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KR-20260065361-A - A HOT PRESS FORMED MEMBER AND METHOD FOR MANUFACTURING THEREOF

KR20260065361AKR 20260065361 AKR20260065361 AKR 20260065361AKR-20260065361-A

Abstract

The present invention provides a hot-formed part, in particular a hot-formed part obtained from an unplated steel sheet, and a method for manufacturing the same.

Inventors

  • 이세웅
  • 김성우
  • 김상헌
  • 김의호
  • 오진근

Assignees

  • 주식회사 포스코

Dates

Publication Date
20260508
Application Date
20241101

Claims (9)

  1. Base steel plate; and It includes an Fe oxide region formed on the surface of the above-mentioned base steel plate, and A hot-formed part having a ratio (C min /C 0) of the minimum carbon content (C min ) existing within 6 μm from the point where Fe content is 80% when measured by GDS on the surface of the steel sheet in the thickness direction of the steel sheet, and the nominal carbon content (C 0 ) at the 45 μm point when measured by GDS on the surface of the steel sheet in the thickness direction of the steel sheet , which is less than 0.60.
  2. In Article 1, A hot-formed part having a ratio (C max /C 0) of the maximum carbon content (C max) existing within 9㎛ from the point where the Fe content is 80% when measured by GDS on the surface of the base steel plate in the thickness direction of the base steel plate, and the nominal carbon content (C 0 ) of 0.60 or more.
  3. In Paragraph 2, A hot-formed part having a ratio (C max /C 0 ) of the maximum carbon content (C max ) and the nominal carbon content (C 0) of 1.50 or less.
  4. In Article 1, A hot-formed part having a ratio (Mn min + Cr min / Mn 0 + Cr 0) of the sum of the minimum Mn content (Mn min ) and minimum Cr content (Cr min ) existing within 1 μm from the point where Fe content is 80% when measured by GDS on the surface of the steel plate in the thickness direction of the steel plate (Mn min + Cr min ) and the sum of the Mn content (Mn 0 ) and Cr content (Cr 0 ) at a 45 μm point when measured by GDS on the surface of the steel plate in the thickness direction of the steel plate (Mn 0 ) and (Mn 0 ) (Mn 0 ) (Mr 0 ) (Mr 0 ) (Mr 0 ) (Mr 0 ) (Mr 0 ) (Mr 0 ) ( Mr 0 ) (Mr 0 ) ( Mr 0 ) (Mr 0 ) (Mr 0 ) (Mr 0 ) (Mr 0 ) (Mr 0 ) (Mr 0 ) (Mr 0 ) (Cr 0 ) when measured by GDS on the surface of the steel plate in the thickness direction of the steel plate in the thickness direction of the steel plate in the above-mentioned surface of
  5. In Paragraph 4, The region where (Mn min +Cr min /Mn 0 +Cr 0 ) is 0.95 or less is a hot-formed part containing ferrite.
  6. In Article 1, The above base steel sheet comprises, in weight%, Carbon (C): 0.02~0.45%, Silicon (Si): 0.50~2.00%, Aluminum (Al): 0.001~1.000%, Manganese (Mn): 0.4~3.0%, Chromium (Cr): 1.0~5.0%, Phosphorus (P): 0.050% or less, Sulfur (S): 0.0200% or less, Nitrogen (N): 0.0100% or less, Titanium (Ti): 0~1.00%, Niobium (Nb): 0~0.10%, Vanadium (V): 0~0.50%, Boron (B): 0~0.0200%, Molybdenum (Mo): 0~1.00%, Tungsten (W): 0~1.00%, Copper (Cu): 0~1.0%, Nickel (Ni): A hot-formed part comprising 0~1.0%, Tin (Sn): 0~1.00%, Antimony (Sb): 0~0.100%, Calcium (Ca): 0~0.10%, Magnesium (Mg): 0~0.10%, Cobalt (Co): 0~1.00%, Arsenic (As): 0~1.00%, Zirconium (Zr): 0~1.00%, Bismuth (Bi): 0~1.00%, Rare Earth Elements (REM): 0~0.3%, and the remainder being Fe and other unavoidable impurities.
  7. The method includes the steps of preparing a steel sheet and heating the steel sheet, The step of heating the above-mentioned steel plate includes a first heating section and a second heating section, and The first heating section is a temperature range of 300℃ to Ae1-50℃, and the second heating section is a temperature range above Ae1-50℃. A method for manufacturing a hot-formed part by controlling the oxygen concentration of the second heating section to 1.00~10.00%.
  8. In Article 7, A method for manufacturing a hot-formed part in which the oxygen concentration of the first heating section is controlled to 3.00~19.00%.
  9. In Article 7, A method for manufacturing a hot-formed part in which the oxygen concentration in the second heating section is lower than the oxygen concentration in the first heating section.

Description

A hot-press formed member and method for manufacturing thereof The present invention relates to a hot-formed part and a method for manufacturing the same. Recently, as regulations regarding passenger protection and fuel efficiency improvement through vehicle weight reduction have become stricter, the application of hot-formed parts as materials for automotive structural components is increasing to achieve these goals. Hot-formed parts are obtained by applying a hot-forming process to steel sheets, which enables them to possess high strength. Accordingly, hot-formed parts are particularly suitable for applications such as bumpers, doors, and pillar reinforcements that require ultra-high strength or significant energy absorption capabilities. Patent Document 1 proposes a technology regarding the hot forming of steel sheets as described above. This document describes a method for securing ultra-high strength with high tensile strength by heating an Al-Si plated steel sheet to 850°C or higher, and then forming the microstructure of a member manufactured by hot forming and rapid cooling using a press into martensite. As such, since the hot-formed member (part) is obtained by forming the steel sheet at a high temperature, it has the advantage of being easily formed when manufacturing parts with complex shapes. Furthermore, since rapid cooling within the form can increase strength, a lightweighting effect resulting from increased strength can be expected. Meanwhile, a technology for manufacturing parts by hot-forming hot-rolled or cold-rolled (annealed) steel sheets, rather than plated steel sheets, as hot-forming steel sheets, is being proposed; that is, a technology for manufacturing hot-formed parts from non-plated steel sheets that are not plated. When heating these non-plated steel sheets for hot forming, carbon on the surface of the steel sheet reacts with oxygen present in the heating equipment, causing decarburization to occur on the surface of the steel sheet. In other words, a decarburized layer is formed on the surface of the non-plated steel sheet, which results in the surface of the hot-formed part becoming uneven, leading to problems such as inferior surface quality and deterioration of physical properties like bendability. Therefore, there is a need to develop technology capable of solving problems such as reduced surface quality, reduced bendability, and reduced fatigue properties when manufacturing hot-formed parts by hot-forming non-plated steel sheets. Figure 1 schematically illustrates the cross-sectional structure of a hot-formed part according to one embodiment of the present invention. FIG. 2 schematically illustrates the cross-sectional structure of a hot-formed part according to another embodiment of the present invention. FIG. 3 is a graph showing the GDS measurement results of a hot-formed part (Invention Example 1) according to one embodiment of the present invention, showing an example of a point where the Fe content is 80% from the surface, a point at C min , and a point at C max . Preferred embodiments of the present invention will be described below with reference to the attached drawings. However, embodiments of the present invention may be modified in various other forms, and the scope of the present invention is not limited to the embodiments described below. In addition, embodiments of the present invention are provided to more fully explain the present invention to those with average knowledge in the relevant technical field. In drawings, the shapes and sizes of elements may be exaggerated for clearer explanation. In describing the embodiments of the present invention, if it is determined that a detailed description of known technology related to the present invention may unnecessarily obscure the essence of the present invention, such detailed description will be omitted. Furthermore, the terms described below are defined considering their functions in the present invention, and these may vary depending on the intentions or conventions of the user or operator. Therefore, such definitions should be based on the content throughout this specification. The terms used in the detailed description are merely for describing the embodiments of the present invention and should not be limited in any way. Unless explicitly stated otherwise, expressions in the singular form include the meaning of the plural form. In this description, expressions such as “include” or “equipped” are intended to refer to certain characteristics, numbers, steps, actions, elements, parts or combinations thereof, and should not be interpreted to exclude the existence or possibility of one or more other characteristics, numbers, steps, actions, elements, parts or combinations thereof other than those described. In addition, in the present invention, the term "steel plate" refers to a coil or sheet material that has not yet been processed into a specific shape, and the term "part" refers to a part that has been pr