What is Steel?

Steel is an?alloy of Iron?(the concept of alloy is explained below) and the principal or main alloying element is?Carbon.?Hence,

The main or base element in steel is:?Iron

Main (principal) alloying element in steel is:?Carbon

Other alloying elements in steel are:?Manganese, Silicon, Nickel, Chromium, Molybdenum, Vanadium, Titanium, Niobium, Aluminum, etc

what is an Alloy?

When different elements are mixed in smaller quantities in the base (main) element, the resulting product is called an alloy of the base element.

Hence steel is an alloy of Iron because Iron is the base element or the main constituent in steel and the main alloying element is Carbon. Some other elements such as?Manganese, Silicon, Nickel, Chromium, Molybdenum, Vanadium, Titanium, Niobium, Aluminum, etc.?are also added in varying quantities to produce different grades (or types) of Steel.

However, there are some exceptions to the above definition of steel like interstitial-free (IF) steels and type 409 ferritic stainless steels, in which carbon is considered an impurity.

What Are the Different Types Of Steel?

Based on the chemical compositions, Steel can be categorized into four (04) basic types:

Carbon Steel

Stainless Steel

Alloy Steel

Tool Steel

1. Carbon Steel:

Carbon steel is the most utilized steel in industries and accounts for over 90% of the total steel production. Based on the carbon content, Carbon steels are further classified into three groups.

Low Carbon Steel/Mild Steel (Up to 0.25%)

Medium Carbon Steel(0.25% to 0.60%)

High Carbon steel (0.60% to 1.5%)

2. Stainless Steel:

Stainless steel is an alloy steel that contains 10.5% Chromium (Minimum). Stainless steel exhibits corrosion resistance properties, due to the formation of a very thin layer of Cr2O3 on its surface. This layer is also known as the passive layer. Increasing the amount of Chromium will further increase the material’s corrosion resistance. In addition to Chromium, Nickel, and Molybdenum are also added to impart desired (or improved) properties. Stainless steel also contains varying amounts of Carbon, Silicon, and Manganese.

Stainless steels are further classified as;

1. Ferritic Stainless Steel

2. Martensitic Stainless Steel

3. Austenitic Stainless Steel

4. Duplex Stainless Steel

5. Precipitation-Hardening (PH) Stainless Steel

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Ferritic Stainless Steel:?Ferritic steels consist of Iron-Chromium alloys with body-centered cubic crystal structures (BCC). These are generally magnetic and cannot be hardened by heat treatment?but can be strengthened by?cold working.

Austenitic Stainless Steel:?Austenitic steels are the most corrosion-resistant. It is non-magnetic and non-heat-treatable. Generally, austenitic steels are highly weldable.

Martensitic Stainless Steel:?Martensitic stainless steels are extremely strong and tough but not as corrosion-resistant as the other two classes. These steels are highly machinable, magnetic, and heat-treatable.

Duplex Stainless Steels:?Duplex stainless steel consists of a two-phase microstructure consisting of grains of ferritic and austenitic stainless steel (i.e Ferrite + Austenite). Duplex steels are about twice as strong as austenitic or ferritic stainless steels.

Precipitation-Hardening (PH) Stainless Steels:?Precipitation-Hardening (PH) Stainless Steels possess Ultra high strength due to precipitation hardening.

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3. Alloy Steel:

In alloy steel, varying proportions of alloying elements are used, to achieve desired (improved) properties such as weldability, ductility, machinability, strength, hardenability, corrosion resistance, etc. Some of the most used alloying elements and their effects are as follows;

Manganese –?Increases strength and hardness, decreases ductility and weldability

Silicon –?Used as deoxidizers used in the steel-making process

Phosphorus –?Increases strength and hardness and decreases ductility and notch impact toughness of steel.

Sulfur –Decreases ductility, notch impact toughness, and weldability. Found in the form of sulfide inclusions.

Copper –?improved corrosion resistance

Nickel –?Increases hardenability and Impact strength of steels.

Molybdenum –?Increases hardenability and enhances the creep resistance of low-alloy steels

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