Title of Invention	A PROCESS TO MANUFACTURE WELDABLE QUALITY STRUCTURAL STEEL FOR JOIST, CHANNEL, ANGLE AND SKELP
Abstract	A process for producing high strength low-alloy structural steel characterized by high strength to weight ratio, superior notch toughness and wettability. The process achieves such characteristic features of high strength low alloy structural steel by lowering carbon content, microalloying with niobium and vanadium singly or combinedly and controlled processing in the mill. The precipitates of micro alloying elements refine the ferrite grain size due to inhibition of austenite grain growth and also cause precipitation strengthening of ferrite matrix. Also in the above process by selecting an appropriate alloy chemistry and controlled processing in the mill, high yield strength coupled with superior notch toughness are obtained.

Title of Invention

A PROCESS TO MANUFACTURE WELDABLE QUALITY STRUCTURAL STEEL FOR JOIST, CHANNEL, ANGLE AND SKELP

Abstract

A process for producing high strength low-alloy structural steel characterized by high strength to weight ratio, superior notch toughness and wettability. The process achieves such characteristic features of high strength low alloy structural steel by lowering carbon content, microalloying with niobium and vanadium singly or combinedly and controlled processing in the mill. The precipitates of micro alloying elements refine the ferrite grain size due to inhibition of austenite grain growth and also cause precipitation strengthening of ferrite matrix. Also in the above process by selecting an appropriate alloy chemistry and controlled processing in the mill, high yield strength coupled with superior notch toughness are obtained.

Full Text	A process to manufacture weldable quality high strength low alloy sm. structuras (joist, channel, angle) and skelp. High strength low-alloy structural steel are characterized by high strength to weight ratio, superior notch toughness and weldability. These benefits are derived by lowering carbon content, microalloying with niobium and vanadium singly or combinedly and controlled processing in the mill. The precipitates of micro alloying elements refine the ferrite grain size due to inhibition of austenite grain growth and also cause precipitation strengthening of ferrite matrix. By selecting an appropriate alloy chemistry and controlled processing in the mill, high yield strength coupled with superior notch toughness can be obtained. Conventional steels have lower strength to weight ration. Their weldability and impact toughness are not as good as low alloy steels. This is due to presence of Nb and V 3ingly or m combination in low alloy steels. These elements refine the gram size and improve strength and impact toughness. They also cause precipitation strengthening and improve strength. Addition of these elements causes amount of carbon in steel to be reduced to low level compared to conventional steels. A lower carbon steel has better weldability. In conventional steel carbon cannot be very low to obtain adequate strength. Mam object of the invention is to produce a weldable quality structural (joist, angle, channel) with minimum room temperature yield strength 300 MPa, 350 MPa, 410 MPa and 450 MPa and weldable quality skelp with minimum room temperature yield strength 410 MPa. Further object of the invention is to produce a structural steel having high strength to weight ratio. Another object is to produce a structural steel having superior weldability and impact toughness. All the' above objects of the invention have been achieved by prolonged study and investigation in the field of sm. variety of steels. The production of sm. grades of steel required different processing sequence, particularly alloy chemistry formulation, pass schedule and temperature of processing. The invention provides a process for producing weldable quality high strength low alloy sm. structural steel for joists, angles, channels and skelp which comprises melting the steel in a furnace and tapping the same in a preheated ladle at 1610 ± 10°C and adding the ferroalloys containing Nb and/or V gradually in the ladle. The liquid steel was cast as ingots which are then soaked at 1350 ± 20°C for 6 hours and rolled into bloom or billets, which are then cooled to room temperature and reheated to 1250 ± 20°C and controlled rolled to obtain the structures/skelp as desired. Micro alloying element Nb to be added should be in the range of 0.005 to 0.05 weight per cent while the weight per cent of V should be 0.10 (max). Other alloying constituent to be present should be such that the final composition may contain, in weight percent C = 0.05 to 0.20 Mn = 0.75 to 1.50 Si = 0.05 to 0.20 S = 0.04 (max) p = 0.04 (max) The process has been developed after extensive trials in plants. The process chart is shown in Fig. 1. The steel was melted in BOFjOHF and tapped in a preheated ladle at 1610 ± 10-C. The addition of ferroniobiumjferro-vanadium was done gradually in the ladle during tapping. The addition started when the ladle was about one-third full of liquid steel to avoid excessive oxidation of microalloying elements. The liquid steel was cast as 8 tonne ingots. The ingots were soaked at 1350 ± 20'C for 6 hours and rolled to blooms. Some of the ingots were rolled to billets. Alternatively molten 1 steel is concast directly into blooms or billets at a tundish temperature of 1540- 1550°C. The blooms were cooled to room temperature, reheated for soaking at 1250 ± 20°C and controlled rolled to beams, angles and channels. The finishing rolling temperature varied between 800-950°C and the reduction per pass was 10 to 20%. The billets were reheated and soaked at 1250 ± 20°C and processed to skelp (size : 216 x 2.7 mm) The finishing rolling temperature was 800 - 850°C, the coiling temperature was 650-700°C and the reduction per pass was 5 to 15%. Typical processing schedules for structural and skelp are shown in Fig. 2. The typical mechanical properties of structural and skelp are shown in Table 1. The optical microstructure of structural showed fine grain polygonal ferrite and pearlite. The ferrite grain size was 3.2 m to 12.0 μm. A mixed structure of polygonal and acicular ferrite with pearlite was observed in beam section having yield stress higher than 450 MPa. The optical microstructure of skelp showed predominanlly a fine polygonal ferrite structure with grain size 5.8 μm to 6.5 μm. The bright field transmsssion electron micrographs showed presence of fine precipitates of microalloying elements in ferrite. The weldability tests of joist section were carried out to establish safe welding procedure for this steel. The structurals of this steel can be welded using properly baked electrode conforming to ASTM E7018 Cl.1 without preheating. Interpass temperature should be about 125X. Using this welding procedure satisfactory fracture toughness can be ensured in the heat affected zone (typical value of HAZ toughness for SAIL-MA 450 joist was 40 Joule at - 55°C). The SAIL-MA joist also showed adequate resistance to hot cracking. The maximum strain below which no hot cracking was observed was 1.2%. From Fig.2 it is clear that blooms for production of angle are to be soaked at 1250°C ± 20°C for 2 to 3 hours in the reheating furnace and rolled to angle of desired size. The reduction per pass will be 20% max. The finishing rolling temperature for angle is 95°C max. The angles after rolling will be cooled in natural air. Blooms for production of joist and channel are to be soaked at 1250°C ± 20°C for 2 to 3 hours and rolled to desired size. The reduction per pass will be 20% maximum. The FRT will be 870°C max. The cooling will be in natural air. Billets for production of skelp are to be soaked at 1250° ± 20°C for 2 to 3 hours and rolled to desired thickness and width. The reduction per pass will be 15% max. The FRT shall be 850°C max. The cooling will be in natural air. The invented process is cost effective as it enables achievement of higher strength (as illustrated in accompanying TABLE 1) without heat treatment through microalloy additions and has been made suitable for implementaiion using the existing equipment of steel plants without the need of additional facilities. We claim: 1. A process for producing weldable quality high strength low alloy sm. structural steel for joists, angles, channels and skelp which comprises melting the steel in a furnace and tapping the same in a preheated ladle at 1610 ± 10°C and adding the ferroalloys to the molten steel containing Nb and/or V and other elements such that final composition may contain in weight per cent. e in the range of 0.05 to 0.20 Mn in the range of 0.75 to 1.50 Si in the range of 0.05 to 0.20 S 0.04 (max) P 0.04 (max) gradually and the molten liquid after complete addition was cast as ingots, which are then soaked at 1350 ± 20°C such as herein described and rolled into bloom or billets, which are then cooled to room temperature and reheated to 1250 ± 20°C and controlled rolled to obtain the structurals/skelp as desired. 2. A process for producing weldable quality high strength low alloy structurals/skelp as claimed in claim 1 in which the weight percent of microalloying element Nb is in the range of 0.005 to 0.05 and weight per cent of V should be 0.10 (max). 3. A process for producing high strength low alloy structural steel as claimed in claim 1 wherein the controlled rolling to produce beams, channels and angles should be carried out at a finishing rolling temperature between 800 to 950°C and the reduction per pass was 10 to 20%. 4. A process for producing high strength low alloy structural steel wherein process parameter for producing the skelp is such that the finishing rolling temperature was 800-850°C, coiling temperature was 650-700e and reduction per pass was 5 to 15%. 5. A process for producing high strength low alloy structural steel as claimed in claim 1 wherein blooms for production of angle are to be soaked at 1250 ± 20°C preferably for 2 to 3 hours in the reheating furnace and rolled to angle of desired size, the reduction per pass will be 20% max and finishing rolling temperature for angle is 950°C max and is then cooled to room temperature in natural air. 6. A process for producing high strength low alloy structural steel as claimed in claim 1 wherein blooms for production of joists and channels are to be soaked at 1250 ± 20°C preferably for 2 to 3 hours and rolled to desired size with reduction per pass being 20% max. and finishing rolling temperature being 870°C max and is then cooled to room temperature in natural air. 7. A process for producing high strength low alloy structural steel as claimed in claim 1 wherein billets for production of skelp are to be soaked at 1250 ± 20°C for 2 to 3 hours and rolled to desired thickness and width. Reduction per pass is 15% max and finishing rolling temperature is 850°C max and is then coiled at temperature of 650- 700°C. 8. A process for producing weldable high strength low alloy sm.structural steel as claimed in anyone of claims 1 to 8 wherein said step orsoaking is carried out for a period of 6 hours. 9. A process for producing high strength weldable quality low alloy sm.structural steel substantially as herein described and ascertained. Dated this 24th day of February 2000.

Full Text

A process to manufacture weldable quality high strength low alloy sm.
structuras (joist, channel, angle) and skelp.
High strength low-alloy structural steel are characterized by high strength to weight
ratio, superior notch toughness and weldability. These benefits are derived by lowering
carbon content, microalloying with niobium and vanadium singly or combinedly and
controlled processing in the mill. The precipitates of micro alloying elements refine the
ferrite grain size due to inhibition of austenite grain growth and also cause
precipitation strengthening of ferrite matrix. By selecting an appropriate alloy
chemistry and controlled processing in the mill, high yield strength coupled with
superior notch toughness can be obtained.
Conventional steels have lower strength to weight ration. Their weldability and impact
toughness are not as good as low alloy steels. This is due to presence of Nb and V
3ingly or m combination in low alloy steels. These elements refine the gram size and
improve strength and impact toughness. They also cause precipitation strengthening
and improve strength. Addition of these elements causes amount of carbon in steel to
be reduced to low level compared to conventional steels. A lower carbon steel has
better weldability. In conventional steel carbon cannot be very low to obtain adequate
strength.
Mam object of the invention is to produce a weldable quality structural (joist, angle,
channel) with minimum room temperature yield strength 300 MPa, 350 MPa, 410 MPa
and 450 MPa and weldable quality skelp with minimum room temperature yield
strength 410 MPa.
Further object of the invention is to produce a structural steel having high strength to
weight ratio.

Another object is to produce a structural steel having superior weldability and impact
toughness.
All the' above objects of the invention have been achieved by prolonged study and
investigation in the field of sm. variety of steels. The production of sm.
grades of steel required different processing sequence, particularly alloy chemistry
formulation, pass schedule and temperature of processing.
The invention provides a process for producing weldable quality high strength low
alloy sm. structural steel for joists, angles, channels and skelp which comprises
melting the steel in a furnace and tapping the same in a preheated ladle at 1610 ±
10°C and adding the ferroalloys containing Nb and/or V gradually in the ladle. The
liquid steel was cast as ingots which are then soaked at 1350 ± 20°C for 6 hours and

rolled into bloom or billets, which are then cooled to room temperature and reheated
to 1250 ± 20°C and controlled rolled to obtain the structures/skelp as desired.
Micro alloying element Nb to be added should be in the range of 0.005 to 0.05 weight
per cent while the weight per cent of V should be 0.10 (max).
Other alloying constituent to be present should be such that the final composition
may contain, in weight percent
C = 0.05 to 0.20
Mn = 0.75 to 1.50
Si = 0.05 to 0.20
S = 0.04 (max)
p = 0.04 (max)
The process has been developed after extensive trials in plants. The process chart is
shown in Fig. 1. The steel was melted in BOFjOHF and tapped in a preheated ladle
at 1610 ± 10-C. The addition of ferroniobiumjferro-vanadium was done gradually in
the ladle during tapping. The addition started when the ladle was about one-third
full of liquid steel to avoid excessive oxidation of microalloying elements. The liquid
steel was cast as 8 tonne ingots. The ingots were soaked at 1350 ± 20'C for 6 hours
and rolled to blooms. Some of the ingots were rolled to billets. Alternatively molten
1 steel is concast directly into blooms or billets at a tundish temperature of 1540-
1550°C.
The blooms were cooled to room temperature, reheated for soaking at 1250 ± 20°C
and controlled rolled to beams, angles and channels. The finishing rolling
temperature varied between 800-950°C and the reduction per pass was 10 to 20%.
The billets were reheated and soaked at 1250 ± 20°C and processed to skelp (size :
216 x 2.7 mm) The finishing rolling temperature was 800 - 850°C, the coiling
temperature was 650-700°C and the reduction per pass was 5 to 15%. Typical
processing schedules for structural and skelp are shown in Fig. 2.
The typical mechanical properties of structural and skelp are shown in Table 1. The
optical microstructure of structural showed fine grain polygonal ferrite and pearlite.

The ferrite grain size was 3.2 m to 12.0 μm. A mixed structure of polygonal and
acicular ferrite with pearlite was observed in beam section having yield stress higher
than 450 MPa. The optical microstructure of skelp showed predominanlly a fine
polygonal ferrite structure with grain size 5.8 μm to 6.5 μm. The bright field
transmsssion electron micrographs showed presence of fine precipitates of
microalloying elements in ferrite.
The weldability tests of joist section were carried out to establish safe welding
procedure for this steel. The structurals of this steel can be welded using properly
baked electrode conforming to ASTM E7018 Cl.1 without preheating. Interpass
temperature should be about 125X. Using this welding procedure satisfactory
fracture toughness can be ensured in the heat affected zone (typical value of HAZ
toughness for SAIL-MA 450 joist was 40 Joule at - 55°C). The SAIL-MA joist also
showed adequate resistance to hot cracking. The maximum strain below which no
hot cracking was observed was 1.2%.
From Fig.2 it is clear that blooms for production of angle are to be soaked at 1250°C
± 20°C for 2 to 3 hours in the reheating furnace and rolled to angle of desired size.
The reduction per pass will be 20% max. The finishing rolling temperature for angle
is 95°C max. The angles after rolling will be cooled in natural air. Blooms for
production of joist and channel are to be soaked at 1250°C ± 20°C for 2 to 3 hours
and rolled to desired size. The reduction per pass will be 20% maximum. The FRT
will be 870°C max. The cooling will be in natural air.
Billets for production of skelp are to be soaked at 1250° ± 20°C for 2 to 3 hours and
rolled to desired thickness and width. The reduction per pass will be 15% max. The
FRT shall be 850°C max. The cooling will be in natural air.
The invented process is cost effective as it enables achievement of higher strength (as
illustrated in accompanying TABLE 1) without heat treatment through microalloy
additions and has been made suitable for implementaiion using the existing
equipment of steel plants without the need of additional facilities.

We claim:
1. A process for producing weldable quality high strength low alloy sm. structural
steel for joists, angles, channels and skelp which comprises melting the steel in a
furnace and tapping the same in a preheated ladle at 1610 ± 10°C and adding the
ferroalloys to the molten steel containing Nb and/or V and other elements such that
final composition may contain in weight per cent.
e in the range of 0.05 to 0.20
Mn in the range of 0.75 to 1.50
Si in the range of 0.05 to 0.20
S 0.04 (max)
P 0.04 (max)
gradually and the molten liquid after complete addition was cast as ingots, which are
then soaked at 1350 ± 20°C such as herein described and rolled into bloom or billets,
which are then cooled to room temperature and reheated to 1250 ± 20°C and controlled
rolled to obtain the structurals/skelp as desired.
2. A process for producing weldable quality high strength low alloy structurals/skelp as
claimed in claim 1 in which the weight percent of microalloying element Nb is in the
range of 0.005 to 0.05 and weight per cent of V should be 0.10 (max).
3. A process for producing high strength low alloy structural steel as claimed in claim 1
wherein the controlled rolling to produce beams, channels and angles should be
carried out at a finishing rolling temperature between 800 to 950°C and the reduction
per pass was 10 to 20%.
4. A process for producing high strength low alloy structural steel wherein process
parameter for producing the skelp is such that the finishing rolling temperature was
800-850°C, coiling temperature was 650-700e and reduction per pass was 5 to
15%.

5. A process for producing high strength low alloy structural steel as claimed in claim 1
wherein blooms for production of angle are to be soaked at 1250 ± 20°C preferably
for 2 to 3 hours in the reheating furnace and rolled to angle of desired size, the
reduction per pass will be 20% max and finishing rolling temperature for angle is
950°C max and is then cooled to room temperature in natural air.
6. A process for producing high strength low alloy structural steel as claimed in claim 1
wherein blooms for production of joists and channels are to be soaked at 1250 ±
20°C preferably for 2 to 3 hours and rolled to desired size with reduction per pass
being 20% max. and finishing rolling temperature being 870°C max and is then
cooled to room temperature in natural air.
7. A process for producing high strength low alloy structural steel as claimed in claim 1
wherein billets for production of skelp are to be soaked at 1250 ± 20°C for 2 to 3
hours and rolled to desired thickness and width. Reduction per pass is 15% max and
finishing rolling temperature is 850°C max and is then coiled at temperature of 650-
700°C.
8. A process for producing weldable high strength low alloy sm.structural steel as
claimed in anyone of claims 1 to 8 wherein said step orsoaking is carried out for a
period of 6 hours.
9. A process for producing high strength weldable quality low alloy sm.structural
steel substantially as herein described and ascertained.
Dated this 24th day of February 2000.

Documents:

112-CAL-2000 (08-07-2003) CORRESPONDENCE.pdf

112-CAL-2000 (10-07-2003) FORM-18.pdf

112-CAL-2000 (22-08-2003) FER.pdf

112-CAL-2000 (24-02-2000) ABSTRACT.pdf

112-CAL-2000 (24-02-2000) CANCELLED DOCUMENT.pdf

112-CAL-2000 (24-02-2000) CLAIMS-1.pdf

112-CAL-2000 (24-02-2000) CLAIMS.pdf

112-CAL-2000 (24-02-2000) CORRESPONDENCE.pdf

112-CAL-2000 (24-02-2000) DESCRIPTION COMPLETE.pdf

112-CAL-2000 (24-02-2000) DRAWINGS.pdf

112-CAL-2000 (24-02-2000) FORM-1.pdf

112-CAL-2000 (24-02-2000) FORM-2.pdf

112-CAL-2000 (24-02-2000) FORM-3.pdf

112-CAL-2000 (24-02-2000) PA.pdf

112-CAL-2000 (24-02-2000) SPECIFICATION.pdf

112-CAL-2000 (24-03-2000) CORRESPONDENCE.pdf

112-CAL-2000 (26-07-2004) CORRESPONDENCE.pdf

112-CAL-2000 (30-10-2003) FER REPLY.pdf

112-CAL-2000 (31-03-2004) CORRESPONDENCE.pdf

112-CAL-2000-(18-12-2013)-CORRESPONDENCE.pdf

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Patent Number

260712

Indian Patent Application Number

112/CAL/2000

PG Journal Number

21/2014

Publication Date

23-May-2014

Grant Date

19-May-2014

Date of Filing

24-Feb-2000

Name of Patentee

STEEL AUTHORITY OF INDIA LIMITED

Applicant Address

RESEARCH & DEVELOPMENT CENTRE FOR IRON & STEEL, DORANDA, RANCHI-834002,BIHAR,INDIA.

Inventors:

#	Inventor's Name	Inventor's Address
1	SEN SANKAR	RESEARCH & DEVELOPMENT CENTRE FOR IRON & STEEL, DORANDA, RANCHI-834002,BIHAR,INDIA.
2	VAIDHNATHA RAMASWAMY	EX EXECUTIVE DIRECTOR OF RESEARCH & DEVELOPMENT CENTRE FOR IRON & STEEL, DORANDA, RANCHI-834002,BIHAR,INDIA. presently working in SHRI VISHNUPRIYA INDUSTRIES LTD., 2ND FLOOR, HOUSE OF ALFA BUSINESS CENTRE, 6/3/349/20, ROAD NO.1, BANJARA HILLS, HYDERABAD-500034.
3	PANIGRAHI BIMAL KUMAR	RESEARCH & DEVELOPMENT CENTRE FOR IRON & STEEL, DORANDA, RANCHI-834002,BIHAR,INDIA.
4	MISHRA KUNJ BIHARI	RESEARCH & DEVELOPMENT CENTRE FOR IRON & STEEL, DORANDA, RANCHI-834002,BIHAR,INDIA.
5	MUKHERJEE DEBASIS	RESEARCH & DEVELOPMENT CENTRE FOR IRON & STEEL, DORANDA, RANCHI-834002,BIHAR,INDIA.

PCT International Classification Number

C21D6/00

PCT International Application Number

N/A

PCT International Filing date

PCT Conventions:

#	PCT Application Number	Date of Convention	Priority Country
1			NA