TMT Bars

Problems associated with High Strength Rebars

TMT Bar

Requirement of High Strength Rebars Problems associated with High Strength Rebars Technological developments in production processes of High Strength Rebars
Comparison of different processes for production of High Strength Rebars TMT Bars Manufacturing process TMT bars vs “Quenched & Tempered” bars
Advantages & Applications International Scenario Indian Scenario

Problems associated with High Strength Rebars

Reinforcement Steel can be in the form of mild steel, medium tensile steel, high tensile steel, deformed bars, high tensile steel wires, hard-drawn steel wire fabric, twisted steel fabric and so on but the mild steel and the deformed bars have remained under most common use.

In the last 15-20 years demand for higher strength deformed bars has been increasing. The most common of these bars is of strength grade Fe 415. Strength grade means the value of yield stress or the 0.2% proof stress.

You may here recall the definitions of yield stress & proof stress; which are as below :

Yield Stress:

Stress (i.e load per unit cross-sectional area) at which elongation first occurs in the test piece without increasing the load in tensile test. In case of steel with no definite yield point, proof stress is applicable.

0.2% Proof Stress:

The stress at which the non proportional elongation equal to 0.2% of the original gauge length takes place.

In India, deformed bars for concrete reinforcement are being produced for many years.

The main processes for their production are hot rolling or hot rolling followed by cold twisting. The increased yield strength was being first achieved by raising carbon & manganese and to a great extent by cold twisting.

These cold twisted bars, though in extensive use at present, continue to have inherent problem of inferior ductility, weldability and increased rate of corrosion due to presence of residual stresses and higher carbon content.

Additionally, cold twisting being labour intensive, enhances cost of production with limitation on production rates.

Increasingly varied & innovative applications have resulted in growing demand for larger diameter bars with similar strength, elongation, weldability and bendability as the small size bars.

Along with this, there is also a need for these steel bars to be welded and fabricated on the site easily.

For this strength & ductility have to be achieved at the lowest possible carbon content.

The most challenging requirement is to achieve all these superior properties at relatively lower cost.

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References:
Latest developments on steel front” by Jagvir Goyal
Thermex Quenching and Tempering Technology” by R.K. Markan, the Chairman and Managing Director of H&K India
Websites of SAIL, Rajuri steel & Evcon

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