| 摘要 |
PROBLEM TO BE SOLVED: To provide a thick steel plate for ultra-low temperature, having excellent fracture resistance safety even under ultra-low temperature environment.SOLUTION: A thick steel plate for ultra-low temperature has a yield strength of 590 MPa or more and contains, by mass%, C:0.01 to 0.12%, Si:0.01 to 0.30%, Mn:0.4 to 2.0%, P:0.05% or less, S:0.008% or less, Ni:5.0% to 7.5%, sol.Al:0.002 to 0.080% and N:0.0050% or less and the remainder being Fe with impurities, and has a residual γ content of 4.0 to 25.0 vol.%, an average circle-equivalent particle diameter of residual γ of 1.0 μm or less, the number of residual γ particles having the average circle-equivalent particle diameter of 0.2 μm or less of 1.0×10/mmor more and a lattice constant of residual γ of 0.3585 nm or more at the 1/4 t position (t:plate thickness). |
