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KR-20260063971-A - COLD HEADING QUALITY WIRE WITHOUT SPHEROIDIZING HEAT TREATMENT AND METHOD FOR MANUFACTURING THEREOF

KR20260063971AKR 20260063971 AKR20260063971 AKR 20260063971AKR-20260063971-A

Abstract

The cold heading wire rod according to the present invention, which allows for the omission of spheroidizing heat treatment, comprises, in weight%, C: 0.05~0.6%, Si: 0.01~2.0%, Mn: 0.01~2.0%, Cr: 0.005~2.0%, Mo: 0.005~0.1%, Ni: 0.005~0.1%, Cu: 0.005~0.5%, Al: 0.005~0.1%, Ti: 0.005~0.1%, N: 0.001~0.03%, and the remainder being Fe and other unavoidable impurities, and when the radius of the wire rod is R, the microstructure measured at the center within (1/5)R from the center of the cross-section of the wire rod comprises 80~99% ferrite and 1~20% spherical cementite.

Inventors

  • 최상우

Assignees

  • 주식회사 포스코

Dates

Publication Date
20260507
Application Date
20241031

Claims (11)

  1. In wt%, it comprises C: 0.05~0.6%, Si: 0.01~2.0%, Mn: 0.01~2.0%, Cr: 0.005~2.0%, Mo: 0.005~0.1%, Ni: 0.005~0.1%, Cu: 0.005~0.5%, Al: 0.005~0.1%, Ti: 0.005~0.1%, N: 0.001~0.03% and the remainder being Fe and other unavoidable impurities, A wire rod for cold heading in which the microstructure measured at the center within (1/5)R from the center of the cross-section of the wire rod, when the radius of the wire rod is R, contains 80~99% ferrite and 1~20% spherical cementite, and the spheroidizing heat treatment can be omitted.
  2. A step of heating and hot rolling a billet comprising, in weight%, C: 0.05~0.6%, Si: 0.01~2.0%, Mn: 0.01~2.0%, Cr: 0.005~2.0%, Mo: 0.005~0.1%, Ni: 0.005~0.1%, Cu: 0.005~0.5%, Al: 0.005~0.1%, Ti: 0.005~0.1%, N: 0.001~0.03%, and the remainder being Fe and other unavoidable impurities; A step of winding the above hot-rolled wire rod into a bar-in-coil form; A step of rapidly cooling the above-mentioned wound wire at 70°C or lower for less than 1 minute; and A method for manufacturing a wire rod for cold heading that can omit spheroidizing heat treatment, comprising the step of tempering the above-mentioned rapidly cooled wire rod at 600 to 800°C for 20 to 300 minutes.
  3. In paragraph 2, A method for manufacturing a wire rod for cold heading that allows for the omission of spheroidizing heat treatment, wherein the wire rod wound in the cooling step above has both ends immersed in a salt bath.
  4. In paragraph 2, A method for manufacturing a wire rod for cold heading that allows for the omission of spheroidizing heat treatment, comprising cooling both ends of the wound wire rod simultaneously in a salt bath during the cooling step.
  5. In paragraph 2, A method for manufacturing a wire rod for cold heading that allows for the omission of spheroidizing heat treatment, wherein the wire rod cooled in the above isothermal heat treatment step has both ends immersed in a salt bath.
  6. In paragraph 2, A method for manufacturing a wire rod for cold heading that allows for the omission of spheroidizing heat treatment, comprising the step of isothermal heat treatment in which both ends of the cooled wire rod are simultaneously isothermal heat treated in a salt bath.
  7. In paragraph 2, The above-mentioned winding step is a method for manufacturing a wire rod for cold heading that can omit the spheroidizing heat treatment performed at a temperature satisfying the following formula (1). Equation (1): X-Al≥100 (Here, X represents the winding temperature)
  8. In paragraph 2, A method for manufacturing a wire rod for cold heading in which the above rapid cooling step can omit spheroidizing heat treatment performed at a speed of 20℃/s or higher.
  9. In paragraph 2, A method for manufacturing a wire rod for cold heading in which the microstructure measured at the center within (1/5)R from the center of the cross-section after the above-mentioned rapid cooling step comprises 70~99% martensite and 1~30% austenite, wherein spheroidizing heat treatment can be omitted.
  10. In paragraph 2, A method for manufacturing a wire rod for cold heading in which the above tempering step can omit spheroidizing heat treatment performed at a speed of 1℃/s or higher.
  11. In paragraph 2, A method for manufacturing a wire rod for cold heading in which the microstructure measured at the center within (1/5)R from the center of the cross-section after the above tempering step comprises 80~99% ferrite and 1~20% spherical cementite, thereby allowing the omission of spheroidizing heat treatment.

Description

Cold heading wire without spheroidizing heat treatment and method for manufacturing the same {COLD HEADING QUALITY WIRE WITHOUT SPHEROIDIZING HEAT TREATMENT AND METHOD FOR MANUFACTURING THEREOF} The present invention relates to a wire rod for cold heading that allows for the omission of spheroidizing heat treatment and a method for manufacturing the same. The microstructure of the wire rod for cold heading, which is generated when the wire rod is rolled and then wound into a ring shape and cooled by Stelmore cooling, or when the wire rod is wound into a bar-in-coil and then cooled by a Garrett line, consists of ferrite and pearlite. Accordingly, in order to process wire rods in drawing and forging lines, a process is required to perform spheroidizing heat treatment before or during drawing to transform the phase into a soft, spheroidized structure. Spheroidizing heat treatment is a process that changes the microstructure of a wire rod from ferrite and pearlite to a form in which ferrite and spheroidal cementite exist. In other words, the parts that existed as pearlite in the initial structure are transformed into ferrite and spheroidal cementite, so that the entire microstructure consists of ferrite and spheroidal cementite. However, in reality, the spheroidizing heat treatment is typically performed by holding the wire coil in a furnace at a temperature near A1 for a long period of time, such as more than 24 hours, and even after the heat treatment is finished, it is removed from the furnace and air-cooled at room temperature for about 1.5 days. Therefore, in order to produce carbon-neutral and eco-friendly products, it is necessary to omit the spheroidizing heat treatment that takes a long time. Figure 1 is a diagram illustrating the spheroidizing heat treatment process typically applied in wire drawing and forging. FIG. 2 is a drawing illustrating a cooling process in which a hot-rolled wire rod is rapidly cooled and then tempered according to one embodiment of the present invention. FIG. 3 is a diagram illustrating a series of processes for winding a hot-rolled wire into a binder coil and then rapidly cooling and tempering it according to one embodiment of the present invention. FIG. 4 is a diagram showing the results of measuring the microstructure of a wire rod for cold heading according to one embodiment of the present invention using an optical microscope. Preferred embodiments of the present invention are described below. However, embodiments of the present invention may be modified in various other forms, and the technical concept of the present invention is not limited to the embodiments described below. Furthermore, the embodiments of the present invention are provided to more completely explain the present invention to those with average knowledge in the relevant technical field. The terms used in this application are used merely to describe specific examples. For this reason, singular expressions include plural expressions unless the context clearly requires them to be singular. Additionally, it should be noted that terms such as “comprising” or “comprising” used in this application are used to clearly indicate the presence of features, steps, functions, components, or combinations thereof described in the specification, and are not used to preliminarily exclude the existence of other features, steps, functions, components, or combinations thereof. Meanwhile, unless otherwise defined, all terms used in this specification shall be understood to have the same meaning as generally understood by those skilled in the art to which the present invention pertains. Accordingly, unless explicitly defined in this specification, specific terms should not be interpreted in an overly ideal or formal sense. For instance, singular expressions in this specification include plural expressions unless the context clearly indicates an exception. Additionally, terms such as "about," "substantially," etc., in this specification are used to mean at or near the stated value when inherent manufacturing and material tolerances are presented in the said sense, and are used to prevent unscrupulous infringers from unfairly exploiting the disclosed content in which precise or absolute values are mentioned to aid in understanding the invention. Figure 1 is a diagram illustrating the spheroidizing heat treatment process typically applied in wire drawing and forging. The spheroidizing heat treatment method shown in Fig. 1 is a heat treatment process that must be omitted to suppress carbon emissions because it utilizes a radiant heating furnace that burns fossil fuels such as LPG, and it requires a long-term heat treatment of more than 24 hours. Furthermore, the spheroidizing heat treatment process is not an essential process applied to secure the physical properties of the final part and product, but rather is intended to secure the drawing and forging processability required to create the shape of the part, so it is desirable