Ultra-high-strength hot-rolled steel sheet, steel pipe, member, and manufacturing methods therefor

Abstract

A preferable aspect of the present invention provides: an ultra-high-strength hot-rolled steel sheet containing, by weight, one or two of 0.40-0.60% of C, 0.7-1.5% of Mn, 0.3% or less (excluding 0%) of Si, 0.03% or less (including 0%) of P, 0.004% or less (including 0%) of S, 0.04% or less (excluding 0%) of Al, 0.3% or less (excluding 0%) of Cr, 0.3% or less (excluding 0%) of Mo, 0.9-1.5% of Ni, and 0.9-1.5% of Cu, 1.1% or more of Cu+Ni, 0.04% or less (excluding 0%) of Ti, 0.005% or less (excluding 0%) of B, 0.006% or less (excluding 0%) of N, and the balance Fe and other impurities, the alloyelements satisfying relational formulas 1 and 2 below, wherein a microstructure of the hot-rolled steel sheet comprises, by volume, 7% or more of ferrite and 93% or less of perlite; a steel pipe anda member each using the same; and manufacturing methods therefor. [Relational formula 1] (Mn / Si) >= 3 (weight ratio) [Relational formula 2] (Ni / Si) >= 1 (weight ratio)

Description

technical field [0001] The present invention relates to a high-strength hot-rolled steel sheet used for automotive component materials, etc., steel pipes and parts using the hot-rolled steel sheet, and their manufacturing methods, and more specifically, to an ultra-high-strength hot-rolled steel sheet, Steel pipes and components of rolled steel sheets having a value of tensile strength×elongation of 20,000 MPa% or more, excellent in resistance to external hydrogen permeation, and exhibiting ultrahigh strength after heat treatment, and their manufacturing methods. Background technique [0002] In order to meet the strengthening of automobile collision safety regulations and the improvement of fuel efficiency, the weight reduction and high strength of automobile components are continuously being carried out. In general, ductility or elongation tends to decrease when the strength of automotive component materials is increased. In addition, in order to simultaneously secure str...

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Problems solved by technology

However, Patent Document 2 proposes that by introducing a ferrite phase into the final microstructure, elongation at the level of 15% and tensile strength at the level of 900-1200 MPa can be ensured, so it is judged that in securing a similar level of elongation At the same time, there are limitations in ensuring ultra-high strength above 1800MPa

[0005] Therefore, according to the analysis of the manufacturing process of the steel plate and steel member proposed in the above-mentioned patent documents, it is not proposed that the steel plate or member has a tensile strength of 1800 MPa or more and a tensile strength of 20000 MPa% or more through quenching-tempering heat treatment A hot-rolled steel sheet, a hot-rolled pickled steel sheet, a steel pipe, and a method for producing the same having a value of × elongation and excellent resistance to hydrogen permeation from the outside such as a corrosive environment

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