JP2013050195A - Spring steel wire and spring - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a spring comprising a fine wire and having superior fatigue properties, and a small-diameter spring steel wire by which the spring having superior the fatigue properties can be obtained.SOLUTION: The spring 1 is ≤6 μm in surface roughness in the circumferential direction of the steel wire constituting the spring 1, and has smoothness. Since the sensitivity of breakage can be lowered by an effect that such as smooth surface can be seen, the spring 1 has superior fatigue properties even if not applied with post-treatment such as shot peening and nitriding treatment. The spring 1 can be obtained by applying electrolyte grinding processing to the spring steel whose wire diameter is smaller than 1 mm, and applying spring processing to the spring steel whose surface roughness in the circumferential direction of the steel wire is ≤6 μm at Rz.

Description

  The present invention relates to a spring steel wire and a spring. In particular, the present invention relates to a spring made of a thin steel wire and excellent in fatigue characteristics, and a thin steel wire for springs from which a spring excellent in fatigue characteristics can be obtained.

  Of the springs used in various fields, springs used in automobile engines and transmissions have excellent fatigue characteristics such as high stress repeatedly applied, high fatigue limit, and difficulty in sag. Desired. For this reason, silicon chrome steel oil tempered wires having excellent fatigue characteristics are widely used as such spring materials (wires) (Patent Documents 1 and 2, etc.).

  Conventionally, in order to improve the fatigue characteristics of the spring, a post-treatment such as shot peening or nitriding has been applied to the spring obtained by spring processing (specifications 0003 and 2 of Patent Document 1). 0035). An electrolytic polishing treatment may be further performed after shot peening (Patent Document 1).

Japanese Patent No. 3301088 JP 2009-235523

  Patent Documents 1 and 2 disclose a spring having excellent fatigue characteristics formed from a spring steel wire having a wire diameter of 1 mm or more, but formed from a steel wire having a small diameter of less than 1 mm and excellent in fatigue characteristics. The spring has not been fully studied.

  A spring formed by a thin wire having a wire diameter of less than 1 mm is also small. For this reason, it is difficult to uniformly apply shot peening to this small spring, and the spring may be deformed by shot peening. Further, the surface of the wire constituting the spring becomes uneven due to shot peening, which may increase wrinkle sensitivity. Furthermore, if post-treatments such as shot peening, nitriding treatment, and electrolytic polishing treatment are performed on the spring after spring processing, the number of steps increases, resulting in a decrease in spring productivity.

  Therefore, the spring is made of a thin steel wire, and the spring having excellent fatigue characteristics and the spring having excellent fatigue characteristics can be obtained without performing post-treatment such as shot peening after the spring processing. Development of spring steel wire is desired.

  Therefore, one of the objects of the present invention is to provide a spring made of a thin steel wire and having excellent fatigue characteristics. Another object of the present invention is to provide a small-diameter spring steel wire from which a spring having excellent fatigue characteristics can be obtained.

  In producing a spring made of a steel wire with a small diameter such as a wire diameter of less than 1 mm, the present inventors satisfy a specific range of the surface roughness of the steel wire before spring processing, and the steel wire surface is smooth, It was also found that the spring after the spring processing substantially maintains the smoothness of the steel wire before the spring processing. In particular, not only is it smooth along the longitudinal direction of the steel wire before spring processing, but also the spring obtained by applying spring processing to the steel wire by keeping it smooth along the circumferential direction of the steel wire. And the knowledge that a smooth thing was obtained in both the longitudinal direction and the circumferential direction of the steel wire which comprises the said spring was acquired. And the spring which consists of a steel wire smooth also in the circumferential direction in this way acquired the knowledge that wrinkle sensitivity fell, and was excellent in a fatigue characteristic, even if it does not give a post-process after a spring process. The present invention is based on the above findings.

  The spring steel wire of the present invention has a wire diameter of less than 1 mm, and the surface roughness in the circumferential direction of this steel wire is 6 μm or less in terms of Rz. The spring of the present invention is manufactured using the steel wire for a spring of the present invention, and this spring substantially maintains the surface roughness of the steel wire for a spring of the present invention, and the steel wire constituting the spring. The surface roughness in the circumferential direction of Rz is 6 μm or less. The spring of the present invention is formed by spirally winding a steel wire having a wire diameter of less than 1 mm, and the surface roughness in the circumferential direction of the steel wire is 6 μm or less in terms of Rz.

  Since the surface of the steel wire which comprises the said spring is smooth over the circumferential direction, this invention spring becomes smooth also in the longitudinal direction of the said steel wire. The cylindrical spring of the present invention formed by spirally winding such a steel wire has a substantially smooth entire circumferential surface. Therefore, the spring of the present invention has low wrinkle sensitivity not only on the inner peripheral region of the spring, which tends to be a starting point of destruction, but also on the entire circumference. For this reason, the spring of the present invention can have a high fatigue limit without being subjected to post-treatment such as shot peening or nitriding, and is excellent in fatigue characteristics. Moreover, when post-processing such as shot peening is not performed after the spring processing, the number of steps to the final product is reduced, and the productivity of the spring is excellent. Furthermore, when the post-treatment is not performed, even if the steel wire is composed of a small diameter steel wire, the steel wire is not deformed by the post-treatment, so that it is possible to prevent generation of defective products due to the deformation. Also from this point, the spring of the present invention is excellent in productivity.

  The steel wire for a spring of the present invention has a smooth surface in the circumferential direction, so that the steel wire for the spring is also smooth in the longitudinal direction of the steel wire, and the entire circumference as described above is substantially smooth. Can be manufactured. Therefore, by using the spring steel wire of the present invention as a spring material, a spring formed from a small diameter steel wire, which has excellent fatigue characteristics without post-treatment such as shot peening after the spring processing, can be produced. Can be manufactured well.

  As one form of this invention steel wire for springs, the form by which the electropolishing process was given over the circumferential direction of the said steel wire for springs is mentioned.

  The electrolytic polishing treatment can easily perform uniform polishing in both the longitudinal direction and the circumferential direction even in a thin steel wire having a wire diameter of less than 1 mm. It is possible to produce a smooth steel wire over both. Therefore, the said form is excellent in productivity at the time of carrying out the spring process of the steel wire for springs of this invention. Further, the electrolytic polishing process is a process in which a residual stress is not substantially generated in the steel wire to be polished, so that a heat treatment for adjusting the residual stress is not necessary. Also from this point, the steel wire for a spring of the present invention is excellent in productivity.

  One form of the spring of the present invention is a form in which nitriding treatment and shot peening are not performed.

  In the above-described embodiment, the spring after the spring processing is not subjected to post-treatment such as nitriding treatment or shot peening, that is, the post-treatment is omitted, thereby reducing the number of steps and improving the productivity of the spring of the present invention. Excellent. The fact that the nitriding treatment is not performed means that the nitrided layer is not substantially present on the surface of the steel wire constituting the spring, and that shot peening is not performed means that the inside of the steel wire constituting the spring is not. It can be determined that the difference between the residual stress and the residual stress on the surface of the steel wire is small (300 MPa or less), or does not substantially have a residual stress.

  The spring of the present invention is excellent in fatigue characteristics. The spring steel wire of the present invention has a small diameter and provides a spring having excellent fatigue characteristics.

It is a schematic perspective view which shows an example of this invention spring. It is explanatory drawing explaining the measuring method of surface roughness.

Hereinafter, the present invention will be described in more detail.
<Composition>
The steel wire for the spring of the present invention and the steel wire constituting the spring of the present invention are typically a silicon chrome steel wire (especially an oil tempered wire for quenching and tempering treatment), a hard drawn wire that is not subjected to quenching and tempering treatment (typical It is composed of piano wire). In addition, a known steel wire, for example, a JIS standard steel wire can be used.

  Typical composition of silicon chrome steel is (%) C: 0.5% -0.8%, Si: 1.0% -2.5%, Mn: 0.20% -1.0%, Cr: 0.5% -2.5% (2) In addition to (1) above, V: 0.05% to 0.50%, Co: 0.02% to 1.00%, Ni: 0.1% to 1.0%, and Mo: 0.05% to 0.50 % Containing at least one selected from%.

<Wire diameter>
The steel wire for the spring of the present invention and the steel wire constituting the spring of the present invention have a wire diameter of less than 1 mm. Depending on the application, it can be 0.8 mm or less, and further 0.6 mm or less. It is advisable to adjust the degree of wire drawing so as to obtain a desired wire diameter and to perform wire drawing.

<Surface roughness>
The steel wire for the spring of the present invention and the steel wire constituting the spring of the present invention have a surface roughness in the circumferential direction of Rz (maximum height, JIS B 0601 (2001)) of 6 μm or less. The surface roughness in the circumferential direction is the length of the steel wire starting from two or more points (preferably three or more) different in the circumferential direction in the end face or cross section (cross section in the direction orthogonal to the axial direction) of the steel wire. The surface roughness is measured along the direction, and the maximum height of the measured surface roughness is said. Examples of the two or more points include two points facing each other in the diameter direction of the steel wire. For the surface roughness, a commercially available measuring device (which may be a contact type or a non-contact type) can be used. The surface roughness Rz is preferably as small as possible, more preferably 5 μm or less, and even more preferably 3 μm or less.

[Method of manufacturing steel wire for springs]
The steel wire for a spring of the present invention is obtained, for example, through a process that overlaps with a conventional oil temper wire manufacturing process. The production process of oil tempered wire is typically caused by melting of raw steel → hot forging → hot rolling → patenting (fine pearlite organization) → skinning (removal of decarburized layer) → annealing (skin peeling) A martensite phase) → wire drawing → quenching and tempering. By this step, a wire material composed of a tempered martensite structure is obtained. Or this invention steel wire for springs is obtained through the process which overlaps with the manufacturing process of the conventional hard drawn wire, for example. Typically, the process of producing hard drawn wire includes the steps of melting raw steel → hot forging → hot rolling → patenting → skinning → annealing → drawing. By this step, a wire material composed of a fine pearlite structure is obtained. Known conditions can be used as the conditions for the above-described steps in the oil tempered wire and the hard drawn wire. Commercially available oil tempered wire or piano wire can be used as the wire material. The steel wire for spring of the present invention is obtained by subjecting the wire material to a smoothing treatment so that the surface roughness is 6 μm or less in Rz over the circumferential direction.

  For the smoothing process, an appropriate means capable of uniformly smoothing the circumferential direction of the wire material can be used. For such a smoothing treatment, an electropolishing treatment is suitable. The surface of the wire material can be uniformly smoothed in the circumferential direction by performing the electropolishing treatment on the wire material before the spring processing, instead of performing the electropolishing treatment on the spring after the spring processing. . Further, by applying spring processing to the wire rod after electropolishing treatment (the steel wire for spring of the present invention), the wire rod constituting the obtained spring can also have a uniform surface roughness over its circumferential direction. .

  In the smoothing treatment, it is preferable to adjust the conditions (in the case of electrolytic polishing treatment, the current value at the time of energization, the type of the electrolytic solution, the energization time, etc.) such that the surface roughness is 6 μm or less.

[Spring manufacturing method]
The spring of the present invention can be obtained by subjecting the steel wire for spring of the present invention to spring processing. The spring specifications (winding diameter, number of windings, free length, etc.) may be selected so as to obtain a desired spring. Since the steel wire for spring of the present invention is uniformly smooth in the circumferential direction as described above, the spring obtained after the spring processing is not subjected to post-treatment such as nitriding treatment or shot peening, so that the fatigue characteristics can be obtained. An excellent spring is obtained. Therefore, in the manufacture of the spring of the present invention, the post-treatment can be omitted. In addition, you may perform the heat processing (strain relief annealing) for removing the distortion accompanying spring processing with respect to the obtained spring after spring processing.

[Test example]
As a wire material, an oil tempered wire (diameter φ0.8 mm) having a composition of JIS standard SWOSC-V was prepared.

(Sample Nos. 1 to 3)
The prepared wire material was electropolished. In all of Sample Nos. 1 to 3, the electrolytic solution used in the electropolishing treatment and the energization current value were the same, and the surface roughness was varied by varying the energization time. When the energization time is increased, the surface roughness tends to decrease.

  The surface roughness of the wire rod (spring steel wire) subjected to electrolytic polishing was measured. Here, it measured as follows. As shown in FIG. 2, one arbitrary point on the circumference is taken on the end face (or cross section) of the wire rod 100, and points shifted by 90 °, 180 °, and 270 ° with respect to this point are taken. Starting from each point, a straight line along the longitudinal direction of the wire 100 is taken as a measurement line. That is, as shown in FIG. 2, the wire 100 is equally divided into four in the circumferential direction, and each of the four equal lines (indicated by a broken line in FIG. 2) is a measurement line. Here, the measurement distance of each measurement line is 10 mm, the displacement is measured for four measurement lines, and the maximum value of the displacement is regarded as Rz (maximum height of the contour curve) in JIS B 0601 (2001). A commercially available laser displacement meter (Keyence LK-G5000 series) was used for measuring the displacement. Table 1 shows the surface roughness Rz.

  The wire rod that had been subjected to electrolytic polishing was subjected to spring processing to produce a spring 1 shown in FIG. The springs of sample Nos. 1 and 2 are not subjected to post-processing after spring processing. The spring of sample No. 3 was shot peened after the spring processing. The shot peening was performed by applying the conditions applied to a spring formed from a known steel wire for springs having a wire diameter of 1 mm or more.

(Sample No. 100-130)
The prepared wire material was subjected to spring processing without being subjected to electrolytic polishing treatment, and springs having the same specifications as Sample Nos. 1 to 3 were produced. The obtained spring was subjected to post-treatment as shown in Table 1. The shot peening and electropolishing were performed by applying the conditions applied to a spring formed from a known steel wire for springs having a wire diameter of 1 mm or more. Sample No. 100 is a spring that has not been post-processed.

  The fatigue limit of each obtained spring was measured (each sample: n = 3). The fatigue limit was measured using a commercially available star spring fatigue tester. And the relative value with respect to the fatigue limit of sample No. 100 was calculated | required about each sample. The results are shown in Table 1. All samples were subjected to strain relief annealing after spring processing.

  As shown in Table 1, by using a spring steel wire whose surface roughness in the circumferential direction of the wire is 6 μm or less as a wire before spring processing, post-processing such as shot peening after spring processing It can be seen that a spring having a high fatigue limit can be obtained without applying. The reason for this is that no post-treatment is applied to the spring after spring processing, so that the wire constituting the spring maintains a smooth surface state in the circumferential direction in the same manner as the spring steel wire before spring processing. This is thought to be due to the decreased susceptibility to sputum. For the springs of sample No. 1 and 2, the surface roughness in the circumferential direction is 6 μm or less in the circumferential direction, similar to the spring steel wire before spring processing, and the surface roughness of the wire rod before spring processing is substantially maintained. It had been.

  Sample No. 3, which was shot peened after spring processing, had a higher fatigue limit than sample No. 100, but the fatigue limit varied. Sample Nos. 120 and 130 subjected to shot peening after spring processing also showed variations in fatigue limit. The reason is considered that at least a part of the surface of the wire constituting the spring is roughened by shot peening, the surface roughness is increased, and wrinkle sensitivity is increased. On the other hand, it can be seen that Samples Nos. 1 and 2 that have not been subjected to shot peening after spring processing stably have a high fatigue limit.

  Moreover, it turns out that the spring which is excellent in a fatigue characteristic is obtained from this test, so that the surface roughness of the steel wire for springs is small.

  From the above test results, it is possible to obtain fatigue characteristics without using post-treatment after spring processing by using a steel wire for spring before spring processing that has a uniformly smooth surface in the circumferential direction. It can be seen that an excellent spring is obtained. It can also be seen that by using a spring steel wire having such a smooth surface, a spring having excellent fatigue characteristics can be manufactured more stably than a spring subjected to post-treatment after spring processing. Furthermore, it can be seen that the obtained spring has a uniform surface over the circumferential direction, like the spring steel wire before spring processing, so that wrinkle sensitivity is reduced and fatigue characteristics are excellent.

  Note that the present invention is not limited to the above-described embodiment, and can be modified as appropriate without departing from the gist of the present invention. For example, the composition, structure, wire diameter, etc. of the steel wire can be changed.

  The spring of the present invention can be suitably used for various springs, in particular, various springs used for automobile parts, specifically, fuel injection nozzle springs, clutch / torque converter springs, and the like. The steel wire for a spring of the present invention can be suitably used as a material for the spring of the present invention.

  1 Spring 100 wire

Claims (5)

The wire diameter is less than 1mm,
A steel wire for a spring characterized by having a surface roughness in the circumferential direction of Rz of 6 μm or less.   2. The spring steel wire according to claim 1, wherein an electrolytic polishing treatment is performed along a circumferential direction of the spring steel wire.   A spring manufactured using the spring steel wire according to claim 1 or 2. Formed by spirally winding a steel wire with a wire diameter of less than 1 mm,
The spring characterized in that the surface roughness in the circumferential direction of the steel wire is 6 μm or less in terms of Rz.   5. The spring according to claim 3, wherein nitriding treatment and shot peening are not performed.

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