Title of Invention	"AN IMPROVED METHOD OF FABRICATING PRODUCTS BY WELDING THE JOINTS BETWEEN STEEL PLATES OF HIGH TENSILE STRENGTH (570 MPA MIN)"
Abstract	An improved method of fabricating products by welding the joints between steel plates of high tensile strength (570 MPa min.) and thickness upto 38 mm in the 'shielded metal arc welding1 (SMAW) technique, such as herein described, characterised in that (a) ends of the plates joined by welding are shaped according to the thickness of the plates in the manner, such as herein described; (b) welding is performed using electrode of type AWS A 5.5 E 8018-G and diameter 3.15, 4.0 and 5.0 mm; (c) eltctrodes are rebaked at 350°C for 2h or 400°C for 1h; (d) the ends of plates of different thickness to be joined by welding are preheated at optimised temperatures and heat input levels, such as herein described; (e) arc between electrode tip and plate ends is produced by welding current and voltage of 110-150A and 20-23V for electrode diameter 3.15 mm, 140-180A and 22-26V for electrode diameter 4.00 mm, and 160-200A and 24-28V for electrode diameter 5.00 mm; (f) electrode is passed over the welded area 5-7 times at an inter pass temperature of 250°C maximum and heat input from the arc into the electrode of 10-14 KJcm-1 for the electrode of diameter 3.15 mm, 14-20 KJcm-1 for the electrode of diameter 4.00 mm and 20-28 KJcm-1 for the electrode of diameter 5.00 mm.

Title of Invention

"AN IMPROVED METHOD OF FABRICATING PRODUCTS BY WELDING THE JOINTS BETWEEN STEEL PLATES OF HIGH TENSILE STRENGTH (570 MPA MIN)"

Abstract

An improved method of fabricating products by welding the joints between steel plates of high tensile strength (570 MPa min.) and thickness upto 38 mm in the 'shielded metal arc welding1 (SMAW) technique, such as herein described, characterised in that (a) ends of the plates joined by welding are shaped according to the thickness of the plates in the manner, such as herein described; (b) welding is performed using electrode of type AWS A 5.5 E 8018-G and diameter 3.15, 4.0 and 5.0 mm; (c) eltctrodes are rebaked at 350°C for 2h or 400°C for 1h; (d) the ends of plates of different thickness to be joined by welding are preheated at optimised temperatures and heat input levels, such as herein described; (e) arc between electrode tip and plate ends is produced by welding current and voltage of 110-150A and 20-23V for electrode diameter 3.15 mm, 140-180A and 22-26V for electrode diameter 4.00 mm, and 160-200A and 24-28V for electrode diameter 5.00 mm; (f) electrode is passed over the welded area 5-7 times at an inter pass temperature of 250°C maximum and heat input from the arc into the electrode of 10-14 KJcm-1 for the electrode of diameter 3.15 mm, 14-20 KJcm-1 for the electrode of diameter 4.00 mm and 20-28 KJcm-1 for the electrode of diameter 5.00 mm.

Full Text	The present invention relates to an improved method of fabricating products by welding the joints between steel plates of high tensile strength (570 MPa min). , The invention relates more particularly to fabricating products from steel plates of tensile strength 570 MPa and above, and of thickness upto 38 mm by optimising the welding technique followed for Joining the ends of the plates to ensure durable performance of the fabricated products in iiaeir end-use applications. In a pending Indian patent applicationNo.1663/DEL/1997 dated 20th June 1997 . by the applicants, a process of producing sound welded joints in atmospheric- and marine- corrosion resistant steel bars using 'shielded metal arc welding' (SMAW) technique has been disolosed. In another pending Indian patent applicationNo. 2023/DEL/1997 dated 21st July 1997 at Patent Branch Office at New Delhi on 29th July.. 1997 by the applicants, a process of producing sound welded joints in atmospheric- and marine- corrosion resistant steel bars using 'gas metal arc welding' (GMAW) technique has been disclosed. The existing products fabricated by welding the joints in steel plates of high tensile strength are generally found to be of relatively low tensile strength and impact emergy at the joints with consequent occasional failures of the products at their joints in end-use applications thereof. The object of the invention is to provide an optimised welding method for joining steel plates of high tensile strength so that the joints in the products fabricated from the plates are of adequate tensile strength and impact energy, to ensure failure-free performance of the joints in end use of the products. The 'shielded metal arc welding1 (SMAW) technique has been followed in welding the joints between the ends of steel plates of high tensile strength by optimising the operating parameters with a view to increasing the tensile strength and impact energy of the welded joints formed in fabricating the products from the steel plates by carrying out extensive investigations on the effects of various parameters of the welding operations on the tensile strength and impact energy of the joints between ends of the steel plates made by welding. In the SMAW technique of welding an electric arc is struckbetween the tip of an electrode rod and the ends of the steel plates to be joined by momentarily touching the plate ends with the tip of the electrode to allow an electric current to flow through the electrode rod into the steel plates, and produce an arc by withdrawing the electrode tip from the ends of the plates to a given distance. The heat generated in the arc melts the steel plate ends and also the metal at the electrode tip. The molten electrode metal mixes with the molten steel at the joinirgends of the plates, and the mixed metal is deposited on cooling to form the welded joint of the steel plates. The electrode rod is coated with a material which on heating melts to form a slag which shields the welded joint, and a gas which envelopes the arc, and thereby prevents oxidation of the welded joint during the welding operation. The specified chemical composition and mechanical properties of the steel plates of high tensile strength used to produce the fabricated products by welding the ends thereof are presented in Tables I and II respectively. The invention is described fully and particularly without restricting the scope of the invention in any manner with reference to the accompanying drawings in which Figure 1 shows the optimum shape of the joined ends of steel plates of thickness t : (A) upto 12.5 mm, (B) between 12.5 and 25.0 mm, and (C) from 25.0 to 32.0 mm; Figure 2 shows the steps followed in the method. Referring to Fig. I(A) showing the optimised shape of the joined end of each plate of thickness t upto 12.5 mm, a lower vertical part v of thickness t/6 is at the bottom and an upper inwardly inclined part 1 of thickness 5t/6 is inclined at an angle a of 35° with the vertical Part. The vertical parts of the joined ends of the two plates p and p' are separated from each other with a gap: of t/5. Referring to Fig. 1(B) showing the optimised shape of the joined end of each plate of thickness t between 12.5 and 25.0 mm, a vertical Part v is of thickness t/6 with the middle point thereof lying at thickness t/2 and the inclined parts i and i' of each plate are inclined inwardly at an angle a of 35° with the vertical Part and each of thickness 5t/12. The vertical parts of the joined ends of the two plates p and p' are separated from each other with a gap of t/5. Referring to Fig. 1(C) showing the optimised shape of the joined end of each plate of thickness from 25.0 to 32.0 mm, a vertical Part v is of thickness t/6with the middle point thereof lying at thickness t/3 from the bottom, and a lower inwardly inclined part i' of the thickness t/A and an upper inwardly inclined parti of thickness 7t/12 of each plate are inclined at an angle a of 35° with the vertical part. The vertical parts of the joined ends of the two plates p and p1 are separated from each other with a gap of t/5. Besides optimising the shape of the ends of plates of different thickness as illustrated and described, the other Parameters of the SMAW technique optimised for welding in the invented method of fabrication are : (i) type of the electrode rod selected (ii) diameter of the electrode rod used (iii) rebaking temperature and time for the electrode rod used (iv) number of passes of the electrode rod tip over the welded area (v) inter-pass temperature of the electrode rod (vi) heat input from the arc into the electrode rod during welding (vii) welding current and voltage for electrode rods of different diameter (viii) preheating temperature and heat input of ends of plate of different thickness and carbon equivalent level. The optimised particulars of the abovementioned parameters of the welding operations followed are presented in Table III. The soundness of the weld formed has been examined by liquid penetration inspection, magnetic particle inspection and radiography, and found to be satisfactory. The mechanical properties at the welded joints have been studied. The tensile strength, impact energy (Charpy V-notch) and bend at the welded joints have been found respectively to be 603-610 MPa; 105-107 J at 25°C, 72-82 J at 0°C and 56-57 J at -20°C; and 3T without any crack. These properties are well above the minimum specified requirements for durable performance of the products in their end-use applications. Field trials conducted on the products fabricated in the invented method have indicated that the chances of their failures in end-use are reduced appreciably. Table I Specified Chemical Composition of Steel Plates. (Table Removed) Table II Specified Mechanical Properties of Steel Plates (Table Removed) * gauge length = 5.65√SO where So is the cross-sectional area. Table III Optimised Welding Parameters (i) type of electrode rod selected:AWS A5.5 E8018-G (coated) (ii) diameter (mm) of electrode rod used: 3.15, 4.00 and 5.00 depending on the welding voltage, current and plate thickness (iii) rebaking temperature and time,of electrode rod: ... 350°C for 2h or 400°C for 1h (iv) number of electrode passes :, 5-7 (v) inter-pass temperature of electrode :.. 250° maximum (vi) heat input from arc into electrode for :- electrode diameter 3.15 mm ... 10-14 KJcm-1 " " A.00 mm ... 14-20 " " " 5.00 mm ... 20-28 " (vii) welding current and voltage for :- electrode diameter 3.15mm ... 110-150A and 20-23V " " 4.00mm ... 14O-180A and 22-26V " " 5.00mm ... 160-200A and 24-28V (viii) heat input level and preheat temperature of plate ends for varying C.E. and plate thickness :- (Table Removed) We Claim :- 1. An improved method of fabricating products by welding the joints between steel plates of high tensile strength (570 MPa min.) and thickness upto 38 mm in the 'shielded metal arc welding' (SMAW) technique, such as herein described, characterised in that (a) ends of the plates joined by welding are shaped according to the thickness of the plates in the manner, such as herein described; (b) welding is performed using electrode of type AWS A 5.5 B 8018-G and diameter 3.15, 4.0 and 5.0 mm; (c) electrodes are re baked at 350°C for 2h or 400° C for 1h; (d) the ends of plates of different thickness to be joined by welding are preheated at optimised temperatures and heat input levels, such as herein described; (e) arc between electrode tip and plate ends is produced by welding current and voltage of 110-150A and 20-23V for electrode diameter 3.15 mm, 140-180A and 22-26V for electrode diameter 4.00 mm, and 160-200A and 24-28V for electrode diameter 5.00 mm; (f) electrode is passed over the welded area 5-7 times at an inter pass temperature of 250°C maximum and heat input from the arc into the electrode of 10-14 KJcm-1 for the electrode of diameter 3.15 mm, 14-20 KJcm-1 for the electrode of diameter 4.00 mm and 20-28 KJcm-1 for the electrode of diameter 5.00 mm, 2. The method as claimed in claim 1, wherein the ends of the plates to be joined are shaped to contain (i) a lower vertical part of 1/6 plate thickness and an upper inwardly inclined part of 5/6 plate thickness for plates of thickness upto 12.5 mm, (ii) a vertical middle part of 1/6 plate thickness, lower and upper inwardly inclined parts each of 5/12 plate thickness for. plates of thickness between 12.5 mm and 25.0 mm, (iii) a vertical part of 1/6 plate thickness having its middle point lying at 1/3 plate thickness from the bottom surface, and lower and upper inwardly inclined parts of respectively 1/4 and 7/12 plate thickness for plates of thickness from 19.0 to 38.0 mm, and wherein the ends of plates to be joined are preheated at 100°C and heat input level 14 KJcm-1 for plate thickness 25-38 mm and carbon equivalent (CE) level >0.38, at 75°C and heat input level

Full Text

The present invention relates to an improved method of fabricating products by welding the joints between steel plates of high tensile strength (570 MPa min). ,
The invention relates more particularly to fabricating products from steel plates of tensile strength 570 MPa and
above, and of thickness upto 38 mm by optimising the welding technique followed for Joining the ends of the plates to ensure durable performance of the fabricated products in iiaeir
end-use applications.
In a pending Indian patent applicationNo.1663/DEL/1997
dated 20th June 1997 .
by the applicants, a process of producing sound welded joints in atmospheric- and marine- corrosion resistant steel bars using 'shielded metal arc welding' (SMAW) technique has been
disolosed.
In another pending Indian patent applicationNo. 2023/DEL/1997
dated 21st July 1997 at Patent Branch Office at New Delhi on 29th July..
1997 by the applicants, a process of producing sound welded
joints in atmospheric- and marine- corrosion resistant steel
bars using 'gas metal arc welding' (GMAW) technique has been disclosed.
The existing products fabricated by welding the joints in steel plates of high tensile strength are generally found to be of relatively low tensile strength and impact emergy at the joints with consequent occasional failures of the products at their joints in end-use applications thereof.

The object of the invention is to provide an optimised welding method for joining steel plates of high tensile strength so that the joints in the products fabricated from the plates are of adequate tensile strength and impact energy, to ensure failure-free performance of the joints in end use of the products.
The 'shielded metal arc welding1 (SMAW) technique has been followed in welding the joints between the ends of steel plates of high tensile strength by optimising the operating parameters with a view to increasing the tensile strength and impact energy of the welded joints formed in fabricating the products from the steel plates by carrying out extensive investigations on the effects of various parameters of the welding operations on the tensile strength and impact energy of the joints between ends of the steel plates made by welding.
In the SMAW technique of welding an electric arc is struckbetween the tip of an electrode rod and the ends of the steel plates to be joined by momentarily touching the plate ends with the tip of the electrode to allow an electric current to flow through the electrode rod into the steel plates, and produce an arc by withdrawing the electrode tip from the ends of the plates to a given distance. The heat generated in the arc melts the steel plate ends and also the metal at the electrode tip. The molten electrode metal mixes with the molten steel at the joinirgends of the plates, and the mixed metal is deposited on cooling to form the welded joint of the

steel plates. The electrode rod is coated with a material
which on heating melts to form a slag which shields the welded joint,
and a gas which envelopes the arc, and thereby prevents oxidation of the welded joint during the welding operation.
The specified chemical composition and mechanical properties of the steel plates of high tensile strength used to produce the fabricated products by welding the ends thereof are presented in Tables I and II respectively.
The invention is described fully and particularly without restricting the scope of the invention in any manner with reference to the accompanying drawings in which
Figure 1 shows the optimum shape of the joined ends of steel plates of thickness t : (A) upto 12.5 mm, (B) between
12.5 and 25.0 mm, and (C) from 25.0 to 32.0 mm; Figure 2 shows the steps followed in the method.
Referring to Fig. I(A) showing the optimised shape
of the joined end of each plate of thickness t upto 12.5 mm, a lower vertical part v of thickness t/6 is at the bottom and an upper inwardly inclined part 1 of thickness 5t/6 is inclined at an angle a of 35° with the vertical Part. The vertical parts of the joined ends of the two plates p and p' are separated from each other with a gap: of t/5.
Referring to Fig. 1(B) showing the optimised shape of the joined end of each plate of thickness t between 12.5 and 25.0 mm, a vertical Part v is of thickness t/6 with the middle point thereof lying at thickness t/2 and the inclined parts i and i' of each plate are inclined inwardly at an angle a of 35° with the vertical Part and each of thickness 5t/12. The vertical parts of the joined ends of the two plates

p and p' are separated from each other with a gap of t/5.
Referring to Fig. 1(C) showing the optimised shape of the joined end of each plate of thickness from 25.0 to 32.0 mm, a vertical Part v is of thickness t/6with the middle point thereof lying at thickness t/3 from the bottom, and a lower inwardly inclined part i' of the thickness t/A and an upper inwardly inclined parti of thickness 7t/12 of each plate are inclined at an angle a of 35° with the vertical part. The vertical parts of the joined ends of the two plates p and p1 are separated from each other with a gap of t/5.
Besides optimising the shape of the ends of plates of different thickness as illustrated and described, the other Parameters of the SMAW technique optimised for welding in the invented method of fabrication are :
(i) type of the electrode rod selected (ii) diameter of the electrode rod used (iii) rebaking temperature and time for the electrode
rod used (iv) number of passes of the electrode rod tip over the
welded area
(v) inter-pass temperature of the electrode rod (vi) heat input from the arc into the electrode rod
during welding (vii) welding current and voltage for electrode rods of
different diameter
(viii) preheating temperature and heat input of ends of plate of different thickness and carbon equivalent level.

The optimised particulars of the abovementioned parameters of the welding operations followed are presented in Table III.
The soundness of the weld formed has been examined by liquid penetration inspection, magnetic particle inspection and radiography, and found to be satisfactory.
The mechanical properties at the welded joints have been studied. The tensile strength, impact energy (Charpy V-notch) and bend at the welded joints have been found respectively to be 603-610 MPa; 105-107 J at 25°C, 72-82 J at 0°C and 56-57 J at -20°C; and 3T without any crack. These properties are well above the minimum specified requirements for durable performance of the products in their end-use applications.
Field trials conducted on the products fabricated in the invented method have indicated that the chances of their failures in end-use are reduced appreciably.

Table I Specified Chemical Composition of Steel Plates.

(Table Removed)
Table II Specified Mechanical Properties of Steel Plates
(Table Removed)
* gauge length = 5.65√SO where So is the cross-sectional area.

Table III
Optimised Welding Parameters (i) type of electrode rod selected:AWS A5.5 E8018-G
(coated)
(ii) diameter (mm) of electrode rod used: 3.15, 4.00 and 5.00 depending on the welding voltage, current and plate thickness (iii) rebaking temperature and time,of electrode rod: ...
350°C for 2h or 400°C for 1h (iv) number of electrode passes :, 5-7
(v) inter-pass temperature of electrode :.. 250° maximum (vi) heat input from arc into electrode for :-
electrode diameter 3.15 mm ... 10-14 KJcm-1
" " A.00 mm ... 14-20 "
" " 5.00 mm ... 20-28 "
(vii) welding current and voltage for :-
electrode diameter 3.15mm ... 110-150A and 20-23V
" " 4.00mm ... 14O-180A and 22-26V
" " 5.00mm ... 160-200A and 24-28V

(viii) heat input level and preheat temperature of plate ends for varying C.E. and plate thickness :-

(Table Removed)

We Claim :-
1. An improved method of fabricating products by welding
the joints between steel plates of high tensile strength
(570 MPa min.) and thickness upto 38 mm in the 'shielded metal arc welding' (SMAW) technique, such as herein described, characterised in that (a) ends of the plates joined by welding are shaped according to the thickness of the plates in the manner, such as herein described; (b) welding is performed using electrode of type AWS A 5.5 B 8018-G and diameter 3.15, 4.0 and 5.0 mm; (c) electrodes are re baked at 350°C for 2h or 400° C for 1h; (d) the ends of plates of different thickness to be joined by welding are preheated at optimised temperatures and heat input levels, such as herein described; (e) arc between electrode tip and plate ends is produced by welding current and voltage of 110-150A and 20-23V for electrode diameter 3.15 mm, 140-180A and 22-26V for electrode diameter 4.00 mm, and 160-200A and 24-28V for electrode diameter 5.00 mm; (f) electrode is passed over the welded area 5-7 times at an inter pass temperature of 250°C maximum and heat input from the arc into the electrode of 10-14 KJcm-1 for the electrode of diameter 3.15 mm, 14-20 KJcm-1 for the electrode of diameter 4.00 mm and 20-28 KJcm-1 for the electrode of diameter 5.00 mm,
2. The method as claimed in claim 1, wherein the ends of
the plates to be joined are shaped to contain (i) a lower vertical
part of 1/6 plate thickness and an upper inwardly inclined part of
5/6 plate thickness for plates of thickness upto 12.5 mm, (ii) a
vertical middle part of 1/6 plate thickness, lower and upper
inwardly inclined parts each of 5/12 plate thickness for.

plates of thickness between 12.5 mm and 25.0 mm, (iii) a vertical part of 1/6 plate thickness having its middle point lying at 1/3 plate thickness from the bottom surface, and lower and upper inwardly inclined parts of respectively 1/4 and 7/12 plate thickness for plates of thickness from 19.0 to 38.0 mm, and wherein the ends of plates to be joined are preheated at 100°C and heat input level 14 KJcm-1 for plate thickness 25-38 mm and carbon equivalent (CE) level >0.38, at 75°C and heat input level

Documents:

9-del-1999-abstract.pdf

9-del-1999-claims.pdf

9-del-1999-correspondence-others.pdf

9-del-1999-correspondence-po.pdf

9-del-1999-description (complete).pdf

9-del-1999-drawings.pdf

9-del-1999-form-1.pdf

9-del-1999-form-19.pdf

9-del-1999-form-2.pdf

9-del-1999-form-4.pdf

9-del-1999-gpa.pdf

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Patent Number

232030

Indian Patent Application Number

9/DEL/1999

PG Journal Number

13/2009

Publication Date

27-Mar-2009

Grant Date

15-Mar-2009

Date of Filing

05-Jan-1999

Name of Patentee

STEEL AUTHORITY OF INDIA LIMITED.

Applicant Address

RESEARCH & DEVELOPMENT CENTRE FOR IRON AND STEEL, ISPAT BHAWAN, LODHI ROAD, NEW DELHI-100093.

Inventors:

#	Inventor's Name	Inventor's Address
1	REMEN DATTA	RDCIS/SAIL, DORANDA, RANCHI-834002.
2	DEBASIS MUKHERJEE	RDCIS/SAIL, DORANDA, RANCHI-834002.
3	SANAK MISHRA	RDCIS/SAIL, DORANDA, RANCHI-834002.
4	VEERARAGHVAN	WELDING RESEARCH INSTITUTE, TIRUCHIRAPALLI-620014.
5	ROHIRA	WELDING RESEARCH INSTITUTE, TIRUCHIRAPALLI-620014.

PCT International Classification Number

B23K 35/00

PCT International Application Number

N/A

PCT International Filing date

PCT Conventions:

#	PCT Application Number	Date of Convention	Priority Country
1			NA