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How is Steel Manufactured? | The Process Explained

Steel Columns and beams of 1 World Trade Center
Steel Columns and beams of 1 World Trade Center Under Construction. Photo: SS

Walk down any city construction site and you’re bound to see a network of steel beams and columns rising from the ground. Why are they using steel? Because steel is strong, durable, and easy to work with, making it the iron alloy of choice for building construction. 

If you’re wondering how steel is manufactured, wonder no more! In this blog post, we’ll explain the process from start to finish. 

History of Steel

The emergence of steel as the foremost material for construction can be traced back to the Iron Age, when it is was used to make swords and other materials. 

With the advent of the railroad construction boom in the 19th century, and it’s subsequent requirement for this resource to make the tracks was proving to be an issue, due to the fact that there wasn’t any automatic production process to fill the need.

The  Initial Making of Steel

Steel does not grow out of thin air. It begins with the mining of iron ore, which then has to be combined with the element carbon via a blast furnace. Let’s get more involved understanding how this process works.

Mining the Iron Mineral

It all begins with the mining of iron ore. An ore represents a mineral where a valuable asset can be extracted.

Once it is taken out from the quarry, the ore is melted and purified  (removing impurities from the ore and leaving only the metal). This is done in a blast furnace.

Enter Carbon

Carbon is an element in the Periodic Table that has an atomic number of six, with four electrons in its outer shell and two electrons in its inner shell.

Atoms that have less than eight electrons in its outer shell, (called the valence shell) tend to look for other atoms to bond with, so that their valence shells can stabilize the atom by balancing the shell to eight electrons. This is based on the Octet Rule.

Iron has eight electrons in its valence shell, so if you bond the carbon atom that has six valence elections with the iron atom, you have a molecule of two different atoms which forms steel.

It is essential to ensure that the correct amount of carbon is used with iron, approximately 0.04%, so that the resultant product is that of steel. If the wrong amount of carbon is mixed with iron, a different product will be produced such as cast iron or wrought iron – both of these are not efficient products to render steel.

When is Carbon Added to Iron?

For steel, this combination of the two elements is done while the iron metal is liquid hot, which then alters the iron’s properties to change to that of steel.

Steel subsequently becomes an alloy (a metal made by combining two or more metallic elements) of iron and carbon.  This causes a distortion of the crystalline lattice structure of iron and subsequently enhances the metal’s strength; specifically, it increases the metal’s tension and compression properties. 

The Manufacturing Process

Steel Cantilever at Chase Bank Headquarters
Steel Cantilever at Chase Bank Headquarters Under Construction. Photo: SS

A breakthrough for manufacturing steel via an automated process materialized in 1856 when Henry Bessemer found a way to  manufacture steel quickly. Bessemer’s steel production process is what inspired the Industrial Revolution

It was the first cost-efficient industrial process for the large scale production of steel from molten pig iron, by taking out impurities from pig iron using an air blast. 

Adding Carbon Produces a Variety of Iron Alloys

As previously mentioned, when mixed with carbon, the iron’s characteristic will be changed, allowing a variety of different types of metal alloys to be created. It all depends upon the amount of carbon that is added to it. Let’s take a look.

Wrought Iron

Wrought iron is softer than cast iron and contains less than 0.1 percent carbon and 1 or 2 percent slag. It was an advancement over bronze and began to replace bronze in Asia Minor by the 2nd century BC. Because iron was far more plentiful as a natural resource, wrought iron was used for a wide variety of implements as well as weapons and armor. 

Cast Iron

Cast iron is an alloy of iron that contains 2 to 4 percent carbon, along with smaller amounts of other elements, such as silicon, manganese and minor traces of sulfur and phosphorus. These minerals are non metallic and are referenced in the industry as slag. Cast iron can be easily molded into a desired shape, known as casting. and has been used to make decorative fences and other aesthetic forms.

Cast iron facades were invented in America in the mid-1800s and were produced quickly, requiring much less time and resources than stone or brick. They were also very efficient for decorative purposes, as the same molds were used for many buildings and a broken piece could be quickly remolded. Because iron is powerful, large windows were utilized, allowing a lot of light into buildings and high ceilings that required only columns for support.

Steel



Steel is an alloy made from iron that usually contains several tenths of a percent of carbon, which increases its strength and durability over the other forms of iron, especially in tensile strength.

Strictly speaking, steel is just another kind of iron alloy, but has much lower carbon than cast iron, and about as much carbon (or sometimes slightly more) than working iron, with other metals frequently added to give it additional properties. 

Most of the steel produced today is called carbon steel, or simple carbon, although it can contain metals other than iron and carbon, like silicon and manganese. 

Summary

The advantages of steel are numerous, from great tensile and compression strength to speed of manufacturing to low cost, it is the metal of choice in construction when compared to iron.

 Although iron and steel appear to be similar, they are two distinct materials that have their own specific characteristics and qualities. Iron is a pure mineral and steel is an alloy material that contains a percentage of carbon.  Depending on the amount of carbon mixed with iron, different products emerge, and this includes the creation of steel. 

Steel is far stronger material and there is no better metal at this time that is used when strength and cost are major factors.

 

What is Iron?

What is Iron?

Iron ore in rock form
iron ore on a rocky base

Did you know that iron is a healthy nutrient for our bodies as well as the main ingredient in the manufacture of steel?

Before we venture into the types of iron, let’s first examine its properties. Iron is a mineral with the symbol Fe and atomic number 26.

On the periodic table, it belongs to the first transition series, which reflects a change in the inner layer of electrons, but we’ll leave that for the chemists since the chemical compound of this mineral is beyond the scope of this article.

Iron is the most common element on Earth when referenced by mass and is very prominently found in the Earth’s outer and inner cores. It is the fourth most common element in the Earth’s crust, but the process to extract it requires kilns or furnaces capable of reaching a temperature of 2,730 °F or higher.

A Little Bit of Iron History

Bronz Statue
Bronze Statue
Wikipedia_Public Domain

The Bronze Age (c. 3300–1200 BC) is characterized by the use of bronze as the metal of choice to create art, tools, and weapons. It was the first time metals were used for these purposes. Prior to this period, stone was used as a tool and for weapons; hence, the Stone Age.

Interestingly enough, the Bronze Age also brought us the first writing system and the invention of the wheel. An intriguing period of creative thought for sure.

Enter Iron

Say goodbye to bronze and hello to iron; hence, the Iron Age, which started around 1200 BC. It should be noted that before the Iron Age was coined, there were occasions when iron was found to be used much earlier.

One historical account was that of the ancient Egyptians. Archeologists found iron beads made from meteorites dating back to 3200 B.C.  Iron is abundant in outer space. But these incidences were rare until the time when iron became the metal of choice.

Iron for Infrastructure

Steel Columns and beams of 1 World Trade Center
Steel  (an alloy of iron) columns and beams of 1 World Trade Center Under Construction. Photo: SS

Once we entered the 19th century, new uses for iron materialized. It was discovered that this mineral, when mixed with carbon, can be used for building purposes, and with the advent of the industrial revolution, where items were being mass-produced, the manufacture of iron became an economical commodity. 

Building Construction

Iron in its pure form is not used for building construction since it would not have the tensile or compressive strength required for infrastructure, but when other elements are added to it, such as carbon, it can become a desirable metal for constructing bridges and buildings, since its tensile and compression strengths are bolstered. Let’s take a look at iron alloys.

Cast Iron

Cast iron has 2 to 4% of carbon mixed in with it along with some small amounts of impurities, such as sulfur and phosphorus. This alloy has an advantage as it is simple to cast (mold). Therefore, cast iron is an excellent choice for decorative ironwork on structures like fencing and benches.  

A good example of the use of cast iron can be found in the SoHo and nearby areas of New York City. There are about 250 cast iron buildings located there. The initial purpose of cast iron facades was to improve older buildings, but they were eventually used in newer construction as well. 

Cast iron fence. Palermo Italy
Cast iron fence. Palermo Italy. Photo SS
Cast Iron’s Disadvantage

Because of iron’s brittleness (subject to fractures under stress) and relatively low tensile (ability to stretch) strength, cast iron is not a suitable material for products that require a high degree of tension or bending moments.

Cast Iron’s Advantage
Cast iron buildings NYC
Cast iron buildings, Lower Manhattan. Photo: SS

Although tension is not a good quality of cast iron, it does have acceptable compressive strength (ability to sustain heavy loads) and it is also durable (ability to withstand wear).

Construction of bridges and buildings using cast iron was very popular in the late 19th and early 20th centuries. In fact, there is a whole section in New York City that is called the Cast Iron District, also known as SOHO.

Later in the mid-20th century and on to today’s building construction techniques, cast iron gave way to steel because of the fact that steel has high tension capabilities as well as high compression.

Wrought Iron 

Wrought iron is not an iron alloy. It is made entirely of iron with no  carbon additions. Wrought iron is malleable, ductile, and corrosion-resistant

This metal is different from cast iron and because of its malleability. it was given the name wrought since it could be hammered into shape while it remained hot. Wrought iron is a prerequisite to mild steel, also called low-carbon steel, and is considered the first of the steel alloys.

As a matter of fact, wrought iron was initially refined into steel. In the 1860s, ironclad warships and railways were built with these iron alloys.

Wrought iron was eventually halted to make way for the less expensive and stronger steel, as steel’s advantage over wrought iron and cast iron is its ability to absorb shocks without breaking.

Steel

Steel Cantilever at Chase Bank Headquarters
Steel Cantilever at Chase Bank Headquarters Under Construction. Photo: SS

Steel is an iron alloy that contains a low amount of carbon, roughly 0.40%; however, that is enough to change iron’s characteristics, and with the advent of the Bessemer process, making steel became less costly to create. 

Steel has good tension and compression factors, as well as being impact resistant. Steel is so strong that it is used to cantilever skyscrapers. This is why you see so many buildings under construction today that have steel as their framework.

Iron for Nutrition

Red Blood Cells
“Red blood cells” by rpongsaj is licensed under CC BY 2.0

Since iron is a mineral, it is also an important nutrient for our bodies. If you have an iron deficiency, you may possibly acquire anemia and also fatigue.

So how much iron do you need on a daily basis? For most people, an adequate amount of iron is consumed daily via the foods that we eat, but to determine your specific iron needs, you can see a chart and information here. One person told us that he eats yogurt and raisins every day. Raisins contain a certain amount of iron. 

Do you know why our blood is red?  It is because there is an interaction between iron and oxygen within the blood creating a red color. Learn more about red blood cells and iron here.

To be sure you have enough iron in your body, check with your doctor to confirm you are not deficient.

Conclusion

Besides being an essential component for healthy blood in our bodies, iron became an essential component for weapons and later, building materials.

Numerous bridges and buildings have been constructed during the 18th, 19th, and 20th centuries using iron, but as the industrial revolution advanced and the making of materials became automated, new alloys of iron were created, specifically, steel and along with concrete, led to the construction of stronger buildings, bridges, and skyscrapers we see today all over the world.