Continuous casting method and continuous casting machine for steel

Abstract

A continuous casting method for steel and a continuous casting machine for steel are disclosed. A continuous casting method for steel includes: applying rolling reduction to a cast piece to be continuously cast at a rolling reduction rate of 0.3 mm/min or more and 2.0 mm/min or less in a range where a center solid phase ratio being a solid phase ratio in a thickness center of the cast piece is at least 0.2 or more and less than 1.0, in which a segment deflection T being a deflection in the thickness direction of a segment frame of the segment (18) where the rolling reduction is applied to the cast piece satisfies Equation (1).2×τ−A/(n−1)≤3.25×2×δ≤1.3  (1)

1 . A continuous casting method for steel,
 the method being a method for continuously casting steel with a continuous casting machine of a curved type continuous casting machine or a vertical bending type continuous casting machine,   the method comprising:   applying rolling reduction to a cast piece to be continuously cast at a rolling reduction rate of 0.3 mm/min or more and 2.0 mm/min or less in a range where a center solid phase ratio being a solid phase ratio in a thickness center of the cast piece is at least 0.2 or more and less than 1.0, wherein   a segment deflection T being a deflection in a thickness direction of a segment frame of a segment where the rolling reduction is applied to the cast piece satisfies Equation (1),   
       
         
           
             
               
                 
                   
                     
                       2 
                       × 
                     
                     ⊤ 
                     
                       
                         
                           - 
                           A 
                         
                         / 
                         
                           ( 
                           
                             n 
                             - 
                             1 
                           
                           ) 
                         
                       
                       ≤ 
                       
                         
                           3 
                           . 
                           2 
                         
                         ⁢ 
                         5 
                         × 
                         2 
                         × 
                         δ 
                       
                       ≤ 
                       1.3 
                     
                   
                 
                 
                   
                     ( 
                     1 
                     ) 
                   
                 
               
             
           
         
         wherein 
         δ represents an actually measured bulging amount (mm), 
         τ represents a segment deflection (mm), 
         A represents a set rolling reduction amount of soft reduction in a soft reduction zone where the center solid phase ratio of the cast piece is 0.2 or more and less than 1.0 (mm), and 
         n represent a number of cast piece supporting roll pairs present in the soft reduction zone where the center solid phase ratio of the cast piece is 0.2 or more and less than 1.0. 
       
     
     
         2 . The continuous casting method for steel according to  claim 1 , wherein, for a segment frame equivalent to a final solidification position, a deflection deviation σ is set to 0.2 mm or less and a lateral displacement difference t of the segment frame is constantly set to 0.2 mm or less. 
     
     
         3 . The continuous casting method for steel according to  claim 1 , comprising:
 bulging long side surfaces of the cast piece with a total bulging amount of 3 mm or more and 20 mm or less by stepwise increasing a roll opening degree of a plurality of pairs of cast piece supporting rolls toward a casting direction downstream side in an intentional bulging zone of the continuous casting machine, wherein   the rolling reduction is applied to the cast piece by stepwise reducing the roll opening degree of the plurality of pairs of cast piece supporting rolls toward the casting direction downstream side in the soft reduction zone on the casting direction downstream side relative to the intentional bulging zone.   
     
     
         4 . The continuous casting method for steel according to  claim 2 , comprising:
 bulging long side surfaces of the cast piece with a total bulging amount of 3 mm or more and 20 mm or less by stepwise increasing a roll opening degree of a plurality of pairs of cast piece supporting rolls toward a casting direction downstream side in an intentional bulging zone of the continuous casting machine, wherein   the rolling reduction is applied to the cast piece by stepwise reducing the roll opening degree of the plurality of pairs of cast piece supporting rolls toward the casting direction downstream side in the soft reduction zone on the casting direction downstream side relative to the intentional bulging zone.   
     
     
         5 . A continuous casting machine for steel,
 the machine being a curved type continuous casting machine or a vertical bending type continuous casting machine for continuously casting steel,   the machine comprising:   a soft reduction zone where a cast piece to be continuously cast is rolling-reduced in a thickness direction, wherein   in the soft reduction zone, the rolling reduction is applied to the cast piece at a rolling reduction rate of 0.3 mm/min or more and 2.0 mm/min or less in a range where a center solid phase ratio being a solid phase ratio in a thickness center of the cast piece is at least 0.2 or more and less than 1.0, and   a segment deflection T being a deflection in the thickness direction of a segment frame of a segment where the rolling reduction is applied to the cast piece in the soft reduction zone satisfies Equation (1),   
       
         
           
             
               
                 
                   
                     
                       2 
                       × 
                     
                     ⊤ 
                     
                       
                         
                           - 
                           A 
                         
                         / 
                         
                           ( 
                           
                             n 
                             - 
                             1 
                           
                           ) 
                         
                       
                       ≤ 
                       
                         
                           3 
                           . 
                           2 
                         
                         ⁢ 
                         5 
                         × 
                         2 
                         × 
                         δ 
                       
                       ≤ 
                       1.3 
                     
                   
                 
                 
                   
                     ( 
                     1 
                     ) 
                   
                 
               
             
           
         
         wherein 
         δ represents an actually measured bulging amount (mm), 
         τ represents a segment deflection (mm), 
         A represents a set rolling reduction amount of soft reduction in the soft reduction zone where the center solid phase ratio of the cast piece is 0.2 or more and less than 1.0 (mm), and 
         n represent a number of cast piece supporting roll pairs present in the soft reduction zone where the center solid phase ratio of the cast piece is 0.2 or more and less than 1.0.