Title of Invention	"A PROCESS OF PRODUCING SOUND WELDED JOINTS FOR ATMOSPHERIC AND MARINE-CORROSION RESISTANT STEEL BARS"
Abstract	The invention provides a process of producing sound welded joints, which are adequately strong and free from welding defects, In atmospheric-corrosion resistant (Cu-TMT) steel bars and marine-corrosion resistant (Cu-Cr-TMT) steel bars, comprising the steps: (a) preparing the joint areas of the steel bars in known methods, (b) selecting the electrode wire of low hydrogen type conforming to AWA A 5.5 E 8018-W code and its coating material of suitable type, (c) using up to 7 passes for butt-welding, (d) following the conditions for butt-welding as (l) both Cu-TME and Cu-Cr-TMT bars are welded without being preheated; (ii) for welding Cu-THT bars, electrodes are used without being rebaked; (iii) for welding Cu-Cr-TMT bars, electrodes are used after baking at 350°C for 2h or at 400°C for 1h; (iv) both Cu-TMT and Cu-Cr-TMT .. bars are welded at a heat input of 7-10 KJcm-1 for electrode diameter of 2,5 mm and 10-15 KTcm1 for electrode diameter of 3.15 mm; (v) both Cu-TMT and Cu-Cr-TMT bars are welded at a current-voltage-heat input combination of 80-1OOA, 20-24V, 7-10 KJcm1 for electrode diameter of 2.5 mm; and of 100-140A, 22-25V, 10-15 KJcm1 for electrode diameter of 3.15 mm; and (vi) both Cu-TMT and Cu-Cr-TMT bars are welded at an electrode inter-pass temperature of 225°C max. and without any post-welding heat treatment of the bars; and for lap welding as (i) both Cu-TMT and Cu-Cr-TMT bars are welded without being preheated; (ii) for welding Cu-TMT bars, electrodes are used without being rebaked and for welding of Cu-Cr-TMT bars, electrodes are rebaked at 350°C - 2 hrs or 400°C - 1 hr before use; (ill) both Cu-TWT and Cu-Cr-TMT bars are welded at heat Input of 7-10 KJcm1 for electrode diameter of 2.5 mm; and (iv) Cu-TMT bars are welded at an overlapped length of 70 mm (min.) and Cu-Cr-TMT bars are welded at an overlapped length of 100 mm (min.).

Title of Invention

"A PROCESS OF PRODUCING SOUND WELDED JOINTS FOR ATMOSPHERIC AND MARINE-CORROSION RESISTANT STEEL BARS"

Abstract

The invention provides a process of producing sound welded joints, which are adequately strong and free from welding defects, In atmospheric-corrosion resistant (Cu-TMT) steel bars and marine-corrosion resistant (Cu-Cr-TMT) steel bars, comprising the steps: (a) preparing the joint areas of the steel bars in known methods, (b) selecting the electrode wire of low hydrogen type conforming to AWA A 5.5 E 8018-W code and its coating material of suitable type, (c) using up to 7 passes for butt-welding, (d) following the conditions for butt-welding as (l) both Cu-TME and Cu-Cr-TMT bars are welded without being preheated; (ii) for welding Cu-THT bars, electrodes are used without being rebaked; (iii) for welding Cu-Cr-TMT bars, electrodes are used after baking at 350°C for 2h or at 400°C for 1h; (iv) both Cu-TMT and Cu-Cr-TMT .. bars are welded at a heat input of 7-10 KJcm-1 for electrode diameter of 2,5 mm and 10-15 KTcm1 for electrode diameter of 3.15 mm; (v) both Cu-TMT and Cu-Cr-TMT bars are welded at a current-voltage-heat input combination of 80-1OOA, 20-24V, 7-10 KJcm1 for electrode diameter of 2.5 mm; and of 100-140A, 22-25V, 10-15 KJcm1 for electrode diameter of 3.15 mm; and (vi) both Cu-TMT and Cu-Cr-TMT bars are welded at an electrode inter-pass temperature of 225°C max. and without any post-welding heat treatment of the bars; and for lap welding as (i) both Cu-TMT and Cu-Cr-TMT bars are welded without being preheated; (ii) for welding Cu-TMT bars, electrodes are used without being rebaked and for welding of Cu-Cr-TMT bars, electrodes are rebaked at 350°C - 2 hrs or 400°C - 1 hr before use; (ill) both Cu-TWT and Cu-Cr-TMT bars are welded at heat Input of 7-10 KJcm1 for electrode diameter of 2.5 mm; and (iv) Cu-TMT bars are welded at an overlapped length of 70 mm (min.) and Cu-Cr-TMT bars are welded at an overlapped length of 100 mm (min.).

Full Text	The present invention relates to a process of producing sound welded Joints_foratmospheric - and marine - corrosion resistant steel bars using SMAW technique. The invention relates more particularly to a process for producing welded joints in TMT r-ebars. The examples of thermo-mechanically treated (TMT) atmospheric - and marine - corrosion resistant steel bars are respectively type Cu - TMT (500) and type Cu - Cr - TMT (500), having chemical compositions as given in Table I from which it is noted tha the only difference between bars is in respect of their Cu/Cr/Ni content. The Joints produced by both butt -and lap - welding of such bacs using the conventional "Shield Metal Arc Welding" (SMAW) method are occasionally associated with welding defects due to improper selection of welding parameters, leading to premature failure of such bars in their end-use applications. The object of the present invention is provide a process for producing adequately strong and defect-free welded Joints in Cu-TMT(500) and Cu-Cr TMT (500) type steel bars. In the conventional SMAW process of welding, an arc is generated between a coated electrode wire and a base metal by momentarily touching the base metal by the electrode wire, which produces enough heat for melting both the base metal and electrode wire at the areas to be welded. The electrode wire metal is thereby transferred into the pool of molten base metal and gets deposited on the base metal surface on solidification of both the molten electrode and base metal as the position of electrode wire end is shifted along the base metal surface to be welded. The electrode wire metal deposited on the base metal gets covered by a slag produced from the heated coating material of the electrode wire. A protective gaseous shield is produced by decomposition of the heated coating material of the electrode to envelop the arc. The main steps followed in the invented process are :-(i) joint preparation and number of passes for butt welding; (ii) selection of electrode wire and its coating material; (iii) optimisation of the conditions for welding; (iv) evaluation of properties and soundness of the welded Joints produced. The invention is described fully and particularly in an unrestricted manner with reference to the accompanying drawings, in which Figure 1 is a schematic lay-out of the conventional SMAW method of welding; Figure 2 is a schematic lay-out of butt-welding process; and Figure 3 is a schematic lay-out of single lap-welding process. Referring to Fig. 1, an arc A is produced between electrode wire E, having a coating C and the region B of the base metal M to melt both the base and electrode wire metal there. The droplets D of the molten electrode wire metal are deposited on the molten base metal pool to form a pool of molten weld metal W there, which on solidification produces a deposit of solidified weld metal S on the base metal M. A layer of slag G is formed on the solidified weld metal S by deposition of heated coating material of the electrode wire E. A protective gaseous shield H is formed by the decomposition products of the heated coating material of the electrode wire. The slag layer G and the protective gaseous shield H prevent the weld metal W from oxidation. The direction T of moving the electrode wire is shown to be from the left-hand end to the right-hand end of the base metal M. The electrode wire used in the process is of a low hydrogen type conforming to AWS A 5.5 E 8018-V code. Table - I Chemical Composition of Cu-TMT (500) and Cu-Cr-TMT (500) type of Steel Bars Welded. (Table Removed) Referring to Fig. 2 the adjacent ends X and Y of two bars M1 and M2 are butt-welded by adopting seven passes of the welding electrode wire under the welding conditions outlined in Table - II. Table - II Conditions for Butt-Welding (Table Removed) Referring to Fig. 3, the adjacent surfaces of two bars M1 and M2 are joined by single lap-welding over the overlapping length V of the bars under conditions followed for the two types of bars, namely, Cu-TMT(500) and Cu-Cr-TMT(500), as outlined in Table - III. Table - III Conditions for Single lap-Welding Welding Conditions. (Table Removed) The properties of the butt- and single lap-welded Joints produced in the process on the two types of steel bars, namely Cu-TMT (500) and Cu-Cr-TMT (500), have been tested and the typical test results are presented in Table - IV. The presence of defects in the welded joints has been evaluated by LEI, . MPI and radiography. The joints welded in the process are found to be substantially defect-free (Table - IV). Table - IV Typical Properties of the Butt- and Single Lap-welded Joints. (Table Removed) * NSD : No significant defects. The results of Table - IV show that ultimate tensile strength (UTS) of the joints produced in the process is appreciably higher than the minimum requirement stipulated for the satisfactory end-use performance of the bars containing the welded joints. Based on the studies conducted, as described above, the optimum conditions for welding of both Cu-TMT and Cu-Cr-TMT bars have been found to be as follows : A. Butt Welding Optimum Conditions (i) Electrode type - AWS A 5.5 E 8018 - W for both Cu-TMT and Cu-Cr-TMT bars, (ii) Preheating of bars - not necessary (iii) Rebaking of electrode - not necessary for Cu-TMT bars; done at 350°C for 2h or at 400°C for 1h for Cu-Cr-TMT bars. (iv) Input of heat - 7 to 10 KJcm1 for electrode diameter of 2.5 mm and 10 to 15 KJcm1 for electrode diameter of 3.15 mm for both of Cu-TMT and Cu-Cr-TMT bars. (v) Current-Voltage-Heat Input Combination for both Cu-TMT and Cu-Cr-TMT bars - Electrode Current Voltage Heat InPut diameter (mm) (A) (V) (kJcm-1 ) (a) 2.5 80-100 20-24 7-10 (b) 3.15 100-140 22-25 10-15 (vi) Electrode Inter-pass temperature - 225°C max. (vii) Post-Welding heat treatment - Normally not necessary; in case of any specific requirement, the heat treatment temperature is chosen so that mechanical strength of the welded joint is not unduly affected. B. Single Lap Welding Optimum Conditions (i) Rebaking of Electrodes - not necessary for Cu-TMT bars; done at 350°C for 2h or at 400°C for 1h for Cu-Cr-TMT bars, (ii) Preheating of bars - not necessary for both Cu-TMT and Cu-Cr-TMT bars, (iii) Input of heat - 7 to 10 KJcm1 for electrode diameter of 2.5 ran for both Cu-TMT and Cu-Cr-TMT bars. (iv) Overlapped length of bars - 70 mm (min.) for Cu-TMT bars and 100 mm (min.) for Cu-Cr-TMT bars. We claim: - 1. A process of producing sound welded joints for atmospheric and marine-corrosion resistant steel bars, where the joints produced are adequately strong and free from welding defects, comprising the steps: - (i) preparing the joint areas of the steel bars, such as herein described, in known methods; (ii) selecting the electrode wire and its coating material to be used, such as herein described; (iii) optimising the conditions for each of butt- and single lap-welding, such as herein described; and (iv) evaluating the properties of and detecting the presence of defects in the welded joints produced, in known methods, such as herein described, Characterized in that the said process is carried out under the conditions followed for butt-welding are: (a) both Cu-TMT and Cu-Cr-TMT bars are welded without being preheated; (b) for welding Cu-TMT bars, electrodes are used without being rebaked; (c) for welding Cu-Cr-TMT bars, electrodes are used after rebaking at 350° C for 2hrs or at 400° C for 1hr; (d) both Cu-TMT and Cu-Cr-TMT bars are welded at a heat input of 7-10 KJ cm1 for electrode diameter of 2.5 mm and of 10-15 KJ cm1 for electrode diameter of 3.15mm; (e) both Cu-TMT and Cu-Cr-TMT bars are welded at a current-voltage-heat input combination of 80-100 A, 20-24 V, 7-10 KJ cm1 for electrode diameter of 2.5 mm and of 100-140A, 22-25V, 101-15 KJ cm1 for electrode diameter of 3.15 mm; and (f) both Cu-TMT and Cu-Cr-TMT bars are welded at an electrode inter-pass temperature of 225 ° C max. and without any post-welding heat treatment of the bars; and for single lap-welding are: (a) both Cu-TMT and Cu-Cr-TMT bars welded without being preheated; (b) for welding.Cu-TMT bars, electrodes are used without being rebaked and for welding of Cu-Cr-TMT bars, electrodes are rebaked at 350° C - 2 hrs or 440 ° C -1 hr before use; (c) both Cu-TMT and Cu-Cr-TMT bars are welded at heat input of 7-10 KJ cm1 for electrode diameter of 2.5 mm; and (d) Cu-TMT bars are welded at an overlapped length of 70mm (min.) and Cu-Cr-TMT bars are welded at an overlapped length of 100 mm (min.). 2. The process as claimed in claim 1, wherein the chemical composition of the atmospheric-corrosion resistant (Cu-TMT) steel bars is (by weight %): C- 0.20 (max), Mn - 1.20 (max), S - 0.045 (max), P- 0.045 (max), Si - 0.40 (max), Cu/Cr/Ni - 0.25 (min) and Fe -balance. 3. The process as claimed in claim 1, wherein the chemical composition of the marine-corrosion resistant (Cu-Cr-TMT) steel bars is(by weight %) : C- 0.20 (max), Mn - 1.20 (max), S- 0.045 (max), P-0.045 (max), Si - 0.40 (max), Cu/Cr/Ni - 0.75 (min) and Fe- balance. 4. The process as claimed in claim 1, wherein the electrode wire used is of a low hydrogen type conforming to AWS A 5.5. E 8018 - W code. 5. The process as claimed in any of the preceding claims, wherein the number of passes of the electrode in butt- welding of bars is upto 7.

Full Text

The present invention relates to a process of producing sound welded Joints_foratmospheric - and marine - corrosion resistant steel bars using SMAW technique.
The invention relates more particularly to a process for producing welded joints in TMT r-ebars.
The examples of thermo-mechanically treated (TMT) atmospheric - and marine - corrosion resistant steel bars are respectively type Cu - TMT (500) and type Cu - Cr - TMT (500),
having chemical compositions as given in Table I from which
it is noted tha the only difference between bars is in respect of
their Cu/Cr/Ni content. The Joints produced by both butt -and lap - welding of such bacs using the conventional "Shield Metal Arc Welding" (SMAW) method are occasionally associated with welding defects due to improper selection of welding parameters, leading to premature failure of such bars in their end-use applications.
The object of the present invention is provide a process for producing adequately strong and defect-free welded Joints in Cu-TMT(500) and Cu-Cr TMT (500) type steel bars.
In the conventional SMAW process of welding, an arc is generated between a coated electrode wire and a base metal by momentarily touching the base metal by the electrode wire, which produces enough heat for melting both the base metal and electrode wire at the areas to be welded.
The electrode wire metal is thereby transferred into the pool of molten base metal and gets deposited on the base metal surface on solidification of both the molten electrode and base

metal as the position of electrode wire end is shifted along the base metal surface to be welded. The electrode wire metal deposited on the base metal gets covered by a slag produced from the heated coating material of the electrode wire. A protective gaseous shield is produced by decomposition of the heated coating material of the electrode to envelop the arc.
The main steps followed in the invented process are :-(i) joint preparation and number of passes for butt welding;
(ii) selection of electrode wire and its coating material; (iii) optimisation of the conditions for welding; (iv) evaluation of properties and soundness of the welded Joints produced.
The invention is described fully and particularly in an unrestricted manner with reference to the accompanying drawings, in which
Figure 1 is a schematic lay-out of the conventional SMAW method of welding;
Figure 2 is a schematic lay-out of butt-welding process; and
Figure 3 is a schematic lay-out of single lap-welding process.
Referring to Fig. 1, an arc A is produced between electrode wire E, having a coating C and the region B of the base metal M to melt both the base and electrode wire metal there. The droplets D of the molten electrode wire metal are deposited on the molten base metal pool to form a pool of

molten weld metal W there, which on solidification produces a deposit of solidified weld metal S on the base metal M. A layer of slag G is formed on the solidified weld metal S by deposition of heated coating material of the electrode wire E. A protective gaseous shield H is formed by the decomposition products of the heated coating material of the electrode wire. The slag layer G and the protective gaseous shield H prevent the weld metal W from oxidation. The direction T of moving the electrode wire is shown to be from the left-hand end to the right-hand end of the base metal M.
The electrode wire used in the process is of a low hydrogen type conforming to AWS A 5.5 E 8018-V code.
Table - I
Chemical Composition of Cu-TMT (500) and Cu-Cr-TMT (500)
type of Steel Bars Welded.
(Table Removed)
Referring to Fig. 2 the adjacent ends X and Y of two bars M1 and M2 are butt-welded by adopting seven passes of the welding electrode wire under the welding conditions outlined in Table - II.
Table - II Conditions for Butt-Welding
(Table Removed)
Referring to Fig. 3, the adjacent surfaces of two bars M1 and M2 are joined by single lap-welding over the overlapping length V of the bars under conditions followed for the two types of bars, namely, Cu-TMT(500) and Cu-Cr-TMT(500), as outlined in Table - III.
Table - III
Conditions for Single lap-Welding
Welding Conditions.
(Table Removed)
The properties of the butt- and single lap-welded Joints produced in the process on the two types of steel bars, namely Cu-TMT (500) and Cu-Cr-TMT (500), have been tested and the typical test results are presented in Table - IV.
The presence of defects in the welded joints has been evaluated by LEI, . MPI and radiography. The joints welded in the process are found to be substantially defect-free (Table - IV).
Table - IV
Typical Properties of the Butt- and Single Lap-welded Joints.
(Table Removed)
* NSD : No significant defects.
The results of Table - IV show that ultimate tensile strength (UTS) of the joints produced in the process is appreciably higher than the minimum requirement stipulated for the satisfactory end-use performance of the bars containing the welded joints.
Based on the studies conducted, as described above, the optimum conditions for welding of both Cu-TMT and Cu-Cr-TMT bars have been found to be as follows :
A. Butt Welding Optimum Conditions (i) Electrode type - AWS A 5.5 E 8018 - W
for both Cu-TMT and Cu-Cr-TMT bars, (ii) Preheating of bars - not necessary (iii) Rebaking of electrode - not necessary for Cu-TMT
bars; done at 350°C for 2h or at 400°C for 1h for Cu-Cr-TMT bars.
(iv) Input of heat - 7 to 10 KJcm1 for electrode
diameter of 2.5 mm and 10 to 15 KJcm1 for electrode diameter of 3.15 mm for both of Cu-TMT and Cu-Cr-TMT bars.
(v) Current-Voltage-Heat Input Combination for both Cu-TMT and Cu-Cr-TMT bars -
Electrode Current Voltage Heat InPut
diameter (mm) (A) (V) (kJcm-1 )
(a) 2.5 80-100 20-24 7-10
(b) 3.15 100-140 22-25 10-15
(vi) Electrode Inter-pass temperature - 225°C max. (vii) Post-Welding heat treatment - Normally not necessary;
in case of any specific requirement, the heat treatment temperature is chosen so that mechanical strength of the welded joint is not unduly affected.

B. Single Lap Welding Optimum Conditions
(i) Rebaking of Electrodes - not necessary for Cu-TMT bars;
done at 350°C for 2h or at 400°C for 1h for Cu-Cr-TMT bars, (ii) Preheating of bars - not necessary for both Cu-TMT and
Cu-Cr-TMT bars, (iii) Input of heat - 7 to 10 KJcm1 for electrode diameter
of 2.5 ran for both Cu-TMT and Cu-Cr-TMT bars.
(iv) Overlapped length of bars - 70 mm (min.) for Cu-TMT
bars and 100 mm (min.) for Cu-Cr-TMT bars.

We claim: -
1. A process of producing sound welded joints for atmospheric and marine-corrosion resistant steel bars, where the joints produced are adequately strong and free from welding defects, comprising the steps: -
(i) preparing the joint areas of the steel bars, such
as herein described, in known methods; (ii) selecting the electrode wire and its coating
material to be used, such as herein described; (iii) optimising the conditions for each of butt- and
single lap-welding, such as herein described; and (iv) evaluating the properties of and detecting the
presence of defects in the welded joints produced, in
known methods, such as herein described,
Characterized in that the said process is carried out under the conditions followed for butt-welding are:
(a) both Cu-TMT and Cu-Cr-TMT bars are welded without
being preheated;
(b) for welding Cu-TMT bars, electrodes are used without
being rebaked;
(c) for welding Cu-Cr-TMT bars, electrodes are used after
rebaking at 350° C for 2hrs or at 400° C for 1hr;
(d) both Cu-TMT and Cu-Cr-TMT bars are welded at a heat
input of 7-10 KJ cm1 for electrode diameter of 2.5 mm and
of 10-15 KJ cm1 for electrode diameter of 3.15mm;
(e) both Cu-TMT and Cu-Cr-TMT bars are welded at a
current-voltage-heat input combination of 80-100 A, 20-24
V, 7-10 KJ cm1 for electrode diameter of 2.5 mm and of
100-140A, 22-25V, 101-15 KJ cm1 for electrode diameter of
3.15 mm; and
(f) both Cu-TMT and Cu-Cr-TMT bars are welded at an
electrode inter-pass temperature of 225 ° C max. and
without any post-welding heat treatment of the bars;
and for single lap-welding are:
(a) both Cu-TMT and Cu-Cr-TMT bars welded without being
preheated;
(b) for welding.Cu-TMT bars, electrodes are used without
being rebaked and for welding of Cu-Cr-TMT bars,
electrodes are rebaked at 350° C - 2 hrs or 440 ° C -1 hr
before use;
(c) both Cu-TMT and Cu-Cr-TMT bars are welded at heat
input of 7-10 KJ cm1 for electrode diameter of 2.5 mm;
and
(d) Cu-TMT bars are welded at an overlapped length of
70mm (min.) and Cu-Cr-TMT bars are welded at an
overlapped length of 100 mm (min.).
2. The process as claimed in claim 1, wherein the chemical
composition of the atmospheric-corrosion resistant (Cu-TMT)
steel bars is (by weight %):
C- 0.20 (max), Mn - 1.20 (max), S - 0.045 (max), P- 0.045 (max), Si - 0.40 (max), Cu/Cr/Ni - 0.25 (min) and Fe -balance.
3. The process as claimed in claim 1, wherein the chemical
composition of the marine-corrosion resistant (Cu-Cr-TMT)
steel bars is(by weight %) : C- 0.20 (max), Mn - 1.20
(max), S- 0.045 (max), P-0.045 (max), Si - 0.40 (max),
Cu/Cr/Ni - 0.75 (min) and Fe- balance.
4. The process as claimed in claim 1, wherein the electrode
wire used is of a low hydrogen type conforming to AWS A
5.5. E 8018 - W code.
5. The process as claimed in any of the preceding claims,
wherein the number of passes of the electrode in butt-
welding of bars is upto 7.

Documents:

1663-del-1997-abstract.pdf

1663-del-1997-claims.pdf

1663-del-1997-correspondence-others.pdf

1663-del-1997-correspondence-po.pdf

1663-del-1997-description (complete).pdf

1663-del-1997-drawings.pdf

1663-del-1997-form-1.pdf

1663-del-1997-form-19.pdf

1663-del-1997-form-2.pdf

1663-del-1997-form-4.pdf

1663-del-1997-gpa.pdf

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Patent Number

212087

Indian Patent Application Number

1663/DEL/1997

PG Journal Number

51/2007

Publication Date

21-Dec-2007

Grant Date

14-Nov-2007

Date of Filing

20-Jun-1997

Name of Patentee

STEEL AUTHORITY OF INDIA LIMITED, RESEARCH AND DEVELOPMENT CENTRE FOR IRON & STEEL, A GOVERNMENT OF INDIA ENTERPRISE

Applicant Address

ISPAT BHAWAN, LODI ROAD, NEW DELHI-110003, INDIA.

Inventors:

#	Inventor's Name	Inventor's Address
1	RAMEN DATTA	RDCIS/SAIL, DORANDA, RANCHI-834002, INDIA.
2	DEBASIS MUKHERJEE	RDCIS/SAIL, DORANDA, RANCHI-834002, INDIA.
3	SANAK MISHRA	RDCIS/SAIL, DORANDA, RANCHI-834002, INDIA.
4	R. VEERARAGHAVAN	WELDING RESEARCH INSTITUTE, TIRUCHIRAPALLI-620014, INDIA.
5	K. L. ROHIRA	WELDING RESEARCH INSTITUTE, TIRUCHIRAPALLI-620014, INDIA.

PCT International Classification Number

B23K 9/38

PCT International Application Number

N/A

PCT International Filing date

PCT Conventions:

#	PCT Application Number	Date of Convention	Priority Country
1			NA