How are buildings kept tall, or bridges made to last decades? Any big structure takes support, and that support all depends on steel of the highest quality. Behind the clan of construction are these hot-rolled deformed bars that have been made to withstand pressure, weather, and time. Strong and trustworthy must justify their heavy-duty classification. Let’s take a glance and see why they are so special.
This blog closely examines hot-rolled deformed bars, their properties, manufacturing, advantages, applications, and more.
What Are Hot-Rolled Deformed Bars?
Hot-rolled deformed bars or Thermo Mechanically Treated Bars (TMT Bars) are steel reinforcement bars that undergo hot rolling and incorporate surface deformations such as ribs or indentations. The surface deformations greatly contribute to the bonding of steel with concrete and thus impart the ability to carry tensile loads better. In terms of processing, hot rolling means that the steel is rolled in its plastic state, being heated more than its recrystallisation temperature, and then passed through the roller.
These bars are usually prefixed by their grade, such as Fe415, Fe500, or Fe550, which indicates their characteristic yield strength. They find larger applications in construction for reinforcing concrete structures like beams, slabs, columns, and foundations.
Properties and Composition of Hot-Rolled Deformed Bars
Composition
Hot-rolled deformed bars consist of low-carbon steel with small percentages of elements like manganese, sulfur, phosphorus, and silicon. Here is the detailed composition of the steel:
| Elements | Typical Range (In Percentage) |
| Carbon | 0.25 to 0.30 |
| Managanese | 0.50 to 1.50 |
| Silicon | 0.10 to 0.30 |
| Sulphur | ≤ 0.050 (Preferably ≤ 0.035) |
| Phosphorous | ≤ 0.050 (Preferably ≤ 0.035) |
Key Properties
- Depending on the type of bars, these bars have a tensile strength of about 415 MPa to 600 MPa.
- Because low carbon content is used in manufacturing, the welded joints provide good weldability.
- It has good bond strength due to surface ribs and deformation on the surface.
- These rebars are ductile and can be bent without fracturing, hence preferred in seismic-prone areas.
- The treating procedures for resistant degradation processes also provide some corrosion resistance, more so when properly treated or coated.
All these properties are crucial for the bar’s performance in compression and tension when reinforced with concrete.
Manufacturing Process of Hot Rolled Deformed Bars
Extraction of Iron and Melting
The manufacturing of hot-rolled deformed bars starts with the step of extraction of iron from iron ore. The ore, together with coke and limestone, is charged into the blast furnace, where the charges are heated to a very high temperature. At higher temperatures, heating is done whereby the melting of the iron takes place, and the separation of the iron and impurities takes place. Conversion of molten iron into steel is the next step in finishing. The steel provides the basic material for the manufacturing process.
Hot Rolling
The steel is cast into rectangular billets and subsequently reheated at temperatures lying between 1100°C and 1250°C in a furnace. The hot billets are rolled in many stages through rolls to give long cylindrical bars. In the latter stages of rolling, ribs or deformations are given on the surface of the bars to provide better bonding with concrete.
Quenching
The red-hot bars are allowed to pass by way of a quenching box, wherein high-pressure water jets cool the bars almost instantly. Such abrupt cooling transforms the outer layer into a hard structure known as martensite, whereas the inner core of the bar stays hot and malleable.
Self Tempering
Upon exiting the quenching zone, heat from the still-hot core flows outward, tempering the outer martensitic layer. Hence, by the process of self-tempering, the brittle martensite becomes tempered martensite, which is strong but not brittle, thus rendering the bars ductile.
Atmospheric Cooling
After which, bars are transferred onto cooling beds and allowed to cool naturally in an open atmosphere. During this period, the inner core begins to slowly transform into a ferrite-pearlite structure that has a ductile inner core and a hard outer shell-just the right combination to reinforce concrete.
Applications of Hot-Rolled Deformed Bars in Construction
The hot-rolled deformed bars are extensively deployed in various types of construction:
- Residential Buildings: Foundation, columns, beams, and slabs.
- Commercial Structures: High-rise structures, commercial complexes, malls, and office spaces.
- Infrastructure Projects: Bridges, tunnels, highways, and dams.
- Industrial Construction: Factories, warehouses, and storage tanks.
- Marine and Coastal Works: Due to corrosion-resistant types, they are useful in humid or saline environments.
Such bars are essential for any structure to act as tensile reinforcement, load-bearing agencies, and those resisting several seismic activities.
Advantages of Using Hot-Rolled Deformed Bars
- Structural Security: They are imbued with the power of a strong bond with the concrete with which they are applied to yield strength and an increased lifespan for the structures.
- Economic Efficiency: Being readily available in standard sizes, they can be carried from site to site. Thus, they cut down labour costs and construction time.
- Versatility: They are used for any type of structure, from a small house to large infrastructure projects.
- Sustainability: Since several companies manufacture the bars with recycled steel, the bars hope to be an environmentally friendly option.
- Compliance with Standards: They are manufactured conforming to various national or international codes, such as ASTM, BIS, or ISO, which together ensure standard quality.
How to Select the Best Hot Rolled Deformed Bars for Your Project?
Grade of Steel
Select the grade based on structural load and design. Most commonly, Fe 500 or Fe 500d grades are used for residential and commercial works, respectively, with the latter being more dense.
Standard Compliance
Make sure the bars meet the standards laid down by your country or international ones such as IS 1786, ASTM A615, or BS 4449.
Corrosion Resistance Requirements
If the project lies in an environment with coastal or chemical aggression, bars need to be considered for an epoxy coating or be corrosion-resistant.
Test Certificates
Always ask for mill test certificates (MTCs) that will state their chemical and mechanical properties.
Visual Inspection
Look for uniform deformations, the presence of rust, and diameter consistency.
Conclusion
The hot-rolled deformed bars are pretty much the workhorses of civil engineering. Given their strength, ductility, and bonding capacity with concrete, they are very important reinforcement materials for protecting life and making structures stand. With TMT processing, micro-alloying, and many other enhancements in manufacturing methods today, these bars are more accessible and better performing than ever.
Choosing an appropriate type of deformed bar affects the finish of your work and its lifespan. Besides, whether you are a contractor, civil engineer, or project manager, knowing the properties and benefits of hot-rolled deformed bars truly helps one make informed decisions to meet safety and performance requirements.