SPRING STEEL, SPRING, AND MANUFACTURING METHOD OF SPRING
A spring steel contains, in terms of mass %, C: 0.35% or more and 0.55% or less, Si: 1.60% or more and 3.00% or less, Mn: 0.20% or more and 1.00% or less, Cr: 0.10% or more and 1.50% or less, Ni: 0.05% or more and 0.30% or less, and Cu: 0.05% or more and 1.00% or less, and substantially does not contain V, the remainder being Fe and unavoidable impurities.
The present application is a related application of, and claims priority to, Japanese Patent Application No. 2013-117874 filed on Jun. 4, 2013, the entire contents of this Japanese patent application are hereby incorporated by reference into the present application.
TECHNICAL FIELDThe present specification relates to a spring steel, a spring, and a manufacturing method of the spring.
BACKGROUND TECHNOLOGYIn recent years, there has been a growing demand for spring steels and springs having high strength. In Patent Literature 1 to 4, springs are disclosed that excel in durability and resistance to sag as well as springs that excel in corrosion fatigue strength.
CITATION LIST Patent Literature
- Patent Literature 1: Japanese Patent Application Laid-Open No. H3-2354
- Patent Literature 2: Japanese Patent Application Laid-Open No. 2008-106365
- Patent Literature 3: Japanese Patent Application Laid-Open No. 2003-55741
- Patent Literature 4: Japanese Patent Application Laid-Open No. 2004-315944
- Patent Literature 5: Japanese Patent Application Laid-Open No. 2004-143482
- Patent Literature 6: Japanese Patent Application Laid-Open No. 2008-202124
However, Ni and V are added in all of the springs described in Patent Literature 1 to 4. Ni is added with the intention of improving corrosion resistance, whereas V is added with the intention of improving toughness and corrosion fatigue resistance. These springs contain 0.30% or more and 3.00% or less of Ni and contain 0.05% or more and 0.50% or less of V, in terms of mass %. Ni and V are costly, and thus the overall cost of such springs tends to be high.
Means for Solving the Problem(s)As a result of conducting various studies on alloy compositions of spring steel, the present inventor discovered an alloy composition that can ensure the performance of a spring even if the added amount of Ni is reduced and V is not added. The following means are provided by the present specification based on these new insights.
In accordance with the present disclosure, a spring steel contains, in terms of mass %, C: 0.35% or more and 0.55% or less, Si: 1.60% or more and 3.00% or less, Mn: 0.20% or more and 1.00% or less, Cr: 0.10% or more and 1.50% or less, Ni: 0.05% or more and 0.30% or less, and Cu: 0.05% or more and 1.00% or less, and substantially does not contain V, the remainder being Fe and unavoidable impurities.
Ni may be 0.18% or more in terms of mass %. Ni may be 0.18% or more and 0.25% or less in terms of mass %. Mn may be 0.45% or more and 0.65% or less in terms of mass %. Cu may be 0.20% or more and 0.30% or less in terms of mass %. Ti may be 0.030% or more and 0.100% or less in terms of mass %. B may be 0.0010% or more and 0.0050% or less in terms of mass %.
P may be 0.015% or less and S may be 0.015% or less in terms of mass %. According to the present disclosure, a spring is also provided that is manufactured using any one of the above-mentioned spring steels.
According to the present disclosure, a manufacturing method of a spring using spring steel is also provided, in which the spring steel contains, in terms of mass %, C: 0.35% or more and 0.55% or less, Si: 1.60% or more and 3.00% or less, Mn: 0.20% or more and 1.00% or less, Cr: 0.10% or more and 1.50% or less, Ni: 0.05% or more and 0.30% or less, and Cu: 0.05% or more and 1.00% or less; and substantially does not contain V, the remainder of the spring steel being Fe and unavoidable impurities.
The manufacturing method may further comprise: a hot setting step in which hot setting is performed on the spring steel, which has been formed into a coil shape and subjected to heat treatment; and a warm shot peening step in which warm shot peening is performed on the spring steel after the hot setting. The manufacturing method of the spring may further comprise: a warm shot peening step in which warm shot peening is performed on the spring steel, which has been formed into a coil shape and subjected to heat treatment; and a hot setting step in which hot setting is performed on the spring steel after the warm shot peening.
According to spring steels disclosed in the present specification (hereinafter referred to as “the present spring steel”), by reducing the added amount of Ni to 0.05% or more and 0.30% or less, in terms of mass %, and not adding V, it is possible to manufacture relatively inexpensive springs. Embodiments disclosed in the present specification will be explained in detail below. Note that, in the following explanation, mass % will be referred to simply as %.
Representative and non-limiting specific examples of the present disclosure will be hereinafter explained in detail with reference to the drawings as appropriate. This detailed explanation is simply intended to show details for implementing preferred examples of the present disclosure to those skilled in the art and is not intended to limit the scope of the present disclosure. Additional features and inventions disclosed below may be used separately from or together with other features and inventions in order to provide a further improved spring steel, a spring, and a manufacturing method of the spring.
Combinations of features and processes disclosed in the following detailed explanation are not always essential in implementing the present disclosure in a broadest meaning and are described only to explain, in particular, representative specific examples of the present disclosure. Further, in providing additional and useful embodiments of the present disclosure, various features of the specific examples explained above and below and various features of matters described in independent and dependent claims do not have to be combined as specified in the specific examples described herein or as specified by enumerated orders.
All features described in the present specification and/or claims are intended to be disclosed individually and independently from one another, separately from configurations of features described in examples and/or claims, as limitations for disclosed or claimed matters specifying the invention as originally filed. Further, descriptions concerning all numerical value ranges and groups or masses are made with the intention of disclosing intermediate configurations of the numerical ranges and the groups or the masses as limitations for disclosed or claimed matters specifying the invention as originally filed.
(Spring Steel)
The present spring steel contains, in terms of mass %, C: 0.35% or more and 0.55% or less, Si: 1.60% or more and 3.00% or less, Mn: 0.20% or more and 1.00% or less, Cr: 0.10% or more and 1.50% or less, Ni: 0.05% or more and 0.30% or less, and Cu: 0.05% or more and 1.00% or less.
(C: Carbon)
The content of C is preferably 0.35% or more and 0.55% or less. If the content of C in the present spring steel is in this range, a spring steel having satisfactory strength can be obtained by quenching and tempering. If the content of C is less than 0.35%, a spring steel having satisfactory strength cannot be obtained by quenching and tempering. If, on the other hand, the content of C is more than 0.55%, toughness may decrease and fatigue strength and corrosion fatigue strength may decrease. While it depends on the relationship with other alloy components, the content of C is preferably 0.40% or more and 0.55% or less. A lower limit value is more preferably 0.43% and still more preferably is 0.45%. Most preferably, the content of C is 0.45% or more and 0.53% or less.
(Si: Silicon)
The content of Si is preferably 1.60% or more and 3.00% or less. If the content of Si in the present spring steel is in this range, Si is effective for improvement of resistance to sag, tempering characteristics, and corrosion fatigue strength. If the content of Si is less than 1.60%, sufficient effects in this regard are less easily obtained. If the content of Si is more than 3.00%, decarburization is promoted during rolling and heat treatment (quenching). In the present spring steel, from a viewpoint of corrosion fatigue strength and the like, a lower limit value is more preferably 1.80% and still more preferably 1.90%. An upper limit value is more preferably 2.50% and still more preferably 2.05%. Most preferably, the content of Si is 1.90% or more and 2.05% or less.
(Mn: Manganese)
The content of Mn is preferably 0.20% or more and 1.00% or less. If the content of Mn is more than 1.00%, toughness tends to decrease. If the content of Mn is less than 0.20%, strength and quenchability tend to be insufficient, and the spring steel tends to crack during rolling. In the present spring steel, from the viewpoint of compensating for a decreased corrosion fatigue strength caused by the decrease in the Ni added amount, a lower limit is more preferably 0.30%, still more preferably 0.40%, and still more preferably 0.45%. An upper limit value is more preferably 0.90%, still more preferably 0.80%, still more preferably 0.70%, and still more preferably 0.65%. Most preferably, the content of Mn is 0.45% or more and 0.65% or less.
(Cr: Chrome)
The content of Cr is preferably 0.10% or more and 1.50% or less. If the content of Cr in the present spring steel is in this range, Cr is effective for securing strength and improving quenchability. If the content of Cr is less than 0.10%, this effect is not provided sufficiently. If the content of Cr is more than 1.50%, the tempered structure becomes heterogeneous and there is greater susceptibility to a risk of impairing the resistance to sag. An upper limit value is more preferably 1.0%, still more preferably 0.50%, and still more preferably 0.40%. A lower limit value is more preferably 0.20% and still more preferably 0.25%. Most preferably, the content of Cr is 0.25% or more and 0.40% or less.
(Ni: Nickel)
The content of Ni is preferably 0.05% or more and 0.30% or less. Ni has the effect of improving the toughness of steel, and also has the effect of suppressing corrosion of steel and improving corrosion fatigue strength. If the content of Ni in the present spring steel is in this range, an inexpensive spring is provided as compared to prior springs. An upper limit value is more preferably less than 0.30%, still more preferably 0.27%, and still more preferably 0.25%. A lower limit value is more preferably 0.10%, more preferably 0.15%, and more preferably 0.18%. Typically, the content of Ni is preferably 0.18% or more and 0.30% or less, more preferably 0.18% or more and less than 0.30%, and still more preferably 0.18% or more and 0.25% or less.
(Cu: Copper)
The content of Cu is preferably 0.05% or more and 1.00% or less. If the content of Cu in the present spring steel is in this range, Cu is effective for improving corrosion resistance and improving quenchability. If the content of Cu is less than 0.05%, this effect is not provided sufficiently. If the content of Cu is more than 1.00%, costs increase. In the present spring steel, from these viewpoints, an upper limit value is more preferably 0.70%, still more preferably 0.50%, and still more preferably 0.30%. A lower limit value is more preferably 0.10%, still more preferably 0.15%, and still more preferably 0.20%. Cu is preferably 0.10% or more and 0.50% or less and more preferably 0.20% or more and 0.30% or less.
(Ti: Titanium)
The content of Ti is preferably 0.030% or more and 0.100% or less. If the content of Ti in the present spring steel is in this range, prior austenite crystal grains after quenching are atomized and toughness is improved. If the content of Ti is less than 0.030%, this effect is not provided sufficiently. If the content of Ti is more than 0.100%, coarse inclusions may precipitate and toughness may decrease. Further, in the present spring steel, for example from the viewpoint that the amount of Ni is reduced and V is substantially not added, an upper limit value is more preferably 0.095%, still more preferably 0.090%, and still more preferably 0.085%. A lower limit value is more preferably 0.045% and still more preferably 0.050%. When the content of Ti is in this range, it is possible to more effectively secure toughness and corrosion fatigue resistance. Most preferably, the content of Ti is 0.050% or more and 0.095% or less.
(B: Boron)
The content of B is preferably 0.0010% or more and 0.0050% or less. If the content of B in the present spring steel is in this range, ductility and toughness of a steel wire are improved. If the content of B is less than 0.0010%, these effects are not provided sufficiently. If the content of B is more than 0.0050%, this effect saturates. Further, in the present spring steel, for example from the viewpoint that the amount of Ni is reduced and V is substantially not added, an upper limit value is more preferably 0.0040% and still more preferably 0.0035%. More preferably, a lower limit is 0.0013%. Most preferably, the content of B is 0.0013% or more and 0.0035% or less.
Further, the present spring steel may contain P (phosphorus). Because P tends to embrittle crystal grain boundaries, the content of P is preferably 0.015% or less and more preferably 0.010% or less.
The present spring steel may contain S (sulfur). Because, like P, S tends to embrittle crystal grain boundaries, the content of S is preferably 0.015% or less and more preferably 0.010% or less.
The present spring steel contains the alloy components explained above but contains substantially no V. Containing substantially no V means that V is included in a same amount as unavoidable impurities. Specifically, the content of V is preferably 0.03% or less. The content of V is more preferably 0.02% or less, still more preferably 0.01% or less, and still more preferably 0.005% or less. In the present spring steel, the remainder is Fe (iron) together with unavoidable impurities.
(Manufacturing Methods of a Spring)
Methods of manufacturing springs using such spring steel will be explained next. Various kinds of springs can be manufactured by applying the present spring steel, a known hot forming method, a cold forming method, a warm forming method, and the like. For example, coil springs can be manufactured as explained below. That is, after the present spring steel is formed into a round steel bar, a wire material or a wire, a plate material, or the like, it is formed into a coil shape. Further, the spring can be manufactured by performing hot setting and warm shot peening on the coil after the forming. The order of performing the hot setting and the warm shot peening may be either order. The method of performing the warm shot peening after performing the hot setting will be referred to as a regular order method; the method of performing the hot setting after performing the warm shot peening will be referred to as a reverse order method. By utilizing such manufacturing methods, it is possible to obtain coil springs for an automobile suspension that excel in resistance to sag and durability.
In particular, according to the regular order method, it is possible to obtain a spring that excels in durability. According to the reverse order method, it is possible to obtain a spring that excels in resistance to sag. That is, the present spring steel can be appropriately used with the regular order method and the reverse order method depending on the use of the spring. In a more specific embodiment, a coil spring for an automobile suspension is manufactured using the present spring steel by performing the processes of: forming; heat treatment; hot setting; warm shot peening; cold shot peening; cold setting; and painting, in this order. The forming process may be performed in a hot state (at a temperature equal to or higher than the recrystallization temperature of the wire material) or may be performed in a warm state (at a temperature lower than the recrystallization temperature of the wire material) or in a cold state (at room temperature). Various previously known methods can be used as the method that forms the present spring steel into a coil shape. For example, the present spring steel may be formed using a coiling machine or may be formed by a method that winds it around a core bar.
In the heat treatment process, heat treatment is performed on the coil that has been formed into the coil shape by the coil forming process. The heat treatment performed in this process differs depending on whether the coil forming process is performed in the hot state or in the warm state or the cold state. That is, when the coil forming process was performed in the hot state, quenching and tempering are performed. Strength and toughness are imparted to the coil by the quenching and the tempering. The temperature condition for the quenching can be set to 800° C. or more and 1000° C. or less. The temperature condition for the tempering can be set to 300° C. or more and 500° C. or less. On the other hand, when the forming process was performed in the cold state, low-temperature annealing is performed. Harmful residual stresses (tensile residual stresses) in the interior and on the surface of the coil can be removed by the low-temperature annealing. The low-temperature annealing can be performed at a temperature of 300° C. or more and 500° C. or less for 20 minutes or more and 60 minutes or less. The processes of quenching and tempering of the coil and low-temperature annealing of the coil can be performed according to any previously known method.
In the hot setting process, the setting is performed while the temperature of the coil is in the warm state. The hot setting applies a directional compressive residual stress to the coil and thus improves durability. Further, the resistance of the coil to sag improves with the presence of relatively large plastic deformations in the coil. Here, the temperature at which the hot setting is performed can be appropriately set within a range of a temperature equal to or lower than the recrystallization temperature of the wire material and higher than room temperature. For example, the hot setting of the coil can be performed in a range in which the temperature of the coil is approximately 150° C. or higher and 400° C. or lower. By performing the setting in such a temperature range, it is possible to increase the amount of plastic deformation imparted to the coil and improve the resistance to sag. The amount of sag δh of the hot setting can be appropriately determined depending on the total length L of the coil spring for automobile suspension (total length Ls at the time of set). Note that, various previously known methods can be used for the setting.
In the warm shot peening process, the coil on which the hot setting has been performed, is subjected to the shot peening in the warm state. Large compressive residual stresses are imparted to the coil surface region by the warm shot peening. Durability and corrosion fatigue resistance of the coil are improved. Here, the temperature at which the shot peening is performed can be appropriately set in a temperature range of a temperature equal to or lower than the recrystallization temperature of the wire material and higher than room temperature. For example, the temperature of the coil can be set to 150° C. or higher and 400° C. or lower. Note that, in the regular order method, it is desirable to perform the warm shot peening at a temperature lower than the temperature at which the hot setting is performed because it is unnecessary to heat the coil after the hot setting. On the other hand, in the reverse order method, it is desirable to perform the hot setting at a temperature lower than the temperature at which the warm shot peening is performed because it is unnecessary to heat the coil after the warm shot peening. Various previously known methods can be used as a steel ball shot peening method.
In the cold shot peening process, the shot peening is performed while the temperature of the coil is at a normal temperature state. Before the cold shot peening process, the coil needs to be cooled to the normal temperature; for example, the coil may be cooled by water or may be allowed to stand and cool. By further performing the cold shot peening in addition to the warm shot peening, it is possible to further improve the durability of the coil. Note that the diameter of the steel balls used in the cold shot peening is preferably set smaller than the diameter of the steel balls used in the warm shot peening. For example, when the diameter of the steel balls used in the warm shot peening is 1.2 mm, the diameter of the steel balls used in the cold shot peening is preferably set to 0.8 mm. By performing the warm shot peening and the cold shot peening, large compressive residual stresses are imparted to the surface region of the coil in the warm shot peening performed first, surface roughness of the coil is improved in the cold shot peening performed later, and compressive residual stresses are imparted to the surface of the coil. As a result, the durability and the corrosion fatigue resistance of the coil are further improved. Note that the conditions of the cold shot peening, that is, projection speed, coverage, projection time, and the number of times of treatment, can be set as appropriate.
In the cold setting process, the setting is performed while the temperature of the coil is at the normal temperature state. By performing the cold setting in addition to the hot setting, the resistance of the coil to sag is further improved. The amount of sag δc of the cold setting can be appropriately determined depending on the total length L (the total length Ls at the time of the set) of the coil spring for an automobile suspension. Note that the amount of sag δc of the cold setting is preferably smaller than the amount of sag δh of the hot setting. When the cold setting process is finished, the coil surface is painted and the coil spring for an automobile suspension is completed.
Note that it is also possible to omit the processes of the cold shot peening and the cold setting and perform only the warm shot peening and the hot setting. It is also possible to omit the processes of the cold shot peening and the hot setting and perform only the warm shot peening and the cold setting. It is also possible to omit the processes of the warm shot peening and the cold setting and perform only the cold shot peening and the hot setting. It is also possible to omit the processes of the warm shot peening and the hot setting and perform only the cold shot peening and the cold setting. That is, at least one or more processes of the shot peening processes (warm and cold) may be performed and at least one or more processes of the setting processes (hot and cold) may be performed. Processes other than the processes explained above also may be included. For example, when the spring steel is formed into a coil shape by hot forming, heat treatment (quenching) may be performed before the hot forming. In addition, when the spring steel is formed into a coil shape by cold forming, heat treatment (induction hardening·tempering) may be performed before the cold forming. In addition, a water cooling process may be performed after the hot setting.
As was explained above, according to the present disclosure, even if the added amount of Ni is reduced and V is not contained, it is possible to obtain a spring steel and a spring in which performances equal to or higher than performances of prior spring steels are secured. Such a spring can be suitably used in a coil spring, a leaf spring, a torsion bar spring, a stabilizer bar, and the like used in an automobile suspension device and the like.
EXAMPLESExamples in which the present disclosure is realized will be explained below. Note that the examples explained below are specific examples for explaining the present disclosure and do not limit the present disclosure.
1. Durability Test(1) Preparation of Springs
Springs 1 to 3 were prepared by using sample 1, which is a spring steel having the chemical composition shown in Table 1 below; comparative spring 1 was prepared by using comparative sample 1. This manufacturing method will be explained. Note that the numbers in Table 1 represent the mass % of each of components with respect to the mass of each of the samples. First, a steel ingot obtained by melting each material in a blast furnace or an electric arc furnace on a scale equivalent to a mass production was split into slabs and rolled, and thereafter rolled into wire materials.
After an oil tempering treatment was applied to the wire materials of the steels of sample 1 and comparative sample 1, cold forming, low-temperature annealing, hot setting, warm shot peening, water cooling, cold shot peening, and cold setting were performed in this order (the regular order method) to manufacture springs 1 and 2 and comparative spring 1. The conditions of the low-temperature annealing were 430° C. and 20 minutes for spring 1 and were 400° C. and 20 minutes for spring 2 and comparative spring 1. The temperature of the coil during the hot setting was set to 330° C. The temperature of the coil during the warm shot peening was set to 300° C. After the oil tempering treatment was applied to the wire material of the steel of sample 1, different from the processes of the regular order method, cold forming, low-temperature annealing, warm shot peening, hot setting, water cooling, cold shot peening, and cold setting were performed in this order (the reverse order method) to manufacture spring 3. The conditions of the low-temperature annealing were 400° C. and 20 minutes. The temperature of the coil during the warm shot peening was set to 350° C. The temperature of the coil during the hot setting was set to 200° C.
(2) Test Method
In a durability test, the load acting on the coil springs was cyclically varied and the number of oscillating cycles (endurance cycles) was measured until breakage of the coil spring. Here, the stress to be applied to the coil springs was set to 735 MPa as the average principal stress, the principal stress amplitude was varied, and the number of endurance cycles was measured. Results of the test are shown in
(1) Preparation of the Springs
Springs 1 to 3 and comparative spring 1 were manufactured by a method that is the same as the method in the durability test.
(2) Test Method
The clamped sag test is conducted with the coil spring clamped at the height at the time of maximum load and placed in a constant temperature vessel for a predetermined time. Changes in load at the mounting height were measured before and after the test to calculate the residual shear strain amount. Here, the clamping stresses were set to 1150 MPa and 1350 MPa. The temperature of the constant temperature vessel was set to 80° C. and the test time was set to 96 hours. In addition, in this clamped sag test, two springs were prepared for each spring and the same test was performed on the respective springs. Results of the test are shown in
(1) Preparation of Springs
First, after an oil tempering treatment was applied to the steels of sample 1 and comparative sample 1, cold forming and low-temperature annealing were performed to respectively prepare spring 4 and comparative spring 2. The spring specifications of spring 4 and comparative spring 2 are as shown in Table 2.
Further, spring 5 and comparative spring 3 were prepared from sample 2 and comparative sample 2 respectively having the chemical compositions shown in Table 3 below. Their manufacturing method will be explained. Note that the numbers in Table 3 represent the mass % of each of the components with respect to the mass of each of the samples. First, a steel ingot obtained by melting each material in a blast furnace or an electric furnace in a scale equivalent to a mass production was split into slabs and rolled and thereafter rolled into wire materials.
After an oil tempering treatment was applied to the wire materials of the steels of sample 2 and comparative sample 2, cold forming and low-temperature annealing were performed to manufacture spring 5 and comparative spring 3. The treatment conditions and treatment temperatures were respectively the same as those in the method of manufacturing spring 1 and comparative spring 1. Note that the spring specifications of spring 5 and comparative spring 3 are as shown in Table 4.
Pits were artificially formed on each of the obtained springs and a fatigue test was conducted in a corrosive environment. The pits were formed by disposing a mask having small holes on the outer surfaces of the springs at a location where the principal stress amplitude is the greatest (2 turns from the coil end in spring 4 and comparative spring 2, and 3.1 turns in spring 5 and comparative spring 3). Further, hemispherical holes (artificial pits) having a diameter of 600 μm and a depth of 300 μm were formed by electrolytic etching. An aqueous ammonium chloride solution was used as the electrolyte. The corrosive environment utilized a 5% NaCl water solution as the corrosive liquid and only portions having the artificial pits were corroded for 16 hours by a misting apparatus. In addition, the circumferences of the artificial pit portions were covered with adsorbent cotton impregnated with the 5% NaCl water solution, and it was prevented from drying out using an ethylene wrap. The fatigue test was conducted in this wrapped state and the number of oscillations until breakage was evaluated. In the fatigue test, the oscillating rate was set to 2 Hz and excitations were applied by parallel compression using a flat base. The test heights were set based upon a principal stress condition of 495±300 MPa that was determined as if there were no artificial pits at locations where artificial pits were formed. Results are shown in
From the above, it has been found that the present spring steel maintains toughness and corrosion fatigue strength, although the content of Ni is reduced and V is substantially not contained. In addition, with regard to resistance to sag, in the present spring steel, the regular order method and the reverse order method can be suitably used depending on the use of the spring.
Claims
1. A spring steel containing, in terms of mass %, C: 0.35% or more and 0.55% or less, Si: 1.60% or more and 3.00% or less, Mn: 0.20% or more and 1.00% or less, Cr: 0.10% or more and 1.50% or less, Ni: 0.05% or more and 0.30% or less, and Cu: 0.05% or more and 1.00% or less, and substantially does not contain V,
- the remainder being Fe and unavoidable impurities.
2. The spring steel according to claim 1, wherein Ni is 0.18% or more in terms of mass %.
3. The spring steel according to claim 1, wherein Ni is 0.18% or more and 0.25% or less in terms of mass %.
4. The spring steel according to claim 1, wherein Mn is 0.45% or more and 0.65% or less in terms of mass %.
5. The spring steel according to claim 1, wherein Cu is 0.20% or more and 0.30% or less in terms of mass %.
6. The spring steel according to claim 1, wherein Ti is 0.030% or more and 0.100% or less in terms of mass %.
7. The spring steel according to claim 1, wherein B is 0.0010% or more and 0.0050% or less in terms of mass %.
8. The spring steel according to claim 1, wherein Cu is 0.10% or more and 0.50% or less and Ni is 0.18% or more and less than 0.30% in terms of mass %.
9. The spring steel according to claim 1, wherein Cu is 0.20% or more and 0.30% or less and Ni is 0.18% or more and 0.25% or less in terms of mass %.
10. A spring manufactured using the spring steel according to claim 1.
11. A method for manufacturing a spring, comprising:
- forming a spring steel into a shape of a spring, wherein
- the spring steel comprises, in terms of mass %, C: 0.35% or more and 0.55% or less, Si: 1.60% or more and 3.00% or less, Mn: 0.20% or more and 1.00% or less, Cr: 0.10% or more and 1.50% or less, Ni: 0.05% or more and 0.30% or less, and Cu: 0.05% or more and 1.00% or less, and substantially does not contain V, and
- the remainder of the spring steel being Fe and unavoidable impurities.
12. The method according to claim 11, further comprising:
- performing hot setting on the spring steel, which has been formed into a coil shape and subjected to heat treatment; and
- performing warm shot peening on the spring steel after the hot setting.
13. The method according to claim 11, further comprising:
- performing warm shot peening on the spring steel, which has been formed into a coil shape and subjected to heat treatment; and
- performing hot setting on the spring steel after the warm shot peening.
14. The method according to claim 11, further comprising:
- performing low-temperature annealing at 430° C. for 20 minutes;
- performing hot setting on the spring steel, which has been formed in a coil shape and subjected to heat treatment; and
- performing warm shot peening on the spring steel after the hot setting.
15. The method according to claim 11, further comprising:
- performing low-temperature annealing at 400° C. for 20 minutes;
- performing hot setting on the spring steel, which has been formed in a coil shape and subjected to heat treatment; and
- performing warm shot peening on the spring steel after the hot setting.
16. The method according to claim 11, further comprising:
- performing hot setting on the spring steel, which has been formed in a coil shape and subjected to heat treatment at 150° C. or higher and 400° C. or lower; and
- performing warm shot peening on the spring steel after the hot setting.
17. The method according to claim 11, further comprising:
- performing hot setting on the spring steel, which has been formed in a coil shape and subjected to heat treatment; and
- after the hot setting, performing warm shot peening on the spring steel at 150° C. or higher and 400° C. or lower.
18. The spring steel according to claim 1, wherein Ni is 0.18% or more and Cu is 0.20% or more and 0.30% or less in terms of mass %.
19. The spring steel according to claim 1, wherein Cu is 0.20% or more and 0.30% or less, Ti is 0.030% or more and 0.100% or less and B is 0.0010% or more and 0.0050% or less in terms of mass %.
20. The spring steel according to claim 19, wherein in terms of mass %:
- C is 0.45% or more and 0.53% or less,
- Si is 1.90% or more and 2.05% or less,
- Mn is 0.45% or more and 0.65% or less,
- Cr is 0.25% or more and 0.40% or less,
- Ni is 0.18% or more and 0.25% or less,
- Ti is 0.050% or more and 0.095% or less,
- B is 0.0013% or more and 0.0035% or less,
- P is 0.010% or less,
- S is 0.010% or less and
- V is 0.03% or less.
Type: Application
Filed: May 8, 2014
Publication Date: May 5, 2016
Inventor: Takanori KUNO (Nagoya-Shi)
Application Number: 14/895,572
