US20200277681A1 - 700MPa CLASS STEEL BAR HAVING EXCELLENT YIELD RATIO AND UNIFORM ELONGATION PROPERTY, AND METHOD FOR MANUFACTURING THE SAME - Google Patents

700MPa CLASS STEEL BAR HAVING EXCELLENT YIELD RATIO AND UNIFORM ELONGATION PROPERTY, AND METHOD FOR MANUFACTURING THE SAME Download PDF

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US20200277681A1
US20200277681A1 US16/617,559 US201816617559A US2020277681A1 US 20200277681 A1 US20200277681 A1 US 20200277681A1 US 201816617559 A US201816617559 A US 201816617559A US 2020277681 A1 US2020277681 A1 US 2020277681A1
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steel bar
cooling
bainite
center
tempcore
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Joonho Lee
SangChul Shim
Byoungchul HWANG
Taeun HONG
Sangin Lee
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Korea University Research and Business Foundation
Foundation for Research and Business of Seoul National University of Science and Technology
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Korea University Research and Business Foundation
Foundation for Research and Business of Seoul National University of Science and Technology
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    • 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
    • C21D6/00—Heat treatment of ferrous alloys
    • C21D6/008—Heat treatment of ferrous alloys containing Si
    • 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
    • C21D9/52—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor for wires; for strips ; for rods of unlimited length
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B21—MECHANICAL METAL-WORKING WITHOUT ESSENTIALLY REMOVING MATERIAL; PUNCHING METAL
    • B21B—ROLLING OF METAL
    • B21B1/00—Metal-rolling methods or mills for making semi-finished products of solid or profiled cross-section; Sequence of operations in milling trains; Layout of rolling-mill plant, e.g. grouping of stands; Succession of passes or of sectional pass alternations
    • B21B1/16—Metal-rolling methods or mills for making semi-finished products of solid or profiled cross-section; Sequence of operations in milling trains; Layout of rolling-mill plant, e.g. grouping of stands; Succession of passes or of sectional pass alternations for rolling wire rods, bars, merchant bars, rounds wire or material of like small cross-section
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B21—MECHANICAL METAL-WORKING WITHOUT ESSENTIALLY REMOVING MATERIAL; PUNCHING METAL
    • B21B—ROLLING OF METAL
    • B21B37/00—Control devices or methods specially adapted for metal-rolling mills or the work produced thereby
    • B21B37/74—Temperature control, e.g. by cooling or heating the rolls or the product
    • 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
    • C21D6/00—Heat treatment of ferrous alloys
    • C21D6/005—Heat treatment of ferrous alloys containing Mn
    • 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
    • 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
    • C21D8/0226—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
    • C21D8/0247—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips characterised by the heat treatment
    • C21D8/0263—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips characterised by the heat treatment following 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
    • C21D8/06—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of rods or wires
    • C21D8/065—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of rods or wires of ferrous alloys
    • 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
    • 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
    • C21D9/0062—Heat-treating apparatus with a cooling or quenching zone
    • 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
    • C21D9/0075—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor for rods of limited length
    • 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
    • C22C38/12—Ferrous alloys, e.g. steel alloys containing tungsten, tantalum, molybdenum, vanadium, or niobium
    • 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
    • C21D2211/002—Bainite
    • 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

Definitions

  • Embodiments of the inventive concept described herein relate to an ultra-high strength steel bar having excellent yield ratio (tensile-to-yield strength, TS/YS) and uniform elongation property and a method of manufacturing the same, more particularly, relate to a steel bar having yield strength of a 700 MPa class having a yield ratio and an excellent uniform elongation property which are suitable for a seismic resistant steel bar, in which a cooling process is improved to increase the yield strength of the steel bar and to increase the yield ratio of the steel bar, and a method of the same.
  • TS/YS yield strength
  • the high strength seismic resistant steel bar is designed to have higher yield strength and yield ratio than a general steel bar, thereby withstanding loads in small amounts and improving seismic resistant performance of the building by securing a margin from a start of plastic deformation after elastic deformation to final fracture, and thus damage of human life is minimized.
  • the seismic resistant performance of the steel bar is related to a deformation capacity of the material and the deformation capacity is determined by yield ratio or uniform elongation property. Therefore, specification related to the deformation capacity will be important in specification of the ultra-high strength seismic resistant steel bar having the yield strength of 700 MPa class or more. Thus, systematic studies on the high yield strength, the yield ratio, and the uniform elongation property are required to develop the high strength seismic resistant steel bar having the yield strength of 700 MPa class or more.
  • the steel bar is manufactured through various methods and an addition of alloying elements to improve the strength and seismic resistant performance of the steel bar.
  • a solid solution strengthening and a precipitation strengthening by the addition of the alloying elements have been mainly utilized to secure the strength and seismic resistant performance in a limited manufacturing process.
  • excessive addition of alloying elements causes some problems in welding and material cost increase during manufacturing, thereby limiting a carbon equivalent (Ceq) to a specific value or less.
  • the ultra-high strength seismic resistant steel bar having the yield strength of 700 MPa class or more has not been developed so far.
  • Embodiments of the inventive concept provide an ultra-high strength seismic resistant steel bar having yield strength of 700 MPa class or more.
  • Embodiments of the inventive concept provide a seismic resistant steel bar having yield strength of 700 MPa or more, yield ratio of 1.25 or more, and excellent uniform elongation property.
  • a steel bar having yield strength of 700 MPa class, excellent yield ratio, and excellent uniform elongation property includes bainite and ferrite included in a center of the steel bar, wherein bainite accounts for 20 or more by volume.
  • the steel bar has the yield strength of 700 to 900 MPa and the yield ratio of 1.25 to 1.50.
  • a bainite structure is formed in the center of the steel bar by a rapid cooling through a Tempcore cooling process.
  • the Tempcore cooling process is performed at a speed of the steel bar of 5 to 20 m/sec, a pressure of cool water of 10 to 30 bar, and an amount of water of 100 to 300 m 3 /hr.
  • a method of manufacturing a steel bar having yield strength of 700 MPa class, excellent yield ratio, and excellent uniform elongation property includes heating a billet for the steel bar, hot-rolling the heated billet to be formed in a steel bar shape, cooling the rolled body having the steel bar shape at a Tempcore; and performing reheating and additional cooling, wherein the cooling at the Tempcore is performed at a speed of the steel bar of 5 to 20 m/sec, a pressure of cool water of 10 to 30 bar, and an amount of water of 100 to 300 m 3 /hr.
  • the billet for the steel bar in the heating of the billet for the steel bar, includes carbon (C) of 0.18 to 0.30 wt %, manganese (Mn) of 0.65 to 2.00 wt %, silicon (Si) of 0.13 to 0.40 wt %, vanadium (V) of 0 to 0.10 wt %, the remaining Fe, and other unavoidable impurity components.
  • a temperature of the center of the steel bar is maintained at 500 to 600° C.
  • a structure of the center of the steel bar includes bainite and ferrite.
  • the steel bar after the reheating and the additional cooling, has the yield strength of 700 to 900 MPa and the yield ratio of 1.25 to 1.50.
  • FIG. 1 shows temperature change of steel bars and structure change by location depending on processes of Examples and Comparative Examples
  • FIG. 2 shows cross-sectional views of steel bars of Examples according to the inventive concept and Comparative Examples
  • FIG. 3 shows optical micrographs of Examples according to the inventive concept and Comparative Examples
  • FIG. 4 shows scanning electron micrographs of Examples according to the inventive concept and Comparative Examples.
  • FIG. 5 shows a graph showing positional hardness of Examples according to the inventive concept and Comparative Examples.
  • the inventive concept provides a method of a steel bar having yield strength of 700 MPa class, which is excellent in yield ratio and uniform elongation property, including heating a billet for a steel bar; hot-rolling the heated billet to be formed in a steel bar shape; cooling the rolled billet having the steel bar shape at a Tempcore; and performing reheating and additional cooling.
  • the billet for the steel bar may include carbon (C) of 0.18 to 0.30 wt %, manganese (Mn) of 0.65 to 2.00 wt %, silicon (Si) of 0.13 to 0.40 wt %, vanadium (V) of 0 to 0.10 wt %, the remaining Fe, and other unavoidable impurity components.
  • Carbon (C) is an effective element for increasing strength.
  • an amount of carbon (C) is low, desired high strength is not obtained and when the amount of carbon (C) is high, the strength is increased but deterioration of toughness and ductility shows a remarkable increase. Therefore, carbon (C) is preferably 0.18 to 0.30 wt % to obtain the high strength.
  • Manganese (Mn) has an effect of increasing the strength during a heat treatment.
  • Manganese (Mn) is an essential element for strength compensation because the amount of C added is limited.
  • the amount of manganese (Mn) is low, the effect of improving hardenability is almost absent.
  • the amount of manganese (Mn) is preferably 0.65 to 2.00 wt %.
  • Silicon (Si) is an element essential for deoxidation of a steel and for improving the strength. When an amount of silicon (Si) is 0.10 wt % or less, the desired high strength is hardly obtained. When the amount of silicon (Si) exceeds a specific range, the toughness and the ductility decrease. Accordingly, the amount of silicon (Si) is preferably 0.13 to 0.40 wt %.
  • Vanadium (V) is added to ensure the strength by solid solution strengthening and precipitation strengthening. Vanadium plays roles of preventing movement at an austenite grain boundary during the heating and the hot-rolling to make austenite grains fine, of suppressing nucleation at the austenite grain boundary to increases the hardenability of the steel bar, and of being combined with carbon or nitrogen and forming a precipitate to improve the strength of the steel bar.
  • vanadium (V) is preferably more than 0 and 0.01 wt % or less.
  • the heated billet After the heating of the billet for the steel bar, the heated billet is subjected to the hot-rolling.
  • the heated billet may be formed in the steel bar shape through a roughing mill, an intermediate mill, and a finishing mill.
  • the hot-rolling process is a method of manufacturing a general steel bar, and a hot-rolling technology is not particularly limited.
  • the cooling at the Tempcore is performed after the hot-rolling.
  • a cooling condition is important in the cooling at the Tempcore.
  • a condition where bainite is sufficiently formed in the center may be satisfied, and thus a bainite structure may be formed.
  • the bainite structure may be formed 20 to 80% by volume.
  • the cooling at the Tempcore may be performed by water cooling.
  • a rolled body of the steel bar, a position of a cooling equipment, and an amount of cooling water are determined.
  • the amount of cooling water and the speed are adjusted to convert austenite to martensite at a surface of the steel bar, and thus a cooling rate may be determined after the rolled body of the steel bar is reheated above a start temperature of bainite formation at the center upon a final reheating.
  • the bainite formation temperature may be 500 to 600° C.
  • the center At an end of the cooling process at the Tempcore, the center maintains the temperature of 500 to 600° C. In the reheating, the center maintains the temperature of 500 to 600° C.
  • the speed of the steel bar, pressure of water, and the amount of water may be adjusted in the cooling at the Tempcore.
  • the speed of the steel bar may be 5 to 20 m/sec
  • the pressure of water may be 10 bar or more, preferably 10 to 20 bar
  • the amount of water may be 100 m 3 /hr or more, preferably 100 to 300 m 3 /hr.
  • the speed of the steel bar, the pressure of water, and the amount of water may be adjusted in the cooling at the Tempcore to form a tempered martensite structure in the surface and a low-temperature metamorphic structure such as tempered martensite and bainite in a boundary, from the first austenite through the cooling process.
  • bainite is mainly formed in the center and ferrite is formed in the rest
  • bainite accounts for 20% by volume or more, and the rest is occupied by ferrite.
  • bainite may account for 20% to 80% by volume. This is possible because the cooling at the Tempcore rapidly lowers to a temperature at which bainite is formed and then the bainite formation temperature is maintained in the reheating.
  • the inventive concept is characterized by maintaining the section, in which bainite is formed in the center of the steel bar, for a long time through the reheating process after the cooling. Therefore, a specific amount or more of bainite is formed and thus the yield strength is improved.
  • the reheating is performed after the cooling at the Tempcore.
  • the reheating may be performed through self-tempering.
  • the temperature of the center of the steel bar may be maintained to be 500 to 600° C., which is a section in which bainite may be formed.
  • the reheating process takes about 0.3 to 1 second after the cooling at the Tempcore.
  • the additional cooling through air cooling is provided.
  • the additional cooling is performed at a cooling rate of 10 ⁇ 20° C./sec to be cooled to 200° C. or less.
  • a flow in the air occurs for quick cooling to be cooled.
  • Example 1 included carbon (C) of 0.34 wt %, manganese (Mn) of 1.07 wt %, silicon (Si) of 0.15 wt %, vanadium (V) of 0.04 wt %, the remaining Fe, and other unavoidable impurity components, which were heated at about 1000° C. (heating a billet for a steel bar)
  • hot-rolling was performed to be formed in a steel bar shape through a roughing mill, an intermediate mill, and a finishing mill.
  • cooling at a Tempcore was performed at a speed of the steel bar of 10 m/sec, a pressure of cool water of 10 bar, and an amount of water of 150 m 3 /hr.
  • the cooling at the Tempcore was carried out at the speed of the steel bar of 5 m/sec, the pressure of cool water of 15 bar, and the amount of water of 150 m 3 /hr.
  • Comparative Example 1 included carbon (C) of 0.29 wt %, manganese (Mn) of 0.52 wt %, silicon (Si) of 0.14 wt %, the remaining Fe, and other unavoidable impurity components.
  • the cooling at the Tempcore was carried out at the speed of the steel bar of 30 m/sec through the air cooling.
  • Comparative Example 2 included carbon (C) of 0.30 wt %, manganese (Mn) of 1.15 wt %, silicon (Si) of 0.16 wt %, vanadium (V) of 0.11 wt %, the remaining Fe, and other unavoidable impurity components.
  • Comparative Example 3 included carbon (C) of 0.32 wt %, manganese (Mn) of 1.08 wt %, silicon (Si) of 0.15 wt %, vanadium (V) of 0.04 wt %, the remaining Fe, and other unavoidable impurity components.
  • the cooling at the Tempcore was carried out at the speed of the steel bar of 30 m/sec through the air cooling.
  • the steel bars of Comparative Examples have a conventional steel bar performance having yield strength of 600 MPa class.
  • the steel bars of Examples 1 and 2 of the inventive concept show yield ratio property of 1.25 or more and high uniform elongation property of 5.0% or more, although having a very high strength of 700 MPa or more.
  • the steel bar according to the inventive concept having the yield strength of 700 MPa or more, which is excellent in the yield ratio and uniform elongation property, may be confirmed that the yield and tensile strength is increased in comparison with the conventional steel bar.
  • the center is formed of the bainite structure of 20% or more and the surface is formed of tempered martensite. Details of an internal structure and hardness characteristics of the steel bars will be described with reference to the drawings.
  • FIG. 1 shows temperature change of steel bars and structure change by location depending on processes of Examples and Comparative Examples.
  • Example 1 in the case of Example 1 and Example 2, after the hot-rolling, in the cooling at the Tempcore, the slow moving speed, rapid quenching degree ‘H’ due to high water pressure, and the reheating cause bainite of 20% by volume or more to be formed in the center and tempered martensite to be formed in the surface
  • the Tempcore process (the rapid cooling through the slow moving speed and the high pressure of water) creates the condition for bainite to be formed in the center of the steel bar and then the condition is maintained for a long time during the reheating, and thus lots of bainite structures are formed in the center.
  • Examples 1 and 2 are adjusted by the section where bainite is formed due to the rapid cooling.
  • the section is maintained to form lots of bainite structures.
  • FIG. 2 shows cross-sectional views of steel bars of Examples according to the inventive concept and Comparative Examples.
  • the steel bars of Example 1 and Example 2 may be confirmed that the boundary is formed between the surface and the center and is defined by a different structure from tempered martensite formed in the surface and bainite and ferrite formed in the center.
  • FIGS. 3 and 4 show optical micrographs and scanning electron micrographs of Examples according to the inventive concept and Comparative Examples.
  • the surface, the boundary, and the center are formed the soft ferrite, pearlite structure, and thus the yield strength is less than 700 MPa.
  • FIG. 5 shows a graph showing positional hardness of Examples according to the inventive concept and Comparative Examples.
  • Example 1 and Example 2 have similar or higher hardness in all positions in comparison with the steel bars of Comparative Example 1 and Comparative Example 3 manufactured through the Tempcore.
  • the steel bar according to the inventive concept is the steel bar having the yield strength of 700 MPa or more, the yield strength of 1.25 or more, and the excellent uniform elongation property because the bainite structure of 20% by volume or more is formed in the center and the tempered martensite is formed in the surface.
  • bainite accounts for 20% by volume or more in the center of the steel bar and thus the steel bar has the yield strength of 700 MPa or more and the yield ratio of 1.25 or more, which is suitable for the seismic resistant steel bar.
  • the steel bar having the yield strength of 700 MPa class, which is excellent in the yield ratio and the uniform elongation property, according to the inventive concept is provided as the seismic resistant steel bar having the yield strength of 700 MPa or more, the high yield ratio, and the high uniform elongation property of 5% or more.
  • the condition of the cooling of the steel bar is changed to form the bainite structure in the center of the steel bar at the specific ratio or more, to increase the uniform elongation property of the steel bar, and to increase the yield ratio of 1.25 or more, thereby greatly improving the quality of the seismic resistant steel bar.

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  • Chemical & Material Sciences (AREA)
  • Engineering & Computer Science (AREA)
  • Mechanical Engineering (AREA)
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  • Crystallography & Structural Chemistry (AREA)
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US16/617,559 2018-11-16 2018-11-23 700MPa CLASS STEEL BAR HAVING EXCELLENT YIELD RATIO AND UNIFORM ELONGATION PROPERTY, AND METHOD FOR MANUFACTURING THE SAME Pending US20200277681A1 (en)

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KR10-2018-0141344 2018-11-16
KR1020180141344A KR102173920B1 (ko) 2018-11-16 2018-11-16 항복비와 균일연신율이 우수한 항복강도 700 MPa급 철근 및 그 제조 방법
PCT/KR2018/014517 WO2020101096A1 (ko) 2018-11-16 2018-11-23 항복비와 균일연신율이 우수한 항복강도 700 MPa급 철근 및 그 제조 방법

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CN112410677A (zh) * 2020-11-30 2021-02-26 武汉钢铁有限公司 一种500MPa级热轧盘螺及其生产方法

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