BIMETALLIC SCREW WITH MARTENSITICALLY HARDENABLE STEEL

Abstract

A method for producing a bimetallic screw with a tip element and a drive element, in which a first blank comprising a steel with 0.07 to 0.14% by weight carbon, 13 to 15% by weight chromium, 1.3 to 1.7% by weight molybdenum, 1.5 to 2.0% by weight nickel and 1.0 to 1.5% by weight manganese is provided and the tip element is made from the first blank. A bimetallic screw with a tip element and a drive element is also provided, the tip element and the drive element having a different material composition, and the tip element comprising at least in some areas a steel with 0.07 to 0.14% by weight carbon, 13 to 15% by weight chromium, 1.3 to 1.7% by weight molybdenum, 1.5 to 2.0% by weight nickel and 1.0 to 1.5% by weight manganese.

Claims

1. A method for producing a bimetallic screw with a tip element and a drive element, the method comprising providing a first blank comprising a steel with 0.07 to 0.14% by weight carbon, 13 to 15% by weight chromium, 1.3 to 1.7% by weight molybdenum, 1.5 to 2.0% by weight nickel and 1.0 to 1.5% by weight manganese, and making the tip element from the first blank.

2. The method as claimed in claim 1, including: case hardening the first blank with nitrogen from a gas phase.

3. The method as claimed in claim 2, including case hardening the first blank with nitrogen from the gas phase in combination with carburizing the first blank with carbon from the gas phase.

4. The method as claimed in claim 2, including thread forming on the first blank before case hardening the first blank.

5. The method as claimed in claim 1, including freezing the first blank at temperatures below minus 80 C. and then tempering the blank at temperatures between 150 C. and 500 C.

6. The method as claimed in claim 1, including providing a second blank comprising a duplex steel or an austenitic stainless steel, and making the drive element from the second blank.

7. The method as claimed in claim 6, including joining the first blank and the second blank together by laser welding or resistance welding.

8. A bimetallic screw with a tip element and a drive element, the tip element and the drive element having a different material composition, wherein the tip element comprises at least in some areas a steel with 0.07 to 0.14% by weight carbon, 13 to 15% by weight chromium, 1.3 to 1.7% by weight molybdenum, 1.5 to 2.0% by weight nickel and 1.0 to 1.5% by weight manganese.

9. The bimetallic screw as claimed in claim 8, wherein the drive element comprises at least in some areas a duplex steel or an austenitic stainless steel.

10. The bimetallic screw as claimed in claim 8, wherein the ratio of an outside diameter (d) of a thread of the bimetallic screw to a thread pitch (p) of the thread is in the range from 1 to 2.

11. The method of claim 2, including case hardening the first blank with nitrogen gas at temperatures between 1000 C. and 1150 C. and/or a nitrogen partial pressure between 0.05 bar and 0.3 bar phase.

12. The method as claimed in claim 3, including thread forming on the first blank before case hardening the first blank.

13. The method as claimed in claim 2, including freezing the first blank at temperatures below minus 80 C. and then tempering the blank at temperatures between 150 C. and 500 C.

14. The method as claimed in claim 3, including freezing the first blank at temperatures below minus 80 C. and then tempering the blank at temperatures between 150 C. and 500 C.

15. The method as claimed in claim 4, including freezing the first blank at temperatures below minus 80 C. and then tempering the blank at temperatures between 150 C. and 500 C.

16. The method as claimed in claim 12, including freezing the first blank at temperatures below minus 80 C. and then tempering the blank at temperatures between 150 C. and 500 C.

17. The method as claimed in claim 2, including providing a second blank comprising a duplex steel or an austenitic stainless steel, and making the drive element from the second blank.

18. The method as claimed in claim 3, including providing a second blank comprising a duplex steel or an austenitic stainless steel, and making the drive element from the second blank.

19. The bimetallic screw as claimed in claim 9, wherein the ratio of an outside diameter (d) of a thread of the bimetallic screw to a thread pitch (p) of the thread is in the range from 1 to 2.

20. The bimetallic screw of claim 10, wherein the ratio of (d) of a thread of the bimetallic screw to (p) of the thread is in the range of from 1.2 to 1.45.

Description

[0035] The invention is explained in more detail below on the basis of preferred exemplary embodiments, which are shown schematically in the accompanying FIGURE, while individual features of the exemplary embodiments that are described below can in principle be implemented individually or in any combination within the scope of the invention. The FIGURE shows schematically:

[0036] FIG. 1: a schematic flow diagram of a production method according to the invention.

[0037] FIG. 1 schematically shows a flow diagram of a possible embodiment of a method according to the invention for producing a bimetallic screw 40 with a tip element 41 and a drive element 42.

[0038] In order to obtain the tip element 41, in step 1 a first blank 31, preferably a wire-shaped first blank 31, made of a steel containing 0.07 to 0.14% by weight, preferably 0.08 to 0.12% by weight, carbon, 13 to 15% by weight chromium, 1.3 to 1.7% by weight molybdenum, 1.5 to 2.0% by weight nickel and 1.0 to 1.5% by weight manganese is provided. In addition, the steel may comprises other elements customary for steel, for example vanadium (in particular <0.2% by weight), niobium (in particular <0.2% by weight), titanium (in particular <0.2% by weight) and/or silicon (in particular <0.5% by weight). The rest is iron with inevitable impurities, for example sulfur and/or phosphorus, in particular in each case <0.02% by weight.

[0039] This is followed in step 2 by thread forming on the first blank 31, whereby an external thread section is formed on the first blank 31. The thread forming may in particular be thread rolling.

[0040] The first blank 31 is then cut to length in step 3 and cleaned in step 4.

[0041] In the subsequent step 5, the first blank 31, which is in the form of a screw, is hardened in a nitrogen-containing gas atmosphere at a temperature greater than 900 C., in particular between 1000 C. and 1150 C., particularly preferably between 1030 C. and 1100 C., the nitrogen partial pressure of the gas atmosphere preferably being between 0.05 bar and 0.6 bar, preferably less than 0.3 bar and particularly preferably less than 0.20 bar. The gas atmosphere may optionally also contain carbon. Following this, still in step 5, the first blank 31 is quenched, in particular gas-quenched, then frozen, in particular at temperatures below minus 80, for example at minus 150 C., and finally tempered, preferably in a temperature range between 150 C. and 500 C., particularly preferably between 200 C. and 250 C., and/or a holding time between 1 hour and 5 hours.

[0042] In order to obtain the drive element 42, in step 11 a second blank 32, preferably a wire-shaped second blank 32, made of a duplex steel or an austenitic stainless steel is provided.

[0043] Then, in step 12, a head is then formed on the second blank 32, for example by upsetting. The head can form the rotary drive 46 on the finished bimetallic screw 40.

[0044] This is then followed in step 13 by thread forming on the second blank 32, as a result of which an external thread section is formed on the second blank 32. The thread forming may in particular be thread rolling.

[0045] The second blank 32 is then cleaned in step 14.

[0046] In step 21, the first blank 31 is arranged in front of the second blank 32 and brought into a position in which the first blank 31 contacts the second blank 32 and the external thread section on the first blank 31 forms an extension of the external thread section on the second blank 32.

[0047] Then, in step 22, the first blank 31 and the second blank 32 are joined together, for example by laser welding or resistance welding.

[0048] The composite comprising the first blank 31 and the second blank 32 can optionally be passivated in step 23.

[0049] Finally, the bimetallic screw 40 shown at 23 is obtained with a metallic tip element 41 and a metallic drive element 42 of a different material, the tip element 41 being obtained from the first blank 31 and the drive element 42 being obtained from the second blank 32. The bimetallic screw 40 has a cylindrical screw shaft 45, at the end of which a hexagon screw head is provided, forming a rotary drive 46. The screw shaft 45 is formed jointly by the drive element 42 and the tip element 41, and the rotary drive 46 is located at the rear end region of the drive element 42. Over the length of the screw shaft 45 there extends along the drive element 42 and the tip element 41 a thread 47 formed as a cutting thread, with an outside diameter d and a pitch p.

[0050] The screw shaft 45 of the bimetallic screw 40 can be screwed into a hole in a mineral substrate, in particular in a concrete substrate, the thread 47, which is formed as a cutting thread, being able to cut a corresponding thread in the substrate when screwed in.