Tenacity excellent high intensity steel for welding heat influenced part

Abstract

Disclosed is a thick steel plate excellent in HAZ toughness even when welding with high heat energy, containing C: 0.03 to 0.12%, Si: 0.2% or less (including 0%), Mn: 1.0 to 2.0%, and P: 0.03% Below (excluding 0%), S: below 0.015% (excluding 0%), Al: below 0.10% (excluding 0%), Ti: 0.015-0.08%, N: 0.0060-0.0120% and B: 0.0010- 0.0050%, in addition to containing Nb: 0.005-0.020% and / or Zr: 0.0001-0.050%, and satisfying the relationship of formula (1), and calculated as 0.05μm or less in circle equivalent diameter, there are 5.0 Ti-containing nitrides per 1mm2 ×106 or more. [Ti]×16[Si]×(12-40[C])<0.38(%)...(1), where [Ti], [Si] and [C] represent the content of Ti, Si and C respectively ( quality%).

Description

Technical field [0001] The present invention relates to steel plates applicable to welded structures such as bridges, high-rise buildings, ships, etc., and particularly relates to steel plates having excellent toughness in the heat-affected zone (hereinafter only referred to as "HAZ") after high-heat welding. Background technique [0002] In recent years, as the various welded structures described above have increased in size, welding of thick steel plates with a plate thickness of 50 mm or more has become inevitable. Therefore, in all fields, from the viewpoint of improving welding efficiency, there is a situation in which high-heat welding with a heat energy of 50 kJ / mm or more is directed. [0003] However, if high-heat welding is performed, the HAZ is added to the high-temperature austenite region and then slowly cooled. Therefore, the structure of the HAZ (especially near the fusion zone of the HAZ) becomes coarser, and there is a problem that the toughness of this part tend...

AI Technical Summary

Problems solved by technology

In order to improve the toughness of the base material, it is known that the effective method is to lower the finish rolling temperature, but as the thickness of the steel plate increases, there is a problem that sufficient toughness cannot be ensured when the plate thickness becomes 80mm or more.

[0010] In addition, the low-temperature toughness of the central part of the steel plate (base material) with reduced reduction has also been pointed out.

In order to improve the toughness of the base material, it is known that the effective method is to lower the finish rolling temperature, but as the thickness of the steel plate increases, there is a problem that sufficient toughness cannot be ensured when the plate thickness becomes 80mm or more.