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Home , Bessemer process, Blast furnace, Cast iron, Electric arc furnace, Henry Bessemer, Open hearth furnace

History of Processing Andrew Ruble Department of & University of Washington Seattle, WA 98195

Abstract Although primitive could make use of , early cast and production methods were time consuming and unpredictable, since the chemistry was not well understood. The important chemistry behind iron processing lies with and reducing , as well as oxygen removing solid carbon as a gas. As the landscape of began to develop, these reactions were understood and utilized to develop processing methods that produced high quality steel in large amounts. Use of a blast reduced the iron ore, and methods like , the , the open-hearth furnace, and the basic oxygen process were used to manipulate the carbon and oxygen reactions to their advantage. steel could also be incorporated such as seen in an furnace.

Module Objectives The objective of the module is to introduce methods of iron processing. The thought process and chemistry behind each method are shown to familiarize students with real world application of chemical reactions. Students will be able to discuss each processing method, how new methods improve the steelmaking process, and the chemistry behind each new method.

Student Learning Objectives The student will be able to

 Recognize the chemistry necessary for iron processing  Differentiate between iron processing methods  Describe the current landscape of iron processing

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MatEd Core Competencies Covered: 7. A Identify the General Nature of 7.I Explain Causes for Differing Materials Properties 9.B Define and Describe Types and Properties of 17.B Describe Techniques used for Metals Processing

Key Words: Iron, Steel, Processing Type: PowerPoint presentation with short online activity and class discussion Time required: one class period Suggested prerequisite: Iron and Steel: Properties and Application

Target grade level: High School; also Introductory College/Technical School

Equipment and Supplies Needed

 PowerPoint projection system

Table of Contents: Abstract 1 Module Objectives 1 Student Learning Objectives 1 MatEd Core Competencies 2 Equipment and Supplies 2 Curriculum Overview 3 Module Procedure 6 Optional Student Activity 8 Supporting Materials 8 Acknowledgements 8 Evaluation 8

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Curriculum Overview The history of iron processing, and therefore steel processing, demonstrates civilization’s demand for a versatile engineering material and the creativity of the engineers of the time. Iron’s high strength and made it much more useful than the brittle materials of history such as wood and ceramic but required a greater scientific understanding and greater technology to implement. Early metallurgists did not understand phase relationships or even concepts of the atom, so processing iron ore was difficult. Small steps in understanding the chemistry led to new processes that allow control over the quality of iron and steel produced while maximizing quantity and quality. Early metallurgists were familiar with melting , so they attempted to melt the iron ore they found. The primitive furnaces, which could melt copper due to its low melting temperature of about 1100 degrees C (around 2000 degrees F), were not able to liquefy the iron ore, which melts just above 1500 degrees C (2700 degrees F). With enough time, however, in a furnace, iron ore would heat up to form a semi-malleable mass which could be hammered and shaped. This took a lot of time and energy, and the product was called wrought iron (wrought meaning worked). Impurities present were worked out by hammering although many still remained, leading to low performance and inconsistency among wrought iron pieces. Each piece needed to be worked individually, which was time consuming. This technique did not oust as the leading of the day but it was a step towards the utilization of iron. The production of wrought iron is a great example of conceptual understanding coming much later than the discovery. Iron ore exists mostly as an , Fe2O3, which is not suitable for any application, but when it is heated with charcoal (carbon) and air (oxygen), the iron ore and reduce to form iron and . This is the main reaction that was slowly understood over time by metallurgists and it is important to remember:

2C + 02 -> 2CO

Fe203 + 3CO -> 2Fe + 3CO2

The reaction between the carbon C and oxygen gas O2 form carbon monoxide CO, which also produces a lot of heat. This is very important as it removes carbon from the iron by turning it into a gas. This carbon monoxide reacts with iron ore Fe2O3, reducing it to pure iron Fe and carbon dioxide CO2 as a gas. As furnace temperatures increased with advances in technology and chemistry, metallurgists were eventually able to fully melt iron to produce cast iron. Since the metal is molten, it can then be ‘cast’ into shapes. As you can see in the phase diagram below, the melting point of iron is lowered significantly as carbon content increases from – for pure iron to – at 4% C. The first cast iron was produced near this point, which allowed the early furnaces to melt it completely. However, once cooled, this material was brittle due to the

3 high carbon percentage. Often, the liquid metal was cast into manageable shapes, such as bars, to be remelted and processed separately from the furnace. This temporary state of the iron is known as , mostly characterized by its high carbon percentage.

Figure 1: Phase diagram of iron and carbon. Notice the lowered melting temperature around 4% carbon.

This processing of iron ore to pig iron was done using a . The blast furnace is a tall cylindrical structure which utilizes a continuous process where a combination of iron ore and (such as ) are inserted into the top of a furnace while air is pumped in from the bottom. The air rises and reacts with the fuel, using the above reactions, reducing the iron ore. Molten iron then flows out the bottom, where it is cast into bars for pig iron. This process needs to be running continuously so blast furnaces often run for many years at a time, and are very difficult to stop and start. As pure oxygen became available, using pre-heated oxygen dramatically improved the pig iron quality and output. One technique for using pig iron was known as puddling. Since no more carbon needed to be added to the iron to decrease the melting temperature, a fuel source was ignited separately from the pig iron to avoid any more additions of carbon or other elements from the fuel to the iron. The heat was directed onto the pig iron, which was melted and combined with iron ore, creating the above and reduction reactions, removing carbon and other contaminates. As the carbon was removed, the melting temperature of the iron increased, effectively solidifying iron with a lower carbon content. The iron

4 solidified into lumps which were extracted. This could be shaped into bars, creating a product similar to wrought iron but without the hammering. While there were a few early techniques for producing steel, none really worked until come up with his technique known as the Bessemer process in the 1850s. Bessemer created a process where air was bubbled up from the bottom through a vessel of molten iron. One might think that this would cool the iron, but the forced air was a better source of oxygen than adding iron ore (like puddling). The added oxygen removed the carbon impurities and created large amounts of heat, which would sustain high temperatures in the molten iron, allowing all the carbon to be removed. This new method took only about 20 minutes and completely revolutionized the steel industry, cutting the price of steel more than 75% and increasing steel production tremendously. This steel was very useful, but since the Bessemer process used air, the iron was exposed to which caused steel to be somewhat brittle. A more advanced version of puddling used a new invention called the , a furnace designed to reuse heat from escaping gas. Similar to puddling, the open hearth furnace was heated separately to avoid any contaminants but, instead of coke, used , which burns near 2000 degrees C to heat the furnace. Combining the new furnace design with gas allowed the furnace to reach and maintain high temperatures, easily melting pig iron and even scrap steel, which was starting to become prevalent. Once the steel was melted, the chemistry was altered until the desired composition was reached. Since the chemistry was carefully controlled, the operators did not need to wait for the iron to solidify, such as in puddling; the iron could be poured out immediately. Each batch took about 8 hours to complete. The open hearth furnace did not replace the Bessemer process, but complemented by using large amounts of scrap steel. When pure oxygen became commercially available, it replaced air in the Bessemer process and, along with some other improvements, became known as the basic oxygen process, and was widely used starting in the 1950s. Often, molten iron direct from the blast furnace could be used. In the basic oxygen process, high pressure oxygen is blown into the steel, either from the top or bottom, which removes carbon while also producing heat to keep the iron molten. Along with adding a few extras, such as and to remove other impurities, this method produced very high quality steel, up to 350 in 40 minutes. Using mostly pig iron, the basic oxygen process did not allow use of large amounts of scrap steel. Some scrap could be used, but scrap was still mostly processed with the open hearth furnace. As new technology created cheaper electricity, a new versatile method of processing steel became available using an . This furnace uses high powered electrodes to melt primarily scrap steel, replacing the open hearth method, since an electric arc furnace did not require the complex construction required for the open hearth furnace. The electrodes can easily reach temperatures near 2000 degrees C and can process a batch in an hour’s time. Similar to the open hearth method, the batch can be heated as long as

5 necessary in order to perfect the chemistry, adding oxygen, carbon, or other elements as necessary. While the electric arc furnace replaced the open hearth furnace, it was also affordable enough to use for small batches of specialized steel or even medium sized batches similar to the basic oxygen process. Today, no one process is solely used to process steel. A blast furnace processes most iron ore, creating pig iron. The basic oxygen process is used to create steel using the pig iron and electric arc is used to produce steel from plentiful scrap, although either method can process pig iron or scrap iron. The cost and convenience of each method dictates which will be used.

Module Procedure:

1. Discussion 1. Where does iron, or any other metal come from? As ore, usually an oxidized form, from the ground. 2. What are some steel applications? 2. Present the slideshow to the students 1. “Steel is desirable” – Steel’s mechanical properties make it desirable, comparing tensile strength to that of other materials. Tensile strength also represents and other mechanical properties. 2. “Getting started with steel” – Comparing the melting temperatures of iron ore, it is definitely higher than other metals’ melting temperatures. Compare with the wood burning furnace max temperature of about 1100 °C. 3. “The iron processing reaction” – As shown in the reaction, C (carbon as a solid) and O2 (oxygen as a gas) combine to form CO (carbon monoxide, a gas). This CO reacts with Fe2O3 (iron ore) to create Fe (iron) and CO2 (carbon dioxide, a gas). So adding carbon and oxygen to raw iron ore reduces it. But also, if there is too much carbon, adding oxygen will remove it, turning solid carbon to a gas. 4. “Wrought Iron” – Before iron could be fully melted, it was just heated and worked into shapes (‘wrought’ meaning ‘worked’). This didn’t do much to remove impurities so it was still weak. Small additions of carbon from the charcoal helped strengthened. 5. “Melting the first iron” – As the carbon content of iron increases, the melting temperature decreases. This allows lower temperature furnaces to melt the iron. Carbon is added through burning the fuel used, either charcoal or coke. 6. “Blast furnace” - The blast furnace builds upon the processing reaction. Carbon fuel and iron ore are added from the top and air is blown in from the

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bottom. The gas rises and the solid falls, and the reaction happens when the two meet. This is a continuous process that is difficult to start or stop. 7. “Cast iron/pig iron” – Molten iron cast immediately from still contains some impurities, but for the first time it could be shaped. Since carbon is added in the blast furnace, it is usually a high percentage. This high carbon iron was cast into bars to be processed later, known as pig iron. Adding improved castability and aided in formation, creating cast iron. 8. “Puddling” – Once the iron was processed from ore, it had too much carbon in it. Puddling essentially did the opposite of early processors: it removed carbon to increase the melting temperature. As the melting temperature increased, iron would solidify and could be gathered into a blob which could be shaped. It was a difficult manual process. The final product had to be worked by hand, and was similar to wrought iron although with a much lower carbon content and fewer impurities. 9. “The Bessemer Process” – Henry Bessemer wanted to create a process better than puddling. By bubbling air up through a vessel of iron at very high temperature, carbon was removed but still stayed in a liquid form which could be easily poured out. The process was also very quick, lasting only around twenty minutes. Carbon could be re-added after the air blow and other elements could be added to create the desired product. 10. “Open Hearth furnace” – The open hearth furnace had a unique furnace design created to reuse heat from escaping gas to keep the molten iron hot. As carbon was removed from oxygen addition, the iron would stay molten instead of solidifying (like puddling), which allowed the iron chemistry to be carefully manipulated. As it stayed hot, the iron could be poured out and shaped as necessary. 11. “Basic oxygen” – The basic oxygen process is very similar to the Bessemer process, replacing pure oxygen for regular air (Bessemer wanted to use pure oxygen, but it was not commercially available at the time). It is also called basic due to additions of high pH elements. After the oxygen is blown through, other elements can be added before pouring out. 12. “Electric Arc furnace” – With abundance of scrap steel and cheap production of electricity, using electricity to melt steel became feasible. The electric arc furnace uses high current between electrodes inserted into scrap steel to melt steel, and maintain a high temperature to keep the steel molten as long as necessary for oxygen additions or other chemical additions to create the desired product. Each batch could be run separately as it was very easy to start and stop, and could be used for individual batches of specialized .

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13. “Today” – Iron ore is processed from the blast furnace to basic oxygen furnace, and scrap processed in EAF. As shown in the chart, these methods have been refined over the years. 14. “Steel locations” – All over the world, here are a few! (see suggested Student Activity below)

At the end of the slide presentation and discussion, you may provide copies of the written curriculum notes to interested students. Also note the potential homework assignment noted below.

Optional Student Activity.

Using the internet, locate a close to your location. Which methods does it use? Try picking a different mill somewhere in the US. Which methods do they use?

Supporting Materials:  “New Science of Strong Materials” by J.E. Gordon. Princeton University Press, 2006.  “Structures or why things don’t fall down” by J.E. Gordon. Da Capo Press, 2002.  Ferrous – https://en.wikipedia.org/wiki/Ferrous_metallurgy

Evaluation

Student evaluation (discussion/quiz)

1. What additions enabled iron ore to be fully melted? 2. What is added to iron ore in order to make iron? 3. Which processing method is mainly used for processing iron ore? 4. How did the open hearth and electric arc furnace allow for the iron’s chemistry to be altered easily? 5. Which processing methods allowed the use of scrap steel?

Instructor evaluation

1. What grade level and class was this module utilized for? 2. Were the students able to grasp the key concepts introduced in the module?

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3. Was the level and rigor of the module acceptable for the grade level of the students? If no, how can it be improved?

Any comments and/or suggestions on improving this module are encouraged.

Course evaluation questions

1. Was the instructor’s explanation comprehensive and thorough? 2. Was the instructor interested in your questions or concerns? 3. Was the instructor able to answer your questions thoroughly and to your satisfaction?

Acknowledgments

The author wishes to thank Professor Tom Stoebe for assistance in developing and editing this module, as well as the assistance of the Materials Science and Engineering department at the University of Washington.

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