METHOD FOR ACHIEVEING VARIABLE PROPERTIES IN A COMPONENT USING UNCOATED FORMAT-HARDENED STEEL

Abstract

A method for achieving variable properties of a component using a coating-free, hot-formed steel comprises: transferring a blank of coating-free, hot-formed steel (CFPHS) material with base blank properties into a heating unit with multiple induction heating coils; heating the blank in the heating unit to produce a modified blank with different modified blank properties throughout the modified blank compared to the base blank properties; moving the modified blank from the heating unit into a die; and forming a molded part by operating the die, producing a finished CFPHS part.

Description

INTRODUCTION

[0001] The present disclosure relates to hot-formed steel used in vehicle structural and vehicle body components.

[0002] Hot-formed steel is used in vehicle construction, including but not limited to passenger cars, trucks, vans, off-road vehicles, autonomous vehicles, battery electric vehicles, agricultural or construction equipment, rail vehicles, and the like, to provide spatially or locally increased material strength in load-bearing components, particularly to mitigate material failure in impact zones of vehicle bodies, such as door panels and body pillars. Previous work on the induction hardening of steel not performed on materials conforming to the American Iron and Steel Institute (AISI) 22MnB5 standard was typically carried out on steels with a higher carbon content. Currently, hot-formed steel (PHS) is formed entirely in a furnace.Before heating, a coating layer, such as zinc, is applied to the steel for cathodic corrosion protection to improve corrosion resistance. In the furnace, the heating rate and final heating temperature must be carefully controlled to prevent melting of the coating layer or the formation of excessive surface oxides, which can define scale on the outer surfaces of the cathodic corrosion protection steel. This scale must then be subsequently removed using a process such as descaling.

[0003] The material properties of currently produced PHS components are uniform throughout the blank and throughout the finished product. Uniform material properties, which are enhanced to maximize material strength in applications such as vehicle crumple zones and pillars, increase the overall component weight and cost and may not allow for the desired component deformation under impact loading to enable localized absorption and distribution of the impact load.

[0004] Although current systems and processes for producing and using hot-formed steel fulfill their intended purpose, there is therefore a need for a new and improved system and process for producing and using hot-formed steel. SUMMARY

[0005] According to several aspects, a process for achieving variable properties of a vehicle component using a coating-free hot-formed steel (CFPHS) includes: transferring a blank made of a CFPHS material with basic blank properties into a heating unit with multiple induction heating coils; heating the blank in the heating unit to create a modified blank with different modified blank properties throughout the modified blank compared to the basic blank properties; moving the modified blank from the heating unit into a die; and forming a molded part by operating the die, producing a finished CFPHS part.

[0006] According to another aspect of the present invention, the method further includes adjusting the mechanical qualities and surface qualities of the finished CFPHS part using localized heating.

[0007] According to another aspect of the present invention, the method further includes performing localized heating, which utilizes a uniform heating rate or an adapted or variable heating rate to achieve a desired temperature profile.

[0008] According to another aspect of the present invention, the method further includes uniform heating across the blank or in predetermined areas in the blank to enable a selective mechanical profile and surface property profile that defines the modified blank.

[0009] According to another aspect of the present invention, the method further comprises applying a voltage to the induction heating coils using a variable power supply with a variable frequency device.

[0010] According to another aspect of the present invention, the method further includes generating varying and localized current intensities in the heating unit and across the blank.

[0011] According to another aspect of the present invention, the method further comprises: generating variable heating speeds using the variable power supply; and providing zoned holding temperatures for the blank.

[0012] According to another aspect of the present invention, the method further includes operating a multi-axis transfer device for manipulating the blank in the heating unit to produce the modified blank.

[0013] According to another aspect of the present invention, the method further comprises producing the CFPHS material by: incorporating carbon (C) into an alloy matrix with a C concentration greater than or equal to about 0.05 wt.% to less than or equal to about 0.35 wt.%; incorporating chromium (Cr) with a Cr concentration greater than or equal to about 1 wt.% to less than or equal to about 9 wt.%; incorporating silicon (Si) with a Si concentration greater than or equal to about 0.5 wt.% to less than or equal to about 2 wt.%; incorporating manganese (Mn) with a Mn concentration greater than or equal to about 0.5 wt.% to less than or equal to about 2.5 wt.%; and providing a residue of iron (Fe).

[0014] According to another aspect of the present invention, the method further comprises producing the CFPHS material by: incorporating martensite greater than or equal to about 95 vol.% in the alloy matrix; placing a first layer directly onto the alloy matrix, wherein the first layer is continuous and has a thickness greater than or equal to about 0.01 µm to less than or equal to about 10 µm; and enriching it with Cr and Si.

[0015] According to several aspects, a method for achieving variable properties of a component using a coating-free, hot-formed steel comprises: transferring a blank of coating-free, hot-formed steel (CFPHS) material into a heating unit with multiple induction heating coils; applying a voltage to the induction heating coils using a variable power supply; generating varying and localized currents within the heating unit and across the blank by operating predetermined induction heating coils; heating the blank within the heating unit to produce a modified blank with different modified properties throughout the modified blank compared to the properties of the blank before transferring the blank into the heating unit;and operating a multi-axis transfer device for manipulating the blank within the heating unit when the blank is heated to produce the modified blank.

[0016] According to another aspect of the present disclosure, the method further includes operating a variable frequency device together with the variable power supply.

[0017] According to another aspect of the present disclosure, the method further includes: moving the modified blank from the heating unit into a molding tool using the multi-axis transfer device; and forming a molded part, which includes operating the molding tool to produce a finished CFPHS part.

[0018] According to another aspect of the present disclosure, the method further includes forming a molded part by operating the molding tool, which produces a finished CFPHS part.

[0019] According to another aspect of the present disclosure, the method further includes adapting the mechanical properties of the modified blank by operating the induction heating coils to achieve an austenitizing temperature in at least one zone of the modified blank and heating the modified blank to subcritical temperatures in areas other than the at least one zone in order to achieve adapted mechanical properties within the modified blank.

[0020] According to another aspect of the present disclosure, the method further includes: mitigating a marginal effect of the overheating risk of the modified blank by tuning a current input and a frequency input into the induction heating coils or controlling a distance from one coil of the multiple induction heating coils for heating; and varying an energy into the induction heating coils to vary material properties throughout a modified blank thickness.

[0021] According to another aspect of the present disclosure, the method further includes adjusting an oxide layer of the CFPHS material to provide an optimal thickness in different areas of the modified blank in a range between no oxide layer and a maximum permissible oxide layer.

[0022] According to several aspects, a method for achieving variable properties of a component using a coating-free, hot-formed steel comprises: transferring a blank of coating-free, hot-formed steel (CFPHS) material into a heating unit with multiple induction coils, the blank having one of several shapes, but not limited to, flat profile, bar, wire, coil, and ingot; applying a voltage to the induction coils using a variable power supply; generating varying and localized currents within the heating unit and across the blank by operating predetermined induction coils to create multiple induction coil patterns across the blank in order to achieve targeted zones of surface properties of the blank;and completing the heating of the blank within the heating unit, in order to produce a modified blank with different modified blank properties everywhere in the modified blank, compared to the properties of the blank before the blank was transferred to the heating unit.

[0023] According to another aspect of the present disclosure, the method further includes: operating a multi-axis transfer device for manipulating the blank within the heating unit during the transformation of the blank into a modified blank; moving the modified blank from the heating unit into a molding tool; and forming a shape of the modified blank, defining a finished CFPHS material component, in the molding tool.

[0024] According to another aspect of the present disclosure, the method further includes: heating the blank within the heating unit from room temperature to a range including approximately 500 °C to approximately 950 °C; and applying a heating rate of approximately 20 °C / second to approximately 500 °C / second when the blank is heated.

[0025] Further areas of applicability will become apparent from the description provided herein. It should be understood that the description and specific examples are intended for illustrative purposes only and are not intended to limit the scope of the present disclosure. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] The drawings described here serve only for illustrative purposes and are not intended to limit the scope of protection of the present disclosure in any way; they show: Fig. 1. A flowchart of a process for achieving variable properties of a component using uncoated, hot-formed steel according to an exemplary aspect; and Fig. 2. A schedule using the procedure of Fig. 1. To produce different material properties. DETAILED DESCRIPTION

[0027] The following description is merely exemplary and is not intended to limit the present disclosure, application or uses.

[0028] When a component, element, or layer is described as "attached to," "interacting with," "connected to," or "coupled with" another element or layer, it may be directly attached to, interacting with, connected to, or coupled with that other component, element, or layer, or there may be intervening elements or layers. Conversely, when an element is described as being "directly attached to," "directly interacting with," "directly connected to," or "directly coupled with" another element or layer, there may be no intervening elements or layers. Other words used to describe the relationship between elements, such as "between" versus "directly between," "adjacent" versus "directly adjacent," and the like, are to be interpreted similarly.As the term “and / or” is used here, it includes any combination of one or more of the associated listed items.

[0029] In Fig. 1 describes a method for achieving variable properties of a component using coating-free, cold-formed steel (CFPHS) 10 of the present disclosure for use, e.g., in a vehicle 11, converting a coating-free, cold-formed steel blank (CFPHS blank) 12, which meets the requirements of US Patent No. 11,539,469, issued on December 20, 2022, into a heating unit 14. As used here, vehicle 11 may include, but is not limited to, passenger cars, trucks, vans, all-terrain vehicles, autonomous vehicles, battery electric vehicles, agricultural or construction equipment, rail vehicles, and the like.

[0030] One material of the CFPHS blank 12 provides an alloy matrix containing carbon (C) in a concentration greater than or equal to 0.05% to less than or equal to approximately 0.35 wt.%, chromium (Cr) in a concentration greater than or equal to approximately 1 wt.% to less than or equal to approximately 9 wt.%, silicon (Si) in a concentration greater than or equal to approximately 0.5 wt.% to less than or equal to approximately 2 wt.%, manganese (Mn) in a concentration greater than or equal to approximately 0.5 wt.% to less than or equal to approximately 2.5 wt.%, and a remainder of iron (Fe). The alloy matrix has a volume greater than or equal to approximately 95 vol.-% martensite, a first layer is arranged directly on the alloy matrix, wherein the first layer is continuous and has a thickness greater than or equal to about 0.01 µm to less than or equal to about 10 µm and contains an oxide enriched with Cr and Si, and a second layer is arranged directly on the first layer, wherein the second layer contains an oxide enriched with Fe.

[0031] According to several aspects, heating unit 14 defines an induction heating oven, the characteristics of which are based on Fig. 2 are further defined. In the heating unit 14, the blank 12 is heated to produce a modified blank 16, which, compared to the homogeneous properties of the blank 12, can have different properties throughout the modified blank 16. A multi-axis transfer device 18, such as a robot, is provided to manipulate the blank 12 in the heating unit 14 during the material property change from the blank 12 to the modified blank 16, and subsequently to transfer the modified blank 16 from the heating unit 14 into a forming or stamping machine, which is referred to below as a forming tool 20. The modified blank 16 is positioned, for example, between an upper base plate 22 and a lower base plate 24 of the forming tool 20 for the subsequent forming process.According to several aspects, the transfer device 18 provides the capability to manipulate the blank 12 within the mold 20 and thereby to position the blank 12 at different locations and in different orientations within the mold 20 during the transformation of the blank 12 into the modified blank 16. Through the operation of the mold 20, a molded part 26 is formed and subsequently removed from the mold 20. The molded part 26 may then undergo additional or final operations to produce the finished CFPHS part 28.

[0032] In Fig. 2 and again from Fig. 1. The CFPHS blank 12 of the present disclosure, without a coating layer and with a stable oxide layer, enables induction hardening without the risk of melting a coating material or generating excessive surface oxide, which defines scale. The present disclosure provides a method and a system for adjusting the mechanical and surface qualities of the finished CFPHS part 28, starting from the blank 12, using localized heating. The localized heating methods can utilize either a uniform heating rate, which essentially maintains a constant heating rate over time, or a variable heating rate, which varies the heating rate at predetermined rates over time and heats with a desired temperature profile.The heating can be carried out uniformly over the blank 12 or in predefined areas in the blank 12 to enable a selective mechanical profile and surface property profile that defines the modified blank 16.

[0033] Induction heating is used for the heat treatment of the CFPHS starting material, which defines the blank 12, according to several aspects. The blank 12 is transferred, for example, by a roller set 30 into the heating unit 14. The heating unit 14 can contain at least one and, according to several aspects, several induction heating coils 32. A voltage is applied to the induction heating coils 32 using a variable power supply 34, which may include a variable frequency device 36. Using the variable power supply 34 with the variable frequency device 36, varying and localized current intensities can be generated within the heating unit 14 and across the blank 12 by applying a voltage or varying the power supplied to the multiple induction heating coils 32.Using the variable power supply 34, variable heating rates can be provided, and holding temperatures can also be set for the blank 12 in zones. The edge effect of the overheating risk is mitigated by using the multiple induction heating coils 32, by fine-tuning the current and frequency input, or by controlling the distance from an exemplary coil 38 of the multiple induction heating coils 32 and / or a coil edge 40 to the heating coil. According to several aspects, the blank 12 is induction heated within the heating unit 14 from room temperature to a temperature range including approximately 500 °C to approximately 950 °C. According to several aspects, a heating rate of approximately 20 °C / second to approximately 500 °C / second is used.

[0034] In Fig.Figure 2 further illustrates examples of different properties across different zones or thicknesses of different modified blanks 16. A first modified blank 16' contains modified surface properties, including an upper blank surface 42 with first properties, a first zone 44 defining a section of the upper blank surface 42 with second properties, and a third zone 46 extending along an entire outer edge 48 of the modified blank 16', which may exhibit third properties. A second modified blank 16" identifies that different properties may be developed anywhere within a blank thickness 50.A central or first bridge section 52 may have properties of a first section, a deck or upper thickness section 54 may have properties of a second section, and a lower or bottom thickness section 56 may have properties of a third section.

[0035] Induction heating achieves targeted surface oxide layer properties within the CFPHS material. The mechanical properties can be varied by induction heating across the CFPHS blank thickness 50. Varying mechanical properties are also generated by using induction heating across the CFPHS blank surface. Furthermore, using induction heating to direct it to different locations within the CFPHS blank or component achieves variable surface properties. Induction heating enables the directing of heat to different locations within a CFPHS component to achieve variable mechanical properties. It is noted that the initial material form of the blank 12 is not limited to flat blanks as shown. Within the scope of this disclosure, other product forms may be used, e.g., but not exclusively: rod, wire, coil, ingot, and the like.

[0036] According to several aspects, the method for achieving variable properties of a component using coating-free, form-hardened steel (CFPHS) 10 of the present disclosure creates variable properties within a CFPHS blank and in a finished component using localized variable heating methods such as induction heating. The method for achieving variable properties of a component using coating-free, form-hardened steel (CFPHS) 10 of the present disclosure allows the adjustment of a CFPHS oxide layer for optimal thickness, from no oxide layer to a maximum permissible oxide layer, in different areas of a component. The use of induction heating on CFPHS to achieve desired form-hardened properties is made possible using the CFPHS material of the present disclosure.The method for achieving variable properties of a component using uncoated cold form-hardened steel (CFPHS) 10 of the present disclosure eliminates the need for conventional furnace heating due to the use of induction heating to achieve the desired heat treatment of CFPHS. It is noted that the desired cold form-hardened properties of the present disclosure cannot be achieved using either conventional coated cold form-hardened steel of any basic grade according to the American Iron and Steel Institute (AISI) or bare (uncoated) cold form-hardened steel without adverse effects on the surface quality of the component or other necessary subsequent or preceding operations, such as descaling for bare material and pre-diffusion for coated material according to AISI.

[0037] The method for achieving variable properties of a component using uncoated cold-formed steel (CFPHS) 10 of the present disclosure makes it possible to achieve mechanical properties adapted to the austenitizing temperatures in one or more areas of the component by means of induction heating, and wherein the component is heated to subcritical temperatures in other areas to achieve adapted mechanical properties within the component. This cannot be achieved using only a conventional furnace. As used here, austenitizing defines a heat treatment process for steel and other ferrous alloys in which a material is heated above its critical temperature and is transformed from ferrite to an austenite crystal structure, which allows the austenite to absorb carbon from the iron carbides in a carbon steel.If a quenching process follows, the austenitized material is hardened.

[0038] Using induction heating, multiple zones with varying mechanical properties can be achieved within the component using induction coils. Current specialized furnaces without induction coils typically produce this effect, but with limitations on the number of possible zones. This effect cannot be achieved using only a conventional furnace.

[0039] Using induction heating, targeted zones with desired surface properties can be achieved by varying the induction heating pattern. Varying the induction heating pattern is not possible using a conventional furnace. A CFPHS without a coating and with a stable oxide layer enables induction hardening without the risk of melting or excessive surface oxide (scale).

[0040] A method for achieving variable properties of a component using coating-free, cold-formed steel (CFPHS) 10 of the present disclosure offers several advantages. These include the use of induction heating for the heat treatment of CFPHS components, reducing capital costs due to the more compact nature of the induction hardening equipment and the reduced complexity of the induction tooling compared to furnace heating. Maintenance of the induction equipment can be less expensive and complicated than that of furnace equipment, resulting in cost savings for the component manufacturer. Varying mechanical properties within a CFPHS blank and a finished component reduces the complexity of an arrangement with multiple components of different material grades.The use of induction heating on a CFPHS component can reduce product costs, increase component performance, and decrease complexity. Furthermore, varying the oxide layer in selected areas of the CFPHS component enables improved joining in specific regions, resulting in a stronger and better integrated assembly. QUOTES INCLUDED IN THE DESCRIPTION

[0000] This list of documents cited by the applicant was automatically generated and is included solely for the reader's convenience. The list is not part of the German patent or utility model application. The DPMA accepts no liability for any errors or omissions. Cited patent literature

[0000] US 11,539,469

[0029]

Claims

[1] A method for achieving variable properties of a vehicle component using a coating-free hot-form hardened steel (CFPHS), comprising: Transferring a blank made of a CFPHS material with basic blank properties into a heating unit with several induction heating coils; Heating the blank in the heating unit to produce a modified blank having different modified blank properties throughout the modified blank compared to the basic blank properties; Moving the modified blank from the heating unit into a forming tool; and Forming a molded part by operating the mold tool, producing a finished CFPHS part. [2] The method of claim 1, further including adjusting mechanical and surface qualities of the finished CFPHS part using localized heating. [3] The method of claim 2, further comprising performing the localized heating using a uniform heating rate or an adjusted or variable heating rate to achieve a desired temperature profile. [4] The method of claim 2, further including heating uniformly across the blank or in predetermined areas within the blank to enable a selective mechanical profile and surface property profile defining the altered blank. [5] The method of claim 1, further including applying a voltage to the induction heating coils using a variable power supply having a variable frequency device. [6] The method of claim 5, further including generating varying and localized current intensities in the heating unit and across the blank. [7] The method of claim 6, further comprising: Generating variable heating rates using the variable power supply; and Providing zoned holding temperatures for the blank. [8] The method of claim 7, further including operating a multi-axis transfer device for manipulating the blank in the heating unit to produce the modified blank. [9] The method of claim 1, further comprising producing the CFPHS material by: Incorporating carbon (C) into an alloy matrix having a C concentration greater than or equal to about 0.05 wt% to less than or equal to about 0.35 wt%; Incorporating chromium (Cr) having a Cr concentration greater than or equal to about 1 wt% to less than or equal to about 9 wt%; Providing silicon (Si) having a Si concentration greater than or equal to about 0.5 wt% to less than or equal to about 2 wt%; Incorporating manganese (Mn) having a Mn concentration greater than or equal to about 0.5 wt% to less than or equal to about 2.5 wt%; and Providing a residue of iron (Fe). [10] The method of claim 9, further comprising producing the CFPHS material by: Incorporation of martensite greater than or equal to about 95 vol% in the alloy matrix; Creating a surface oxide layer on the alloy matrix, wherein the surface oxide layer is continuous and has a thickness greater than or equal to about 0.01 µm to less than or equal to about 10 µm; and Enrichment with Cr and Si.

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