What is iron? What is steel? And how they are produced.
Hey Engineering Lovers, my name is Gustavo Pereira and have you ever wondered how people refine iron and steel? You've probably heard of iron ore, but how do we turn a mound of earth into a set of stainless steel surgical instruments or a locomotive? If you had to name the technologies that have had the greatest effect on modern society, refining the heavy metal element iron would have to be near the top.
Iron makes up a huge variety of modern products. Especially carbon-rich commercial iron, which we call steel. Cars, tractors, bridges, trains, tools, skyscrapers, weapons and many other items rely on iron and steel to make them strong.
Iron is so important that primitive societies are measured by the extent to which they learn to refine it. This is where the classification "Iron Age" comes from. Iron is an incredibly useful substance, extremely strong, and at the same time malleable.
If properly heated, iron is also relatively easy to shape into various shapes, as well as refine, using simple tools. And speaking of these tools, unlike wood, iron can withstand high temperatures without combusting, being useful for services that need to work with high temperatures. Unlike most substances, you can also magnetize iron, making it useful in creating electric motors and generators.
Finally, there is certainly no iron shortage to worry about. The earth's crust has 5% iron and, in some areas, the element is concentrated in ores that contain up to 70% iron. Iron is very important to human history as it can be created relatively easily with tools that were available in primitive societies.
There will likely come a day when humans become so technologically advanced that iron will be completely replaced by aluminum, plastics, and things like carbon and fiberglass. But now, the economic equation gives cheap iron and steel a huge advantage over these much more expensive alternatives. Humans have invented countless uses for iron, from carpentry tools and cooking equipment to complicated machines and spaceships.
But before iron can be used for any of these uses, it needs to be extracted from the ground. Before many ancient civilizations began making the transition from the Bronze Age to the Iron Age, some toolmakers were already creating iron implements from a cosmic source: meteorites. Called "black copper" by the Egyptians, meteoric iron is not the kind of substance found in massive, consolidated sites.
Instead, craftsmen found pieces of it scattered over vast distances. Most of Earth's iron, however, exists in iron ore. Mined directly from the ground, raw ore is a mixture of proprietary ore and loose earth.
The ore itself can usually be separated by crushing the raw ore and simply washing away the lighter soil. Decomposing the ore itself is more difficult, however, as it is a chemical compound of carbonates, hydrates, oxides, silicates, sulfides, and various impurities. To get to the pieces of iron in the ore, you have to smelt it.
Smelting involves heating the ore until the metal becomes spongy and the chemical compounds in the ore begin to break down. More importantly, it releases oxygen from the iron ore, which makes up a high percentage of common iron ores. The most primitive facility used to smelt iron is a forge.
There, a blacksmith burns coal with iron ore and a good supply of oxygen that was provided by a bellows or blower. Coal is essentially pure carbon. Carbon combines with oxygen to create carbon dioxide and carbon monoxide, which releases a lot of heat in the process.
The carbon and carbon monoxide combine with the oxygen in the iron ore and carry it away, leaving the iron metal. In a forge, the fire is not hot enough to completely melt the iron. Instead, the iron heats up into a spongy mass containing iron and silicates from the ore.
Heating and hammering this mass forces the impurities out and mixes the glassy silicates into the iron metal to create wrought iron. Wrought iron is tough and easy to work with, making it perfect for crafting tools. Tool and weapon makers learned to smelt copper long before iron became the dominant metal.
Archaeological evidence suggests that blacksmiths in the Middle East were smelting iron as early as 2500 BC, although it was over a thousand years before iron became the dominant metal in the region. To create higher grades of iron, blacksmiths would need better furnaces. Technology has developed gradually over the centuries.
In the mid-1300s, taller furnaces and hand-operated bellows allowed European furnaces to burn hot enough to not only soften iron, but melt it. Today, the most advanced way to smelt iron is in a blast furnace. A blast furnace is charged with iron ore, charcoal or coke and limestone.
Large amounts of air blow across the bottom of the kiln, and the calcium in the limestone combines with the silicates to form slag. Liquid iron accumulates at the bottom of the blast furnace, under a layer of slag. The blacksmith periodically lets the liquid iron flow and cool.
At this point, liquid iron normally flows through a channel or mold made of sand. Once it cools, this metal is known as pig iron. The basic recipe to create a ton of pig iron, you would need 2 tons of ore, 1 ton of coke and half a ton of limestone.
The temperature in the center of the blast furnace can reach around 1,600 degrees Celsius. This pig iron contains 4 to 5 percent carbon and is so hard and brittle that it is almost useless. If you want to do anything with it, you have three options.
First, you can melt it down, mix it with slag, and hammer it to remove most of the carbon and create strong, malleable wrought iron. The second option is to melt pig iron and combine it with scrap metal, melt impurities and add alloys to form cast iron. This metal contains 2 to 4 percent carbon, along with amounts of silicon, manganese, and trace impurities.
Cast iron, as the name implies, is typically cast in molds to form a wide variety of parts and products. The third option for pig iron is to take the refining process even further and create steel. Steel is the iron that has the most impurities removed.
Steel also has a consistent carbon concentration of 0. 5 to 1. 5 percent.
Impurities such as silica, phosphorus and sulfur weaken steel tremendously, so they must be eliminated. The advantage of steel over iron is strength. The open-pit furnace is a way to create steel from pig iron.
The pig iron, limestone and iron ore go to an open-air furnace. It is heated to about 871 degrees C. The limestone and ore form a slag that floats on the surface.
Impurities, including carbon, are oxidized and float from the iron to the dross. When the carbon content is correct, you have carbon steel. A variety of metals can be alloyed with the steel at this point to create different properties.
For example, adding 10 to 30 percent chromium creates stainless steel, which is very resistant to rust. The addition of chromium and molybdenum creates chromium-molybdenum steel, which is both strong and light. And you, can you think of your life today without steel?
Have you noticed the amount of items in our daily lives that take this material? Leave it here in the comments and I want to know. I'm going to leave two videos on the side that you might also like and that complement the subject, so be sure to check them out.
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