WEAR-RESISTANT HIGH-STRENGTH ROLL-FORMED COMPONENTS

Abstract

A method of forming a component having a cross-section with a bend radius includes providing a work-piece blank from press-hardened steel (PHS). The method also includes austenitizing the work-piece blank in a furnace via heating the strip of sheet metal to achieve therein an austenite microstructure, including soaking the work-piece blank for a predetermined amount of time. The method additionally includes quenching the austenitized work-piece blank to achieve therein a martensitic matrix microstructure with dispersed chromium-enriched carbide. The method also includes roll-forming the austenitized and quenched work-piece blank to generate the cross-section and the bend radius. The method may further include locally heating the bend radius area during the roll-forming of the cross-section to reduce an amount of chromium-enriched carbide in the martensitic matrix microstructure inside the bend radius area relative to the microstructure outside the bend, and thereby generating the component having high strength, ductility, and wear resistance.

Claims

1. A method of forming a component having a cross-section having a bend characterized by a bend radius, the method comprising: providing a work-piece blank from press-hardened steel (PHS); austenitizing the work-piece blank in a furnace via heating the work-piece blank to achieve therein an austenite microstructure, including soaking the strip of PHS for a predetermined amount of time; quenching the austenitized work-piece blank to achieve therein a martensitic matrix microstructure with dispersed chromium-enriched carbide; and roll-forming the austenitized and quenched work-piece blank via at least one set of rolls to generate the cross-section having the bend radius.

2. The method of forming the component of claim 1, locally heating an area of the bend radius during the roll-forming of the cross-section to reduce an amount of chromium-enriched carbide in the martensitic matrix microstructure inside the bend radius relative to the martensitic matrix microstructure outside the bend radius, and thereby generating the component having high strength, ductility, and wear resistance.

3. The method of forming the component of claim 1, wherein the predetermined amount of time is in a range of 1-1000 seconds.

4. The method of forming the component of claim 1, wherein the quenching is performed at a rate greater than 10° C. per second.

5. The method of forming the component of claim 1, wherein the cross-section has a 1:1 ratio of material thickness to the bend radius without cracks or tears.

6. The method of forming the component of claim 1, wherein locally heating the austenitized and quenched work-piece blank is performed via one of a laser, a microwave, and an infrared device during the roll-forming.

7. The method of forming the component of claim 1, wherein the PHS of the work-piece blank includes carbon (C) in a range of 0.05-0.45% by weight, manganese (Mn) in a range of 0-4.5% by weight, chromium (Cr) in a range of 0.5-6% by weight, and silicon (Si) in a range of 0.5-2.5% by weight.

8. The method of forming the component of claim 1, wherein an amount of chromium in the chromium-enriched carbide is greater than 2% by weight, and wherein particles of the chromium-enriched carbide have a diameter in a range of 5 nm-1.5 μm.

9. The method of forming the component of claim 1, wherein the martensitic matrix microstructure with dispersed chromium-enriched carbide includes: martensite (with optional austenite at less than 10% by volume and optional ferrite at less than 5% by volume) at greater than 85% by volume; and chromium-enriched carbide in a range of 0.2-10% by volume.

10. The method of forming the component of claim 1, wherein the austenitized and quenched work-piece blank has a tensile strength in a range of 1000-2000 MPa.

11. A roll-formed high strength, ductility, and wear resistant component comprising: a cross-section having a bend characterized by a bend radius roll-formed from austenitized and quenched work-piece blank from a press-hardened steel (PHS) having a martensitic matrix microstructure with dispersed chromium-enriched carbide; wherein, relative to the martensitic matrix microstructure outside the bend radius, the martensitic matrix microstructure in the bend radius has a reduced amount of the chromium-enriched carbide.

12. The component of claim 11, wherein the cross-section has a 1:1 ratio of material thickness to the bend radius without cracks or tears.

13. The component of claim 11, wherein the PHS of the work-piece blank includes carbon (C) in a range of 0.05-0.45% by weight, manganese (Mn) in a range of 0-4.5% by weight, chromium (Cr) in a range of 0.5-6% by weight, and silicon (Si) in a range of 0.5-2.5% by weight.

14. The component of claim 11, wherein an amount of chromium in the chromium-enriched carbide is greater than 2% by weight.

15. The component of claim 14, wherein particles of the chromium-enriched carbide have a diameter in a range of 5 nm-1.5 μm.

16. The component of claim 11, wherein the martensitic matrix microstructure with dispersed carbide includes: martensite (with optional austenite at less than 10% by volume and optional ferrite at less than 5% by volume) at greater than 85% by volume; and chromium-enriched carbide in a range of 0.2-10% by volume.

17. The component of claim 11, wherein the austenitized and quenched work-piece blank from has a tensile strength in a range of 1000-2000 MPa.

18. A method of forming a structural component including a cross-section having a bend characterized by a bend radius, the method comprising: providing a work-piece blank from press-hardened steel (PHS) having carbide enriched with an amount of chromium greater than 2% by weight; austenitizing the work-piece blank in a furnace via heating the strip of sheet metal to achieve therein an austenite microstructure, including soaking the work-piece blank for 200-500 seconds; quenching the austenitized work-piece blank at a rate greater than 10° C. per second to achieve therein a martensitic matrix microstructure with dispersed chromium-enriched carbide to achieve ultimate tensile strength thereof in a range of 1000-2000 MPa; roll-forming the austenitized and quenched work-piece blank via at least one set of rolls to generate the cross-section including the bend radius; and locally heating an area of the bend radius during the roll-forming of the cross-section to reduce an amount of the chromium-enriched carbide in the martensitic matrix microstructure inside the bend radius area relative to the martensitic matrix microstructure outside the bend radius, and thereby generating the structural component having high strength, ductility, and wear resistance.

19. The method of forming the structural component of claim 18, wherein the PHS of the work-piece blank includes carbon (C) in a range of 0.05-0.45% by weight, manganese (Mn) in a range of 0-4.5% by weight, chromium (Cr) in a range of 0.5-6% by weight, and silicon (Si) in a range of 0.5-2.5% by weight.

20. The method of forming the structural component of claim 18, wherein the martensitic matrix microstructure with dispersed chromium-enriched carbide includes: martensite (with optional austenite at less than 10% by volume and optional ferrite at less than 5% by volume) at greater than 85% by volume; and chromium-enriched carbide in a range of 0.2-10% by volume.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0017] FIG. 1 is a schematic perspective illustration of roll-forming and localized heating a press-hardened steel (PHS) work-piece blank to generate a structural component having a small radius bend, according to the disclosure.

[0018] FIG. 2 is a schematic close-up illustration of a cross-section of the structural component roll-formed from the work-piece blank as shown in FIG. 1, according to the disclosure.

[0019] FIG. 3 is an illustration of a martensitic matrix microstructure with dispersed chromium-enriched carbide of the structural component roll-formed from the PHS work-piece blank.

[0020] FIG. 4A is a data plot depicting stress vs strain comparison of PHS without carbide and PHS enriched with carbide.

[0021] FIG. 4B is a data plot depicting wear resistance comparison of PHS without carbide and PHS enriched with carbide.

[0022] FIG. 4C is a data plot depicting impact toughness comparison of PHS without carbide and PHS enriched with carbide.

[0023] FIG. 5 is a flow chart illustrating a method of roll-forming the structural component from the PHS work-piece blank shown in FIGS. 1-4.

[0024] FIG. 6 is a data plot depicting austenitizing temperature versus time for the structural component formed from the PHS work-piece blank having the martensitic matrix microstructure with dispersed chromium-enriched carbide shown in FIG. 3, according to the disclosure.

DETAILED DESCRIPTION

[0025] Referring to the drawings in which like elements are identified with identical numerals throughout, FIG. 1 illustrates, in detail, processing and forming of a work-piece blank 10. Such work-piece blanks 10 are frequently used in manufacturing processes, such as metal stamping or roll-forming, to produce specifically shaped high strength components. Typically, such components are formed from work-piece blanks 10. Each work-piece blank 10 is typically a pre-cut piece of formable material, for example sheet metal, such as cold rolled steel.

[0026] Specifically, the formable material may be a press-hardened steel (PHS) selected for the subject work-piece blank 10 used in manufacture of a structural component 12. The component 12 is a high strength and wear resistant part having high ductility or fracture toughness. The structural component 12 may, for example, be an automotive body frame rail shown in FIG. 1 or a cross-member (not shown). PHS is a high-strength steel typically delivered in rolls or coils of various sizes for blanking, austenitizing, and additional processing. Generally, austenitization and quenching is a hardening process used on iron-based metals to promote better mechanical properties of the material. The purpose of austenitizing steel and other ferrous alloys is to soften the materials for forming them into the required shape, while the purpose of quenching is to provide strength and resistance to the material.

[0027] The temperature at which steel and other ferrous alloys are heated above their critical temperatures is called the austenitizing temperature. The austenitizing temperature range varies for different grades of carbon, alloys, and tool steels. After the metal is heated into the austenite region, it is then quenched in a heat extraction medium. Generally, press hardening, a.k.a., hot stamping or hot press forming, allows PHS steels to be formed into complex shapes not commonly possible with regular cold stamping operations. However, PHS is typically not used for roll-formed part due to likelihood of material splits and tears, especially in tight radii of the component cross-sections generated by forming rolls.

[0028] The work-piece blank 10 is generally cut from a strip or coil 14 of PHS described above to be subsequently austenitized, quenched, and roll-formed to produce the structural component 12. The unformed work-piece blank 10 may be initially austenitized in a furnace 16 (shown in FIG. 1). To achieve a martensitic matrix microstructure which will be described in detail below, austenitization of the work-piece blank 10 may be performed at a predetermined temperature, above austenitizing temperature Ac3 (shown in FIG. 6), with the work-piece blank 10 soaked at the specific temperature for a predetermined amount of time. The resultant tensile strength of the austenitized and quenched work-piece blank 10 may be in a range of 1000-2000 MPa (shown in FIG. 4A).

[0029] Following austenitization, the work-piece blank 10 may be quenched at a rate of greater than 10° C. per second and transferred to a system of rolls 18 (shown in FIG. 1) having at least one set of rolls 18A. As shown, the system of rolls 18 may include multiple sets of rolls mounted on consecutive stands, with each set of rolls generating an incremental part of the component 12. The austenitized and quenched work-piece blank 10 may be locally heated during roll-forming via a heating device 20, such as a laser, a microwave, or an infrared source, in the area where the rolls 18A come into contact with the blank material. In a system 18 employing multiple rolls, each respective roll 18A may be paired with a corresponding heating device 20 to locally heat the area of the work-piece blank 10 undergoing deformation. Localized heating is intended to improve roll-formability of the work-piece blank 10, especially when generated from high-strength steel, such as austenitized and quenched PHS. The local heating thus enables the PHS work-piece blank 10 to be formed into the component 12 having the desired shape along with high strength, ductility, and wear resistance.

[0030] As used to manufacture the component 12, PHS includes carbon (C) in a range of 0.05-0.45% by weight, manganese (Mn) in a range of 0-4.5% by weight, chromium (Cr) in a range of 0.5-6% by weight, and silicon (Si) in a range of 0.5-2.5% by weight. The structural component 12 has a desired final shape or contour 12A (shown in FIG. 1) and a cross-section or profile 12B with one or more bends 22 characterized by a radius R (shown in FIG. 2). The component 12 material has a martensitic matrix microstructure 24 with dispersed chromium-enriched carbide 26, shown in FIG. 3. While PHS without carbide has similar tensile properties to PHS enriched with carbide (stress vs strain comparison shown in FIG. 4A), and specifically with chromium-enriched carbide, PHS enriched with carbide will provide comparatively higher strength and wear resistance (wear resistance comparison shown in FIG. 4B and impact toughness comparison shown in FIG. 4C).

[0031] The martensitic matrix microstructure 24 with dispersed chromium-enriched carbide 26 may specifically include martensite (with optional austenite at less than 10.sup.0/by volume and optional ferrite at less than 5% by volume) at greater than 85% by volume, and further at greater than 90% by volume. The martensitic matrix microstructure 24 with dispersed chromium-enriched carbide 26 may additionally include chromium-enriched carbide in a range of 0.2-10% by volume, austenite at less than 10% by volume, and ferrite at less than 5% by volume. The martensite in the martensitic matrix microstructure 24 may also, optionally, include austenite/ferrite martensite. The amount of chromium in the chromium-enriched carbide 26 may be greater than 2% by weight. Particles of the chromium-enriched carbide 26 may have a diameter in a range of 5 nm-1.5 μm.

[0032] An area of the cross-section or profile 12B proximate and surrounding the bend radius R is indicated in FIG. 2 as area A1, wherein an area outside the area A1, is indicated in FIG. 2 as area A2. Local heating of the area A1 proximate the bend radius R during the roll-forming of the cross-section 12B is configured to reduce an amount of the chromium-enriched carbide 26 in the martensitic matrix microstructure 24 inside the bend radius R relative to the martensitic matrix microstructure outside the bend radius. Specifically, before local heating is applied to area A1 the chromium-enriched carbide 26 is present in both areas A1 and A2, and subsequent local heating dissolves the carbides in A1. While the reduction of chromium-enriched carbide 26 in the bend radius R permits higher ductility for forming, the dispersed chromium-enriched carbide 26 in adjacent area A2 generates increased strength and wear resistance of the component 12 outside the bend(s).

[0033] As additionally shown in FIG. 2, the local heating of PHS material in area A1 during roll-forming permits the radius R to have a relatively small magnitude, i.e., the cross-section 12B may have a small ratio of material thickness t to the bend radius R without cracks or tears having developed in the bend 22. Specifically, the ratio of material thickness t to the bend radius R may be 1:1. Typically, the ratio of PHS material thickness to bend radius in formed parts exceeds 1:1.5 to reduce the likelihood of cracks and tears. The subject advantageous ratio of material thickness t to the bend radius R in the cross-section 12B roll-formed from PHS is specifically enabled by enhanced material formability at higher temperatures, i.e., higher plasticity of martensite, enabled by the localized heating described above.

[0034] FIG. 5 depicts a method 100 of forming the component 12 from the work-piece blank 10 shown in and described above with respect to FIGS. 1-4. The forming of the component 12 is initiated in frame 102 with providing a strip of press-hardened steel (PHS). As described above, the work-piece blank 10 may be cut out or blanked from a roll or coil of the PHS. Following frame 102, the method proceeds to frame 104. In frame 104 the method includes austenitizing the work-piece blank 10 via heating the work-piece blank in the furnace 16 at a predetermined austenitization temperature 28, above temperature Ac3, as shown in FIG. 6.

[0035] In frame 104 the method further includes soaking the work-piece blank at the subject predetermined temperature 28 for a predetermined amount of time 30 (shown in FIG. 6) to achieve an austenite microstructure in the cross-section 12B. The predetermined temperature 28 may be in a range of 880-950° C. The predetermined amount of soak time 30 may be in a range of 1-1000 seconds, and may be further constrained to a range of 200-500 seconds. After austenitizing the work-piece blank 10, the method proceeds to frame 106. In frame 106 the method includes quenching the austenitized work-piece blank 10 to achieve therein the martensitic matrix microstructure 24 with dispersed chromium-enriched carbide 26. As described with respect to FIGS. 1-4, quenching may be performed at a rate greater than 10° C. per second. Specifically, quenching of the work-piece blank 10 may be performed in a salt bath, mixed liquid and air quenching, or via water-cooled die quenching. It is intended for the austenitized and quenched PHS work-piece blank 10 to have tensile strength in a range of 1000-2000 MPa.

[0036] Following frame 106, the method moves on to frame 108, where the method includes roll-forming the austenitized and quenched work-piece blank 10 via the system of rolls 18 to generate the cross-section 12B having the bend radius R. After frame 108, the method may proceed to frame 110. In frame 110 the method includes locally heating the area A1 of the bend radius R during the roll-forming of the cross-section 12B. Local heating of the area A1 acts to reduce an amount of chromium-enriched carbide in and around the bend radius R relative to the martensitic matrix microstructure 24 outside the bend 22 by dissolving the chromium-enriched carbide 26 in the area A1. As described with respect to FIGS. 1-4, the austenitized and quenched work-piece blank 10 may be locally heated via the heating device 20, for example a laser, a microwave, or an infrared source.

[0037] Following frame 108 or 110, the method may proceed to frame 112. In frame 112 the method includes cooling the roll-formed component 12, such as by permitting the component to reach equilibrium with ambient temperature. Following frame 112, the method may proceed to and conclude in frame 114 with trimming excess material, washing, and/or packaging the final component 12. Generally, the above-disclosed method applied to the PHS work-piece blank 10, specifically using local heating of the austenitized and quenched work-piece blank 10 in the area A1 of the bend radius R, is intended to produce a roll-formed component 12 having high strength, ductility (fracture toughness), and wear resistance in requisite areas.

[0038] The detailed description and the drawings or figures are supportive and descriptive of the disclosure, but the scope of the disclosure is defined solely by the claims. While some of the best modes and other embodiments for carrying out the claimed disclosure have been described in detail, various alternative designs and embodiments exist for practicing the disclosure defined in the appended claims. Furthermore, the embodiments shown in the drawings or the characteristics of various embodiments mentioned in the present description are not necessarily to be understood as embodiments independent of each other. Rather, it is possible that each of the characteristics described in one of the examples of an embodiment can be combined with one or a plurality of other desired characteristics from other embodiments, resulting in other embodiments not described in words or by reference to the drawings. Accordingly, such other embodiments fall within the framework of the scope of the appended claims.