with a proof roller, place on the bed of a copy press, cover with "glossy art paper," overlay with two thicknesses of broadcloth, and apply pressure.

This solution acts by attacking the purer portions which solidified first with greater vigor, leaving in relief the major and minor segregates, which thus print black on the proof. Some very beautiful examples of work on shell forgings are illustrated in the original paper.

GRAPHITIZATION IN IRON-CARBON ALLOYS

Whether graphite or cementite is the stable constituent of pure iron-carbon alloys was again discussed by K. Tawara and G. Asohara of Tokyo University. They cast a number of triangular ingots, in preheated clay molds, and studied the effect of six variables with regard to graphitization. First, chemical composition (that is to say, carbon content, the amount of silicon being held at 0.05 per cent or less, while the other impurities were very low) appeared not to be a decisive factor in graphitization. Graphite was always seen in a slowly cooled ingot containing from 2 to 3 per cent carbon, although in relatively larger amounts in higher carbon irons, which would be expected if the constituents appearing at primary solidification were austenite and graphite only. Second, the maximum temperature attained by the molten iron appeared to have no effect. Thus no excess decomposition of Fe,C by superheating appeared to persist at the liquidus. Third, temperatures of casting up to 1400 deg. C. for a 3.3 per cent C appeared to cause no differences. Fourth, temperature of the mold had a large effect due to the speed at which it cooled the metal through the solidification range. Thus no graphite was found after pouring in a mold heated to 900 deg. C., held for 7 hr. at that temperature and then quenched. When cast in a mold heated to 1000 deg. C., held for 8 hr. and then quenched, graphite appeared in spots only. When cast in a mold heated to 1100 deg. C., held for 1 hr. and then quenched there was plenty of graphite. However, the same procedure in a mold at 1125-1128 deg. C. gave no graphite. The authors interpret the last results as meaning that the metal (3.3 per cent C) was held liquid in the mold, and when quenched it was white iron; a mold at 1100 deg. C. giving an optimum cooling rate through the mushy stage for graphitization. Fifth, when the mold is 1100 deg. C. and the subsequent cooling is slow, the metal is completely graphitized independently of the time it is held at 1100 deg. C. Sixth, with a mold at 1100 deg. C., the speed of subsequent cooling merely affects the method of deposition of the primary austenite, water quenching producing martensitic ground mass, and slow cooling producing pearlite and needle cementite.

From these experiments the authors conclude that homogeneous graphitization takes place during the slow cooling of the metal down to 1100 deg. C., covering a time longer than 30 min., and when uninfluenced by such accelerators as silicon and manganese, does not occur at 1000 deg. C. even after 8 hours' uniform heating. Consequently they believe that cementite in the melt is at least partially dissociated, and if time be given during solidification, the free carbon thus in existence will crystallize as graphite particles causing more cementite to decompose, enriching the melt in ferrite, the contemporaneous product of dissociation, when finally the remaining melt will have the composition of saturated austenite. Thus is the stable alloy produced. On more rapid cooling, decomposition of molten cementite is incomplete, whence the metastable "mottled" iron. The

authors consider a graphite crystal as being an element of the eutectic; the lamellar structure ordinarily expected of a eutectic is thus absent due to the slow cooling of the melt. Such crystals are surrounded by resolved austenite (needle cementite plus pearlite), as they should be, and not by ferrite resulting from a hypothetical decomposition of Fe,C.

INFLUENCE OF RATE OF COOLING ON HARDENING
CARBON STEEL

"An Experimental Investigation of the Influence of the Rate of Cooling on the Hardening of Carbon Steels" was described at considerable length by the prominent French metallurgist, A. M. Portevin of the Ecole Centrale des Arts et Manufactures, Paris, and his associate, M. Garvin. In a preliminary part the authors describe in detail their apparatus and method of tracing cooling curves at very rapid rates. A platinum couple whose elements were but 0.1 mm. in diameter was used in order that its heat capacity be negligible, and actual contact at the center of the cylindrical test piece was periodically verified by measuring the resistance, couple to specimen. In order that this contact might not be disturbed, the specimen and couple were both held stationary by a nickel-steel tube fixed to the upper head of a standard. Heating was done by a Meker blast lamp; when a predetermined temperature was reached the lamp was rapidly lowered, a quenching cup swung into place, and the specimen was cooled by a uniform flow of water. Automatic records were made photographically by a beam of light from a galvanometer mirror; the paper contains information as to necessary precautions and corrections to insure proper time and temperature registration.

Their problem was to determine for a given steel how the transformations, structure and hardness vary with different rates of quenching ( from 700 to 200 deg. C. was the unit of comparison) and the initial temperature of quenching. Different speeds of quenching were had by using geometrically similar specimens of varying diameter; after quenching the pieces were broken across their center and the microscopy and Brinell hardness of the spot directly in contact with the thermocouple junction examined. A series of such curves for 1.07 C steel is illustrated in Fig. 1, and it is seen that rapid cooling suppresses transformations until 300 to 350 deg. C. Such cylinders are entirely martensitic and their hardness is uniformly close to 600. On cylinders 14 mm. in diameter and larger, however, this lower transformation Ar" is suppressed and an upper one, Ar', at

635 to 665 (depending upon the speed) appears. Such cylinders show uniformly a troostitic core, of hardness, 400, surrounded by a shell of martensite of thickness decreasing as the diameter increases. There is therefore a critical range in the rate of cooling (in this particular steel, about 7 sec. from 700 to 200 deg. C.) at which the interval transformations suddenly change their nature and position on the temperature scale. When quenching at speeds near this rate, the same steel will sometimes appear troostitic, sometimes martensitic, and sometimes both Ar' and Ar" are in evidence, giving a martensite-troostite complex.

Experiments by the authors demonstrate that composition has much to do with the critical rate. Particularly manganese will increase the critical time between 700 and 200, imparting quasi self-hardening properties. Variations in carbon also appear to have a marked influence. Eutectoid steels have slow critical rate as compared with either hypo-eutectoid or hyper-eutectoid, either of which tends to become troostitic with the separation of the pro-eutectoid constituents, ferrite or cementite respectively. This excess constituent may well be the cause of the phenomena, presenting nuclei unabsorbed into the austenite around which crystallization proceeds, correspondingly inducing formation of troostite. Unabsorbed nuclei may be the reason why previous heat treatment, mechanical working, method of manufacture, duration of heat and temperature of quenching all have an effect upon the speed of quenching.

In particular, raising the quenching temperature in the neighborhood of the critical rate tends to make Ar' disappear, as does also a second quenching. Also the authors point out that various facts already determined about quenching hold true at rates somewhat distant from the critical-thus varies as diameter of geometrically similar cylinders except at the critical rate, nor does hardness vary as the temperature of quenching (except at the critical rate), and with the same provision, the agitation, rate of circulation, or temperature of cooling water will not affect the hardness of drastic quenchings. By interrupting the quenching at various temperatures, the authors were also able to form troostite (Y iron-carbon solution - Fe,Ca iron complex) at temperatures as slow as 400 deg. recalescence is exhibited in such curves, and microscopically the troostite is strongly marked and bulky, both the characteristics of a sharply defined reaction, much different from that which occurs when annealing martensite to troostite, osmondite or sorbite.

TWO PAPERS ON TOOL STEEL

Strong

"The Manufacture and Working of High-Speed Steel" was described in a paper by J. H. Andrew and G. W. Green of the Metallurgical Research Dept., Armstrong, Whitworth & Co., wherein they gave the practice at the Openshaw works in manufacture of steel bars with 14 per cent W, 3.8 per cent Cr, 0.5 per cent V, and 0.6 per cent C. Such material is melted in crucibles, and poured at 1420 20 deg. C. into ladles, wherefrom it teemed at 1335 5 deg. C. into chills, making a top-cast ingot 6 in. square and weighing 350 lb. After 30 min. the ingots are stripped, being then at 650 deg. and annealed in a gas-fired furnace for 48 hr. at 800 deg. C. Microsections now show excessive carbide segregation at the skin, and fine structure at the outer portion of the ingot. In the center is coarse-grained structure with thick walls of carbide.

Drillings from various parts of the ingots and croppings show practically no measurable segregation. This, as well as the entire absence of blowholes. is probably due to the small size of ingot, and the very quick solidification, due to the chill-mold and high alloy con

tent.

Mechanical and heat treatment are resorted to in order to reduce this crystalline structure to an extremely fine grain, it having been found that 88 per cent reduction is necessary before the distorted carbide envelopes lose their dangerous form of loops and hooks. Whether reduction is done by rolling or forging is immaterial, as long as the working temperatures are correct, which, by the way, are greater than generally thought to be correct.

A good practice is cited as folows: After annealing, the ingots are preheated, attaining 820 deg. C. in 24 hr., then transferred to another furnace and brought to 1170 deg. in 4 or 5 hr. Cogging from 6 to 3 in. square was done under a 1-ton hammer, occupying about 4 min., at which time the temperature was 1000 deg. C. Ten per cent of the head was cropped off; and any surface cracks gouged out with a steel tool, as is done after each reduction. Microsections now show well disseminated carbide in the outer portions, but at the center the envelopes are merely distorted.

After the 31-in. billets are cut in half, they are aired under the fire-bars and finally charged into a cool-fired furnace, attaining a temperature of 1150 ± 20 deg. C. and soaking until the forge is ready for them. Forging one end to 1 in. requires slightly less than 2 min., during which time the temperature falls 50 deg. The large end is reheated and drawn under the same conditions. Microscopically, the carbide now is in laminated, bandlike zones, occasionally appearing as semi-decomposed austenite.

From 1 in. the bars are tilted or rolled to 1 in., rolling starting at 1030 deg. C. and requiring 15 to 18 passes, consuming nearly 2 min., the temperature dropping about 10 deg. per pass. Tilting is done on each end separately as before, requiring about 2 min., during which the temperature drops from 1100 deg. to 850

50 deg. At this point the carbide envelopes are broken up into grains, but these still assume laminated arrangement as to position.

In older practice the 11-in. bars were then annealed by heating to 800 deg. C. in 24 hr., then damp the furnace from 3 to 6 hr., when the bars were furnace cooled during 36 hr. This required 3 days, and the structure was not refined (800 deg. being lower than the transformation range). Newer practice heats slowly to 900 deg. C., soaking a little time, cooling in furnace to 700 deg. C., and cooling in air. Cast structure is now eliminated, the bars have been softened from Brinell 616 to 250, and are ready for shaping into machine tools.

Lathe tools are hardened by gradually heating to a medium red heat, then quickly heating the nose to 12901300 deg. C., when it is quickly withdrawn and cooled in air-blast or oil attaining Brinell 650. Quick heating, consistent with adequate soaking, is desirable, since high and prolonged temperatures promote grain growth, without materially affecting any improper carbide distribution persisting to this point. A difference of 5 deg. in the maximum will increase the grain size 15 diameters (Figs. 2 and 3), while 10 deg. to 1310 will liquefy the carbide eutectics. At 1350 deg. the specimen is completely "crozzled." (Fig. 4.) Tool failures may be due to persistent dendritic structure inherited

from too hot casting, rare segregations of slag or manganese sulphide, forging cracks, but most often carbide segregations forming banded laminations or grain envelopes.

A study of the microscopic and mechanical properties of several tool steels was presented by Dean J. O. Arnold, and Fred Ibbotson, of the University of Sheffield. Previous researches on plain carbon steels with the addition of a single alloying element has already distinguished the various carbides of chromium, vanadium, tungsten and molybdenum. In the complex mixtures used in these experiments, the same methods were used, namely, electrolysis of the tool steel in HCl (sq.gr. 1.02). The residue of carbides was then analyzed, whence formulæ could be ascribed.

It appears that the relative affinity of carbon for the alloying elements is V, Mo, W, Cr, and lastly Fe. Consequently, with the modest amount of carbon present (0.65 per cent) Fe,C may be entirely absent in high W-V steels, the hard Cr,C, also giving way to Cr,C.

Micro

scopically, all the steels in annealed condition are similar, showing a pale background of an intermetallic solution overlaid by dark troostitic and paler sorbitic varieties of a pearlite of unknown composition, the whole being overlaid by nodules (sometimes streaks) of a brilliant white metaral; doubtless a mixture of segregated carbides. When quenched from 1300 deg. C., the Mo-V steel shows well-marked allotriomorphic crystals of a mixed hardenite, which, here and there, are partially surrounded by a unique dark-etching pearlitic constituent, possibly a troostitic vanadium pearlite which does not transform into its hardenite until 1400 deg. A molybdenum steel with no vanadium does not show these areas. Other steels showed allotriomorphic crystals of hardenite of varying sizes, surrounded with thincell walls with fairly thick and very broken cell walls of cementite more or less segregated into nodules (sometimes in the crystals themselves).

Chemically the steels were designed to have constant carbon 0.65 per cent, chromium 2.85, silicon 0.4, manganese 0.2, phosphorus 0.015, sulphur 0.06. Vanadium when present was 1.25 per cent, molybdenum either 2 or 6 per cent and tungsten either 12 or 16 per cent. Efficiency tests were made by speeding up a lathe tool until it broke, and measuring the amount of steel removed, with the results shown in the accompanying table.

From the results molybdenum appears to be an ac

STEEL HARDENED AT 1350 DEG. C. X 200, REDUCED ONETHIRD

creases with temperature. When clear melted and very hot the slag will contain about 48 per cent SiO,, 33 per cent FeO and 16 per cent MnO, the latter variable as to the nature of the pig melted. At this point ore may be added to maintain basicity, complete the elimination of silicon and to speed the "boil." As the heat progresses the slag gets lighter in color and more viscous, until finally Si0, becomes supersaturated and it is reduced by the metallic iron, this state of affairs evidencing itself by blowholes on the under surface of metal samples. Then limestone is added sparingly, with the ore, the former to satisfy the SiO, and the latter to continue to lower the carbon content of the bath. This method, by the way, is far better than to liquefy the slag by lowering the flame or by chilling with scrap, either of which increases the FeO in the slag by oxidizing metal. At a continuously high temperature, therefore, the decarbonization proceeds, a proper slag being about SiO,, 58 per cent; FeO, 21 per cent; CaO, 5 per cent; MnO, 12 per cent, and appearing light green in a quenched sample, the metal being watched for bubbles, meanwhile, and fresh additions of lime made as they appear.

As the carbon content approaches that desired in the finished metal, lime additions are made with caution, and only as indicated by the appearance of blowholes from the reaction

is the only plausible reaction in which the percentage of iron in a slag can be raised. Since this actually occurs in the finishing stages, when C is below 0.15, it possibly is the predominant reaction. It doubtless also occurs during the boil, counteracting somewhat the effect of the then more prominent reaction

Fe,0,3 C3 CO+2 Fe

or possibly Fe,0, + C = CO + 2 FeO

The authors conclude that the rapid reduction in carbon is due to gas reduction either direct or by Fe,O, acting as a carrier; the latter being formed on the surface layers of the slag, and reacting with the slagiron interface, most particularly of metal shot dancing in the slag whose quantity equals ton in a 100-ton bath. Therefore the use of a rich gas with as much air as the furnace can carry will afford best conditions for carbon removal that is, rapid thickening of slag after more frequent ore additions. Consideration of the rate at which the bath is decarbonized after the boil (entirely by Fe,O,), and during the boil, also leads to the assumption that perhaps of the decarbonization by gasreduction is due to contact between gas and metal shot during the boiling period.

MODERN STEEL METALLURGY

Mr. C. H. F. Bagley, technical supervisor for the South Durham Steel Co., presented a discussion of "Modern Steel Metallurgy," a calculation and comparison of processes, particularly as refers to the slags formed. In brief, it is a treatise on the metallurgical calculations of steelfurnace slags, so collated that given unit prices for different qualities of the necessary constituents, the the best combination for any modern process may be actually determined with confidence, or, on the other

1 Acid Basie Bess. Bess.

4.4 1.21 4.5 8.45 7.5 7.3 13.0 8.0 11.2 11.6 19.1 13.6 14.45 31.1 12.2 13.2 102.2 89.8 91.4 102.8 101.3101.3 105.1 91.0 92.8 9.4 8.10 9.6 16.9 15 0 14.6 17.3 13.5 13.4 1.2 19.7 22.8 22.7 19.7 22.8 22.7

hand, the best process for a given set of conditions may be found when planning a new works. The author pays particular attention to the slag produced, laying emphasis upon the fact that steel making also involves slag making, and, other things being equal, it is true that any factor which lessens the quantity of slag made will at the same time increase the output of iron and lower its cost.

There is nothing particularly novel in the method of calculations. In general, given the analysis of metal charged and the amount of metal tapped, the amount of oxidation can easily be figured. Oxygen comes either from blast or ore; in the latter case, additional slagforming impurities are added. These, with the impurities from the bath, will form a slag which in a given process varies within rather narrow limits at the end of the operation (whatever it may have been meanwhile) in order that it may be thin enough to pour, quiet, stable and non-corrosive. From such known composition, and a little auxiliary data as to mechanical losses, a metallic and non-metallic balance sheet can easily be obtained, giving the yield in metal per unit charged, the slag make and the weight of all additions.

Principal data are assembled in Tables I and II. As an instance of the results Table III summarizes the author's calculations on the various styles of duplex proc

esses.

Lignite Utilization Board of Canada

Although Canada possesses large coal deposits, it has been necessary to import about 500,000 tons of anthracite from Pennsylvania at a cost of about $5,000,000 per annum. The lignite deposits underlying various districts of the Provinces of Saskatchewan and Alberta are unsuited in the raw state to household use. By carbonizing, however, a coke is obtained which briquettes readily; two tons of the inferior fuel giving one ton of briquettes which approximate anthracite in heating value.

The Lignite Utilization Board was created to investigate machines and processes for carbonizing, briquetting, etc., and to construct a plant of commercial size for the production of domestic fuel. Consideration will also be given to the utilization of by-products and of powdered fuel for commercial power production.

Ramsay Memorial Fund

The committee for the Ramsay Memorial Fund for the United States reports the receipt of contributions totaling $4700, which, after deduction of current expenses for printing, postage, etc., will leave about £900 for transmission to the Fund headquarters in London. The committee had hoped to be able to transmit at least £1500 at this time, and will therefore wercome further contributions. Checks should be sent to the chairman, Dr. Charles Baskerville, 140th St. and Convent Ave., New York, or to the treasurer, Mr. William J. Matheson, 21 Burling Slip, New York.