Tenacity excellent high intensity thick steel plate for high heat energy input welding heat influenced part

Abstract

The invention provides a high-tension plate steel with excellent HAZ toughness. In respect of quality percent, the chemical composition thereof contains 0.02-0.12 percent of C, 0-0.40 percent of Si, 1.0-2.0 percent of Mn, 0-0.030 percent of P, 0.001-0.025 percent of S, 0-0.050 percent of Al, 0.005-0.100 percent of Ti, 0.0001-0.0500 percent of REM, 0.0001-0.0500 percent of Zr, 0.0020-0.0300 percent of N, and 0.0005-0.0100 percent of O; remnant parts are Fe and inevitable impurities; when content of oxide with a circle diameter measured to be less than 2 [mu]m is 500 / mm<2>, content of oxysulfide with a circle diameter measured to be more than 2 [mu]m is 40-1000 / cm<2>, and when REM and Mn and the like specified oxide for forming oxysulfide with a circle diameter measured to be more than 2 [mu]m are respectively REM2O3 and MnO2, etc., conversion value of oxide of REM, conversion value of oxide of Mn, oxide conversion value of each specified oxide conversion value calculated according to concentration of S relative to average concentration of each element forming the xoysulfide, and proportion of total value of mean concentration of S in oxysulfide are: oxide equivalent value of REM is over 10 percent; oxide equivalent value of Mn is less than 20 percent; oxide equivalent value of S is 3-20 percent.

Description

technical field [0001] The present invention relates to a high-tensile high-tensile thick steel plate for welding that is used as a structural material in the fields of shipbuilding and construction, and has excellent toughness in the welding heat-affected zone (hereinafter referred to as "HAZ") during high heat energy input welding. Background technique [0002] Generally speaking, steel materials used as structural materials in fields such as shipbuilding and construction are joined into desired shapes by welding. Therefore, in addition to the toughness of the base metal, these steels must also have excellent HAZ toughness. [0003] In recent years, with the enlargement of welded structures in the construction and shipbuilding fields, the scope of application of thick steel plates with a plate thickness of 50 mm or more has been expanded. At the same time, high heat input welding is required for the purpose of improving welding efficiency and reducing construction costs. ...

AI Technical Summary

Problems solved by technology

[0018] However, until now, TiN has been mainly used as a means to ensure HAZ toughness. The increase in welding heat energy input in recent years has led to the disappearance or coarsening of TiN particles during welding, making it difficult to achieve sufficient microstructure.

In addition, for the microstructure technology that suppresses the coarsening of γ grains and promotes intragranular α transformation by using intermediates such as oxides or sulfides that are stable at high temperatures compared to TiN, it is important to suppress the coarsening of γ grains and promote intragranular α transformation. The alpha metamorphosis also makes it difficult to disperse oxysulfides

In addition, as oxysulfides effective in promoting intragranular α transformation, oxysulfides having good lattice integration with the α phase have been proposed, but the obtained HAZ toughness is limited when focusing only on the lattice integration.

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