WO2009082149A2 - High strength cold-rolled steel sheet having excellent weather resistance and method manufacturing the same - Google Patents

High strength cold-rolled steel sheet having excellent weather resistance and method manufacturing the same Download PDF

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Publication number
WO2009082149A2
WO2009082149A2 PCT/KR2008/007581 KR2008007581W WO2009082149A2 WO 2009082149 A2 WO2009082149 A2 WO 2009082149A2 KR 2008007581 W KR2008007581 W KR 2008007581W WO 2009082149 A2 WO2009082149 A2 WO 2009082149A2
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steel
steel sheet
cold
rolled steel
rolled
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PCT/KR2008/007581
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English (en)
French (fr)
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WO2009082149A3 (en
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Jai-Ik Kim
Kee-Jo Jeong
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Posco
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Publication of WO2009082149A2 publication Critical patent/WO2009082149A2/en
Publication of WO2009082149A3 publication Critical patent/WO2009082149A3/en

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    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
    • C22C38/20—Ferrous alloys, e.g. steel alloys containing chromium with copper
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D8/00—Modifying the physical properties by deformation combined with, or followed by, heat treatment
    • C21D8/02—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips
    • C21D8/04—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips to produce plates or strips for deep-drawing
    • C21D8/041—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips to produce plates or strips for deep-drawing involving a particular fabrication or treatment of ingot or slab
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D8/00—Modifying the physical properties by deformation combined with, or followed by, heat treatment
    • C21D8/02—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips
    • C21D8/04—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips to produce plates or strips for deep-drawing
    • C21D8/0421—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips to produce plates or strips for deep-drawing characterised by the working steps
    • C21D8/0426—Hot rolling
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D8/00—Modifying the physical properties by deformation combined with, or followed by, heat treatment
    • C21D8/02—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips
    • C21D8/04—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips to produce plates or strips for deep-drawing
    • C21D8/0421—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips to produce plates or strips for deep-drawing characterised by the working steps
    • C21D8/0436—Cold rolling
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D8/00—Modifying the physical properties by deformation combined with, or followed by, heat treatment
    • C21D8/02—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips
    • C21D8/04—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips to produce plates or strips for deep-drawing
    • C21D8/0447—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips to produce plates or strips for deep-drawing characterised by the heat treatment
    • C21D8/0473—Final recrystallisation annealing
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D9/00—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor
    • C21D9/46—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor for sheet metals
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D9/00—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor
    • C21D9/46—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor for sheet metals
    • C21D9/48—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor for sheet metals deep-drawing sheets
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/02—Ferrous alloys, e.g. steel alloys containing silicon
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/04—Ferrous alloys, e.g. steel alloys containing manganese
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/06—Ferrous alloys, e.g. steel alloys containing aluminium
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
    • C22C38/22—Ferrous alloys, e.g. steel alloys containing chromium with molybdenum or tungsten
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
    • C22C38/24—Ferrous alloys, e.g. steel alloys containing chromium with vanadium
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
    • C22C38/28—Ferrous alloys, e.g. steel alloys containing chromium with titanium or zirconium
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
    • C22C38/30—Ferrous alloys, e.g. steel alloys containing chromium with cobalt
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D2211/00—Microstructure comprising significant phases
    • C21D2211/005—Ferrite
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D8/00—Modifying the physical properties by deformation combined with, or followed by, heat treatment
    • C21D8/02—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips
    • C21D8/0221—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips characterised by the working steps
    • C21D8/0236—Cold rolling
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D8/00—Modifying the physical properties by deformation combined with, or followed by, heat treatment
    • C21D8/02—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips
    • C21D8/0247—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips characterised by the heat treatment
    • C21D8/0273—Final recrystallisation annealing

Definitions

  • the present invention relates to a high strength cold-rolled steel sheet having excellent impact resistance for use in railway vehicles and containers, and a manufacturing method thereof, and more particularly, to a cold-rolled steel sheet having high strength characteristic as well as weather resistance by controlling components of a steel and manufacturing conditions, and a method of manufacturing the cold-rolled steel sheet.
  • a yield ratio is defined as a ratio of tensile strength to yield strength, among material parameters obtained through a tensile test.
  • a higher yield ratio at the same tensile strength means higher yield strength of the steel. That is, a steel with a high yield ratio has greater resistance against deformation when impact is imposed, due to its high yield strength which is characteristic of an elastic material, thereby further capable of suppressing deformation.
  • the steel may have a yield ratio of at least 80%.
  • the containers should withstand various climatic conditions on the ground or sea depending on transportation circumstances. This has led to a demand for the steel with excellent weather resistance.
  • SPA-C Korean standard KS-D3542 and Japanese standard JIS-G3125
  • a steel has a low tensile strength of 50 kg/mm , thus leading to an increase in the weight of the container when the steel is used to manufacture a large- sized container, e.g., 50-feet container.
  • a high-strength cold-rolled steel having a tensile strength of 60 to 80 kg/mm has been used for structural members of a car.
  • this type of steel does not have desired excellent weather resistance because much attention is still paid on the increase of strength.
  • Japanese Patent Laid-open Publication No. Hei 7-207408 discloses a method of manufacturing a hot-rolled steel sheet.
  • a steel containing ⁇ 0.008% C, 0.5 to 2.5% Si, 0.1 to 3.5% Mn, 0.03 to 0.20% P, ⁇ 0.01% S, 0.05 to 2.0% Cu, 0.005 to 0.1% Al, ⁇ 0.008% N, 0.05 to 6.0% Cr, 0.05 to 2.0% Ni, 0.05 to 3.0% Mo, and 0.0003 to 0.002% B is heated to 1,100 to 1,300 0 C. Then, the steel is finish-rolled at 800 to 950 0 C and then coiled at 400 to 700 0 C.
  • Japanese Patent Laid-open Publication No. Hei 11-21622 discloses a method of manufacturing a steel product.
  • a steel having a composition consisting of, by weight, ⁇ 0.15% C, ⁇ 0.7% Si, 0.2 to 1.5% Mn, 0.03 to 0.15% P, ⁇ 0.02% S, ⁇ 0.4% Cu, 0.01 to 0.1% Al, ⁇ 0.1% Cr, 0.4 to 4.0% Ni and 0.1 to 1.5% Mo is heated to 1,050 to 1,300 0 C. Thereafter, the steel is hot-rolled at 950 0 C or higher by at least 40%, then finish-rolled at 900 to 750 0 C and followed by air cooling.
  • An aspect of the present invention provides a high strength cold-rolled steel sheet ha ving a tensile strength of at least 80 kg/mm as well as excellent impact resistance and weather resistance by controlling added amounts of steel components such as Co, V, Zr and W and optimizing rolling and annealing conditions, and a method of manufacturing the high strength cold-rolled steel sheet.
  • a high strength cold-rolled steel sheet comprising, by weight, 0.08 to 0.20% C, 0.1 to 0.5% Si, 1.2 to 2.0% Mn, ⁇ 0.03% P, ⁇ 0.01% S, 0.02 to 0.07% Al, 0.02 to 0.06% V, 0.2 to 0.5% Cu, 0.3 to 0.8% Cr, 0.04 to 0.08% Zr, 0.02 to 0.08% Co, 0.02 to 0.07% W, the balance being Fe and unavoidable impurities, and there is also provided a method of manufacturing a high strength cold-rolled steel sheet with excellent impact resistance and weather resistance, the method including: reheating the high strength cold-rolled steel sheet to 1,150 to 1,300 0 C; finish-rolling the reheated steel at a temperature of 800 0 C to 950 0 C; cooling the finish-rolled steel at a cooling rate of 20 to 40 0 C per second; coiling the steel at 500 to 650 0 C, and cold-rolling the coiled steel
  • a high strength cold-rolled steel sheet with excellent weather resistance, mechanical properties and high yield ratio can be obtained by appropriately controlling components and process conditions. Therefore, it is possible to manufacture a high value-added steel sheet for use in outdoor structures requiring high impact resistance.
  • an annealing process is performed in a relatively low-temperature range, thereby saving energy and improving annealing efficiency.
  • steel components may have chemical compositions as follows.
  • C carbon
  • a greater amount of C increases tensile strength and yield strength of the steel sheet.
  • an excessive amount of C degrades workability of the steel, and thus an upper limit of C is set to amount of 0.20%.
  • the amount of C may be set to a range of 0.08 to 0.20%.
  • Si is effective for deoxidizing molten steel and strengthening solid solution.
  • Si forms a compact Fe SiO oxide with Fe on a surface layer of the steel at a high temperature, thus serving to improve corrosion resistance.
  • Si may be added in an amount of at least 0.1%. Therefore, Si should be necessarily added to improve weather resistance, but an excessive amount of Si degrades weldability and coating properties.
  • Si may be added in an amount of up to 0.5%, and therefore the addition amount of Si is limited to a range of 0.1 to 0.5%.
  • Mn Manganese
  • MnS Manganese S
  • a small amount of Mn is advantageous for workability but leads to insufficient strength of the steel. Therefore, Mn should be added in an amount of at least 0.5% to achieve desired strength.
  • an excessive amount of Mn degrades economic efficiency and causes poor weldability.
  • the upper limit of Mn amount is set to 2.0%.
  • Phosphorous (P) enhances corrosion resistance of the steel and thus may be added in a great amount to increase corrosion resistance.
  • P creates central segregation during casting of the steel.
  • a great amount of P degrades weldability and tensile strength. Therefore, the addition amount of P may be limited to 0.03% or less.
  • S Sulfur
  • Si is known to be effective for increasing corrosion resistance.
  • Si may be added into the steel as small as possible. Accordingly, S may be added in an amount of up to 0.01%, more particularly, up to 0.005%.
  • Aluminum (Al) is generally effective for deoxidizing molten steel and increasing corrosion resistance, but an excessive amount of Al increases an amount of inclusion in the steel, thereby deteriorating workability.
  • the amount of Al may be set to a range of 0.02 to 0.07%.
  • Vanadium (V) delays recrystallization of ferrite and also enhances the strength of the steel sheet because it binds with C and N in the steel to be precipitated.
  • V should be added in an amount of 0.02% or more. Meanwhile, the addition amount of V exceeding 0.06% may increase manufacturing costs and deteriorate hot-rolling workability. Therefore, the addition amount of V is limited to a range of 0.02 to 0.06%.
  • Copper (Cu) forms a stable rust layer in a corrosion atmosphere to thereby improve corrosion resistance.
  • Cu may be added in an amount of 0.02% or more.
  • the Cu amount exceeding 0.5% may result in grain boundary cracks during continuous casting and roughen a surface of a hot-rolled steel sheet as well. Therefore, the addition amount of Cu is limited to a range of 0.2 to 0.5%.
  • Chromium (Cr) serves to form a stable rust layer like Cu. To achieve corrosion resistance and strength, Cr may be added in an amount of 0.3% or more. Meanwhile, if the addition amount of Cr is 0.8% or more, crevice corrosion is generated and manufacturing cost is dramatically increased. Therefore, Cr may be added in an amount of 0.3 to 0.8%.
  • Zirconium (Zr), which delays recrystallization of ferrite, may be added in an amount of 0.04% or more to obtain desired strength. Meanwhile, Zr amount exceeding 0.08% cannot ensure rolling property of the steel, and therefore, the addition amount of V is limited up to 0.08%.
  • Co Co
  • Cu and Cr added to attain corrosion resistance of the steel thereby to facilitate formation of a product inhibiting corrosion of a surface layer.
  • Co may be added in an amount of 0.02% or more.
  • the amount of Co exceeding 0.08% leads to higher manufacturing costs rather than brings about better corrosion resistance. Therefore, the addition amount of Co is limited to a range of 0.02 to 0.08%.
  • tungsten (W) which is added to ensure hardenability and strength characteristics, should be added in an amount of at least 0.02% to attain a desired strength in a low temperature range.
  • the upper limit of W amount may be limited to 0.07%, and thus the addition amount of W is set to a range of 0.02 to 0.07%.
  • the steel having the above-described composition may have a corrosion resistance index (CI) of 6.62 or higher. Furthermore, the steel may have a tensile strength of at least 80 kgf/mm , a yield ratio of at least 80%, and an elongation ratio of at least 10%.
  • CI corrosion resistance index
  • the steel having the above composition may be manufactured under following conditions.
  • the steel is cooled at a cooling rate of 20 0 C to 40 0 C per second. Subsequently, the steel is coiled at 500 0 C to 650 0 C and followed by cold-rolling. Thereafter, the steel is thermally treated at 550 0 C to an A transformation point, thereby manufacturing a high strength cold-rolled steel sheet with excellent weather resistance and impact resistance having a high tensile strength of at least 80kg/mm .
  • the steel when reheated to less than 1,150 0 C, is prone to central segregation due to insufficient destruction of a solidification grain structure formed during casting. Therefore, the finally formed grains are mixed to significantly degrade workability and impact toughness of the steel. Meanwhile, the steel, when reheated to above 1,300 0 C, accelerates scale formation due to oxidization, resulting in significant decrease in thickness of a slab and coarsening grains. Also, in this case, much heat should be consumed to lead to a great economic loss, and thus the reheating temperature may be in a range of 1,150 to 1,300 0 C.
  • the finish hot-rolling temperature is above 950 0 C
  • the steel is not hot-rolled uniformly across an entire thickness thereof.
  • grains are not sufficiently refined so that the steel is degraded in impact toughness due to the coarse grains.
  • the finish hot-rolling temperature is below 800 0 C
  • the steel is finish hot-rolled at a low temperature, thereby accelerating the admixture of grains thereof. This deteriorates corrosion resistance and workability, and therefore the finish hot-rolling temperature may be set to a range of 800 to 950 0 C.
  • the cooling rate of the steel may be set to 20 0 C or less per second.
  • the cooling rate exceeding 40 0 C per second leads to formation of a hard second phase like bainite, thereby significantly deteriorating cold- rolling properties. Therefore, the cooling temperature of the steel may be set to a range of 20 to 40 0 C per second.
  • a hot-rolling coiling temperature exceeding 650 0 C does not bring about sufficient precipitation effects, thereby making it difficult to stably ensure a desired strength of 80 kg/mm .
  • the coiling temperature is below 500 0 C, a hard phase is formed while the steel is cooled and maintained so that a roll force of a rolling mill sharply increases during the cold-rolling. This makes it difficult to roll the steel and thus the coiling temperature of the steel may be set to a range of 500 to 650 0C.
  • the hot-rolled steel is rolled under general cold-rolling conditions and then subjected to continuous annealing.
  • the steel needs to be annealed at a proper temperature.
  • the annealing temperature is lower than 550 0 C during the continuous annealing, deformed grains in the cold-rolling still remain, sharply decreasing ductility and thus deteriorating workability.
  • an annealing temperature exceeding an A transformation point results in formation of martensite because the steel is transformed when cooled after being annealed. This decreases yield strength of the steel to 60% or less, and thus the impact resistance of the steel becomes poorer. Therefore, the upper limit of the annealing temperature of the steel is set to the A transformation point.
  • the corrosion resistance index (CI) is an indicator for estimating weather resistance in accordance with ASTM GlOl. A higher corrosion resistance index means stronger weather resistance.
  • the corrosion resistance index (CI) is derived primarily based on alloy elements and defined as following Equation.
  • Corrosion resistance index (CI) 26.01(%Cu) + 3.88(%Ni) + 1.2(%Cr) + 1.49(%Si) + 17.28(%P) - 7.29(%Cu)(%Ni) - 9.10(%Ni)(%P) - 33.39(%Cu) 2 [40] Table 1 [Table 1]
  • Comparative steels 2, 3 and 4 are low in corrosion resistance index and their corrosion-induced weight losses were 0.030 g/cm or more in the salt spray test, and therefore they are not suitable for weather-resistant steels. In contrast, it can be observed that Inventive steels 1 and 2 and Comparative steel 1 exhibit excellent weather resistance characteristics in terms of corrosion-induced weight loss and corrosion resistance index.
  • Comparative examples 1 to 5 whose chemical compositions satisfy the conditions of Inventive steels but whose manufacturing conditions fall out of the range of the present invention did not achieve desired characteristics. That is, Comparative example 2 and Comparative example 5 whose annealing temperatures were higher than the annealing condition of the present invention attained desired tensile strength, but were reduced in a yield ratio to 70% or less. This is because the second phase is formed by transformation in a cooling process due to the high annealing temperature and resultantly yield strength is lowered. That is, Comparative Example 2 and Comparative Example 5 did not achieve a yield ratio of at least 80%, leading to a decrease in impact resistance.
  • Comparative Example 4 whose annealing temperature was lower than the annealing condition of the present invention, most deformed grains produced during cold-rolling are not recovered, thus not ensuring desired workability. Moreover, Comparative Example 1 whose finish hot-rolling temperature and coiling temperature fall out of the ranges of the present invention and Comparative Example 3 whose cooling rate is higher than the cooling condition of the present invention demonstrated a ductility of less than 5%, thus not achieving appropriate workability.
  • Comparative steel 1 of which W and Mn compositional ranges fell out of the requirement of the present invention but which had relatively excellent weather resistance was manufactured under the conditions of the present invention (Comparative example 7)
  • Comparative example 6 when increased in the annealing temperature to ensure ductility and workability, was reduced in yield strength due to the creation of dual phase such as martensite, thus making it difficult to attain a yield ratio of 80% or higher.

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  • Chemical & Material Sciences (AREA)
  • Engineering & Computer Science (AREA)
  • Materials Engineering (AREA)
  • Mechanical Engineering (AREA)
  • Metallurgy (AREA)
  • Organic Chemistry (AREA)
  • Physics & Mathematics (AREA)
  • Thermal Sciences (AREA)
  • Crystallography & Structural Chemistry (AREA)
  • Heat Treatment Of Sheet Steel (AREA)
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PCT/KR2008/007581 2007-12-24 2008-12-22 High strength cold-rolled steel sheet having excellent weather resistance and method manufacturing the same WO2009082149A2 (en)

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Cited By (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CN101994063A (zh) * 2009-08-18 2011-03-30 宝山钢铁股份有限公司 屈服强度在700MPa以上的耐候钢及其制造方法

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Publication number Priority date Publication date Assignee Title
CN114107785B (zh) 2020-08-27 2022-10-21 宝山钢铁股份有限公司 一种具有超高屈强比的吉帕级贝氏体钢及其制造方法
CN113637903A (zh) * 2021-07-28 2021-11-12 武汉钢铁有限公司 一种含稀土的屈服强度为310MPa级冷轧汽车用耐候钢及生产方法
CN113637901A (zh) * 2021-07-28 2021-11-12 武汉钢铁有限公司 一种屈服强度为280MPa级冷轧汽车用经济耐候钢及生产方法

Citations (6)

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