Claims:WE CLAIM:

1. A seismic resistant reinforced steel bar having :

a steel composition comprising :
C 0.25-0.32;
Mn 0.6-1.0;
S Upto 0.04 max;
P Upto 0.04 max;
Si 0.10-0.40;
N upto 0.012 max and balance Fe which is substantially free of costly microalloy/ferro alloy addition and having a microstructure of an outer peripheral tempered Martensite layer and a core of Ferrite and Pearlite structure providing for UTS/YS ratio > 1.25 and % Uniform Elongation > 8 %.

2. A seismic resistant reinforced steel bar as claimed in claim 1 wherein variation in said carbon content selectively provides variable outer layer thickness of said tempered Martensite layer and desired strength of the said core Ferrite and Pearlite structure.

3. A reinforced steel bar as claimed in anyone of claims 1 or 2 having yield strength of 500 (min) N/mm2 and 650(max) N/mm2 and UTS 625 (min) N/mm2 preferably YS in the range of 525 N/mm2 to 575 N/mm2.

4. A seismic resistant reinforced steel bar as claimed in anyone of claims 1 to 3 wherein the %El is >16% preferably in the range of 17% to 25% and uniform elanogation is in the range of >8% to 15%.
5. A seismic resistant reinforced steel bar as claimed in anyone of claims 1 to 4 wherein said rebar diameter comprises 8 to 40 mm.

6. A seismic resistant reinforced steel bar as claimed in anyone of claims 1 to 5 wherein the carbon content is based on desired hardening of temper martensite layer and martensite layer thickness.

7. A process for manufacture of seismic resistant reinforced steel bar as claimed in anyone of claims 1 to 6 comprising:

providing selective steel composition comprising:

high C content in the range of 0.25-0.32;
Mn 0.6-1.0;
S Upto 0.04 max;
P Upto 0.04 max;
Si 0.10-0.40;
N upto 0.012 max and balance Fe which is substantially free of ferro alloys and processing to cast into billets;

subjecting said billets to processing including reheating furnace,rolling stages and controlled water quenching to develop a peripheral tempered martensite and a ferrite pearlite structure in the core and wherein the said peripheral tempered Martensite layer thickness is controlled involving selectively the said high carbon content in the steel composition substantially free of any ferro alloys and water flow rate under controlled quenching and said selective high carbon content free of ferro alloys generating core strength of Ferrite and Pearlite such as to achieve desired peripheral tempered Martensite layer thickness and Ferrite and Pearlite core combination favouring generation of said reinforced steel bar having UTS/YS ratio > 1.25 and % Uniform Elongation > 8 %.

8. A process as claimed in claim 7 wherein said peripheral tempered Martensite layer is reduced by controlled reducing water flow in said water quenching and also increasing the carbon content in the ferror alloy free steel composition.

9. A process as claimed in anyone of claims 7 or 8 comprising involving said selective increased carbon content in said ferro alloy free steel composition the said peripheral tempered martensite layer formation start temperature is decreased and thus less martensite ring thickness is achieved in combination with controlled reduced water flow during quenching while the said selective carbon content in the ferro alloy free steel composition ensured desired hardness of martensite whereby drop in YS due to less tempered martensite ring is compensated by the increase hardness of martensite layer.

10. A process as claimed in anyone of claims 7 to 9 wherein the step of controlled water quenching includes quenching in water boxes and self-tempering comprises temperature in the range of 550 to 650°C and water flow rate in the range of 200 to 2000 liter /min depending on mill speed and size of rebars.

11. A process as claimed in anyone of claims 7 to 10 comprising processing involving bar rod rolling parameters comprising :

Furnace temperature (soaking) in the range of 1050-11500C;
Cooling bed temperature in the range of 550-6500C;
Finishing rolling temperature < 10000C; and
Controlled cooling involving thermo-mechanical treatment under reduced water in the range of 200 to 2000 liter/min cooling in water box.

Dated this the 16th day of December, 2017
Anjan Sen
Of Anjan Sen & Associates
(Applicants Agent)
IN/PA-199

, Description:FIELD OF THE INVENTION:

Present invention relates to seismic resistant TMT(Thermo-mechanically-treated) Rebars. More particularly, the present invention is directed to provide seismic resistant TMT Rebars conforming to IS 1786 Fe500S grade for concrete reinforcement application under seismic condition and method of producing the same. This can be produced in the form of bar, coils and rod and can be used for reinforcement in concrete and similar application. The seismic resistant steel according to present invention is obtained by increased carbon content in C-Mn steel composition without any microalloy addition to achieve desired microstructure, improved mechanical properties and is characterized by high UTS/YS ratio and high uniform elongation (also called Total Elongation as per standard).

BACKGROUND OF THE INVENTION
In concrete reinforcement, steel rebar is used to impart tensile strength whereas concrete takes the compressive loads. Therefore steel rebar is a vital material in any construction industry whether it is high rise building, bridges or engineering projects. TMT rebar is very popular and replacing CTD (Cold-twisted-deformed) bars in construction industry because of high strength coupled with moderate elongation. TMT rebar is produced by thermo mechanically treatment which includes, rolling through a sequence of rolling stands comprising roughing,intermediate, and finishing stands which progressively reducethe billet to the final size and shape of the reinforcing bar. In the final rolling pass the bar is ribbed to give a good joint strength between steel and concrete. The high strength and moderate elongation is achieved in TMT rebar by a process called QST (Quench & Self Tempered). After the hot rolling is finished the hot rebar is “Quenched” by passing through a series of water box. This converts the surface layer of the bar to “Martensite” whereas the core remains as “Austenite”. In the second stage of ‘Self Tempering’ begins whenthe bar leaves the water box with a temperature gradientthrough its cross section, the temperature of the core beinghigher than that of the surface. This allows heat to flow fromthe core to the surface, resulting in tempering of the surface,giving a structure called ‘Tempered Martensite’ which is strong and tough. At that time the core converts to (Ferrite + Pearlite) microstructure.
As per IS 1786, There are several grades of high strength deformed steel wires for various applications in construction field. Depending upon the mechanical properties (mainly YS) requirement, grade is designated as Fe415, Fe500, Fe550, Fe600, Fe650 and Fe700 (number such as 415, 500 etc. denotes the minimum YS requirement) grades. Higher the grade (i.e. min. YS), lower is the required minimum elongation. But over the years, for grades 415 / 500 / 550, more ductile grades such as Fe415D, Fe500D & Fe550D are developed and being used.

For earthquake resistant reinforcement concrete (RC) structure, the RC member i.e. TMT rebar are expected to undergo large inelastic/ plastic deformations before failure for adequate seismic energy dissipation. Since post-yield behaviour of an RC structure is largely controlled by steel reinforcing bars, it places certain special requirements on their properties, such as high ultimate tensile strength to yield strength ratio (UTS/YS ratio) and uniform elongation. The larger the UTS/YS ratio, the better is energy absorption capability before failure. Larger deformations are experienced which could serve as a visible warning to the building occupants prior to failure or collapse.
Fe500S is the grade incorporated in IS 1786 for such earthquake resistant application in seismic zone. Its min. YS & Elongation requirement is same as that of Fe500D; but UTS / YS ratio requirement is = 1.25 against = 1.10 for Fe500D.
The present invention is thus directed to developing a cost effective Fe500S grade seismic resistant steel in C-Mn steel with higher carbon content but without addition of any costly alloying/ micro alloying elements, and its processing involving suitable water quenching + self-tempering after thermo mechanical rolling to achive desired microstructure along with critical UTS / YS ratio and specified range of YS & min. elongation properties suitable for application under seismic condition.
OBJECTS OF INVENTION

The basic object of the present invention is directed to provideseismic resistant reinforcementTMTRebars with minimum of 500 MPa yield strength and improved UTS/YS ratio of at least 1.25, high uniform elongation (more than 8%) conforming to IS 1786 Fe500S grade for construction applications at seismic conditions and a method of its production.
Another object of the present invention is to provide seismic resistant TMT Rebars having C-Mn steel composition without micro-alloy addition so that cost of the production is not increased.
A further object of the present invention is to providea process of producing the said grade of reinforced steel rebar following selective process steps and parameters to achieve desired microstructure to ensure the required strength and elongation properties as per the applicable standard.
A still further object of the present invention is to providea process of producing the said grade of reinforced steel rebarwithin the same set up such as mill speed and with minor adjustment in water flow so that mill set up is not hampered.
A still further object of the present invention is to providea process of producing the said grade of reinforced steel rebar wherein billets casted to 165*165 mm from steel melting shop are reheated in the reheating furnace and are subjected to different reduction ratios upto final diameter as per customer requirement in the Bar Rod Mill.
A still further object of the present invention is to providea process of producing the said grade of reinforced steel rebar wherein selection of proper chemistry within BIS specification with combination of controlled cooling is the key to achieve the critical UTS / YS ratio along with specified range of YS & min. elongation.
SUMMARY OF THE INVENTION

The basic aspect of the present invention is directed to provide a seismic resistant reinforced steel bar having:

a steel composition comprising :
C 0.25-0.32;
Mn 0.6-1.0;
S Upto 0.04 max;
P Upto 0.04 max;
Si 0.10-0.40;
N upto 0.012 max and balance Fe which is substantially free of costly microalloy/ferro alloy addition and having a microstructure of an outer peripheral tempered Martensite layer and a core of Ferrite and Pearlite structure providing for UTS/YS ratio > 1.25 and % Uniform Elongation > 8 %.

A further aspect of the present invention is directed to provide said seismic resistant reinforced steel bar wherein variation in said carbon content selectively provides variable outer layer thickness of said tempered Martensite layer and desired strength of the said core Ferrite and Pearlite structure.

A still further aspect of the present invention is directed to provide said seismic resistant reinforced steel bar having yield strength of 500 (min) N/mm2 and 650(max) N/mm2 and UTS 625 (min) N/mm2, preferably YS in the range of 525 N/mm2 to 575 N/mm2.

A still further aspect of the present invention is directed to provide said seismic resistant reinforced steel bar wherein the %El is >16% preferably in the range of 17 to 25 % and uniform elanogation is in the range of >8% to 15 %.

Another aspect of the present invention is directed to said seismic resistant reinforced steel bar wherein said rebar diameter comprises 8 to 40 mm.

Yet another aspect of the present invention is directed to said seismic resistant reinforced steel bar wherein the carbon content is based on desired hardening of temper martensite layer and martensite layer thickness.

A further aspect of the present invention is directed to a process for manufacture of seismic resistant reinforced steel bar comprising:

providing selective steel composition comprising:

high C content in the range of 0.25-0.32;
Mn 0.6-1.0;
S Upto 0.04 max;
P Upto 0.04 max;
Si 0.10-0.40;
N upto 0.012 max and balance Fe which is substantially free of ferro alloys and processing to cast into billets;

subjecting said billets to processing including reheating furnace,rolling stages and controlled water quenching to develop a peripheral tempered martensite and a ferrite pearlite structure in the core and wherein the said peripheral tempered Martensite layer thickness is controlled involving selectively the said high carbon content in the steel composition substantially free of any ferro alloys and water flow rate under controlled quenching and said selective high carbon content free of ferro alloys generating core strength of Ferrite and Pearlite such as to achieve desired peripheral tempered Martensite layer thickness and Ferrite and Pearlite core combination favouring generation of said reinforced steel bar having UTS/YS ratio > 1.25 and % Uniform Elongation > 8 %.

A still further aspect of the present invention is directed to said process wherein said peripheral tempered Martensite layer is reduced by controlled reducing water flow in said water quenching and also increasing the carbon content in the ferror alloy free steel composition.

A still further aspect of the present invention is directed to said process comprising involving said selective increased carbon content in said ferro alloy free steel composition the said peripheral tempered martensite layer formation start temperature is decreased and thus less martensite ring thickness is achieved in combination with controlled reduced water flow during quenching while the said selective carbon content in the ferro alloy free steel composition ensured desired hardness of martensite whereby drop in YS due to less tempered martensite ring is compensated by the increase hardness of martensite layer.

Another aspect of the present invention is directed to said process wherein the step of controlled water quenching includes quenching in water boxes and self tempering comprisetemperature in the range of 550 to 650°C and water flow rate in the range of 200 to 2000 liter /min depending on mill speed and diameter of rebar.

Yet another aspect of the present invention is directed to said process comprising processing involving bar rod rolling parameters comprising:

Furnace temperature (soaking) in the range of 1050-11500C;
Cooling bed temperature in the range of 550-6500C;
Finishing rolling temperature < 10000C; and
Controlled cooling involving thermos-mechanical treatment under reduced water in the range of 200 to 2000 liter/min cooling in water box.

The above and other objects and advantages of the present invention are described hereunder in greater details with reference to following accompanying non limiting illustrative drawings.

BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS
Figure 1: Process flow chart for Fe500 S grade steel rebars according to present invention.

Figure 2: Comparative illustration of Macrostructure of normal TMT Rebar versus the inventive seismic resistant TMT rebras of Fe500s grade having narrower Martensite layer Thickness.

Figure 3: showing the Microstructure Comparison of core (Ferrite + Pearlite Core) wherein normal TMT rebars having ferrite dominated core as compared to Fe500S grade obtained according to present invention having pearlite dominated core giving more strength.

Figure 4: shows load Vs Displacement graph for Seismic resistant grade (Fe500S) steel according to present invention.

Figure 5: shows Load Vs Displacement graph of normal reinforcement grade.

DETAILED DESCRIPTION OF THE INVENTION WITH REFERENCE TO ACCOMPANYING DRAWINGS

The present invention is directed to provide seismic resistant TMT Rebars conforming to IS 1786 Fe500S grade with minimum of 500 MPa yield strength and improved UTS/YS ratio of at least 1.25, high uniform elongation (more than 8%) for concrete reinforcement application under seismic condition and method of producing the same. As already described herein before that since post-yield behaviour of an RC structure is largely controlled by steel reinforcing bars, it requires certain special requirements of the rebars such as high ultimate tensile strength to yield strength ratio (UTS/YS ratio) and uniform elongation. The larger the UTS/YS ratio, the better is energy absorption capability before failure.

The present invention relates to development of Fe500S in C-Mn steel without addition of any alloying / micro alloying elements, suitable water quenching + self-tempering after thermo mechanical rolling. The billets casted to 165*165 mm from steel melting shop are reheated in the reheating furnace and are subjected to different reduction ratios upto final diameter as per customer requirement in the Bar Rod Mill. Selection of proper chemistry within BIS specification with combination of controlled cooling is the key to achieve the critical UTS / YS ratio along with specified range of YS & min. elongation.
This new steel reinforced grade is made through ConArc furnace steel making and Ladle RefiningFurnace (LRF) route. It is further cast into billets through continuous casting process. These billets are processed through reheating furnace andBar Rolling Mill(BRM) followed by controlled Quenching. The hot rolled reinforced bars are inspected manually. Samples are collected from the bars. These samples are tested in laboratory for cleanliness of steel and mechanical properties.
Normally in TMT rebar, the strength is achieved by the peripheral tempered martensitic rim developed by fast water quenching in the water boxes and self-tempering in the cooling bed and ductility is achieved by ferrite-pearlite structure in the core. More is the martensite ring thickness, more is the yield strength and less ductility because this hard martensite phases. To increase the UTS/YS ratio either a single phase structure is desired or controlled the martensite layer thickness. Single phase structure can be achieved by air cooling, but it lowers the yield strength. To compensate the strength, it requires to add costly ferro-alloys such as Mn and V/ Nb. Other option is controlling the tempered martensite layer thickness. Tempered Martensite layer thickness can be controlled by reducing the water flow and increase the carbon content.
Accordingly, the C-Mn steel compositionof new reinforced bar grade in weight % without any microalloyingselected for the present invention is as presented in following table 1:

Table 1:

C Mn S max. P max. Si N max.
0.25-0.32 0.6-1.0 0.04 0.04 0.10-0.40 0.012

The balance is Fe and unavoidable impurities.

Increasing Carbon content will decrease the martensite start temperature and thus less martensite ring thickness but due to increase Carbon, hardness of martensite will be high. Reduce water flow will also reduce the layer thickness. Thus drop in YS due to less tempered martensite ring will be compensated by the increase hardness of martensite layer. Due to high Carbon concentration, the core Ferrite + Pearlite structure got strengthen due to higher fraction of pearlite. This will improve the UTS/YS ratio as well as uniform elongation. In the present invention the tempered martensitic ring is controlled by reducing the water flow by 10 % as compared to normal rolling. This combination of chemical composition and water flow gives UTS/YS ratio > 1.25 and % Uniform Elongation > 8 %.
Now, the essential components of the steel grade for seismic resistance TMT rebarsaccording to present invention are described hereinafter with reasoning for selecting the respective concentration rangein weight percent.

Carbon (C) :0.25% or more and less than 0.32% by weight

Carbon is an essential element that provides strength and hardness to steel further maintains Pearlite structure. Carbon content is useful in achieving better balance between the strength and the elongation property. The carbon content needs to be more than 0.25 as increased C content will reduce the martensite start temperature and thus less martensite ring thickness. In the same time increased Carbon content will increase the hardness of tempered martensite. Thus controlling tempered martensite layer thickness and increased hardness of tempered martensite layer, desired YS and UTS/ YS is achieved.
The carbon content needs to below 0.32 % as (i) IS 1786 Fe500S standard requirement, (ii) Weldability will be poor.Accordingly C content is kept 0.25-0.32

Silicon (Si) : 0.1% or more and less than 0.4% by weight

Silicon is added as de-oxidiser for purity of Steel and has a strong solid solution strengthening effect hence acts to reinforce steel. Silicon needs to be contained within 0.4 % as excess of Silicon will deteriorate toughness and weldability of Steel. Further if, excessive silicon will deteriorate the surface quality of the rebar by making sticky scale during reheating of billet and difficult to remove during descaling. Accordingly, the Si content is kept 0.1-0.4, preferably 0.15-0.25 % by weight.

Manganese (Mn) : 0.6 % or more and 1.0% or less by weight

Mn acts as solid solution strengther. Further Manganese improves hardenability and access to critical alloying elements forming precipitate and acts pearlite stabilizer. It compensate the strength loss which arises due to less tempered martensite ring layer. Hence to ensure required strength, Mn content is kept as 0.6 % minimum. Increasing Mn content will increase the cost of the production. Also increased Mn has a high tendency of segregation so it’s content should not be very high. N this present invention, Mn content is kept as 0.6-1.0 %

Phosphorus (P) : 0.04% max or less by weight

Phosphorus improves the atmospheric corrosion resistance of the structural steel material, acts as solid solution strengthener and improves the shape-forming workability of the steel, such rib forming in Construction steel. But Phosphorous, when added in large amount deteriorates the toughness and rollability. In addition, the segregation of phosphorus at grain boundaries has been found to result in brittleness of the steel bar. For these reasons, the upper limit of phosphorus content in the present steel composition is kept as 0.04% by weight maximum. This is also requirement of IS1786 Fe500S grade.

Sulphur (S): 0.04% max or less by weight

As per standard requirement, sulfur content should not exceed 0.04%, Accordingly, the S content is restricted to less than 0.04% by weight.

Nitrogen (N): not more than 0.012% by weight

Nitrogen acts as solid solution strengthener. It also combines with micro alloy such as Nb/V/Ti to form Nitride/ Carbonitride precipitates and thus increase strength. Excess nitrogen causes a large amount of nitride to precipitate, thereby deteriorating ductility and hardenability and induces the phenomenon of room temperature ageing, which will cause the change of the mechanical properties of the steel and the restoration of the yield point elongation of the steel. In this present composition, as there is no microalloy used, so chances of precipitation is less. Therefore, the amount of nitrogen should be no more than 0.012%. This is also requirement of IS1786 normal Fe500 grade.

The composition may further include the following elements optionally:

Copper (Cu) : 0% or more and 0.30% or less by weight
Copper is an element that improves the atmospheric corrosion resistance of the structural steel material. In this present case copper is not added intentionally and its maximal limit is restricted to 0.30%.

Chromium (Cr) : 0% or more and 0.5% or less by weight

Chromium is generally added to steel to increase corrosion resistance and oxidation resistance. Chromium also increases hardenability and improves high temperature strength. In this present case chromium is not added intentionally and its maximal limit is restricted to 0.50%.

Nickel (Ni) : 0 % or more and 0.3% or less by weight

Nickel addition to the chemical composition of steel improves the red hot strength and corrosion resistance properties. In this present case nickel is not added intentionally and its maximal limit is restricted to 0.30%.

The balance is Fe and unavoidable impurities.

Details of the process of manufacturing:

Aseismic resistant reinforcement steel having the composition described above is prepared by obtaining molten steel through steel making, followed by ingot making or continuous casting in billets. To produce a seismic resistant reinforcement steel having desired properties, the billet is subjected to reheating, descaling, rough rolling, Bar rod rolling, Thermal mechanical treatment and bundling, details of which will be described hereinafter.

The process route followed to produce the seismic resistant TMT Rebars according to present invention comprising the steps of:
a) Primary Steel Making by ConArc or similar furnace
b) Secondary steel making: Ladle Refining Furnace.
c) Continuous billet casting into (165 x 165 mm)
d)Re-heating, bar rod rolling, controlled cooling and cut to length with set optimum processing parameters.

Accompanying Figure 1 illustrates the process flow chart for producing Fe500S grade TMT Rebars according to present invention.

The Bar rod rolling parameters specified for processing are presented in the following Table 2:

Table 2:
1 Furnace Temperature (Soaking) 1050 – 1150 °C
2 Cooling bed Temperature 550-650 °C
3 Finish Rolling Temperature < 1000 °C
4 Controlled cooling Thermo Mechanical Treatment (reduced water cooling in water box)

The material specifications of the TMT Rebars produced according to above process of present invention in supply conditions are as presented in the following Table 3:

Table 3:

1 Chemical Composition As per Table 1
2 Rebar Diameter 8 - 40 mm
4 Yield Strength 500 (min) N/mm2 and 650(max) N/mm2
5 UTS 625 (min) N/mm2
6 UTS/YS >1.25
7 %El >16%
8 %Uniform El ? 8%
9 Weight per meter As per sample diameter
10 Bend Test OK
11 Rebend Test OK
112 Microstructure Tempered Martensite + (Ferrite + Pearlite)

Trials were conducted with various steel composition with the normal grade vis-a vis the Fe 500S grade according to present invention and the comparison of Normal and Invention Chemistry and Mechanical properties are presented in the following Table 4 wherein the samples marked as “invented” in remarks column conform to the specification and properties according to IS 1786 Fe500S grade:

Table 4:

It would be apparent from data provided in Table 4 that:

Sr No 1- 11, where Carbon is lower than the selected range and with no ferro alloy addition and water level as per conventional, the properties not conforming to desired standard for Fe500S grade.

Sr No 12-17, where Carbon is in the selected range and water flow beyond the claim range, the properties not conforming to standard for Fe500S grade.

Sr No 18-24, where Carbon range is in selected range and water flow reduced by 10 %, the properties of resulting steel grade conform to applicable standard for Fe500S grade according to present invention.

Mechanical Tests and Metallography

The tensile properties (yield strength and ultimate tensile strength) are measured using 600 mm long and gauge length = 5 d ( where d is the nominal diameter of the rebar)test specimens on a universal testing machine. Bend rebend test is also conducted as per the standard requirement of IS1786. All tests are performed at room temperature.

Metallographic analysis is carried out rate the cleanliness of steel. Metallographic samples prepared are polished and etched with 5% nital. A simple light optical microscope is used to record the core and outer microstructure comprising the material.

Accompanying Figure 2 shows thecomparative illustration of Macrostructure of normal TMT Rebar versus the inventive seismic resistant TMT rebars of Fe500S grade, where(a)normal TMT Rebar having Martensite layer thickness comparatively higher, while (b) Invented TMT rebar( Fe500S) having Martensite layer thickness is lower.

Accompanying Figure 3 showing the Microstructure Comparison of core (Ferrite + Pearlite Core) wherein (a)normal TMT rebarsare having ferrite dominated core as compared to (b) Fe500S grade obtained according to present invention having pearlite dominated core giving more strength.

Accompanying Figure 4 shows load Vs Displacement graph for Seismic resistant grade (Fe500S) steel according to present invention, the details of the test parameters and results as shown in graph favouring higher UTS/YS ratio with improved uniform elongation are as follows:

Diameter 40 mm
Proof Load 685 kN
0.2% Proof Stress (YS) 551 Mpa
Load at Peak 877 kN
Tensile Strength (UTS) 705 Mpa
UTS/YS ratio 1.28
%El 17
% Uniform Elongation 8.3

Accompanying Figure 5 shows Load Vs Displacement graph of normal reinforcement grade, the details of the test parameters and results as shown in graph are as follows:

Diameter 40 mm
Proof Load 700 kN
0.2% Proof Stress (YS) 569 Mpa
Load at Peak 855 kN
Tensile Strength (UTS) 694 Mpa
UTS/YS Ratio 1.22
%El 17
% Uniform Elongation 6.8

It is thus possible by way of the present invention to provide seismic resistant reinforcementTMTRebars with minimum of 500 MPa yield strength and improved UTS/YS ratio of more than 1.25, high uniform elongation (more than 8%) for construction applications at seismic conditions conforming to IS 1786 Fe500S, having cost effective high carbon containing C-Mn steel composition without any microalloy addition selectively processed with controlled bar rolling and thermo mechanical treatment involving reduced water flow at cooling bed to ensure a microstructure with narrower and harder martensite rim and pearlite dominated Ferrite + Pearlite core structure resulting in higher energy absorption capability before failure.