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Lesson: Learn about Steel with Harry Kane

Examine the wonders and history of steel, the material central to the strength of modern football stadiums.

Learn about Steel with Tottenham's Harry Kane
Lesson
Revision Notes

Football goal-scoring phenomenon, Harry Kane, is currently Tottenham Hotspurs’ leading-scorer and third on their all-time list. He is vice-captain of Spurs and captain of England, his national team.

Harry plies his trade at Spurs new, Tottenham Hotspur Stadium, a wonder of modern stadium design. Central to the strength and elegance of Spurs’ stadium, and almost every other modern building, is Steel.

The story of steel tells us so much about the way the modern world developed. Follow its journey in this video.

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Harry Kane

Harry Edward Kane was born July 28th, 1993. He is an English professional footballer who plays for Tottenham Hotspur and is captain of England. Born and raised in Walthamstow, East London, Kane has been at Spurs throughout his career, but as a young player was out on loan at several clubs.

In his first full season at the club, Kane scored 31 goals across all competitions, and finished as the league's second highest goalscorer. He has continued to be a prolific goalscorer. In the 2017-18 season, Kane registered his best campaign to date, with 41 goals scored in 48 games in all competitions. In November 2019, he became Tottenham's third highest all-time goalscorer.

Kane has scored 32 goals in 45 games for England. He appeared and scored at every youth level and made his senior debut in March 2015, aged 21, scoring in that game. He was made the squad's captain in  May 2018, prior to the 2018 FIFA World Cup. In that tournament Kane led England to fourth place, their highest finish since 1990. He also finished as the top goalscorer, winning the Golden Boot.

Tottenham Hotspur Stadium

The Tottenham Hotspur Stadium is the Club’s new stadium, replacing the club's previous stadium, White Hart Lane. It has a capacity of 62,303, making it one of the biggest stadiums in the Premier League. It is designed to be a multi-purpose venue and features the world's first dividing, retractable football pitch, which reveals a synthetic turf pitch underneath for NFL London games, concerts, and other events.

The construction of the stadium was initiated as the centrepiece of the Northumberland Development Project, intended to be the catalyst for a 20-year regeneration plan for the Tottenham area. The project covers the site of the now demolished ground of White Hart Lane and areas adjacent to it. The project was first conceived in 2007 and announced in 2008, but the plan was revised several times, and the construction of the stadium, did not commence until 2015. The stadium subsequently opened in April 2019 with a ceremony before the first Premier League game held at the stadium.

The name ‘Tottenham Hotspur stadium’ is temporary, the intention being to sell the naming rights, so that it will be named after a sponsor.

Steel

The development of steel can be traced back 4000 years to the beginning of the Iron Age. Proving to be harder and stronger than bronze, which had previously been the most widely used metal, iron began to displace bronze in weaponry and tools.

For the following few thousand years, however, the quality of iron produced would depend as much on the ore available as on the production methods.

By the 17th century, iron's properties were well understood, but increasing urbanisation in Europe demanded a more versatile structural metal. And by the 19th century, the amount of iron being consumed by the growth of the railways gave manufacturers the financial incentive to find a solution to iron's brittleness and inefficient production processes.

The breakthrough in steel production came in 1856 when Henry Bessemer developed an effective way to use oxygen to reduce the carbon content in iron: The modern steel industry was born.

Early Iron

At very high temperatures, iron begins to absorb carbon, which lowers the melting point of the metal, resulting in cast iron, usually between 2.5 to 4.5% carbon. The development of blast furnaces, first used by the Chinese in the 6th century BC and in Europe during the Middle Ages, increased the production of cast iron.

Cast iron is strong but suffers from brittleness because of its carbon content, making it less than ideal for working and shaping. As manufacturers became aware that the high carbon content in iron was central to the problem of brittleness, they experimented with new methods for reducing the carbon content to make iron more workable.

By the late 18th century, ironmakers learned how to transform cast iron into a low-carbon content wrought iron using puddling furnaces. The idea was developed by Henry Cort in 1784. The furnaces heated molten iron, which had to be stirred by ‘puddlers’ using long, oar-shaped tools, allowing oxygen to combine with and slowly remove the carbon.

The iron would be removed and worked with a forge hammer by the puddler before being rolled into sheets or rails. By 1860, there were over 3000 puddling furnaces in Britain, but the process remained hindered by its labour and fuel costs.

One of the earliest forms of steel, blister steel, began production in Germany and England in the 17th century and was produced by increasing the carbon content in iron using a process known as cementation. In this process, bars of wrought iron were layered with powdered charcoal in stone boxes and heated.

After about a week, the iron would absorb the carbon in the charcoal. Repeated heating would distribute carbon more evenly and the result, after cooling, was blister steel. The higher carbon content made blister steel much more workable than pig iron, allowing it to be pressed or rolled.

Blister steel production advanced in the 1740s when English clockmaker, Benjamin Huntsman, while trying to develop high-quality steel for his clock springs, found that the metal could be melted in clay crucibles and refined with a special flux to remove slag that the cementation process left behind. The result was a crucible, or cast steel. But due to the cost of production, both blister and cast steel were only ever used in speciality applications.

As a result, cast iron made in puddling furnaces remained the primary structural metal in industrialising Britain during most of the 19th century.

Modern Steelmaking

The growth of railways during the 19th century in both Europe and America put enormous pressure on the iron industry, which still struggled with inefficient production processes. Steel was still unproven as a structural metal and production of the product was slow and costly. That was until 1856 when Henry Bessemer came up with a more effective way to introduce oxygen into molten iron to reduce the carbon content.

Now known as the Bessemer Process, Bessemer designed a pear-shaped receptacle, referred to as a 'converter' in which iron could be heated while oxygen could be blown through the molten metal. As oxygen passed through the molten metal, it would react with the carbon, releasing carbon dioxide and producing a purer form of iron.

The process was fast and inexpensive, removing carbon and silicon from iron in a matter of minutes but suffered from being too successful. Too much carbon was removed, and too much oxygen remained in the final product. Bessemer ultimately had to repay his investors until he could find a method to increase the carbon content and remove the unwanted oxygen.

At about the same time, British metallurgist Robert Mushet acquired and began testing a compound of iron, carbon, and manganese, known as spiegeleisen. Manganese was known to remove oxygen from molten iron and the carbon content in the spiegeleisen, so, if added in the right quantities, would provide the solution to Bessemer's problems. Bessemer began adding it to his conversion process with great success.

One problem remained. Bessemer had failed to find a way to remove phosphorus, a harmful impurity that makes steel brittle, from his end product. Consequently, only phosphorus-free ore from Sweden and Wales could be used.

In 1876, Welshman, Sidney Gilchrist Thomas, came up with the solution by adding limestone, to the Bessemer process. The limestone drew phosphorus from the iron into the slag, allowing the unwanted element to be removed.

This innovation meant that, finally, iron ore from anywhere in the world could be used to make steel. Not surprisingly, steel production costs began decreasing significantly. Prices for steel rail dropped more than 80% between 1867 and 1884, as a result of the new steel producing techniques, initiating the growth of the world steel industry.

The Open Hearth Process

In the 1860s, German engineer, Karl Wilhelm Siemens, further enhanced steel production through his creation of the open-hearth process. The open-hearth process produced steel from cast iron in large shallow furnaces.

The process, using high temperatures to burn off excess carbon and other impurities, relied on heated brick chambers below the hearth. Regenerative furnaces later used exhaust gasses from the furnace to maintain high temperatures in the brick chambers below.

This method allowed for the production of much larger quantities (50-100 metric tons could be produced in one furnace), periodic testing of the molten steel so that it could be made to meet particular specifications and the use of scrap steel as a raw material. Although the process itself was much slower, by 1900, the open-hearth process had primarily replaced the Bessemer process.

Birth of the Steel Industry

The revolution in steel production that provided cheaper, higher quality material, was recognised by many businessmen of the day as an investment opportunity. Capitalists of the late 19th century, including Americans Andrew Carnegie and Charles Schwab, invested, and made millions (billions in the case of Carnegie) in the steel industry. Carnegie's US Steel Corporation, founded in 1901, was the first corporation ever launched valued at over one billion dollars.

Electric Arc Furnace Steelmaking

Just after the turn of the century, another development occurred that would have a strong influence on the evolution of steel production. French scientist, Paul Heroult's electric arc furnace (EAF) was designed to pass an electric current through charged material, resulting in exothermic oxidation and temperatures up to 1800°C more than sufficient to heat steel production.

Initially used for specialty steels, EAFs grew in use and, by World War II, were being used for the manufacturing of steel alloys. The low investment cost involved in setting up EAF mills allowed them to compete with the major US producers like the US Steel Corporation and Bethlehem Steel, especially in carbon steels, or long products.

Because EAFs can produce steel from 100% scrap, less energy per unit of production is needed. As opposed to basic oxygen hearths, operations can also be stopped and started with little-associated cost. For these reasons, production via EAFs has been steadily increasing for over 50 years and now accounts for about 33% of global steel production.

Oxygen Steelmaking

The majority of global steel production, about 66%, is now produced in basic oxygen facilities. It is a method to separate oxygen from nitrogen on an industrial scale, developed in the 1960s. It allowed major advances in the development of basic oxygen furnaces.

Basic oxygen furnaces blow oxygen into large quantities of molten iron and scrap steel and can complete a charge much more quickly than open-hearth methods. Large vessels holding up to 350 metric tons of iron can complete conversion to steel in less than one hour.

The cost efficiencies of oxygen steelmaking made open-hearth factories uncompetitive and, following the advent of oxygen steelmaking in the 1960s, open-hearth operations began closing. The last open-hearth facility in the US closed in 1992 and in China in 2001.

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