Classifications

• • 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 of ferrous metals or ferrous alloys by deformation combined with, or followed by, heat treatment
  • C21D8/02—Modifying the physical properties of ferrous metals or ferrous alloys by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips
  • C21D8/0221—Modifying the physical properties of ferrous metals or ferrous alloys by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips characterised by the working steps
  • C21D8/0226—Hot rolling
• • 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
• • 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 of ferrous metals or ferrous alloys by deformation combined with, or followed by, heat treatment
  • C21D8/02—Modifying the physical properties of ferrous metals or ferrous alloys 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 of ferrous metals or ferrous alloys by deformation combined with, or followed by, heat treatment
  • C21D8/06—Modifying the physical properties of ferrous metals or ferrous alloys by deformation combined with, or followed by, heat treatment during manufacturing of rods or wires
• • 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 of ferrous metals or ferrous alloys by deformation combined with, or followed by, heat treatment
  • C21D8/06—Modifying the physical properties of ferrous metals or ferrous alloys by deformation combined with, or followed by, heat treatment during manufacturing of rods or wires
  • C21D8/08—Modifying the physical properties of ferrous metals or ferrous alloys by deformation combined with, or followed by, heat treatment during manufacturing of rods or wires for concrete reinforcement
• • 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
  • 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
• • 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
  • C22C38/002—Ferrous alloys, e.g. steel alloys containing In, Mg, or other elements not provided for in one single group C22C38/001 - C22C38/60
• • 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
  • C22C38/004—Very low carbon steels, i.e. having a carbon content of less than 0,01%
• • 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
  • C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
• • 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
  • C22C38/60—Ferrous alloys, e.g. steel alloys containing lead, selenium, tellurium, or antimony, or more than 0.04% by weight of sulfur
• • 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
  • C21D2211/00—Microstructure comprising significant phases
  • C21D2211/009—Pearlite

Definitions

• the present invention relates to a wire rod for concrete reinforcing steel fibers that are used as concrete reinforcements in tunnels, floors, and the like, steel fibers, and a method for manufacturing the same.
• Si forms firelite (Fe 2 SiO 4 ) at the boundary between the scale and the base material, which degrades the scale removability, and thus it is important to minimize SI.
• the present invention is directed to providing a wire rod for concrete reinforcing steel fibers, steel fibers, and a method for manufacturing the same, which have a tensile strength of 1700 MPa or more and do not fracture after at least 10 repeated applications of 90-degree bending, through dry drawing and wet drawing without a lead patenting (LP) heat treatment by controlling Expression1 and microstructure through an alloy composition and a manufacturing process.
• LP lead patenting
• a microstructure thereof may include, in area fraction, more than 98% and less than 100% quasi polygonal ferrite and more than 0% and less than 2% cementite.
• an average grain size of the quasi polygonal ferrite in a range of 1/4D based on a cross-section may be more than 0 ⁇ m and 35 ⁇ m or less.
• D refers to a diameter of the wire rod.
• the wire rod may satisfy Expression 1 below, C + 0.17 * Mn + 0.25 * Cr ⁇ 0.62 ⁇ 0 ,
• [C], [Mn], and [Cr] represent the content (wt%) of each element.
• no fracture occurs after at least 10 repeated applications of 90-degree bending.
• [C], [Mn], and [Cr] represent the content (wt%) of each element.
• a wire rod for concrete reinforcing steel fibers, steel fibers, and a method for manufacturing the same according to an embodiment of the present invention can ensure a tensile strength of 1700 MPa or more and not fracture after at least 10 repeated applications of 90-degree bending, through dry drawing and wet drawing without a lead patenting (LP) heat treatment during processing.
• LP lead patenting
• FIG. 1 is a photograph showing the microstructure observed in Inventive Example 4.
• a wire rod for concrete reinforcing steel fibers may include, in percent by weight (wt%), 0.005 to 0.035% of C, 0.07 to 0.3% of Si, 0.07 to 0.2% of Mn, 1.0 to 2.2% of Cr, 0.05% or less of P, 0.05% or less of S, and the balance of Fe and other inevitable impurities.
• the content of C may be 0.005 to 0.035 wt%.
• C is an element that greatly improves strength during the formation of pearlite or cementite, but an increase in the C content may lead to the formation of pearlite that may cause wire breakage during wet drawing. Therefore, when the C content is less than 0.005%, it is difficult to achieve the target strength, and when the C content exceeds 0.035%, cementite having an area fraction of 2% or more may form along grain boundaries, which may cause wire breakage during drawing. Accordingly, it is desirable to control the C content to less than or equal to 0.035%.
• the content of Si may be 0.07 to 0.3 wt%.
• the content of Mn may be 0.07 to 0.2 wt%.
• Mn is an element that contributes to solid solution strengthening and hardenability, and may combine with S present in steel to form MnS, and thus, it may be included in an amount of 0.07% or more. However, since the addition of Mn has a limited effect on strengthening improvement and increase the costs, it is desirable to set the maximum content to 0.2%.
• Cr is a primary solid solution strengthening element that is present in ferrite and increases the strength of the material.
• the tensile strength may increase by about 40 MPa.
• the addition of Cr may increase the work hardening rate during drawing by 300 or more, enabling strength improvement also in the final product.
• the Cr content is less than 1.0%, it is difficult to achieve the target strength, and when the Cr content exceeds 2.2%, cracks may occur due to stress difference between the surface and the center caused by martensite formation in the central region, when a continuously cast bloom is charged into a high-temperature furnace at a low temperature. Therefore, it is desirable to control the Cr content to 2.2% or less.
• the remaining component(s) of the disclosed invention is iron (Fe).
• Fe iron
• unintended impurities may inevitably be introduced from raw materials or the surrounding environment in a typical manufacturing process, and thus cannot be excluded. Since such impurities may be well known to those skilled in the art of conventional manufacturing processes, details thereof are not described in this specification.
• the wire rod for concrete reinforcing steel fibers according to an embodiment of the present invention may satisfy Expression 1.
• [C], [Mn], and [Cr] represent the content (wt%) of each element.
• C, Mn, and Cr are elements related to the strength of the material.
• the addition of Cr at a high content of 1.0% or more which has an excellent solid solution strengthening effect, may increase the initial material strength and work hardening rate.
• excessive addition of Cr content may cause internal cracks when the billet is cooled and then charged into the heating furnace, which may lead to breakage inside the heating furnace or cause cobbling during rolling. Therefore, Expression 1 represents a relationship for appropriate contents of C, Mn, and Cr, and when the value of Expression 1 is more than 0, billet cracks may occur, resulting in cobbling formation during wire rod rolling. Therefore, it is desirable to control the value to be less than or equal to 0.
• the microstructure of the wire rod for concrete reinforcing steel fibers may include, in area fraction, more than 98% and less than 100% of quasi polygonal ferrite and more than 0% and less than 2% of cementite.
• the primary structure of the steel is composed of quasi polygonal ferrite, which is a low-temperature transformation structure, through a large amount of Cr content, wire breakage under load may be prevented even when a lead patenting (LP) heat treatment is omitted, and compared to when the primary structure is composed of polygonal ferrite, the strength reduction may be suppressed without inhibition of elongation, and the like, thereby enabling a higher tensile strength.
• the formation of carbides such as CrC due to the addition of Cr reduces the cementite formation compared to when Cr is not added, which may lower the probability of wire breakage during drawing.
• an average grain size of the quasi polygonal ferrite in a range of 1/4D based on a cross-section may be more than 0 ⁇ m and 35 ⁇ m or less.
• D refers to a diameter of the wire rod.
• the average grain size of the quasi-polygonal ferrite is more than 0 ⁇ m and 35 ⁇ m or less, a wire breakage may be prevented during drawing, and the 90-degree bending performance of the final steel fiber may be greatly improved to withstand at least 10 repetition.
• the wire rod for concrete reinforcing steel fiber according to an embodiment of the present invention may have a tensile strength of 850 MPa or more.
• the wire rod for concrete reinforcing steel fibers may be manufactured by preparing a billet having the alloy composition described above, and then subjecting the billet to reheating, wire rod rolling, coiling, and cooling processes.
• the method for manufacturing a wire rod for concrete reinforcing steel fibers may include maintaining a billet comprising, in percent by weight (wt%), 0.005 to 0.035% of C, 0.07 to 0.3% of Si, 0.07 to 0.2% of Mn, 1.0 to 2.2% of Cr, 0.05% or less of P, 0.05% or less of S, and the balance of Fe and other inevitable impurities at a temperature range of 1,000 to 1,250°C for 90 to 120 minutes, and then rolling the billet to produce a wire rod; coiling the produced wire rod at a temperature range of 880 to 950°C, wherein cooling after the coiling includes a first cooling of cooling the wire rod to a temperature of 800°C at a rate of 1°C/s or less, and a second cooling of finally cooling the wire rod to a temperature of 300°C at a rate of 20°C/s or more.
• the billet After preparing the billet having the above-described alloy composition, in order to achieve normalizing and austenite formation, the billet is maintained at a heating temperature of 1,000 to 1,250°C for 90 to 120 minutes and then rolled.
• a heating temperature 1,000 to 1,250°C for 90 to 120 minutes and then rolled.
• the temperature When the temperature is maintained below 1,000°C, the charging time becomes long, and when the temperature is maintained above 1,250°C, it imposes an increased thermal load. Therefore, it is desirable to control the temperature to 1,000 to 1,250°C.
• the temperature when the temperature is maintained below 90 minutes, it may be difficult to form central austenite, and when the temperature is maintained above 120 minutes, coarse grain growth may occur. Therefore, it is desirable to maintain the temperature for 90 to 120 minutes.
• the heated billet is rolled under conventional rolling conditions. That is, the heated billet is subjected to hot rolling sequentially including rough rolling, intermediate rough rolling/finish rolling, and final rolling to produce a wire rod.
• the coiling temperature is controlled to 880°C ⁇ 950°C through water cooling.
• the minimum thickness of 8um is not achieved, and when the temperature is above 950°C, the thickness of 20um is achieved, but a coiling shape defect (requiring equipment investment) occurs. Therefore, it is desirable to control the coiling temperature within the range.
• the wire rod is cooled to 300°C at a rate of 20°C/s or more using a reforming tube in a Stelmore cooling zone, thereby suppressing the transformation and increasing the tensile strength.
• the cooling rate in the second cooling may be 30°C/s or less. When the cooling rate exceeds 30°C/s, the tensile strength targeted by the present invention may not be achieved.
• the wire rod may satisfy Expression 1.
• [C], [Mn], and [Cr] represent the content (wt%) of each element.
• the concrete reinforcing steel fiber according to the present invention may include, in percent by weight (wt%), 0.005 to 0.035% of C, 0.07 to 0.3% of Si, 0.07 to 0.2% of Mn, 1.0 to 2.2% of Cr, 0.05% or less of P, 0.05% or less of S, and the balance of Fe and other inevitable impurities, and satisfy Expression 1 below, and have a tensile strength of 1700 MPa or more, C + 0.17 * Mn + 0.25 * Cr ⁇ 0.62 ⁇ 0
• [C], [Mn], and [Cr] represent the content (wt%) of each element.
• the concrete reinforcing steel fiber according to the present invention may have no fracture after at least 10 repeated applications of 90-degree bending.
• [C], [Mn], and [Cr] represent the content (wt%) of each element.
• a steel having the alloy composition shown in Table 1 below was refined in a converter and cast under conventional conditions to produce a 160 x 160mm 2 continuous casting billet.
• the billet was maintained at a temperature of 1,080°C for 98 minutes, followed by rolling under conventional conditions, and after finish rolling, the coiling temperature was controlled to 905°Cthrough cooling in a water cooling zone.
• the first cooling was performed up to a temperature of 800°C at a rate of 0.08°C/s in the Stelmore cooling zone, and the second cooling was performed at a rate of 22°C/s to the reforming tube to complete the cooling and produce a wire rod.
• Tables 1 and 2 show the test compositions, the microstructures of the wire rod observed under an optical microscope in a 1/4D region of the wire rod cross-section, and the mechanical properties of the wire rod, in which D represents the diameter of the wire rod.
• the average grain size of quasi-polygonal ferrite was defined by measuring the area of all grains measured at 100 x magnification, converting the area into a grain size while assuming it as a circular shape, and then dividing the grain size by the number of grains.
• Table 3 shows the properties of steel fibers manufactured by removing scale on the surface of the manufactured wire rod using a mechanical descaling method, and performing dry drawing and then wet drawing without performing a LP heat treatment.
• the tensile test was conducted in accordance with ISO 6892-1 standard, and the tensile speed (cross head speed) was 50 m/min.
• the test specimen had a length of 300 mm, and was continuously cut into 20 pieces, whose tensile strengths were measured, and the average and deviation were checked.
• the 90-degree bending test was performed using steel fibers having a length of 300 mm as test specimens.
• a pin having a size of 2.5R (R is the diameter of the steel fiber: 0.55 mm) was fixed at the midpoint along the length, and 90-degree bending was repeated in one direction. The number of times until fracture occurred during the repeated 90-degree bending is shown in Table 3 below.

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• Chemical & Material Sciences (AREA)
• Engineering & Computer Science (AREA)
• Mechanical Engineering (AREA)
• Materials Engineering (AREA)
• Metallurgy (AREA)
• Organic Chemistry (AREA)
• Physics & Mathematics (AREA)
• Thermal Sciences (AREA)
• Crystallography & Structural Chemistry (AREA)
• Manufacturing & Machinery (AREA)
• Heat Treatment Of Steel (AREA)

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• 2022
  • 2022-12-21 KR KR1020220180140A patent/KR20240098409A/ko active Pending
• 2023
  • 2023-11-24 JP JP2025532898A patent/JP2025539890A/ja active Pending
  • 2023-11-24 CN CN202380087285.4A patent/CN120418470A/zh active Pending
  • 2023-11-24 WO PCT/KR2023/019121 patent/WO2024136173A1/fr not_active Ceased
  • 2023-11-24 EP EP23907459.4A patent/EP4613902A4/fr active Pending

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