Steelmaking Technologies

Summary

Steelmaking technologies are processes, such as the Bessemer, open-hearth, and basic oxygen furnace, designed to make an alloy of iron and a small amount of carbon. Depending on the properties desired in the steel, other alloys can be made with such elements as chromium, cobalt, copper, molybdenum, nickel, silicon, and tungsten. Steel is commonly produced as rods, bars, sheets, and wires, which are employed in constructing automobiles, railroads, ships, and machinery. Steel has also been used to make numerous other things, from delicate surgical instruments to skyscrapers.

Definition and Basic Principles

Steel is an alloy of pure iron, such as wrought iron, and a small but crucial amount of carbon, which transforms the iron into a material that can hold a sharp edge and tolerate tension, friction, and bending. Even before the chemical nature of steel was understood, artisans had developed steelmaking technologies that resulted in such sophisticated products as samurai swords and fine cutlery. After physicists and chemists discovered and developed phase diagrams, they possessed the principles that allowed them to predict the properties of multicomponent systems, including steel alloys.

Carbon steels could then be described as iron with less than .8 percent carbon, though the carbon content could vary from .2 to 2.1 percent by weight. Low-alloy steels, generally made in the same way as ordinary carbon steels, have less than 5 percent of such elements as chromium, molybdenum, and nickel. High-alloy steels require special processing and have large percentages of alloying elements. For example, some stainless steels contain 18 percent chromium and 8 percent nickel. The evolution of steelmaking technologies has led to a diversification of methods and a multiplication of products, with the manufacturing techniques increasingly well adapted to the wide variety of complex steels demanded by many modern industries.

Background and History

Although science and technology historians often combine their treatment of iron and steel, the two substances had a different, though related, evolution, especially in the modern period. Iron was first smelted from its ore more than 4,000 years ago, and archaeologists have found steel artifacts in several locales during the second millennium BCE. Some groups in Africa and Asia made steel weapons, and the Greek philosopher Aristotle discussed steel in the fourth century BCE. In the early centuries of the Common Era, certain steels made in the Middle East, such as Damascus steel, became famous for their beauty and ability to maintain a sharp edge.

During the medieval period, European iron makers developed improved methods for producing pig and wrought iron as well as steel for tools like scythes, sickles, spades, and hoes. Ironworks multiplied in Eastern Europe into the sixteenth century, and from the sixteenth to the eighteenth centuries, blast furnaces transformed iron and steel manufacturing in central and western Europe. In Colonial America, steel was made by baking wrought-iron strips with charcoal in sealed clay containers—the cementation process.

Modern steelmaking began in nineteenth-century England with the introduction of the Bessemer process and Germany's open-hearth process. These methods of making massive amounts of high-quality steel spread to other countries, especially the United States, which adopted and improved the techniques. The country became the world's largest steel producer by 1900 following the discovery of rich iron-ore deposits in Minnesota’s Mesabi Range. The United States maintained this position well into the second half of the twentieth century. However, mismanagement, domestic and international competition, and failure to implement new technologies like electric furnaces and minimills resulted in the decline of American steel and the ascendance of steelmakers like China, Japan, India, and Brazil in the late twentieth century.

How It Works

Conceptually, the creation of steel, an alloy of iron and carbon, is readily understood since it involves either the removal of impurities and adjusting the carbon content in iron or adding the proper amount of carbon to very pure iron. In the long history of steelmaking before the modern era, these subtractive and additive techniques were discovered empirically, by trial and error. As chemists and physicists developed a deeper understanding of elemental metals and alloys, they could facilitate the production of traditional steels and create many new steel alloys, which stimulated the industry's progress in the twentieth century.

Bessemer Process. In the middle of the nineteenth century, British inventor Henry Bessemer discovered a method of converting pig iron into steel by eliminating impurities and lowering carbon content. He accomplished this through a converter, a pear-shaped container with nozzles at its base, through which compressed air was bubbled into the molten iron to oxidize impurities and excess carbon. The American mechanical engineer Alexander Lyman Holley was chiefly responsible for adapting the Bessemer process for US mills, where it became part of a system for manufacturing steel rails for the booming railroad business.

Open-Hearth Process. During the first half of the twentieth century, the open-hearth steelmaking method replaced the Bessemer process in Europe and America. German inventor Karl Siemens and French engineer Pierre- Émile Martin developed this process (also called the Siemens-Martin process), in which the primary agent for transforming iron into steel was a large open-hearth furnace in which a natural-gas flame was directed downward onto the predominantly metal mix, which, in time, was transformed into steel. Although this process took much longer than the Bessemer process, it resulted in large amounts of steel and allowed technicians to monitor the molten steel, permitting precision steel to be made. Americans increased the sizes of open-hearth furnaces, replaced natural gas with heavy fuel oil, improved the circulatory system, and created efficient instrumentation that controlled the entire process. By the 1930s, more than 80 percent of steel made in the United States was produced using the open-hearth method.

Oxygen Steelmaking. During the decades after World War II, oxygen steelmaking replaced the open-hearth process in many countries. The device for transforming a mixture of pig iron and scrap into steel was the basic oxygen furnace, a large, closed barrel-shaped container in which oxygen was directed downward into the heated metals via a water-cooled lance. Within thirty years of its introduction in 1958, 97 percent of US steel was made by oxygen furnaces and the remaining 3 percent by open-hearth furnaces.

Minimills. During the final decades of the twentieth and the first decades of the twenty-first century, a "minimill revolution" transformed the world steel industry. The central component in a minimill is the electric arc furnace, where scrap metal is melted, purified, and processed into various steel products. Because minimills do not have to make such intermediate products as pig iron, they can minimize expenses for raw materials. New technologies in minimills allow the manufacture of a wide variety of products, from low- and high-carbon steels to specialized alloy steels. In 1970, minimills accounted for about 10 percent of US steel production, but their popularity increased in the following decades, accounting for more than half of the produced steel. These gains were due not so much to expansions in scale but to the development of more and better steel products.

Energy Efficient Steel Production. Steelmaking through the mid-2020s produced 7 to 11 percent of total global greenhouse gas emissions. Demand for cleaner steel production increased throughout the early twentieth century with stricter governmental regulations on industry standards and public scrutiny on corporate social responsibility. This resulted in companies testing new, green steel production techniques, like renewable hydrogen reduction. The Swedish company SSAB AB created HYBRIT—Hydrogen Breakthrough Ironmaking Technology—which uses hydrogen to chemically reduce iron ore combined with carbon. The only byproduct is water vapor. The process is more expensive on the front end, but considering the cost of traditional steel production's emissions taxes in some countries, the costs are nearly equal.

Applications and Products

Throughout the history of steelmaking, changing markets have played a pivotal role in determining which applications are viable and which products succeed or fail. Initially, markets existed for military applications such as swords and bayonets and agricultural artifacts like scythes and plows. With the development of the railroad industry, the original demand for iron was replaced by increasing orders for steel, since Bessemer steel rails were superior to iron ones in durability and overall cost-effectiveness. However, the railroad industry was eventually replaced by the automotive industry as the leading steel buyer in all advanced industrialized societies.

As plastics substituted for steel in many automobile parts in the second half of the twentieth century, and as aluminum wrested more and more of the market for metal containers from steel, demand declined. Some scholars classify steelmaking applications in terms of the products sold to other businesses for processing—for example, sheets, strips, bars, rods, pipes, wires, plates, and other structural shapes. Others classify applications in terms of the chief industries using steel, such as the railroad, automotive, construction, and machinery industries. The following are representative industrial applications of steel.

Railroad and Shipbuilding Industries. In the United States and other countries, the early history of the railroad industry was dominated by iron. As thousands of miles of iron rails were laid down and heavily used, they needed to be constantly replaced. In the second half of the nineteenth century and beyond, steel rails proved their superiority, leading to this massive application along with steel wheels and others. Similarly, shipbuilding passed from an iron to a steel age. During the American Civil War, the famous battle of the ironcladsthe USS Monitor and the CSS Virginiaproved wooden ships were no match for an ironclad, causing navies around the world to abandon wooden ships in favor of their iron successors. In the late nineteenth century, steel began to replace iron in military and commercial ships because it created lighter and stronger hulls. In the twentieth century, ships constructed mainly of steel became the norm, though steel compositions later changed to increase durability in harsh environments with large temperature fluctuations. In the late twentieth and early twenty-first centuries, aluminum became a serious competitor of steel for high-speed ships.

Automobile Industry. Throughout most of the twentieth century, a major consumer of steel has been the automotive industry, particularly in the United States. Steel has been, and continues to be, the chief constituent of car bodies, and hot-rolled sheet steel has become a staple of the auto industry. Steel use in this industry grew after World War II, but a decline developed during the latter decades of the century. Because of the oil and environmental crises, cars were, on the whole, downsized, and steel began to be replaced by plastics and aluminum to reduce weight and increase energy efficiency. The steel industry responded by developing better and lighter steel. Furthermore, other materials failed to replace steel in the framework, body panels, and several auto parts under the hood.

Construction Industries. From the end of the nineteenth to the start of the twenty-first century construction has constituted one of the largest steel markets. It has often rivaled and sometimes surpassed the auto industry in terms of tons of steel purchased and used in constructing high-rise office buildings, bridges, and, increasingly, private homes. Structural steel played an essential role in building American skyscrapers, like the 1931 construction of the Empire State Building. With 102 stories and a height of 1,250 feet, it was the tallest building in the world until the 1972 completion of the north tower of the World Trade Center. Civil engineer John Augustus Roebling and his son, Washington Roebling, were the designer and chief engineer of the Brooklyn Bridge, which opened in 1883. The longest bridge in the world at the time, it proved the value of steel wire with its massive suspension cables and suspenders. In the 1930s, the Bethlehem Steel Corporation supplied the structural steel for the George Washington Bridge in New York City and the Golden Gate Bridge in San Francisco.

Special-Purpose Steel-Alloy Applications. Although carbon steels are involved in major applications, the ever-growing variety of alloy steels has resulted in successful products because of their desirable properties and low cost. A good example is stainless steel, sometimes called corrosion-resistant steel, which is conventionally defined as having 11 percent chromium, but austenitic stainless steel is a complex alloy made with iron, chromium, nickel, manganese, silicon, carbon, phosphorus, and sulfur. Elemental components in alloy steels can be varied to suit certain industrial and domestic requirements. Some steels alloyed with cobalt or silicon have applications as permanent magnets. Several heat-resistant steel alloys have been made and successfully marketed, some of which have greater strength and dimensional stability at high temperatures.

Careers and Course Work

In the early history of steelmaking, workers were trained on the job, first through the apprenticeship system and later through participation in what came to be called "shop culture." As steelmaking became professionalized in the late nineteenth century, jobs in production were increasingly staffed with individuals having associate's or bachelor's degrees. Besides general courses in mathematics, physics, chemistry, and materials science, these students also learn practical crafts like welding and blueprint reading. As steelmaking technologies became more complex, with the introduction of minimills, electric arc furnaces, continuous casting, and computerized control of processing and product fabrication, master's and doctoral degrees have become essential for students hoping for good jobs in government, industrial administration, and academic research. With employment declining in the developed world and increasing in the developing world, job opportunities for American and European students with advanced degrees and the requisite language skills are becoming available in countries such as China, India, and Brazil.

The rate of decline in US steel industry jobs slowed somewhat in the first decade of the twenty-first century, though it remained volatile. Even the depleted industry remained a prominent cultural touchstone, however, and it often figures highly in political considerations. Because ore and coal deposits were located largely in eastern and midwestern states, these were the places where steelmaking careers were traditionally and often still are forged. Compensation varies by education, experience, and job level. Some companies still prefer hiring vocational school graduates for processing jobs. Those desiring to become machinists, millwrights, or pipefitters generally have to serve an apprenticeship. Nevertheless, executives tend to favor those who have taken physics, chemistry, and metallurgy courses, and engineers must possess graduate degrees.

Social Context and Future Prospects

Analysts studying the social, political, and economic future of the steelmaking industry usually make two points. First, steelmaking has been and will continue to be necessary for technological and industrial progress in the developed and developing worlds. Second, steelmaking faces serious challenges, such as rising energy and raw materials costs, the expense of adopting new technologies, and the burden of stricter regulations concerning environmental pollution and job safety. For those who see deleterious competition and unfair trade practices as harming steelmaking's progress, the answer is reducing barriers between countries and encouraging technological, economic, and political cooperation. Others believe that the American steel industry can be reinvigorated by effective leaders willing to invest in the research and development of new technologies, particularly those that are energy-efficient, emphasizing that the United States must be a leader, not a follower. Steelmaking is a capital-intensive industry, and to be profitable it is necessary to make wise use of its most precious resources—technological, economic, and human.

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