High-strength hot-dip galvanized steel sheet excellent in impact resistance property and high-strength alloyed hot-dip galvanized steel sheet
View Patent ↗A base steel sheet has a hot-dip galvanized layer formed on a surface thereof, in which, in a steel sheet structure in a range of ⅛ thickness to ⅜ thickness centered around ¼ thickness of a sheet thickness from a surface, a volume fraction of a retained austenite phase is 5% or less, and a total volume fraction of phases of bainite, bainitic ferrite, fresh martensite, and tempered martensite is 40% or more, an average effective crystal grain diameter is 5.0 μm or less, a maximum effective crystal grain diameter is 20 μm or less, and a decarburized layer with a thickness of 0.01 μm to 10.0 μm is formed on a surface layer portion, in which a density of oxides dispersed in the decarburized layer is 1.0×10 12 to 1.0×10 16 oxides/m 2 , and an average grain diameter of the oxides is 500 nm or less.
1. A high-strength hot-dip galvanized steel sheet excellent in impact resistance property, comprising
a hot-dip galvanized layer formed on a surface of a base steel sheet containing, by mass %,
C: 0.075 to 0.400%,
Si: 0.01 to 2.00%,
Mn: 0.80 to 3.50%,
P: 0.0001 to 0.100%,
S: 0.0001 to 0.0100%,
Al: 0.001 to 2.00%,
O: 0.0001 to 0.0100%,
N: 0.0001 to 0.0100%, and
a balance composed of Fe and inevitable impurities, wherein:
the base steel sheet has a steel sheet structure in a range of ⅛ thickness to ⅜ thickness centered around ¼ thickness of a sheet thickness from a surface, in which a volume fraction of a retained austenite phase is 5% or less, and a total volume fraction of a bainite phase, a bainitic ferrite phase, a fresh martensite phase and a tempered martensite phase is 40% or more;
an average effective crystal grain diameter and a maximum effective crystal grain diameter in the range of ⅛ thickness to ⅜ thickness centered around ¼ thickness of the sheet thickness from the surface are 5.0 μm or less and 20 μm or less, respectively; and
a decarburized layer with a thickness of 0.01 μm to 10.0 μm is formed on a surface layer portion, in which a density of oxides dispersed in the decarburized layer is 1.0×10 12 to 1.0×10 16 oxides/m 2 , and an average grain diameter of the oxides is 500 nm or less.
2. The high-strength hot-dip galvanized steel sheet excellent in impact resistance property according to claim 1 , wherein
the base steel sheet further contains, by mass %, one or two or more selected from
Ti: 0.001 to 0.150%,
Nb: 0.001 to 0.100%, and
V: 0.001 to 0.300%.
3. The high-strength hot-dip galvanized steel sheet excellent in impact resistance property according to claim 1 , wherein
the base steel sheet further contains one or two or more selected from
Cr: 0.01 to 2.00%,
Ni: 0.01 to 2.00%,
Cu: 0.01 to 2.00%,
Mo: 0.01 to 2.00%,
B: 0.0001 to 0.0100%, and
W: 0.01 to 2.00%.
4. The high-strength hot-dip galvanized steel sheet excellent in impact resistance property according to claim 1 , wherein
the base steel sheet further contains 0.0001 to 0.0100% in total of one or two or more selected from Ca, Ce, Mg, Zr, La, and REM.
5. A high-strength alloyed hot-dip galvanized steel sheet excellent in impact resistance property, comprising
the hot-dip galvanized layer of the high-strength hot-dip galvanized steel sheet according to claim 1 , the hot-dip galvanized layer being alloyed.