Posco

Posco Co., Ltd

Posco Holdings Inc.

Jin-Ho Bae

The present invention provides a high strength hot rolled steel sheet and a method for manufacturing same, the steel sheet containing, in weight percentage, 0.11-0.14% of C, 0.20-0.50% of Si, 1.8-2.0% of Mn, 0.03% or less of P, 0.02% or less of S, 0.01-0.04% of Nb, 0.5-0.8% of Cr, 0.01-0.03% of Ti, 0.2-0.4% of Cu, 0.1-0.4% of Ni, 0.2-0.4% of Mo, 0.007% or less of N, 0.001-0.006% of Ca, 0.01-0.05% of Al, a balance of Fe and inevitable impurities, wherein relational expressions 1 to 3 below are satisfied, and a microstructure includes, by area percentage, 88% or more of bainite, 10% or less of ferrite, 2% or less of pearlite, and 0.8% or less of island martensite. [Relational Expression 1] 7≤(Mo/93)/(P/31)≤16. [Relational Expression 2] 1.6≤Cr+3Mo+2Ni≤2. [Relational Expression 3] 6≤(3C/12+Mn/55)×100≤7.

High strength hot rolled steel sheet having excellent elongation and method for manufacturing the same

A preferable aspect of the present invention provides a high-strength high-toughness hot-rolled steel sheet and a manufacturing method therefor, wherein the hot-rolled steel sheet contains, by weight, 0.07-0.13% C, 0.20-0.50% Si, 0.5-0.9% Mn, 0.03% or less P, 0.02% or less S, 0.005-0.03% Nb, 0.3-0.6% Cr, 0.005-0.03% Ti, 0.1-0.35% Cu, 0.05-0.3% Ni, 0.01-0.15% Mo, 0.007% or less N, 0.001-0.006% Ca, 0.01-0.05% Al, and the balance Fe and other unavoidable impurities, the alloy elements satisfying the following relational formulas [Relational formula 1] 1.6&#x2264;(Mo/96)/(P/31)&#x2264;6, [Relational formula 2] 1.6&#x2264;(Ca/S)&#x2264;3, and [Relational formula 3] 3.5&#x2264;(3*C/12+Mn/55)*100&#x2264;5; wherein a microstructure comprises, by area fraction, 85% or more of polygonal ferrite and 15% or less of pearlite, the crystal grain size of the polygonal ferrite being 10 &#x3bc;m or less; and wherein a variation in yield strength in a width direction is 35 MPa or lower.

High-strength high-toughness hot-rolled steel sheet and manufacturing method therefor

A preferable aspect of the present invention provides a hot-rolled steel sheet with excellent low-temperature toughness, a steel pipe using the same, and a manufacturing method therefor, wherein the hot-rolled steel sheet contains, by weight, 0.35-0.65% C, 0.01-0.4% Si, 13-26% Mn, 0.01-0.3% Ti, 0.01% or less B, 4% or less Al, 1-6% Cr, 0.05% or less P, 0.02% or less S, 0.01% or less N, 0.01-2% Cu, 0.001-0.015% Nb, and the balance Fe and other unavoidable impurities, the alloy elements satisfying the following relational formulas&#x2014;[Relational formula 1] 70&#x3c;[10*(C/12)+(Mn/55)+(Al/27)]*100&#x3c;95 and [Relational formula 2] 4&#x3c;100*(Cr/52+100*(Nb/93))&#x3c;9; wherein a microstructure comprises, by area fraction, 97% or more (including 100%) of austenite and 3% or less (including 0%) of a carbide, the crystal grain size of the austenite being 18-30 &#x3bc;m or less; and wherein the size of the carbide is 0.5 &#x3bc;m or less.

Hot-rolled steel sheet with excellent low-temperature toughness, steel pipe, and manufacturing method therefor

The present invention relates to a method for manufacturing a high strength and high toughness steel material which is mainly used at an extremely low temperature and used in various parts of ships for LNG transport and LNG fuel vehicles.

High manganese steel having superior low-temperature toughness and yield strength and manufacturing method thereof

A steel material for a low yield ratio, high-strength steel pipe having excellent low-temperature toughness according to an aspect of the present invention comprises, by weight %, 0.03-0.065% of C, 0.05-0.3% of Si, 1.7-2.2% of Mn, 0.01-0.04% of Al, 0.005-0.025% of Ti, 0.008% or less of N, 0.08-0.12% of Nb, 0.02% or less of P, 0.002% or less of S, 0.05-0.3% of Cr, 0.4-0.9% of Ni, 0.3-0.5% of Mo, 0.05-0.3% of Cu, 0.0005-0.006% of Ca, 0.001-0.04% of V, and the balance of Fe and inevitable impurities, wherein a number of deposits having an average diameter of 20 nm or less per unit area in a cross section of the steel material may be 6.5*10/mmor greater.

Growing community of inventors

Gwangyang-si, South Korea

Jin-Ho Bae