Hot stamping alloy, method of making hot stamped parts with such alloy, and parts made from such alloy
A novel alloy composition for hot stamping forms a thin, uniform oxide layer, addressing the issues of thick coatings and electrode damage in existing alloys, thereby simplifying manufacturing and improving spot welding performance.
Patent Information
- Application Number
- US18/436610
- Authority / Receiving Office
- US · United States
- Patent Type
- Applications(United States)
- Current Assignee / Owner
- Priority Date
- 2023-12-22
- Filing Date
- 2024-02-08
- Publication Date
- 2025-06-26
AI Technical Summary
Existing hot stamping alloys for automotive parts result in thick and uneven oxide coatings, necessitating additional processing steps like blasting, which complicates the manufacturing process and increases costs, and are difficult to spot weld due to non-uniform surface oxides that damage electrodes.
A novel alloy composition comprising 0.05-0.45 wt% C, 0.5-6 wt% Cr, 0.5-2.5 wt% Si, 0.1-0.5 wt% Ce, balance Fe, which forms a thin and uniform oxide layer during hot stamping, reducing the need for protective atmospheres and improving spot welding performance.
The alloy achieves a thin, uniform oxide coating that enhances spot welding durability and prevents electrode damage, eliminating the need for additional processing steps and reducing manufacturing complexity and costs.
Smart Images
Figure US20250207233A1-D00000_ABST
Abstract
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application claims the benefit of Chinese Patent Application No. 202311785026.7, filed on Dec. 22, 2023. The entire disclosure of the application referenced above is incorporated herein by reference.INTRODUCTION
[0002] The information provided in this section is for the purpose of generally presenting the context of the disclosure. Work of the presently named inventors, to the extent it is described in this section, as well as aspects of the description that may not otherwise qualify as prior art at the time of filing, are neither expressly nor impliedly admitted as prior art against the present disclosure.
[0003] The present disclosure relates to alloys for hot stamping of structural parts, such as structural automotive parts, and to the hot stamping of such structural parts, and the resulting structural parts themselves.
[0004] A common method of manufacturing structural automotive parts is hot stamping, also referred to 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, which require further processing such as blasting. To reduce the formation of these oxide coatings, the 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 cost.
[0005] Hot stamping alloys have been developed which are more resistant to the formation of oxides during the hot stamping process. One 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, the balance being iron. However, these alloys are difficult to later spot weld during subsequent manufacturing, because the non-uniform surface oxides causes build-up on spot welding electrodes, which reduces the electrode life, and can result in welding artifacts on the surface.SUMMARY
[0006] Further areas of applicability of the present disclosure will become apparent from the detailed description, the claims and the drawings. The detailed description and specific examples are intended for purposes of illustration only and are not intended to limit the scope of the disclosure.
[0007] Embodiments of this disclosure provide an improved metal alloy suitable for hot stamping. According to a first preferred embodiment, the alloy can comprise between about 0.05 and about 0.45 wt % carbon; between about 0.5 and about 4.5 wt % manganese; between about 0.5 and about 6 wt % chromium; between about 0.5 and about 2.5 wt % Si, between about 0.1 and about 0.5 wt % cerium, the balance being iron and impurities.
[0008] The cerium content is preferably above about 0.1 wt % to improve the quality of the surface after hot stamping. The cerium content is preferably less than about 0.5 wt % to maintain steel casting and rolling quality. In some versions of this first embodiment, it may be desirable to keep the total of the Cr and Si content to less than or equal to about 5 wt % for easier scale removal in steel mill. In some versions of this first embodiment, it may be desirable to keep the ratio of Cr:Si between about 1.25:1 and about 3:1 for high temperature oxidation resistance during hot stamping.
[0009] The alloy does not need to be processed in a protective atmosphere such as nitrogen or argon, and processing generally results in a thin, uniform oxide coating less the 1 μm thick, typically less than 0.5 μm thick and often between 0.1 and 0.2 μm thick. The thin uniform oxide layer is less damaging to spot welding tips than the thicker and / or less uniform oxide coatings that develop on existing hot stamping alloys.
[0010] According to a second preferred embodiment of this disclosure, a method of making structural parts, such as automobile structural parts, is disclosed. The method according to this second preferred embodiment comprises: heating a blank of a metal alloy comprising between about 0.05 and about 0.45 wt % carbon; between about 0.5 and about 4.5 wt % manganese; between about 0.5 and about 6 wt % chromium; between about 0.5 and about 2.5 wt % Si, between about 0.1 and about 0.5 wt % cerium, the balance being iron and impurities.
[0011] The heated metal blank is then hot stamped into the desired structural part. This composition provides a wider processing window, both in terms of temperature and duration. For example, in one version, the heating occurs in the space bounded by the time, temperature points (300 s, 870° C.), (200 s, 980° C.), (800 s, 870° C.), and (1000 s, 980° C.). In another version, the heating occurs in the space bounded by the time, temperature points (300 s, 870° C.), (200 s, 980° C.), (1000 s, 870° C.), and (800 s, 980° C.). In some instances, the heating can be performed in an inert atmosphere, such as in a nitrogen or argon atmosphere, but this generally is not necessary.
[0012] According to a third preferred embodiment of this disclosure, structural parts are provided. According to the third embodiment, a structural part, such as an automotive structural part, made of between about 0.05 and about 0.45 wt % carbon; between about 0.5 and about 4.5 wt % manganese; between about 0.5 and about 6 wt % chromium; between about 0.5 and about 2.5 wt % Si, between about 0.1 and about 0.5 wt % cerium, the balance being iron and impurities, shaped by hot stamping with a substantially uniform oxidation thickness after hot stamping of less than about 0.5 μm. This part can be, for example, automotive pillars, door beams and bumper beams.
[0013] Hot stamping products from blanks of this alloy results in parts with a thin, uniform oxide coating that does not need blasting or other processing steps. The thin, substantially uniform oxide coating improves spot welding, extending the life of spot-welding electrodes, and suppresses spot weld melting / expulsion, resulting in smoother surfaces.BRIEF DESCRIPTION OF THE DRAWINGS
[0014] The present disclosure will become more fully understood from the detailed description and the accompanying drawings, wherein:
[0015] FIG. 1 is a photomicrograph of 22MnB5 with thick oxides after soaking at 930° C. for 300 seconds, showing thick oxidation layer of ˜5 μm;
[0016] FIG. 2 is a photomicrograph of an alloy of 0.05-0.45 wt % C, 0-0.45 wt % Mn, 0.5-6 wt % Cr, 0.5-2.5 wt % Si, the balance being iron, after soaking at 930° C. for 300 seconds, showing non-uniform oxidization of between 0.2 μm and 3 μm;
[0017] FIG. 3 is a photomicrograph of an alloy according to this disclosure, after soaking at 930° C. for 640 seconds, showing uniform oxidization of about 0.14 μm;
[0018] FIG. 4 is a photomicrograph of an alloy according to this disclosure, after soaking at 930° C. for 720 seconds, showing uniform oxidization of about 0.16 μm;
[0019] FIG. 5 is a photomicrograph of an alloy according to this disclosure, after soaking at 930° C. for 300 seconds, showing uniform oxidization of about 0.13 μm;
[0020] FIG. 6 is a photomicrograph of an alloy according to this disclosure, after soaking at 950° C. for 360 seconds, showing uniform oxidization of about 0.13 μm;
[0021] FIGS. 7A and 7B are photomicrographs comparing the surface of an alloy of this disclosure (7A) versus 22MnB5 (7B) using a spot-welding electrode after 25 spot welds;
[0022] FIGS. 8A and 8B are photomicrographs comparing the surface of an alloy of this disclosure (8A) versus 22MnB5 (8B) using a spot-welding electrode after 59 spot welds;
[0023] FIGS. 9A and 9B are photomicrographs comparing the surface of an alloy of this disclosure (9A) versus 22MnB5 (9B) using a spot-welding electrode after 75 spot welds;
[0024] FIGS. 10A and 10B are photomicrographs comparing the surface of an alloy of this disclosure (10A) versus 22MnB5 (10B) using a spot-welding electrode after 100 spot welds; and
[0025] FIGS. 11A and 11B are depictions of a spot welding electrode after 100 spot welds of a current alloy (11A) versus an alloy of this disclosure.
[0026] In the drawings, reference numbers may be reused to identify similar and / or identical elements.DETAILED DESCRIPTION
[0027] Embodiments of this disclosure provide an improved metal alloy suitable for hot stamping. According to a first preferred embodiment, the alloy can comprise between about 0.05 and about 0.45 wt % carbon; between about 0.5 and about 4.5 wt % manganese; between about 0.5 and about 6 wt % chromium; between about 0.5 and about 2.5 wt % Si, between about 0.1 and about 0.5 wt % cerium, the balance being iron and impurities.
[0028] The cerium content is preferably above about 0.1 wt % to improve the quality of the surface after hot stamping. The cerium content is preferably less than about 0.5 wt % to maintain steel casting and rolling quality. In some versions of this first embodiment, it may be desirable to keep the total of the Cr and Si content to less than or equal to about 5 wt % for easier scale removal in steel mill. In some versions of this first embodiment it may be desirable to keep the ratio of Cr:Si between about 1.25:1 and about 3:1 for high temperature oxidation resistance during hot stamping. Of course other rare earth materials could be used in place of cerium.
[0029] The alloy does not need to be processed in a protective atmosphere such as in nitrogen or argon, and processing generally results in a thin, uniform oxide coating less the 1 μm thick, typically less than 0.5 μm thick, and often between 0.1 and 0.2 μm thick. The thin uniform oxide layer is less damaging to spot welding tips the thicker and / or less uniform oxide coatings the develop on existing hot stamping alloys.
[0030] According to a second preferred embodiment of this disclosure, a method of making a structural part, such as automobile structural parts, is disclosed. The method according to this second preferred embodiment comprises: heating a blank of a metal alloy comprising between about 0.05 and about 0.45 wt % carbon; between about 0.5 and about 4.5 wt % manganese; between about 0.5 and about 6 wt % chromium; between about 0.5 and about 2.5 wt % Si, between about 0.1 and about 0.5 wt % cerium, the balance being iron and impurities.
[0031] The alloy is heated above its austenization temperature (˜900° C.). The heated metal blank is then hot stamped into the desired structural part. This composition provides a wider processing window, both in terms of temperature and duration. For example, in one version, the heating occurs in the space bounded by the time, temperature points (300 s, 870° C.), (200 s, 980° C.), (800 s, 870° C.), and (1000 s, 980° C.). In another version, the heating occurs in the space bounded by the time, temperature points (300 s, 870° C.), (200 s, 980° C.), (1000 s, 870° C.), and (800 s, 980° C.). In some instances, the heating can be performed in an inert atmosphere, such as in a nitrogen or argon atmosphere.
[0032] According to a third preferred embodiment of this disclosure, automotive parts are provided. According to the third embodiment, a structural part, such as an automotive structural part, made of between about 0.05 and about 0.45 wt % carbon; between about 0.5 and about 4.5 wt % manganese; between about 0.5 and about 6 wt % chromium; between about 0.5 and about 2.5 wt % Si, between about 0.1 and about 0.5 wt % cerium, the balance being iron and impurities, shaped by hot stamping with a substantially uniform oxidation thickness after hot stamping of less than about 0.5 μm. This part can be, for example, automotive pillars, door beams and bumper beams.
[0033] The thin, substantially uniform oxide coating improves spot welding, and extends the life of spot-welding electrodes, and suppresses spot weld melting / expulsion, resulting in smoother surfaces.
[0034] The foregoing description is merely illustrative in nature and is in no way intended to limit the disclosure, its application, or uses. The broad teachings of the disclosure can be implemented in a variety of forms. Therefore, while this disclosure includes particular examples, the true scope of the disclosure should not be so limited since other modifications will become apparent upon a study of the drawings, the specification, and the following claims. It should be understood that one or more steps within a method may be executed in different order (or concurrently) without altering the principles of the present disclosure. Further, although each of the embodiments is described above as having certain features, any one or more of those features described with respect to any embodiment of the disclosure can be implemented in and / or combined with features of any of the other embodiments, even if that combination is not explicitly described. In other words, the described embodiments are not mutually exclusive, and permutations of one or more embodiments with one another remain within the scope of this disclosure.
Claims
1. A metal alloy suitable for hot stamping, the alloy comprising between about 0.05 and about 0.45 wt % carbon; between about 0.5 and about 4.5 wt % manganese; between about 0.5 and about 6 wt % chromium; between about 0.5 and about 2.5 wt % Si, between about 0.1 and about 0.5 wt % cerium, the balance being iron and impurities.
2. The metal alloy according to claim 1 wherein the total of Cr and Si content is less than or equal to about 5 wt %.
3. The metal alloy according to claim 2 wherein the ratio of Cr:Si is between about 1.25 and about 3.
4. The metal alloy according to claim 1 wherein the ratio of Cr:Si is between about 1.25 and about 3.
5. A method of making a structural automobile part comprising: heating a blank of a metal alloy comprising between about 0.05 and about 0.45 wt % carbon; between about 0.5 and about 4.5 wt % manganese; between about 0.5 and about 6 wt % chromium; between about 0.5 and about 2.5 wt % Si, between about 0.1 and about 0.5 wt % cerium, the balance being iron and impurities; and hot stamping the blank into the desired structural automotive part.
6. The method of claim 5 wherein the heating occurs in the space bounded by the time, temperature points (300 s, 870° C.), (200 s, 980° C.), (800 s, 870° C.), and (1000 s, 980° C.).
7. The method of claim 5 wherein the heating occurs in the space bounded by the time, temperature points (300 s, 870° C.), (200 s, 980° C.), (1000 s, 870° C.), and (800 s, 980° C.).
8. The method of claim 5 wherein the heating occurs in an inert atmosphere.
9. The method according to claim 5 wherein the composition of the blank has a total of Cr and Si content is less than or equal to about 5 wt %.
10. The method according to claim 9 wherein the composition of the blank has a ratio of Cr:Si is between about 1.25 and about 3.
11. The method according to claim 5 wherein the ratio of Cr:Si is between about 1.25 and about 3.
12. An automotive structural part made of between about 0.05 and about 0.45 wt % carbon; between about 0.5 and about 4.5 wt % manganese; between about 0.5 and about 6 wt % chromium; between about 0.5 and about 2.5 wt % Si, between about 0.1 and about 0.5 wt % cerium, the balance being iron and impurities, shaped by hot stamping with a uniform oxidation thickness after hot stamping of 0.5 μm.
13. The automotive structural part according to claim 12 wherein the total of Cr and Si content is less than or equal to about 5 wt %.
14. The automotive structural part according to claim 13 wherein the ratio of Cr:Si is between about 1.25 and about 3.
15. The automotive structural part according to claim 12 wherein the ratio of Cr:Si is between about 1.25 and about 3.
16. The automotive structural part according to claim 11, wherein the part is an automotive pillar, a door beam, or a bumper beam.