Since the beginning of human civilization, steel has been the most widely used metal. It’s inexpensive, durable, and highly versatile.
Steel is a sustainable material since it is 100 percent recyclable and uses very little energy to produce. Now, to address the elephant in the room, does steel rust?
Yes, steel rusts, but not all of it. There are various kinds of steel. For rusting to take place, three factors are necessary. Iron, followed by water and oxygen, its scientific name is iron oxide, and it has an orange-brown color, sometimes green. Steel is a mixture of Iron and Carbon.
So, what exactly is steel? Why do some of them rust while others don’t? These and other questions make for an interesting topic. Let’s look into them.
What Is Steel?
Steel is a purified form of iron mixed mainly with carbon. The amount of carbon can vary from 0.02% to 2%. Depending on the type of steel, iron can also be mixed with other elements such as silicon, phosphorus, sulfur, and oxygen.
The primary difference between iron and steel is that the former is metal. In contrast, the latter is an alloy—precisely, an iron alloy, a mixture of iron (main element), carbon, and others (sub-elements). Alloys are helpful because they have different properties than the original metal.
A strong molecular structure forms when carbon interacts with iron. The resulting lattice microstructure aids in the achievement of specific qualities such as tensile strength, flexibility, and hardness.
A pure metal has a massive metallic structure in its solid-state. Layers of atoms are organized. The layers may slide over each other if a force is applied. Conversely, the atoms are different sizes in an iron alloy (steel).
The size of carbon atoms is less than that of iron atoms. They are found in the interstitial regions of the iron crystal lattice. These are the spaces that exist between the iron atoms.
However, the carbon atoms do not fit together perfectly, causing the iron crystal’s lattice to be distorted. And this distortion makes it stronger in many ways.
Production of Steel
By now, we know that sprinkling other elements onto iron gives us steel. But how do we go from excavating metals to producing the globally used finished product?
The journey begins with a blast. Impure iron ore is extracted from the earth. It is then transported onto the raw materials dock and into the blast furnace. Limestone and various types of coal are added. The carbon mostly comes from coal.
The blast furnace’s molten iron is loaded into a torpedo vehicle and dumped into a converter furnace. At this stage, the liquid iron has 4% to 4.2% carbon and other impurities. But it’s not steel yet.
Oxygen is added to the molten iron in the converter furnace. It helps with two things.
Firstly, it removes the impurities from the molten iron. Secondly, it reduces the carbon content from approximately ±4% to ± 2%. And now we have steel.
Fun fact: Oxygen is blown in the furnace at approximately three times the speed of sound!
Other elements, such as chromium, manganese, nickel, etc., are added according to need. The temperature is adjusted inside the furnace. The molten steel is poured into different molds for various shapes.
The process described above uses a blast furnace to produce steel. But there is another way, using electric arc furnaces (EAF). This process is more or less the same, except that it uses a large amount of electricity and electrodes.
Note: We can use recycled materials to make steel besides iron ores. They are a common source of iron for steel production. Making steel with recycled material uses EAF.
4 Common Types of Steel
Because steel is a metal alloy made of iron and carbon, there can be numerous types of steel depending on the ratio of the mixture.
We determine steel grade by checking the composition amount of iron and carbon and other elements like nickel, magnesium, molybdenum, silicon, etc.
Reportedly, there are 3500 different varieties of steel. The following paragraphs will look at four common types of steel.
1. Alloy Steel
Alloy steels consist of alloying elements like chromium, manganese, nickel, tungsten, etc. Different alloying elements introduce different properties to the steel. Due to this, alloy steel is highly customizable.
There are two types of alloy steel:
• Low alloy steel – Contains less than 10% alloying elements.
• High alloy steel – Contains less than 10% alloying elements.
The following are the most commonly used alloy steels.
• Tungsten Steel – Heat resistant. Improved grain structure.
• Nickel Steel – Tough. Corrosion-resistant.
• Vanadium Steel – High shock and vibration resistant.
• Silicon Steel -Induces magnetic properties.
• Aluminium Steel – Low density. High strength.
2. Stainless Steel
Stainless steel is the most popular type of steel due to its shiny appearance and extensive use. Previously known as ‘rustless steel.’
Due to its high chromium content and mixture of other metals, stainless steel is highly non-corrosive. One everyday use is in kitchen sinks.
There are mainly four different types of stainless steel. They are austenitic, ferritic, martensitic, and duplex stainless steel. They vary due to their crystalline structure and composition.
You must also read the article on does stainless steel rust.
3. Carbon Steel
Carbon steel accounts for 90% of total steel production. Carbon steel’s most common use is in the construction industry, to build infrastructure.
The three main types are low, medium, and high carbon steels, all based on their carbon content. The greater the amount of carbon, the harder the alloy.
• Low Carbon Steel – Contains 0.04% to 0.30% carbon content.
• Medium Carbon Steel – Has a carbon range of 0.31% to 0.60% and manganese ranging from 0.60% to 1.65%.
• High Carbon Steel: Carbon range between 0.61% and 1.50%.
4. Tool Steel
Tool steels, as the name suggests, are used for tool manufacturing. They’re abrasion-resistant and are customarily used in high-impact environments.
Molybdenum, vanadium, tungsten, and cobalt are common alloying elements in tool steels, making them heat resistant, durable, and robust.
Six types of tool steel grades are widely used in industry.
• Air-hardening tool steels
• High Speed
• Shock-resisting types
Why and How Steel Rusts?
Material made of iron is rust-prone when exposed to oxygen and water. Since steel is mostly iron, it is subject to rust. But why does steel rust?
Before that, we must know what oxidation is. Oxidation is the process by which an element gains oxygen. The element that gains oxygen is said to be oxidized.
Rusting is an oxidation reaction where iron gains oxygen in the presence of water. The simplified chemical reaction is –
iron + water + oxygen → hydrated iron (III) oxide (rust).
4Fe +2xH2O + 3O2 → 2Fe2O3.xH2O
But why would iron react with water and air? Elements tend to have eight electrons in their outer shell for their stability. Most of them don’t have eight, so they mutually share them with other elements.
To illustrate, water consists of one oxygen and two hydrogen atoms. An oxygen atom has six outer electrons in its outer shell, while hydrogen atoms have one electron.
The two hydrogen atoms provide two electrons. Therefore, oxygen and hydrogen combine, filling their outer shells (6+2=8).
Similarly, iron has two electrons in its outer shell. Thus, it tends to have a full outer shell. Therefore, reacting together, they form FeO (OH), the most common form of rust.
Rusting of steel is a chemical change. The bond between iron and carbon atoms weakens over time. It is important to note that the change is not rapid.
Must Read: Is Rusting of Iron a Chemical Change
Steel can be severely corroded by rust. It can thin steel to the point where it is no longer appropriate for its intended use.
Excessive corrosion can lead to the collapse of structures and the burst of pipelines. Rust can also detract from the steel’s aesthetics.
How To Prevent Steel from Rusting?
Rust is a familiar issue. However, there are ways to avoid it.
Rusting is essentially prevented by preventing moisture from coming into contact with the metal. Let’s have a look at some options for doing so.
Painting creates a protective layer over metal objects and prevents moisture from reaching them. Before painting, degrease the surface with sandpaper or any other cleaner.
Make sure to paint multiple times and in narrow areas too. Any gap will allow air and water to come into contact, eventually corroding the whole thing.
Oil lubricates steel parts, allowing them to move with less friction and forming a rust-resistant barrier. Because oil and water are not miscible, they do not mix.
Applying a layer of oil to steel creates a barrier that prevents water or humidity from getting to the material, preventing rust.
Galvanizing is the process of coating steel with a protective zinc layer. Zinc corrodes thirty times slower than iron.
The zinc coating prevents corrosive substances from penetrating further into the metal. Galvanized steel, along with stainless steel, is rust-free.
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Rusting is a very troublesome issue when working with steel. But if you know the proper preventive measures or just use the right types of steel, it can be easily managed. By now you should know does steel rust, how it can be prevented and what types of steel are rust-free.
I hope this article came to your aid and thanks for stopping by.