Hot roll forming system for high strength component production

Abstract

A method including loading coating-free press-hardened steel (CFPHS) into a roll forming system. The CFPHS includes: an alloy matrix of carbon (C); a first layer directly on the alloy matrix, the first layer is continuous, has a first thickness of greater than or equal to about 0.01 µm to less than or equal to about 10 µm, and including an oxide enriched with Cr and Si; and a second layer disposed directly on the first layer, the second layer is continuous, has a second thickness of greater than or equal to about 0.01 µm to less than or equal to about 30 µm, and including an oxide enriched with Fe. The method further includes: heating the CFPHS prior to roll forming the CFPHS into the part; and roll forming the CFPHS into the part with rollers after heating the CFPHS. The heating is performed inline with the roll forming.

Description

CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application claims the benefit of Chinese Patent Application No. 202510106626.9 filed on January 22, 2025. 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 systems and methods for forming high strength components from coating-free press-hardened steel (CFPHS) by hot roll forming.

[0004] Roll forming is a continuous metal forming process that includes bending a long strip of sheet metal, typically coiled steel, into a desired cross-section. This is achieved by passing the metal through a series of rollers. Each roller performs an incremental part of the bend until the final shape is obtained. The metal strip is fed through multiple roller stations, each gradually shaping the metal until the desired profile is achieved. Roll forming is used in various industries, including automotive and non-automotive industries. With respect to automotive applications, roll forming may be used to form reinforced safety structures, bumpers, door frames, etc. Non-automotive applications for roll forming include, but are not limited to, construction (for beams and studs), aerospace (for wing supports), appliances (for refrigerator and oven parts), etc. Roll forming provides, for example, for high-volume production, precise and consistent shapes, minimal waste, and the ability to handle complex profiles. SUMMARY

[0005] The present disclosure provides for, in various features, a method including loading coating-free press-hardened steel (CFPHS) into a roll forming system. The CFPHS includes: an alloy matrix of carbon (C) at a concentration of greater than or equal to about 0.05 wt.% to less than or equal to about 0.35 wt.%, chromium (Cr) at a concentration of greater than or equal to about 0.6 wt.% to less than or equal to about 4.0 wt.%, silicon (Si) at a concentration of greater than or equal to about 0.5 wt.% to less than or equal to about 2.0 wt.%, and a balance of iron (Fe); a first layer directly on the alloy matrix, the first layer is continuous, has a first thickness of greater than or equal to about 0.01 µm to less than or equal to about 10 µm, and including an oxide enriched with Cr and Si; and a second layer disposed directly on the first layer, the second layer is continuous, has a second thickness of greater than or equal to about 0.01 µm to less than or equal to about 30 µm, and including an oxide enriched with Fe. The method further includes: heating the CFPHS prior to roll forming the CFPHS into the part; and roll forming the CFPHS into the part with rollers after heating the CFPHS. The heating is performed inline with the roll forming on a common roll forming line.

[0006] In further features, the alloy matrix is greater than or equal to about 95 vol.% martensite when fully hardened.

[0007] In further features, the alloy matrix further includes at least one of the following: manganese (Mn) at a concentration of greater than or equal to about 0.5 wt.% to less than or equal to about 5.0 wt.%; and niobium (Nb) at a concentration of greater than or equal to about 0.0 wt.% to less than or equal to about 0.05 wt.%.

[0008] In further features, the alloy matrix further includes yttrium (Y) at a concentration of greater than or equal to about 0.0 wt.% to less than or equal to about 0.3 wt.%.

[0009] In further features, the alloy matrix further includes cerium (Ce) at a concentration of greater than or equal to about 0.0 wt.% to less than or equal to about 0.3 wt.%.

[0010] In further features, the alloy matrix includes a yield strength of 700– 1.8 GPa, an ultimate tensile strength of 1.0 – 2.1 GPa; and a hardness of 300-600 HV.

[0011] In further features, the alloy matrix includes a surface oxidation of 0.1 – 5.0 µm.

[0012] In further features, the part defines a gap between a first surface and a second surface of the part, the method further comprising laser welding the first surface and the second surface together at the gap to close the gap.

[0013] In further features, prior to the laser welding the gap is less than, or equal to, 0.1 mm.

[0014] In further features, roll forming the CFPHS into the part includes roll forming the part to include a corner radii of less than, or equal to, 2.0t.

[0015] In further features, the heating includes induction heating.

[0016] In further features, the heating is 850°C – 980°C for 1-100 seconds.

[0017] In further features, the heating includes at least one of: heating the CFPHS to an austenitizing temperature of least at A3 to provide the part with a first strength of greater than 1,500 MPa; heating the CFPHS to an inter critical temperature of between A1 and A3 to provide the part with a second strength of between 1,000 – 1,500 MPa; and heating the heating the CFPHS to a sub critical temperature of below A1 to provide the part with a second strength of between 500 – 1,000 MPa.

[0018] In further features, the heating includes heating a first area of the CFPHS to a first temperature and heating a second area of the CFPHS to a second temperature that is different from the first temperature.

[0019] In further features, the heating of the CFPHS prior to roll forming the CFPHS into the part is a primary heating, the method further including a secondary heating during the roll forming.

[0020] In further features, the part is configured for inclusion in a battery protection case of a vehicle.

[0021] The present disclosure also provides for, in various features, a method for forming a part by roll forming. The method includes loading coating-free press-hardened steel (CFPHS) into a roll forming system. The CFPHS includes: an alloy matrix of carbon (C) at a concentration of greater than or equal to about 0.05 wt.% to less than or equal to about 0.35 wt.%, chromium (Cr) at a concentration of greater than or equal to about 0.6 wt.% to less than or equal to about 4.0 wt.%, silicon (Si) at a concentration of greater than or equal to about 0.5 wt.% to less than or equal to about 2.0 wt.%, manganese (Mn) at a concentration of greater than or equal to about 0.5 wt.% to less than or equal to about 5.0 wt.%, niobium (Nb) at a concentration of greater than or equal to about 0.0 wt.% to less than or equal to about 0.05 wt.%, and a balance of iron (Fe), the alloy matrix being greater than or equal to about 95 vol.% martensite when fully hardened. The CFPHS further includes: a first layer directly on the alloy matrix, the first layer is continuous, has a first thickness of greater than or equal to about 0.01 µm to less than or equal to about 10 µm, and including an oxide enriched with Cr and Si; and a second layer disposed directly on the first layer, the second layer is continuous, has a second thickness of greater than or equal to about 0.01 µm to less than or equal to about 30 µm, and including an oxide enriched with Fe. The method further includes: heating the CFPHS with an induction heater prior to roll forming the CFPHS into the part, the heating includes heating a first portion of the CFPHS to a first temperature and heating a second portion of the CFPHS to a second temperature that is different from the first temperature; roll forming the CFPHS into the part with rollers after heating the CFPHS, the part defining a gap between a first surface and a second surface of the part that is less than, or equal to, 1.5 mm; and welding the first surface and the second surface together at the gap to close the gap. The heating is performed inline with the roll forming on a common roll forming line.

[0022] In further features, the heating of the CFPHS prior to roll forming the CFPHS into the part is a primary heating, the method further including a secondary heating during the roll forming.

[0023] The present disclosure also provides for, in various features, a system for forming a part by roll forming. The system includes coating-free press-hardened steel (CFPHS) including: an alloy matrix of carbon (C) at a concentration of greater than or equal to about 0.05 wt.% to less than or equal to about 0.35 wt.%, chromium (Cr) at a concentration of greater than or equal to about 0.6 wt.% to less than or equal to about 4.0 wt.%, silicon (Si) at a concentration of greater than or equal to about 0.5 wt.% to less than or equal to about 2.0 wt.%, and a balance of iron (Fe), the alloy matrix being greater than or equal to about 95 vol.% martensite when fully hardened. The CFPHS further includes: a first layer directly on the alloy matrix, the first layer is continuous, has a first thickness of greater than or equal to about 0.01 µm to less than or equal to about 10 µm, and including an oxide enriched with Cr and Si; and a second layer disposed directly on the first layer, the second layer is continuous, has a second thickness of greater than or equal to about 0.01 µm to less than or equal to about 30 µm, and including an oxide enriched with Fe. The method further includes: heating the CFPHS with an induction heater prior to roll forming the CFPHS into the part, the heating includes heating a first portion of the CFPHS to a first temperature and heating a second portion of the CFPHS to a second temperature that is different from the first temperature; roll forming the CFPHS into the part with rollers after heating the CFPHS, the part defining a gap between a first surface and a second surface of the part that is less than, or equal to, 1.5 mm; and welding the first surface and the second surface together at the gap to close the gap. The heating is performed inline with the roll forming on a common roll forming line.

[0024] In further features, the heater includes a plurality of heating elements configured to heat a first area of the CFPHS to a first temperature and heat a second area of the CFPHS to a second temperature that is different from the first temperature.

[0025] 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.BRIEF DESCRIPTION OF THE DRAWINGS

[0026] The present disclosure will become more fully understood from the detailed description and the accompanying drawings, wherein:

[0027] FIG. 1 illustrates an exemplary roll forming system in accordance with the present disclosure;

[0028] FIG. 2 illustrates a plurality of heating elements of the roll forming system of FIG. 1 configured to heat different areas of coating free press hardened steel (CFPHS) to different temperatures;

[0029] FIG. 3 illustrates an exemplary method in accordance with the present disclosure for roll forming parts from CFPHS;

[0030] FIG. 4 is a perspective view of an exemplary part formed from CFPHS by roll forming in accordance with the present disclosure;

[0031] FIG. 5 illustrates area 5 of FIG. 4;

[0032] FIG. 6 is a perspective view of an exemplary battery protection case formed from CFPHS by roll forming in accordance with the present disclosure; and

[0033] FIG. 7 illustrates coating-free press-hardened steel (CFPHS) in accordance with the present disclosure.

[0034] In the drawings, reference numbers may be reused to identify similar and / or identical elements.DETAILED DESCRIPTION

[0035] The present disclosure generally provides for methods and systems for forming parts from coating-free press-hardened steel (CFPHS) by roll forming. The parts may be any suitable automotive or non-automotive parts. Suitable automotive parts include, but are not limited to, structural components that enhance vehicle safety. For example, the parts may be any suitable structural components at or proximate to a vehicle A-pillar, B-pillar, door frame, etc. The part may also be a portion of a protective case for a battery pack, such as side rails of the protective case.

[0036] Prior to forming the part by roll forming, the CFPHS is heated. Heating the CFPHS softens the material, which enables acceleration of the bending process during rolling with fewer rolling stations. Heating prior to roll-forming also allows the part to be formed with sharp corner radii, such as radii of less than, or equal to, 2.0t. The heating further allows the part to be formed with a consistent and narrow gap (such as less than, or equal to 1.5mm) between opposing edges of the part after roll forming, which facilitates joining of the edges by laser welding. Use of CFPHS allows the use of rapid heating methods and systems, such as induction heating, with a short soaking time (5s, for example) to achieve a high strength component of greater than, or equal to, 1,500 MPa, for example.

[0037] FIG. 1 and FIG. 2 illustrate examples of a roll forming system 10 in accordance with the present disclosure. FIG. 3 illustrates a method 110 in accordance with the present disclosure for using the roll forming system 10, or any other suitable roll forming system, to form a part from coating-free press-hardened steel (CFPHS). FIGS. 4, 5, and 6 illustrate exemplary parts formed from CFPHS using the roll forming system 10 and / or the method 110. FIG. 7 illustrates an exemplary piece of CFPHS 310.

[0038] The roll forming system 10 of FIG. 1 is configured to roll form CFPHS 310 into any suitable part. In the example of FIG. 1, coils 320 of the CFPHS 310 are processed by the roll forming system 10. The coils 320 are uncoiled (or unrolled) by an uncoiling device 20. The uncoiling device 20 is any suitable device configured to uncoil the CFPHS 310 from the coils 320. From the uncoiling device 20, the CFPHS 310 is transferred in-line to a flattening device 30. The flattening device 30 is any suitable device configured to flatten or level the CFPHS 310 that has been uncoiled from the coils 320. From the flattening device 30, the CFPHS 310 is transferred in-line to a punch device 40. The punch device 40 is any suitable device configured to punch holes in the CFPHS 310, or provide the CFPHS 310 with any other surface features to be included with the part to be roll formed. After the roll forming is complete, and opposing edges are welded together, the roll-formed part may be subject to any suitable additional processing, such as, but not limited to, additional hole piercing, laser cutting, etc.

[0039] From the punch device 40, the CFPHS 310 is transferred in-line to a heater 50. The heater 50 is any suitable device configured to heat the CFPHS 310 in-line prior to reaching a roll forming assembly 60. The heater 50 may be an induction heater, for example. The heater 50 is configured to heat the CFPHS 310 to any suitable temperature for any suitable period of time. For example, the heater 50 is configured to heat the CFPHS 310 to 850°C – 980°C for 5 seconds, or about 5 seconds. The temperature to which the CFPHS 310 is heated may be varied based on a desired strength or hardness of the CFPHS 310. For example, the heater 50 may be configured to heat the CFPHS 310 to an austenitizing temperature of least at A3 to provide the part with a first strength of greater than 1,500 MPa. The heater 50 may be configured to heat the CFPHS 310 to an inter critical temperature of between A1 and A3 to provide the part with a second strength of between 1,000 – 1,500 MPa. The heater 50 may be configured to heat the CFPHS 310 to a sub critical temperature of below A1 to provide the part with a third strength of between 500 – 1,000 MPa.

[0040] With reference to FIG. 2, the heater 50 may include one or more heating elements to heat the CFPHS 310. In the example of FIG. 2, six heating elements 52A, 52B, 52C, 52D, 52E, and 52F are included. Each one of the heating elements 52A-52F is arranged to heat a different area of the CFPHS 310. For example and as illustrated in FIG. 2, a first heating element 52A is arranged to heat a first area 312A of the CFPHS 310, a second heating element 52B is arranged to heat a second area 312B, a third heating element 52C is arranged to heat a third area 312C, a fourth heating element 52D is arranged to heat a fourth area 312D, a fifth heating element 52E is arranged to heat a fifth area 312E, and a sixth heating element 52F is arranged to heat a sixth area 312F. The heating elements 52A-52F are controlled by any suitable controller 100. The controller 100 is configured to individually control the temperature of each one of the heating elements 52A-52F in order to heat the different areas 312A-312F of the CFPHS 310 to different temperatures. Heating the areas 312A-312F to different temperatures facilitates roll forming of the CFPHS 310 into a particular part. The heating elements 52A-52F may be arranged side-by-side in a direction perpendicular to a length of the CFPHS 310, arranged side-by-side in a direction parallel to a length of the CFPHS 310, or arranged in any other suitable orientation to heat any desired areas of the CFPHS 310.

[0041] From the heater 50, the CFPHS 310 is transferred in-line to a roll forming assembly 60. The roll forming assembly 60 includes any suitable number of rollers configured to roll-form the CFPHS 310 into a desired part. In the example illustrated, the roll forming assembly 60 includes first rollers 62A, second rollers 62B, third rollers 62C, and fourth rollers 62D. The rollers 62A-62D may include rollers on one both sides of the CFPHS 310. Heating the CFPHS 310 with the heater 50 may reduce the number of rollers needed for the roll forming assembly 60 to form the part. The roll forming assembly 60 may include a secondary heater 54, which may be the same as, or substantially similar to, the heater 50. The secondary heater 54 is controlled by the controller 100. The secondary heater 54 may be included to maintain the CFPHS 310 heated to a desired temperature throughout the roll forming process performed by the roll forming assembly 60. The CFPHS workpiece is then either air cooled, water cooled, or roller quenched post heating, depending on the desired physical property profile.

[0042] From the roll forming assembly 60, the CFPHS 310 is transferred in-line to a cutting device 70. The cutting device 70 is any suitable device configured to cut the CFPHS 310 to separate the different parts formed by the roll forming assembly 60. From the cutting device 70, the roll formed parts proceed to a run-out table 80. At the run-out table 80, or subsequent to the run-out table 80, the roll formed part may be welded using any suitable welder 90, such as a laser welder, or any other suitable joining method or device, such as resistance spot welding or high frequency welding. The welder 90 is configured to weld together opposing surfaces of the roll formed part. The welding will be further described herein in conjunction with the exemplary parts illustrated in FIG. 5 and FIG. 6. An optional operation of hole piercing may be added to add holes to the component using laser cutting.

[0043] The method 110 of FIG. 3 for forming a part by roll forming will now be described in further detail. The method 110 may be performed by the roll forming system 10 and the controller 100 of FIG. 1, or any other suitable roll forming system and controller. The method 110 will now be described with reference to the roll forming system 10 and the controller 100 for exemplary purposes only. The method 110 begins at block 120, where the controller 100 is operated to start the roll forming system 10. At block 130, the coils 320 of the CFPHS 310 are loaded into the roll forming system 10, and at block 140 the controller 100 operates the flattening device 30 to flatten and / or level the coils 320 into generally flat and generally level sheets of the CFPHS 310. From block 140, the method 110 proceeds to block 150. At block 150, the controller 100 operates the punch device 40 to punch any holes (or form any other surface features) included with the final part to be formed. From block 150, the method 110 proceeds to block 160. At block 160, the heater 50 and / or the secondary heater 54 are operated by the controller 100 to heat the CFPHS 310 as described above. The heating of block 160 includes individually actuating one or more of the different heating elements 52A-52F to heat the different areas 312A-312F to different temperatures to facilitate roll forming as appropriate.

[0044] From block 160, the method 110 proceeds to block 170. At block 170, the controller 100 operates the roll forming assembly 60 to form the part by roll forming. The roll forming process includes operation by the controller 100 of the different rollers 62A-62D. The rollers 62A-62D may include sets of rollers, such as provided on opposite sides of the CFPHS 310, for example. The rollers 62A-62D are arranged, operated, and otherwise configured to form the part by roll forming. To maintain the CFPHS 310 at an elevated temperature during roll forming, the secondary heater 54 may be included with the roll forming assembly, such as between adjacent ones of the rollers 62A-62D. Any suitable number of the secondary heaters 54 may be included. The secondary heater 54 is operated by the controller 100 in a manner that is the same as, or similar to, operation of the heater 50. From block 170, the method 110 proceeds to block 180 where the part is cooled as appropriate, such as by air-cooling or with any suitable cooling device.

[0045] From block 180, the method 110 proceeds to block 190. At block 190, the controller 100 operates the cutting device 70 to cut the CFPHS 310 and separate the parts formed therein by roll forming. From block 190, the method 110 proceeds to block 210. At block 210, the controller 100 operates the laser welder 90, or any other suitable joining methods, to weld edges of the part together and close gaps formed between the edges, as described below. From block 210, the method 110 proceeds to block 220 where the controller 100 ends the method 110 when all of the desired parts have been formed by roll forming the CFPHS 310. Prior to the method 110 ending, however, any suitable hole piercing operation may be added to the roll formed part.

[0046] FIG. 4 illustrates an example of a part 410 formed in accordance with the present disclosure by one or both of the roll forming system 10 and the method 110. The part 410 may be any suitable automotive or non-automotive part. With respect to automotive parts, the part 410 may be a structural reinforcement member, such as an A-pillar, B-pillar, or included with a battery protection case. The part 410 is roll formed from the flat and level (or generally flat and generally level) sheet of the CFPHS 310. With particular reference to FIG. 5, the part 410 includes a first edge 420 and a second edge 422 separated by a gap 424. By heating the CFPHS 310 prior to roll forming with the heater 50 (and / or during the roll forming with the secondary heater 54), the first edge 420 and the second edge 422 are able to be formed sharp and parallel, and the gap 424 is very small. For example, the gap 424 may be less than, or equal to, 1.5mm. The gap 424 is filled and closed by a weld 430. The weld 430 is formed by the welder 90, such as a laser welder, or any other suitable joining methods. Because the gap 424 is very small, and the first edge 420 and the second edge 422 are sharp and parallel, the weld 430 has a high integrity. Any other suitable welding techniques may be used, however, such as high frequency welding. With high frequency welding, no such gap is present (the two edges are pressed together for welding). The part 410 further includes a corner 440 with a corner radii of less than, or equal to, 2.0t. The tight corner radii is made possible by heating the CFPHS 310 with the heater 50 and / or the secondary heater 54 as described above.

[0047] FIG. 6 illustrates a battery pack 510, such as for a vehicle battery. The battery pack 510 is protected by a battery protection case 520. The battery protection case 520 may be any suitable structure configured to protect the battery pack 510. The battery protection case 520 includes, in the example illustrated, a first side rail 530, a second side rail 532, and a base plate 534. One or both of the first side rail 530 and the second side rail 532 is formed from the CFPHS 310 by roll forming using the system 10 and / or the method 110. The first side rail 530 and / or the second side rail 532 may each include the first edge 420, the second edge 422, the gap 424, the weld 430, and the corner 440 of FIGS. 4 and 5.

[0048] With reference to FIG. 7, the CFPHS 310 will be described in additional detail. The CFPHS 310 generally includes an alloy matrix 340, a first layer 350, and a second layer 360. The alloy matrix 340 is in the form of a coil or sheet and includes carbon (C), chromium (Cr), silicon (Si), and iron (Fe). During a hot stamping process, portions of the Cr and Si combine with atmospheric oxygen to form a first layer 350 comprising an oxide enriched with the portions of the Cr and Si. When there is sufficient oxygen in the atmosphere, a portion of the Fe combines with atmospheric oxygen to form the second layer 360 comprising an oxide enriched with Fe. As used in regard to the first layer 350 and the second layer 360, the terms “first” and “second” distinguish the layers structurally from each other and do not relate to an order of formation during hot stamping. Therefore, when the first layer 350 and the second layer 360 are both formed during hot stamping, the first layer 350 may be formed prior to the formation of the second layer 360, the second layer 360 may be formed prior to the formation of the first layer 350, or the first layer 350 and the second layer 360 may be formed simultaneously. The first and second layers prevent, inhibit, or minimize further oxidation so that descaling steps, such as shot blasting or sand blasting, are not required.

[0049] The C is present in the steel alloy matrix 340 at concentration of greater than or equal to about 0.05 wt.% to less than or equal to about 0.35 wt.%, at a concentration of greater than or equal to about 0.01 wt.% to less than or equal to about 0.35 wt.%, and subranges thereof. In various embodiments, the steel alloy matrix 340 comprises C at a concentration of about 0.01 wt.%, about 0.02 wt.%, about 0.04 wt.%, about 0.06 wt.%, about 0.08 wt.%, about 0.1 wt.%, about 0.12 wt.%, about 0.14 wt.%, about 0.16 wt.%, about 0.18 wt.%, about 0.2 wt.%, about 0.22 wt.%, about 0.24 wt.%, about 0.26 wt.%, about 0.28 wt.%, about 0.3 wt.%, 0.32 wt.%, about 0.34 wt.%, or about 0.35 wt.%.

[0050] The Cr is present in the steel alloy matrix 340 at a concentration of greater than or equal to about 0.6 wt.% to less than or equal to about 4.0 wt.%, of greater than or equal to about 1 wt.% to less than or equal to about 9 wt.%, greater than or equal to about 1 wt.% to less than or equal to about 6 wt.%, greater than or equal to about 1 wt.% to less than or equal to about 4 wt.%, or greater than or equal to about 1 wt.% to less than or equal to about 3 wt.%. In various embodiments, the steel alloy matrix 340 comprises Cr at a concentration of about 1 wt.%, about 1.2 wt.%, about 1.4 wt.%, about 1.5 wt.%, about 1.6 wt.%, about 1.8 wt.%, about 2 wt.%, about 2.2 wt.%, about 2.4 wt.%, about 2.5 wt.%, about 2.6 wt.%, about 2.8 wt.%, about 3 wt.%, about 3.2 wt.%, about 3.4 wt.%, about 3.5 wt.%, about 3.6 wt.%, about 3.8 wt.%, about 4 wt.%, about 4.2 wt.%, about 4.4 wt.%, about 4.5 wt.%, about 4.6 wt.%, about 4.8 wt.%, about 5 wt.%, about 5.2 wt.%, about 5.4 wt.%, about 5.5 wt.%, about 5.6 wt.%, about 5.8 wt.%, about 6 wt.%, about 6.2 wt.%, about 6.4 wt.%, about 6.5 wt.%, about 6.6 wt.%, about 6.8 wt.%, about 7 wt.%, about 7.2 wt.%, about 7.4 wt.%, about 7.5 wt.%, about 7.6 wt.%, about 7.8 wt.%, about 8 wt.%, about 8.2 wt.%, about 8.4 wt.%, about 8.5 wt.%, about 8.6 wt.%, about 8.8 wt.%, or about 9 wt.%.

[0051] The Si is present in the steel alloy matrix 340 at a concentration of greater than or equal to about 0.5 wt.% to less than or equal to about 2.0 wt.%, at a concentration of greater than or equal to about 0.5 wt.% to less than or equal to about 2 wt.%, or greater than or equal to about 0.6 wt.% to less than or equal to about 1.8 wt.%. In various embodiments, the steel alloy comprises Si at a concentration of about 0.5 wt.%, about 0.6 wt.%, about 0.7 wt.%, about 0.8 wt.%, about 0.9 wt.%, about 1 wt.%, about 1.1 wt.%, about 1.2 wt.%, about 1.3 wt.%, about 1.4 wt.%, about 1.5 wt.%, about 1.6 wt.%, about 1.7 wt.%, about 1.8 wt.%, about 1.9 wt.%, or about 2 wt.%.

[0052] The Fe makes up the balance of the steel alloy matrix 340. The steel alloy matrix 340 microstructure, when fully hardened, is greater than, or equal to, about 95 vol.% martensite. In its original state (as received from the steel mill), the material consists of a mixture of ferrite, carbides and bainite. Heat treatment of the raw CFPHS material can result in microstructures that have varying combinations of ferrite, bainite, retained austenite, martensite and carbides. The CFPHS 310 is free of, and does not include, for example, a layer of zinc (Zn) or an aluminum-silicon (Al-Si) coating.

[0053] In various embodiments, the steel alloy further comprises manganese (Mn) at a concentration of greater than or equal to about 0.5 wt.% to less than or equal to about 5.0 wt.%, at a concentration of greater than or equal to about 0 wt.% to less than or equal to about 3 wt.%, greater than or equal to about 0.2 wt.% to less than or equal to about 3 wt.%, greater than or equal to about 0.25 wt.% to less than or equal to about 2.5 wt.%, greater than or equal to about 0.5 wt.% to less than or equal to about 2 wt.%, greater than or equal to about 0.75 wt.% to less than or equal to about 1.5 wt.%, or greater than or equal to about 1 wt.% to less than or equal to about 1.5 wt.%. In some embodiments, the steel alloy matrix 340 is substantially free of Mn. As used herein, “substantially free” refers to trace component levels, such as levels of less than or equal to about 1.5%, less than or equal to about 1%, less than or equal to about 0.5%, or levels that are not detectable. In various embodiments, the steel alloy is substantially free of Mn or comprises Mn at a concentration of less than or equal to about 3 wt.%, less than or equal to about 2.5 wt.%, less than or equal to about 2 wt.%, less than or equal to about 1.5 wt.%, less than or equal to about 1 wt.%, or less than or equal to about 0.5 wt.%, such as at a concentration of about 3 wt.%, about 2.8 wt.%, about 2.6 wt.%, about 2.4 wt.%, about 2.2 wt.%, about 2 wt.%, about 1.8 wt.%, about 1.6 wt.%, about 1.4 wt.%, about 1.2 wt.%, about 1 wt.%, about 0.8 wt.%, about 0.6 wt.%, about 0.4 wt.%, about 0.2 wt.%, or lower.

[0054] In various embodiments, the steel alloy matrix 340 further comprises nitrogen (N) at a concentration of greater than or equal to about 0 wt.% to less than or equal to about 0.01 wt.% or greater than or equal to about 0.0001 wt.% to less than or equal to about 0.01 wt.%. For example, in various embodiments, the steel alloy matrix 340 is substantially free of N or comprises N at a concentration of less than or equal to about 0.01 wt.%, less than or equal to 0.009 wt.%, less than or equal to 0.008 wt.%, less than or equal to 0.007 wt.%, less than or equal to 0.006 wt.%, less than or equal to 0.005 wt.%, less than or equal to 0.004 wt.%, less than or equal to 0.003 wt.%, less than or equal to 0.002 wt.%, or less than or equal to 0.001 wt.%, such as at a concentration of about 0.01 wt.%, about 0.009 wt.%, about 0.008 wt.%, about 0.007 wt.%, about 0.006 wt.%, about 0.005 wt.%, about 0.004 wt.%, about 0.003 wt.%, about 0.002 wt.%, about 0.001 wt.%, or lower.

[0055] In various embodiments, the steel alloy matrix 340 further comprises molybdenum (Mo) at a concentration of greater than or equal to about 0 wt.% to less than or equal to about 0.8 wt.%, greater than or equal to about 0.01 wt.% to less than or equal to about 0.8 wt.%, or less than or equal to about 0.8 wt.%. For example, in various embodiments, the steel alloy matrix 340 is substantially free of Mo or comprises Mo at a concentration of less than or equal to about 0.8 wt.%, less than or equal to about 0.7 wt.%, less than or equal to about 0.6 wt.%, less than or equal to about 0.5 wt.%, less than or equal to about 0.4 wt.%, less than or equal to about 0.3 wt.%, less than or equal to about 0.2 wt.%, or less than or equal to about 0.1 wt.%, such as at a concentration of about 0.8 wt.%, about 0.7 wt.%, about 0.6 wt.%, about 0.5 wt.%, about 0.4 wt.%, about 0.3 wt.%, about 0.2 wt.%, about 0.1 wt.%, or lower.

[0056] In various embodiments, the steel alloy matrix 340 further comprises boron (B) at a concentration of greater than or equal to about 0 wt.% to less than or equal to about 0.005 wt.%, greater than or equal to about 0.0001 wt.% to less than or equal to about 0.005 wt.%, or less than or equal to about 0.005 wt.%. For example, in various embodiments, the steel alloy matrix 340 is substantially free of B or comprises B at a concentration of less than or equal to about 0.005 wt.%, less than or equal to about 0.004 wt.%, less than or equal to about 0.003 wt.%, less than or equal to about 0.002 wt.%, or less than or equal to about 0.001 wt.%, such as at a concentration of about 0.005 wt.%, about 0.004 wt.%, about 0.003 wt.%, about 0.002 wt.%, about 0.001 wt.%, about 0.0005 wt.%, about 0.0001 wt.%, or lower.

[0057] In various embodiments, the steel alloy matrix 340 further comprises niobium (Nb) at a concentration of greater than or equal to about 0.0 wt.% to less than or equal to about 0.05 wt.%, at a concentration of greater than or equal to about 0 wt.% to less than or equal to about 0.3 wt.%, greater than or equal to about 0.01 to less than or equal to about 0.3 wt.%, or less than or equal to about 0.3 wt.%. For example, in various embodiments, the steel alloy is substantially free of Nb or comprises Nb at a concentration of less than or equal to about 0.3 wt.%, less than or equal to about 0.25 wt.%, less than or equal to about 0.2 wt.%, less than or equal to about 0.15 wt.%, or less than or equal to about 0.1 wt.%, such as at a concentration of about 0.3 wt.%, about 0.25 wt.%, about 0.2 wt.%, about 0.15 wt.%, about 0.1 wt.%, or lower.

[0058] In various embodiments, the steel alloy matrix 340 further comprises vanadium (V) at a concentration of greater than or equal to about 0 wt.% to less than or equal to about 0.3 wt.%, greater than or equal to about 0.01 to less than or equal to about 0.3 wt.%, or less than or equal to about 0.3 wt.%. For example, in various embodiments, the steel alloy matrix 340 is substantially free of V or comprises V at a concentration of less than or equal to about 0.3 wt.%, less than or equal to about 0.25 wt.%, less than or equal to about 0.2 wt.%, less than or equal to about 0.15 wt.%, or less than or equal to about 0.1 wt.%, such as at a concentration of about 0.3 wt.%, about 0.25 wt.%, about 0.2 wt.%, about 0.15 wt.%, about 0.1 wt.%, or lower.

[0059] The steel alloy matrix 340 may further include yttrium (Y) at any suitable concentration, such as at a concentration of greater than or equal to about 0.0 wt.% to less than or equal to about 0.3 wt.%. The steel alloy matrix 340 may also include cerium (Ce) at any suitable concentration, such as at a concentration of greater than or equal to about 0.0 wt.% to less than or equal to about 0.3 wt.%.

[0060] The CFPHS 310 results from hot pressing the alloy matrix 340. The CFPHS 310 thus includes the alloy matrix 340, the first layer 350, and a second layer 360, which is optional. FIG. 7 shows a cross section illustration of a portion of the CFPHS 310, and shows that the first layer 350 and the second layer 360 (which is optional) surround the alloy matrix 340. The CFPHS 310 has an ultimate tensile strength (UTS) of greater than or equal to about 500 MPa, greater than or equal to about 750 MPa, greater than or equal to about 1,000 MPa, greater than or equal to about 1,250 MPa, greater than or equal to about 1,600 MPa, greater than or equal to about 1,700 MPa, or greater than or equal to about 1,800 MPa. In some embodiments, the CFPHS 310 has a UTS of greater than or equal to about 1,600 MPa and less than or equal to about 2000 MPa. The steel alloy matrix 340 microstructure when fully hardened is greater than, or equal to, about 95 vol.% martensite. In its original state (as received from the steel mill), the material consists of a mixture of ferrite, carbides and bainite. Heat treatment of the raw CFPHS material can result in microstructures that have varying combinations of ferrite, bainite, retained austenite, martensite and carbides. The alloy matrix 340 in accordance with the present disclosure includes, in various configurations, a yield strength of 700 – 1.8 GPa, an ultimate tensile strength of 1.0 – 2.1 GPa, and a hardness of 300 – 600 HV.

[0061] The first layer 350 is disposed directly on the alloy matrix 340 during a hot pressing process and comprises an oxide enriched with Cr and Si, including Cr oxides and Si oxides. In the first layer 350, the oxide enriched with Cr has a concentration of greater than or equal to about 1 wt.% to less than or equal to about 30 wt.%, such as a concentration of about 1 wt.%, about 2 wt.%, about 4 wt.%, about 6 wt.%, about 8 wt.%, about 10 wt.%, about 12 wt.%, about 14 wt.%, about 16 wt.%, about 18 wt.%, about 20 wt.%, about 22 wt.%, about 24 wt.%, about 26 wt.%, about 28 wt.%, or about 30 wt.%. In the first layer 350, the oxide enriched with Si has a concentration of greater than or equal to about 1 wt.% to less than or equal to about 30 wt.%, such as a concentration of about 1 wt.%, about 2 wt.%, about 4 wt.%, about 6 wt.%, about 8 wt.%, about 10 wt.%, about 12 wt.%, about 14 wt.%, about 16 wt.%, about 18 wt.%, about 20 wt.%, about 22 wt.%, about 24 wt.%, about 26 wt.%, about 28 wt.%, or about 30 wt.%, The Cr and Si in the first layer 350 originate within and migrate from the alloy matrix 340 into the oxide. In this regard, the Cr and Si of the enriched oxide of the first layer 350 are derived from the steel alloy or the alloy matrix 340. Put another way, the first layer 350 is formed from portions of the Cr and the Si included in the steel alloy or the alloy matrix 340.

[0062] The first layer 350 has a thickness TL1 of greater than or equal to about 0.01 μm to less than or equal to about 10 μm, such as a thickness of about 0.01 μm, about 0.05 μm, about 0.1 μm, about 0.15 μm, about 0.25 μm, about 0.3 μm, about 0.35 μm, about 0.4 μm, about 0.45 μm, about 0.5 μm, about 0.55 μm, about 0.6 μm, about 0.65 μm, about 0.7 μm, about 0.75 μm, about 0.8 μm, about 0.85 μm, about 0.9 μm, about 0.95 μm, about 1 μm, about 1.5 μm, about 2 μm, about 2.5 μm, about 3 μm, about 3.5 μm, about 4 μm, about 4.5 μm, about 5 μm, about 5.5 μm, about 6 μm, about 6.5 μm, about 7 μm, about 7.5 μm, about 8 μm, about 8.5 μm, about 9 μm, about 9.5 μm, or about 10 μm.

[0063] In certain variations, the first layer 350 is continuous and homogenous. Therefore, in embodiments where the second layer 360 is absent, the first layer 350 provides an exposed surface, and there is no need for it to be descaled by, for example, shot blasting or sand blasting. Moreover, when the second layer 360 is absent, the first layer 350 prevents, inhibits, or minimizes further surface oxidation.

[0064] When processed under various conditions, the CFPHS 310 comprises the second layer 360. The second layer 360 is disposed directly on the first layer 350 during the hot pressing process and comprises an oxide enriched with Fe. In various embodiments, the oxide enriched with Fe comprises FeO, Fe2O3, Fe3O4, or a combination thereof. In the second layer 360, the oxide enriched with Fe has a concentration of Fe of greater than or equal to about 10 wt.%, greater than or equal to about 15 wt.%, greater than or equal to about 20 wt.%, greater than or equal to about 25 wt.%, or greater than or equal to about 30 wt.%. The Fe in the second layer 360 originates within and migrates from the alloy matrix 340 into the oxide. In this regard, the Fe of the second layer 360 is derived from the steel alloy or the alloy matrix 340. Put another way, the second layer 360 is formed from a portion of the Fe included in the steel alloy or the alloy matrix 340.

[0065] The second layer 360 has a thickness TL2 of greater than or equal to about 0 μm to less than or equal to about 30 μm or greater than or equal to about 0.01 μm to less than or equal to about 30 μm, such as a thickness of about 0.01 μm, about 0.05 μm, about 0.1 μm, about 0.15 μm, about 0.25 μm, about 0.3 μm, about 0.35 μm, about 0.4 μm, about 0.45 μm, about 0.5 μm, about 0.55 μm, about 0.6 μm, about 0.65 μm, about 0.7 μm, about 0.75 μm, about 0.8 μm, about 0.85 μm, about 0.9 μm, about 0.95 μm, about 1 μm, about 1.5 μm, about 2 μm, about 2.5 μm, about 3 μm, about 3.5 μm, about 4 μm, about 4.5 μm, about 5 μm, about 5.5 μm, about 6 μm, about 6.5 μm, about 7 μm, about 7.5 μm, about 8 μm, about 8.5 μm, about 9 μm, about 9.5 μm, about 10 μm, about 12 μm, about 14 μm, about 16 μm, about 18 μm, about 20 μm, about 22 μm, about 24 μm, about 26 μm, about 28 μm, or about 30 μm.

[0066] The second layer 360 is continuous and homogenous. Therefore, the second layer 360 provides an exposed surface, and there is no need for it to be descaled by, for example, shot blasting or sand blasting. Moreover, the second layer 360 prevent, inhibits, or minimizes further surface oxidation. When the first layer 350 and the second layers 360 are both formed during hot stamping, the first layer 350 may be formed prior to the formation of the second layer 360, the second layer 360 may be formed prior to the formation of the first layer 350, or the first layer 350 and the second layer 360 may be formed simultaneously. The CFPHS 310 does not include or is free of any layer that is not derived from the steel alloy or the alloy matrix 82. Nonetheless, it does not require descaling.

[0067] 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.

[0068] Spatial and functional relationships between elements (for example, between modules, circuit elements, semiconductor layers, etc.) are described using various terms, including “connected,”“engaged,”“coupled,”“adjacent,”“next to,”“on top of,”“above,”“below,” and “disposed.” Unless explicitly described as being “direct,” when a relationship between first and second elements is described in the above disclosure, that relationship can be a direct relationship where no other intervening elements are present between the first and second elements, but can also be an indirect relationship where one or more intervening elements are present (either spatially or functionally) between the first and second elements. As used herein, the phrase at least one of A, B, and C should be construed to mean a logical (A OR B OR C), using a non-exclusive logical OR, and should not be construed to mean “at least one of A, at least one of B, and at least one of C.”

[0069] In the figures, the direction of an arrow, as indicated by the arrowhead, generally demonstrates the flow of information (such as data or instructions) that is of interest to the illustration. For example, when element A and element B exchange a variety of information but information transmitted from element A to element B is relevant to the illustration, the arrow may point from element A to element B. This unidirectional arrow does not imply that no other information is transmitted from element B to element A. Further, for information sent from element A to element B, element B may send requests for, or receipt acknowledgements of, the information to element A.

[0070] In this application, including the definitions below, the term “module” or the term “controller” may be replaced with the term “circuit.” The term “module” may refer to, be part of, or include: an Application Specific Integrated Circuit (ASIC); a digital, analog, or mixed analog / digital discrete circuit; a digital, analog, or mixed analog / digital integrated circuit; a combinational logic circuit; a field programmable gate array (FPGA); a processor circuit (shared, dedicated, or group) that executes code; a memory circuit (shared, dedicated, or group) that stores code executed by the processor circuit; other suitable hardware components that provide the described functionality; or a combination of some or all of the above, such as in a system-on-chip.

[0071] The module may include one or more interface circuits. In some examples, the interface circuits may include wired or wireless interfaces that are connected to a local area network (LAN), the Internet, a wide area network (WAN), or combinations thereof. The functionality of any given module of the present disclosure may be distributed among multiple modules that are connected via interface circuits. For example, multiple modules may allow load balancing. In a further example, a server (also known as remote, or cloud) module may accomplish some functionality on behalf of a client module.

[0072] The term code, as used above, may include software, firmware, and / or microcode, and may refer to programs, routines, functions, classes, data structures, and / or objects. The term shared processor circuit encompasses a single processor circuit that executes some or all code from multiple modules. The term group processor circuit encompasses a processor circuit that, in combination with additional processor circuits, executes some or all code from one or more modules. References to multiple processor circuits encompass multiple processor circuits on discrete dies, multiple processor circuits on a single die, multiple cores of a single processor circuit, multiple threads of a single processor circuit, or a combination of the above. The term shared memory circuit encompasses a single memory circuit that stores some or all code from multiple modules. The term group memory circuit encompasses a memory circuit that, in combination with additional memories, stores some or all code from one or more modules.

[0073] The term memory circuit is a subset of the term computer-readable medium. The term computer-readable medium, as used herein, does not encompass transitory electrical or electromagnetic signals propagating through a medium (such as on a carrier wave); the term computer-readable medium may therefore be considered tangible and non-transitory. Non-limiting examples of a non-transitory, tangible computer-readable medium are nonvolatile memory circuits (such as a flash memory circuit, an erasable programmable read-only memory circuit, or a mask read-only memory circuit), volatile memory circuits (such as a static random access memory circuit or a dynamic random access memory circuit), magnetic storage media (such as an analog or digital magnetic tape or a hard disk drive), and optical storage media (such as a CD, a DVD, or a Blu-ray Disc).

[0074] The apparatuses and methods described in this application may be partially or fully implemented by a special purpose computer created by configuring a general purpose computer to execute one or more particular functions embodied in computer programs. The functional blocks, flowchart components, and other elements described above serve as software specifications, which can be translated into the computer programs by the routine work of a skilled technician or programmer.

[0075] The computer programs include processor-executable instructions that are stored on at least one non-transitory, tangible computer-readable medium. The computer programs may also include or rely on stored data. The computer programs may encompass a basic input / output system (BIOS) that interacts with hardware of the special purpose computer, device drivers that interact with particular devices of the special purpose computer, one or more operating systems, user applications, background services, background applications, etc.

[0076] The computer programs may include: (i) descriptive text to be parsed, such as HTML (hypertext markup language), XML (extensible markup language), or JSON (JavaScript Object Notation) (ii) assembly code, (iii) object code generated from source code by a compiler, (iv) source code for execution by an interpreter, (v) source code for compilation and execution by a just-in-time compiler, etc. As examples only, source code may be written using syntax from languages including C, C++, C#, Objective-C, Swift, Haskell, Go, SQL, R, Lisp, Java®, Fortran, Perl, Pascal, Curl, OCaml, Javascript®, HTML5 (Hypertext Markup Language 5th revision), Ada, ASP (Active Server Pages), PHP (PHP: Hypertext Preprocessor), Scala, Eiffel, Smalltalk, Erlang, Ruby, Flash®, Visual Basic®, Lua, MATLAB, SIMULINK, and Python®.

Claims

1. A method for forming a part by roll forming, the method comprising: loading coating-free press-hardened steel (CFPHS) into a roll forming system, the CFPHS including:an alloy matrix of carbon (C) at a concentration of greater than or equal to about 0.05 wt.% to less than or equal to about 0.35 wt.%, chromium (Cr) at a concentration of greater than or equal to about 0.6 wt.% to less than or equal to about 4.0 wt.%, silicon (Si) at a concentration of greater than or equal to about 0.5 wt.% to less than or equal to about 2.0 wt.%, and a balance of iron (Fe);a first layer directly on the alloy matrix, the first layer is continuous, has a first thickness of greater than or equal to about 0.01 µm to less than or equal to about 10 µm, and including an oxide enriched with Cr and Si; anda second layer disposed directly on the first layer, the second layer is continuous, has a second thickness of greater than or equal to about 0.01 µm to less than or equal to about 30 µm, and including an oxide enriched with Fe;heating the CFPHS prior to roll forming the CFPHS into the part; androll forming the CFPHS into the part with rollers after heating the CFPHS,wherein the heating is performed inline with the roll forming on a common roll forming line.

2. The method of claim 1, wherein the alloy matrix is greater than or equal to about 95 vol.% martensite when fully hardened.

3. The method of claim 1, wherein the alloy matrix further includes at least one of the following: manganese (Mn) at a concentration of greater than or equal to about 0.5 wt.% to less than or equal to about 5.0 wt.%; andniobium (Nb) at a concentration of greater than or equal to about 0.0 wt.% to less than or equal to about 0.05 wt.%.

4. The method of claim 1, wherein the alloy matrix further includes yttrium (Y) at a concentration of greater than or equal to about 0.0 wt.% to less than or equal to about 0.3 wt.%.

5. The method of claim 1, wherein the alloy matrix further includes cerium (Ce) at a concentration of greater than or equal to about 0.0 wt.% to less than or equal to about 0.3 wt.%.

6. The method of claim 1, wherein the alloy matrix includes a yield strength of 700 – 1.8 GPa, an ultimate tensile strength of 1.0 – 2.1 GPa; and a hardness of 300-600 HV.

7. The method of claim 1, wherein the alloy matrix includes a surface oxidation of 0.1 – 5.0 µm.

8. The method of claim 1, wherein the part defines a gap between a first surface and a second surface of the part, the method further comprising laser welding the first surface and the second surface together at the gap to close the gap.

9. The method of claim 8, wherein prior to the laser welding the gap is less than, or equal to, 0.1 mm.

10. The method of claim 1, wherein roll forming the CFPHS into the part includes roll forming the part to include a corner radii of less than, or equal to, 2.0t.

11. The method of claim 1, wherein the heating includes induction heating.

12. The method of claim 11, wherein the heating is 850°C – 980°C for 1-100 seconds.

13. The method of claim 1, wherein the heating includes at least one of: heating the CFPHS to an austenitizing temperature of least at A3 to provide the part with a first strength of greater than 1,500 MPa; heating the CFPHS to an inter critical temperature of between A1 and A3 to provide the part with a second strength of between 1,000 – 1,500 MPa; andheating the heating the CFPHS to a sub critical temperature of below A1 to provide the part with a second strength of between 500 – 1,000 MPa.

14. The method of claim 1, wherein the heating includes heating a first area of the CFPHS to a first temperature and heating a second area of the CFPHS to a second temperature that is different from the first temperature.

15. The method of claim 1, wherein the heating of the CFPHS prior to roll forming the CFPHS into the part is a primary heating, the method further including a secondary heating during the roll forming.

16. The method of claim 1, wherein the part is configured for inclusion in a battery protection case of a vehicle.

17. A method for forming a part by roll forming, the method comprising: loading coating-free press-hardened steel (CFPHS) into a roll forming system, the CFPHS including: an alloy matrix of carbon (C) at a concentration of greater than or equal to about 0.05 wt.% to less than or equal to about 0.35 wt.%, chromium (Cr) at a concentration of greater than or equal to about 0.6 wt.% to less than or equal to about 4.0 wt.%, silicon (Si) at a concentration of greater than or equal to about 0.5 wt.% to less than or equal to about 2.0 wt.%, manganese (Mn) at a concentration of greater than or equal to about 0.5 wt.% to less than or equal to about 5.0 wt.%, niobium (Nb) at a concentration of greater than or equal to about 0.0 wt.% to less than or equal to about 0.05 wt.%, and a balance of iron (Fe), the alloy matrix being greater than or equal to about 95 vol.% martensite when fully hardened;a first layer directly on the alloy matrix, the first layer is continuous, has a first thickness of greater than or equal to about 0.01 µm to less than or equal to about 10 µm, and including an oxide enriched with Cr and Si; anda second layer disposed directly on the first layer, the second layer is continuous, has a second thickness of greater than or equal to about 0.01 µm to less than or equal to about 30 µm, and including an oxide enriched with Fe;heating the CFPHS with an induction heater prior to roll forming the CFPHS into the part, the heating includes heating a first portion of the CFPHS to a first temperature and heating a second portion of the CFPHS to a second temperature that is different from the first temperature; roll forming the CFPHS into the part with rollers after heating the CFPHS, the part defining a gap between a first surface and a second surface of the part that is less than, or equal to, 1.5 mm; andwelding the first surface and the second surface together at the gap to close the gap,wherein the heating is performed inline with the roll forming on a common roll forming line.

18. The method of claim 17, wherein the heating of the CFPHS prior to roll forming the CFPHS into the part is a primary heating, the method further including a secondary heating during the roll forming.

19. A system for forming a part by roll forming, the system comprising: coating-free press-hardened steel (CFPHS) including: an alloy matrix of carbon (C) at a concentration of greater than or equal to about 0.05 wt.% to less than or equal to about 0.35 wt.%, chromium (Cr) at a concentration of greater than or equal to about 0.6 wt.% to less than or equal to about 4.0 wt.%, silicon (Si) at a concentration of greater than or equal to about 0.5 wt.% to less than or equal to about 2.0 wt.%, and a balance of iron (Fe), the alloy matrix being greater than or equal to about 95 vol.% martensite when fully hardened;a first layer directly on the alloy matrix, the first layer is continuous, has a first thickness of greater than or equal to about 0.01 µm to less than or equal to about 10 µm, and including an oxide enriched with Cr and Si; anda second layer disposed directly on the first layer, the second layer is continuous, has a second thickness of greater than or equal to about 0.01 µm to less than or equal to about 30 µm, and including an oxide enriched with Fe;an uncoiling device configured to uncoil the CFPHS;a flattening device configured to flatten the CFPHS;a punching device configured to punch openings in the CFPHS;a plurality of rollers configured to roll form the CFPHS into the part; anda heater between, the punching device and the plurality of rollers, the heater configured to heat the CFPHS after bring punched by the punching device and prior to being roll formed by the plurality of rollers,wherein the uncoiling device, the flattening device, the punching device, the plurality of rollers, and the heater are all on a common roll forming line.

20. The system of claim 19, wherein the heater includes a plurality of heating elements configured to heat a first area of the CFPHS to a first temperature and heat a second area of the CFPHS to a second temperature that is different from the first temperature.

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