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By C. A. Heberlein

C. A. HEBERLEIN, New York, N. Y.-The results stated by Rey and Brevers are so startling that they are of great interest, as the concentration of a low percentage of cinnabar by differential flotation yields a high-grade concentrate in the presence of either arsenical or iron pyrite. The authors say: "Cyanide can thus be used to depress arsenopyrite and make a good cinnabar-arsenopyrite separation. A cinnabar-pyrite separation could probably be effected in the same way." Corrosive sublimate at the present price of mercury would be a very expensive reagent but the expense would be justifiable if a high rate of concentration could be obtained with a high extraction. On my request, special tests were made in the Punitaqui mill in Chile along the line suggested by the authors, without any improvement of either grade or extraction. As the recovery of the cinnabar in a complex sulphide of chalcopyrite and pyrite gave unsatisfactory results, I had tests made at the testing laboratory of the American Cyanamid Co. at Stamford, Conn. As these tests turned out to be highly satisfactory, not only at Stamford but later at the mine, they are presented here. [ ] The pulp had a density of 22 and a pH of 7.8. Total time of conditioning was one minute. The reagent added was Texas fuel oil, 0.116lb. of 33.7 Bé. gravity containing 0.9 per cent sulphur. Frother, 0.062 lb. of No. 5 pine oil. Rate of concentration of mercury was 25.7: 11. [ ]

Jan 1, 1941

By John Tyssowski

IN 1925, Harry Howard Stout, then metallurgist for Phelps Dodge Corporation, while investigating the cleaning of cathode copper by various gases at elevated temper-atures below the melting point of the metal, observed in the laboratory that particles of pure copper heated in a closed tube filled with hydrogen seemingly "stuck together." By further investigation he found that there was actual crystal growth across the boundaries of the particles of pure metal; in other words, there was a complete new crystal realignment and growth throughout the newly formed copper mass. It was coalescence, not adhesion; the several parti-cles had become one unit. From this dis-covery has been developed the coalescence process, whereby copper of cathode purity is squirted out in semifabricated form from an extrusion press, by the appli-cation of about 30c0 tons pressure on a 10-in. piston. Stout decided that cathode copper pro-duced by electrolytic deposition was the logical source of the pure copper required for the coalescence process, but as there was no way of reducing the ordinary tough commercial cathodes to the small particles required he was confronted by a serious problem at the outset. Under his direction, this problem was solved by William H, Osborn and Harry Howard Stout, Jr. They developed the process and technique for producing cathode copper in brittle, friable form, and to them must be given the greater part of the credit for this phase of the development program as well as for that relating to the gas cleaning of the cathode particles.

Jan 1, 1940

By John S. Crandall

Occurrence: small crystals in alluvial sands from the eroding Belt Series mica schists. Flowsheet: dragline, trommel screen, jigs, drier, crusher, screens. Value: ground, $2.50 per cu yd, garnet sand gross $60. per ton. Costs: production and sales $48. per ton. Uses: blasting sand in aircraft plants, monumental works, foundries. Efficiency comparison: superior to silica sand. Future: possibilities only touched upon, research continuing.

Jan 1, 1950

By Raymond Mancha

The use of blower fans and tubina- for auxiliary face ventilation is a somewhat controversial subject. Most authorities agree upon the advantages of this system over the maintenance of line brattice for dead-end ventilation. They also recognize the system's disadvantages. However, there is considerable disagreement as to the proper relation of the advantages to the disadvantages. It is the purpose of this report to present the opinions of four authorities of diversified occupation and permit the reader to form his own opinions on the subject. ORsErvers Carel Robinson is a mining engineer consultant of wide repute, who has a background of operating experience. Thomas G. Fear is a mine operator whose present position is that of chief engineer for the Hanna Coal Co. at St. Clairsville, Ohio. E. H. Denny is chief of the Coal Mine Inspection Division of the U. S. Bureau of Mines, and is a very able engineer whose past experience well qualifies him to appraise this problem. Cloyd M. Smith, editor of the periodical Mechanization, is a ventilation consultant. For a number of years he was a member of the Mining Department of the University of Illinois and has studied mine ventilation for many years. It is Mr. Robinson,s opinion that closely spaced breakthroughs, although conducive to low gas accumulation past the last open crosscut during the driving of entries, are difficult to maintain and are constant Sources of fugitive air. Jute or canvas brattice is suitable for entry driving with

Jan 1, 1944

By Raymond Mancha

The use of blower fans and tubina- for auxiliary face ventilation is a somewhat controversial subject. Most authorities agree upon the advantages of this system over the maintenance of line brattice for dead-end ventilation. They also recognize the system's disadvantages. However, there is considerable disagreement as to the proper relation of the advantages to the disadvantages. It is the purpose of this report to present the opinions of four authorities of diversified occupation and permit the reader to form his own opinions on the subject. ORsErvers Carel Robinson is a mining engineer consultant of wide repute, who has a background of operating experience. Thomas G. Fear is a mine operator whose present position is that of chief engineer for the Hanna Coal Co. at St. Clairsville, Ohio. E. H. Denny is chief of the Coal Mine Inspection Division of the U. S. Bureau of Mines, and is a very able engineer whose past experience well qualifies him to appraise this problem. Cloyd M. Smith, editor of the periodical Mechanization, is a ventilation consultant. For a number of years he was a member of the Mining Department of the University of Illinois and has studied mine ventilation for many years. It is Mr. Robinson,s opinion that closely spaced breakthroughs, although conducive to low gas accumulation past the last open crosscut during the driving of entries, are difficult to maintain and are constant Sources of fugitive air. Jute or canvas brattice is suitable for entry driving with

Jan 1, 1944

By William Fink

THE investigation of aluminum alloy systems prior to 1923 was severely handicapped by the low purity of the best aluminum available. However, by that time, the electrolytic purification of aluminum had been developed by the Aluminum Company of America,(1)? and in May, 1923, there was initiated, under the direction of E. H. Dix, Jr.,(2) a program for the investigation of the aluminum-alloy systems using the purest electrolytically refined aluminum. Up to the present time 15 papers (a) have been published, most of which are on the binary aluminum systems. Work is now in progress on the ternary systems, and it seems probable that most of the future work will be on ternary systems. Therefore this survey of the binary aluminum systems investigated up to the present time (the sixteenth paper of the series) concludes the first phase of this program. Certain qualitative relations between corresponding portions of the various binary diagrams as well as between different parts of the same diagram were noted some time ago by R. S. Archer.(4) In the present . paper these relations and others are considered quantitatively by the application of well-known thermodynamic equations or by newly discovered empirical relations No attempt will be made here to present the history of the develop-ment of the thermodynamic equations defining equilibrium or their application to metallic systems, although a list of references is given at the end of this paper for those who are interested in this phase of the

Jan 1, 1934

By C. L. Warwick, A. B. Parsons

The papers and discussion appearing in this volume were presented at a symposium jointly sponsored by the American Society for Testing Materials and the American Institute of Mining and Metallurgical Engineers and held at Philadelphia, Pa., November 29, 30, and December 1, 1944. Late in January, 1944, Lieut. Col. C. H. Greenall, Officer-in-Charge of the Laboratory Division, Frankford Arsenal, Ordnance Department, U.S.A., suggested to the American Society for Testing Materials that it might be a propitious time to arrange for a symposium on stress-corrosion cracking at the Annual Meeting of the Society in June, and agreed to make available a number of papers relating to work being carried out at that Arsenal. The Society's Committee B-5 on Copper and Copper Alloys, Cast and Wrought expressed keen interest in the symposium, and other Society committees were contacted and agreed to cooperate. Since the subject is one of primary interest also to the American Institute of Mining and Metallurgical Engineers, it was arranged that the two organizations would jointly sponsor the symposium. A Symposium Committee was formed under the joint leadership, for A.S.T.M., of Carter S. Cole, then Chief of the Metals Branch, Conservation Division, War Production Board and now Engineer on the Headquarters Staff of the Society; and, for A.I.M.E., of E. A. Anderson, Chief of Metals Section, Research Division, New Jersey Zinc Co. (of Pa.) and chairman of the Program Committee of the Institute of Metals Division. The Symposium Committee was constituted as follows:

Jan 1, 1945

By Emil Gathmann

Discussion of the paper of EMIL GATHMANN, presented at the San Francisco meeting September, 1915, and printed in Bulletin No. 104, August, 1915, pp. 1485 to 1492 H. W. LASH, Cleveland, 0.-I have found in practical experience that it is not objectionable to have some blow-holes in ingots. They enlarge during solidification and have a tendency to cause the steel to rise. If they are of fairly small size they weld up quite readily, especially where they are some distance from the surface. In that way a pipe, which is much more detrimental than a few small blow-holes, is prevented. There is a very great difference in the formation of blow-holes in steel. You get one condition in soft steel and entirely another condition in rail carbon, or the still higher grades. The figures that are given in Mr. Gathmann's paper I imagine are taken from the higher carbons, as it is very seldom that piping occurs in soft steel. J. W. RICHARDS, South Bethlehem,, Pa.-This contribution is very welcome, and I understand that the process of Mr. Gathmann is in practical use and has proven successful. I believe the experience of steel makers is that an ingot which has a pipe is of more solid structure, and therefore takes a great deal more work in the rolls and in mechanical treatment, than an ingot which has some blow-holes. The density of the piped steel is undoubtedly increased. My opinion is that it is un-

Jan 12, 1915

By AIME AIME

CHARLES WASHINGTON MERRILL, the second to be honored by the award of the James Douglas gold medal, throughout his entire professional career has been identified with the cyanide method of extracting gold from ore. To his efforts this branch of the metallurgical industry owes a large measure of its success in continuing to treat some gold ores profitably, in spite of economic adversities. Mr. Merrill was born at Concord, N. H., Dec. 21, 1869, and received the degree of B. S. from the School of Mines at the University of California in 1891. Among his first professional connections was the Standard Mining Co., at Bodie, Cal., followed by a short engagement at Harqua Hala, Ariz. From 1895 to 1899 he was connected with the Montana Mining Co., at Marysvale, Mont., and then followed his nine years of fruitful association with the Homestake Mining Co. In 1909, the Merrill Co. was formed, to exploit more than a score of patents granted to Mr. Merrill, covering various phases of the cyanide process and numerous pieces of equipment for its operation; among the most noteworthy of these innovations were the Merrill filter-press, and the use of zinc dust as a precipitant. The Merrill Co. has a long record of successful accomplishments in its chosen field, to mention only the plants at the Dome mines of Ontario and at the Sta. Gertrudis mines of Mexico as among the more recent. Mr. Merrill is president also of the Western Ore Purchasing Co.; and a director in two gold dredging companies of California.

Jan 1, 1924

By D. Harrington

TheRe has been, during the past year, a wealth of report data and discussion relating directly or indirectly to various phases of ventilation of metal mines, and many of the data are from foreign sources. The phase of the subject most generously accorded the attention of the technical press is that of cooling mine air, with much less attention to other fairly intimately associated features such as fan performance, friction factors, fires, mine gases, mine lighting, health of miners, and ventilation standards. Cooling Mine Air South Africa, with its very deep mining on the Rand and with fairly high working temperatures, 'contributes the most definite data on the subject of cooling mine air, and undoubtedly the most interesting issued are those from a paper by J. H. Dobson,' in which he gives a comprehensive review of the subject as gleaned largely by analyzing the data in three papers.2 Dr. Dobson's summation is decidedly interesting. In general it is recognized that the introducing into the mine and circulating to the working places of large volumes of pure air is the most effective method of giving deep, hot metal-mine workings reasonably efficient working conditions. A tabulation as to the cost of securing various amounts of cooling by circulating various volumes, from 230,000 to 760,000 cu. ft. per min., indicates that there are cost limits beyond which increase of quantity of air in circulation is impracticable, as the annual cost of circulating 230,000 cu. ft. of air per min. in a certain mine at a depth of

Jan 1, 1928

By AIME AIME

THE year 1940 was an important one in the life of Carl Swartz. At the annual Institute meeting in February of that year, he was inducted into the office of Vice-Chairman of the Institute of Metals Division, and a few months later he assumed another and possibly even more important responsibility-he became the son-in-law of Robert H. Leach, genial vice-president of Handy and Harman, who had just ended his term as Chairman of the Division. The young man who took on this dual obligation in 1940, and who is now commander-in-chief of I.M.D., was born near Danville, Ill., and graduated with honors from the University of Illinois in 1923. (Ed. note: It's a small world. About the time Carl was a freshman in high school at Danville, or slightly before, the University of Illinois students held beer parties in Danville's hotel. We know; we were there.) Continuing his education at another of our fine Middle-Western colleges, Carl received his Master's degree from the University of Wisconsin and his Ph.D. from the same school in 1926. For the next nine years he worked in that splendid training school for non-ferrous metallurgists-the research laboratory of the American Smelting and Refining Co., at Barber, N. J., leaving there in 1935 to take the position of metallurgist of the Cleveland Graphite Bronze Co. in Cleveland, where he is still working (in a modern, air-conditioned office and laboratory) today.

Jan 1, 1942

Department of Conservation and Development, State of North Carolina, Raleigh, N C H J Bryson, State Geologist. The latest list of publications will be sent upon request. Of the many Bulletins, Economic Papers, Circulars and Volumes issued by the Department of Conservation and Development, the following are available and relate to mining and geology of the state ? Bulletin 18, Bibliography of North Carolina geology, mineralogy and geography (1909), 50 cents, 21, The Gold Hill mining district (1910), 15 cents, 22, Report on Cid mining district (1911), 15 cents, cloth 75 cents, 25, Zircon, monazite and other minerals, 15 cents, cloth, 75 cents, 28, Limestones and marls, 15 cents, 29, Kaolins of North Carolina, 50 cents, 31, Deposits of brown iron ore, 50 cents, 32, Magnetic iron ores, 15 cents, 33, The Deep River coal field, 50 cents, 37, Pyrophyllite deposits, 35 cents A series of the Economic Papers review the mining industry in North Carolina for the years cited Those now available are Economic Paper 23 (1908-1909-1910), 10 cents, cloth, 50 cents, 49 (1913-1917), 20 cents, 55 (1918-1923), 25 cents, 60 (1924¬1925), 15 cents, 63 (1927-1928), 25 cents. Other available Economic Papers on geology and mining are No 3, Talc and pyrophyllite deposits (1900), 25 cents; 58, Oil prospecting well near Havelock (1927), 5 cents, 59, Oil-bearing shales of Deep River Valley (1927), 10 cents Available volumes on geology. Vol 1, Corundum and the basic magnesian rocks (1905), 35 cents, cloth, $150, 5, The Cretaceous formations of North Carolina (1923), cloth $1 75

Jan 1, 1933

A tentative plan for the Colorado Meeting has been formulated as follows: One day will be spent at Denver, one day at Colorado Springs, one day at Cripple Creek, a trip by automobile to the top of Pike's Peak, one day at Pueblo, one day at Leadville. All the principal mines and mills of the districts mentioned will be visited, including the gold mines in Cripple Creek, the lead, zinc, and steel works. of Pueblo, the production of ferro-molybdenum by electric furnace at Leadville, etc. Special arrangements are being made for the social entertainment of ladies at all points; one evening at Colorado Springs will be devoted to a reception and dance, and the usual dinner will he given on another evening. The following papers have already been accepted for the Colorado Meeting, and some have already been published: Fireproofing Mine Shafts by the Anaconda Copper Mining Co. By E. M. Norris. (March Bulletin.) Air Blasts in the Kolar Gold Field, India. By E. S. Moore. (March Bulletin.) The Use of Coal in Pulverized Form. By H. R. Collins. (April Bulletin.) Coal Mining in Washington. By F. A. Hill. (April Bulletin.) Carbocoal. By C. T. Malcolmson. (May Bulletin.) Gaging and Storage of Oil in the Mid-continent Field. By O. U. Bradley. (March Bulletin.) An Interpretation of the So-called Paraffin Dirt of the Gulf Coast Oil Fields. By A. D. Brokaw. (April Bulletin.) The Theory of Volcanic Origin of Salt Domes. By. E. DeGolyer. (May Bulletin.)

Jan 5, 1918

C. H. BIERBAUM,* Buffalo, N. Y.--I agree with Dr. Merica that the eutectoid has a distinct effect upon the alloy and also that, as yet, it is difficult to say at just what point this eutectoid occurs or the conditions under which it appears; that is, the percentages of copper, tin, zinc, lead, and the other elements together with the temperature of pouring and the rate of cooling that is necessary; all seem to have a contributing effect. Some authorities, Law for instance, gives it as 9 per cent. of tin, yet under certain conditions I have found it with a lower percentage of tin to copper contents than that. The hard delta and the soft alpha crystals are both necessary for a bearing alloy; the one supplements the other. I am not inclined to think that phosphorus has any effect upon the eutectoid forming. The phosphide, PCu3, forms in and around the delta but is and remains distinct and separated from it. Etching with ferric chloride and then with nitric acid shows this very distinctly; it darkens the eutectoid and the other parts and leaves the phosphide bright. The rate of cooling determines the size of the crystals and the eutectoid together with their distribution and orientation. It is possible to chill the alloy to such an extent Where no eutectoid appears. I think it has been positively demonstrated that only an alpha and a beta appear. when this copper-tin alloy has been poured between two polished ingots

Jan 1, 1919

Discussion of the paper of CHESTER W. WASHBURNE, presented at the New York meeting, February, 1915, and printed in Bulletin No. 9S, February, 1915, pp. 469 to 471. ROSWELL H. JOHNSON, Pittsburgh, Pa.-I hope that this contribution of Mr. Washburne's is only the first of a series dealing more in detail with the very important problems involved. Pores are of two kinds: Those which are entirely inclosed, so that they do not belong to a system of communicating pores tapped by the bore hole or shot hole; second, those which do so communicate. Porosity, of course, includes both. But since pores of the first class are valueless to us, we should confine our attention to the latter, for which I propose the term "effective porosity." This should be measured by the Wisconsin method, based on the quantity of fluid that can be introduced by the aid of vacuum. Another factor which requires attention in this connection is the dependence of the extractability upon the rate of loss of pressure, as affected by the number of holes, and the rapidity of their completion, the existence of uncontrolled wells, the use by other operators of vacuum pumps upon the casing head, the exhaustion of a gas field in the same reservoir prior to the discovery of the oil, etc. The extractability depends upon the pressure available for the exclusion of the oil from the reservoir into the hole. The action of gravity in bringing oil into the hole is relatively small where the pores are very small, as is so frequently the case.

Jan 5, 1915

During the year terminating at the date for the third annual meeting of Engineering Foundation, the Board completed, its undertaking to sustain the National Research Council for one year. Assistance given in the organization of the National Research Council has been amply justified by the results. The Council is now well established in a 4¬story building at 1023 16th Street, N. W., Washington, and has recently secured another similar building near by in order to house its increasing force. The breadth, importance and volume of work done have steadily grown. Foreign offices have recently been established in London and Paris, Dr. H. A. Bumstead being in charge of the former and Dr. William F. Durand of the latter. The total expenditure by Engineering Foundation for the National Research Council was $9,036, derived partly from income of the endowment fund and partly from special gifts from Ambrose Swasey and Edward D. Adams. In May, Walter M. Gilbert was appointed Assistant Secretary of Engineering. Foundation, with headquarters in Washington, his services being contributed by the Carnegie Institution. He also became and has remained to date Assistant Secretary of the National Research Council. In September, resolutions were exchanged between the Engineering Foundation Board and the National Research Council, setting forth a policy of continuing reciprocal relationship, and a conference committee, Chairman M. I. Pupin, Dr. Charles Warren Hunt, and Gano Dunn, was appointed to inform the National Research Council of the readiness of Engineering Foundation to work upon definite problems sug-gested by the Council. No problems have yet been suggested.

Jan 5, 1918

By E. S. Machlin

RECENTLY, there has been much activity in the field of nucleation of martensitic transformations.'- One of the problems in this field is the calculation of the rate of nucleation (number of plates nucleated per unit untransformed volume per unit time) in terms of observable parameters. Two such observable parameters are the fraction of the length of a straight line which corresponds to the portion of the total length of the line that lies in the martensitic phase and the number of plates intersected by this straight line per unit length of line. Because of the necessity of a valid answer to this problem, the following investigation was undertaken. Although this problem has been treated in the past, a derivation of the relation between the volume and linear fractions of martensite will be described to illustrate the method used in the succeeding analyses. It is assumed that the martensitic plates are in the form of a right circular cylinder having a small height relative to the radius of the base. The volume fraction of martensite is then: fr = lXNl,hjAl [1] where f, is the volume fraction of martensite, and Nij is the number of plates per unit total volume having the area Ai and the height hi. The linear fraction of martensite is obtained as follows. For the plates having the particular area A, and height h,, the fraction sin 0 dB* will have their cylinder axes between the angles 0 and 0 + d0 to the straight line along which the linear fraction of mar-

Jan 1, 1953

By J. PARK

Discussion of the paper of J. PARSE CHANNING, presented at the New York meeting, February, 1915, and printed in Bulletin No. 99, March, 1915, pp. 529 to 538. FRED H. RINDGE, JR., * New York, N. Y.-It is interesting to note that although this movement was started only seven years ago at Yale, it has spread in that brief time to 200 colleges and technical schools, anti thousands of men are interested in it. There are 3,000 graduates who became acquainted with the movement in college days anti are now promoting the industrial betterment idea all over the country. Some of these men are employed entirely in this work, and the number of such workers is constantly increasing. We feel we are really doing a very fundamental thing in getting so many coming engineers and prospective employers of labor to interest themselves in these things which we have been discussing this morning; these things which are so vital to efficiency and success in any line of business or engineering to-clay. Of course the institutions located in our large industrial centers have the greatest opportunity for practical service. But I have just returned from one college, Pennsylvania State College, where 300 engineering students in three clays signed up as interested in this movement and as anxious to take active part in the work this summer. That is one of a number of colleges situated in towns where there are 110 industrial opportunities. Therefore, their field of service must be where they work

Jan 5, 1915

By Mark David Rankin

This paper represents a general assessment of the primary factors driving the market for mobile offshore drilling rigs and the utility of those factors as choice variables for the offshore drilling program planner.

Jan 1, 1982

By M. E. Nicholson

IN order to understand how alloying elements influence hardenability through their effect on the rate of pearlite nucleation, it is advantageous to use a model to describe the mechanism of pearlite nucleation. The model which currently is most widely accepted has been described, among others, by Mehl et a1.1-3 and by Hultgren.4 Pearlite nucleation involves both the nucleation of ferrite and cementite.4,5 Cementite nucleates first, followed rapidly by the formation of ferrite at the cementite-austenite interface. The conclusion that cementite is the first phase to form during the process of pearlite nucleation is based, in part, on the observation that proeutectoid cementite is continuous with pearlitic cementite and that the orientation relationship between proeutectoid ferrite and austenite is not the same as that between pearlitic: ferrite and austenite.6,7 Recently, Smith" has suggested that the dissimilarity in orientation relations, instead of indicating the pearlite nucleation sequence, may be evidence that pearlite is nucleated in a grain adjacent to the one in which it is growing. Also, Modin9 as shown that ferrite in pearlite may be continuous with proeutectoid ferrite, and he has also shown that proeutectoid cementite is not always continuous with pearlitic cementite. Thus, it appears that the conclusion that cementite always initiates the pearlite nucleation process is open to serious question. The author believes that important evidence on the question of how pearlite is nucleated exists in the rates of pearlite nucleation of different steels. The following is a review and analysis of this evidence. If the nucleation of pearlite is considered as requiring the nucleation of both cementite and ferrite, then the time to nucleate pearlite consists of the time to nucleate the first phase to form, plus the time to nucleate the second phase at the advancing interface of the first. In the absence of a visible proeutectoid constituent, the second phase must be nucleated very soon after the first. If cementite is the first phase to form, the time to nucleate pearlite will be approximately equal to the time to nucleate cementite. Since the nucleation rate of a phase precipitating from solid solution increases with the degree of supersaturation, it would be expected that the rate of pearlite nucleation should increase with increasing carbon content. Digges10 has shown that the reverse is true. He determined the quenching velocity necessary to suppress pearlite formation in plain carbon steels as a function of carbon content. His results showed that pearlite formation could be suppressed with lower quenching velocities as the carbon content of the steel increased, at least up to 1.25 pct C, the highest carbon content he studied. Thus, it would appear that in plain carbon steels, in which pearlite is formed at the nose of the C-curve, the hypothesis that cementite nucleates first does not predict the observed change in nucleation rate. The validity of the current model of pearlite nucleation may be tested also by determining whether or not it predicts the relative influence of alloying elements on the nucleation of ferrite and pearlite. This can be done best by a consideration of the changes in a TTT diagram produced by a change in alloy content. Hultgren4 suggests that the general shape of a TTT diagram, as well as what constituents will form from austenite, can be predicted from the relative nucleation rates of ferrite and cementite. This is illustrated in the schematic diagram for a hypoeutectoid low alloy or plain carbon steel shown in Fig. 1. The C-curves for ferrite nucleation and for cementite nucleation are represented by AA' and CC', respectively, and the start of ferrite formation and pearlite formation are represented by AX and BC respectively. Adopting the current theory, Hultgren suggests that between X and C pearlite forms directly from austenite, since cementite nucleates more rapidly than ferrite in this temperature range. Conversely, at temperatures above Tx, ferrite is the first to nucleate and proeutectoid ferrite is formed. As proeutectoid ferrite grows, austenite becomes enriched in carbon, so that the cementite nucleation rate is increased. As a result, pearlite nucleation above temperature Tx is accelerated, beginning along BX and not along C'X. Temperature T, represents the temperature at which the nucleation rate of ferrite equals that of cementite. By extending this type of reasoning, using the principle that the nucleation rates of ferrite and cementite increase with increasing supersaturation of austenite with respect to these phases, it should be possible to predict the influence of carbon content on the shape of the isothermal transformation diagram. For a slightly higher carbon content than that of Fig. 1, the curve A A' representing the beginning of ferrite formation should be moved to the right, whereas the curve CC' representing the beginning of cementite formation should be moved to the left. For hypoeutectoid plain carbon and low alloy steels, this prediction does not agree with existing data. Instead, as the carbon content is increased, the pearlite curve moves to the right along with the ferrite curve and always appears to join it tangen-tially. This behavior is demonstrated by the TTT-curves of a series of manganese steels" shown in Fig. 2. In this figure, TTT-curves for four alloys containing 0.20, 0.40, 0.60, and 1.20 pct C are superimposed. The curves are identified in the figure legend. The letters F, P, and C are used to indicate the start of ferrite, pearlite, and cementite formation, respectively. In these steels, it appears that the nucleation of ferrite and of pearlite are related processes. As a result of the foregoing evidence, it is proposed that the formation of pearlite be considered as follows: Either ferrite or cementite may nucleate from austenite, then grow until the remaining phase is nucleated at the interface between the growing phase and austenite. (The growth of the first phase to form is assumed to be accompanied by a composition change in the adjoining austenite.) According to this model there are two modes of nucleating pearlite: 1—where cementite initiates the succession

Jan 1, 1955