plays a significant role in the field of mining subsidence engineering. This applies both to the assessment of the affected area by underground mining activities as well as applied methods for the prediction of ground movements.Recent observations using remote sensing show that ground movements outside the affected area defined by the angle of draw have been detected in German hard coal mining. Since the affected area by underground mining activities also plays an essential role regarding claims of landowners with damages to their houses and infrastructures, possible solutions for limiting the size of the affected area will be presented in this paper.Ground movements which exceed the affected area of an underground coal mine, as defined by the angle of draw will be shown in an exemplary manner. Present knowledge indicates an expectation that ground movements outside the affected area will not cause damage of major significance.This paper outlines the consequences for all affected parties regarding ground movements due to underground coal mining that exceed the extent of the area defined by the currently assumed angle of draw. This will be visualized in a case study.INTRODUCTIONGermany has a long tradition of coal mining, especially in the mining area of the Ruhr district. Following a long period of mining activity, the area is now highly populated and densely developed. In such an environment, it is of utmost importance to calculate and predict ground movements initiated by mining activities; therefore, the research here focused on the prediction of ground movement for the last decades. Special attention was given to the development of accurate ground movement models, which can be utilized in all mining areas. These models are based on different influencing factors such as depth of mining, worked thickness and the angle of draw.Depending on these models, the mining companies calculate the area of land subsidence; the predicted results are used for financial calculations and planning. For structures on top of zones with a high risk of deformation, structural measures can be applied, construction warnings can be given and, in cases of damage, compensation can be planned. The technical and economic planning was performed for all areas of mining subsidence. The most important factor for the outer limits of mining subsidence is the angle of draw (Ger. Grenzwinkel), which plots the border of the area of mining subsidence."

Jan 1, 2015

By H Zhang, A Lawrence

To accommodate the fast growing need for services in Singapore’s Marina Bay downtown area, Marina South, the construction of a common services tunnel (CST) was required. The CST includes various services such as telecom cables, power lines and water pipes. A deep excavation and temporary earth retaining system (TERS) was required to facilitate the construction of the tunnels. Marina Bay is reclaimed land over thick soft marine clay which is likely to be still consolidating. The deep soft marine clay poses a big challenge for deep excavations in downtown areas where highways and sensitive structures are close by. This paper presents a case study of part of the CST Phase 1B and 2 at Marina South, in particular a 26 m deep excavation supported by a 46 m diameter temporary caisson. The construction started in late 2006 and the basic structure was completed in early 2011. The caisson was formed by 1.0 m thick overlapping diaphragm wall panels with a capping beam and three ring beams at different depths. Two-dimensional finite element analyses were conducted to predict the ground settlement, lateral displacement, bending moment and hoop stresses in the diaphragm wall and ring beams during different excavation stages. A comprehensive instrumentation and monitoring scheme was established to verify the design predictions, control excavation safety and trigger the contingency plan to protect public safety. The impact of construction activity, unbalanced temporary stockpiles and adjacent deep excavation for a mole removal will be discussed.CITATION:Zhang, H and Lawrence, A, 2014. A case history of a deep excavation in a big circular shaft in Singapore marine clay, in Proceedings 15th Australasian Tunnelling Conference 2014, pp 581–588 (The Australasian Institute of Mining and Metallurgy: Melbourne).

Sep 17, 2014

By Pedro Boson Gambogi

Aços com microestrutura completamente perlítica são utilizados para fabricação de componentes submetidos a condições severas de carregamento mecânico frequentemente combinado com atrito. Estes aços têm desempenho mecânico afetado principalmente pelo espaçamento interlamelar da perlita. O objetivo deste trabalho foi demonstrar os benefícios do uso da Microscopia de Força Atômica para determinar o espaçamento interlamelar da perlita de um aço eutetóide laminado a quente. Para tal, imagens da microestrutura de amostras retiradas na direção longitudinal e transversal à laminação foram obtidas e processadas com auxílio de um Microscópio de Força Atômica. Como resultado, destaca-se o fato da técnica utilizada ter se mostrado uma ferramenta versátil para caracterização quantitativa do espaçamento interlamelar da perlita. Foi observado espalhamento dos valores medidos do espaçamento interlamelar principalmente influenciado pelas condições de resfriamento do aço durante a transformação austenita-perlita.

Aug 16, 2017

By Bruna Helena Malovini Loiola

O presente trabalho apresenta os resultados de têmpera a partir da temperatura de transformação da austenita para ferrita em um aço microligado seguido de revenido de 200 a 550°C. Foram avaliadas as fases presentes no equilíbrio termodinâmico em função da temperatura de formação para verificar quais fases foram solubilizadas nas condições de tratamento térmico. Após os tratamentos de têmpera e revenido, foram realizadas caracterizações microestruturais e de microdureza. Os resultados indicaram presença de ferrita poligonal em conjunto com constituintes displacivos como ferrita acicular, bainita e martensita em baixa fração volumétrica. Ambos os constituintes apresentaram variação de microdureza com o revenido e apresentaram envelhecimento na temperatura de 550°C. Este envelhecimento foi atribuído à precipitação de carbonetos tipos M7C3 e MC com base nas simulações termodinâmicas.

Oct 30, 2017

By Emerson J

Drilling has always been one of the most important parts of the exploration process with most companies spending around 25% of their budget on drilling. Although superficially there appears to be little difference in drills and drilling practice a number of major refinements have taken place over the last decade that have significantly changed the drilling scene. One of the most important advances has been in hydraulic engineering giving rise to the Dual Purpose top drive drilling rigs. These have led to significant productivity increases with the high rotation speeds and longer fleets. Downhole technology has also advanced with better hammers, stronger drill rods, impregnated coring bits and improved drilling fluids. Although geologists continue to measure drilling performance on a cost per metre basis, greater consideration is at last being paid to the quality of sample produced. This is particularly the case with RC drilling where quite sophisticated automatic and semi automatic splitting devices have been developed. Drill operators are now required to be experienced in both Diamond coring and air drilling and be better qualified to maintain the more sophisticated machinery. Management of drilling companies or drilling divisions has also had to change to accommodate both the high capital cost of equipment and the demands of keeping drilling a cost effective exercise.

Jan 1, 1987

By Paulo Santiago

Redução dos custos de operação e a produção de aço com menor impacto ambiental são diretrizes unânimes na siderurgia atual. A tecnologia das Turbinas de Recuperação de Topo (Top Recovery Turbines – TRT) é um aliado importante para seguir nessas direções. As TRTs produzem energia elétrica a partir do gás de alta pressão proveniente do topo dos Altos Fornos, gerando energia elétrica sem impacto em emissões. Durante a campanha de operação da turbina, a mesma pode perder eficiência operacional devido a, dentre outros, deposição sobre as palhetas. Com o intuito de melhorar o desempenho da turbina estabilizando sua geração durante toda sua campanha, foi desenvolvido um trabalho de dosagem de polímero dispersante na água de spray da turbina (para turbinas com tecnologia de água de spray na admissão do gás). A dosagem do polímero dispersante visa reduzir a deposição e incrustração nas palhetas, reduzindo assim a perda de performance durante a campanha causadas pelo incremento de massa nas palhetas. Os resultados alcançados em um teste de campo em uma siderúrgica no Brasil foram um incremento de 52% na geração durante a campanha onde o polímero dispersante foi aplicado. Com a aplicação do polímero, uma melhora significativa na confiabilidade e performance da turbina assim como a possibilidade da redução no consumo de água foram atingidos

Oct 30, 2017

By M S. Stern, R Aguila

To control direct blasting costs many open pit mines dewater and line wet blastholes before loading them with ANFO or Heavy ANFO blends of explosives. The plastic lay-flat tubing used for these liners can be punctured during loading and allow water to partly dissolve and desensitise the explosive column which reduces blasting performance.

Jan 1, 1997

By André Nogueira

A etapa de flotação convencional do Concentrador 2 ocorre em um circuito com 13 tanques de flotação que recebem o produto dos ciclones limpadores (-0,15mm +0,030mm). O concentrado desta etapa contribui com aproximadamente 80% do volume de produção do concentrador. A necessidade da implantação do sistema de controle avançado de processos (SCAP) advém da alta heterogeneidade na alimentação do concentrador, uma vez que a Samarco não conta com pilha de homogeneização. O objetivo principal do projeto foi maximizar a recuperação metálica da flotação convencional e reduzir a variabilidade do teor de sílica no concentrado final. Aliado ao sistema de análise de imagem de espuma e ao analisador de sílica online, a ferramenta demostrou que, além de atingir os objetivos esperados, trouxe estabilização ao processo e padronização da operação.

Aug 16, 2017

By Bob Robinson

In 1990, the European Space Agency (ESA) initiated a technology transfer program to stimulate the wider use of technology developed by the European and Canadian space communities. This paper focuses on the method of technology transfer from the space industry to terrestrial industries, with a focus on the mining resource sector within a program called the Harsh Environments Initiative (HEI) created in 1997. Other resource sector applications include forestry and oil & gas. C-CORE in partnership with the Mining Innovation, Rehabilitation and Applied Research Corporation (MIRARCO) supported by ESA, Canadian Space Agency (CSA) and European R&D organizations conduct projects to promote and demonstrate the transfer of innovative technologies from space to non-space industries. Space programs have and continue to develop new knowledge for extra-terrestrial application, e.g., satellite earth observation, manned missions and unmanned planetary exploration. Many of which hold the potential for application on land and ocean. Currently, space technologies of interest to the mine sector range from robotics and image analysis to sensors, software and advanced materials. The HEI works to identify and apply these types of technologies in the areas of automated/tele-controlled mine operations and mine monitoring.

May 1, 2001

By Leslie F. Sawatsky

Each potential oil sands developer deals with the question of optional sources of raw water to supply large water demands that range from 50 to 80 million cubic metres per year for each of six existing and planned developments. The Athabasca River currently supplies nearly all of the water to the existing mines via conventional bank intakes, which has resulted in some concern over the effects of reduced river flows. This paper describes the various water supply options, and the likely scenario for future oil sands water supply projects. Various water supply options have been suggested including Athabasca River water via infiltration galleries, groundwater, combined Athabasca River water and alluvial groundwater using wells (i.e. bank filtration systems), diversion of tributary rivers, utilization of large lakes in the region and pumping from other large rivers in the region. Investigations show that the size of river catchment needed to support raw water usage by a typical oil sands mines exceeds 5,000 km2 eliminating all tributary rivers that are located in the oil sands region except those rivers with large drainage areas like Firebag and MacKay Rivers. Lakes cannot be used as a source of supply due to large water deficits for smaller lakes and the large cost of sourcing water from a lake as large as Lake Athabasca. A groundwater source alone would not likely meet the large water demands. River intakes on the Athabasca River will likely continue to be the most practical water supply option for oil sands mines north of Fort McMurray, although various types of Athabasca River intakes are possible. Existing intake systems include screened riverbank intakes, forebay intakes, and river bottom intakes. Infiltration galleries are not feasible for most sites, though some bank-filtration-type systems using high capacity wells may be an option if there is sufficient thickness of high-permeability alluvium at a suitable location in the Athabasca River valley.

May 1, 2004

By T. Tamagawa

A gaseous chlorination process for hydrometallurgical treatment of a chalcopyrite concentrate was investigated. The overall process is visualized to consist of low temperature chlorination-selective oxidation, followed by aqueous chloride leaching and SX-EW for producing electrolytic copper elemental sulfur and ferric oxide. In this article, the chlorination phase of the processes is described. Initially, the chlorination behavior of chalcopyrite-concentrate micro-pellets was investigated using a small batch-type fluidized bed reactor. The optimum conditions thereby established was used in continuous chlorination tests. The chlorinated products thus prepared were used in the selective oxidation phase of the investigation.

Jan 1, 1999

By S. K. Sharma, R. Markandeya, G. Venkateswara

"In this study, a three level Box- Behnken factorial design combined with Response surface methodology (RSM) for modeling of process parameters of Multi Gravity Separator (MGS) for recovery Iron values from sub grade iron ore, Deposit No. 5, Bailadila complex has been developed. The three significant operational parameters of MGS, Drum rotational speed (RPM), Drum inclination (degrees) and quantity of wash water (LPM) were considered in the experimental work. Other parameters like feed percent solids, shake frequency and shake amplitude were maintained constant. The ‘as received’ sub grade iron ore sample is admixture of lump and fines and chemically assayed 40.80% Fe, 40.90% SiO2, 0.24% Al2O3 and 0.22% Loss on Ignition (LOI). The obtained results were evaluated with the Box-Behnken factorial design, RSM and also Quadratic programming(QP). Second order response functions were produced for Fe in terms of grade (%) and recovery (%) of the concentrate fraction. Taking advantage of QP, it was observed that maximum grade of 62.21% Fe achieved at an inclination of 4.3degrees, 2.7LPM of wash water and at a drum speed of 198 RPM. Similarly a maximum Fe recovery of 65.37% weight can be achieved at 4.3degrees inclination, 2.6LPM wash water and at a rotational speed of 212 RPM Predicted values of responses obtained using model equations were in good agreement with the experimental values. The influence of the process variables of the multi gravity separator concentrator on grade and recovery of concentrate fraction were presented and discussed."

Jan 1, 2014

By F. N. Bender

Percolation leaching of wad-type manganese ores was investigated, using a novel system of alternate upward passage of sulfur dioxide gas through moistened ore and downward percolation of wash solutions to extract solubilized manganese. Bench and large-scale tests designed to simulate vat and heap leaching were made on four wad ores from Arizona and Nevada and on a pailomelane ore from Arizona. Three of the wad ores required prebaking at 500° to 600° C. to produce a permeable agglomerate that would not slake during percolation washing. The hard-type ore and one of the wad ores that contained a large amount of granular gangue did not require prior roasting. The deportment of the different ores toward leaching and percolation was studied with particular reference to the influence of the sulfur dioxide - oxygen ratio and the effect of gas dilution on the rate of manganese dissolution, dithionate formation, and acid production. Crushed charges of the ores, as coarse as 1 inch and as fine as 1/4 inch, were treated for periods of 5 to 11 days. Percolation of the gas and leach solutions through the charges was achieved without difficulty. The manganese extractions varied between 78 and 97 percent and depended upon the size and type of ore leached. The average quantity of sulfur dioxide required in the larger scale tests was about 2.6 pounds per pound of manganese recovered. The dithionate formation varied from 0.35 to 0.9 pound per pound of manganese extracted depending upon the strength of leaching gas.

Jan 1, 1957

By F. E. Diebold

The methodology for describing the geochemistry of elements in a coal seam have been developed. This has been applied to the Rosebud Coal Seam, which is an economically important member of the subbituminous coals of the Fort Union Formation in Eastern Montana. The method development has involved a detailed study of two popular techniques for determining the metal geochemistry of coal, namely, whole coal analyses and coal physical fractionation. The mathematically contrived element associations (whole coal analyses technique) and the element concentration trends in the float and sink fractions (physical fractionation technique) are considered to lead to only qualitative conclusions concerning the chemical associations of the elements in coals. Additionally, the processes taking place with the coal during low temperature ashing in an oxygen plasma are experimentally investigated and shown to be of sufficeint extent that the use of such low temperature ash for deciphering element geochemistry is questionable. The method developed in this study is a chemical fractionation that involves the sequential leaching of coal with water, 0.5 N HC1, 3 N HC1, 2 N HNO3, and 48% HF. These leach solutions are shown to selectively dissolve the predominate inorganic phases, sulfates, Ca and Mg carbonates, Fe sulfides and K alumino-silicates and quartz, respectively. These phases were identified with the use of XRD, SEM, EM and leaches (water and 0.3 N HC1) of whole coal and low temperature ash. The incorporation of the anion-exchange step in the leaching scheme was investigated and was observed to warrant further study of such intensity to be, at the time, unuseable. The use of this sequential leaching technique on several coal samples from the same seam generates element concentration trends that can be quantitatively interpreted with respect to the chemical associations of the minor and trace metals in the coal seam. The properties of the various seams of economic importance in the Fort Union Formation in Eastern Montana are compiled and presented. The subsequent conclusion is that there is not a large variation in the properties of these coal seams and that the variations within the Rosebud are within one order of magnitude. The chemical fractionation technique, investigated in this study, was applied to composite tipple samples of the Rosebud seam. Each composite sample represented 76,800 tons of coal. A minimum of 32% of the Ca and Mg are present as separate water soluble sulfates. An excess of the sulfate ion in the water extracts shows the predominating influence of the ion exchange capacity of the organic compounds in the coal. Based upon the CO content of the coal and the HC1 leachate data, 25 to 30% of the alkaline earth elements exist as separate carbonates and the remainder are associated with the organic compounds. The small fraction of the illite that dissolves in the HC1 and HNO3 leachates accounts for the K and Al. Slight dissolution of the pyrite in the HCl solvent occurs, the small amounts of Li and As do not relate to any known phase and Mn is present as a separate carbonate phase. Fe and a significant amount of the As exist in the pyrite that is dissolved in the HNO. Se is equally partitioned between the pyrite and the organic compound~. Most of the trace elements are found in the HF solutions. Li, V, and Cr were interpreted to be associated with the clay minerals (kaolinite and illite). Ni and Pb appear to be present as separate phases and 50% of the Hg is HF soluble but is not chemically related to any known inorganic phase.

Jan 1, 1983

By G. Deschênes

In Part I of the work, gold and silver were shown to be efficiently extracted from Kupol samples using lead nitrate in a cyanide leach system. In Part II, a comparison of the technical and economic merits of a new technology called CELP (CANMET Enhanced Leaching Process) was made with the cyanidation/AVR(Acidification-Volatilization-Recycling) process using 8 metallurgical variability samples as well as a large composite sample which represented initial two years of Kupol mill feed. The composite sample had 33.4 g/t Au and 289 g/t Ag. The metallurgical demonstrated that the CELP produced very similar gold and silver leach extractions compared to the standard Cyanidation /AVR leach conditions at 1/2 the cyanide concentration (1000 ppm NaCN in CELP vs. 2000 ppm for cyanidation/AVR leach conditions). It was estimated that the total cost per ton, were approximately the same for the two technologies (total cost of the CELP with the use of Merrill-Crowe at $46.48/ton, with cyanidation/AVR at $46.13/ton). However, the implementation of the CELP would eliminate a capital expenditure of approximately $5 million. Eight variability samples used to confirm the previous results showed that on average the gold and silver leach extractions with the CELP and the feasibility leach conditions were very similar for gold extractions, but 4.6% higher for silver extractions compared to the conventional cyanidation. The decision was made to remove AVR cyanide recovery from the Kupol flowsheet and implement the CELP at Kupol. The ability to use conventional leach equipment with the CELP and simplify the flowsheet was also a factor, given the remote location of the Kupol Mine.

Jan 1, 2009

By H. E. Cross

In a minerals-recovery context, the object of exercising control over milling operations must be threefold, 1) To achieve maximum recovery at 2) minimum operating costs and 3) making maximum use of installed equipment, Milling is one of a sequence of operations which have as their objective the economic recovery of minerals from mined ores, All operations in the sequence are interdependent and each is both influenced by and itself affects all other unit processes. The part which grinding plays in achieving each of the above objectives is indicated in the following analysis: In South Africa, the most important mining operations are still the gold mines, A vast reservoir of knowledge and experience in treating the Witwatersrand and associated ores has been accumulated. and recoveries are consistently high, However residue values do vary and frequently this is due to fluctuations in the degree of grind, The significance of changes in residue values is indicated by the following example: On a modern mine, the residue values varied from 0,25 to 0,33 dwi; per 2000 lb, during a period of 6 months, The cash value of the gold thus lost varied therefore between $0.44 and $0.58 per 2000 lb, ton. A residue which assays 0.30 dwt per ton would contain approximately 0.26 dwt as undissolved gold and 0,040 dwt per ton as dissolved gold present in residual solution after filtration. This dissolved gold loss is a function of efficiency of filtration and varies from 0.030 to 0,.070 dwt per ton of residue.

Jan 1, 1970

By W. S. Holt, E. T. Tkac, R. A. Grange

QUANTITATIVE knowledge of the time element involved in austenite transformation in a particular steel provides a sound basis for understanding and planning heat-treatment. Such knowledge is conveniently obtained by measurement of austenite transformation as it occurs at each of a series of temperature levels. The results of these measurements usually are summarized in the form of the now familiar isothermal transformation diagram (I-T diagram, TTT diagram, or S-curve). Although a considerable number of such diagrams already have appeared in the literature, there remain many compositions of commercial importance for which no I-T diagram is available. The diagram for many such steels may be predicted from published data with sufficient accuracy for most practical purposes, but for others no satisfactory prediction can be made because the effect on austenite transformation of one or more of the important alloying elements present is not well enough known. Such a steel is Nitralloy, Type 135-Modified, which, containing about 1.25 per cent aluminum, differs from any whose I-T diagram has been published. This paper presents results of a study of the isothermal transformation behavior of a sample from a commercial heat of this aluminum-chromium-molybdenum steel, together with pertinent supplementary data including the equilibrium transformation temperatures (Ae3 and Ae1), the temperature range of martensite formation, and the end-quench hardenability. These data are directly applicable to the heat-treatment of this type of steel and are of interest in revealing some of the fundamental effects of aluminum as an alloying element in steel. MATERIAL All specimens were prepared from a 13-in. diam bar forged from a 5 by 5-in. billet from a commercial heat made in an electric arc furnace. The composition of the bar was; C, 0.41 per cent: Mn, 0.57: P, 0.016: S, 0.005: Si, 0.24: Ni, 0.17: Cr, i.57: MO, 0.36: Al, 1.26. The forged bar was normalized from 1750°F (955°C) and then tempered for one hour at 1200°F (650°C), this tempering treatment having been given to facilitate the machining of specimens. EQUILIBRIUM TRANSFORMATION TEMPERATURES In hypoeutectoid steel the minimum temperature at which austenite is completely stable, Ae3, and the maximum temperature at which austenite is completely unstable, Ae1, are of great significance in heat-treatment. Since these temperatures are dependent upon com-

Jan 1, 1946

By K. A. Grange, W. S. Holt, E. T. Tkac

Quantitative knowledge of the time clement involved in austenite transformation in a particular steel provides a sound basis for understanding and planning heat-treatment. Such knowledge is conveniently obtained by measurement of austenite transformation as it occurs at each of a series of temperature levels. The results of these measurements usually are summarized in the form of the now familiar isothermal transformation diagram (I-T diagram, TTT diagram, or S-curve). Although a considerable number of such diagrams already have appeared in the literature, there remain many compositions of commercial importance for which no I-T diagram is available. The diagram for many such steels may be predicted from published data with sufficient accuracy for most practical purposes, but for others no satisfactory prediction can be made because the effect on austenite transformation of one or more of the important alloying elements present is not well enough known. Such a steel is Nitralloy, Type 13s-Modified, which, containing about 1.25 per cent aluminum, differs from any whose I-T diagram has been published. This paper presents results of a study of the isothermal transformation behavior of a sample from a commercial heat of this aluminum-chromium-molybdenum steel, together with pertinent supplementary data including the equilibrium transformation temperatures (Aeaand Ae,), the temperature range of martensite formation, and the end-quench harden-ability. These data are directly applicable to the hcat-treatment of this type of steel and are of interest in revealing some of the fundamental effects of aluminum as an alloying element in steel. Material All specimens were prepared from a 1 1/4 i-in. diam bar forged from a 5 by 5-in. billet from a commercial heat made in an electric arc furnace. The composition of the bar was; C, 0.41 per cent: AIn, 0.57: P, 0.016: S, 0.005: Si, 0.24: Ni, 0.17: Cr, I.j7: Mo, 0.36: All 1.26. The forged bar was normalized from r750°F (95s°C) and then tempered for one hour at rzoo°F (650°C), this tempering treatment having been given to facilitate the machining of specimens. Equilibrium Transformation Temperatures In hypoeutectoid steel the minimum temperature at which austenite is completely stable, Aep, and the maximum temperature at which austenite is completely unstable, Ael, are of great significance in heat-treatment. Since these temperatures are dependent upon com-

Jan 1, 1948

By W. S. Holt, K. A. Grange, E. T. Tkac

Quantitative knowledge of the time clement involved in austenite transformation in a particular steel provides a sound basis for understanding and planning heat-treatment. Such knowledge is conveniently obtained by measurement of austenite transformation as it occurs at each of a series of temperature levels. The results of these measurements usually are summarized in the form of the now familiar isothermal transformation diagram (I-T diagram, TTT diagram, or S-curve). Although a considerable number of such diagrams already have appeared in the literature, there remain many compositions of commercial importance for which no I-T diagram is available. The diagram for many such steels may be predicted from published data with sufficient accuracy for most practical purposes, but for others no satisfactory prediction can be made because the effect on austenite transformation of one or more of the important alloying elements present is not well enough known. Such a steel is Nitralloy, Type 13s-Modified, which, containing about 1.25 per cent aluminum, differs from any whose I-T diagram has been published. This paper presents results of a study of the isothermal transformation behavior of a sample from a commercial heat of this aluminum-chromium-molybdenum steel, together with pertinent supplementary data including the equilibrium transformation temperatures (Aeaand Ae,), the temperature range of martensite formation, and the end-quench harden-ability. These data are directly applicable to the hcat-treatment of this type of steel and are of interest in revealing some of the fundamental effects of aluminum as an alloying element in steel. Material All specimens were prepared from a 1 1/4 i-in. diam bar forged from a 5 by 5-in. billet from a commercial heat made in an electric arc furnace. The composition of the bar was; C, 0.41 per cent: AIn, 0.57: P, 0.016: S, 0.005: Si, 0.24: Ni, 0.17: Cr, I.j7: Mo, 0.36: All 1.26. The forged bar was normalized from r750°F (95s°C) and then tempered for one hour at rzoo°F (650°C), this tempering treatment having been given to facilitate the machining of specimens. Equilibrium Transformation Temperatures In hypoeutectoid steel the minimum temperature at which austenite is completely stable, Aep, and the maximum temperature at which austenite is completely unstable, Ael, are of great significance in heat-treatment. Since these temperatures are dependent upon com-

Jan 1, 1948