What Are the Different Types Of Steel?
Based on the chemical compositions, Steel can be categorized into four (04) basic types:
1. CARBON STEEL:
Carbon steel is the most utilized steel in the industries and accounts for more than 90% of the total steel production. Based on the carbon content, Carbon steels are further classified into three groups.
Low Carbon Steel/Mild Steel
Medium Carbon Steel
High Carbon steel
Carbon content is given in the table below:
|S.No.||Type of carbon steel||Percentage of Carbon|
|1||Low Carbon Steel/Mild steel||Up to 0.25%|
|2||Medium Carbon Steel||0.25% to 0.60%|
|3||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 corrosion resistance of the material. 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 Steels
2. Martensitic Stainless Steels
3. Austenitic Stainless Steels
4. Duplex Stainless Steels
5. Precipitation-Hardening (PH) Stainless Steels
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 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.
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 and 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
4. TOOL STEEL:
Tool steels have high carbon content (0.5% to 1.5%). Higher carbon content provides higher hardness and strength. These steels are mostly used to make tools and dies. Tool steel contains various amounts of tungsten, cobalt, molybdenum, and vanadium to increase the heat and wear resistance, and durability of the metal. This makes tool steels very ideal for use as cutting and drilling tools.