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.

What is claimed is: 
     
         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° C., a liquidus temperature between 1150 and 1350° C., and a freezing range between 100 and 250° 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 2  and heat flux after 25 milliseconds of greater than 8 Mw/m 2  to provide a weighted average heat flux of at least 10 Mw/m 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° C., a liquidus temperature between 1150 and 1350° C., and a freezing range between 100 and 250° 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 2  and heat flux after 25 milliseconds of greater than 8 Mw/m 2  to provide a weighted average heat flux of at least 10 Mw/m 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 u R′ v Cr w M x B y (P,C,Si) 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 2  and heat flux after 25 milliseconds of greater than 8 Mw/m 2  to provide a weighted average heat flux of at least 10 Mw/m 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 u R′ v Cr w M x B y (P,C,Si) 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 2  and heat flux after 25 milliseconds of greater than 8 Mw/m 2  to provide a weighted average heat flux of at least 10 Mw/m 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° C., a liquidus temperature between 1150 and 1350° C., and a freezing range between 100 and 250° 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 2  and heat flux after 25 milliseconds of greater than 8 Mw/m 2  to provide a weighted average heat flux of at least 10 Mw/m 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° C., a liquidus temperature between 1150 and 1350° C., and a freezing range between 100 and 250° 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 2  and heat flux after 25 milliseconds of greater than 8 Mw/m 2  to provide a weighted average heat flux of at least 10 Mw/m 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 u R′ v Cr w M x B y (P,C,Si) 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 2  and heat flux after 25 milliseconds of greater than 8 Mw/m 2  to provide a weighted average heat flux of at least 10 Mw/m 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 u R′ v Cr w M x B y (P,C,Si) 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 2  and heat flux after 25 milliseconds of greater than 8 Mw/m 2  to provide a weighted average heat flux of at least 10 Mw/m 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° C., a liquidus temperature between 1150 and 1350° C., and a freezing range between 100 and 250° 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 2  and heat flux after 25 milliseconds of greater than 8 Mw/m 2  to provide a weighted average heat flux of at least 10 Mw/m 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° C., a liquidus temperature between 1150 and 1350° C., and a freezing range between 100 and 250° 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 2  and heat flux after 25 milliseconds of greater than 8 Mw/m 2  to provide a weighted average heat flux of at least 10 Mw/m 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 u R′ v Cr w M x B y (P,C,Si) 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 2  and heat flux after 25 milliseconds of greater than 8 Mw/m 2  to provide a weighted average heat flux of at least 10 Mw/m 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 u R′ v Cr w M x B y (P,C,Si) 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 2  and heat flux after 25 milliseconds of greater than 8 Mw/m 2  to provide a weighted average heat flux of at least 10 Mw/m 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.