THICK STEEL PLATE HAVING EXCELLENT MACHINABILITY AND SURFACE WORKABILITY

摘要

PROBLEM TO BE SOLVED: To provide a thick steel plate in which the formation of coarse MnS causing working spots is suppressed without reducing the machinability of the steel, and the extension of MnS on hot working is suppressed.;SOLUTION: (1) The thick steel plate satisfies the concentration of solid solution Al in 0.01 to 0.07%, and the concentration of total Mg in 0.0005 to 0.01%, and in which, provided that the number of MnS inclusions with a minor axis of ≥5 μm containing compound oxide containing both of Al and Mg is defined as a, and the total number of MnS inclusions with a minor axis of ≥5 μm is defined as b, (a/b)×100≥30% is satisfied. (2) Alternatively, the thick steel plate satisfies the concentration of solid solution Al in 0.01 to 0.07%, and the concentration of solid solution Mg in 0.00001 to 0.0001%, and in which, provided that the number of MnS inclusions with a minor axis of ≥5 μm containing compound oxide containing both of Al and Mg is defined as a, and the total number of MnS inclusions with a minor axis of ≥5 μm is defined as b, (a/b)×100≥30% is satisfied.;COPYRIGHT: (C)2003,JPO