I was watching the Discovery Channel the other day and came across a show about steel. Living in today’s technologically advanced era often leads me into thinking that cars, boats, bridges, pots and pans are very ordinary, but I’ve never realized just how ubiquitous steel is (or the fact that steel isn’t an element). I was so intrigued by steel that day that I actually sat for over an hour to watch the show. So how is steel made and why is it used so widely? Curious, I decided to learn more about steelmaking and hope to provide some insight into this ‘ordinary’ material.
Steel is essentially an alloy of iron, the second most abundant metal on Earth (Iron Fact-ite, n.d.), and 0.5 to 1.5 percent concentration of carbon (Brain & Lamb, 2000). It is used widely for its strength, durability, affordability, flexibility, and recyclability. What got me interested was also the connection between its manufacturing process and redox reactions, which is what we are currently learning about in IB Chemistry.
The two visuals below sum up steelmaking in a nutshell.
To make steel, coal is first converted to coke, or pure carbon, as a source of energy for the blast furnace, where iron ore is turned into molten iron and limestone is added. Inside the blast furnace, carbon and carbon monoxide act as reducing agents in reducing iron (III) oxide, the ore, into iron. Because carbon is above iron on the reactivity series, carbon, being more reactive, is oxidized and iron is reduced, as seen below. (Brown, n.d.)
Fe2O3(s) + 3CO(g) à 2Fe(l/s) + 3CO2(g)
Fe2O3(s) + 3C(g) à 2Fe(l/s) + 3CO(g) (Brown, n.d.)
At the same time, limestone (CaCO3) is used to remove impurities, such as silica, in the iron ore.
CaCO3 + SiO2 à CaSiO3 + CO2 (Brown, n.d.)
In the next stage, the molten iron is mixed with recycled steel and alloys based on the customers’ needs. This then enters either a basic oxygen furnace, where 70 percent iron is mixed with 30 percent recycled steel, or an electric arc furnace, where 70 to 100 percent recycled steel is used (Making Steel, n.d.). The molten steel produced is then sent to a slab caster to be casted into solid steel slabs, which is later reheated to ensure that the slabs were all at the same temperature before being rolled into strips. The steel slabs then go to the roughing mill and finishing mill, which reduces the slabs’ thickness and rolls them into strips, and become hot rolled products. Then hydrochloric acid (HCl) is applied to remove surface scales before the steel strips are cooled, and now they are ready for sale for construction, automotive, appliances, and manufacturing. (Steel Builds a Better World, n.d.)
I found steel’s manufacturing process rather interesting, but what was more also interesting was the fact that steel is 100 percent recyclable and can be “recycled infinitely without ever affecting its strength or durability” (Steel Builds a Better World, n.d.). As someone who cares about environmental health, I was very happy to know about this. In fact, manufacturing using recycled metals not only reduces greenhouse gas emissions but also saves up to 56 percent the energy used to make steel from iron ore. Moreover, it is also beneficial to the economy in that in 2008 alone, the “scrap recycling industry generated $86 billion and supported 85,000 jobs” (West, n.d.).
On the other hand, however, iron and steel manufacturing also raises environmental concerns. The iron and steel industry release air pollutants, such as sulphur dioxide, nitrogen dioxide and carbon monoxide, and particulates, such as soot and dust, into the air. Moreover, steel works also releases large volumes of wastewater, which, if retained in unsealed ponds, may contaminate other local water ecosystems. Additionally, the consumption of 21.1 gigajoules per tonne of energy (used by US scrap-based plants in 1988) also brings up the issue of energy conservation. (Spiegel, n.d.)
I realized that it is important to consider both merits and shortcomings before reaching conclusions. As much as steel is useful and recyclable, its manufacturing also harms our environment. This research was an eye opener for me as I found a real-life application, steelmaking, for what we’re learning in class!
Brain, M., & Lamb, R. (2000, April 1). How Iron and Steel Work. HowStuffWorks. Retrieved October 9, 2013, from science.howstuffworks.com/iron4.htm
Brown, D. (n.d.). The Extraction of Iron.Doc Brown. Retrieved October 9, 2013, from http://www.docbrown.info/page04/Mextracta.htm
Iron Fact-ite. (n.d.). Planet Earth. Retrieved October 9, 2013, from www.gsa.org.au/resources/factites/factitesIron.pdf
Making Steel: How It’s Made. (n.d.).SteelWorks. Retrieved October 9, 2013, from www.steel.org/en/Making%20Steel/How%20Its%20Made.aspx
Spiegel, J. (n.d.). Environmental and Public Health Issues. International Labour Organization. Retrieved October 9, 2013, from http://www.ilo.org/oshenc/part-xi/iron-and-steel/item/593-environmental-and-public-health-issues
Steel Builds a Better World. (n.d.).Dofasco. Retrieved October 9, 2013, from www.dofasco.ca/HOW_STEEL_IS_MADE/html/Steel.pdf
The Chemistry of Steelmaking. (n.d.).School Science. Retrieved October 9, 2013, from resources.schoolscience.co.uk/Corus/14-16/steel/msch1pg1.html
West, L. (n.d.). Metal Recycling – Benefits of Metal Recycling – Why Recycle Metal?.Environmental Issues – News and Information about the Environment. Retrieved October 9, 2013, from http://environment.about.com/od/recycling/a/metal-recycling.htm
Steel Finishing Flowline. (n.d.). Steel Works. Retrieved October 9, 2013, from www.steel.org/Making%20Steel/How%20Its%20Made/Steelmaking%20Finishing%20Flowline.aspx
Steelmaking Flowline. (n.d.). Steel Works. Retrieved October 9, 2013, from www.steel.org/Making%20Steel/How%20Its%20Made/Steelmaking%20Flowlines.aspx