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By Claus G. Goetzel

Pressing of powdered metal parts is best done in the direction of the shortest extension of the piece, to avoid too great a loss of pressing force through internal iriction. As long as curved surfaces, re-cessej, or offsets occur only parallel to this shortest axis of pressure, no special difficulties arise: the cross sections, perpendicular to the pressure, do not vary, nor does the shape of the parts change during compression except for a gradually reduced thickness (Fig. IA). The problem becomes more dificult, however, when the curved surfaces or recesses are perpendicular to the shortest axis of the part (Fig. IB) Two processes for molding uniformly dense parts with complicated shapes from powdered metals are described in detail in this paper. Both can be employed successfully by those trained in the art. The first refers to curved parts; the second is especially adapted to parts having one or more recesses or steps. Both methods, as set forth here, are applied under the condition that presents the more difficult problem. For clarity, before description of the two practical methods, the variable factors in molding powdered metal parts will be reviewed, then an idealized procedure will be considered briefly. Variable Factors in Molding Powdered Metal Parts Compression Ratio Compression ratio is defined as the proportion of the final relative density of the compact to the apparent density of the powder. For iron powder of an apparent density of 3.0, for example, a compression ratio of 2 1/2:1 would be required to produce a compressed compact of 7.5 density; whereas for another iron powder having an apparent density of only 1.5, a compression ratio of 5:1 would be required to produce the same density. The lower the powder's apparent density, the greater must be the compression ratio for pressing compacts of high density.

Jan 1, 1946

By F. N. Rhines

Sintering may be defined as the process by which powders bond themselves into coherent bodies, usually, although not necessarily, under the influence of pressure and elevated temperature. For the sake of clarity and simplicity, the present survey will exclude from consideration the sintering of mixed or alloyed powders, with attendant complications, but at the risk of overlooking information of general applicability. Sintering in the presence of a liquid phase is thus automatically eliminated. The sintering of alloys involves much additional subject matter and deserves separate consideration. Since the literature of the subject is extensive and widely scattered, it will not be feasible to consider the contributions individually. Instead, the subject matter will be classified according to experimental observations and theory, and will be presented in summary form. It should be noted that the appended list of references does not constitute a complete bibliography; it includes only those works quoted below. More extensive bibliographies are included in several of the references; see particularly references 7, 9, 28, 34, 38, 50, 52, 54, a "Bibliography on Powder Metallurgy" published by the Library of Congress and a pamphlet published by the Metals Disintegrating Co. entitled "The Field of Powder Metallurgy and Bibliography." 11. Summary of Experimental Observations The following classified list is composed of general statements of established fact derived from the experimental results reported in the published literature. A few contested observations are included, because of their potential importance; these are labeled as such. Any satisfactory and complete theory must be capable of explaining all of the uncontested facts. Obviously, some important facts may be missing from this list and these may hold the key to the correct explanation of the sintering process, but the possible lack of such material should not deter attempts to understand the subject on the basis of what is available here. A, The Initial Bond at Room Temperature a. To a limited extent uncompressed powders and massive metals adhere at room temperature. Clean tin powder forms a weak "cake" on standing at room temperature, the strength increasing with time. Clean gold surfaces adhere on light con-tact, as do those of many other substances, including nickel.27 b. Upon compression the strength of the bond- is increased progres-ivelv. There is a limit of pressure

Jan 1, 1946

By F. N. Rhines

Sintering may be defined as the process by which powders bond themselves into coherent bodies, usually, although not necessarily, under the influence of pressure and elevated temperature. For the sake of clarity and simplicity, the present survey will exclude from consideration the sintering of mixed or alloyed powders, with attendant complications, but at the risk of overlooking information of general applicability. Sintering in the presence of a liquid phase is thus automatically eliminated. The sintering of alloys involves much additional subject matter and deserves separate consideration. Since the literature of the subject is extensive and widely scattered, it will not be feasible to consider the contributions individually. Instead, the subject matter will be classified according to experimental observations and theory, and will be presented in summary form. It should be noted that the appended list of references does not constitute a complete bibliography; it includes only those works quoted below. More extensive bibliographies are included in several of the references; see particularly references 7, 9, 28, 34, 38, 50, 52, 54, a "Bibliography on Powder Metallurgy" published by the Library of Congress and a pamphlet published by the Metals Disintegrating Co. entitled "The Field of Powder Metallurgy and Bibliography." 11. Summary of Experimental Observations The following classified list is composed of general statements of established fact derived from the experimental results reported in the published literature. A few contested observations are included, because of their potential importance; these are labeled as such. Any satisfactory and complete theory must be capable of explaining all of the uncontested facts. Obviously, some important facts may be missing from this list and these may hold the key to the correct explanation of the sintering process, but the possible lack of such material should not deter attempts to understand the subject on the basis of what is available here. A, The Initial Bond at Room Temperature a. To a limited extent uncompressed powders and massive metals adhere at room temperature. Clean tin powder forms a weak "cake" on standing at room temperature, the strength increasing with time. Clean gold surfaces adhere on light con-tact, as do those of many other substances, including nickel.27 b. Upon compression the strength of the bond- is increased progres-ivelv. There is a limit of pressure

Jan 1, 1946

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

Experience has indicated that hard bronzes are not suitable for bearing applications where high bearing loads and speeds are involved. It is the general practice to utilize softer materials for these purposes, such as copper, lead, silver, babbitt, lead-base alloys, and more recently aluminum-base alloys, preferably supported by a steel backing. It was the objective of the present investigation to study a new material produced by powder metallurgical methods susceptible to precipitation-hardening. Test MAteriaIs Preliminary tests were made with compacts containing copper, nickel and silicon in quantities sufficient to form 3 to 5 per cent nickel silicide. It mas found that this type of alloy was susceptible to the formation of a soft surface shell when sintered in tank hydrogen. The depth of the shell depended On the length of sintering time and sintering temperature, and varied in thickness from a few thousandths to as much as One eighth inch. This soft shell resulted from the preferential oxidation of silicon, thereby reducing the efficiency of age-hardening by the nickel silicide compound. The body of the sintered compacts below the soft shell could be precipitation-hardened to a hardness of 70 to 85 Rockwell B, by quenching from goo°C. and age-hardening at 450°C. A series of tests was made with various addition agents, in order to decrease the rate of preferential oxidation, and it was found that phosphorus was most beneficial in this respect. After considerable experimentation, the following nominal com-position was accepted as standard: 2.4 per cent nickel; 0.8 silicon; 0.3 phosphorus; balance copper. The physical propertties and certain bearing properties of this alloy are described in the present paper Preparation of Compacts Several methods of incorporating the hardening ingredient (nickel silicide) were studied. Compacts formed from copper, nickel and silicon powders were found to be inferior to those fabricated from prealloyed nickel silicide master alloys, because of the rapid oxidation of pure silicon during sintering. The use of a prealloyed nickel silicide hardener containing 25 per cent silicon and 75 per cent nickel could be further improved by preparing a master alloy, incorporating nickel, silicon, phosphorus and copper, having the following nominal composition~ 25 per cent nickel; 7 silicon; 3 phosphorus 64 copper. This alloy is brittle in the cast condition and can be readily powdered. Sintering Procedure The blended powders were pressed at '5 to 40 tons per sq' in., the pressure depending on the size and shape of the compacts. Sintering was carried out in hydrogen or cracked ammonia atmospheres at

Jan 1, 1946

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

Experience has indicated that hard bronzes are not suitable for bearing applications where high bearing loads and speeds are involved. It is the general practice to utilize softer materials for these purposes, such as copper, lead, silver, babbitt, lead-base alloys, and more recently aluminum-base alloys, preferably supported by a steel backing. It was the objective of the present investigation to study a new material produced by powder metallurgical methods susceptible to precipitation-hardening. Test MAteriaIs Preliminary tests were made with compacts containing copper, nickel and silicon in quantities sufficient to form 3 to 5 per cent nickel silicide. It mas found that this type of alloy was susceptible to the formation of a soft surface shell when sintered in tank hydrogen. The depth of the shell depended On the length of sintering time and sintering temperature, and varied in thickness from a few thousandths to as much as One eighth inch. This soft shell resulted from the preferential oxidation of silicon, thereby reducing the efficiency of age-hardening by the nickel silicide compound. The body of the sintered compacts below the soft shell could be precipitation-hardened to a hardness of 70 to 85 Rockwell B, by quenching from goo°C. and age-hardening at 450°C. A series of tests was made with various addition agents, in order to decrease the rate of preferential oxidation, and it was found that phosphorus was most beneficial in this respect. After considerable experimentation, the following nominal com-position was accepted as standard: 2.4 per cent nickel; 0.8 silicon; 0.3 phosphorus; balance copper. The physical propertties and certain bearing properties of this alloy are described in the present paper Preparation of Compacts Several methods of incorporating the hardening ingredient (nickel silicide) were studied. Compacts formed from copper, nickel and silicon powders were found to be inferior to those fabricated from prealloyed nickel silicide master alloys, because of the rapid oxidation of pure silicon during sintering. The use of a prealloyed nickel silicide hardener containing 25 per cent silicon and 75 per cent nickel could be further improved by preparing a master alloy, incorporating nickel, silicon, phosphorus and copper, having the following nominal composition~ 25 per cent nickel; 7 silicon; 3 phosphorus 64 copper. This alloy is brittle in the cast condition and can be readily powdered. Sintering Procedure The blended powders were pressed at '5 to 40 tons per sq' in., the pressure depending on the size and shape of the compacts. Sintering was carried out in hydrogen or cracked ammonia atmospheres at

Jan 1, 1946

By John Wulff, Richard P. Seelig

The importance of the pressing operation in the forming of articles by powder metallurgy depends to a great extent on the type of product to be made. While in some few cases the pressing is merely a means of compacting loose powder particles into a solid mass preliminary to a sintering treatment, in most applications it constitutes a molding operation with the purpose of shaping the raw material in powder form into a certain predetermined, accurately defined part not altered in shape by subsequent sintering. In still other cases, no pressing at all but sintering in molds gives useful articles. A limited number of products are made by the simultaneous application of pressure and heat. The factors that control the product of the pressing operation are raw material, lubricant, type, size and shape of die and compact, magnitude and time of application of pressure, as well as temperature of pressing. All such factors need to be controlled; yet, depending on the function of the pressing operation, greater emphasis may be placed on processing factors other than the pressing operation. In any complete discussion of pressing, subsequent sintering cannot be disregarded. For the sake of brevity, the present paper has been limited to the mechanics of pressing and only occasionally refers to sintering. For the same reason, hot-pressing has been omitted as beyond the scope of this paper In any survey of the literature on the pressing of metal powders, the 1938 paper of Balshinl on the theory of the process of pressing deserves mention. The first attempts at an interpretation of pressing phenomena were made by Balshin' and RakovskL2 The experimental results of both are of great interest. Since the experimental results are not described, the work was repeated, using our own interpretation of the possible techniques, and is reported in the following pages. The basic theory of Balshin,' based on a hydro-dynamic analogy, however, leads to hut another way of plotting density and pres- , sure against height of a pressed compact. Since it does not give any new insight into the phenomena, nor account for the influence of side-wall friction, a discussion of the theory has been omitted from this paper. Density Gradients in Compacts The process of pressing metal powders in a die (disregarding for this consideration the powder filling and ejection operations) may be divided into three phases: (I) packing, (2) elastic and plastic deformation, (3) cold-working with or without fragmentation. It must be emphasized that these three steps do not follow each other in sequence; on the contrary, in practice

Jan 1, 1946

By John Wulff, Richard P. Seelig

The importance of the pressing operation in the forming of articles by powder metallurgy depends to a great extent on the type of product to be made. While in some few cases the pressing is merely a means of compacting loose powder particles into a solid mass preliminary to a sintering treatment, in most applications it constitutes a molding operation with the purpose of shaping the raw material in powder form into a certain predetermined, accurately defined part not altered in shape by subsequent sintering. In still other cases, no pressing at all but sintering in molds gives useful articles. A limited number of products are made by the simultaneous application of pressure and heat. The factors that control the product of the pressing operation are raw material, lubricant, type, size and shape of die and compact, magnitude and time of application of pressure, as well as temperature of pressing. All such factors need to be controlled; yet, depending on the function of the pressing operation, greater emphasis may be placed on processing factors other than the pressing operation. In any complete discussion of pressing, subsequent sintering cannot be disregarded. For the sake of brevity, the present paper has been limited to the mechanics of pressing and only occasionally refers to sintering. For the same reason, hot-pressing has been omitted as beyond the scope of this paper In any survey of the literature on the pressing of metal powders, the 1938 paper of Balshinl on the theory of the process of pressing deserves mention. The first attempts at an interpretation of pressing phenomena were made by Balshin' and RakovskL2 The experimental results of both are of great interest. Since the experimental results are not described, the work was repeated, using our own interpretation of the possible techniques, and is reported in the following pages. The basic theory of Balshin,' based on a hydro-dynamic analogy, however, leads to hut another way of plotting density and pres- , sure against height of a pressed compact. Since it does not give any new insight into the phenomena, nor account for the influence of side-wall friction, a discussion of the theory has been omitted from this paper. Density Gradients in Compacts The process of pressing metal powders in a die (disregarding for this consideration the powder filling and ejection operations) may be divided into three phases: (I) packing, (2) elastic and plastic deformation, (3) cold-working with or without fragmentation. It must be emphasized that these three steps do not follow each other in sequence; on the contrary, in practice

Jan 1, 1946

A High-speed Dilatometer and the Transformational Behavior of Six Steels in Cooling. By Arthur L. Christenson, Edward C. Nelson and Clarence E. Jackson. (With discussion).................................606 Dilatometric Studies of the Graphitization of Cast Iron. By N. A. Ziegler. With discussion) 627 An Interferometer Type of Dilatometer and Some Typical Results. By- L. '4. WIlley and W. L. Fink. (With discussion).........................642 The meeting was held in the Pine Room of the Statler Hotel, Cleveland, Ohio, on Tuesday afternoon, October 17, 1944. The chairmen were F. M. Walters, Jr. and Howard Scott. Introduction F. M. Walters, Jr.—The principal advantages of the dilatometric method perhaps are two, as compared with the method of thermal analysis. One is that the dilatometric method can be applied with a large variety of rates of heating and cooling, whereas thermal analysis—that is, the study of the transformational characteristics by means of heat evolution—is limited to the rates of heating and cooling that reveal the evolution of heat. The dilatometer can be used for the study Of reactions at zero rates of heating and cooling; that is, isothermal reactions. As you will hear this afternoon, the rates have been pushed up as far as 500°C. a second. The other advantage is that the dilatometric method shows that a two-phase region is a two-phase region, whereas the thermal analysis merely reveals the temperature at which the rates of heat evolution are greatest.

Jan 1, 1945

By D. J. McAdam, R. W. Mebs

The technical cohesive strength of a metal means, not the interatomic forces, but the technically estimated resistance to fracture. An example of such resistance to fracture is the so-called "true" breaking stress of a tension-test specimen, the breaking load divided by the sectional area at fracture. According to the prevalent view,8 the technical cohesive strength of a metal. in any particular state as regards prior mecharlical treatment and heat-treatment, is determined by a limiting value of the algebraically greatest principal stress. In two previous papers by one of the authors, evidence was presented to indicate that the technical cohesive strength of a metal cannot be represented by a single stress value, but that it comprises an infinite number of values corresponding to the infinite number of possible combinations of the principal stresses. The technical cohesive strength thus comprises an infinite number of technical cohesion Limits, each representing a specific stress combination at fracture. In the same papers, evidence was presented that plastic extension causes a continuous increase in the technical cohesive strength. Such a variation is not in accordance with the prevalent view that plastic extension first increases, then decreases, the technical cohesive strength.' In this paper, as in the previous papers,14.15 the algebraically greatest principal stress will be designated S1, the least principal stress will be designated 33, and the intermediate principal stress will be designated S². The technical cohesion limit under polarsymmetric tension (S1 = S2 = S3) will be termed the "disruptive stress," and the cohesion limit under unidirectional tension (S2 and S3 = o) will be termed the "severing stress."l4, .l5 The yield strength of a metal, according to the generally accepted theory, may be represented by a constant value of the shearing-strain energy, and hence by a constant value of the sum of the squares of the three principal stress differences. In the second of the previous papers,15 however, evidence was presented that the limiting yield stress decreases with increase in the volume stress, the algebraic average Of the three principal stresses.* This in fluence of the volume stress becomes prominent only in the field of triaxial tension. In the two previous papers,".'5 diagrams were presented to show the variation of the technical cohesion limit, yield stress, and ultimate stress with the combination of principal stresses and with plastic extension. Those diagrams and the resultant • Any stress system ma? be resolved into a polarsymmetric stress causing pure volume strain and a combination of pure shearing stresses. which cause no change of volum

Jan 1, 1945

Page Fundamental Principles Involved in Segregation in Alloy Castings. By R. M. Brick. (With discussion)............................* Review of Factors Underlying Segregation in Steel Ingots. By B. M. LarseX.. (With discussion)............................. 4x4 Introduction to the Session on Segregation in Steel. By Earle C. Smith......436 Relation of Open-hearth Practice to Segregation in Rimmed Steel. By J. W. HaLley and G. L. Plimpton, Jr. (With discussion)................438 Segregation in a Large Alloy-steel Ingot. By S. W. Poole and J. .4. Rosa. (With discussion) .............................459

Jan 1, 1945

By Earle C. Smith

The Chairman.—Mr. Earle Smith has kindly offered to make some remarks in connection with segregation in the product, Mr. Smith: E. C. Smith,* Cleveland, Ohio—I will start this Off by a story oF the code days of the American Iron and Steel Institute. In those days, Republic did not have a big strip mill, and the question came up of the check analysis of rimmed steel. I suggested that they let me be the chairman of the Committee on Accumulating the Information on the Variation of the Composition of the Ingots of Rimmed Steel. Somebody wanted to know why I wanted to be the chairman. I said, "we don't make any of the big ingots of rimmed steel, and no matter who makes them they are so bad that you don't dare publish the information. So if 1 collect it and hide it you can't charge me with having done anything that really disrupted the commercial situation." So, everybody furnished me with a rather complete story as to the horrible variations in big rimmed ingots. I took it out to my house and put it away, and it is still there. Now, segregation in the big ingot is no longer an "academic " matter as far as I am concerned. I am in a situation like that of the German who was told in 1956 about the coming war. He said: "until it is your throat that is going to be cut, you don't pay any attention to what is happening to the otherman." 'That is the way with the problem that we have in front of us. Recently I have been told that the 'Omptroller was questioning the payment for certain articles of stamped steel that had been made from rimmed steel, because upon check analysis of the rimmed steel it had been determined that these stamped articles were nut within the compositions that were included in the specification, and therefore he as the camptroller had no alternative. It was not meeting the specification; therefore, no payment. So I I say to all of you: You can very seriously consider this matter of segregation now and on into the future on the basis of the fact that it is actually going to cost your companies, which are making these products, money unless there is some new idea about the infallibility of quantitative , chemists who analyze some of these products or lawyers who read specifications, I don't know which man is going to be the major factor in the future. if the National Bureau of Standards could in some way show the specification writers the variation between good chemists analyzing for That they expect to be umpire eel. the writers would certainly realize that some of the to to which we have calmly signed our names as being O.K. are— well, as one man said to me, they might be filled by the devil, and they certainly could be filled by the Lord, but they could not he me by mankind. I would like to inject two or three things into a segregation study which I Want you to think about, because 1 would be a little surprised if there is very much discussion of them, In the first place, we generslly make steel in the United States in the basic open hearth, and I do not think there has bee,, nearly enough consideration given to segregation German the bath before it moves into the ladle. I am sure that any of the people who handled the 9400 series of the NE series when it contained the 0,60 per cent silicon have more respect than they had previously for the segregation that is within, the ladle; that is, before the metal reaches the ingot mold, the frozen ingots and the segregation in them. Another pint to which I think We ought to sis serious consideration is the segregation of iron oxide in the ingot-iron type of material, where the distinction between that and the steel segregation is that it is actually segregat. ing iron oxide, Normally we are segregating some form of carbon or sulphur, or something like that, with the stamping steel industry now coming down into the ranges of chemistry, where the segregation of iron oxide will be just

Jan 1, 1945

By J. W. Halley, G. L. Plimpton

Because of the two distinct stages in the solidification of rimmed steel, segregation in the rimmed ingot is more complex than that in the killed or semikilled ingot. In the earlier stage, chemical reactions, resulting in evolution of gas and vigorous stirring of the metal, effect a degree of negative segregation unique to rimmed steel. The composition of this zone constitutes the principal quality advantage of this type of steel. In the later stage of solidification, after the evolution of gas has ceased, the segregation follows the general pattern of a more completely deoxidized steel. However, the composition of the liquid remaining after the first solidification stage varies markedly from that of the original melt, some constituents having been partially removed as reaction products while the concentration of others has been intensified by rejection from the metal solidifying in the first zone. The aim, from the standpoint of segregation, in rimmed steel of high quality is to effect a maximum negative segregation in the rim zone without excessive concentration of undesirable elements at the center of the ingot. To achieve this aim, the composition of the melt may be varied and the furnace and pouring practice may be adjusted within certain limits. It is the purpose of this study to discuss segregation in rimmed steel from the standpoint of the mechanisms that produce it and to survey the phases of open-hearth practice that influence those mechanisms. Mechanisms Producing Segregation The mechanisms that determine the degree of segregation in the rimmed ingot are closely interrelated, making it difficult to select the primary factors and to determine a satisfactory order for presenting them. For instance, the question of sulphur segregation is relatively simple, since sulphur is not directly involved in chemical reactions in the ingot; but its concentration in the rim zone is dependent not only on its original analysis in the melt, its segregation coefficient, and the freezing rate, but also on the rate of its removal from the impure film on the solidifying surface. This washing action involves all the factors (such as freezing rate, the carbon-oxygen product, pressure, etc.) that determine the rate of gas evolution and hence the efficiency of film removal. Sulphur distribution between the rim and core is affected by the volumetric ratio between the two zones, and its segregation in the core is a function not only of the freezing rate of the core but also of all the foregoing factors that determine its concentration in the metal when solidification of the core starts. To simplify the presentation, it is proposed to treat the mechanisms affecting segregation independently in this section, reserving a discussion of their over-all effects for the section in which actual segregation data are given. The factors affecting segregation will be treated in the following order: (I) differential solidification, (2) removal of constituents as

Jan 1, 1945

By B. M. Larsen

Attempting to review the fundamental aspects of segregation in steel ingots of all types in a paper of reasonable length, we encounter two difficulties: (I) the fact that a large number of different physical and chemical effects are involved, and (2) rather incomplete and confusing evidence on certain aspects of detail and mechanism in the freezing process in which the segregation effect is involved. The best solution seemed to be to link together most of the underlying factors into a simplified theoretical picture that appears to the writer to explain most of the observed data, in the hope that this will serve as a reasonably good target for discussion and criticism. Segregation effects, especially in steel ingots or castings, are often divided into " microscopic" and "macroscopic," depending on whether the variations in concentration of solutes or dissolved elements in the iron occur as: (I) a periodic variation over the small distances between the nuclei and the surfaces of the primary grains, or (2) as a larger scale effect involving concentration gradients over distances of the order of several inches, more or less. The reason for this somewhat artificial division is, of course, that it is only the macroscopic scale effect that has much practical importance. About the only effect of practical importance that results from microscopic segregation is the banded structure often left in rolled sections, and even this is relatively harmless in most cases. However, the causes of microscopic segregation also untlerly the larger scale effect, so we must first consider matters such as the formation and growth of crystal nuclei, selective freezing and diffusion, and others that are fundamental to all sepregation effects. Undercooling and Nuclei Formation It is probable that although the degree of undercooling is small in iron, as in metals in general, a certain amount of it takes place, and also that the number of crystal nuclei increases very rapidly with increased undercooling below the liquidus temperature. In practical terms this means that the nuclei number illcreases very rapidly with increased cooling or freezing rate, thus being dependent on the rate of heat flow out from the zone of crystallization. Temperature Gradients and Heat Dissipation during Freezing Each pound of steel evolves about 100 B.t.u. when freezing. In addition to this, the temperature gradient in the solidified portion (required to dissipate the heat as freezing progresses into the axis) necessitates a loss of heat required to cool the solid metal below its freezing range, which is equivalent to an amount of not so much less in magnitude. In a 5-ton ingot, the total would include about one million B.t.u. for freezing alone and about 0.4 to 0.5 million B.t.u. for the gradient, up to the end of the freezing period. Thus the rate of freezing depends primarily on the rate of heat dissipation. In the ordinary ingot shapes, the axial rate of growth of the solid

Jan 1, 1945

By S. W. Poole, J. A. Rosa

The object of this investigation was to determine the distribution of chemical elements within a large, killed alloy-steel ingot, by sulphur printing and quantitative chemical analysis. With regard to segregation in steel ingots, the factors of melting practice, pouring temperatures, mold design, etc., and the mechanics of solidification and its attendant functions, have been the subject of intensive study over a period of years by many investigators. Notable among these is the Sub-committee of the No. 5 Committee of the British Iron and Steel Institute. For an exposition of the many problems awaiting the researcher on the heterogeneity of steel ingots, the methods of attacking these problems, together with some of the answers, the reader is referred to the nine reports and numerous papers of that committee and its membership. Steelmaking Data Melt.—The heat was made in a 70-ton direct arc-type basic electric furnace. Furnace charge consisted of nickel-chromium-molybdenum steel, most of it in the form of heavy mill scrap. All of the scrap was charged cold. The standard double-slag method was employed, the heat being finished under a strong carbide slag. Aluminum was used as the deoxidizing agent. Tapping tempera- ture, as observed with an optical pyrometer, was 3000°F. Detail of Mold and Ingot Size.—Details of the ingot mold and the ingot itself are given in Fig. I. Teeming.—Teeming temperature of the subject ingot as observed with an optical pyrometer was 2830°F. The ingot was top-poured directly through a 1 1/2-in. nozzle and required 7 min., 44 sec. to fill up to the hot top. An additional 2 min., 30 sec. were required to fill the hot top. The ingot was stripped hot and charged with the remainder of the heat into an annealing furnace. There it was given the standard annealing cycle used for these ingots. Subsequent heat-treatments are described elsewhere in this paper. Sectioning and Preparation for Sulphur Printing Because of previous favorable experience in sectioning ingots up to 21 1/2 in. square with an oxyacetylene torch, it was decided to use this method to section the subject ingot. The ingot was preheated to 900°F. for 12 hr. It was then placed on a steel bed in a horizontal position so that the longitudinal axis was level and parallel to the track of the motor-driven torch carrier. Two cuts were made, one 2 in. above the longitudinal axis and the other 2 in. below. The time required to make each cut was approximately 75 min. The cutting operation is shown in Figs. 2 and 3. The 4-in. thick slab was mmediately charged into a furnace standing at 1200F.

Jan 1, 1945

By W. D. Brown

Newell1 has shown that hydrogen is removed from steel in a vacuum at a temperature of 500° to 900° C. within 136 hr. Holm and Thompson2 also state that, especially when the hydrogen is high, the results obtained by extraction at 800°C. agree with those obtained by vacuum fusion. In this laboratory, an apparatus was designed (Oct. 1940) and used wherein the piece of steel was heated at 100°F. in a Torricellian vacuum (Fig. I). This vacuum was produced by raising and lowering a "leveling bottle or bulb" containing mercury. Extensive tests were made with this apparatus. The weakness of the procedure was the possibility of leakage of air into the tube around the rubber stopper at the bottom. The present plan is to raise and lower the mercury by applying vacuum from a mechanical pump, to the top of the tube and then to a bottle of mercury in which the bottom of the tube is immersed. The Apparatus The extraction is made in a Pyrex tube A, I in. i.d. It is drawn down at the top at N and an 8-mm. i.d. tube is welded on it. To this a Pyrex stopcock E, 4-mm. bore, is welded. The tube between N and E is preferably 8 in. long and is graduated in milliliters. The total length of A to the stopcock is 28 inches. Heat is supplied by a split-tube furnace. 0 in. long by 6 in. in diameter, hinged on the side. A short pyrometer couple P is inserted through the walls of the furnace. In use this is standardized by comparison with a standard couple in a I-in. tube, just opposite this short couple. In the I-in. tube A a glass rod R, flattened at one end, supports the sample S and the length of R is so adjusted that the sample is in proper place. (It may float in the mercury.) The tube A is inserted in a large rubber stopper to fit the bottle B and extends nearly to the bottom. It is so placed that the handle of the stopcock faces the operator. In this stopper also is a short tube D bent at right angles for the application of vacuum. Also in this stopper is an 8-mm. tube C reaching nearly to the bottom; this is bent so as to miss the heater and again bent to bring it in line with and as near as possible to the upper and reduced part of tube A. On this tube C is welded a 4-mm.-bore stopcock H. In order that the two tubes may be as near as possible, the handle of stopcock H faces the back, or is the reverse of stopcock E. The total height of II above the bottom is 28 in. As explained later, this is the pressure-measuring tube C. The bottle B is about half full of mercury. The mercury must cover the ends of A and C by about I in. when they are evacuated. By tees T and rubber tubing RT the tubes A, C and D, the latter through the three-way stopcock M, are connected to the vacuum pump. A sheet of asbestos at K prevents the stopcocks E and H from becoming so hot that they leak. A good grade of vacuum lubricant prevents leakage of E and H. In order to measure the pressure of the

Jan 1, 1945

By John Naughton

At the General Electric ResearchLabora-tories, we have been interested in the iron-manganese system and the effect of hydrogen on the properties of these alloys. Dr. H. H. Uhlig previously has presented some of these results.' We wish now to offer some other of the data that have a bearing on the subject of this symposium. In the determination of hydrogen in the iron-manganese system by any heating Method we are presented with the problem of the evaporation of volatile manganese and the consequent adsorption of hydrogen by this evaporated metal. It seems wise. therefore, to extract gas at as low a temperature as feasible. Consequently we chose the vacuum or hot extraction method for the analyses of these alloys. The apparatus used is shown in Fig. I. The design is a modification of the apparatus described by Holm and Thompson. To limit loss of hydrogen, samples are stored in a chamber immersed in liquid air. We recommend this procedure whenever there is a question of loss of hydrogen at room temperature. Thence they are moved to the quartz furnace by means of a small magnet, where they are heated by induction to 700' to 800°C. The extracted gas is removed by the circulating pump and placed in the known volume VI (or V2). The circulating pump has been described.3 It is so designed that in spite of the fact that the outlet portion of the pump is part of the known volume, this volume is affected neither by the speed of pumping nor by the pressure of stored gas. The pump also serves to circulate the gases for analysis. The analytical system consists of a

Jan 1, 1945

By J. G. Thompson

Determinations of the hydrogen content of irons and steels invariably are subject to two serious difficulties: (I) the determination of amounts of 0.001 per cent or less of any constituent requires an analytical procedure of unusual precision and accuracy, and (2) the hydrogen content of many samples is dccidedly not stable; i.e., there is no assurance that the content at the time the analysis is made is the same as it was when the sample was taken or at some previous time in the history of the piece. In respect to both the precision and speed of the determination, the vacuum-extraction procedure for the determination of hydrogen possesses advantages over the vacuum-fusion procedure, which has been the recognized standard for the detcrmination of other gaseous elements in sted-— oxygen and nitrogen for example. The basic facts upon which the vacuum-extraction procedure is based—i.e., the evolution of gas from solid steel when it is heated in vacuum, and the fact that the evolved gas is rich in hydrogen—were observed by Graham1 many years ago. Subsequent investigations have shown that hydrogen exists in steel chiefly as interstitial solid solution (i.e., in atomic dispersion) and perhaps to some extent as hydridcs that are unstable and decompose to form atomic hydrogen. In either case practically all of the hydrogen in steel at elevated temperatures exists in the atomic condition and consequently is able to diffuse readily through the metal. In contrast to this, other gaseous elements, such as oxygen and nitrogen, normally are present in steel chiefly in the form of relatively stable compounds such as oxides or silicates and nitrates; i.e., the oxygen and nitrogen atoms are fixed in stable combinations and are not free to migrate. The only oxygen or nitrogen that can diffuse in steel is the small amount in solution (atomically dispersed) and the rate of diffusion of these atoms is much less than that of hydrogen because of their greater atomic volume and lower mobility. Consequently, it is possible to extract most or all of the hydrogen from solid steel in a reasonable time at moderately elevated temperatures, but the procedure is not applicable to the determination of oxygen or nitrogen. It is only within the last decade that these observations have been developed into an analytical procedure for the determination of hydrogen. Apparatus and Procedure The apparatus used at the National Bureau of Standards,6 for the determination of hydrogen by the vacuum-extraction procedure, is shown schematically in Fig. I. The specimen, freshly cleaned and dried,* is suspended on a fine wire within the quartz furnace tube that is connected to the reservoir system and analytical train.

Jan 1, 1945

By J. G. Mravec

The SO-called gas-tube method as developed by Hare, Peterson and Soler for determining the type and content of gases in molten steel is particularly adapted for determining the hydrogen content in molten steel. The development of this method has been quite completely discussed in a paper published by these co-workers in 1937.' The purpose of this paper, therefore, is to familiarize with this method those who arc not well acquainted with it. The principle of the gas-tube method is as fol1ows: One end of an evacuated gas tube is sealed with a very thin copper disk. when this end of the tube is immersed in a test spoonful of molten steel, the copper disk melts almost immediately, allowing a portion of the steel to be drawn up into the evacuated space. Any dissolved gases, and those produced by reactions between the components of the steel during freezing, are liberated into the unfilled portion of the sampling tube. A blob of steel that forms on the immersed end of the tube after the sample is drawn up seals up the end, making it airtight again. The evolved gases are subsequently drawn out of the gas tube through a suitable valve and analyzed by means of an Orsat apparatus. The volume of the sampling tube is sufficiently large so that a pressure considerably below atmospheric is produced after the gas evolution. The low pressure is necessary to effect a nearly complete removal of gases from the steel. Construction oF Sampling Tube The sampling gas-tube apparatus is illustrated in Fig. I. Seamless S.A.E. tubing used for section A is first cut into 7-ft. lengths. Through cxperiencc it was found necessary to use two sizes of tubing for this part, "is-in. and 3/4-in., respectively. The smaller tubing is generally used on the hotter or lower carbon steels. If the inside wall of the tube A is coated with grease or oil, it should be burned out before being machined as follows: One end is machined on the inside diameter to a depth of 34 in., so as to form a seat for a 7/8-in copper disk, which is stamped out from 0.005 to 0.007-in. thick copper sheet. The other end is machined on the outside diameter to a diameter of 1 5/16 in., to take a small reservoir or trap member I?. About 4 in. below the same end, a 1/2-in. hole is drilled to receive the 1/2-in. copper tubing leading to the large reservoir C. The inside of tube A is then thoroughly cleaned with a round wire brush, such as is generally used to clean out shotgun barrels. It is very important that the surface be absolutely free of rust or any nonmetallic coating. Next, the thin copper disk is soldered in place with low-melting silver solder.

Jan 1, 1945

By R. M. Scafe

Although hydrogen has been intensively studied in its relation to steel quality, the methods of sampling and determinations are still open to question. It is true that various procedures have been proposed but actually there has not been sufficient agreement to establish a common base from which to work. As a result, it is difficult, to say the least, to correlate the reported results of some of the investigators in this field. The present symposium, premised on methods rather than effects, should prove of considerable value. For the purpose of this discussion two methods of sampling and analysis will be considered. First, sampling of molten steel in the ingot mold by use of an evacuated tube and cylinder using conventional methods of analysis for the gases collected; second, analysis by vacuum extraction involving the use of heating equipment and the determination of the amount of hydrogen evolved from solid steel samples by measurement at reduced pressures. Both methods have been used at Duquesne Steel Works and it is believed that either may be used with considerable benefit if the limitations of each method are recognized. Evacuated Tube and Cylinder Sampling devices for gases in molten steel suggested by various investigators range from very cumbersome and complicated devices to the relatively simple evacuated tube and cylinder used by Soler for deter- mining the CO content of the bath. This latter device was adopted (Fig. I) and modified to meet conditions at Duquesne Works. The principal modifications were in placing the cylinder at the side of the tube and the use of a sleeve on the immersion end of the tube. The first modification was made so that the cylinder could be readily detached and taken to the laboratory; the second, because of the difficulty encountered in obtaining an airtight seal after sampling and because of our practice of re-using the tube. Rigid control of the method of sampling and of the handling of the sample according to plan are of primary importance in hydrogen determinations. This applies to both the sampling of molten steel and the determination of the hydrogen content of cold steel samples. Except for a few preliminary samples taken from spoons, all work on molten steels using the evacuated tube was confined to the sampling and analysis of molten steel during the pour. As mentioned, uniformity of sampling was a basic consideration. As a result, every effort was made to follow definite sampling techniques and procedures. These included control of the depth below the surface from which the sample was taken, the timing between the shutoff and taking of the sample, as well as maintenance and care of the equipment. The distance below the surface at which the sample was taken was readily controlled bv means of a crosspiece and centering device attached to the tube. The steel was poured into the mold to the hot-top junction, the tube was then lowered into the 75

Jan 1, 1945

By C. B. Post, D. G. Schoffstall

A determinatioil of the hydrogen content of molten steel by means of the Vacuum-extraction method, as reported here, consists in first casting a sample of the bath in a bomb, so that the gases evolved during solidification are trapped for analysis. A portion of the cast steel sample is then prepared and heated at a temperature of 600" to 800°C. under high vacuum, and the gaser given off during this vacuum extraction (which are shown to be hydrogen), are collected and measured. Analysis of the gases evolved on solidification and the gases in the solid sample enables an accurate determination of hydrogen in the molten steel. Fig. I shows the bomb and accessories that have been found suitable for trapping the gases evolved on solidification. The bomb is made of scamless steel pipe, approximately 7 in. long by 136 in. i.d., and welded at the bottom. An ordinary pipe cap has a vacuuni-type metal stopcock threaded and brazed in its upper end. This pipe cap fits onto the bomb by means of machined threads. A flange is brazed to the pipe at the point where the cap starts to tighten up, and a rubber gasket is placed between the flange and cap. Heavy vacuum grease is used between the flange and gasket and the gasket and cap. The weight of the complete bomb and it? interval volume is known before the sample is cast. In practice, a sample of about 400 grams of steel is poured into the bomb, the funnel quickly swung out of the way, the bomb cap spun down the threads and tightened against the gasket, and the bomb set in a pail of water to keep the gasket and vacuum grease cool. It is estimated that at least 80 per cent 01 the gases evolved from the liquid sample during solidification are trapped in the bomb."

Jan 1, 1945