High-strength steel having excellent low-yield-ratio characteristics, and manufacturing method therefor

Abstract

A high-strength steel having excellent low-yield-ratio characteristics, according to one embodiment of the present invention, comprises, by wt%, 0.06-0.12% of C, 0.2-0.5% of Si, 1.5-2.0% of Mn, 0.003-0.05% of Al, 0.01% or less of N, 0.02% or less of P, 0.003% or less of S, 0.05-0.5% of Cr, 0.05-0.5% of Mo, 0.01-0.05% of Nb, 0.0005-0.005% of Ca and the balance of Fe and other inevitable impurities,and comprises polygonal ferrite as a microstructure, wherein the area fraction of the polygonal ferrite is 10-30% and the average hardness of the polygonal ferrite can be 180 Hv or less.

Description

technical field [0001] The present invention relates to a steel material for pipelines and a manufacturing method thereof, in particular, to a high-strength steel material excellent in low yield ratio and a manufacturing method thereof. Background technique [0002] Steel materials for pipes are formed into pipes by various methods. When forming a pipe, not only is it easy to plastically deform, but the plastic deformation of the entire pipe is uniform, and as long as no cracks or breaks occur during the pipe forming process, it can be evaluated as excellent pipe-making performance. In addition, when a pipe is used, if the pipe is not broken and deformed even when the delivery pressure changes rapidly, it can be evaluated that the safety performance of the pipe is excellent. In order to improve the pipe-making performance and safety performance of steel materials for pipes, the required physical properties are to reduce the yield ratio. The lower the yield ratio of the ste...

AI Technical Summary

Problems solved by technology

[0004] However, in the case of steel materials for pipes, especially steel materials for line pipes, not only the yield ratio but also a certain level of strength and toughness are required, so it is not possible to control the fineness by considering only the yield ratio. organize

If the fraction of polygonal ferrite, which is a phase with low hardness, is increased more than necessary, the problem of lower yield strength will occur; if the fraction of martensite or bainite, which is a phase with high hardness, is increased, The problem of deterioration of toughness will occur

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