Blank for hot-stamped automotive parts and method for producing hot-stamped automotive parts

Abstract

The invention relates to a rolled blank for a hot-stamped automotive component and a method of manufacturing a hot-stamped automotive component. A roll blank for hot stamping automotive parts, the blank being made from an alloy comprising from about 0.05 to about 0.35 weight percent carbon, from about 0.5 to about 5.0 weight percent manganese, from about 0.5 to about 2.0 weight percent silicon, from about 0.6 to about 4.0 weight percent chromium, optionally from about 0.02 to 0.05 weight percent niobium, and optionally from about 0.03 to about 0.3 weight percent yttrium and / or cerium, with the balance being iron and impurities. The blank is cold rolled to have at least one of the geometric features: (a) a maximum thickness difference greater than about 0.8 mm and less than about 2.0 mm; (b) a maximum ratio of thickest to thinnest regions greater than about 1.2 and less than about 2.5; and (c) at least one transition zone between adjacent regions of different thicknesses, the transition zone having a length greater than 10 times but less than 80 times the difference in thickness between the regions.

Description

Technical Field

[0001] This disclosure relates to hot-stamped automotive parts, and more particularly to rolled blanks for hot-stamped automotive parts, and methods for manufacturing hot-stamped automotive parts. Background Technology

[0002] The information provided in this section is for the purpose of generally presenting the background of this disclosure. The work of the currently named inventors (to the extent described in this section) and aspects of the description that may not constitute prior art at the time of filing are neither expressly nor implied to be considered prior art to this disclosure.

[0003] Many automotive structural components are manufactured through hot stamping or die-hardening. The steel commonly used in this method is 22MnB5, which has a nominal composition of 0.22 wt% carbon, 1.59 wt% manganese, 0.25 wt% silicon, 0.006 wt% chromium, 0.002 wt% copper, 0.001 wt% sulfur, 0.015 wt% phosphorus, 0.082 wt% aluminum, 0.026 wt% titanium, and 0.0027 wt% boron. However, this alloy is prone to oxidation during high-temperature processing, and therefore typically has a protective aluminum-silicon coating.

[0004] While effective in reducing oxidation, the coating interferes with preheating stamping processes such as cold rolling. The amount of cold rolling reduction of the coated alloy must be limited (both in absolute and relative terms) to avoid excessive thinning of the coating. Summary of the Invention

[0005] The embodiments disclosed herein provide a rolled blank for hot-stamping automotive parts, a method for manufacturing the rolled blank, and an automotive part made from the rolled blank.

[0006] According to a first embodiment of this disclosure, a rolled blank for hot-stamping automotive parts is provided. The blank is made of an alloy comprising about 0.05 to about 0.35 wt% carbon, about 0.5 to about 5.0 wt% manganese, about 0.5 to about 2.0 wt% silicon, about 0.6 to about 4.0 wt% chromium, optionally about 0.02-0.05 wt% niobium, and optionally about 0.03 to about 0.3 wt% yttrium and / or cerium, with the balance being iron and impurities. This blank does not require a coating to resist excessive oxidation during subsequent hot stamping, and thus its thickness can be reduced by a greater amount and a greater percentage than with a coated alloy. Furthermore, the alloy can harden at a slow cooling rate, allowing for a more abrupt transition in thickness because the surface of the blank does not need to remain in contact with the die during hot stamping. The alloy is cold-rolled to form a rolled billet having one or more of the following geometric features: (a) the maximum thickness difference between the thinnest and thickest regions of the billet can be from about 0.8 mm to about 2.0 mm; (b) the thickest region is from 1.4 to 3.2 mm and the thinnest region is from 0.8 to 1.5 mm, with a thickness ratio (thickest / thinnest) of 1.2 to 2.5; and (c) at least one transition region between adjacent regions of the billet with different thicknesses, the transition region having a length less than 80 times but greater than 10 times the thickness difference between the regions.

[0007] In some forms of the first embodiment, the rolled billet optionally contains about 0.02-0.05% by weight of niobium, and in other forms of the first embodiment, the billet optionally contains about 0.03 to about 0.3% by weight of yttrium and / or cerium. In still other forms of the first embodiment, the rolled billet optionally contains about 0.02-0.05% by weight of niobium and about 0.03 to about 0.3% by weight of yttrium and / or cerium.

[0008] According to a second embodiment of this disclosure, structural components for automobiles are provided by hot stamping any form of rolled blank according to the first embodiment.

[0009] According to a third embodiment of this disclosure, a method for manufacturing a rolled blank for hot-stamped automotive structural components is provided. Typically, the method of the third embodiment includes forming a rolled blank suitable for hot-stamped automotive components by cold rolling a blank made of an alloy comprising about 0.05 to about 0.35 wt% carbon, about 0.5 to about 5.0 wt% manganese, about 0.5 to about 2.0 wt% silicon, about 0.6 to about 4.0 wt% chromium, optionally about 0.02-0.05 wt% niobium, and optionally about 0.03 to about 0.3 wt% yttrium and / or cerium, having one or more of these geometric characteristics: (a) the blank (a) the maximum thickness difference between the thinnest region and the thickest region of the billet is greater than about 0.8 mm and about 1.5 mm; (b) the maximum ratio between the thinnest region of the billet and the thickest region of the billet is about 1.2 and less than about 2.5 (including the endpoints); and (c) at least one transition zone between adjacent regions of the billet with different thicknesses, the length of which is less than 80 times the thickness difference between the regions but greater than 10 times the thickness difference between the regions; and hot stamping the rolled billet to form a structural component for automobiles.

[0010] Compared to conventionally hot-stamped parts, the automotive parts obtained from the second embodiment and the automotive parts obtained from the third embodiment can be manufactured more cost-effectively and are lighter in weight. Because the rolled blanks of the embodiments of this disclosure allow for greater thickness variation, the blanks can be manufactured thinner in less critical areas of the part while maintaining appropriate thickness in critical areas of the finished part, reducing the amount of material used and the weight of the final part. Furthermore, the increased ability to vary the thickness of the rolled blank eliminates the need to reinforce multiple areas of the blank. Moreover, the transition between areas of different thicknesses can be much shorter while still achieving desirable strength and hardness properties, since die contact is not critical for achieving a desirable cooling profile.

[0011] The present invention discloses the following solutions:

[0012] Option 1. A rolled billet for hot-stamped automotive parts, said billet being made of an alloy comprising about 0.05 to about 0.35 wt% carbon, about 0.5 to about 5.0 wt% manganese, about 0.5 to about 2.0 wt% silicon, about 0.6 to about 4.0 wt% chromium, optionally about 0.02-0.05 wt% niobium, and optionally about 0.03 to about 0.3 wt% yttrium and / or cerium, with the balance being iron and impurities, wherein said rolled billet is cold-rolled to have one or more of these geometric characteristics:

[0013] The maximum thickness difference between the thinnest and thickest regions of the billet is greater than approximately 0.8 mm and less than approximately 2.0 mm;

[0014] The maximum ratio of the thickest region to the thinnest region of the billet is greater than about 1.2 and less than about 2.5; and

[0015] At least one transition zone between adjacent regions of different thicknesses in a billet, the transition zone having a length less than 80 times but greater than 10 times the thickness difference between the regions.

[0016] Option 2. The rolled billet according to Option 1 contains about 0.02 to 0.05% by weight of niobium.

[0017] Option 3. The rolled billet according to Option 2 contains about 0.03 to about 0.3% by weight of yttrium and / or cerium.

[0018] Option 4. The rolled billet according to Option 1 contains about 0.03 to about 0.3% by weight of yttrium and / or cerium.

[0019] Option 5. A structural component for automobiles made by hot stamping of the rolled blank as described in Option 1.

[0020] Option 6. The structural component for automobiles according to Option 5, wherein the component has an ultimate tensile strength greater than about 1500 MPa.

[0021] Option 7. A structural component for an automobile according to Option 6, wherein the component has a hardness of approximately 400 to 560 HV.

[0022] Option 8. A structural component for an automobile according to Option 5, wherein the component has a hardness higher than about 400 and 560 HV.

[0023] Option 9. A method for manufacturing structural components for automobiles, comprising:

[0024] A rolled billet suitable for hot-stamped automotive parts is formed by cold rolling a billet made of an alloy comprising about 0.05 to about 0.35 wt% carbon, about 0.5 to about 5.0 wt% manganese, about 0.5 to about 2.0 wt% silicon, about 0.6 to about 4.0 wt% chromium, optionally about 0.02-0.05 wt% niobium, and optionally about 0.03 to about 0.3 wt% yttrium and / or cerium, wherein the rolled billet is cold rolled to have one or more of the following geometric characteristics: (a) a maximum thickness difference between the thinnest region and the thickest region of the billet greater than about 0.8 mm and less than about 2.0 mm; (b) a maximum ratio between the thickest region and the thinnest region of the billet greater than about 1.2 and less than about 2.5; and (c) at least one transition region between adjacent regions of the billet with different thicknesses, the transition region having a length less than 80 times but greater than 10 times the thickness difference between the regions; and

[0025] The rolled blank is hot-stamped to form structural components for automobiles.

[0026] Option 10. A method for manufacturing a structural component for an automobile according to Option 9, wherein the blank is made of an alloy containing about 0.02-0.05% by weight of niobium.

[0027] Option 11. A method for manufacturing a structural component for an automobile according to Option 10, wherein the blank is made of an alloy containing about 0.03 to about 0.3% by weight of yttrium and / or cerium.

[0028] Option 12. A method for manufacturing a structural component for an automobile according to Option 9, wherein the blank is made of an alloy containing about 0.03 to about 0.3% by weight of yttrium and / or cerium. Attached Figure Description

[0029] This disclosure will be more fully understood from the detailed description and accompanying drawings, in which:

[0030] Figure 1 illustrates an implementation scheme using this disclosure ( Figure 1B Shorter transition zones between regions of varying thicknesses that can be achieved vs. existing technologies ( Figure 1A The longer transition zone required in the mold to maintain mold contact, achieve a sufficient cooling rate, and thus achieve the desired properties;

[0031] Figure 2 illustrates an implementation scheme using this disclosure ( Figure 2B The improvements in absolute thickness difference and thickness ratio that can be achieved compared to existing technologies, and the improvements in existing technologies ( Figure 2A The longer transition zone required to maintain mold contact for sufficient cooling rate and thus achieve desired properties; and

[0032] Figure 3 This is a flowchart of a method for manufacturing structural automotive components.

[0033] In the accompanying drawings, reference numerals may be used repeatedly to identify similar and / or identical elements. Detailed Implementation

[0034] The embodiments disclosed herein provide a rolled blank for hot-stamping automotive parts, a method for manufacturing the rolled blank, and an automotive part made from the rolled blank.

[0035] According to a first embodiment of this disclosure, a rolled billet for manufacturing automotive parts by hot stamping is provided. The rolled billet is obtained by cold rolling an alloy comprising about 0.05 to about 0.35 wt% carbon, about 0.5 to about 5.0 wt% manganese, about 0.5 to about 2.0 wt% silicon, about 0.6 to about 4.0 wt% chromium, optionally about 0.02-0.05 wt% niobium, and optionally about 0.03 to about 0.3 wt% yttrium and / or cerium, with the balance being iron and impurities.

[0036] The cold rolling process produces a smoother surface (e.g., Ra of about 0.3) than hot rolling (e.g., Ra of about 2.5). Furthermore, because the alloy lacks a protective aluminum-silicon coating to resist excessive oxidation during subsequent hot stamping, the alloy billet can be cold-rolled to achieve greater thickness reductions (either in absolute terms or as a ratio). For example, the alloy can be cold-rolled to thickness differences greater than 0.8 mm and up to 2.0 mm, with a thickness difference ratio (thickest / thinnest) of 1.2 to about 2.5 (including endpoints), because there is no surface coating that would be thinned or damaged (e.g., by inversion or breakage).

[0037] Furthermore, during hot stamping, it is difficult for the die to perfectly match the transition zone. Air gaps between the die and the transition zone can reduce the cooling rate. The alloy of this disclosure can harden at a much slower cooling rate than conventional alloys (such as coated 22MnB5), thus allowing for a more abrupt transition between areas of different thicknesses, since the blank surface does not need to remain in contact with the die during cooling. To achieve desired physical properties, conventional alloys such as 22MnB5 require a cooling rate of 30°C / s for hardening, while the alloy of this invention achieves satisfactory hardening at a cooling rate of about 5°C / s to about 20°C / s. Moreover, after hot stamping, the alloy of this disclosure can achieve a yield strength of about 900 to about 1400 MPa and an ultimate tensile strength of about 1300-1900 MPa, while coated 22MnB5 has an ultimate tensile strength of 1350-1550 MPa. Furthermore, the microhardness of the hot-stamping alloy of this disclosure is 400 HV to 560 HV, including the transition zone and corners on the hot-stamped assembly.

[0038] Surface oxidation may occur during hot stamping. This oxidation is more pronounced when the blank is thinner and less pronounced when the blank is thicker. This variation is greater than 0.1 times the thickness ratio.

[0039] Therefore, the alloy of this disclosure can be cold-rolled to achieve one or more geometries beneficial to the final hot-stamped product, which cannot be achieved with existing coated alloys such as coated 22MnB5, said geometries including one or more of the following: (a) a maximum thickness difference between the thinnest region and the thickest region of the billet greater than about 0.8 mm and less than about 2.0 mm; (b) a maximum ratio between the thinnest region and the thickest region of the billet of about 1.2 to about 2.5 (including the endpoints); and (c) at least one transition region between adjacent regions of the billet with different thicknesses, the transition region having a length less than 80 times but greater than 10 times the thickness difference between the regions.

[0040] The ability to form billets with greater thickness reduction and a greater thickness reduction ratio allows for thinner rolling of the billet in less critical areas of the part, while maintaining appropriate thickness in critical areas, reducing the amount of material used and the weight of the final part. Furthermore, the wider range of allowable variations in billet thickness means that no reinforcement or other post-manufacturing modifications to the billet are required. Similarly, shorter transitions between areas of different thicknesses mean that the billet can be manufactured with less material, resulting in lighter parts.

[0041] In some forms of the first embodiment, the rolled billet contains about 0.02-0.05% by weight of niobium, and in other forms of the first embodiment, the billet contains about 0.03 to about 0.3% by weight of yttrium and / or cerium. In still other forms of the first embodiment, the rolled billet contains about 0.02-0.05% by weight of niobium and about 0.03 to about 0.3% by weight of yttrium and / or cerium.

[0042] According to a second embodiment of this disclosure, structural components for automobiles are provided by hot stamping a rolled billet of any form according to the first embodiment. The rolled billet and the resulting structural component are made of an alloy that does not require a coating to protect it from excessive oxidation during hot stamping. This allows the billet to be cold-rolled to provide a greater thickness variation (from about 0.8 mm to about 2.0 mm) and a greater thickness variation ratio (thickest / thinnest) (up to 2.5 or greater), reducing the amount of material used and lightening the weight of the rolled billet and the resulting structural component. Furthermore, the alloy's ability to harden during relatively slow cooling allows for shorter transitions between adjacent areas of different thicknesses, as die contact is not critical for cooling. Thus, while conventional alloys such as coated 22MnB5 require transition zones longer than 80 times the thickness variation, the alloys used in this disclosure can have transition zones ranging from 10 times to less than 80 times the thickness variation.

[0043] According to a third embodiment of this disclosure, a method for manufacturing rolled blanks for hot-stamped automotive structural components is provided. Figure 3 The method of the third embodiment, generally shown as 100, at 102 includes forming a rolled billet suitable for hot-stamped automotive parts by cold rolling a billet made of an alloy comprising about 0.05 to about 0.35 wt% carbon, about 0.5 to about 5.0 wt% manganese, about 0.5 to about 2.0 wt% silicon, about 0.6 to about 4.0 wt% chromium, optionally about 0.02-0.05 wt% niobium, and optionally about 0.03 to about 0.3 wt% yttrium and / or cerium, having one or more of these geometric characteristics: (a) a maximum thickness difference between the thinnest region and the thickest region of the billet greater than about 0.8 mm and less than about 2.0 mm; (b) a maximum ratio between the thickest region of the billet and the thinnest region of the billet of about 1.2 to about 2.5; and (c) at least one transition zone between adjacent regions of the billet with different thicknesses, the transition zone having a length less than 80 times but greater than 10 times the thickness difference between the regions. Subsequently, at point 104, the rolled blank is hot-stamped to form a structural component for automobiles.

[0044] Compared to conventional hot-stamped parts, the automotive parts obtained from the second embodiment and those obtained from the method of the third embodiment can be manufactured more cost-effectively and are lighter in weight. Because the rolled blanks of the embodiments of this disclosure allow for greater thickness variation, the blanks can be manufactured thinner in less critical areas of the part while maintaining appropriate thickness in critical areas, reducing the amount of material used and the weight of the final part. Furthermore, the increased ability to vary the thickness of the rolled blank eliminates the need to reinforce multiple areas of the blank. Moreover, the transition between areas of different thicknesses can be much shorter, while still achieving desirable strength and hardness properties, since die contact is not critical for the cooling profile required to achieve the desired properties. The resulting parts can have an ultimate tensile strength greater than about 1500 MPa and / or a hardness higher than about 45 HRC (about 400 to 560 HV).

[0045] This disclosure can be applied to any vehicle body structure, including center pillars, door beams, and floor longitudinal beams, to reduce costs, lighten weight, and enhance impact resistance.

[0046] The foregoing description is merely illustrative and is by no means intended to limit this disclosure, its application, or its use. The broad teachings of this disclosure can be implemented in various forms. Therefore, while this disclosure includes specific examples, its true scope should not be so limited, as other modifications will become apparent upon examination of the drawings, description, and appended claims. It should be understood that one or more steps within the method may be performed in different orders (or simultaneously) without altering the principles of this disclosure. Furthermore, although each embodiment is described above as having certain features, any one or more of those features described with respect to any embodiment of the invention may be implemented in any of other embodiments and / or combined with features of any of other embodiments, even if such combinations are not explicitly described. In other words, the described embodiments are not mutually exclusive, and substitution of one or more embodiments for each other remains within the scope of this disclosure.

Claims

1. A rolled billet for hot-stamped automotive parts, said billet being made of an alloy comprising about 0.05 to about 0.35 wt% carbon, about 0.5 to about 5.0 wt% manganese, about 0.5 to about 2.0 wt% silicon, about 0.6 to about 4.0 wt% chromium, optionally about 0.02-0.05 wt% niobium, and optionally about 0.03 to about 0.3 wt% yttrium and / or cerium, with the balance being iron and impurities, said rolled billet being cold-rolled to have one or more of these geometries: The maximum thickness difference between the thinnest and thickest areas of the billet is greater than approximately 0.8 mm and less than approximately 2.0 mm; The maximum ratio of the thickest region to the thinnest region of the billet is greater than about 1.2 and less than about 2.5; and At least one transition zone between adjacent regions of different thicknesses in a billet, the transition zone having a length less than 80 times but greater than 10 times the thickness difference between the regions.

2. The rolled billet according to claim 1, comprising about 0.02 to 0.05% by weight of niobium.

3. The rolled billet according to claim 2, comprising about 0.03 to about 0.3% by weight of yttrium and / or cerium.

4. The rolled billet according to claim 1, comprising about 0.03 to about 0.3% by weight of yttrium and / or cerium.

5. A structural component for automobiles, manufactured by hot stamping of the rolled blank according to claim 1.

6. The structural component for automobiles according to claim 5, wherein the component has an ultimate tensile strength greater than about 1500 MPa.

7. The structural component for automobiles according to claim 6, wherein the component has a hardness of about 400 to 560 HV.

8. The structural component for automobiles according to claim 5, wherein the component has a hardness higher than about 400 and 560 HV.

9. A method for manufacturing a structural component for an automobile, comprising: A rolled billet suitable for hot-stamped automotive parts is formed by cold rolling a billet made of an alloy comprising about 0.05 to about 0.35 wt% carbon, about 0.5 to about 5.0 wt% manganese, about 0.5 to about 2.0 wt% silicon, about 0.6 to about 4.0 wt% chromium, optionally about 0.02-0.05 wt% niobium, and optionally about 0.03 to about 0.3 wt% yttrium and / or cerium, wherein the rolled billet is cold rolled to have one or more of the following geometric characteristics: (a) a maximum thickness difference between the thinnest region and the thickest region of the billet greater than about 0.8 mm and less than about 2.0 mm; (b) a maximum ratio between the thickest region and the thinnest region of the billet greater than about 1.2 and less than about 2.5; and (c) at least one transition region between adjacent regions of the billet with different thicknesses, the transition region having a length less than 80 times but greater than 10 times the thickness difference between the regions. as well as The rolled blank is hot-stamped to form structural components for automobiles.

10. The method of manufacturing a structural component for an automobile according to claim 9, wherein the blank is made of an alloy containing about 0.02-0.05% by weight of niobium.

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