Ferritic stainless steel sheet for fuel tank and fuel pipe and method for making the same

Abstract

A ferritic stainless steel sheet for fuel tanks and fuel pipes comprises, by mass percent, about 0.1 % or less of C; about 1.0 % or less of Si; about 1.5 % or less of Mn; about 0.06 % or less of P; about 0.03 % or less of S; about 1.0 % or less of Al; about 11% to about 20% Cr; about 2.0% or less of Ni; about 0.5% to about 3.0% Mo; about 0.02% to about 1.0% V; about 0.04% or less of N; at least one of about 0.01% to about 0.8% Nb and about 0.01% to about 1.0% Ti; and the balance being Fe and incidental impurities. The ferritic stainless steel sheet is produced by rough-rolling a slab having the above composition; hot-rolling the rough-rolled sheet under a linear pressure of at least about 3.5 MN/m at a final pass in the finish rolling; cold-rolling the hot-rolled sheet at a gross reduction rate of at least about 75%; and annealing the cold-rolled sheet. The cold-rolling step includes one rolling stage or at least two rolling stages including intermediate annealing.

What is claimed is:  
     
         1 . A ferritic stainless steel sheet for fuel tanks and fuel pipes comprising, by mass percent: about 0.1% or less of C; about 1.0% or less of Si; about 1.5% or less of Mn; about 0.06% or less of P; about 0.03% or less of S; about 1.0% or less of Al; about 11% to about 20% Cr; about 2.0% or less of Ni; about 0.5% to about 3.0% Mo; about 0.02% to about 1.0% V; about 0.04% or less of N; at least one of about 0.01% to about 0.8% Nb and about 0.01% to about 1.0% Ti; and the balance being Fe and incidental impurities.  
     
     
         2 . The ferritic stainless steel sheet according to  claim 1 , wherein the ferritic stainless steel sheet has a ridging height of about 50 μm or less at a 25% deformation in uniaxial stretching.  
     
     
         3 . The ferritic stainless steel sheet according to  claim 1 , wherein a lubricant coat comprising an acrylic resin, calcium stearate, and polyethylene wax is coated and baked on at least one surface of the ferritic stainless steel sheet in a coating amount of about 0.5 g/m 2  to about 4.0 g/m 2 .  
     
     
         4 . The ferritic stainless steel sheet according to  claim 2 , wherein a lubricant coat comprising an acrylic resin, calcium stearate, and polyethylene wax is coated and baked on at least one surface of the ferritic stainless steel sheet in a coating amount of about 0.5 g/m 2  to about 4.0 g/m 2 .  
     
     
         5 . A fuel tank comprising the ferritic stainless steel sheet according to  claim 1 .  
     
     
         6 . A fuel pipe comprising the ferritic stainless steel sheet according to  claim 1 .  
     
     
         7 . The ferritic stainless steel sheet according to  claim 1 , wherein the ferritic stainless steel sheet has an r-value of at least about 1.5.  
     
     
         8 . A method for making a ferritic stainless steel sheet for fuel tanks and fuel pipes, comprising the steps of: 
 rough-rolling a slab comprising, by mass percent, about 0.1% or less of C, about 1.0% or less of Si, about 1.5% or less of Mn, about 0.6% or less of P, about 0.03% or less of S, about 1.0% or less of Al, about 11% to about 20% Cr, about 2.0% or less of Ni, about 0.5% to about 3.0% Mo, about 0.02% to about 1.0% V, about 0.04% or less of N, at least one of about 0.01% to about 0.8% Nb and about 0.01% to about 1.0% Ti, and the balance being Fe and incidental impurities;    hot-rolling the rough-rolled sheet under a linear pressure of at least about 3.5 MN/m at a final pass in the finish rolling;    cold-rolling the hot-rolled sheet at a gross reduction rate of at least about 75%, the cold-rolling including one rolling stage or at least two rolling stages including intermediate annealing; and    annealing the cold-rolled sheet.    
     
     
         9 . The method according to  claim 8 , wherein the hot-rolled sheet is subjected to hot-rolled sheet annealing according to the following equations, cold roiling, and finish annealing:  
       900 ≦T+ 20 t 1,150 and t≦10  
       wherein T is annealing temperature (° C) and t is holding time (minutes).  
     
     
         10 . The method according to  claim 8 , wherein a lubricant coat comprising an acrylic resin, calcium stearate, and polyethylene wax is coated and baked on at least one surface of the hot-rolled or annealed hot-rolled sheet in a coating amount of about 0.5 g/m 2  to about 4.0 g/m 2 .  
     
     
         11 . The method according to  claim 9 , wherein a lubricant coat comprising an acrylic resin, calcium stearate, and polyethylene wax is coated and baked on at least one surface of the hot-rolled or annealed hot-rolled sheet in a coating amount of about 0.5 g/m 2  to about 4.0 g/m 2 .  
     
     
         12 . A fuel tank comprising a ferritic stainless steel sheet made from the method according to  claim 8 .  
     
     
         13 . A fuel pipe comprising a ferritic stainless steel sheet made from the method according to  claim 8.