Abstract: A thick steel plate for high heat input welding and having great heat-affected area toughness and a manufacturing method therefor, comprising the steps of smelting, casting, rolling, and cooling. Chemical composition is properly controlled for the steel plate and satisfies 1?Ti/N?6 and Mg/Ti>0.017, where effective S content in steel=S?1.3 Mg?0.8 Ca?0.34 REM?0.35 Zr, and effective S content in steel: 0.0003-0.003%; finely dispersed inclusions may be formed in the steel plate, and the amount of composite inclusion MgO+Ti2O3+MnS in the steel plate is controlled at a proportion greater than or equal to 5%. The tensile strength of a base material so acquired is ?510 MPa, insofar as welding input energy is 200-400 kJ/cm, the average Charpy impact work of the steel plate at ?40 ° C. is 100 J or more, at the same time, the average Charpy aging impact work of the base material of ½ thickness at ?40° C. is 46 J or more.

Abstract: A thick steel plate for high heat input welding and having great heat-affected area toughness and a manufacturing method therefor, comprising the steps of smelting, casting, rolling, and cooling. Also, the chemical composition of the steel plate satisfies 1?Ti/N?6 and (Ca+REM+Zr)/Al?0.11, where the effective S content in steel=S-0.8Ca-0.34REM-0.35Zr. and the effective S content in steel: 0.0006-0.005%; finely dispersed inclusions may be formed, and the amount of composite inclusion CaO+Al2O3+MnS+TiN in the steel plate is at a proportion of ?12%. With respect to welding in which the thickness of the steel plate is 50-70 mm, the tensile strength of a base material is ?510 MPa. and welding input energy is 200-400 kJ/cm, the average Charpy impact work of a welding heat-affected area of the steel plate at ?40° C. is 100 J or more, and at the same time, the average Charpy aging impact work of the base material of ½ thickness at ?40° C. is 46 J or more.

Abstract: A thick steel plate for high heat input welding and having great heat-affected area toughness and a manufacturing method therefor, comprising the steps of smelting, casting, rolling, and cooling. Also, the chemical composition of the steel plate satisfies 1?Ti/N?6 and (Ca+REM+Zr)/Al?0.11, where the effective S content in steel=S-0.8Ca-0.34REM-0.35Zr. and the effective S content in steel: 0.0006-0.005%; finely dispersed inclusions may be formed, and the amount of composite inclusion CaO+Al2O3+MnS+TiN in the steel plate is at a proportion of ?12%. With respect to welding in which the thickness of the steel plate is 50-70 mm, the tensile strength of a base material is ?510 MPa. and welding input energy is 200-400 kJ/cm, the average Charpy impact work of a welding heat-affected area of the steel plate at ?40 ° C. is 100 J or more, and at the same time, the average Charpy aging impact work of the base material of ½ thickness at ?40° C. is 46 J or more.

Abstract: A thick steel plate for high heat input welding and having great heat-affected area toughness and a manufacturing method therefor, comprising the steps of smelting, casting, rolling, and cooling. Chemical composition is properly controlled for the steel plate and satisfies 1?Ti/N?6 and Mg/Ti>0.017, where effective S content in steel=S?1.3 Mg?0.8 Ca?0.34 REM?0.35 Zr, and effective S content in steel: 0.0003-0.003%; finely dispersed inclusions may be formed in the steel plate, and the amount of composite inclusion MgO+Ti2O3+MnS in the steel plate is controlled at a proportion greater than or equal to 5%. The tensile strength of a base material so acquired is ?510 MPa, insofar as welding input energy is 200?400 kJ/cm, the average Charpy impact work of the steel plate at ?40 ° C. is 100 J or more, at the same time, the average Charpy aging impact work of the base material of ½ thickness at ?40° C. is 46 J or more.