WO2018184855A1

WO2018184855A1 - An elongated steel wire with a metal coating and a polymer coating

Info

Publication number: WO2018184855A1
Application number: PCT/EP2018/057258
Authority: WO
Inventors: Xiaojiang Liu; Li Shen
Original assignee: Nv Bekaert Sa; Bekaert Jiangyin Wire Products Co. Ltd.
Priority date: 2017-04-05
Filing date: 2018-03-22
Publication date: 2018-10-11
Also published as: CN110520544A

Abstract

An elongated steel wire is provided, the elongated steel wire comprises a steel filament, a metal coating for corrosion resistance upon the steel filament and a polymer coating for corrosion resistance upon the metal coating, the steel filament has a microstructure comprising more than 96% tempered martensite. The elongated steel wire is an environment friend product, and it has good corrosion resistance, abrasion resistance, hardness and strength.

Description

Title An elongated steel wire with a metal coating and a polymer coating

Description

Technical Field

[1 ] The invention relates to an elongated steel wire with a metal coating and a polymer coating, and its manufacturing method. The invention relates to the application of an elongated steel wire with high corrosion resistance as carding wire or brush wire. The invention also relates to a flexible clothing, fixed carding flat or wire brush comprising an elongated steel wire with high corrosion resistance.

Background Art

[2] In general, there are two types of so-called carding wires: steel wires for so-called flexible tops or flexible clothing and steel wires to be worked into toothed wires for fixed carding flats.

[3] In the production of textiles, a carding process is for arranging the fibers in a uniform state, i.e. uniform density and uniform thickness, and removing impurities. This can be done by means of flexible clothings or by means of fixed flats.

[4] Flexible clothings comprise small hooks which are set into resilient, multiply fabric layers and are made of steel wires bent into a U shape and provided with a knee. The flexible clothings bend when subjected to loading and return to their original position when no longer loaded. The steel wires for the flexible clothings are usually very hard and are bare steel filament without any coating. The steel wires either have a tempered martensitic structure over their whole volume and length or they have been locally hardened at their tops so that tempered martensite only present at the top.

[5] Similarly the toothed carding wire, is installed in the fixed flats, also has a hardened structure, either locally or over its volume.

[6] Both the toothed carding wire and the steel wire for flexible clothing is not easy to be corroded during the process of carding the fibers, as the friction between the wire and the fibers help to prevent the corrosion of the wire.

However, these steel wires may get sometimes corroded during the transport or installation. The iron oxides on the surface of the steel wire present hard particles, as a consequence of which a corroded carding wire may cause the failure of the carding wire during carding process.

[7] To improve the corrosion resistance, one solution is to provide a carding wire with zinc or zinc alloy coating which can be done by means of a hot dip process However, passing the steel wires through a hot dip bath, means exposing the steel wire to temperatures above the melt

temperature of zinc or zinc alloy. This heat treatment is not desired as it may soften or even change the tempered martensitic structure to be sorbite or tempered sorbite structure, and this leads to less hardness, strength and abrasion resistance.

[8] The present carding wire either is a steel wire with tempered martensite structure without metal coating or a steel wire with a metal coating and sorbite and tempered sorbite structure.

Disclosure of Invention

[9] The primary object of the invention is to provide an elongated steel wire having high corrosion resistance without above drawbacks.

[10] A second object of the invention is to provide an elongated steel wire

having a high corrosion resistance in an environment friendly way but without destroying the metal structure of the steel wire.

[1 1 ] A third object of the invention is to provide a method of manufacturing the elongated steel wire having high corrosion resistance without destroying the metal structure of the steel wire.

[12] A fourth object of the invention is to provide a flexible clothing or fixed flats with high corrosion resistance and proper metal structure.

[13] A fifth object of the invention is to provide a wire brush with high corrosion resistance and proper metal structure.

[14] According to the first aspect of the invention, an elongated steel wire is provided, the elongated steel wire comprises a steel filament, the steel filament has a metal coating for corrosion resistance upon the steel filament, the steel filament further has a polymer coating for corrosion resistance upon the metal coating, the steel filament has a microstructure comprising more than 96% tempered martensite. [15] The elongated steel wire according to the present invention has good performance of corrosion resistance, abrasion resistance, strength and hardness. Furthermore elongated steel wire is an environment friendly product. By applying both a metal coating and a polymer coating, the corrosion resistance of the elongated steel wire is improved, particular the short term corrosion resistance is improved quite a lot, and this makes the elongated steel wire resisting the corrosion during the transport and the installation for the end user ("for the end user" means no heavy

deformation will be applied on the elongated steel wire anymore and the mechanical property of elongated steel wire won't be changed very much).

[16] The metal coating is applied by a method which is different from the

existing way. The existing way of applying metal coating of the steel filament is so-called hot dip, which leads to a steel wire having a

microstructure of more sorbite and tempered sorbite, because the high temperature of hot dip process makes the elongated steel wire going through an unwanted patenting process, and this patenting process makes the metal structure of steel wires being changed to be sorbite and tempered sorbite. The present invention is different, the metal coating upon the elongated steel wire is done with a very low temperature, and this low temperature does not change the metal structure of steel filament, so the metallic structure of the steel filament is kept to be of more than 96% tempered martensite thereby to obtain high hardness, strength and abrasion resistance which are benefit for the further application. During the manufacturing of the invention elongated steel wire, no waste acid, waste gas or heavy metal is generated.

[17] The application of the polymer coating upon the metal coating also doesn't change the metallic structure of the steel filament.

[18] Therefore, the metallic structure in the steel filament has more than 96% tempered martensite. And this makes the elongated steel wire having high hardness, strength and abrasion resistance which are benefit for the further application such as carding wire or brush wire.

[19] Compared with the conventional steel wire with zinc coating made by hot dip, the invention elongated steel wire provides a new solution with less environment pollution, comparable corrosion resistance and higher hardness, abrasion resistance and strength. Compared with the

conventional steel wire without metal coating, the invention elongated steel wire has better corrosion resistance.

[20] The polymer coating could be a coating of anyone of existing polymer for corrosion resistance, and it can also be a co-polymer or a homo-polymer. Preferably the polymer of the polymer coating is polyethylene or polypropylene.

[21 ] Preferably the polymer coating has a thickness being less than 15μηη.

More preferably the polymer coating has a thickness ranging from 1 to 10μΐη.

[22] The polymer can alternatively contain pigment. Either inorganic or organic pigment, the pigment can be special pigment such as luminescent pigment. The elongated steel wire can be applied with the whole visible spectrum, from violet to red.

[23] According to the present invention, the metal coating for corrosion

resistance is for improving the performance of corrosion resistance of the elongated steel wire. The metal inside the metal coating could be any one of the existing metal which can prevent the corrosion of the steel wire. Preferably, the metal coating comprises one or more metal element selected from the group consisting of aluminium, zinc, magnesium and zinc alloy. The different metal elements inside the metal coating are not alloyed with each other, instead, they are separately presenting in the coating.

[24] According to the present invention, the metal element in the metal coating is in the form of flakes and/or particles which are observed in

microstructure. "Flake" means the metal presents a laminar-like shape. The flakes and/or particles of metal, preferably zinc and aluminium, form a closed layer to prevent the corrosion of steel filament. The closed layer of metal coating helps to prevent the corrosion of the elongated steel wire. Particularly for the application of carding wire, the metal coating provides a corrosion resistance enough for preventing the corrosion during the transport and the process of making the flexible cloth or fixed flat.

[25] Although it is called "metal coating", it is not a coating purely consisting of metal, instead there is a binding agent presenting inside the coating to adhere the metal flakes and/or particles, and the coating also has the unavoidable impurities. The binding agent could be any one of the known binding agents, such as organic resin, i.e. epoxy resin.

[26] According to the present invention, there is no alloy in the boundary of the metal coating and the surface of the steel filament, this means the metal element of the metal coating and Fe of the steel wire are not alloyed. This is different from the metal coating made by conventional hot dip method. Even though there is no alloy generated in the boundary of the metal coating and the surface of the steel filament, the adhesion between the metal coating and the steel filament is good and acceptable.

[27] For one preferable embodiment, the metal coating is a coating comprising zinc and aluminium, and both zinc and aluminium are in the form of flakes and/or particles which are observed in microstructure. Preferably, the weight ratio of zinc to aluminium ranges from 0.6 to 160. More preferably, the weight ratio of zinc to aluminium ranges from 3 to 50. In the preferable range, the metal coating has better performance of corrosion resistance and better adhesion with the steel filament. As an alternative, the metal coating is a coating comprising zinc and magnesium, and both zinc and magnesium are in the form of flakes and/or particles which are observed in microstructure

[28] The thickness of the metal coating depends on the requirement of the corrosion resistance of the elongated steel wire. The thicker the metal coating, the better the corrosion resistance, but the higher the production cost. Preferably, the metal coating has a thickness ranging from Ο.δμηη to 50μΐη. More preferably, the metal coating has a thickness ranging from Ο.δμηη to 5μηη.

[29] Preferably, the steel filament has a microstructure comprising more than 99% tempered martensite, or even less than or equal to 100% tempered martensite. Such elongated steel filament has a higher strength, abrasion resistance and hardness, and it is more suitable for the application of flexible clothing, flexible top, raising fillet, fixed flats and wire brush.

[30] The steel filament for the elongated steel wire is carbon steel filament with a certain strength. The carbon content of the steel filament is preferably higher than 0.20% by weight, more preferably ranging from 0.50% to 1 .2%, most preferably ranging from 0.6% to 1 .1 %. The higher the carbon content, the higher the tensile strength. Besides the carbon content, the steel filament comprises one or more other elements, for example, silicon, preferably ranging from 0.10 % to 2.5 %, more preferably ranging from 0.15 to 1 .60 %; manganese, preferably ranging from 0.10 % to 2.0 %, more preferably ranging from 0.50 to 0.90 %; chromium, preferably ranging from 0.0 % to 2.0 %, more preferably ranging from 0.10 % to 1 .50 %; vanadium, preferably ranging from 0.0 % to 2.0 %, more

preferably ranging from 0.05 % to 0.60 %; tungsten, preferably ranging from 0.0 % to 1 .5 %, more preferably ranging from 0.1 % to 0.70 %. The above contents are calculated by weight.

[31 ] The steel filament of the elongated steel wire has any one of existing

cross-sections, for example, round, triangle, oval or flat. The cross-section of the steel filament may have slight convex or concave curve caused by the manufacturing process. Preferably, steel filament has an equivalent diameter ranging from 0.2mm to 6.0mm, more preferably ranging from 0.2mm to 0.8mm. For the round steel filament, the equivalent diameter is its diameter measured by micrometer; for other shaped steel filament, the equivalent diameter is the diameter of a circle of equivalent cross-sectional area.

[32] A further layer can be applied upon the polymer layer depending on the requirement of the steel filament.

[33] According to the second object of the invention, a method of making an elongated steel wire is provided. This method is a continuous process which is very suitable for coating the elongated steel filament which is thin and very long, it comprises:

- step 1 , provide an oil quenched and tempered steel filament, a first bath, a second bath and two heat devices, the first bath comprises organic solvent and metal particles;

- step 2, lead the oil quenched and tempered steel filament through the first bath at atmospheric temperature to provide a metal coating on the surface of the oil quenched and tempered steel filament; - step 3, lead the oil quenched and tempered steel filament through one heat device at a temperature in the range of 150-400 ^°C to dry the metal coating and volatilize the organic solvent;

- step 4, leading said oil quenched and tempered steel filament through a second bath to provide a polymer coating;

- step 5, leading said oil quenched and tempered steel filament through another heat device at a temperature in the range of 150-300 ^°C to dry said polymer coating.

[34] In step 3, the passing of the steel filament through the heat device is very short, the tempered martensitic structure of the steel filament is not changed to a great extent. In addition, the short time avoids waste of energy.

[35] Preferably the heating temperature in step 3 is 150-300 ^°C. Preferably the heating in third step is done with a time ranging from 2 to 8 seconds.

[36] The method doesn't use acid and heavy metal, so it doesn't generate

waste acid, waste gas and heavy metal, and it is environmental friendly. Furthermore this method is a continuous process, and it is fit for the thin and long steel filament. Additionally, both the metal coating process and polymer coating process are done with a low temperature, the metallic structure won't be changed obviously , i.e. the metal structure of the oil quenched and tempered steel filament has a metallic structure of more than 96% tempered martensite, the metal and polymer coated elongated steel wire still has a metallic structure of more than 96% tempered martensite; and thereby the mechanical properties of the steel filament won't be changed obviously, i.e. the strength, abrasion resistance and hardness of the metal and polymer coated elongated steel wire are almost the same as the original oil quenched and tempered steel filament.

[37] The metal coating obtained by the above method doesn't generate any alloy in the boundary between the metal coating and the surface of the steel filament, and the metal in the metal coating is in the form of flakes and/or particles observed in microstructure. This is completely different from a metal coating obtained by conventional hot dip process. [38] According to the present invention, the method further comprises a thickness control step following the step 2 and/or the step 4. The thickness control step is to control the thickness of the metal coating and/or the polymer coating and make the thickness of the metal coating and/or the polymer coating being uniform, and it is done by leading the oil quenched and tempered steel filament through a blowing device or a wiping device. The thickness control step can be done in horizontal direction or vertical direction.

[39] The oil quenched and tempered steel filament is preferably to be cleaned before being coated (the second step). The cleaning of the oil quenched and tempered steel filament makes the metal coating being easier adhering on. The cleaning process can be any one of existing cleaning method.

[40] The above-mentioned organic solvent is a carrier of metal particles to keep the metal particles in the liquid, and it is volatilized after the third step, namely the short heating step. The organic solvent could be any one of existing organic solvent for carrying the metal particles. According to the present invention, preferably the organic solvent is hexyl propionate or propyl acetate.

[41 ] In Step 1 , besides metal particles and organic solvent, the first bath

comprise other additives to contribute to the coating process, such as a binding agent to adhere the metal flakes and/or particles in the coating.

[42] The invention elongated steel wire has many applications, and it can be applied in any field which requires the final steel wire has a certain corrosion resistance performance, such as carding wire, brush wire and control cable wire.

[43] According to the third object of the invention, a fixed flat with toothed steel wire is provided. The fixed flat comprises an elongated steel wire, the elongated steel wire comprises a steel filament, the steel filament has a metal coating for corrosion resistance upon the steel filament, the steel filament further has a polymer coating upon the metal coating, the steel filament has a microstructure comprising more than 96% tempered martensite. The fixed flat is an environment friend product, as its manufacturing method doesn't generate waste acid, waste gas and heavy metal.

[44] According to the present invention, a flexible top is provided. The flexible clothing comprises small hooks or needles, a base comprising multi-ply layers of fabric and rubber and an aluminium holder, the hooks or needles are set into the base, and the base with the hooks or needles is held in said aluminium holder, the hooks or needles are made of elongated steel wires, the elongated steel wire comprises a steel filament, the steel filament has a metal coating for corrosion resistance upon the steel filament, the steel filament further has a polymer coating upon the metal coating, the steel filament has a microstructure comprising more than 96% tempered nnartensite. The top of the hooks or needles may be grinded, thereby the metal coating and the polymer coating are removed, however, this is only occurred in the top end of the hooks or needles.

[45] According to the fourth object of the invention, a wire brush is provided.

The wire brush comprises the wires and a holder, the wires are fixed on the holder, the wires are made of elongated steel wires, the elongated steel wire comprises a steel filament, the steel filament has a metal coating for corrosion resistance upon the steel filament, the steel filament further has a polymer coating upon the metal coating, the steel filament has a microstructure comprising more than 96% tempered martensite. The wire brush is an environment friend product, as its manufacturing method doesn't generate waste acid, waste gas and heavy metal.

[46] According to the present invention, a raising fillet is provided. The raise fillet comprises hooks or needles and a base comprising multi-ply layers of fabric and rubber, the hooks or needles are set into the base, the hooks or needles are made of elongated steel wires, the elongated steel wire comprises a steel filament, the steel filament has a metal coating for corrosion resistance upon the steel filament, the steel filament further has a polymer coating upon the metal coating, the steel filament has a microstructure comprising more than 96% tempered martensite.

[47] "Elongated" is understood to be thin and long, i.e. the length is more than ten times, e.g. more than fifty times the biggest dimension of the cross- section. [48] "Carding wire" is the wire for the application of carding.

[49] "Brush wire" is the wire for the application of brush.

Mode(s) for Carrying Out the Invention

[50] The manufacturing of the elongated steel wire can be done as follows.

[51 ] First, providing an oil quenched and tempered steel filament, a first bath, a second bath and two heat devices, the first bath comprises organic solvent, and metal particles, the second bath comprises polymer.

[52] The oil quenched and tempered steel filament can be made by drawing wire rod together with heat treatments, and it has a metal structure of more than 96% martensite.

[53] The wire rod is firstly cleaned by mechanical descaling and / or by

chemical pickling in a H2SO₄ or HCI solution in order to remove the oxides present on the surface. The wire rod is then rinsed in water and is dried. The dried wire rod is then subjected to a first series of dry drawing operations in order to reduce the diameter until a first intermediate diameter.

[54] At this first intermediate diameter d1 , e.g. at about 2.30 to 3.50 mm, the dry drawn steel filament is subjected to a first intermediate heat treatment, called patenting. Patenting means first austenitizing until a temperature of about 1000^°C followed by a transformation phase from austenite to pearlite at a temperature of about 580 - 650^°C . The steel filament is then ready for further mechanical deformation.

[55] Thereafter the steel filament is further dry drawn from the first intermediate diameter d1 until a second intermediate diameter d2 in a second number of diameter reduction steps. The second diameter d2 typically ranges from 1 .0 mm to 1 .60 mm.

[56] At this second intermediate diameter d2, the steel filament is subjected to a second patenting treatment, i.e. austenitizing again at a temperature of about 1000^°C and thereafter quenching at a temperature of 580 to 650 ^°C to allow for transformation to pearlite.

[57] If the total reduction in the first and second dry drawing step is not too big a direct drawing operation can be done from wire rod till diameter d2. [58] Thereafter the steel filament is further dry drawn or wet drawn from the second intermediate diameter d2 until a final diameter d3 in a third number of diameter reduction steps. The final diameter d3 typically ranges from 0.20 mm to 0.80 mm. More than the round steel filament, the steel filament can also be a non-round shape, e.g. flat, rectangle, double convex, triangle, egg-shape, rhombus and etc, and the non-round filament has an equivalent diameter ranging from 0.20 mm to 0.80 mm.

[59] Thereafter the steel filament is subjected to the oil-quenching and

tempering process. Oil quenching and tempering mean that first

austenitizing until a temperature of about 1000^°C following by a

transformation phase from austenite to martensite at a temperature of about 40 - 150^°C in the quenching oil, then finally going through a tempering process at a temperature of about 300 - 400 ^°C for a final transformation phase of tempered martensite.

[60] The oil quenched and tempered steel filament is provided, and it has a microstructure comprising more than 96% tempered martensite, even more than 99% tempered martensite, or even less than or equal to 100% tempered martensite.

[61 ] A first bath and a heat device are also provided. The first bath comprises organic solvent, binding agent and metal particles, the metal particles are kept in the liquid of organic solvent. The metal particles could be any one or any combination of the elements selected from zinc, zinc alloy, magnesium and alumium particles. The organic solvent could be hexyl propionate or propyl acetate. The heat device is an on-line heating device, could be a heating furnace. The first bath and the heat device are continuously set to make the coating process being continuous.

[62] Following the oil-quenching and tempering process, the steel filament is subjected to a metal coating process. The steel filament is led through the first bath at atmospheric temperature to provide a metal coating on the surface of the oil quenched and tempered steel filament, then it is led through the heat device at a temperature in the range of 150-400 ^°C to dry the metal coating and volatilize the organic solvent. The speed of the steel filament going through the heat device is controlled, preferably, the stay of the steel filament in the heat device is less than 10 seconds, or in the range of 2-8 seconds or even 3-5 seconds. Then the metal coating is fixed on the surface of the steel filament, and an elongated steel wire with a metal coating for corrosion resistance is obtained.

[63] Then the metal coated steel filament is subjected to a polymer coating process. The steel filament goes into the second bath with a certain polymer concentration, for example 30vol%, and a temperature lower than 100^°C to get a thin polymer coating, for example less than 15μηη. And then the steel filament is led through the heat device at a temperature in the range of 150-300 ^°C to dry the polymer coating.

[64] The final elongated steel wire has a carbon content above 0.20% by

weight (preferably less than 1 .2%), a tensile strength typically above 1800 MPa, and a metal coating with a coating thickness ranging from Ο.δμηη to 50μΐη, a polymer coating with a thickness less than 15μηη. The final elongated steel wire has good corrosion resistance, abrasion resistance, strength and hardness.

[65] A first embodiment of the invention is an elongated steel wire. The

elongated steel wire has a steel filament, a metal coating upon the steel filament and a polymer coating upon the metal coating. The steel filament has a microstructure comprising 99.1 % tempered martensite, and it has a carbon content of 0.65%. The steel filament has a round cross-section, and it has a diameter of 0.33mm. The metal coating is a closed coating comprising zinc flakes and/or particles and aluminium flakes and/or particles, and it has a thickness of 1 .1 μηη. An organic resin as a binding agent of the metal flakes and particles is presenting in the metal coating. There is no alloy in the boundary of the metal coating and the surface of the steel filament. The polymer coating comprises polypropylene, and it has a thickness of 3μηη.

[66] A second embodiment of the invention is an elongated steel wire. The elongated steel wire has a steel filament, a metal coating upon the steel filament and a polymer coating upon the metal coating. The steel filament has a microstructure comprising more than 98.2% tempered martensite, and it has a carbon content of 0.72%. The steel filament has a triangular cross-section, and it has an equivalent diameter of 0.35mm. The metal coating is a closed coating comprising zinc flakes and/or particles and aluminium flakes and/or particles, and it has a thickness of 6μηη. An organic resin as a binding agent of the metal flakes and particles is presenting in the metal coating. The polymer coating comprises

polyethylene and it has a thickness of 2μηη. There is no alloy in the boundary of the metal coating and the surface of the steel filament.

[67] A test is done to know the anticorrosion performance of the invention

elongated steel wire. Two prior elongated steel wires are as reference, one is an elongated steel wire without any coating ("Reference 1 "), another is an elongated steel wire with a zinc coating which is coated by hot-dip and has a coating thickness of 3.5μηη ("Reference 2"). A third reference is an elongated steel wire with metal coating comprising zinc flakes and aluminium flakes and having a thickness of 3.0μηη without polymer coating upon the metal coating, the way of applying the metal coating is the same as the method in the present invention. The test is so- called salt spray test according to ASTM B1 17. The time when the corrosion started and severe corrosion occurred is recorded.

From the above table, it is clear that the invention elongated steel wire has a corrosion resistance much better than Reference 1 and 3, and it has a comparable corrosion resistance with Reference 2. Reference 2 has the highest production cost, and furthermore the manufacturing of Reference 2 leads environment pollution (waste gas, waste acid and heavy metal), Reference 2 is not good choice for the future sustainable development. It is clear that the combination of metal coating and polymer coating provides a very good corrosion resistance solution, while with less environment pollution. Additionally, the invention elongated steel wire shows good and comparable hardness, strength and abrasion resistance. The invention elongated steel wire is more suitable for the market.

[69] Another embodiment of the invention is an elongated steel wire. The

elongated steel wire has a steel filament, a metal coating upon the steel filament and a polymer coating upon the metal coating. The steel filament has a microstructure comprising more than 98.5% tempered martensite, and it has a carbon content of 0.8%. The steel filament has a round cross- section, and it has a diameter of 0.40mm. The metal coating is a closed coating comprising zinc flakes and particles, and it has a thickness of 2.5μπη. There is no alloy in the boundary of the metal coating and the surface of the steel filament. The polymer coating is a co-polymer coating based on polyethylene and polyacrylate, and it has a thickness of 3μηη.

[70] A flexible top is provided. The flexible clothing comprises hooks or

needles, a base comprising multiple ply layers of fabric and rubber and an aluminium holder, the hooks or needles are set into the base, and the base with the hooks or needles is held in said aluminium holder. The hooks are made by cutting the elongated steel wire of the first embodiment into a short length and thereafter being bent into U-shape. The tops of the hooks can be grinded or not.

[71 ] A wire brush is provided. The wire brush comprises wires and a holder which is fixed with the wires. The wires are made by cutting the elongated steel wire of the second embodiment into a short length. The wires can be crimped or not.

A raising fillet is provided. The raise fillet comprises hooks or needles and a base comprising multi-ply layers of fabric and rubber, the hooks or needles are set into the base, the hooks or needles are made by cutting the elongated steel wire of the second embodiment into a short length.

Claims

1 . An elongated steel wire, said elongated steel wire comprising a steel filament, said steel filament having a metal coating for corrosion resistance upon said steel filament, characterized in that said steel filament further having a polymer coating for corrosion resistance upon said metal coating, and said steel filament has a microstructure comprising more than 96% tempered martensite.

2. An elongated steel wire according to claim 1 , characterized in that the polymer of said polymer coating is polypropylene or polyethylene.

3. An elongated steel wire according to claim 1 or 2, characterized in that said polymer coating has a thickness being less than 15μηη.

4. An elongated steel wire according to claim 3, characterized in that said polymer coating has a thickness ranging from 1 to 10μηη.

5. An elongated steel wire according to any one of claims 1 to 4, characterized in that said metal coating comprises metal flakes and/or particles observed in microstructure

6. An elongated steel wire according to any one of claims 1 to 5, characterized in that said metal coating comprises organic resin.

7. An elongated steel wire according to any one of claims 1 to 6, characterized in that said steel filament has a microstructure comprising more than 99% tempered martensite.

8. An elongated steel wire according to any one of claims 1 to 7, characterized in that said metal coating is a coating comprising zinc and aluminium.

9. An elongated steel wire according to claim 8, characterized in that the weight ratio of said zinc to said aluminium ranges from 3 to 50.

10. An elongated steel wire according to any one of claims 1 to 9, characterized in that said metal coating has a thickness ranging from Ο.δμηη to 50μηη.

1 1 .An elongated steel wire according to claim 10, characterized in that said metal coating has a thickness ranging from Ο.δμηη to 5μηη.

12. A method of making an elongated steel wire according to any one of previous claims, said method is a continuous process comprising:

- step 1 , providing an oil quenched and tempered steel filament, a first bath, two heat devices and a second bath, said first bath comprising organic solvent and metal particles, and second bath comprising polymer;

- step 2, leading said oil quenched and tempered steel filament through said first bath at atmospheric temperature to provide a metal coating on the surface of said oil quenched and tempered steel filament;

- step 3, leading said oil quenched and tempered steel filament through one said heat device at a temperature in the range of 150-400 ^°C to dry said metal coating and volatilize said organic solvent;

- step 4, leading said oil quenched and tempered steel filament through said second bath to provide a polymer coating;

- step 5, leading said oil quenched and tempered steel filament through another said heat device at a temperature in the range of 150-300 ^°C to dry said polymer coating.

13. A flexible top comprising hooks or needles, resilient and a base comprising multi-ply layers of fabric and rubber and an aluminium holder, said hooks or needles are set into said base, said base with said hooks or needles is held in said aluminium holder, hooks or needles are made of elongated steel wires according to any one of claims 1 to 1 1 .

14. A wire brush comprising the wires and a holder, said wires being fixed on said holder, said wires are made of elongated steel wires according to any one of claims 1 to 1 1 .

15. A raising fillet comprising hooks or needles and a base comprising multi-ply layers of fabric and rubber, said hooks or needles are set into said base, said hooks or needles are made of elongated steel wires according to any one of claims 1 to 1 1 .