JP2010138456A - Ni-PLATED STEEL WIRE FOR SPRING, AND METHOD FOR PRODUCING THE SAME - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a steel wire, particularly a steel wire for a spring, whose heat resistance is improved, and to which corrosion resistance is imparted as well, and to provide a method for producing the same. <P>SOLUTION: The Ni-plated steel wire for a spring comprises, by weight, 0.5 to 0.8% C, 1.2 to 2.5% Si, 0.5 to 1.5% Mn, and 0.05 to 1.5% Cr, and the balance Fe with inevitable impurities, and in which an Ni plating layer with a thickness of ≥2 μm is formed on the surface. The Ni plating steel wire for a spring may comprise either or both of V and Ni as well, and, in this case, regarding their contents, 0.05 to 0.25% V, and 0.05 to 1.5% Ni are satisfied. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a Ni-plated steel wire for a spring and a method for producing the same.

  The hard steel wire described in JIS G 3521 and the piano wire described in JIS G 3522 are used as steel wires for springs, and exhibit excellent tensile strength by performing cold drawing. . However, hard steel wires and piano wires may lose mechanical strength over time in a high-temperature environment, and are therefore unreliable in terms of heat resistance. Moreover, since rust is generated in a corrosive environment, the reliability is low in terms of corrosion resistance.

As a spring steel wire having higher heat resistance than hard steel wire and piano wire, for example, one disclosed in Patent Document 1 is known. The steel wire of Patent Document 1 has improved heat resistance by increasing the Si content in the range of 0.5 to 1.5% by weight. Thereby, strength can be maintained in a high temperature environment of around 200 ° C.
Japanese Patent No. 3539875

  However, the steel wire of Patent Document 1 cannot be said to have sufficient heat resistance because the strength decreases in a high temperature environment exceeding 300 ° C., for example. In addition, the corrosion resistance is the same as the conventional product.

  In view of the above circumstances, an object of the present invention is to provide a steel wire, particularly a spring steel wire, which has improved heat resistance and corrosion resistance, and a manufacturing method thereof.

  In order to achieve the above object, the Ni-plated steel wire for springs according to the present invention is, by weight, C: 0.5 to 0.8%, Si: 1.2 to 2.5%, Mn: 0.00. A Ni plating layer containing 5 to 1.5%, Cr: 0.05 to 1.5%, the balance being Fe and inevitable impurities, and having a thickness of 2 μm or more is formed on the surface.

  The Ni-plated steel wire for springs according to the present invention contains Cr in addition to the above contents C, Si and Mn, and the content is set to 0.05 to 1.5% by weight. It is possible to improve heat resistance as compared with a steel wire for springs that does not contain. In addition, since the Ni plated steel wire for springs according to the present invention has a Ni plated layer with a thickness of 2 μm or more formed on the surface, it is possible to improve the corrosion resistance as compared with a bare spring steel wire. . Thus, the Ni-plated steel wire for springs according to the present invention has heat resistance and corrosion resistance.

  In a preferred embodiment of the present invention, the Ni-plated steel wire for spring includes one or both of V and Ni, and the contents thereof are V: 0.05 to 0.25% and Ni: 0.05 to, respectively. 1.5%.

  According to this configuration, since the Ni-plated steel wire for spring contains one or both of V and Ni having the above contents, it is possible to further improve the heat resistance.

  In addition, the method for producing the Ni-plated steel wire for springs according to the present invention is in wt%, C: 0.5 to 0.8%, Si: 1.2 to 2.5%, Mn: 0.5 to Applying a patenting treatment to a wire produced by hot rolling steel containing 1.5%, Cr: 0.05 to 1.5%, the balance being Fe and inevitable impurities, and the patenting After pre-drawing the treated wire as necessary, a step of performing Ni plating treatment on the surface thereof, and finishing wire drawing of the Ni-plated wire to give a steel wire In the wire drawing process, the area reduction rate after the Ni plating treatment of the wire is set to 10% or more, and the layer thickness of the Ni plating is 2 μm or more after the wire drawing process. Is set to

  According to the method for manufacturing a Ni-plated steel wire for springs according to the present invention, the area reduction rate after the Ni plating treatment of the wire is set to 10% or more, and the layer thickness of the Ni plating layer after the wire drawing is 2 μm. By setting as described above, it is possible to impart corrosion resistance and gloss to the spring steel wire. Further, as described above, it is possible to impart heat resistance to the steel wire by the composition component having the above content rate. Furthermore, one or both of V having a content of 0.05 to 0.25% and Ni having a content of 0.05 to 1.5% are used as necessary.

  According to the Ni-plated steel wire for springs and the method for producing the same according to the present invention, it is possible to provide a steel wire for springs having heat resistance, corrosion resistance and gloss.

  Hereinafter, the steel wire which concerns on embodiment of this invention is demonstrated in detail.

The steel wire of this embodiment is a steel wire for springs, and contains C, Si, Mn, and Cr as main composition components, and the balance consists of Fe and inevitable impurities. The steel wire for spring has an electric Ni plating layer on the surface. Below, each content rate of C, Si, Mn, and Cr is shown by weight%.
C: 0.5 to 0.8%
Si: 1.2-2.5%
Mn: 0.5 to 1.5%
Cr: 0.05 to 1.5%

The steel wire for spring includes one or both of V and Ni as necessary in addition to the above-described composition components. Below, each content rate of V and Ni is shown by weight%.
V: 0.05-0.25%
Ni: 0.05 to 1.5%

  Next, the reason why the content (% by weight) of each composition component is defined in the above range will be described.

C: 0.5 to 0.8%
C is an essential element for securing the strength required for the steel wire for springs, and at least 0.5% or more is necessary for securing the strength. On the other hand, if it exceeds 0.8%, pro-eutectoid cementite is likely to be generated during patenting, and the toughness and ductility are reduced.

Si: 1.2-2.5%
Si is an element used as a deoxidizer during steel making, and has an effect of increasing the heat resistance by dissolving in ferrite in pearlite, and thus is an essential element in the spring steel wire of this embodiment. . In order to increase the heat resistance, it is necessary to add at least 1.2%. On the other hand, when it exceeds 2.5%, toughness and ductility are lowered. Moreover, excessive addition of Si promotes decarburization of the steel wire surface layer during patenting, and thus reduces the fatigue strength of the spring.

Mn: 0.5 to 1.5%
Mn is an element used as a deoxidizer at the time of steel making, and since it has the effect of improving hardenability and strength, it is an essential element in the spring steel wire of this embodiment. In order to obtain the effect, it is necessary to add at least 0.5% or more. On the other hand, if it exceeds 1.5%, the hardenability is unnecessarily increased, so that patenting for a long time is required, and a supercooled structure such as bainite is easily generated. descend.

Cr: 0.05 to 1.5%
Cr has the effect of increasing heat resistance by precipitating as carbide or carbonitride on ferrite in pearlite, and increasing the strength by reducing the lamella spacing of pearlite, so the spring steel wire of this embodiment Then it is an essential element. In order to obtain the effect, it is necessary to add at least 0.05% or more. On the other hand, if it exceeds 1.5%, the hardenability is unnecessarily increased, so that patenting for a long time is required, and a supercooled structure such as bainite is easily generated. descend.

V: 0.05-0.25%
V is an element having an effect of increasing heat resistance by precipitating as a carbide or carbonitride on ferrite in pearlite. In order to obtain the effect, it is necessary to add at least 0.05% or more. On the other hand, if it exceeds 0.25%, a supercooled structure is likely to be generated at the time of patenting, so that the wire drawing workability is lowered.

Ni: 0.05 to 1.5%
Ni is an element having an effect of improving hardenability. In order to obtain the effect, it is necessary to add at least 0.05% or more. On the other hand, if it exceeds 1.5%, a supercooled structure is likely to be generated during patenting, so that the wire drawing workability is lowered.

  In this embodiment, the spring steel wire is given heat resistance mainly by the addition of Si and Cr having the above-mentioned contents, and is given corrosion resistance and appearance gloss by the electric Ni plating layer.

Next, the manufacturing process of the Ni plating steel wire for springs is demonstrated. The Ni-plated steel wire for spring is manufactured by the following manufacturing process (A) or (B).
・ Manufacturing process (A)
Steel melting → Hot rolling → Patenting treatment → Electric Ni plating treatment → Wire drawing → Spring steel wire manufacturing and manufacturing process (B)
Steel melting → Hot rolling → Patenting → Pre-drawing → Electrical Ni plating → Finish drawing → Manufacturing of spring steel wire

  In the manufacturing step (A), first, a steel containing C, Si, Mn and Cr having the above contents is melted, and the steel is hot-rolled to manufacture a wire having a predetermined diameter. Next, a patenting process is performed on the wire, and then an electric Ni plating process is performed. By this electric Ni plating treatment, a Ni plating layer is formed on the surface of the wire. Then, the wire rod having the Ni plating layer is subjected to wire drawing to produce a spring steel wire having a predetermined diameter. The wire drawing process is performed at an appropriate wire drawing degree corresponding to the strength required for the spring steel wire.

  Depending on the degree of wire drawing, the Ni plating layer of the steel wire after wire drawing may become thin, and it may be difficult to ensure corrosion resistance. In such a case, the manufacturing process (B) is applied. The manufacturing process (B) differs from the manufacturing process (A) in that a preliminary wire drawing process is performed before the electric Ni plating treatment. The preliminary wire drawing process is a process in which a wire drawing process is performed in advance at a predetermined degree of processing before the electric Ni plating process, and the degree of finishing wire drawing after the electric Ni plating process is increased by the amount of the preliminary wire drawing process. Since it can make small, it can prevent that the layer thickness of Ni plating layer becomes thin too much.

  Thus, the Ni-plated steel wire for springs is manufactured by the manufacturing process (A) or (B), but the manufacturing processes (A) and (B) include, for example, the thickness of the Ni-plated layer, and the steel wire for springs. Is selected according to the strength required.

  Further, the wire drawing process (finish wire drawing process) needs to be performed at least one pass after the electric Ni plating process in any of the manufacturing steps (A) and (B). If only the electric Ni plating process is performed, the surface of the Ni plating layer is rough. Therefore, the accuracy of the thickness of the Ni plating layer is low, which causes a decrease in corrosion resistance. Moreover, it is difficult to give the Ni plating layer gloss. Therefore, in this embodiment, the surface of the Ni plating layer is smoothed to ensure corrosion resistance and gloss. Specifically, the Ni plating layer is smoothed by performing a wire drawing process with a reduction in area of 10% or more. That is, the wire drawing is performed at a cross-section reduction rate in which the cross-sectional area of the wire before the wire drawing process is 10% or more smaller than the cross-sectional area of the wire after the wire drawing process. The Ni plating layer after the wire drawing is smoothed to have corrosion resistance and gloss. In this embodiment, the thickness of the Ni plating layer is set to be 2 μm or more.

  Next, an experiment conducted for evaluating the heat resistance of the Ni-plated steel wire for spring according to the present embodiment and the result thereof will be described with reference to Table 1 and FIG.

(Heat resistance evaluation experiment 1)
Table 1 shows the composition components of Examples 1 to 4 and Comparative Examples 1 to 3 used in this experiment. Each of Examples 1-4 and Comparative Examples 1-3 was manufactured by the manufacturing process (A). Specifically, steel having the composition components shown in Table 1 was melted, and a wire having a diameter of 5.5 mm was manufactured by hot rolling. Next, a patenting process was performed on each wire. In the patenting treatment, the austenitizing heating temperature was set to 930 ° C., and the pearlite transformation bath temperature was selected from the range of 530 to 650 ° C. according to the composition components so that bainite was not generated. After the patenting treatment, each wire was subjected to an electric Ni plating treatment to form a Ni plating layer having a thickness of about 15 μm on the surface of each wire. Thereafter, each wire was drawn to produce a steel wire for a spring having a diameter of 1.8 mm (Examples 1 to 4 and Comparative Examples 1 to 3). In the wire drawing, a normal continuous wire drawing machine and a die made of cemented carbide were used. Further, the wire drawing was performed so that the thickness of the Ni plating layer after the wire drawing was 3 μm.

  Tensile tests were performed on Examples 1 to 4 and Comparative Examples 1 to 3 after wire drawing. Since the strength after patenting the wire varies depending on the examples, the tensile strength after wire drawing was also different as shown in Table 1.

  In this heat resistance evaluation experiment, in order to evaluate heat resistance, a tensile test was performed on Examples 1 to 4 and Comparative Examples 1 to 3 after performing a temper treatment for 20 minutes within a range of 250 to 500 ° C. Carried out and compared the tensile strength. The result is shown in FIG.

  In FIG. 1, the horizontal axis indicates the temper temperature, and the vertical axis indicates the tensile strength. As is clear from FIG. 1, Examples 1 to 4 maintained a tensile strength substantially equal to or higher than the tensile strength before treatment even when tempered at 350 ° C. Thereby, Examples 1-4 can expect the heat resistance calculated | required as a steel wire for springs. Therefore, improvement in the sag resistance of a spring manufactured by secondary processing of the spring steel wire can be expected.

  Moreover, even if Examples 1-4 were tempered at the temperature exceeding 350 degreeC, the fall of tensile strength was moderate. The tensile strength after the temper treatment was lower in the order of Example 4, Example 3, Example 2, and Example 1. Examples 2 and 3 are more tensile than Example 1 because V is added in view of the composition component of Example 1, and Example 4 is more than V 1 and Ni is added in view of the composition component of Example 1. It was confirmed that the strength was high and the heat resistance was improved.

  On the other hand, the fall of the tensile strength after the temper process of Comparative Examples 1-3 is remarkable. Since the content rate of Si is lower than the content rate prescribed | regulated by this embodiment and the comparative example 1 does not contain Cr, the fall of the tensile strength after a temper process is the most remarkable. Comparative Example 2 has a higher Si content than Comparative Example 1, but does not contain Cr, so the tensile strength after tempering is significantly reduced. In Comparative Example 3, the Cr content is in the range (0.05 to 1.5%) defined in the present embodiment, but since the Si content is small, the tensile strength decreases after tempering. Is remarkable. As is clear from these results, Comparative Examples 1 to 3 have lower heat resistance than Examples 1 to 5. Based on this experimental result, the spring steel wire according to the present embodiment contains Cr, and each content rate of Si and Cr is set in the above range in order to improve heat resistance.

  Next, another experiment conducted for evaluating the heat resistance of the Ni-plated steel wire for spring according to the present embodiment and the result thereof will be described with reference to FIG.

(Heat resistance evaluation test 2)
Examples 5 to 7 used in the heat resistance evaluation test 2 are steel wires having the same composition components as those of Example 2 shown in Table 1 and manufactured by drawing a wire having a diameter of 5.5 mm. In Example 5, the wire drawing degree was set to 52%, in Example 6, the wire drawing degree was set to 81%, and in Example 7, the wire drawing degree was set to 90%. For Examples 5 to 7, a temper treatment was performed for 20 minutes in the range of 250 to 500 ° C., and then a tensile test was performed to compare the tensile strength. The result is shown in FIG.

  As shown in FIG. 2, the increase in strength due to strain aging caused by the temper treatment at 250 ° C. was the largest in Example 7 with a large degree of wire drawing, and the smallest in Example 5 with a low degree of wire drawing. Further, the decrease in strength due to the temper at 300 ° C. or higher was greatest in Example 7 having a large degree of wire drawing, and was smallest in Example 5 having a small degree of wire drawing. As a result, Examples 5-7 all maintained a tensile strength substantially equal to or higher than the tensile strength before treatment even after tempering at 350 ° C. Thereby, Examples 5-7 can expect the heat resistance calculated | required as a steel wire for springs irrespective of the magnitude of the wire drawing work degree in a manufacturing process. Therefore, improvement in the sag resistance of a spring manufactured by secondary processing of the spring steel wire can be expected.

  Next, Experiments I and II conducted for evaluating the corrosion resistance of the Ni-plated steel wire for spring according to the present embodiment and the results thereof will be described with reference to Tables 2 and 3 and FIGS.

(Corrosion resistance evaluation experiment I)
In this experiment I, as shown in Table 2, using Examples 8 to 11 in which the thicknesses of the electric Ni plating layers were different from each other, a salt spray test was performed on those Examples 8 to 11 to obtain corrosion resistance. Compared. Examples 8 to 11 are steel wires having a diameter of 1.8 mm manufactured by drawing a wire having a diameter of 5.5 mm and having the same composition components as those of Example 1 shown in Table 1. Example 8 is manufactured by the manufacturing process (A), and the layer thickness of the Ni plating layer is set to 2 μm. Example 9 is manufactured by the manufacturing process (B), and the layer thickness of the Ni plating layer is set to 5 μm. And Example 10 did not have a Ni plating layer, Example 11 was manufactured by the manufacturing process (A), and the layer thickness of the Ni plating layer was set to 1 μm.

  FIG. 3 shows the results of the salt spray test, where the horizontal axis represents the test time and the vertical axis represents the red rust occurrence area ratio. As is clear from FIG. 3, Examples 8 and 9 having a Ni plating layer thickness of 2 μm or more as defined in this embodiment exhibited an excellent rust prevention effect. In particular, Example 9 having a Ni plating layer thickness of 5 μm has a high antirust effect. In contrast, Example 11 having a Ni plating layer thickness of less than 1 μm, which is less than the layer thickness defined in the present embodiment, has a significantly lower rust prevention effect than Example 8 having a Ni plating layer thickness of 2 μm. It was confirmed that the antirust effect was as low as in Example 10 that did not have a Ni plating layer.

  Based on the result of this corrosion resistance evaluation experiment I, in the Ni-plated steel wire for springs of this embodiment, the layer thickness of the Ni plating layer is set to 2 μm or more as described above, preferably 5 μm or more.

(Corrosion resistance evaluation experiment II)
In this experiment II, as shown in Table 3, Examples 12 to 15 in which the finishing wire drawing degree of the manufacturing process (B), that is, the surface area reduction rate was made different from each other, were used. A salt spray test was conducted to compare the corrosion resistance. Examples 12 to 15 are steel wires having a diameter of 1.8 mm manufactured from a wire having a diameter of 5.5 mm according to the manufacturing process (B), having the same composition components as those of Example 1 shown in Table 1. No. 12 is the finishing wire drawing degree after electric Ni plating treatment is set to 10%, Example 13 is the finishing wire drawing degree after electric Ni plating treatment is set to 20%, and Example 14 is electric The finish drawing degree after Ni plating was set to 5%. Further, Example 15 is a steel wire that is not subjected to finish wire drawing after the electric Ni plating treatment but is subjected to electric Ni plating treatment after the wire drawing. In addition, the layer thickness of Ni plating of Examples 12-15 was set to 2 micrometers.

  FIG. 4 shows the results of the salt spray test, where the horizontal axis represents the test time and the vertical axis represents the red rust occurrence area ratio. FIG. 4 also shows data of Example 8 in Table 2 for comparison. As shown in FIG. 4, Examples 12 and 13 were confirmed to have the same degree of corrosion resistance as Example 8 manufactured according to the manufacturing process (A). On the other hand, Examples 14 and 15 were confirmed to be significantly inferior to Examples 12 and 13 in corrosion resistance.

  Based on the result of this corrosion resistance evaluation test II, the finish wire drawing degree (area reduction rate) is set to 10% or more in the Ni-plated steel wire for springs of this embodiment.

  As is apparent from the above description, the Ni-plated steel wire for springs according to this embodiment includes Cr, the Cr content is set to 0.05 to 1.5%, and the Si content is 1.2. It is a steel wire that has acquired sufficient heat resistance by setting it to ˜2.5%, and has acquired corrosion resistance and glossiness by setting the thickness of the Ni plating layer to 2 μm or more.

It is a figure which shows the tensile strength after the temper process of the Ni plating steel wire for springs which concerns on this embodiment. It is a figure which shows the tensile strength after the temper process of the Ni plating steel wire for springs which varied the degree of wire drawing. It is a figure which shows the corrosion resistance of the steel wire for springs which made the thickness of the electric nickel plating layer differ mutually. It is a figure which shows the corrosion resistance of the steel wire for springs which made the finish wire drawing degree differ mutually.

Claims (4)

  In weight percent, C: 0.5-0.8%, Si: 1.2-2.5%, Mn: 0.5-1.5%, Cr: 0.05-1.5%, A Ni-plated steel wire for a spring, wherein the balance is made of Fe and inevitable impurities, and a Ni plating layer having a thickness of 2 μm or more is formed on the surface.   2. The Ni-plated steel wire for spring according to claim 1, wherein one or both of V and Ni are contained, and the contents thereof are V: 0.05 to 0.25% and Ni: 0.05 to 1 respectively. Ni-plated steel wire for springs, characterized in that it is 5%. A method of manufacturing a Ni-plated steel wire for a spring,
In weight percent, C: 0.5-0.8%, Si: 1.2-2.5%, Mn: 0.5-1.5%, Cr: 0.05-1.5%, Applying a patenting treatment to a wire produced by hot rolling steel comprising the balance Fe and inevitable impurities;
Performing a preliminary wire drawing process on the patented wire rod as necessary, and then performing a Ni plating process on the surface;
Producing a steel wire by subjecting the Ni-plated wire to a finish drawing;
Including
In the wire drawing process, the area reduction rate after the Ni plating treatment of the wire is set to 10% or more,
The method for producing a Ni-plated steel wire for a spring, wherein the layer thickness of the Ni plating is set to be 2 μm or more after the wire drawing.   In the manufacturing method of the Ni plating steel wire for springs of Claim 3, the said steel contains one or both of V and Ni, and these content is respectively V: 0.05-0.25% and Ni : 0.05-1.5% of the manufacturing method of the Ni plating steel wire for springs characterized by the above-mentioned.

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