WO2022034964A1 - 초고강도 철근 및 이의 제조방법 - Google Patents
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- WO2022034964A1 WO2022034964A1 PCT/KR2020/013596 KR2020013596W WO2022034964A1 WO 2022034964 A1 WO2022034964 A1 WO 2022034964A1 KR 2020013596 W KR2020013596 W KR 2020013596W WO 2022034964 A1 WO2022034964 A1 WO 2022034964A1
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- C—CHEMISTRY; METALLURGY
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- C21D1/00—General methods or devices for heat treatment, e.g. annealing, hardening, quenching or tempering
- C21D1/18—Hardening; Quenching with or without subsequent tempering
- C21D1/19—Hardening; Quenching with or without subsequent tempering by interrupted quenching
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- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
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- 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
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- 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
- B21B1/163—Rolling or cold-forming of concrete reinforcement bars or wire ; Rolls therefor
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- 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
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- C21D6/00—Heat treatment of ferrous alloys
- C21D6/004—Heat treatment of ferrous alloys containing Cr and Ni
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- C21D6/00—Heat treatment of ferrous alloys
- C21D6/005—Heat treatment of ferrous alloys containing Mn
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- C21D6/00—Heat treatment of ferrous alloys
- C21D6/008—Heat treatment of ferrous alloys containing Si
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- 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
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- 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
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- 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
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- 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
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- 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
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- 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
- C21D8/08—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of rods or wires for concrete reinforcement
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- 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
- C21D9/525—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor for wires; for strips ; for rods of unlimited length for wire, for rods
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- 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
- C21D9/54—Furnaces for treating strips or wire
- C21D9/56—Continuous furnaces for strip or wire
- C21D9/573—Continuous furnaces for strip or wire with cooling
- C21D9/5732—Continuous furnaces for strip or wire with cooling of wires; of rods
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- C22C—ALLOYS
- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/001—Ferrous alloys, e.g. steel alloys containing N
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- C22C—ALLOYS
- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/002—Ferrous alloys, e.g. steel alloys containing In, Mg, or other elements not provided for in one single group C22C38/001 - C22C38/60
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- C—CHEMISTRY; METALLURGY
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- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/008—Ferrous alloys, e.g. steel alloys containing tin
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- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/02—Ferrous alloys, e.g. steel alloys containing silicon
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- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/04—Ferrous alloys, e.g. steel alloys containing manganese
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- C—CHEMISTRY; METALLURGY
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- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/06—Ferrous alloys, e.g. steel alloys containing aluminium
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- C—CHEMISTRY; METALLURGY
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- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
- C22C38/40—Ferrous alloys, e.g. steel alloys containing chromium with nickel
- C22C38/42—Ferrous alloys, e.g. steel alloys containing chromium with nickel with copper
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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
- C22C38/40—Ferrous alloys, e.g. steel alloys containing chromium with nickel
- C22C38/44—Ferrous alloys, e.g. steel alloys containing chromium with nickel with molybdenum or tungsten
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- 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
- C22C38/40—Ferrous alloys, e.g. steel alloys containing chromium with nickel
- C22C38/46—Ferrous alloys, e.g. steel alloys containing chromium with nickel with vanadium
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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
- C22C38/40—Ferrous alloys, e.g. steel alloys containing chromium with nickel
- C22C38/48—Ferrous alloys, e.g. steel alloys containing chromium with nickel with niobium or tantalum
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- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
- C22C38/40—Ferrous alloys, e.g. steel alloys containing chromium with nickel
- C22C38/58—Ferrous alloys, e.g. steel alloys containing chromium with nickel with more than 1.5% by weight of manganese
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- E—FIXED CONSTRUCTIONS
- E04—BUILDING
- E04C—STRUCTURAL ELEMENTS; BUILDING MATERIALS
- E04C5/00—Reinforcing elements, e.g. for concrete; Auxiliary elements therefor
- E04C5/01—Reinforcing elements of metal, e.g. with non-structural coatings
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- E—FIXED CONSTRUCTIONS
- E04—BUILDING
- E04C—STRUCTURAL ELEMENTS; BUILDING MATERIALS
- E04C5/00—Reinforcing elements, e.g. for concrete; Auxiliary elements therefor
- E04C5/01—Reinforcing elements of metal, e.g. with non-structural coatings
- E04C5/06—Reinforcing elements of metal, e.g. with non-structural coatings of high bending resistance, i.e. of essentially three-dimensional extent, e.g. lattice girders
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- C21D2211/00—Microstructure comprising significant phases
- C21D2211/002—Bainite
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- 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
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- C21D2211/00—Microstructure comprising significant phases
- C21D2211/008—Martensite
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- C21D2211/00—Microstructure comprising significant phases
- C21D2211/009—Pearlite
Definitions
- the present invention relates to an ultra-high strength reinforcing bar and a method for manufacturing the same. More particularly, it relates to an ultra-high-strength reinforcing bar for a building structure having excellent seismic resistance and a method for manufacturing the same.
- reinforcing bars with higher strength are required.
- reinforcing bars with a yield strength of 500 MPa were required based on the yield strength, but recently rebars with a yield strength of 600 to 700 MPa are required.
- it is to provide an ultra-high strength reinforcing bar excellent in high strength and earthquake resistance and a method for manufacturing the same.
- it is to provide an ultra-high-strength reinforcing bar excellent in productivity and cost reduction effect through reduction of alloy element addition amount and process simplification and a method for manufacturing the same.
- the ultra-high strength reinforcing bar is carbon (C): 0.10 to 0.45 wt%, silicon (Si): 0.5 to 1.0 wt%, manganese (Mn): 0.40 to 1.80 wt%, chromium (Cr): 0.10 to 1.0 wt%, vanadium (V): more than 0 and less than 0.2 wt%, copper (Cu): more than 0 and less than 0.4 wt%, molybdenum (Mo): more than 0 and less than or equal to 0.5 wt%, aluminum (Al): 0.015 to 0.070 wt%, Nickel (Ni): greater than 0 and less than or equal to 0.25% by weight, tin (Sn): greater than 0 and less than or equal to 0.1% by weight, phosphorus (P): greater than 0 and less than or equal to 0.05% by weight
- the ultra-high strength reinforcing bar may have a yield strength (YS) of 700 to 850 MPa, a tensile strength/yield strength (TS/YS) of 1.25 to 1.35, and an elongation (El) of 10% or more.
- the center may be formed of a microstructure comprising 30 to 45% by volume of ferrite, 30 to 45% by volume of pearlite, and 15 to 25% by volume of bainite.
- the reinforcing bar may include 5 to 15 area% of the surface layer part and 85 to 95 area% of the central part based on the cross-section.
- the central portion may include a hardened core layer having a hardness of 350Hv or more.
- the hardened core layer may have a microstructure including lower bainite and fine ferrite having an average size of 5 to 10 ⁇ m.
- the hardened core layer may have a hardness of 350 to 400Hv, a central portion excluding the hardened core layer may have a hardness of 240 to 280Hv, and the surface layer may have a hardness of 330 to 360Hv.
- the reinforcing bar may include 15 to 30 area% of the hardened core layer based on the cross-section.
- the ultra-high strength rebar manufacturing method is carbon (C): 0.10 to 0.45 wt%, silicon (Si): 0.5 to 1.0 wt%, manganese (Mn): 0.40 to 1.80 wt%, chromium (Cr): 0.10 ⁇ 1.0 wt%, vanadium (V): more than 0 and 0.2 wt% or less, copper (Cu): more than 0 and up to 0.4 wt%, molybdenum (Mo): more than 0 and up to 0.5 wt%, aluminum (Al): 0.015 to 0.070 wt% %, nickel (Ni): greater than 0 and less than or equal to 0.25% by weight, tin (Sn): greater than 0 and less than or equal to 0.1% by weight, phosphorus (P): greater than 0 and less than or equal to
- the cooling may be carried out under the conditions of a line speed of 6.7 to 7.2 m/s and a specific water amount of 3.7 to 3.9 l/kg of the rolled material.
- the reheating may be carried out at 1050 ⁇ 1250 °C.
- the central portion may include a hardened core layer having a hardness of 350Hv or more.
- the ultra-high strength reinforcing bar of the present invention has excellent high strength and seismic resistance, and has excellent productivity and cost reduction effects through reduction of alloy element addition amount and process simplification. delay, the effect of shortening the construction period and reducing the construction cost can be excellent.
- FIG. 1 shows a method for manufacturing ultra-high strength reinforcing bars according to an embodiment of the present invention.
- FIG. 2 is a cross-sectional view of an ultra-high strength reinforcing bar according to an embodiment of the present invention.
- Figure 4 (a) is the microstructure of the surface layer part of the reinforcing bar of the example
- Figure 4 (b) is the microstructure of the center of the reinforcing bar of the example
- Figure 4 (c) is a microstructure photograph of the hardened core layer of the reinforcing bar of the example.
- Figure 5 (a) is the microstructure of the surface layer of the reinforcing bar of Comparative Example 1
- Figure 5 (b) is the microstructure of the center of the rebar of Comparative Example 1
- Figure 5 (c) is a microstructure photograph of the center of the reinforcing bar of Comparative Example 1.
- the ultra-high strength reinforcing bar is carbon (C): 0.10 to 0.45 wt%, silicon (Si): 0.5 to 1.0 wt%, manganese (Mn): 0.40 to 1.80 wt%, chromium (Cr): 0.10 to 1.0 wt%, vanadium (V): more than 0 and less than 0.2 wt%, copper (Cu): more than 0 and less than 0.4 wt%, molybdenum (Mo): more than 0 and less than or equal to 0.5 wt%, aluminum (Al): 0.015 to 0.070 wt%, Nickel (Ni): greater than 0 and less than or equal to 0.25% by weight, tin (Sn): greater than 0 and less than or equal to 0.1% by weight, phosphorus (P): greater than 0 and less than or equal to 0.05% by weight
- the carbon (C) is the most effective for increasing the strength of steel and is an important element for increasing the tensile strength in particular.
- the carbon is dissolved in austenite to form a martensitic structure during quenching. As the amount of carbon increases, the quenching hardness is improved, but the possibility of deformation during quenching is increased. It is combined with elements such as iron (Fe), chromium (Cr), vanadium (V) and titanium (Ti) to form carbides, improving strength and hardness.
- the carbon is included in an amount of 0.10 to 0.45% by weight based on the total weight of the ultra-high strength reinforcing bar.
- the carbon content is less than 0.10% by weight, it is difficult to secure strength and hardness, and when it contains more than 0.45% by weight, the possibility of deformation during quenching increases, and it may be difficult to secure elongation and low-temperature toughness.
- 0.35 to 0.40% by weight may be included.
- the silicon (Si) is an element that increases hardenability, such as molybdenum and chromium, and is used as a deoxidizer.
- the silicon is a strong deoxidizer, and when 2 wt% or more is added, toughness is lowered and plastic workability is impaired, so there is a limit to the amount added.
- the silicon has an effect of increasing the softening resistance during tempering (tempering).
- a hardening phase can be formed in a specific controlled cooling range.
- the silicon is included in an amount of 0.5 to 1.0% by weight based on the total weight of the ultra-high strength reinforcing bar.
- austenite ( ⁇ ) ⁇ ferrite ( ⁇ ) phase transformation temperature change and carbon solid solution change in ferrite prevent grain boundary movement and prevent grain coarsening, and complex ferrite (polygonal and needle-shaped)
- V vanadium
- C, N carbon and nitrogen
- the silicon When the silicon is included in an amount of less than 0.5 wt%, the effect of the addition is insignificant, and when the silicon is included in an amount exceeding 1.0 wt%, an oxide is formed on the surface of the steel to reduce ductility and workability of the steel. Preferably 0.50 to 0.65 wt% may be included.
- the manganese (Mn) is an austenite stabilizing element in steel and is effective in improving hardenability. A part of manganese is dissolved in steel, and a part is combined with sulfur contained in the steel to form MnS, a non-metallic inclusion, which is ductile and elongates in the machining direction during plastic working. However, as the sulfur component in the steel decreases due to the formation of MnS, the crystal grains become weak and the formation of FeS, a low-melting-point compound, can be suppressed.
- the manganese is included in an amount of 0.40 to 1.80% by weight based on the total weight of the ultra-high strength reinforcing bar.
- the manganese is included in an amount of less than 0.40 wt%, the effect of the addition is insignificant, and when the manganese is included in an amount exceeding 1.80 wt%, the content of non-metallic inclusions such as MnS increases, so defects such as cracks may occur during welding.
- 1.2 to 1.5% by weight may be included.
- the chromium (Cr) is a ferrite stabilizing element. When added to the carbon and manganese-containing steel of the present invention, it delays the diffusion of carbon due to a solute-interfering effect, thereby affecting particle size refinement, and improving hardenability.
- the chromium is included in an amount of 0.10 to 1.0% by weight based on the total weight of the ultra-high strength reinforcing bar.
- the chromium is included in an amount of less than 0.10 wt %, the effect of the addition is insignificant, and when the chromium is included in an amount exceeding 1.0 wt %, weldability or toughness of the heat-affected zone may be reduced.
- 0.2 to 0.5 wt% may be included.
- the vanadium (V) has a stronger carbide formation ability than chromium, and since it refines crystal grains, it is also used to improve stainless steel or cutting tool steel. In addition, it is also used for precipitation hardening steels and permanent magnets because it forms a compound with other metal elements and has a remarkable precipitation hardening effect.
- the vanadium is contained in an amount greater than 0 and 0.2 wt% or less based on the total weight of the ultra-high strength reinforcing bar.
- the vanadium is included in an amount exceeding 0.2% by weight, the production cost increases, thereby reducing economic efficiency and lowering low-temperature impact toughness.
- it may be included in an amount of 0.08 to 0.15% by weight.
- the copper (Cu) is dissolved up to about 0.35% by weight in ferrite at room temperature and exhibits a solid solution strengthening effect, so that strength and hardness are slightly improved, but elongation may be reduced.
- hot workability is a problem, and in particular, when it contains 0.5 wt% or more, it causes red hot brittleness.
- corrosion resistance is significantly increased in the air or seawater, and when more than 0.4% is added, a precipitation hardening effect occurs due to fine precipitation of copper. is making
- the copper is included in an amount greater than 0 and 0.4% by weight or less based on the total weight of the ultra-high strength reinforcing bar.
- the copper is included in an amount exceeding 0.4 wt %, hot workability and elongation may be reduced or red hot brittleness may occur.
- 0.1 to 0.3% by weight may be included.
- the molybdenum (Mo) is used as an element for increasing hardenability, and in the present invention, it can improve strength, toughness, and hardenability of steel.
- the molybdenum is included in an amount greater than 0 and 0.5% by weight or less based on the total weight of the ultra-high strength reinforcing bar.
- the molybdenum is included in an amount exceeding 0.5% by weight, weldability may be deteriorated.
- it may be included in an amount of 0.001 to 0.1% by weight.
- the aluminum (Al) may function as a deoxidizer.
- the aluminum is included in an amount of 0.015 to 0.070% by weight based on the total weight of the ultra-high strength reinforcing bar.
- the aluminum is included in an amount of less than 0.015% by weight, the effect of the addition is insignificant, and when it is included in an amount exceeding 0.070% by weight, the amount of non-metallic inclusions such as aluminum oxide (Al 2 O 3 ) can be increased.
- Preferably 0.015 to 0.025% by weight may be included.
- the nickel (Ni) increases the strength of the steel and ensures a low-temperature impact value.
- the nickel is included in more than 0 0.25% by weight based on the total weight of the ultra-high strength reinforcing bar.
- the nickel may be included in an amount of 0.0001 to 0.005% by weight.
- the tin (Sn) may be added to secure corrosion resistance.
- the tin is included in an amount greater than 0 and 0.1% by weight or less based on the total weight of the ultra-high strength reinforcing bar.
- the tin is included in an amount exceeding 0.1 wt %, elongation may be significantly reduced.
- it may be included in an amount of 0.0001 to 0.005% by weight.
- the phosphorus (P) is not a problem if it is uniformly distributed in the steel, but usually forms Fe 3 P.
- the Fe 3 P is extremely fragile and segregated, so it is not homogenized even after annealing, and is elongated during processing such as forging and rolling.
- the phosphorus lowers impact resistance, promotes temper brittleness, and improves machinability in free-cutting steel, but is generally treated as an element harmful to steel.
- the phosphorus is included in an amount greater than 0 and 0.05% by weight or less based on the total weight of the ultra-high strength reinforcing bar.
- the phosphorus is included in an amount exceeding 0.05 wt %, central segregation and fine segregation are formed, which adversely affects the material and may deteriorate ductility.
- it may be included in an amount greater than 0 and 0.03% by weight or less.
- the sulfur (S) is combined with manganese (Mn), zinc (Zn), titanium (Ti) and molybdenum (Mo) to improve the machinability of steel, and is combined with manganese to form MnS inclusions.
- Mn manganese
- Zn zinc
- Ti titanium
- Mo molybdenum
- the ratio of manganese to sulfur may be about 5:1.
- the sulfur is contained in an amount greater than 0 and 0.03% by weight or less based on the total weight of the ultra-high strength reinforcing bar.
- the sulfur is included in an amount exceeding 0.03 wt%, ductility is greatly reduced, and the amount of non-metallic inclusions such as MnS may be significantly increased.
- it may be included in an amount greater than 0 and 0.025% by weight or less.
- the nitrogen (N) has a great effect on the mechanical properties of steel even in a very small amount, while increasing the tensile strength and yield strength, while decreasing the elongation. In particular, the decrease in the impact value and the increase in the transition temperature are remarkable.
- nitrogen has a fast diffusion rate and shows a continuous solubility change from 0.1 wt% to 0.003 wt% in ferrite.
- the nitrogen forms nitrides such as titanium, zirconium, vanadium and niobium to refine crystal grains.
- the nitrogen is contained in an amount of 0.005 to 0.02% by weight based on the total weight of the ultra-high strength reinforcing bar.
- the nitrogen is included in an amount of less than 0.005% by weight, the effect of its addition is insignificant, and when it is included in an amount exceeding 0.02% by weight, the elongation and formability of the steel may be reduced.
- the ultra-high strength reinforcing bar has a carbon equivalent (Ceq) of 0.7 or more, which is expressed by the following formula 1:
- the carbon equivalent When the carbon equivalent is 0.7 or more, the seismic performance and yield strength required for the reinforcing bar of the present invention can be achieved. If the carbon equivalent is less than 0.7, the seismic performance and strength of the reinforcing bar of the present invention may be reduced.
- the carbon equivalent may be 0.7 to 0.8.
- the ultra-high strength reinforcing bar has a central portion 20; and a surface layer portion 10 formed on the outer circumferential surface of the central portion 20 .
- the surface layer includes tempered martensite.
- the central portion is made of a microstructure including ferrite, pearlite, and bainite.
- the center may be formed of a microstructure containing 30 to 45% by volume of ferrite, 30 to 45% by volume of pearlite, and 15 to 25% by volume of bainite.
- both strength and seismic resistance may be excellent.
- the ferrite includes at least one of polygonal ferrite and acicular ferrite.
- the ultra-high strength reinforcing bar may include 5 to 15 area% of the surface layer part and 85 to 95 area% of the central part based on the cross-section. Under the above conditions, strength and seismic resistance may be excellent. For example, it may include 5 to 10 area% of the surface layer and 90 to 95 area% of the central part.
- the central portion 20 may include a hardened core layer 22 .
- the hardened core layer is formed through stress-induced transformation, and may have excellent seismic resistance and strength at the same time.
- the hardened core layer may have a microstructure including lower bainite and fine ferrite having an average size of 5 to 10 ⁇ m.
- the hardened nose layer is made of the microstructure, seismic resistance and strength may be excellent at the same time.
- the fine ferrite may have an average size of 6 to 8 ⁇ m.
- the hardened core layer may have a hardness of 350Hv or more. Under the above conditions, the seismic resistance and strength of the super-strength rebar of the present invention may be excellent at the same time.
- the hardened core layer may have a hardness of 350 to 400Hv
- a central portion excluding the hardened core layer may have a hardness of 240 to 280Hv
- the surface layer may have a hardness of 330 to 360Hv.
- the ultra-high strength reinforcing bar may include 15 to 30 area% of the hardened core layer based on the cross-section.
- the hardened core layer may be included in an area of 15 to 25%.
- the ultra-high strength reinforcing bar has a yield strength (YS) of 700 MPa or more, a tensile strength/yield strength (TS/YS) of 1.25 or more, and an elongation (El) of 10% or more. Under the above conditions, both strength and seismic resistance may be excellent.
- the ultra-high strength reinforcing bar may have a yield strength (YS) of 700 to 850 MPa, a tensile strength/yield strength (TS/YS) of 1.25 to 1.35, and an elongation (El) of 10 to 20%.
- the ultra-high strength rebar manufacturing method includes (S10) semi-finished product reheating; (S20) rolling material manufacturing step; (S30) cooling step; includes.
- the ultra-high strength rebar manufacturing method is (S10) carbon (C): 0.10 to 0.45 wt%, silicon (Si): 0.5 to 1.0 wt%, manganese (Mn): 0.40 to 1.80 wt%, chromium (Cr) : 0.10 to 1.0 wt%, vanadium (V): more than 0 and 0.2 wt% or less, copper (Cu): more than 0 to 0.4 wt% or less, molybdenum (Mo): more than 0 to 0.5 wt% or less, aluminum (Al): 0.015 to 0.070 wt %, Nickel (Ni): More than 0 0.25 wt %, Tin (Sn): More than 0, 0.1 wt %, Phosphorus (P): More than 0, 0.05 wt %, Sulfur (S): More than 0 0.03 wt %
- the manufactured ultra-high-strength reinforcing bar includes a central portion; and a surface layer portion formed on the outer circumferential surface of the central portion, wherein the surface portion includes tempered martensite, and the center portion is formed of a microstructure including ferrite, pearlite and bainite, wherein the ferrite is polygonal ferrite and needles It contains at least one of type ferrite, and yield strength (YS): 700 MPa or more and tensile strength/yield strength (TS/YS): 1.25 or more.
- the step is carbon (C): 0.10 to 0.45 wt%, silicon (Si): 0.5 to 1.0 wt%, manganese (Mn): 0.40 to 1.80 wt%, chromium (Cr): 0.10 to 1.0 wt%, vanadium (V) ): greater than 0 and less than or equal to 0.2% by weight, copper (Cu): greater than 0 and less than or equal to 0.4% by weight, molybdenum (Mo): greater than 0 and less than or equal to 0.5% by weight, aluminum (Al): 0.015 to 0.070% by weight, nickel (Ni): 0 More than 0.25% by weight, tin (Sn): greater than 0 and less than or equal to 0.1% by weight, phosphorus (P): greater than 0 and less than or equal to 0.05% by weight, sulfur (S): greater than 0 and less than or equal to 0.03% by weight, nitrogen (N): 0.005 to 0.02 It is a
- the semi-finished product may be a bloom or a billet manufactured by continuously casting molten steel of the above-described alloy component.
- the semi-finished product has a carbon equivalent (Ceq) of 0.7 or more, which is expressed by the following formula 1:
- the carbon equivalent When the carbon equivalent is 0.7 or more, the seismic performance and yield strength required for the reinforcing bar of the present invention can be achieved. If the carbon equivalent is less than 0.7, the seismic performance and strength of the reinforcing bar of the present invention may be reduced.
- the carbon equivalent may be 0.7 to 0.8. For example, it may be 0.70, 0.71, 0.72, 0.73, 0.74, 0.75, 0.76, 0.77, 0.78, 0.79 or 0.80.
- the reheating may be carried out at 1050 ⁇ 1250 °C.
- the reheating may be carried out at 1050 ⁇ 1150 °C.
- the step is a step of producing a rolled material by hot rolling the reheated semi-finished product at a finish rolling temperature: 850 ⁇ 1000 °C condition.
- the rolled material may be manufactured by starting the hot-rolling of the reheated semi-finished product at a temperature of 1050 to 1150° C. and ending the finish rolling temperature: 850 to 1000° C.
- the hot rolling may be performed through rough rolling (RM), intermediate finishing rolling (IM), and finishing rolling (FM).
- the hot rolling is carried out at a finish rolling temperature of less than 850 ° C.
- a rolling load is caused to decrease productivity and reduce the heat treatment effect.
- the finish rolling temperature is carried out in excess of 1000 ° C.
- a coarse pearlite structure is formed strength may be reduced.
- the finish rolling temperature can be carried out under the conditions of 940 ⁇ 1000 °C.
- the step is a step of cooling the rolled material to below the Ms temperature through the temp core.
- the rolled material may be subjected to a tempcore process to cool the surface temperature of the rolled material to a martensitic transformation starting temperature (Ms temperature) or less.
- Ms temperature martensitic transformation starting temperature
- the temp core process comprises the step of recuperating the cooled rolled material to 500 ⁇ 700 °C. If the recuperation temperature cannot be ensured, the thickness of the hardened layer in the target surface layer portion cannot be secured.
- the cooled rolled material may be reheated to 630 to 680 °C.
- the rolled material may be air-cooled after the recuperation.
- the surface of the rolled material is cooled to Ms or less through a temp core process to form a surface layer portion, and the central portion of the rolled material except for the surface layer portion may induce stress-induced transformation through controlled cooling.
- the central portion is formed with a complex microstructure comprising 30 to 45% by volume of ferrite, 30 to 45% by volume of pearlite, and 15 to 25% by volume of bainite at least one of polygonal and needle-shaped, lower bainite in the center (stress-induced bainite) and a core hardened layer composed of fine ferrite may be formed.
- the temp core process during the temp core process, it may be carried out under the conditions of a line speed of 6.7 to 7.2 m/s and a specific water amount of 3.7 to 3.9 l/kg (or 3.7 to 3.9 l/rolling material-kg) of the rolled material.
- the specific water quantity and the flux are controlled under the above conditions, it is possible to achieve the target recuperation temperature of the present invention, control the formation of the surface layer of the ultra-high-strength rebar, and bainite and bainite in the center of the ultra-high-strength rebar through organic stress transformation It is possible to induce the formation of a hardened core layer made of a microstructure including fine ferrite.
- cooling is sufficiently performed under the conditions of the flux and specific amount of the rolled material to achieve the target recuperation temperature range of the present invention.
- the ultra-high strength reinforcing bar may include 5 to 15 area% of the surface layer part and 85 to 95 area% of the central part based on the cross-section. Under the above conditions, strength and seismic resistance may be excellent. For example, it may include 5 to 10 area% of the surface layer and 90 to 95 area% of the central part.
- the central portion may include a hardened core layer.
- the hardened core layer is formed through stress-induced transformation, and may have excellent seismic resistance and strength at the same time.
- the hardened core layer may have a microstructure including lower bainite and fine ferrite having an average size of 5 to 10 ⁇ m.
- the “size” may mean the maximum length of the fine ferrite.
- the fine ferrite may have an average size of 6 to 8 ⁇ m.
- the hardened core layer may have a hardness of 350Hv or more. Under the above conditions, the seismic resistance and strength of the super-strength rebar of the present invention may be excellent at the same time.
- the hardened core layer may have a hardness of 350 to 400Hv
- a central portion excluding the hardened core layer may have a hardness of 240 to 280Hv
- the surface layer may have a hardness of 330 to 360Hv.
- the ultra-high strength reinforcing bar may include 15 to 30 area% of the hardened core layer based on the cross-section.
- the hardened core layer may be included in an area of 15 to 25%.
- the ultra-high strength reinforcing bar may have a yield strength (YS) of 700 MPa or more, a tensile strength/yield strength (TS/YS) of 1.25 or more, and an elongation (El) of 10% or more. Under the above conditions, both strength and seismic resistance may be excellent.
- the ultra-high strength reinforcing bar may have a yield strength (YS) of 700 to 850 MPa, a tensile strength/yield strength (TS/YS) of 1.25 to 1.35, and an elongation (El) of 10 to 20%.
- Example 1 the silicon (Si) content was increased even though the vanadium (V) content was reduced compared to Comparative Examples 1 and 2, and it was found that it was possible to secure a sufficient material for the reinforcing bar. .
- the increase in the content of silicon prevents grain boundary movement due to austenite ( ⁇ ) ⁇ ferrite ( ⁇ ) phase transformation temperature change and carbon solid solution change in ferrite to prevent grain coarsening, and complex (polygon+) Needle-shaped) It is considered that the bonding of residual vanadium (V) with carbon and nitrogen (C, N) was induced in the temperature range where ferrite and bainite were formed, and VCN precipitates were formed inside the ferrite, contributing to the material increase.
- the above embodiment does not follow the conventional cooling in order to secure the required properties of the reinforcing bar, but controls the surface layer part by controlling the specific water quantity and the beam speed during temp core, and a hardened core layer composed of bainite and fine ferrite at the center of the rebar induced the formation of
- the reinforcing bar of the embodiment of the present invention has a central portion 20 made of a microstructure including 42% by volume of ferrite, 34% by volume of pearlite and 24% by volume of bainite, and the central portion 20 Formed on the outer peripheral surface of the, including a surface layer portion 10 consisting of a microstructure containing tempered martensite, the central portion 20 is a hardened core layer 22 consisting of a composite microstructure containing lower bainite and fine ferrite It can be seen that this was formed.
- the reinforcing bar of Comparative Example 1 is formed on the outer surface of the central portion 2 and the central portion 2 containing 35% by volume of polygonal ferrite and 65% by volume of pearlite, and includes tempered martensite It can be seen that it includes a surface layer portion 1 made of a microstructure.
- FIG. 4 (a) is the microstructure of the surface layer of the reinforcing bar of Example
- FIG. 4 (b) is the microstructure of the center of the reinforcing bar of Example
- FIG. . is the microstructure of the surface layer of the reinforcing bar of Comparative Example 1
- Fig. 5 (b) is the microstructure of the center of the rebar of Comparative Example 1
- Fig. 5 (c) is a microstructure photograph of the center of the reinforcing bar of Comparative Example 1. .
- the reinforcing bar of the embodiment has a surface layer portion (hardness 370Hv) having a microstructure containing martensite, and a central portion (hardness 260Hv) containing ferrite, pearlite and bainite was formed, and the It was found that a hardened core layer (hardness of 350 Hv) of about 15 to 25 area% was formed in the center of the reinforcing bar cross-section. In addition, it was found that the hardened core layer had a microstructure including lower bainite and fine ferrite having an average size of about 7 to 8 ⁇ m.
- the reinforcing bar of Example and Comparative Example 1 can confirm a clear difference in microstructure, and even in the microhardness measurement result, the central hardness value of the reinforcing bar of Example 1 is about 100 Hv higher than that of Comparative Example 1.
- the hardened core layer of the above embodiment is formed through phase control through Stress Induced Transformation (SIT) as a link effect between strain energy accumulated during finish hot rolling and cooling control, and specific quantity of the present invention 3.7 It was found that it was possible to secure the hardened core layer under the condition of ⁇ 3.9 l/rolling material-kg.
- SIT Stress Induced Transformation
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Abstract
Description
Claims (12)
- 탄소(C): 0.10~0.45 중량%, 실리콘(Si): 0.5~1.0 중량%, 망간(Mn): 0.40~1.80 중량%, 크롬(Cr): 0.10~1.0 중량%, 바나듐(V): 0 초과 0.2 중량% 이하, 구리(Cu): 0 초과 0.4 중량% 이하, 몰리브덴(Mo): 0 초과 0.5 중량% 이하, 알루미늄(Al): 0.015~0.070 중량%, 니켈(Ni): 0 초과 0.25 중량% 이하, 주석(Sn): 0 초과 0.1 중량% 이하, 인(P): 0 초과 0.05 중량% 이하, 황(S): 0 초과 0.03 중량% 이하, 질소(N): 0.005~0.02 중량%, 잔량의 철(Fe) 및 기타 불가피한 불순물을 포함하며, 하기 식 1에 따른 탄소당량(Ceq): 0.7 이상인 초고강도 철근이며,상기 초고강도 철근은 중심부; 및 상기 중심부의 외주면에 형성되는 표층부;를 포함하며,상기 표층부는 템퍼드 마르텐사이트를 포함하고, 상기 중심부는 페라이트, 펄라이트 및 베이나이트를 포함하는 미세조직으로 이루어지며,상기 페라이트는 다각형 페라이트 및 침상형 페라이트 중 하나 이상을 포함하고,항복강도(YS): 700MPa 이상 및 인장강도/항복강도(TS/YS): 1.25 이상인 것을 특징으로 하는 초고강도 철근:[식 1]Ceq = [C] + [Mn]/6 + ([Cr]+[V]+[Mo])/5 + ([Cu]+[Ni])/15(상기 식 1에서, 상기 [C], [Mn], [Cr], [V], [Mo], [Cu] 및 [Ni]는 상기 철근에 포함되는 탄소(C), 망간(Mn), 크롬(Cr), 바나듐(V), 몰리브덴(Mo), 구리(Cu) 및 니켈(Ni)의 함량(중량%) 이다).
- 제1항에 있어서,항복강도(YS) 700~850MPa, 인장강도/항복강도(TS/YS) 1.25~1.35 및 연신율(El) 10% 이상인 것을 특징으로 하는 초고강도 철근.
- 제1항에 있어서,상기 중심부는 페라이트 30~45 부피%, 펄라이트 30~45 부피% 및 베이나이트 15~25 부피%를 포함하는 미세조직으로 이루어지는 것을 특징으로 하는 초고강도 철근.
- 제1항에 있어서,상기 철근은 횡단면 기준 표층부 5~15 면적% 및 중심부 85~95 면적%를 포함하는 것을 특징으로 하는 초고강도 철근.
- 제1항에 있어서,상기 중심부는 경도 350Hv 이상인 코어경화층을 포함하는 것을 특징으로 하는 초고강도 철근.
- 제5항에 있어서,상기 코어경화층은 하부 베이나이트(lower bainite) 및 평균 크기 5~10㎛인 미세 페라이트를 포함하는 미세조직으로 이루어지는 것을 특징으로 하는 초고강도 철근.
- 제5항에 있어서,상기 코어경화층은 경도 350~400Hv이고,상기 코어경화층을 제외한 중심부는 경도 240~280Hv 이며,표층부는 경도 330~360Hv인 것을 특징으로 하는 초고강도 철근.
- 제5항에 있어서,상기 철근은 횡단면 기준 상기 코어경화층을 15~30 면적%로 포함하는 것을 특징으로 하는 초고강도 철근.
- 탄소(C): 0.10~0.45 중량%, 실리콘(Si): 0.5~1.0 중량%, 망간(Mn): 0.40~1.80 중량%, 크롬(Cr): 0.10~1.0 중량%, 바나듐(V): 0 초과 0.2 중량% 이하, 구리(Cu): 0 초과 0.4 중량% 이하, 몰리브덴(Mo): 0 초과 0.5 중량% 이하, 알루미늄(Al): 0.015~0.070 중량%, 니켈(Ni): 0 초과 0.25 중량% 이하, 주석(Sn): 0 초과 0.1 중량% 이하, 인(P): 0 초과 0.05 중량% 이하, 황(S): 0 초과 0.03 중량% 이하, 질소(N): 0.005~0.02 중량%, 잔량의 철(Fe) 및 기타 불가피한 불순물을 포함하며, 하기 식 1에 따른 탄소당량(Ceq): 0.7 이상인 반제품을 재가열하는 단계;상기 재가열된 반제품을 마무리 압연온도: 850~1000℃ 조건으로 열간압연하여 압연재를 제조하는 단계; 및상기 압연재를 Ms 온도 이하까지 냉각하는 단계;를 포함하되,상기 냉각은 상기 압연재를 500~700℃까지 복열하는 단계;를 포함하여 이루어지는 초고강도 철근 제조방법이며,상기 초고강도 철근은 중심부; 및 상기 중심부의 외주면에 형성되는 표층부;를 포함하며,상기 표층부는 템퍼드 마르텐사이트를 포함하고, 상기 중심부는 페라이트, 펄라이트 및 베이나이트를 포함하는 미세조직으로 이루어지며,상기 페라이트는 다각형 페라이트 및 침상형 페라이트 중 하나 이상을 포함하며,항복강도(YS): 700MPa 이상 및 인장강도/항복강도(TS/YS): 1.25 이상인 것을 특징으로 하는 초고강도 철근 제조방법:[식 1]Ceq = [C] + [Mn]/6 + ([Cr]+[V]+[Mo])/5 + ([Cu]+[Ni])/15(상기 식 1에서, 상기 [C], [Mn], [Cr], [V], [Mo], [Cu] 및 [Ni]는 상기 반제품에 포함되는 탄소(C), 망간(Mn), 크롬(Cr), 바나듐(V), 몰리브덴(Mo), 구리(Cu) 및 니켈(Ni)의 함량(중량%) 이다).
- 제9항에 있어서,상기 냉각시 상기 압연재의 선속 6.7~7.2m/s 및 비수량 3.7~3.9 l/kg 조건으로 실시하는 것을 특징으로 하는 초고강도 철근 제조방법.
- 제9항에 있어서,상기 재가열은 1050~1250℃에서 실시하는 것을 특징으로 하는 초고강도 철근 제조방법.
- 제9항에 있어서,상기 중심부는 경도 350Hv 이상인 코어경화층을 포함하는 것을 특징으로 하는 초고강도 철근 제조방법.
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