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
  • C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
  • C22C38/40—Ferrous alloys, e.g. steel alloys containing chromium with nickel
• • 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
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B21—MECHANICAL METAL-WORKING WITHOUT ESSENTIALLY REMOVING MATERIAL; PUNCHING METAL
  • B21C—MANUFACTURE OF METAL SHEETS, WIRE, RODS, TUBES OR PROFILES, OTHERWISE THAN BY ROLLING; AUXILIARY OPERATIONS USED IN CONNECTION WITH METAL-WORKING WITHOUT ESSENTIALLY REMOVING MATERIAL
  • B21C1/00—Manufacture of metal sheets, metal wire, metal rods, metal tubes by drawing
  • B21C1/003—Drawing materials of special alloys so far as the composition of the alloy requires or permits special drawing methods or sequences
• • 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
  • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
  • C22C—ALLOYS
  • C22C38/00—Ferrous alloys, e.g. steel alloys
  • C22C38/001—Ferrous alloys, e.g. steel alloys containing N
• • 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
  • 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 drawing having superior strength and ductility, the wire rod being used for a tire cord, a wire rope, a piano wire, a bridge steel wire and the like, and a method for manufacturing the same, and more particularly, to a wire rod for drawing having high strength and high ductility by controlling a C content to a suitable range and simultaneously adding Si and Cr together to produce a lamella structure of pearlite into a fine pearlite microstructure, and a method for manufacturing the same.
• the strength of a base steel may be enhanced by adding a large amount of a strengthening element to the base steel.
• Carbon (C) is a representative example of the strengthening element.
• the strength of a desired wire rod is increasingly enhanced as the content of C increases from a hypoeutectoid zone to a eutectoid zone, and from a eutectoid zone to a hypereutectoid zone.
• a wire rod for drawing is prepared by drawing and heat-treating a rolled wire rod and finally processing the rolled wire rod into a wire rod.
• the rolled wire rod may be cured to drastically improve its strength. Since a lamellar spacing of the pearlite structure becomes fine, a strain-hardening coefficient increases, and a potential is piled up in the process of the wire rod, it is possible to cure the wire rod.
• strength of a wire rod may be enhanced by increasing a wire drawing strain of material, regardless of the above-mentioned processes.
• the wire drawing strain of material is closely associated with the ductility of material. Where a material is not dis- connected while being drawn, the steel material may be easily processed and the strength of a wire rod may be favorably improved.
• the present invention is designed to solve the problems of the prior art, and therefore it is an object of the present invention to provide a wire rod for drawing having high strength and high ductility by controlling a C content to a suitable range and simultaneously adding Si and Cr together to produce a lamella structure of pearlite into a fine pearlite microstructure.
• a wire rod for drawing which has superior strength and ductility, including, by weight: carbon (C): 0.87 to 1.0%, manganese (Mn): 0.1 to 0.60%, silicon (Si): 0.3 to 1.0%, sulfur (S): 0.010% or less (excluding 0%), phosphorus (P): 0.011% or less (excluding 0%), chromium (Cr): 0.1 to 0.5%, nitrogen (N): 0.007% or less (excluding 0%), and the balance of iron (Fe) and other inevitable impurities, wherein the sum (% by weight) of the Si and Cr contents satisfies the following equation: 0.6 ⁇ Si+Cr ⁇ 1.2, and the wire rod has a pearlite structure.
• one exemplary embodiment of the present invention may provide a wire rod for drawing, which has high strength and high ductility, by controlling a C content to a suitable range and simultaneously adding Si and Cr together.
• another exemplary embodiment of the present invention may provide a method for manufacturing a wire rod for drawing having high strength and high ductility.
• FIG. 1 is a graph illustrating tensile strength and reduction of area of a wire rod for drawing according to the content of carbon (C).
• FIG. 2 is a graph illustrating tensile strength and reduction of area of a wire rod for drawing according to the compositional ranges of components in the wire rod.
• FIG. 1 is a graph illustrating tensile strength and reduction of area of a wire rod according to the content of carbon (C). Referring to FIG. 1, when the content of C increase to a level of constant C content, it is difficult to expect improvement of the strength of the wire rod, and the strength of the wire rod is not enhanced, or rather decreased due to the small reduction of area.
• the strength and ductility of the wire rod for drawing may be secured by adjusting the C content to a content level at which the reduction of area of the wire rod may be secured without the continuous increases in the C content, and simultaneously adding other alloy elements, particularly Si and Cr, to produce a lamella structure of pearlite into a fine pearlite microstructure.
• compositional ranges of components in the steel sheet according to one exemplary embodiment of the present invention are described in more detail.
• the term 'percentage (%)' used in the exemplary embodiments represents '% by weight', unless indicated otherwise.
• Carbon (C) is a core element to secure strength of steel.
• a content of C exceeds 1.0%, the reduction of area (RA) of the steel is decreased, which makes it impossible to expect the improvement of the strength of steel by a drawing process, whereas, when the content of C is less than 0.87%, it is difficult to secure a desired strength of steel. Therefore, it is desirable to define the C content to 0.87 to 1.0%.
• Manganese (Mn) is an element that is effective at enhancing hardenability of steel but causes severe center segregation. In this case, when a content of Mn exceeds 0.6%, Mn has high possibility to induce formation of a low-temperature structure. On the contrary, when the content of Mn is less than 0.1%, an addition effect of Mn may not be shown sufficiently. Therefore, it is desirable to define the Mn content to 0.1 to 0.6%.
• Si silicon
• C functions to enhance the strength of steel with its increasing content, but results in the decrease in reduction of area of steel, which appears as limits on the improvement of the strength of steel.
• C functions to precipitate coarse proeutectoid cementite beyond a hypereutectoid compositional range, which provides a main crack initiation position during a drawing process.
• the addition of Si does not facilitate the formation of proeutectoid cementite within the hypereutectoid compositional range, but functions to enhance the strength of steel by means of the solution strengthening.
• Si is used as a deoxidizing agent in a steel-making process, a trace of Si is included in steel.
• Si is added at a content of less than 0.3%, the strength and ductility of steel are not improved effectively.
• the content of the added Si exceeds 1.0%, the ductility of lamellar ferrite may be deteriorated severely, thereby degrading wire drawability. Therefore, it is desirable to define the Si content to 0.3 to 1.0%.
• Cr chromium
• Cr functions to improve the strength and ductility of steel by producing a lamella structure of pearlite into a fine pearlite mi- crostructure.
• a content of Cr is less than 0.1%, the lamellar structure of pearlite into a fine pearlite microstructure is not achieved sufficiently, whereas, when the content of Cr exceeds 0.5%, a pearlite transformation rate at constant temperature is slow, which adversely affects productivity of steel. Therefore, it is desirable to define the Cr content to 0.1 to 0.5%.
• S Sulfur
• P Phosphorus
• N Nitrogen
• the wire rod satisfying the requirements regarding the above-mentioned compositional ranges may further include nickel (Ni).
• Ni functions to improve the strength and ductility of a wire rod since it facilitates the plastic deformation of cementite during a drawing process by driving one more slip system of cementite.
• Ni When a content of Ni is less than 0.3%, the strength and ductility of a wire rod are not significantly changed when compared to those of the wire rod that does not include Ni but satisfies the requirements regarding the above-mentioned compositional ranges. Therefore, it is desirable for the wire rod to include 0.3% or more of Ni.
• Ni may be more preferably used at a content of 0.3 to 1.0%.
• the wire rod for drawing includes the balance of iron (Fe) and other inevitable impurities.
• the wire rod having the above-mentioned compositional ranges has a tensile strength of 1300 MPa or more and a 30% or more reduction of area.
• a pearlite structure has an interlamellar spacing of 130 nm or less.
• the pearlite structure of the wire rod has an interlamellar spacing of 50 nm or less. The finer the interlamellar spacing of the pearlite structure is, the higher the strength of the wire rod is.
• each of steel billets having components and their contents as listed in the following Table 1 was heated at 1100 to 1300 0 C, and hot-rolled, and then cooled at a rate of 10 to 20 °C/s to obtain a wire rod. Then, each of the prepared wire rods was measured for tensile strength (TS), reduction of area (RA), and interlamellar spacing of a pearlite structure.
• FIG. 2 is a graph illustrating tensile strength and reduction of area of a wire rod for drawing according to the addition of Cr and Si in addition to 0.92% by weight of C.
• the rightmost bar graph represents a tensile strength and a reduction of area of the Inventive steel 1.
• Inventive steel 4 shows its superior strength and ductility, i.e. a tensile strength of 1364 MPa and a 38.7% reduction of area. Also, it was seen that the Inventive steel 4 has a tensile strength of 1300 MP or more and a 30% or more reduction of area when the sum of the Si and Cr contents is in a range of 0.6 to 1.2 % by weight. Also, it was revealed that the Inventive steel 5 shows its superior tensile strength and reduction of area when Ni is added at a content of 0.5 % by weight.
• Example 2 (Example 2) [93] Each of the wire rods (Inventive steel 1, Comparative steels 4 and 5) prepared in the method of Example 1 was austenized at 1050 0 C, lead-patented at a solder pot temperature of 55O 0 C to obtain a steel sheet. Then, each of the steel sheets was measured for tensile strength and interlamellar spacing. The results are listed in the following Table 2.
• the twists represent the workability or ductility of a steel wire at maintaining its superior strength.
• the superior ductility of a wire rod functions to reduce a disconnection rate of the wire rod during the drawing process and suppress the delamination in the wire rod.
• the fatigue property represents the increase in service life and durability of the wire rod.
• the fatigue property is two times higher in the Inventive steels than the Comparative steels. Therefore, it was seen that, owing to the combined addition of Si and Cr, the Inventive steel 1 shows its superior ductility and fatigue property as well as the tensile strength even after the drawing process.

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

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• 2007
  • 2007-12-27 KR KR1020070139434A patent/KR100979006B1/ko active IP Right Grant
• 2008
  • 2008-11-12 CN CN200880123271.9A patent/CN101910440A/zh active Pending
  • 2008-11-12 EP EP08867709.1A patent/EP2238271A4/de not_active Withdrawn
  • 2008-11-12 JP JP2010540556A patent/JP2011509345A/ja active Pending
  • 2008-11-12 US US12/810,061 patent/US20100263772A1/en not_active Abandoned
  • 2008-11-12 WO PCT/KR2008/006660 patent/WO2009084811A1/en active Application Filing

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