Continuous annealing line, continuous hot-dip galvanizing line, and steel sheet production method

Abstract

Provided is a continuous annealing line capable of producing a steel sheet excellent in hydrogen embrittlement resistance. A continuous annealing line 100 includes: a payoff reel 10 to feed a cold-rolled steel sheet S; an annealing furnace 20 to continuously anneal the cold-rolled steel sheet S and including a heating zone 22 , a soaking zone 24 , and a cooling zone 26 ; a downstream line 30 ; a tension reel 50 configured to coil the cold-rolled steel sheet S; and a vibration application device 60 or 70 configured to apply vibration to the cold-rolled steel sheet S being passed from the cooling zone 26 to the tension reel 50 so that the cold-rolled steel sheet is caused to vibrate at a frequency of 100 Hz or more and 100,000 Hz or less and a maximum amplitude of 10 nm or more and 500 μm or less.

1 . A continuous annealing line comprising:
 a payoff reel configured to uncoil a cold-rolled coil to feed a cold-rolled steel sheet;   an annealing furnace configured to pass the cold-rolled steel sheet therethrough to continuously anneal the cold-rolled steel sheet and including a heating zone, a soaking zone, and a cooling zone that are arranged from an upstream side in a sheet passing direction, the cold-rolled steel sheet being annealed in a reducing atmosphere containing hydrogen in the heating zone and the soaking zone, and cooled in the cooling zone;   a downstream line configured to continuously pass the cold-rolled steel sheet discharged from the annealing furnace therethrough;   a tension reel configured to coil the cold-rolled steel sheet being passed through the downstream line; and   a vibration application device configured to apply vibration to the cold-rolled steel sheet being passed from the cooling zone to the tension reel so that the cold-rolled steel sheet is caused to vibrate at a frequency of 100 Hz or more and 100,000 Hz or less and a maximum amplitude of 10 nm or more and 500 μm or less.   
     
     
         2 - 6 . (canceled) 
     
     
         7 . A continuous hot-dip galvanizing line comprising:
 the continuous annealing line according to claim  1 ; and   a hot-dip galvanizing bath located, as the downstream line, downstream of the annealing furnace in the sheet passing direction, and configured to immerse the cold-rolled steel sheet therein to apply a hot-dip galvanized coating onto the cold-rolled steel sheet.   
     
     
         8 . The continuous hot-dip galvanizing line according to  claim 7 , wherein the vibration application device is located at a position that enables applying vibration to the cold-rolled steel sheet being passed upstream of the hot-dip galvanizing bath. 
     
     
         9 . The continuous hot-dip galvanizing line according to  claim 7 , wherein the vibration application device is located at a position that enables applying vibration to the cold-rolled steel sheet being passed downstream of the hot-dip galvanizing bath. 
     
     
         10 . The continuous hot-dip galvanizing line according to  claim 7 , comprising
 an alloying furnace located, as the downstream line, downstream of the hot-dip galvanizing bath in the sheet passing direction, and configured to pass the cold-rolled steel sheet therethrough to heat and alloy the hot-dip galvanized coating.   
     
     
         11 . The continuous hot-dip galvanizing line according to  claim 10 , wherein the vibration application device is located at a position that enables applying vibration to the cold-rolled steel sheet being passed upstream of the hot-dip galvanizing bath. 
     
     
         12 . The continuous hot-dip galvanizing line according to  claim 10 , wherein the vibration application device is located at a position that enables applying vibration to the cold-rolled steel sheet being passed downstream of the hot-dip galvanizing bath. 
     
     
         13 . The continuous hot-dip galvanizing line according to  claim 7 , wherein an arrangement of the vibration application device and a sheet passing speed of the cold-rolled steel sheet are set so that a vibration application time for the cold-rolled steel sheet will be 1 second or more. 
     
     
         14 . The continuous hot-dip galvanizing line according to  claim 7 , wherein the vibration application device comprises an electromagnet having a magnetic pole surface spaced from and facing a surface of the cold-rolled steel sheet, and the vibration application device is configured to cause the cold-rolled steel sheet to vibrate in response to an external force exerted by the electromagnet on the cold-rolled steel sheet. 
     
     
         15 . (canceled) 
     
     
         16 . A steel sheet production method comprising, in the following order:
 a step (A) of uncoiling a cold-rolled coil to feed a cold-rolled steel sheet by a payoff reel;   a step (B) of passing the cold-rolled steel sheet through an annealing furnace in which a heating zone, a soaking zone, and a cooling zone are arranged from an upstream side in a sheet passing direction, to continuously anneal the cold-rolled steel sheet by a step (B-1) of annealing the cold-rolled steel sheet in a reducing atmosphere containing hydrogen in the heating zone and the soaking zone and a step (B-2) of cooling the cold-rolled steel sheet in the cooling zone;   a step (C) of continuously passing the cold-rolled steel sheet discharged from the annealing furnace; and   a step (D) of coiling the cold-rolled steel sheet by a tension reel to obtain a product coil,   wherein the steel sheet production method comprises   a vibration application step of applying vibration to the cold-rolled steel sheet being passed in or after the step (B-2) and before the step (D) so that the cold-rolled steel sheet is caused to vibrate at a frequency of 100 Hz or more and 100,000 Hz or less and a maximum amplitude of 10 nm or more and 500 μm or less.   
     
     
         17 - 18 . (canceled) 
     
     
         19 . The steel sheet production method according to  claim 16 , wherein the step (C) includes a step (C-1) of immersing the cold-rolled steel sheet in a hot-dip galvanizing bath located downstream of the annealing furnace in the sheet passing direction to apply a hot-dip galvanized coating onto the cold-rolled steel sheet. 
     
     
         20 . The steel sheet production method according to  claim 19 , wherein the vibration application step is performed before the step (C-1). 
     
     
         21 . The steel sheet production method according to  claim 19 , wherein the vibration application step is performed after the step (C-1). 
     
     
         22 . The steel sheet production method according to  claim 19 , wherein the step (C) includes, following the step (C-1), a step (C-2) of passing the cold-rolled steel sheet through an alloying furnace located downstream of the hot-dip galvanizing bath in the sheet passing direction to heat and alloy the hot-dip galvanized coating. 
     
     
         23 . The steel sheet production method according to  claim 22 , wherein the vibration application step is performed before the step (C-1). 
     
     
         24 . The steel sheet production method according to  claim 22 , wherein the vibration application step is performed after the step (C-1). 
     
     
         25 . The steel sheet production method according to  claim 16 , wherein in the vibration application step, a vibration application time for the cold-rolled steel sheet is 1 second or more. 
     
     
         26 . The steel sheet production method according to  claim 16 , wherein in the vibration application step, the cold-rolled steel sheet is caused to vibrate in response to an external force exerted by an electromagnet on the cold-rolled steel sheet, the electromagnet having a magnetic pole surface spaced from and facing a surface of the cold-rolled steel sheet. 
     
     
         27 . (canceled) 
     
     
         28 . The steel sheet production method according to  claim 16 , wherein the cold-rolled steel sheet is a high strength steel sheet having a tensile strength of 590 MPa or more. 
     
     
         29 . The steel sheet production method according to  claim 16 , wherein the cold-rolled steel sheet has a chemical composition containing, in mass %,
 C: 0.030% to 0.800%,   Si: 0.01% to 3.00%,   Mn: 0.01% to 10.00%,   P: 0.001% to 0.100%   S: 0.0001% to 0.0200%,   N: 0.0005% to 0.0100%, and   Al: 0.001% to 2.000%,   with the balance being Fe and inevitable impurities.   
     
     
         30 . The steel sheet production method according to  claim 29 , wherein the chemical composition further contains, in mass %, at least one element selected from the group consisting of
 Ti: 0.200% or less,   Nb: 0.200% or less,   V: 0.500% or less,   W: 0.500% or less,   B: 0.0050% or less,   Ni: 1.000% or less,   Cr: 1.000% or less,   Mo: 1.000% or less,   Cu: 1.000% or less,   Sn: 0.200% or less,   Sb: 0.200% or less,   Ta: 0.100% or less,   Ca: 0.0050% or less,   Mg: 0.0050% or less,   Zr: 0.1000% or less, and   REM: 0.0050% or less.   
     
     
         31 - 32 . (canceled) 
     
     
         33 . The steel sheet production method according to  claim 16 , wherein the product coil has a diffusible hydrogen content of 0.50 mass ppm or less.