| 摘要 |
<p><P>PROBLEM TO BE SOLVED: To provide a steel material for very low temperature use, which is excellent in fracture toughness; to provide a method for manufacturing the steel material; and to provide an LNG tank to which the steel material is applied. <P>SOLUTION: The steel material for very low temperature includes, by mass, 0.01-0.12% of C, 0.01-0.3% of Si, 0.4-2.0% of Mn,≤0.05% of P,≤0.008% of S, >5.0 and <10.0% of Ni, 0.002-0.08% of Al, 0.0015-0.0040% of N, and the balance Fe with impurities, and is characterized in that the residualγquantity at a position of (1/4)t of the plate thickness t is≥3.0 vol.%, the value represented by formula (1) below is≥1.3, and the reduction rate of the residualγquantity is≤25% when the steel material is subjected to a plastic strain of 1% under an environment of -165°C. (1):σ<SB POS="POST">y,-165°C</SB>/σ<SB POS="POST">y,RT</SB>, wherein,σ<SB POS="POST">y,-165°C</SB>represents yield strength [MPa] at -165°C, andσ<SB POS="POST">y,RT</SB>represents yield strength [MPa] at room temperature. <P>COPYRIGHT: (C)2013,JPO&INPIT</p> |
