High strength and low yield ratio steel for structure having excellent low temperature toughness

Abstract

There is provided a high strength and low yield ratio steel for structure that is used as steel for structures of buildings and has excellent characteristics such as low temperature toughness, a tensile strength of approximately 600 MPa or more and a low yield ratio of 80% or less. The high strength and low yield ratio steel includes, by weight percent: C: 0.02 to 0.12%, Si: 0.01 to 0.8%, Mn: 0.3 to 2.5%, P: 0.02% or less, S: 0.01% or less, Al: 0.005 to 0.5%, Nb: 0.005 to 0.10%, B: 3 to 50 ppm, Ti: 0.005 to 0.1%, N: 15 to 150 ppm, Ca: 60 ppm or less, and the balance of Fe and inevitable impurities, and further includes at least one component selected from the group consisting of, by weight percent: Cr: 0.05 to 1.0%, Mo: 0.01 to 1.0%, Ni: 0.01 to 2.0%, Cu: 0.01 to 1.0% and V: 0.005 to 0.3%, wherein a finish cooling temperature is limited to 500 to 600 DEG C after the finish-rolling process. The high strength and low yield ratio steel satisfying characteristics such as low temperature toughness, brittle crack arrestabi lity and low yield ratio, and the manufacturing method thereof may be provided.

Description

technical field [0001] The present invention relates to a high-strength and low-yield-ratio structural steel with excellent properties such as low-temperature toughness and a preparation method thereof, more specifically, to a steel that satisfies excellent main properties such as low-temperature toughness and low yield-ratio— - Both of these properties are required for steels for structural use - High strength steels and methods for their preparation, said superior main properties being obtained by using bainitic ferrite and granular bainite structures as the matrix structure of the steel And it is achieved by using a dual-phase method with high hardness. Background technique [0002] Structures such as buildings and bridges mainly require high strength because of their high loads. With the continuing demand to reduce the cost of building materials used to construct building structures, the overall weight of steel used tends to decrease as well. Therefore, there is an inc...

AI Technical Summary

Problems solved by technology

In this case, low productivity problems may occur in the production line

The method of obtaining the MA structure by heat-treating the bainitic ferrite structure in the critical temperature range after the rolling process has problems in that product supply is delayed, production cost increases, yield decreases, etc.

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