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By John Wulff, Robert Kamm, Steinberg Morris

In powder metallurgy it has often been observed that shrinkage may occur in one direction and growth in another during sintering. Even in long-time sintering experiments the rate of shrinkage may be different in different parts of the compact. In the fabrication of some parts requiring a constant permeability it is even questionable in some cases whether pressing from one direction should be attempted. These observations require for their interpretation a more detailed study of green or pressed density than has heretofore been available. Usually average density measurements of the whole compact are made and in some cases carefully cut sections are measured. A different approach to the problem was first mentioned by Rakowskil and also used by Balshin.2 Balshin's diagram is reproduced in Fig I and schematically shows the result of pressing three layers of metal powder with fine intervening layers of graphite. The retarding effect of the die walls and a qualitative example of the density distribution is evident. More quantitative information about the distribution of density within a cold-pressed powder compact would be useful in showing the variation in density in as as influenced by the type of poKder, shape of die, lubricatioll during the process, and other variables. Furthermore, information about the cracking of cold-pressed compacts may be obtained from an analysis of the stress distribution within a, powder compact, and some information about the stress distribution can be obtained in turn from the derlsity and strain distributions. A more detailed report on some of the present experiments appears in reference 3. Present Investigation In order to ascertain the density gradients in cold-pressed metal powders, a deformable lead grid within the powder was employed. After pressing in cylindrical di" the ejected compact was radiographed, giving a pattern of the deformed grid. From the radiograph density and deformation from point to point is readily measured. From the radiograph strain distribution and stress trajectories were also determined. The latter also permits the determination of the coefficient of friction at the die wall. This technique indicates that the densest Part of a compact pressed from one side is at the top outer circumference and the least dense region at the bottom circumfercnce near the stationary plunger. For Some heights of compacts the density at the axis is such that the lower density is at the top rather than at the bottom. SO irregular a density distribution is due primarily to die-wall friction. As the ratio - diameter to height of compact is increased the die walls play a correspondingly smaller role. More uniform density

Jan 1, 1947

By John Wulff, Steinberg Morris, Robert Kamm

In powder metallurgy it has often been observed that shrinkage may occur in one direction and growth in another during sintering. Even in long-time sintering experiments the rate of shrinkage may be different in different parts of the compact. In the fabrication of some parts requiring a constant permeability it is even questionable in some cases whether pressing from one direction should be attempted. These observations require for their interpretation a more detailed study of green or pressed density than has heretofore been available. Usually average density measurements of the whole compact are made and in some cases carefully cut sections are measured. A different approach to the problem was first mentioned by Rakowskil and also used by Balshin.2 Balshin's diagram is reproduced in Fig I and schematically shows the result of pressing three layers of metal powder with fine intervening layers of graphite. The retarding effect of the die walls and a qualitative example of the density distribution is evident. More quantitative information about the distribution of density within a cold-pressed powder compact would be useful in showing the variation in density in as as influenced by the type of poKder, shape of die, lubricatioll during the process, and other variables. Furthermore, information about the cracking of cold-pressed compacts may be obtained from an analysis of the stress distribution within a, powder compact, and some information about the stress distribution can be obtained in turn from the derlsity and strain distributions. A more detailed report on some of the present experiments appears in reference 3. Present Investigation In order to ascertain the density gradients in cold-pressed metal powders, a deformable lead grid within the powder was employed. After pressing in cylindrical di" the ejected compact was radiographed, giving a pattern of the deformed grid. From the radiograph density and deformation from point to point is readily measured. From the radiograph strain distribution and stress trajectories were also determined. The latter also permits the determination of the coefficient of friction at the die wall. This technique indicates that the densest Part of a compact pressed from one side is at the top outer circumference and the least dense region at the bottom circumfercnce near the stationary plunger. For Some heights of compacts the density at the axis is such that the lower density is at the top rather than at the bottom. SO irregular a density distribution is due primarily to die-wall friction. As the ratio - diameter to height of compact is increased the die walls play a correspondingly smaller role. More uniform density

Jan 1, 1947

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Jan 1, 1907

By Paul W. Zimmer, Carl E. Dutton

Iron ore in the Menominee district is mined from two iron-formations of middle Precambrian age. The older formation is present in the northeastern part; is composed mainly of hematite, magnetite, quartz, and minor silicates; and contains about 34 per cent iron. The rock has been so coarsened by meta- morphism that concentration of magnetite and hematite is feasib!e, and pellets containing more than 60 per cent iron are being produced. The older formation is also present in the southeastern part where it has 1:een only slightly metamorphosed. Ore containing more than 50 per cent iron was formerly mined from local residual concentrations of iron oxides from which silica had been sufficiently leached, or replaced by iron oxide, or affected by combinations of these processes. The younger iron-formation occurs in the western part of the district and, if unaltered, is interlayered siderite and chert. The ore in this area also contains more than 50 per cent iron and formed as local residual concentrations but in two stages. The siderite was converted to iron oxides (hematite and "limonite"), and silica was contemporaneously or subsequently removed by leaching, or replacement, or combinations of these processes.

Jan 1, 1968

Jan 1, 1916

By Bert S. Sandell

Much has been said and written about the various uses of die castings, their applications in the various industries and their advantages and disadvantages. Examination of this literature, however, fails to disclose any data concerning the effect of temperature upon any of the physical properties of die-casting alloys. The uses and applications of die castings are so numerous, and of such a varied nature, that far too lengthy a manuscript would be required to list all of them. Brief mention of some specific cases will suffice to illustrate the temperature ranges in which certain die castings function. Automobile hardware, such as hub caps, door handles, radiator caps, etc., can be used as one example. Castings of this type are constantly exposed to varying climatic conditions, temperatures ranging from below zero to upwards of 100" F. Refrigerator parts, such as ice-cube trays, etc., form another example. Approaching the other temperature extreme, we encounter conditions such as are found in kitchens in which oven-heat indicator parts, cooking utensils, waffle grids, etc., embody use of die castings, where temperatures as high as 500" F. are often met with. Because of this variation in service temperatures, it was felt necessary to ascertain the effect of these temperatures upon the physical properties of die-casting alloys. The Charpy impact test was chosen first because of its simplicity, and because of the fact that brittleness is more likely to be objectionable in die castings than hardness or other physical properties. Alloys Investigated Two types of alloys were used in this investigation—zinc-base and aluminum-base alloys. Two alloys of each group were included. Those most generally employed in the industry at present were selected. Alloys A and B are of the same nominal composition, and correspond to A. S. T. M. alloy XXI, containing 4 per cent aluminum, 3 per cent copper, 0.1 per cent magnesium, and the balance zinc of 99.99 per cent

Jan 1, 1932

By R. I. Jaffee, H. P. Nielsen

In recent years much attention has been given to high melting alloy systems. It has been of interest in this respect to investigate the alloys of platinum and tungsten, which were known from the literature to have very high melting points up to about 50 pct tungsten, but about which little had been published on the high-tungsten side of the system. Powder metallurgical methods were used throughout this investigation for the preparation of the alloys, utilizing electrical sintering techniques such as are used for tungsten and molybdenum. In the course of the work it was found desirable to determine fusion temperatures of the alloys, and it was possible from these and other data to draw a tentative constitutional diagram (solidus, mostly) applicable to the high-temperature part of the system. No attempt was made to determine solid solubility vs. temperature data, nor to investigate the lower temperature transformations in the solid state. Data on the microstructure, hardness, and a note on oxidation resistance of the sintered alloys were obtained. Past Work Miillerl determined liquidus temperatures of platinum-rich alloys to 50 pct tungsten, using a radiation method employing a photoelectric cell, and found that the melting points increased progressively from I771 C for platinum to 2350°C for the 50 pct alloy. Microscopic evidence by Miiller that complete solid solutions exist to 50 pct tungsten was not checked by Kremer2 who, according to Vines and Wise,3 found that "although the 8 pct tungsten alloy was a solid solution, the 26 pct tungsten alloy contained a eutectic or an intermediate phase." Hultgren and Jaffee4 using X ray methods found continuous solid solutions to at least 33.6 pct tungsten (35 at. pct) after annealing in vacuum for 6 days at I000 C. Vines and WiseS report work communicated to them by E. C. Rhodes on wrought alloys to 7 pct tungsten, which showed that tungsten hardened platinum extremely rapidly, and was one of the most potent hardeners of the binary additions to platinum. Considerable quantities of 4 pct tungsten platinum wire have been produced for grids in radar tubes and for aircraft spark plugs. Some of the alloy for the latter application is made by sintering, the remainder by smelting and casting. Materials The platinum powder used in this work was kindly supplied by the Research and Development Laboratory of the Owens-Corning Fiberglas Corp., Newark, Ohio. It was prepared from scrap platinum. After dissolving in aqua regia and evaporating almost to dryness, the solution was worked up several times with concentrated HC1. The resultant platinic chloride was diluted considerably, and metallic zinc was added, which precipitated the platinum in a very finely divided form. After dissolving the

Jan 1, 1949

By C. C. Wright, R. J. Day

ALTHOUGH data on the exact tonnage of recoverable coal silt are not known, the quantity produced in 1943 was estimated to be over five million tons for the anthracite region of Pennsylvania alone. Since that time the recovery of the No. 5 buck- wheat size previously included in silt estimates has increased greatly thus reducing the total silt tonnage. As a compensating factor, however, the methods of recovering silt previously escaping into the rivers and streams have been markedly improved so that the net figure may not have changed materially. Comparable estimates for bituminous coal are lacking, but undoubtedly the silt represents a significant tonnage. With the trend toward increased wet cleaning of the smaller sizes of bituminous coal, it is to be expected that even greater quantities of silt will be available in the future. The raw silt from anthracite collieries usually contains a high mineral matter content, but technological developments in fine coal cleaning have been making rapid advances and it appears probable that more extensive use of these methods will be employed in the near future. Bituminous coal silt in many instances contains a similar high mineral matter content. As with anthracite silt, however, the cleaning of this material, where necessary, appears both technologically and economically feasible. With a view to upgrading the size and value of silt, considerable laboratory and pilot plant work has been conducted by a number of organizations on what is commonly known as pelletization. Actually the process is one of extrusion in which the moist silt is extruded from a die in the form of rods, which usually break into relatively short lengths-a few inches long-as they fall from the die. Fig I is a photograph of some extruded 3/8-in. diam pellets and of the anthracite silt from which they were produced. This technique of producing larger sized material from fines is by no means new, having been used extensively by the industrial carbon and clay industries for years.' The application of the process to coal silt appears, however, to be relatively new. The first major program of investigation dates back only to July 1945, when a group of engineers representing the Anthracite Institute, The Pennsylvania State College and the J. F. Pritchard and Co. conducted preliminary tests on the extrusion of anthracite silt at the Floridin Co. plant at Warren, Pa. Since that time these three organizations-individually, together, and in co- operation with other interested groups- have actively pursued work on various phases of the problem. Much of the early history and details of the laboratory and pilot plant work by the Anthracite Institute, has been reported by Mulcey and Eckerd.2 It is the purpose of this paper to report additional information on the process, especially with respect to the factors influencing the quality and use properties of the product, and the current develop

Jan 1, 1948

By J. Blodget Britton

To the question, " Do the Pennsylvania anthracites contain phosphorus?" asked at the last meeting of the Institute during the discussion on the metallurgical value of Western lignites, I can now give a definite answer. Through the kindness of a gentleman connected with the Philadelphia and Reading Railroad, and another connected with one of the principal ironworks on the Lehigh, there was sent to the Ironmasters' Laboratory a number of samples of the coals now largely shipped from the Schuylkill and Lehigh regions. Seventeen of these I examined for their contents of ash and phosphorus, and obtained results as follows : Ash. Phosphorus. No. 1, . 4.10 .0063 2, . . . . 7.97 .0209 113, . 5.53 .0049 114, . . . . . . . 6.55 .0056 . 5, . 5.39 .0761 . . . . . . . 11 6, 14.15 .0593 7, . 10 43 ,0049 rl 8, . . . . . . . 5.29 .0354 9, . . . . . . . 3.01 .0042 6L10, . . . . . . 3.03 .0042 1 1 . 275 .0014 12, . 2.82 ,0111 l'13, . .3.69 trace L1 14, . . .2.35 trace 15, . . . . . . . 7.22 .0014 16, . . . . . . . 3.49 .0167 17, . 4.63 trace

. F. W. SPERR, JR.,* Pittsburgh, Pa.--Mr. Malcolmson states that the Carbocoal process produces ammonium sulfate in excess of that normally recovered in the ordinary byproduct coke process. Table 3 indicates that 20,000 to 25,000 lb. of sulfate of ammonia are obtained in carbonizing 1000 tons of Clinchfield coal. This is a high-grade coal and yields from 26 to 28 lb. of ammonium sulfate per ton in a modern byproduct coke oven. On the next page, 21 lb. is stated as the yield of ammonium sulfate per short ton of raw coal; this is less than the average production from any well operated byproduct coke-oven plant treating coal of the character usually coked, in Pennsylvania and Ohio. The statement as to the comparative yields of light oil is somewhat misleading in view of the results obtained during the past year or two by the more modern byproduct coke plants. The plants put in operation by the H. Koppers Co., during the past two years, are producing about 3.5 gal. of light oil per short ton of coal, and several of these plants are producing more than 4 gal. per ton. The yield of pure toluene runs from 0.45 gal. to 0.55 gal. per ton. .The quality of the light oil .obtained from the Carbocoal process is of much greater importance than would be inferred by one not closely familiar with the subject. The presence of paraffins in the benzol and toluol fractions seriously detracts from their commercial value; the benzol and toluol fractions derived fro in the Carbocoal process contain about 50 per cent, of paraffins. It should be thoroughly understood what these paraffins are. They are simply hydrocarbons that go to make up ordinary petroleum, and if a successful method for the removal of paraffins from benzol and toluol has been developed, this can at once be applied to several well known processes by which benzol and toluol can be made directly from petroleum, which have as yet been total failures on account of the contamination of these products by paraffins.

Jan 11, 1918

Jan 1, 1968

Henry Louis, Newcastle-upon-Tyne, England (communica, tion to the Secretary): I have been much interested in Mr. Schmitz's description of the copper-ore bed in the Permian formation of Texas. He compares it with the Mansfeld Kupferschiefer; but it seems to me to present closer analogies with a small deposit on the same side of the Atlantic, in Nova Scotia, which I examined in 1877. I quote entirely from my fieldnotes, made then, and from specimens still in my possession. These copper-deposits are known in several places; but I examined them at the village of New Annan, on the banks of the French river. This district has been determined by Sir J. W. Dawson as being of Permian age, and this determination seems to have been confirmed as recently as 1891 by the operations of the Canadian Geological Survey. The following is the section, very imperfectly exposed in a few shallow levels, described in ascending order: Red sandstone, moderately fissile and markedly false-bedded. Lower nodule-bed, 1 inch to 6 inches thick, of fissile mica, ceous sandstone, containing obscure plant-remains converted into anthracite, chalcopyrite, chalcocite and iron pyrites. Very coarse grit or, in places, red sandstone; thickness and character variable. Upper nodule-bed, 6 inches to 2 feet thick exceptionally, generally about 10 inches. Soft, gray, friable shaly sandstone, with nodules of copper-ore. Red sandstone. All these strata lie flat, in places quite horizontal, in places dipping towards the river at 5° to 10°.

Jan 1, 1897

By Waldemar Lindgeen

PART I.—General Features. PAGE Purpose and Extent of Inquiry ; Definitions (Fissure-Veins, Metamorphism, Metasomatism, Impregnation, Cementation, Weathering); Metasomatism in Connection with Mineral Deposits, Especially Fissure-Veins; Calcu lation of Analyses ; Criteria of Metasomatism; Crystallization of Sec ondary Minerals in Other Bodies; Secondary Alteration of Veins; Structure and Composition of Metasomatic Vein-Rocks and Their Rela tion to General Metamorphism,.759 PART 11.—Minerals Developed by Metasomatic Processes in Fissure-Veins. Quartz, including Chalcedonite and Opal; Rutile and Anatase; Fluorite; Calcite ; Magnesite and Dolomite ; Siderite; Muscovite and Sericite ; Biotite; Chlorite; Pyroxene and A mphibole; Garnet; Epidote ; Ortho clase ; Albite ; Tourmaline ; Topaz ; Kaolinite ; Zeolites ; Pyrite ; Mar casite ; Chalcopyrite ; Arsenopyrite; Pyrrhotite ; Galena; Zinc-blende and Other Sulphides; Tellurides; Native Copper ; Gold and Silver,. 601 Resistant Minerals,........... 619 PART III.—The Fissure-Veins Classified According to Metasomatic Processes. 1. Topaz-Cassiterite Veins (Altenberg and Zinnwald, Saxony ; Mt. Bischoff, Tasmania),..........620 2. Scapolite-Apatite Veins,.........625 3. Tourmalinic Gold-Copper Veins,.. 626 4. Biotitic Gold-Copper Veins,........ 641 5. Propylitic Gold and Silver Veins (General Features; Comstock Lode; The Veins of Nagyág, Hungary; Pachuca, Mexico ; New Zealand; Alaska ; Silver Cliff, Colorado; Silver City, Idaho),. .. .645 6. Fluoritic Gold-Tellurium Veins (Cripple Creek ; Other Occurrences),. 654 7. Sericitic and Kaolinitic Gold- and Silver-Veins (General Remarks; The Freiberg Veins ; De Lamar, Idaho; Summit District, Colorado),. . 6.58 8. Sericitic and Calcitic Gold-Silver Veins (The Gold-Quartz Veins of Cali fornia ; Idaho Types ; San Juan, Colorado ; Treadwell Mine, Alaska ; Gold Veins of Ontario, Canada; Schwarzwald Fissure-Veins),. . 664

Jan 1, 1901

THOSE MARKED THUS * ARE MEMBERS, MARKED THUS ?ARE ASSOCIATES. THESE SIGNS DOUBLED INDICATE LIFE MEMBERS AND ASSOCIATES RESPECTIVELY. THE FIGURES AT THE END OF THE ADDRESS INDICATE THE YEAR OF ELECTION. HEAVY-FACED TYPE SIGNIFIES HONORARY MEMBERSHIP. *AARONS, J. BOYD, Vivian Gold Mining Co., Ltd., Harris, West. Australia. '05 *ABADIE, EMILE R., Cons. and Min. Engr., 214 Union Savings Bank Bldg., Oakland, Cal. '76 ?ABBÉ, MAX F., Prest., Abbé Engineering Co, 220 Broadway, New York, N.Y. '07 *ABBOTT, CHARLES W., Min. Engr. Pioche, Nev. ?08 *ABBOTT, JAMES W., Min. Engr: Ploche, Lincoln Co., Nev. '94

Jan 1, 1917

By E. I. Larsen, F. R. Hensel

According to statements by Guertler1 Smith and Hamilton were the first to study the copper-titanium alloys, but owing to the presence of large amounts of impurities their data are inconclusive. M. A. Hunter and I. W. Bacon later investigated the electrical conductivity and the temperature coefficients at room temperature. The present writers reported their results2 in November, 1930. Recently Kroll published data on copper-titanium alloys3 which agree closely with those obtained by the authors. Material Tested The titanium used was in the form of square sintered rods, the analysis of which runs as follows: titanium, 95.4 per cent; silicon, 0.7; iron,l.8; aluminum, 1.4; copper, 0.1; manganese, 0.05. The ingots were prepared in a high-frequency induction furnace in air atmosphere. Their analyses are given in Table 1. Up to 5 per cent titanium the alloys could be forged. Above that amount they were red short and broke up easily. Owing to their rapid absorption of nitrogen and oxygen from the air, the alloys with the higher amounts of titanium tend to form surface films which greatly increase the casting difficulties, especially when small masses of metal are handled. It was, however, possible to prepare sound ingots up to 25 per cent titanium. Thermal and X-ray Investigation The cooling curves of some of the alloys are plotted in Fig. 1, and R tentative diagram constructed from these data is given in Fig. 2. From this it is evident that the solid solubility of copper for titanium is approxi-mately 4 to 5 weight per cent titanium at 878" C., which is the eutectic temperature. The melting point of copper is lowered gradually by adding

Jan 1, 1932

By Chester Wells Purington

Situation.—The Camp Bird mine is in Imogene basin† (Fig. 1) at the head-waters of Canon creek, a branch of the Gunnison, in the southern part of Ouray county, Colorado, towards the northern edge of the region known as the San Juan mountains, and about 10 miles W. of the continental divide. It is 8 miles by wagon-road from Ouray, the terminus of a branch of the Rio Grande' Southern railway. The distance from Denver to Ouray is 387 miles by rail. In an air-line, the mine is 190 miles SW. of Denver. The altitude of the town, tunnel and buildings is 11,200 ft., and level No. 2 is 11,500 ft., and No. 1 is 11,670 ft., above sea-level. The lowest point of the lode-ontcrop, which crosses the basin E. and W., has an elevation of 11,850 ft., and that of the highest point, on the divide between Imogene and Tomboy basins, is 13,250 ft. On the eastern slope of the Imogene basin (towards Ironton) the vein is less clearly defined on the surface. Ownership and Extent.—At the time of the writing of this paper, the property is owned by Mr. Thomas I?. Walsh, and operated under the management of Mr. J. W. Benson. It

Jan 1, 1903

By M. G. Corson

THE iron-silicon alloy series has always been one of the most puzzling among the binary alloys. Examining the well known mechanical properties of the iron-rich alloys only we meet the following situation: The ultimate strength and yield point of alloys worked and annealed under the usual conditions represent nearly a straight line function of the silicon content up to 4.5 per cent. silicon (Fig. 1). Starting at the ultimate strength of 35,000 lb. and at a yield point of 16,000 lb. for pure electrolytic iron, one reaches a maximum strength of 93,000 lb. and a maximum yield point of 74,000 lb. at 4.5 per cent. silicon. This corresponds to an increase in ultimate strength by 13,000 lb. per each per cent. of silicon added and nearly the same rate applies to the yield point. The data mentioned are taken from the investigation by T. D. Yensen,1 and while they do not exactly corroborate the results obtained by earlier investigators, they seem to be the most correct. Plastic properties of the alloys are controlled by a much more complicated relationship. Up to 2.5 per cent. Si, the elongation stays close to 50 per cent. (in 2 in.) and the area reduction amounts to 85 per cent;, a situation that forms the usual feature of all alloys representing strictly solid solutions. The plasticity of the latter is always nearly equal to that of their base metal. Beyond 2.5 per cent. silicon, the situation becomes much more complicated. Yensen observed an enormous drop in elongation and area reduction at about 2.65 per cent. silicon, where the first hardly reaches 10 per cent. and the second is still lower; he found, however, a considerable recovery in plasticity at about 2.8 per cent. Si and up to 4.5 per cent. Si it is represented by 20 per cent. for the elongation and 30 per cent. for area reduction.

Jan 1, 1928

By Arthur V. Corry

GOLD was discovered in Alder Gulch, Virginia. City, Mont., on May 26, 1863. In a short time some 6000 people flocked to the new discovery, and on the banks of Alder Gulch six settlements sprang into existence, the principal one, Virginia City, alone surviving. This town today has a population of 800, and is the county seat of Madison County. It is estimated that between forty and fifty million dollars in gold was produced up to 1904. Virginia City is situated at the mouth of Alder Creek where that stream leaves the narrow canyon that cuts the steep foothills flanking Old Baldy Mountain, elevation 9572 ft., 12 mi. south. Virginia City itself is 5700 ft. above sea level.

Jan 1, 1936

By Graham P. Crutchfield

The W. I. Cook pool in Shackelford County, Texas, has been the subject of a number of papers and articles. Its unique position both as to operation and development has made it an ideal location for unit repressuring. The major portion of the pool is located on the W. I. Cook ranch and most of the oil leases are owned by Roeser & Pendleton, Inc. and the Continental Oil Co. and operated by Roeser & Pendleton, Inc. The Humble Oil & Refining Co. and Tom James operate producing leases which have a vital bearing on the unity of the pool. Both have cooperated in the repressuring project. Practically the entire royalty is owned by Mrs. W. I. Cook and she has given the operators her entire cooperation in all phases of unit repressuring.

Jan 1, 1931

By A. B. Kinzel

IT is with sincere appreciation and a deep sense of responsibility that I accept the honor of delivering the Howe Memorial Lecture. In our time metallurgical research has delved into phenomena ever more complex in character, so that much of this work must be done by organized teams. We, of the Union Carbide and Carbon Research Laboratories and the Electro Metallurgical Co., are truly a team and the lecture which is to follow is due largely to a few of the outstanding members of that team here cited and well known to you in their own right: John Lamont, whose work deserves special recognition, Walter Crafts, William Forgeng, William Binder, Robert Fowler, and David Swan. Thus it is a fitting pleasure to accept this honor for the research institution which I represent. Henry Marion Howe was truly inspirational and his breadth of view was such that he could use either the method of rigid proof or implied mechanism to further the broad understanding. But perhaps his outstanding characteristic was his sound judgment and his ability to weigh observations. The following is replete with observations and judgment as to their implication. We would like to feel that it is the type of dissertation which Howe, himself, would have enjoyed. Chromium carbides in stainless steel have, in a sense, been a key to the progress of the stainless steel industry. Brearley's first stainless steel, containing approximately 0.30 pct C, was successful because it differed from previous Fe-Cr alloys in that the carbides were present in such amount and form as to provide the stainless and cutting properties. Again, the 12 pct Cr die steels with a carbon content of 1.5 pct or more achieved their properties by virtue of the form and distribution of the chromium carbides. In the straight chromium steels with from 12 to 25 pct Cr, chromium carbide amount and distribution are once more the determinants with respect to physical properties and corrosion resistance. In each of the cases just cited the role of the carbide is in essence similar to that of iron carbide in carbon steel and this story is so well known that we need not dwell on it. In the austenitic stainless steels, the chromium carbide plays only a minor positive role with respect to mechanical properties, and for corrosion resistance the objective is to achieve maximum homogeneity. Thus the tendency has been to ever lower the carbon and correlatively the chromium carbide content of the austenitic steels. Today stainless steels with carbon less than 0.03 pct are beginning to find their true place, and this is being aided in major degree by our Company's introduction of a new type of ferrochromium having negligible carbon. The role of carbon in these austenitic steels has long been recognized, and a truly enormous amount of research has been devoted to the subject. Much has been learned about corrosion resistance, but the attack on the problem from the point of view of carbide precipitation and the nature thereof has left much to be understood. Because of its fundamental importance to the future of stainless steels, further study of the mechanism of carbide formation in austenitic steels is of interest. In the 18-8 Cr-Ni steels, which are typical of the austenitic class of steel, carbon is soluble in the aus-tenite to the extent of approximately 0.15 pct at 1832°F (1000°C). The solubility becomes less with decreasing temperature, so that at 1652°F (900°C) the solubility limit is approximately 0.06 pct, at 1472°F (800°C) it is about 0.03 pct, and at 932°F (500°C) it is approximately 0.01 pct. Obviously this is the ideal situation for the classical precipitation phenomenon. It is true that, in a sense, 18-8 austenite resulting from annealing is in a metastable state, and the phenomenon of ferritic precipitation from this austenite should be considered. However, in a so-called fully austenitic 18-8 steel this is secondary with respect to the carbides and can be neglected. A wide variety of chromium carbides is known. Only one chromium carbide, Cr,,C,,, frequently referred to as Cr,C, has been found in unmodified low carbon 18-8 steel. This, fortunately, simplifies the study of the precipitation phenomena. For this study an A.I.S.I. type 304 stainless steel of commercial quality was selected. Analysis showed C 0.07 pct, Mn 0.49 pct, Si 0.33 pct, Ni 9.34 pct, Cr 18.91 pct, and N 0.033 pct. As expected with this composition the steel was homogeneous after annealing except for a few pools of ferrite, which were disregarded in that their location was not coincident with subsequent carbide precipitation areas. On corrosion testing the steel was normal and typical of good commercial quality. Specimens 1/2xlx4 in. were annealed and subjected to precipitation heat treatment for 100 hr at 100" temperature intervals from 1000° to 1500°F and for ten selected intervals ranging from 5 min to 64 hr at 1300°F. These blocks were then cut into small pieces for metallographic studies. The first problem

Jan 1, 1953