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Table of contents:
Weldability, tensile strength, ductility, toughness, malleability – these are some of the common mechanical properties of steel that determines the type of steel that will be used in a project. While the toughness of Fe 550 TMT bars is what makes it suitable for infrastructure development projects such as bridges, the properties of anti-rusting and durability makes galvanised steel suitable for automotive body parts. In brief, the composition of steel gives it its unique properties, and it’s on the basis of these characteristics of steel that it is used in applications and industries.
In this short guide, we take a look at the mechanical and physical properties of steel, what makes different steel types suitable for specific applications, and as a business owner / buyer of steel, how to determine which steel type is the best choice for your business.
Before looking at the properties of steel, let’s understand the meaning of the same.
What is the meaning of mechanical properties of steel?
If you are familiar with how is steel produced or even the steel fabrication process, then you will know that based on its properties, steel will behave in a certain way under various forces and environments.
Its mechanical properties will determine how steel will deform, resist impact, or bear load without breaking. For instance, ductile steel can bend or stretch without snapping, making it suitable for construction of earthquake resistant buildings. TMT bars can provide building safety against natural disasters for this very property.
These mechanical properties gives steel its versatility in engineering and construction projects. It allows it to meet the diverse design requirements and maintain safety standards and longevity.
Now let us take a closer look at steel’s different mechanical properties and physical properties. Physical properties refer to those properties that can be measured (e.g., melting point). Mechanical properties refer to those properties which explain how a metal performs under force (e.g., strength, resistance to corrosion).
1. Tensile strength of steel
Tensile strength refers to the maximum amount of tensile stress steel can take before it cracks, breaks or fails. For instance, TMT bars, especially grades Fe 550 and Fe 600, come with high tensile strength. Reinforced TMT bars as such are often used for the construction of buildings and bridges where it is exposed to high stress and is able to withstand force without breaking.
The ability to not deform or break under extreme pressure, enables the steel to withstand heavy loads and harsh weather conditions, while providing stability and safety. The different grades of TMT bars offer different levels of tensile strength and and hence used accordingly.
2. Elongation or ductility
When steel has low tensile strength, it will break or deform under stress. Elongation or ductility as such is another key mechanical property of steel that refers to the degree to which steel can stretched or compressed before it breaks.
For instance, mild steel is ductile making it suitable for projects in areas prone to seismic activities. Since it can bend without breaking, it is resilient and can absorb and dissipate the earthquake shocks.
Similarly, among TMT bars, Fe 415 is more ductile than Fe 600.
TMT bars ductility or elongation (%)
| Fe 415 | Fe 500 | Fe 550 | Fe 600 |
| ~14.5% | ~12% | ~10% (more for the other variations, i.e., Fe 550D) | ~10% |
In simple terms, elongation refers to how flexible a particular grade of steel is.
3. Toughness
The next characteristic of steel we will look at is toughness or the amount of force that can be applied before the steel breaks.
Toughness refers to the metal’s ability to absorb energy and be able to deform without any fracture. This basically means that during bending, the steel should be able to resist any breakage or deformation. For instance, mild steel, along with being ductile, also demonstrates properties of toughness. Similarly, carbon steel is also tough, and hence used for making cutting tools, high-strength wires, etc.
Toughness in steel refers to unbreakability. That is, the extent to which steel can take and withstand impact (force) and not break. For instance, making anti-crash or crash-resistant car frames that can withstand force/pressure, take a hit and perform optimally.
Example of steel toughness:
- Automotive sector: High-toughness steel is used in the automotive sector to make roll cages, crumple zones, etc. These parts are able to absorb energy and withstand high impact, protect passengers, and prevent the vehicle from breakage and deformity. Usually, dual-phase (DP) steel is used for making automotive safety components.
- Construction sector: Various types of steel is used in the construction sector. TMT bars, especially Fe 415 and Fe500 are often used in constructing earthquake resistant buildings for reinforcement. TMT bars have high toughness and flexibility and can withstand the impact of an earthquake or natural callamity in seismic zones. As it can bend without breaking, TMT bars can absorb the energy, minimise damage to concrete buildings, and provide safety.
In general, low alloy steel are high on toughness. This explains why they are more suited for making heavy machinery and defence equipment, where metal performance is critical and there’s no room for failure or errors.
4. Hardness
Hardness is another characteristic of steel that makes certain types of steel suitable for wear-resistant applications. Hardness also makes steel suited for industries that require building components that are long-lasting and durable.
Common example is tool steel, which is hard and resistant to heat and abrasion. In general, alloy steel and high-carbon steel have properties of hardness. Tool steel as such is a suitable option for making tools like saws, hammers, cutting tools, etc. and can resist abrasion during impact.
5. Weldability
The carbon content in steel determines its weldability – the higher the carbon content, the lower is the steel’s weldability. Low carbon percentage (i.e., 0.04% to 0.30%) will increase the weldability property of steel.
In simple terms, weldability refers to how easily steel can be joined without its mechanical properties being affected. TMX steel has high weldability and elongation (16% – 23%) properties.
The composition of stainless steel, particularly grade 316 austenitic stainless steel is a highly weld-friendly steel type. It contains a high percentage of chromium (16% to 18%) and nickel (10% to 14%), and low percentage of molybdenum (2% to 3%) and carbon, making it highly weldable. It’s as such a suitable metal for use in making pipelines, tanks, and other complex structures.
6. Corrosion resistance in steel
Of the different mechanical properties of steel, resistant to rust and corrosion is the next property we will study.
This means that when exposed to specific environmental conditions, especially moisture and humidity, steel does not corrode, rust or degrade easily. That is, there is minimum chemical reaction or damage caused to steel. This is critical mechanical property of steel that makes it safe to be used in specific environments such as marine climate and coastal areas, for longevity.
For instance, corten steel (also known as weathering steel) is rust and corrosion resistant and has high tensile strength. It is commonly used in roofing solutions, landscape design, marine transport, bridges, etc. Similarly, stainless steel is corrosion resistant, making SS chequered plates preferable for use in food processing units
7. Yield strength
The yield strength of steel refers to steel’s ability to maintain its shape and form under stress. It’s the stress point at which steel begins to behave like a plastic and deform. It’s for this reason that carbon steel and certain alloy steel, with low yield strength, are used in the construction and manufacturing sector.
This property allows steel to keep its shape and form under force, making it suitable for projects that require design aesthetics and structural stability. This is especially important in the construction sector, when building high rises and skyscrapers, where it is critical to use material that can withstand stress without breaking.
8. Fatigue resistance
When we talk about steel’s resistance to fatigue, it refers to any weakness when under repeated stress or load. This can occur due to repeated load straining.
For instance, alloy steel and tool steel have high fatigue resistance. That is, it can withstand high stress and load for a long time without failure. This why, steel is used in making certain machine equipment such as cranes, required for material loading and unloading.
It is for this characteristic of steel that it is also used the aerospace sector for making components like aero turbines and engines.
9. Malleability
Malleability is another important mechanical property of steel. Put simply, it refers to steel’s ability to be rolled into sheets or compressed without breaking when pressure or stress is applied to it.
For instance:
- Galvanised steel is known for its malleability and is commonly used in making steel roofing and siding solutions.
- Galvanised steel is also used in the automotive sector for making body panels. It can be moulded into different shapes without tearing and is also corrosion resistant.
- Tin-plated steel is used in the food and packaging industry for making food cans. These are highly malleable and corrosion resistant. They can also easily be moulded into various sizes. There’s minimal contamination and the food can be kept safe in an air-tight environment.
The characteristic of malleability in steel, allows it to take intricate shapes and forms, to make the final product functional and aesthetically pleasing. Malleability is a key property for making steel sheets and steel plates.
How mechanical properties of steel impacts buying decisions?
Now that we understand the primary mechanical properties of steel, the question is, does this impact your buying decisions? And if so, how?
To answer this question, it’s important to understand that any given type of steel with come with a mix of all these properties. This means that any given type of steel will contain the mechanical properties of hardness, ductility, tensile strength, toughness, malleability and so on. What will vary is the proportion, composition and degree.
As such, as a business owner, when you decide to buy steel for your project, it’s advisable to learn about the different characteristics of steel types and make an informed decision. You can also consider alternatives to any specific steel type or the difference between its grades (e.g., difference between 304 and 316 stainless steel, or Fe 415 vs Fe 500 TMT bars).
Knowledge about the different types and grades based on the properties of steel will enable you to make smarter buying decisions.
Sohini is a seasoned content writer with 12 years’ experience in developing marketing and business content across multiple formats. At Tata nexarc, she leverages her skills in crafting curated content on the Indian MSME sector, steel procurement, and logistics. In her personal time, she enjoys reading fiction and being up-to-date on trends in digital marketing and the Indian business ecosystem.
