High strength thin steel sheet having high hydrogen embrittlement resisting property
The purpose of the present invention is to provide a high strength thin steel sheet that has high hydrogen embrittlement resisting property. In order to achieve the above purpose, a high strength thin steel sheet having high hydrogen embrittlement resisting property comprises: C: 0.10 to 0.25%; Si: 1.0 to 3.0%; Mn: 1.0 to 3.5%; P: 0.15% or less; S: 0.02% or less; and Al: 1.5% or less (higher than 0%) in terms of percentage by weight, with balance of iron and inevitable impurities; and the metal structure comprises: residual austenite; 1% by area or more in proportion to the entire structure; bainitic ferrite and martensite: 80% or more in total; and ferrite and pearlite: 9% or less (may be 0%) in total, while the mean axis ratio (major axis/minor axis) of said residual austenite grains is 5 or higher, and the steel has tensile strength of 1180 MPa or higher.
1 . A high strength thin steel sheet having high hydrogen embrittlement resisting property, which comprises:
C: 0.10 to 0.25%;
Si: 1.0 to 3.0%;
Mn: 1.0 to 3.5%;
P: 0.15% or less;
S: 0.02% or less; and
Al: 1.5% or less (higher than 0%) in terms of percentage by weight, with balance of iron and inevitable impurities; wherein the metal structure comprises:
residual austenite; 1% by area or more in proportion to the entire structure;
bainitic ferrite and martensite: 80% or more in total; and ferrite and pearlite: 9% or less (may be 0%) in total, while the mean axis ratio (major axis/minor axis) of said residual austenite grains is 5 or higher, and the steel has tensile strength of 1180 MPa or higher.
2 . The high strength thin steel sheet according to claim 1 , wherein the metal structure further satisfies the requirements that:
mean length of minor axes of said residual austenite grains is 1 μm or less; and
minimum distance between said residual austenite grains is 1 μm or less.
3 . The high strength thin steel sheet according to claim 1 , wherein 0.5% or less (higher than 0%) by weight of Al is contained.
4 . The high strength thin steel sheet according to claim 1 , wherein
0.003 to 0.5% of Cu and/or
0.003 to 1.0% of Ni
in terms of percentage by weight are further contained.
5 . The high strength thin steel sheet according to claim 1 , wherein
0.003 to 1.0% of Ti and/or V
in terms of percentage by weight are further contained.
6 . The high strength thin steel sheet according to claim 1 , wherein
1.0% or less (higher than 0%) of Mo and
0.1% or less (higher than 0%) of Nb
in terms of percentage by weight are further contained.
7 . The high strength thin steel sheet according to claim 1 , wherein 0.0002 to 0.01% of B in terms of percentage by weight is further contained.
8 . The high strength thin steel sheet according to claim 1 , wherein at least one element selected from the group consisting of:
0.0005 to 0.005% of Ca;
0.0005 to 0.01% of Mg; and
0.0005 to 0.01% of REM
in terms of percentage by weight is further contained.
9 . A high strength thin steel sheet having high hydrogen embrittlement resisting property, which comprises:
C: 0.10 to 0.25%;
Si: 1.0 to 3.0%;
Mn: 1.0 to 3.5%;
P: 0.15% or less;
S: 0.02% or less; and
Al: 1.5% or less (higher than 0%) in terms of percentage by weight,
with balance of iron and inevitable impurities,
wherein the metal structure comprises: residual austenite of 1% by area or more in proportion to the entire structure,
while the mean axis ratio (major axis/minor axis) of said residual austenite grains is 5 or higher;
mean length of minor axes of said residual austenite grains is 1 μm or less; and
minimum distance between said residual austenite grains is 1 μm or less; and
the steel has tensile strength of 1180 MPa or higher.
10 . The high strength thin steel sheet according to claim 9 , wherein 0.5% or less (higher than 0%) by weight of Al is contained.
11 . The high strength thin steel sheet according to claim 9 , wherein
0.003 to 0.5% of Cu and/or
0.003 to 1.0% of Ni
in terms of percentage by weight are further contained.
12 . The high strength thin steel sheet according to claim 9 , wherein
0.003 to 1.0% of Ti and/or V
in terms of percentage by weight are further contained.
13 . The high strength thin steel sheet according to claim 9 , wherein
1.0% or less (higher than 0%) of Mo and
0.1% or less (higher than 0%) of Nb
in terms of percentage by weight are further contained.
14 . The high strength thin steel sheet according to claim 9 , wherein 0.0002 to 0.01% of B in terms of percentage by weight is further contained.
15 . The high strength thin steel sheet according to claim 9 , wherein at least one element selected from the group consisting of:
0.0005 to 0.005% of Ca;
0.0005 to 0.01% of Mg; and
0.0005 to 0.01% of REM
in terms of percentage by weight is further contained.