Search Documents

By S. R. Goodman, Hsun Hu

The formation of secondary - recrystallization tex-tlires in cube-textured 18-8 stain less steel (Type 304) Ilas been studied at three temperatures. Prolonged annealing at 100°'C protluces a PredoninanGly (520) [OOZJ-type texture, which is related to the cube te.ture of the primary lnatrix by a rotation of approxivzately 22 deg around the [001] axis in the rolling direction. Annealing at 1200 or 1300°C facers the formation of the (123)[272/-type texture, which is related to the matrix texture by a [111] rotation of app.voxiniately 40 deg. These observations suggest that in the secondary recrystallization of cube-texlut-ed stainless steel an apparent actilation energy for growth is higher for grains related to the tncrtuix Og [111] rotations thun those reloted by [100] rotations. THE formation of secondary-recrystallization textures in cube-textured primary matrices of fcc metals has been studied widely by various investigators. For Fe-40 pct Ni alloys, Pawlek' and wassermann2 reported that the orientations of secondary grains were related to the cube texture by rotations of 30 and 38 deg around [001] in the rolling direction. However, Rathenau and custers3 found that, while in one Fe-48 pct Ni alloy, most of the secondary grains were oriented with respect to the cube-textured matrix by rotations around [001] of 26.5 deg, in another alloy of a different origin, the orientations of secondary grains were related to the cube texture by rotations of approximately 35 deg around a [lll] axis. Similar orientation relationships were also observed between the secondary grains and the cube-textured primary matrices of copper.4"a No attempt was made to differentiate these two types of orientation relationships; reorientation by either a [111] or a [100] rotation was considered to be equally favored. The present investigation consisted of a study of the secondary recrystallization textures in cube-textured stainless steel. It was noted that the secondary grains formed in stainless steel were considerably smaller than those of Fe-Ni alloys or copper. This offered the advantage that the secondary recrystallization texture could be determined by the texture-goniometer technique, and a more detailed study of the textural development during the course of secondary recrystallization could be made. The effect of annealing temperature on the formation of secondary-recrystallization textures was also investigated. MATERLAL AND METHOD It was shown earlier"-" that a strong cube texture can be obtained in 18-8 stainless steels by rolling at 800°C to produce the copper-type deformation texture, followed by annealing at 800" to 1000°C for recrystallization. To improve the cube texture for the present study, a commercial-grade 18-8 stainless steel (Type 304) was rolled at 800°C first to 5 mm (0.2 in.) thick plates. Three of these plates were then stacked and welded together along the edges into a sandwich assembly. After annealing at 900°C for 20 min: the assembly was finally rolled at 800'C to 90 pct reduction in thickness with reheats and end-for-end reversals after each pass. Only the central strip, which was reduced from 5.0 to 0.50 mm (0.7 in. to 0.020 in.) thick, was used. The chemical composition of the steel in weight percent was as follows: C, 0.06; Mn, 0.38: Cr, 18.71; Ni, 9.56: P, 0.011; S, 0.009; and Si, 0.39. The purpose of rolling the strip in a sandwich assembly was to prevent direct contact between the central strip and the rolls. It was observed earlier" that, when the strip was rolled at 800°C without being enclosed in a sandwich assembly, the cube texture obtained by subsequent annealing at 900" or 1000° C for recrystallization was largely confined to the central section of the strip, while most of the recrystallized grains formed in the surface section of the strip were not cube-textured. This was obviously due to the fact that the actual temperature at the strip surface during rolling, as a result of direct contact between the strip and the cold and massive rolls, was considerably lower than 800°C. By using a sandwich assembly for hot rolling, the cube texture obtained upon subsequent annealing for recrystallization was found to extend through the entire thickness of the strip. After rolling, the central strip was taken from the sandwich assembly. and cut into specimens. Prior to annealing. the specimens were etched to 0.25 mm (0.010 in.) thick. A tube furnace provided with a purified, dry argon atmosphere was used for annealing. Textures were determined by the reflection technique. using a Siemens automatic texture-goniometer and ZrOz-filtered MoKa radiation. With a time constant of 4 sec. the preferred orientation of the secondary grains could be measured satisfactorily by the integrated intensities. Both (111) and (200) reflections were measured, and corresponding pole figures were constructed according to the techniques described previously.10 The agreement between results deduced from these two reflections was excellent. RESULTS AND DISCUSSION Secondary-Recrystallization Texture due to Prolonged Annealing at 1000°C. Fig. 1 shows the primary-recrystallization texture of a specimen annealed at 1000°C for 30 min. A substantial improvement in both sharpness and intensity of the cube texture, owing to the present processing method, can be noted readily by comparing Fig. 1 with similar pole figures shown earlier in Refs. 9 and 11. Secondary recrystallization

Jan 1, 1967

By Wenya Du, Qingbo Yu, Peng Li, Qin Qin

"A new heat recovery system is proposed. This system uses the endothermic heat of gasification reaction instead of sensible heat to recover the energy of molten blast furnace slag. The gasification technological parameter in molten blast furnace was calculated and the exergy of the system was analyzed. The gasification reactions were studied kinetically by the isothermal thermogravimetry using STA409PC thermal analyzer. The results showed that, according to different gasification agent, this system can produce syngas with different C-H ratio. The exergy efficiency of this system is high and its internal exergy loss rate is about 11%. This method can bring huge economic and environmental benefits which are important to the survival and sustainable development of iron-steel enterprises. The molten BF slag acts as not only thermal media but also good catalyst. The kinetic parameters on gasification reaction with different types of coal used differ from each other.IntroductionEnergy consumption in the iron-making process is about 50%~60% of the total energy input. The blast furnace is very important in the iron & steel process. So energy conservation and emission reduction about blast furnace is very important. In recent years, in order to recovery energy, many new technologies such as TRT (Top gas pressure Recovery Turbine) and CCPP (Combined Cycle Power Plant) were used in iron-making. But the energy of molten blast furnace (BF) slag has only been used limitedly so far.Molten BF (Blast Furnace) slag is the byproduct of iron-making at the high temperatures range from 1723 to 1923K, and has a large amount of sensible heat remaining. The yield of molten BF slag is about 300 kg per ton of pig iron. In conventional processes, molten BF slag is quenched rapidly using a large amount of water to produce a glassy-granulated slag. The quenching slag must be dried before it can be used in cement manufacture. During the process, a large amount of water was consumed and the energy of molten slag can not be recovered. At the same time, it causes environmental pollution problems. So the critical problems of the process are not only energy recovery of molten slag and reducing emission of H2S and SO2, but also guaranteeing the subsequent use value of slag. For this propose, many new technologies were investigated to recover the thermal energy of molten slag. The promising methods are dry granulation [1-4] and reforming of methane [5-9]. The method, utilization of reaction heat instead of latent heat and sensible heat, is quite attractive from viewpoints of energy storage without heat loss, and makes a connection to other industry. But both of them are in laboratory. In this paper, coal gasification in molten BF slag was used to recover the energy of molten BF slag. The gasification technological parameter in molten BF was calculated and the exergy of the system was analyzed. The gasification reactions were studied kinetically by the isothermal thermogravimetry using STA409PC thermal analyzer."

Jan 1, 2011

Fault detection and identification are major challenges in process engineering and manufacturing and the key component of abnormal event management systems. Timely detection, diagnosis and rectification of abnormal or faulty process conditions can lead to savings of billions of dollars in equipment damage and lost productivity, not to mention the prevention of injury and loss of human life associated with industrial accidents. A major contributing factor to current losses in industry is the reliance on human operators to interpret high-frequency samples from hundreds or thousands of variables simultaneously. As a result, the automation of fault detection and diagnosis is seen as crucial to the successful implementation of abnormal event management, the need for which is becoming all the more urgent given the increased complexity associated with modem industrial plants. In this paper, a methodology for process monitoring that uses support vector methods to extract nonlinear features from data is discussed and applied in the diagnostic monitoring of an industrial liquid-liquid extraction column.

Jan 1, 2005

By C. Caballero, A. Warczok, K. Itagaki, A. Moyano, J. Font

The Codelco Norte Smelter process 2,500 tpd of arsenic-bearing concentrates with an arsenic content of up to 1.5% in one of its two main smelting units, the Teniente Converter. The product, 1,100 tpd high-grade matte or white metal, is traditionally fed to the PS converters, while the 1,700 tpd of slag is fed to the slag cleaning electric furnace for copper recovery. This is achieved in a very reductive environment which reduces the viscosity of the slag and enhances the sedimentation of the high-grade matte droplets. The behavior of arsenic in this non-oxidative environment was studied at lab-scale and fundamental thermodynamic data were obtained. Based on these data a thermodynamicbase model to assess the arsenic behavior in reductive environment was developed. It is based on a mass balance for the reduction and sedimentation stages performed in an electric furnace which allows the recovery of high-grade matte droplets after decreasing the viscosity of the slag. This model can be a very suitable tool for predicting fractional distribution of arsenic in the slag cleaning electric furnace, when the distribution ratio, vapor saturation degree, temperature, y As and pO2 are given.

Jan 1, 2007

By C. H. Green

Recently two papers on the structure of eutectics were read before thc British Institute of Metals, one by F. L. Bradyl and the other by A. Portevin. 2 In the preparation of photomicrographs of laboratory specimens as illustrations for student work, and in connection with various researches, the writer has been working along the same line for some time and, therefore, was much interested in the results given, especially those of Portevin. He has correlated the information on the subject and has outlined a broad scientific basis for future work along this line. It is largely with the idea of adding something by way of illustration to the work already done that this paper is written. The eutectic is generally understood to mean the alloy having the lowest melting point of any alloy of the system, and in which the melt becomes supersaturated with reference to the two or more phases which separate out simultaneously or alternately. From the surface pattern, the eutectic means a structure with no primary crystals. It is not always easy to get the exact eutectic composition in making any alloy; in fact, a slight range in composition may be expected and some of the coarser particles may be richer in either of the composing metals. Even when chemical analysis shows the right composition, differences in density of the pure metals may cause segregation, or supercooling resulting from different crystallizing properties may give a surface pattern the appearance of being on one side of the eutectic point. However, the alloys on either side of the eutectic composition, showing primary crystals of one of the phases and the effect of the proeutectic form on the surface pattern of the eutectic make a very interesting study, which is slightly touched upon in this paper. The phases, or microconstituents, of a eutectic may be pure metals (Pb-Sb, Tl-Au), solid solutions (Cd-Zn), a pure metal and a solid solution (Ag-Sn), or a pure metal or solid solution with an intermetallic compound (Sb-Mg, Sb-Cu, As-Cu, Bi-Te, etc.).

Jan 1, 1925

By George Verley

A new and important task in assisting developing countries is the transfer of microcomputer technology applied to mineral exploration and mining. With this objective in mind, three micro- computers have been introduced in Niger and a training program has been put into place. The core of the program consists of two seminars in Niamey, Niger, after which the attendants will be able to operate a microcomputer and use a small library of application software.

Jan 1, 1987

By C. H. Herty

AN earlier paper on absorption of sulfur by the slag in the basic open-hearth furnace included a brief discussion of the absorption of sulfur during the melting period. The data available at that time showed that the amount of sulfur absorbed by the melting scrap was proportional to the sulfur content of the furnace gases, and the following statement was made: "The conclusion may be drawn from these results that if a gas entirely free from sulfur were used during the melting, any iron in direct contact with the gases would be completely, or nearly completely, desulfurized before it reached the bath proper." The experimental work discussed herein deals with absorption of sulfur by the melting scrap when fuels with both high and low-sulfur content were used. Before taking up the experimental work let us consider the process as a whole as to the "flow" of sulfur. The input of sulfur occurs in: 1, the hot metal charged; 2, the scrap; 3, the stone or lime charged; 4, the ores charged; and 5, the gas. Sulfur goes out of the furnace in the steel, the slag and the gas. The distribution of sulfur in the furnace depends on the sulfur concentration in each of these materials and on the equilibrium conditions between them.

Jan 1, 1926

By C. E. Saxon, F. E. Cash

"Adequate lighting for all mining operations would unquestionably tend to promote both safety and efficiency; this would be true not only for men but also for the animals that man impresses into service in mines. The Markeeta Coal Co. and the Alabama Fuel & Iron Co. both operating mines in Alabama, have found that equipping mine mules with portable electric lights is more efficient, much more humane, and far more safe for both men and animals then the more or less usual method of forcing the animal to do its work essentially in darkness.This report is intended to give the mining industry data, that will aid in trying to bring about safe and efficient operation of mines.The authors desire to thank Charles F. DeBardeleben, president, Fred R. Bell, general manager, Hewett Smith, C. H. Shepherd, and R. A. Sensing, superintendents for the Alabama Fuel & Iron Co.; and Charles F. DeBardeleben, Jr., president, and H. M. House, superintendent for the Markeeta Coal Co., for their cooperation in furnishing the data for this paper.The eight mines operated by the Alabama Fuel & Iron Co. and one operated by the Markeeta Coal Co. in Jefferson and St. Clair Counties, Ala., are the only mines in Alabama where mules are provided with portable electric lights, and there are few if any mines in other States in which this system is in use.These two companies are convinced that equipping all mine mules with good lights decreases underground haulage cost by animals by prolonging the useful life of the animals, increasing their efficiency, lessening haulage wrecks and delays on haulage, and increasing production. Last but not least of the advantages would be the more humane treatment of the animals.The nine mines are developed by slopes along the dip of the coal bed, with double-room entries on 200- to 300-foot centers turned right and left off the slopes and with approximately 1 per cent grade in favor of the loads. Rooms are driven up or diagonally up the pitch from these entries.A surface hoist delivers the empties from the surface to the entry sidetracks at the slope and pulls the loads to the surface. From these sidetracks, mules pull one to four wooden cars, each of which holds 1-1/2 to 2-1/2 tons of coal, deliver the empties to the rooms and entry faces, and pull the loads to the slope sidetracks. The mule haul varies from 100 to 3,000 feet; there are no locomotives or trolley wires in any of these nine mines, seven of which are rated as gassy and two as nongassy by the Alabama state Mining Department."

May 1, 1933

By W. B. Mather

A SURVEY of the technical literature concerned with oil well drilling methods and particularly with rate of penetration by various cutting media on different types of rock provides a mass of conflicting data. This is especially true with respect to, (1) the relative efficiency of diamond, rotary and percussion drilling operations; (2) the costs of the various types of drilling; and (3) the hardness factor of various types of rock and cutting media. The latter is the particular phase of the subject discussed here. The cause of the confusion may be attributed partially to a lack of 'basic knowledge concerning the physical properties of the cutting media and of individual types of rock. It is also due in part to a general lack of uniform standards in the industry for evaluating the hardness versus drillability of rocks while possible errors in interpretation by the authors of the various papers pertaining to the subject may be an additional cause of misunderstanding. The hardness of a mineral is defined by Dana' as "the resistance which a smooth surface offers to abrasion." Webster' states that hardness is "the cohesion of the particles on the surface of a body (as a mineral) as determined by its capacity to scratch another or be itself scratched." Rock hardness, although not usually defined in publications describing rocks, is assumed to be the same as the minerals which compose the rock or the resistance of the rock to abrasion. Drillability of a rock may be defined arbitrarily as the rate at which rock is penetrated by a definite type of drilling tool with the assistance of a specific type of cutting surface or medium and under speci- fied conditions as to speed of rotation and applications of pressure. Eventually the term penetrability may have to be employed to include any method of making boreholes in rocks, since methods other than those using conventional cutting surfaces are already in operation. A case in point is the jet piercing methoda which employs an oxy-acetylene flame as a means of penetration. The word hardness as used by the drilling fraternity has a variety of meanings which depend upon the type of drilling method employed. For example, in diamond drilling, hardness is interpretated as resistance to abrasion. In percussion drilling the term implies resistance to impact or indentation, while in rotary drilling, hardness is considered anal-agous to compressive strength. The three types of hardness—abrasion, impact and compression—are conflicting variables for different types of rock. Nevertheless, the term hardness is applied indiscriminately by the industry for the resistance of rock to penetration by any type of drilling technique. Abrasion Hardness Since 1818, Moh's scale of hardness, although only relative in nature, has been accepted universally as the method of measuring mineral and therefore rock hardness. In 1933, Ridgway, Ballard and

Jan 1, 1952

By O. W. Bilharz

INTRODUCTION ACID mine-water drainage is a serious problem with many mines in the Tri-State zinc and lead mining district. Particularly is this true when large volumes must be considered in unwatering old mines that have refilled with water which has dissolved the products of oxidation and has become chalybeate in character. The experiences discussed in this paper have to do specifically with the unwatering of a comparatively small area west of the town of Baxter Springs, Kans., where the pumping job was complicated by water of this type and where the extremely high sulphate content particularly effected that phase of mine drainage having to do with stream pollution. LOCATION, GEOLOGY AND HISTORY The Baxter Springs area of the Tri-State mining field is situated just west of the town of Baxter Springs and is a northeasterly extension of the main mineralized zones of the Oklahoma part of the district (Fig I). The mining area is traversed with well defined shear zones which provide easy circulation of ground waters and the ore bodies are found along these shear zones as localized enrichments wherever the structural conditions are favorable (Fig 2). The ore-bearing strata is Mississippian with an overlain capping of shale of Pennsylvanian age. This shale strata carries much pyrite and marcasite at its base and undoubtedly was a contributing factor to the subsequent high iron content of the water. The area originally contained a sulphide water which discharged as an artesian flow in springs within the town and gave Baxter Springs its name. These springs were famed for many years for their mineral water. This original sulphide water was first removed about 1917 and active mining was carried on west of the town during subsequent high metal price periods. Many small mines were opened, with each localized enrichment becoming a separate mine. During the depression mining ceased and all mines in the west Baxter area were allowed to flood. No serious effort was made to again unwater until higher prices caused from the demand for metal for World War II once more focused attention on this part of the field. ORIGINAL MINING RESULTS IN OXIDATION As plans for unwatering progressed, it soon developed that the mine-water pools had become strongly acid in character and carried large amounts of sulphates in solution. This occurred in the following way. When the original sulphide water was removed, shafts sunk, and mining carried on over a number of years, ferrous sulphate was formed by the spontaneous oxidation of the pyrite beds in contact with air admitted through churn-drill holes and mine openings. These products of oxidation can be seen today in the old mines of the district as crusts of crystalline sulphates

Jan 1, 1947

By H. J. Wu

The optimum performance in mineral processing plants usually demands the optimum size reduction, which is frequently achieved by a closed grinding circuit. Due to the difficulty associated with fine size classification, the size separation efficiency in closed grinding circuit is usually very low, which leads to huge circulating load and significant overgrinding. Recent development of Der-rick Stack Sizer has made an efficient fine size separation down to 200 mesh with a satisfactory screening capacity. With the efficient fine size separation with Derrick Stack sizer, the problems commonly associated with typical closed grinding circuit, including high circulating load and over-grinding, have been eliminated. Feedback from numerous Stack Sizer applications in iron ore industry indicated that, compared with conventional fine size classification equipment, the circulating load achieved by Derrick screen was usually decreased from approximate 300% down to 60% or so, while the iron recovery has been increased by 6% to 8% only by more efficient size separation in the closed grinding circuit. To study this phenomenon, this paper discusses the relationship between size classification, circulating load and mineral recovery in the closed grinding circuit. A simulation model to predict the improvement in the grinding circuit from more efficient screening is also introduced with this paper.

Jan 1, 2014

By P. Forrest

Based on the results of mathematical analysis, photoelastic modelling, and case studies, the mechanisms of longwall under- mining interaction has been thoroughly investigated. The effects of using yield pillars in combination with rigid pillars in lower seam mine design have been found to provide significant improvement in ground conditions during undermining. Off- setting of solemnized longwall panel entries relative to upper-seam remnant structures has proven to be effective in alleviating adverse stress conditions.

Jan 1, 1988

By C. L. Karr

The U.S. Bureau of Mines is optimizing the design of an air-sparged hydrocyclone. This report summarizes the initial stage of the project-the prediction of collision efficiencies for use in a comprehensive air-sparged hydrocyclone model. The equations of motion are presented in nondimensional form and solved numerically for a small spherical particle passing around a larger bubble in an infinite fluid under the influence of a strong force field. Collision efficiencies are determined from the calculated particle trajectories for values of Stokes' number, K, between 0.01 and 100 and for values of the nondimensional force, W, between 0.0 and 100. These large values of K and Ware needed to model high-performance flotation devices like the air-sparged hydrocyclone; solutions for the required K and W values have not appeared in the literature prior to this study. Effects of changes in particle-to-bubble radius ratio are considered for both viscous and potential flows. The results help predict the improved recovery of fine particles when flotation is performed in a strong force field.

Jan 1, 1990

By J. D. Price, W. M. Bertholf

Making maximum possible use of available equipment and material, CF&I placed a high-efficiency, high-capacity washery unit in the existing buildings to gain simplified operation, reduced manpower requirements, raised efficiency, and boosted production. THE central washing plant of the Colorado Fuel & Iron Corp. was first operated in 1918 to furnish coal for two 60-oven batteries of Koppers design. Prior to that time the coke for the blast furnaces had been secured from a number of beehive operations, some with their own washeries. The original washery had four Elmore jigs, which did not do as well as had been expected. In 1923 the jigs were taken out and replaced by Deister Plat-O tables, with various changes in auxiliary equipment. In 1936 the throughput of the plant was considerably increased by the installation of vibrating filters for recovery and drying of fine coal, thereby reducing a large recirculating load of fine coal which passed through the screens of the Carpenter driers. In the late 1940's it became evident that something would have to be done to keep the washery abreast of progress at Pueblo and other washeries. Coal requirements were nearly two and one-half times the original requirements of the 120 small ovens, as additional ovens had been built in 1930, 1938, and 1945, whereas no additional coal washing capacity had been added since the 1936 modifications. Much of the equipment, moreover, had seen better days. One answer to the problem was to build a new and completely up-to-the-minute plant, with sep- arate sections for coarse, medium fine, fine, and very fine coal. On the other hand, it might be financially more profitable to place a high-efficiency, high-capacity unit in the existing buildings. The washing problem at Pueblo is not unique, but it is approached differently. There are no established specifications for coke ash and sulphur. The plant is operated on the principle that if it is more economical to wash it out than to slag it out, wash it out; otherwise, send it on to the blast furnaces. With coals at the Pueblo plant costing what they do, the benefits of washing at a low gravity are questionable. Hence the primary problem is to eliminate the high-ash components and retain all the low and medium-ash components. Sulphur is no problem at all, averaging 0.6 pct in the coke. Since a good proportion of the free impurity in the coals is as large as the coal or bone or larger, it appeared that it would be safe to go to jig washing and discontinue crushing the coal before washing, as had been the practice with the tables. This would boost the throughput. It might also decrease manpower requirements and washing costs considerably. It was assumed at the start and has been demonstrated in the first year of operation that a jig will do as well on the fines as the tables had been doing. It would not be necessary to discount any gains due to increased efficiency in washing the coarse material because of incapacity to wash the fines. By washing at —2+0 mesh it would be possible to dewater, by screening, a considerable tonnage satisfactorily, for example, at —2 + % or —2 + l/4, and then crush it in a hammer mill. The —?+20 could be dewatered in centrifugal driers and the remain-

Jan 1, 1955

By H. Larson, J. Chipman

The ferrous and ferric oxide concentrations of slags, expressed as j = Fe+++/(Fe+++ + Fe++), have been established through gas-slag equilibrium at 1550°C in a range of oxygen pressure of 10-I to 10-9 equilibriumatm. The value of j is increased by basic additions (BaO, CaO, MgO, MnO) and decreased by acidic oxides (SiO2 and TiO2). Oxygen pressure is shown graphically as a function of composition for slags which are analogous to those at the slag-gas interface of the open hearth furnace. THE progress which has been made in recent years in understanding the chemistry of metallurgical slags has been based largely on studies of slag-metal and slag-gas equilibria. There is a considerable body of knowledge which is applicable to reactions occurring at the slag-metal interface in open hearth steelmaking. There is little information concerning reactions of the slag with the furnace atmosphere and hence little basis for an understanding of the transfer of oxygen, sulphur, or hydrogen between gas and slag. The oxygen pressure of the open hearth atmosphere is normally of the order of 10-1 to 10-3 atm which differs by several orders of magnitude from that of about 10" atm at the slag-metal interface. The chemical properties of the slag, for example, the ratio of ferric to ferrous iron and the ability of the slag to hold sulphur in solution, are greatly affected by changes in oxygen pressure. This investigation was undertaken to enlarge our knowledge of the effect of oxygen Pressure on steel-making slags. Using air or controlled mixtures of CO a CO2 a range of oxygen Pressures from 10.' to 10.' was covered. Review of the Literature There are only a few references in the literature which pertain directly to this investigation. The most important is that of Darken and Gurry1,2 on the system iron-oxygen. This work included the determination of the phase diagram of the system and also a study of the field of homogeneous melts and their oxygen pressures. Their apparatus and procedure were very similar to that used in this study. Iron oxide was melted in a platinum crucible under an atmosphere of CO2:CO, CO2:H2, H2O, CO2, air or O2 depending upon the partial pressure of oxygen desired. After equilibrium was reached, the sample was quenched and analyzed for ferrous and ferric oxide. By appropriate calculations these authors were able to determine the oxygen and iron activities in the various slags, heats of formation of the oxides of iron, and heats of solution of iron and oxygen in the liquid slags. In a subsequent paper' the same authors made a less thorough investigation of the effects of additions of lime and manganese oxide on the composition of iron oxide melts. Only a few experiments were made and those in a narrower range of temperature and oxygen pressure. Darken' has investigated the fusion temperature of iron oxide in contact with silica under various atmospheres. He found that the temperature changes from 1120° to 1447°C as the gas composition changes from CO2/CO equal to 20.8 to pure oxygen. A comprehensive paper by White" predates the work of Darken and Gurry. The decomposition of ferric oxide into oxygen and lower oxides of iron was studied from 1000° to 1650°C and under oxygen pressures from 2 to 76 cm of mercury. The effect of

Jan 1, 1954

By E. S. Machlin, Morris Cohen

GRENINGER and Troiano' were the first to establish the fact that the habit planes of mar-tensitic products are usually planes of high indices. In steels containing 0.55 to 1.4 pct C, the habit plane indices are {225}A.* In steels with more than 1.5 pct C and in Fe-Ni alloys, the indices are {259In. The presence of both habits in certain alloy steels has been reported recently." Several investigators"-" have subsequently attempted to provide an understanding of these complex habit relations. Bowles'6 work is the most recent and the most successful. Like Greninger and Troiano, Bowles concluded that the transformation occurs in two steps, the first, a strain (or displacement) that is homogeneous throughout the volume of the martensitic plate, while the second is a strain that is homogeneous only within relatively small portions of the martensitic plate. The first strain yields the measured tilt of the specimen surface, but does not produce the final martensitic structure. This and the correct lattice orientations are achieved by the second strain. Bowles also reasoned that each strain could be described by the motion of a plane of no rotation and no distortion (hereinafter called the invariant plane) in a direction not necessarily contained in the plane.** In applying these considerations to steels with {225}a habits, Bowles found that the habit plane coincided with the invariant plane of the first strain, a result which signified that the atoms move along certain paths during the transformation. Whether this correlation results from the existence of some sort of a plate nucleus6 lying along the invariant plane of the first strain, or whether the invariant plane primarily defines the preferred directions of propagation of the first strain, will be discussed in a later section. There are two obstacles to the general acceptance of Bowles' treatment: 1—it has not been shown that elements of his double-strain analysis are unique, and 2—it is not known whether his treatment applies to transformations yielding the {2591A habit. Unless these two questions are resolved, the correlation between the habit and invariant planes in the {225}A systems might be regarded as coincidental. Experimental Procedure Using a 70 pct Fe-30 pct Ni alloy as an example of a {2591A habit system, preliminary attempts were made to obtain a double-strain solution based on a Nishiyamax** set of orientation relations and on a Greninger-Troianot set, adopting the stereographic technique described by Bowles" who used the Kurd-jumow-Sachstt set in connection with the {225}A habit. These attempts were unsuccessful because the method is essentially one of trial and error and requires either exceedingly good luck or a prior knowledge of the results being sought. Consequently it was decided to measure independently the strain associated with the formation of a martensitic plate as well as the habit-plane indices of the particular plate. By means of matrix algebra, the measured strain was applied to the austenite lattice, whose orientation with respect to the strain was determined, in order to ascertain whether the resultant structure would have the lattice of martensite. This was not found to be the case, and hence it was assumed that the measured strain was the first of two Bowles-type strains, characterized by the motion of an invariant plane. A solution of this displacement was obtained in terms of the invariant-plane indices and the direction of motion of the atoms. Then the second strain

Jan 1, 1952

By M. Garfinkle, W. D. Klopp, W. R. Witzke

The tensile properties of binary W-Re alloys containing up to 33 at. pct Re were determined at temperatures from 78" to 3630°F. Elongations as high as 260 pct were observed in electron-beam-melted tungsten containing 23 at. pct Re when tensile-tested at 3630°F after a 1-hr anneal at 3090°F. All alloys tested under these conditions with rhenium contents between 20 and 28 at. pct exhibited elongations of at least 200 pct. These alloys also showed enhanced grain growth rates. The values of strain-rate sensitivity ranged between 0.2 and 0.3 for the alloys exhibiting high elongations. Houlezler, for swaged alloys tested just above the re-crystallization temperature, strain-rate sensitivities as high as 0.8 were observed. The high-temperature strengths of the high-rhenium-content alloys were also less than those of alloys with intermediate rhenium contents. ALLOYING with rhenium has two distinct effects on the mechanical properties of tungsten. One effect occurs in dilute solid solutions and is most clearly seen in the lowering of the hardness and of the ductile-brittle transition temperature at about 5 at. pct Re.1-3 The second effect occurs in the concentrated solid solution at about 25 at. pct Re, and is characterized by twinning and a larger decrease in the ductile-brittle transition temperature. An aspect of the high-rhenium-content alloy which has received little attention is the higher-than-usual tensile ductility at 3500°F.3 Anomalous high ductility has been observed in several other alloy systems. usually associated with a phase transformation or a solid-solubility limit.4'5 The phenomenon is now commonly termed superplasticity. High-strain-rate sensitivities6 and grain boundary sliding7 have been reported for materials that undergo superplastic deformation. Also, it has been found that superplastic materials usually have a very fine grain structure (less than 10 pm).8 and it has been proposedg that such a structure alone is sufficient for superplasticity. The purpose of the present study was to further characterize the high-temperature tensile properties of W-Re alloys to determine the conditions under which they might be superplastic. Tensile and selected strain-rate sensitivity tests were conducted on alloys containing 0 to 33.3 at. pct Re at temperatures from 78" to 3630°F. Grain-growth rates were also determined on most alloys at 3630°F. Fig. 1 indicates the compositions evaluated and their locations relative to the solvus line in the tungsten-rich end of the W-Re phase diagram. Twelve binary W-Re alloys containing up to 33.3 at pct Re were double electron-beam-melted and subsequently fabricated to 0.3-in. rod by extrusion and swaging. The starting materials were commercial powders of tungsten and rhenium with impurity levels as listed in Table I. The various blended W-Re compositions were hydrostatically pressed at 70 ksi. The pressed bars were drip-melted into 1.5-in.-diam ingots and then remelted into 2-in.-diam ingots at a chamber pressure of 10~5 torr. The ingots were canned in molybdenum and extruded to round bar at a reduction ratio of 6:l. The alloy extrusions were swaged to about an 80 pct reduction at 2100" to 2900°F. Buttonhead tensile specimens with a reduced section diameter of 0.16 in. and a gage length of 1.0 in. were centerless-ground from the swaged bars

Jan 1, 1970

By C. McCulloch

OPEN-PIT mining of coal is relatively a recent innovation; men still active in the industry can trace its development. Re- viewing the growth of operations from the original horse-drawn scrapers, through the various stages of power equipment to the huge strip- ping shovels of today, one also notes changes in the methods of what the coal man calls preparation at the face. We really should not call it face preparation because, in contrast to underground mining, a face does not exist in strip mining. Further, preparation of the coal for market at the loading point has already, in but a few years, become largely of historic interest only and modern mines as well as old mines recently modernized rely almost entirely on separate and elaborate preparation plants to produce marketable coal. This practice was not voluntarily adopted by the producer but was forced upon him by the inadequacy of previous

Jan 1, 1939

By Flor De Cock

The paper reflects part of the work from the European Regional Technical Committee on Piles (ERTC3) during its mandate between 1994 and 1999, and, in particular, describes the find­ings from an International Seminar held in 1997 in Brussels on European practice for design­ing axially loaded piles. The seminar included contributions from 17 European countries, each of which provided a synopsis of their respective national design approaches. This paper pays particular attention to the design methods based on laboratory and in-situ test data for both bored and displacement piles.

Jan 1, 2002

By J. E. Harris

By elimination of other possible nucleation processes, it has been demonstrated, for commercially pure magnesium and a Mg-Al alloy, that at stresses less than that necessary for triple-point cracking creep cavities are most probably nucleated heterogeneously at second-phase particles. Evidence for the existence of such particles is presented and the role of grain boundary sliding in the nucleation process is examined quantitatively. DURING creep deformation of polycrystalline magnesium and its dilute alloys in the temperature range 0.45 to 0.7 Tm (Tm = absolute melting temperature) cavities form mainly along grain boundaries oriented normal to the stress axis and failure eventually occurs by their growth and impingement.' The possibility of low-ductility creep failure of magnesium-alloy reactor cans during service has prompted a number of studies of cavity formation in these materials.2-5 In this paper divergent theories of cavity nucleation6-10 are examined critically and conclusions drawn regarding the most probable mechanism of formation of cavities in magnesium. The paper is divided into two parts. The first section consists of the review and quantitative assessment of the possible role of grain boundary sliding in the nucleation process. In the second part an experimental program is described where an electron-microscope technique has been used to determine if second-phase particles exist in as-received commercially pure magnesium and in a magnesium alloy 1) THEORETICAL REVIEW Possible nucleation sites for creep cavities are: a) high-angle grain boundary triple points,11-14 b) subboundary/grain boundary intersections,15-18 c) ledges in the grain boundary, 19-25 d) second-phase particles. 9,26-30 Each of these possibilities is now considered with special reference to deformation of magnesium. 1.1) Triple-Point Cracking. The stroh31 condition to nucleate fracture is: " > vr [1] where ss = applied shear stress, ? = surface energy, C = shear modulus, L = length of sliding interface. This relationship is independent of the nature of the interface and it is possible to calculate the stress concentration at the end of a sliding high-angle grain boundary and thus deduce, approximately,* the minimum applied stress necessary to nucleate triple-point cracking. Such theoretical predictions for Nimonic alloys have been made by McLean13 and found to agree quite closely with the minimum stress determined by experiment. Stresses capable of nucleating triple-point cracking should also be sufficient to nucleate fracture at a grain boundary due to intragranular slip, for the lengths of sliding interface in the two cases are approximately equal. Thus the minimum stress for triple-point cracking should represent a demarcation between failure due to general "cracking" and that due to cavitation. Hauser, Landon, and Dorn32 have demonstrated that for polycrystalline magnesium in the temperature range 78° to 298°K the fracture stress is inversely proportional to the square root of the mean grain diameter. As pointed out by stroh31 this result indicates that Eq. [I] describes the fracture characteristics of magnesium at low temperatures. Heal3 has reported that for rapid deformation (112 pct hr-1) of polycrystalline magnesium the transition from cracking to cavitation occurs in the temperature range 175" to 275°C. He also presented the fracture-stress values for the same material tested under similar conditions. From Eq. [I] taking G = 1.3 x 10" dynes , ? = 600 ergs . cm-2,33 and L = 0.017 cm, a Stroh-McLean13,31 tensile stress of -266 kg. cm-2 is calculated, corresponding to a transition temperature of -190°C; this is in

Jan 1, 1965