Mild steel comes with some excellent properties as you can weld and bend it conveniently according to your requirements. Therefore, it has a wide range of applications across different industries.
Ease in machining and welding makes mild steel one of the most popular forms of steel available.
In this guide, we are going to break down EVERYTHING about mild steel in terms of:
- What is mild steel.
- How it’s made.
- What its types and grades are.
- What is mild steel’s chemical composition and properties.
- And what are its use cases and applications.
- How to deal with surface finishes of mild steel
So without further ado let’s get started.
What is Mild Steel?
Mild steel is a kind of steel that has low carbon content in it. Most of the carbon steels have a very small percentage of this element which goes up to 2.1%. Hence, this steel has more properties of iron in it.
Carbon content is going to vary immensely according to the requirements and application for which the steel is going to be used. Low carbon steels like mild or soft steel have a very low carbon content in them that ranges between 0.05% to 0.25%.
But there are different grades of mild steel as well and they all have a carbon content in them that ranges between 0.5% to 0.25% like we just mentioned. However, other elements are also added to improve various useful properties including wear resistivity, tensile strength, and corrosion resistivity.
And its surface hardness can be achieved through carburizing. It is a top choice for structural steel. It has a density of around 7.85 grams per cubic centimeter. For improving tensile strength more metal alloys are added to their composition.
It also improves the overall wear and corrosion resistivity as well. Alloying is primarily done with the use of silicon, molybdenum, chromium, copper, nickel, vanadium, and aluminum. Other impurities like sulfur and phosphorus are restricted in their proportions.
When you compare mild steel with higher carbon steel, it has higher tensile strength and it will not break. But it will deform or bend because there is not going to be any crystal deformation that occurs due to higher carbon content. Because of this, mild steel is highly useful in a variety of applications across different industries.
How Low Carbon Steel is Made
A uniform increase in the carbon content of steel can be achieved with the help of heat treatment. This treatment is a process that involves heating and then cooling metals. And there are various methods and techniques to achieve it. Non-ferrous and ferrous metals can both go through this treatment before they can be used.
With the increase in carbon content steel hardens but it loses its ductility. Consequently, the steel becomes brittle and it might fracture when you bend it by applying excessive load. But the manufacturing process of mild steel is similar to all other carbon steels.
However, higher carbon steel only has more carbon content in it and they also have different physical properties. These include higher strength and higher hardness value especially if you compare them with mild steel. With time, new processes and methods have been introduced and they are continuously evolving as well.
But primarily, there are three different steps involved in the process of making mild steel right out of pure iron.
● Primary steelmaking
This step involves the mixing of iron ore with lime and coal and then it is heated inside a blast furnace that comes with a capacity ranging from 100 tons to 400 tons. Lime works as a flux as it develops a protective layer over the molten metal.
The modern methods of steelmaking involve BOS (Basic Oxygen Furnace) or EAF (Electric Arc Furnace). The BOS process involves blowing oxygen through the molten metal with the inclusion of scrap steel.
Doing this reduces the carbon content to around 1.5%. While the EAF process involves feeding of scrap steel through electric arcs of high power. And it significantly improves the overall quality of the resulting steel.
● Secondary Steelmaking
This step involves a further reduction of carbon content by adding various alloy elements. It is achieved by manipulating the furnace conditions by altering temperature and pressure. And to get the required type of mild steel various processes are used during this step. These include degassing, CAS-OB, Ladle injection, ladle furnace, and stirring.
● Mild Steel Casting & Primary Forming
When the specified carbon continent is achieved and other elements have been added to enhance its physical properties according to the requirements, the molten metal is then poured out into the mold.
In this mold, the molten metal is given a shape and then allowed to cool down and solidify. At the end, when the steel has cooled down, cutting takes place into different shapes such as billets, blooms, and slabs to improve the surface quality, a hot rolling process is used.
● Secondary Forming
Though we have the complete mild steel in the previous step, usually, it is formed once again for improving its mechanical properties according to the requirements and applications. In this step, the mild steel gets its final properties and shape. The procedures that are used to finalize this step includes machining, shaping through cold rolling, coating, surface treatment, and tempering.
Mild Steel Grades
Here are some of the most common grades or types of mild steel.
● EN 1.0301
This grade contains 0.1% of carbon, 0.4% of manganese, 0.4% or silicon. Apart from that, there are some small proportions of other elements as well, including aluminum, copper, chromium, nickel, molybdenum. The equivalent grades of this alloy steel here are AISI 1008, AISI C10, and AISI DC01. It is frequently used in furniture, appliances, and the automotive industry.
● EN 1.1121
This mild steel grade features carbon content ranging from 0.08% to 0,13% and manganese content ranging from 0.3% to 0.6%. And its equivalent grade is AISI 1010. It has a wide range of applications in the automotive industry.
● EB 1.0402
This mild steel grade has a carbon content ranging from 0.18% to 0.23%. Manganese content ranges from 0.3% to 0.6%. Its equivalent grades are AISI 1020, and AISI C22. It is a suitable choice for hydraulic parts and camshafts.
Mild Steel Properties
● Chemical Properties
As we have mentioned above, mild steel features very low carbon content especially if you compare it with medium or high carbon steel. The carbon content doesn’t exceed 0.25% but according to some schools of thought carbon continents can reach up to 0.45% as well.
However, mild steel composition might also have some other elements and metals in it. These include various proportions of cobalt, chromium, copper, sulfur, phosphorus, aluminum, nickel, molybdenum, and manganese. These elements equip the final product with different properties
For instance, chromium is useful in enhancing the corrosion resistivity of mild steel and it also increases its overall hardness. Chromium is essential because, in its purest form, mild steel can easily corrode as it has been oxidized.
With chromium, a layer of iron oxide doesn’t form on the steel. Instead with exposure a layer of chromium oxide develops and it is not going to fall off. Therefore this layer also prevents any further corrosion.
Similarly, chromium oxide also does the same thing. Mild steel might also be galvanized for better wear resistivity, excellent tensile strength, and heat resistivity.
| Chemical Composition | |
|---|---|
| Iron | 98.81% to 99.26% |
| Carbon | 0.14% to 0.20% |
| Manganese | 0.60% to 0.90% |
| Phosphorus | <= 0.04% |
| Sulfur | <= 0.05% |
● Physical Properties
With this low carbon content, this metal becomes very machinable and easy to weld. Easy cutting and forming into various shapes without any proportional stresses is one of the primary features of this steel.
It also means that mild steel strength is not that much especially if you compare it with high carbon or medium carbon steel. Plus, mild steel density and mild steel weight are going to be on the lower side as well as compared to its higher carbon counterparts. The melting point of mild steel is also significantly lower than other carbon steels.
Mild steel has very impressive physical properties, and for that reason, it has been increasingly used in various industries. Mild steel is,
- High strength to handle impacts.
- High tensile strength.
- Excellent weldability and ductility.
- Magnetic metal because of the ferrite content in it.
- Cold forming possibilities for excellent malleability.
- Not the best option for heat treatment for improving physical properties.
- Almost impossible to harden during quenching and eating.
- Subject to corrosion if not treated with a proper coating.
- More affordable as compared to other forms of steel.
Mild Steel Strength, Density & Melting Point
Mild steel is extremely strong as it has very low carbon content. It means that this metal has high resistivity against breakage. Even when it is cold, it’s quite malleable and therefore, it has high impact and tensile strength. Under high pressure, it will not break but will deform or bend. Mild steel density is around 0.248 pounds per cubic inch, and the melting point of mild steel is 2570F.
| Mild Steel Mechanical & Electrical Properties | |
|---|---|
| Hardness Brinell (Knoop, Rockwell B, & Vickers) 126 (145, 71, & 131) | 126 (145, 71, & 131) |
| Ultimate Tensile Strength (Yield) | 63800 PSI (53700 PSI) |
| Elongation @ Break (within 50mm) | 15% |
| Ductility | High |
| Machinability | 78% (based on 100% machinability of AISI 1212 steel |
| Weldability | Instant welding (but not recommended when carburized or nitrided) |
| Corrosion Resistance | High with alloying |
| Affordability | Cheaper than most steels |
| Magnetism | Yes |
| Cutting | Flame, disc, and plasma cutting |
| Hardening/Strengthening | Impossible through quenching or heating |
| Heat Resistivity | High (up to 540C/ 1000F) |
Use Cases & Applications of Mild Steel
Mild steel has been used across different industries for a variety of purposes. It is the most common form of metal that we see around our houses and workplaces.
● Construction
There are some grades of mild steel that are called structural steels because they offer a tremendous amount of resistivity against loads and pressure. Mild steel also meets the wind and seismic requirements and it can resist corrosion and fire as well. Plus, it is far cheaper as compared to other forms of steel as well.
● Machinery applications
In automobile manufacturing and machinery application, mild steel is frequently used. It works well with different coating requirements and cutting techniques. It also has excellent weldability and is an ideal choice for making panels and frames.
● Poles and pipelines
Due to its maximum ductility, mild steel is a top choice for making pipelines and poles. Plus, it can also handle extreme weather conditions pretty well.
● Cookware and cutlery
In the past, the chefs of the modern age loved to use stainless steel cutlery.
But that is changing quite rapidly as more and more of them have found mild steel cutlery far more advantageous.
With mild steel, the cutting equipment is easier to clean and be sharpened. It also has a higher temperature limit and will not stick to materials.
● Fencing
This type of steel can be shaped into anything pretty easily and for that reason, it is a top choice for fencing. Mild steel also has a visual appeal as it looks pretty eye-catching.
Product Forms Available of Mild Steel
Mild steel is available in different product forms. Apart from the sheet, it is available in box section channel, angle, flat, square, hexagon, round, tube, T-section, pipe, mesh, threaded bar, telescopic tube, and half-round molds.
It means that it can be used in a range of different applications according to the needs and requirements.
Mild Steel Surface Finishes
As there is a wide range of case uses and applications of mild steel there are different surface finishes available as well. All these processes are equally effective and anyone of them can be used based on aesthetics and usage requirements.
Apart from that, mild steel is known for rusting and corrosion due to the oxidation process and it is very much similar to wrought iron.
Therefore, there are some surface finishes to prevent the oxidation process and keep the metal safe from corrosion and rusting.
– Priming
It is one of the surface finishes that involves painting the metal with paint containing zinc phosphate. This finish works as an active rust-resistant coating. The zinc phosphate compound tends to disrupt the formation of anodes on the surface of the metal.
This is achieved by hydrolyzing water to start producing zinc and phosphate ions. Phosphate ions act as anodic while zinc ions work as cathodic inhibitors. But for the best results, this paint has to be applied with a thickness in a layer that measures to be around 125 microns.
It can be achieved by applying it to different layers with the help of a roller. But keep in mind, this is only a suitable finish for indoor use and not for extreme conditions.
– Galvanizing
This process only involves coating the steel with a layer of zinc.
This can be done by dipping that steel into molten zinc. Zinc will start to react with steel when it cools down and forms zinc carbonate. After this process, it is called galvanized steel.
This layer will protect the steel in two different ways,
- The base metal underneath the layer is not exposed to the atmosphere and its different elements.
- The zinc coating of galvanized steel behaves as a sacrificial safety layer. It means that zinc will start corroding first because it has a greater electronegativity than the steel that it is protecting underneath.
Galvanizing is one of the best surface finishes that will work for the steel that is going to be used in outdoor areas, as it can handle harsh conditions pretty well. With this surface finish, the metal can handle rains, sun, and winds pretty well
– Intumescent Coating
These coatings are pretty much like paints and they are inert at cold temperatures but they work as insulation due to a complex chemical reaction at temperatures around 200C to 250C. These temperatures don’t influence steel. The reaction causes the coating to swell and expand the layer of low conductivity.
There are two different types of these intumescent coatings: thick and thin films. Thick films are developed for hydrocarbon and off-shore industries to be used in buildings. On the other hand, thin films are water or solvent-based layers that are useful for building fires. These films are very useful to make mild steel fire-resistant.
Pros & Cons of Using Mild Steel
Pros:
- Mild steel is extremely light as compared to other forms of steel.
- It is pretty cheap as well in comparison to other carbon steels.
- Mild steel is more malleable and ductile than other steels.
- It is more convenient to recycle mild steel as compared to other forms of steel.
- It can be used for a variety of purposes and is highly versatile.
Cons:
- One cannot heat treat mild steel.
- It doesn’t handle high-stress applications and beds or deforms easily.
Frequently Asked Questions
Can you harden mild steel?
Yes, you can harden mild steel if you increase the carbon content in it.
But due to the oxidation process hardening becomes a tough task as the steel has been processed to reduce its carbon content.
Mild steel is alloy steel or a pure metal?
Mild steel is not a pure metal. It has large iron content in it with other elements including carbon, nickel, chromium, aluminum, etc. In the purest form, it is iron.
How is mild steel different from high carbon steel and medium carbon steel?
Mild steel has a very low carob continent in it as compared to medium and high carbon steels. It has a carbon content that ranges from 0.5% to 0.25%. Whereas, high and mediums carbon steels have higher carbon content.
Is mild steel stronger than stainless steel?
The strength of metal has different meanings in different contexts. For instance, if you compare mild steel with stainless steel than mild steel is much more ductile and malleable than stainless steel. It doesn’t break easily but you can bend and deform it.
On the other hand, stainless steel is much more brittle due to the higher carbon content in it. It’s more prone to breakage at high pressures than mild steel but it has high corrosion resistivity as well. And both these properties have different uses.
Final thoughts
Due to its high ductility and malleability, you need to consider using mild steel for various applications. Mild steel is quite frequently used across different industries due to its physical properties. It has high machinability and weldability and is a top choice for various manufacturing industries.
Mild steel has much lower carbon content in it and can be easily treated for wear and corrosion resistivity by the addition of different alloys. Due to its easy handling mild steel is one of the most versatile metals to be used for a variety of applications.
