HOT FOUNTAINING ALLOY AND METHOD FOR PRODUCEING HOT FOUNTAINED PARTS WITH SUCH AN ALLOY

Abstract

A metal alloy suitable for hot stamping contains between approximately 0.05 and approximately 0.45 wt% carbon, between approximately 0.5 and approximately 4.5 wt% manganese, between approximately 0.5 and approximately 6 wt% chromium, between approximately 0.5 and approximately 2.5 wt% silicon, between approximately 0.1 and approximately 0.5 wt% cerium, with the remainder being iron and impurities. A process for manufacturing an automotive component involves heating a blank made from the metal alloy and hot stamping the blank into the desired automotive component. A structural part is produced by hot stamping a blank made from a metal alloy.

Description

INTRODUCTION

[0001] The present disclosure relates to alloys for hot stamping structural parts, such as structural parts for motor vehicles, and to the hot stamping (process) of such structural parts.

[0002] A common process for manufacturing structural parts for the automotive industry is hot stamping, also known as press hardening. However, with commonly used alloys such as 22MnB5, hot stamping can result in heavily oxidized parts—parts with thick and / or uneven oxide coatings that require further processing such as shot blasting. To reduce the formation of these oxide coatings, hot stamping can be performed in an inert atmosphere, but this complicates the manufacturing process and increases costs. Alternatively, coatings such as AlSi can be applied to the blanks from which the parts are hot stamped, but this also complicates the manufacturing process and increases costs.

[0003] Hot stamping alloys have been developed that are more resistant to the formation of oxides during the hot stamping process. An example of such an alloy has a nominal composition of 0.05–0.45 wt% C, 0–0.45 wt% Mn, 0.5–6 wt% Cr, 0.5–2.5 wt% Si, and the balance iron. However, these alloys are difficult to spot weld during subsequent production because the uneven surface oxides deposit on the spot welding electrodes, reducing electrode life and potentially leading to surface weld defects.

[0004] Known metal alloys suitable for hot stamping and / or methods for producing an automotive structural part are described, for example, in DE 10 2020 204 356 A1 and DE 10 2020 131 993 A1. SUMMARY

[0005] Further areas of applicability of the present disclosure will become apparent from the detailed description, claims, and drawings. The detailed description and specific examples are provided for illustrative purposes only and are not intended to limit the scope of the disclosure.

[0006] According to the invention, an improved metal alloy suitable for hot stamping is disclosed. According to a first preferred embodiment, the alloy may contain between 0.05 and 0.45 wt.% carbon, between 0.5 and 4.5 wt.% manganese, between 0.5 and 6 wt.% chromium, between 0.5 and 2.5 wt.% Si, between more than 0.1 and 0.5 wt.% cerium, and the balance iron and impurities.

[0007] The cerium content is above 0.1 wt.% to improve the surface quality after hot stamping. The cerium content is below 0.5 wt.% to maintain the quality of the steel casting and rolling. In some versions of this first embodiment, it may be desirable to keep the total Cr and Si content less than or equal to 5 wt.% to facilitate scale removal in the steel mill. In some versions of this first embodiment, it may be desirable to keep the Cr:Si ratio between 1.25:1 and 3:1 to ensure oxidation resistance at high temperatures during hot stamping.

[0008] The alloy does not require processing in a protective atmosphere such as nitrogen or argon, and processing generally results in a thin, uniform oxide coating with a thickness of less than 1 µm, typically less than 0.5 µm, and often between 0.1 and 0.2 µm. This thin, uniform oxide layer is less damaging to spot welding tips than the thicker and / or less uniform oxide layers that form on existing hot stamping alloys.

[0009] According to a second inventive embodiment of this invention, a method for manufacturing structural parts, such as automotive structural parts, is disclosed. The method according to this second preferred embodiment comprises: heating a blank made of a metal alloy containing between 0.05 and 0.45 wt.% carbon, between 0.5 and 4.5 wt.% manganese, between 0.5 and 6 wt.% chromium, between 0.5 and 2.5 wt.% Si, between more than 0.1 and 0.5 wt.% cerium, and the balance iron and impurities.

[0010] The heated metal blank is then hot-stamped into the desired component. This combination provides a wider processing window, both in terms of temperature and duration. In one version, for example, heating occurs in the space defined by the time and temperature points (300 s, 870 °C), (200 s, 980 °C), (800 s, 870 °C), and (1000 s, 980 °C). In another version, heating occurs in the space defined by the time and temperature points (300 s, 870 °C), (200 s, 980 °C), (1000 s, 870 °C), and (800 s, 980 °C). In some cases, heating can be performed in an inert atmosphere, such as nitrogen or argon, but this is generally not required.

[0011] Structural parts are also not described here according to the invention. A structural part, such as an automotive structural part, is made from between 0.05 and 0.45 wt.% carbon, between 0.5 and 4.5 wt.% manganese, between 0.5 and 6 wt.% chromium, between 0.5 and 2.5 wt.% Si, between 0.1 and 0.5 wt.% cerium, the remainder being iron and impurities, formed by hot stamping with a substantially uniform oxidation thickness after hot stamping of less than 0.5 µm. This part can be, for example, vehicle pillars, door beams, and bumper beams.

[0012] Hot stamping products from this alloy blanks results in parts with a thin, uniform oxide coating that requires no blasting or other finishing. The thin, essentially uniform oxide coating improves spot welding, extends the life of spot welding electrodes, and suppresses melting / stripping of weld spots, resulting in smoother surfaces. BRIEF DESCRIPTION OF THE DRAWINGS

[0013] The present disclosure will become more fully understood from the detailed description and the accompanying drawings, in which: Fig. Figure 1 is a micrograph of 22MnB5 with thick oxides after a 300-second soak at 930°C, showing a thick oxidation coating of ~5 µm; Fig. Figure 2 is a micrograph of an alloy containing 0.05-0.45 wt% C, 0-0.45 wt% Mn, 0.5-6 wt% Cr, 0.5-2.5 wt% Si, balance iron, after a 300 second soak at 930°C showing non-uniform oxidation of 0.2 µm to 3 µm; Fig. 3 is a micrograph of an alloy according to the disclosure after a 640 second soak at 930°C showing a uniform oxidation of about 0.14 µm; Fig. 4 is a micrograph of an alloy according to the disclosure after a 720 second soak at 930°C showing a uniform oxidation of about 0.16 µm; Fig. 5 is a micrograph of an alloy according to the disclosure after a 300 second soak at 930°C showing a uniform oxidation of about 0.13 µm Fig. 6 is a micrograph of an alloy according to the disclosure after a 360 second soak at 950°C showing a uniform oxidation of about 0.13 µm; Fig. 7A and Fig. 7B are micrographs comparing the surface of an alloy of this disclosure (7A) with that of 22MnB5 (7B) using a spot welding electrode after 25 spot welds; Fig. 8A and Fig. 8B are micrographs comparing the surface of an alloy of this disclosure (8A) with that of 22MnB5 (8B) using a spot welding electrode after 59 spot welds; Fig. 9A and Fig. 9B are micrographs comparing the surface of an alloy of this disclosure (9A) with that of 22MnB5 (9B) using a spot welding electrode after 75 spot welds; Fig. 10A and Fig. 10B are micrographs comparing the surface of an alloy of this disclosure (10A) with that of 22MnB5 (10B) using a spot welding electrode after 100 spot welds; and Fig. 11A and Fig. 11B are illustrations of a spot welding electrode after 100 spot welds of a common alloy (11A) compared to an alloy of this disclosure.

[0014] Reference symbols may be reused in the drawings to identify similar and / or identical elements. DETAILED DESCRIPTION

[0015] Embodiments of this invention provide an improved metal alloy suitable for hot stamping. According to a first preferred embodiment, the alloy may contain between 0.05 and 0.45 wt.% carbon, between 0.5 and 4.5 wt.% manganese, between 0.5 and 6 wt.% chromium, between 0.5 and 2.5 wt.% Si, between more than 0.1 and 0.5 wt.% cerium, and the balance iron and impurities.

[0016] The cerium content is above 0.1 wt.% to improve the surface quality after hot stamping. The cerium content is below 0.5 wt.% to maintain the quality of steel casting and rolling. In some versions of this first embodiment, it may be desirable to keep the total content of Cr and Si less than or equal to 5 wt.% to facilitate scale removal in the steel mill. In some versions of this first embodiment, it may be desirable to keep the Cr:Si ratio between 1.25:1 and 3:1 to ensure oxidation resistance at high temperatures during hot stamping. Of course, other rare earths could be used instead of cerium.

[0017] The alloy does not require processing in a protective atmosphere such as nitrogen or argon, and processing generally results in a thin, uniform oxide coating with a thickness of less than 1 µm, typically less than 0.5 µm, and often between 0.1 and 0.2 µm. This thin, uniform oxide coating is less damaging to spot welding tips than the thicker and / or less uniform oxide coatings that form on existing hot stamping alloys.

[0018] According to a second preferred embodiment of this disclosure, a method for manufacturing a component, such as an automotive structural part, is disclosed. The method according to this second preferred embodiment comprises: heating a blank made of a metal alloy containing between 0.05 and 0.45 wt% carbon, between 0.5 and 4.5 wt% manganese, between 0.5 and 6 wt% chromium, between 0.5 and 2.5 wt% Si, between more than 0.1 and 0.5 wt% cerium, and the balance iron and impurities.

[0019] The alloy is heated above its austenitizing temperature (~900 °C). The heated metal blank is then hot stamped into the desired component. This composition provides a wider processing window, both in terms of temperature and duration. In one version, for example, heating occurs in the space bounded by the time and temperature points (300 s, 870 °C), (200 s, 980 °C), (800 s, 870 °C) and (1000 s, 980 °C). In another version, heating occurs in the space bounded by the time and temperature points (300 s, 870 °C), (200 s, 980 °C), (1000 s, 870 °C) and (800 s, 980 °C). In some cases, heating can be carried out in an inert atmosphere, e.g. B. in a nitrogen or argon atmosphere.

[0020] Automotive parts are not provided according to the invention. A structural part, such as an automotive structural part, is made from between 0.05 and 0.45 wt.% carbon, between 0.5 and 4.5 wt.% manganese, between 0.5 and 6 wt.% chromium, between 0.5 and 2.5 wt.% Si, between 0.1 and 0.5 wt.% cerium, the balance iron and impurities, formed by hot stamping with a substantially uniform oxidation thickness after hot stamping of less than 0.5 µm. This part can be, for example, vehicle pillars, door beams and bumper beams.

[0021] The thin, essentially uniform oxide coating improves spot welding, extends the life of spot welding electrodes, and suppresses melting / expansion of the weld spots, resulting in smoother surfaces.

Claims

[1] Metal alloy suitable for hot stamping, the alloy containing between 0.05 and 0.45 wt% carbon, between 0.5 and 4.5 wt% manganese, between 0.5 and 6 wt% chromium, between 0.5 and 2.5 wt% Si, between more than 0.1 and 0.5 wt% cerium and the balance iron and impurities. [2] The metal alloy according to claim 1, wherein the total content of Cr and Si is less than or equal to 5 wt%. [3] Metal alloy according to claim 2, wherein the ratio of Cr:Si is between 1.25 and 3. [4] Metal alloy according to claim 1, wherein the ratio of Cr:Si is between 1.25 and 3. [5] A method of manufacturing an automotive structural part, comprising: Heating a blank made of a metal alloy containing between 0.05 and 0.45 wt% carbon, between 0.5 and 4.5 wt% manganese, between 0.5 and 6 wt% chromium, between 0.5 and 2.5 wt% Si, between more than 0.1 and 0.5 wt% cerium, and the balance iron and impurities; and Hot stamping the blank into the desired automotive structural part. [6] The method of claim 5, wherein the heating takes place in the space defined by the time and temperature points (300s, 870°C), (200s, 980°C), (800s, 870°C) and (1000s, 980°C). [7] The method of claim 5, wherein the heating takes place in the space defined by the time and temperature points (300s, 870°C), (200s, 980°C), (1000s, 870°C) and (800s, 980°C). [8] The method of claim 5, further comprising heating in an inert atmosphere. [9] The method according to claim 5, wherein the composition of the blank has a total content of Cr and Si of less than or equal to 5 wt%. [10] The method of claim 9, wherein the composition of the blank has a Cr:Si ratio of between 1.25 and 3.

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