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the drivers behind the steel

For millennia the quest for better metals to make better lives has driven the development of cultures. Here are highlights of how steel technology has responded to socioeconomic needs from the time of Andrew Carnegie to the present.

In 1848, in the midst of the Age of Manifest Destiny, a Scottish weaver named William Carnegie and his family immigrated to Pittsburgh from a village in Scotland where a disruptive technology called steam power had decimated the cottage weaving industry. It is ironic that steam power, the cause of William Carnegie’s occupational misfortune, would become the key to his son, Andrew’s, fortunes. Andrew Carnegie’s uncanny knack for recognizing socio-economic needs and matching them with emerging technologies would become a way of doing business for the companies he founded and their successor, United States Steel, for more than a century.

Early methods of iron production

In ancient times, the discovery that charcoal mixed with iron ore and burned in a pit with an air draft would yield a “puddle” of “sponge iron” opened the door to the Iron Age. Although nobody claims to know when iron first came into regular use, written evidence of the deliberate reduction of iron ore to produce metallic iron goes back two thousand years.

Early methods of iron production were not significantly different than those used today. In principle, heat from burning solid carbon liberates oxygen in iron oxides and promotes its association with gas phase carbon to form carbon dioxide and metallic iron. A flux, such as burned limestone, is used to catalyze the process.  Until recently, the metal component was naturally occurring iron-bearing ore; today the same ore is ground and separated magnetically, mixed with a flux binder and formed into pellets.  Until the nineteenth century, carbon was supplied in the form of charcoal — wood with the volatiles baked out. Since then carbon has been supplied in the form of coke — coal with the volatiles baked out.

Through the centuries iron technology improved gradually through empirical practice as open puddles gave way to closed pits, closed pits morphed into open hearths, hearths became shafts, shafts became stacks, stacks were optimized for induction and pressure control; while blow pipes became wind tunnels, wind tunnels became air bellows, air bellows became steam driven blowing engines, steam driven blowing engines became stove-preheated air delivered by large volume steam-driven turbo blowers; while sponge iron evolved into bloom iron, bloom iron to cast iron, cast iron to wrought iron, which evolved in turn into liquid iron pouring from the tapped base of today’s giant blast furnaces.

At the time of the Carnegie family’s arrival in the United States, cast iron and wrought iron were the ferrous metals of the day. Iron furnaces yielded iron castings and pig iron for remelting and refining into wrought iron. Wrought iron was made by recasting pig iron into bars and annealing them in contact with charcoal for weeks. Steel was produced in small quantities by remelting and recasting broken wrought iron bars and hand beating carbon into them over a charcoal fire. Arduous production methods and limited output resulted in high prices for all ferrous metal products. Then, in 1856, the renowned English industrialist/inventor, Henry Bessmer, proved his method for making cheap steel by decarburizing molten pig iron in a semi-rotating crucible by forcing air into the melt.

In 1864, after having risen meteorically as an employee of the in the Pennsylvania Railroad, Andrew Carnegie quit the railroad to devote himself wholeheartedly to the iron industry. Earlier, in 1862, he and other mangers from the railroad had formed the Keystone Bridge Company. Through acquisitions, mergers  and buyouts the company prospered from contracts with the railroads to replace wooden bridges with iron ones. As a result of his experience with railroad bridges Carnegie saw that long lasting steel rails would eventually and inevitably supplant the wear-prone cast iron and ironclad wooden rails in  use at that time. In 1873, he met Henry Bessemer and became convinced that his cost-efficient process for producing large quantities of liquid phase steel was the answer to the rail wear problem.

Although the Bessemer process efficiently removed silicon and carbon from the steel, it did not remove phosphorous, which makes steel brittle. Consequently, low phosphorus iron ore was needed to make the Bessemer process work. Large deposits of such ore were to be found in the Upper Michigan Peninsula and had just recently become available by means of large-scale transport to the lower states.

As a consequence of the convergence of Carnegie’s association with the Pennsylvania Railroad and the Keystone Bridge Company, the availability of the Bessemer converter to make cheap steel rail, Pittsburgh’s renowned supply of high quality coal for coking, the availability of low phosphorus iron ore and efficient means of transporting it to Pittsburgh, in 1872 Carnegie resolved to construct a steel mill dedicated to the manufacture of steel rails. The new rail mill would be named after the president of the Pennsylvania Railroad. Located in Braddock, Pennsylvania, it was called then, as it is now, the Edgar Thompson Works.

Once in operation, the designated mastermind behind the new mill was Captain William R. Jones, an expert in the Bessemer process, hard driving manager and fiercely competitive businessman. Jones was responsible for many process improvements at the plant, one of the most significant being the Jones Mixer, which stored up to 100 tons of molten pig iron in a vessel that dispensed 10 ton charges into the Bessemer converters as needed, thereby making the process continuous.

In addition to the original two Bessemer converters, the Edgar Thompson Works was equipped with two open hearth furnaces. Although primitive open hearths had been used centuries earlier, in the 1880’s in Europe, the ancient process was resurrected, redesigned, scaled up and transformed by the addition of a low roof, furnace doors and a logistics system that enabled the efficient movement of materials through the steelmaking process. In the open hearth process, cold scrap followed by molten iron, several hours later, went from the charging floor through the furnace doors into the hearth where it was heated from above and, eight hours later, flowed as molten steel through a tapping spout into a ladle on the pouring floor on the other side. The ladle was hoisted to the nearby mold yard, where molten steel flowed from a nozzle in the ladle bottom into ingot molds. While Bessemer converters had been capable of ten-ton charges, open hearth furnaces were capable of charges as high as 350 tons.   In addition, open hearths tolerated wide variations in the ratio of cold scrap to molten iron in the charge. The ability to add alloying materials and to take samples for laboratory testing at any time during the process enabled the production of finely tuned steels. As a consequence of tremendous increases in production output and process improvements, in the first decade of the twentieth century, open hearths supplanted Bessemer converters as the technology of choice among steelmakers around the world.

In the early decades of the twentieth century the emerging automotive industry needed sheet steel for automobile bodies. At that time however, sheet steel was still produced by primitive, arduous methods of manual rolling, turning and re-rolling ingots that were, as a matter of necessity, cast sufficiently light in weight for several men to carry. Output was limited and costs were high until the development of the continuous hot strip mill by the American Rolling Mill Company (Armco), in the early 1920s, With the advent of continuous milling, massive slabs of high quality steel could be rolled while hot through a progression of rollers, each flattening the metal to a thinner gauge, while elongating the slab into a strip and, finally, rolling it into a coil. By the 1930s, cold rolling of previously manufactured hot rolled steel coils came on to the scene. Using the same machine principles as hot rolling, cold rolling enabled the further reduction in thickness below hot roll’s physical limit of about .050 inches, as well as the enhancement of the steel’s surface finish.

Although the steel industry had made tremendous progress over a period of about fifty years, a seemingly intractable problem lingered. In the words of U.S. Steel’s current Director of Product Technology, Joseph Defilippi, the problem can be summed up in two words: “Iron rusts.” In response to that lingering problem, in 1938 U.S. Steel opened its first experimental tinplating line for the production of tin cans for the food processing industry. Tin cans had come into popular use after World War I as a consequence of returning doughboys having grown accustomed to them while overseas. The result of the company’s experimental electrolytic tinplating line was the patented and globally licensed U. S. Steel Electrolytic Tinplating process which employs a sulphonic acid electrolyte to carry the stannous tin before it is reduced to a zero-valence state and electrodeposited onto the steel substrate.

The thirties also saw the early development of vitreous enamel coatings for the appliance industry and both electrolytic and hot-dip zinc galvanizing processes.

War II brought the steel-hulled Victory Ships, which experience proved, tended to crack in cold, rough seas.  Following the war, the United States government authorized a unified steel industry effort to find the cause of the problem and come up with solutions. Between 1945 and 1965, this industry- wide effort led to tremendous advances in the understanding of steel microstructures with the resultant development of techniques to control the opposing characteristics of brittleness and ductility. Principal among those techniques were the fine control of grain size and the elimination of embrittling nitrogen from the steel, which was entrained from the air used to oxidize the molten mix during manufacture.

In the mid 1950s, the Basic Oxygen Process (BOP) came to the rescue when Union Carbide developed an inexpensive process for producing oxygen. Today, having replaced the open hearth process, the Basic Oxygen Process employs a removable lance to blow pure oxygen, rather than air, into the molten iron in a large refractory lined vessel, called a BOP furnace, before tapping into a portable covered ladle in which the deoxidized, reduced nitrogen, tuned and alloyed molten steel is stored before transport to the continuous caster. At the caster, the steel is dispensed into a tundish, which acts a reservoir for the continuous process, and then into caster molds for solidification into long continuous slabs, which are subsequently torch cut to size in-line before delivery to the slab yard.

The construction of oil and gas pipelines during the 1950s and 60s required steel pipe with high fracture toughness, especially in Arctic and desert environments. With earlier steel pipe, a small fracture in a pressurized line could expand along grain boundaries in the steel microstructure, resulting in a mile long crack. Researchers at U.S. Steel found that the addition of nanoscale niobium and titanium particles to the steel formula promoted both nucleation and controlled inhibition of crystal growth during cooling. The result was small grain size which greatly increased fracture toughness.

Beginning in the 1970s, with the demise of the practice of planned obsolescence, demand for corrosion resistant sheet steel for the automotive industry took an upswing. The impetus from that trend led to increases in research and development as well as investments in production capacity for both electrolytic and hot dip galvanizing facilities for U.S. Steel, worldwide.

Today, researchers at U.S. Steel manipulate steel formulations at nanoscale levels both within the mass and on the surface of steel products to produce heretofore unavailable performance and aesthetic characteristics including: corrosion and dent resistance, surface integrated color and reflective coatings, bake hardenability, superior strength, impact resistance, easy formability and light weight.

Of the forty-some grades of steel that U.S. Steel produces today for hot-dip automotive galvanizing, thirty were not available ten years ago. Twelve new automotive grades are under development. Over 950 total steel grades are produced at U. S. Steel Gary Works for all sheet and tin products.

Back in 1927, U.S. Steel’s board of directors declared that henceforth, the company would engage in the formal practice of research and development. Through the years that declaration would prove to be prophetic. True to the board’s vision and in keeping with Andrew Carnegie’s aptitude for recognizing opportunity and matching it with technology, today United States Steel employs analytical science in conjunction with advanced technology to meet the needs of customers around the world. Lighter, stronger, more formable, more beautiful steels are the holy grails of the company today. Mr. Carnegie would be proud.

This story first appeared as a feature article in Pittsburgh Engineer magazine.

© Copyright 2005, Thomas P. Imerito / dba Science Communications

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