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.

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

Classification	Approximate Equivalents	Key Points
AISI 1008	DIN 1.0204	Excellent cold formability
AISI 1010	DIN 1.0301	Low strength, used for magnet cores
AISI 1015	DIN 1.0401	Wear-resistant, good machinability
AISI 1018	DIN 1.0419	Excellent for carburizing applications, good machinability
AISI 1020	DIN 1.0044	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 Steel	Modulus of Elasticity (GPa)	Brinell Hardness	Ultimate Tensile Strength (MPa)	Yield Strength (MPa)	Elongation at Break (%)	Steel Density kg/m3
AISI 1008	200	95	340	285	20	7.87
AISI 1010	205	105	365	305	20	7.87
AISI 1015	205	111	385	325	18	7.87
AISI 1018	205	126	440	370	15	7.87
AISI 1020	186	121	420	350	15	7.87
S275 J0	205	121	430 - 580	275	21	7.85
S355 J0	210	146	510 - 680	355	20	7.80

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

Classification	Carbon Content (% Weight)	Secondary Alloying Elements (% Weight)
AISI 1008	<0.1	0.3 to 0.5 Mn; 0.04 P; 0.05 S
AISI 1010	0.08 to 0.13	0.3 to 0.6 Mn; 0.04 P; 0.05 S
AISI 1015	0.13 to 0.18	0.3 to 0.6 Mn; 0.04 P; 0.05 S
AISI 1018	0.14 to 0.2	0.6 to 0.9 Mn; 0.04 P; 0.05 S
AISI 1020	0.17 to 0.23	0.3 to 0.6 Mn; 0.04 P; 0.05 S
S275	0.18	1.5 Mn; 0.030 P; 0.030 S; 0.012 N; 0.55 Cu
S355	0.2	1.6 Mn; 0.030 P; 0.030 S; 0.012 N; 0.55 Cu

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.