JP-7856890-B2 - Hot stamped molded parts

Inventors

• 土井 教史

Assignees

• 日本製鉄株式会社

Dates

Publication Date

20260512

Application Date

20220330

Claims (1)

1. Steel base material and The steel substrate is formed on an Al coating, The aforementioned Al coating is An interface layer formed at the interface with the steel substrate, having a structure in which a portion of αFe is replaced with Al and Si, An intermediate layer formed on the aforementioned interface layer, The intermediate layer includes an oxide film layer formed on the intermediate layer, The aforementioned intermediate layer includes an Fe-Al-Si phase having a structure in which a portion of αFe is replaced with Al and Si. The Fe-Al-Si phase contains at least one of Ni and Cr, The Si content in the Fe-Al-Si phase is 13 to 17 % by mass, and the total content of Ni and Cr is 0.10 to 5.0% by mass. The oxide film layer contains Mg, The ratio of Mg in the components of the oxide film layer, excluding carbon and oxygen, is 10.0 to 35.0 % by mass. A hot-stamped molded article wherein the peak intensity α of α- Al₂O₃ (10⁻²) and the peak intensity γ of γ- Al₂O₃ (11¹) detected by XRD in the oxide film layer satisfy the following relationship. γ/(α+γ)≧0.50

Description

This invention relates to a hot-stamped molded body. Hot stamping (also known as hot pressing, die quenching, or press quenching) is a known method for forming high-strength steel materials with high dimensional accuracy. Hot stamping involves heating steel materials such as steel plates to the austenite region and forming them while hot, then obtaining the desired properties through cooling after forming. In hot stamping, scale can form on the surface of the steel during heating, and this needs to be removed in a subsequent process. To avoid this, a technique is known in which aluminum plating is applied to the steel for hot stamping to suppress scale formation. Japanese Patent Publication No. 63-3929 discloses a method for manufacturing a hot-dip aluminum-plated steel sheet that exhibits a low oxidation weight gain during high-temperature oxidation. Japanese Patent Publication No. 2943021 discloses a method for manufacturing an austenitic stainless steel sheet strip having a NiAl intermetallic compound on its surface, by coating the surface of the austenitic stainless steel sheet strip with Al and then performing diffusion heat treatment in a non-oxidizing atmosphere at a temperature range of 700-800°C. International Publication No. 2018/221738 discloses a hot-stamped component comprising a steel material, an Al-Fe intermetallic compound layer, and an oxide film layer, wherein the oxide film layer contains one or more elements selected from the group consisting of Be, Mg, Ca, Sr, Ba, Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, and Zn, in an amount of 0.01 atomic% to 80 atomic% excluding oxygen. Japanese Patent Publication No. 2017-536472 discloses a flat steel product for hot forming, comprising a steel substrate and a protective coating mainly composed of Al. The publication states that the protective coating contains at least one alkaline earth metal or transition metal in a total amount of 0.1% to 0.5% by weight, and that oxides of the alkaline earth metal or transition metal are formed on the outer surface of the protective coating during hot forming. Special Publication No. 63-3929Patent No. 2943021International Publication No. 2018/221738Special Publication No. 2017-536472 Figure 1 is a schematic cross-sectional view showing the structure of a hot-stamped molded body according to one embodiment of the present invention.Figure 2 is an example of an XRD pattern that includes (10-2) of α- Al₂O₃ and (111) of γ- Al₂O₃ . The inventors focused on the crystalline structure of the oxide film layer formed when hot stamping is performed on an Al-plated steel sheet and conducted a detailed analysis using XRD. Specifically, they focused on α- Al₂O₃ and γ- Al₂O₃ . As a result, they found that by adding predetermined amounts of Mg and Ni , or predetermined amounts of Mg and Cr, to the Al-based plating layer, the formation of α- Al₂O₃ , which should be a stable oxide in the temperature range during hot stamping , is suppressed, and γ- Al₂O₃ is formed in large quantities. Furthermore, they found that by creating an oxide film layer with a large amount of γ- Al₂O₃ , the amount of hydrogen absorbed from the atmosphere can be reduced. This invention was completed based on the above findings. A hot-stamped molded article according to one embodiment of the present invention will be described in detail below. Figure 1 is a schematic cross-sectional view showing the structure of a hot-stamped molded body 1 according to one embodiment of the present invention. The hot-stamped molded body 1 is a molded body formed by hot stamping a steel material coated with Al. The hot-stamped molded body 1 comprises a steel base material 10 and an Al coating 20 formed on the steel base material 10. The Al coating 20 includes an interface layer 21 formed at the interface with the steel substrate 10, an intermediate layer 22 formed on the interface layer 21, and an oxide film layer 23 formed on the intermediate layer 22. The Al coating 20 of the hot-stamped molded body 1 according to this embodiment contains at least one of Ni and Mg, and Mg. However, these elements are not uniformly distributed throughout the Al coating 20; Ni and Cr tend to be concentrated in the intermediate layer 22, and Mg tends to be concentrated in the oxide layer 23. Furthermore, Ni and Cr tend to be concentrated in the Fe-Al-Si phase 22a of the intermediate layer 22, which will be described later. [Interfacial layer] The interface layer 21 is formed at the interface with the steel substrate 10. The interface layer 21 has a structure in which a part of the αFe bcc structure is replaced with Al and Si. The chemical composition of the interface layer 21 has a distribution that changes along the thickness direction. For example, the average chemical composition of the interface layer 21 in the thickness direction is Fe: 60.0 to 98.0 mass%, Al: 1.0 to 40.0 mass%, and Si: 1.0 to 20.0 mass%. The interface layer 21 may contain small amounts of elements other than Si, Fe, and Al. The