| 摘要 |
PURPOSE: A thick steel sheet with the excellent cryogenic temperature toughness is provided to have the excellent cryogenic temperature toughness at a temperature of -196°C, and to implement that the rate of brittle fracture surface is 10% or less. CONSTITUTION: A thick steel sheet with the excellent cryogenic temperature toughness contains 0.02 to 0.10 mass% of C, 0.40 mass% or less of Si, 0.50 to 2.0 mass% of Mn, 0.007 mass% or less of P, 0.007 mass% or less of S, 0.005 to 0.050 mass% of Al, 5.0 to 7.5 mass% of Ni, 0.010 mass% or less of N, and the remaining material having Fe and unavoidable impurities. The remaining austenite phase that is present at a temperature of -196°C is 2.0 vol% to 12.0 vol%. Moreover, the average diameter per original state of the inclusion that has the diameter per original state is above 2.0 μm is 3.5 μm or less. The remaining austenite phase that is present at a temperature of -196°C is 4.0 vol% to 12.0 vol%. |
