US20170283904A1

US20170283904A1 - Method for producing cold-formed steel springs

Info

Publication number: US20170283904A1
Application number: US15/508,356
Authority: US
Inventors: Dieter Lechner; Marcel Groß; Heinz Georg Gabor; Marco Roland
Original assignee: ThyssenKrupp AG; ThyssenKrupp Federn und Stabilisatoren GmbH
Current assignee: ThyssenKrupp AG; ThyssenKrupp Federn und Stabilisatoren GmbH
Priority date: 2014-09-04
Filing date: 2015-07-15
Publication date: 2017-10-05
Also published as: US20170275721A1; JP2017532450A; KR20170051472A; BR112017004212B1; CN106605000B; RU2017104701A; RU2682882C1; EP3686295A1; CN106795576B; EP3686294A1; KR20170052612A; CN106795576A; KR102332298B1; CN106605000A; HUE052643T2; BR112017004224B1; EP3189165A1; KR102326352B1; HUE050515T2; RU2664847C2

Abstract

A process for producing a spring and/or torsion bar from a steel wire by cold forming may involve providing a steel wire; thermomechanically forming the steel wire above a minimum recrystallization temperature of the steel wire; cooling the steel wire; tempering the steel wire, which may involve heating, quenching, reheating, and cooling the steel wire; cold forming the steel wire at a cold forming temperature, the cold forming temperature being a temperature below the minimum recrystallization temperature of the steel wire; and separating the steel wire. With respect to the cooling of the steel wire, the steel wire may be cooled to a temperature below the minimum recrystallization temperature such that at least a partly ferritic-pearlitic structure is formed in the steel wire.

Description

The present invention relates to cold-formed springs and/or torsion bars, to a process for producing cold-formed springs and/or torsion bars, and to the use of a steel wire for production of cold-formed springs and/or torsion bars.

PRIOR ART

Springs and torsion bars made from formed steel wire are known in the prior art in a multitude of embodiments. Torsion bars are also referred to, for example, as torque rod springs, stabilization torque rods or torsion bar springs. Steel springs and torsion bar springs are used especially in motor vehicles, where steel springs are used, for example, to absorb road unevenness in shock absorber systems, and torsion bar springs to provide stabilization against tilting and distortion of the chassis, especially on motor vehicle cornering, on motor vehicle journeys over varying road surfaces and in the event of road unevenness. The shaping of the steel wire to give springs and torsion bars can be effected by a cold and/or hot forming method. Prior to this shaping, the steel wire can undergo various preparation steps which affect the spring and strength properties. For example, the spring steel used for production of a steel spring and/or torsion bar spring is subjected to a thermomechanical forming (TMF) operation, in order to increase its strength and toughness usable for construction purposes and to improve further specific use properties of a material. For instance, springs and/or torsion bars having high strength(s) can be produced with lower material input and hence low weight and material costs. The prior art discloses a number of different methods which comprise a thermal treatment and then a forming operation. In the case of cold forming, the formability of the steel wire is limited, since the toughness and formability thereof decreases as a result of cold solidification with an increasing degree of forming.
In the mass production of hot-formed helical springs, the TMF is already used in the form of a skew rolling process, but here only on prefabricated individualized spring rods. Such a process is disclosed in DE 103 15 418 B3. The TMF is effected on the spring rod by a one-stage skew rolling process directly prior to the hot winding of the helical springs. The hot-formed spring is quenched in oil, which results in a martensitic structure.
In the cold forming of helical springs, no spring rods are used. Instead, a pre-tempered, i.e. already hardened and annealed, wire in the cold state, is converted to the ultimate helical form by cold winding; only then is it separated from the continuing wire and hence the material is separated.
DE 198 39 383 C2 describes a process for thermomechanical treatment of steel for torsion-stressed spring elements. A starting material is rapidly heated to a temperature of 1080° C. and austenitized. Subsequently, the starting material is subjected to a TMF, which achieves recrystallization. Subsequently, without intermediate cooling, the starting material is hardened by quenching.
This process is conducted in an integral manufacturing line in which all steps are conducted from the TMF up to the quenching. The direct concatenation of thermomechanical forming and tempering which is thus required results in the following disadvantages:

1. Changes in the length of the wire resulting from the thermomechanical forming, usually rolling, have a direct effect on the process parameters of the immediately subsequent tempering.
2. The process times and temperatures of the thermomechanical forming and the tempering would have to be matched to one another, which is difficult to implement in terms of process technology. This is because a preferred temperature for the thermomechanical forming is only just above the austenitization temperature of the wire material, while heating to a much higher temperature is advantageous for the tempering.
3. The rolling apparatus for the TMF and the tempering apparatus have different throughput times per unit wire length; in order to solve this conflict, very complex regulation and control problems have to be solved.
4. The throughput of the manufacturing line would then be defined by the slowest process component; the quicker process components are therefore working not at capacity and therefore uneconomically.
5. The one-stage skew rolling operation employed in the manufacturing of springs for thermomechanical forming (corresponding to the abovementioned DE 103 15 418 B3) leads to rotation of the wire about its longitudinal axis at a speed of 400 rpm or more. This can be conducted with individualized spring rods, but not in the processing of continuous wires. In the subsequent process steps such as quenching, annealing and coiling, the wire would correspondingly rotate, which would make at least greatly elevated demands on these units. In practice, the implementability of such an integrated process with continuous wire has not yet been tested. It is already known that a two-stage caliber rolling operation can also be used instead of skew rolling. However, the above disadvantages 1 to 4 also exist when caliber rolling is employed.

DE 198 39 383 C2 suggests, in one variant (column 3 lines 4-20), after the thermomechanical forming, quenching the spring steel at first to low temperature and then sending it to another tempering process with significant heating and quenching. However, this variant has substantially the disadvantages addressed above.
It is therefore an object of the present invention to provide an improved spring and/or torsion bar and an improved process for producing the improved spring and/or torsion bar where the aforementioned disadvantages are avoided. More particularly, the improved process for producing the improved spring and/or torsion bar is to provide a more stable manufacturing process with reliable fulfilment of high quality demands. Moreover, the improved process for producing the improved spring and/or torsion bar is to be implementable in a simple and reliable manner in existing processes.

DISCLOSURE OF THE INVENTION

This object is achieved by a spring and/or torsion bar as claimed in claim 1, and a process as claimed in claim 5.
The spring of the invention has the advantage over conventional springs that the spring wire of the invention has higher toughness compared to conventional spring wires. Because of the higher toughness of the spring wire, the spring of the invention can be subjected to higher stresses. Further advantages of the spring of the invention are a lower weight compared to conventional springs and a longer lifetime. Moreover, the spring of the invention, compared to conventional springs, can especially be designed with smaller dimensions and a shorter spring length, which means that the spring of the invention can also be disposed in small spaces.
The torsion bar of the invention has the advantage over conventional torsion bars that the spring wire of the invention has higher toughness compared to conventional spring wires. Because of the higher toughness of the spring wire, the torsion bar of the invention can be subjected to higher stresses. A further advantage of the torsion bar of the invention is a longer lifetime compared to conventional torsion bars.
The process of the invention for producing springs and/or torsion bars has the advantage over conventional processes that the spring and/or torsion bar of the invention has a spring wire having a higher toughness compared to conventional spring wires. A further advantage of the process of the invention is that it can be integrated simply and reliably into existing processes. Moreover, the process of the invention has the advantages that

- the separation of TMF and tempering in the process allows the optimal process parameters, for example temperatures, to be established for each of the two steps,
- the separation of TMF from the downstream manufacturing steps in the process allows the optimal throughput rates to be established for each of the steps,
- any processing steps additionally needed on the steel wire and/or rod, for example precise cutting to a desired length or the production of non-constant steel wire and/or rod diameters, can be undertaken without prolonging the duration of the process before the quench hardening,
- the risk that there will be adverse changes in structure in the steel wire and/or rod as a result of holding at very high temperature for a long period is reduced,
- the shutdown of any process component (for example for maintenance or because of a defect) does not have any direct effects on the entire manufacturing line and the other process steps can continue production,
- there is no need to keep a separate TMF unit ready for every winding system, and the flexibility of production is increased since the selection of winding system to be used can be made independently of the TMF unit,
- the processing of spring rods at a non-constant, especially varying, wire diameter is possible by the process of the invention in a simple manner and without increased complexity.

The invention therefore provides a spring and/or torsion bar produced from a steel wire by cold forming by a process comprising the following steps:

- a) providing a steel wire;
- b) thermomechanically forming the steel wire provided in step a) above the minimum recrystallization temperature of the steel wire, said steel wire having an at least partly austenitic structure;
- c) cooling the steel wire thermomechanically formed in step b);
- d) tempering the steel wire, comprising
  - I. heating the steel wire cooled in step c) at least to a hardening temperature equal to or greater than the austenite start temperature;
  - II. quenching the steel wire heated at least to the hardening temperature in step I. to a first cooling temperature, the first cooling temperature being a temperature below the minimum recrystallization temperature of the steel wire, and an at least partly martensitic structure being established;
  - III. reheating the steel wire quenched in step II. to a first annealing temperature which is less than the austenite start temperature;
  - IV. cooling the steel wire reheated in step III. to a second cooling temperature, the second cooling temperature being at least less than the first annealing temperature;
- e) cold forming the metal wire tempered in step d) at a cold forming temperature, the cold forming temperature being a temperature below the minimum recrystallization temperature of the steel wire;
- f) separating the steel wire cold-formed in step e), wherein with cooling of the steel wire in step c) to a temperature below the minimum recrystallization temperature it is cooled such that at least a partly ferritic-pearlitic structure is established in the steel wire.

The invention further provides a process for producing a spring and/or torsion bar, comprising the steps of:

The invention further provides for the use of a steel wire for production of cold-formed springs and/or torsion bars, comprising the steps of:

The formation of the pearlitic-ferritic structure puts the wire in an intermediate state in which the wire features high softness and hence also good amenability to handling. Because of this softness, it is possible to achieve separation of the TMF from the subsequent tempering in the process. In the period between the TMF and the tempering, the wire has much better amenability to handling, since it is not in a hardened form.
The invention can be implemented either in a spring or in a torsion bar, or else in a spring wire of the invention, or else in a process for producing the spring and/or torsion bar, or else the spring wire, and also in the use of a steel wire for production of the spring and/or torsion bar.

DETAILED DESCRIPTION OF THE INVENTION

In the context of the present invention, a spring is understood to mean a component made from a steel wire which yields under stress and, after the stress is relieved, returns to its original state. More particularly, a spring may be a component wound in helical or spiral form from steel wire or stretched or bent in the form of a rod. Examples of springs are selected from a group of helical springs, especially helical compression springs, helical tension springs, conical springs, elastic springs, flexible springs, especially spiral springs, wound torsion springs and combinations thereof.
In the context of the present invention, a torsion bar is understood to mean a bar element wherein, when the torsion bar is fixed at both ends, the secured ends perform a pivoting motion about the axis of the bar element with respect to one another. More particularly, the mechanical stress takes place to a crucial degree through a torque that engages tangentially with respect to the rod element axis. Torsion bars are also understood, for example, to mean a straight torsion bar, an angular torsion bar, a torsion bar spring, a torsion spring, a stabilization torsion bar, a stabilizer, a separated stabilizer and combinations thereof.
Cold forming in the context of the present invention is understood to mean forming of the steel wire below the recrystallization temperature. More particularly, formability is limited in cold forming since, as a result of the cold solidification, there is a decrease in the toughness and formability of a material, for example steel, with an increasing degree of forming. Examples of cold forming are cold winding, cold bending and combinations thereof.
The recrystallization temperature is that calcining temperature which, in the case of a cold-formed structure with a given degree of forming, leads to complete recrystallization within a limited period of time. The recrystallization temperature does not have a fixed value but depends on the extent of the prior cold forming and the melting temperature of the material, especially the melting temperatures of steels. For example, in the case of steels, the recrystallization temperature is also dependent on the carbon content and the alloy of the particular steel.
The minimum recrystallization temperature is understood to mean the lowermost temperature at which there is still recrystallization, especially recrystallization of the structure of a steel wire.
Austenite start temperature in the context of the invention is understood to mean a temperature at which there is transformation to an at least partly austenitic structure. More particularly, at an austenitization temperature, there is transformation to an at least partly austenitic structure.
Tempering in the context of the present invention may be partial or complete tempering.
A heat transfer, as occurs, for example, in step b) in the thermomechanical forming, in step d)I. in the heating, in step d)III. in the reheating and/or another heat transfer in the context of the invention, is understood to mean one selected from conduction of heat, especially conductive heating, radiation of heat, especially infrared radiation, heating by induction, convection, especially a heated fan, and combinations thereof.
A stabilizer in the context of the invention is also understood to mean a stabilization torsion bar. More particularly, sections of stabilizers and/or separated stabilizers are also understood to mean stabilizers of the invention.
In a preferred embodiment of the invention, the production of the spring and/or torsion bar is conducted with a steel wire having a carbon content in the range from 0.02% to 0.8% by weight. More particularly, in the context of the invention, steels having a carbon content in the range from 0.02% to 0.8% by weight are understood to mean hypoeutectoid steels.
In a preferred embodiment of the invention, the sequence of steps e) and f) is as desired.
In a preferred embodiment of the invention, the thermomechanical forming in step b) is effected at a temperature equal to or greater than the austenite start temperature, preferably equal to or greater than the austenite end temperature, more preferably in the range from the austenite end temperature to 50° C. greater than the austenite end temperature.
Austenite end temperature in the context of the invention is understood to mean a temperature at which the transformation to an austenitic structure is complete.
Thus, in a preferred embodiment, it is envisaged that, in this intermediate state, i.e. after the TMF and prior to the tempering, the wire, which is still in the form of a continuous wire, is rolled up, especially coiled, for storage or transport purposes. The softer the wire, the more easily this is possible. For the subsequent tempering, the wire is uncoiled again. The subsequent tempering is thus completely decoupled from the TMF.
The process sequence of the invention also enables decoupling of the tempering from the TMF with regard to the temperature range. While the optimal forming temperature during the TMF is just above the austenitization temperature of the wire material, especially less than 50° C. above the austenitization temperature of the wire material, heating to significantly higher temperatures is advantageous for the tempering. Thus, in a preferred configuration, the tempering temperature is above the forming temperature, especially more than 50° C. above the austenitization temperature of the wire material. The separation of TMF and tempering in the process allows the optimal temperature to be established for each of the two steps.
A further advantage of the process sequence of the invention is that the decoupling of the two processes of tempering and TMF allows both processes to be conducted at (required) throughput rates of the wire that are optimal for the particular process. The throughput rate of the wire in the TMF is not necessarily the same as in the tempering. In the integral manufacturing line, by contrast, the slower of the two processes sets the throughput rate for both processes, meaning that one of the two processes does not work under optimal conditions, i.e. in an uneconomic manner.
A further advantage of the process of the invention and of the spring of the invention and/or the torsion bar is that the spring wire of the invention has a finer-grain structure compared to conventional spring wires.
In a preferred embodiment of the invention, the cooling of the wire in step c) is effected at least to a temperature below the minimum recrystallization temperature, preferably below a temperature of 200° C., more preferably below a temperature of 50° C.
The cooling after the TMF is preferably effected at such a low cooling rate as to ensure that a pearlitic-ferritic structure is established. For this purpose, the person skilled in the art is able to employ the TTT diagram corresponding to the material, from which it is possible to read off the cooling rate.
In principle, the procedure proposed appears to be uneconomic compared to the known process, since the wire now has to be reheated for the cold forming process after the intermediate cooling. However, it has been found that the decoupling achieved thereby can avoid the disadvantages mentioned at the outset, which can be assessed as being better in technical terms and more economically advantageous than the advantages resulting from the integral manufacture. In addition, the intermediate cooling can also be effected in a controlled manner with involvement of a heat exchanger, by means of which the waste heat from the cooling can again be available to the TMF or the subsequent tempering with quite a high efficiency.
According to the invention, it is now possible to use an already pretreated wire for production of cold-formed steel springs, especially helical springs or torsion bar springs made from steel. The wire has a temperature of less than 200° C., especially room temperature. Moreover, the wire has already been subjected to a thermomechanical forming operation and has a pearlitic-ferritic structure. This wire is then tempered, the tempering comprising the following steps: heating of the wire to a tempering temperature above the austenitization temperature of the wire material and austenitization; quenching of the wire heated to tempering temperature for formation of a martensitic structure in the wire; annealing of the wire. This is followed by the cold forming of the wire for production of the cold-formed steel springs. The advantages and developments that have been mentioned with regard to the process are applicable to this use.
In a preferred embodiment of the invention, the steel wire is heated in step d)I. to a temperature equal to or greater than the austenite start temperature, preferably equal to or greater than the austenite end temperature.
In a preferred embodiment of the invention, the quenching of the wire in step d)II. causes the steel wire structure to undergo at least partial conversion to martensite and the steel wire to be exposed to at least a martensite start temperature, whereby the quenching of the steel wire is preferably carried out to the first cooling temperature of the steel wire of less than or equal to 200° C.
Martensite start temperature in the context of the invention is understood to mean a temperature at which there is transformation to an at least partly martensitic structure.
In a preferred embodiment of the invention, the tempering of the steel wire in step d) establishes the hardness profile over the cross section of the steel wire. For example, the hardness of the steel wire can vary from the edge to the core of the steel wire. More particularly, the hardness can drop or rise or else be equal from the edge to the core of the steel wire. Preferably, the hardness drops from the edge to the core of the steel wire. For example, this can be effected by edge heating of the steel wire with subsequent recooling after one of steps d) to f).
Preferably, the process is employed in the production of cold-formed helical springs. This involves cold winding of the wire to give steel springs; only after the cold winding of the helical springs are they separated from the wire, especially individualized.
Likewise preferably, the process is employed in the production of cold-formed torsion bar springs. This involves cutting the wire to length to give rods after the tempering. Thereafter, the rods are processed further by cold bending to give torsion bar springs, especially stabilizers for motor vehicle chassis.
In a preferred embodiment of the invention, after one of steps d) to f), in a further step g), edge heating and subsequent recooling of the steel wire is carried out, whereby the hardness increases from the edge to the core of the steel wire.
In a preferred embodiment of the invention, after one of steps c) to f), in a further step h), the steel wire is coiled.
In a preferred embodiment of the invention, after one of steps c) to g), in a further step i), a surface treatment of the steel wire is carried out, in which the surface of the steel wire is at least partly removed.
In a preferred embodiment of the invention, the spring produced by the process of the invention and/or the torsion bar have a martensite content of greater than 40% by volume, preferably greater than 80% by volume, more preferably greater than 90% by volume, most preferably greater than 95% by volume.
In a preferred embodiment of the invention, the process is conducted using a steel wire with a carbon content in the range from 0.02% to 0.8% by weight.
In a preferred embodiment of the invention, production of cold-formed springs and/or torsion bars is accomplished using a steel wire having a carbon content in the range from 0.02% to 0.8% by weight.

PREFERRED WORKING EXAMPLE OF THE INVENTION

Further measures which improve the invention will be discussed in detail hereinafter together with the description of a preferred working example of the invention and with reference to the figures. The figures show:

FIG. 1 a schematic diagram of the process of the invention in one embodiment of the invention,

FIG. 2 a schematic diagram of the process of the invention in one embodiment of the invention,

FIG. 3 a temperature profile for the embodiments according to FIGS. 1 and 2.

FIGS. 1 to 3 are described together hereinafter. A wound steel wire 1, especially a wire rod, is provided on a ring 10. The steel wire 1 is at first heated to a forming temperature T1 of about 800° C., which is above the minimum recrystallization temperature of the steel wire, especially above the austenitization temperature Ac3 of in the present case 785° C., 11. Then the steel wire 1 is subjected to thermomechanical forming (TMF) 12. The heating 11 can be dispensed with when the TMF immediately follows a steel wire rolling process and the temperature of the steel wire is still at the desired forming temperature T1.
The thermomechanical forming 12 can be effected by multistage caliber rolling. Subsequently, the steel wire 1 is cooled 13 at such a slow rate that a partly ferritic-pearlitic structure, i.e. a soft structure, is established in the steel wire. The cooling can be effected without any further intervention by simple storage at room temperature or ambient temperature, but the cooling is preferably effected in a controlled manner. Before, during or after the cooling, the steel wire 1 is coiled 14, which is readily possible because of the soft microstructural state. For cooling, it is also possible to provide a heat exchanger, such that the waste heat can be fed back to the process.
When the steel wire 1 is then coiled, it can be transported from one processing site to the next processing site and processed further there. In FIG. 3, this is illustrated by a gap in the temperature profile after the coiling 14. A spring manufacturer can then purchase the steel wire 1 pretreated by thermomechanical forming from a steel wire manufacturer, and need not keep the equipment required for the TMF in house. This saves space and capital costs for the spring manufacturer.
After any desired period of storage and/or transport, the tempering of the steel wire 1 commences, and consequently need not follow the TMF directly (or even in terms of location). Coiling 15 may also be followed by a processing operation, for example grinding 16, prior to the tempering. Subsequently, for commencement of the tempering, the steel wire is heated 17 to a hardening temperature T2 distinctly above the austenitization temperature Ac3 or the forming temperature T1. In the present case, the hardening temperature T2 is about 950° C. The heating is effected very quickly and is preferably conducted by inductive means. The heating is effected at a heating rate of at least 50 K/s, preferably at least 100 K/s. This is followed by quenching 18, for example in a water or oil bath, which establishes an at least partly martensitic structure. Subsequently, the steel wire 1 is annealed 19.
In a first configuration as shown in FIG. 1, the tempered steel wire 1 is then subjected to cold winding 20′ to give helical springs 3′ and then cut 21 from the steel wire 1. In an alternative configuration as shown in FIG. 2, the tempered steel wire 1 is first cut 21 into individual spring rods 22 and then subjected to cold bending 20″ to give torsion bar springs 3″.
In terms of its execution, the invention is not restricted to the preferred working example specified above. Instead, there is a number of conceivable variants which make use of the solution presented even in executions of a fundamentally different kind. All the features and/or advantages that are apparent from the claims, description or drawings, including details of construction or three-dimensional arrangements, may be essential to the invention either on their own or in a wide variety of different combinations.

INDUSTRIAL APPLICABILITY

Springs and/or torsion bars of the above-described type are used, for example, in the production of motor vehicles, especially of motor vehicle chassis.

LIST OF REFERENCE SIGNS

1 steel wire
2 spring rod
3′ helical spring
3″ torsion bar spring
10 ring
11 heating
12 thermomechanical forming (TMF)
13 cooling
14 coiling
15 uncoiling
16 grinding
17 heating
18 quenching
19 annealing
20′ cold winding
20″ cold bending
21 cutting
22 spring rod

Claims

1.-15. (canceled)

16. A process for producing a spring or torsion bar from a steel wire by cold forming, the process comprising:

providing a steel wire;

thermomechanically forming the steel wire above a minimum recrystallization temperature of the steel wire, the steel wire having an at least partly austenitic structure;

cooling the thermomechanically-formed steel wire such that an at least partly ferritic-pearlitic structure forms in the steel wire;

tempering the steel wire that has been cooled, wherein the tempering comprises:

heating the steel wire at least to a hardening temperature equal to or greater than an austenite start temperature,

quenching the heated steel wire to a first cooling temperature, the first cooling temperature being a temperature below the minimum recrystallization temperature of the steel wire, wherein an at least partly martensitic structure forms in the steel wire,

reheating the quenched steel wire to a first annealing temperature that is less than the austenite start temperature, and

cooling the reheated steel wire to a second cooling temperature, the second cooling temperature being less than the first annealing temperature;

cold forming the steel wire at a cold forming temperature, the cold forming temperature being a temperature below the minimum recrystallization temperature of the steel wire; and

separating the steel wire.

17. The process of claim 16 wherein the cold forming is performed prior to the separating.

18. The process of claim 16 wherein the separating is performed prior to the cold forming.

19. The process of claim 16 wherein the thermomechanically forming of the steel wire is effected at a temperature equal to or greater than the austenite start temperature.

20. The process of claim 16 wherein the thermomechanically forming of the steel wire is effected at a temperature equal to or greater than an austenite end temperature.

21. The process of claim 16 wherein the thermomechanically forming of the steel wire is effected at a temperature between an austenite end temperature and 50° C. above the austenite end temperature.

22. The process of claim 16 wherein the cooling of the thermomechanically-formed steel wire comprises cooling the steel wire to a temperature below the minimum recrystallization temperature.

23. The process of claim 16 wherein the cooling of the thermomechanically-formed steel wire comprises cooling the steel wire to below 200° C.

24. The process of claim 16 wherein the cooling of the thermomechanically-formed steel wire comprises cooling the steel wire to below 50° C.

25. The process of claim 16 wherein the heating of the steel wire comprises heating the steel wire to a temperature equal to or greater than an austenite end temperature.

26. The process of claim 16 wherein the quenching of the heated steel wire causes a structure of the steel wire to at least partially convert to martensite and causes the steel wire to be exposed to at least a martensite start temperature.

27. The process of claim 26 wherein the quenching is carried out to the first cooling temperature of the steel wire of less than or equal to 200° C.

28. The process of claim 16 wherein the tempering of the steel wire establishes a hardness profile over a cross section of the steel wire.

29. The process of claim 16 further comprising edge heating the steel wire and subsequently recooling the steel wire after tempering, cold forming, or separating the steel wire, wherein a hardness of the steel wire increases from an edge of the steel wire to a core of the steel wire.

30. The process of claim 16 further comprising coiling the steel wire after cooling, tempering, cold forming, or separating the steel wire.

31. The process of claim 16 further comprising surface treating the steel wire wherein a surface of the steel wire is at least partly removed, wherein the surface treating of the steel wire is performed after cooling, tempering, cold forming, or separating the steel wire.