Posco

Posco Co., Ltd

Postech Academy-industry Foundation

Jai-Hyun Kwak

Jin-Keun Oh

Yeol-Rae Cho

Kyoo-Young Lee

Hang-Sik Cho

Joo-Hyun Ryu

Dong-Seoug Sin

Kwang-Geun Chin

Min-Seo Koo

Man-Young Park

Sang-Ho Han

Young-Roc Im

Jong-Chan Park

Han-Soo Kim

Bruno C De Cooman

Ki-Soo Kim

Se-Don Choo

Tae-Jin Song

One aspect of the present invention provides a method for preventing spot welding crack of a galvanized steel plate, which can reduce crack occurring due molten zinc having a low melting point when a galvanized advanced high strength steel (AHSS) plate is spot-welded, and can thus improve welding strength and fatigue life.

Method for preventing spot welding crack of galvanized steel plate

A high strength cold rolled steel sheet having excellent burring properties includes: by weight %, 0.13-0.25% of carbon (C), 1.0-2.0% of silicon (Si), 1.5-3.0% of manganese (Mn), 0.08-1.5% of aluminum (Al)+chromium (Cr)+molybdenum (Mo), 0.1% or less of phosphorus (P), 0.01% or less of sulfur(S), 0.01% or less of nitrogen (N), and the balance of Fe and inevitable impurities; and, by area fraction, 3-25% of ferrite, 20-40% of martensite, 5-20% of residual austenite. The ferrite has an average grain size of 2 μm or less at the reference point of t/(wherein t refers to a steel sheet thickness), with the average ratio between lengths in the thickness direction and in the rolling direction being 1.5 or less.

High-strength cold rolled steel sheet and galvannealed steel sheet having excellent burring property, and manufacturing method therefor

Provided is a high-strength cold rolled steel sheet, a high-strength hot-dip galvanized steel sheet manufactured using the cold rolled steel sheet, and manufacturing methods therefor, the high-strength cold rolled steel sheet comprising, by wt %, 0.17-0.21% of carbon (C), 0.3-0.8% of silicon (Si), 2.7-3.3% of manganese (Mn), 0.3-0.7% of chromium (Cr), 0.01-0.3% of aluminum (Al), 0.01-0.03% of titanium (Ti), 0.001-0.003% of boron (B), 0.04% or less of phosphorus (P), 0.02% or less of sulfur (S), 0.01% or less of nitrogen (N) and the balance of iron (Fe) and other inevitable impurities, wherein the amounts of carbon (C), silicon (Si) and aluminum (Al) satisfy the following mathematical relation (1). [Mathematical relation (1)] [C]+([Si]+[Al])/5&#x2264;0.35% (wherein [C], [Si] and [Al] respectively mean the wt % of C, Si and Al.)

High-strength cold rolled steel sheet having high hole expansion ratio, highstrength hot-dip galvanized steel sheet, and manufacturing methods therefor

Provided are a high-strength cold-rolled steel sheet and a hot-dip galvanized steel sheet comprising in % by weight: 0.05 to 0.3% of carbon (C); 0.6 to 2.5% of silicon (Si); 0.01 to 0.5% of aluminum (Al); 1.5 to 3.0% of manganese (Mn); and the remainder being Fe and unavoidable impurities, the steel sheet has a microstructure comprised of, in an area fraction, ferrite in an amount of 60% or less, lath-type bainite of 25% or more, martensite of 5% or more, and lath-type retained austenite in an amount of 5%, wherein the ferrite has an average grain diameter of 2 &#x3bc;m or less and the ferrite satisfies Fn2, defined by relational expression 1, is 89% or more and Fa5, defined by relational expression 2, is 70% or less.

High strength cold-rolled steel sheet and hot-dip galvanized steel sheet having excellent hole expansion, ductility and surface treatment properties, and method for manufacturing same

Provided is a method of continuously annealing a strip. The method includes: firstly heating a strip in a first heating zone; firstly cooling the firstly heated strip or maintaining the firstly heated strip at a constant temperature in a first cooling or constant temperature maintaining zone; secondarily heating and soaking the strip, firstly cooled or remaining at the constant temperature, in a second heating and soaking zone; and secondarily cooling the strip, secondarily heated and soaked, in a second cooling zone.

Method of continuously annealing a strip

The present invention relates to: a high-strength steel sheet used for construction materials and transportation means such as vehicles and trains and, more specifically, to a high-strength cold rolled steel sheet having excellent ductility, a hot-dip galvanized steel sheet, and a method for manufacturing the same.

High-strength cold rolled steel sheet having excellent ductility, hot-dip galvanized steel sheet and method for manufacturing same

The present invention relates to an apparatus for continuous annealing of a strip, capable of manufacturing a high-strength and highly ductile cold-rolled steel sheet having both excellent strength and ductility, and to a method for continuous annealing of a strip. The continuous annealing apparatus, according to the present invention, is capable of continuous annealing by cooling after heating, and then reheating, unlike an existing continuous annealing apparatus which heats only once and then cools or provides an overaging treatment. As a result, the continuous annealing apparatus, according to the present invention, can preliminarily render a homogeneous texture or control the texture as desired, and then perform another reheating heat treatment to stabilize the texture or control the shape thereof to a desired state. Also, provided is a continuous annealing apparatus and a continuous annealing method using the apparatus, the continuous annealing apparatus also capable of manufacturing high-strength steel having excellent processability and strength by using a low alloy, and capable of manufacturing a zinc-plated strip having excellent plated surfaces by controlling the thickness of elements and oxides enriched on the surface of the strip.

Apparatus for continuous annealing of strip and method for continuous annealing of same

The present invention relates to a lightweight steel sheet and a method of manufacturing the same, wherein high strength and ductility can be achieved in the lightweight steel sheet even when a small amount of carbon and manganese is added, by preventing loss of austenite due to decarburizing through inhibiting decarburization, which occurs during a heat treatment step of a steel sheet containing austenite.

Lightweight steel sheet having excellent strength and ductility and method for manufacturing same

Provided is a ferritic lightweight high-strength steel sheet having excellent stiffness and ductility and a method of manufacturing the same. The steel sheet including 0.02 wt % to 0.1 wt % of carbon (C), 4 wt % to 15 wt % of manganese (Mn), 4 wt % to 10 wt % of aluminum (Al), 2.0 wt % or less (excluding 0) of silicon (Si), 0.01 wt % to 0.3 wt % of titanium (Ti), 0.005 wt % to 0.2 wt % of antimony (Sb), and iron (Fe) as well as unavoidable impurities as a remainder, and having a value of 0.25&#xd7;Ti/C ranging from 0.17 to 1.0 and a value of Mn/Al&#xd7;Log(C&#xd7;Ti&#xd7;10000) ranging from 1.0 to 10.

Ferritic lightweight high-strength steel sheet having excellent stiffness and ductility, and method of manufacturing the same

Provided is an austenitic, lightweight, high-strength steel sheet having a high yield ratio and ductility and a method for producing the same, and more particularly, to a high-strength steel sheet for automotive interior panels, exterior panels, and structural parts, and a method for producing the steel sheet. The steel sheet may be a hot-rolled steel sheet, a cold-rolled steel sheet, or a plated steel sheet. The steel sheet includes, by weight %, C: 0.6% to 1.0%, Si: 0.1% to 2.5%, Mn: 10% to 15%, P: 0.02% or less, S: 0.015% or less, Al: 5% to 8%, Ti: 0.01% to 0.20%, N: 0.02% or less, and the balance of Fe and inevitable impurities, wherein the steel sheet has a specific gravity of 7.4 g/cmand a Mn/Al ratio of 2 to 3.

Austenitic, lightweight, high-strength steel sheet having high yield ratio and ductility, and method for producing the same

The present invention relates to a hot dip galvanized steel sheet and a manufacturing method thereof. The hot dip galvanize steel sheet includes a steel sheet including a martensitic structure as a matrix, and a hot dip galvanized layer formed on the steel sheet. The steel sheet includes C of 0.05 wt % to 0.30 wt %, Mn of 0.5 wt % to 3.5 wt %, Si of 0.1 wt % to 0.8 wt %, Al of 0.01 wt % to 1.5 wt %, Cr of 0.01 wt % to 1.5 wt %, Mo of 0.01 wt % to 1.5 wt %, Ti of 0.001 wt % to 0.10 wt %, N of 5 ppm to 120 ppm, B of 3 ppm to 80 ppm, an impurity, and the remainder of Fe.

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Gwangyang-si, South Korea

Jai-Hyun Kwak