CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a National Phase application filed under 35 USC 371 of PCT International Application No. PCT/KR2019/018501 with an International Filing Date of Dec. 26, 2019, which claims the benefit of Korean Patent Application No. 10-2019-0050165 filed on Apr. 30, 2019. The entire contents of these applications are incorporated herein by reference in their entirety.

TECHNICAL FIELD

The present invention relates to a hot-stamped part and a method for manufacturing the same, and more particularly, to a hot-stamped part having excellent weldability, high delayed fracture resistance and high tensile strength, and a method for manufacturing the same.

BACKGROUND

In the current automobile industry, environmental and fuel economy regulations and safety standards have become more stringent. Accordingly, the application rate of ultra-high strength steel and hot-stamped steel has steadily increased. In particular, in the case of hot-stamped steel, including conventional 1.5 G hot-stamped steel, research and development has been conducted to increase toughness and strength. A hot stamping process generally includes heating, molding, cooling and trimming, and phase transformation and microstructural change of material are used during the process.

Technologies related thereto include Korean Patent Application Publication No. 10-2018-0095757 (entitled “Method for Manufacturing Hot-Stamped Parts”).

SUMMARY OF THE INVENTION

Technical Problem

An object of the present invention is to provide a hot-stamped part having excellent weldability, high delayed fracture resistance and high tensile strength, and a method for manufacturing the same.

Technical Solution

A hot-stamped part according to an exemplary embodiment of the present invention for achieving the above object includes, as a base layer, a steel material having a composition including an amount of 0.28 to 0.38 wt % of carbon (C), an amount of 0.1 to 0.4 wt % of silicon (Si), an amount of 1.2 to 2.0 wt % of manganese (Mn), an amount of greater than 0 but not greater than 0.020 wt % of phosphorus (P), an amount greater than 0 but not greater than 0.003 wt % of sulfur (S), an amount of 0.1 to 0.5 wt % of chromium (Cr), an amount of 0.0015 to 0.0040 wt % of boron (B), an amount of 0.025 to 0.05 wt % of titanium (Ti), and the balance of iron (Fe) and unavoidable impurities, all the wt % based on the total weight of the composition, and the microstructure of the base layer is full martensite.

The hot-stamped part may further include an Al—Si-based coating layer on the base layer, in which the fraction of a Fe—Al—Si-based intermetallic compound layer in the coating layer may be less than 40%.

In the hot-stamped part, the steel material may have a tensile strength (TS) of 1,700 MPa or greater, a yield strength (YS) of 1,200 MPa or greater, and an elongation (El) of 6% or greater.

A method for manufacturing a hot-stamped part according to an exemplary embodiment of the present invention for achieving the above object includes steps of: (a) preparing a blank including an amount of 0.28 to 0.38 wt % of carbon (C), an amount of 0.1 to 0.4 wt % of silicon (Si), an amount of 1.2 to 2.0 wt % of manganese (Mn), an amount greater than 0 but not greater than 0.020 wt % of phosphorus (P), an amount greater than 0 but not greater than 0.003 wt % of sulfur (S), an amount of 0.1 to 0.5 wt % of chromium (Cr), an amount of 0.0015 to 0.0040 wt % of boron (B), an amount of 0.025 to 0.05 wt % of titanium (Ti), and the balance of iron (Fe) and unavoidable impurities, all the wt % based on the total weight of the blank; (b) heating the blank; (c) forming a molded body by hot-stamping the heated blank in a press mold; and (d) forming a hot-stamped part by cooling the molded body.

In the method for manufacturing a hot-stamped part, step (b) may include: when the thickness of the blank is 1.2 mm, heating the blank in a preheated furnace for a time and at a temperature defined by the diagram having heating time-temperature coordinates of I (175 sec, 880° C.), II (210 sec, 820° C.), III (745 sec, 820° C.) and IV (455 sec, 880° C.) as apexes; when the thickness of the blank decreases by 0.1 mm from 1.2 mm, heating the blank for a time that is decreased by 12 sec from the time defined by the diagram and when the thickness of the blank increases by 0.1 mm from 1.2 mm, heating the blank for a time that is increased by 12 sec from the time defined by the diagram I-II-III-IV.

In the method for manufacturing a hot-stamped part, a heating condition for heating the blank may be set to 6.0×105° C.·sec/mm or less per thickness of the blank.

In the method for manufacturing a hot-stamped part, the cooling of the molded body in step (d) may be performed at a rate of at least 10° C./sec.

Advantageous Effects

According to the embodiments of the present invention, there may be provided a hot-stamped part having excellent weldability, high delayed fracture resistance and high tensile strength, and a method for manufacturing the same. It is to be understood that the scope of the present invention is not limited by this effect.

