Abstract: The high-strength thick steel plate for storage container contains: C: 0.12-0.16% (means mass %, hereinafter the same), Si: 0.05-0.5%, Mn: 1-1.5%, Al: 0.01-0.05%, Nb: 0.003-0.02%, Mo: 0.03-0.3%, V: 0.025-0.04%, Cr: 0.05-0.3%, Cu: 0.05-0.5%, Ni: 0.15-0.55%, Ca: 0.0005-0.006% respectively, and the RP value as defined by an equation (1) below satisfies the relation of RP?4.5×10?8. RP={[Nb]/93+1/60×[V]/51}×[Mo]/96??(1) where [Nb], [V] and [Mo] respectively represent the content (mass %) of Nb, V and Mo.

Abstract: A high-strength steel sheet is provided which, even when subjected to long-term stress-relief annealing after welding, decreases little in strength and which has satisfactory low-temperature HAZ toughness. The high-strength steel sheet has a chemical composition adequately regulated and has a CP value defined by the following equation (1) of 5.40% or higher and a carbon equivalent (Ceq) defined by the following equation (2) of 0.45% or lower. CP value=125[Ti]+111[Nb]+60[V]+15[Mo] (1) ([Ti], [Nb], [V], and [Mo] indicate the contents (mass %) of Ti, Nb, V, and Mo, respectively.) Ceq=[C]+[Mn]/6+([Cr]+[Mo]+[V])/5+([Cu]+[Ni])/15 (2) ([C], [Mn], [Cr], [Mo], [V], [Cu], and [Ni] indicate the contents (mass %) of C, Mn, Cr, Mo, V, Cu, and Ni, respectively.

Abstract: A high-strength steel sheet according to the present invention not only is suitably adjusted in its chemical elements composition, but also has a DE value defined by the following Equation (1) of 0.0340% or more, and a carbon equivalent Ceq defined by the following Equation (2) of 0.45% or less: DE value=[Ti]+[Nb]+0.3[V]+0.0075[Cr]??(1) where, [Ti], [Nb], [V], and [Cr] represent contents (mass %) of Ti, Nb, V, and Cr, respectively; Ceq=[C]+[Mn]/6+([Cr]+[Mo]+[V])/5+([Cu]+[Ni])/15 ??(2) where, [C], [Mn], [Cr], [Mo], [V], [Cu], and [Ni] represent contents (mass %) of C, Mn, Cr, Mo, V, Cu, and Ni, respectively. A high-strength steel sheet resistant to strength reduction and good in low-temperature toughness of HAZ even when subjected for a long time to a stress-relief annealing process after being processed by welding, is provided.

Abstract: The high-strength thick steel plate for storage container contains: C: 0.12-0.16% (means mass %, hereinafter the same), Si: 0.05-0.5%, Mn: 1-1.5%, Al: 0.01-0.05%, Nb: 0.003-0.02%, Mo: 0.03-0.3%, V: 0.025-0.04%, Cr: 0.05-0.3%, Cu: 0.05-0.5%, Ni: 0.15-0.55%, Ca: 0.0005-0.006% respectively, and the RP value as defined by an equation (1) below satisfies the relation of RP?4.5×10?8. RP?{[Nb]/93+ 1/60×[V]/51}×[Mo]/96??(1) where [Nb], [V] and [Mo] respectively represent the content (mass %) of Nb, V and Mo.

Abstract: A high-strength steel sheet is provided which, even when subjected to long-term stress-relief annealing after welding, decreases little in strength and which has satisfactory low-temperature HAZ toughness. The high-strength steel sheet has a chemical composition adequately regulated and has a CP value defined by the following equation (1) of 5.40% or higher and a carbon equivalent (Ceq) defined by the following equation (2) of 0.45% or lower. CP value=125[Ti]+111[Nb]+60[V]+15[Mo] (1) ([Ti], [Nb], [V], and [Mo] indicate the contents (mass %) of Ti, Nb, V, and Mo, respectively.) Ceq=[C]+[Mn]/6+([Cr]+[Mo]+[V])/5+([Cu]+[Ni])/15 (2) ([C], [Mn], [Cr], [Mo], [V], [Cu], and [Ni] indicate the contents (mass %) of C, Mn, Cr, Mo, V, Cu, and Ni, respectively.

Abstract: A high-strength steel sheet according to the present invention not only is suitably adjusted in its chemical elements composition, but also has a DE value defined by the following Equation (1) of 0.0340% or more, and a carbon equivalent Ceq defined by the following Equation (2) of 0.45% or less: DE value=[Ti]+[Nb]+0.3[V]+0.0075[Cr]??(1) where, [Ti], [Nb], [V], and [Cr] represent contents (mass %) of Ti, Nb, V, and Cr, respectively; Ceq=[C]+[Mn]/6+([Cr]+[Mo]+[V])/5+([Cu]+[Ni])/15 ??(2) where, [C], [Mn], [Cr], [Mo], [V], [Cu], and [Ni] represent contents (mass %) of C, Mn, Cr, Mo, V, Cu, and Ni, respectively. A high-strength steel sheet resistant to strength reduction and good in low-temperature toughness of HAZ even when subjected for a long time to a stress-relief annealing process after being processed by welding, is provided.