KR20060129019A - Steel wire for spring - Google Patents

Abstract

A steel wire for a spring being produced through quenching and tempering and having a tempered martensite structure, which is produced with a value of reduction of area of 40 % or more, and exhibits a shear yield stress of 1000 MPa or more after the heat treatment at 420 to 480°C for two hours or longer, wherein the steel wire preferably has a chemical composition, in mass %, that C: 0.50 to 0.75 %, Si: 1.80 to 2.70 %, Mn: 0. 1 to 0.7 %, Cr: 0.70 to 1.50 %, Co: 0.02 to 1.00%, and the balance: Fe and impurities, or that C: 0.50 to 0.75 %, Si: 1.80 to 2.70 %, Mn: more than 0.7% and 1.5 % or less, Cr: 0.70 to 1.50 %, and the balance: Fe and impurities.

Description

Steel Wire for Spring {STEEL WIRE FOR SPRING}

The present invention relates to a spring steel wire having a tempering martensite structure by quenching tempering, a method for producing a spring steel wire suitable for the production of this spring steel wire, and a spring produced by the steel wire It is about. In particular, the present invention relates to a high-strength spring steel wire having excellent fatigue characteristics with a high strength suitable for a spring used for an engine valve spring or a transmission inside an automobile.

In response to the low fuel consumption of automobiles, in recent years, miniaturization and weight reduction of components such as engines and transmissions of automobiles have been advanced. In connection with this, the stress applied to springs, such as an engine valve spring and a transmission spring, is increasing year by year, and the spring material used is further required to improve fatigue characteristics. Conventionally, silicon chrome oil temper wires are used for valve springs and transmission springs of these engines. For example, those described in Patent Documents 1 to 3 are known.

[Patent Document 1]

Japanese Patent No. 2842579

[Patent Document 2]

Japanese Patent Application Laid-Open No. 2002-194496

[Patent Document 3]

Japanese Patent No. 3045795

However, the characteristics required for springs such as valve springs of engines and springs for transmissions have become strict in recent years, and further improvements are required for spring steel wires and springs. In particular, it is desired that the spring steel wire and the spring have more balanced fatigue characteristics and toughness.

On the other hand, in recent years, with the request of improving fatigue strength (fatigue limit), after a spring process, the spring is heat-treated (nitriding treatment) of high temperature (specifically, about 420-480 degreeC).

In the technique of patent document 1, toughness is aimed at by making content of C (carbon) of a steel wire into 0.3-0.5 weight%. However, since the heat resistance is lowered by lowering the content of carbon to less than 0.50% by weight, for example, when the steel wire is subjected to the high temperature nitriding treatment on the spring, the fatigue strength is lowered. When used, it causes internal breakage.

In the technique described in Patent Literature 2, fatigue strength is improved by setting the average grain size of austenite after quenching to a microstructure of 1.0 to 7.0 µm. However, in order to make austenite grain size smaller, when the temperature at the time of quenching is made low, unsolubilized carbide will remain and it will become a factor which reduces toughness. Moreover, since toughness falls, breakage tends to occur at the time of steel working of a spring, and it adversely affects the mass productivity of a spring.

In the technique described in Patent Literature 3, the surface hardness is reduced by intentionally decarburizing the surface of the steel wire during oil tempering, thereby improving the spring workability, but it is difficult to obtain a uniform decarburized layer on the surface. Unsuitable for mass production of steel wires or springs. In addition, the oxygen concentration must be controlled at the time of heating the steel wire (oil tempering), which entails an increase in cost.

In addition, neither of the techniques described in the literature has been examined for the internal stress in the torsional direction inside the material (spring), that is, the shear yield stress of the spring after the nitriding treatment performed after the spring processing of the steel wire.

Then, the main object of this invention is to provide the high strength spring steel wire which is excellent in both fatigue strength and toughness. Another object of the present invention is to provide a spring manufactured by the spring steel wire and a manufacturing method suitable for the production of the spring steel wire.

The steel wire for spring of this invention achieves the said objective by defining the cross-sectional shrinkage value of the steel wire after quenching tempering, and the shear yield stress of the steel wire which performed the heat processing corresponded to the nitriding treatment after said quenching tempering to a specific value.

That is, this invention is a steel wire for spring which has a tempered martensite structure by hardening tempering. The steel wire for spring has a cross-sectional shrinkage of 40% or more and a shear yield stress of the steel wire after heat treatment for 2 hours or more at 420 ° C or more and 480 ° C or less is 1000 MPa or more.

As for the said steel wire for spring, it is more preferable to consist especially in any one of the following 1-6 chemical components.

1.% by mass C: 0.50 to 0.75%, Si: 1.80 to 2.70%, Mn: 0.1 to 0.7%, Cr: 0.70 to 1.50%, Co: 0.02 to 1.00%, the balance being Fe and impurities

2. By mass%, C: 0.50-0.75%, Si: 1.80-2.70%, Mn: more than 0.7-1.5%, Cr: 0.70-1.50%, and remainder is Fe and an impurity

3. As mass%, at least of C: 0.50 to 0.75%, Si: 1.80 to 2.70%, Mn: over 0.7 to 1.5%, Cr: 0.70 to 1.50%, Ni: 0.1 to 1.0% and Co: 0.02 to 1.00% It contains one element, and the balance is Fe and impurities

4.% by mass C: 0.50 to 0.75%, Si: 1.80 to 2.70%, Mn: 0.1 to 0.7%, Cr: 0.70 to 1.50%, Co: 0.02 to 1.00% and V by mass: 0.05 to 0.50% , Mo: 0.05% to 0.50%, W: 0.05% to 0.15%, Nb: 0.05% to 0.15%, and Ti: 0.01% to 0.20%. impurities

5. By mass%, C: 0.50 to 0.75%, Si: 1.80 to 2.70%, Mn: over 0.7 to 1.5%, Cr: 0.70 to 1.50%, and by mass% V: 0.05 to 0.50%, Mo: 0.05 to At least one element selected from the group of five elements consisting of 0.50%, W: 0.05-0.15%, Nb: 0.05-0.15%, and Ti: 0.01-0.20%, with the balance being Fe and impurities

6. By mass%, at least of C: 0.50 to 0.75%, Si: 1.80 to 2.70%, Mn: over 0.7 to 1.5%, Cr: 0.70 to 1.50%, Ni: 0.1 to 1.0% and Co: 0.02 to 1.00% From one element and five element groups consisting of V: 0.05-0.50%, Mo: 0.05-0.50%, W: 0.05-0.15%, Nb: 0.05-0.15%, and Ti: 0.01-0.20% Contains at least one element selected, and the balance is Fe and impurities

Moreover, as a manufacturing method suitable for manufacture of the said steel wire for springs of this invention, the following is proposed. That is, the manufacturing method of the steel wire for springs of this invention is a process of patterning the steel materials of the chemical component as described in any one of the following (A)-(C), and drawing the said patterned steel material. And a step of performing quenching and tempering on the freshly processed steel wire. The patterning, the austenitization step of heating for 60 to 180 seconds at 900 ~ 1050 ℃, and the constant temperature transformation step of heating for 20 to 100 seconds at 600 ~ 750 ℃ after the austenitization process I shall do it.

(A) Mass: C: 0.50 to 0.75%, Si: 1.80 to 2.70%, Mn: 0.1 to 0.7%, Cr: 0.70 to 1.50%, Co: 0.02 to 1.00%, the balance being Fe and impurities Steel

(B) Steel material containing C: 0.50 to 0.75%, Si: 1.80 to 2.70%, Mn: over 0.7 to 1.5%, Cr: 0.70 to 1.50% by mass, and the balance being Fe and impurities

(C) in mass% in C: 0.50 to 0.75%, Si: 1.80 to 2.70%, Mn: over 0.7 to 1.5%, Cr: 0.70 to 1.50%, Ni: 0.1 to 1.0% and Co: 0.02 to 1.00% Steel material containing at least one element and remainder consisting of Fe and impurities

In addition to the chemical components of the above (A) to (C), the steel material is also in mass%, V: 0.05-0.50%, Mo: 0.05-0.50%, W: 0.05-0.15%, Nb: 0.05-0.15% , And Ti: may contain at least one element selected from five element groups consisting of 0.01 to 0.20%.

Hereinafter, the present invention will be described in more detail.

(Improved fatigue characteristic)

In order to improve the fatigue characteristics of the spring, it is desired to suppress the fatigue fracture of the spring. When the spring is used repeatedly, the spring is subjected to cyclic stress in the shear direction simultaneously with the tension direction and the compression direction. In this way, due to the externally added cyclic stress, the spring causes the sliding deformation (plastic deformation) locally or intensively repeatedly, generates irregularities in the vicinity of the surface of the spring, and cracks occur, leading to breakage, that is, Fatigue failure. Therefore, in order to suppress fatigue failure of the spring, it is effective to suppress the local or intensive plastic deformation. In order to suppress such plastic deformation, conventionally, after steel-stretching a steel wire, it heat-processes, such as nitriding, and raises the surface hardness of a spring, and improves a fatigue limit. However, these days, the spring is permanently deformed and cannot be used only by increasing the fatigue limit. It is considered that this is because even if the hardened nitride layer of the spring surface layer formed by the heat treatment such as the nitriding treatment is not permanently deformed, the strength inside the spring is deteriorated due to the large stress, thereby causing permanent deformation. For such reasons, in addition to being high in strength, it is desired to improve not only the fatigue limit but also the torsional resistance, that is, the shear yield stress itself. Thus, the inventors have studied variously and found that after the heat treatment of the nitriding treatment or the like, the inside of the material (spring) should have an appropriate torsional strength. Specifically, it has been found that the fatigue properties of the spring can be improved if the shear yield stress of the spring is higher than 1000 MPa after the heat treatment such as nitriding treatment. Based on this knowledge, the spring steel wire of this invention defines the shear yield stress of the steel wire after specific heat processing after quenching tempering to 1000 Mpa or more.

(Toughness)

No matter how high the steel wire is, even if the toughness is low, the steel wire breaks at the time of spring processing, thereby impairing the mass productivity of the spring. Moreover, the fatigue property of a spring will also fall by the fall of the toughness of the steel wire used as a material. Therefore, the inventors have studied variously, and it has been found that setting the cross-sectional shrinkage value of the steel wire after quenching to 40% or more is effective in preventing the breakage of the steel wire at the time of spring processing and excellent in the mass productivity of the spring. Got. Based on this knowledge, the present invention defines the section shrinkage value of the steel wire to be 40% or more. When the cross-sectional shrinkage value is less than 40%, breakage of the steel wire is likely to occur at the time of spring machining, and there is a risk of disturbing the mass productivity of the spring. In addition, the cross-sectional shrinkage value may decrease slightly by subjecting the steel wire to a specific heat treatment of 420 ° C or more and 480 ° C or less corresponding to the nitriding treatment for 2 hours or more after quenching and tempering. However, as described above, if the cross-sectional shrinkage value is 40% or more, the steel wire can maintain the cross-sectional shrinkage value of 35% or more even after the heat treatment, and the spring obtained by the steel wire can obtain high fatigue characteristics. have.

Thus, the steel wire for spring of this invention defines the cross-sectional shrinkage value, and the shear yield stress after heat-processing corresponded to nitriding treatment to this steel wire, and the fatigue strength and the high fatigue strength of the spring obtained by this steel wire and this steel wire are We try to balance performance.

In order to obtain the steel wire for the present invention and the spring excellent in both the fatigue properties and the toughness, the optimum chemical composition and manufacturing conditions, especially patterning conditions of the steel wire is specified.

<Chemical composition>

First, after the steel wire is subjected to spring processing, heat treatment such as nitriding treatment performed on the spring improves the spring fatigue limit by improving the surface hardness of the spring. Loss may occur. Therefore, in this invention, in order to improve the heat resistance of the mother phase of the steel wire processed by a spring, it shall contain C and Si in a predetermined range (mass%). Further, when tempering the steel wire, a predetermined amount of Cr is contained in order to form carbide in the steel wire structure to increase the softening resistance of the steel wire. It is also effective to increase the softening resistance in addition to containing a predetermined amount of Cr and to further contain a predetermined amount of Mo, V, Nb, W, and Ti. In addition, it is effective to improve the shear yield stress of the spring of the steel wire of the present invention or the steel wire of the present invention, which contains 0.02 to 1.00 mass% of Co or abundantly Mn (greater than 0.7 to 1.5 mass%). Found. Therefore, content of Mn and Co is prescribed | regulated. The detailed component range and the reason for limitation of a range are mentioned later.

<Production Conditions>

The steel wire for a spring of this invention is obtained by performing a solvent → hot forging → hot rolling → patterning → drawing → quenching tempering to steel materials which have the said chemical component.

(Patterning condition)

In the present invention, the patterning of specific conditions is performed prior to drawing, thereby sufficiently austenitizing the steel structure, dissolving the unsolubilized carbide, and obtaining a uniform perlite structure by appropriate constant temperature transformation. Insufficient austenitization causes a decrease in the toughness of the steel wire and the shear yield stress. Therefore, in order to fully austenitize, it is suitable to heat for 60 to 180 seconds at the temperature of 900-1050 degreeC. If the heating temperature is less than 900 ° C., or if the heating time is less than 60 seconds at the heating temperature of 900 to 1050 ° C., sufficient austenitization cannot be performed, and the unsolubilized carbide remains. When the heating temperature is higher than 1050 ° C or the heating time is longer than 180 seconds at the heating temperature of 900 to 1050 ° C, the austenite particles are coarsened and martensite is formed during transformation. It is easy to produce, and at the time of fresh processing, the freshness is impaired.

It is preferable that the constant temperature transformation of the steel material performed after austenitization is heated at 600-750 degreeC for 20 to 100 second. When the heating temperature is higher than 750 ° C. or when the heating time is longer than 100 seconds at the heating temperature of 600 to 750 ° C., cementite is spheroidized in the steel structure, resulting in the freshness of the steel. It becomes a factor to inhibit. On the other hand, when the heating temperature is lower than 600 ° C. or when the heating time is shorter than 20 seconds at the heating temperature of 600 to 750 ° C., transformation to pearlite is not completed and martensite is produced, thereby inhibiting freshness. It becomes a factor to throw away.

(Quenching, tempering)

If the temperature at the time of quenching the steel wire obtained by drawing the said patterning steel is too low, unsoluble carbide will remain in a steel wire structure, and the toughness of steel wire will fall. On the contrary, if the temperature at the time of quenching is too high, austenite crystal grains grow and enlarge, thereby reducing the fatigue limit of the steel wire or the spring obtained by the steel wire. Therefore, it is preferable that the temperature at the time of quenching shall be more than 850 degreeC and less than 1050 degreeC.

<Organization>

The steel wire for spring of this invention shall have a tempered martensite structure. Further, if the austenite grains (former austenite grains) of the steel wire after quenching and tempering are refined, the steel wire and the spring obtained by the steel wire become difficult to produce localized and concentrated slipping deformation even if cyclic stress is applied. That is, the shear yield stress of the steel wire and the spring can be improved, and as a result, finer austenite grains (former austenite grains) can contribute to the improvement of the fatigue characteristics.

Specifically, the average grain size of the austenite grains (former austenite grains) is preferably 3.0 to 7.0 µm. The average grain size can be changed by changing the temperature of the patterning performed on steel materials. More specifically, when the temperature at the time of austenitization is lowered in patterning, the grain size decreases, and when the same temperature is increased, the grain size tends to increase. If the average crystal grain size is less than 3.0 µm, the austenitization temperature is low, so that the unsolubilized carbide remains and the toughness of the steel wire tends to decrease. In addition, when the average grain size exceeds 7.0 µm, the fatigue limit of the spring obtained by the steel wire or the steel wire is hardly improved. In addition, an average grain size shall be the value measured after tempering by fresh steel wire.

Hereinafter, the reason for selecting the member element and limiting the component range in the present invention will be described. In addition, the unit of the numerical value described in the vicinity of an element is mass%.

C: 0.50-0.75

C is an important element for determining the strength of steel, and if the content of carbon is less than 0.50% by mass with respect to the whole steel, steel wire of sufficient strength is not obtained, and if it exceeds 0.75% by mass, the toughness is impaired. 0.50 mass% or more and 0.75 mass% or less.

Si: 1.80 ~ 2.70

Si is used as a deoxidizer at the time of dissolution refining of steel materials. In addition, Si has an effect of improving the heat resistance by dissolving in ferrite to prevent a decrease in hardness inside the steel wire (spring) by heat treatment such as stress relief annealing or nitriding treatment performed on the spring after spring processing. In order to maintain heat resistance, 1.80 mass% or more is required, and when it exceeds 2.70 mass%, toughness will fall, Therefore, content of Si shall be 1.80 mass% or more and 2.70 mass% or less.

Mn: 0.1 ~ 1.5

Mn, like Si, is used as a deoxidizer in dissolution refining. In such condensed milk, the lower limit is made 0.1 mass% as the content of Mn required for the deoxidizer. In addition, Mn improves the hardenability of the steel wire, increases the strength of the steel wire, and has an effect of improving the shear yield stress of the spring obtained by the steel wire or the steel wire. However, if the content of Mn is more than 1.5% by mass with respect to the whole steel, martensite is easily formed in the steel material during patterning, and the upper limit of the content of Mn is caused because it causes disconnection at the time of drawing. Let 1.5 mass%. In particular, in the case of containing Co described later in steel, the content of Mn may be as low as 0.1 to 0.7% by mass, and when not containing Co, it is preferable to contain Mn sufficiently as over 0.7 to 1.5% by mass. . It may contain Co sufficiently and contain Mn.

Cr: 0.70-1.50

Since Cr improves hardenability of steel and increases softening resistance, it is effective for preventing the softening of the spring when the spring is subjected to heat treatment such as tempering treatment or nitriding treatment after the spring processing. If the content of Cr is less than 0.70% by mass relative to the whole steel, sufficient effect for the prevention of softening cannot be obtained. Therefore, the content of Cr is 0.70% by mass or more, and if it exceeds 1.50% by mass, martensite is formed during patterning. It becomes easy to generate | occur | produce, and becomes a cause of disconnection at the time of drawing, and becomes a factor which reduces the toughness of steel materials after patterning (oil tempering). Therefore, content of Cr is prescribed | regulated to 0.70 to 1.50%.

Co: 0.02 ~ 1.00

Co contains a small amount in steel to improve the shear yield stress of the steel wire and the spring. Moreover, Co has the effect of improving heat resistance, and is effective in preventing the softening of the tempered or nitrided spring after the spring processing. In addition, when the Co content is small, the toughness of the steel wire is not lowered. If the Co content is less than 0.02% by mass, it is difficult to obtain effects such as improvement of the shear yield stress of the steel wire or the spring, improvement of heat resistance of the steel wire, and even if Co content is added more than 1.00% by mass, 1.00% by mass or less Compared with the case where it is made, the effect by containing Co does not change, but since steel wire manufacture and spring manufacture become expensive, Co content is made into 0.02 mass% or more and 1.00 mass% or less. In addition, when Co is contained in steel, content of Mn may be made low as 0.1-0.7 mass% as mentioned above.

Ni: 0.1 ~ 1.0

By containing Ni in steel, there exists an effect which improves the corrosion resistance and toughness of steel wire. If the content of Ni is less than 0.1% by mass, the steel wire effect is hardly obtained, and even if the content of Ni exceeds 1.0% by mass, the steel wire production becomes expensive, and further improvement effects of the toughness of the steel wire cannot be obtained. In such condensed milk, the content of Ni is made 0.1 mass% or more and 1.0 mass% or less.

Mo, V: 0.05-0.50

W, Nb: 0.05-0.15

These elements tend to form carbides in the wire structure when the wire is tempered and to increase the softening resistance of the wire. When content of Mo, content of V, content of W, and content of Nb are less than 0.05 mass% with respect to the whole steel, respectively, the said effect is hard to be acquired. Moreover, when content of Mo exceeds 0.50 mass%, When content of V exceeds 0.50 mass%, When content of W exceeds 0.15 mass%, When content of Nb exceeds 0.15 mass%, Both of them tend to lower the toughness of the steel wire.

Ti: 0.01 ~ 0.20

Ti has an effect of forming carbide at tempering and increasing softening resistance of the steel wire. If the content of Ti is less than 0.01% by mass, the above effect cannot be obtained. If the content of Ti is more than 0.20% by mass, the high-melting point nonmetallic inclusion TiO is formed in the steel wire structure, thereby reducing the toughness of the steel wire. Therefore, content of Ti is made into 0.01 mass% or more and 0.20 mass% or less.

The shape of the cross section perpendicular to the steel wire longitudinal direction (new wire direction) of the steel wire for spring of the present invention may be a shape of an unshaped cross section such as an ellipse, a trapezoid, a square, a rectangle, as well as a circular shape.

The spring of the present invention can be obtained by subjecting the spring steel wire to spring processing such as coiling. In particular, after the spring steel wire of the present invention is subjected to spring processing, the obtained spring is subjected to heat treatment such as nitriding treatment, whereby the surface hardness of the spring is improved, and thus the fatigue limit can be excellent.

<Embodiment of the Invention>

EMBODIMENT OF THE INVENTION Hereinafter, embodiment of this invention is described.

The steel material which consists of a chemical component shown in Table 1, and remainder Fe and an impurity was melted by the vacuum melting furnace, and the wire rod of ø6.5 mm was produced by hot forging and hot rolling. Subsequently, a wire having a diameter of 3.0 mm was obtained by subjecting the wire to patterning (austenitic → constant temperature transformation), peeling, annealing, and drawing. Table 2 shows the patterning conditions. In this example, the patterning performed on the wire rod of ø6.5 mm is a condition for austenizing the wire rod as shown in Table 2, and a plurality of conditions in which the heating time and the holding time of the wire rod are prepared are prepared. As a condition for constant temperature transformation of the wire rod after austenitization, a plurality of conditions having different heating time and holding time of the wire rod were prepared.

Quenching and tempering was performed to the obtained wire (ø3.0 mm). Quenching was performed on the conditions shown in Table 3, and tempering performed the heating temperature as 450-530 degreeC in any wire. In the wire after quenching and tempering, the average crystal grain size (average? Particle size) of the cross-sectional shrinkage value RA and austenite grains (former austenite grains) was measured. The results are shown in Table 3. Also, by changing the quenching temperature of the wire, the average grain size of the austenite grains (former austenite grains) was changed. The average grain size of the austenite grains was calculated by the cutting method specified in JIS G0522.

After quenching and tempering, the shear yield stress and fatigue characteristics (fatigue limit) were measured for the steel wire subjected to heat treatment (420 ° C. × 2 hours, or 480 ° C. × 2 hours) corresponding to the nitriding treatment. The results are shown in Table 3. The shear yield stress of the steel wire subjected to the heat treatment was subjected to a banquet test with a sample length of 10 Od (d: sample diameter), and was determined from a torque-θ curve. The fatigue limit was evaluated by the Nakamura rotary bending fatigue test.

As shown in Table 3, it can be seen that all the steel wires of Sample Nos. 13 to 21 whose cross-sectional shrinkage values (RA) are 40% or more and the shear yield stress after heat treatment corresponding to the nitriding treatment are 1000 MPa or more. . Moreover, these steel wires are considered to be excellent in permanent deformation because of their high shear yield stress. Therefore, it turns out that the steel wire for springs of this invention is excellent in a fatigue characteristic, having high toughness.

On the other hand, Sample Nos. 1 to 4, 6, and 8 resulted in low shear yield stress after heat treatment corresponding to nitriding treatment and low fatigue limit. In particular, sample Nos. 2 and 4 also had low cross-sectional shrinkage values, and were inferior in toughness. In addition, the samples No. 5 and 7 stopped the experiment because martensite was generated in the wire structure during patterning, and a large number of disconnections were generated by the peeling of the next step. Sample No. 11 had not only a low shear yield stress after heat treatment, but also a large amount of V in the steel, so that the cross-sectional shrinkage of the steel wire was lowered and the fatigue limit was lowered. Sample No. 12 had a low shear yield stress after heat treatment and a high Ti content, resulting in a lower fatigue limit due to breakage caused by Ti-based inclusions.

Sample No. 9 had a low shear yield stress after heat treatment and a small average particle diameter of the austenite grains (former austenite grains), resulting in lower cross-sectional shrinkage. On the other hand, in sample No. 10, the shear yield stress after heat treatment was low, and the fatigue limit was lowered because the average particle diameter of the austenite grains (former austenite grains) was large.

About the steel material which has the chemical component of the sample K of Table 1, the wire rod of ø6.5 mm was produced similarly to the above, and the wire of ø3.0 mm was prepared similarly to the above. At this time, the conditions of patterning were changed as shown in Table 2. Quenching tempering was performed to the obtained wire (quenching: 940 degreeC, tempering: 450-530 degreeC), and the average particle diameter of the cross-sectional shrinkage value (RA) and austenite crystal grain (former austenite crystal grain) of the obtained wire were measured. The results are shown in Table 4. In addition, the shear yield stress and the fatigue characteristic (fatigue limit) were measured for the steel wire subjected to the heat treatment (420 ° C. × 2 hours, or 480 ° C. × 2 hours) corresponding to the nitriding treatment after quenching the wire. The results are also shown in Table 4. The measurement of each physical property was performed similarly to the above.

As shown in Table 4, samples No. 22 and 23 subjected to patterning under specific conditions (austenitic: from 60 to 180 seconds at 900 to 1050 ° C and constant temperature transformation from 20 to 100 seconds at 600 to 750 ° C) In all, it can be seen that the fatigue limit is high.

On the other hand, since all the samples No. 25 and 27-29 had martensite generate | occur | produced in the wire structure when patterning, and many disconnection generate | occur | produced in the drawing process, the experiment was stopped. In samples Nos. 24 and 26, unsolubilized carbide remained, so that the cross-sectional shrinkage of the wire decreased and the fatigue limit decreased. In addition, samples No. 24 and 26 had low shear yield stress. In sample Nos. 30 and 31, since cementite was spheroidized in the wire structure, unsolubilized carbide remained, the section shrinkage decreased, and the shear yield stress of the steel wire was also small.

Since the steel wire for springs of this invention is excellent in a fatigue characteristic and toughness, it is suitable for the material of the spring used for the site | part to which fatigue strength is calculated | required.

Claims (13)

As a steel wire for a spring having a tempering martensite structure by quenching tempering, Sectional shrinkage is over 40% A spring steel wire, characterized in that the shear yield stress of the steel wire after heat treatment at 420 ° C. or higher and 480 ° C. or lower for 2 hours is 1000 MPa or more. The method of claim 1, The steel wire contains, in mass%, C: 0.50 to 0.75%, Si: 1.80 to 2.70%, Mn: 0.1 to 0.7%, Cr: 0.70 to 1.50%, Co: 0.02 to 1.00%, and the balance is Fe and impurities. Spring steel wire, characterized in that consisting of. The method of claim 1, The steel wire contains, in mass%, C: 0.50 to 0.75%, Si: 1.80 to 2.70%, Mn: over 0.7 to 1.5%, and Cr: 0.70 to 1.50%, and the balance is made of Fe and impurities. Steel wire for spring. The method of claim 1, The steel wire is, in mass%, C: 0.50 to 0.75%, Si: 1.80 to 2.70%, Mn: over 0.7 to 1.5%, Cr: 0.70 to 1.50%, It contains at least one of Ni: 0.1-1.0% and Co: 0.02-1.00% by mass, Steel wire for spring, characterized in that the balance is made of Fe and impurities. The method of claim 1, The steel wire is, in mass%, C: 0.50 to 0.75%, Si: 1.80 to 2.70%, Mn: 0.1 to 0.7%, Cr: 0.70 to 1.50%, Co: 0.02 to 1.00%, At least one selected from five element groups consisting of V: 0.05-0.50%, Mo: 0.05-0.50%, W: 0.05-0.15%, Nb: 0.05-0.15%, and Ti: 0.01-0.20% by mass. Contains elements, Steel wire for spring, characterized in that the balance is made of Fe and impurities. The method of claim 1, The steel wire is, in mass%, C: 0.50 to 0.75%, Si: 1.80 to 2.70%, Mn: over 0.7 to 1.5%, Cr: 0.70 to 1.50%, At least one selected from five element groups consisting of V: 0.05-0.50%, Mo: 0.05-0.50%, W: 0.05-0.15%, Nb: 0.05-0.15%, and Ti: 0.01-0.20% by mass. Contains elements, Steel wire for spring, characterized in that the balance is made of Fe and impurities. The method of claim 1, The steel wire is, in mass%, C: 0.50 to 0.75%, Si: 1.80 to 2.70%, Mn: over 0.7 to 1.5%, Cr: 0.70 to 1.50%, and mass: Ni: 0.1 to 1.0% and Co: 0.02 At least one element of 1.00% and the mass% of V: 0.05-0.50%, Mo: 0.05-0.50%, W: 0.05-0.15%, Nb: 0.05-0.15%, and Ti: 0.01-0.20% A steel wire for spring, containing at least one element selected from five element groups, and the balance consisting of Fe and impurities. The method according to any one of claims 1 to 7, A steel wire for springs, characterized in that the average grain size of the austenite grains (formerly austenite grains) of the steel wire is 3.0 to 7.0 µm. The spring produced using the steel wire for springs in any one of Claims 1-7. The spring produced using the steel wire for springs of Claim 8. Steel material containing C: 0.50 to 0.75%, Si: 1.80 to 2.70%, Mn: 0.1 to 0.7%, Cr: 0.70 to 1.50%, Co: 0.02 to 1.00% by mass, and the balance being Fe and impurities. I) patterning (patenting), A process of drawing the patterned steel in a fresh line, And quenching tempering on the freshly processed steel wire, The patterning is, An austenite process for heating at 900-1050 ° C. for 60-180 seconds, And a constant temperature transformation step of heating at 600 to 750 ° C. for 20 to 100 seconds after the austenitization step. C: 0.50 to 0.75% by mass, Si: 1.80 to 2.70%, Mn: greater than 0.7 to 1.5%, Cr: 0.70 to 1.50%, and the remainder is patterned for the steel material consisting of Fe and impurities, Fresh process the patterned steel, And quenching tempering on the freshly processed steel wire, The patterning is, An austenitization process for heating at 900 to 1050 ° C. for 60 to 180 seconds, Method for producing a steel wire for the spring characterized in that it comprises a constant temperature transformation process for heating for 20 to 100 seconds at 600 ~ 750 ℃ after the austenitization process. In mass%, at least one of C: 0.50 to 0.75%, Si: 1.80 to 2.70%, Mn: over 0.7 to 1.5%, Cr: 0.70 to 1.50%, Ni: 0.1 to 1.0% and Co: 0.02 to 1.00% Patterning a steel material containing an element, the balance being made of Fe and impurities; Fresh process the patterned steel, And quenching tempering on the freshly processed steel wire, The patterning is, An austenitization process for heating at 900 to 1050 ° C. for 60 to 180 seconds, Method for producing a steel wire for the spring characterized in that it comprises a constant temperature transformation process for heating for 20 to 100 seconds at 600 ~ 750 ℃ after the austenitization process.