Steel goes into making myriad objects. It provides structural support for skyscrapers and other buildings, makes up automobiles and can be found in any average household in appliances and canned goods. Steel is integral to making everyday things we often take for granted—buildings, cars, tools, packaging—but the life of steel begins long before the average person utilizes it.
Steel is one of the few construction materials that has an infinite lifecycle and does not degrade when it is recycled; it does not lose strength or functionality. Because of its magnetic properties, iron and steel easily are diverted from the waste stream. Almost 69 percent of all discarded steel is recycled in North America each year, which is more than paper, aluminum, plastic and glass combined, amounting to about 80 million tons of steel recycled per year.
How It’s MadeAlthough each steel mill has a slightly different process for making steel, they all follow the same general concept. Philip K. Bell, director of external communications and public affairs at the Tampa, Fla., Gerdau AmeriSteel location, explains the process his company uses. “The process begins with scrap collection and processing to segregate the usable ferrous material from non-ferrous metals and non-metal materials,” he says. “The usable scrap is collected and placed in a large bucket, which can hold up to 25 tons of material, and is then charged into a furnace in the melt shop. Carbon electrodes are inserted through the furnace roof, causing the scrap to melt. Alloys are added to meet material specification and then any impurities are removed. The molten steel is tapped into a refractory lined bucket and transferred to a casting area. The bucket is tapped from the underside, allowing the material to pour into a continuous casting process which produces an initial shape, called a billet, of the desired material specification. These billets then are reheated and sent through a rolling process to achieve the desired final shape. Once rolled, the material goes through a finishing process where it is cooled in a cooling bed, tested to assure it meets specification, marked with a mill identification, cut, bundled and stored on site until it is transported for delivery.”
From the time the scrap goes into the melt shop, it takes four to eight hours to complete the process. Most of Gerdau AmeriSteel’s products then are sold to steel service centers or directly to steel fabricators to be processed further for use in construction. The remainder is sold to original equipment manufacturers for commercial and industrial use. All of Gerdau AmeriSteel’s North American mills use electric arc furnace technology, which relies on recycled scrap metal as the feedstock. A majority of the recycling scrap comes from post-consumer scrap such as automobiles and appliances, with the remainder coming from pre-consumer scrap such as manufacturing and construction waste.
Mini MillThe mini mill steel production process with Charlotte, N.C.-based Nucor Steel begins in the scrap yard; Nucor uses 75 to 90 percent scrap steel as its raw material. The scrap then goes into a charge bucket. Each heat, or batch, can be custom-made so the composition can vary from bucket to bucket. Bucket contents then are dropped into an electric arc furnace, where it takes two charges to make a heat of up to 170 tons of molten steel. After the furnace is covered, electrodes are lowered through the top and electricity arcs to the steel. The electric charge is anywhere from 130 to 170 megawatts. Within 45 minutes, the scrap steel becomes molten steel at approximately 3,000 F.
Molten steel then is tapped through the bottom of the furnace into a ladle where it is processed at the ladle metallurgy furnace. There, the exact chemistry and temperature are achieved by adding and trimming alloying elements. Nucor also can deoxidize, desulfurize and modify inclusions. Alloys are added in bulk or wire form. The temperature is adjusted with a set of electrodes similar to those at the electric furnace. An electromagnetic stirring process and argon gas mix the additions and remove inclusions.
From the ladle it enters the tundish, which is like a funnel that helps prevent splashing, gives a smoother flow and helps precisely regulate the flow of metal to be cast in the mold. From there, it’s put it through the submerged entry nozzle, which delivers the steel beneath a layer of mold powder, protecting it from re-oxidation, regulating heat transfer and lubricating the slab mold interface. The cast slab thickness at an integrated steel maker is between 8 and 12 inches; mini mills cast between 2 and 3 inches, which helps reduce costs, increase productivity and make American steel manufacturers globally competitive. After this, it goes through a water spray chamber then through the tunnel furnace, ending up in the hot-strip mill where the steel is rolled to customer gauge or pre-cold rolled thicknesses.
Processes have become more efficient throughout the years. According to the Pittsburgh-based American Iron and Steel Institute’s Web site, the North American steel industry has reduced its energy intensity by 60 percent since World War II. It also has achieved a 90 percent reduction in the discharge and air and water emissions versus only 10 years ago.
Technological AdvancementsChris Moor, industry mobilization director with the Chicago-based American Institute of Steel Construction, has been involved with the steel industry for the past 26 years. He started out in England on the shop floor as a welder and also has been a steel worker, project manager and detailer. Moor also worked in the software world and worked for a long time with building information modeling software.
Throughout the years, Moor has seen a significant shift in automation and detailing. “At one point I was a detailer and we produced drawings of each individual steel piece with a pencil and paper,” he recalls. “I then got into the software world where you started producing those drawings with a computer. That grew into BIM. The automation the steel industry has taken from that is tremendous, from producing drawings automatically, building 3-D models of the whole structure before the pieces are made and downloading all that information to the shop floor so it’s automatically punched, drilled out and cut to length.
“Is it easier now? Yes. It’s easier, quicker and much more efficient. And it’s getting better all the time. We still need experienced people to use these advanced tools, though. We rely on people who understand the business and who understand the impact of what they are entering into the computer. There was a time when we didn’t have calculators to do equations for us so maybe people understood what they were doing a bit better,” he explains. “Sometimes things go into a little black box and they come out on the other end and look great, but what happened in that black box?”
Looking AheadMoor predicts the steel industry will continue its advancement. “I was in a fabricator shop just a few weeks ago and I saw a robotic welder,” he says. “What needs to be recognized, however, is that technology is just a tool. Processes will have to change to make better use of those tools.”
Fabricators today, however, are working mostly off backlogs. “Our industry is at the back end of any recovery,” asserts Moor. “Having said that, we’re at the back end of any downslide as well.” When the architect receives a job, he designs it then passes it down to the engineer who continually passes the job down the flow; the fabricator doesn’t get the job until perhaps nine months to one year after the architect does. “It’s a ripple effect,” says Moor. “It’s good on the way down but not so good on the way up.”
Moor sums the current economic climate. “The time to start marketing isn’t when the market is great,” he says. “The time to start marketing is when the market is down because that’s the only time you can win market share. When things are great and you’re selling every week, well guess what, every other company is selling a lot too and no one gains any market share. The only time you can gain market share is when the market slows down. You don’t necessarily gain market share then, but you prepare yourself to gain market share in the future.”