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KR-20260067238-A - Full Hard Cold rolled steel sheet and manufacturing method of the same

KR20260067238AKR 20260067238 AKR20260067238 AKR 20260067238AKR-20260067238-A

Abstract

The present invention provides a hard cold-rolled steel sheet comprising carbon (C) 0.001 wt% or more and 0.005 wt% or less, silicon (Si) 0 wt% or more and 0.02 wt% or less, manganese (Mn) 0.05 wt% or more and 0.15 wt% or less, phosphorus (P) 0 wt% or more and 0.02 wt% or less, sulfur (S) greater than 0 wt% and 0.01 wt% or less, aluminum (Al) 0.01 wt% or more and 0.06 wt% or less, niobium (Nb) 0.005 wt% or more and 0.02 wt% or less, titanium (Ti) 0.01 wt% or more and 0.04 wt% or less, and the remainder being iron (Fe) and other unavoidable impurities.

Inventors

  • 배철준

Assignees

  • 현대제철 주식회사

Dates

Publication Date
20260512
Application Date
20241105

Claims (10)

  1. Hard cold-rolled steel sheet comprising carbon (C) 0.001 wt% or more and 0.005 wt% or less, silicon (Si) 0 wt% or more and 0.02 wt% or less, manganese (Mn) 0.05 wt% or more and 0.15 wt% or less, phosphorus (P) 0 wt% or more and 0.02 wt% or less, sulfur (S) greater than 0 wt% and 0.01 wt% or less, aluminum (Al) 0.01 wt% or more and 0.06 wt% or less, niobium (Nb) 0.005 wt% or more and 0.02 wt% or less, titanium (Ti) 0.01 wt% or more and 0.04 wt% or less, and the remainder being iron (Fe) and other unavoidable impurities.
  2. In paragraph 1, A hard cold-rolled steel sheet having a yield strength of 410 MPa or more and 580 MPa or less.
  3. A hot rolling step for manufacturing a hot-rolled plate by hot rolling a slab containing carbon (C) 0.001 wt% or more and 0.005 wt% or less, silicon (Si) 0 wt% or more and 0.02 wt% or less, manganese (Mn) 0.05 wt% or more and 0.15 wt% or less, phosphorus (P) 0 wt% or more and 0.02 wt% or less, sulfur (S) greater than 0 wt% and 0.01 wt% or less, aluminum (Al) 0.01 wt% or more and 0.06 wt% or less, niobium (Nb) 0.005 wt% or more and 0.02 wt% or less, titanium (Ti) 0.01 wt% or more and 0.04 wt% or less, and the remainder being iron (Fe) and other unavoidable impurities; A cold rolling step for manufacturing a cold rolled plate by pressing the above hot rolled plate; A heat treatment step of heating the above cold-rolled plate to a target surface temperature of more than 100 ℃ and less than 450 ℃; and A cooling step for cooling the heat-treated cold-rolled plate to prevent heat from spreading to the center of the cold-rolled plate; A method for manufacturing hard cold-rolled steel sheets, comprising
  4. In paragraph 3, A method for manufacturing a hard cold-rolled steel sheet, wherein, in the heat treatment step above, when the surface of the cold-rolled sheet reaches the target surface temperature, it is maintained for a holding time according to Formula 1 below. <Equation 1> 0< t < 1.90*exp(d/1.75) + 2.49 (Here, t represents the holding time and d represents the thickness of the cold-rolled sheet)
  5. In paragraph 3, A method for manufacturing a hard cold-rolled steel sheet, wherein, in the heat treatment step above, the surface of the cold-rolled sheet is heated using a resistance heating method.
  6. In paragraph 5, A method for manufacturing a hard cold-rolled steel sheet, wherein, in the heat treatment step above, the surface of the cold-rolled sheet is heated using an indirect heating method.
  7. In paragraph 3, A method for manufacturing a hard cold-rolled steel sheet, wherein the hot rolling step comprises: a step of reheating the slab at a temperature of 1,100 ℃ or higher and 1,250 ℃ or lower; a step of finish rolling at a temperature of Ar3 or higher and Ar3+100 ℃ or lower; and a step of coiling at a temperature of 600 ℃ or higher and 750 ℃ or lower.
  8. In paragraph 3, A method for manufacturing a hard cold-rolled steel sheet, wherein in the cooling step above, the cold-rolled sheet is cooled at a cooling rate of 10 ℃/s or more and 30 ℃/s or less.
  9. In paragraph 8, A method for manufacturing a hard cold-rolled steel sheet, wherein the cold-rolled sheet is cooled by a water cooling method in the above cooling step.
  10. In paragraph 3, A method for manufacturing a hard cold-rolled steel sheet, wherein the yield strength of the hard cold-rolled steel sheet after the cooling step and the yield strength of the hard cold-rolled steel sheet before the heat treatment step satisfy the following Equation 2. <Equation 2> 0.95*Y0 < Y (Here, Y0 represents the yield strength of the cold-rolled sheet before heat treatment [MPa], and Y represents the yield strength of the hard cold-rolled steel sheet after the cooling stage [MPa])

Description

Full Hard Cold Rolled Steel Sheet and Manufacturing Method of the Same The present invention relates to a method for manufacturing a hard cold-rolled steel sheet that can maintain high strength characteristics while simultaneously improving surface irregularity in the bending portion. Full Hard Cold-rolled Steel Sheet is a steel sheet produced by cold-rolling a hot-rolled steel sheet that has the characteristics of a semi-finished product, such as an annealed cold-rolled steel sheet or a hot-dip galvanized steel sheet. Hard cold-rolled steel sheets exhibit work hardening characteristics through cold rolling and possess superior yield strength and tensile strength properties compared to annealed steel of the same compositional system. Meanwhile, hard cold-rolled steel sheets exhibit lower elongation compared to annealed steel of the same compositional system. While these hard cold-rolled steel sheets can be applied to parts utilizing forming processes such as simple bending and roll forming, there is a problem in that they are difficult to apply to automotive body panels that require high formability. However, since it possesses high strength characteristics compared to hot-rolled steel sheets, it has high utility value due to the advantage of enabling the realization of high-strength thin materials. However, since hard cold-rolled steel sheets have a microstructure in a work-hardened state due to rolling, surface irregularities called grooves occur on the surface during bending, which acts as a factor that degrades the appearance quality of the final product. FIG. 1 is a flowchart schematically illustrating a method for manufacturing a hard cold-rolled steel sheet according to one embodiment of the present invention. FIG. 2 is a drawing showing the surface condition during bending process according to one embodiment of the present invention. FIG. 3 is a drawing showing the surface condition during bending process according to one comparative example of the present invention. The present invention will be described in detail below. However, in describing the present invention, if it is determined that a detailed description of related known technologies or configurations may unnecessarily obscure the essence of the present invention, such detailed description will be omitted. In the following embodiments, terms such as first, second, etc. are used not in a limiting sense, but for the purpose of distinguishing one component from another component. In the following examples, singular expressions include plural expressions unless the context clearly indicates otherwise. In the following embodiments, when various components such as layers, films, regions, and plates are described as being "on" another component, this includes not only cases where they are "directly on" another component, but also cases where another component is interposed between them. In the drawings, the size of components may be exaggerated or reduced for convenience of explanation. For example, the size and thickness of each component shown in the drawings are depicted arbitrarily for convenience of explanation, and therefore the present invention is not necessarily limited to what is illustrated. In the following embodiments, terms such as "include" or "have" mean that the features or components described in the specification are present, and do not preclude the possibility that one or more other features or components may be added. In this specification, "A and/or B" indicates the case where it is A, B, or both A and B. Additionally, in this specification, "at least one of A and B" indicates the case where it is A, B, or both A and B. Unless otherwise defined, all terms used herein, including technical and scientific terms, have the same meaning as generally understood by those skilled in the art to which this invention pertains. Terms defined in commonly used dictionaries are further interpreted to have meanings consistent with relevant technical literature and the present disclosure, and are not interpreted in an ideal or highly formal sense unless otherwise defined. Hereinafter, embodiments of the present invention are described in detail so that those skilled in the art can easily implement the invention. However, the present invention may be embodied in various different forms and is not limited to the embodiments described herein. FIG. 1 is a flowchart schematically illustrating a method for manufacturing a hard cold-rolled steel sheet according to one embodiment of the present invention. The following describes a process for manufacturing a hard cold-rolled steel sheet according to one embodiment of the present invention. Conditions not specifically described below shall be assumed to be ordinary conditions. Referring to FIG. 1, a method for manufacturing a hard cold-rolled steel sheet according to one embodiment of the present invention may include a hot rolling step (S100), a cold rolling step (S200), a heat treatment step (S300)