Ferritic stainless steel strip excellent in freeze of shape formed by working

Abstract

A ferritic stainless steel sheet, which is press-formed to a product shape without such dimensional defects as spring-back or torsion, has an alloying composition consisting of C up to 0.10%, Si up to 1.0%, Mn up to 1.0%, P up to 0.050%, S up to 0.020%, Ni up to 2.0%, 8.0-22.0% of Cr, N up to 0.05%, optionally one or more of Al up to 0.10%, Mo up to 1.0%, Cu up to 1.0%, 0.010-0.50% of Ti, 0.010-0.50% of Nb, 0.010-0.30% of V, 0.010-0.30% of Zr and 0.0010-0.0100% of B, and the balance being essentially Fe with the provision that a value-FM defined by the formula (1) is adjusted to 0 or less. Its mechanical properties are controlled to a plane anisotropic degree (r max −r min ) of Lankford value (r) ≦0.80 and an anisotropic degree (σ max −σ min ) of 0.2%-yield strength ≦20 N/mm 2 . The stainless steel sheet is manufactured by hot-rolling a stainless steel having the specified composition and then batch-annealing the hot-rolled steel sheet 1-24 hours at 700-800° C. FM = 420  C - 11.5     Si + 7  Mn + 23  Ni - 3.5  Cr - 12  Mo + 9  Cu - 49  Ti - 50  Nb - 23  V - 52  Al + 470  N + 20 ( 1 )

1 . A ferritic stainless steel sheet, which has: 
 alloying composition consisting of C up to 0.10 mass %, Si up to 1.0 mass %, Mn up to 1.0 mass %, P up to 0.050 mass %, S up to 0.020 mass %, Ni up to 2.0 mass %, 8.0-22.0 mass % of Cr, N up to 0.05 mass % and the balance being essentially Fe, with the provision that a value-FM defined by the formula (1) is adjusted to 0 or less, and    the mechanical properties that a plane anisotropic degree (r max −r min ) of Lankford value (r) and an anisotropic degree (σ max −σ min ) of 0.2%-yield strength are controlled not more than 0.80 and 20 N/mm 2 , respectively.                  FM   =       420      C     -     11.5                 Si     +     7      Mn     +     23      Ni     -     3.5      Cr     -     12      Mo     +     9      Cu     -     49      Ti     -     50      Nb     -     23      V     -     52      Al     +     470      N     +   20             (   1   )                           
     
     
         2 . The ferritic stainless steel sheet defined by  claim 1 , wherein the alloying composition further contains one or more of Al up to 0.10 mass %, Mo up to 1.0 mass %, Cu up to 1.0 mass %, 0.01-0.50 mass % of Ti, 0.01-0.50 mass % of Nb, 0.01-0.30 mass % of V, 0.01-0.30 mass % of Zr and 0.0010-0.0100 mass % of B.  
     
     
         3 . The ferritic stainless steel sheet defined by  claim 1 , wherein 0.2%-yield strength is not more than 350 N/mm 2  along any of a rolling direction, directions crossing said rolling direction with an angle of 45 degrees and a direction crossing said rolling direction with a right angle.  
     
     
         4 . A method of manufacturing a ferritic stainless steel sheet good of shape-freezability during plastic reformation, which comprises the steps of: 
 hot-rolling a ferritic stainless steel having the alloying composition defined by  claim 1  or  2 , and then    batch-annealing the hot-rolled steel sheet 1-24 hours at 700-800 ° C.