WO2018233986A1

WO2018233986A1 - Wire with steel core and metal alloy coating

Info

Publication number: WO2018233986A1
Application number: PCT/EP2018/063955
Authority: WO
Inventors: Simone Agresti
Original assignee: Nv Bekaert Sa
Priority date: 2017-06-22
Filing date: 2018-05-28
Publication date: 2018-12-27
Also published as: CN110785510B; HUE053878T2; EP3642382B1; CN110785510A; ES2860579T3; EP3642382A1

Abstract

A wire (30) has a core (32) of steel with a diameter ranging from 0.30 mm to 3.0 mm. The wire (30) has two layers (34, 36) of metal coating: - a first layer (34) of a zinc alloy around the core (32) and clearly showing a zinc gradient with zinc being more present at the outer side, - a second layer (36) of copper around the first layer (34). This wire is an intermediate product that allows manufacturing of steel filaments for rubber reinforcement in an efficient way.

Description

Title: Wire with steel core and metal alloy coating

Description

Technical Field

[0001 ] The invention relates to a wire having a core of steel and a metal coating and to a method of manufacturing and further processing such a wire.

Background Art

[0002] Steel wires with a metal alloy coating, e.g. a brass coating, are known for the reinforcement of rubber products, such as rubber tires. The alloy coating is obtained by first plating the separate metals one after the other, followed by a heat treatment to diffuse the metals into an alloy. High demands are made upon these steel wires such as a high tensile strength and a high level of adhesion to rubber.

[0003] Steel wires with a metal alloy coating, e.g. a brass coating, are also known for use as loose abrasive sawing wire for the cutting of silicon ingots. As with the steel wires for rubber reinforcement, the alloy coating is here also obtained by first plating the separate metals one of the other, followed by a heat treatment to diffuse the metals into an alloy. High demands are also made upon these sawing wires such as, particularly, a high tensile strength.

[0004] It is known in the art that high tensile strengths are obtained by applying a high degree of cold deformation to the steel wires, more particularly, by means of a wet wire drawing operation with a high degree of cross-section reduction.

The state of the art of cold deformation, however, has its own inherent limits.

In order to obtain a high tensile strength, the degree of drawing has to be high. The higher the degree of drawing, the higher the losses of metal coating as a consequence of the drawing operation, more particularly as a result of the contacts between the steel wire and the drawing dies. These high losses of metal coating might be compensated by applying a thicker coating. However, this thicker coating will require a more intense heat treatment to diffuse the two metals into an alloy. The more intense this heat treatment, the higher the losses in tensile strength for the steel wire. This means that the starting tensile strength is lower, which need to be compensated by even higher degrees of drawing.

As a result, according to the state of the art and without changing other parameters such as the steel composition, there is somewhere an optimum of the obtainable final tensile strength, which is difficult to further increase without deteriorating processing.

Disclosure of Invention

[0005] It is a primary object of the invention to further increase the obtainable tensile strength.

It is a further object of the invention to improve the deformability of steel wires.

It is also an object of the invention to reduce coating losses during deformation.

It is yet another object of the invention to reduce drawing die consumption. Viewed from another point of view, the invention also aims to reduce drawing lubricant consumption.

Still another object of the invention is to keep the adhesion in rubber products.

[0006] According to a first aspect of the present invention, there is provided a steel wire with a core of steel with a diameter ranging from 0.30 mm to 3.0 mm. The steel wire has two layers of metal coating:

1 ) a first layer of a zinc alloy around the steel core and clearly showing a zinc gradient with zinc being more present at the outer side;

2) a second layer of copper around this first layer.

Steel wires with a diameter ranging from 0.30 mm to 1 .0 mm are suitable intermediate products to make loose abrasive sawing wire.

Steel wires with a diameter ranging from 0.90 mm to 3.0 mm are suitable intermediate products to make steel filaments adapted for rubber reinforcement.

[0007] Due to the fact that the first layer of the zinc alloy clearly shows a zinc gradient, the heating treatment for diffusion of the two or more metals in the alloy can be less intense. Hence loss of tensile strength can either be avoided or even not be present. So the intermediate steel wires have a higher starting tensile strength. As a result, for equal degrees of deformation, the final tensile strength is higher or for equal final tensile strengths, the degree of deformation can be lower.

The second top layer of copper above the first layer improves the deformability, reduces coating losses, reduces die wear and reduces lubricant consumption.

[0008] Prior art documents JP-A2-62-246425, EP-A2-0 185 492, JP-A2-61 -

284321 , J P-A2-61 -28432 and JP-A2-61 -241027 all disclose steel wires adapted for electro-discharge machining (EDM). These steel wires have a zinc alloy coating having a zinc gradient, with zinc density becoming high towards the outer surface. Due to the fact that zinc causes a higher friction than copper and to the fact that more zinc is present at the surface, these steel wires will not have an improved drawability and neither will lead to a reduction in coating loss, a reduction in lube consumption or a reduction in die wear, on the contrary.

[0009] Prior art document WO-A1 -201 1/076746 discloses a brass coated steel wire with a zinc gradient in the coating. The zinc gradient is such that, in contrast to the invention, less zinc is present at the surface of the brass layer.

[0010] Prior art document EP-B1 -1 295 985 discloses a steel wire with two layers of metal coating. The first layer is a brass coating, the second top layer is a copper layer. EP-B1 -1 295 985 does not teach the presence of a zinc gradient in the first layer. In addition, the top layer of copper has a thickness which is smaller than 0.02 μιτι.

[001 1 ] In an embodiment of the invention, the first layer is a copper-M-zinc alloy, where M is one or more metals selected from the group consisting of cobalt, nickel, tin, indium, manganese, iron, bismuth and molybdenum. The first layer and the second layer together may have a copper content ranging from 58 wt% to 75 wt%, e.g. from 61 wt% to 70 wt%. The content of the one or two metals M may range from 0.5 wt% to 10 wt%, e.g. from 2 wt% to 8 wt%.

[0012] In a preferable embodiment of the invention, the first layer is a copper-zinc alloy, only having copper and zinc as main elements.

The first layer and the second layer together may have a copper content ranging from 60 wt% to 70 wt%, e.g. from 61 wt% to 69 wt%.

[0013] The terms "clearly showing a zinc gradient with zinc being more present at the outer side" preferably refer to a configuration where there is Xout per cent of zinc at the outer side of the first layer and Xin per cent of zinc at the inner side of the first layer and where the difference Xout - Xin is more than 15 percent, e.g. more than 16 per cent, e.g. more than 17 per cent, e.g. more than 18 per cent.

[0014] In a preferable embodiment of the invention, the weight percentage of copper over the first and the second layer is more than 58 wt%.

In a preferable embodiment of the invention, the weight percentage of copper is lower than 70 wt%.

[0015] The second layer of copper has preferably a thickness more than 0.10 μιτι, e.g. more than 0.12 μιτι, e.g. more than 0.15 μιτι.

[0016] According to a second aspect of the invention, there is provided a method of manufacturing a steel wire. This method comprises the following steps: a. providing a steel core with a diameter ranging between 0.30 mm and 3.0 mm;

b. plating this steel core with two or more metals, one of them being zinc; c. heating the thus plated steel core so that the two or more metals

partially diffuse and form a first layer, clearly showing a zinc gradient with zinc being more present at the outer side than the inner side;

d. plating a second layer of copper around the first layer.

[0017] Preferably, regarding the zinc gradient, there is Xout per cent of zinc at the outer side of the first layer and Xin per cent of zinc at the inner side of the first layer and where the difference Xout - Xin is more than 15 percent, e.g. more than 16 per cent, e.g. more than 17 per cent, e.g. more than 18 per cent.

[0018] In a preferable embodiment of the invention, the method further comprises the step of drawing the steel wire so that the copper of the second layer and the two or more metals of the first layer diffuse into each other and form one global layer.

[0019] Most preferably, the diffusion as a result of the drawing operation is such that the outer side of the global layer has Xgout per cent of zinc and the inner side of the global layer has Xgin per cent of zinc, where Xgout - Xgin is less than 15 per cent, e.g. less than 14 per cent, e.g. less than 12 per cent.

Brief Description of Figures in the Drawings

[0020] Figure 1 schematically shows steps to manufacture an intermediate steel wire according to the prior art;

[0021 ] Figure 2 schematically shows steps to manufacture an intermediate steel wire according to the invention;

[0022] Figure 3 shows a cross-section of an intermediate steel wire according to the invention;

[0023] Figure 4 shows a cross-section of a final steel filament; Mode(s) for Carrying Out the Invention

[0024] Figure 1 illustrates in a schematic way a prior art process. A steel wire 10 is first plated with copper (Cu) in a copper plating installation 12 in an amount equal to the final amount of copper needed or desired. The copper plated wire is then coated with zinc (Zn) in a zinc plating

installation 14 in an amount equal to the final amount of zinc needed or desired. The steel wire with the double coating is then subjected to a thermodiffusion treatment, e.g. by means of a mid-frequent installation 16. The thickness of the brass coating is represented in 17. The amount of thermodiffusion energy spent is such that a full alloying of copper with zinc is obtained, or at least approximated. This means that a gradient of zinc throughout this brass coating is non-existent or limited to maximum 15%, preferably maximum 10%. The result of this prior art process is a steel wire 18 with a more or less homogeneous brass coating.

[0025] Figure 2 illustrates the present invention. A steel wire 20 enters into a copper plating bath 22 where only 75% to 85% of the amount of finally desired or needed copper is deposited on the steel 20. Thereafter the steel wire enters into a zinc plating installation 24 where 100% of the amount of the finally desired or needed zinc is deposited. The steel wire with the double layer is then subjected to a thermodiffusion treatment in, e.g. a mid-frequent installation 26. In distinction with the prior art, only a partial alloying is aimed at, which means that only a partial diffusion is carried out thus saving 15 to 30% of thermodiffusion energy. The thickness of the partially alloyed copper-zinc coating is illustrated in 27. After the thermodiffusion step, the steel wire is plated with the remaining 25% to 15% of copper in a second copper plating installation 28.

[0026] The result is an intermediate wire 30 with a first layer of a copper-zinc alloy that is showing a clear gradient of zinc with zinc being more present at the outer side and a second layer of copper on top and around of the first layer. Due to its top copper coating, this intermediate wire 30 has a color that is more red than a wire with a common brass coating.

[0027] The partial diffusion treatment in the installation 26 bounds the zinc to

copper, despite the presence of a zinc gradient. This bounding prevents the zinc from dissolving in the second copper bath 28.

[0028] Next to the degree of energy saving, the less intense thermodiffusion

treatment has as additional advantage that the loss in tensile strength of the intermediate steel wire is either non-existent or substantially reduced. All other parameters being unchanged, this means that the tensile strength before the beginning of the wet wire drawing operation is higher than it is in the prior art. Tests have shown differences in tensile strength between the prior art and the invention that vary between 10 MPa and 25 MPa.

[0029] A cross-section of the double coated intermediate steel wire 30 is shown in Figure 3. The steel wire 30 has a steel core 32, a first layer of a partially alloyed copper-zinc coating 34 and a second layer of copper 36 on top of the first layer 34.

[0030] Figure 4 shows a cross-section of a final steel filament 40. It has a steel core 42 and a single 'global' layer of brass 44 without gradient or with a gradient that is less pronounced than the gradient of the intermediate steel wire 30.

[0031 ] As mentioned, wet wire drawing is the process that transforms the

intermediate steel wire 30 into the final steel filament 40. The heat generated during the wet wire drawing process causes the first layer and the second to diffuse with each other in order to result in a brass coating that is more or less homogeneous.

In comparison with the prior art, following differences are apparent when drawing an intermediate steel wire according to the invention.

A loss of only 3% to 4% of the coating is noticed. The wet wire drawing process consumes less lubricant.

Less energy is needed in the wet wire drawing process.

Less die wear is noticed.

These advantages can be attributed to the top copper coating 36 that causes less slip than a brass or a zinc coating.

[0032] Next to advantages experienced during wet wire drawing, the further downstream processing such as the cord twisting also has its advantages when handling a steel filament that originates from an intermediate steel wire according to the invention. More particularly, a substantial reduction in the number of fractures has been noticed. For one particular steel cord construction made by a double-twisting ("bunching") process, the level of fractures per ton was reduced with 50%.

[0033] Table 1 hereunder mentions following values and parameters:

- wire diameter of the intermediate steel wire;

- amount and thickness of the copper in the 1 ^st layer;

- amount and thickness of the zinc in the 1 ^st layer;

- amount and thickness of the copper in the 2^nd layer;

- Xout the percentage of zinc at the radially outer side of the 1^st layer after thermodiffusion;

- Xin the percentage of zinc at the radially inner side of the 1^st layer after thermodiffusion;

- Xout - Xin the gradient of Zn;

- the percentage of thermodiffusion energy saved in an invention process compared with the prior art.

The percentages of Zn have been measured by means of an X-ray photo electron spectroscopy (XPS) in combination with depth profiling with an argon ion gun.

Table 1

Wire 1st layer 2nd layer Xout Xin Xout - energy

Diameter Cu Zn Cu Xin saved

(mm) (g/kg) (nm) (g/kg) (nm) (g/kg) (nm) (%) (%) (%) (%) 1,65 2,08 755 1,51 688 0,52 189 50,3 27,9 22,4 20

1,09 3,01 722 2,09 629 0,53 127 54,1 17,7 36,4 17

1,85 1,9 773 1,36 694 0,41 167 49,7 26 23,7 25

[0034] For a final steel filament 40 the single brass coating has a zinc gradient that is much smaller than that of the first layer of an intermediate steel wire 30.

For a 0.30 mm final steel filament, a gradient Xgout - Xgin of 10% was measured, and for a 0.175 mm final steel filament, a gradient Xgout - Xgin of 1 1 % was measured.

[0035] A suitable steel composition is e.g. a minimum carbon content of 0.65%, a manganese content ranging from 0.10% to 0.70%, a silicon content ranging from 0.05% to 0.50%, a maximum sulphur content of 0.03%, a maximum phosphorus content of 0.03%, even of 0.02%, all percentages being percentages by weight. There are only traces of copper, nickel and / or chromium. The remainder is always iron.

[0036] Micro-alloyed steel compositions may also be suitable such as

compositions further comprising one or more of following elements:

- chromium (%Cr): in amounts ranging from 0.10% to 1.0%, e.g. from 0.10 to 0.50%;

- nickel (%Ni): in amounts ranging from 0.05% to 2.0%, e.g. from 0.10% to 0.60%;

- cobalt (%Co): in amounts ranging from 0.05% to 3.0%; e.g. from 0.10% to 0.60%;

- vanadium (%V): in amounts ranging from 0.05% to 1.0%, e.g. from 0.05% to 0.30%;

- molybdenum (%Mo): in amounts ranging from 0.05% to 0.60%, e.g. from 0.10% to 0.30%;

- copper (%Cu): in amounts ranging from 0.10% to 0.40%, e.g. from 0.15% to 0.30%;

- boron (%B): in amounts ranging from 0.001 % to 0.010%, e.g. from 0.002% to 0.006%;

- niobium (%Nb): in amounts ranging from 0.001 % to 0.50%, e.g. from 0.02% to 0.05%;

- titanium (%Ti): in amounts ranging from 0.001 % to 0.50%, e.g. from 0.001 % to 0.010%;

- antimony (%Sb): in amounts ranging from 0.0005% to 0.08%, e.g. from 0.0005% to 0.05%;

- calcium (%Ca): in amounts ranging from 0.001 % to 0.05%, e.g. from 0.0001 % to 0.01 %;

- tungsten (%W): e.g. in an amount of about 0.20%;

- zirconium (%Zr): e.g. in an amount ranging from 0.01 % to 0.10%;

- aluminum (%AI): preferably in amounts lower than 0.035%, e.g. lower than 0.015%, e.g. lower than 0.005%;

- nitrogen (%N): in amounts less than 0.005%;

- rare earth metals (%REM): in amounts ranging from 0.010% to 0.050%.

[0037] Within the context of the present invention low-carbon steel compositions such as disclosed in EP-A-2 268 839 are not excluded. Such a steel compositions has a carbon content of less than 0.20 %. An example is a carbon content ranging between 0.04 % and 0.08 %, a silicon content of 0.166 %, a chromium content of 0.042 %, a copper content of 0.173 %, a manganese content of 0.382 %, a molybdenum content of 0.013 %, a nitrogen content of 0.006 %, a nickel content of 0.077 %, a phosphorus content of 0.007 %, a sulphur content of 0.013 %, all percentages being percentages by weight.

[0038] Reference numbers

10 steel wire

12 copper (Cu) plating

14 zinc (Zn) plating

16 thermodiffusion

17 brass coating CuZn

18 brass coated steel wire

20 steel wire

22 copper (Cu) plating but not to its full extent 24 zinc (Zn) plating

26 thermodiffusion but not to its full extent

28 top copper (Cu) plating

30 brass + top copper plated steel wire

32 steel core

34 first layer of brass

36 second layer of copper

40 final steel wire

42 steel core

44 layer of brass

Claims

1 . A wire

having a core of steel with a diameter ranging from 0.30 mm to 3.0 mm, said wire having two layers of metal coating:

- a first layer of a zinc alloy around said core and clearly showing a zinc gradient with zinc being more present at the outer side,

- a second layer of copper around said first layer.

2. A wire according to claim 1 ,

wherein said first layer is a copper-M-zinc alloy, where M is one or two metals selected from the group consisting of cobalt, nickel, tin, indium, manganese, iron, bismuth and molybdenum.

3. A wire according to claim 1 ,

wherein said first layer is a copper-zinc alloy.

4. A wire according to any one of the preceding claims,

wherein said outer side of said first layer has Xout per cent of zinc and said inner side of said first layer has Xin per cent of zinc, Xout - Xin being more than 15 per cent.

5. A wire according to any one of claims 2 to 4,

wherein the weight percentage of copper over both the first and the second layer is more than 58 wt%.

6. A wire according to claim 5,

wherein the weight percentage of copper over the first and the second layer is lower than 70 wt%.

7. A wire according to any one of the preceding claims,

wherein the second layer has a thickness being more than 0.10 μιτι.

8. A method of manufacturing a wire, said method comprising the following steps a. providing a steel core with a diameter ranging between 0.30 mm and 3.0 mm;

b. plating said steel core with two or more metals, one of them being zinc;

c. heating the thus plated steel core so that the two or more metals partially diffuse and form a first layer, clearly showing a zinc gradient with zinc being more present at the outer side than the inner side; d. plating a second layer of copper around said first layer.

9. A method according to claim 8,

10. A method according to claim 8 or 9,

said method further comprising the step:

e. drawing said steel wire so that the copper of the second layer and the two or more metals of the first layer diffuse into each other and form one global layer.

1 1 .A method according to claim 10,

wherein the diffusion as a result of said drawing is such that said outer side of said global layer has Xgout per cent of zinc and said inner side of said global layer has Xgin per cent of zinc, Xgout - Xgin being less than 15 per cent.