Title of Invention	"A PROCESS FOR PRODUCING COPPER-BEARING, AGE-HARDENED STEEL OF INCREASED YIELD STRENGTH, BENDABILITY AND WELDABILITY"
Abstract	A process for producing copper-bearing age-hardened steel of increased yield strength, bendability and weldability, comprising the following steps in sequence: (a) making steel in Electric Arc Furnace/LD furnace by charging scraf containing cuttings of mild steel plates, bars and sheets, which is reasonably free from residual elements like Arsenic, Tin and Lead, lime, petroleum coke, sponge iron, iron ore and/or hot metal in required quantities in the furnace and melting the said raw materials by electric arc or oxygen lancing with addition of 0.5-3.0% by weight quantity of Fe-Mn-Nickel sinter and Fe-Mo in the BOF(LD) furnace and 3 to 4 times slag off; (b) adding Cu, Fe-Mo, Fe-Mn (high carbon), Fe-Min (low carbon), Fe-V to molten steel in ladle; (c) further adding FeMn, FeNb in VAD-I by arc degassing (below 5 torr) for 10 minutes and adjusting the composition of steel in VAD-II at 1625-1630°C; (d) injecting CaSi wire into molten steel in ladle; (e) casting the molten steel into slabs in a continuous casting machine; (f) cross-rolling the slabs into plates, as herein described; and (g) ageing the plates, as herein described; characterised in that (i) the chemical composition of the steel produced is (by weight %): C-0.045 to 0.055, Mn-0.75 to 0.90, P-0.005 to 0.010, S-0.005 to 0.010, Si-0.20 to 0.35, Ni-0.95 to 1.25, Cr-0.70 to 0.85, Mo-0.25 to 0.35, Cu-1.10 to 1.30, Nb-0.03 to 0.04, Al-0.015 to 0.020, Ti-0.005 max, V-0.02 to 0.03 and Fe-the balance; (ii) CaSi wire is injected into molten steel at a rate of 0.7 to 1.0 kg per Ton and to a depth of 2.7 to 3.0 m in ladle; (iii) slabs are cast at a speed of 0.7 to 0.8 m/min and at a superheat of 15-20°C; (iv) the slabs are conditioned by heating to 600/650°C in a walking-beam furnace, soaking for 2 hours, re-heating at a rate of 50-60°C/hour to 1280/1300°C and re-soaking for 2.5 to 3.0 hours; (v) the slabs are cross-rolled into plates of width 1700 to 1850 mm in 20 to 22 passes; (vi) plates are finish-rolled at 900-930°C, solution-treated at 920-930°C for 30 to 45 minutes, and oil-quenched; and (vii) plate are aged by soaking oil-quenched plates in a walking beam furnace having soaking temperature of 630 ± 10°C.

Title of Invention

"A PROCESS FOR PRODUCING COPPER-BEARING, AGE-HARDENED STEEL OF INCREASED YIELD STRENGTH, BENDABILITY AND WELDABILITY"

Abstract

A process for producing copper-bearing age-hardened steel of increased yield strength, bendability and weldability, comprising the following steps in sequence: (a) making steel in Electric Arc Furnace/LD furnace by charging scraf containing cuttings of mild steel plates, bars and sheets, which is reasonably free from residual elements like Arsenic, Tin and Lead, lime, petroleum coke, sponge iron, iron ore and/or hot metal in required quantities in the furnace and melting the said raw materials by electric arc or oxygen lancing with addition of 0.5-3.0% by weight quantity of Fe-Mn-Nickel sinter and Fe-Mo in the BOF(LD) furnace and 3 to 4 times slag off; (b) adding Cu, Fe-Mo, Fe-Mn (high carbon), Fe-Min (low carbon), Fe-V to molten steel in ladle; (c) further adding FeMn, FeNb in VAD-I by arc degassing (below 5 torr) for 10 minutes and adjusting the composition of steel in VAD-II at 1625-1630°C; (d) injecting CaSi wire into molten steel in ladle; (e) casting the molten steel into slabs in a continuous casting machine; (f) cross-rolling the slabs into plates, as herein described; and (g) ageing the plates, as herein described; characterised in that (i) the chemical composition of the steel produced is (by weight %): C-0.045 to 0.055, Mn-0.75 to 0.90, P-0.005 to 0.010, S-0.005 to 0.010, Si-0.20 to 0.35, Ni-0.95 to 1.25, Cr-0.70 to 0.85, Mo-0.25 to 0.35, Cu-1.10 to 1.30, Nb-0.03 to 0.04, Al-0.015 to 0.020, Ti-0.005 max, V-0.02 to 0.03 and Fe-the balance; (ii) CaSi wire is injected into molten steel at a rate of 0.7 to 1.0 kg per Ton and to a depth of 2.7 to 3.0 m in ladle; (iii) slabs are cast at a speed of 0.7 to 0.8 m/min and at a superheat of 15-20°C; (iv) the slabs are conditioned by heating to 600/650°C in a walking-beam furnace, soaking for 2 hours, re-heating at a rate of 50-60°C/hour to 1280/1300°C and re-soaking for 2.5 to 3.0 hours; (v) the slabs are cross-rolled into plates of width 1700 to 1850 mm in 20 to 22 passes; (vi) plates are finish-rolled at 900-930°C, solution-treated at 920-930°C for 30 to 45 minutes, and oil-quenched; and (vii) plate are aged by soaking oil-quenched plates in a walking beam furnace having soaking temperature of 630 ± 10°C.

Full Text	The present invention relates to a process for producing copper-bearing, age-hardened steel of increased yield strength, bendability and weldability. The ateel having high yield strength, corrosion resistance, bendability and weldability is required particularly for the construction of ocean going vessels, bridges and structures used in coastal areas. The conventional HSLA grades of steel containing copper and chromium used for the purpose has the following drawbacks s (i) the yield strength is not adequately high ; (ii) the pre- and post-welding treatment is required with increase in fabrication cost; (iii) bending is associated with surface cracks; and (iv) fracture toughness is low. The conventional HSLA grades of steel of chemical composition (by weight %) : C-0,07, Mn-0.40 to 0.70, P-0.025, S-0.010, Si-O.4O, Ni-0,70 to 1.00, Cr-O.60-0.90, Mo-0.15 to 0.25, Cu-1.00 to 1.30, Nb-0.02 to 0.06, Al-0.02 to 0.06 and the balance-Fe is produced from ingots/slabs prepared in EAF/BOF route and rendered to be of fine-grain microstructure by killing the steel fully. The object of the present invention is to provide a process for producing steel of increased yield strength, bendabilityand fracture toughness, which is particularly suitable for the construction of ships, bridges and structures erected at coastal regions. 2 In the invented process the chemical composition of the conventional HSLA grades of steel has been optimised by conducting extensive experiments in pilot mill and steel plants, as given in Table 1, which also contains the composition of the conventional HSLA grades of steel for comparison. It is noted from Table 1 that the content of C, S, P and Al is reduced, that of Mn, Ni and Mo is increased, that of Cr, Cu and Nb is kept unchanged and new elements Ti and V are added in the optimised composition of steel produced in the invented process. The steps followed in sequence in the invented process are :- (a) Steel is made in Electric Arc Furnace/LD furnace by charging scraf containing cuttings of mild steel plates, bars and sheets,which is reasonably free from residual elements like Arsenic, Tin and Lead, lime, petroleum coke, sponge iron, iron ore and/or hot metal, in required quantities in the furnace and melting the said raw materials by electric arc or oxygen lancing with addition of 0.5 to 3.0% by weight of Fe-Mn-Nickel sinter and Fe-Mo in the BOF(LD) furnace and 3 to 4 times slag off; (b) Cu, Fe-Mo, Fe-Mn (high carbon), Fe-Mn (low carbon), Fe-V are added to molten steel in ladle; (c) Fe-Mn, Fe-Nb are further added in VAD-I by are degassing (below 5 torr) for 10 minutes and adjusting the composition in VAD-II at 1625-1635°C; (d) CaSi wire is injected into molten steel at a rate of 0.7-1.0 kg per Ton and to a depth of 2.7-3.0 m in ladle; (e) Molten steel at a temperature of 1535-154O°C is cast into slabs of preferred cross section 900 x 170 mm and length 2.05-2.15 m in a vertical (BOW-type) continuous casting machine by applying the standard powder on the tundish and mould surface, at a preferred casting speed of 0.7 - 0.8 m/min, and at a superheat of 15-20°C maintained during casting; 3 (f) the slabs are conditioned by heating to 600/650°C in a walking-beam furnace and soaked for 2 hours, and re-heated at a rate of 50-60°C/hour to 1280/1300°C and re-soaked for 2,5 to 3.0 hours; (g) the slabs are cross-rolled !fea the temperature range of 1050 to 970°C to increase the width to 1700-1850 mm at thickness in the range of 10 to 16 mm after 3 passes in the temperature range of 1150-1070°C and thickness 10-16 mm, in total 20 to 22 passes, by controlling the oxygen level in reheating furnaces to be below 2%; (h) plates are finish-rolled at 900-930°C ; (i) finish-rolled plates are cut to the required size such as 1600 x '6200 mm and solution-treated at 920-930°C for 30 to 45 minutes and oil-quenched; (j) for ageing, oil-quenched plates are tempered in a walking beam furnace whose soaking zone temperature is maintained at 630 ± 10°C for tempering (ageing) plates of thickness 10 mm, 12 mm, 14 mm and 16mm at 630 ± 10°C for 110, 120, 135 ana 150 minutes respectively, to achieve uniform distribution of copper precipitates in the matrix of the plate's; The mechanical properties of the steel produced in the invented process are presented in Table 2 which includes also the requisite/targetted values thereof. It is noted from Table 2 that the mechanical properties of the steel produced in the invented process are superior to the requisite/targetted values thereof. The yield strength (YS) of the steel produced being appreciately higher than the minimum value 550 MPa of the conventional HSLA grades of steel, the plates of lesser thickness produced in the invented process will be suitable for use 4 compared with the plates of conventional HSLA grades of steel, leading to a saving in the consumption of steel for a given application. Moreover, in the case of the steel produced in the invented process, the pre- and post-welding treatment is not required with the resultant saving in the cost of fabrication of welded structures made from this steel. A sizeable quantity of steel produced in the invented process has been evaluated for performance at consumer's level and found to be satisfactorily. 5 Table 1 : Chemical composition of conventional HSLA grades of steel and the steel produced in the invented process. Content by weight % Ingredients Conventional HSLA grades of steel Steel produced in the invented process. C 0.07 0.045-0.055 Mn 0.40_0.70 0.75-0.90 P 0.025 0.005-0.010 S 0.010 0.005-0.010 Si 0.40 0.20-0.35 Ni 0.70-1.00 0.95-1.25 Cr 0.60-0.90 0.70-0.85 Mo 0.15-0.25 0.25-0.35 Cu 1.00-1.30 1.10-1.30 Nb 0.02-0.06 0.03-0.04 Al 0.02-0.06 0.015-0.020 Ti - 0.005 max V - 0.02-0.03 Fe Balance Balance Table 2 : Mechanical Properties of Steel Produced in the Invented Process. Properties Requisite/Targetted Observed Values - Values t. YS 575 MPa 605 - 635 MPa 2. UTS - 690 - 718 MPa 3. % EL 20 22 - 26 4. % RA* 50 62 - 67 5. Impact Energy (CVN) (Joules) (a) at 25°C - 190 - 225 (b) at -18°C 100 135 - 165 (c) at -62°C 85 109 - 114 (d) at -84°C - 85 - 95 6. Vickers Hardness (a) oil-quenched - 150 - 180 V£N ** (b) age-hardened 235 - 265 VPI 7. Bendability - 1T without surface cracks 8. Fracture toughness (a) static at 25°C (K1c) 273 MPa /m (b) Dynamic at 25°C. (K1d) - 130 MPa.. ? RA - Reduction in Area V£N - Vickers Penetration Number. 605 - 635 MPa 690 - 718 MPa 22 - 26 62 - 67 190 - 225 135 - 165 109 - 114 85 - 95 150 - 180 VPN 235 - 265 VPN 1T without surface cracks 7 We Claim :- 1. A process for producing copper-bearing age-hardened steel of increased yield strength, bendability and weldability, comprising the following steps in sequence: (a) making steel in Electric Arc Furnace/LD furnace by charging scraf containing cuttings of mild steel plates, bars and sheets.which is reasonably free from residual elements like Arsenic, Tin and Lead, lime, petroleum coke, sponge iron, iron ore and/or hot metal, in required quantities in the furnace and melting the said raw materials by electric arc or oxygen lancing with addition of 0.5-3.0% by weight quantity of Fe-Mn-Nickel sinter and Fe-Mo in the BOF(LD) furnace and 3 to 4 times slag off; (b) adding Cu, Fe-Mo, Fe-Mn (high carbon), Fe-Min (low carbon), Fe-V to molten steel in ladle; (c) further adding FeMn, FeNb in VAD-I by arc degassing (below 5 torr) for 10 minutes and adjusting the composition of steel in VAD-II at 1625-163O°C; (d) injecting CaSi wire into molten steel in ladle; (e) casting the molten steel into slabs in a continuous casting machine; (f) cross- rolling the slabs into plates, as herein described; and (g) ageing the plates, as herein described; characterised in that (i) the chemical composition of the steel produced is (by weight %): C-0.045 to 0.055, Mn-0.75 to 0.90, P-0.005 to 0.010, S-0.005 to 0.010, Si-0.20 to 0.35, Ni-0.95 to 1.25, 8 Cr-0.70 to 0.85, Mo-0.25 to 0.35, Cu-1,10 to 1.30, Nb-0.03 to 0.04, Al-0.015 to 0.020, Ti-0.005 max, V-0.02 to 0.03 and Fe-the balance; (ii) CaSi wire is injected into molten steel at a rate of 0.7 to 1.0 kg per Ton and to a depth of 2.7 to 3.0 m in ladle; (iii) slabs are cast at a speed of 0.7 to 0.8 m/min and at a superheat of 15-20°C; (iv) the slabs are conditioned by heating to 600/650°C in a walking-beam furnace, soaking for 2 hours, re-heating at a rate of 50-60°C/hour to 128O/13OO°C and re-soaking for 2.5 to 3.0 hours; (v) the slabs are cross-rolled into plates of width 1700 to 1850 ram in 20 to 22 passes; (vi) plates are finish-rolled at 900-930°C, solution-treated at 920-930°C for 30 to 45 minutes, and oil-quenched; and (vii) plates are aged by soaking oil-quenched plates in a walking beam furnace having soaking temperature of 630 + 10°C. 2. The process as claimed in claim 1, wherein the slabs are cross-rolled into plates of width 1700 to 1850 mm and thickness 10 to 16 mm after three passes in the temperature range of 1150-1070°C. 3. The process as claimed in claim 1 or 2, wherein the slabs are cross-rolled at oxygen level below 2% in the furnace. 9 4. The process as claimed in any of the preceding claims, wherein the oil-quenched plates of thickness 10 mm are soaked for 110 minutes, those of thickness 12 mm for 120 minutes, those of thickness 14 mm for 135 minutes and those of thickness 16 mm for 150 minutes. 10 A process for producing copper-bearing age-hardened steel of increased yield strength, bendability and weldability, comprising the following steps in sequence: (a) making steel in Electric Arc Furnace/LD furnace by charging scraf containing cuttings of mild steel plates, bars and sheets, which is reasonably free from residual elements like Arsenic, Tin and Lead, lime, petroleum coke, sponge iron, iron ore and/or hot metal in required quantities in the furnace and melting the said raw materials by electric arc or oxygen lancing with addition of 0.5-3.0% by weight quantity of Fe-Mn-Nickel sinter and Fe-Mo in the BOF(LD) furnace and 3 to 4 times slag off; (b) adding Cu, Fe-Mo, Fe-Mn (high carbon), Fe-Min (low carbon), Fe-V to molten steel in ladle; (c) further adding FeMn, FeNb in VAD-I by arc degassing (below 5 torr) for 10 minutes and adjusting the composition of steel in VAD-II at 1625-1630°C; (d) injecting CaSi wire into molten steel in ladle; (e) casting the molten steel into slabs in a continuous casting machine; (f) cross-rolling the slabs into plates, as herein described; and (g) ageing the plates, as herein described; characterised in that (i) the chemical composition of the steel produced is (by weight %): C-0.045 to 0.055, Mn-0.75 to 0.90, P-0.005 to 0.010, S-0.005 to 0.010, Si-0.20 to 0.35, Ni-0.95 to 1.25, Cr-0.70 to 0.85, Mo-0.25 to 0.35, Cu-1.10 to 1.30, Nb-0.03 to 0.04, Al-0.015 to 0.020, Ti-0.005 max, V-0.02 to 0.03 and Fe-the balance; (ii) CaSi wire is injected into molten steel at a rate of 0.7 to 1.0 kg per Ton and to a depth of 2.7 to 3.0 m in ladle; (iii) slabs are cast at a speed of 0.7 to 0.8 m/min and at a superheat of 15-20°C; (iv) the slabs are conditioned by heating to 600/650°C in a walking-beam furnace, soaking for 2 hours, re-heating at a rate of 50-60°C/hour to 1280/1300°C and re-soaking for 2.5 to 3.0 hours; (v) the slabs are cross-rolled into plates of width 1700 to 1850 mm in 20 to 22 passes; (vi) plates are finish-rolled at 900-930°C, solution-treated at 920-930°C for 30 to 45 minutes, and oil-quenched; and (vii) plate are aged by soaking oil-quenched plates in a walking beam furnace having soaking temperature of 630 ± 10°C.

Full Text

The present invention relates to a process for producing copper-bearing, age-hardened steel of increased yield strength, bendability and weldability.
The ateel having high yield strength, corrosion
resistance, bendability and weldability is required particularly for the construction of ocean going vessels, bridges and structures used in coastal areas. The conventional HSLA grades of steel containing copper and chromium used for the purpose has the following drawbacks s (i) the yield strength is not adequately high ; (ii) the pre- and post-welding treatment is required with increase in fabrication cost; (iii) bending is associated with surface cracks; and (iv) fracture toughness is low.
The conventional HSLA grades of steel of chemical composition (by weight %) : C-0,07, Mn-0.40 to 0.70, P-0.025, S-0.010, Si-O.4O, Ni-0,70 to 1.00, Cr-O.60-0.90, Mo-0.15 to 0.25, Cu-1.00 to 1.30, Nb-0.02 to 0.06, Al-0.02 to 0.06 and the balance-Fe is produced from ingots/slabs prepared in EAF/BOF route and rendered to be of fine-grain microstructure by killing the steel fully.
The object of the present invention is to provide a process for producing steel of increased yield strength, bendabilityand fracture toughness, which is particularly suitable for the construction of ships, bridges and structures erected at coastal regions.
2

In the invented process the chemical composition of the conventional HSLA grades of steel has been optimised by conducting extensive experiments in pilot mill and steel plants, as given in
Table 1, which also contains the composition of the conventional HSLA grades of steel for comparison. It is noted from Table 1 that the content of C, S, P and Al is reduced, that of Mn, Ni and Mo is increased, that of Cr, Cu and Nb is kept unchanged and new elements Ti and V are added in the optimised composition of steel produced in the invented process. The steps followed in sequence in the invented process are :-
(a) Steel is made in Electric Arc Furnace/LD furnace by
charging scraf containing cuttings of mild steel plates, bars and
sheets,which is reasonably free from residual elements like Arsenic,
Tin and Lead, lime, petroleum coke, sponge iron, iron ore and/or
hot metal, in required quantities in the furnace and melting the
said raw materials by electric arc or oxygen lancing with addition
of 0.5 to 3.0% by weight of Fe-Mn-Nickel sinter and Fe-Mo in the
BOF(LD) furnace and 3 to 4 times slag off;
(b) Cu, Fe-Mo, Fe-Mn (high carbon), Fe-Mn (low carbon),
Fe-V are added to molten steel in ladle;
(c) Fe-Mn, Fe-Nb are further added in VAD-I by are degassing
(below 5 torr) for 10 minutes and adjusting the composition in
VAD-II at 1625-1635°C;
(d) CaSi wire is injected into molten steel at a rate of
0.7-1.0 kg per Ton and to a depth of 2.7-3.0 m in ladle;
(e) Molten steel at a temperature of 1535-154O°C is cast
into slabs of preferred cross section 900 x 170 mm and length
2.05-2.15 m in a vertical (BOW-type) continuous casting machine
by applying the standard powder on the tundish and mould surface,
at a preferred casting speed of 0.7 - 0.8 m/min, and at a
superheat of 15-20°C maintained during casting;
3

(f) the slabs are conditioned by heating to 600/650°C in
a walking-beam furnace and soaked for 2 hours, and re-heated at
a rate of 50-60°C/hour to 1280/1300°C and re-soaked for 2,5 to
3.0 hours;
(g) the slabs are cross-rolled !fea the temperature range of
1050 to 970°C to increase the width to 1700-1850 mm at thickness
in the range of 10 to 16 mm after 3 passes in the temperature
range of 1150-1070°C and thickness 10-16 mm, in total 20 to 22
passes, by controlling the oxygen level in reheating furnaces
to be below 2%;
(h) plates are finish-rolled at 900-930°C ;
(i) finish-rolled plates are cut to the required size such as 1600 x '6200 mm and solution-treated at 920-930°C for 30 to 45 minutes and oil-quenched;
(j) for ageing, oil-quenched plates are tempered in a walking beam furnace whose soaking zone temperature is maintained at 630 ± 10°C for tempering (ageing) plates of thickness 10 mm, 12 mm, 14 mm and 16mm at 630 ± 10°C for 110, 120, 135 ana 150 minutes respectively, to achieve uniform distribution of copper precipitates in the matrix of the plate's;
The mechanical properties of the steel produced in the invented process are presented in Table 2 which includes also the requisite/targetted values thereof. It is noted from Table 2 that the mechanical properties of the steel produced in the invented process are superior to the requisite/targetted values thereof. The yield strength (YS) of the steel produced being appreciately higher than the minimum value 550 MPa of the conventional HSLA grades of steel, the plates of lesser thickness produced in the invented process will be suitable for use
4

compared with the plates of conventional HSLA grades of steel, leading to a saving in the consumption of steel for a given application.
Moreover, in the case of the steel produced in the invented process, the pre- and post-welding treatment is not required with the resultant saving in the cost of fabrication of welded structures made from this steel.
A sizeable quantity of steel produced in the invented process has been evaluated for performance at consumer's level and found to be satisfactorily.
5

Table 1 : Chemical composition of conventional HSLA grades
of steel and the steel produced in the invented
process.
Content by weight %

Ingredients Conventional HSLA grades of steel Steel produced in the invented process.

C 0.07 0.045-0.055
Mn 0.40_0.70 0.75-0.90
P 0.025 0.005-0.010
S 0.010 0.005-0.010
Si 0.40 0.20-0.35
Ni 0.70-1.00 0.95-1.25
Cr 0.60-0.90 0.70-0.85
Mo 0.15-0.25 0.25-0.35
Cu 1.00-1.30 1.10-1.30
Nb 0.02-0.06 0.03-0.04
Al 0.02-0.06 0.015-0.020
Ti - 0.005 max
V - 0.02-0.03
Fe Balance Balance

Table 2 : Mechanical Properties of Steel Produced
in the Invented Process.
Properties Requisite/Targetted Observed Values -
Values

t. YS
575 MPa
605 - 635 MPa
2. UTS -
690 - 718 MPa
3. % EL 20
22 - 26
4. % RA* 50
62 - 67
5. Impact Energy (CVN) (Joules)

(a) at 25°C -
190 - 225
(b) at -18°C 100
135 - 165
(c) at -62°C 85
109 - 114
(d) at -84°C -
85 - 95
6. Vickers Hardness

(a) oil-quenched -
150 - 180 V£N **
(b) age-hardened
235 - 265 VP*I
7. Bendability -
1T without surface cracks
8. Fracture toughness
(a) static at 25°C (K1c)
273 MPa */m
(b) Dynamic at 25°C. (K1d) -
130 MPa..
? RA - Reduction in Area

** V£N - Vickers Penetration Number.

605 - 635 MPa
690 - 718 MPa
22 - 26
62 - 67
190 - 225 135 - 165 109 - 114 85 - 95
150 - 180 VPN **
235 - 265 VPN
1T without surface cracks

7

We Claim :-
1. A process for producing copper-bearing age-hardened steel of increased yield strength, bendability and weldability, comprising the following steps in sequence: (a) making steel in Electric Arc Furnace/LD furnace by charging scraf containing cuttings of mild steel plates, bars and sheets.which is reasonably free from residual elements like Arsenic, Tin and Lead, lime, petroleum coke, sponge iron, iron ore and/or hot metal, in required quantities in the furnace and melting the said raw materials by electric arc or oxygen lancing with addition of 0.5-3.0% by weight quantity of Fe-Mn-Nickel sinter and Fe-Mo in the BOF(LD) furnace and 3 to 4 times slag off; (b) adding Cu, Fe-Mo, Fe-Mn (high carbon), Fe-Min (low carbon), Fe-V to molten steel in ladle; (c) further adding FeMn, FeNb in VAD-I by arc degassing (below 5 torr) for 10 minutes and adjusting the composition of steel in VAD-II at 1625-163O°C; (d) injecting CaSi wire into molten steel in ladle; (e) casting the molten steel into slabs in a continuous casting machine; (f) cross- rolling the slabs into plates, as herein described; and (g) ageing the plates, as herein described; characterised in that (i) the chemical composition of the steel produced is (by weight %): C-0.045 to 0.055, Mn-0.75 to 0.90, P-0.005 to 0.010, S-0.005 to 0.010, Si-0.20 to 0.35, Ni-0.95 to 1.25,
8

Cr-0.70 to 0.85, Mo-0.25 to 0.35, Cu-1,10 to 1.30, Nb-0.03 to 0.04, Al-0.015 to 0.020, Ti-0.005 max, V-0.02 to 0.03 and Fe-the balance; (ii) CaSi wire is injected into molten steel at a rate of 0.7 to 1.0 kg per Ton and to a depth of 2.7 to 3.0 m in ladle; (iii) slabs are cast at a speed of 0.7 to 0.8 m/min and at a superheat of 15-20°C; (iv) the slabs are conditioned by heating to 600/650°C in a walking-beam furnace, soaking for 2 hours, re-heating at a rate of 50-60°C/hour to 128O/13OO°C and re-soaking for 2.5 to 3.0 hours; (v) the slabs are cross-rolled into plates of width 1700 to 1850 ram in 20 to 22 passes; (vi) plates are finish-rolled at 900-930°C, solution-treated at 920-930°C for 30 to 45 minutes, and oil-quenched; and (vii) plates are aged by soaking oil-quenched plates in a walking beam furnace having soaking temperature of 630 + 10°C.
2. The process as claimed in claim 1, wherein
the slabs are cross-rolled into plates of width 1700
to 1850 mm and thickness 10 to 16 mm after three
passes in the temperature range of 1150-1070°C.
3. The process as claimed in claim 1 or 2,
wherein the slabs are cross-rolled at oxygen level
below 2% in the furnace.
9

4. The process as claimed in any of the preceding claims, wherein the oil-quenched plates of thickness 10 mm are soaked for 110 minutes, those of thickness 12 mm for 120 minutes, those of thickness 14 mm for 135 minutes and those of thickness 16 mm for 150 minutes.
10
A process for producing copper-bearing age-hardened steel of increased yield strength, bendability and weldability, comprising the following steps in sequence: (a) making steel in Electric Arc Furnace/LD furnace by charging scraf containing cuttings of mild steel plates, bars and sheets, which is reasonably free from residual elements like Arsenic, Tin and Lead, lime, petroleum coke, sponge iron, iron ore and/or hot metal in required quantities in the furnace and melting the said raw materials by electric arc or oxygen lancing with addition of 0.5-3.0% by weight quantity of Fe-Mn-Nickel sinter and Fe-Mo in the BOF(LD) furnace and 3 to 4 times slag off; (b) adding Cu, Fe-Mo, Fe-Mn (high carbon), Fe-Min (low carbon), Fe-V to molten steel in ladle; (c) further adding FeMn, FeNb in VAD-I by arc degassing (below 5 torr) for 10 minutes and adjusting the composition of steel in VAD-II at 1625-1630°C; (d) injecting CaSi wire into molten steel in ladle; (e) casting the molten steel into slabs in a continuous casting machine; (f) cross-rolling the slabs into plates, as herein described; and (g) ageing the plates, as herein described; characterised in that (i) the chemical composition of the steel produced is (by weight %): C-0.045 to 0.055, Mn-0.75 to 0.90, P-0.005 to 0.010, S-0.005 to 0.010, Si-0.20 to 0.35, Ni-0.95 to 1.25, Cr-0.70 to 0.85, Mo-0.25 to 0.35, Cu-1.10 to 1.30, Nb-0.03 to 0.04, Al-0.015 to 0.020, Ti-0.005 max, V-0.02 to 0.03 and Fe-the balance; (ii) CaSi wire is injected into molten steel at a rate of 0.7 to 1.0 kg per Ton and to a depth of 2.7 to 3.0 m in ladle; (iii) slabs are cast at a speed of 0.7 to 0.8 m/min and at a superheat of 15-20°C; (iv) the slabs are conditioned by heating to 600/650°C in a walking-beam furnace, soaking for 2 hours, re-heating at a rate of 50-60°C/hour to 1280/1300°C and re-soaking for 2.5 to 3.0 hours; (v) the slabs are cross-rolled into plates of width 1700 to 1850 mm in 20 to 22 passes; (vi) plates are finish-rolled at 900-930°C, solution-treated at 920-930°C for 30 to 45 minutes, and oil-quenched; and (vii) plate are aged by soaking oil-quenched plates in a walking beam furnace having soaking temperature of 630 ± 10°C.

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Patent Number

205865

Indian Patent Application Number

00106/CAL/1999

PG Journal Number

15/2007

Publication Date

13-Apr-2007

Grant Date

13-Apr-2007

Date of Filing

12-Feb-1999

Name of Patentee

STEEL AUTHORITY OF INDIA LIMITED

Applicant Address

RESEARCH AND DEVELOPMENT CENTRE FOR IRON AND STEEL, A GOVT. OF INDIA ENTERPRISE, ISPAT BHAWAN, LODHI ROAD, NEW DELHI

Inventors:

#	Inventor's Name	Inventor's Address
1	SUSIL KUMAR SEN	RDCIS/SAIL, DORANDA, RANCHI
2	RAM AVTAR	RDCIS/SAIL, DORANDA, RANCHI-834002
3	AMITAVA ROY	RDCIS/SAIL, DORANDA, RANCHI-834002
4	SANJAY KUMAR DHUA	RDCIS/SAIL, DORANDA, RANCHI-834002
5	MOKAPATTY SATYENDRA PRASAD	RDCIS/SAIL, DORANDA, RANCHI-834002
6	GANGESHWAR SINGH	ROURKELA STEEL PLANT, SAIL, ROURKELA
7	SUDHAKER JHA	RDCIS/SAIL, DORANDA, RANCHI-834002

PCT International Classification Number

C 22 C 9/00

PCT International Application Number

N/A

PCT International Filing date

PCT Conventions:

#	PCT Application Number	Date of Convention	Priority Country
1			NA