U.S. patent application number 13/838465 was filed with the patent office on 2014-09-18 for method of thin strip casting.
This patent application is currently assigned to CASTRIP, LLC. The applicant listed for this patent is Walter N. Blejde, Daniel Geoffrey Edelman, Rama Ballav Mahapatra. Invention is credited to Walter N. Blejde, Daniel Geoffrey Edelman, Rama Ballav Mahapatra.
Application Number | 20140261905 13/838465 |
Document ID | / |
Family ID | 51522086 |
Filed Date | 2014-09-18 |
United States Patent
Application |
20140261905 |
Kind Code |
A1 |
Blejde; Walter N. ; et
al. |
September 18, 2014 |
METHOD OF THIN STRIP CASTING
Abstract
A method for making alloy strip by continuous casting with
tensile strength of at least 900 MPa and total elongation of at
least 30%, strip with tensile strength of at least 1200 MPa and
total elongation of at least 20%, or strip with tensile strength of
at least 1500 MPa and total elongation of at least 15%. Molten
metal is introduced forming a casting pool supported on the casting
rolls and counter-rotating the A heat flux is provided with a peak
heat flux >20 Mw/m2. The strip is cooled at 1000-3000 K/sec. A
roll biasing force >40 kN/meter of casting roll length is
applied to form thin metal strip. The strip is then conveyed
through a first enclosure with an atmosphere having an oxygen
content of <5%. The cast strip is rolled through a rolling mill
and reduced and modification of the microstructure is
initiated.
Inventors: |
Blejde; Walter N.;
(Brownsburg, IN) ; Mahapatra; Rama Ballav;
(Brighton-Le-Sands, AU) ; Edelman; Daniel Geoffrey;
(Brownsburg, IN) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Blejde; Walter N.
Mahapatra; Rama Ballav
Edelman; Daniel Geoffrey |
Brownsburg
Brighton-Le-Sands
Brownsburg |
IN
IN |
US
AU
US |
|
|
Assignee: |
CASTRIP, LLC
Charlotte
NC
|
Family ID: |
51522086 |
Appl. No.: |
13/838465 |
Filed: |
March 15, 2013 |
Current U.S.
Class: |
148/541 ;
148/556; 148/557; 164/463 |
Current CPC
Class: |
B22D 11/0622 20130101;
B22D 11/1206 20130101 |
Class at
Publication: |
148/541 ;
164/463; 148/557; 148/556 |
International
Class: |
B22D 11/06 20060101
B22D011/06; B22D 11/12 20060101 B22D011/12 |
Claims
1. A method of making alloy strip with tensile strength of at least
900 MPa and total elongation of at least 30% produced by continuous
casting comprising: (a) assembling a twin roll caster having a pair
of counter-rotating casting rolls laterally positioned to provide a
nip there between, (b) introducing molten metal to form a casting
pool supported on the casting rolls above the nip and
counter-rotating the casting rolls where the composition has a
solidus temperature between 950 and 1200.degree. C., a liquidus
temperature between 1150 and 1350.degree. C., and a freezing range
between 100 and 250.degree. C., (c) providing a heat flux in
forming the thin strip on the casting rolls with a peak heat flux
of greater than 20 Mw/m.sup.2 and heat flux after 25 milliseconds
of greater than 8 Mw/m.sup.2 to provide a weighted average heat
flux of at least 10 Mw/m.sup.2, and cooling the strip at 1000 to
3000 K/sec until the strip exits the nip between the casting rolls,
(d) applying a roll biasing force greater than 40 kN/meter of
casting roll length to form thin metal strip downwardly at the nip,
(e) conveying the thin cast strip through a first enclosure with an
atmosphere having an oxygen content of less than 5% immediately
downstream of the casting rolls and on to a roller table while
forming a loop of the cast strip with a strain of not more than
0.4% to form a thin steel strip, and (f) rolling the cast strip
through a rolling mill to impart between 10 and 40% reduction and
initiating a modification of the microstructure of the cast strip
to provide strip with tensile strength of at least 900 MPa and
total elongation of at least 30%.
2. The method of making steel strip as claimed in claim 1 where the
loop in the enclosure is between 2.8 and 3 meters.
3. A method of making alloy strip as claimed in claim 1 where the
strip after step (c) has an unresolved microstructure at the
surfaces, an equiaxed in the central portions and columnar
intermediate portions.
4. A method of making alloy strip as claimed in claim 1 where the
casting rolls have crown shape such that the cast strip within 25
millimeters of the edge of the strip have a higher temperature than
the strip in the center portion of the strip width.
5. A method of making alloy strip with tensile strength of at least
900 MPa and total elongation of at least 30% produced by continuous
casting comprising: (a) assembling a twin roll caster having a pair
of counter-rotating casting rolls laterally positioned to provide a
nip there between, (b) introducing molten metal to form a casting
pool supported on the casting rolls above the nip and
counter-rotating the casting rolls where the composition has a
solidus temperature between 950 and 1200.degree. C., a liquidus
temperature between 1150 and 1350.degree. C., and a freezing range
between 100 and 250.degree. C., (c) providing a heat flux in
forming the thin strip on the casting rolls with a peak heat flux
of greater than 20 Mw/m.sup.2 and heat flux after 25 milliseconds
of greater than 8 Mw/m.sup.2 to provide a weighted average heat
flux of at least 10 Mw/m.sup.2, and cooling the strip at 1000 to
3000 K/sec until the strip exits the nip between the casting rolls,
(d) applying a roll biasing force greater than 40 kN/meter of
casting roll length to form thin metal strip downwardly at the nip,
(e) conveying the thin cast strip through a first enclosure with an
atmosphere having an oxygen content of less than 5% immediately
downstream of the casting rolls and on to a roller table while
forming a loop of the cast strip with a strain of not more than
0.4%, and (f) subjecting the cast strip to heating post casting to
at least 70% of the alloy's melting point to modify the
microstructure of the cast strip to provide strip with tensile
strength of at least 900 MPa and total elongation of at least
30%.
6. The method of making alloy strip with tensile strength of at
least 900 MPa and total elongation of at least 30% as claimed in
claim 5 where the loop in the enclosure is between 2.8 and 3
meters.
7. The method of making alloy strip with tensile strength of at
least 900 MPa and total elongation of at least 30% as claimed in
claim 5 where the loop in the enclosure has a strain of not more
than 0.2%.
8. A method of making alloy strip with tensile strength of at least
900 MPa and total elongation of at least 30% as claimed in claim 5
where the strip after step (c) has an unresolved microstructure at
the surfaces, an equiaxed in the central portions, and columnar
intermediate portions.
9. A method of making alloy strip with tensile strength of at least
900 MPa and total elongation of at least 30% as claimed in claim 5
where the casting roll have crown shape such that the cast strip
within 25 millimeters of the edge of the strip have a higher
temperature than the strip in the center portion of the strip
width.
10. A method of making alloy strip with tensile strength of at
least 900 MPa and total elongation of at least 30% produced by
continuous casting comprising: (a) assembling a twin roll caster
having a pair of counter-rotating casting rolls laterally
positioned to provide a nip there between, (b) introducing molten
metal to form a casting pool supported on the casting rolls above
the nip and counter-rotating the casting rolls where the
composition is of the formula:
R.sub.uR'.sub.vCr.sub.wM.sub.xB.sub.y(P,C,Si).sub.z, Where R is one
of iron, cobalt or nickel, R' is one or two iron of iron, cobalt or
nickel other than R, Cr, B, P, C, and Si respectively represent
chromium, boron, phosphorus, carbon and silicon, M is one or more
of molybdenum, vanadium, niobium, titanium, aluminum, tin,
manganese and copper, u, v, w, x, y and z represent atom percent of
R, R', Cr, M, B and (P, C, Si), respectively, and having the
following values: u=30-85 v=0-30 w=0-45 x=0-30 y=0-12 z=0-7.5 with
the provisions that (1) the sum of v+w+x is at least 5, (2) when x
is larger than 20, then w must be less than 20, (3) the amount of
each of vanadium, manganese, copper, tin, magnesium may not exceed
10 atom percent, and (4) the combined amount of boron, phosphorus,
carbon and silicon may not exceed about 13 atom percent. (c)
providing a heat flux in forming the thin strip on the casting
rolls with a peak heat flux of greater than 20 Mw/m.sup.2 and heat
flux after 25 milliseconds of greater than 8 Mw/m.sup.2 to provide
a weighted average heat flux of at least 10 Mw/m.sup.2, and cooling
the strip at 1000 to 3000 K/sec until the strip exits the nip
between the casting rolls, (d) applying a roll biasing force
greater than 40 kN/meter of casting roll length to form thin metal
strip downwardly at the nip, (e) conveying the thin cast strip
through a first enclosure with an atmosphere having an oxygen
content of less than 5% immediately downstream of the casting rolls
and on to a roller table while forming a loop of the cast strip
with a strain of not more than 0.4% to form a thin steel strip, and
(f) rolling the cast strip through a rolling mill to impart between
10 and 40% reduction and initiating a modification of the
microstructure of the cast strip to provide strip with tensile
strength of at least 900 MPa and total elongation of at least
30%.
11. The method of making alloy strip as claimed in claim 10 where
the loop in the enclosure is between 2.8 and 3 meters.
12. A method of making alloy strip as claimed in claim 10 where the
strip after step (c) has an unresolved microstructure at the
surfaces, an equiaxed in the central portions and columnar
intermediate portions.
13. A method of making alloy strip as claimed in claim 10 where the
casting roll have crown shape such that the cast strip within 25
millimeters of the edge of the strip have a higher temperature than
the strip in the center portion of the strip width.
14. A method of making alloy strip with tensile strength of at
least 900 MPa and total elongation of at least 30% produced by
continuous casting comprising: (a) assembling a twin roll caster
having a pair of counter-rotating casting rolls laterally
positioned to provide a nip there between, (b) introducing molten
metal to form a casting pool supported on the casting rolls above
the nip and counter-rotating the casting rolls where the
composition is of the formula:
R.sub.uR'.sub.vCr.sub.wM.sub.xB.sub.y(P,C,Si).sub.z, Where R is one
of iron, cobalt or nickel, R' is one or two iron of iron, cobalt or
nickel other than R, Cr, B, P, C, and Si respectively represent
chromium, boron, phosphorus, carbon and silicon, M is one or more
of molybdenum, vanadium, niobium, titanium, aluminum, tin,
manganese and copper, u, v, w, x, y and z represent atom percent of
R, R', Cr, M, B and (P, C, Si), respectively, and having the
following values: u=30-85 v=0-30 w=0-45 x=0-30 y=0-12 z=0-7.5 with
the provisions that (1) the sum of v+w+x is at least 5, (2) when x
is larger than 20, then w must be less than 20, (3) the amount of
each of vanadium, manganese, copper, tin, magnesium may not exceed
10 atom percent, and (4) the combined amount of boron, phosphorus,
carbon and silicon may not exceed about 13 atom percent. (c)
providing a heat flux in forming the thin strip on the casting
rolls with a peak heat flux of greater than 20 Mw/m.sup.2 and heat
flux after 25 milliseconds of greater than 8 Mw/m.sup.2 to provide
a weighted average heat flux of at least 10 Mw/m.sup.2, and cooling
the strip at 1000 to 3000 K/sec until the strip exits the nip
between the casting rolls, (d) applying a roll biasing force
greater than 40 kN/meter of casting roll length to form thin metal
strip downwardly at the nip, (e) conveying the thin cast strip
through a first enclosure with an atmosphere having an oxygen
content of less than 5% immediately downstream of the casting rolls
and on to a roller table while forming a loop of the cast strip
with a strain of not more than 0.4% to form a thin steel strip, and
(f) subjecting the cast strip to heating post casting to at least
70% of the alloy's melting point to modify the microstructure of
the cast strip to provide strip with tensile strength of at least
900 MPa and total elongation of at least 30%.
15. The method of making alloy strip as claimed in claim 14 where
the loop in the enclosure is between 2.8 and 3 meters.
16. The method of making alloy strip as claimed in claim 14 where
the loop in the enclosure has a strain of not more than 0.2%.
17. A method of making alloy strip as claimed in claim 14 where the
strip after step (c) has an unresolved microstructure at the
surfaces, an equiaxed in the central portions and columnar
intermediate portions.
18. A method of making alloy strip as claimed in claim 14 where the
casting roll have crown shape such that the cast strip within 25
millimeters of the edge of the strip have a higher temperature than
the strip in the center portion of the strip width.
19. A method of making alloy strip with tensile strength of at
least 1200 MPa and total elongation of at least 20% produced by
continuous casting comprising: (a) assembling a twin roll caster
having a pair of counter-rotating casting rolls laterally
positioned to provide a nip there between, (b) introducing molten
metal to form a casting pool supported on the casting rolls above
the nip and counter-rotating the casting rolls where the
composition has a solidus temperature between 950 and 1200.degree.
C., a liquidus temperature between 1150 and 1350.degree. C., and a
freezing range between 100 and 250.degree. C., (c) providing a heat
flux in forming the thin strip on the casting rolls with a peak
heat flux of greater than 20 Mw/m.sup.2 and heat flux after 25
milliseconds of greater than 8 Mw/m.sup.2 to provide a weighted
average heat flux of at least 10 Mw/m.sup.2, and cooling the strip
at 1000 to 3000 K/sec until the strip exits the nip between the
casting rolls, (d) applying a roll biasing force greater than 40
kN/meter of casting roll length to form thin metal strip downwardly
at the nip, (e) conveying the thin cast strip through a first
enclosure with an atmosphere having an oxygen content of less than
5% immediately downstream of the casting rolls and on to a roller
table while forming a loop of the cast strip with a strain of not
more than 0.4% to form a thin steel strip, and (f) rolling the cast
strip through a rolling mill to impart between 10 and 40% reduction
and initiating a modification of the microstructure of the cast
strip to provide strip with tensile strength of at least 1200 MPa
and total elongation of at least 20%.
20. The method of making steel strip as claimed in claim 19 where
the loop in the enclosure is between 2.8 and 3 meters.
21. A method of making alloy strip as claimed in claim 19 where the
strip after step (c) has an unresolved microstructure at the
surfaces, an equiaxed in the central portions and columnar
intermediate portions.
22. A method of making alloy strip as claimed in claim 19 where the
casting rolls have crown shape such that the cast strip within 25
millimeters of the edge of the strip have a higher temperature than
the strip in the center portion of the strip width.
23. A method of making alloy strip with tensile strength of at
least 1200 MPa and total elongation of at least 20% produced by
continuous casting comprising: (a) assembling a twin roll caster
having a pair of counter-rotating casting rolls laterally
positioned to provide a nip there between, (b) introducing molten
metal to form a casting pool supported on the casting rolls above
the nip and counter-rotating the casting rolls where the
composition has a solidus temperature between 950 and 1200.degree.
C., a liquidus temperature between 1150 and 1350.degree. C., and a
freezing range between 100 and 250.degree. C., (c) providing a heat
flux in forming the thin strip on the casting rolls with a peak
heat flux of greater than 20 Mw/m.sup.2 and heat flux after 25
milliseconds of greater than 8 Mw/m.sup.2 to provide a weighted
average heat flux of at least 10 Mw/m.sup.2, and cooling the strip
at 1000 to 3000 K/sec until the strip exits the nip between the
casting rolls, (d) applying a roll biasing force greater than 40
kN/meter of casting roll length to form thin metal strip downwardly
at the nip, (e) conveying the thin cast strip through a first
enclosure with an atmosphere having an oxygen content of less than
5% immediately downstream of the casting rolls and on to a roller
table while forming a loop of the cast strip with a strain of not
more than 0.4%, and (f) subjecting the cast strip to heating post
casting to at least 70% of the alloy's melting point to modify the
microstructure of the cast strip to provide strip with tensile
strength of at least 1200 MPa and total elongation of at least
20%.
24. The method of making alloy strip with tensile strength of at
least 1200 MPa and total elongation of at least 20% as claimed in
claim 23 where the loop in the enclosure is between 2.8 and 3
meters.
25. The method of making alloy strip as claimed in claim 23 where
the loop in the enclosure has a strain of not more than 0.2%.
26. A method of making alloy strip with tensile strength of at
least 1200 MPa and total elongation of at least 20% as claimed in
claim 23 where the strip after step (c) has an unresolved
microstructure at the surfaces, an equiaxed in the central
portions, and columnar intermediate portions.
27. A method of making alloy strip with tensile strength of at
least 1200 MPa and total elongation of at least 20% as claimed in
claim 23 where the casting roll have crown shape such that the cast
strip within 25 millimeters of the edge of the strip have a higher
temperature than the strip in the center portion of the strip
width.
28. A method of making alloy strip with tensile strength of at
least 1200 MPa and total elongation of at least 20% produced by
continuous casting comprising: (a) assembling a twin roll caster
having a pair of counter-rotating casting rolls laterally
positioned to provide a nip there between, (b) introducing molten
metal to form a casting pool supported on the casting rolls above
the nip and counter-rotating the casting rolls where the
composition is of the formula:
R.sub.uR'.sub.vCr.sub.wM.sub.xB.sub.y(P,C,Si).sub.z, Where R is one
of iron, cobalt or nickel, R' is one or two iron of iron, cobalt or
nickel other than R, Cr, B, P, C, and Si respectively represent
chromium, boron, phosphorus, carbon and silicon, M is one or more
of molybdenum, vanadium, niobium, titanium, aluminum, tin,
manganese and copper, u, v, w, x, y and z represent atom percent of
R, R', Cr, M, B and (P, C, Si), respectively, and having the
following values: u=30-85 v=0-30 w=0-45 x=0-30 y=0-12 z=0-7.5 with
the provisions that (1) the sum of v+w+x is at least 5, (2) when x
is larger than 20, then w must be less than 20, (3) the amount of
each of vanadium, manganese, copper, tin, magnesium may not exceed
10 atom percent, and (4) the combined amount of boron, phosphorus,
carbon and silicon may not exceed about 13 atom percent. (c)
providing a heat flux in forming the thin strip on the casting
rolls with a peak heat flux of greater than 20 Mw/m.sup.2 and heat
flux after 25 milliseconds of greater than 8 Mw/m.sup.2 to provide
a weighted average heat flux of at least 10 Mw/m.sup.2, and cooling
the strip at 1000 to 3000 K/sec until the strip exits the nip
between the casting rolls, (d) applying a roll biasing force
greater than 40 kN/meter of casting roll length to form thin metal
strip downwardly at the nip, (e) conveying the thin cast strip
through a first enclosure with an atmosphere having an oxygen
content of less than 5% immediately downstream of the casting rolls
and on to a roller table while forming a loop of the cast strip
with a strain of not more than 0.4% to form a thin steel strip, and
(f) rolling the cast strip through a rolling mill to impart between
10 and 40% reduction and initiating a modification of the
microstructure of the cast strip to provide strip with tensile
strength of at least 1200 MPa and total elongation of at least
20%.
29. The method of making alloy strip as claimed in claim 28 where
the loop in the enclosure is between 2.8 and 3 meters.
30. A method of making alloy strip as claimed in claim 28 where the
strip after step (c) has an unresolved microstructure at the
surfaces, an equiaxed in the central portions and columnar
intermediate portions.
31. A method of making alloy strip as claimed in claim 28 where the
casting roll have crown shape such that the cast strip within 25
millimeters of the edge of the strip have a higher temperature than
the strip in the center portion of the strip width.
32. A method of making alloy strip with tensile strength of at
least 1200 MPa and total elongation of at least 20% produced by
continuous casting comprising: (a) assembling a twin roll caster
having a pair of counter-rotating casting rolls laterally
positioned to provide a nip there between, (b) introducing molten
metal to form a casting pool supported on the casting rolls above
the nip and counter-rotating the casting rolls where the
composition is of the formula:
R.sub.uR'.sub.vCr.sub.wM.sub.xB.sub.y(P,C,Si).sub.z, Where R is one
of iron, cobalt or nickel, R' is one or two iron of iron, cobalt or
nickel other than R, Cr, B, P, C, and Si respectively represent
chromium, boron, phosphorus, carbon and silicon, M is one or more
of molybdenum, vanadium, niobium, titanium, aluminum, tin,
manganese and copper, u, v, w, x, y and z represent atom percent of
R, R', Cr, M, B and (P, C, Si), respectively, and having the
following values: u=30-85 v=0-30 w=0-45 x=0-30 y=0-12 z=0-7.5 with
the provisions that (1) the sum of v+w+x is at least 5, (2) when x
is larger than 20, then w must be less than 20, (3) the amount of
each of vanadium, manganese, copper, tin, magnesium may not exceed
10 atom percent, and (4) the combined amount of boron, phosphorus,
carbon and silicon may not exceed about 13 atom percent. (c)
providing a heat flux in forming the thin strip on the casting
rolls with a peak heat flux of greater than 20 Mw/m.sup.2 and heat
flux after 25 milliseconds of greater than 8 Mw/m.sup.2 to provide
a weighted average heat flux of at least 10 Mw/m.sup.2, and cooling
the strip at 1000 to 3000 K/sec until the strip exits the nip
between the casting rolls, (d) applying a roll biasing force
greater than 40 kN/meter of casting roll length to form thin metal
strip downwardly at the nip, (e) conveying the thin cast strip
through a first enclosure with an atmosphere having an oxygen
content of less than 5% immediately downstream of the casting rolls
and on to a roller table while forming a loop of the cast strip
with a strain of not more than 0.4% to form a thin steel strip, and
(f) subjecting the cast strip to heating post casting to at least
70% of the alloy's melting point to modify the microstructure of
the cast strip to provide strip with tensile strength of at least
1200 MPa and total elongation of at least 20%.
33. The method of making alloy strip as claimed in claim 32 where
the loop in the enclosure is between 2.8 and 3 meters.
34. The method of making alloy strip as claimed in claim 32 where
the loop in the enclosure has a strain of not more than 0.2%.
35. A method of making alloy strip as claimed in claim 32 where the
strip after step (c) has an unresolved microstructure at the
surfaces, an equiaxed in the central portions and columnar
intermediate portions.
36. A method of making alloy strip as claimed in claim 32 where the
casting roll have crown shape such that the cast strip within 25
millimeters of the edge of the strip have a higher temperature than
the strip in the center portion of the strip width.
37. A method of making alloy strip with tensile strength of at
least 1500 MPa and total elongation of at least 15% produced by
continuous casting comprising: (a) assembling a twin roll caster
having a pair of counter-rotating casting rolls laterally
positioned to provide a nip there between, (b) introducing molten
metal to form a casting pool supported on the casting rolls above
the nip and counter-rotating the casting rolls where the
composition has a solidus temperature between 950 and 1200.degree.
C., a liquidus temperature between 1150 and 1350.degree. C., and a
freezing range between 100 and 250.degree. C., (c) providing a heat
flux in forming the thin strip on the casting rolls with a peak
heat flux of greater than 20 Mw/m.sup.2 and heat flux after 25
milliseconds of greater than 8 Mw/m.sup.2 to provide a weighted
average heat flux of at least 10 Mw/m.sup.2, and cooling the strip
at 1000 to 3000 K/sec until the strip exits the nip between the
casting rolls, (d) applying a roll biasing force greater than 40
kN/meter of casting roll length to form thin metal strip downwardly
at the nip, (e) conveying the thin cast strip through a first
enclosure with an atmosphere having an oxygen content of less than
5% immediately downstream of the casting rolls and on to a roller
table while forming a loop of the cast strip with a strain of not
more than 0.4% to form a thin steel strip, and (f) rolling the cast
strip through a rolling mill to impart between 10 and 40% reduction
and initiating a modification of the microstructure of the cast
strip to provide strip with tensile strength of at least 1500 MPa
and total elongation of at least 15%.
38. The method of making steel strip as claimed in claim 37 where
the loop in the enclosure is between 2.8 and 3 meters.
39. A method of making alloy strip as claimed in claim 37 where the
strip after step (c) has an unresolved microstructure at the
surfaces, an equiaxed in the central portions and columnar
intermediate portions.
40. A method of making alloy strip as claimed in claim 37 where the
casting rolls have crown shape such that the cast strip within 25
millimeters of the edge of the strip have a higher temperature than
the strip in the center portion of the strip width.
41. A method of making alloy strip with tensile strength of at
least 1500 MPa and total elongation of at least 15% produced by
continuous casting comprising: (a) assembling a twin roll caster
having a pair of counter-rotating casting rolls laterally
positioned to provide a nip there between, (b) introducing molten
metal to form a casting pool supported on the casting rolls above
the nip and counter-rotating the casting rolls where the
composition has a solidus temperature between 950 and 1200.degree.
C., a liquidus temperature between 1150 and 1350.degree. C., and a
freezing range between 100 and 250.degree. C., (c) providing a heat
flux in forming the thin strip on the casting rolls with a peak
heat flux of greater than 20 Mw/m.sup.2 and heat flux after 25
milliseconds of greater than 8 Mw/m.sup.2 to provide a weighted
average heat flux of at least 10 Mw/m.sup.2, and cooling the strip
at 1000 to 3000 K/sec until the strip exits the nip between the
casting rolls, (d) applying a roll biasing force greater than 40
kN/meter of casting roll length to form thin metal strip downwardly
at the nip, (e) conveying the thin cast strip through a first
enclosure with an atmosphere having an oxygen content of less than
5% immediately downstream of the casting rolls and on to a roller
table while forming a loop of the cast strip with a strain of not
more than 0.4%, and (f) subjecting the cast strip to heating post
casting to at least 70% of the alloy's melting point to modify the
microstructure of the cast strip to provide strip with tensile
strength of at least 1500 MPa and total elongation of at least
15%.
42. The method of making alloy strip with tensile strength of at
least 1500 MPa and total elongation of at least 15% as claimed in
claim 41 where the loop in the enclosure is between 2.8 and 3
meters.
43. The method of making alloy strip as claimed in claim 41 where
the loop in the enclosure has a strain of not more than 0.2%.
44. A method of making alloy strip with tensile strength of at
least 1500 MPa and total elongation of at least 15% as claimed in
claim 41 where the strip after step (c) has an unresolved
microstructure at the surfaces, an equiaxed in the central
portions, and columnar intermediate portions.
45. A method of making alloy strip with tensile strength of at
least 1500 MPa and total elongation of at least 15% as claimed in
claim 41 where the casting roll have crown shape such that the cast
strip within 25 millimeters of the edge of the strip have a higher
temperature than the strip in the center portion of the strip
width.
46. A method of making alloy strip with tensile strength of at
least 1500 MPa and total elongation of at least 15% produced by
continuous casting comprising: (a) assembling a twin roll caster
having a pair of counter-rotating casting rolls laterally
positioned to provide a nip there between, (b) introducing molten
metal to form a casting pool supported on the casting rolls above
the nip and counter-rotating the casting rolls where the
composition is of the formula:
R.sub.uR'.sub.vCr.sub.wM.sub.xB.sub.y(P,C,Si).sub.z, Where R is one
of iron, cobalt or nickel, R' is one or two iron of iron, cobalt or
nickel other than R, Cr, B, P, C, and Si respectively represent
chromium, boron, phosphorus, carbon and silicon, M is one or more
of molybdenum, vanadium, niobium, titanium, aluminum, tin,
manganese and copper, u, v, w, x, y and z represent atom percent of
R, R', Cr, M, B and (P, C, Si), respectively, and having the
following values: u=30-85 v=0-30 w=0-45 x=0-30 y=0-12 z=0-7.5 with
the provisions that (1) the sum of v+w+x is at least 5, (2) when x
is larger than 20, then w must be less than 20, (3) the amount of
each of vanadium, manganese, copper, tin, magnesium may not exceed
10 atom percent, and (4) the combined amount of boron, phosphorus,
carbon and silicon may not exceed about 13 atom percent. (c)
providing a heat flux in forming the thin strip on the casting
rolls with a peak heat flux of greater than 20 Mw/m.sup.2 and heat
flux after 25 milliseconds of greater than 8 Mw/m.sup.2 to provide
a weighted average heat flux of at least 10 Mw/m.sup.2, and cooling
the strip at 1000 to 3000 K/sec until the strip exits the nip
between the casting rolls, (d) applying a roll biasing force
greater than 40 kN/meter of casting roll length to form thin metal
strip downwardly at the nip, (e) conveying the thin cast strip
through a first enclosure with an atmosphere having an oxygen
content of less than 5% immediately downstream of the casting rolls
and on to a roller table while forming a loop of the cast strip
with a strain of not more than 0.4% to form a thin steel strip, and
(f) rolling the cast strip through a rolling mill to impart between
10 and 40% reduction and initiating a modification of the
microstructure of the cast strip to provide strip with tensile
strength of at least 1500 MPa and total elongation of at least
15%.
47. The method of making alloy strip as claimed in claim 46 where
the loop in the enclosure is between 2.8 and 3 meters.
48. A method of making alloy strip as claimed in claim 46 where the
strip after step (c) has an unresolved microstructure at the
surfaces, an equiaxed in the central portions and columnar
intermediate portions.
49. A method of making alloy strip as claimed in claim 46 where the
casting roll have crown shape such that the cast strip within 25
millimeters of the edge of the strip have a higher temperature than
the strip in the center portion of the strip width.
50. A method of making alloy strip with tensile strength of at
least 1500 MPa and total elongation of at least 15% produced by
continuous casting comprising: (a) assembling a twin roll caster
having a pair of counter-rotating casting rolls laterally
positioned to provide a nip there between, (b) introducing molten
metal to form a casting pool supported on the casting rolls above
the nip and counter-rotating the casting rolls where the
composition is of the formula:
R.sub.uR'.sub.vCr.sub.wM.sub.xB.sub.y(P,C,Si).sub.z, Where R is one
of iron, cobalt or nickel R' is one or two iron of iron, cobalt or
nickel other than R, Cr, B, P, C, and Si respectively represent
chromium, boron, phosphorus, carbon and silicon, M is one or more
of molybdenum, vanadium, niobium, titanium, aluminum, tin,
manganese and copper, u, v, w, x, y and z represent atom percent of
R, R', Cr, M, B and (P, C, Si), respectively, and having the
following values: u=30-85 v=0-30 w=0-40 x=0-30 y=0-12 z=0-7.5 with
the provisions that (1) the sum of v+w+x is at least 5, (2) when x
is larger than 20, then w must be less than 20, (3) the amount of
each of vanadium, manganese, copper, tin, magnesium may not exceed
10 atom percent, and (4) the combined amount of boron, phosphorus,
carbon and silicon may not exceed about 13 atom percent. (c)
providing a heat flux in forming the thin strip on the casting
rolls with a peak heat flux of greater than 20 Mw/m.sup.2 and heat
flux after 25 milliseconds of greater than 8 Mw/m.sup.2 to provide
a weighted average heat flux of at least 10 Mw/m.sup.2, and cooling
the strip at 1000 to 3000 K/sec until the strip exits the nip
between the casting rolls, (d) applying a roll biasing force
greater than 40 kN/meter of casting roll length to form thin metal
strip downwardly at the nip, (e) conveying the thin cast strip
through a first enclosure with an atmosphere having an oxygen
content of less than 5% immediately downstream of the casting rolls
and on to a roller table while forming a loop of the cast strip
with a strain of not more than 0.4% to form a thin steel strip, and
(f) subjecting the cast strip to heating post casting to at least
70% of the alloy's melting point to modify the microstructure of
the cast strip to provide strip with tensile strength of at least
1500 MPa and total elongation of at least 15%.
51. The method of making alloy strip as claimed in claim 50 where
the loop in the enclosure is between 2.8 and 3 meters.
52. The method of making alloy strip as claimed in claim 50 where
the loop in the enclosure has a strain of not more than 0.2%.
53. A method of making alloy strip as claimed in claim 50 where the
strip after step (c) has an unresolved microstructure at the
surfaces, an equiaxed in the central portions and columnar
intermediate portions.
54. A method of making alloy strip as claimed in claim 50 where the
casting roll have crown shape such that the cast strip within 25
millimeters of the edge of the strip have a higher temperature than
the strip in the center portion of the strip width.
Description
BACKGROUND AND SUMMARY
[0001] This invention relates to making thin strip and more
particularly casting of thin strip by a twin roll caster.
[0002] It is known to cast metal strip by continuous casting in a
twin roll caster. Molten metal is introduced between a pair of
counter-rotating laterally positioned casting rolls with a nip
there between, which are cooled so that metal shells solidify on
the moving roll surfaces and are brought together at the nip
between the rolls to produce solidified strip product delivered
downwardly from the nip between the rolls. The term "nip" is used
herein to refer to the general region at which the rolls are
closest together. The molten metal may be poured from a ladle into
a smaller vessel, or tundish, from which it flows through a
transition piece to a metal delivery nozzle positioned above the
nip, longitudinally between the casting rolls, which delivers the
molten metal to the region above the nip to form a casting pool of
molten metal. The casting pool of molten metal is supported on the
casting surfaces of the rolls above the nip. The casting pool is
typically confined at the ends of the casting rolls by side plates
or dams held in sliding engagement adjacent the ends of the casting
rolls.
[0003] In casting thin strip by twin roll casting, the metal
delivery nozzles receive molten metal from the moveable tundish
through the transition piece and delivers the molten metal in the
casting pool in a desired flow pattern. As the casting rolls
rotate, metal from the casting pool solidifies into shells on the
casting rolls and the shells are brought close together at the nip
to produce a solidified cast strip below the nip. The gap between
the casting rolls maintains separation between the solidified
shells at the nip with semi-solid metal present in the space
between the shells at the nip, so that at least part of the strip
between the shells is subsequently solidified below the nip. The
mushy or semi-solid center portion is thus "swallowed" between the
shells and solidified downstream of the nip as the thin strip is
cooled. The thickness of the shells and indirectly the thickness of
the mush center portion is therefore determined and controlled by
the amount of heat flux transferred from the shells to the casting
rolls as the shells are formed in moving through the casting pool.
In the past, these parameters limited the steel compositions that
could be cast into thin strip by twin roll caster to those with
freezing range (i.e. temperature between the liquidus temperature
and the solidus temperature) less than 100.degree. C. and typically
less than 50.degree. C.
[0004] A related concern has been the biasing forces that could be
exerted on the thin strip at the nip by the casting rolls. The
biasing forces exerted by the casting rolls were limited to those
that could maintain the cast shells (with a mushy center portion)
as a cast strip with sufficient strength to maintain itself. Again
this parameter limited the compositions of steel that could be cast
in the twin roll caster to those with a freezing range less than
100.degree. C. and typically less than 50.degree. C.
[0005] Another limitation in the past on casting thin strip by the
twin roll caster was cooling the cast strip immediately after
casting in an enclosure, where oxygen levels were limited to
inhibit the formation of scale as the thin strip during cooling. At
the same time, the just casted thin strip had to be fed onto a
roller table to pinch rolls to exiting the enclosure for downstream
processing. This transition had been previously done by a moveable
apron that swung up into the strip path moving downward from the
nip to feed the strip laterally onto the roller table to the pinch
rolls, and when the apron was swung back out of the path of the
thin strip following initial feeding the strip to the pinch rolls,
a loop was provided through which the thin strip traveled from the
casting rolls to the roller table. The strip had to be maintained
within a certain level of strain so that the strip did not break at
the loop during the casting. This feature again limited the steel
compositions that could be cast into thin strip by twin roll caster
to those with a freezing range less than 100.degree. C. and
typically less than 50.degree. C.
[0006] There is therefore a need for development of twin roll
casting methods and casting equipment to be able to cast previously
known and new steel compositions that have a freezing range greater
than 50.degree. C. and preferable greater than 100.degree. C. and
that are high in both tensile strength and percent elongation to
overcome the previously mentioned limitations.
[0007] Currently disclosed is a method for making alloy strip with
tensile strength of at least 900 MPa and total elongation of at
least 30% produced by continuous casting. The method of casting the
alloy strip comprises the steps of: assembling a twin roll caster
having a pair of counter-rotating casting rolls laterally
positioned to provide a nip there between; introducing molten metal
to form a casting pool supported on the casting rolls above the nip
and counter-rotating the casting rolls where the composition has a
solidus temperature between 950 and 1200.degree. C., a liquidus
temperature between 1150 and 1350.degree. C., and a freezing range
between 100 and 250.degree. C.; providing a heat flux in forming
the thin strip on the casting rolls with a peak heat flux of
greater than 20 Mw/m.sup.2 and heat flux after 25 milliseconds of
greater than 8 Mw/m.sup.2 to provide a weighted average heat flux
of at least 10 Mw/m.sup.2, and cooling the strip at 1000 to 3000
K/sec until the strip exits the nip between the casting rolls;
applying a roll biasing force greater than 40 kN/meter of casting
roll length to form thin metal strip downwardly at the nip;
conveying the thin cast strip through a first enclosure with an
atmosphere having an oxygen content of less than 5% immediately
downstream of the casting rolls and on to a roller table while
forming a loop of the cast strip with a strain of not more than
0.4% or not more than 0.2% to form a continuous thin steel strip;
and rolling the cast strip through a rolling mill to impart between
10% and 40% reduction and initiating a modification of the
microstructure of the cast strip to provide strip with tensile
strength of at least 900 MPa and total elongation of at least 30%,
strip with tensile strength of at least 1200 MPa and total
elongation of at least 20%, or strip with tensile strength of at
least 1500 MPa and total elongation of at least 15%.
[0008] Alternatively, a method of making alloy strip with tensile
strength of at least 900 MPa and total elongation of at least 30%
strip with tensile strength of at least 1200 MPa and total
elongation of at least 20%, or strip with tensile strength of at
least 1500 MPa and total elongation of at least 15% is produced by
continuous casting which comprises assembling a twin roll caster
having a pair of counter-rotating casting rolls laterally
positioned to provide a nip there between; introducing molten metal
to form a casting pool supported on the casting rolls above the nip
and counter-rotating the casting rolls where the composition has a
solidus temperature between 950 and 1200.degree. C., a liquidus
temperature between 1150 and 1350.degree. C., and a freezing range
between 100 and 250.degree. C.; providing a heat flux in forming
the thin strip on the casting rolls with a peak heat flux of
greater than 20 Mw/m.sup.2 and heat flux after 25 milliseconds of
greater than 8 Mw/m.sup.2 to provide a weighted average heat flux
of at least 10 Mw/m.sup.2, and cooling the strip at 1000 to 3000
K/sec until the strip exits the nip between the casting rolls;
applying a roll biasing force greater than 40 kN/meter of casting
roll length to form thin metal strip downwardly at the nip,
conveying the thin cast strip through a first enclosure with an
atmosphere having an oxygen content of less than 5% immediately
downstream of the casting rolls and on to a roller table while
forming a loop of the cast strip with a strain of not more than
0.4% or not more than 0.2%; and heating post cast strip to at least
70% of the melting point of the alloy forming the strip to modify
the microstructure of the cast strip to provide strip with tensile
strength of at least 900 MPa and total elongation of at least 30%,
strip with tensile strength of at least 1200 MPa and total
elongation of at least 20%, or strip with tensile strength of at
least 1500 MPa and total elongation of at least 15%.
[0009] Further, a method of making alloy strip with tensile
strength of at least 900 MPa and total elongation of at least 30%
produced by continuous casting comprising:
[0010] assembling a twin roll caster having a pair of
counter-rotating casting rolls laterally positioned to provide a
nip there between,
[0011] introducing molten metal to form a casting pool supported on
the casting rolls above the nip and counter-rotating the casting
rolls where the composition is of the formula:
R.sub.uR'.sub.vCr.sub.wM.sub.xB.sub.y(P,C,Si).sub.z,
[0012] Where R is one of iron, cobalt or nickel, [0013] R' is one
or two iron of iron, cobalt or nickel other than R, [0014] Cr, B,
P, C, and Si respectively represent chromium, boron, phosphorus,
carbon and silicon, [0015] M is one or more of molybdenum,
vanadium, niobium, titanium, aluminum, tin, manganese and copper,
[0016] u, v, w, x, y and z represent atom percent of R, R', Cr, M,
B and (P, C, Si), respectively, and having the following values:
[0017] u=30-85 [0018] v=0-30 [0019] w=0-45 [0020] x=0-30 [0021]
y=0-12 [0022] z=0-7.5 with the provisions that (1) the sum of v+w+x
is at least 5, (2) when x is larger than 20, then w must be less
than 20, (3) the amount of each of vanadium, manganese, copper,
tin, magnesium may not exceed 10 atom percent, and (4) the combined
amount of boron, phosphorus, carbon and silicon may not exceed 13
atom percent.
[0023] providing a heat flux in forming the thin strip on the
casting rolls with a peak heat flux of greater than 20 Mw/m.sup.2
and heat flux after 25 milliseconds of greater than 8 Mw/m.sup.2 to
provide a weighted average heat flux of at least 10 Mw/m.sup.2, and
cooling the strip at 1000 to 3000 K/sec until the strip exits the
nip between the casting rolls,
[0024] applying a roll biasing force greater than 40 kN/meter of
casting roll length to form thin metal strip downwardly at the
nip,
[0025] conveying the thin cast strip through a first enclosure with
an atmosphere having an oxygen content of less than 5% immediately
downstream of the casting rolls and on to a roller table while
forming a loop of the cast strip with a strain of not more than
0.2% to form a thin steel strip, and
[0026] rolling the cast strip through a rolling mill to impart
between 10 and 40% reduction or heating the post cast strip to at
least 70% of the melting point of the alloy forming the strip
initiating a modification of the microstructure of the cast strip
to provide strip with tensile strength of at least 900 MPa and
total elongation of at least 30%, strip with tensile strength of at
least 1200 MPa and total elongation of at least 20%, or strip with
tensile strength of at least 1500 MPa and total elongation of at
least 15%.
[0027] These and other advantages and novel features of the present
invention, as well as details of an illustrated embodiment thereof,
will be more fully understood from the following description and
drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
[0028] The accompanying drawings illustrate the disclosed method
and are referred to as the following more detailed description of
the disclosed method proceeds:
[0029] FIG. 1 is a diagrammatical side view of a portion of twin
roll caster system for practicing the disclosed method;
[0030] FIG. 1A is a diagrammatical view of a portion of twin roll
caster for practicing the disclosed method in accordance with an
embodiment of the present invention;
[0031] FIG. 2 is a partial sectional view through the casting rolls
mounted in a roll cassette in the casting position of the caster
system of FIG. 1;
[0032] FIG. 3 is diagrammatical plan view of the roll cassette of
FIG. 2 removed from the caster system;
[0033] FIG. 4 is a transverse partial sectional view through the
portion marked 4-4 in FIG. 3;
[0034] FIG. 5 is an enlarged view of marked detail 5 in FIG. 4;
[0035] FIG. 6 is a cross-section of a cast steel strip made as
described herein, in accordance with an embodiment of the present
invention;
[0036] FIG. 7A is a cross-section of a cast steel strip as
illustrated in FIG. 6; and
[0037] FIG. 7B is an enlarged view of marked detail A in FIG.
7A.
DETAILED DESCRIPTION OF THE DRAWINGS
[0038] The embodiments are described with reference to a twin roll
caster shown in FIGS. 1 through 5. Referring now to FIGS. 1 and 2,
a twin roll caster is illustrated that comprises a main machine
frame 10 that stands up from the factory floor and supports a pair
of casting rolls mounted in a module in a roll cassette 11. The
casting rolls 12 are mounted in the roll cassette 11 for ease of
operation and movement as described below. The roll cassette
facilitates rapid movement of the casting rolls ready for casting
from a setup position into an operative casting position in the
caster as a unit, and ready removal of the casting rolls from the
casting position when the casting rolls are to be replaced. There
is no particular configuration of the roll cassette that is
desired, so long as it performs that function of facilitating
movement and positioning of the casting rolls as described
herein.
[0039] The casting apparatus for continuously casting of thin alloy
strip with tensile strength of at least 900 MPa and total
elongation of at least 30%, with tensile strength of at least 1200
MPa and total elongation of at least 20%, or with tensile strength
of at least 1500 MPa and total elongation of at least 15% includes
a pair of counter-rotatable casting rolls 12 having shafts 22 (FIG.
3) and casting surfaces 12A laterally positioned to form a nip 18
there between. Molten metal with a solidus temperature between 950
and 1200.degree. C., a liquidus temperature between 1150 and
1350.degree. C., and a freezing range between 100 and 250.degree.
C., is supplied from a ladle 13 through a metal delivery system to
a metal delivery nozzle 17, core nozzle, positioned between the
casting rolls 12 above the nip 18. Molten metal thus delivered
forms a casting pool 19 of molten metal above the nip supported on
the casting surfaces 12A of the casting rolls 12. This casting pool
19 is confined in the casting area at the ends of the casting rolls
12 by a pair of side closure plates, or side dams 20, (shown in
dotted line in FIG. 2). The upper surface of the casting pool 19
(generally referred to as the "meniscus" level) may rise above the
lower end of the delivery nozzle 17 so that the lower end of the
delivery nozzle is immersed within the casting pool. The casting
area includes the addition of a protective atmosphere above the
casting pool 19 to inhibit oxidation of the molten metal in the
casting area.
[0040] The ladle 13 typically is of a conventional construction
supported on a rotating turret 40. For metal delivery, the ladle 13
is positioned over a movable tundish 14 in the casting position to
fill the tundish with molten metal. The movable tundish 14 may be
positioned on a tundish car 66 capable of transferring the tundish
from a heating station (not shown), where the tundish is heated to
near a casting temperature, to the casting position. A tundish
guide, such as rails, may be positioned beneath the tundish car 66
to enable moving the movable tundish 14 from the heating station to
the casting position.
[0041] The movable tundish 14 may be fitted with a slide gate 25,
actuable by a servo mechanism, to allow molten metal to flow from
the tundish 14 through the slide gate 25, and then through a
refractory outlet shroud 15 to a transition piece or distributor 16
in the casting position. From the distributor 16, the molten metal
flows to the delivery nozzle 17 positioned between the casting
rolls 12 above the nip 18.
[0042] The casting rolls 12 are internally water cooled so that as
the casting rolls 12 are counter-rotated, shells solidify on the
casting surfaces 12A as the casting surfaces move into contact with
and through the casting pool 19 with each revolution of the casting
rolls 12. The shells are brought close together at the nip 18
between the casting rolls to produce a thin cast strip product 21
delivered downwardly from the nip. The gap between the casting
rolls is such as to maintain separation between the solidified
shells at the nip so that mushy metal is present in the space
between the shells through the nip, and is, at least in part,
subsequently solidified between the solidified shells within the
cast strip below the nip.
[0043] It is important to achieve rapid cooling of the molten metal
over the casting surfaces of the rolls in order to form solidified
shells in the short period of exposure on the casting surfaces to
the molten metal casting pool during each revolution of the casting
rolls. Moreover, it is important to achieve even solidification so
as to avoid distortion of the solidifying shells which come
together at the nip to form the steel strip. The present method
involves a heat flux in forming the thin strip on the casting rolls
with a peak heat flux of greater than 20 Mw/m.sup.2 and heat flux
after 25 milliseconds of greater than 8 Mw/m.sup.2 to provide a
weighted average heat flux of at least 10 Mw/m.sup.2, and cooling
the strip at 1000 to 3000 K/sec until the strip exits the nip
between the casting rolls. The heat flux between the molten metal
and the casting surfaces of the casting rolls may be initially
measured and continually measured by methods as described in U.S.
Pat. No. 7,299,857. Although this is one way for measuring the heat
flux, the heat flux can be measured by any available method.
[0044] As shown in FIG. 6, the alloy strip with tensile strength of
at least 900 MPa and total elongation of at least 30%, with tensile
strength of at least 1200 MPa and total elongation of at least 20%,
or with tensile strength of at least 1500 MPa and total elongation
of at least 15% made in accordance the present invention may have
an unresolved microstructure at the surfaces, an equiaxed in the
central portions and columnar intermediate portions. These
microstructures are illustrated in FIGS. 7A and 7B, where FIG. 7B
is an enlarged view of marked detail A in FIG. 7A.
[0045] The casting rolls should be set to an appropriate separation
or gap of the casting rolls at the nip to allow the casting rolls
to move against the action of biasing force to enable the rolls to
move to accommodate fluctuations in casting roll separation and
strip thickness. The casting roll separation force or biasing force
may be used to control the characteristics of the strip.
Significant amount of reheating occurs below the roll nip due to
the presence of mushy material. The greater the amount of mushy
material or the wider the mushy center portion, the longer the
strip remains hot. The amount of mushy material between the shells
below the nip is controlled by applying a roll biasing force
greater than 40 kN/meter of casting roll length to form thin metal
strip downwardly at the nip. The bias force restricts the amount of
mushy material in the center portion between the shells of the
strip allowing the strip to cool sufficiently so there is no
effective strength transited in conjunction with the strain on the
strip in the loop in the enclosure immediately following casting
and the strain is not more than 0.4% or 0.2%, as explained
below.
[0046] When the amount of mushy material in the center portion
between the shells is limited by the biasing force, the temperature
of the strip near the edges can be increased relative to the center
portion of the strip width. In one embodiment, the crown of the
casting rolls may be shaped such that the cast strip within 25
millimeters of the edge of the strip have a higher temperature that
the strip in the center portion of the strip width. The crown shape
of the casting rolls 12 in combination with the casting roll
biasing force is capable of forming the cast strip with mushy metal
between the shells so that the cast strip within 25 millimeters of
the edge of the strip have a higher temperature that the strip in
the center portion of the strip width.
[0047] Once the strip exists the nip, the formed cast strip is
delivered downwardly from the nip of the casting rolls into a first
enclosure containing a protective atmosphere where the strip
commences a cooling process after leaving the nip. The strip
typically hangs in the enclosure in a loop before moving over a
roller table through a first pinch rolls. The disclosed method
provides for the thin strip to withstand the transition from the
first enclosure to the roller table without breaking. Below the
twin roll caster, the cast strip passes through a first enclosure
with an atmosphere having an oxygen content of less than 5%
immediately downstream of the casting rolls and on to a roller
table while forming a loop of the cast strip with a strain of not
more than 0.4% to form a thin steel strip. The loop in the
enclosure may be between 2.8 and 3 meters.
[0048] Alternatively, below the twin roll caster, the cast strip
may pass through a first enclosure with an atmosphere having an
oxygen content of less than 5% immediately downstream of the
casting rolls and on to a roller table while forming a loop of the
cast strip with a strain of not more than 0.2% to form a thin steel
strip. The loop in the enclosure may be between 2.8 and 3
meters.
[0049] After exiting the first enclosure, the strip may pass
through further sealed enclosures after the pinch roll stand, which
may include a hot rolling mill as shown in FIG. 1. FIG. 1 shows the
twin roll caster producing the thin cast strip 21, and passing
across guide table 30 to pinch roll stand 31 having pinch rolls
31A. Upon exiting the pinch roll stand 31, the thin cast strip may
pass through a hot rolling mill 32, comprising a pair of work rolls
32A, and backup rolls 32B, forming a gap capable of hot rolling the
cast strip delivered from the casting roll. In the rolling mill 32,
the cast strip may be hot rolled to reduce the strip to a desired
thickness, improve the strip surface, improve the strip flatness
and inducing enough strain to cause modification of the
microstructure of the strip. Moreover, the cast strip in hot rolled
can have imparted between 10 and 40% reduction initiating a
modification of the microstructure of the cast strip to provide
strip with tensile strength of at least 900 MPa and total
elongation of at least 30%, strip with tensile strength of at least
1200 MPa and total elongation of at least 20%, or strip with
tensile strength of at least 1500 MPa and total elongation of at
least 15%. The work rolls 32A have work surfaces providing the
desired strip profile across the work rolls.
[0050] Alternatively, as shown in FIG. 1A, instead of hot rolling
the strip in rolling mill 32, the casted strip may be subject to
heating by induction heating 200, or other form of heat as to
desired, post casting to heat the strip to at least 70% of the
melting point of the alloy forming the strip to modify the
microstructure of the cast strip and provide strip with of at least
900 MPa tensile strength and total elongation of at least 30%,
strip with tensile strength of at least 1200 MPa and total
elongation of at least 20%, or strip with tensile strength of at
least 1500 MPa and total elongation of at least 15%. Note that the
strip may be cooled after casting and before proceeding with this
heating step.
[0051] In either embodiment, the cast strip then passes onto a
run-out table 33, where it may be cooled by contact with a coolant,
such as water, supplied via water jets 90 or other suitable means,
and by convection and radiation. In any event, the cast strip may
then pass through a second pinch roll stand 91 having rollers 91A
to provide tension of the cast strip, and then to a coiler 92. The
thin strip may be typically between about 0.3 and 2.0 millimeters
in thickness on coiling.
[0052] At the start of the casting operation, a short length of
imperfect strip is typically produced as casting conditions
stabilize. After continuous casting is established, the casting
rolls are moved apart slightly and then brought together again to
cause this leading end of the cast strip to break away forming a
clean head end of the following cast strip. The imperfect material
drops into a scrap receptacle 26, which is movable on a scrap
receptacle guide. The scrap receptacle 26 is located in a scrap
receiving position beneath the caster and forms part of a sealed
enclosure 27 as described below. The enclosure 27 is typically
water cooled. At this time, a water-cooled apron 28 that normally
hangs downwardly from a pivot 29 to one side in the enclosure 27 is
swung into position to guide the clean end of the cast strip 21
onto the guide table 30 that feeds it to the pinch roll stand 31.
The apron 28 is then retracted back to its hanging position to
allow the cast strip 21 to hang in a loop beneath the casting rolls
in enclosure 27 before it passes to the guide table 30 where it
engages a succession of guide rollers.
[0053] An overflow container 38 may be provided beneath the movable
tundish 14 to receive molten material that may spill from the
tundish. As shown in FIG. 1, the overflow container 38 may be
movable on rails 39 or another guide such that the overflow
container 38 may be placed beneath the movable tundish 14 as
desired in casting locations. Additionally, an overflow container
may be provided for the distributor 16 adjacent the distributor
(not shown).
[0054] The sealed enclosure 27 is formed by a number of separate
wall sections that fit together at various seal connections to form
a continuous enclosure wall that permits control of the atmosphere
within the enclosure. Additionally, the scrap receptacle 26 may be
capable of attaching with the enclosure 27 so that the enclosure is
capable of supporting a protective atmosphere immediately beneath
the casting rolls 12 in the casting position. The enclosure 27
includes an opening in the lower portion of the enclosure, lower
enclosure portion 44, providing an outlet for scrap to pass from
the enclosure 27 into the scrap receptacle 26 in the scrap
receiving position. The lower enclosure portion 44 may extend
downwardly as a part of the enclosure 27, the opening being
positioned above the scrap receptacle 26 in the scrap receiving
position. As used in the specification and claims herein, "seal,"
"sealed," "sealing," and "sealingly" in reference to the scrap
receptacle 26, enclosure 27, and related features may not be a
complete seal so as to prevent leakage, but rather is usually less
than a perfect seal as appropriate to allow control and support of
the atmosphere within the enclosure as desired with some tolerable
leakage.
[0055] A rim portion 45 may surround the opening of the lower
enclosure portion 44 and may be movably positioned above the scrap
receptacle, capable of sealingly engaging and/or attaching to the
scrap receptacle 26 in the scrap receiving position. The rim
portion 45 may be movable between a sealing position in which the
rim portion engages the scrap receptacle, and a clearance position
in which the rim portion 45 is disengaged from the scrap
receptacle. Alternately, the caster or the scrap receptacle may
include a lifting mechanism to raise the scrap receptacle into
sealing engagement with the rim portion 45 of the enclosure, and
then lower the scrap receptacle into the clearance position. When
sealed, the enclosure 27 and scrap receptacle 26 are filled with a
desired gas, such as nitrogen, to reduce the amount of oxygen in
the enclosure and provide a protective atmosphere for the cast
strip.
[0056] The enclosure 27 may include an upper collar portion 27A
supporting a protective atmosphere immediately beneath the casting
rolls in the casting position. When the casting rolls 12 are in the
casting position, the upper collar portion is moved to the extended
position closing the space between a housing portion adjacent the
casting rolls 12, as shown in FIG. 2, and the enclosure 27. The
upper collar portion may be provided within or adjacent the
enclosure 27 and adjacent the casting rolls, and may be moved by a
plurality of actuators (not shown) such as servo-mechanisms,
hydraulic mechanisms, pneumatic mechanisms, and rotating
actuators.
[0057] As shown in FIGS. 2-3, cleaning brushes 36 are disposed
adjacent the pair of casting rolls 12, such that the periphery of
the cleaning brushes 36 may be brought into contact with the
casting surfaces 12A of the casting rolls 12 to clean oxides from
the casting surfaces during casting. The cleaning brushes 36 are
positioned at opposite sides of the casting area adjacent the
casting rolls 12, between the nip 18 and the casting area where the
casting rolls enter the protective atmosphere in contact with the
molten metal casting pool 19.
[0058] The side dams 20 may be mounted on and actuated by plate
holders 100 positioned one at each end of the roll assembly and
moveable toward and away from one another. The plate holders 100
and side dams 20 may be positioned on a core nozzle plate 106
mounted on the roll cassette 11 so as to extend horizontally above
the casting rolls, as shown in FIG. 3. The core nozzle plate 106 is
positioned beneath the distributor 16 in the casting position and
has a central opening 107 to receive the metal delivery nozzle 17.
The metal delivery nozzle 17 may be provided in two or more
segments, and at least a portion of each metal delivery nozzle 17
segment may be supported by the core nozzle plate 106. The outer
end of each metal delivery nozzle 17 is supported by a bridge
portion (not shown) positioned adjacent the side dams 20 and
capable of supporting and moving the delivery nozzle 17 during
casting.
[0059] There is shown in FIG. 4 a pair of delivery nozzles 17
formed as substantially identical segments made of a refractory
material such as zirconia graphite, alumina graphite or any other
suitable material. It must be understood that more than two
delivery nozzles 17 may be used in any different sizes and shapes
if desired. The delivery nozzles 17 need not be substantially
identical in size and shape, although generally such is desirable
to facilitate fabrication and installation. Two delivery nozzles 17
may be provided, each capable of moving independently of the other
above the casting rolls 12.
[0060] Typically where two delivery nozzles 17 are used, the
nozzles 17 are disposed and supported in end-to-end relationship as
shown in FIG. 4 along the nip 18 with a gap 34 therebetween, so
that each delivery nozzle 17 can be moved inwardly toward each
other during a casting campaign as explained below. It must be
understood, however, that any suitable number of delivery nozzles
17 may be used, including two delivery nozzles 17 as described
below and including any additional number of nozzles 17 disposed
therebetween. For example, there may be a central nozzle segment
adjacent to outer nozzle segments on either side.
[0061] Each delivery nozzle 17 may be formed in one piece or
multiple pieces. As shown, each nozzle 17 includes an end wall 23
positioned nearest a confining side dam 20 as explained below. Each
end wall 23 may be configured to achieve a particular desired
molten metal flow in the triple point region between the casting
rolls 12 and the respective side dam 20.
[0062] The side dams 20 may be made from a refractory material such
as zirconia graphite, graphite alumina, boron nitride, boron
nitride-zirconia, or other suitable composites. The side dams 20
have a face surface capable of physical contact with the casting
rolls and molten metal in the casting pool.
[0063] A pair of carriage assemblies, generally indicated at 104,
are provided to position the side dams 20 and the delivery nozzles
17. As illustrated, the twin roll caster is generally symmetrical,
although such is not required. Referring to FIG. 5, one carriage
assembly 104 is illustrated and described below, with the other
carriage assembly 104 being generally similar. It is understood
that the twin roll caster may utilize any number of carriage
assemblies 104 configured in any suitable manner to provide a flow
of molten metal to the casting pool 19. Each carriage assembly 104
is disposed at one end of the pair of casting rolls 12. Each
carriage assembly 104 may be mounted fixed relative to the machine
frame 10, or may be moveable axially toward and away from the
casting rolls 12 to enable the spacing between the carriage
assembly 104 and the casting rolls 12 to be adjusted. The carriage
assemblies 104 may be preset in final position before a casting
campaign to suit the width of the casting rolls 12 for the strip to
be cast, or the position of the carriage assemblies 104 may be
adjusted as desired during a casting campaign. The carriage
assemblies 104 may be positioned one at each end of the roll
assembly and moveable toward and away from one another to enable
the spacing between them to be adjusted. The carriage assemblies
104 can be preset before a casting operation according to the width
of the casting rolls and to allow quick roll changes for differing
strip widths. The carriage assemblies 104 may be positioned so as
to extend horizontally above the casting rolls with the nozzles 17
positioned beneath the distributor 16 in the casting position and
at a central position to receive the molten metal.
[0064] For example the carriage assembly 104 may be positioned from
tracks (not shown) on the machine frame 10, which may be mounted by
clamps or any other suitable mechanism. Alternatively, the carriage
assembly 104 may be supported by its own support structure relative
to the casting rolls 12.
[0065] The carriage assembly 104 includes a support frame 125. A
nozzle bridge 108 is moveably connected to the support frame 125
and engages the delivery nozzles 17 for selective movement thereof.
A nozzle actuator 110 is mounted to the support frame 125 and
connected to the nozzle bridge 108 for moving the nozzle bridge 108
and thus moving the delivery nozzles 17 to position the end wall 23
relative to the side dam 20. The nozzle actuator 110 is thus
capable of positioning the delivery nozzles 17. The nozzle actuator
110 is a conventional servo mechanism. It must be understood,
however, that the nozzle actuator 110 may be any drive mechanism
suitable to move and adjust delivery nozzles 17. For example, the
nozzle actuator 110 may be a screw jack drive operated by an
electric motor, a hydraulic mechanism, a pneumatic mechanism, a
gear mechanisms, a cog, a drive chain mechanism, a pulley and cable
mechanism, a drive screw mechanism, a jack actuator, a rack and
pinion mechanism, an electro-mechanical actuator, an electric
motor, a linear actuator, a rotating actuator, or any other
suitable device.
[0066] A nozzle position sensor 113 senses the position of the
delivery nozzles 17. The nozzle position sensor 113 is a linear
displacement sensor to measure the change in position of the nozzle
bridge 108 relative to the support frame 125. The nozzle position
sensor 113 may be any sensor suitable to indicate any parameter
representative of a position of the delivery nozzles 17. For
example, the nozzle position sensor 113 may be a linear variable
displacement transformer to respond to the extension of the nozzle
actuator 110 to provide signals indicative of movement of the
delivery nozzles 17, or an optical imaging device for tracking the
position of the delivery nozzles 17 or any other suitable device
for determining the location of the delivery nozzles 17.
[0067] Each side dam 20 is mounted to a plate holder 100 which is
moveably connected to the support frame 125 and engages the side
dam 20 for selective movement thereof. A side dam actuator 102 is
mounted to the support frame 125 and connected to the plate holder
100 for moving the plate holder 100 and thus moving each side dam
20 to position the side dam 20 relative to the casting rolls 12.
The side dam actuator 102 is thus capable of positioning the side
dam 20 and capable of cyclically varying the axial force of the
side dams as described below. The side dam actuator 102 is a
hydraulic force cylinder. It must be understood, however, that the
side dam actuator 102 may be any suitable drive mechanism to
position the plate holder 100 to bring the side dam 20 into
engagement with the casting rolls 12 to confine the casting pool 19
formed on the casting surfaces 12A during a casting operation. Such
a suitable drive mechanism, for example, may be a servo mechanism,
a screw jack drive operated by electric motor, a pneumatic
mechanism, a gear mechanisms, a cog, a drive chain mechanism, a
pulley and cable mechanism, a drive screw mechanism, a jack
actuator, a rack and pinion mechanism, an electro-mechanical
actuator, an electric motor, a linear actuator, a rotating
actuator, or any other suitable device. Thus, the side dams 20 are
mounted in side dam plate holders 100, which are movable by side
dam actuators 102, such as a servo mechanism, to bring the side
dams 20 into engagement with the ends of the casting rolls.
Additionally, the side dam actuators 102 are capable of positioning
the side dams 20 during casting. The side dams 20 thus form end
closures for the molten pool of metal on the casting rolls during
the casting operation.
[0068] A side dam position sensor 112 senses the position of the
side dam 20. The side dam position sensor 112 is a linear
displacement sensor to measure the actual change in position of the
plate holder 100 relative to the support frame 125. The side dam
position sensor 112 may be any sensor suitable to indicate any
parameter representative of a position of the side dam 20. For
example, the side dam position sensor 112 may be a linear variable
displacement transducer to respond to the extension of the side dam
actuator 102 to provide signals indicative of position of the side
dam 20, or an optical imaging device for tracking the position of
the side dam 20 or any other suitable device for determining the
location of the side dam 20. The side dam position sensor 112 may
also or alternatively include a force sensor, or load cell for
determining the force urging the side dam 20 against the casting
rolls 12 and providing electrical signals indicative of the force
urging the side dam against the casting rolls.
[0069] In any case the actuators 110 and 102 and the sensors 113
and 112 may be connected into a control system in the form of a
circuit receiving control signals determined by measurement of the
distance variation between the delivery nozzles 17 and the
confining side dams 20, and between the side dams 20 and the
casting rolls 12. For example, small water cooled video cameras may
be installed on the nozzle bridge 108, or any other suitable
structure, to directly observe the distance between the delivery
nozzles 17 and the confining side dams 20 and the side dams 20 and
the casting rolls 12, and to produce control signals to be fed to
position encoders on the actuators 110 and 102. With any
arrangement, precise control of the distance between the end walls
23 of the delivery nozzle 17 and the side dams 20 and the side dams
20 and the casting rolls 12 may be maintained. Moreover these
distances can be accurately set and maintained by independent
operation of the actuators 110 and 102 during casting. For example,
the distance between the end wall 23 and the side dam 20 may be set
so that a discharge of molten metal is positioned to a target area
on the side dam 20 relative to the triple point regions.
[0070] During a casting campaign the control system of the twin
roll caster is capable of actuating the side dam actuators 102 to
vary the apply force on the side dams 20 against the ends of the
casting rolls 12 in the axial direction, i.e. along the axis of the
centerlines of the two casting rolls. The apply force is not varied
such that the side dams 20 develop a clearance at edges of the
casting rolls 12 that may cause leakage of molten metal from the
casting pool. The control system may receive position or force
information from the sensors 112 or from direct feedback of the
actuator 102.
[0071] In accordance with an alternative embodiment of the present
invention, a method of making alloy strip with tensile strength of
at least 900 MPa and total elongation of at least 30%, strip with
tensile strength of at least 1200 MPa and total elongation of at
least 20%, or strip with tensile strength of at least 1500 MPa and
total elongation of at least 15% produced by continuous casting
comprises: assembling a twin roll caster having a pair of
counter-rotating casting rolls laterally positioned to provide a
nip there between, introducing molten metal to form a casting pool
supported on the casting rolls above the nip and counter-rotating
the casting rolls where the composition is of the formula:
R.sub.uR.sub.'vC.sub.rwM.sub.xB.sub.y(P,C,Si).sub.z, where R is one
of iron, cobalt or nickel; R' is one or two iron of iron, cobalt or
nickel other than R; Cr, B, P, C, and Si respectively represent
chromium, boron, phosphorus, carbon and silicon; M is one or more
of molybdenum, vanadium, niobium, titanium, aluminum, tin,
manganese and copper; u, v, w, x, y and z represent atom percent of
R, R', Cr, M, B and (P, C, Si), respectively, and having the
following values: u=30-85, v=0-30, w=0-40, x=0-30, y=0-12, and
z=0-7.5, with the provisions that (1) the sum of v+w+x is at least
5, (2) when x is larger than 20, then w must be less than 20, (3)
the amount of each of vanadium, manganese, copper, tin, magnesium
may not exceed 10 atom percent, and (4) the combined amount of
boron, phosphorus, carbon and silicon may not exceed about 13 atom
percent.
[0072] The molten metal thus delivered forms a casting pool of
molten metal above the nip supported on the casting surfaces of the
casting rolls. A heat flux in forming the thin strip on the casting
rolls is provided with a peak heat flux of greater than 20
Mw/m.sup.2 and heat flux after 25 milliseconds of greater than 8
Mw/m.sup.2 to provide a weighted average heat flux of at least 10
Mw/m.sup.2, and cooling the strip at 1000 to 3000 K/sec until the
strip exits the nip between the casting rolls. A roll biasing force
greater than 40 kN/meter of casting roll length is applied to form
thin metal strip downwardly at the nip.
[0073] Once the strip exists the nip, the thin cast strip is
conveyed through a first enclosure with an atmosphere having an
oxygen content of less than 5% immediately downstream of the
casting rolls and on to a roller table while forming a loop of the
cast strip with a strain of not more than 0.4% or 0.2% to form a
thin steel strip. In one embodiment, the loop in the enclosure is
between 2.8 and 3 meters. The cast strip is rolled through a
rolling mill to impart between 10 and 40% reduction or heating the
post cast strip to at least 70% of the melting point of the alloy
forming the strip and initiating a modification of the
microstructure of the cast strip to provide strip with of at least
900 MPa tensile strength and total elongation of at least 30%%,
strip with tensile strength of at least 1200 MPa and total
elongation of at least 20%, or strip with tensile strength of at
least 1500 MPa and total elongation of at least 15%. The strip may
have an unresolved microstructure at the surfaces, an equiaxed in
the central portions, and columnar intermediate portions.
[0074] While the principle and mode of operation of this invention
have been explained and illustrated with regard to particular
embodiments, it must be understood, however, that this invention
may be practiced otherwise than as specifically explained and
illustrated without departing from its spirit or scope
* * * * *