Ferritic stainless steel and method for manufacturing the same

Abstract

A ferritic stainless steel having sufficient corrosion resistance and excellent formability and ridging resistance. The ferritic stainless steel having a chemical composition comprising, by mass %, C: 0.005% or more and 0.035% or less, Si: 0.25% or more and less than 0.40%, Mn: 0.05% or more and 0.35% or less, P: 0.040% or less, S: 0.01% or less, Cr: 15.5% or more and 18.0% or less, Al: 0.001% or more and 0.10% or less, N: 0.01% or more and 0.06% or less, and the balance being Fe and inevitable impurities. Si and Mn satisfy the relational expression 29.5×Si−50×Mn+6≥0, where Si and Mn in the relational expression respectively denote the content, by mass %, of the corresponding chemical element.

1 . Ferritic stainless steel having a chemical composition comprising, by mass %:
 C: 0.005% or more and 0.035% or less;   Si: 0.25% or more and less than 0.40%;   Mn: 0.05% or more and 0.35% or less;   P: 0.040% or less;   S: 0.01% or less;   Cr: 15.5% or more and 18.0% or less;   Al: 0.001% or more and 0.10% or less;   N: 0.01% or more and 0.06% or less; and   the balance being Fe and inevitable impurities,   wherein Si and Mn satisfy the relational expression (1)
   29.5×Si−50×Mn+6≥0   (1)
 
   (where Si and Mn respectively denote the content, by mass %, of the corresponding chemical element.   
     
     
         2 . The ferritic stainless steel according to  claim 1 , the chemical composition further comprising, by mass %, at least one selected from the group consisting of Cu: 0.1% or more and 0.5% or less, Ni: 0.1% or more and 0.6% or less, Mo: 0.1% or more and 0.5% or less, and Co: 0.01% or more and 0.3% or less. 
     
     
         3 . The ferritic stainless steel according to  claim 1 , the chemical composition further comprising, by mass %, at least one selected from the group consisting of V: 0.01% or more and 0.10% or less, Ti: 0.001% or more and 0.05% or less, Nb: 0.001% or more and 0.05% or less, Ca: 0.0002% or more and 0.0020% or less, Mg: 0.0002% or more and 0.0050% or less, B: 0.0002% or more and 0.0050% or less, and REM: 0.01% or more and 0.10% or less. 
     
     
         4 . The ferritic stainless steel according to  claim 1 , wherein the steel has an elongation after fracture in a direction at a right angle to a rolling direction of 28% or more, an average Lankford value of 0.70 or more, and a ridging height of 2.5 μm or less. 
     
     
         5 . A method for manufacturing the ferritic stainless steel according to  claim 1 , the method comprising:
 performing hot rolling on a steel slab to form a hot-rolled steel sheet;   then performing annealing in which the hot-rolled steel sheet is held at a temperature in a range of 900° C. or higher and 1050° C. or lower for 5 seconds or more and 15 minutes or less;   then performing cold rolling; and   then performing annealing in which the cold-rolled steel sheet is held at a temperature in a range of 800° C. or higher and 950° C. or lower for 5 seconds or more and 5 minutes or less.   
     
     
         6 . The ferritic stainless steel according to  claim 2 , the chemical composition further comprising, by mass %, at least one selected from the group consisting of V: 0.01% or more and 0.10% or less, Ti: 0.001% or more and 0.05% or less, Nb: 0.001% or more and 0.05% or less, Ca: 0.0002% or more and 0.0020% or less, Mg: 0.0002% or more and 0.0050% or less, B: 0.0002% or more and 0.0050% or less, and REM: 0.01% or more and 0.10% or less. 
     
     
         7 . The ferritic stainless steel according to  claim 2 , wherein the steel has an elongation after fracture in a direction at a right angle to a rolling direction of 28% or more, an average Lankford value of 0.70 or more, and a ridging height of 2.5 μm or less. 
     
     
         8 . The ferritic stainless steel according to  claim 3 , wherein the steel has an elongation after fracture in a direction at a right angle to a rolling direction of 28% or more, an average Lankford value of 0.70 or more, and a ridging height of 2.5 μm or less. 
     
     
         9 . The ferritic stainless steel according to  claim 6 , wherein the steel has an elongation after fracture in a direction at a right angle to a rolling direction of 28% or more, an average Lankford value of 0.70 or more, and a ridging height of 2.5 μm or less. 
     
     
         10 . A method for manufacturing the ferritic stainless steel according to  claim 2 , the method comprising:
 performing hot rolling on a steel slab to form a hot-rolled steel sheet;   then performing annealing in which the hot-rolled steel sheet is held at a temperature in a range of 900° C. or higher and 1050° C. or lower for 5 seconds or more and 15 minutes or less;   then performing cold rolling; and   then performing annealing in which the cold-rolled steel sheet is held at a temperature in a range of 800° C. or higher and 950° C. or lower for 5 seconds or more and 5 minutes or less.   
     
     
         11 . A method for manufacturing the ferritic stainless steel according to  claim 3 , the method comprising:
 performing hot rolling on a steel slab to form a hot-rolled steel sheet;   then performing annealing in which the hot-rolled steel sheet is held at a temperature in a range of 900° C. or higher and 1050° C. or lower for 5 seconds or more and 15 minutes or less;   then performing cold rolling; and   then performing annealing in which the cold-rolled steel sheet is held at a temperature in a range of 800° C. or higher and 950° C. or lower for 5 seconds or more and 5 minutes or less.   
     
     
         12 . A method for manufacturing the ferritic stainless steel according to  claim 4 , the method comprising:
 performing hot rolling on a steel slab to form a hot-rolled steel sheet;   then performing annealing in which the hot-rolled steel sheet is held at a temperature in a range of 900° C. or higher and 1050° C. or lower for 5 seconds or more and 15 minutes or less;   then performing cold rolling; and   then performing annealing in which the cold-rolled steel sheet is held at a temperature in a range of 800° C. or higher and 950° C. or lower for 5 seconds or more and 5 minutes or less.   
     
     
         13 . A method for manufacturing the ferritic stainless steel according to  claim 6 , the method comprising:
 performing hot rolling on a steel slab to form a hot-rolled steel sheet;   then performing annealing in which the hot-rolled steel sheet is held at a temperature in a range of 900° C. or higher and 1050° C. or lower for 5 seconds or more and 15 minutes or less;   then performing cold rolling; and   then performing annealing in which the cold-rolled steel sheet is held at a temperature in a range of 800° C. or higher and 950° C. or lower for 5 seconds or more and 5 minutes or less.   
     
     
         14 . A method for manufacturing the ferritic stainless steel according to  claim 7 , the method comprising:
 performing hot rolling on a steel slab to form a hot-rolled steel sheet;   then performing annealing in which the hot-rolled steel sheet is held at a temperature in a range of 900° C. or higher and 1050° C. or lower for 5 seconds or more and 15 minutes or less;   then performing cold rolling; and   then performing annealing in which the cold-rolled steel sheet is held at a temperature in a range of 800° C. or higher and 950° C. or lower for 5 seconds or more and 5 minutes or less.   
     
     
         15 . A method for manufacturing the ferritic stainless steel according to  claim 8 , the method comprising:
 performing hot rolling on a steel slab to form a hot-rolled steel sheet;   then performing annealing in which the hot-rolled steel sheet is held at a temperature in a range of 900° C. or higher and 1050° C. or lower for 5 seconds or more and 15 minutes or less;   then performing cold rolling; and   then performing annealing in which the cold-rolled steel sheet is held at a temperature in a range of 800° C. or higher and 950° C. or lower for 5 seconds or more and 5 minutes or less.   
     
     
         16 . A method for manufacturing the ferritic stainless steel according to  claim 9 , the method comprising: