Nickel-containing steel for low temperature service and low-temperature tank
A nickel-containing steel for low temperature service having a determined chemical composition of a Ni content of from 5.0 to 8.0%, in which the volume fraction of retained austenite in a region of 1.5 mm from a surface in the thickness direction is from 3.0 to 20.0% by volume, and the ratio of the hardness in a region of 1.0 mm from a surface in the thickness direction to the hardness in a region of ¼ of the thickness from a surface in the thickness direction is 1.1 or less, and a low-temperature tank using the nickel-containing steel for low temperature service.
1. A nickel-containing, steel for low temperature service, the steel comprising, in percentage by mass:
from 0.01 to 0.15% of C,
from 0.01 to 2.00% of Si,
from 0.20 to 2.00% of Mn,
0.010% or less of P,
0.0100% or less of S,
from 5.0 to 8.0% of Ni,
from 0.005 to 2.000% of Al
from 0.0010 to 0.0100% of N,
from 0 to 1.00% of Cu,
from 0 to 0.80% of Sn,
from 0 to 0.80% of Sb,
from 0 to 2.00% of Cr,
from 0 to 1.00% of Mo,
from 0 to 1.00% of W,
from 0 to 1.00% of V,
from 0 to 0.100% of Nb,
from 0 to 0.100% of Ti,
from 0 to 0.0200% of Ca,
from 0 to 0.0500% of B,
from 0 to 0.0100% of Mg,
from 0 to 0.0200% of REM, and
a balance being Fe and impurities,
wherein a volume fraction of retained austenite in a region 1.5 mm from a surface of the steel in a thickness direction, is from 3.0 to 20.0% by volume, and
wherein a ratio of a hardness in a region 1.0 mm from the surface in the thickness direction to a hardness in a region ¼ of the thickness from the surface in the thickness direction, is 1.1 or less.
2. The nickel-containing steel for low temperature service according to claim 1 ,
wherein a content of Si is from 0.01 to 0.60% by mass.
3. The nickel-containing steel for low temperature service according to claim 1 , wherein a content of Al is from 0.005 to 0.100% by mass.
4. The nickel-containing steel for low temperature service according to claim 1 , having a yield strength of from 590 to 800 MPa, a tensile strength of from 690 to 830 MPa, and a Charpy impact absorbed energy at −196° C., of 150 J or more.
5. The nickel-containing steel for low temperature service according to claim 1 , having a thickness of from 6 to 50 mm.
6. A low-temperature tank comprising the nickel-containing steel for low temperature service according to claim 1 .
7. The low-temperature tank according to claim 6 , wherein a content of Si is from 0.01 to 0.60% by mass.
8. The low-temperature tank according to claim 6 , wherein a content of Al is from 0.005 to 0.100% by mass.
9. The low-temperature tank according to claim 6 , the nickel-containing steel for low temperature service having a yield strength of from 590 to 800 MPa, a tensile strength of from 690 to 830 MPa, and a Charpy impact absorbed energy at −196° C., of 150 J or more.
10. The low-temperature tank according to claim 6 , the nickel-containing steel for low temperature service having a thickness of from 6 to 50 mm.