Ferritic stainless steel sheet for automobile brake disk rotors, automobile brake disk rotor, and hot-stamped article for automobile brake disk rotors

Abstract

A ferritic stainless steel sheet for an automobile brake disc rotor includes: 0.001 to 0.05 mass % of C; 0.001 to 0.05 mass % of N; 0.3 to 4.0 mass % of Si; 0.01 to 2.0 mass % of Mn; 0.01 to 0.05 mass % of P; 0.0001 to 0.02 mass % of S; 10 to 20 mass % of Cr; one or both of 0.001 to 0.5 mass % of Ti and 0.01 to 0.8 mass % of Nb; and a balance consisting of Fe and impurities. After a hot stamping treatment, a crystal grain size is in a range from 100 to 200 μm, and precipitates each having a grain size of 500 nm or less are present at a density of 0.01 to 20 pieces per square micrometer.

1 . A ferritic stainless steel sheet for an automobile brake disc rotor, comprising:
 0.001 to 0.05 mass % of C;   0.001 to 0.05 mass % of N;   0.3 to 4.0 mass % of Si;   0.01 to 2.0 mass % of Mn;   0.01 to 0.05 mass % of P;   0.0001 to 0.02 mass % of S;   10 to 20 mass % of Cr;   one or both of 0.001 to 0.5 mass % of Ti and 0.01 to 0.8 mass % of Nb; and   a balance consisting of Fe and impurities, wherein   through a heat treatment (hereinafter referred to as a “hot stamping pseudo heat treatment”) in which the steel sheet is heated to 1000 degrees C. and subsequently cooled by being retained in a range from 890 to 700 degrees C. for one to ten minutes, a crystal grain size is in a range from 100 to 200 μm, and precipitates each having a grain size of 500 nm or less are at a density of 0.01 to 20 pieces per square micrometer, and   the ferritic stainless steel sheet is a ferritic stainless steel for hot stamping.   
     
     
         2 . A ferritic stainless steel sheet for an automobile brake disc rotor, comprising:
 0.001 to 0.05 mass % of C;   0.001 to 0.05 mass % of N;   0.3 to 4.0 mass % of Si;   0.01 to 2.0 mass % of Mn;   0.01 to 0.05 mass % of P;   0.0001 to 0.02 mass % of S;   10 to 20 mass % of Cr;   one or both of 0.001 to 0.5 mass % of Ti and 0.01 to 0.8 mass % of Nb; and   a balance consisting of Fe and impurities, wherein   the ferritic stainless steel sheet in which a crystal grain size is in a range from 100 to 200 μm and precipitates each having a grain size of 500 nm or less are present at a density of 0.01 to 20 pieces per square micrometer is in a form of a hot-stamped product.   
     
     
         3 - 4 . (canceled) 
     
     
         5 . The ferritic stainless steel sheet for an automobile brake disc rotor according to  claim 1 , wherein fracture elongation at 1000 degrees C. is 50% or more, and 0.2% proof strength at 700 degrees C. after the hot stamping pseudo heat treatment is 80 MPa or more. 
     
     
         6 . The ferritic stainless steel sheet for an automobile brake disc rotor according to  claim 2 , wherein 0.2% proof strength at 700 degrees C. is 80 MPa or more. 
     
     
         7 . The ferritic stainless steel sheet for an automobile brake disc rotor according to  claim 1 , wherein the crystal grain size is in a range from 130 to 200 μm. 
     
     
         8 . (canceled) 
     
     
         9 . The ferritic stainless steel sheet for an automobile brake disc rotor according to  claim 7 , wherein 0.2% proof strength at 300 degrees C. is 170 MPa or more. 
     
     
         10 . The ferritic stainless steel sheet for an automobile brake disc rotor according to  claim 1 , further comprising, in place of a part of Fe, at least one of 0.0001 to 0.0030 mass % of B, 0.001 to 4.0 mass % of Al, 0.01 to 3.0 mass % of Cu, 0.01 to 3.0 mass % of Mo, 0.001 to 2.0 mass % of W, 0.001 to 1.0 mass % of V, 0.01 to 0.5 mass % of Sn, 0.01 to 1.0 mass % of Ni, 0.0001 to 0.01 mass % of Mg, 0.005 to 0.5 mass % of Sb, 0.001 to 0.3 mass % of Zr, 0.001 to 0.3 mass % of Ta, 0.001 to 0.3 mass % of Hf, 0.001 to 0.3 mass % of Co, 0.0001 to 0.01 mass % of Ca, 0.001 to 0.2 mass % of REM, and 0.0002 to 0.3 mass % of Ga. 
     
     
         11 . An automobile brake disc rotor being made of the stainless steel sheet according to  claim 1 . 
     
     
         12 . A hot-stamped product for an automobile brake disc rotor, the hot-stamped product made of the stainless steel sheet according to  claim 1 . 
     
     
         13 . The ferritic stainless steel sheet for an automobile brake disc rotor according to  claim 2 , wherein the crystal grain size is in a range from 130 to 200 μm. 
     
     
         14 . The ferritic stainless steel sheet for an automobile brake disc rotor according to  claim 13 , wherein 0.2% proof strength at 300 degrees C. is 170 MPa or more. 
     
     
         15 . The ferritic stainless steel sheet for an automobile brake disc rotor according to  claim 2 , further comprising, in place of a part of Fe, at least one of 0.0001 to 0.0030 mass % of B, 0.001 to 4.0 mass % of Al, 0.01 to 3.0 mass % of Cu, 0.01 to 3.0 mass % of Mo, 0.001 to 2.0 mass % of W, 0.001 to 1.0 mass % of V, 0.01 to 0.5 mass % of Sn, 0.01 to 1.0 mass % of Ni, 0.0001 to 0.01 mass % of Mg, 0.005 to 0.5 mass % of Sb, 0.001 to 0.3 mass % of Zr, 0.001 to 0.3 mass % of Ta, 0.001 to 0.3 mass % of Hf, 0.001 to 0.3 mass % of Co, 0.0001 to 0.01 mass % of Ca, 0.001 to 0.2 mass % of REM, and 0.0002 to 0.3 mass % of Ga. 
     
     
         16 . An automobile brake disc rotor made of the stainless steel sheet according to  claim 2 . 
     
     
         17 . A hot-stamped product for an automobile brake disc rotor, the hot-stamped product made of the stainless steel sheet according to  claim 2 .