High-strength screw including an unhardened thread end

Abstract

A high-strength screw (1) includes a head (2) and a threaded portion (5) including a thread (6) and a thread end (9) facing away from the head (2) in an axial direction. The threaded portion (5) includes an unhardened portion (12) starting at the thread end (9) and extending in an axial direction. The unhardened portion (12) has a hardness being reduced compared to an axial middle portion (11) of the threaded portion (5).

Claims

1. A high-strength screw, comprising: a head; and a shank defining an axial direction and including a threaded portion including a thread, the threaded portion having a first thread end facing away from the head in the axial direction, the threaded portion having a second thread end facing the head in the axial direction, the threaded portion having an axial middle portion being located in the middle between the first thread end and the second thread end, the axial middle portion having a first hardness, and the threaded portion including an unhardened portion, the unhardened portion starting at the first thread end and extending in the axial direction towards the head, the unhardened portion having a second hardness being reduced compared to the first hardness of the axial middle portion.

2. The screw of claim 1, wherein the second hardness of the unhardened portion is at least 50 HV lower than the first hardness of the axial middle portion.

3. The screw of claim 1, wherein the second hardness of the unhardened portion is between 50 HV and 300 HV lower than the first hardness of the axial middle portion.

4. The screw of claim 1, wherein the second hardness of the unhardened portion is between 100 HV and 250 HV lower than the first hardness of the axial middle portion.

5. The screw of claim 1, wherein the axial middle portion has a first tensile strength, the unhardened portion has a second tensile strength, the second tensile strength of the unhardened portion being at least 100 N/mm.sup.2 lower than the first tensile strength of the axial middle portion.

6. The screw of claim 1, wherein the axial middle portion has a first tensile strength, the unhardened portion has a second tensile strength, the second tensile strength of the unhardened portion being between 100 N/mm.sup.2 and 700 N/mm.sup.2 lower than the first tensile strength of the axial middle portion.

7. The screw of claim 1, wherein the axial middle portion has a first tensile strength, the unhardened portion has a second tensile strength, the second tensile strength of the unhardened portion being between 200 N/mm.sup.2 and 500 N/mm.sup.2 lower than the first tensile strength of the axial middle portion.

8. The screw of claim 1, wherein the second hardness of the unhardened portion is between 15% and 50% lower than the first hardness of the axial middle portion.

9. The screw of claim 1, wherein the second hardness of the unhardened portion is between 20% and 40% lower than the first hardness of the axial middle portion.

10. The screw of claim 1, wherein the axial middle portion has a first tensile strength, the unhardened portion has a second tensile strength, the second tensile strength of the unhardened portion being between 15% and 50% lower than the second tensile strength of the axial middle portion.

11. The screw of claim 1, wherein the axial middle portion has a first tensile strength, the unhardened portion has a second tensile strength, the second tensile strength of the unhardened portion being between 20% and 40% lower than the second tensile strength of the axial middle portion.

12. The screw of claim 1, wherein the thread has a pitch, the unhardened portion has an axial length, the axial length extending over at least twice the pitch.

13. The screw of claim 1, wherein the thread has a pitch, the unhardened portion has an axial length, the axial length extending over at least three times the pitch.

14. The screw of claim 12, wherein the axial length extends over a maximum of one selected from the group consisting of: eight times, seven times and six times the pitch.

15. The screw of claim 13, wherein the axial length extends over a maximum of one selected from the group consisting of: eight times, seven times and six times the pitch.

16. The screw of claim 1, wherein the thread being located in the unhardened portion has a standard design as far as geometry is concerned.

17. The screw of claim 16, wherein no bore is arranged in the unhardened portion.

18. The screw of claim 1, wherein the screw includes a bainite structure.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) In the following, the invention is further explained and described with respect to preferred exemplary embodiments illustrated in the drawings.

(2) FIG. 1 illustrates a view of an exemplary embodiment of the new high-strength screw.

(3) FIG. 2 illustrates detail A of the threaded portion of the screw according to FIG. 1.

(4) FIG. 3 illustrates a sectional view of the screw according to FIG. 1.

(5) FIG. 4 illustrates detail B of the threaded portion of the screw according to FIG. 3.

DETAILED DESCRIPTION

(6) FIG. 1-4 illustrate different views of an exemplary embodiment of a new high-strength screw 1. The screw 1 is a high-strength screw 1 having a tensile strength of at least 800 N/mm.sup.2, especially an ultra-high-strength screw 1 having a tensile strength of at least 1400 N/mm.sup.2. The screw 1 includes a bainite structure that has especially been produced by austempering and that extends substantially over the entire cross-section of the screw 1.

(7) The screw 1 includes a head 2 and shaft 3. The head 2 includes a usual tool engagement contour. The shaft 3 includes a threadless shaft portion 4 and a threaded portion 5 including a thread 6. In this case, the thread 6 is designed as a metric thread. However, it could also be designed as a different thread 6.

(8) The threaded portion 5 includes a thread run-in 7 and a thread run-out 8. It furthermore includes a thread end 9 facing away from the head 2 and a thread end 10 facing the head 2. Correspondently, an axial middle portion 11 of the threaded portion 5 is arranged in the middle between these two thread ends 9, 10.

(9) As it is indicated by reference numeral 12, the threaded portion 5 includes an unhardened portion 12. The unhardened portion 12 starts at the thread end 9 and extends in an axial direction over a partial length of the threaded portion 5. There is reduced hardness and tensile strength in the unhardened portion 12 compared to the axial middle portion 11 of the threaded portion 5. The hardness of the unhardened portion 12 may be between 15% and 50% lower compared to the axial middle portion 11 of the threaded portion 5.

(10) The unhardened portion 12 extends in the axial direction at least to and beyond a dome 13 of the threaded portion 5, i. e. the region of the threaded portion 5 in which the thread 6 reaches its maximum outer diameter for the first time.

(11) As it is emphasized by way of example by the two lines 14, 15, the unhardened portion 12 may extend in the sense of line 14 over a minimum length of at least three times the pitch of the thread 6.

(12) According to line 15, the unhardened portion 12 may extend over a maximum length corresponding to the maximums of six times the pitch of the thread 6. However, it is to be understood that other numerical values and especially the other numerical values mentioned in this application may be used.

(13) Many variations and modifications may be made to the preferred embodiments of the invention without departing substantially from the spirit and principles of the invention. All such modifications and variations are intended to be included herein within the scope of the present invention, as defined by the following claims.