High-carbon steel sheet and method of manufacturing the same

Abstract

A high-carbon steel sheet includes: a chemical composition represented by, in mass %, C: 0.30% to 0.70%, B: 0.0004% to 0.0035%, and others; and a structure represented by a spheroidized ratio of cementite: 80% or more; and an average diameter of cementite: 0.3 μm to 2.2 μm, wherein a coefficient of micro-friction of ferrite on a surface of the steel sheet is less than 0.5.

1 . A high-carbon steel sheet, comprising:
 a chemical composition represented by, in mass %:   C: 0.30% to 0.70%,   Si: 0.07% to 1.00%,   Mn: 0.20% to 3.00%,   Ti: 0.010% to 0.500%,   Cr: 0.01% to 1.50%,   B: 0.0004% to 0.0035%,   P: 0.025% or less,   Al: 0.100% or less,   S: 0.0100% or less,   N: 0.010% or less,   Cu: 0.500% or less,   Nb: 0.000% to 0.500%,   Mo: 0.000% to 0.500%,   V: 0.000% to 0.500%,   W: 0.000% to 0.500%,   Ta: 0.000% to 0.500%,   Ni: 0.000% to 0.500%,   Mg: 0.000% to 0.500%,   Ca: 0.000% to 0.500%,   Y: 0.000% to 0.500%,   Zr: 0.000% to 0.500%,   La: 0.000% to 0.500%,   Ce: 0.000% to 0.500%, and   balance: Fe and impurities; and   a structure represented by:   a spheroidized ratio of cementite: 80% or more; and   an average diameter of cementite: 0.3 μm to 2.2 μm, wherein   a coefficient of micro-friction of ferrite on a surface of the steel sheet is less than 0.5.   
     
     
         2 . The high-carbon steel sheet according to  claim 1 , wherein
 the high-carbon steel sheet contains one or more selected from the group consisting of:   Nb: 0.001% to 0.500%;   Mo: 0.001% to 0.500%;   V: 0.001% to 0.500%;   W: 0.001% to 0.500%;   Ta: 0.001% to 0.500%;   Ni: 0.001% to 0.500%;   Mg: 0.001% to 0.500%;   Ca: 0.001% to 0.500%;   Y: 0.001% to 0.500%;   Zr: 0.001% to 0.500%;   La: 0.001% to 0.500%; and   Ce: 0.001% to 0.500%.   
     
     
         3 . A method of manufacturing a high-carbon steel sheet, comprising:
 hot-rolling of a slab so as to obtain a hot-rolled steel sheet;   pickling of the hot-rolled steel sheet; and   annealing of the hot-rolled steel sheet after the pickling,   the slab comprising a chemical composition represented by, in mass %:   C: 0.30% to 0.70%,   Si: 0.07% to 1.00%,   Mn: 0.20% to 3.00%,   Ti: 0.010% to 0.500%,   Cr: 0.01% to 1.50%,   B: 0.0004% to 0.0035%,   P: 0.025% or less,   Al: 0.100% or less,   S: 0.0100% or less,   N: 0.010% or less,   Cu: 0.500% or less,   Nb: 0.000% to 0.500%,   Mo: 0.000% to 0.500%,   V: 0.000% to 0.500%,   W: 0.000% to 0.500%,   Ta: 0.000% to 0.500%,   Ni: 0.000% to 0.500%,   Mg: 0.000% to 0.500%,   Ca: 0.000% to 0.500%,   Y: 0.000% to 0.500%,   Zr: 0.000% to 0.500%,   La: 0.000% to 0.500%,   Ce: 0.000% to 0.500%, and   balance: Fe and impurities, wherein   in the hot-rolling,   the slab is heated at a temperature of 1000° C. or more and less than 1150° C.,   a finish rolling temperature is 830° C. or more and 950° C. or less, and   a coiling temperature is 450° C. or more and 700° C. or less, and   the annealing comprises:   retaining the hot-rolled steel sheet at a temperature of 730° C. or more and 770° C. or less for 3 hours or more and 60 hours or less; and   then cooling the hot-rolled steel sheet down to 650° C. at a cooling rate of 1° C./hr or more and 60° C./hr or less.   
     
     
         4 . The method of manufacturing the high-carbon steel sheet according to  claim 3 , wherein
 the slab contains one or more selected from the group consisting of:   Nb: 0.001% to 0.500%;   Mo: 0.001% to 0.500%;   V: 0.001% to 0.500%;   W: 0.001% to 0.500%;   Ta: 0.001% to 0.500%;   Ni: 0.001% to 0.500%;   Mg: 0.001% to 0.500%;   Ca: 0.001% to 0.500%;   Y: 0.001% to 0.500%;   Zr: 0.001% to 0.500%;   La: 0.001% to 0.500%; and   Ce: 0.001% to 0.500%.