High tension steel plate for high heat energy input with excellent low temperature toughness base metal

Abstract

The invention relates to a steel plate with compositions in prescriptive range, which mainly comprises Bainite phase. In a t / 4 (t represents thickness of the plate, the same below) deep position from surface, when region enclosed by two crystallized large angle grain boundary with 15 DEG C azimuth error is used as grain, average equivalent weight circle diameter DA of the grain measured by an electron backscatter diffraction imaging method is less than 10 mum, and predictive largest grain size DM obtained by calculating grain size of the grain measured by the electron backscatter diffraction imaging method according to an extremum statistical method is less than 80 mum. According to the composition, problems of cost and production are not occurred, strength and toughness of parent metal are excellent, and toughness of welding heat infection part is also excellent when carrying high heat energy input welding.

Description

technical field [0001] The present invention relates to a high-tensile steel plate mainly used as an extremely thick material (thickness: 50 to 80 mm) used for ships, and in particular to a heat-affected zone of a base material that has excellent strength and toughness and is welded with high heat energy input High tensile steel sheet for high heat input welding with excellent toughness. Background technique [0002] In recent years, the large-scale propulsion of the main ship types, especially the ultra-large-scale propulsion of the container ship with a stacked number from 6,000TEU to 10,000TEU, is the type of ship with the most stringent longitudinal strength of the large deck opening, which requires the use of high tension Steel plate and extremely thick material. In addition, in the use of high-tensile steel sheets, in order to suppress brittle fracture, the toughness level has to be considered. Even for important parts used to ensure longitudinal strength in container...

AI Technical Summary

Problems solved by technology

However, in order to make the microstructure into ultra-fine ferrite, it is necessary to experience 3 It is not preferable from the viewpoint of productivity to stop cooling at a temperature below the phase transition point and reheat the reverse phase transition process more than once.

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