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Common mild steel Galvalume roof - Image Credit: Shutterstock/Hamid Rustanto

All About Mild Steel: Definition, Composition, and Properties

Learn more about mild steel and how it's used in manufacturing.

Xomety X
By Team Xometry
October 24, 2022
 5 min read
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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:

Slide 1 of 1
Figure 1: Mild Steel - Image Credit: Shutterstock/studiovin
Figure 1: Mild Steel - Image Credit: Shutterstock/studiovin
Figure 1: Mild Steel - Image Credit: Shutterstock/studiovin

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:

Table 1: Mild Steel Grades
ClassificationApproximate EquivalentsKey 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,

Where is Mild Steel Used?

Mild steel is a general-purpose material that can be found in most industries. Some typical applications include: car bodies, furniture, wire, rebar, and fasteners. Higher strength mild steel is used for structures and storage tank plating.

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:

Table 2: Mild Steel Properties
Type of Mild SteelModulus of Elasticity (GPa)Brinell HardnessUltimate 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

What is the Chemical Composition of Mild Steel?

Table 3 below lists the secondary elements present in the various grades of mild steels:

Table 3: Mild Steel Chemical Composition
ClassificationCarbon 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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Xomety X
Team Xometry
This article was written by various Xometry contributors. Xometry is a leading resource on manufacturing with CNC machining, sheet metal fabrication, 3D printing, injection molding, urethane casting, and more.