High-strength ferritic stainless steel for clamp, and manufacturing method therefor

Abstract

Disclosed are high-strength ferritic stainless steel STS430, which has a yield strength of 350 MPa or greater and can be applied to a clamp of a vehicle or a common hose, and a manufacturing method thereof. The high-strength ferritic stainless steel for a clamp, according to one embodiment of the present invention, comprises, by weight, 0.04-0.1% of C, 0.2-0.6% of Si, 0.01-1.5% of Mn, 14.0-18.0% of Cr, 0.005-0.2% of Al, 0.005-0.2% of V, 0.02-0.1% of N, and the remainder as Fe and inevitable impurities, satisfies Expressions (1) and (2), and has at least 2.5×106 precipitates having a mean diameter of 0.5 μm or less per mm2. (1) 0.35%≤Si+Al+V≤0.6% (2) 0.09%≤C+N≤0.12%

1 . A method of manufacturing high-strength ferritic stainless steel for a clamp, the method comprising:
 hot-rolling a slab, which includes, by weight, 0.04 to 0.1% of C, 0.2 to 0.6% of Si, 0.01 to 1.5% of Mn, 14.0 to 18.0% of Cr, 0.005 to 0.2% of Al, 0.005 to 0.2% of V, 0.02 to 0.1% of N, and the remainder as Fe and inevitable impurities and satisfies the following Expressions (1) and (2), by reheating at 1,000 to 1,200° C.;   winding the hot-rolled steel sheet at 700° C. or more;   cold-rolling the wound hot-rolled steel sheet at a reduction ratio of 60% or more without performing annealing;   annealing the cold-rolled steel sheet at 550 to 950° C. for 10 minutes or less; and   skin-pass rolling the cold-rolled annealed steel sheet at a reduction ratio of 2 to 8%.
   0.35%≤Si+Al+V≤0.6%   (1)
 
   0.09%≤C+N≤0.12%   (2)
 
   (wherein, Si, Al, V, C, and N refer to contents (% by weight) of respective elements)   
     
     
         2 . The method of  claim 1 , wherein the cold-rolled annealed steel sheet includes at least 2.5×10 6  (Cr,Fe)-carbonitride precipitates having an average diameter of 0.5 μm or less per mm 2 . 
     
     
         3 . The method of  claim 1 , wherein the slab further includes any one or more selected from the group consisting of 0.001 to 0.5% of Ni, 0.05% or less of P, and 0.005% or less of S. 
     
     
         4 . The method of  claim 1 , wherein the cold-rolled annealed steel sheet has a yield strength of 320 MPa or more, a tensile strength of 510 MPa or more, and an elongation rate of 20% or more. 
     
     
         5 . The method of  claim 1 , wherein the cold-rolled annealed steel sheet having been skin-pass rolled has a yield strength of 350 MPa or more, a tensile strength of 510 MPa or more, and an elongation rate of 20% or more. 
     
     
         6 . High-strength ferritic stainless steel for a clamp, comprising, by weight, 0.04 to 0.1% of C, 0.2 to 0.6% of Si, 0.01 to 1.5% of Mn, 14.0 to 18.0% of Cr, 0.005 to 0.2% of Al, 0.005 to 0.2% of V, 0.02 to 0.1% of N, and the remainder as Fe and inevitable impurities, satisfying the following Expressions (1) and (2), and having a yield strength of 350 MPa or more.
   0.35%≤Si+Al+V≤0.6%   (1)
     0.09%≤C+N≤0.12%   (2)
   (wherein, Si, Al, V, C, and N refer to contents (% by weight) of respective elements)   
     
     
         7 . The high-strength ferritic stainless steel of  claim 6 , further comprising any one or more selected from the group consisting of 0.001 to 0.5% of Ni, 0.05% or less of P, and 0.005% or less of S. 
     
     
         8 . The high-strength ferritic stainless steel of  claim 6 , which includes (Cr,Fe)-carbonitride precipitates, wherein at least 2.5×10 6  (Cr,Fe)-carbonitride precipitates having an average diameter of 0.5 μm or less per mm 2  are distributed. 
     
     
         9 . The high-strength ferritic stainless steel of  claim 6 , which has a tensile strength of 510 MPa or more and an elongation rate of 20% or more.