Steel material having superior toughness of welded heat-affected zone, and method for manufacturing same

Abstract

This steel material satisfies the following conditions:(a) the ZrO2 content is 5-50%, the REM oxide content is 5-50%, and the CaO content is 50% or less (excluding 0%) when the composition of all oxide-based inclusions is measured and then expressed in terms of the mass of the individual oxides; (b) among all the inclusions, those having a circle equivalent diameter of 0.1-2 [mu]m are present in an amount of 120 / mm2 or greater, oxides larger than 3 [mu]m are present in an amount of 5.0 / mm2 or less, and oxides larger than 5 [mu]m are present in an amount of 5.0 / mm2 or less; and, when the composition of all the inclusions is measured, (c-1) the number of REM- and Zr-containing inclusions I that satisfy the REM / Zr molar ratio of 0.6-1.4 is 30% or greater in relation to the entire number of inclusions, and / or (c-2) the number of REM-, Zr-, Al-, Ca-, and Ti-containing inclusions II is 40% or greater in relation to the entire number of inclusions, inclusions II satisfying the condition in which the ratio of the total number of moles of REM and Zr and the total number of moles of Al, Ca, and Ti is 0.5-1.2. The HAZ toughness is thereby kept at a very high level even when the material is welded with a high heat input of 50 kJ / mm or greater.

Description

technical field [0001] The present invention relates to a steel material used in bridges, high-rise buildings, ships, etc., and more particularly to a part (hereinafter, sometimes referred to as "welding heat-affected zone" or "HAZ") that is affected by heat during welding. A steel material with superior toughness and a method for manufacturing the same. Background technique [0002] The properties required of steel materials used in bridges, high-rise buildings, ships, etc. have become increasingly strict in recent years, and particularly good toughness is required. These steel materials are generally joined by welding, but among the welded joints, especially the HAZ is affected by heat during welding, and there is a problem that the toughness tends to deteriorate. This deterioration in toughness becomes more pronounced as the heat input during welding increases. The reason for this is considered to be that when the heat input during welding increases, the cooling rate of ...

AI Technical Summary

Problems solved by technology

These steel materials are generally joined by welding, but the welded joints, especially the HAZ, are affected by heat during welding, and there is a problem that the toughness tends to deteriorate.

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