Method for achieving variable characteristics within component using plating-free press-hardened steel

Abstract

A method of achieving variable characteristics of a component using plating-free press hardened steel, the method comprising: transferring a blank of plating-free press hardened steel (CFPHS) material having base characteristics into a heating unit having a plurality of induction heating coils; heating the blank within the heating unit to produce a modified blank, the modified blank having a modified blank characteristic that is different than the base characteristic throughout the modified blank; moving the modified blank from the heating unit into a mold; and a molded part is formed by operating the mold, so that a finished CFPHS part is manufactured.

Description

Technical Field

[0001] The disclosure relates to press-hardened steels for vehicle structural and body components. Background Art

[0002] Press-hardened steels are used in vehicle designs, including but not limited to automobiles, trucks, vans, sport utility vehicles, autonomous vehicles, fully electric vehicles, farm or construction equipment, railroad cars, and the like, to provide regional or localized increased material strength in load-bearing components, particularly to mitigate material collapse in body impact areas such as door panels and body pillars. Steel induction hardening work, which has not previously been performed on 22MnB5 American Iron and Steel Institute (AISI) material, is typically performed on higher carbon steels. Current press-hardened steels (PHS) are formed entirely in a furnace. Prior to heating, a coating such as zinc is applied to the steel for cathodic protection and thus improved corrosion resistance. In the furnace, the heating rate and final heating temperature must be carefully controlled to avoid melting the coating or producing excessive surface oxides, which define an oxide scale that can form on the outer surface of the PHS, which must then be removed using processes such as shot peening.

[0003] The material properties of currently manufactured PHS are uniform throughout the blank and throughout the finished shape of the article. The increase in uniform material properties to maximize material strength, such as in vehicle crush areas and pillars, increases the overall weight and cost of the part and may not allow the part to deform as desired under impact loads, thereby failing to achieve localized absorption and distribution of impact loads.

[0004] Therefore, while current systems and methods for producing and using press-hardened steel achieve their intended purposes, a new and improved system and method for producing and using press-hardened steel is needed. Summary of the invention

[0005] According to several aspects, a method for achieving variable properties of a vehicle component using a coating-free press hardened steel (CFPHS) includes: transferring a blank of CFPHS material having base blank properties to a heating unit having a plurality of induction heating coils; heating the blank within the heating unit to produce a modified blank having different modified blank properties throughout the modified blank compared to the base blank properties; moving the modified blank from the heating unit to a die; and forming a formed part through die operation to produce a finished CFPHS part.

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

[0007] In another aspect of the present disclosure, the method further includes performing local heating using one of a uniform heating rate and an adjusted heating rate or a variable heating rate to achieve a desired temperature distribution.

[0008] In another aspect of the present disclosure, the method further includes uniformly heating the entire billet or a predetermined area within the billet to achieve a selective mechanical property profile and a surface property profile that defines a modified billet.

[0009] In another aspect of the present disclosure, the method further includes energizing the induction heating coil using a variable power supply having a variable frequency device.

[0010] In another aspect of the present disclosure, the method further includes generating varying local current intensities within the heating unit and on the blank.

[0011] In another aspect of the present disclosure, the method further includes: generating a variable heating rate using a variable power supply; and providing a zoned holding temperature for the blank.

[0012] In another aspect of the present disclosure, the method further includes operating a multi-axis conveyor to manipulate the billet within the heating unit to produce the modified billet.

[0013] In another aspect of the present disclosure, the method also includes manufacturing the CFPHS material by: incorporating carbon (C) into the alloy matrix, the C concentration being greater than or equal to about 0.05 wt.% to less than or equal to about 0.35 wt.%; including chromium (Cr) having a Cr concentration of greater than or equal to about 1 wt.% to less than or equal to about 9 wt.%; including silicon (Si) having a Si concentration of greater than or equal to about 0.5 wt.% to less than or equal to about 2 wt.%; including manganese (Mn) having a Mn concentration of greater than or equal to about 0.5 wt.% to less than or equal to about 2.5 wt.%; and providing a balance of iron (Fe).

[0014] In another aspect of the present disclosure, the method also includes manufacturing a CFPHS material by: including an alloy matrix having greater than or equal to about 95 vol.% martensite; directly providing a first layer on the alloy matrix, the first layer being continuous and having a thickness greater than or equal to about 0.01 μm to less than or equal to about 10 μm; and enriching Cr and Si.

[0015] According to several aspects, a method for achieving variable properties of a component using a non-coated press hardened steel includes: transferring a blank of non-coated press hardened steel (CFPHS) material to a heating unit having multiple induction heating coils; powering the induction heating coils using a variable power supply; generating varying local current intensities within the heating unit and on the blank by operating one of the predetermined induction heating coils; heating the blank within the heating unit to produce a modified blank having different modified blank properties throughout the modified blank compared to the blank properties before the blank was transferred to the heating unit; and operating a multi-axis conveyor to manipulate the blank within the heating unit while heating the blank to produce the modified blank.

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

[0017] In another aspect of the present disclosure, the method further includes: moving the modified blank from the heating unit into a mold using a multi-axis conveyor; and forming the molded part, including operating the mold to produce a finished CFPHS part.

[0018] In another aspect of the present disclosure, the method further includes forming a molded part by operating the mold to produce a finished CFPHS part.

[0019] In another aspect of the present disclosure, the method further includes adjusting the mechanical properties of the modified billet by operation of the induction heating coil to achieve an austenitizing temperature in at least one region of the modified billet, and heating the modified billet to a subcritical temperature in a region outside the at least one region to achieve the adjusted mechanical properties within the modified billet.

[0020] In another aspect of the present disclosure, the method also includes: mitigating the edge effect of the risk of overheating of the modified blank by adjusting the current input and frequency input of the induction heating coil or controlling the distance from one of the multiple induction heating coils used for heating; and changing the energy entering the induction heating coil to change the material properties throughout the thickness of the modified blank.

[0021] In another aspect of the present disclosure, the method further includes adjusting the oxide layer of the CFPHS material to provide an optimal thickness ranging from no oxide layer to a maximum allowable oxide layer in different regions of the modified blank.

[0022] According to several aspects, a method for achieving variable properties of a component using a non-coated press hardened steel includes: transferring a blank of a non-coated press hardened steel (CFPHS) material into a heating unit having a plurality of induction heating coils, the blank having one of a plurality of shapes, including but not limited to flat stock, rod stock, wire stock, coil stock, and bar stock; powering the induction heating coils using a variable power supply; generating varying local current intensities within the heating unit and on the blank by operating predetermined induction heating coils to form a plurality of induction heating patterns on the blank to achieve a target area having blank surface properties; and completing heating of the blank within the heating unit to produce a modified blank having different modified blank properties throughout the modified blank compared to the properties of the blank before the blank was transferred to the heating unit.

[0023] In another aspect of the present disclosure, the method further includes: during the process of modifying the blank into a modified blank, operating a multi-axis conveyor to manipulate the blank within a heating unit, moving the modified blank from the heating unit to a mold; and forming a shape of the modified blank defining a finished CFPHS material part in the mold.

[0024] In another aspect of the present disclosure, the method further comprises: heating the blank from room temperature to a range including about 500°C to about 950°C in a heating unit; when heating the blank, a heating rate of about 20°C / sec to about 500°C / sec is employed.

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

[0026] The drawings described in the present disclosure are for illustration purposes only and are not intended to limit the scope of the present disclosure in any way.

[0027] Figure 1 is a flow chart of a method of achieving variable properties of a component using uncoated press-hardened steel according to an exemplary aspect; and

[0028] Figure 2 is used Figure 1 A method to generate flow charts of different material properties. DETAILED DESCRIPTION

[0029] The following description is merely exemplary in nature and is not intended to limit the present disclosure, application, or uses.

[0030] When a component, element or layer is referred to as being "on," "engaged to," "connected to," or "coupled to" another component or layer, it may be directly on or engaged, connected or coupled to the other component, element or layer, or there may be intervening elements or layers. In contrast, when an element is referred to as being "directly on," "directly engaged to," "directly connected to," or "directly coupled to" another element or layer, there may be no intervening elements or layers. Other words used to describe the relationship between elements should be interpreted in a similar manner (e.g., "between" versus "directly between," "adjacent" versus "directly adjacent," etc.). The term "and / or" used in this disclosure includes any and all combinations of one or more of the associated enumerated items.

[0031] Reference Figure 1 , a method of achieving variable properties of a component using the CFPHS 10 of the present disclosure, for example, for a vehicle 11, transferring a CFPHS 10 blank 12 that meets the requirements of U.S. Patent 11,539,469 issued on December 20, 2022 to a heating unit 14. As used in the present disclosure, the vehicle 11 may include, but is not limited to, an automobile, a truck, a van, a sport utility vehicle, an autonomous vehicle, a fully electric vehicle, farm or construction equipment, a rail vehicle, and the like.

[0032] The material of the CFPHS billet 12 provides an alloy matrix including carbon (C) at a concentration of greater than or equal to 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 1 wt.% to less than or equal to about 9 wt.%, silicon (Si) at a concentration of greater than or equal to about 0.5 wt.% to less than or equal to about 2 wt.%, manganese (Mn) at a concentration of greater than or equal to about 0.5 wt.% to less than or equal to about 2.5 wt.%, and a balance of iron (Fe). The alloy matrix is ​​greater than or equal to about 95 vol.% martensite, a first layer is directly disposed on the alloy matrix, the first layer is continuous, has a thickness of greater than or equal to about 0.01 μm to less than or equal to about 10 μm, and includes oxides rich in Cr and Si, and a second layer is directly disposed on the first layer, the second layer includes an oxide rich in Fe.

[0033] According to several aspects, the heating unit 14 defines an induction heating furnace, the characteristics of which refer to Figure 2The invention further defines a method for manufacturing a modified blank 16. Within the heating unit 14, the heated blank 12 is heated to produce a modified blank 16, which may include different properties throughout the modified blank 16 compared to the uniform properties of the blank 12. A multi-axis conveyor 18, such as a robot, is provided to manipulate the blank 12 within the heating unit 14 during the process of modifying the material properties of the blank 12 into the modified blank 16, and then transfer the modified blank 16 from the heating unit 14 to a forming machine or stamping machine, hereinafter referred to as a die 20. The modified blank 16 is located between, for example, an upper die seat 22 and a lower die seat 24 of the die 20 for subsequent forming of the modified blank 16. According to several aspects, the conveyor 18 provides the ability to manipulate the blank 12 within the die 20, thereby positioning the blank 12 at different locations and different orientations within the die 20 during the process of modifying the blank 12 into the modified blank 16. A molded part 26 is formed by the operation of the die 20 and then removed from the die 20. Additional or final operations may then be performed on the molded part 26 to produce a finished CFPHS part 28 .

[0034] Reference Figure 2 And refer again Figure 1 The blank 12 formed by the CFPHS of the present disclosure is capable of induction hardening without a coating but with a stable oxide layer without the risk of melting the coating material or producing excessive surface oxide (defined as scale). The present disclosure provides a method and system for adjusting the mechanical quality and surface quality of a finished CFPHS part 28 starting from the blank 12 using local heating. The local heating method can use a uniform heating rate that maintains a substantially constant heating rate over time, or an adjusted heating rate that changes the heating rate at a predetermined heating rate over time, to heat to a desired temperature distribution. The heating can be performed uniformly throughout the blank 12 or in predetermined areas within the blank 12 to achieve a selective mechanical property distribution and surface property distribution that defines the modified blank 16.

[0035] According to several aspects, induction heating is used to define the heat treatment of the CFPHS substrate of the blank 12. The blank 12 is transferred to the heating unit 14 (such as by the roller set 30). The heating unit 14 may include at least one (according to several aspects, a plurality of) induction heating coils 32. The induction heating coils 32 are energized using a variable power supply 34 that may have a frequency conversion device 36. Using the variable power supply 34 with the frequency conversion device 36, by energizing predetermined coils of the plurality of induction heating coils 32 or changing the power supplied to predetermined coils of the plurality of induction heating coils 32, a variable local current intensity can be generated within the heating unit 14 and on the blank 12. Using the variable power supply 34 can provide a variable heating rate and can also provide a zoned holding temperature for the blank 12. By using a plurality of induction heating coils 32, the edge effect of the risk of overheating is mitigated by fine-tuning the current and frequency input, or controlling the distance of the exemplary coils 38 and / or coil edges 40 of the plurality of induction heating coils 32 for heating. According to several aspects, the blank 12 is inductively heated within the heating unit 14 from room temperature to a range including about 500° C. to about 950° C. According to several aspects, a heating rate of about 20° C. / second up to about 500° C. / second is used.

[0036] Continue to refer to Figure 2 , examples of different properties for different regions or thicknesses of different modified blanks 16 are shown. A first modified blank 16' includes a modified surface property including a blank upper surface 42 having a first property, a first region 44 defining a portion of the blank upper surface 42 within the upper surface 42 having a second property, and a third region 46 extending along the entire outer edge 48 of the modified blank 16' may have a third property. A second modified blank 16" illustrates that different properties may be formed throughout the blank thickness 50. A center or first thickness portion 52 may have a first portion property, a top or upper thickness portion 54 may have a second portion property, and a lower or bottom thickness portion 56 may have a third portion property.

[0037] Induction heating can achieve targeted surface oxide layer characteristics within the CFPHS material. Through induction heating, mechanical properties can be changed throughout the CFPHS billet thickness 50. Different mechanical properties can also be produced using induction heating of the CFPHS billet surface. Variable surface features are further achieved by using induction heating to target different locations within a CFPHS billet or component. Induction heating allows variable mechanical properties to be achieved for different locations within a CFPHS component. It should be noted that the initial material form of the billet 12 is not limited to the flat billet shown. Other product shapes can be used, such as but not limited to: rods, wires, coils, bars, etc. within the scope of the present disclosure.

[0038] According to various aspects, a method of achieving variable properties of a component using the uncoated press-hardened steel (CFPHS) 10 of the present disclosure provides variable properties within the CFPHS blank and within the finished component using a local variable heating method such as induction heating. The method of achieving variable properties of a component using the uncoated press-hardened steel (CFPHS) 10 of the present disclosure allows the CFPHS oxide layer to be adjusted in different areas of the component to obtain an optimal thickness from no oxide layer to a maximum allowable oxide layer. The use of the CFPHS material of the present disclosure enables the use of induction heating on the CFPHS to achieve the desired press-hardening properties. The method of achieving variable properties of a component using the uncoated press-hardened steel (CFPHS) 10 of the present disclosure makes conventional furnace heating unnecessary due to the use of induction heating to achieve the desired heat treatment of the CFPHS. It is noteworthy that the desired press-hardening properties of the present disclosure cannot be achieved using any base grade of conventional AISI plated press-hardened steel or using bare (uncoated) press-hardened steel without adversely affecting the surface quality of the component or other necessary subsequent or prior operations, such as shot peening of bare material and pre-diffusion of AlSI plated material.

[0039] The method of achieving variable properties of a component using the CFPHS10 of the present disclosure allows for the achievement of adjusted mechanical properties by induction heating, for example, reaching an austenitizing temperature in one or more regions of a component, and wherein the component is heated to a subcritical temperature in other regions to achieve the adjusted mechanical properties within the component. This is not achievable using only a conventional furnace. As used in the present disclosure, austenitizing defines a heat treatment process for steel and other ferrous alloys in which the material is heated above its critical temperature and transformed from ferrite to an austenite crystal structure, enabling the austenite to absorb carbon from the iron carbide in the carbon steel. When a quenching process is subsequently performed, the austenitized material becomes hardened.

[0040] With induction heating, multiple zones with different mechanical properties can be achieved in a component using an induction coil. Current dedicated non-induction coil furnaces often produce this effect with a limited number of zones possible. This effect cannot be achieved using conventional furnaces alone.

[0041] Using induction heating, it is possible to achieve targeted areas with desired surface properties by changing the induction heating pattern. Changing the induction heating pattern is not possible using only a conventional furnace. Uncoated CFPHS with a stable oxide layer enables induction hardening without the risk of melting or excessive surface oxide (scale).

[0042] The method of achieving variable properties of a component using the CFPHS10 of the present disclosure provides a number of advantages. Among them are the use of induction heating to heat treat CFPHS components to reduce capital investment costs because induction hardening equipment is more compact and the complexity of induction tools is reduced relative to furnace heating. Maintenance of induction equipment may be cheaper and simpler than furnace equipment, thereby reducing costs for component manufacturers. Different mechanical properties within CFPHS billets and finished components reduce the complexity of assembling multiple components with different material grades. Using induction heating on CFPHS components can reduce product costs and can improve component performance and reduce complexity. Changing the oxide layer of selected areas of the CFPHS component can also improve the connection of predetermined areas, making the assembly more robust and better integrated.

Claims

1. A method for achieving variable characteristics of vehicle components using uncoated press hardened steel (CFPHS), comprising: transferring a blank of CFPHS material having the characteristics of a base blank to a heating unit having a plurality of 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 base blank properties; moving the modified blank from the heating unit into a mold; as well as The molded part is formed by the operation of the mold, thereby manufacturing a finished CFPHS part.

2. The method of claim 1 further comprising using localized heating to adjust the mechanical and surface qualities of the finished CFPHS part.

3. The method of claim 2, further comprising performing the local heating using one of a uniform heating rate and an adjusted heating rate or a variable heating rate to achieve a desired temperature distribution.

4. The method of claim 2, further comprising uniformly heating the blank or in predetermined areas within the blank to achieve a selective mechanical and surface property profile that defines the modified blank.

5. The method of claim 1, further comprising energizing the induction heating coil using a variable power supply having a variable frequency device.

6. The method of claim 5, further comprising generating a variable local current intensity in the heating unit and on the blank.

7. The method according to claim 6, further comprising: producing a variable heating rate using the variable power supply; as well as A zoned holding temperature is provided for the billet.

8. The method of claim 7, further comprising operating a multi-axis conveyor to manipulate the blank within the heating unit to produce the modified blank.

9. The method according to claim 1, further comprising manufacturing the CFPHS material by: Incorporating carbon (C) into the alloy matrix, wherein the C concentration is greater than or equal to about 0.05 wt. % and less than or equal to about 0.35 wt. %; chromium (Cr) including a Cr concentration of greater than or equal to about 1 wt. % to less than or equal to about 9 wt. %; providing silicon (Si) having a Si concentration of greater than or equal to about 0.5 wt. % to less than or equal to about 2 wt. %; Manganese (Mn) including a Mn concentration of greater than or equal to about 0.5 wt. % to less than or equal to about 2.5 wt. %; and The balance of iron (Fe) is provided.

10. The method according to claim 9, further comprising manufacturing the CFPHS material by: including an alloy matrix having greater than or equal to about 95 vol.% martensite; providing a surface oxide layer on the alloy substrate, the surface oxide layer being continuous and having a thickness of greater than or equal to about 0.01 μm to less than or equal to about 10 μm; and Enriched in Cr and Si.

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