US20180230563A1 - Methods of forming components utilizing ultra-high strength steel and components formed thereby - Google Patents

Methods of forming components utilizing ultra-high strength steel and components formed thereby Download PDF

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US20180230563A1
US20180230563A1 US15/875,042 US201815875042A US2018230563A1 US 20180230563 A1 US20180230563 A1 US 20180230563A1 US 201815875042 A US201815875042 A US 201815875042A US 2018230563 A1 US2018230563 A1 US 2018230563A1
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component
unfinished
coating
forth
blank
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US15/875,042
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John Sabo
Sokol Sulaj
David Dorigo
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Magna Powertrain Inc
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Magna Powertrain Inc
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Priority to US15/875,042 priority patent/US20180230563A1/en
Assigned to MAGNA POWERTRAIN, INC. reassignment MAGNA POWERTRAIN, INC. ASSIGNMENT OF ASSIGNORS INTEREST (SEE DOCUMENT FOR DETAILS). Assignors: DORIGO, DAVID, SULAJ, Sokol, SABO, JOHN
Priority claimed from DE102018202151.1A external-priority patent/DE102018202151A1/en
Publication of US20180230563A1 publication Critical patent/US20180230563A1/en
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    • CCHEMISTRY; METALLURGY
    • C21METALLURGY OF IRON
    • C21DMODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D1/00General methods or devices for heat treatment, e.g. annealing, hardening, quenching or tempering
    • C21D1/68Temporary coatings or embedding materials applied before or during heat treatment
    • C21D1/70Temporary coatings or embedding materials applied before or during heat treatment while heating or quenching
    • CCHEMISTRY; METALLURGY
    • C21METALLURGY OF IRON
    • C21DMODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D1/00General methods or devices for heat treatment, e.g. annealing, hardening, quenching or tempering
    • C21D1/62Quenching devices
    • C21D1/673Quenching devices for die quenching
    • CCHEMISTRY; METALLURGY
    • C21METALLURGY OF IRON
    • C21DMODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D6/00Heat treatment of ferrous alloys
    • CCHEMISTRY; METALLURGY
    • C21METALLURGY OF IRON
    • C21DMODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D7/00Modifying the physical properties of iron or steel by deformation
    • C21D7/02Modifying the physical properties of iron or steel by deformation by cold working
    • CCHEMISTRY; METALLURGY
    • C21METALLURGY OF IRON
    • C21DMODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D8/00Modifying the physical properties by deformation combined with, or followed by, heat treatment
    • C21D8/005Modifying the physical properties by deformation combined with, or followed by, heat treatment of ferrous alloys
    • CCHEMISTRY; METALLURGY
    • C21METALLURGY OF IRON
    • C21DMODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D9/00Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor
    • C21D9/0068Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor for particular articles not mentioned below
    • CCHEMISTRY; METALLURGY
    • C22METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22CALLOYS
    • C22C38/00Ferrous alloys, e.g. steel alloys
    • C22C38/18Ferrous alloys, e.g. steel alloys containing chromium
    • C22C38/32Ferrous alloys, e.g. steel alloys containing chromium with boron
    • CCHEMISTRY; METALLURGY
    • C21METALLURGY OF IRON
    • C21DMODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D2201/00Treatment for obtaining particular effects
    • CCHEMISTRY; METALLURGY
    • C22METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22CALLOYS
    • C22C2202/00Physical properties

Abstract

Components and methods for forming components utilizing ultra-high strength steel are provided. A first method includes the steps of providing a blank of ultra-high strength steel, cold forming the blank into an unfinished component, and applying a coating to the outer surface of the unfinished component that is adapted to inhibit the formation of a ferrite soft layer on the component during heating thereof. A second method includes the steps of providing a blank of heavy gauge thickness ultra-high strength steel, cold forming the blank into a finished component, heating the finished component and quenching the component without the use of tooling.

Description

    CROSS-REFERENCE TO RELATED APPLICATIONS
  • This application claims the benefit of U.S. Provisional Patent Application Ser. No. 62/459,262 filed on Feb. 15, 2017, and titled “Methods of Forming Components Utilizing Ultra-High Strength Steel and Components Formed Thereby”, the entire disclosure of which is hereby incorporated by reference.
  • FIELD
  • The present disclosure relates generally to methods of forming components from ultra-high strength steel, such as boron steel, and to components formed by such methods.
  • BACKGROUND
  • Ultra-high strength steel is currently used in building construction and static automotive structures, e.g., vehicle bodies and frames. The use of ultra-high strength steel generally allows the weights of these structures to be reduced. Additionally, in automotive structures, the ultra-high strength steel enables the absorption of impact energy and minimizes intrusion into occupant seating areas. Although ultra-high strength steel can be made extremely strong, other properties such as formability, weldability, and impact toughness may be negatively affected, resulting in structures which may be more prone to cracking and fracture.
  • Power transmission components for automotive vehicles, such as clutch assemblies having clutch plates within a clutch housing and clutch hub are well-known. Such clutch housings have a generally cylindrical or cup-shaped body and an open end. The cylindrical or cup-shaped body is formed from a sheet metal blank and has a plurality of spline teeth formed thereon. The clutch plates fit within the clutch housing and engage the spline teeth. The clutch hub can also be a formed sheet metal component and is typically connected to a transmission shaft.
  • Powertrain components including clutch housings and hubs are commonly made of aluminum or high strength low alloy steel (HSLA) rather than ultra-high strength steel, such as boron steel. Aluminum or HSLA steel is used primarily because of its formability. Specifically, these types of materials are high strength materials which can achieve a specific geometric dimension or shape and have a specific tolerance required. Consequently, aluminum or HSLA may be used in powertrain components including parts of an automatic transmission easily, efficiently, and at a low-cost.
  • Typically, components such as reaction shells, clutch housings, and hubs made of aluminum or HSLA are formed using one or a combination of cold-forming or stamping processes and thermal heat treatments to obtain the desired shape, performance, and strength characteristics. Additionally, the structures such as the plurality of spline teeth of the clutch housing may be formed easily by using a series of rollers. Similar processes also may be used to form other powertrain components such as planetary carriers used in differentials and various covers used in a vehicle powertrain.
  • Ultra-high strength steel lacks formability using the conventional cold-forming technologies discussed above. Use of conventional cold-forming technologies with ultra-high strength steel typically does not result in the formation of required geometric dimensions and tolerances. However, there is a desire by manufacturers and suppliers to utilize ultra-high strength steel in forming automotive components such as power transmission components for similar reasons as those discussed above when used in static applications of automotive structures (e.g. reduced component weight and improved absorption of impact energy).
  • As such, a need exists for components, such as clutch housings and hubs, to be formed from ultra-high strength steel, such as boron steel. Additionally, there is a need for an improved method for forming the same.
  • SUMMARY
  • This section provides a general summary of the inventive concepts associated with the present disclosure and is not intended to represent a comprehensive disclosure of its full scope or all of its features, object, aspects and advantages. Components formed with ultra-high strength steel and methods of forming these components from ultra-high strength steel are provided.
  • In accordance with one aspect of the present disclosure, a method for forming a component from ultra-high strength steel includes pre-forming, such as via cold-forming, a blank of ultra-high strength steel, such as a flat blank of ultra-high strength steel, into a predetermined shape. The method also includes applying a coating to the outer surface and/or other exposed areas of the component, wherein the coating is configured to eliminate or reduce the formation of a ferrite soft layer that can be formed as a result of scale/decarburization during heat treatments of the component. The application of the coating therefore increases the strength of the component by preventing the formation of the ferrite soft layer.
  • In accordance with another aspect of present disclosure, a further method for forming a component utilizing ultra-high strength steel is provided. The method includes the step of providing a blank of heavy gauge, ultra-high strength steel and forming the blank into a component. Next, the method includes the steps of heating the component. The method proceeds with quenching the component without the use of tooling. The use of tooling is not required for thicker walled components according to the subject method because the thicker material undergoes minimal distortion during cooling and such components are typically machined to final critical tolerances. Utilizing the subject method provides a quicker quenching process which leads to decreased overall cycle time
  • DRAWINGS
  • Other advantages of the present disclosure will be readily appreciated, as the same becomes better understood by reference to the following detailed description when considered in connection with the accompanying drawings wherein:
  • FIG. 1 is a perspective view of a clutch housing and a clutch hub in accordance with an exemplary embodiment of the present disclosure;
  • FIG. 2 is a cross-sectional view along 2-2 of FIG. 1;
  • FIG. 3 is a perspective view of a clutch housing having a plurality of spline teeth for engaging a clutch plate in accordance with the exemplary embodiment of the present disclosure;
  • FIG. 4 is a flowchart of a method for forming a power transmission component utilizing ultra-high strength steel in accordance with the exemplary embodiment of the present disclosure;
  • FIG. 5 is a flowchart of a method for forming a power transmission component utilizing ultra-high strength steel in accordance with the exemplary embodiment of the present disclosure;
  • FIG. 6 is a flowchart of a method for forming a power transmission component utilizing ultra-high strength steel in accordance with an exemplary embodiment of the present disclosure;
  • FIG. 7 is a flowchart of a method for forming a power transmission component utilizing ultra-high strength steel in accordance with an exemplary embodiment of the present disclosure;
  • FIG. 8 is a perspective view of a clutch hub in accordance with a second embodiment of the present disclosure;
  • FIG. 9 is a perspective view of a continuously variable transmission (CVT) plunger in accordance with a third embodiment of the present disclosure;
  • FIG. 10 is a perspective view of a CVT cylinder in accordance with a fourth embodiment of the present disclosure;
  • FIG. 11 is a perspective view of a planetary carrier in accordance with a fifth embodiment of the present disclosure;
  • FIG. 12A is a perspective view of a reaction shell in accordance with a sixth embodiment of the present disclosure;
  • FIG. 12B is a perspective view of a reaction shell in accordance with the sixth embodiment of the present disclosure;
  • FIG. 13A is a perspective view of a differential housing in accordance with a seventh embodiment of the present disclosure;
  • FIG. 13B is a cross-sectional view along 13B-13B of FIG. 13A;
  • FIG. 13C is a cross-sectional view along 13C-13C of FIG. 13A;
  • FIG. 14 is a perspective view of a differential cover in accordance with a eighth embodiment of the present disclosure;
  • FIG. 15A is a perspective view of a torque converter cover in accordance with a ninth embodiment of the present disclosure;
  • FIG. 15B is a front view of a front portion of the torque converter cover shown in FIG. 15A;
  • FIG. 15C is a front view of a back portion of the torque converter cover shown in FIG. 15A;
  • FIG. 16 is a perspective view of an oil pan in accordance with an eleventh embodiment of the present disclosure;
  • FIG. 17 is a perspective view of a CVT plunger in accordance with an eleventh embodiment of the present disclosure;
  • FIG. 18 is a perspective view of a housing of a differential in accordance with a twelth embodiment of the present disclosure;
  • FIG. 19 is a perspective view of a reaction shell in accordance with a thirteenth embodiment of the present disclosure;
  • FIG. 20 is a flowchart of a method for forming a power transmission component utilizing ultra-high strength steel wherein a coating is applied to the component prior to heat treating in accordance with an exemplary embodiment of the present disclosure;
  • FIG. 21 is a magnified view of a component that was partially coated in accordance with the method illustrated in FIG. 20, illustrating the fatigue strength of the coated and uncoated regions;
  • FIG. 22 is a magnified view of a component that was partially coated in accordance with the method illustrated in FIG. 20, illustrating the fatigue strength of the coated and uncoated regions;
  • FIG. 23 is a perspective view of a cylinder of a CVT transmission in accordance with a fourteenth embodiment of the present disclosure;
  • FIG. 24 is a perspective view of a housing of a CVT transmission in accordance with a fifteenth embodiment of the present disclosure;
  • FIG. 25 is a perspective view of a planetary carrier in accordance with a sixteenth embodiment of the present disclosure;
  • FIG. 26 is a perspective view of a rotary carrier in accordance with a seventeenth embodiment of the present disclosure;
  • FIG. 27 is a flowchart of a method for forming a power transmission component utilizing ultra-high strength steel wherein no tooling is used during quenching in accordance with an exemplary embodiment of the present disclosure;
  • FIG. 28 is a chart illustrating temperature vs carbon content of parts made in accordance with an exemplary method of the present disclosure;
  • FIG. 29 a top view of a component made in accordance with an exemplary method of the present disclosure, wherein testing points are labeled; and
  • FIG. 30 is a chart illustrating testing data for hardness vs distance at the testing points labeled in FIG. 29.
  • DETAILED DESCRIPTION
  • Detailed examples of the present disclosure are disclosed herein; however, it is to be understood that the disclosed examples are merely exemplary and may be embodied in various and alternative forms. It is not intended that these examples illustrate and describe all possible forms of the disclosure. Rather, the words used in the specification are words of description rather than limitation, and it is understood that various changes may be made without departing from the spirit and scope of the disclosure.
  • As those of ordinary skill in the art will understand various features of the present disclosure as illustrated and described with reference to any of the Figures may be combined with features illustrated in one or more other Figures to produce examples of the present disclosure that are not explicitly illustrated or described. The combinations of features illustrated provide representative examples for typical applications. However, various combinations and modifications of the features consistent with the teachings of the present disclosure may be desired for particular applications or implementations.
  • Example embodiments of components formed from ultra-high strength steel constructed in accordance with the present disclosure will now be more fully described. These example embodiments are primarily directed to powertrain components. Moreover, each of the exemplary embodiments is provided so that this disclosure is thorough and fully conveys the scope of the inventive concepts, features and advantages to those skilled in the art. To this end, numerous specific details are set forth to provide a thorough understanding of each of the embodiments associated with the present disclosure. However, as will be apparent to those skilled in the art, not all specific details described herein need to be employed, the example embodiments may be embodied in many different forms, and that neither should be construed or interpreted to limit the scope of the disclosure.
  • FIGS. 1-3 show various views of a clutch housing 10 in accordance with an exemplary embodiment of the present disclosure. In particular, FIG. 1 shows a perspective view of a clutch housing 10, FIG. 2 shows a cross-sectional view of the clutch housing 10 and hub 12, and FIG. 3 shows a perspective view of the clutch housing 10 having a plurality of spline teeth 16 disposed thereon. In FIGS. 1 and 2, the clutch housing 10 is shown without the plurality of spline teeth 16. The clutch housing 10 has a generally cylindrical or cup-like shape having a radial ring portion 12 and a cylindrical drum portion 15. Housing 10 is formed from a strip (i.e. blank) of ultra-high strength steel 14, one preferred type of ultra-high strength steel 14 includes 22MnB5 boron steel. The ultra-high strength steel may be pre-coated with aluminum silicon (AlSi) or other material to prevent corrosion and decarburization during the heating and quenching steps. The clutch housing 10 may be a single piece or may be two pieces joined together by a weld or may be pressed-formed. To form the clutch housing 10, a blank of boron steel 14 is preformed, specifically cold-formed, into a predetermined shape. The predetermined shape may be a cylindrical shape or any shape known in the art related for clutch housings. After the blank 14 is cold-formed into a predetermined shape, the predetermined shape is heat treated in an inert environment. The inert environment may be an induction oven or induction chamber. Heat treatment may include, but is not limited to, any or a combination of annealing, case hardening, tempering, quenching, hot forming, or welding. Next, the clutch housing 10 is exposed to a water cooled quenching tool die to form a plurality of spline teeth 16 thereon, as shown in FIG. 3. Alternatively, the water cooled quenching die may form a second predetermined shape instead of a plurality of spline teeth 16, as shown in FIGS. 1-2 where the clutch housing 10 is smooth. It is important to note in FIG. 2 that the cross-sectional view shows a reduction in materials used compared to conventional methods using HSLA steel. A clutch hub may be formed in the same manner as will be described further below.
  • With respect to FIG. 4, a flowchart of a method for forming a component utilizing ultra-high strength steel in accordance with an exemplary embodiment of the present disclosure is provided. As illustrated by additional embodiments described in more detail below, the component may be, but is not limited to, a clutch housing, clutch hub, planetary gear carrier, or a torque converter cover. In the exemplary embodiment, the component is the clutch housing 10 described above. First, the method includes the 100 pre-forming a flat blank of steel into a predetermined shape having a plurality of spline teeth 16. Specifically, the pre-forming of the flat blank of steel is carried out by cold-forming techniques. The predetermined or unfinished shape is based on the type of component. For example, if the component is a clutch housing 10, the steel may be cold-formed into a cylindrical or cup-like shape. The flat blank of steel may be 22MnB5 boron steel and may be pre-coated to prevent corrosion. After the flat blank of steel has been pre-formed into a predetermined shape with the plurality of spline teeth 16, the pre-formed predetermined shape is 102 heat treated in an inert atmosphere to alter the properties of the steel. The heat treated steel is then sized and calibrated using a quenching tool 104. In particular, a water cooled quenching die.
  • With respect to FIG. 5, a flowchart with a method for forming a component utilizing ultra-high strength steel in accordance with an exemplary embodiment of the present disclosure is provided. The method includes 200 pre-forming a flat blank of steel into a cup-shaped body. As discussed above, the flat blank of steel may be a 22MnB5 boron steel blank. The cup-shaped body is then 202 heat treated in an inert environment. The inert environment may be an induction chamber or oven. Next, the method includes 204 water cooled quenching the cup-shape body to form a plurality of spline teeth thereon.
  • FIGS. 6-7 also show flowcharts of methods for forming a component utilizing ultra-high strength steel in accordance with an exemplary embodiment of the present disclosure. Like the methods shown in FIGS. 4-5, the methods shown in FIGS. 6-7 utilize 22MnB5 boron steel. However, it is appreciated by one skilled in the art that any type of ultra-high strength steel or any type of boron steel may be used in conjunction with these methods. In FIG. 6, the method includes 300 pre-forming or cold-forming the flat blank of steel into a predetermined shape. The predetermined or unfinished shape of the method shown in FIG. 6 does not include a plurality of spline teeth 16. The cold-formed steel is then 302 heat treated in an inert atmosphere. The heat treatment may be localized to a certain portion of the steel. The method further includes 304 forming a plurality of spline teeth 16 within the heat treated steel using a quenching tool. The quenching tool is a water-cooled quenching die.
  • With respect to FIG. 7, the method for forming a component utilizing ultra-high strength steel in accordance with an exemplary embodiment of the present disclosure includes 400 heat treating a flat blank of steel in an inert atmosphere and 402 quenching the heat treated flat blank into a predetermined shape using a quenching tool.
  • The method discussed above may also include, but is not limited to cold-forming the clutch housing 10 without a plurality of spline teeth 16, heat treating the unfinished shape of the clutch housing 10 using localized induction heating, and forming and sizing the plurality of spline teeth 16 using the quenching die. Alternatively, the method may include pre-forming/cold-forming the clutch housing 10 with a plurality of spline teeth 16, heating the unfinished shape of the clutch housing 10 in an inert environment, and sizing and finalizing the shape of the housing 10 in the quenching die. Similarly, planetary gear carriers and other components may be partially or completely cold formed and then heated using either localized or entire part heating.
  • In addition to the clutch housing 10 disclosed above, other embodiments of components from ultra-high strength steel constructed in accordance with the present disclosure are described in more detail below. FIG. 8 shows a clutch hub 500 in accordance with a second embodiment of the present disclosure. The clutch hub 500 has a cup-like shape having a radial ring portion 502 and a cylindrical drum portion 504. A tubular neck 506 extends longitudinally from the radial ring portion 502 and a drive gear 508 is attached to the tubular neck 506. Like the clutch housing 10, the clutch hub 500 may be formed from a strip (i.e. blank) of ultra-high strength steel. The ultra-high strength steel may also be pre-coated with aluminum silicon (AlSi) or other material to prevent corrosion and decarburization during the heating and quenching steps. The clutch hub 500 may be a single piece or may be two pieces joined together by a weld or may be pressed-formed. To form the clutch hub 500, a blank of boron steel can be cold-formed into a predetermined or unfinished shape. A plurality of generally triangular openings 510 can be formed in the radial ring portion during cold forming for weight reduction. The predetermined shape may then be heat treated in an inert environment. Next, the clutch hub 500 may be exposed to a water cooled quenching tool die to form a plurality of radially outwardly extending spline teeth 512 disposed about the cylindrical drum portion 504.
  • FIG. 9 shows a continuously variable transmission (CVT) plunger 520 in accordance with a third embodiment of the present disclosure. The CVT plunger 520 includes a generally bell-shaped body defining a centrally disposed opening 522. The CVT plunger 520 is formed from a preformed flat blank of ultra-high strength steel, preferably 22MnB5 boron steel. The blank of boron steel may be cold-formed into a predetermined or unfinished shape with a thick center and outer edge. The predetermined shape shape can then be heat treated in an inert environment. Next, the CVT plunger 520 can be exposed to a water cooled quenching tool die.
  • FIG. 10 shows a CVT cylinder 540 in accordance with a fourth embodiment of the present disclosure. The CVT cylinder 540 includes an annular or cylindrically shaped body having a first end 542 and a second end 544 and including a shoulder 546 formed at the first end 542. The body of the CVT cylinder 540 defines an opening 548 longitudinally extending from the first end 542 to the second end 544. The CVT cylinder 540 begins as a preformed flat blank of ultra-high strength steel, preferably 22MnB5 boron steel, with the centrally disposed material removed and discarded. Next, the preformed blank or unfinished shape is heat treated in an inert environment. Then, the CVT cylinder 540 is exposed to a water cooled quenching tool die.
  • FIG. 11 shows a planetary carrier 560 in accordance with a fifth embodiment of the present disclosure. The planetary carrier 560 comprises a first piece 562 and a second piece 564 joined together by a weld. A plurality of apertures 566 are circumferentially disposed in a spaced relationship to each other about the perimeter of each piece 562, 564. The first piece 562 includes a plurality of legs 568 extending longitudinally. To form the first piece 562 of the planetary carrier 560, a flat blank of boron steel can be cold-formed into a predetermined or unfinished shape with the plurality of apertures 566 and including the legs 568. To form the second piece 564 of the planetary carrier 560, a flat blank of boron steel can be cold-formed into a an unfinished shape with the plurality of apertures 566. The unfinished shapes of the pieces 562, 564 are heat treated in an inert environment. Next, each piece 562, 564 of the carrier 560 may be exposed to a water cooled quenching tool die. The planetary carrier 560 is completed by joining or welding the legs 568 of the first piece 562 to the second piece 564.
  • FIGS. 12A and 12B show two reaction shells 580 in accordance with a sixth embodiment of the present disclosure. Each reaction shell 580 comprises a body including a cylindrical first portion 582 of a first diameter and a cylindrical second portion 584 of a second diameter being larger than the first diameter. A plurality of radially outwardly extending spline teeth 586 are disposed about the cylindrical second portion 584. A plurality of bores 588 are defined by the cylindrical first portion 582 and the cylindrical second portion 584. To form the reaction shell 580, a flat blank of boron steel is cold-formed into a predetermined tubular shape or unfinished shape having the bores. The predetermined tubular shape is then heat treated in an inert environment. Although the bores 588 are formed while cold-forming, it should be understood that the bores 588 may also be formed while the predetermined tubular shape is hot. Next, the reaction shell is exposed to a water cooled quenching tool die to hold the geometry and form the radially outwardly extending spline teeth 586 disposed about cylindrical second portion 584.
  • FIG. 13A shows a differential housing 600 in accordance with a seventh embodiment of the present disclosure. The differential housing 600 is generally cup or drum shaped with a tubular neck portion 602 defining a central opening 604 and including a plurality of arms 606 extending radially and longitudinally from the neck portion 602. The arms 606 alternate circumferentially between the arm 606 including a radially inwardly extending shoulder 608 (FIG. 13C) and the arm 606 having a generally L shaped cross section (FIG. 13B). Each arm 606 also includes at least one aperture 610. The differential housing 600 begins as a preformed flat blank of ultra-high strength steel, preferably 22MnB5 boron steel, with an extrusion forming the neck portion 602 and the central opening 604. The preformed blank or unfinished shape is heat treated in an inert environment. Then the differential housing 600 is exposed to a water cooled quenching tool die.
  • FIG. 14 shows a differential cover 620 in accordance with an eighth embodiment of the present disclosure. The differential cover 620 comprises a generally bell shaped body 622 extending between a generally cylindrical first end 624 and an opposite annular second end 626. A ring gear 628 is attached to the second end 626 of the cover 620. The cover 620 is for enclosing a plurality of pinion gears 630. The cover 620 is formed with a flat blank of boron steel that is cold-formed into a unfinished flat or cup shape having an extrusion extending longitudinally at its center. Next, the cover 620 is heat treated in an inert environment. Then the cover 620 is exposed to a water cooled quenching tool die. The ring gear 628 may initially be two pieces which are welded to the outer diameter of the cover 620.
  • FIG. 15A shows a torque converter cover 640 in accordance with a ninth embodiment of the present disclosure. The torque converter cover 640 comprises a front portion 642 (FIG. 15B) and a back portion 644 (FIG. 15C). The front portion 642 is generally drum-shaped and includes a radial wall 646 having an outer peripheral portion defining a lock-up surface. An integral cylindrical portion 648 of the front portion 642 has an inner surface that extends longitudinally from the radial wall 646. The inner surface of the front portion may also define an internal spline. The back portion 644 is ring shaped and has a center opening 650 and a curved cross-section or half round shape. Each portion 642, 644 begins as a flat blank of boron steel which is cold-formed into a predetermined shape. The predetermined or unfinished shapes may then be heat treated in an inert environment. Next, each portion 642, 644 of the cover can be exposed to a water cooled quenching tool die. Such torque converter covers 640 using higher strength steel allow for a thinner wall which reduces weight compared to covers made from other materials.
  • FIG. 16 shows an oil pan 660 in accordance with a tenth embodiment of the present disclosure. The oil pan 660 comprises a generally rectangular base 662 with a side wall 664 disposed around the periphery of the base 662 and extending generally perpendicularly from the base 662 to an upper continuous flange 668 adapted to be secured to a block of an engine. A plurality of openings 670 are defined by the flange 668 and spaced from each other circumferentially about the flange 668. The oil pan 660 may be formed from a flat blank of boron steel which is cold-formed into a predetermined shape. The predetermined or unfinished shape may then be heat treated in an inert environment. Then the oil pan 660 can be exposed to a water cooled quenching tool die. The use of high strength steel in this type of application allows for a thinner base 662 and side wall 664 and can also allow for ribbing features.
  • In each of the aforementioned embodiments, the components may be formed from 22MnB5 steel, however, it should be understood that the amount of boron (B5-B50) may be selected depending on the type of component or strength desired. Additionally, the amount of other materials which comprise the ultra-high strength steel, such as carbon, may cause variation in the martensitic percentage and hardness after quenching. During the heat treatment, the heating temperature is approximately 850-950 degrees C. More specifically, the target heating temperature for 22MnB5 steel is 900 degrees C., however, the heating temperature may be increased as the amount of boron is increased. As described above, the heat treating may be partially or completely localized. The heating method may be induction or by other techniques. When it is desirable to localize strength in one particular area of a component, the heat treatment may be localized to that area. In other instances, localized heat treatment may be used for sections of a component having a thicker cross section.
  • During the quenching step that may be used in forming each of the aforementioned embodiments, the quench press/die defines the final shape of the part. The release temperature may range between approximately 150-250 degrees C., with a preferred target temperature of 200 degrees C. The components generally remain in the quench press/die for approximately 6-20 seconds depending on the cross sectional thickness and desired strength.
  • In general, materials having a strength of approximately 1000 Mpa will crack or spring back during cold forming, therefore the aforementioned methods are advantageous when forming such high strength materials. Additionally, due to a reduction of cross section, the geometry of components formed with heat assisted calibration (HAC) methods disclosed herein may be more complex (i.e. ribs). Consequently, the manufacturing of some components (e.g. planetary carrier described in the fifth embodiment above) that is not possible using cold forming is made possible with HAC processes.
  • According to another aspect of the present disclosure, a method is provided for applying a coating to the outer surfaces and other exposed areas of the components prior to heat treating. Applying such a coating eliminates or reduces the formation of a ferrite soft layer on the component that can be formed as a result of scale/decarburization during heat treatments of the component which is known to affect the strength of the component in its final form.
  • More particularly, the coating is applied to areas such as windows, holes or cutouts of components, such as those found on the components illustrated in FIGS. 17-19. The coating may be comprised of materials such as a nickel electrolyte coating, oils applied to form an unfoliated oxide layer, high-temperature graphite oil, water-based ceramic coatings, and other high-temperature protective coatings that are adapted to control oxidation and decarburization. Nickel coatings may remain as a layer after final production of the component, while oil or water-based ceramics may be washed off or absorbed after heat treatment. It should be appreciated that the coating may be applied by spraying or brushing. Furthermore, the coating may be applied to only targeted portions, or to the entire component. For example, a first portion that is coated may include the areas around windows, while a second portion that is uncoated may include the rest of the component.
  • With respect to FIG. 20, a flowchart of a method for forming a component in accordance with an exemplary embodiment of the present disclosure is provided. The method may include the step of 1000 providing a blank of ultra-high strength steel. The method proceeds with 1002 cold forming the blank into an unfinished component. The method continues with 1004 applying a coating to the outer surface of the unfinished component, wherein the coating is adapted to inhibit the formation of a ferrite soft layer on the unfinished component during heating of the component. The method continues with 1006 heating the unfinished component. Finally, the method proceeds with 1008 quenching the unfinished component.
  • It should be appreciated that applying a coating in accordance with the subject method allows the mechanical properties of the component to be tailored by applying the coating to predetermined regions. More particularly, the coating may be applied to a first portion of the unfinished component, while a second portion of the unfinished component remains uncoated. As illustrated in FIGS. 21 and 22, tests were conducted on components that were coated in accordance with the subject method at certain regions, while other regions of the components were allowed to remain uncoated. As illustrated in these figures, an optical microscopy of the surface microstructure of the component can be utilized to identify where a coating was applied. The tests revealed a fatigue strength of approximately 475 Mpa in coated regions, and only 305 Mpa in uncoated regions. The tests further affirmed that components that are coated in accordance with the subject method can meet strength requirements, and surface and core hardness of minimum 400 HV requirements.
  • In view of the foregoing, it should be appreciated that an advantage of utilizing the subject coating method include the prevention of the formation of a ferrite soft layer on the component, which reduces thickness and improves the fatigue strength of the component.
  • According to a further aspect of the disclosure, a method is provided wherein thicker walled, heavy gauge components are directly quenched, i.e., without the use of tooling, after being heat treated to provide a more cost effective process. More particularly, as discussed in the foregoing, thinner walled components can be held with tooling during quenching to reduce distortion. Such tooling is not required for thicker walled components according to the subject method because the thicker material undergoes minimal distortion during cooling and because thicker walled components are typically machined to final critical tolerances. Utilizing the subject method provides a quicker quenching process which leads to decreased overall cycle time.
  • Thicker walled, heavy gauge components according to the subject method have a wall thickness between approximately 3.5 to 6.5 mm. Such components may include, but are not limited to, a CVT plunger 520, 1520 such as that presented in FIGS. 9 and 17, a CVT cylinder 540, 1540 such as that presented in FIGS. 10 and 23, a differential housing 600, 1600 such as that presented in FIGS. 13A-13C, a differential cover 620 such as that presented in FIG. 14, a CVT housing 1542 such as that presented in FIG. 24, a planetary carrier 1544 such as that that presented in FIG. 25, and a rotary carrier 1546 such as that presented in FIG. 26. Furthermore, such heavy gauge components may have the following composition:
  • Carbon 0.08 to 0.33%;
  • Manganese 0.8 to 1.50%;
  • Boron 0.0005 to 0.005%;
  • Silicon 0.50% max;
  • Phosphorous 0.030% max;
  • Sulfar 0025% max; and
  • Chromium 0.35% max.
  • With respect to FIG. 26, a flowchart of a method for forming a component in accordance with an exemplary embodiment of the present disclosure is provided. The subject method may include step 2000 of pre-forming or cold-forming, such as with a roller or cam die, a flat blank of steel into a final shape. The method continues with step 2002 heating the formed blank such as with an electrical or gas furnace or induction heating source. For example, the blank may be heated up to 930 degrees Celsius. The method continues with quickly transferring the component to a quenching media, and step 2004 quenching the component without the use of tooling. The component may be fully or partially quenched. After quenching is complete, the component is removed from the quenching media.
  • It should be appreciated that the subject method allows the mechanical properties of components to be tailored for specific purposes and for the overall weight of the component to be reduced. As illustrated in FIGS. 27-29, by utilizing the subject method, components were able to meet strength and hardness minimum requirements of 400 HC, and core hardness minimum requirements of 200 HV.
  • While examples of the disclosure have been illustrated and described, it is not intended that these examples illustrate and describe all possible forms of the disclosure. Rather, the words used in the specification are words of description rather than limitation, and it is understood that various changes may be made without departing from the spirit and scope of the disclosure. Additionally, the features and various implementing embodiments may be combined to form further examples of the disclosure.

Claims (20)

What is claimed is:
1. A method of forming a component utilizing ultra-high strength steel including the steps of:
providing a blank of ultra-high strength steel;
cold forming the blank into an unfinished component;
applying a coating to the outer surface of the unfinished component, wherein the coating is adapted to inhibit the formation of a ferrite soft layer on the unfinished component during heating of the component;
heating the unfinished component; and
quenching the unfinished component.
2. The method as set forth in claim 1 wherein the outer surface of the unfinished component includes at least a first portion and a second portion, and wherein applying a coating to the outer surface of the unfinished component includes applying the coating to only the first portion of the outer surface of the component.
3. The method as set forth in claim 2 wherein the first portion of the outer surface of the unfinished component extends about an opening defined by the outer surface such that the coating is applied about the opening.
4. The method as set forth in claim 1 wherein the coating is applied to at least substantially the entire outer surface of the unfinished component.
5. The method as set forth in claim 1 wherein the coating includes at least one of a nickel electrolyte coating, a high-temperature graphite oil, or a water-based ceramic coating.
6. The method as set forth in claim 1 wherein the component is at least one of a differential housing, a CVT plunger, inner diameter splines of a clutch housing, and external gears.
7. A method of forming a component utilizing ultra-high strength steel including the steps of:
providing a blank of heavy gauge thickness ultra-high strength steel;
cold forming the blank into a finished component;
heating the finished component; and
quenching the finished component without the use of tooling.
8. The method as set forth in claim 7 wherein a thickness of the blank is between approximately 3.5 and 6.5 mm.
9. The method as set forth in claim 7 wherein the blank has the composition of:
carbon 0.08 to 0.33 wt %;
manganese 0.8 to 1.50 wt %;
boron 0.0005 to 0.005 wt %;
silicon less than or equal to 0.50 wt %;
phosphorous less than or equal to 0.030 wt %;
sulfar less than or equal to 0.0025 wt %; and
chromium less than or equal to 0.35 wt %.
10. The method as set forth in claim 7 wherein the component is at least one of a differential housing, a CVT plunger, inner diameter splines of a clutch housing, and external gears.
11. The method as set forth in claim 7 wherein heating the finished component includes heating the component with one of an electric furnace, a gas furnace, or an induction heat source.
12. The method as set forth in claim 7 wherein heating the finished component includes heating the finished component to 930 degrees Celsius.
13. The method as set forth in claim 7 wherein quenching the finished component includes quenching only a portion of the finished component.
14. The method as set forth in claim 7 wherein quenching the finished component includes quenching the entire finished component.
15. A method of forming a powertrain component for a vehicle utilizing ultra-high strength steel including the steps of:
providing a blank of ultra-high strength steel;
cold forming the blank into an unfinished powertrain component;
applying a coating to the outer surface of the unfinished powertrain component, wherein the coating is adapted to inhibit the formation of a ferrite soft layer on the unfinished component during heating of the component;
heating the unfinished powertrain component; and
quenching the unfinished powertrain component.
16. The method as set forth in claim 15 wherein the outer surface of the unfinished powertrain component includes at least a first portion and a second portion, and wherein applying a coating to the outer surface of the unfinished powertrain component includes applying the coating to only the first portion of the outer surface of the component.
17. The method as set forth in claim 6 wherein the first portion of the outer surface of the unfinished powertrain component extends about an opening defined by the outer surface such that the coating is applied about the opening.
18. The method as set forth in claim 15 wherein the coating is applied to at least substantially the entire outer surface of the unfinished powertrain component.
19. The method as set forth in claim 15 wherein the coating includes at least one of a nickel electrolyte coating, a high-temperature graphite oil, or a water-based ceramic coating.
20. The method as set forth in claim 15 wherein the unfinished powertrain component is at least one of a differential housing, a CVT plunger, inner diameter splines of a clutch housing, and external gears.
US15/875,042 2017-02-15 2018-01-19 Methods of forming components utilizing ultra-high strength steel and components formed thereby Pending US20180230563A1 (en)

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