Thick high strength steel plate having excellent low temperature toughness in welding heat affected zone caused by high heat input welding

Abstract

A thick high strength steel plate having excellent low temperature toughness in a welding heat affected zone caused by high heat input welding, which is characterized in that it has a chemical composition, in mass %, that C: 0.03 to 0.14 %, Si: 0.30 % or less, Mn: 0.8 to 2.0 %, P: 0.02 % or less, S: 0.005 % or less, Ni: 0.8 to 4.0 %, Nb: 0.003 to 0.040 %, Al: 0.001 to 0.040 %, N: 0.0010 to 0.0100 %, Ti: 0.005 to 0.030 %, with the proviso that the contents of Ni and Mn satisfy the following formula [1], and the balance: iron and inevitable impurities, Ni / Mn >= 10 X Ceq - 3 (0.36 < Ceq < 0.42) wherein Ceq = C + Mn / 6 + (Cr + Mo + V) / 5 + (Ni + Cu) / 15. The use of the above thick high strength steel plate can achieve excellent welding HAZ toughness, even when a welding is carried out with a welding heat input of 20 to 100 kJ / mm on a steel plate having a thickness of 50 to 80 mm and exhibiting a base material tensile strength of about 490 to 570 Mpa.

Description

technical field [0001] The present invention relates to a thick and high-strength steel plate with excellent low-temperature toughness in the welded heat-affected zone (Heat Affected Zone, hereinafter referred to as HAZ) used in ships, marine structures, middle and high-rise buildings, bridges, etc. It is a steel plate that has an excellent welded joint area even when the steel plate with a base metal tensile strength of 490-570 MPa is welded with a welding input energy of 20-100 kJ / mm. Background technique [0002] In recent years, the requirements for the material properties of welding steel used in large structures such as ships, marine structures, mid-rise buildings, and bridges have become increasingly stringent. In particular, among these structures, thick steel plates having a plate thickness exceeding 50 mm and a base material having a tensile strength of 570 MPa class are increasingly used. In addition, in order to promote high-efficiency welding, for the welding o...

AI Technical Summary

Problems solved by technology

However, if only Ti is added to steel, it is difficult to control the number and degree of dispersion of Ti oxides in steel, and it is also difficult to control the number and degree of dispersion of precipitates such as TiN and MnS.

For this reason, in a steel in which Ti oxides are dispersed by deoxidizing only Ti, for example, the number of Ti oxides cannot be obtained sufficiently, or the toughness in the thickness direction of a thick plate fluctuates.

Images