Steel is an essential material used across a wide range of industries. If you are in construction, manufacturing, automotive, aerospace, and more, you will require steel. As such, learning how steel is made will help you decide which steel products are best suited to your needs. In this article, we will explore everything else you need to know about steel manufacturing.
How Steel is Made: The Ironmaking Process
Did you know that steel is an alloy of iron and carbon? This is why the ironmaking process is a crucial step. Manufacturers start by obtaining raw iron from iron ores. This is done through either;
- Direct reduction or
- Blast furnaces processes.
The end products of these processes are sponge iron and pig iron, respectively.
Comparison of Direct Reduction and Blast Furnace Iron Extraction Methods
|Direct Reduction||Blast Furnace|
|Raw Material||Iron Ore Pellets or Lump Ore||Iron Ore and Coke|
|Fuel||Natural Gas or Coal||Coke|
|Purity of Iron Produced||Up to 95%||Up to 90%|
|Temperature||800 – 1200 °C||1500 – 2000 °C|
|Scale||Small to Medium||Large|
Blast furnace iron extraction method
The blast furnace is the oldest iron extraction method. You will find that most iron manufacturers use this method for large-scale iron production. Blast furnaces involve a series of steps to acquire pig iron.
To start with, iron ore, coke, and limestone are layered in a furnace and heated with hot air for several hours.
During this heating stage, the coke forms carbon dioxide with the hot air. This gas then reacts with the iron ore to remove oxygen and leave behind iron. Limestone on the other hand facilitates the removal of impurities from iron. The process ends with pig iron settling at the bottom of the furnace.
Direct reduction iron extraction method
Unlike blast furnaces, direct reduction is a modern iron extraction method. Most manufacturers prefer it to blast furnaces due to its low-energy consumption and negligible carbon footprint. As you will see, it happens in a series of steps too.
Here are the steps in the process. It starts the removal of oxygen from iron ore. Crushed iron ore is added into a furnace which is heated within 800 – 1200 °C temperature ranges.
Consequently, this ore is subjected to the reducing gasses which remove the oxygen from the ore. Sponge iron forms at this point. The direct reduction method produces iron that is up to 95% pure. You already know that the higher the purity, the better the mechanical properties of steel.
How Steel is Made: The Steelmaking Process
After the iron is extracted, it now undergoes the steelmaking process. Sponge and pig iron have high concentrations of carbon and impurities. These elements need to be reduced to the desired amount to produce steel.
You might be curious why these elements, particularly carbon need to be reduced. Well, the carbon content regulation is done because too little of it makes steel weak while too much makes steel brittle.
The carbon left in the final product is what accounts for the durability, ductility, and strength of steel.
Two major processes are used to produce steel. These are;
- Basic oxygen furnace (BOF) and
- Electric arc furnace (EAF) processes.
While other methods exist, these two are the most widely used.
Basic Oxygen Furnace (BOF) Process
BOF is a refining procedure primarily used to convert pig iron to steel. It is a lengthy chemical reaction that occurs inside a vessel known as a BOF converter. This process is also known as the oxygen converter process or basic oxygen steelmaking.
For your information, pig iron has different grades that can be refined using the BOF converter. These include;
- Gray iron
- Ductile iron
- White iron
The BOF process occurs as follows. High-pressure oxygen is blown into the molten pig iron inside the BOF converter. As this oxygen combines with iron, the carbon present leads to the formation of CO2 gas. This exothermic reaction leads to temperature increases in the vessel. Coincidentally, these high temperatures are vital in the steelmaking process.
The high temperatures burn off excess carbon and other impurities. As this is happening, other elements, such as silicon and aluminum, are introduced into the vessel. Their purpose is to improve the final steel properties.
When this process is complete, molten steel is tapped from the vessel for sampling and quality assessment. This follows a secondary refining process in steelmaking where the steel is further purified and modified for your quality standards. Common secondary steelmaking techniques include degassing, decarburization, and desulfurization.
Electric Arc Furnace (EAF) Process
If you have ever wondered how used steel products are recycled, the answer is the EAF process. In other words, while the BOF process is used to primarily produce virgin steel, the EAF process is particularly used for turning scrap steel into new steel products.
However, feedstock in the EAF is not restricted to scrap steel. Other steel precursors such as sponge or pig iron can be used in this process.
Here is a look at how steel is made in the EAF process. First, is getting the feedstock, in this case, scrap. Scrap steel is obtained from one of three common sources：
- Obsolete scrap
- Industrial scrap
- Revert scrap
Firstly, scrap is loaded into the EAF furnace. This furnace contains electric arcs which heat and melt the scrap at high temperatures. Depending on the composition and grade of scrap, the melting temperatures reach between 1500 – 1550 °C.
Refining the melted steel scrap is the second step. This process is meant to adjust the chemical composition of the scrap and lower its impurities. Engineers carefully add refining agents such as fluorspar or lime into the molten metal.
You need to note that alloying is also done during the refining process. Elements such as nickel and manganese are added to the molten scrap to improve the steel properties of the final product. Remember, the EAF process produces specialty steel products.
The scrap or other steel predecessors have been turned into steel at this stage. What’s left now is to adjust temperatures in the furnace to aid further processing and casting.
Pros and Cons of the BOF and EAF Processes
Take a look at the following table showing the pros and cons of the BOF and EAF steelmaking processes.
How Steel is Made into Different Types of Steel
Understanding how different steel types are made will help you get valuable insights required when making important decisions. It will also help you communicate more effectively about your needs with your steel supplier. Here is a look at how different steel products are made.
How Stainless Steel is Made
Typically, you will find steel manufacturers using the EAF process to produce stainless steel, and for good reasons. This type of steel requires specific alloys such as iron, nickel, and chromium.
Stainless steel is made in two major steps, EAF and AOD. To start with, the scrap is melted in the EAF furnace. Refining the scrap occurs in the AOD, (argon-oxygen decarburization) process. Here, argon gas and oxygen are introduced to lower steel impurities such as carbon. Note that stainless steel has lower carbon content than regular steel.
Casting and surface finishing are the final steps in the stainless steel-making processes where manufacturers shape and treat the end products as needed.
How Galvanized Steel is Made
The galvanization process involves coating regular steel with a layer of zinc. If you are looking for a more corrosion-resistant steel product, consider galvanized steel. This is because this coating serves as a protective barrier against corrosion.
Let’s look at how this process works.
- Step 1: Cleaning the regular steel rod or bar in special solutions to remove grease or surface dirt.
- Step 2: The steel surface is prepped with a solution of zinc ammonium chloride, a process called fluxing. This helps the molten zinc wet the surface properly.
- Step 3: The steel is dipped in the molten zinc and allowed for the galvanization process to occur.
Some steel manufacturers perform a post-treatment to further enhance the protective barrier, but it’s an optional stage. This treatment could be necessary if you use steel in highly aggressive settings such as in the construction and automotive industries.
How Damascus Steel is Made
Damascus steel constitutes multiple sheets of different types of steel forged together. This type of steel requires intricate manufacturing. As such, you won’t find many companies producing it at an industrial scale.
The process of making Damascus Steel starts with selecting the types of steel to be forged together. Selection is made based on properties. Subsequently, they are heated together and pressed to form a billet.
Depending on the manufacturer and tools being used, the billet is folded, forged, and welded repeatedly. This process is what forms the characteristic layers as observed in Damascus steel products.
Finally, a process called acid etching ensues. This involves cleaning the steel and treating it with an acid solution to reveal the patterns formed by the layering of multiple sheets of steel.
How AR500 Steel is Made
If you require abrasion-resistant steel metals, AR500 could be your best bet. This includes the manufacture of armored equipment like vehicles and vests. Therefore, it undergoes specific processing to achieve the required strength and durability.
High-quality, low-alloy steel is used as the raw material in the AR500 steel production process. Its production involves special heating and cooling techniques.
A particular heat treatment procedure known as quenching and tempering is applied in the production of AR500. In simpler terms, this involves heating the alloy to a certain temperature, then rapidly cooling it with oil or water to harden it.
During the refining process in the EAF, the carbon content of steel is also not greatly reduced. This is because carbon counts for the hardness of AR500 steel.
FAQs about Steelmaking
Q: How is steel formed into products?
A: The method of forming steel into products depends on how the steel is intended to be used. Some of the common methods used include casting, rolling, and forging. If you are looking for steel sheets, the rolling method will be applied. Rolling is the most common method, especially for large-scale steel production.
Q: How are steel properties determined?
A: Two broad tests can be used to determine steel properties; mechanical and non-destructive tests. Mechanical tests are done to ascertain the physical properties of steel while non-destructive tests detect flaws in the structure of the finished product. Mechanical testing uses special test equipment while the latter uses ultrasonic and radiography testing
Q: What are some common applications of steel products?
A: The usage of steel is rather diverse and versatile. Whether you are a stainless steel kitchenware maker or a construction company, you will need steel products. Other industries where steel is used include marine, medical, aerospace, transportation, power, and much more. Steel has excellent properties that make it highly versatile.
This article provided you with an in-depth look at how steel is made. We have seen how it is produced from the main precursors which are iron-rich ores and recycled steel scrap. We have also explored how specific types of steel products are made. With this knowledge, you are a step closer to making the right choice when buying steel.
The intricate processes which are employed by manufacturers are meant to make the final product suitable for your needs. Steelmakers spend huge capital and manpower to ensure the production of high-quality and standard steel for your benefit.
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