Continuous annealing line, continuous annealing method, method of producing cold-rolled steel sheet, and method of producing coated or plated steel sheet

Abstract

Provided is a continuous annealing line, a continuous annealing method, a method of producing a cold-rolled steel sheet, and a method of producing a coated or plated steel sheet that can respond quickly to variation in material properties and substantially reduce variation in mechanical properties of products. The continuous annealing line is for a steel sheet and includes a heating zone (6), a soaking zone (7), and a cooling zone (8), in this order, at least one induction heating device (9) disposed between the soaking zone (7) and the cooling zone (8), and a measuring device (phase transformation rate meter (10)) disposed at or after an exit from the induction heating device (9) and configured to measure at least one phase fraction of the steel sheet.

1 . A continuous annealing line for a steel sheet, comprising a heating zone, a soaking zone, and a cooling zone, in this order, and further comprising:
 at least one induction heating device disposed between the soaking zone and the cooling zone; and   a measuring device disposed at or after an exit from the induction heating device and configured to measure at least one phase fraction of the steel sheet.   
     
     
         2 . The continuous annealing line according to  claim 1 , further comprising a control device configured to determine an operating condition of the induction heating device based on a measurement result of the measuring device. 
     
     
         3 . The continuous annealing line according to  claim 1 , wherein a heating rate of the induction heater is 10° C./s or more and is 200° C./s or less. 
     
     
         4 . A continuous annealing method for a steel sheet that is conveyed through a heating zone, a soaking zone, and a cooling zone, in this order, the method comprising:
 after holding the temperature of the steel sheet in a recrystallization temperature range in the soaking zone,   a step of rapidly heating the steel sheet by at least one induction heating device disposed between the soaking zone and the cooling zone; and   a step of controlling an operating condition of the induction heating device based on a phase fraction of the steel sheet obtained between an exit from the soaking zone and entry to the cooling zone.   
     
     
         5 . The continuous annealing method according to  claim 4 , wherein the induction heater heats the steel sheet at a rate of 10° C./s or more and 200° C./s or less. 
     
     
         6 . A method of producing a cold-rolled steel sheet, the method comprising a step of annealing the steel sheet that is a cold-rolled steel sheet at an annealing temperature adjusted by the continuous annealing method according to  claim 4 . 
     
     
         7 . A method of producing a coated or plated steel sheet, the method comprising a step of applying a coating or plating treatment to a surface of the steel sheet annealed by the method of producing a cold-rolled steel sheet according to  claim 6 . 
     
     
         8 . The method of producing a coated or plated steel sheet according to  claim 7 , wherein the coating or plating treatment is electrogalvanization treatment, hot-dip galvanizing treatment, or galvannealing treatment.