A new unbeatable combination of high yield strength and high tensile strength
A builder wants to create a robust construction. He picks a high grade steel for its strength. It is not rare that he then discovers it is not a suitable one and would fall short of the required performance. Now where did such a customer make an error? What is the confusion that caused him to reach an incorrect decision about the steel?
The main thing to bear in mind is your project’s need : where is it located, and what are the load parameters. About 54% of our country is in Zone 4 and Zone 5 category of seismic activity – this means that they are highly earthquake prone. Even in Zone 3, there is moderate seismic activity which is a challenge to the civil structures we put up.
Other than the important factor of the location, your choice of construction steel is directly related to the load aspects such as dead load, live load, wind load, and quake load – engineers have to ensure that material strength matches the load. In doing this, they have to provide for maximum safety without opting for an uneconomical choice.
TMT parameters and construction safety
What is the benchmark for safety, and for earthquake safety? Not only does it mean the building will not collapse even in a severe earthquake, it means that if there are frequent tremors in the region, the structure will not have any damage at all.
In March 2017, the Bureau of Indian Standards has specified various TMT grades in its amendment to IS 1786:2008, which address the need for ductility and seismic safety. It has also set the ductility values in terms of percentage elongation for grades – Fe415: 14.5%, Fe500 : 12%, and Fe550 : 8%.
The challenge is for higher grades from Fe500 to offer the ideal combination of tensile stength and ductility so that the structures can withstand dynamic and seismic loads for several decades.
Maintaining a safe ratio for better strength
At Icon Steel, with our experience and commitment to new product development, we took up the challenge of producing a steel with a high yield strength as well as a very high ultimate tensile strength (UTS). By maintaining a good ratio between them, our newly launched Icon DS 500 TMT bar is unique in its versatile combination of ductility ( with an elongation percentage of 18%) and strength with UTS of 535 N/sq.mm.
The manufacturing secret in the higher TMT grade is about how to form the outer martensite layer. The percentage of tempered martensite formed should not exceed 5-9%, otherwise it becomes quite brittle. This usually shows up in bending the bar as the ribs will spit up.
A TMT Bar with multiple advantages for the customer
Another practical advantage of the Icon DS 500 TMT bar is in its handling on site. It does not show the problems that are seen sometimes with Fe500 bars of hard bending or cracking and rib damage in bending. It happens because the martensite layer gets weakened in the bend. Similarly, there are issues related to welding as well.
If you are using a higher grade TMT bar and have to ensure both safety and a high tensile strength, you should select a bar with an elongation that is well over 14.5%. With an elongation of 18%, our Icon DS 500 sets a new standard in terms of customer satisfaction by assuring them of a secure construction and lower maintenance.
We can produce the rebar of desired Yield Strength by controlling the Rim Thickness and Hardness of the rebar. Thus we get the required percentage of elongation for a seismic load by maintaining a high UTS to YS ratio. In addition to a thicker martensite layer, it retains the thickness of the core for a superior ductility, thus resulting in a one-of-its-kind TMT bar – Icon DS 500 – that scores on both ultimate strength as well as safety.
This is in contrast with a common practice of creating a thicker martensite rim through additional quenching. The result of that practice is that strength is increased but the ductility is reduced. Icon Steels has avoided this compromise to develop a stronger and safer TMT bar that can be used across geographic regions and applications.