ULTRA HIGH STRENGTH BODY AND CHASSIS COMPONENTS

Abstract

A structural component for an automotive vehicle formed from a single-piece of steel material and having a closed, complex cross-section with increased strength, for example a strength of greater than 650 MPa, and thus improved performance, is provided. The structural component typically has an elongation of greater than 5%. The structural component is formed by expanding a boron-containing steel material, for example heating or hydroforming a tube of the steel material. The boron-containing steel material expands by least 2% during the forming process and thus achieves the closed, complex cross-section, while also achieving the high strength. In addition, the structural component can be formed with zones of varying thickness, strength, hardness, elongation, and/or other varying properties to achieve the desired performance.

Description

BACKGROUND OF THE INVENTION

1. Field of the Invention

The invention relates generally to structural components for automotive vehicles, more particularly to high strength body and chassis components formed of steel, and methods of manufacturing the same.

2. Related Art

High strength structural components formed of steel for automotive vehicles, such as rails, beams, and pillars of the vehicle body or chassis, are oftentimes formed with complex closed cross-sections, for example cross-sections which vary in shape and/or thickness. A high strength component is typically required when used in a vehicle body or chassis application. In addition, the strength, elongation, or another material property is oftentimes varied along the length of the component to enhance performance. For example, the component can include a first zone having a high strength, and a second zone having a high ductility.

One process currently used to produce a component formed of steel and having a complex cross-section includes forming a first part with a U-shaped cross-section, forming a second part with a U-shaped cross-section, and then welding the first part to the second part to provide a tubular cross-section. Hydroforming is another process used to form a steel component having a complex cross-section, for example a closed cross-section having a shape which varies along the length of the component. This process includes disposing a tube of the steel material between two dies of a hydroforming press, closing the dies, and injecting high pressure water into the ends of the tube such that the tube expands and conforms to the shape of the dies. However, the current hydroforming process is limited to use with low carbon steel, which has a low expansion during the forming process and a limited strength. A process for forming a steel component having a closed, complex, or varying cross-section with higher strength is desired.

SUMMARY OF THE INVENTION

The invention provides a method of manufacturing a structural component having a closed, complex, or varying cross-section with higher strength. The method includes providing a tube surrounding a hollow opening and extending between opposite ends, wherein the tube is formed of a steel material including boron; and expanding the steel material.

The invention also provides the structural component comprising a steel material surrounding a hollow opening and extending between opposite ends, wherein the steel material contains boron, and a cross-section of the steel material varies between the opposite ends.

BRIEF DESCRIPTION OF THE DRAWINGS

Other advantages of the present invention 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. 1A illustrates a comparative front or rear rail for an automotive vehicle having a closed cross-section and formed by joining two pieces of steel material without boron;

FIG. 1B illustrates a front or rear rail for an automotive vehicle having a closed cross-section formed by expanding a single-piece of boron-containing steel material according to a first example embodiment of the invention;

FIG. 2A illustrates a comparative front or rear frame rail for an automotive vehicle having a closed cross-section and formed by joining two pieces of steel material without boron:

FIG. 2B illustrates a front or rear frame rail for an automotive vehicle having a closed cross-section formed by expanding a single-piece of boron-containing steel material according to a second example embodiment of the invention;

FIG. 3A illustrates a comparative front end shotgun structure for an automotive vehicle formed from a steel material without boron;

FIG. 3B illustrates a front end shotgun structure for an automotive vehicle having a closed cross-section formed by expanding a single-piece of boron-containing steel material according to a third example embodiment of the invention;

FIG. 4A illustrates a comparative B-pillar for an automotive vehicle having a closed cross-section and formed by joining two pieces of steel material without boron;

FIG. 4B illustrates a B-pillar for an automotive vehicle having a closed cross-section formed by expanding a single-piece of boron-containing steel material according to a fourth example embodiment of the invention;

FIG. 5A illustrates a comparative roof rail for an automotive vehicle having a closed cross-section and formed from a steel material without boron;

FIG. 5B illustrates a roof rail for an automotive vehicle having a closed cross-section formed by expanding a single-piece of boron-containing steel material according to a fifth example embodiment of the invention;

FIG. 6A illustrates a comparative rail for an automotive vehicle having a closed cross-section and formed by joining two pieces of steel material without boron; and

FIG. 6B illustrates a rail for an automotive vehicle having a closed cross-section formed by expanding a single-piece of boron-containing steel material according to a sixth example embodiment of the invention;

DESCRIPTION OF THE EXAMPLE EMBODIMENTS

The invention provides an ultra-high strength structural component 20 for an automotive vehicle having a closed, complex cross-section formed by heating and expanding a single-piece of steel material. The steel material contains boron which provides the high strength and an expansion of 2% to 50% during the forming process. The structural component 20 can be used in various automotive vehicle applications, such as body or chassis applications. For example the structural component 20 can be used as a rail, beam, pillar, or frame. Example structural components 20 which can be formed according to embodiments of the invention, for example to replace the structural components of FIGS. 1A-6A, are shown in FIGS. 1B-6B.

The structural component 20 is formed from a boron-containing or boron-based steel material, for example medium or high carbon steel alloyed with boron. The steel material is typically iron-based, or contains iron in an amount greater than the individual amount, or possibly the total amount, of every other element present in the steel material. Medium and high carbon steels are typically preferred for automotive vehicle applications compared to low carbon steel due to the higher strength. Various boron-containing compositions can be used to form the structural component 20, for example 22MnB5 steel, 30MnB5 steel, 38MnB5 steel, or steel of the xxBxx series. The steel material is typically a boron-alloyed quenched and tempered steel.

When the steel material is 22MnB5 steel, the composition of the steel material can include carbon in an amount of 0.19 to 0.25 percent by weight (wt. %), silicon in an amount up to 0.40 wt. %, manganese in an amount of 1.10 to 1.40 wt. %, phosphorous in an amount up to 0.025 wt. %, sulfur in an amount up to 0.015 wt. %, aluminum in an amount up to 0.08 wt. %, nitrogen in an amount up to 0.01 wt. %, chromium in an amount up to 0.30 wt. %, and boron in an amount of 0.0008 to 0.0050 wt. %, based on the total weight of the steel material.

When the steel material is 30MnB5 steel, the composition of the steel material can include carbon in an amount of 0.27 to 0.32 percent by weight (wt. %), silicon in an amount of 0.15 to 0.35 wt. %, manganese in an amount of 1.15 to 1.40 wt. %, phosphorous in an amount up to 0.023 wt. %, sulfur in an amount up to 0.010 wt. %, aluminum in an amount up to 0.080 wt. %, nitrogen in an amount up to 0.010 wt. %, chromium in an amount of 0.10 to 0.25 wt. %, titanium in an amount of 0.015 to 0.045 wt. %, and boron in an amount of 0.0015 to 0.0040 wt. %, based on the total weight of the steel material.

When the steel material is 38MnB5 steel, the composition can include carbon in an amount of 0.36 to 0.40 percent by weight (wt. %), silicon in an amount of 0.15 to 0.35 wt. %, manganese in an amount of 1.20 to 1.40 wt %, phosphorous in an amount up to 0.020 wt. %, sulfur in an amount up to 0.010 wt. %, aluminum in an amount up to 0.060 wt. %, nitrogen in an amount up to 0.010 wt. %, chromium in an amount of 0.10 to 0.25 wt. %, titanium in an amount of 0.015 to 0.045 wt. %, and boron in an amount of 0.0015 to 0.0045 wt. %, based on the total weight of the steel material.

According to one example embodiment, the structural component 20 is formed by providing a tube of the steel material, heating the tube, and expanding the tube to achieve the structural component 20 having the desired complex or varying cross-sectional shape along its length. The heating step typically includes heating the tube to a temperature of 900 to 950° C. During the expansion step, at least one dimension of the tube increases by 2% to 50%. For example, the diameter, width, length, and/or height of the tube can increase by at least 2%. The structural component 20 formed typically has a width extending across a center axis A which varies along the length of the component 20. The cross-sectional shape achieved can be referred to as closed and non-circular, tubular, or O-shaped.

The boron-containing steel material is able to flow better when heated, compared to in colder states. The boron-containing steel material has an expansion of at least 2% or greater than 2%, typically greater than 10%, and up to 50% when heated to a temperature greater than 400° C. The presence of boron in the steel material allows for the formation of complex or varying cross-sectional shapes, even when the steel material has a medium or high carbon content. The expansion of at least 2% is an improvement over the expansion achieved by other steel materials which have been used in an expansion forming process, such as low carbon steels without boron. The steel material used to form the comparative structural components of FIGS. 1A-6A, for example, has an expansion of less than 2% during the forming process when heated to the same temperature. Thus, to achieve the complex, closed cross-section, two separate pieces of the comparative steel material need to be laser welded or otherwise joined together.

The boron-containing steel material used to form the single-piece structural components 20 of FIGS. 1B-6B also provides a yield strength of greater than 550 MPa and a tensile strength of greater than 650 MPa after the expansion process. The strength provided by the boron-containing steel material after the expansion process is an improvement over the comparative steel materials without boron, which provide a yield strength of less than 550 MPa and a tensile strength of less than 650 MPa after the expansion process.

In another example embodiment, a hydro-forming process is used to form the structural component 20. This process typically includes disposing the tube of boron-containing steel material between two dies of a hydroforming press, closing the dies, and injecting high pressure water into the ends of the tube such that the tube expands and conforms to the shape of the dies. The hydroforming press is typically a low tonnage press. The shape of the dies is designed to achieve the complex cross-sectional shape along the length of the structural component 20. Alternatively, another type of forming process which includes expanding the boron-containing steel material can be used to obtain the desired shape.

In addition to a cross-sectional shape which varies along the length of the component 20, the structural component 20 can also have a varying thickness along its length. For example, the example structural component 20 of FIG. 1B is formed with a first zone 26 extending from a first end 22 toward a second end 24 which has a greater thickness than a second zone 28 extending from the first zone 26 to a second end 24. Varying the thickness along the length of the component 20 can reduce weight and achieve properties which enhance performance of the structural component 20.

The structural component 20 can also be formed to have a homogenous or varying hardness, strength, elongation, ductility, and/or another varying property along its length. For example, the first zone 26 can have a higher strength and hardness than the second zone 28, and the second zone 28 can have a higher elongation and ductility. A yield strength of greater than 550 MPa, a tensile strength of greater than 650 MPa, and an elongation of greater than 5% can be achieved using the boron-containing steel material. Thus, the structural component 20 can be referred to as an ultra-high strength component.

The varying hardness, strength, elongation, and/or ductility along the length of the structural component 20 can be achieved by cooling different zones of the structural component 20 at different rates after the heating and/or forming steps. For example, the first zone 26 of the structural component 20 can be cooled to room temperature or below faster than the second zone 28

As alluded to above, the structural component 20 of the first example embodiment shown in FIG. 1B can be used in place of the comparative structural component shown in FIG. 1A. In this embodiment, the comparative structural component is formed by welding two pieces of steel material without boron together to achieve the closed cross-section. The structural component 20 of the first example embodiment shown in FIG. 1B is formed by heating and expanding a single piece of boron-containing steel material to achieve the closed and varying cross-section. The boron-containing steel material has an expansion of at least 2% during the forming process. In addition, the example structural component 20 is formed with the first zone 26 having a higher hardness and strength, for example, a yield strength of 500 MPa to 1500 MPa, and the second zone 28 having a higher ductility and elongation. Alternatively, the structural component 20 could have a homogenous yield strength of 500 MPa to 1500 MPa and an expansion of greater than 2%. In addition to being formed with a variable cross-section and strength, the structural component 20 can be formed with a variable thickness, for example a lower thickness along the second zone 28 to reduce weight. The structural components of FIGS. 1A and 1B are typically used as a front or rear rail for an automotive vehicle.

FIGS. 2B-6B illustrate other example structural components 20 which can be used in place of the structural components shown in FIGS. 2A-6A. The structural component 20 of the second example embodiment shown in FIG. 2B can be used in place of the comparative structural component shown in FIG. 2A. In this embodiment, the comparative structural component is formed by welding two pieces of steel material without boron together to achieve the closed cross-section. The structural component 20 of the second example embodiment shown in FIG. 2B is formed by heating and expanding a single tube of boron-containing steel material to achieve the closed and varying cross-section. The boron-containing steel material has an expansion of at least 2% during the forming process. In addition, the example structural component 20 is formed with several first zones 26 having a higher hardness and strength, for example a yield strength of 650 MPa to 2000 MPa, and two second zones 28 having a lower strength but higher ductility and elongation, for example an elongation of greater than 5%. The first zones 26 could have a strength, elongation, and other properties the same as or different from one another. The two second zones 28 could also have a strength, elongation, and other properties the same as or different from one another. Alternatively, the structural component 20 can be formed with a homogenous strength, hardness, ductility, and/or elongation along its length, for example a yield strength of 650 MPa to 2000 MPa, or 950 MPa to 2000 MPa, and an elongation of greater than 5%. The structural components of FIGS. 2A and 2B are typically used as a front or rear frame rail for an automotive vehicle.

The structural component 20 of the third example embodiment shown in FIG. 3B can be used in place of a comparative structural component formed using the part shown in FIG. 3A. In this embodiment, the comparative structural component is formed by welding two of the parts of steel material without boron together to achieve the closed cross-section. If the comparative structural component of FIG. 3A is formed by an expansion process, then the comparative structural component has a limited expansion and/or limited strength. The structural component 20 of the third example embodiment shown in FIG. 3B is formed by heating and expanding a tube of boron-containing steel material to achieve the closed and varying cross-section. The boron-containing steel material has an expansion of at least 2% during the forming process. This example structural component 20 also has a yield strength 700 MPa to 2000 MPa, for example 780 MPa or greater, and an elongation of greater than 5%, for example around 10% or greater. The structural components of FIGS. 3A and 3B are typically used as a front end shotgun structure for an automotive vehicle. The properties and shape of the example structural component 20 provide for narrow offset in the event of a crash.

The structural component 20 of the fourth example embodiment shown in FIG. 4B can be used in place of the comparative structural component shown in FIG. 4A. In this embodiment, the comparative structural component is formed by welding two pieces of steel material without boron together to achieve the closed cross-section. The structural component 20 of the fourth example embodiment shown in FIG. 4B is formed by heating and expanding three pieces of boron-containing steel material together to achieve the closed cross-section, and then tailor welding the three pieces together. The boron-containing steel material has an expansion of at least 2% during the forming process. The three pieces provide two first zones 26 having a higher strength spaced from one another by a second zone 28 having a lower strength. The first zones 26 have a tensile strength of 980 MPa to 2000 MPa, and the second zone has a tensile strength of 610 MPa to 980 MPa. The three pieces also have different cross-sectional shapes. During the tailor welding process, transition zones 30 are formed between the different zones. The tailor welding process also provides a varying thickness along the length of the structural component 20. The structural components of FIGS. 4A and 4B are typically used as a B-pillar along the side body of an automotive vehicle.

The structural component 20 of the fifth example embodiment shown in FIG. 5B can be used in place of the comparative structural component shown in FIG. 5A. In this embodiment, the comparative structural component is formed by expanding a tube of steel material without boron to achieve the closed cross-section. However, in this case, the expansion provided by the steel material without boron is limited to around or below 2%. The structural component 20 of the fifth example embodiment shown in FIG. 5B is formed by heating and expanding a tube of boron-containing steel material to achieve the closed and varying cross-section. The boron-containing steel material has an expansion of at least 3% during the forming process. The material located in the center of the structural component 20 has an expansion of up to 30%. This example structural component 20 also achieves a yield strength 980 MPa to 2000 MPa and an elongation of greater than 5%. The structural components of FIGS. 5A and 5B are typically used as a roof rail of an automotive vehicle.

The structural component 20 of the sixth example embodiment shown in FIG. 6B can be used in place of the comparative structural component shown in FIG. 6A. In this embodiment, the comparative structural component is formed by welding two pieces of steel material without boron together to achieve the closed cross-section. If the structural component of FIG. 6A is formed by an expansion process, then the comparative structural component has a limited expansion and/or limited strength. The structural component 20 of the sixth example embodiment shown in FIG. 6B is formed by heating and expanding a single tube of boron-containing steel material to achieve the closed cross-section. The boron-containing steel material has an expansion of at least 2% during the forming process. This example structural component 20 also achieves a yield strength 700 MPa to 2000 MPa, for example 1500 MPa, and an elongation of greater than 5%. The structural components of FIGS. 6A and 6B are typically used as a beam for an automotive vehicle. The components of FIGS. 6A and 6B are also formed with holes to reduce weight.

Many modifications and variations of the present disclosure are possible in light of the above teachings and may be practiced otherwise than as specifically described while within the scope of the claims.

Claims

1. A method of manufacturing a structural component, comprising the steps of: providing a tube surrounding a hollow opening and extending between opposite ends, the tube being formed of a steel material including boron; andexpanding the steel material.

2. The method of claim 1, wherein the expanding step includes disposing the tube between a pair of dies and injecting water under pressure into the hollow opening of the tube.

3. The method of claim 1, wherein the expanding step includes heating the steel material to a temperature greater than 400° C.

4. The method of claim 1, wherein the steel material expands by at least 2% when heated to a temperature greater than 400° C. or when the hollow opening is filled with water under pressure.

5. The method of claim 1, wherein the steel material expands by greater than 10% and up to 50% when heated to a temperature greater than 400° C. or when the hollow opening is filled with water under pressure.

6. The method of claim 1, wherein the expanding step includes increasing the area of the cross-sectional opening between the opposite ends.

7. The method of claim 1, wherein the expanding step includes varying the thickness of the tube between the opposite ends.

8. The method of claim 1, wherein the steel material of at least one zone of the tube has a yield strength of greater than 550 MPa and a tensile strength of greater than 650 MPa after the expanding step.

9. A structural component, comprising: a steel material surrounding a hollow opening and extending between opposite ends;the steel material containing boron; anda cross-section of the steel material varying between the opposite ends.

10. The structural component of claim 9, wherein the steel material has a yield strength of greater than 550 MPa and a tensile strength of greater than 650 MPa.

11. The structural component of claim 9, wherein at least one of the thickness of the structural component and the cross-sectional area of the hollow opening varies between the opposite ends.

12. The structural component of claim 9, wherein at least one of the strength, hardness, elongation, and ductility of the structural component varies between the opposite ends.

13. The structural component of claim 9, wherein the steel material includes carbon in an amount of 0.19 to 0.25 percent by weight (wt. %), silicon in an amount up to 0.40 wt. %, manganese in an amount of 1.10 to 1.40 wt. %, phosphorous in an amount up to 0.025 wt. %, sulfur in an amount up to 0.015 wt. %, aluminum in an amount up to 0.08 wt. %, nitrogen in an amount up to 0.01 wt. %, chromium in an amount up to 0.30 wt. %, and boron in an amount of 0.0008 to 0.0050 wt. %, based on the total weight of the steel material.

14. The structural component of claim 9, wherein the steel material includes carbon in an amount of 0.27 to 0.32 percent by weight (wt. %), silicon in an amount of 0.15 to 0.35 wt. %, manganese in an amount of 1.15 to 1.40 wt. %, phosphorous in an amount up to 0.023 wt. %, sulfur in an amount up to 0.010 wt. %, aluminum in an amount up to 0.080 wt. %, nitrogen in an amount up to 0.010 wt. %, chromium in an amount of 0.10 to 0.25 wt. %, titanium in an amount of 0.015 to 0.045 wt. %, and boron in an amount of 0.0015 to 0.0040 wt. %, based on the total weight of the steel material.

15. The structural component of claim 9, wherein the steel material includes carbon in an amount of 0.36 to 0.40 percent by weight (wt. %), silicon in an amount of 0.15 to 0.35 wt. %, manganese in an amount of 1.20 to 1.40 wt. %, phosphorous in an amount up to 0.020 wt. %, sulfur in an amount up to 0.010 wt. %, aluminum in an amount up to 0.060 wt. %, nitrogen in an amount up to 0.010 wt. %, chromium in an amount of 0.10 to 0.25 wt. %, titanium in an amount of 0.015 to 0.045 wt. %, and boron in an amount of 0.0015 to 0.0045 wt. %, based on the total weight of the steel material.

16. The method of claim 1, wherein at least one of the thickness of the structural component and the cross-sectional area of the hollow opening varies between the opposite ends.

17. The method of claim 1, wherein at least one of the strength, hardness, elongation, and ductility of the structural component varies between the opposite ends.

18. The method of claim 1, wherein the steel material includes carbon in an amount of 0.19 to 0.25 percent by weight (wt. %), silicon in an amount up to 0.40 wt. %, manganese in an amount of 1.10 to 1.40 wt. %, phosphorous in an amount up to 0.025 wt. %, sulfur in an amount up to 0.015 wt. %, aluminum in an amount up to 0.08 wt. %, nitrogen in an amount up to 0.01 wt. %, chromium in an amount up to 0.30 wt. %, and boron in an amount of 0.0008 to 0.0050 wt. %, based on the total weight of the steel material.

19. The method of claim 1, wherein the steel material includes carbon in an amount of 0.27 to 0.32 percent by weight (wt. %), silicon in an amount of 0.15 to 0.35 wt. %, manganese in an amount of 1.15 to 1.40 wt. %, phosphorous in an amount up to 0.023 wt. %, sulfur in an amount up to 0.010 wt. %, aluminum in an amount up to 0.080 wt. %, nitrogen in an amount up to 0.010 wt. %, chromium in an amount of 0.10 to 0.25 wt. %, titanium in an amount of 0.015 to 0.045 wt. %, and boron in an amount of 0.0015 to 0.0040 wt. %, based on the total weight of the steel material.

20. The method of claim 1, wherein the steel material includes carbon in an amount of 0.36 to 0.40 percent by weight (wt. %), silicon in an amount of 0.15 to 0.35 wt. %, manganese in an amount of 1.20 to 1.40 wt. %, phosphorous in an amount up to 0.020 wt. %, sulfur in an amount up to 0.010 wt. %, aluminum in an amount up to 0.060 wt. %, nitrogen in an amount up to 0.010 wt. %, chromium in an amount of 0.10 to 0.25 wt. %, titanium in an amount of 0.015 to 0.045 wt. %, and boron in an amount of 0.0015 to 0.0045 wt. %, based on the total weight of the steel material.