Steel is a versatile material with many different types, each having their own unique properties and uses. Carbon steel, stainless steel, alloy steel, and tool steel are four of the most commonly used types. In fact, carbon steel is the most widely used steel globally, containing iron, carbon, and other alloying elements in specific amounts. Carbon accounts for approximately 90% of all steel production and is the primary alloying element in carbon steels. Overall, there are 14 main types of steel, which can be further classified into subcategories within each category.

• We have heard phrases like steel bridges, steel frames, or commonly stainless steel. Now, steel is an alloy of iron and carbon to derive improved strength and resistance to fracture. There are different types of steel. Here, an alloy is formed by elements that are either metals or chemical elements, but one of them is always metal.

In this article, we shall discuss the types of steel necessary for the SSC JE ME and GATE ME examinations. We will also study the composition of each type of steel, their advantages and disadvantages, and finally applications of each type.It also helps in RRB JE Mechanical engineering examinations too.

Steel changes its mechanical properties based on the chemical composition or alloying element. The types of steel discussed here is based on the composition. Let us refer to the classification tree below for our study on the various types.

Fig 1: Types of Steel

According to the syllabus of the AE/JE Mechanical exam, we will be discussing only Mild and Alloy steel. But let us have an understanding of the other types as well.

Carbon Steel

Steel with a carbon content of between 0.05 wt % and 2.1 wt % is known as carbon steel. These are the most used type in the manufacturing industries. Based on the composition of carbon, classification can be done into four types of carbon steel.

• Mild Steel (Low Carbon steel) - 0.05 wt % to 0.30 wt % carbon
• Medium Carbon Steel - 0.3 wt % to 0.5 wt % carbon
• High Carbon Steel - 0.5 wt % to 1.5 wt % carbon
• Ultra High Carbon Steel - 1.5 wt % to 2.1 wt % carbon.

​Stainless Steel

Stainless steel is a steel alloy containing 10.5% chromium. With a thin coating of \((Cr_2 O_3)\) on its surface, stainless steel shows corrosion-resistant qualities. Stainless steel also contains other elements like Nickel and manganese to improve the properties. Due to its good durability, stainless steel is widely used in kitchen utensils and medical instruments. The recyclability and low maintenance make stainless steel an environmentally friendly type of steel. There are various types of stainless steel: Ferritic, Martensitic, Austenitic, Duplex, and Precipitation-Hardening (PH) Stainless Steels.

Tool Steel

Tool steels contain between 0.5 wt % and 1.5 wt % carbon. Increased carbon content increases hardness and strength. Typically, these steels are used to manufacture tools and die. There are not many types of tool steel but one prominent is High-Speed Steel (HSS), which is mostly used in the manufacturing of cutting tools for machines.

Let us study the other types of steel in detail as it is necessary for AE/JE Mechanical exams.

Mild Steel

Low carbon steel or mild steel offers excellent cold-forming capabilities, remarkable ductility and weldability, and great impact strength. Due to these characteristics, mild steel is simpler for machining using CNC machines than other forms of steel. It has 0.16 wt % and 0.29 wt % of carbon content and a relatively high melting point of between \(1450 (^{circ} C) \)to 1\(520 (^{circ} C)\). Because mild steel has a high melting point and is more ductile under heat, it is perfect for forging, drilling, welding, and other fabrication procedures.

The manufacturing of mild steel is simple. Steel is heat treated to enhance the carbon content uniformly. When the carbon content increases, steel becomes tougher but less ductile. This indicates that the metal becomes brittle and may fracture rather than bend when an external load is applied.

Types of Mild Steel

There are different types of mild steel, each with its unique properties and characteristics as listed below.

• (a) Hot Rolled Mild Steel: This type of mild steel is produced by rolling the steel at a high temperature, typically above \(927(^{circ} C)\). It is commonly used in structural applications as it has a rougher surface texture than cold-rolled mild steel.
• (b) Cold Rolled Mild Steel: This type of mild steel is produced by rolling the steel at a low temperature, typically below room temperature. It has a smoother surface texture than hot-rolled mild steel and is commonly used in applications that require a high level of precision
• (c) Galvanized Mild Steel: This type of mild steel is coated with a layer of zinc to protect it from corrosion. It is commonly used in outdoor applications, such as fences and guardrails.

Advantages of Mild Steel

Mild steel is a popular choice of material in a wide range of industries due to its many advantages, which are listed below.

• Mild Steel is inexpensive compared to other types of steel and is readily available in large quantities.
• It is easily formed and shaped without breaking. This makes it a versatile material for a wide range of applications.
• They can be easily welded and fabricated using a variety of techniques. 
• Mild steel is strong and durable, with high tensile strength and resistance to deformation. It can withstand heavy loads and is highly resistant to wear and tear.
• It can be coated with a layer of zinc or other materials to make it highly resistant to corrosion. 
• It is a highly recyclable material, which means it can be melted down and reused multiple times without losing its properties or quality.

Disadvantages of Mild Steel

While mild steel has many advantages, it also has some disadvantages that should be considered before choosing it for a particular application which are discussed below.

• While mild steel can be coated to make it more corrosion-resistant, it is still more prone to rust and corrosion than other types of steel, particularly in harsh environments. 
• It has relatively low impact strength compared to other types of steel, which means it can be more prone to cracking or breaking under heavy loads or impacts.
• It has a relatively low melting point and poor heat resistance compared to other types of steel, which can limit its use in high-temperature applications.
• It has a relatively low level of hardness compared to other types of steel, which can limit its use in applications where high wear resistance or cutting ability is required.
• Due to its relatively low strength and stiffness, mild steel may not be suitable for those applications that require very thin or lightweight structures.
• Its production can have environmental impacts, particularly in terms of greenhouse gas emissions and water usage.

Applications of Mild Steel

The idea that everything visible from your window is made of mild steel is not unrealistic. Almost all man-made objects are made from this metal. The use of mild steel is widespread, from structural elements in buildings to the hulls of enormous ships. The uses listed below are only a few examples.

• Mild steel is commonly used in construction for building frameworks, reinforcement bars, and other structural elements.
• It is used in the manufacturing of

Automobile components like chassis, engine parts, rivets, and suspension systems

1. Everyday components like chairs, tables, and shelves
2. Industrial needs like pipes, tubes, wires, chains, and sheet metals.
3. Agricultural equipment like ploughs and cultivators.
4. Kitchen appliances, home electronics, and bicycles.
5. Generally, fencing is done using mild steel these days.
6. It is used in the manufacture of various transportation equipment, such as trailers and shipping containers.

Alloy Steel

Carbon steel is combined with one or more alloying elements, such as manganese, silicon, nickel, titanium, copper, chromium, and aluminium, to produce alloy steel. The elements are called alloying elements, added to the steel to improve its hardness, strength, toughness, high-temperature performance, corrosion resistance, and wear resistance, among other physical and/or mechanical properties.

Types of Alloy Steel

There are many types of alloy steel, which are classified based on their chemical composition, properties, and intended use. Some of the types of alloy steel are listed below.

• Low Alloy Steel: They contain small amounts of alloying elements, typically less than 8 %. Titanium, copper, niobium, and vanadium are common elements that are added to obtain ‘Low Alloy Steels’ to improve their strength and toughness. Low-alloy steels undergo heat treatment, normalising, and tempering during the manufacturing process.
• High Alloy Steel: They contain more than 8% of alloying elements, which are typically added to improve their corrosion resistance, high-temperature strength, and wear resistance. Examples of high alloy steel include stainless steel and tool steel, which we have discussed already.

Steel Classification Based on Various Properties

Steel Properties depend on various parameters. Before choosing the type of steel, it is important to check all the properties related to it. A broader classification of steel based on carbon content, alloying elements and applications is provided in the table below. 

Effect of Alloying Elements Types of Steels

Typically, the alloying elements account for 1 wt % to 50 wt % of the alloy steel's composition. Let us study the effects of each alloying element in the alloy steel.

Advantages of Alloy Steel

A renowned usage of anything reflects its exceptional qualities. As alloy steel is also widely used for many applications, let us see some of its advantages:

• Alloy steel contains alloying elements that improve its strength and hardness, making it stronger than other types of steel.
• They are highly resistant to wear and tear, making them ideal for use in applications where parts are subjected to high stress and friction. 
• Some types of alloy steel, such as stainless steel, are highly resistant to corrosion, making them ideal for use in harsh environments.
• Alloy steel is capable of withstanding high temperatures without losing its strength or other properties, making it ideal for use in high-temperature applications.
• It is a versatile material that can be customized to meet the specific needs of various applications. By adjusting the alloying elements and heat treatment, manufacturers can create alloy steel with specific properties.

Disadvantages of Alloy Steel

While alloy steel offers many advantages, there are also some disadvantages to consider, depending on the specific application which are discussed below.

• Alloy steel can be more expensive than other types of steel, especially when specialized alloys are required. This can be a significant factor in some applications where cost is a primary concern.
• Certain types of alloy steel can be difficult to weld due to their high carbon content, which can cause cracking and other problems during the welding process. This can increase the time and cost of manufacturing.
• In some cases, alloy steel can be susceptible to brittle fracture, which can lead to sudden and catastrophic failure of the component. This is particularly true for alloys with high carbon content, which can be prone to cracking under certain conditions.
• Some specialized alloys of alloy steel may not be readily available, which can make them difficult to source for some applications.

However, for many applications, the benefits of alloy steel far outweigh the disadvantages, making it a popular choice for a wide range of industries.

Applications of Alloy Steel

The applications cannot be listed as a whole as there are numerous applications for each alloy element. Let us look at some of the most notable.

Nomenclature of Steel

It is required to follow the specifications set forth by the American Iron and Steel Institute or AISI steel. There are various types of steel, each of which is identified by a three-digit acronym and perhaps a letter.

• The first digit represents the principal alloying element
• The second digit represents the subgroup alloying element or the relative percent of the principal alloying element.
• The final two digits represent the estimated amount of carbon in the alloy.

AISI steels are classified into

• 2XX: Austenitic steel with chromium, nickel, and manganese content
• 3XX: austenitic steel with chromium and nickel content
• 4XX: Chrome steel that is ferritic or martensitic
• 5XX: Medium-format martensitic steel.
• 6XX: Steel is hardened by chrome precipitation.

According to AISI SAE, these are the most used grades of stainless steel

1. AISI 304 stainless steel: Austenitic and non-magnetic steel
2. AISI 430 stainless steel: ferritic type with higher thermal stability
3. AISI 316 stainless steel: Austenitic alloy with nickel, chromium, and molybdenum.

Conclusion

There is a lot to learn about the types of steel from the AE/JE Mechanical previous year's question mock tests. With steel like support from our Super teachers, you can crack the AE/JE Mechanical exams with ease. 

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