Hot pressed member and method of producing same, and coated steel sheet for hot press forming

Abstract

A hot pressed member disclosed herein includes: a base steel sheet; a Fe—Zn—Al—Mg-based alloy coated layer containing an α-Fe phase and a Γ phase and formed on at least one surface of the base steel sheet; and an oxide layer containing Zn, Al, and Mg and formed on the Fe—Zn—Al—Mg-based alloy coated layer, in which a ratio of IΓ/Iα is 0.5 or less when measured by X-ray diffraction using a Co-Kα (wavelength: 1.79021 Å) radiation source at an incident angle of 25°, where IF is an intensity of a diffraction peak of (411) plane of the Γ phase present in an angular range of 41.5°≤2θ≤43.0° and Iα is an intensity of a diffraction peak of (110) plane of the α-Fe phase present in an angular range of 51.0°≤2θ≤52.0°, and a sum of Al and Mg concentrations in the oxide layer is 28 atomic % or more.

1 . A hot pressed member comprising:
 a base steel sheet;   a Fe—Zn—Al—Mg-based alloy coated layer containing an α-Fe phase and a Γ phase and formed on at least one surface of the base steel sheet at a coating weight per surface of 40 g/m 2  to 400 g/m 2 ; and   an oxide layer containing Zn, Al, and Mg and formed on the Fe—Zn—Al—Mg-based alloy coated layer, wherein   a ratio of I Γ /I α  is 0.5 or less when measured by X-ray diffraction using a Co-Kα (wavelength: 1.79021 Å) radiation source at an incident angle of 25°, where I Γ  is an intensity of a diffraction peak of (411) plane of the Γ phase present in an angular range of 41.5°≤2θ≤43.0° and I α  is an intensity of a diffraction peak of (110) plane of the α-Fe phase present in an angular range of 51.0°≤2θ≤52.0°, and   a sum of Al and Mg concentrations in the oxide layer is 28 atomic % or more.   
     
     
         2 . A method of producing a hot pressed member, the method comprising:
 heating a coated steel sheet for hot press forming to a temperature range of Ac 3  transformation point to 1000° C., the coated steel sheet for hot press forming comprising:
 a base steel sheet; and 
 a Zn—Al—Mg-based alloy coated layer formed on at least one surface of the base steel sheet at a coating weight per surface of 30 g/m 2  to 180 g/m 2 , having a chemical composition containing, in mass %, Al: 3% to 10% and Mg: 0.2% to 0.8%, with the balance being Zn and inevitable impurities, and having a liquidus temperature in an air atmosphere of 400° C. or lower, and 
   then subjecting the coated steel sheet to hot press forming.   
     
     
         3 . The method of producing a hot pressed member according to  claim 2 , wherein the chemical composition of the Zn—Al—Mg-based alloy coated layer further contains at least one selected from the group consisting of Ca, Sr, Mn, V, Cr, Mo, Ti, Ni, Co, Sb, Zr, and B in a total amount of 1 mass % or less. 
     
     
         4 . A coated steel sheet for hot press forming comprising:
 a base steel sheet; and   a Zn—Al—Mg-based alloy coated layer formed on at least one surface of the base steel sheet at a coating weight per surface of 30 g/m 2  to 180 g/m 2 , having a chemical composition containing, in mass %, Al: 3% to 10% and Mg: 0.2% to 0.8%, with the balance being Zn and inevitable impurities, and having a liquidus temperature in an air atmosphere of 400° C. or lower.   
     
     
         5 . The coated steel sheet for hot press forming according to  claim 4 , wherein the chemical composition of the Zn—Al—Mg-based alloy coated layer further contains at least one selected from the group consisting of Ca, Sr, Mn, V, Cr, Mo, Ti, Ni, Co, Sb, Zr, and B in a total amount of 1 mass % or less.