All About Mild Steel: Definition, Composition, and Properties
Learn more about mild steel and how it's used in manufacturing.
Mild steel, also known as low-carbon steel, is one of the most widely used steel. It is used in the construction and automotive industries, and for fencing, signs, and innumerable other applications. It is valued for its weldability, machinability, and ductility. Mild steel is primarily characterized by having a carbon content of less than 0.2 % by weight. The 4-digit AISI (American Iron and Steel Institute) classification codes for mild steel start with "10" and end with two digits that are less than 20, indicating the approximate carbon content of the steel in hundredths.
This article will explore the chemical composition, mechanical properties, grades, and characteristics of mild steel.
What is Mild Steel?
Mild steel is an iron alloy with carbon as its main alloying element. It is one of the most widely used forms of steel and can be applied to a range of general-purpose applications. Mild steel owes its popularity to its adequate strength at low cost, in addition to its excellent machinability and weldability. Various grades of mild steel have differing amounts of carbon with higher carbon contents wrestling in increased strength at the expense of ductility. In some cases, additional alloying elements are added to improve properties such as tensile strength, corrosion resistance, and wear resistance. Figure 1 shows some examples of mild steel products:
Figure 1: Mild Steel - Image Credit: Shutterstock/studiovin
What is the Composition of Mild Steel?
Mild steel is made up of an iron (Fe) base with the addition of small amounts of carbon. Low-carbon steel is typically defined as having less than 0.2 % carbon by ASM International. Different grades of mild steel are defined by their differing levels of carbon. Another common alloying element is manganese (Mn).
What Are the Different Grades of Mild Steel?
There are many different grades of mild steel. Mild steels classified according to the AISI (American Iron and Steel Institute) numbering system will all begin with “10” as their first two digits signifying their low carbon content. Low-carbon steel, and by extension mild steel, will have the final 2 digits of the designation as any number less than 20 (approximate carbon content multiplied by 100). Most mild steel has low (<1%) quantities of phosphorus and sulfur and these elements are actively limited as they are considered impurities. Some common grades are listed in Table 1 below:
| Classification | Approximate Equivalents | Key Points |
|---|---|---|
Classification AISI 1008 | Approximate Equivalents DIN 1.0204 | Key Points Excellent cold formability |
Classification AISI 1010 | Approximate Equivalents DIN 1.0301 | Key Points Low strength, used for magnet cores |
Classification AISI 1015 | Approximate Equivalents DIN 1.0401 | Key Points Wear-resistant, good machinability |
Classification AISI 1018 | Approximate Equivalents DIN 1.0419 | Key Points Excellent for carburizing applications, good machinability |
Classification AISI 1020 | Approximate Equivalents DIN 1.0044 | Key Points A good balance of strength and ductility, |
How Much Carbon is in Mild Steel?
The amount of carbon in mild steel is less than 0.2 % by weight. According to AISI (American Iron and Steel Institute), low-carbon steel is a type of mild steel.
What is the Mechanical Properties of Mild Steel?
The mechanical properties of some of the common types of mild steels are listed in Table 2 below:
| Type of Mild Steel | Modulus of Elasticity (GPa) | Brinell Hardness | Ultimate Tensile Strength (MPa) | Yield Strength (MPa) | Elongation at Break (%) | Steel Density kg/m3 |
|---|---|---|---|---|---|---|
Type of Mild Steel AISI 1008 | Modulus of Elasticity (GPa) 200 | Brinell Hardness 95 | Ultimate Tensile Strength (MPa) 340 | Yield Strength (MPa) 285 | Elongation at Break (%) 20 | Steel Density kg/m3 7.87 |
Type of Mild Steel AISI 1010 | Modulus of Elasticity (GPa) 205 | Brinell Hardness 105 | Ultimate Tensile Strength (MPa) 365 | Yield Strength (MPa) 305 | Elongation at Break (%) 20 | Steel Density kg/m3 7.87 |
Type of Mild Steel AISI 1015 | Modulus of Elasticity (GPa) 205 | Brinell Hardness 111 | Ultimate Tensile Strength (MPa) 385 | Yield Strength (MPa) 325 | Elongation at Break (%) 18 | Steel Density kg/m3 7.87 |
Type of Mild Steel AISI 1018 | Modulus of Elasticity (GPa) 205 | Brinell Hardness 126 | Ultimate Tensile Strength (MPa) 440 | Yield Strength (MPa) 370 | Elongation at Break (%) 15 | Steel Density kg/m3 7.87 |
Type of Mild Steel AISI 1020 | Modulus of Elasticity (GPa) 186 | Brinell Hardness 121 | Ultimate Tensile Strength (MPa) 420 | Yield Strength (MPa) 350 | Elongation at Break (%) 15 | Steel Density kg/m3 7.87 |
Type of Mild Steel S275 J0 | Modulus of Elasticity (GPa) 205 | Brinell Hardness 121 | Ultimate Tensile Strength (MPa) 430 - 580 | Yield Strength (MPa) 275 | Elongation at Break (%) 21 | Steel Density kg/m3 7.85 |
Type of Mild Steel S355 J0 | Modulus of Elasticity (GPa) 210 | Brinell Hardness 146 | Ultimate Tensile Strength (MPa) 510 - 680 | Yield Strength (MPa) 355 | Elongation at Break (%) 20 | Steel Density kg/m3 7.80 |
Table Credit: matweb.com
| Classification | Carbon Content (% Weight) | Secondary Alloying Elements (% Weight) |
|---|---|---|
Classification AISI 1008 | Carbon Content (% Weight) <0.1 | Secondary Alloying Elements (% Weight) 0.3 to 0.5 Mn; 0.04 P; 0.05 S |
Classification AISI 1010 | Carbon Content (% Weight) 0.08 to 0.13 | Secondary Alloying Elements (% Weight) 0.3 to 0.6 Mn; 0.04 P; 0.05 S |
Classification AISI 1015 | Carbon Content (% Weight) 0.13 to 0.18 | Secondary Alloying Elements (% Weight) 0.3 to 0.6 Mn; 0.04 P; 0.05 S |
Classification AISI 1018 | Carbon Content (% Weight) 0.14 to 0.2 | Secondary Alloying Elements (% Weight) 0.6 to 0.9 Mn; 0.04 P; 0.05 S |
Classification AISI 1020 | Carbon Content (% Weight) 0.17 to 0.23 | Secondary Alloying Elements (% Weight) 0.3 to 0.6 Mn; 0.04 P; 0.05 S |
Classification S275 | Carbon Content (% Weight) 0.18 | Secondary Alloying Elements (% Weight) 1.5 Mn; 0.030 P; 0.030 S; 0.012 N; 0.55 Cu |
Classification S355 | Carbon Content (% Weight) 0.2 | Secondary Alloying Elements (% Weight) 1.6 Mn; 0.030 P; 0.030 S; 0.012 N; 0.55 Cu |
Table 3: matweb.com
What is the Density of Mild Steel?
The density of all grades of mild steel hovers near 7.8 c/cm3. This is because the density of mild steel, which is more than 98% iron, is dominated by the density of iron (7.87 g/cm3). Alloys that fit under the mild steel umbrella that contain small amounts of alloying elements other than iron will have slightly different densities.
What Is the Toughness of Mild Steel?
Mild steel is both ductile and strong and is, therefore, a very tough material. The toughness of mild steel varies according to the type and classification. Toughness is defined as how much energy can be absorbed without fracture. It is calculated as the area beneath a material's stress-strain curve as defined up to the fracture point. The mechanical property commonly used to define a material's toughness is the Charpy impact strength. For 1020, for example, the Charpy impact strength would be 24 J at 10 °C.
Which Mild Steel Grade is the Strongest?
The strongest grade of mild steel is 1020. It must be noted that this grade of mild steel also has the highest carbon content which gives it strength at the expense of ductility.
What is Mild Steel's High Melting Point?
The temperature at which mild steel becomes completely liquid varies between 1450 and 1530 °C, depending on the carbon and alloy content of the particular grade of steel.
Is Mild Steel Suitable for Welding?
Yes, mild steel is suitable for welding. Grades with additional silicon and manganese further improve the weldability of mild steel. Mild steel’s weldability is one of the reasons for its widespread use as it can be easily welded on site with a simple stick welding machine (Shielded Metal Arc Welding) using ER70S-3 & ER70S-6 rods.
To learn more about which mild steel is best suited to your unique application, contact a Xometry expert today or check our quoting tool.
Summary
This article presented mild steel explained what it is, and discussed its different attributes. To learn more about mild steel, contact a Xometry representative.
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