JPH0417616A - Production of stainless steel wire - Google Patents

Abstract

PURPOSE:To produce the stainless steel wire with which spark flaws, contact flaws and plating flaws are prevented by subjecting the stainless steel wire to a surface hardening treatment prior to the execution of an Ni plating treatment, then subjecting the wire to the Ni plating treatment in the state of applying tension thereto. CONSTITUTION:The austenitic stainless steel wire is subjected to an under drawing treatment at need then to a soln. heat treatment (heating to about 110 deg.C) by the conventional method. The wire is then subjected to the surface hardening treatment by rolling, etc., by which the Vickers hardness is improved to about 50 to 150; thereafter, the tension is applied to the wire and while the wire is held straight, the wire is subjected to the Ni plating. After the plating layer is formed, the wire is further subjected to finish drawing so that alpha' martensite is incorporated at 60 to 90% into the structure of the wire. The stainless steel wire which has the good workability and is improved in the electrical conductivity and corrosion resistance is obtd. This steel wire is useful for coil springs, etc.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a method for manufacturing a stainless steel wire that has good workability and is mainly used for coil springs with improved conductivity and corrosion resistance.

[Prior Art] Stainless steel wire is widely used in coil springs and the like because of its good corrosion resistance. The surface of this stainless steel wire has poor lubricity during wire drawing and even during spring forming, so during manufacturing, the surface of the stainless steel wire is coated with a resin film and metal plating with lead, copper, nickel, etc. to improve lubricity. is increasing.

Among them, the most common is nickel plating.

There are two ways to condition the stainless steel wire before nickel plating: one is to plate the hard wire itself, and the other is to plate it in a soft state through solution treatment. Each method has its advantages and disadvantages. In other words, when a hard wire is subjected to nickel plating and then subjected to solution treatment, the hydrogen gas absorbed during the plating process is released and contributes to improving the properties of the wire afterwards, or the nickel plating and stainless steel base material are mixed. This has the advantage of creating a metal diffusion layer between the layers to improve adhesion. However, in this method, the hard wire is plated, so the wire tends to be curly and the plating wire may get tangled with neighboring wires in the plating tank, touch the contact part with the electrode rod, or come apart, causing sparks. There are many problems such as scratches occurring in this part. Therefore, as a countermeasure, there is a method of solution treatment and nickel plating (for example,
No. 278). In this case, the generatrix is too soft and scratches occur in the guide of the plating device, and when winding the bobbin during solution treatment, the overlapping portions of the bobbin body may form nicks (micro islands). , this may meander in the plating bath and come off the electrode rod, causing sparks. Furthermore, since the bus bar before plating is subjected to solution treatment at about 1100° C., the surface layer of the stainless steel is soft and many grain boundaries are exposed to the outside, providing many places for hydrogen to enter during plating. Also, if the stainless steel base material is too soft, when the nickel that has precipitated on it comes into contact with the die during subsequent wire drawing, the nickel may sink into the base material before the nickel itself can fully demonstrate its lubricity. There is.

In that case, the gaps between the precipitated nickel crystal grains, that is, the gaps into which the lubricant powder fits, decrease, resulting in a decrease in lubricity.

Furthermore, if a stainless steel bus bar is plated with a metal such as nickel, the corrosion resistance of the stainless steel itself may be adversely affected depending on the operating environment.

[Problems to be Solved by the Invention] The purpose of the present invention is to surface harden the stainless steel wire before nickel plating and perform the nickel plating under tension. An object of the present invention is to provide a method for manufacturing stainless steel wire that prevents spark flaws, contact flaws, and scratch flaws.

Another object of the present invention is to surface harden the stainless steel wire before nickel plating.
It is an object of the present invention to provide a method for manufacturing a stainless steel wire that prevents hydrogen from entering the steel wire during nickel plating treatment, thereby preventing embrittlement of the stainless steel wire.

A further object of the present invention is to surface harden the stainless steel wire before nickel plating.
By making the steel wire harder than the nickel plating layer formed on the surface, it prevents the nickel plating layer from being embedded in the steel wire during finishing, and also prevents many cracks from forming in the nickel plating layer. In addition, it is an object of the present invention to provide a method for producing a stainless steel wire, which can increase the penetration area of the lubricant through the effects of both of the above and improve the lubricity.

A further object of the present invention is to provide a method for manufacturing a stainless steel wire that improves the corrosion resistance of a styrene steel wire by forming the plating layer into a three-layer structure of a semi-bright nickel plating layer, a copper plating layer, and a bright nickel plating layer. That's true.

[Means for Solving the Problems] In order to achieve this object, the method for manufacturing a stainless steel wire of the present invention includes a step of solution-treating an austenitic stainless steel wire, and a surface treatment of the solution-treated steel wire. A stainless steel wire manufacturing process that includes a hardening process, a nickel plating process with tension applied to the surface hardened steel wire, and a final wire drawing process on the nickel plated steel wire. This is the manufacturing method.

In the method for manufacturing a stainless steel M wire according to an embodiment of the present invention, the plating treatment on the stainless steel wire is semi-bright nickel plating,
This is a process in which copper plating and bright nickel plating are performed in sequence.

A method for manufacturing a stainless steel wire according to another embodiment of the present invention includes:
The steel wire to be solution-treated is subjected to underdrawing.

A method for manufacturing a stainless steel wire according to another embodiment of the present invention includes:
Surface hardening is performed so that the surface hardness of the steel wire obtained by surface hardening of the steel wire is higher than the hardness of the nickel plating layer obtained by nickel plating.

In the method for producing a stainless steel wire according to an embodiment of the present invention, in the finishing wire drawing treatment, alpha martensite is present in the structure of the steel wire from 60 to 60%.
This is done to ensure that it contains 90%.

[Operations and Effects] According to the method for manufacturing a stainless steel wire of the present invention, the stainless steel wire is subjected to a surface hardening treatment before being nickel plated, and the nickel plating treatment is performed under tension. Therefore, nickel plating treatment is
The surface of the stainless steel wire being treated is hard and straight. This prevents the stainless steel wire from coming into contact with the guides and electrodes of the nickel plating equipment, and even if contact occurs, the stainless steel wire is less likely to be damaged. That is, spark flaws, contact flaws, and scratch flaws on the stainless steel wire during plating can be prevented.

According to the method for manufacturing a stainless steel wire of the present invention, the stainless steel wire is subjected to surface hardening treatment before being subjected to nickel plating treatment. For this reason, the grain boundaries formed on the surface of the stainless steel wire (this becomes the entry route for hydrogen)
By crushing the stainless steel wire, it is possible to prevent hydrogen from penetrating and being trapped inside the steel wire during the nickel plating process, thereby preventing the stainless steel wire from becoming brittle. Although hydrogen embrittlement may be promoted by hardening the material, this does not pose a problem in the processing of the present invention, and rather, crushing grain boundaries is more effective in preventing embrittlement.

Furthermore, according to the method for manufacturing a stainless steel wire of the present invention, by subjecting the stainless steel wire to surface hardening treatment before performing the nickel plating treatment, the hardness of the steel wire can be improved by applying a nickel plating layer formed on the surface. It can be made harder. As a result, since the stainless steel wire is hard, the nickel plating layer is not embedded in the steel wire during the initial wire drawing process, and a large amount of lubricant gets stuck in the grain boundaries of the precipitated nickel crystals. The soft nickel plating layer is plastically deformed, causing many cracks in the nickel plating layer, and the lubricant also penetrates into these cracks, increasing the area where the lubricant can penetrate and improving lubricity. can. According to another method of manufacturing stainless steel wire of the present invention,
By making the plating layer a three-layer structure of semi-bright nickel plating layer, copper plating layer, and bright nickel plating layer, when the plated stainless steel wire is placed in a corrosive environment, the base bright plating layer becomes an anode. When melted, the copper and semi-bright plating layer acting as a cathode prevents corrosion, thereby protecting the underlying stainless steel wire and improving its corrosion resistance.

[Detailed Description of the Invention] In the method for producing a stainless steel wire of the present invention, an austenitic stainless steel wire is first prepared, and if necessary, this steel wire is subjected to underdrawing treatment according to a conventional method. After solution treatment (heating to about 1100° C.) according to a conventional method, a surface hardening treatment is performed (hereinafter, the steel wire obtained by this treatment will be referred to as a generatrix). This surface hardening treatment is performed so that the hardness of the generatrix is higher than that of the plating layer formed on the surface of the generatrix, and it is usually preferable to perform the treatment to increase the Vickers hardness by about 50 to 150. . In other words, the hardness of the generatrix varies depending on the wire diameter, but is generally Hv170.
It is about ~230. In addition, the hardness of the nickel plating layer deposited and formed on the surface of this generatrix varies depending on the plating conditions (solution composition, solution pH, solution temperature, presence or absence of additives, etc.), but in normal plating, the hardness is Hv190 to 250. That's about it. Therefore, by increasing the Vickers hardness by about 50 to 150, the hardness of the generatrix becomes approximately harder than the nickel plating layer. The surface hardening treatment may be performed, for example, by rolling the generatrix, or by reducing the wire diameter to 1/2 using a wire drawing die.
This is done by making it thinner by about 10 to 1/30. After or at the same time as this surface hardening treatment, tension is applied to the generatrix and the generatrix is held straight and passed through the plating bath.

When plating the generatrix, hydrogen tries to penetrate into the generatrix, but the grain boundaries of the austenite structure exposed on the surface of the base metal due to the above surface hardening treatment (this is where hydrogen easily penetrates). is crushed, and the amount of hydrogen stored in the bus bar decreases. The plating of the bus bar may be performed by ordinary nickel plating according to a conventional method, or by sequentially performing semi-bright nickel plating, copper plating, and bright nickel plating to form three plating layers. good. When a three-layer plating layer is formed, when a plated stainless steel wire is placed in a corrosive environment, the base bright plating layer acts as an anode and dissolves, and the responsible copper or semi-bright nickel plating layer acts as a cathode to prevent corrosion. As a result, the underlying stainless steel wire is protected and its corrosion resistance is improved.

After forming the plating layer, when finishing wire drawing is performed, the hardness of the generatrix is higher than that of the plating layer, so the nickel plating layer is not embedded in the steel wire, and the relatively soft nickel plating layer undergoes plastic deformation. As a result, many cracks are generated in the nickel plating layer, and the lubricant penetrates into these cracks, thereby increasing the area into which the lubricant penetrates and improving lubricity.

When the stainless steel wire produced in this manner is subjected to wire drawing, the austenitic structure changes to a martensitic structure, increasing hardness and strength. The degree of change from austenite to martensitic structure varies depending on the amount of elements such as nickel, chromium, and carbon that make up the stainless steel.For the spring circumferential wire, nickel 8
%, 18% chromium, 0.07% carbon, and 18-8 stainless steel is the most common. When using this component as a spring wire material, the amount of martensite generated by processing is 60% or more.
A tissue mechanical property of 90% is most suitable. In order to generate this amount of martensite, it is sufficient to stretch the wire to a finished diameter that is approximately 1/2 to 1/4 of the diameter of the generatrix in a normal temperature environment. The amount of martensite is 60%
If it is less than 90%, the strength will be insufficient, and if it is less than 90%, it will become brittle, which is not preferable. The degree to which martensite is formed from austenite varies significantly depending not only on the degree of processing but also on the temperature at the time of processing, so it is important to adequately control the processing temperature during wire drawing.

Stainless steel wires for springs manufactured using these various unique manufacturing methods have good lubricity on the surface, making them easy to form afterward, and the finished springs also have good electrical conductivity, corrosion resistance, and It can be said to be the optimal product in terms of strength.

[Example code] Next, the present invention will be specifically explained with reference to Examples.

Examples and Comparative Examples Stainless steel wires were manufactured using austenitic stainless steel materials containing the elements shown in Table 1 by the following various methods.

A. (Conventional method: No surface hardening treatment or application of tension to the busbar) After applying 5.0μm nickel plating to the solution-treated busbar wound on a bobbin with a diameter of 1.5mmφ, the diameter was reduced to 1/3.
The wire was drawn to 0.5 mm and processed into a coil spring.

B: (Conventional method: No surface hardening treatment or application of tension to the generatrix) 1.5mmφ hard drawn wire with strong wire drawing process
After applying nickel plating to the thickness indicated by μ, solution treatment was performed, and wire drawing was performed to a diameter of 1/3, ie, 0.5 mm.

C: (Method of the present invention) A bobbin-wound generatrix with a diameter of 1.61 mmφ that has been solution-treated is lightly rolled to a diameter of 1.5 mm, and then nickel plated to a thickness of 5.0 μm to reduce the diameter by 1/1.
3 was drawn to a diameter of 0.5 mm and processed into a coil spring. In addition, back tension of about 30 dazzles was added during the metsuki. The hardness of the generatrix after light rolling is 28
The hardness of the nickel plating layer was 190Hv.

D: (Method of the present invention) A bobbin-wound generatrix with a diameter of 1.5 mm that has been solution-treated is lightly rolled to a diameter of 1.4 mm, and a 2 μm thick semi-bright nickel plating is applied thereon.
Copper plating with the mark was applied, and then 2 μm bright nickel plating was applied thereon, and the wire was then drawn to 1/3 of the diameter, 0.50 mmφ, and this was processed into a coil spring. In addition, about 30 kg of pack tension was added during the metsuki. The hardness of the bus bar after light rolling was 290 Hv, and the hardness of the nickel plating layer was 200 Hv.

The plating line used here is shown in FIG. In the figure, 1 is the bus bar, 2 is the rolling roller, 3 is the bowed capstan, 4 is the pretreatment layer, 5 is the semi-bright nickel plating layer, 6
7 shows a copper plating layer, 7 shows a bright nickel plating layer, 8 shows a drawer capstan, and 9 shows a stainless steel wire after plating.

Table 2 shows the mechanical properties and flatness of these test products after wire drawing and surface observation.

From this table, when comparing the conventional method and the method of the present invention, it is clear that the flatness ratio of the product C of the present invention is particularly small and has good lubricity. In addition, although the product C of the present invention has high strength, the drawing ratio is large. Furthermore, the product of the present invention is similar to conventional products A and B.
It can be seen that the flatness ratio is smaller, the reduction ratio is larger, and the lubricity and toughness are superior compared to the above.

Table 3 shows spark defects caused in the plating process at 5,000
Flaws with a depth of 30 μm or more were confirmed using an eddy current flaw detector during wire drawing on a separate line.

Significantly more spark defects were observed in B, which was clearly plated with hard wire, and no spark defects were observed in C and D, which were solution-treated and lightly rolled and then plated. This is thought to be because the line has been straightened and because pack tension is added to the line so that it runs straight on the line. Residual spark defects may cause breakage during spring forming.

Table 4 shows the measured and compared values of the electrical conductivity of each test material.

The conductivity of the copper-plated product of the present invention is clearly recognized to be improved.

[Spring coiling property] Using A, C, and D as test materials, two springs as shown in Fig.
As a result of manufacturing 000 pieces and measuring the free length distribution, a distribution as shown in FIG. 2 was obtained.

As a result, C has the least variation, next is D, and A is C.
The dispersion was somewhat larger than that for D and D.

[Corrosion resistance by salt spray test]

A salt spray test according to JIS z2371 was conducted using A and D as test materials. The results are shown in Table-5.

As can be seen from this result, the product invented by D, that is, the composite plated product of semi-bright nickel + copper + bright nickel, clearly takes a longer time to develop red rust than the conventional plated product with nickel alone. It can be said that the degree of total rust after that is small and the corrosion resistance is excellent.

As explained above, the quality of the present invention is stable during the manufacturing process, and as a result, the conductivity and corrosion resistance of the stainless steel wire produced are improved, and the shape of the final product spring is also stable and good quality. .

Hereinafter, the effects of the present invention were confirmed by the following experimental examples.

Experimental Example 1 (Relationship between surface hardness and flaws) When the electrode rod weighs 750 gr and a 2.0 mmφ wire is run at a speed of 10 m/min by IHr, the surface hardness of the stainless steel wire is changed and flaws occur. (only friction scratches with the electrode rod were investigated).

The types of flaws targeted were “eyeballs of 50 μm or more” and “width 1
"Oyster scratches of 00 μm or more", [continuous width 50, czn
These are the above flaws (seen as 1 flaw per 100 rn), and spark flaws (regardless of size).

Obviously, the number of scratches decreases rapidly when the stainless steel skin becomes harder than the electrode rod, almost disappears when there is a difference of about 100 in Hv, and conversely increases rapidly when the stainless steel skin becomes softer by only about 50 Hv. (See Figure 4).

Experimental example 2 (relationship between back tension size and flaw) 2.0mmφ was applied to the actual plating line at 10m/alin.
I ran it and tested it. In solution-treated materials, if the back tension is too loose, spark defects at the cathode rod and paper contact with guides along the way can be seen.

The hardened material clearly has fewer scratches than the solution treated material, and even in this case, the larger the back tension, the fewer the defects, and they are almost gone at 30 kg (see Figure 5). Note that if the hardening treatment is performed by pulling out with a die and the pulling force required in this case is used as it is for back tension, the back tension will be about 90 kg with an area reduction rate of 20%.

Experimental Example 3 (Maximum penetration rate of nickel into the base material during hardening treatment) The hardness of the precipitated nickel was set to Hv220, the surface hardness of the stainless steel bus bar was changed, nickel plating was applied to this, and the hardening was performed by drawing with an area reduction rate of 20%. When the treatment was applied, the maximum penetration rate of nickel into the stainless steel substrate was determined using a metallurgical microscope. As a result, if the hardness of the generatrix is approximately Hv230 or higher, the penetration rate will be small, and on the contrary, some penetration of the substrate into the plating layer will be observed. The ``maximum penetration rate'', which measures the degree of penetration of the second layer into the substrate, is as follows. That is, the penetration of nickel into the substrate is represented by a plus sign, the penetration of the substrate into nickel is represented by a minus sign, and the failure to sink into either is represented by O. That is, immediately after plating, it is O, but when wire drawing is added to this, some of the wires sink in, and as the degree of processing increases, the absolute value of the thickness of the plating layer gradually decreases.

The maximum penetration rate is the ratio of the initial plating thickness to the deepest penetration in either direction due to the wire drawing process on a cross section. For example, if expressed using symbols A and BSC in Figure 7, (1-
B/A)X100 or (1-C/A)X100-maximum penetration rate.

However, if there is a condition of IBI≦IAI≦IcI, in the case of A-B>C - the base plate sinks into the plating layer, and when A-B<C + the plating sinks into the base plate, this state is shown in an actual micrograph. Figures 8 to 11 are shown.

However, this concept can be applied to the initial stage of wire drawing, that is, up to a reduction in area of 50% (processing that results in a diameter that is approximately 70% of the diameter of the generatrix before wire drawing). The surface lubricity is largely determined by the processing up to this stage.

If the wire drawing process exceeds that level, the processing effect of the wire and the nickel plating layer will be different, and the plating layer will become very thin, so it will become complicated because it will sink into each other. will no longer be possible. FIG. 8 shows a micrograph of the cross section of the generatrix immediately after plating.

Figure 9 shows a state in which the hardness of the plating layer and the substrate are almost the same;
The figure shows a case where nickel plating is harder than stainless steel wire (
Figure 11 shows the plated wire (conventional product) and the plated wire in which the stainless steel wire is harder than the nickel plating (product of the present invention).
% (Fig. 9), 35% (Fig. 10), and 35% (Fig. 11). Note that the difference in hardness between the nickel plating and the stainless steel wire is approximately ±70 in Hv.

Example 4 (Influence of surface hardening treatment on hydrogen embrittlement) If the surface of the stainless steel wire has dirt, oxide film, oil, etc. that are resistant to adhesion during handling, it is necessary to completely remove them. This may adversely affect the adhesion of the subsequent nickel plating, resulting in peeling.

Therefore, an excellent electrolytic treatment method must be used to clean the surface of stainless steel wire. When using the most recent electrolytic cleaning method, there is a non-contact alternating electrolytic method that performs powerful electrolytic cleaning without contacting the wire being treated.
In this case, a current density 10 to 20 times higher than that of ordinary cathodic or anodic electrolytic cleaning methods can be used, so that stronger surface treatment is possible. However, on the other hand, when a material becomes a cathode, the amount of hydrogen generated from its surface is extremely large, and the amount of hydrogen generated in normal catalytic cathode electrolysis is said to be relatively insensitive. Even in the case of austenitic stainless steel wire, it is necessary to be careful. Furthermore, in the case of austenitic stainless steel wire that generates α-martensite during subsequent wire drawing,
If hydrogen enters, even if the amount is small, the effect of hydrogen on embrittlement becomes large. In solution-treated stainless steel, fresh grain boundaries after recrystallization play a major role as an entry route for hydrogen to enter the interior from the stainless steel surface.

Therefore, crushing the grain boundaries exposed on the surface and reducing the paths for hydrogen to penetrate will greatly contribute to reducing the amount of hydrogen penetrating into the interior. It is generally said that if strong processing is performed, hydrogen embrittlement is likely to occur due to subsequent plating, but there is no problem with processing to the extent of the present invention.

Therefore, in the present invention, the stainless steel surface is rolled with a rolling roller to crush the grain boundaries, and the effects of this experiment will be described below.

First, a solution-treated stainless steel wire with a diameter of 3.8 mm was heated with 200 ml of sulfuric acid.
Using a non-contact alternating electrolytic cleaning method with a bath composition of gzJ, 60
Busbars treated for 30 s at a current density of A/c-, and 4
A solution-treated stainless steel wire with a diameter of 0.05 mm was rolled to a diameter of 3.8 with a roller die, and then treated under exactly the same conditions as the method described above, two types of wire were plated with nickel to a thickness of 3 μm, and both The amount of hydrogen absorbed was measured and compared, and these wires were drawn using a continuous wire drawing machine to a thickness of 1.8 mm, and the twist values and drawing ratios of these wires were measured and compared. The results are shown in FIGS. 12, 13, and 14. From the figure, it can be seen that the method of the present invention absorbs less gas and improves the twist value and narrowing ratio.

Table 1 Chemical composition of sample material (wt%) Table 3 Spark flaw investigation results Table 4 conductivity Reference stainless steel = 2.4

[Brief explanation of drawings]

Fig. 1 is a diagram showing an example of a coil spring made of stainless steel wire according to the method of the present invention, Fig. 2 is a distribution diagram showing variations in the free length of this coil spring, and Fig. 3 is a plating treatment according to the method of the present invention. Figure 4 is a diagram showing the relationship between the surface hardness (Hv) of stainless steel wire and the number of flaws, and a model diagram of the experiment. Figure 5 is a diagram showing the relationship between the pack tension (kg) and the number of flaws. Figure 6 is a diagram showing the relationship between the surface hardness (Hv) of stainless steel wire and the maximum penetration rate (%) into the base, and Figure 7 is a diagram showing the state of penetration of plating particles into the base. Figures 8 to 11 are micrographs of the metal structure near the surface layer showing different states of penetration of the plating particles into the substrate, and Figures 12 to 14 are the hydrogen gas-containing stainless steel wires of the present invention. FIG. 3 is a diagram showing the ratio, twist value of the strands, and drawing rate % of the strands in comparison with conventional stainless steel wires. Applicant's representative Patent attorney Suzue Takehiko Number 2 Harakuchi〉 John (Ni9) Figure 6 δ Figure 11 ← Hama 9 Shun - Masu Irisa w - Gunohe - ¥ - 4 cases of general color

Claims (5)

[Claims] (1) A step of solution-treating an austenitic stainless steel wire, a step of surface-hardening the solution-treated steel wire, and a step of applying nickel to the surface-hardened steel wire under tension. A method for producing stainless steel wire, which includes a plating process and a finish drawing process of a nickel-plated steel wire. (2) A step of applying solution treatment to the austenitic stainless steel wire, a step of applying surface hardening treatment to the solution treated steel wire, and a state in which tension is applied to the surface hardened steel wire, A method for producing a stainless steel wire, comprising a step of sequentially performing semi-bright nickel plating, copper plating, and bright nickel plating, and a step of finishing wire drawing the steel wire on which the plating layer has been formed. (3) The method for manufacturing a stainless steel wire according to claim 1 or 2, wherein the steel wire to be subjected to solution treatment is subjected to underdrawing wire drawing processing. (4) The surface hardening treatment of the steel wire is performed in such a manner that the surface hardness of the steel wire obtained by this treatment is higher than the hardness of the nickel plating layer obtained by the nickel plating treatment. The method for manufacturing stainless steel wire described in . (5) The method for manufacturing a stainless steel wire according to any one of claims 1 to 4, wherein the finishing wire drawing treatment is performed so that 60 to 90% of α' martensite is contained in the structure of the steel wire.