STEEL MATERIAL HAVING SUPERIOR TOUGHNESS IN WELD HEAT-AFFECTED ZONE AND PROCESS FOR PRODUCING THE SA

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PURPOSE : A steel material having excellent toughness in a weld heat-affected zone, which can improve toughness of the weld heat-affected zone by compositely adding a rare earth metal and/or Ca and Zr to the steel material such that the steel material contains an oxide of the rare earth metal and/or CaO and ZrO2, and a method for producing the same are provided. CONSTITUTION : A steel material having excellent toughness in a weld heat-affected zone comprises, by mass percent, 0.01 to 0.2%% of C, 0.5%% or less(with 0%% being excluded) of Si, 2.5%% or less(with 0%% being excluded) of Mn and 0.01%% or less(with 0%% being excluded) of N, satisfies 0.02%% or less(with 0%% being included) of P, 0.015%% or less(with 0%% being included) of S and 0.01%% or less(with 0%% being included) of Al at the same time, and further comprises 0.001 to 0.1%% of a REM(rare earth metal) and/or 0.0003 to 0.02%% of Ca, 0.001 to 0.05%% of Zr, and Fe and inevitable impurities, wherein the steel material contains an oxide of the REM and/or CaO and ZrO2 as oxides in steel. © KIPO 2007