METALLURGY-A CHALLENGE AND AN OPPORTUNITY HERBERT H. UHLIG Massachusetts Institute of Technology Cambridge, Massachusetts
IN1819, a brilliant young man destined to become one of the most famous scientists of all time began a painstaking investigation of iron alloys. He sought, as he stated it, ". . .to ascertain whether any alloy could be artificially formed better, for the purpose of making instmments, than steel in its purest state; and second, whether any such alloy would, under similar circumstances, prove less susceptible of oxidation. New metallic combinations for reflecting mirrors were also a collateral object of research".' With cmde furnaces, operated by hand bellows, alloys of iron containing platinum, rhodium, silver, nickel, chromium, and other metals were melted and cast. Some steels seemed notably bright and hard, and were well suited to experimental straight-edge razors. They compared favorably with razors of the famous Wootz steel that came f ~ the magical furnaces of India. They even showed some of the desired damascened surface on etching with acid, typical of the Wootz steel. The corrosion resistance of the alloys, however, was disappointing since they behaved much like iron unless highly alloyed with an expensive element such as platinum. It had been claimed that meteorites of natural iron-nickel alloy composition had phenomenal resistance to msting, but this was undoubtedly exaggerated, since the artificially prepared alloys containing as much as 10 per cent nickel proved not unusual in this respect. Michael Faraday was not the @st scientist to turn his attention to metallurgy, but he was certainly one of the most famous. Working with James Stodart, he gave undivided attention for a period of five years to the metallurgical research described above. Equipment for melting was primitive, and pure metals for alloying scarce. Hence, platinum and platinum-group metals were used, since they were available as pure metals. Had more chromium been available and of better purity, the stainless steels (iron-base alloys containing a t least 12 per cent chromium) would probably have been discovered by Faraday rather than by Harry Brearley about 100 years later, and the corrosion resistance so much desired thereby accomplished. As it was, the low-chromium alloys showed no superior propertie; that seemed to justify the extra trouble of alloying. This investi~ationof Faradav had onlv limited influence on metallurgical practice of his times; nevertheless, the foundation was laid for many recognized objectives of
-
,
M~~~~~~~~~~~ on the Alloys of Steel with a View to Its Improvernents," Qmrterlg Journal of Sn'acea, IX,319 (1820).
alloy research, the success of which has been especially evident within the last 30 years. Metallurgical research today with x-ray diiraction equipment, the electron microscope, and vacuum furnace is a far cry from research in Michael Faraday's time. The type of research Faraday began under great di5culty has now gained tremendous momentum in supplying the specialized needs for metals in anything from a small vacuum tube or miniature magnet to the critical blades of a steam turbine. The more extensive research on alloys is only recent, and the science of metals is correspondingly new, having started actually after the 20th century began. Hence, many important discoveries in this field were made very recently, and many new developments are still to come. m It is logical that systematic study of metals should in large measure have begun in chemical laboratories, since the problems often concern chemical properties and hence have natural appeal to the chemist. The metals, after all, make up more than three-quarters of the elements in the Periodic Table. Of the several chemical laboratpries in this.country, England, and Germany serving to launch the science of metals in the early 19001s,Gustav Tammann's laboratory of physical chemistry in Gottingen was one of the first and in many respects was typical. Tarnmann assembled a large amount of data on phase diagrams, microstrncture of metals, oxidation, aqueous corrosion, galvanic potentials, and what was subsequently known as orderdisorder in alloys. Many well-known American chemists and metallurgists completed their graduate studies in his laboratory working on a subject that later came to be known as physical metallurgy. Much of the work then started is continuing today in greater detail and with considerable refinement by metallurgists in university and industrial laboratories. Physical metallurgy now, in the tradition of those who early founded the science, has continued to be essentially the physical chemistry of metals, and in recent years has also included much of the information classified under physics of the solid state. PHYSICAL METALLURGY AND PROCESS METALLURGY
The problems of the metallurgist, therefore, cut broadly across the boundaries of physics and chemistry. Since metallurgy also includes extraction of metals from ores, and their refinement or alloying to produce de-
668
DECEMBER. 1948
sired properties, the subject, in addition, overlaps the techniques and approaches of the chemical engineer. It is convenient, accord'mgly, with a spectrum of activity so broad, that metallurgy should be divided into process metallurgy and physical metallurgy. The process metallurgist is concerned with producing or refinmg metals, beginning with ore a t the mines or open pits, and finishing with the reduction furnaces and electrolytic tanks that provide metals for subsequent fabrication. The metals are then rolled, cast, extruded, or shaped in other ways to suit the final application. The latter activity, namely fabrication or shaping of metals, is now a separate branch called mechanical metallurgy. As the name indicates, this subdivision overlaps the activities of the mechanical engineer. Le Chatel..r was probably one of the first modern process metallurgists. He applied thermodynamics to the operation of the blast furnace, and reported the equilibria between carbon, ferric oxide, carbon monoxide, and molten iron, pointing out that one could expect the reduction of iron oxide to proceed only to the equilibrium concentration of carbon monoxide beyond which the reaction would not go. Today, thermodynamics is applied in much greater detail, not only to the blast furnace, but to the control of metal production generally. With the open-hearth furnace, for example, a detailed chemistry of equilibria and reaction rates between metal, slag, and gas has been worked out and applied. As a result, steel today is produced a t less cost and of much better quality than that produced earlier in the century without benefit of scientific control. Chemistry of the open-hearth in an inferno of 1600°C. is both unusual and interesting, considering the fact that elements like zinc and magnesium are treated as gases rather than solids, and nitrogen becomes a chemically active element combining spontaneously with chromium, aluminum, titanium, and other elements that may be present in the molten metal. Most metal ores today are not of.adequate quality for reduction directly in the furnace. More often, they require concentration or "beneficiation." ru beneficiating ores, the metallurgist often applies surface chemistry or colloid chemistry to the over-all problem. He adds to water suspensions of ores, for example, surface active compounds that wet some constituentsmore than others, so that the concentrate "floats" away from the residue and can then be separated by skimming off or by other means. Thus concentrated, the ore is usually in satisfactory condition for the reducing furnace. The "flotation" process has become an important development the world over, and is especially critical to this country today. Most of our high-grade ores are used up, and the ores remaining require considerable beneficiation before they can be economically reduced to metals. The physical metallurgist, as indicated previously, usually deals with metals after the process metallurgist has finished with them. He busies himself largely in the laboratory examining small sections of metals for determination of their properties. By automatically
669
indenting a small diamond point or steel ball, he determines the hardness of the metal. If the metal is a carbon steel, he thereby automatically learns somethmg of its tensile strength and ductility, its proper heat treatment, and the maximum stress (endurance limit) that can safely be applied when the steel is subject to vibration. By examining an etched piece under the microscope, he gains further knowledge of metal properties, or corroboration of properties estimated from other sources. He gains information of past thermal history, the number and kinds of phases present, the types and quantities of inclusions, and the crystal or grain size as well as crystal orientation. Should a steel. have been surface hardened by reaction with methane or carbon monoxide a t elevated temperatures (carburized) or by reaction with ammonia (nitrided), he can use the microscope to measure the thickness of the hardened surface or case (hence, case hardening). He may also be concerned with determining magnetic data if the steel is one to be used in transformer cores. If dealing with stainless steels, he may run corrosion tests in concentrated nitric acid to learn if previous heat treatment was proper for optimum corrosion resistance. If a brass, he may immerse a sample in mercurous nitrate to determine if the alloy is susceptible to cracking. Should it crack, the brass will be further annealed to avoid possible failure in case it comes in contact with a dilute ammonia atmosphere in service. If aluminum or magnesium, he may immerse the metal for a few minutes in sodium chloride solution and, alternately, a few minutes in air, continuing the cycle until appreciable weight loss occurs by corrosion. From this, he learns something of corrosion resistance, and, if the metal is stressed, its susceptibility to cracking. There are many other tests of a similar nature. If the physical metallurgist is engaged in research, he may study the nature of or the rate of precipitation of chemical compounds, not in water or organic solvents, but in the solid metal itself. This precipitation withm the solid is important because the precipitates drastically affectstrength, hardness, andductility of themetal. They penetrate the lattice planes on which slip occurs when a metal is deformed and "key" them, so that further slip is difficult and the metal is thereby stronger and harder. Research of this kmd is also used in preparing better permanent magnets, since precipitates in metals also account for magnetic qualities found, for example, in Alnico alloys. The problem may be one of diffusion of nonmetals, or metals in other metals, using refined chemical analysis or radioactive isotopes to identify the substance doing the diffusing. This iuformation is significant to many metallurgical operations including heat treatment of alloys for improved strength or better corrosion resistance, surface-hardening operations, and sinteriug of powder compacts whereby metals are shaped by pressing the powders, and the particles then bonded a t high temperatures. Still further, the physical metallurgist may be engaged in preparing new alloys for corrosion or oxidation resistance. He applies to such studies modern fundamental knowledge of
670
chemistry and physics; for example, he may consider electron interaction between components of an alloy, or between the alloy and its environment, and the nature of electrolytic cells taking part in high-temperature oxidation where the electrolyte is a solid, the cathode is an oxygen electrode a t the oxide-oxygen interface, and the anode is the interface between metal and oxide. These problems are physical chemistry of the highest order. Other problems include phase transformation studies and the relation between grain orientation and magnetic properties, the latter having considerable commercial value in the production of high-efficiency -motors and transformers. JOBS AVAILABLE
Positions in metallurgy, both in industry and in teachmg, have taken a sharp turn upward during and since the war-in greater proportion than many other fields of science and engineering. The reason is obvious in that industry and government have suddenly increased their requests for men with metallurgical training, far in excess of the number of men who are being trained. The educational program in metallurgy, therefore, has not yet begun to catch up with the demands for graduates who are able to assume and direct the investigation of metal problems facing industry. One of the main reasons why supply of men lags so much behind demand is that few students choosing their- life profession realize the opportunities that metallurgy provides. The subject is not one taught as such in the high schools, and only relatively few colleges offer undergraduate or graduate courses leading to a degree in metallurgy. The entering student, for that reason, may have fair knowledge of what chemistry, nucleonics, and electrical engineering mean, but he is usually not quite sure whether metallurgy trains one to operate a blast furnace or predict the weather. As a result, many men who major in physical chemistry or chemical engineering, later learning what the subject of metallurgy comprises, enter the field because they find the opportunities attractive and the subject one t h a t naturally appeals to their interests. This is essentially what happened to the writer. GRADUATE STUDIES
In the same sense, the field of metallurgy is attractive to chemists or chemical engineers going on to their graduate degrees. Training in chemistry provides an excellent background for courses in metallography (studies of metal microstructure), process metallurgy, physics of metals, thermodynamics of metal systems, etc., and leads directly to often familiar techniques in advanced phases of metallurgical research. Research assistantships in several graduate schools are available
JOURNAL OF CHEMICAL EDUCATION
to men who have good records in chemistry, with the added advantage that departments of metallurgy are apt to be less crowded than departments in fields receiving popular acclaim of the press during the war years. The B.S. graduate in chemistry can readily make up the required preparatory courses in metallurgy, and, by continuing his research during summers, receive the Master's degree, frequently not longer than one year from the time he registers, or in three years if he goes on to his doctorate. INDUSTRIES EMPLOYING METALLURGISTS
The industries employing metallurgists are far more varied than one might first suppose. Fundamental work of a scientific nature is carried on by metallurgists in laboratories of the Bell Telephone Company, the General Electric Company, and the Westinghouse Electric Corporation. The National Bureau of Standards and the Naval Research Laboratory are examples of government laboratories employing metallurgists for fundamental research. The Bureau of Mines likewise has extensive programs in process metallurgy. Practically all of the oil companies now employ metallurgists, and are expanding their activities along these lines. The Union Carbide and Carbon Company and the du Pont Company pursue both fundamental and practical investigations in the field of metals, employing many metallurgists for research or production. The Dow Chemical Company employs metallurgists for research or production in connection with their Magnesium Division. All these companies provide jobs in addition to opportunities offered by the many metalproducing and fabricating industries, represented, for example, by thesteel, aluminum, and brass companies, and by the automobile and aircraft industries. The varieties of jobs and their locations, in other ~vords,are by no means restricted. The chemist and chemical engineer, therefore, find that circumstances surrounding prdessional activity in metallurgy are not much different from those in chemistry. The opportunities in industry and in universities are similar. The training periods are the same, and courses of instruction are allied. The apparatus used for metallurgical research such as x-ray diffraction equipment, the potentiometer, high-frequency furnaces, and vacuum systems may be itlready familiar to the chemist. By the same token, the chemical engineer finds himself a t home with roasting and reducing furnaces, kilns, converters, filters, crushing and grindmg apparatus, electrolytic refining equipment, and Dorr thickeners. The types of problems coming from metallurgy are new, varied, and some different and dificult, but all add together as offering to the chemist both a challenge and an opportunity.
