Everyone knows that steel is made from iron ore, but how is it made? Do you know it? If not, this guide is for you, where you will learn how iron can be converted into shiny stainless steel. Two processes of converting iron ore into steel are discussed here.
The World Steel Association reckons we churned out a whopping 1,869.9 million tonnes of steel in 2019. That's a tidy 3.4% jump from 2018 and more than double what we managed back in 1999. Blimey, the world just can't get enough of the stuff! From building bridges to brewing beer kegs, steel's everywhere you look. Strong, cheap, and versatile, it's the backbone of all sorts of manufacturing.
What is steel made of?
Iron, the star ingredient of steel, is as common as muck on Earth. All steel alloys are essentially iron with a sprinkle of carbon, between 0.002% and 2.1% by weight. This magical mix bonds the iron atoms together, creating a lattice structure that gives steel its incredible strength and hardness.
Now, while "iron + carbon" is the basic formula, different types of steel have different ratios. We can also throw in other elements like nickel, molybdenum, or even a dash of vanadium, each of which gives the steel its own special talent. And just like baking a cake, how we make and treat the steel plays a part in its final properties.
One particularly flashy group of steel alloys are the ones with chromium – stainless steel, that's the one. Doesn't rust, shines like a polished shilling, and tough as nails to boot.
How to make steel
At its core, making steel is all about mixing iron and carbon at temperatures hot enough to melt a dragon's beard (over 2600°F).
First up, we get our hands on some "pig iron" – basically, iron smelted from ore, but with a bit too much carbon for our liking. So, we bubble oxygen through the molten metal, giving it a good stir and evening out the carbon content. This also burns off any unwanted nasties like silicon and phosphorus.
Next comes the "in-the-ladle" trickery. We can melt down scrap steel or pick up where the pig iron left off. This is where we add extra elements for fancy alloys or skim off any impurities floating on top. Then, it's all about heating and cooling the ladle like a well-seasoned chef to get the chemical reactions just right.
And voila! Out comes the steel, ready to be shaped, bent, and hammered into all sorts of wonderful things.
Finishing steel
When steel leaves the fiery belly of a foundry or mill, it's not quite ready to strut its stuff in the big wide world. Before it graces bridges, cars, or cutlery, it needs a bit of finishing.
In the foundry, molten steel takes shape in sand or investment casts, forming intricate patterns. The steel mill, on the other hand, uses a continuous caster to churn out raw building blocks like sheets, billets, bars, and blooms. Think of them as the Lego bricks of the steel world, ready to be assembled into something grand.
The mill might then give our steel a workout with hot-rolling or cold-rolling processes, each shaping and smoothing it differently. Imagine it like a rolling pin for metal, squeezing and stretching it into the desired form.
Before shipping out, the steel gets prepped for its journey. Some get sliced into manageable lengths, others coiled up like a metal python, and some bundled together for strength.
Both foundry and mill might give the steel a good heat treatment, like a spa day for fiery alloys. Processes like quenching, tempering, normalizing, and annealing change the way the steel behaves, making it tough for bridges, flexible for car springs, or anything in between.
Invention of steel
Steel's been around for a while, with archaeologists unearthing evidence of its presence in Turkey 4,000 years ago. Back then, making steel was a right old palaver. Imagine tending a furnace hot enough to melt rocks, battling impurities, and spending hours coaxing the metal into shape. It was a laborious dance with fire and hammer.
Bessemer's Breakthrough:
Then came Henry Bessemer in 1856, a true metal maestro. He invented the Bessemer converter, a magical contraption that bubbled air through molten steel, burning away impurities and keeping the heat cranked up. What used to take days now took a mere 20 minutes, and out popped five tons of strong, high-quality steel. Bessemer's brainchild fueled the Industrial Revolution, showing the world the ironclad potential of this versatile metal.
Is steel magnetic?
Most steel exhibits magnetic properties, although not all types do. Since steel is primarily composed of iron, and iron is inherently magnetic, the magnetic characteristic is common. The discovery of ferromagnetism was initially observed in lodestones, which consist of magnetite, an iron oxide. Other elements like cobalt and nickel also display ferromagnetic properties and are occasionally present in steel.
Stainless steel, known for its non-magnetic properties, contains iron, with many types also containing nickel. However, not all stainless alloys are non-magnetic. Austenitic stainless steel, comprising nickel, is typically non-magnetic (though it may exhibit very slight magnetism when worked). Conversely, ferritic or martensitic alloys, also stainless, can be magnetic.
Properties of steel
Steel's widespread usage is owed to its specific material traits combined with its relatively affordable cost. Compared to various building and tool-making materials like wood, stone, concrete, or cast iron, steel alloys offer:
- Hardness: Resisting indentation under increasing pressure
- Toughness: Describing how much deformation a material can endure before fracturing
- Yield strength: Resistance to shape change under gradual pressure
- Tensile strength: Ability to withstand pulling forces before breaking
- Malleability: Capacity to be shaped by hammering or pressing without breaking
- Ductility: Ability to be shaped without losing toughness, even through working processes that might otherwise make it more brittle
Although the specific range of these properties differs among alloys, steel overall tends to be harder and less brittle than many other materials, making it both resilient and durable.
Types of steel
There are four primary classifications of steel alloys: carbon, tool, alloy, and stainless steels.
- Carbon Steel—Mild, medium, and high carbon steels differ mainly in hardness and ductility. Mild or low carbon steels tend to be more ductile but offer lower hardness. Conversely, high carbon steels are harder but usually have lower ductility.
- Tool Steel—High carbon steel with additional elements like tungsten, vanadium, or molybdenum, heat-treated and quenched, achieves superior hardness, ideal for tool steels.
- Alloy Steel—This category denotes steels blended with specific elements for exceptional material properties, beyond those common in other groups. While all steels are alloys, alloy steels are distinct, designed for specific applications, varying from standard formulations to exotic alloys for purposes like jet engines.
- Stainless Steel—These steels are alloyed with chromium for rust resistance via passivation.
Steel production: a story of recycling
One of steel’s notable attributes (and that of other metals) lies in the fact that scrap can be transformed into entirely new, high-quality metal. Secondary steelmaking generates alloys as excellent as those from pig iron. While metal items may degrade from use, their elemental composition allows for complete transformation through melting and alloying.
Growth in steelmaking output doesn’t necessarily rely on increased ore smelting. Reclaiming and processing scrap steel means yesterday’s car panel can become tomorrow’s I-beam.
With 98% recyclability, steel ranks among the world’s most reusable materials. However, environmental challenges persist. Coke, a coal derivative, is the typical carbon input for steelmaking. Moreover, the substantial energy required for melting or smelting, along with oxidation in production, generates chemicals and carbon dioxide. Thankfully, ongoing research in the steelmaking sector aims to address these issues. Solutions include recycling carbon dioxide back into steel, reducing reliance on sources like coke.
As these technologies evolve and are adopted, steelmaking will remain a key industry of the future, forming the foundation of our economy.
