Patent Application
20250197958
The present disclosure relates to tubular coating free press-hardened steel used in vehicle structural and body members.
Press hardened steel is used in vehicles including automobiles, trucks, vans, sport utility vehicles, autonomous vehicles, battery electric vehicles, farm or construction equipment, railway vehicles, and the like to provide regional or local increased material strength in load-bearing components and to mitigate against material collapse in impact zones of vehicle bodies, for example door beams and body pillars. Current press hardened steel (PHS) is entirely formed in a furnace. A coating layer, such as aluminum-silicon, is applied to the steel prior to heating for barrier protection from corrosion and to prevent surface scale development and decarburization during the hot forming process. In the furnace, a heating rate and final heating temperature must be carefully controlled to avoid melting the coating, and to control the interdiffusion layer thickness between substrate and coating, and to achieve the desired strength after hot forming. For uncoated press hardened steel (PHS), the scale developed during heating must be subsequently removed using a process such as shot-blasting after hot forming
Material properties of presently prepared PHS are uniform throughout a blank and throughout a finished form of the item. Uniform material properties are increased to maximize material strength, for example in vehicle crush zones and pillars.
Thus, while current systems and methods to produce and utilize press hardened steel achieve their intended purpose, there is a need for a new and improved system and method to produce and use press hardened steel.
According to several aspects of the present disclosure, a method for producing a tubular component using a coating free press hardened steel (CFPHS) is provided. The method includes feeding a CFPHS continuous tubular component into a heating unit and heating the CFPHS continuous tubular component with the heating unit. The method then includes bending the CFPHS continuous tubular component using a bending unit before the continuous tubular component is cooled. After the bending step, the method includes cooling the CFPHS continuous tubular component using a cooling unit with ambient air.
In accordance with another aspect of the disclosure, the method includes a heating unit including at least one of an induction heating coil, a laser-based heater, or a flame-based heater.
In accordance with another aspect of the disclosure, the method includes a heating unit including multiple induction heating coils arranged in series along the CFPHS continuous tubular component.
In accordance with another aspect of the disclosure, the method includes a heating unit including multiple induction heating coils arranged in parallel along the CFPHS continuous tubular component.
In accordance with another aspect of the disclosure, the method includes a CFPHS continuous tubular component including at least one of concentric CFPHS tubing or square CFPHS tubing.
In accordance with another aspect of the disclosure, the method includes heating the CFPHS continuous tubular component including heating a portion of the CFPHS continuous tubular component with at least one induction heating coil to a uniform temperature.
In accordance with another aspect of the disclosure, the method includes heating the CFPHS continuous tubular component including heating the CFPHS continuous tubular component to varying temperatures along a length of the CFPHS continuous tubular component to produce variable mechanical properties.
In accordance with another aspect of the disclosure, the method includes heating the CFPHS continuous tubular component including heating the CFPHS continuous tubular component to varying temperatures along a circumference of the CFPHS continuous tubular component to produce variable mechanical properties.
In accordance with another aspect of the disclosure, the method includes heating the CFPHS continuous tubular component including employing a variable heating rate to achieve a specific temperature profile.
In accordance with another aspect of the disclosure, the method further includes soaking the CFPHS continuous tubular component for less than 30 seconds subsequent to heating the CFPHS continuous tubular component and before cooling the CFPHS continuous tubular component.
In accordance with another aspect of the disclosure, the method further includes soaking the CFPHS continuous tubular component at a temperature between 875° C. and 1200° C. to produce a fully austenitized microstructure, subsequent to heating the CFPHS continuous tubular component and before cooling the CFPHS continuous tubular component.
In accordance with another aspect of the disclosure, the method further includes soaking the CFPHS continuous tubular component at a temperature between 750° C. and 875° C., to achieve partial austenitization, subsequent to heating the CFPHS continuous tubular component and before cooling the CFPHS continuous tubular component.
In accordance with another aspect of the disclosure, the method includes bending the CFPHS continuous tubular component including at least one of roll bending or mandrel bending.
In accordance with another aspect of the disclosure, the method includes cooling the CFPHS continuous tubular component including using forced air cooling.
In accordance with another aspect of the disclosure, the method includes cooling the continuous tubular component including using tunnel furnace cooling to retard a cooling rate.
In accordance with another aspect of the disclosure, the method includes using a quenching media including cooled air.
In accordance with another aspect of the disclosure, the method includes a CFPHS continuous tubular component having a tube elongation of greater than 4% after cooling the CFPHS continuous tubular component.
According to several aspects of the present disclosure, a method to achieve variable properties of a tubular component using a coating free press hardened steel (CFPHS) is provided. The method includes feeding a CFPHS continuous tubular component into a heating unit having induction heating coils and energizing the induction heating coils using a variable power supply. The method then includes heating the CFPHS continuous tubular component by generating varying and localized current intensities within the heating unit and across the CFPHS continuous tubular component by operating predetermined ones of the induction heating coils. The method then proceeds to bending the CFPHS continuous tubular component using a bending unit and cooling the CFPHS continuous tubular component using ambient air.
In accordance with another aspect of the disclosure, the method further includes soaking the CFPHS continuous tubular component for less than 30 seconds subsequent to heating the CFPHS continuous tubular component and before cooling the CFPHS continuous tubular component.
According to several aspects of the present disclosure, a method for producing induction-hardened tubular components using a coating free press hardened steel (CFPHS) is provided. The method includes feeding a CFPHS continuous tubular component into a heating unit having at least one induction heating coil. The CFPHS continuous tubular component is then heated using the heating unit having at least one induction heating coil. The at least one induction heating coil provides varying temperatures along a length of the CFPHS continuous tubular component to produce tailored properties. The method then includes soaking the CFPHS continuous tubular component between 875° C. and 1200° C. for less than 30 seconds to achieve a fully austenitized microstructure. After the soaking step, the method then includes bending the CFPHS continuous tubular component using a bending unit before the CFPHS continuous tubular component is cooled. The bending unit includes roll bending. Subsequent the bending step, the method includes cooling the CFPHS continuous tubular component using ambient air to transform the fully austenitized microstructure to martensite.
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 purposes of illustration only and are not intended to limit the scope of the present disclosure.
The drawings described herein are for illustration purposes only and are not intended to limit the scope of the present disclosure in any way.
The following description is merely exemplary in nature and is not intended to limit the present disclosure, application, or uses.
When a component, element or layer is referred to as being “on”, “engaged to”, “connected to”, or “coupled to” another element or layer, it may be directly on, engaged, connected or coupled to the other component, element, or layer, or intervening elements or layers may be present. 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 in intervening elements or layers present. Other words used to describe the relationship between elements should be interpreted in a like fashion, such as “between” versus “directly between”, “adjacent” versus “directly adjacent”, and the like. As used herein, the term “and/or” includes any and all combinations of one or more of the associated listed items.
Referring to
CFPHS is uncoated steel with a low carbon (C) content and additions of chromium and silicon, which form a dense oxide layer on a surface of the CFPHS after hot forming. CFPHS is an alternative to conventional aluminum silicon (Al—Si) coated press hardened steel, in which aluminum silicon (Al—Si) coating is applied to sheet steel before hot forming. Additionally, CFPHS is an uncoated PHS, in which an oxidation resistant layer would be developed during heating to protect the surface, thus eliminating a need for Al—Si coating or shot blasting, in the case of traditional uncoated (bare) PHS, post processing to maintain surface quality.
A material composition of the CFPHS continuous tubular component 12 includes an alloy matrix including carbon (C) at a concentration of greater than or equal to 0.05% to less than or equal to about 0.35 percent weight (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 Mn 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). In this context, the term “about” is known to those skilled in the art. Alternatively, the term “about” may be read to mean plus or minus 0.5% by weight.
With reference to
In the heating unit 14, the CFPHS continuous tubular component 12 is heated to transform the crystal structure of the steel from ferrite to austenite. Austenite is a more open and flexible structure that can absorb more carbon from iron-carbides in carbon steel. Transforming the ferrite to austenite, or austenitization, enables subsequent transformation to martensite upon cooling, which modifies the mechanical properties of the CFPHS continuous tubular component 12 so that it is suitable for use in, for example, vehicular structural components.
The induction heating coils 20 are energized using a variable power supply 22, which may include a variable frequency device 24. Varying and localized current intensities are generated by the variable power supply 22 and the variable frequency device 24 across the CFPHS continuous tubular component 12 by energizing or varying a power supplied to predetermined ones of the multiple induction heating coils 20. Using the variable power supply 22, variable heating rates and zoned hold temperatures may be provided to the CFPHS continuous tubular component 12. For example, a variable heating rate can include heating the CFPHS continuous tubular component 12 at a rate of 500° C./second for a first amount of time and then heating at a rate of 100° C./second for a second amount of time. It should be appreciated that other variable heating rates can be used.
In some aspects, the heating unit 14 can include other heating devices, for example a laser-based heating device or a flame-based heating device. When a laser-based heating device is used, the device directs a laser onto the CFPHS continuous tubular component 12 for heating. When a flame-based heating device is used, a flame directed toward the CFPHS continuous tubular component 12 is used for heating.
Induction heating achieves targeted surface oxide layer properties within the CFPHS continuous tubular component 12. Mechanical properties may be varied via induction heating through the CFPHS continuous tubular component 12 thickness. Varying mechanical properties are also produced using induction heating across the CFPHS continuous tubular component 12 surface. Using induction heating to target different locations within the CFPHS continuous tubular component 12 further achieves variable surface characteristics. Induction heating permits targeting different locations within a CFPHS continuous tubular component 12 to achieve variable mechanical properties.
The heating unit 14 may include multiple stages of heating. For example, a first induction heating coil can heat the CFPHS continuous tubular component 12, which may be subsequently cooled and then reheated or heated at a different rate by a second induction heating coil. The heating unit 14 may include multiple induction heating coils 20 in series and/or in parallel.
Within the heating unit 14, the CFPHS continuous tubular component 12 is heated and, when using multiple stages of heating, may include differing properties throughout after heating and hardening compared to the homogeneous properties of the pre-heat treated CFPHS continuous tubular component 12. For example, induction heating can provide differing properties across different zones, lengths, or thicknesses of the CFPHS continuous tubular component 12. In a specific example, after heating, a first side of the CFPHS continuous tubular component 12 includes a first set of modified surface properties and a second side of the CFPHS continuous tubular component 12 includes a second set of modified surface properties. In another specific example, a radially inner portion of the CFPHS continuous tubular component 12 has a first set of modified properties, and a radially outer portion of the CFPHS continuous tubular component 12 has a second set of modified properties.
After a heating and/or a soaking step with the heating unit 14, the CFPHS continuous tubular component 12 is fed to the bending unit 16 while pliable. The bending unit 16 includes multiple rollers 26, for example, that the CFPHS continuous tubular component 12 is fed and directed through to achieve a desired bend or shape. In the example shown in
The cooling unit 18 receives and cools the CFPHS continuous tubular component 12 directly after bending with bending unit 16 using a quenching media for cooling. Preferably, ambient air is used for cooling the CFPHS continuous tubular component 12. For example, the cooling unit 18 may include an air blast cooling unit that uses forced air, and so forth.
The CFPHS continuous tubular component 12 of the present disclosure, having minimal or no oxidation and without a coating layer, enables induction hardening without the risk of melting a coating material or without generation of excess surface oxide, defining scale. The present disclosure provides a method and system to tailor mechanical and surface qualities of the finished CFPHS continuous tubular component 12 using localized heating. Localized heating methods may employ either a uniform heating rate maintaining a substantially constant heating rate over time, or a tailored heating rate varying the heating rate at predetermined rates of heating over time, heating to a desired temperature profile. An example temperature profile can include keeping the CFPHS continuous tubular component 12 at a temperature of 1000° C. for 20 seconds. Heating may be performed uniformly across the CFPHS continuous tubular component 12 or in predetermined areas within the CFPHS continuous tubular component 12 to enable a selective mechanical and surface property profile defining the heated and induction-hardened CFPHS continuous tubular component 12.
At block 104, method 100 includes energizing induction heating coils in the heating unit 14 using a variable power supply 22. The variable power supply 22 can be initialized by a controller (not shown) or other automated device for determining supply of electricity to the variable power supply 22. The method then proceeds to block 106.
At block 106, method 100 includes heating the CFPHS continuous tubular component 12 with the heating unit 14. Heating the CFPHS continuous tubular component 12 can include using at least one induction heating coil to provide uniform and/or varying temperatures along a length of the CFPHS continuous tubular component 12 to produce tailored properties. Additionally, heating the CFPHS continuous tubular component can include using at least one of an induction heating coil, a laser-based heater, or a flame-based heater. Further, heating the CFPHS continuous tubular component can include using multiple induction heating coils arranged in series along and/or in parallel along the CFPHS continuous tubular component. In one example, heating the CFPHS continuous tubular component includes heating the CFPHS continuous tubular component to varying temperatures along a circumference of the CFPHS continuous tubular component to produce variable mechanical properties. The method 100 then may proceed to block 108.
At block 108, method 100 includes soaking the CFPHS continuous tubular component 12. Soaking the CFPHS continuous tubular component 12 includes maintaining temperature of the heated CFPHS continuous tubular component 12 for a duration of time to achieve a desired property. In a specific example, the CFPHS continuous tubular component 12 can be soaked for less than 30 seconds at a temperature between 875° C. and 1200° C. to achieve a fully austenitized microstructure, which transforms to martensite upon cooling. In another specific example, soaking the CFPHS continuous tubular component 12 includes soaking the CFPHS continuous tubular component at a temperature between 750° C. and 875° C. to achieve partial austenitization. The method 100 then proceeds to block 110.
At block 110, method 100 includes bending the CFPHS continuous tubular component 12 using the bending unit 16. Bending the CFPHS continuous tubular component 12 can include using at least one of roll bending (e.g., three roll push bending) and/or mandrel bending, for example. Roll bending, as shown in
At block 112, method 100 includes cooling the CFPHS continuous tubular component 12 using a cooling unit 18. The cooling unit 18 can cool the CFPHS continuous tubular component 12 using ambient air, quenching media (e.g., cooled air), and/or forced air cooling. In some instances, a tunnel furnace cooling unit can be used to retard a rate of cooling of the CFPHS continuous tubular component 12. Retarding the rate of cooling can develop microstructures from a fully austenitized condition with less than 95% martensite and increasing amounts of ferrite, pearlite, bainite, and/or retained austenite. In one example, the CFPHS continuous tubular component 12 after the cooling step has a tube elongation of greater than 4%. The CFPHS continuous tubular component 12 after the cooling step may have a local tube ultimate tensile strength (UTS) greater than 1300 MPa. In some instances, the CFPHS continuous tubular component 12 may have a UTS lower than 1300 MPa due to the presence of phases or microconstituents other than martensite in amounts greater than 5% volume. The method 100 then ends.
According to several aspects, the method to achieve variable properties of a component using CFPHS of the present disclosure provides variable properties within a CFPHS continuous tubular component 12 using localized variable heating methods such as induction heating. The method to achieve variable properties of a component using CFPHS of the present disclosure allows tailoring a CFPHS oxide layer for optimal thickness from a no oxide layer to a maximum allowable oxide layer in different areas of the CFPHS continuous tubular component 12. The use of induction heating on CFPHS to achieve desired press hardened properties is enabled using CFPHS material of the present disclosure. The method to achieve variable properties of a component using the CFPHS of the present disclosure renders conventional furnace heating unnecessary due to use of induction heating to achieve the desired heat treatment of CFPHS. It is noted the desired press hardened properties of the present disclosure cannot be achieved using conventional aluminum-silicon (Al—Si) coated press hardened steel of any base grade, nor with bare (uncoated) press hardened steel without detrimental effects on a surface quality of the component or other necessary subsequent or preceding operations, such as shot blasting for bare material and pre-diffusion for Al—Si coated material.
The method to achieve variable properties of the CFPHS continuous tubular component 12 of the present disclosure permits tailored mechanical properties to be accomplished via induction heating, for example, to the austenitization temperatures in one or more areas of the component and wherein the component is heated to sub-critical temperatures in other areas to achieve tailored mechanical properties within the component. This is not achievable by using only a conventional furnace. As used herein, austenitization defines a heat treatment process for steel and other ferrous alloys where a material is heated above its critical temperature and transformed from ferrite to an austenite crystal structure which allows the austenite to absorb carbon from the iron carbides in a carbon steel. When followed by a quenching process, the austenitized material becomes hardened due to transformation of austenite to martensite.
Using induction heating, multiple zones of varying mechanical properties may be achieved in the component using induction coils. Current specialized non-induction coil furnaces typically produce this effect with limitations on the number of zones possible. This effect is not achievable using only a conventional furnace.
Using induction heating, targeted zones of desired surface properties may be achieved by varying an induction heating pattern. Varying an induction heating pattern is not achievable using only a conventional furnace. A CFPHS continuous tubular component 12 without a coating (and with a stable oxide layer formed during heating and soaking at elevated temperatures) enables induction hardening without the risk of melting or of excess surface oxide (scale).
A method to achieve variable properties of a component using the CFPHS continuous tubular component 12 of the present disclosure offers several advantages. These include using induction heating to heat treat CFPHS continuous tubular component 12 to reduce a cost of capital investment due to a more compact nature of induction hardening equipment and a reduced complexity of induction tooling over furnace heating. Maintenance of the induction equipment may be less expensive and involved than furnace equipment, leading to cost reduction for the component producer. Varying mechanical properties within the CFPHS continuous tubular component 12 reduces the complexity of an assembly with multiple components of separate material grades. Using induction heating on the CFPHS continuous tubular component 12 may reduce product cost and may increase performance of the component and provide a complexity reduction. Controlling an oxide layer in selected areas of the CFPHS component also allows for improved joining in predetermined areas which allows an assembly to be stronger and better integrated.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2023117376783 | Dec 2023 | CN | national |
