NON-PNEUMATIC TIRE HAVING CURVED SPOKES AND METHOD FOR MAKING SAME - Patent application

Abstract

The non-pneumatic tire includes a lower ring having a first diameter and an upper ring having a second diameter greater than the first diameter. The upper ring is substantially coaxial with the lower ring. The non-pneumatic tire further includes a plurality of curved steel spokes extending between the lower ring and the upper ring. Each of the plurality of curved steel spokes has a 0.2% yield strength of at least 1300 MPA, a tensile strength of at least 1400 MPa, and a hardness of at least 50 HRC.

Description

[Technical field]

[0001] FIELD OF THE DISCLOSURE This disclosure relates to non-pneumatic tires having curved spokes and methods of making same, and more particularly, to non-pneumatic tires having curved steel spokes and methods of making same. Summary of the Invention [Problem to be solved by the invention]

[0002] Various tire constructions have been developed that allow the tire to run in an uninflated or underinflated state. Non-pneumatic tires do not require inflation, but "run-flat tires" can continue to operate at relatively high speeds for extended periods of time after a puncture that results in a complete or partial loss of pressurized air. Non-pneumatic tires may include a number of spokes, webbing, or other support structures connecting an inner ring to an outer ring.

[0003] In one embodiment, a method of making a non-pneumatic tire includes providing a rolled sheet of steel having a carbon content of 0.20% to 0.60%. The sheet has a thickness of 1.5 mm to 7 mm. The method further includes unrolling the rolled sheet of steel and tailor rolling the sheet of steel such that the thickness of the sheet varies periodically along its length between a minimum thickness and a maximum thickness. The minimum thickness is at least 1.2 mm and the maximum thickness is no greater than 4.5 mm. The method also includes cutting the sheet into blanks including one or more thick sections and one or more thin sections of steel. The length of each blank is equal to the width of the sheet. The method further includes rotating each blank 90 degrees and roll forming each blank to form a curve along the width of the blank with the one or more thick sections and the one or more thin sections parallel along the length of the blank. The method also includes heating each blank to a temperature between 950°C and 1400°C for 2 to 10 seconds, and cooling each blank to a temperature less than 200°C within 10 seconds. The method further includes cutting each blank into a plurality of steel spokes having widths between 80mm and 400mm. The method also includes providing a lower ring and an upper ring, and disposing the plurality of steel spokes between the lower ring and the upper ring.

[0004] In another embodiment, a non-pneumatic tire includes a lower ring having a first diameter and an upper ring having a second diameter greater than the first diameter. The upper ring is substantially coaxial with the lower ring. The non-pneumatic tire further includes a plurality of curved steel spokes extending between the lower ring and the upper ring. Each of the plurality of curved steel spokes has a 0.2% yield strength of at least 1300 MPA, a tensile strength of at least 1400 MPa, and a hardness of at least 50 HRC.

[0005] In yet another embodiment, a method of manufacturing spokes for a non-pneumatic tire includes providing a rolled sheet of steel having a carbon content of 0.28% to 0.50%, unrolling the rolled sheet of steel, and roll forming the steel sheet to form a curve along its width. The method also includes heating the steel sheet to a temperature of 950°C to 1400°C for 2 to 10 seconds, and cooling the steel sheet to a temperature of less than 200°C within 10 seconds. The method further includes cutting steel spokes from the steel sheet, the steel spokes having a width of 80mm to 400mm. [Brief description of the drawings]

[0006] The accompanying drawings, together with the detailed description provided below, illustrate structures that describe exemplary embodiments of the claimed invention. Similar elements are identified with the same reference numerals. It should be understood that elements shown as a single component may be replaced with multiple components, and elements shown as multiple components may be replaced with a single component. The drawings are not to scale, and the proportions of certain elements may be exaggerated for illustrative purposes.

[0007] [Figure 1] FIG. 1 is a front view of one embodiment of a non-pneumatic tire. [Diagram 2] FIG. 2 is a flow chart illustrating one embodiment of a method for making spokes for a non-pneumatic tire. [Diagram 3] FIG. 3 is a pictorial diagram of the method illustrated in the flow chart of FIG. [Figure 4] FIG. 4 is a flow chart illustrating an alternative embodiment of a method for making spokes for a non-pneumatic tire. [Diagram 5] FIG. 5 is a pictorial diagram of the method illustrated in the flow chart of FIG. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0008] The following contains definitions of select terms used herein. These definitions include various examples and / or forms of components that fall within the scope of the term and may be used for implementation. The examples are not intended to be limiting. Both the singular and plural forms of a term may be within the scope of the definition.

[0009] "Axial" and "axially" refer to the direction parallel to the axis of rotation of the tire.

[0010] "Circumferential" and "circumferentially" refer to a direction extending along the perimeter of the surface of the tread perpendicular to the axial direction.

[0011] "Radial" and "radially" refer to directions perpendicular to the axis of rotation of the tire.

[0012] As used herein, "tread" refers to that portion of the tire that comes into contact with the road or ground under normal inflation and normal load.

[0013] It should be understood that, although similar terms are used in the following description to describe typical tire components, the terms, of course, have slightly different connotations and one of ordinary skill in the art would not consider any of the following terms to be purely interchangeable with another term used to describe typical tire components.

[0014] As used herein, directions are stated with reference to the tire's axis of rotation. The terms "upward" and "upwardly" refer to the general direction toward the tire's tread, and "downward" and "downwardly" refer to the general direction toward the tire's axis of rotation. Thus, when relative directional terms such as "upper" and "lower" or "top" and "bottom" are used in connection with elements, the "upper" or "top" element is spaced closer to the tread than the "lower" or "bottom" element. Additionally, when relative directional terms such as "on" or "under" are used in connection with elements, an element that is "on" another element is closer to the tread than the other element.

[0015] The terms "inward" and "inwardly" refer to the general direction toward the tire's equatorial plane, and "outward" and "outwardly" refer to the general direction away from the tire's equatorial plane, toward the tire's sidewall. Thus, when relative directional terms such as "inner" and "outer" are used in connection with elements, the "inner" elements are spaced closer to the tire's equatorial plane than the "outer" elements.

[0016] 1 is a front view of one embodiment of a non-pneumatic tire 100. The non-pneumatic tire 100 includes a lower ring 130 having a first diameter and an upper ring 140 having a second diameter larger than the first diameter. The upper ring 140 is coaxial with the lower ring 130. The lower ring 130 can be engaged with a vehicle hub (not shown) for mounting the non-pneumatic tire 100 to a vehicle.

[0017] The spokes 200 extend between the lower ring 130 and the upper ring 140 and connect the lower ring 130 to the upper ring 140. In the illustrated embodiment, the spokes 200 are curved. In alternative embodiments, the spokes may have a more pronounced curve, such as being substantially C-shaped. In other alternative embodiments, the spokes may have any desired shape. For example, the spokes may be substantially V-shaped or serpentine-shaped. In yet other alternative embodiments, the non-pneumatic tire may include spokes of two or more different shapes. For example, the non-pneumatic tire may include C-shaped spokes alternating with V-shaped spokes along the circumference of the non-pneumatic tire. In yet another alternative embodiment, the spokes may be replaced with webbing or other support structure.

[0018] A circumferential tread 210 is attached to the top ring 140. The circumferential tread 210 may be constructed of rubber or other elastomeric material and may include tread elements (not shown), such as grooves, ribs, blocks, lugs, sipes, studs, or any other desired elements. In alternative embodiments, the tread layer may be omitted and the tread elements may be formed directly on the top ring.

[0019] The other components of the non-pneumatic tire 100 may be made from a variety of materials. The lower ring 130 or upper ring 140 may be made from an elastomeric material, plastic, composite material, or metal. The spokes 200 may also be made from an elastomeric material, plastic, composite material, or metal. In alternative embodiments, the lower ring, upper ring, or tread band may be made from any desired material. Particular materials may be selected for particular components to provide a non-pneumatic tire with desired performance characteristics.

[0020] In some embodiments, it is desirable to construct the spokes from very high strength steel. However, it is difficult to form very high strength steel into curved shapes (such as a constant radius) because the steel has a tendency to return to its previous shape after bending. This property is sometimes referred to as the "springback" of the steel. This tendency becomes stronger as the strength of the steel increases. Forming ultra-high strength steel requires much higher pressing forces than conventional steels, thus necessitating the use of specialized high tonnage presses or roll forming equipment. This need for specialized equipment significantly increases processing costs and may therefore limit the number of companies with the capability to produce such parts.

[0021] Very high strength steels are often over-bent beyond the desired shape to allow them to relax back to the desired shape due to their tendency to spring back. In practice, the relaxation is often inconsistent between different coils of steel, resulting in poor dimensional control. Thus, over-bent steel components must often be reconditioned. Forming operations must also be adjusted to compensate for springback differences between coils. Residual stresses from the forming process may also vary due to the forming and reconditioning processes, causing inconsistencies in fatigue durability.

[0022] One known solution to this problem is to use hot forming grade steels, which can be formed at high temperatures and then quenched to form a martensitic structure with the required mechanical properties. An example of a hot forming grade steel is the Usibor grade press hardened steel from ArcelorMittal. This steel can only be used in a hot stamping process where individual flat blanks are heated to about 950°C, then quickly stamped in a die and rapidly cooled to below 200°C while under pressure in the die to form the individual spokes. This process is very slow and expensive due to the high temperatures and the complexity of the cooling system required for the die.

[0023] Another known solution is to form the steel into a low strength structure and then increase the strength by using a heat treatment process to change the crystal structure of the steel to martensite or bainite. For conventional steels classified as high strength, with an ultimate tensile strength of about 400-600 MPa, it is possible to roll form bends or C-shapes in successive cross sections and achieve consistent results. Adjustments to compensate for slight differences in strength between coils can be made using laser measurement systems and direct feedback to tighten or loosen the forming rolls. This process can be done from a coil of steel as a continuous process. The formed channels can then either be cut into individual components or cut as longer lengths. For practical reasons, handling lengths over 4m or 5m becomes very difficult.

[0024] Existing processes of roll forming steel and then heat treating the rolled steel can cause thermal distortion of the component as it is gradually heated and the residual stresses are relieved. Rapid cooling to "harden" the microstructure can then induce further residual stresses that can cause distortion or lead to premature fatigue failure due to residual tensile stress concentrations in localized areas. Taking steps such as clamping and supporting the component to prevent distortion can be successful, but this is expensive and impractical for high volume production.

[0025] An improved solution to the springback problem is disclosed herein. In this improved solution, the component is rapidly heated using induction heating and then rapidly cooled by water cooling or quenching. The process of rapidly heating and cooling the component within a few seconds creates a bainite structure in the steel. The rapid heating and rapid cooling - or flash process - reduces the opportunity for thermal distortion or residual stresses to occur. In one test using 4140 steel components, the flash process described above resulted in a significant increase in strength compared to the conventional process, as shown in Table 1. [Table 1]

[0026] Figure 2 is a flow chart illustrating one embodiment of such a method 300 for manufacturing spokes for non-pneumatic tires. The method 300 includes providing (310) a heat treatable rolled sheet. The sheet has a thickness between 1.5 mm and 7 mm. In one embodiment, the sheet has a width of 1.5 m or less.

[0027] In one embodiment, the heat treatable steel is 4130 steel. In an alternative embodiment, the heat treatable steel may be 4140 or 4150 steel. The heat treatable steel may have a carbon content of 0.28% to 0.50%. In an alternative embodiment, the heat treatable steel may have a carbon content of 0.20% to 0.55%. In another alternative embodiment, the heat treatable steel may have a carbon content of 0.20% to 0.60%. The heat treatable steel may also have a manganese content of 0.40% to 1.0%.

[0028] Although the disclosed process is described for very high strength steels, it should be understood that other steel options may be used, such as 1080 steel. Thus, in an alternative embodiment, the process may be used with steels having a carbon content of 0.001% to 4.0%. Additionally, the method may be used with steels having a manganese content of 0.30% to 1.0%.

[0029] The rolled sheet is unrolled and then roll formed to impart a curve, bend, or other shape along its width. The roll forming process may form any desired spoke shape in the strip (320). In one embodiment, an arc is formed in the strip, where the arc is defined by a single radius. In an alternative embodiment, a curvature is formed in the strip, where the curvature is defined by multiple radii. In another alternative embodiment, a V-shaped bend is formed in the strip. It should be understood that multiple arcs or bends may be formed in the strip.

[0030] The strip is then optionally preheated. In one embodiment, the strip is preheated to a temperature of between 450° C. and 650° C. Preheating may be performed in an electric furnace or a gas furnace. Alternatively, the preheating step may be omitted.

[0031] The strip is then heated (330) to a temperature of 950°C to 1400°C. The strip may be heated to this temperature for 2 to 10 seconds. Thus, this is sometimes referred to as a rapid heating step. The heating step may be performed in a heating unit. Exemplary heating units include, but are not limited to, electrical resistance heaters, fluidized beds, electric furnaces, plasma furnaces, microwave ovens, open environment propane burners, gas combustion units, solid fuels, hot salt baths, torches, induction heaters, and any combination thereof.

[0032] The strip is heated to a temperature between 950°C and 1400°C and then cooled (340) to a temperature below 200°C. The strip may be cooled to this temperature in less than 10 seconds. Therefore, this step may be referred to as a rapid cooling step. In one embodiment, the strip is cooled by quenching the strip in a quenching agent. Exemplary quenching agents include, but are not limited to, water, aqueous solutions containing water, oil, brine solutions, air, and powders.

[0033] After the strip has been rapidly heated and then rapidly cooled, it is cut 350 into a plurality of steel spokes. In one embodiment, each spoke has a width of between 80 mm and 400 mm. However, it should be understood that the strip may be cut to any desired width.

[0034] After the strip is cut, any finishing process may be applied. For example, at least one edge of the spokes may be machined (360). The machining process may impart a rounded or chamfered edge. Alternatively, the machining may impart square corners or any geometric shape to the edge. As another example, one or more surfaces may be peened (370), such as by a shot peening or laser peening process. Those skilled in the art will appreciate that other known finishing processes may be applied to each spoke.

[0035] Spokes resulting from this process have been shown to have a tensile strength of at least 1400 MPa, a 0.2% yield strength of at least 1300 MPA, and a hardness of at least 50 HRC. These properties can be altered by adjusting any number of steps in the flash process.

[0036] In another embodiment, a non-pneumatic tire includes a lower ring having a first diameter and an upper ring having a second diameter larger than the first diameter. The tire manufacturer may then arrange the lower and upper rings so that they are coaxial and extend a plurality of steel spokes between the lower and upper rings. The plurality of spokes may be attached to the lower and upper rings by a welding or brazing process. Alternatively, the plurality of spokes may be connected to the lower and upper rings by pins, adhesives, or other fasteners. For example, the plurality of spokes may be hinged to one or both of the lower and upper rings. In one known embodiment, one or more of the upper and lower rings may have slots for receiving the spokes.

[0037] When the spokes are assembled to the upper and lower rings, each spoke may extend axially across the entire width of the lower ring and across the entire width of the upper ring. Alternatively, one or more of the spokes may extend less than the entire width of the lower ring and across the entire width of the upper ring. In certain embodiments, two or more rows of spokes may extend axially across the entire upper and lower rings. When two or more rows of spokes are used, the spokes in adjacent rows may bend in opposite directions. Alternatively, when two or more rows of spokes are used, the spokes in adjacent rows may bend in the same direction.

[0038] An elastomeric tread may then be extended around the upper ring, and the resulting non-pneumatic tire may be similar to the non-pneumatic tire 100 shown in FIG.

[0039] Figure 3 is a pictorial diagram of a method (400) for making spokes. This method is substantially similar to the method 300 shown in the flow chart of Figure 2. As seen in this figure, the method 400 includes providing a steel coil (410). The steel coil may have the same properties as described above with respect to Figure 2. The steel is then roll formed (420), rapidly heated (430), and quenched (440). The steel is then cut to the desired spoke length (450).

[0040] 4 is a flow chart illustrating an alternative embodiment of a method 500 for making spokes for a non-pneumatic tire. The method 500 includes providing 510 a heat treatable rolled sheet. The sheet has a thickness between 1.5 mm and 7 mm. In one embodiment, the sheet has a width of 2.0 mm or less.

[0041] In one embodiment, the heat treatable steel is 4130 steel. In an alternative embodiment, the heat treatable steel may be 4140 or 4150 steel. The heat treatable steel may have a carbon content of 0.28% to 0.50%. In an alternative embodiment, the heat treatable steel may have a carbon content of 0.20% to 0.55%. In another alternative embodiment, the heat treatable steel may have a carbon content of 0.20% to 0.60%. The heat treatable steel may also have a manganese content of 0.40% to 1.0%.

[0042] Although the disclosed process is described for very high strength steels, it should be understood that other steel options may be used, such as 1080 steel. Thus, in an alternative embodiment, the process may be used with steels having a carbon content of 0.001% to 4.0%. Additionally, the method may be used with steels having a manganese content of 0.30% to 1.0%.

[0043] The rolled sheet of steel is unwound and then tailor rolled (520). The tailor rolling process imparts a continuous thickness transition between a minimum thickness and a maximum thickness. In one embodiment, the sheet of steel is tailor rolled such that the thickness varies periodically along its length between a minimum thickness of 1.2 mm and a maximum thickness of 4.5 mm.

[0044] The sheet of steel is then cut into blanks that include one or more thick sections and one or more thin sections of steel (530). The blanks may be cut to a length equal to the width of the coil. After each blank is cut, it is rotated 90 degrees (540).

[0045] The turned blank is then roll formed to impart a curve, bend, or other shape along its width. The roll forming process may form any desired spoke shape in the blank (550). In one embodiment, an arc is formed in the blank, the arc being defined by a single radius. In an alternative embodiment, a curve is formed in the blank, the curve being defined by multiple radii. In another alternative embodiment, a V-shaped bend is formed in the blank. It should be understood that multiple arcs or bends may be formed in the blank.

[0046] The blank is then optionally preheated. In one embodiment, the blank is preheated to a temperature between 450° C. and 650° C. Preheating can be performed in an electric furnace or a gas furnace. Also, the preheating step can be omitted.

[0047] The blank is then heated (560) to a temperature of 950°C to 1400°C. The blank may be heated to this temperature for 2 to 10 seconds. Thus, this is sometimes referred to as a rapid heating step. The heating step may be performed in a heating unit. Exemplary heating units include, but are not limited to, electrical resistance heaters, fluidized beds, electric furnaces, plasma furnaces, microwave ovens, open environment propane burners, gas combustion units, solid fuels, high temperature salt baths, torches, induction heaters, and any combination thereof.

[0048] The blank is heated to a temperature between 950°C and 1400°C and then cooled (570) to a temperature below 200°C. The blank can be cooled to this temperature in less than 10 seconds. Therefore, this step is sometimes referred to as a rapid cooling step. In one embodiment, the blank is cooled by quenching the blank in a quench material. Exemplary quench materials include, but are not limited to, water, aqueous solutions containing water, oil, brine solutions, air, and powders.

[0049] The blank is rapidly heated and then rapidly cooled before being cut (580) into a plurality of steel spokes. In one embodiment, each spoke has a width of between 80 mm and 400 mm. However, it should be understood that the blank may be cut to any desired width.

[0050] Due to the tailor rolling and rotating of the blanks prior to the roll forming process, each blank has a thickness that varies along its length, in one embodiment the thickness varies from a minimum thickness of 1.2 mm to a maximum thickness of 4.5 mm.

[0051] After the blank is cut, any finishing process may be applied. For example, at least one edge of the spoke may be machined (590). The machining process may impart a rounded or chamfered edge. Alternatively, the machining may impart square corners or any geometric shape to the edge. As another example, one or more surfaces may be peened (595), such as by a shot peening or laser peening process. Those skilled in the art will appreciate that other known finishing processes may be applied to each spoke.

[0052] Spokes resulting from this process have been shown to have a tensile stress of at least 1400 MPa, a 0.2% yield strength of at least 1300 MPA, and a hardness of at least 50 HRC. These properties can be altered by adjusting any number of steps in the flash process.

[0053] In another embodiment, a non-pneumatic tire includes a lower ring having a first diameter and an upper ring having a second diameter larger than the first diameter. The tire manufacturer may then arrange the lower and upper rings so that they are coaxial and extend a plurality of steel spokes between the lower and upper rings. The plurality of spokes may be attached to the lower and upper rings by a welding or brazing process. Alternatively, the plurality of spokes may be connected to the lower and upper rings by pins, adhesives, or other fasteners. For example, the plurality of spokes may be hinged to one or both of the lower and upper rings. In one known embodiment, one or more of the upper and lower rings may have slots for receiving the spokes.

[0054] When the spokes are assembled to the upper and lower rings, each spoke may extend axially across the entire width of the lower ring and across the entire width of the upper ring. Alternatively, one or more of the spokes may extend less than the entire width of the lower ring and across the entire width of the upper ring. In certain embodiments, two or more rows of spokes may extend axially across the entire upper and lower rings. When two or more rows of spokes are used, the spokes in adjacent rows may bend in opposite directions. Alternatively, when two or more rows of spokes are used, the spokes in adjacent rows may bend in the same direction.

[0055] An elastomeric tread may then be extended around the upper ring. The resulting non-pneumatic tire may be similar to the non-pneumatic tire 100 shown in FIG. 1. It should be understood that the method 500 of FIG. 4 is merely exemplary. In alternative embodiments, the hub may be rolled or certain steps may be omitted. For example, the strip may be cut into blanks without undergoing a tailor rolling process.

[0056] FIG. 5 is a pictorial diagram of a method (600) for making spokes. This method is substantially similar to the method 500 shown in the flow chart of FIG. 4. As seen in this figure, the method 600 includes providing a steel coil (610). The steel coil may have the same characteristics as described above with respect to FIG. 4. The steel coil is tailor rolled (620), cut (630), and turned (640). The steel coil is then roll formed (650), flash heated (660), and quenched (670). The steel coil is then cut to the desired spoke length (680).

[0057] The terms "includes" or "including", to the extent that they are used in this specification or in the claims, are intended to be inclusive, similar to the term "comprising", as interpreted when used as a transitional term in the claims. Furthermore, to the extent that the term "or" is used (e.g., A or B), it is intended to mean "A or B, or both". When applicants intend to indicate "only A or B but not both", the term "only A or B but not both" is used. Thus, the use of the term "or" herein is inclusive, not exclusive. See Bryan A. Garner, A Dictionary of Modern Legal Usage 624 (2d.Ed.1995). Also, the terms "in" or "into", to the extent that they are used in this specification or in the claims, are intended to additionally mean "on" or "onto". Furthermore, to the extent the term "connect" is used in this specification or the claims, it is intended to mean not only "directly connected to," but also "indirectly connected to," such as connected via one or more other components.

[0058] While the present application has been illustrated by the description of its embodiments, and those embodiments have been described in considerable detail, it is not the intention of the applicants to restrict or in any manner limit the scope of the appended claims to such details. Additional advantages and modifications will be readily apparent to those skilled in the art. Thus, the present application in its broader aspects is not limited to the specific details, representative apparatus and methods, and examples shown and described. Thus, departures may be made from such details without departing from the spirit or scope of the applicants' general inventive concept.

Claims

1. 1. A method of making a non-pneumatic tire, the method comprising: Providing a rolled sheet of steel having a carbon content of 0.20% to 0.60%, said sheet having a thickness of 1.5 mm to 7 mm; unwinding the rolled sheet of steel; tailor rolling the steel sheet such that the thickness of the sheet varies periodically along its length between a minimum thickness and a maximum thickness; said minimum thickness being at least 1.2 mm; said maximum thickness being 4.5 mm or less; and cutting the sheet into blanks including one or more thick sections and one or more thin sections of steel, the length of each blank being equal to the width of the sheet; rotating each blank 90 degrees; roll forming each blank to form a curve along a width of the blank with one or more thick portions and one or more thin portions parallel along the length of the blank; heating each blank to a temperature of 950°C to 1400°C for 2 to 10 seconds; Cooling each blank to a temperature below 200° C. within 10 seconds; cutting each blank into a plurality of steel spokes having a width between 80 mm and 400 mm; Providing a lower ring and an upper ring; and disposing the plurality of steel spokes between the lower ring and the upper ring.

2. 10. The method of claim 1, wherein the step of heating each blank comprises heating each blank with a heating unit selected from the group consisting of an electric resistance heater, a fluidized bed, an electric furnace, a plasma furnace, a microwave oven, an open environment propane burner, a gas combustion unit, a solid fuel, a high temperature salt bath, a torch, an induction heater, and any combination thereof.

3. 10. The method of claim 1, wherein the step of cooling each blank comprises rapidly quenching the blank with a quenching material selected from the group consisting of water, a water-containing aqueous solution, oil, a brine solution, air, and a powder.

4. The method of claim 1 , further comprising the step of machining at least one edge of each of said plurality of steel spokes.

5. The method of claim 1 , further comprising the step of peening at least one surface of each of said plurality of steel spokes.

6. The method of claim 1 , wherein the steps of heating and cooling each blank result in a blank having a tensile strength of at least 1400 MPa.

7. 2. The method of claim 1, wherein the steps of heating and cooling each blank result in a blank having a 0.2% yield strength of at least 1300 MPA.

8. The method of claim 1 , wherein the steps of heating and cooling each blank result in a sheet of steel having a hardness of at least 50 HRC.

9. The method of claim 1 further comprising circumferentially installing a tread around the upper ring.

10. 2. The method of claim 1, further comprising preheating each blank to a temperature of between 450°C and 650°C prior to heating each blank to a temperature of between 950°C and 1400°C.

11. The method of claim 10, wherein preheating the blank to a temperature of between 450°C and 650°C is performed using one of an electric furnace and a gas furnace.

12. A non-pneumatic tire, a lower ring having a first diameter; an upper ring having a second diameter greater than the first diameter and substantially coaxial with the lower ring; a plurality of curved steel spokes extending between the lower ring and the upper ring; 2. A non-pneumatic tire, wherein each of said plurality of curved steel spokes has a 0.2% yield strength of at least 1300 MPA, a tensile strength of at least 1400 MPa, and a hardness of at least 50 HRC.

13. 13. The non-pneumatic tire of claim 12, wherein each of said plurality of curved steel spokes has a carbon content of between 0.28% and 0.50%.

14. The non-pneumatic tire of claim 12 wherein at least one of said plurality of curved steel spokes has a variable thickness.

15. 15. The non-pneumatic tire of claim 14, wherein said at least one of said plurality of curved steel spokes having variable thickness has a minimum thickness of 1.2 mm and a maximum thickness of 4.5 mm.

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