Classifications

• • 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
  • 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
  • C21D1/00—General methods or devices for heat treatment, e.g. annealing, hardening, quenching or tempering
  • C21D1/84—Controlled slow cooling
• • 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
• • 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
• • 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
  • C22C38/04—Ferrous alloys, e.g. steel alloys containing manganese
• • 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
  • C21D1/00—General methods or devices for heat treatment, e.g. annealing, hardening, quenching or tempering
  • C21D1/02—Hardening articles or materials formed by forging or rolling, with no further heating beyond that required for the formation
• • 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
  • C21D2211/003—Cementite
• • 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
• • 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
  • C21D7/00—Modifying the physical properties of iron or steel by deformation
  • C21D7/13—Modifying the physical properties of iron or steel by deformation by hot working

Definitions

• the present invention relates to a steel wire with improved drawability and a method for manufacturing the same, and more specifically, to a steel wire without delamination and with improved torsion properties and drawability, and a method for manufacturing the same.
• a method of increasing the strength of the material itself may be used. That is, as one of the methods for obtaining a high-strength steel wire, a method of increasing the strength of the material itself by adding a large amount of a reinforcing element that increases the strength of the steel may be used.
• a typical example of such a reinforcing element is carbon.
• a carbon content is increased, a fraction of cementite, which is a hard phase, inside a wire rod increases and the lamellar spacing of a pearlite structure becomes denser, so that the strength of the material is improved.
• Techniques for adding various alloying elements in addition to carbon have been proposed.
• strength can be improved by increasing the drawing strain of the steel wire.
• the drawing strain of the material is closely related to the ductility of the material, and it is advantageous to improve the strength as the material itself is easily processed without disconnection during drawing.
• the most economical method among methods for increasing the strength of the steel wire is a method of reducing the amount of alloying elements and increasing the drawing strain.
• delamination usually occurs when the drawing strain increases, and when delamination occurs during a torsion test of a steel wire, it is regarded as a defect, and the maximum drawing strain at which delamination does not occur is defined as a drawing limit.
• the occurrence of delamination is related to cementite decomposition, and when cementite decomposition occurs due to an increase in drawing strain, carbon from cementite is released into ferrite, thereby rapidly reducing the plastic deformability of ferrite and generating cracks. This acts as a major obstacle to the high strength of the steel wire.
• the present invention is directed to providing a steel wire with improved drawability by controlling the strength of a wire rod and slowing down a decomposition rate of cementite, and a method for manufacturing the same.
• a steel wire having improved drawability according to one embodiment of the present invention includes, in weight percent, C: 0.52 to 0.69%, Mn: 0.3 to 0.8%, Si: 0.1 to 0.5%, a balance of Fe, and unavoidable impurities, has a carbon content of cementite in pearlite of 7 at% or more, and satisfies the following Expression (1).
• TS denotes a tensile strength (MPa) of a wire rod before drawing
• ⁇ denotes a drawing strain
• a tensile strength of a wire rod may be 700 to 1,000 MPa.
• the torsion number of the steel wire may be 30 or more.
• Delamination may not occur in the steel wire at a drawing strain of 4.02 or less.
• a method for manufacturing a steel wire for a spring with improved fatigue life and toughness includes: hot-rolling a billet including, in weight percent, C: 0.52 to 0.69%, Mn: 0.3 to 0.8%, Si: 0.1 to 0.5%, a balance of Fe, and unavoidable impurities to obtain a wire rod; cooling the hot-rolled wire rod at a cooling rate of 3 to 20 °C/s; and obtaining a steel wire by drawing the cooled wire rod to satisfy the following Expression (1).
• [TS] denotes a tensile strength (MPa) of a wire rod before drawing
• ⁇ denotes a drawing strain
• delamination may not occur at a drawing strain of 4.02 or less.
• the occurrence of delamination can be suppressed and torsion properties and a drawing limit can be increased even during drawing with a high drawing strain by controlling the strength of a wire rod and slowing down a decomposition rate of cementite.
• the steel wire according to the embodiment of the present invention can secure a torsion number of 27 or more even at a drawing strain of 4.02, and since delamination does not occur during drawing, a drawing limit can be increased and, ultimately, a steel wire having ultra-high strength can be provided.
• a steel wire having improved drawability according to an embodiment of the present invention includes, in weight percent, C: 0.52 to 0.69%, Mn: 0.3 to 0.8%, Si: 0.1 to 0.5%, a balance of Fe, and unavoidable impurities, has a carbon content of cementite in pearlite of 7 at% or more, and satisfies the following Expression (1).
• TS denotes a tensile strength (MPa) of a wire rod before drawing
• ⁇ denotes a drawing strain
• a steel wire having improved drawability according to an embodiment of the present invention includes, in weight percent, C: 0.52 to 0.69%, Mn: 0.3 to 0.8%, Si: 0.1 to 0.5%, a balance of Fe and unavoidable impurities, has a carbon content of cementite in pearlite of 7 at% or more after drawing, and satisfies the following Expression (1).
• [TS] denotes a tensile strength (MPa) of the wire rod before drawing
• ⁇ denotes the drawing strain
• a content of C is 0.52 to 0.69%.
• C is an element added to improve the strength of the steel wire.
• a C content is less than 0.52%, a strength improvement effect is not sufficient, and when the C content exceeds 0.69%, the strength of the steel can be secured but ductility is reduced, so that in the present invention, it is preferable to control the C content to 0.52 to 0.69%.
• a content of Mn is 0.3 to 0.8%.
• Mn is an effective element for increasing hardenability.
• an Mn content is less than 0.3%, the above-mentioned effect cannot be sufficiently obtained, and when the Mn content exceeds 0.8%, centerline segregation may occur, and the possibility of causing a low-temperature structure is very high, so that it is preferable to control the Mn content to 0.3 to 0.8% in the present invention.
• a content of Si is 0.1 to 0.5%.
• Si is an effective element for increasing the cleanliness of a wire rod and strengthening steel by being employed in ferrite, which is a base structure, to improve strength.
• ferrite which is a base structure
• the Si content is preferably controlled to 0.1 to 0.5%.
• the remainder is Fe, and includes other impurities inevitably mixed in manufacturing processes.
• the addition of other alloying elements other than the above-mentioned alloy composition is not excluded.
• the steel wire having improved drawability according to one embodiment of the present invention may have a carbon content of cementite in perlite of 7 at% or more after drawing.
• the carbon content of cementite (Fe 3 C) in pearlite is 25 at%, but the carbon content of cementite in pearlite becomes lower than 25 at% through the drawing process.
• the carbon content in cementite is less than 7 at%, delamination may occur, so that the carbon content in cementite is limited to 7 at% or more.
• the steel wire with improved drawability according to one embodiment of the present invention satisfies the following Expression (1).
• [TS] denotes a tensile strength (MPa) of a wire rod before drawing
• ⁇ denotes a drawing strain
• the drawing strain ( ⁇ ) is expressed as 2ln(di/df).
• di denotes an initial diameter of the steel wire before drawing
• df denotes a diameter of the steel wire after drawing.
• the present invention can slow down a decomposition rate of cementite and suppress the occurrence of delamination by controlling the tensile strength and drawing strain of the wire rod so that the value of Expression (1) is less than 1,500.
• the cementite decomposition rate can slow down even at a high drawing strain, and thus delamination can be suppressed.
• the drawing strain is 3.0 or more is considered excessive deformation when drawing is performed, but in the present invention, even when a severe drawing strain of 4.02 is applied during drawing, it is possible to provide a steel wire having a torsion number of 27 or more and having ultra-high strength.
• the ultra-high strength steel wire with an increased drawing limit of the present invention can be applied to products such as tire cord, saw wire, wire rope, piano wire, and steel wire for bridges.
• the tensile strength of the wire rod according to the present invention may be in the range of 700 to 1,000 MPa.
• a method for manufacturing a steel wire with improved drawability includes: hot-rolling a billet including, in weight percent, C: 0.52 to 0.69%, Mn: 0.3 to 0.8%, Si: 0.1 to 0.5%, a balance of Fe, and unavoidable impurities to obtain a wire rod; cooling the hot-rolled wire rod at a cooling rate of 3 to 20 °C/s; and obtaining a steel wire by drawing the cooled wire rod to satisfy the following Expression (1).
• [TS] denotes a tensile strength (MPa) of a wire rod before drawing
• ⁇ denotes a drawing strain
• the steel wire with improved drawability according to the present invention can be manufactured by hot-rolling a billet including the alloy composition described above to obtain a wire rod, cooling the hot-rolled wire rod, and drawing the cooled wire rod to satisfy Expression (1).
• the billet can be hot-rolled at a temperature range of 800 °C to 1200 °C after heating to a temperature range of 900 to 1100 °C
• cooling of the wire rod may be performed at a cooling rate of 3 to 20 °C/s.
• the cooling rate is less than 3 °C/s, there is a problem that segmented and coarse pearlite is generated, and when the cooling rate exceeds 20 °C/s, there is a problem in that a low temperature structure such as martensite is caused. Therefore, in the present invention, it is preferable to control the cooling rate of the wire rod to 3 to 20 °C/s.
• the cooled wire rod may be drawn to satisfy the above-described Expression (1).
• the torsion number of the steel wire was determined by the number of turns until the steel wire broke during a torsion test applying transverse stress, and the presence or absence of delamination was indicated by checking whether a spiral fracture defect appeared at a wire fracture portion.
• Inventive Example 1 856 3.57 12 36 Did not occur 1211
• Inventive Example 2 844 3.79 11 34 Did not occur 1287
• Inventive Example 3 848 4.02 9 30 Did not occur 1405
• Inventive Example 4 948 3.57 10 35 Did not occur 1303
• Inventive Example 5 950 3.79 9 33 Did not occur 1393 Comparative Example 1 967 4.02 6 24 Occurred 1524

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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)
• Heat Treatment Of Strip Materials And Filament Materials (AREA)

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• 2020
  • 2020-12-15 KR KR1020200175304A patent/KR102464611B1/ko active Active
• 2021
  • 2021-11-18 EP EP21906896.2A patent/EP4265768A4/fr active Pending
  • 2021-11-18 US US18/267,237 patent/US20240117459A1/en active Pending
  • 2021-11-18 WO PCT/KR2021/016988 patent/WO2022131591A1/fr not_active Ceased
  • 2021-11-18 CN CN202180084212.0A patent/CN116829754A/zh active Pending

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