LASER SPOT HARDENING
A hardened/stiffened steel component includes a steel substrate having a bulk region and a steel substrate surface. Plurality of localized martensite-enriched regions is located at the steel substrate surface. Characteristically, the plurality of localized martensite-enriched regions has higher martensite content than the bulk region. Centers of adjacent localized martensite-enriched regions in the plurality of martensite-enriched localized regions are separated by a separation distance that is from about 0.5 to 5 mm. A method for forming the steel component by laser spot hardening is also provided.
In at least one aspect, the present invention is related to steel components that are laser spot hardened.
BACKGROUNDIt is known that motor vehicles have a large number of metal and, in particular, steel components. Such components are used because of the easy formability of metal into automobile parts and the strength provided. However, automobile manufacturers are under pressure to reduce a vehicles weight in order to improve fuel efficiency. Therefore, reducing the thickness of metal components is desirable. However, a thickness reduction can lower the rigidity of such components.
Accordingly, there is a need for steel components that maintain rigidity while also decreasing weight.
SUMMARYThe present invention solves one or more problems of the prior art by providing in at least one embodiment, a steel component with improved stiffness and hardness. The steel component includes a steel substrate having a bulk region and a steel substrate surface. Plurality of localized martensite-enriched regions is located at the steel substrate surface. Characteristically, the plurality of localized martensite-enriched regions has higher martensite content than the bulk region. Centers of adjacent localized martensite-enriched regions in the plurality of martensite-enriched localized regions are separated by a separation distance that is from about 0.5 to 5 mm.
In another embodiment, a method for forming the hardened/stiffened steel component set forth above is provided. The method includes a step of providing a steel substrate having a bulk region and a steel substrate surface. The steel substrate is laser spot hardened at a plurality of locations on the steel substrate surface with a laser welding system that includes a laser to form a plurality of localized martensite-enriched regions located at the steel substrate surface. The plurality of localized martensite-enriched regions has higher martensite content than the bulk region. Centers of adjacent localized martensite-enriched regions in the plurality of localized martensite-enriched regions are separated by a separation distance that is from about 0.5 to 5 mm. Advantageously, the increase or decrease of the components strength and stiffness is controlled by the distribution and the size of the laser spot weld. Automotive seat structures or components exhibit predictable and repeatable load path performance with zero increase in mass.
Reference will now be made in detail to presently preferred compositions, embodiments and methods of the present invention, which constitute the best modes of practicing the invention presently known to the inventors. The Figures are not necessarily to scale. However, it is to be understood that the disclosed embodiments are merely exemplary of the invention that may be embodied in various and alternative forms. Therefore, specific details disclosed herein are not to be interpreted as limiting, but merely as a representative basis for any aspect of the invention and/or as a representative basis for teaching one skilled in the art to variously employ the present invention.
Except in the examples, or where otherwise expressly indicated, all numerical quantities in this description indicating amounts of material or conditions of reaction and/or use are to be understood as modified by the word “about” in describing the broadest scope of the invention. Practice within the numerical limits stated is generally preferred. Also, unless expressly stated to the contrary: the description of a group or class of materials as suitable or preferred for a given purpose in connection with the invention implies that mixtures of any two or more of the members of the group or class are equally suitable or preferred; description of constituents in chemical terms refers to the constituents at the time of addition to any combination specified in the description, and does not necessarily preclude chemical interactions among the constituents of a mixture once mixed; the first definition of an acronym or other abbreviation applies to all subsequent uses herein of the same abbreviation and applies mutatis mutandis to normal grammatical variations of the initially defined abbreviation; and, unless expressly stated to the contrary, measurement of a property is determined by the same technique as previously or later referenced for the same property.
It is also to be understood that this invention is not limited to the specific embodiments and methods described below, as specific components and/or conditions may, of course, vary. Furthermore, the terminology used herein is used only for the purpose of describing particular embodiments of the present invention and is not intended to be limiting in any way.
It must also be noted that, as used in the specification and the appended claims, the singular form “a,” “an,” and “the” comprise plural referents unless the context clearly indicates otherwise. For example, reference to a component in the singular is intended to comprise a plurality of components.
The term “comprising” is synonymous with “including,” “having,” “containing,” or “characterized by.” These terms are inclusive and open-ended and do not exclude additional, unrecited elements or method steps.
The phrase “consisting of” excludes any element, step, or ingredient not specified in the claim. When this phrase appears in a clause of the body of a claim, rather than immediately following the preamble, it limits only the element set forth in that clause; other elements are not excluded from the claim as a whole.
The phrase “consisting essentially of” limits the scope of a claim to the specified materials or steps, plus those that do not materially affect the basic and novel characteristic(s) of the claimed subject matter.
With respect to the terms “comprising,” “consisting of,” and “consisting essentially of,” where one of these three terms is used herein, the presently disclosed and claimed subject matter can include the use of either of the other two terms.
With reference to
Still referring to
The steel component of the present embodiment is advantageously stiffer and more rigid than a steel component of the same bulk region composition without having a plurality of localized martensite-enriched regions 18. In this regard, the localized martensite-enriched regions 18 have an average Rockwell hardness value from about 35 to 60 HRC as measured on the C scale and the bulk region has an average Rockwell hardness value less 35 HRC as measured on the C scale. In a refinement, the steel component has a deflection that is at most 50 percent of the deflection of a steel component (of the same type and dimensions) without the localized martensite-enriched regions for a 1 mm thick sample as determined by the three point bend tests set forth below with a load of 300 N. In another refinement, the steel component has a deflection that is at most 40 percent of the deflection of a steel component (of the same type and dimensions) without the localized martensite-enriched regions for a 1 mm thick sample as determined by the three point bend tests set forth below with a load of 300 N. In still another refinement, the steel component has a deflection that is from 20 to 50 percent of the deflection of a steel component (of the same type and dimensions) without the localized martensite-enriched regions for a 1 mm thick sample as determined by the three point bend tests set forth below with a load of 300 N.
With reference to
With reference to
Table 2 provides values of the ultimate tensile strength (UTS) for the base material and the laser spots for several steel samples. In general, the UTS is increased by over 100 percent.
Finally, Table 3 provides micro hardness values in the laser spot harden zone at several distances from the steel surface. In general, the micro hardness was higher than the value of the base material (i.e., the bulk region).
While exemplary embodiments are described above, it is not intended that these embodiments describe all possible forms of the invention. 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 invention. Additionally, the features of various implementing embodiments may be combined to form further embodiments of the invention.
Claims
1. A steel component comprising:
- a steel substrate having a bulk region and a steel substrate surface; and
- a plurality of localized martensite-enriched regions located at the steel substrate surface, the plurality of localized martensite-enriched regions having higher martensite content than the bulk region, wherein centers of adjacent localized martensite-enriched regions in the plurality of martensite-enriched localized region are separated by a separation distance that is from about 0.5 to 5 mm.
2. The steel component of claim 1 wherein the separation distance is from about 1 to 4 mm.
3. The steel component of claim 1 wherein the separation distance is from about 1.5 to 3 mm.
4. The steel component of claim 1 wherein at least a portion of the plurality of martensite-enriched localized regions are arranged in a rectangular array.
5. The steel component of claim 1 wherein at least a portion of the plurality of martensite-enriched localized regions are arranged in a hexagonal array.
6. The steel component of claim 1 wherein each localized martensite-enriched region has a maximum spatial extent parallel to the steel substrate surface less than 4 mm.
7. The steel component of claim 1 wherein the steel substrate comprises a multiphase steel or dual phase steel.
8. The steel component of claim 1 wherein the localized martensite-enriched regions have a maximum spatial extent parallel to the steel substrate surface less than 3 mm.
9. The steel component of claim 1 wherein the localized martensite-enriched regions have an average Rockwell hardness value from about 35 to 60 HRC as measured on the C scale and the bulk region has an average Rockwell hardness value less 35 HRC as measured on the C scale.
10. The steel component of claim 1 wherein the localized martensite-enriched regions extend below the steel substrate surface to a depth from about 50 to 600 micrometers.
11. A method for hardening a steel component comprising:
- providing a steel substrate having a bulk region and a steel substrate surface; and
- laser spot hardening the steel substrate at a plurality of locations on the steel substrate surface with a laser welding system that includes a laser to form a plurality of localized martensite-enriched regions located at the steel substrate surface, the plurality of localized martensite-enriched regions having higher martensite contents than the bulk region, wherein centers of adjacent localized martensite-enriched regions in the plurality of localized martensite-enriched region are separated by a separation distance that is from about 0.5 to 5 mm.
12. The method of claim 11 wherein the laser melts the steel substrate within 5 ms which upon solidification creates the plurality of localized martensite-enriched regions.
13. The method of claim 11 wherein the laser welding system includes a fiber laser.
14. The method of claim 11 wherein the laser has a power output from about 0.1 to 3 MW/cm2.
15. The method of claim 11 wherein light from the laser is sequentially directed to the plurality of locations on the steel substrate surface.
16. The method of claim 11 wherein the steel substrate is sequentially moved to direct light onto a plurality of locations on the steel substrate surface.
17. The method of claim 11 wherein the separation distance is from about 1 to 4 mm.
18. The method of claim 11 wherein the separation distance is from about 1.5 to 3 mm.
19. The method of claim 11 wherein at least a portion of the plurality of martensite-enriched localized regions are arranged in a rectangular array or a hexagonal array.
20. The method of claim 11 wherein the steel substrate comprises a multiphase steel, dual phase and HSLA grades of steel.
Type: Application
Filed: Sep 30, 2016
Publication Date: Apr 5, 2018
Inventors: Mark Anthony HARRIS (West Bloomfield, MI), Bozdar BRKOVIC (Belle River), Michael HADDAD (Royal Oak, MI)
Application Number: 15/281,467