TMT steel bars compliments “Reinforced Cement Concrete” (RCC) which has become an integral part of every structure, be it a multi-storied building, a tunnel, a flyover, a TV tower etc. Here are some of the most frequently asked questions about TMT bars answered

1. FAQs
1. What is TMT?
Thermo Mechanical Processing, also known as Thermo-Mechanical Treatment (TMT), is
a metallurgical process that integrates work hardening and heat treatment into a single
process.
The quenching process produces a high strength bar from low carbon steel. The
process quenches the surface layer of the bar, which pressurizes and deforms the
crystal structure of intermediate layers, and simultaneously begins to temper the
quenched layers using the heat from the bar's core.
2. What is the need for TMT?
TMT steel bars compliments “Reinforced Cement Concrete” (RCC) which has become an
integral part of every structure, be it a multi-storied building, a tunnel, a flyover, a TV
tower etc.
With TMT, RCC can be molded into any desired shape and steel Rebars gain the ability
to withstand any load made to act upon them.
These unnecessary forces can be developed by any live or dead load acting upon the
structures thus causing loss of life and property.
In order to secure creations of mankind and to make them ever lasting for generations
to come the steel Rebars should conform to quality standards best in class.
3. What is the process involved in TMT?
Thermo-mechanical treatment involves three stage:
Stage 1: Quenching
The hot rolled bar leaves the finishing mill stand at 1050 deg Celsius which is rapidly
quenched by special split style nozzle cooling process. The quenching converts the
billet's surface layer to martensite, and causes it to shrink. The shrinkage pressurizes the
core helping to form the correct crystal structures, while the core remains hot and
austenitic.
Stage 2: Self Tempering
The bar leaves the quench box with a temperature gradient through its cross section
and as the bar cools, heat flows from the bar's centre to its surface so that the bar's
heat and pressure correctly tempers an intermediate ring of martensite and bainite
Stage 3: Atmospheric Cooling
Finally, the slow cooling after quenching automatically tempers the austenitic core to
ferrite and Pearlite on the cooling bed which is having strong, tough, tempered

2. martensite in the surface layer of the bar, an intermediate layer of martensite and
bainite, and a refined, tough and ductile ferrite and pearlite core.
4. What is the advantage of using CRS (corrosion Resistance steel) rebar?
Advantages of using CRS Rebar:
 Longer Life
 High yield strength coupled with good ductility and bendability
 No extra precaution required in material handling and transportation
 No maintenance required during fabrication
 More suitable under poor workmanship conditions at site
 No extra precaution during welding
 Can be bent and re-bent around very small mandrels.
 Fatigue tests show it can be used as reinforcement material in seismic zones.
5. What is the advantage of De-scaling the Billets before rolling?
When TMT bars are produced by descaled billets with the help of high pressure Descaler
(working at more than 230 bar pressure) placed at the exit of reheating furnace. This
eliminates the possibility of rolled –in-scale in the finished rebar.
Descaling ensures uniform development of martensitic rim depth of up to 25% of the
diameter in the finished rebar after quenching and ensures high strength and ductility in
the finished rebar as yield strength increase with the rim thickness and also reduces
hardness from the outer surface reducing the brittle nature of the rebar as the more the
hardness, more is the brittleness.
In Rebars manufactured without descaling, the scales get rolled in with the product and
during mechanical working peels off from the surface of the rebar and hence making the
rebar surface more prone to corrosion.

3. 6. What is the influence of different chemical ingredient in steel on the properties of
rebar?
S.NO CHEMICAL ELEMENT
EFFECT ON REBAR
CONTROLLING PROPERTY ACTUAL EFFECT
1 Carbon (C)
Hardness, strength, weldability and
brittleness
Higher carbon contributes to the tensile strength of
steel, that is, higher load bearing capacity and vice
versa. Lower carbon content less than 0.1% will reduce
the strength. Higher carbon content 0f 0.3% and above
makes the steel bar unweldable and brittle.
2 Manganese(Mn) Strength and yield strength
The manganese content in steel is not specified as per
IS:1786-2008,however higher manganese content in steel
increases the tensile strength and also the carbon
equivalent property
3 Sulphur (S)
Present as an impurity in steel which
increases its brittleness
Presence of Sulphur should be limited as per IS:1786-
2008.Presence of higher Sulphur makes the bar brittle
during twisting, as higher Sulphur content brings the hot
shot problem during rolling.
4 Phosphorus(P)
Present as an impurity in steel which
increases strength and brittleness
Higher phosphorous content leads to increase in strength
and corrosion resistance properties but brings brittleness
due to the formation of low euctoid phosphicles in the
grain boundary. Also lowers the impact value at sub-zero
temperature level(transition temperature)
5 Copper (Cu)
Strength and corrosion resistance
properties
Being a pearlite stabilizer it increases the strength and
corrosion resistance property.
6 Chromium(Cr) Weldability and corrosion resistance
Present as an impurity and influences carbon equivalent
and increases corrosion resistance property.
7
Carbon
Equivalent(CE)
Hardness, tensile strength and
weldability
Carbon Equivalent is measure of the tendency of the
weld to form martensite on cooling and suffer brittle
fracture. It is directly related to hydrogen induced cold
cracking which is a most common weld defect for steel.
Higher concentration of carbon and other alloying
element tend to increase hardness and decrease
weldability

4. 7. What is Carbon Equivalent and how does it enhances the weldability of Jindal Panther
TMT?
Carbon Equivalent is measure of the tendency of the weld to form martensite on cooling
and suffer brittle fracture. It is directly related to hydrogen induced cold cracking which
is a most common weld defect for steel. Higher concentration of carbon and other
alloying element tend to increase hardness and decrease weldability
TMT process can produce the desired yield strength with steel of relatively lower carbon
equivalent by adjusting the on-line heat treatment parameters.
CARBON EQUIVALENT WELDABILITY
Up to 0.35 Excellent(JSPL’S CE)
0.36-0.40 Very good
0.41-0.45 Good
.46-0.50 Fair
Over 0.500 Poor
8. Why low level of Sulphur and Phosphorous makes TMT bars superior in quality?
Lower the level of Sulphur and Phosphorous, more is the strength of steel.
Effect of Sulphur & Phosphorous:
Phospho
rous
Excess level of P can lead to cold shortness wherein the steel
undergoes brittle fracture while working in extremely cold condition
and hence becomes more prone to cracking.
Sulphur Excess level of S can lead to hot shortness wherein the melting point
of steel gets lowered and hence making steel more prone to failure
under extreme high temperature conditions and steel strength gets
lowered drastically.

5. 9. What is Stress-Strain curve and what is the importance of YS, UTS and Percentage
Elongation?
Stress-strain curve is an extremely important graphical measure of material’s
mechanical properties
Yield stress: The stress a material can withstand without permanent deformation, Yield
strength is usually stated as the stress at which a permanent deformation of 0.2% of the
original dimension will result, known as the 0.2% yield stress.
OR
The stress at which a non-proportional elongation equals to 0.2 % of the original gauge
length takes place (where gauge length is 5.65sqrt A.’A’ is the cross sectional area of the
test piece).
Ultimate Tensile Strength: The maximum stress a material can withstand in a tensile
test.
OR
The maximum load (force) reached in a tensile test divided by the effective cross
sectional area of gauge length portion of the test piece.
Percentage Elongation: When a material is tested for tensile strength it elongates a
certain amount before fracture takes place. The two pieces are placed together and the
amount of extension is measured against marks made before starting the test and is
expressed as a percentage of the original gauge length.
10. What is the misconception about the reddish color of TMT Rebar?
Often due to interaction of the rebar with moisture and air, the surface of the rebar
develops a reddish colour which is being misunderstood as corrosion. In fact, reddish
rebar can be used for construction without any hesitation so long they are in proper
physical shape, weight and strength.