FIELD OF INVENTION
The present invention relates to a method of welding for thermo-mechanically
treated (TMT) rebar. More specifically the proposed invention is related to develop a
welding procedure to secure metal strength throughout its thickness including the
welding zone after welding of rebar of aforesaid genre.
BACKGROUND OF INVENTION
For 010,IS:9417 is applicable but for TMT, TMT CRS- no such specification was
available. The proposed invention has been developed by customer demand. The
producer and supplier of TMT rebar are frequently been asked by their customer to
advise for appropriate welding procedure as well as selection of welding electrode
for welding of TMT rebar due to non-availability of any IS standard or in any prior
published literature, in respect of welding of TMT rebar (suitable for concrete
reinforcement application) without any failure due to impairment of metal strength,
weld bead, microstructural properties and heat affected zone at the weld.
There is no specific procedure available for welding TMT bar. Welding procedure for
cold twisted deformed (CTD)bars have been provided in IS-1786-1985 and IS 9417-
1989 as follows:
i) Welding procedure - 3.2.2 of IS 1786-1985
ii) Butt welding procedure by shielded metal are welding process- inter pass
temperature to be maintained -10.3.4.1 (paragraph 1) of IS 9417-1989
iii) Electrodes -10.5.3 of IS 9417-1989
iv) Welding procedure for Lap Joint -10.5.4 of IS 9417-1989

The above standards laid down in IS standard was so far considered as the
base level input as guidelines for strength characteristics to be maintained for
welding of TMT bar.
There has been always a controversy about the maximum interpass
temperature to be maintained as provided by IS 9417-1989 which has
indicated that the interpass temperature should be restricted within 250s C as
stated in article 10.3.4.1 that 'That temperature of the bars at a distance about
one bar diameter from the joints shall not exceed 300° C immediately after the
bead is made. Before commencing the next bead, the temperature shall not
exceed 250o C".
The said standard provided by IS as has not given a specific guideline in
particular stages, has caused a serious concern to an industry in effect as if
somehow to maintain interpass temperature around 300° C or slightly more.
The said guideline being not sufficient for welding of TMT rebar, an upgraded
testing procedure over the IS procedure of welding in this respect was a long
felt need of the industry to be developed on investigation, recording and
assessment on fresh practical welding condition for better understanding and
securing of strength characteristics after welding of TMT rebar.
The present invention has proposed to remove the above difficulties of prior
state of art as laid down in IS guide lines by developing a testing procedure
for evaluating strength characteristics of TMT rebar after welding to secure
any failure in practical conditions of those welded TMT rebars in the above
context.
DESCRIPTION OF THE INVENTION
It is well known that inter pass temperature is just as important, as if not more
important than preheat temperature with regard to the mechanical and

micro structure properties of weld. For instance yield and ultimate tensile strength of
the weld metal are both related with maintenance of inter pass temperature
securely. High values of inter pass temperature tend to reduce the weld metal
strength. It is important to impose control over the maximum inter pass
temperature when certain mechanical weld metal properties are required. Those
criteria are as follows:
■ The effects of the welding process, procedures, and sequence of welding
must always be taken into account to maintain inter pass temperature with
the proper range.
■ The effects of both minimum and maximum inter pass temperature should be
considered with regard to the mechanical and microstructure properties of
the weld metal and the heat affected zone (HAZ).
The inter pass temperature should be maintained throughout the full thickness of
the base metal and some reasonable distance away from the weld, approximately
equal to one -inch, unless the codes specify otherwise.
One object of the invention is to carry out welding of TMT rebar maintaining
interpass temperature within the range of 234 to 310°C through out the thickness of
the test bar specimens along with the effect of minimum and maximum interpass
temperature with regard to the mechanical and microstructural properties of the
weld metal and the heat affected zone.
Another object of the invention is to study the input of higher interpass temperature
than that mentioned in IS 9417, on tensile properties of the TMT rebar before and
after welding and the interpass temperature being monitored by infrared
thermometer (CMSS 2000 infrared thermometer SKF).
A further object of the invention is to determine appropriate electrode specification
and TMT bar composition for welding of TMT bars without leading any defect in the
welded zone.

Yet another object of the invention is to provide welding procedure for obtaining
uniform cross sectional mechanical properties of welded TMT rebar for welding
procedure followed for lap joint (single side) with actual current 180 amperes
against current 140/180 amperes specified by proprietor for electrodes.
A still another object of the invention is to evaluate the performance of welding as
prescribed for AWS/SFA 5.5 E 8018.
The invention will be better understood from the following description with examples
and accompanying drawing in which.
Figure 1 is attached Welding (lap joint) of TMT rebar with diameter 20mm (d) and
interpass temperature 234 degree Centigrade, and length of weld X and Z and
overlap X, Y and Z each > 5d where X+Y+Z = 300 mm.
Figure 2 is attached Welding (lap joint) of TMT rebar with diameter 20mm (d) and
interpass temperature 310 degree Centigrade, and length of weld X and Z and
overlap X, Y and Z each > 5d where X+Y+Z = 300 mm.
Chemical composition of the TMT rebar is as shown in the table-1. Tensile properties
are evaluated against the specification as laid down in IS: 1608:2005/ISO:6892:1998
"Metallic Material Tensile Testing at ambient temperature" through YS, UTS, and %
elongation on inspection before welding.


Tensile properties before welding of TMT rebar of the above mentioned composition
is tested as follows:-

The chemical composition and tensile properties of the TMT rebar test specimen
conformed to IS: 1786:85 for grade Fe415. As no specific procedure was available
for welding of TMT rebar the following guidelines were followed during the welding:
10.3.4.1 (paragraph 1) [IS 9414-1989] for inter-pass temperature, 10.5.3 [IS 9417-
1989] for Electrodes and 10.5.4 [IS 9417-1989] for welding procedure were
followed for lap joint (single side) with actual current 180 amperes against current
140/180 amperes, specified by proprietor.

Paragraph 10.3.4.1 of IS 9417-89 for interpass temperature has stated as the
sequence of welding beads. The temperature of the bar at a distance of about one
bar diameter from the joints shall not exceed 310 degree Centigrade immediately
after the bead is made. Before commencing the next bead, the temperature shall
not exceed 234 degree Centigrade (contrary to the range of 250-300 degree
Centigrade mentioned in IS:9417-1989). The temperature may be checked
approximately by using temperature indicating crayons. However, in the absence of
temperature indicating devices, the bar may be allowed to cool down to hand hot
temperature before the next bead is deposited.
After completing bead 4, the bars are turned through 1800 and the beads 5 to 7 are
made in the same manner as described above. The top bead 8 is deposited as joint
is continuously rotated and the size of the reinforcement should be approximately as
indicated in Fig.2.
Paragraph 10.5.3 of IS 9417-1989 for electrode has specified the size of electrodes
according to the diameter of the bar to be welded shall be as follows:
Nominal Diameter of bar, d mm Size of Electrode, Max
Up to and including 10 2.5
Over 10 up to and 3.15
Including 18
Over18 up to and 4.0
Including 28
Over 28 5.0
Paragraph 10.5.4 of IS:9417-1989 for welding procedure of lap joint has specified
that the arc should be struck somewhere in the middle of the joint and not at its
beginning.

The various lap joints used to connect are shown in the Fig-1 and Fig-2.
Welding electrode is maintained confirming specification AWS/SF A 5.5. E 8018 with
composition in weight % C-0.05-0.10, Mn-1.4-1.85, S-0.030 Max, P-0.030 Max, Si-
0.20-0.48 and Ni-0.45-0.80 and size 4mm x 450mm.
Tensile properties inspected after welding of TMT rebar is narrated as follows in
table 3.


It was observed that no TMT rebar sample 1 to 6 above broke from the
welded region while maintained with interpass temperature from 234oC to
310° C.
The welding of TMT test piece following welding procedure for CTD bars
according to IS 9417:1989 is shown in Figure 1.
The above test procedure for welding test of TMT rebar was carried out with
inspection stages of
i. Prelim inary stage i.e. before commencing fabrication of welding,
ii. In process stage i.e. during fabrication by welding and
iii. After welding, followed by evaluation of mechanical properties after
welding.
From the test investigations as narrated above it is assessed and concluded that
Conclusion:
The above test results show that TMT rebar can be welded following the
above process without any detrimental impact.
Welding electrode: AWS/ SF A 5.5. E 8018 was found appropriate for
welding of TMT rebar.
The material can be welded satisfactorily even at the interpass temperature of
310° C without any detrimental effect on tensile properties.
The invention as narrated though described with a particular embodiment
should not be read and construed in a restrictive manner as some
modifications, alterations and changes are possible within the scope and limit
of the invention as defined in the encompassed appended claims.

WE CLAIM
1. A method of welding of thermo mechanically treated (TMT) welded metal
rebar with uniform strength maintaining throughout the thickness of welded
rebar comprising the steps of;
selecting the electrode as specified in AWS/SFA 5.5 E8018 after carrying out
test and evaluating suitable performance of welding of lap joint TMT rebar
specimens as specified in IS for CTD bars;
Characterized in that;
Expanded interpass temperature range of 234-310°C is provided throughout
the thickness of the test bar specimen and between bead to bead formation
than that of the range of 250-300°C as laid down in the IS specification to
secure the improved welding characters of TMT rebars.
2. A method of welding as claimed in claim 1, wherein the welding procedure for
welding of test pieces of TMT rebar is carried out with inspection stages of
i) preliminary stage i.e. before commencing fabrication of welding,
ii) in process stage i.e. during fabrication by welding and
iii) after welding, followed by evaluation of mechanical properties after
welding.
3. A method of welding as claimed in claim 1, wherein the interpass
temperature is monitored by infrared thermometer.

Abstract

A METHOD FOR WELDING THERMO-MECHANICALLY TREATED (TMT)
REBAR
An electrode as specified in AWS/SFA 5.5 E8018 is selected after
carrying out test and evaluating suitable performance of welding of TMT rebar (lap
joint) specimens with other standards for electrode as specified in IS for CTD bars.
Next, expanded interpass temperature range of 234-310°C is provided throughout
the thickness of the test bar specimen and between bead to bead formation than
that of the range of 250-300°C as laid down in the IS specification to secure the
improved welding characters of TMT rebar.