Hot-rolled ferritic stainless steel sheet with excellent cold cracking resistance and manufacturing process therefor

Abstract

This hot-rolled ferritic stainless steel sheet contains, in terms of % by mass: 0.0150% or less of C, 0.01% to 2.00% of Si, 0.01% to 2.00% of Mn, less than 0.040% of P, 0.010% or less of S, 10.0% to 30.0% of Cr, 0.001% to 0.100% of Al, and 0.0200% or less of N, with a balance being Fe and unavoidable impurities, wherein in a cross section in a range of ¼ to ¾ of a sheet thickness, a length L of all crystal grain boundaries having orientation differences of 1° or more to less than 180° and a length La of subgrain boundaries having orientation differences of 1° or more to less than 15° satisfy a relation of La/L≧0.20.

1 . A hot-rolled ferritic stainless steel sheet with excellent cold cracking resistance, comprising, in terms of % by mass:
 0.0150% or less of C;   0.01% to 2.00% of Si;   0.01% to 2.00% of Mn;   less than 0.040% of P;   0.010% or less of S;   10.0% to 30.0% of Cr;   0.001% to 3.00% ofAl; and   0.0200% or less of N,   with a balance being Fe and unavoidable impurities,   wherein in a cross section in a range of ¼ to ¾ of a sheet thickness, a length L of all crystal grain boundaries having orientation differences of 1° or more to less than 180° and a length La of subgrain boundaries having orientation differences of 1° or more to less than 15° satisfy a relation of La/L≧0.20.   
     
     
         2 . The hot-rolled ferritic stainless steel sheet with excellent cold cracking resistance according to  claim 1 , which further comprises one or more selected from, in terms of % by mass:
 0.05% to 0.70% of Nb;   0.05% to 0.30% of Ti;   0.1% to 2.5% of Mo;   0.1% to 1.5% of Ni;   0.0001% to 0.0025% of B;   0.1% to 2.0% of Cu; and   0.03% to 0.35% of Sn,   wherein in a case where either one or both of Nb and Ti are included, the following formula (1) is satisfied,
   Nb/93+Ti/48≧C/12+N/14   (1)
 
   element symbols in the formula (1) indicate contents of the respective elements in terms of % by mass.   
     
     
         3 . The hot-rolled ferritic stainless steel sheet with excellent cold cracking resistance according to  claim 1  or  2 , wherein the content of Al is in a range of more than 0.10% to 3.00%. 
     
     
         4 . A method for manufacturing the hot-rolled ferritic stainless steel sheet with excellent cold cracking resistance according to any one of  claims 1  to  3 , the method comprising:
 casting ferritic stainless steel having the steel composition according to any one of  claims 1  to  3  to generate a semi-finished product and subjecting the semi-finished product to hot rolling under a condition where a finishing temperature is in a range of 800° C. to 1000° C. to generate a hot-rolled steel sheet; 
 subsequently, coiling the hot-rolled steel sheet in a coil shape at a temperature of more than 650° C. to 800° C.; and 
 immersing the hot-rolled sheet coiled in a coil shape in a water tank within 1 hour after the coiling, maintaining the hot-rolled sheet in the water tank for 1 hour or more, and taking out the hot-rolled steel sheet.