Title of Invention	"AN IMPROVED PROCESS FOR PRODUCING WELDABLE QUALITY STEEL OF INCREASED YIELD STRENGTH AND CORROSION RESISTANCE"
Abstract	An improved process for producing weldable quality steel of increased yield strength and corrosion resistance, suitable for construction of bridges and buildings, characterised in that the process comprises the following steps in sequence : (a) producing primary steel of minimum sulphur content 0.04% by weight in a L.D. converter of Basic Oxygen France (BOF); (b) tapping the molten primary steel into a pre-heated ladle with addition of ferro-alloys like low- and high-carbon ferro-manganese, ferro-silicon, ferro-vanadium and silicon- manganese, and alloying metals like Nickel, Copper and Aluminium to the extent of 4 to 5% by weight and in proportion required to produce molten steel of composition (by weight %): C-0.08 to 0.15, Mn-0.80 to 1.25, S-0.03 max., P-0.03 max., Si-0.32 to 0.60, Cr-0.42 to 0.65, Ni-0.20 to 0.30, Cu-0.25 to 0.40, V-0.02 to 0.06 and Fe- the balance; (c) casting the molten steel into ingots in moulds with addition of known misch metal in required quantity to the molten steel during teeming thereof into the moulds; (d) soaking the ingots in soaking pits at 1320°C for 6 to 8 hours; (e) hot rolling the ingots into slabs of size 150/160 mm x 1490 mm followed by hot shearing, cooling in stacks and scarf in thereof; (f) reheating the slabs to 1280°C in an atmosphere containing 0.5% oxygen by volume; and (g) finish rolling the slabs at 870 ± 10°C, followed by coiling thereof at 640 + 10°C.

Title of Invention

"AN IMPROVED PROCESS FOR PRODUCING WELDABLE QUALITY STEEL OF INCREASED YIELD STRENGTH AND CORROSION RESISTANCE"

Abstract

An improved process for producing weldable quality steel of increased yield strength and corrosion resistance, suitable for construction of bridges and buildings, characterised in that the process comprises the following steps in sequence : (a) producing primary steel of minimum sulphur content 0.04% by weight in a L.D. converter of Basic Oxygen France (BOF); (b) tapping the molten primary steel into a pre-heated ladle with addition of ferro-alloys like low- and high-carbon ferro-manganese, ferro-silicon, ferro-vanadium and silicon- manganese, and alloying metals like Nickel, Copper and Aluminium to the extent of 4 to 5% by weight and in proportion required to produce molten steel of composition (by weight %): C-0.08 to 0.15, Mn-0.80 to 1.25, S-0.03 max., P-0.03 max., Si-0.32 to 0.60, Cr-0.42 to 0.65, Ni-0.20 to 0.30, Cu-0.25 to 0.40, V-0.02 to 0.06 and Fe- the balance; (c) casting the molten steel into ingots in moulds with addition of known misch metal in required quantity to the molten steel during teeming thereof into the moulds; (d) soaking the ingots in soaking pits at 1320°C for 6 to 8 hours; (e) hot rolling the ingots into slabs of size 150/160 mm x 1490 mm followed by hot shearing, cooling in stacks and scarf in thereof; (f) reheating the slabs to 1280°C in an atmosphere containing 0.5% oxygen by volume; and (g) finish rolling the slabs at 870 ± 10°C, followed by coiling thereof at 640 + 10°C.

Full Text	The invention relates to an improved process for producing weldable quality steel of increased yield strength and corrosion resistance. The invention relates more particularly to a process for producing weldable quality steel of corrosion resistance higher than that of carbon structural steel and minimum yield strength of 340 MPa, to make the same suitable for use in the construction of bridges, buildings and various other equipment which are vulnerable to corrosion by atmosphere and/or flue gases using primary steel of relatively high sulphur content i.e. 0.04% and above by weight as the starting material. The existing process for producing steel for the abovementioned applications comprises preparation of molten steel of relatively low sulphur content i.e. less than 0.03% by weight in a basic oxygen furnace (BOF); addition of alloying elements such as carbon, manganese and vanadium in a relatively high proportion to the molten steel in a vacuum are degassing (VAD) ladle; continuous casting (CC) of the molten steel into slabs; hot rolling of the slabs into strips in horizontal slabbing machine (HSM); hot finishing and coiling of the strips; and cooling the coils to ambient temperature. The main drawbacks of the existing process are that because of addition of the alloying elements, particularly carbon, manganese and vanadium in a relatively high proportion to the molten steel the weldability and corrosion resistance properties of the steel produced are adversely affected and that the cost of production is increased owing to the addition - 2 - of the relatively expensive alloying elements like manganese and vanadium in increased proportion to the molten steel in ladle. The objective of the present invention is to provide an improved process for producing weldable quality steel plates of increased yield strength and corrosion resistance at a reduced cost from primary steel containing a relatively high percentage of sulphur by weight i.e. 0.04% and above. The invented process has been developed by conducting extensive research work in laboratory, followed by plant level trials and evaluation of the end use performance of the product. The basic steps followed in the invented process are :- (i) determining the chemical composition of the steel suitable for meeting the end use requirements; (ii) producing primary steel of sulphur content 0.04% and above (by weight) in a BOF and adding ferro-alloys and alloying metals to the molten steel in a ladle; (iii) producing refined secondary steel ingots by Argon rinsing of the molten steel in the ladle and casting in a mould with addition of misch metal to the molten steel at the time of teeming the same into the mould; and (iv) soaking, slabbing, scarfing, controlled hot rolling and coiling, and cooling. Distinguishing features of the present invention v/ith reference to prior art are :- (i) As compared to maximum specified carbon content of 0.19% for this grade of steel (ASTM 588), carbon content is limited to be in the range of 0.08 to 0.15 percent in the invented process - 3 - for ensuring increased weldability of the steel produced. (ii) To minimise the adverse effect of increased sulphur content, the molten steel is tapped from L.D. convertor (BOF) with reduced sulphur content of about 0.04% by treating the steel with Misch metal during its transfer from BOF to ladle to convert the sulphide inclusions into globular shape particles, which improves the ductility of steel. In other words, even if proper desulfurisation facilities is not available in the plant, and the sulphur level of steel is as high as 0.04%, it is possible in the invented process to get good ductility by treating steel with Misch metal. (iii) Cr-Si containing steels, like the one produced, have a tendency to form sticky scale during reheating of the slabs for hot rolling. The problem is overcome in the invented process by maintaining a controlled amount of oxygen (0.5%) in the reheating furnace for forming a non-sticky scale on the steel, which can be easily removed during high pressure descaling operation. (iv) By using 870 ± 10°C temperature as hot finishing temperature along with delayed cooling on the run out table (ROT), followed by coiling at a temperature of 640 ± 10°C, a fine grain pearlite-ferrite grain structure steel which has higher yield strength and toughness,as compared to steel produced in the prior art, is produced. The invented process is described fully and particularly in an unrestricted manner with reference to the accompanying drawings in which Figure 1 is a flow diagram - 3A - depicting the various steps followed in sequence in the invented process : Referring to Fig. 1, the invented process comprises the following steps in sequence ;- (a) heats of primary steel having sulphur content of 0.04% or more by weight are produced in a BOF having a L.D. converter of 60 tonne capacity, lined with basic refractories, by blowing oxygen of 99.50% purity into the converter for oxidising the impurities like silicon, phosphorus, manganese and carbon present in the molten steel therein and reducing their content in the molten steel by double deslagging; (b) the molten steel is tapped into a pre-heated ladle in which ferro-alloys such as low carbon ferro-manganese [Fe - Mn (Low C)], high carbon ferro-manganese [Fe - Mn (Low C)], ferro-silicon (Fe-Si), ferro-chromium (Fe-Cr), ferro-vahadium (Fe-V), silicon-manganese (Si-Mn) and alloying metals such as Nickel (Ni), copper (Cu) and aluminium (Al) are added in quantities such as,to the extent of 4 to 5% by weight required for producing steel of chemical composition (by weight %)i C-0.08 to 0.15, Mn-0.80 to 1.25, S-0.03 max, P-0.03 max., Si-0.32 to 0.60, Cr-0.42 to 0.65, Ni-0.20 to 0.30, Cu-0,25 to 0.40, V-0.02 to 0,06 and Fe-the balance, the said additions of ferro-alloys and alloying metals being made during filling of the ladle with molten steel from one-third to two-third of the height of the ladle; (c) the molten steel in ladle is transferred to a secondary refining furnace in which Argon gas rinsing of the _ 4 - steel is carried out by blowing Argon through a porus plug to homogenise the composition and temperature of the steel in the furnace; (d) the refined molten steel is cast into ingots in a mould of 12.5 tonne capacity, the top part of the mould being Kept hot for reducing pipe formation during solidification of the ingots, with addition of known misch metal at a preferred rate of 1.5 kg per tonne of the steel produced in the mould during teeming of the molten steel into the mould; casting of ingots instead of continuous casting (CC) of slabs has been adopted to make the process more flexible for using heats of primary steel containing relatively high sulphur inclusion and more versatile for adoption in steel plants having no facility for continuous casting; (e) hot ingots are charged into soaking pits which are lined with ceramic fibre and of recuperative type, provided with side burners using either mixed gases from blast furnaces and coke ovens or coke oven gases alone, of calorific value 400 K cal/NM3, for heating the charge, and soaked for 6 to 8 hours at a preferred temperature of 1320 C; (f) the soaked ingots are hot rolled into slabs of preferred size 15O/16Omm x 1490mm in a slabbing mill provided with two rolls each of diameter 1200mm and two manipulators disposed one on each side of the mill for positioning of the slabs on their stand; (g) the slabs are hot sheared to remove the pipes and other defects formed therein and cooled in stocks for preventing cracks being formed therein; -5- (h) the cooled slabs are inspected for the presence of defects therein and subjected to scarfing ; (i) the scarfed slabs are charged into a reheating furnace maintained at a preferred temperature of 1280°C and having an atmosphere containing O.5% oxygen by volume for reducing the formation of sticky scale for preventing rolled-in scale in the finished product; (j) the reheated slabs are hot rolled into strips and coils of size 5 to 10mm x 1510mm in a hot strip mill provided with lamilar water cooling arrangement maintaining the finishing temperature preferably at 870 + 10°C and the coiling temperature preferably at 640 + 1O°C during rolling for producing relatively fine grain steel of increased yield and ultimate strength with enhanced weldability; (k) the coils are allowed to cool to the ambient temperature in natural air. The properties of the steel plates produced are tested. The test results along with the specified minimum values are presented in Table I from which it is noted that the yield strength, ultimate tensile strength and elongation % at break of the product are each appreciably higher than the corresponding minimum specified values. Extensive shearing, bending and welding operations performed on the steel produced in the invented process in a plant for manufacturing 'Louver Dampers' and like articles have proved the satisfactory end use performance of the product. The corrosion resistance of the steel plates has been found to be 4 to 5 times higher than that of the carbon structural steel* — 6 — Table I -7- Test Results and Specified Minimum Values of the properties of the Steel Produced. We Claim :- 1. An improved process lor producing weldable quality steel of increased yield strength and corrosion resistance, suitable for construction of bridges and buildings, characterised in that the process comprises the following steps in sequences (a) producing primary steel of minimum sulphur content 0.04 % by weight in a L.D. converter of Basic Oxygen Furnace (BOP); (b) tapping the molten primary steel into a pre-heated ladle with addition of ferro-alloys like low- and high-carbon ferro-manganese, ferro-silicon, ferro-vanadium and silicon- manganese, and alloying metals like Nickel, Copper and Aluminium to the extant of 4 to 5% by weight and in proportion required to produce molten steel of composition (by weight %): C-0.08 to 0.15, Mn-0.80 to 1.25, S-0.03 max., P-0.03 max., Si-0.32 to 0.60, Cr-0.42 to 0,65, Ni-0.20 to 0,30, Cu-0,25 to 0.40, Y-0.02 to 0.06 and Fe- the balance; (c) casting the molten steel into ingots in moulds with addition of known misch metal in required quantity to the molten steel during teeming thereof into the moulds; (d) soaking the ingots in soaking pits at 1320°C for 6 to 8 hours; (e) hot rolling the ingots into slabs of size 150/160 mm x 1490 mm , followed by hot shearing, cooling in stacks and scarfing thereof; (f) reheating the slabs to 1280°C in an atmosphere containing 0.5% oxygen by volume; and - 8 - (g) finish rolling the slabs at 870 + 10°C, followed by coiling thereof at 640 + 10°C. 2. The process as claimed in claim 1, wherein the primary steel is produced in a L.D. converter of 60 tome capacity, lined with basic refractories, by blowing oxygen of 99.50% purity into the converter and double deslagging of the molten steel. 3. The process as claimed in claim 1 or 2, wherein the ferro-alloys and alloying metals are added to the molten steel during filling of the ladle with the molten steel from one- third to two-third of the height of the ladle, 4. The process as claimed in any preceding claim, wherein the misch metal is added at the rate of 1.5 kg per tonne of the steel produced. 5. The process as claimed in any preceding claim, wherein the ingots are cast in moulds of 12.5 tonne capacity, the top part of which is kept hot during solidification of the ingots therein. 6. The process as claimed in any preceding claim, wherein the ingots are soaked in soaking pits at a temperature of 1320°C for 7 hours. 7. The process as claimed in claim 6, wherein the ingots are soaked in soaking pits which are lined with ceramic fibre, of recuperative type and heated with side burners provided therein. 8. The process as claimed in claim 7, wherein the burners are supplied with either mixed gases from blast furnaces and coke ovens or with gases from coke ovens alone, of calorific value 400 K cal/NM3. - 9 - 9. The process as claimed in any preceding claim, wherein the soaked ingots are hot rolled into slabs in a slabbing mill provided with two rolls each of diameter 1200 mm and, two manipulators disposed one on each side of the slabs for positioning of the slabs on the stand therefor. - 10 - 10. The process as claimed in any preceding claim, wherein the re-heated slabs are rolled into coils in a hot strip mill provided with lamilar water cooling arrangenent. An improved process for producing weldable quality steel of increased yield strength and corrosion resistance, suitable for construction of bridges and buildings, characterised in that the process comprises the following steps in sequence : (a) producing primary steel of minimum sulphur content 0.04% by weight in a L.D. converter of Basic Oxygen France (BOF); (b) tapping the molten primary steel into a pre-heated ladle with addition of ferro-alloys like low- and high-carbon ferro-manganese, ferro-silicon, ferro-vanadium and silicon- manganese, and alloying metals like Nickel, Copper and Aluminium to the extent of 4 to 5% by weight and in proportion required to produce molten steel of composition (by weight %): C-0.08 to 0.15, Mn-0.80 to 1.25, S-0.03 max., P-0.03 max., Si-0.32 to 0.60, Cr-0.42 to 0.65, Ni-0.20 to 0.30, Cu-0.25 to 0.40, V-0.02 to 0.06 and Fe- the balance; (c) casting the molten steel into ingots in moulds with addition of known misch metal in required quantity to the molten steel during teeming thereof into the moulds; (d) soaking the ingots in soaking pits at 1320°C for 6 to 8 hours; (e) hot rolling the ingots into slabs of size 150/160 mm x 1490 mm followed by hot shearing, cooling in stacks and scarf in thereof; (f) reheating the slabs to 1280°C in an atmosphere containing 0.5% oxygen by volume; and (g) finish rolling the slabs at 870 ± 10°C, followed by coiling thereof at 640 + 10°C.

Full Text

The invention relates to an improved process for producing weldable quality steel of increased yield strength and corrosion resistance.
The invention relates more particularly to a process for producing weldable quality steel of corrosion resistance higher than that of carbon structural steel and minimum yield strength of 340 MPa, to make the same suitable for use in the construction of bridges, buildings and various other equipment which are vulnerable to corrosion by atmosphere and/or flue gases using primary steel of relatively high sulphur content i.e. 0.04% and above by weight as the starting material.
The existing process for producing steel for the abovementioned applications comprises preparation of molten steel of relatively low sulphur content i.e. less than 0.03% by weight in a basic oxygen furnace (BOF); addition of alloying elements such as carbon, manganese and vanadium in a relatively high proportion to the molten steel in a vacuum are degassing (VAD) ladle; continuous casting (CC) of the molten steel into slabs; hot rolling of the slabs into strips in horizontal slabbing machine (HSM); hot finishing and coiling of the strips; and cooling the coils to ambient temperature.
The main drawbacks of the existing process are that because of addition of the alloying elements, particularly carbon, manganese and vanadium in a relatively high proportion to the molten steel the weldability and corrosion resistance properties of the steel produced are adversely affected and that the cost of production is increased owing to the addition
- 2 -

of the relatively expensive alloying elements like manganese and vanadium in increased proportion to the molten steel in ladle.
The objective of the present invention is to provide an improved process for producing weldable quality steel plates of increased yield strength and corrosion resistance at a reduced cost from primary steel containing a relatively high percentage of sulphur by weight i.e. 0.04% and above.
The invented process has been developed by conducting extensive research work in laboratory, followed by plant level trials and evaluation of the end use performance of the product. The basic steps followed in the invented process are :-
(i) determining the chemical composition of the steel suitable for meeting the end use requirements;
(ii) producing primary steel of sulphur content 0.04% and above (by weight) in a BOF and adding ferro-alloys and alloying metals to the molten steel in a ladle;
(iii) producing refined secondary steel ingots by Argon rinsing of the molten steel in the ladle and casting in a mould with addition of misch metal to the molten steel at the time of teeming the same into the mould; and
(iv) soaking, slabbing, scarfing, controlled hot rolling and coiling, and cooling.
Distinguishing features of the present invention v/ith reference to prior art are :-
(i) As compared to maximum specified carbon content of 0.19% for this grade of steel (ASTM 588), carbon content is limited to be in the range of 0.08 to 0.15 percent in the invented process
- 3 -

for ensuring increased weldability of the steel produced.
(ii) To minimise the adverse effect of increased sulphur content, the molten steel is tapped from L.D. convertor (BOF) with reduced sulphur content of about 0.04% by treating the steel with Misch metal during its transfer from BOF to ladle to convert the sulphide inclusions into globular shape particles, which improves the ductility of steel. In other words, even if proper desulfurisation facilities is not available in the plant, and the sulphur level of steel is as high as 0.04%, it is possible in the invented process to get good ductility by treating steel with Misch metal.
(iii) Cr-Si containing steels, like the one produced, have a tendency to form sticky scale during reheating of the slabs for hot rolling. The problem is overcome in the invented process by maintaining a controlled amount of oxygen (0.5%) in the reheating furnace for forming a non-sticky scale on the steel, which can be easily removed during high pressure descaling operation.
(iv) By using 870 ± 10°C temperature as hot finishing temperature along with delayed cooling on the run out table (ROT), followed by coiling at a temperature of 640 ± 10°C, a fine grain pearlite-ferrite grain structure steel which has higher yield strength and toughness,as compared to steel produced in the prior art, is produced.
The invented process is described fully and particularly in an unrestricted manner with reference to the accompanying drawings in which Figure 1 is a flow diagram
- 3A -

depicting the various steps followed in sequence in the invented process :
Referring to Fig. 1, the invented process comprises the following steps in sequence ;-
(a) heats of primary steel having sulphur content of
0.04% or more by weight are produced in a BOF having a L.D.
converter of 60 tonne capacity, lined with basic refractories,
by blowing oxygen of 99.50% purity into the converter for
oxidising the impurities like silicon, phosphorus, manganese
and carbon present in the molten steel therein and reducing
their content in the molten steel by double deslagging;
(b) the molten steel is tapped into a pre-heated ladle in
which ferro-alloys such as low carbon ferro-manganese
[Fe - Mn (Low C)], high carbon ferro-manganese
[Fe - Mn (Low C)], ferro-silicon (Fe-Si), ferro-chromium
(Fe-Cr), ferro-vahadium (Fe-V), silicon-manganese (Si-Mn) and
alloying metals such as Nickel (Ni), copper (Cu) and aluminium

(Al) are added in quantities such as,to the extent of 4 to 5% by weight required for producing steel of
chemical composition (by weight %)i C-0.08 to 0.15, Mn-0.80 to 1.25, S-0.03 max, P-0.03 max., Si-0.32 to 0.60, Cr-0.42 to 0.65, Ni-0.20 to 0.30, Cu-0,25 to 0.40, V-0.02 to 0,06 and Fe-the balance, the said additions of ferro-alloys and alloying metals being made during filling of the ladle with molten steel from one-third to two-third of the height of the ladle;
(c) the molten steel in ladle is transferred to a
secondary refining furnace in which Argon gas rinsing of the
_ 4 -

steel is carried out by blowing Argon through a porus plug to homogenise the composition and temperature of the steel in the furnace;
(d) the refined molten steel is cast into ingots in a
mould of 12.5 tonne capacity, the top part of the mould being
Kept hot for reducing pipe formation during solidification of
the ingots, with addition of known misch metal at a preferred rate
of 1.5 kg per tonne of the steel produced in the mould during
teeming of the molten steel into the mould; casting of ingots
instead of continuous casting (CC) of slabs has been adopted
to make the process more flexible for using heats of primary
steel containing relatively high sulphur inclusion and more
versatile for adoption in steel plants having no facility for
continuous casting;
(e) hot ingots are charged into soaking pits which are
lined with ceramic fibre and of recuperative type, provided
with side burners using either mixed gases from blast furnaces
and coke ovens or coke oven gases alone, of calorific value
400 K cal/NM3, for heating the charge, and soaked for 6 to 8
hours at a preferred temperature of 1320 C;
(f) the soaked ingots are hot rolled into slabs of
preferred size 15O/16Omm x 1490mm in a slabbing
mill provided with two rolls each of diameter 1200mm and two manipulators disposed one on each side of the mill for positioning of the slabs on their stand;
(g) the slabs are hot sheared to remove the pipes and
other defects formed therein and cooled in stocks for preventing
cracks being formed therein;
-5-

(h) the cooled slabs are inspected for the presence of defects therein and subjected to scarfing ;
(i) the scarfed slabs are charged into a reheating furnace maintained at a preferred temperature of 1280°C and having an atmosphere containing O.5% oxygen by volume for reducing the formation of sticky scale for preventing rolled-in scale in the finished product;
(j) the reheated slabs are hot rolled into strips and coils of size 5 to 10mm x 1510mm in a hot strip mill provided with lamilar water cooling arrangement maintaining the finishing temperature preferably at 870 + 10°C and the coiling temperature preferably at 640 + 1O°C during rolling for producing relatively fine grain steel of increased yield and ultimate strength with enhanced weldability;
(k) the coils are allowed to cool to the ambient temperature in natural air.
The properties of the steel plates produced are tested. The test results along with the specified minimum values are presented in Table I from which it is noted that the yield strength, ultimate tensile strength and elongation % at break of the product are each appreciably higher than the corresponding minimum specified values.
Extensive shearing, bending and welding operations performed on the steel produced in the invented process in a plant for manufacturing 'Louver Dampers' and like articles have proved the satisfactory end use performance of the product. The corrosion resistance of the steel plates has been found to be 4 to 5 times higher than that of the carbon structural steel*
— 6 —

Table I
-7-
Test Results and Specified Minimum Values of the properties of the Steel Produced.

We Claim :-
1. An improved process lor producing weldable quality steel of increased yield strength and corrosion resistance, suitable for construction of bridges and buildings, characterised in that the process comprises the following steps in sequences
(a) producing primary steel of minimum sulphur content
0.04 % by weight in a L.D. converter of Basic Oxygen Furnace
(BOP);
(b) tapping the molten primary steel into a pre-heated
ladle with addition of ferro-alloys like low- and high-carbon
ferro-manganese, ferro-silicon, ferro-vanadium and silicon-
manganese, and alloying metals like Nickel, Copper and Aluminium
to the extant of 4 to 5% by weight and in proportion required
to produce molten steel of composition (by weight %): C-0.08 to
0.15, Mn-0.80 to 1.25, S-0.03 max., P-0.03 max., Si-0.32 to
0.60, Cr-0.42 to 0,65, Ni-0.20 to 0,30, Cu-0,25 to 0.40, Y-0.02
to 0.06 and Fe- the balance;
(c) casting the molten steel into ingots in moulds with
addition of known misch metal in required quantity to the molten
steel during teeming thereof into the moulds;
(d) soaking the ingots in soaking pits at 1320°C for 6 to 8
hours;
(e) hot rolling the ingots into slabs of size 150/160 mm x
1490 mm , followed by hot shearing, cooling in stacks and scarfing
thereof;
(f) reheating the slabs to 1280°C in an atmosphere
containing 0.5% oxygen by volume; and
- 8 -

(g) finish rolling the slabs at 870 + 10°C, followed by coiling thereof at 640 + 10°C.
2. The process as claimed in claim 1, wherein the primary
steel is produced in a L.D. converter of 60 tome capacity,
lined with basic refractories, by blowing oxygen of 99.50% purity
into the converter and double deslagging of the molten steel.
3. The process as claimed in claim 1 or 2, wherein the
ferro-alloys and alloying metals are added to the molten steel
during filling of the ladle with the molten steel from one-
third to two-third of the height of the ladle,
4. The process as claimed in any preceding claim, wherein the misch metal is added at the rate of 1.5 kg per tonne of the steel produced.
5. The process as claimed in any preceding claim, wherein the ingots are cast in moulds of 12.5 tonne capacity, the top part of which is kept hot during solidification of the ingots therein.
6. The process as claimed in any preceding claim, wherein the ingots are soaked in soaking pits at a temperature of 1320°C for 7 hours.
7. The process as claimed in claim 6, wherein the ingots
are soaked in soaking pits which are lined with ceramic fibre,
of recuperative type and heated with side burners provided
therein.
8. The process as claimed in claim 7, wherein the burners
are supplied with either mixed gases from blast furnaces and coke
ovens or with gases from coke ovens alone, of calorific value
400 K cal/NM3.
- 9 -

9. The process as claimed in any preceding claim, wherein the soaked ingots are hot rolled into slabs in a slabbing mill provided with two rolls each of diameter 1200 mm and, two manipulators disposed one on each side of the slabs for positioning of the slabs on the stand therefor.
- 10 -
10. The process as claimed in any preceding claim, wherein the re-heated slabs are rolled into coils in a hot strip mill provided with lamilar water cooling arrangenent.
An improved process for producing weldable quality steel of increased yield strength and corrosion resistance, suitable for construction of bridges and buildings, characterised in that the process comprises the following steps in sequence :
(a) producing primary steel of minimum sulphur content
0.04% by weight in a L.D. converter of Basic Oxygen France (BOF);
(b) tapping the molten primary steel into a pre-heated
ladle with addition of ferro-alloys like low- and high-carbon
ferro-manganese, ferro-silicon, ferro-vanadium and silicon-
manganese, and alloying metals like Nickel, Copper and Aluminium
to the extent of 4 to 5% by weight and in proportion required to
produce molten steel of composition (by weight %): C-0.08 to
0.15, Mn-0.80 to 1.25, S-0.03 max., P-0.03 max., Si-0.32 to 0.60,
Cr-0.42 to 0.65, Ni-0.20 to 0.30, Cu-0.25 to 0.40, V-0.02 to 0.06
and Fe- the balance;
(c) casting the molten steel into ingots in moulds with
addition of known misch metal in required quantity to the molten
steel during teeming thereof into the moulds;
(d) soaking the ingots in soaking pits at 1320°C for
6 to 8 hours;
(e) hot rolling the ingots into slabs of size 150/160 mm x
1490 mm followed by hot shearing, cooling in stacks and scarf in
thereof;
(f) reheating the slabs to 1280°C in an atmosphere
containing 0.5% oxygen by volume; and
(g) finish rolling the slabs at 870 ± 10°C, followed by
coiling thereof at 640 + 10°C.

Documents:

02324-cal-1997-abstract.pdf

02324-cal-1997-assignment.pdf

02324-cal-1997-claims.pdf

02324-cal-1997-correspondence.pdf

02324-cal-1997-description(complete).pdf

02324-cal-1997-drawings.pdf

02324-cal-1997-form-1.pdf

02324-cal-1997-form-2.pdf

02324-cal-1997-form-3.pdf

02324-cal-1997-letters patent.pdf

02324-cal-1997-p.a.pdf

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Patent Number

202601

Indian Patent Application Number

2324/CAL/1997

PG Journal Number

09/2007

Publication Date

02-Mar-2007

Grant Date

02-Mar-2007

Date of Filing

09-Dec-1997

Name of Patentee

STEEL AUTHORITY OF INDIA LIMITED

Applicant Address

CENTER FOR IRON AND STEEL,AT ISPAT BHAWAN, LODHI ROAD, NEW DELHI-110003

Inventors:

#	Inventor's Name	Inventor's Address
1	MADAN LAL NARULA	RDCIS/SAIL,DORANDA,RANCHI-834002.
2	ATUL SAXENA	RDCIS/SAIL,DORANDA,RANCHI-834002.
3	BALBIR SINGH	RDCIS/SAIL,DORANDA,RANCHI-834002.
4	SANAK MISHRA	RDCIS/SAIL,DORANDA,RANCHI-834002.

PCT International Classification Number

C22C 38/02

PCT International Application Number

N/A

PCT International Filing date

PCT Conventions:

#	PCT Application Number	Date of Convention	Priority Country
1			NA