Fe3C diagram for PWHT

Types of carbon steel and its contents

Carbon steel is steel with the element carbon (C) as its main alloy with a concentration of up to 2%. In fact most of the steel is carbon steel. This carbon steel is divided into three types according to its carbon content.

First, Low Carbon Steel which only contains about 0.1% – 0.3% carbon is known to be soft and weak as well as ductile and tough. This steel is easy to weld and work with, and is relatively inexpensive compared to other types of carbon steel. Examples of this type of carbon steel are ship plate, sheet and structural profiles, such as I, L, H, and C.

Second, Medium Carbon Steel with a carbon content of about 0.3% -0.8%. The micro structure is louder and stronger. The high amount of carbon makes this steel more responsive to various heat treatment processes to improve its mechanical properties. Examples are railroad tracks, gears, and various engine components.
Third, there is High Carbon Steel, the carbon content is around 0.8% -2%. Its qualities — hardness, strength, and ductility — are higher than the other two types of steel. Examples of application for various tools, especially cutting tools.

Alloy Steel

Alloy steel (alloy steel) is steel that is added with other alloying elements besides carbon in order to obtain special properties, such as strength, resistance to rust, weldability, and others. Types of elements that are commonly combined include Manganese, Chromium, Nickel, Phosphorus, Sulfur, and others. The addition of other elements is present in a small percentage, usually less than the element carbon.

Despite the addition of other elements, carbon remains the dominant alloying element. According to the percentage of carbon there are three groups of alloy steels, namely low carbon alloy steels (element C ≤2.5%); medium carbon alloy steel (C element 2.5% -10%); and high carbon alloy steel (element C> 10%).

Fe3C diagram
carbon steel for pipeline

When viewed from the content of elements other than carbon, special alloy steels and high speed steels are known. Special Alloy Steel (special alloy steel) is an alloy steel that adds one or more elements to obtain special properties. Meanwhile, High-speed Steel is an alloy steel developed as a raw material for high-speed machine tools. At high temperatures its hardness can withstand better than other types of steel.

Each alloying element has a different effect when combined with different elements and in different quantities. As a result, there are many types of alloy steel with different mechanical properties.

Even in small amounts – if heat treated, cooling, and so on – each element of the alloy will affect the mechanical properties of the steel. We will first examine the various elements that are relatively always present in steel, namely carbon, manganese, phosphorus, sulfur and silicon and their significant effects.

Carbon (C)
It can be said that carbon (C) is the most important alloying element present in all steels. The amount is relatively dominant compared to other elements. The term carbon steel (carbon steel) refers to steel with a carbon content as the main mixture with a percentage reaching the range 0.12% to 2%. In carbon-element steels, the role is given to increase the hardness, tensile strength, and their reaction to heat treatment. The increase in carbon content is directly proportional to the increase in the melting point of the steel, but it also reduces toughness and makes it brittle / brittle and decreases its weldability. In most steel welds the carbon content is less than 0.5%.

Manganese (Mn)
Manganese (Mn) is an alloying element that is no less important than carbon. Its presence has the potential to improve steel structure and increase its strength by increasing hardening and making steel resistant to wear. The addition of manganese also anticipates oxidation and the formation of iron sulfide and dissolved impurities (inclusions) in the manufacturing process. The amount of manganese contained in steel is usually around 0.3%, but in some types of carbon steel the content can be up to 1.5%.

Phospor (P)
The phosphorus (P) content of most carbon steels averages about 0.04%. In excessive amounts the elemental phosphorus tends to be considered an impurity because it has the potential to reduce the hardness / toughness of the steel. That’s why phosphorus is only added in small amounts. The addition of up to 0.1% phosphorus to low high-strength alloys aims to increase strength and resistance to corrosion.

Sulfur (S)
Sulfur or sulfur (S) is an element that tends to be considered an impurity, but in small amounts (<0.05%) it has a positive effect, such as making steel malleable. However, excessive amounts have an impact on brittleness and decrease the ability of the steel to be welded and / or increase the risk of weld crack formation.

Silicon (Si)
Silicon (Si) has the potential to improve steel structure as well as elemental manganese (Mn), but to a relatively small degree. The silicon element will increase the strength and hardness of the steel. This element can be a carbide stabilizer that is formed due to the addition of other alloys. Silicon also acts as a deoxidizer – binder / remover of oxygen or other dissolved gases (nitrogen) – to anticipate damage and / or defects. The approximate normal percentage for sulfur content is around 0.4%.


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