Steel is a very popular construction and engineering material. Steel is a strong, hard, bluish-gray metal alloy of iron and is one of the most widely used materials around the world.
Different Types of Steel are manufactured from carbon content from 0.2 to 2.1 percent (by weight), depending on classification according to composition and their physical properties.
The major element in steel is carbon but other alloying elements i.e. tungsten, chromium, vanadium, magnesium and a small amount of sulfur, silicon, phosphorus, and oxygen are also present.
Steel is mainly used for structural and fabricating material. In steel manufacturing, carbon, and other alloying material are used for creating hardening and preventing dislocations in the iron atom.
The important properties of steel like ductility, hardness, and tensile strength of steel depend on the amount of alloying materials and their form presence in iron.
An increasing amount of carbon makes the steel harden and strong, but less ductile. Steel is a versatile, strong, and resilient material.
The biggest advantage is that steel can be recycled over and over again without losing its properties. Steel is one of the essential materials in construction, infrastructure, and bridges as well as used in household appliances. Steel industries are playing a vital role in economic development.
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Types of Steel In Construction
The following are major types of steel as per composition,
- Carbon steel
- Alloy steel
1. Carbon Steel
Carbon steel is generally contested less than 1 % carbon and traces of manganese, sulfur, silicon, and phosphorus.
The properties and characteristics of carbon steel mainly depend on the carbon content in steel and there is a minor influence on this type of carbon due to the alloying and residual materials. Plain carbon steel is further classified into four categories.
Following are the types of carbon steel,
1) Low-carbon steel
2) Medium carbon steel
3) High-carbon steel
4) Very high-carbon steel
Low Carbon Steel
In low carbon steel types of steel, carbon % is limited to 0.30 and is the most commonly used grade. These types of steel can be machined and welded easily and also has a ductile property higher than high-carbon steel.
Medium Carbon Steel
In medium carbon steel, the amount of carbon is kept between 0.30 to 0.45 percent carbons. As there is an increase in the amount of carbon content there is an increase in hardness and tensile strength and a decrease in ductility.
But, because of the higher carbon content, its machining and welding are more difficult than low-carbon steel due to the increased content of carbon.
High Carbon Steel
In high-carbon steel, the amount of carbon content is between 0.45 to 0.75 percent. So, these types of steel face the challenge of welding and machining this type of steel.
So, for any type of molding work heating is necessary to produce acceptable welds and is also used to control the mechanical properties of steel after welding.
Very high Carbon Steel
In very high-carbon steel, the amount of carbon content is up to 1.50 percent. Because of the high carbon in the steel, it requires heat before, during, and after welding to control its mechanical properties.
So, its major application is in the production of hard steel products such as metal cutting tools and truck springs.
Designation System of Carbon Steel
A four-digit designation system has been introduced by the American Iron and Steel Institute (AISI) together with the Society of Automotive Engineers (SAE). Also as per ASTM a240
SAE 1XXX
First digit:
1st letter of the digit indicates that either it is carbon steel or alloy steel.
1 indicate represents carbon steel and 2-9 is for alloy steel.
Second digit:
2nd digit indicates the modification of steel:
0 – Plain carbon, non-modified
1 – Resulfurized
2 – Resulfurized and phosphorized
5 – Non-resulfurized, Mn over 1.0%
Last two digits:
The last 2 digits show the carbon concentration at 0.01%.
Example:
SAE 1045: In which 1 represents the plain carbon (non-modified) steel and contains 0.45% carbon in this type of steel.
2. Alloy Steel
Alloy steel is the type of carbon steel in which one or more elements other than carbon have been intentionally added, to produce a desired physical property or characteristic.
Generally, molybdenum, manganese, nickel, silicon, boron, chromium, boron, and vanadium are added as external elements. There are two types of alloy steel
Following are the types of alloy steel,
- Low alloy steel
- High alloy steel
1. Low Alloy Steel
In low alloy steel, the carbon content is generally kept at 0.25 % and often at 0.15 % for special welding applications.
There are some alloying elements like manganese, nickel, chromium, molybdenum, silicon, vanadium, and boron and the less common alloying elements are aluminum, cobalt, copper, titanium, tungsten, tin, and zirconium.
Most popularly low alloy steel is used to achieve better hardenability and increased corrosion resistance in certain environments. There is one drawback is that the low alloy steels are difficult to weld.
If we lower the carbon content up to 0.10 percent along with other alloying materials increases the strength of the material.
2. High Alloy Steel
Generally, steel having other elements more than 8% by weight of total other than carbon and iron is classified as high alloy steel.
High alloy steel essentially has two chemical elements and the properties of this type of steel depend on the percentage of the chemical element present in 5 it.
Its major advantage, it offers high corrosion resistance with high reliability. These types of high-carbon steel are largely used in nuclear power plants, heat exchangers, centrifugal separators, driers, pipelines, couplings, valves, bolts, salt manufacturing, exhaust gas desulfurizes, petrochemical, pharmaceutical, and semiconductor cleaning equipment.
Designation System of Alloy Steel
The four-digit designation system for alloy steel has been developed by the American Iron and Steel Institute (AISI) together with the Society of Automotive Engineers (SAE).
As per the four-digit classification SAE-AISI system:
First digit
The first digit shows the class of alloy steel:
2- Nickel steel
3- Nickel-chromium steels
4- Molybdenum steels
5- Chromium steels
6- Chromium-vanadium steels
7- Tungsten-chromium steels
9- Silicon-manganese steels
Second digit
The second digit indicates the concentration of the major element in percentages. if the 2nd element is 1 or 2 it means 1% and 2%.
Last two digits
The last two digits indicate carbon concentration by 0.01%.
Example:
SAE 6230
It shows the alloy of Chromium-vanadium steel, containing 2% of chromium and 0.30% of carbon.
Types of Steel According to Application
As per application of steel is classified as under,
1. Stainless steel
2. Tool and die steel
1. Stainless steel
Stainless steel is a type of steel that comes with a minimum of 10% chromium content. This steel is more resistant to stains, corrosion, and rust than ordinary steel.
It was invented or made in 1913 by Harry Brearley of Sheffield, England, but the discovery was not announced to the world until 1915.
It is called corrosion-resistant steel when the alloy type and grade are not detailed, particularly in the aviation industry.
It is mainly utilized where the properties of steel, as well as the resistance to corrosion, are required. Stainless steel has almost 150 grades out of which 15 are the most commonly used.
This type of steel is mainly used in watchbands, watches, handgun models, pistols, storage tanks, tankers, table cutlery, jewelry, food processing plant, surgical instruments as well as in the aviation industry.
Designation system of Alloy Steel
AISI has introduced a three-digit system for stainless steel:
2XX series – chromium-nickel-manganese austenitic stainless steels
3XX series – chromium-nickel austenitic stainless steels
4XX series – ferritic stainless steels and chromium martensitic stainless steels
5XX series – low chromium martensitic stainless steels
2. Tool And Die Steel
This is very high carbon steel (either carbon or alloy) possessing high hardness, strength, and wear resistance.
Tools and die steel generally have a carbon content between 0.7% to 1.5%, tool steels are manufactured under carefully controlled conditions to produce the required quality of steel. Tool steels are heat treatable.
To increase the hardness of steel tool alloying elements forming hard and stable carbides are added to the composition. It is used to shape other metals by cutting, forming, machining, and die casting.
Tool and die steel is mainly utilized for making chisels, forging dies, hummers, drills, cutters, shear blades, drills, and razors.
Tool and die steels can be divided based on their use, mechanical properties, composition, and method of heat treatment. There are various grades of tools and die steel available for different applications.
Selection of grade mainly depends on whether a keen cutting edge is necessary or not, as in stamping dies, or whether the tool has to withstand impact loading and service conditions encountered with such hand tools as axes, pickaxes, and quarrying implements or not.
Designation System of Tool Steel
One-letter system in combination with a number for tool steel system has been developed by the American Iron and Steel Institute (AISI) together with the Society of Automotive Engineers (SAE).
The letter means;
W- Water-hardened plain carbon tool steel
O- Oil hardening cold work alloy steel
A- Air hardening cold work alloy steel
D- Diffused hardening cold work alloy steel
S- Shock resistance low carbon tool steel
T- High-speed tungsten tool steel
M- High speed molybdenum tool steel
H- Hot work tool steel
P- Plastic mold tool steel
Conclusion:
In conclusion, the existence of 10 different types of steel, encompassing both alloyed steel and carbon steel, highlights the versatility and adaptability of this essential material in various industries, each types of steel possesses distinct characteristics and properties which make it suitable for specific applications.
Carbon steel with its high carbon content, it offers excellent strength and hardness, making it ideal for structural component and tools, on the other hand alloyed steel, which incorporates elements like chromium, molybdenum, exhibits enhanced properties such as corrosion resistance, improved tensile strength, and heat resistance.
The availability of diverse steel types enables engineers and manufactures to choose the most appropriate steel for their proper use, ensuring optimal performance and longevity in a various application, from automotive industries, construction industries and manufacturing sectors.
FAQs:
What is carbon steel?
Carbon steel is a type of steel that primarily consists of carbon as the main alloying element, with small amounts of other elements. It is widely used in various applications due to its strength and affordability.
What are the different grades of carbon steel?
Carbon steel is categorized into several grades based on its carbon content and mechanical properties. Some common grades include low carbon steel, medium carbon steel, and high carbon steel.
What is alloyed steel?
Alloyed steel is a type of steel that contains additional alloying elements besides carbon, such as manganese, silicon, nickel, chromium, or vanadium. These elements enhance specific properties, such as strength, corrosion resistance, or heat resistance.
What is stainless steel?
Stainless steel is a popular type of alloyed steel that contains a minimum of 10.5% chromium by mass. It exhibits excellent corrosion resistance and is widely used in various applications, including kitchenware, construction, and medical equipment.
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