Structural steel and method for manufacturing same

Abstract

A structural steel material according to one aspect of the present invention contains, in wt%, 0.12 to 0.18% of C, 0.02 to 0.5% of Si, 0.6 to 1.6% of Mn, 0.002 to 0.06% of Sol.Al, 0.001 to 0.05% of Nb, 0.001 to 0.06% of V, 0.003 to 0.009% of Ti, 0.0002 to 0.006% of Ca, 0.0002 to 0.0005% of B, 0.001 to 0.006% of N, 0.02% or less of P, 0.003% or less of S, and the balance of Fe and unavoidable impurities, and satisfies the following relational expression 1: the microstructure contains a composite structure in which the main phase is ferrite, the second phase is pearlite, and the balance is a hard structure, the ferrite may have an average grain size of 20 [mu] m or less. [relational expression 1] [N]-0.3 * [Ti]-0.1 * [Nb] < = 0.001 (wt%) In the relational expression 1, [N], [Ti], and [Nb] represent the contents (wt%) of N, Ti, and Nb contained in the steel material, respectively.

Description

technical field [0001] The present invention relates to a structural steel material and a manufacturing method thereof. In particular, the present invention relates to a structural normalizing heat treatment thick steel plate with excellent low-temperature impact toughness after plastic deformation and a method for producing the same. Background technique [0002] For large structures such as ships or offshore factories, various technical measures have been proposed to improve the economics of the entire project. [0003] Conventionally, in order to manufacture a structure with a curved surface such as a column, welding is mainly used, but there are disadvantages in terms of manufacturing time and cost. As a solution, a technique for producing steel with curved surfaces by hot or cold bending has been developed, but such plastically deformed steel has poor impact toughness and cannot provide performance suitable for large-scale structures such as ships or offshore plants. ...

AI Technical Summary

Problems solved by technology

However, these methods require a large amount of expensive elements to be added, so they are not economically desirable

[0006] In particular, compared with the steel produced by the thermo-mechanical controlled process, the steel produced by normalizing heat treatment not only has a relatively coarse structure, but also adds a relatively large amount of carbon (C) to ensure strength, There is a problem of ensuring low-temperature impact toughness, especially low-temperature impact toughness after plastic deformation

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