Zinc-plated steel sheet and method for producing same

Abstract

The zinc-plated steel sheet includes a base steel sheet having a predetermined chemical composition, a Fe—Al alloy layer formed on at least a part of a surface of the base steel sheet, and a zinc-plated layer formed on the base steel sheet surface or a surface of the Fe—Al alloy layer, the base steel sheet has an internal oxide layer of 0.2 μm or more in a sheet thickness direction from the base steel sheet surface, the Fe—Al alloy layer has an average thickness of 1 nm or more and less than 100 nm, and in a cross section in a thickness direction, the grain boundary coverage by an oxide is 60% or more in the internal oxide layer, a coverage of the base steel sheet surface by the Fe—Al alloy layer is 40% or more, and the tensile strength is 980 MPa or more and 2000 MPa or less.

What is claimed is: 
     
         1 . A zinc-plated steel sheet comprising:
 a base steel sheet;   a Fe—Al alloy layer formed on at least a part of a surface of the base steel sheet; and   a zinc-plated layer formed on the surface of the base steel sheet or a surface of the Fe—Al alloy layer,   wherein, the base steel sheet has a chemical composition including, in mass %,   C: 0.10 to 0.40%,   Si: 0.10 to 3.00%,   Mn: 1.00 to 5.00%,   sol.Al: 0.001 to 1.500%,   P: 0.0010 to 0.0300%,   S: 0.0200% or less,   N: 0.0100% or less,   O: 0.0100% or less,   Ti: 0 to 0.200%,   B: 0 to 0.0100%,   Cr: 0 to 1.000%,   Mo: 0 to 1.000%,   Ni: 0 to 1.000%,   Cu: 0 to 1.000%,   Sn: 0 to 0.500%,   Nb: 0 to 0.200%,   V: 0 to 0.500%,   W: 0 to 0.500%,   Ca: 0 to 0.0100%,   Mg: 0 to 0.0100%,   Bi: 0 to 0.0100%,   Sb: 0 to 0.1000%,   Zr: 0 to 0.0100%,   REM: 0 to 0.1000%, and   a remainder: Fe and an impurity,   the base steel sheet has an internal oxide layer of 0.2 μm or more in a sheet thickness direction from the surface of the base steel sheet,   the Fe—Al alloy layer has an average thickness of 1 nm or more and less than 100 nm,   in a cross section in a thickness direction,   a grain boundary coverage by an oxide is 60% or more in the internal oxide layer,   a coverage of the surface of the base steel sheet by the Fe—Al alloy layer is 40% or more, and   a tensile strength is 980 MPa or more and 2000 MPa or less.   
     
     
         2 . The zinc-plated steel sheet according to  claim 1 , wherein
 the chemical composition of the base steel sheet contains, in mass %, one or more selected from the group consisting of   Ti: 0.005 to 0.200%,   B: 0.0005 to 0.0100%,   Cr: 0.001 to 1.000%,   Mo: 0.001 to 1.000%,   Ni: 0.001 to 1.000%,   Cu: 0.001 to 1.000%,   Sn: 0.001 to 0.500%,   Nb: 0.001 to 0.200%,   V: 0.001 to 0.500%,   W: 0.001 to 0.500%,   Ca: 0.0001 to 0.0100%,   Mg: 0.0001 to 0.0100%,   Bi: 0.0001 to 0.0100%,   Sb: 0.0001 to 0.1000%,   Zr: 0.0001 to 0.0100%, and   REM: 0.0001 to 0.1000%.   
     
     
         3 . A method for manufacturing a zinc-plated steel sheet, the method comprising:
 an annealing step of holding a steel sheet at an annealing temperature of 700 to 1000° C. for 1 second or more to anneal the steel sheet, the steel sheet having a chemical composition including, in mass %, C: 0.10 to 0.40%, Si: 0.10 to 3.00%, Mn: 1.00 to 5.00%, sol.Al: 0.001 to 1.500%, P; 0.0010 to 0.0300%, S: 0.0200% or less, N: 0.0100% or less, O: 0.0100% or less, Ti: 0 to 0.200%, B: 0 to 0.0100%, Cr: 0 to 1.000%, Mo: 0 to 1.000%, Ni: 0 to 1.000%, Cu: 0 to 1.000%, Sn: 0 to 0.500%, Nb: 0 to 0.200%, V: 0 to 0.500%, W: 0 to 0.500%, Ca: 0 to 0.0100%, Mg: 0 to 0.0100%, Bi: 0 to 0.0100%, Sb: 0 to 0.1000%, Zr: 0 to 0.0100%, REM: 0 to 0.1000%, and a remainder: Fe and an impurity; and   a plating step of forming a zinc-plated layer on a surface of the steel sheet after the annealing step, wherein   in the annealing step, in a heating process to the annealing temperature, an average heating rate in a first temperature range of 400 to 650° C. is 2.0° C./sec or more, and an average heating rate in a second temperature range of 650° C. to the annealing temperature is 0.5 to 5.0° C./sec and an atmosphere having (P(H2O)/P(H2)) in the second temperature range is 0.05 to 2.00,   in the plating step, the steel sheet is cooled to a temperature of 440 to 550° C. at an average cooling rate of 0.5° C./sec or more, is immersed in a plating bath containing Zn as a main component and having an effective Al amount of 0.050 to 0.250 mass %, is pulled up from the plating bath, then is cooled so that a temperature of the steel sheet reaches 400° C. within 10 seconds, and subsequently is cooled to 350° C. or less so that at an average cooling rate from 400° C. to 350° C. is 1.0° C./sec or more and 5.0° C./sec or less.