KR-102962865-B1 - WELDED BLANK AND MANUFACTURING METHOD FOR THE SAME

KR102962865B1KR 102962865 B1KR102962865 B1KR 102962865B1KR-102962865-B1

Abstract

The present invention aims to provide a welded blank and a method for manufacturing the same, wherein the difference in heating rate between the thicker part (the thickest part when viewed in cross-section) and the thinner part (the thinnest part when viewed in cross-section) is reduced, and the difference in heating rate is reduced, and uniform heat treatment characteristics are secured across the entire area of the blank, in a welded blank manufactured by welding two or more base materials of different thicknesses.

Inventors

박계정
박재명
공제열
윤승채

Assignees

현대제철 주식회사

Dates

Publication Date: 20260512
Application Date: 20250307

Claims (7)

In a welded blank formed by welding two or more base materials of different thicknesses, The above-mentioned weld blank comprises: a thicker section having the thickest thickness when viewed from a cross-section of the weld blank; and a thinner section having the thinnest thickness when viewed from a cross-section of the weld blank. A zinc plating layer is disposed on at least a portion of the surface of the above-mentioned thick section, and An Al-Si plating layer is disposed on at least a portion of the surface of the above-mentioned thin film, and In the case of hot stamping the above-mentioned welded blank, the zinc plating layer and the Al-Si plating layer are arranged such that the ratio (Vb/Va) of the heating rate (Vb) of the thin part to the heating rate (Va) of the thick part satisfies the following equations (1) and (2). Welding blank. Equation (1) (2) (V a is the heating rate of the thick section, V b is the heating rate of the thin section, t 1 is the time taken for the temperature of the thick or thin section to reach T 1 ℃ from room temperature, t 2 is the time taken for the temperature of the thick or thin section to reach T 2 ℃ from room temperature, and T 2 ℃ is a temperature higher than T 1 ℃)
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In Article 1, The above zinc plating layer is arranged to cover the entire surface of the above-mentioned thick portion, and The above Al-Si plating layer is arranged to cover the entire surface of the above thin film, Welding blank.
In Paragraph 3, The sum of the thickness of the above zinc plating layer and the thickness of the thick part is 0.8 mm or more and 4.6 mm or less, and The sum of the thickness of the above Al-Si plating layer and the thickness of the thin section is 0.8 mm or more and 2.3 mm or less, Welding blank.
In Article 1, The gamma phase fraction in the above zinc plating layer is greater than 0% and less than or equal to 40% in area %, Welding blank.
A method for manufacturing a welded blank by welding two or more base materials of different thicknesses, (a) A step of preparing a first base material and a second base material having different thicknesses; (b) a step of manufacturing a welded blank by welding the first base material and the second base material; (c) A step of measuring the thickness of a plurality of parts when viewing the welded blank from a cross-section; (d) A thick section plating step of plating zinc (Zn) on at least a portion of the surface of the thick section, which is the thickest part measured in each of the plurality of parts; (e) A thin film plating step of plating Al-Si on at least a portion of the surface area of the thin film, which is the part with the smallest thickness measured in each of the plurality of parts; including, Method for manufacturing a welding blank.
In Article 6, (f) a heating step for heating the welding blank; further comprising, In the above heating step, the ratio (Vb/Va) of the heating rate (Vb) of the thin section to the heating rate (Va) of the thick section satisfies the following equations (1) and (2). Method for manufacturing a welding blank. Equation (1) (2) (Va is the heating rate of the thick section, Vb is the heating rate of the thin section, t1 is the time taken for the temperature of the thick or thin section to reach T1℃ from room temperature, t2 is the time taken for the temperature of the thick or thin section to reach T2℃ from room temperature, where T2℃ is a higher temperature than T1℃)

Description

Welded Blank and Manufacturing Method for the Same The present invention relates to a welded blank and a method for manufacturing the same, and more specifically, to a technology for improving manufacturing quality by reducing the difference in heating rates of each base material during a hot stamping process in a welded blank formed by welding two or more base materials of different thicknesses. Traditionally, Tailor Welded Blank (TWB) and Patchwork Blank technologies, which involve joining metal materials of different strengths and thicknesses and performing a hot stamping process to manufacture lightweight and high-strength parts used in various industrial fields such as automotive, aerospace, and construction, have been widely applied. These technologies are designed to secure customized hot stamping characteristics and are particularly useful for reinforcing mechanical properties in specific areas or achieving weight reduction by joining base materials of different thicknesses or strengths. However, due to the nature of the hot stamping process, there is a problem in that the heating rate during the heating process varies depending on the thickness of the bonded blank material. Generally, thin materials have a high thermal conductivity and therefore a fast heating rate, whereas thick materials have a relatively slower heating rate because they have a large heat capacity. Due to these characteristics, thick materials require a heating process at high temperatures for a longer period of time to secure the required mechanical properties. The problem is that during the long heating process required to secure the physical properties of thick materials, thin materials, which are relatively sensitive to heat, are exposed to excessive heat, resulting in overheating. Overheating of thin materials can accelerate thermal transformation of the material's microstructure or induce the formation of an oxide layer, ultimately degrading the material's strength, ductility, and surface quality. This leads to quality non-uniformity throughout the bonded blank and can negatively affect the durability and performance of the final product during the hot stamping process. In particular, for Tailor Welded Blank and Patchwork Blank, the heating time is set based on the thicker material rather than the thinner material. The greater the difference in thickness between the thicker material and the thinner material, the longer the cycle time of the entire heating process becomes, resulting in the thinner material being overheated relatively. Such overheating can adversely affect the quality and mechanical properties of the final product due to excessive softening or oxidation of the thinner material. Furthermore, the difference in heating rate due to the difference in thickness between thin and thick materials causes local differences in phase transformation. Due to the difference in volume change between thin and thick materials resulting from the difference in phase transformation between thin and thick materials, the blank material undergoes thermal deformation (warping) during heating, and this deformation can cause serious defects such as the material deviating from its path or becoming misaligned during transport within the furnace. Furthermore, this problem intensifies as blank sizes increase and the thickness difference between thin and thick materials widens. In large blanks, localized thermal stress acts more significantly, leading to increased product deformation and a higher likelihood of reduced production efficiency and precision. Therefore, in conventional technology, there has been a need to resolve issues such as differences in heating rates caused by thickness differences between thin and thick materials, non-uniformity of phase transformation, thermal deformation, and process defects. By improving these problems, there is a need for the development of technology that can simultaneously ensure production efficiency and product quality in the hot stamping process. As one of the related technologies, the following prior art document, International Publication No. 2023-224123, discloses a method of reducing the difference in heating rates between the overlapping blank portion and the non-overlapping portion by providing a separate carbon-based black film when only aluminum-based plated steel sheets are used as the material for an overlapping blank for hot stamping; however, this is not efficient in that it requires performing a process of additionally installing a separate film on the aluminum-plated blank. Figure 1 is a drawing showing a Tailor Welded Blank and a Patchwork Blank. Figure 2 is a graph showing the material temperature over time of Comparative Example 1 of the present invention. Figure 3 is a graph showing the material temperature over time in Example 1 of the present invention. Figure 4 is a graph showing the material temperature over time of Comparative Example 2 of the present invention. Figure 5 is