Low surface roughness cast strip and method and apparatus for making the same

Abstract

A thin cast strip is formed having at least one microstructure selected from the group consisting of polygonal ferrite, acicular ferrite, Widmanstatten, bainite and martinsite, a surface roughness of less than 1.5 microns Ra and a scale thickness of less than about 10 microns by applying a mixture of water and oil on the work rolls of the hot rolling mill, passing the thin cast strip at a temperature of less than 1100° C. through the hot rolling mill while the mixture of oil and water is applied to the work rolls, and shrouding the thin cast strip from the casting rolls through the hot rolling mill in an atmosphere of less than 5% oxygen to form the thin cast strip.

1 . A thin cast strip having at least one microstructure selected from the group consisting of polygonal ferrite, acicular ferrite, Widmanstatten, bainite and martinsite, a surface roughness of less than 1.5 microns Ra and a scale thickness of less than about 10 microns made by the steps comprising: 
 a. assembling a twin roll caster having laterally positioned caster rolls forming a nip between them and a hot rolling mill having work rolls and back-up rolls adjacent the twin roll caster,    b. forming a thin cast strip from the nip between the casting rolls of the twin roll caster,    c. applying a mixture of water and oil on the work rolls of the hot rolling mill,    d. passing the thin cast strip at a temperature of less than 1100° C. through the hot rolling mill while the mixture of oil and water is applied to the work rolls, and    e. shrouding the thin cast strip from the casting rolls through the hot rolling mill in an atmosphere of less than 5% oxygen forming a thin cast strip having: at least one microstructure selected from the group consisting of polygonal ferrite, acicular ferrite, Widmanstatten, bainite and martinsite, a surface roughness of less than 1.5 microns Ra, and a scale thickness of less than 10 microns.    
   
   
       2 . A thin cast strip as described in  claim 1  wherein the thin cast strip is passed through the hot rolling mill at a temperature less than 1050° C. while the mixture of oil and water is applied to the work rolls.  
   
   
       3 . A thin cast strip as described in  claim 1  wherein the surface roughness is less than 1.0 microns Ra.  
   
   
       4 . A thin cast strip as described in  claim 1  wherein the surface roughness is less than 0.7 microns Ra.  
   
   
       5 . A thin cast strip as described in  claim 1  wherein the surface roughness is less than 0.5 microns Ra.  
   
   
       6 . A thin cast strip as described in  claim 1  wherein the scale thickness is less than 7 microns.  
   
   
       7 . A thin cast strip as described in  claim 1  wherein the scale thickness is less than 4 microns.  
   
   
       8 . A thin cast strip as described in  claim 1  wherein the mixture of oil and water is applied by spying the work rolls.  
   
   
       9 . A thin cast strip as described in  claim 1  wherein the mixture of oil and water is applied to the work rolls by applying the mixture of oil and water to the back-up rolls.  
   
   
       10 . A thin cast strip as described in  claim 1  wherein the mixture of oil and water is less than 5% oil and the low surface roughness is less than 1.5 microns Ra.  
   
   
       11 . A thin cast steel strip with reduced surface roughness below 1.5 microns Ra, produced by the steps comprising: 
 a. assembling a strip caster having a pair of casting rolls having a nip there between;    b. assembling a metal delivery system capable of forming a casting pool between the cast rolls above the nip with side dams adjacent the ends of the nip to confine said casting pool;    c. assembling adjacent the strip caster a hot rolling mill having work rolls with work surfaces forming a gap between them through which hot strip is rolled;    d. assembling spray nozzles positioned adjacent the work rolls capable of providing a mixture of water and oil to the work rolls;    e. introducing molten steel between the pair of casting rolls to form a casting pool supported on casting surfaces of the casting rolls confined by said first side dams;    f. counter-rotating the casting rolls to form solidified metal shells on the surfaces of the casting rolls and cast steel strip through the nip between the casting rolls from said solidified shells;    g. spraying the mixture of oil and water as the strip enters the hot rolling mill; and    h. rolling the cast strip between the work rolls of the hot rolling mill to produce a cast strip having a surface roughness less than 1 microns Ra.    
   
   
       12 . The thin cast steel strip with reduced surface roughness as claimed in  claim 11  where the rate of production of the cast strip in above 80 meters per minute.  
   
   
       13 . The thin cast steel strip with reduced surface roughness as claimed in  claim 11  where the rolling temperature is below 900° C.  
   
   
       14 . The thin cast steel strip with reduced surface roughness as claimed in  claim 11  where the rate of spray by the nozzles is between 10 and 30 gallons per minute.  
   
   
       15 . The thin cast steel strip with reduced surface roughness as claimed in  claim 11  where the surface roughness below 0.7 microns Ra.  
   
   
       16 . The thin cast steel strip with reduced surface roughness as claimed in  claim 11  where the surface roughness below 0.4 microns Ra.  
   
   
       17 . The thin cast steel strip with reduced surface roughness as claimed in  claim 11  where the rate of production of the cast strip in above 80 meters per minute.  
   
   
       18 . A thin cast steel strip with reduced surface roughness below 1.5 microns Ra, produced by the steps comprising: 
 a. assembling a strip caster having a pair of casting rolls having a nip there between;    b. assembling a metal delivery system capable of forming a casting pool between the cast rolls above the nip with side dams adjacent the ends of the nip to confine said casting pool;    c. assembling adjacent the strip caster a hot rolling mill having back-up rolls and work rolls with work surfaces forming a gap between the work rolls through which hot strip is rolled;    d. assembling spray nozzles positioned upstream of the work rolls capable of spraying a mixture of water and oil the back-up rolls;    e. introducing molten steel between the pair of casting rolls to form a casting pool supported on casting surfaces of the casting rolls confined by said first side dams;    f. counter-rotating the casting rolls to form solidified metal shells on the surfaces of the casting rolls and cast steel strip through the nip between the casting rolls from the solidified shells;    g spraying the mixture of oil and water as the cast strip enters the hot rolling mill; and    h. rolling the cast strip between the work rolls of the hot rolling mill to produce a cast strip having a surface roughness less than 1.5 microns Ra.    
   
   
       19 . The thin cast steel strip with reduced surface roughness below 1.5 microns Ra as claimed in  claim 18  where the rate of production of the cast strip in above 80 meters per minute.  
   
   
       20 . The thin cast steel strip with reduced surface roughness below 1.5 microns Ra as claimed in  claim 18  where the rolling temperature is below 10° C.  
   
   
       21 . The thin cast steel strip with reduced surface roughness as claimed in  claim 18  where the rolling temperature is below 1050° C.  
   
   
       22 . The thin cast steel strip with reduced surface roughness as claimed in  claim 18  where the rolling temperature is below 900° C.  
   
   
       23 . The thin cast steel strip with reduced surface roughness as claimed in  claim 18  where the rate of spray by the nozzles is between 10 and 30 gallons per minute.  
   
   
       24 . The thin cast steel strip with reduced surface roughness as claimed in  claim 18  where the surface roughness below 0.7 microns Ra.  
   
   
       25 . The thin cast steel strip with reduced surface roughness as claimed in  claim 24  where the rate of production of the cast strip in above 80 meters per minute.  
   
   
       26 . The thin cast steel strip with reduced surface roughness as claimed in  claim 24  where the rolling temperature is below 1100° C.  
   
   
       27 . The thin cast steel strip with reduced surface roughness as claimed in  claim 24  where the rolling temperature is below 1050° C.  
   
   
       28 . The thin cast steel strip with reduced surface roughness as claimed in  claim 24  where the rolling temperature is below 900° C.  
   
   
       29 . The thin cast steel strip with reduced surface roughness as claimed in  claim 24  where the rate of spray by the nozzles is between 10 and 30 gallons per minute.  
   
   
       30 . The thin cast steel strip with reduced surface roughness as claimed in  claim 18  where the mixture of oil and water is less than 5% oil.  
   
   
       31 . The thin cast steel strip with reduced surface roughness below 1 microns Ra as claimed in  claim 18  where the thin cast steel strip has a surface scale thickness of less than about 7 microns.