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By R. P. Abendroth

This study is concerned with the kinetics of selective oxidation of chromium in a commercial Fe-Cr-Ni alloy. Selective oxidation of chromium in this alloy, by use of a low oxygen-potential atmosphere, leads to the formation of a compact, protective layer of Cr2O3. This layer serves to protect this alloy from gross scaling when it is subsequently exposed to severe oxidizing conditions at high temperature. The interaction of low oxygen-potential atmospheres close to equilibrium with Fe-Cr and Ni-Cr alloys has been studied by others."' These studies werk concerned with the surface-structure variations under slightly oxidizing conditions. NO detailed study was made of the oxide scale formation kinetics, however. The alloy samples were cut from 0.012-in.-thick sheet, with an apparent surface area of 7.1 sq cm. These sheet samples were abraded through 4/0 metallographic paper, and washed in alcohol and acetone. The analysis of the sheet alloy is (in weight percent): 42 pct Ni, 5.5 pct Cr, 0.09 pct C, 0.18 pct Al, 0.36 pct Si, 0.26 pct Mn, balance Fe. The weight gain vs time data were obtained with a 2-g capacity fused-silica spring—cathetometer system. The spring deflection was optically magnified ten times before being read by the cathetometer. A sensitivity of about 0.01 mg was attainable. The spring was enclosed in a water jacket maintained at 60°C to minimize the effect of temperature changes. The sample was suspended from the spring with a fused-silica hangdown and was positioned in the thermal center of a mullite furnace tube. Sample temperature was read with the aid of a thermocouple placed outside the mullite tube and an inside vs outside temperature calibration. Temperature change during the course of a run was ±0.25°C, with a temperature gradient of less than l.O°C over the length of the sample. Total temperature uncertainty was no more than ±3.0°C. Alignment difficulties between the hangdown and radiation shields in the furnace tube required that the sample be positioned in the furnace when cold, and heated with the furnace until the temperature stabilized at the desired point. This required 5 to 6 hr, and was carried out in Matheson ultrahigh-purity hydrogen. Oxidation was started, after evacuation, by introducing a hydrogen-water vapor mixture, obtained by saturating hydrogen with water vapor at 31.00o ± 0.02oC. Oxidation was continued for 90 min. Gas flow was 300 ml per min during heat up and oxidation. Since only several milligrams of oxide are formed on each sample, chemical analysis of the oxide is difficult. A representative analysis is: 80 pct Cr2O3, 5 pct Fe2O3, 3 pct Al2O3, 4 pct MnO, 7 pct SiO2, 1 pct or less NiO. X-ray diffraction analysis of the oxide as formed on the alloy gives rhombohedra1 Cr2O3, and barely distinguishable amounts of a cubic spinel phase, and possibly AlZOs and SO2. The identification of these latter two compounds is by no means certain. The spinel phase could be based on iron or manganese as these elements are present in significant amounts in the oxide. The results of the kinetic studies using 31°C dew-point hydrogen-water vapor mixtures were found to conform to a parabolic rate law. In many cases the parabolic plot consisted of two intersecting straight lines, defining an early and a late rate for a particular run, and in the other cases the parabolic plot consisted of one straight line for the entire run. The slopes of the various straight lines were determined by the method of least squares. Reproducibility of the data was good enough for multiple runs at the same temperature such that the value given for the rate constant is the average for two or more closely similar values, rather than widely varying values of the rate, where more than one determination is indicated in Table I. The exhibition of only one or of two rate constants during a run can happen at the same temperature. Thus, Table I shows that at 11'74°C a single rate constant was obtained from one sample, while other samples oxidized at the same temperature gave an early and a late rate constant. It should be noted that the single rate constant corresponds very closely with the early rate constant. This is also true at 1153°C. The time at which the late rate started to appear was variable, usually occurring 20 to 40 min after oxidation had started.

Jan 1, 1964

By James J. Scott

INTRODUCTION This paper presents the basic principles which must be followed to create a truly inherently safe mining system. The need to relate the support mechanism to be employed to the ground reaction curve and basic rock mechanics principles will be pointed out. The support system must function in concert with the deformations that are inherent in the selected mining system. Following the support selection, the mechanics for installing support must be developed. This is best done through a cooperative effort between mine engineers, mine operators, safety personnel, equipment sup- pliers, and government inspectors both state and federal. Accident statistics, near miss statistics, review of equipment used by others, geologic features, etc. will necessarily have to be studied. The goal of equipment development and selection should be to develop inherent safety by removing the miner from the hazard area or by providing absolute protection for the miner if he must work in close proximity to the potential fall of ground. The role of good productivity in reducing the numbers of men exposed to hazards is emphasized as a good safety measure ROCK MECHANICS PRINCIPLES A thorough understanding of the ground reaction curve surrounding openings to be created is essential in the

Jan 1, 1982

By A. Q. Tool

THE necessity of accurate temperature measurements in the glass-making industries is today being much more widely appreciated than in the past. The introduction of the modern simplified and perfected pyrometric methods in connection with exact regulation of furnace temperatures has caused a marked improvement in the glass product with a quickened rate of production. An example of the processes in which much improvement has been and still can be made is that of annealing or heat-treating the glass. This is one of the most delicate processes in glass manufacture and one that requires a most careful furnace control. The heat treatment is undertaken to decrease the possibility of breakage and, in glass for fine optical instruments, to prevent serious warping of accurately ground and polished surfaces and to make the glass more uniform throughout to the passage of light waves. These objects are accomplished by removing all the harmful stresses that exist in a piece of glass when it has been cooled too quickly or unevenly. Such stresses exist, for example, after it has been pressed, cast, or otherwise worked. Thus the process of annealing consists of heating the glass evenly to the temperature at which it softens just enough to relieve these stresses in a reasonable time and then cooling slowly and uniformly until the glass hardens again. Accordingly, the things that must be investigated and determined in order to anneal glass without loss of time are, the annealing temperature, the time that the glass should be held at this temperature while the stresses relax, and the quickest cooling procedure that will give satisfactory results. After these characteristics of the glass are known the problem is one of pyrometry and temperature control entirely. In cases when it is known that a glass article will be required to withstand some definite type of heat or mechanical shock it is often possible, by a proper heat treatment, to produce such a distribution of the stresses in the glass that it will be enabled to resist these shocks more effectively.

Jan 9, 1919

CHARGING of an open-hearth heat is begun as soon as possible after the previous heat has been tapped. Ordinarily, about 40 min is required to drain and dress the furnace hearth, make up the taphole, and perform routine repairs of the banks. Repairs to the upper back wall and to the front wall and jambs can ordinarily be done while the first scrap charge is being heated and are therefore allowed to wait in order to save furnace time. Any major repairs required on the hearth or other parts of the furnace necessitate longer delays because such repairs must be made while the furnace is empty. Although charging practice varies considerably in detail with the type and proportions of scrap and iron used, many factors are common to all varieties of charge. Such general considerations are dealt with first. CHARGING EQUIPMENT AND STOCK HANDLING The physical equipment available for loading and weighing the stock, transporting it to the furnace, and charging it, may have a major effect on charging practice. Limestone, scrap, and all other solid melting stock are charged mechanically by means of equipment illustrated in Fig 2-1. The charging of hot metal is shown in the background of this figure. Mechanical equipment and plant layout for stock handling are described in Chapter 1. It is generally desirable to charge the scrap about as fast as the physical volume can be put into the furnace. Charging scrap that is too heavy or adding the charge too rapidly (less than 45 min) may be detrimental to melting rate because of excessive chilling of the entire furnace system and also because of poor conduction of heat to the lower layers in the furnace; but the more common problem is the reverse one of charging light 'scrap fast enough to maintain a normal heat time. A limiting factor may be the height to which the scrap may he piled in the fur-

Jan 1, 1951

CHARGING of an open-hearth heat is begun as soon as possible after the previous heat has been tapped. Ordinarily, about 40 min is required to drain and dress the furnace hearth, make up the taphole, and perform routine repairs of the banks. Repairs to the upper back wall and to the front wall and jambs can ordinarily be done while the first scrap charge is being heated and are therefore allowed to wait in order to save furnace time. Any major repairs required on the hearth or other parts of the furnace necessitate longer delays because such repairs must be made while the furnace is empty. Although charging practice varies considerably in detail with the type and proportions of scrap and iron used, many factors are common to all varieties of charge. Such general considerations are dealt with first. CHARGING EQUIPMENT AND STOCK HANDLING The physical equipment available for loading and weighing the stock, transporting it to the furnace, and charging it, may have a major effect on charging practice. Limestone, scrap, and all other solid melting stock are charged mechanically by means of equipment illustrated in Fig 2-1. The charging of hot metal is shown in- the background of this figure. Mechanical equipment and plant layout for stock handling are described in Chapter 1. It is generally desirable to charge the scrap about as fast as the physical volume can be put into the furnace. Charging scrap that is too heavy or adding the charge too rapidly (less than 45 min) may be detrimental to melting rate because of excessive chilling of the entire furnace system and also because of poor conduction of heat to the lower layers in the furnace; but the more common problem is the reverse one of charging light scrap fast enough to maintain a normal heat time. A limiting factor may be the height to which the scrap may he piled in the fur-

Jan 1, 1964

By George W. Doffing

Numerous contradictory statements have been made in the past regarding the importance of the seasonal influence of demand for motor fuel on prices of oil securities. It has often been said that the time to buy oil securities is in the spring, or just prior to the heavy consuming season for gasoline. The fallacy of this argument is brought out in the following paragraphs. Seasonality of Oil-security Prices The indexes used in this paper as indicators of prices of oil securities and general industrials are those compiled by Standard Statistics Co. The oil producing and refining stock index includes 14 representative petroleum companies, while the all-industrials index is made up of 347 issues. All figures are stated as relatives, with 1926 = 100. The primary basis of the index, and one that gives a good weighting of the relative importance of the company within the industry, is the total market value of the stock issue outstanding; i.e., the market price times the number of shares outstanding. Adjustments are made for the addition or elimination of issues from the group index, for stock dividends, split-ups, stock rights, et cetera. At the present time the oil producing and refining index includes the following companies: Atlantic Refining Co., Consolidated Oil Corporation, Continental Oil Co., Gulf Oil Corporation, Humble Oil & Refining Co., Ohio Oil Co., Royal Dutch Co., Shell Union Oil Corporation, Socony-Vacuum Oil Co., Standard Oil Company of California, Standard Oil Co. (Indiana), Standard Oil Co. (New Jersey), Texas Corporation, Union Oil Company of California. In calculating the seasonal for oil-security prices several periods have been selected as indicat,ive of major changes in the industry, as follows: 1. 1918 through 1936. This gives an over-all picture of the industry during the motor-vehicle, motor-fuel era. 2. 1927 through 1936. This period includes the control stages, both voluntary and coercive. 3. 1927 to September, 1933. This is the pre-code period of control.

Jan 1, 1937

By Richard H. Hopkins, R. W. Kraft

A new technique facilitating the rapid determination of the three-dimensional morphology of phases suspended in an opaque matrix is described. The vapidity of the technique is based upon continuous cinephotomicrographic recording of specimen microstructure as the specimen surface is removed under controlled conditions in an electrolytic cell. The advantages of the technique for determining spatial morphologies in opaque materials are illustrated by application of this method to the study of the configuration of faults in a specimen of directionally solidified CuAl2-Al eutectic alloy. A spatial model of the eutectic fault network deduced in this manner has substantiated the facts that faults in this alloy tend to lie parallel to one another in a direction close to that of the specimen growth axis and that the majority of faults tend to bridge lamellae rather than run parallel to them as growth proceeds. For the specimen studied fault density decreased as growth proceeded. ALTHOUGH metallographic observation is a powerful tool for investigating the correlation between structure and properties in metallic alloys, ordinary metallographic methods suffer the fundamental limitation that any conclusions concerning the three-dimensional structure of these opaque materials must rely upon inference from two-dimensional microsections. For this reason it is frequently impossible to make valid judgments regarding the true spatial distribution of the micro-constituents in specimens under investigation. Several techniques have been devised to circumvent the basic limitation of planar microsec-tioning and employed with varying success. These include construction of three-dimensional models of alloy microstructure from sequences of photomicrographs,1-3 quantitative deduction of spatial features based upon statistical studies of data from random and/or selected plane microsections,4-6 and selective dissolution of one phase in a two-phase alloy to reveal the topography of the phase remaining.' However these techniques also have certain obvious disadvantages. Construction of three-dimensional models is a very time-con- suming procedure due to the tedious polish-etch-photograph cycle needed to obtain the necessary photomicrographs to portray the spatial microstructure. Statistical methods by their very nature give only average values of the quantities being studied and cannot therefore give a detailed physical picture of the microstructure to be observed. Finally, the technique of selective dissolution is only applicable in systems where the phases are of vastly different chemical reactivity; it is of little use in the study of single-phase alloys. Since the determination of the three-dimensional structure of opaque materials is hindered by two facts—the materials are opaque to radiation in the visible spectrum and construction of spatial models of microstructure is quite laborious—two solutions to the problem suggest themselves: 1) use radiation of energy great enough to render the alloy transparent, i.e., some microradio-graphic method, or, 2) devise a rapid means to section and record alloy microstructure. Stereomicroradiography has indeed been used to study internal arrangements of phases in several materials8,9 but the method, in general, is limited to very thin specimens (due to X-ray absorption) and simple microstructures. It would seem then that development of a rapid, simple, and generally applicable technique for studying the details of alloy microstructures in three dimensions can best be undertaken by following the second approach above. Using this idea a new technique for rapid evaluation of spatial microstructures was developed based upon cinephotomicrographic recording of the micro-structure of a specimen undergoing controlled electrolytic dissolution. It was further felt that application of this technique to the careful study of the spatial configuration of faults in a CuAl2-Al eutectic alloy would yield information that could be correlated with the extensive data3,6,10-12 already compiled concerning the solidification and crystallography of this eutectic. The practicality and usefulness of similar methods for studying three-dimensional features in alloys has recently been illustrated by the study of dislocation loops in zinc13 and spheroidized structure in steel.14

Jan 1, 1965

There were present twelve- Directors, the Secretary and the Assistant Secretary of the Institute, and fifteen guests. A committee of three was appointed to draft a suitable resolution of memorial of the services of Joseph Esrey Johnson, Jr. The committee consists of Joseph W. Richards, Chairman, J. V. N. Dorr and Allen H. Rogers. William R. Walker was elected a Director in place of J. E. Johnson, Jr., and Edwin Ludlow was elected a member of the Executive Committee in his stead. George C. Stone was appointed Chairman of the Committee on Membership in place of Mr. Johnson. The following resolutions were then adopted: RESOLVED, That a special business meeting of the Institute be and the same hereby is appointed to be, held at the office of the Institute, No. 29 West 39th Street, Borough of Manhattan, City of New York, on the 27th day of June, 1919, it 8.30 o'clock in the P. M. to consider and take action upon the proposal to change the name of the Institute to "American Institute of Mining and Metallurgical Engineers, Incor-porated," and the further proposal to extend the corporate purposes of the Institute so that it shall, in addition to its other powers, be empowered to promote the arts and sciences connected with the economic production of the useful minerals and metals, and the welfare of, those employed in these industries, by all lawful means.

Jan 6, 1919

Among the bills now pending in Congress is one to authorize exploration for and disposition of coal, phosphate, sodium, oil, oil shale, and gas on, public domain. One, to provide protection and government revenue for potash and for zinc ores and products. One to prevent withdrawal of mineral lands from entry and occupancy by law, also to promote, production of quicksilver, tungsten, sulfate, pyrites, and sulfur, and of manganese and manganiferous ores. Three resolutions have been introduced to suspend requirements of annual assessment work on mining claims during year 1919 and one to relieve owners of mining claims mustered into military service.

Jan 8, 1919

Robert W. Hunt, Chicago, Ill.:—It has been my good fortune to know of this development of Mr. York's for some time, and I think he will permit me to say that this is not the first demonstration that he has made of his method for rolling difficult shapes, and which, as he has stated, had in the past been regarded as practically impossible. I have good reason to know that Mr. York has been successful on other lines, because I myself went through a period of professional disrepute for having reported favorably on his methods, which received discredit up to the time that it was practically demonstrated that his claims were true ones. Years ago Mr. York built a mill at Duluth, Minn., for the production of structural shapes, and notably of what might be called balanced beams—beams that did not have flanges of restricted width. His scheme was to produce beams with flanges so wide that they could be used in place of built-up beams. The mill, of course, went through the difficulties that such a mill would have to encounter. I mas called upon to make an examination of the property and report. These beams were rolled on a universal mill—a mill which would admit of various-sized sections without change of rolls. I was convinced that Mr. York could do it, and I so reported. Having received condemnation and ridicule for having taken that position, later on I was glad to find that Mr. John Fritz had come to the same conclusion, and had so reported. I concluded we both could rest content, while awaiting developments. Later still, as we all know, there was another difficulty that Mr. York met with—namely, that the architects or structural engineers would not accept his proposed sections. That is still a great difficulty in America. Later, the Grey mill came into successful operation in Luxemburg, producing such sections, which are being used in England and on the Continent. In fact, the whole process, both from a commercial and a mechanical point of view, is a success. The Bethlehem Steel Co., Bethlehem, Pa.,

Jan 1, 1907

By W. R. Ingalls

THE paramount subject of interest and concern at the present time is the readjustment in economic conditions following the cataclysmic disturbance produced by the war and the misconceptions leading to an orgy of extravagance that prevailed during two years following the armistice he, time is too short for me to undertake to review the nature and extent of the upheavals occurring between August, 1914, and October, 1920. Bulky volumes will be written about them. . But I shall have to refer to some of the results in order to outline a prognosis. It is the future, not the past;' that is of most interest to us. Let me be so bold as to say, without further preface, that I am not optimistic as to the near future. .We shall, indeed, have revivals in trade, but they will be delusive if their nature be not 'understood. We shall build hopes and expectations upon political maneuvers and events, only to find in the end that they were folly. In the meanwhile fundamental economic influences will continue to exert their steady and irresistible pressure. The new administratiow at Washington has no magic wand with which to kindle the fires in our idle steel furnaces, or create a million new houses for the people; nor can the premiers of Europe put into motion the spindles of the cotton and woolen mills, or by any incantations compel the people of the Orient to buy goods. The people of the Orient, and of, Europe, and of the two Americas are in the grip of the same economic forces. The readjustment has proceeded further in some parts of the world than in others. In the United States I do not think we, have gone more than over the threshold. I shall tell you why 1 think thus, but in telling you I shall be limited, in view of the immensity of the subject, to a series of bald statements, without much elucidation.

Jan 1, 1921

By A. L. Field

WOOLSEY McA. JOHNSON, Hartford, Conn. (written discussion).¬When ;we regard the number of British thermal units running into the billions that-must be applied to metallurgical slags in the United States, we cannot but conclude that the physical chemistry of-slags is a very important subject when measured in dollars and cents. A further contemplation of the subject shows us that it has been hitherto treated in too purely a practical manner. It is needless to comment at length on the cost of these heat units and on the cost of fluxes to produce these metallurgical slags, for, it amounts to tens of millions of dollars annually. Accordingly, this research is of value to the country. But we must,all balance our results against our efforts. Therefore, while the speaker is unwilling to criticise unduly this meritorious research, lie does criticise it in the interest of the profession for the reason that it seems to him too highly theoretical. The article is much too, scientific to produce results at a minimum cost. Let us explain our meaning. It has been said that there are always two sides to a question. It may be further said that there are always three sides to a question, the two extremes and the middle ground. In any industrial research there are the highly theoretical side, the purely practical side, and the theoretico-practical side. To study a slag and be practical in the studying, there is something needed that represents in the laboratory (or in microcosm) what actually happens macrocosmically in the blast furnace. There is such a thing as the art of metallurgical research occupying the middle ground between theory and practice.

Jan 4, 1917

By E. G. Schempp, W. A. Morgan

The influence of modifications in the molybdenum, vanadium and, to a limited degree, carbon and boron content to a basic composition of 5 pct Cr, 0.75 pct Mo, 1 pct V hot-work tool steel composition, was studied in respect to hardenability, grpain- coarsening temperature, and tempering charactevistics. Tensile, impact, and fatigue pvoperties were studied for the most promising compositions. An alloy with a typical composition of 0.43 pct C, 4.97 pct CI-, 0.33 pct Si, 2.25 pct Mo, and 1.00 pct V uas found to offer the most favorable combination of properties in respect to high-strength applicntions when tempered at 1100°F. MANY 5 pct Cr high-strength steels are at present being manufactured in North America which fit well into the classification of the AISI-SAE system. Much interest has been shown in these materials as ultra-high-strength steels for use at elevated temperatures. The limiting temperature of use lies at the point where the steels begin to soften rapidly. Although a great deal of information has been made available in the past two years on the properties of selected alloys in this series, little information exists on the effect of systematically varying the ccntent of one or more elements in the 5 pct Cr-base alloy. This paper presents the results of an investigation of the effect of variations of the carbon, molybdenum, vanadium, and, to a limited extent, the silicon, manganese, boron, and niobium content of a 5 pct Cr steel to the AISI H-13 base analysis. EXPERIMENTAL PROCEDURE All experimental heats were melted in a 50-lb. induction furnace. The melting stock consisted of

Jan 1, 1962

The following outline has been prepared by request with the help of leading professors, business men, and social workers. It is arranged to cover 64 or preferably 96 class periods-four to eight month's work at the rate of two or three periods a week. More time would be desirable, but less time would be better than nothing. Certain topics must be omitted, especially if the assigned number of periods are lessened, where time is lacking. Many subjects are suggested in order to permit of choice and adaptation to local conditions; this is merely a suggestive outline. The course should be supplemented y engineering trips to study certain industrial conditions and the betterment work of selected companies-and social agencies. It should also be accompanied by brief surveys and practical service by students along the lines indicated. Reports and essays should be written. This is not a regular course in sociology and economics. It is a course in "human engineering" and should probably be directed by an engineering professor of large practical experience. Other members of the faculty, sociologists, economists, selected engineers, employers, labor leaders or others may be requested to lead certain periods, as desired. Care has been taken to avoid biased judgment in selection of topics and references.* * The authors of this outline have compiled an exhaustive list of references to books and periodicals relating to each group of topics. Lack of space prevents the publication of these lists in the BULLETIN, but they will gladly be supplied on request.-Ed.

Jan 12, 1917

By T. Egleston

The manufacture of charcoal in kilns was declared many years ago, after a series of experiments made in poorly constructed furnaces, to be unprofitable, and the subject is dismissed by most writers with the remark that in order to use the method economically the products of distillation, both liquid and gaseous, must be collected. It is asserted with truth that the number of kilns required for a large production of iron would be so great that it is doubtful whether any works would be justified in making the necessary outlay for their constructiou, but it can also be asserted with equal truth that for any such production in a given locality the use of charcoal as fuel would be eqnally unjustifiable. It appears to have been forgotten that there were other manufactures besides iron in which large amounts of charcoal were used, but these consumers seen] to have been guided entirely by the results of the experiments of the iron men, who necessarily made the largest qnantity of it. Some authors speak in a doubtful way of the quality of the charcoal produced, and a few concede that with great care good charcoal can he made in kilns, but that most of the workmen do not like kiln 'charcoal. This is the real secret of the opposition to this method of manufacture. Most of these objections were written when charcoal was the most important fuel used by the iron manufacturer, and when what was a largeproduction of iron for several furnaces was less than that produced by a single modern one, in localities where other fuels can be had. Almost all that has been written on the subject related to the use of the fuel for the manufacture of iron in the blast furnace, where very peculiar properties are required, and where the qnantity produced is limited by the height of the furnace, and this in turn by the crushing resistance of the charcoal. A large production was, therefore, only possible when the best and hardest woods were used. Of all these objections there is not a single one which is not eqnally applicable to any method of charcoal manufacture, whether it be meilers, pits, or furnaces. Until recently, therefore, the manufacturers of charcoal iron

Jan 1, 1880

By F. Weinberg

Lead single crystals have been deformed in tension over the temperature range of 4.2°K to the melting point. Changes in flow stress resulting from temperature cycling and strain rate cycling have been measured as a function of temperature for crystals of different orientations and purity. It was found that the flow stress ratio, after correcting for the temperature dependence of the shear modulus, decreased progressively with temperature above approximately 0.5Tm. The activation energy calculated from the high-temperature portion of the curve was found to be markedly higher than that of self-diffusion. For single glide crystals, the corrected flow stress showed an increase above 0.5 Tm before decreasitzg with temperature. This increase is attributed to static recovery occurrittg during temperature cycling. THE temperature dependence of the flow stress, based on temperature cycling and strain rate cycling, has been extensively investigated,' and on the basis of these results dislocation models of the work-hardening process have been proposed. In general, the flow stress is divided into two parts, ts, the short-range interaction term, which is only effective at low temperatures and which decreases with increasing temperature, and TG, the long-range stress term, which is independent of temperature after allowing for the temperature dependence of the shear modulus. The observations demonstrating that tG/µ is independent of temperature were generally carried out at low temperatures to minimize recovery effects. Several investigations have been reported on flow stress measurements at high temperatures2"5 which demonstrate that TG/µ does not remain constant at temperatures above 0.5Tm (where Tm is the melting temperature of the material in OK). Specifically, Hirsch and warrington3 carried out temperature cycling tests at two strain rates on single and polycrystalline aluminum up to 0.8 Tm and on polycrystalline copper. For aluminum they found that the flow stress ratio (the flow stress at temperature T2, divided by the flow stress at the reference temperature T1 in one temperature cycle) dropped progressively with increasing temperature above 0.5Tm. From the slopes of the high-temperature portions of the curves, they determined an activation energy for the deformation process of 1.6 ev (at best) which they considered was in agreement with the activation energy of self-diffusion, 1.35 ev. Calculations of the activation volume demonstrated that the deformation was not controlled by dislocation climb. They proposed a mechanism in which the rate-controlling process at high temperatures was due to the rate of move- ment of vacancies away from jogs, i.e., that of self-diffusion. Results of Lucke and Buhler4 on single crystals of aluminum confirmed this conclusion. They measured the critical resolved shear stress of aluminum over a wide range of temperature and strain rates. They found that the temperature dependence of the critical resolved shear stress was similar to that of the flow stress ratio, as determined by Hirsch and Warrington, and from their data calculated an activation energy for high-temperature deformation of 1.35 ev identical to that of self-diffusion. More recently Gallagher5 has carried out a detailed investigation of the temperature dependence of the flow stress ratio of copper, silver, and gold. In all cases, he found that the flow stress ratio, after adjusting for the shear modulus temperature change, drops at high temperatures. The activation energies he determined were found to be appreciably higher than the activation energy of self-diffusion of the material being considered. The flow stress ratio was found to be dependent on the orientation of the material, and, in addition, an anomalous increase in the flow stress ratio for copper, oriented for single glide, was observed above 0.5Tm. The purpose of the present investigation was to measure the critical resolved shear stress, the flow stress ratio, and the strain rate sensitivity of lead, primarily as a function of temperature. The results should indicate whether, following Lucke and Buhler, the critical resolved shear stress of lead has the same temperature dependence as the flow stress, and, following Hirsch and Warrington, whether the activation energy for high-temperature deformation in lead is the same as that of self-diffusion. Lead deforms as a normal fee material,6'7 is available in high-purity form, can readily be grown as single crystals, and, for this investigation, has the very considerable advantage of having a low melting point, 327°C. The observations of the critical resolved shear stress of lead have been published elsewhere.' EXPERIMENTAL PROCEDURE The experimental procedure was essentially the same as that used in the critical resolved shear stress measurements.' Single crystals of 99.999 pct (59) and 99.9999 pct (69) lead were deformed in tension with a table-model Instron in a silicone oil bath above room temperatures and in a cooled methyl alcohol or liquid-nitrogen bath below room temperatures. The test specimens were rectangular in section, 0.65 by 0.33 cm, and had a 5-cm gage length. The specimens were grown as single crystals with tapered ends, which fitted into matched tapered grips for testing. To obtain the flow stress between two temperatures, specimens were first deformed approximately 1.0 pct at the higher temperature. The test was then stopped, the load relaxed, the oil bath removed without disturbing the specimen, the grips and specimen cooled with a fan and then immersed in liquid nitro-

Jan 1, 1969

By R. A. Bosch, F. V. Lenel, G. S. Ansell

RECENTLY, Ansell and aenel' proposed a dislocation model to account for the yielding behavior of dispersion-strengthened alloys. The criterion for yielding used in this model was that yielding occurs when the shear stress due to arrays of piled-up dislocations fractures or plastically deforms the dispersed second-phase particles. Calculations based on this model predict that the yield strength, uysof a dispersion-strengthened alloy containing particles whose geometry permits them to be considered as straight, i.e. not curved, barriers to dislocations follows the relation where and are the shear moduli of the matrix and dispersed phase respectively, b is the Burger vector of a dislocation in the matrix, A is the mean free path between dispersed phase particles and C is a constant. This yield stress, ys, is closely approximated in polycrystalline alloys by the proportional limit. The offset yield stress, uoy, is the yield stress, uys, plus the increase of stress due to strain hardening in the offset strain increment. Previous investigation1 has shown that Eq. [I] describes the yielding behavior of several different dispersion-strengthened alloys as a function of the mean free path between dispersed phase particles at a constant temperature. The purpose of this investigation was to investigate the temperature dependence of the yielding behavior of dispersion-strengthened alloys. The alloys studied, MD2100 and MD5100, are SAP-type alloys containing flake shaped aluminum oxide particles dispersed in a matrix of commercial purity aluminum. The proportional limit and 0.2 pct offset stress of both of these alloys were determined as a function of temperature over the temperature range from -190" to 500 C. All tests were conducted on an Instron tensile testing machine. Stress was measured by means of the Instron load cell. Strain was measured by means of SR-4 strain gages attached to the tensile specimens. Stress sensitivity was 80 psi. Strain sensitivity was 2 x 10F Fig. 1 shows the values received for the proportional limit and 0.2 pct offset yield stress plotted as a function of homologous temperature for both the MD2100 and MD5100 alloys. Inspection of Eq. [I] shows that of the terms which determine the theoretically predicted yield stress, uy,, only the shear moduli have an appreciable temperature dependence. From Eq. [I] the yield stress at any temperature T, UT, may be predicted from the yield stress at any arbitrary reference temperature, in this case 25 OC, u25, by the relation where the subscripts T and 25 refer to the values of the property at test temperature and at 25"C, respectively. The temperature dependence of the yield stress predicted by Eq. 121, based on the observed value for the proportional limit at 25OC, is also shown in Fig. 1. In evaluating Eq. [2] the following data was used. The values for the shear modulus of

Jan 1, 1962

By D. H. Woodard, G. W. Geil, W. D. Jenkins

In a series of papers, the authors and their associates have shown the influence of four important factors on the technical cohesion limit.3-l6 By "technical cohesion limitv is meant the technically determin-able resistance to fracture. The four importarlt factors are the stress system, plastic deformation, temperature, and the strain rate, The influence of any one of these factors may be represented by a curve of cohesion limits, although only one point on the curve may represent actual fracture. As the term "fracture stress" has come into general use with the same significance as technical cohesion limit, the authors are here using the shorter term with the understanding that it does not always refer to actual fracture. The previously mentioned series of papers contains ample evidence that plastic extension increases the fracture stress of any polycrystalline metal, In a recent paper of the series,l5 moreover, it has been shown that the effect of plastic deformation on the fracture stress cannot be attributed to reorientation of internal flaws but is a work-strengthening effect, similar to the effect on the flow stress, $ Plastic deformation of steels, however, may not only cause work hardening, but may result in additional hardness because of strain aging. Some evidence that strain aging affects not only the flow stress but also the fracture stress, has been presented in a recent paper.14 In that paper, a study is made of the influence Of Plastic deformstion at room temperature on the fracture stress of ferritic steels at -188°C. The study is based on the results Of two-stage tests. In the first stage each specimen was extended a predetermined amount at room temperature; in the second stage the specimen was tested to fracture in liquid air. In most Of these tests the specimen remained in the testing machine during the interval of about one hour between the first and second stages, it was kept under a tensile load of about 500 lb and maintained at liquid air temperature. The effects of various amounts of .plastic deformation on the fracture stress were thus determined and curves were obtained to represent the influence of plastic deformation at room temperature on the stress at brittle fracture in liquid air.14 Two specimens Of ingot iron, however, were removed from the testing machine at the end of the first stage and several days elapsed before the specimens were tested to fracture in liquid air, As shown in Fig 8 of that paper," the points representing fracture of these specimens are far above the curve representing the results of two-stage tests without a rest interval between the stages. The evidence thus indicated that the fracture stresses of these two specimens were increased not

Jan 1, 1949

By G. W. Geil, D. H. Woodard, W. D. Jenkins

In a series of papers, the authors and their associates have shown the influence of four important factors on the technical cohesion limit.3-l6 By "technical cohesion limitv is meant the technically determin-able resistance to fracture. The four importarlt factors are the stress system, plastic deformation, temperature, and the strain rate, The influence of any one of these factors may be represented by a curve of cohesion limits, although only one point on the curve may represent actual fracture. As the term "fracture stress" has come into general use with the same significance as technical cohesion limit, the authors are here using the shorter term with the understanding that it does not always refer to actual fracture. The previously mentioned series of papers contains ample evidence that plastic extension increases the fracture stress of any polycrystalline metal, In a recent paper of the series,l5 moreover, it has been shown that the effect of plastic deformation on the fracture stress cannot be attributed to reorientation of internal flaws but is a work-strengthening effect, similar to the effect on the flow stress, $ Plastic deformation of steels, however, may not only cause work hardening, but may result in additional hardness because of strain aging. Some evidence that strain aging affects not only the flow stress but also the fracture stress, has been presented in a recent paper.14 In that paper, a study is made of the influence Of Plastic deformstion at room temperature on the fracture stress of ferritic steels at -188°C. The study is based on the results Of two-stage tests. In the first stage each specimen was extended a predetermined amount at room temperature; in the second stage the specimen was tested to fracture in liquid air. In most Of these tests the specimen remained in the testing machine during the interval of about one hour between the first and second stages, it was kept under a tensile load of about 500 lb and maintained at liquid air temperature. The effects of various amounts of .plastic deformation on the fracture stress were thus determined and curves were obtained to represent the influence of plastic deformation at room temperature on the stress at brittle fracture in liquid air.14 Two specimens Of ingot iron, however, were removed from the testing machine at the end of the first stage and several days elapsed before the specimens were tested to fracture in liquid air, As shown in Fig 8 of that paper," the points representing fracture of these specimens are far above the curve representing the results of two-stage tests without a rest interval between the stages. The evidence thus indicated that the fracture stresses of these two specimens were increased not

Jan 1, 1949

By G. W. Jones

THIS paper describes experiments in which eight test samples of gelatin dynamite were fired in three different types of apparatus and the quantity and composition of the gaseous products of detonation determined. The special dynamites were so prepared that the oxygen balance of the samples varied from -35.0 to +6.0 g. per 100 g. of explosive, including the wrapper. By means of this graded series of explosives, the relation between oxygen balance and gaseous products of detonation could be studied explicitly. The effect of varying oxygen balance on explosive strength has-been discussed in another paper.1 The apparatus employed in the work described in the present paper included (1) the Bichel gage, a steel bomb of 15-1 volume; (2) the Crawshaw-Jones confined detonation apparatus, a steel cannon from which the explosive is fired into a pipe of 904 volume; and (3) the Hercules tank, an apparatus in which the explosive is confined in a quartz block which is placed in a steel tank of about 4500-1. volume. A full description of the apparatus is given later. VARIABLES AFFECTING COMPOSITION OF DETONATION PRODUCTS The character of the detonation products of commercial explosives is governed in part by the same factors that affect the combustion products from explosive mixtures of air with gases or vapors. In either case, combustible materials-namely, carbon, hydrogen, and sometimes sulfur-are present and combined variously. In an exploding gas mixture the combustibles are oxidized by oxygen in the admixed air, whereas with explosives the necessary oxygen is provided by oxygen-carrying materials in the explosive ingredients.

Jan 1, 1928