MARTENSITICALLY HARDENABLE STEEL AND USE THEREOF, IN PARTICULAR FOR PRODUCING A SCREW

Abstract

A steel comprising 0.07 to 0.14 wt. % of carbon, 13 to 15 wt. % of chromium, 1.3 to 1.7 wt. % of molybdenum, 1.5 to 2.0 wt. % of nickel and 1.0 to 1.5 wt. % of manganese and use of the steel for producing screws is provided.

Claims

1. A method for producing a shaped body, the method comprising producing a blank comprising a steel with 0.07 to 0.14 wt % carbon, 13 to 15 wt % chromium, 1.3 to 1.7 wt % molybdenum, 1.5 to 2.0 wt % nickel and 1.0 to 1.5 wt % manganese.

2. The method according to claim 1, including case-hardening the blank with nitrogen from the gas phase.

3. The method according to claim 2, including the case-hardening the blank with nitrogen from the gas phase in combination with carburizing the blank with carbon from the gas phase.

4. The method according to claim 2, including processing the blank, wherein case-hardening the blank is performed subsequent to processing the blank.

5. The method according to claim 1, including deep-freezing the blank at temperatures below minus 80 C. and subsequently annealing the blank at temperatures between 150 C. and 500 C.

6. The method according to claim 1, wherein the shaped body is a screw shape.

7. The method according to claim 6, including local induction hardening of a tip portion of the screw shape.

8. A steel comprising 0.07 to 0.14 wt % carbon, 13 to 15 wt % chromium, 1.3 to 1.7 wt % molybdenum, 1.5 to 2.0 wt % nickel and 1.0 to 1.5 wt % manganese.

9. A screw produced using the steel of claim 8.

10. A screw at least partially comprising a steel obtainable in the method according to claim 1.

11. A screw according to claim 10, having a ratio of an outside diameter (d) of a thread of the screw to a thread pitch (p) of the thread is in the range of 1 to 2.

12. The method according to claim 2, comprising case-hardening the blank with nitrogen from the gas phase at temperatures between 1,000 C. and 1,150 C.

13. The method according to claim 2, comprising case-hardening the blank with nitrogen from the gas phase at a nitrogen partial pressure between 0.05 and 0.3 bar.

14. The method according to claim 12, comprising case-hardening the blank with nitrogen from the gas phase at a nitrogen partial pressure between 0.05 and 0.3 bar.

15. The method according to claim 3, including processing the blank, wherein case-hardening the blank is performed subsequent to processing the blank.

16. The method according claim 2, including deep-freezing the blank at temperatures below minus 80 C. and subsequently annealing the blank at temperatures between 150 C. and 500.

17. The method according claim 3, including deep-freezing the blank at temperatures below minus 80 C. and subsequently annealing the blank at temperatures between 150 C. and 500.

18. The method according claim 4, including deep-freezing the blank at temperatures below minus 80 C. and subsequently annealing the blank at temperatures between 150 C. and 500.

19. The method according to claim 2, wherein the shaped body is a screw shape.

20. The screw according to claim 11, wherein the ratio of the outside diameter of the thread to the thread pitch is in the range of 1.2 to 1.45.

Description

[0039] The invention is explained in more detail below with reference to preferred exemplary embodiments, which are shown schematically in the accompanying figures, wherein individual features of the exemplary embodiments shown below can be basically realized individually or in any desired combination in the context of the invention. The figures show schematic illustrations, in which:

[0040] FIG. 1 shows a schematic flow diagram of a production method according to the invention; and

[0041] FIG. 2 shows a schematic representation of a screw according to the invention, produced in a production method according to the invention.

[0042] FIG. 1 schematically shows the sequence of steps of a possible embodiment of a production method according to the invention. First, in step 1, a blank, preferably wire-shaped, made of a steel containing 0.07 to 0.14% carbon by weight, preferably 0.08 to 0.12 wt % carbon, 13 to 15 wt % chromium, 1.3 to 1.7 wt % molybdenum, 1.5 to 2.0 wt % nickel, and 1.0 to 1.5 wt % manganese. In addition, the steel may have other admixtures customary in 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 remainder is iron with unavoidable impurities, for example sulfur and/or phosphorus, in particular <0.02% by weight in each case.

[0043] Then, the blank is processed in step 2, for example, formed, preferably rolled, and the blank thereby made into the shape of a shaped body, in particular in the form of a screw shape with a screw shaft 20 and a thread 21 arranged on the screw shaft 20. Optionally, the screw shape may also have a rotary drive 15, for example a screw head, arranged on the screw shaft 20. In this case, step 2 of the processing may include, in addition to rolling, compression of the blank.

[0044] The blank formed as a screw shape is then hardened in step 3 at a temperature greater than 900 C., especially between 1,000 C. and 1,150 C., more preferably between 1,030 C. and 1,100 C., in a nitrogenous gas atmosphere, wherein the nitrogen partial pressure of the gas atmosphere is preferably between 0.05 bar and 0.6 bar, more preferably less than 0.3 bar and particularly preferably less than 0.20 bar. Optionally, the gas atmosphere may also contain carbon.

[0045] Subsequently, the blank formed as a screw shape is quenched in step 4, in particular gas-quenched.

[0046] In the subsequent step 5, a deep-freeze treatment of the form of a screw blank follows at temperatures below minus 80, for example at minus 150 C.

[0047] Finally, the blank formed as a screw shape is annealed in step 6, preferably in a temperature range between 150 C. and 500 C., more preferably between 200 C. and 250 C., and/or for a holding time between 1 hour and 5 hours.

[0048] Optionally, in a subsequent step 7, a local, preferably inductive, hardening can be provided at a tip region of the blank designed as a screw shape, and preferably a subsequent deep-freezing of the blank formed as a screw shape can be provided.

[0049] An exemplary embodiment of a screw according to the invention, which is formed as a concrete screw, is shown in FIG. 2.

[0050] The screw 10 has a cylindrical screw shaft 20, at the end of which a hexagonal screw head is provided which forms a rotary drive 15. Along the screw shaft 20, a thread 21 formed as a cutting thread extends with an outer diameter d and a pitch p. Optionally, a smaller-diameter support thread 28 may be provided on the screw shaft 20.

[0051] The screw shaft 20 of the screw is screwed into a bore in a mineral substrate 50, in particular in a concrete substrate, wherein the thread 21 formed as a cutting thread has cut open a corresponding thread in the substrate 50 during screwing. The screw shaft 20 is guided through a hole in an attachment 53 which is secured to the substrate 50 by the rotary drive 15 formed as a screw head.