JP4612527B2 - Hollow spring - Google Patents

Description

The present invention relates to a hollow spring that is a hollow coil spring or a hollow rod-shaped spring.

In recent years, with the wave of weight reduction of automobiles, panel materials have been made aluminum, chassis and main bodies have been made high tensile, and so on. The need for weight reduction has further increased as global warming due to exhaust gas from automobiles has been taken up internationally, and reduction of CO ₂ contained in exhaust gas has attracted attention as a major issue.
In automobiles, measures taken as a CO ₂ reduction method can be divided into development of a new power source (hybrid engine, fuel cell motor system, battery motor system) or current improvements. The means that have been greatly taken up in this current improvement are “improvement of combustion method” and “labor saving of power source by weight reduction”. Particularly in Europe, fuel regulations will be introduced in 2010, so automakers are striving to reduce the weight of the entire vehicle that has immediate effects.
In order to meet such demands, the weight of springs used in automobiles has been reduced in recent years. For example, proposals have been made regarding hollow coil springs.
However, only a relatively low carbon (0.45% or less) and low alloy steel has been put to practical use as a spring element tube, and the material cleanliness and surface properties are low. For this reason, the material strength is low, and spring stress (permanent deformation) or breakage occurs at high stress, so the design stress has to be lowered, and the weight reduction effect is low.

Japanese Patent Laid-Open No. 11-230221 Japanese Patent Laid-Open No. 7-12160

  The problem to be solved is that the material strength is low, and the spring stress (permanent deformation) or breakage occurs at high stress, so the design stress has to be lowered, and the weight reduction effect is low.

The present invention uses a seamless spring steel pipe obtained by extruding a heated spring steel material by hydraulic pressure in order to increase the material cleanliness and surface properties in order to achieve both a light weight effect of the hollow spring and an increase in fatigue strength. The most important feature is that a hollow body formed into a coil shape, a rod shape, or a rod shape having a bent portion is subjected to a surface treatment for imparting compressive residual stress.

The hollow spring of the present invention is a hollow body formed into a rod shape having a coil shape, a rod shape, or a bent portion by using a seamless spring steel pipe obtained by extruding a heated spring steel material with a hydraulic pressure in order to enhance material cleanliness and surface properties. In addition, since the surface treatment for imparting compressive residual stress is applied, the material strength of the hollow spring is high, and the design stress can be increased because the hollow spring sag (permanent deformation) and breakage are suppressed even at high stress. It is possible to achieve both a light weight effect and an increased fatigue strength.

  The objective of achieving both a light weight effect and improved fatigue strength was achieved using seamless spring steel pipes with improved material cleanliness and surface properties.

[Hollow coil spring]
FIG. 1 is a cross-sectional view of a hollow coil spring as a hollow spring according to Embodiment 1 of the present invention. The hollow coil spring 1 is used as a suspension spring or a valve spring for an automobile, and is coiled using a seamless spring steel pipe in which a heated spring steel material is extruded by hydraulic pressure to improve material cleanliness and surface properties. A surface treatment was applied to form a compressive residual stress.

  The ratio of the thickness t and the outer diameter D of the cross section of the hollow body constituting the hollow coil spring 1 was set to t / D = 0.10 to 0.35, preferably 0.20 to 0.30. 2 is a chart showing the relationship between t / D and weight reduction rate, etc. FIG. 3 is a graph showing the relationship between t / D, weight reduction rate and hole stress, and FIG. It is a graph which shows the relationship between a height increase rate and a hole part stress.

  As shown in FIGS. 2 to 4, when t / D is reduced to increase the weight reduction rate, the inner diameter side stress of the hole portion 3 is also relatively increased (FIG. 3). The height is also increased (FIG. 4). Therefore, it is important to increase the weight reduction rate while suppressing the contact height.

  Here, when compressive residual stress is applied to the inner surface of the hole 3 of the hollow coil spring 1, the fatigue strength is 970 MPa, and otherwise 600 MPa. Therefore, when compressive residual stress is not applied to the inner surface of the hole 3 of the hollow coil spring 1, the setting of t / D = 0.25 is the limit in strength as shown in FIG. Lightweight. When compressive residual stress is applied to the inner surface of the hole 3 of the hollow coil spring 1, t / D = 0.10 can be set, which is lighter than t / D = 0.25. Although the setting of t / D = 0.35 is heavier than the setting of t / D = 0.25, the weight can be reduced as compared with the conventional setting, which is an allowable range.

  These were judged comprehensively, the point where an inflection point was seen in the change of the weight reduction rate was specified, and the range of t / D = 0.10-0.35 was determined.

The hollow coil spring 1 has a hardness of H _V = 500 or more. As shown in FIG. 1, the cross-sectional outer shape 5 (outer peripheral circle) and the inner cross-sectional shape 6 (inner peripheral circle of the hole 3) are relatively The position is almost circular concentric. The relative positions of the cross-sectional outer shape 5 and the cross-sectional inner shape 6 of the hollow coil spring 1 were secured by setting the coil diameter and material hardness of the hollow body constituting the hollow coil spring 1.

[Hollow coil spring manufacturing process]
FIG. 5 is a block diagram showing a manufacturing process of the hollow coil spring 1. As shown in FIG. 5, the hollow coil spring 1 includes a hot isostatic pressing process 7, a skinning process 9, a rolling process 11, a coil forming process 13, a heat treatment process 15, an end face grinding process 17, a shot peening process 19, and a setting. It forms through the process 21 and the coating process 23 in order.

  In the hot isostatic pressing step 7, a heated spring steel material is extruded by a hydraulic pressure, for example, an isostatic pressure, to form a seamless spring steel pipe having improved material cleanliness and surface properties. In addition, although the more detailed description of the hot isostatic pressing process 7 is mentioned later, the heating of a spring steel raw material is 1050 degreeC or more and less than 1300 degreeC, and when using the lubrication agent which added graphite to the fats and oils at the time of extrusion processing The extrusion resistance can be reduced and the seamless spring steel pipe can be smoothly extruded. Therefore, it is possible to obtain a seamless spring steel pipe with less non-metallic inclusions and no rough skin.

  In the skin-cutting step 9, at least the outer surface of the seamless spring steel pipe is ground to decarburize the surface and scrape fine wrinkles to further enhance the surface properties. In the skinning step 9, both the outer surface and the inner surface can be ground.

  In the rolling step 11, the seamless spring steel pipe after shaving is extended by rolling. This rolling step 11 can reduce the amount of processing in the next coil forming step 13.

  In the coil forming step 13, the rolled seamless spring steel pipe is formed into a coiled hollow body.

In the heat treatment step 15, the coiled hollow body is given elasticity as a spring by quenching and tempering heat treatment. In this step, surface treatment by nitriding treatment can be performed after quenching and tempering heat treatment, and compressive residual stress of about 100 MPa can be applied to the inner surface of the hole 3. Therefore, in this embodiment, the surface treatment for applying the compressive residual stress is applied to the outer surface of the hollow coil spring 1 and the inner surface of the hole portion 3 together with the shot peening step 19 in the subsequent step. However, the application of compressive residual stress on the inner surface can be omitted.
In the heat treatment step 15, a compressive residual stress of 200 MPa or less can be applied to the inner surface of the hole portion 3 by carburizing quenching / tempering heat treatment. Alternatively, after the quenching and tempering heat treatment, the inner surface of the hole 3 can be subjected to an inner surface shot, which will be described later, to give a compressive residual stress.
Furthermore, after the seamless spring steel pipe is treated with oil tempering, it is formed into a coiled hollow body by the coil forming step 13, and after the heat treatment for strain relief, the quenching, tempering heat treatment + nitriding treatment, or carburizing quenching, A tempering heat treatment, or quenching, a tempering heat treatment + inner surface shot can be applied to impart compressive residual stress to the inner surface of the hole 3.
In the end surface grinding step 17, the end surface treatment is performed by grinding the end surface of the coiled hollow body.
In the shot and pinning step 19, a surface treatment is performed in which hard fine particles are collided and compressive residual stress is applied to the outer surface of the coiled hollow pair.
In the setting step 21, the coiled hollow body is compressed and then released to prevent sag as a spring.
In the coating step 23, coating is performed as necessary to complete the hollow coil spring 1.
[Hot isostatic pressing process]
FIG. 6 is a process diagram of the hot isostatic pressing process, and FIG. 7 is a cross-sectional view of the hot isostatic extrusion processing apparatus.

  The seamless spring steel pipe according to the present embodiment can be manufactured by a manufacturing process including each process shown in FIG. For example, the process (A) in FIG. 6 is a billet forming process, the process (B) in FIG. 6 is a first heating process, the process (C) in FIG. 6 is a hot isostatic extrusion process, and the process in FIG. (D) is the second heating step, step (E) in FIG. 6 is the grinding step, steps (F) and (G) in FIG. 6 are the extension steps, and step (H) in FIG. The heating step, step (I) in FIG. 6 is a pickling step, and step (J) in FIG. 6 is a grinding step.

  In this embodiment, as shown in FIG. 6, the (J) bending correction process is included after the pickling process (I), and the grinding process (E) is included after the second heating process (D). However, these can be omitted.

  In the billet forming step (A), the spring steel material 25 is formed into a hollow, for example, cylindrical billet 27 (hollow billet). Such molding can be performed by forging or the like.

  In a 1st heating process (B), this billet 27 is put into a heating furnace, and heat processing are performed at 1050 degreeC or more and less than 1300 degreeC, and it softens. As the heating furnace, an electric furnace, a gas furnace, or the like can be used.

  The heating time at this time is not particularly limited as long as the billet 27 can be sufficiently softened. Further, the heating time can be appropriately changed in consideration of the size of the billet 27 and the like.

  In this way, by defining the hot isostatic pressing temperature within a specific range, the maximum size of non-metallic inclusions and the number per unit area can be appropriately controlled and have excellent durability. Seamless steel pipe can be manufactured.

  In the hot isostatic extrusion process (C), the hot isostatic extrusion apparatus 29 is used to extrude the billet 27 heated to 1050 ° C. or more and less than 1300 ° C. with a hydraulic pressure. Thus, the seamless steel pipe intermediate body 41 is manufactured.

  In addition, the extrusion temperature of the billet 27 in the hot isostatic extrusion process (C) is preferably set to the heating temperature of the first heating process (B), that is, 1050 ° C. or more and less than 1300 ° C. From the viewpoint of the number and size of inclusions in the steel that affect the durability of the spring, the extrusion temperature is most preferably between 1100 ° C and less than 1280 ° C. The advantage of reducing the damage to the tool can be obtained by performing on the side. Therefore, the recommended range of the extrusion temperature should be set at 1050 ° C. or more and less than 1200 ° C. by slightly lowering the lower limit range. However, if more importance is attached to quality, it should be set at 1100 ° C. or more and less than 1200 ° C.

  The reason why the extrusion temperature is set from the viewpoint of the number and size (maximum thickness) per unit area of nonmetallic inclusions in the metal structure is as follows. When the extrusion temperature rises, the non-metallic inclusions are softened, and are deformed and divided by the extrusion, so that miniaturization proceeds. However, since crystallization and accompanying crystal growth proceed simultaneously, if the extrusion temperature is too high, there is a concern that the nonmetallic inclusions become coarse due to crystallization. On the other hand, the softening temperature of the nonmetallic inclusion is 1100 ° C. or higher and lower than 1280 ° C. in the case of a spring steel material, and it is recommended to set an extrusion temperature equal to or higher than the softening temperature. Further, the deformation / splitting effect of the nonmetallic inclusions due to the deformation of the metal structure depends on the relative strength difference between the nonmetallic inclusions and the metal structure. Therefore, if the strength of the metal structure is lowered more than the nonmetallic inclusions softened due to the extrusion temperature being too high, the effect of refining is impaired simultaneously with the progress of crystallization. Therefore, it is preferable that the extrusion temperature be equal to or higher than the softening temperature of the nonmetallic inclusions and as low as possible.

    On the other hand, since the die life at the time of hot isostatic extrusion becomes shorter as the extrusion temperature becomes higher, it is better to set the extrusion temperature lower when the total cost is taken into consideration. Therefore, the extrusion temperature is set low by 50 ° C., and 1050 ° C. is set as the lower limit of the extrusion temperature. If the extrusion temperature is lower than this, the adverse effects of non-metallic inclusions cannot be ignored, and the pressing force becomes too large, causing problems such as poor quality and increased load on the equipment. .

  Further, the feature of hot isostatic extrusion is that when hot isostatic extrusion is performed in the specific temperature range described above, the friction between the spring steel material and the tool of the hot isostatic extrusion device 29 is usually Therefore, the surface state of the seamless steel pipe intermediate body 41 can be smoothed. As a result, for example, the surface of the seamless steel pipe intermediate body 41 is beautiful, the average roughness Ra can be 50 μm or less, and the crystal grains on the surface tend to be small. Therefore, when the seamless spring steel pipe 47 manufactured thereby is processed into a product called a coil spring, for example, since the stress is maximized on the outermost surface of the hollow spring, it has fine crystal grains. Small surface roughness and few surface defects (such as wrinkles and wrinkles) lead to longer spring life.

  In the second heating step (D), the seamless steel pipe intermediate 41 is heated in a heating furnace. The heating temperature at this time is preferably 650 to 750 ° C. The heating time is not particularly limited as long as the entire seamless steel pipe is heated. For example, the heating time is preferably 0.1 to 1.0 hour. If the heating temperature is less than 650 ° C. or the heating time is less than 0.1 hour, the seamless steel pipe intermediate 41 is not sufficiently heated, so that the next process cannot be smoothly ground or extended. . On the other hand, when the heating temperature exceeds 750 ° C., the quenching temperature is reached, which is not preferable. Moreover, even if heating time exceeds 1 hour, the effect of a heating will be saturated and it is not economically preferable.

  In a grinding process (E), the grinding process for removing the decarburization layer formed in the internal peripheral surface of the heated seamless steel pipe intermediate body 41 is performed. In addition, since a grinding dimension changes with the kind of spring steel raw material to be used, a 1st heating process, and a 2nd heating process, it is preferable to perform an experiment etc. beforehand and to set conditions suitably.

  The manufacturing method of the seamless spring steel pipe of the present embodiment further includes a grinding step (E) for grinding the inner peripheral surface of the heated seamless steel pipe intermediate 41 intermediate after the second heating step (D). Yes.

  In this way, the decarburized layer generated by the second heating step (D) heat treatment is ground to eliminate the portion that is not quenched, and the surface hardness is made uniform, resulting in excellent durability and reliability. A high seamless steel pipe intermediate body 41 can be manufactured.

  In the extension process, the heated seamless steel pipe intermediate body 41 is extended. The seamless steel pipe intermediate body 41 can be extended by at least one of pilger mill rolling (F) and drawing (G).

  For example, after performing moderate rolling by drawing (G), drawing (drawing) using a die may be performed by pilger mill rolling (F).

  Pilger mill rolling (F) is a process in which the seamless steel pipe intermediate body 41 is pressed and flattened from both sides. However, since the seamless steel pipe intermediate body 41 is elongated by this, the drawing process in the next step can be reduced. Here, the pilger mill rolling (F) is not performed by simply pressing the seamless steel pipe intermediate body 41 flatly from two directions, but, for example, pressing uniformly from three directions, four directions or more. By rolling and rolling, the seamless steel pipe intermediate body 41 can be extended with higher roundness, and the drawing process (G) can be more actively labor-saving.

  In addition, if this pilger mill rolling (F) is performed excessively, for example, when it is drawn, a variation in thickness occurs in the circumferential direction of the seamless steel pipe intermediate body 41. Therefore, it can be omitted. In the case where the drawing process (G) is repeatedly performed, a pilger mill rolling (F) rolling process can be used instead. However, even in this case, it is preferable to finally perform drawing by drawing (G) so as to ensure the roundness of the seamless steel pipe intermediate 41 subjected to surface reduction.

  Next, since the stretched (drawn) seamless steel pipe intermediate 41 is work-hardened, the seamless steel pipe intermediate 41 is annealed by heating to 650-750 ° C. in the third heating step (H). If the third heat treatment temperature is less than 650 ° C., the annealing is insufficient, which is not preferable. On the other hand, when the third heat treatment temperature exceeds 750 ° C., the effect of the earliest annealing is saturated, which is not economically preferable.

  In the pickling step (I), the annealed seamless steel pipe intermediate 41 is pickled to remove oils and fats (pressure medium 44), scales, and the like attached to the seamless steel pipe intermediate 41.

  Since the drawing process (G) can only perform a diameter reduction process of 25% or less per time, the above-described drawing process (G), the third heating process (H), and the pickling process (I) are performed a predetermined number of times. By repeating, it is preferable to manufacture a seamless spring steel pipe 47 having a desired diameter.

  In addition, it is more preferable to finally perform the bending correction in the bending correction step (J) to manufacture the hollow spring seamless steel pipe intermediate 41 as a product.

  Moreover, in the manufacturing method of the seamless steel pipe for hollow springs of a present Example, it replaces with said 2nd heating process (D), and also as a slow cooling process (not shown) which anneals the heated seamless steel pipe intermediate body 41. Good.

  Normally, the seamless steel pipe intermediate body 41 subjected to hot isostatic pressing and reduced in diameter is exposed to the atmosphere, and thus rapidly cooled from the temperature of 1050 to 1300 ° C. described above. Therefore, since the seamless steel pipe intermediate body 41 is in a quenched state, the hardness becomes very high. In such a state, subsequent processes such as a grinding process (E) and an extension process (Pilger mill rolling (F), drawing process (G)) and the like cannot be performed.

  Therefore, after heating in the first heating step (C) to temporarily change the state of the metal structure to an austenite structure, annealing is performed by gradually cooling the seamless steel pipe intermediate 41 in the slow cooling step (not shown). Is what you do.

  As a result, the residual stress can be removed, the seamless steel pipe intermediate body 41 can be softened, the machinability can be improved, and the cold workability can be improved. For example, the extension process (drawing process) can be performed without performing the second heating process. (G), Pilger mill rolling (F)) can be performed. That is, there is an advantage in that the number of manufacturing steps can be simplified.

  Slow cooling can be performed by using a heat retaining device capable of temperature control and slow cooling rate control so that the seamless steel pipe intermediate 41 subjected to hot isostatic pressing does not rapidly cool.

  The slow cooling rate at this time is preferably 0.1 to 0.3 ° C./second. When the slow cooling rate is faster than 0.3 ° C./second, the annealing effect by slow cooling cannot be obtained. On the other hand, if the slow cooling rate is slower than 0.1 ° C./second, the time required for proceeding to the extension process becomes longer, and the production efficiency becomes worse.

  In the manufacturing method of the seamless spring steel pipe 47 of the present embodiment, instead of the second heating step (D), a slow cooling step of gradually cooling the seamless steel pipe intermediate body 41 subjected to hot isostatic pressing may be used. .

  Thus, it changes to a 2nd heating process (D), and also performs the process which spheroidizes the carbide | carbonized_material in the metal structure also by gradually cooling the seamless steel pipe intermediate body 41 by which the hot isostatic extrusion process was carried out. Therefore, the seamless spring steel pipe 47 with improved cold workability, grindability (machinability), toughness and the like as well as excellent durability as described above can be manufactured.

  As described above, the seamless spring steel pipe 47 of this example is manufactured by hot isostatic pressing, and thus has a smooth outer peripheral surface and inner peripheral surface. Even if it exists, it has excellent durability such as fatigue life as a result of not having a place that tends to be a starting point of destruction.

  Moreover, the seamless spring steel pipe 47 of a present Example can achieve weight reduction of about 30 to 40% compared with the solid steel pipe of the same diameter.

  According to the manufacturing method of the seamless spring steel pipe 47 of the present embodiment, since the seamless spring steel pipe 47 is easily manufactured by hot isostatic pressing without performing drilling or the like, the number of steps can be reduced. As a result, production efficiency can be increased and it can be manufactured at low cost.

  Moreover, since the manufacturing method of the seamless spring steel pipe 47 of a present Example performs a hot isostatic extrusion process, an outer peripheral surface and an inner peripheral surface are smooth, and a high quality seamless steel pipe can be manufactured.

  Furthermore, since the manufacturing method of the seamless spring steel pipe 47 of this embodiment does not perform Mannesmann drilling or mandrel mill rolling, the seamless spring steel pipe 47 can be easily manufactured.

  FIG. 7 is a cross-sectional view of the hot isostatic extrusion device 29 used in the hot isostatic extrusion step (C).

  The seamless spring steel pipe 47 used in the present example was manufactured based on a seamless steel pipe intermediate 41 obtained by hot isostatic extrusion processing of a hollow cylindrical spring steel billet 27, for example.

  The seamless spring steel pipe 47 can have a very smooth surface (outer peripheral surface and inner peripheral surface) from the hot working stage by hot isostatic pressing.

  In this hot isostatic extrusion process, the viscoplastic pressure medium 44 is used when extruding the seamless steel pipe intermediate 41 by the hot isostatic extrusion apparatus 29. For example, a large pressure around 1 GPa (10,000 atm) is used. It is possible to greatly reduce the friction between the hot isostatic extrusion device 29 and the seamless steel pipe intermediate 41 even when pressure is applied, and there is no continuous wrinkles or rough skin, and the seamless spring steel pipe 47 has excellent surface properties. Can be manufactured.

  As the pressure medium 44 used here, it is preferable to use a lubricant obtained by adding graphite to an oil and fat system.

  The depth of continuous ridges formed on the inner and outer peripheral surfaces of the seamless spring steel pipe 47 is 50 μm or less from the surface.

  Note that the continuous rod means that the seamless spring steel pipe 47 is brought into contact with a part of the hot isostatic extrusion device at the time of manufacture, and the seamless spring steel pipe 47 is directed from one end side to the other end side in the pipe axis direction. A sliding rod formed continuously on the outer peripheral surface or inner peripheral surface for a long time.

  Here, for example, when the coil spring is continuously expanded and contracted to cause breakage or the like, it is usually caused by surface anomalies such as continuous wrinkles on the surface of the coil spring or breakage or cracks from non-metallic inclusions. Often becomes.

Therefore, in this embodiment, the depth of the continuous wrinkles is 50 μm or less, preferably 45 μm or less, more preferably 40 μm or less, and even more preferably 35 μm or less from each surface of the outer peripheral surface and the inner peripheral surface. It is possible to eliminate almost all of the points that are likely to be the starting point of.
In this way, the depth of the continuous ridge formed on the outer peripheral surface and inner peripheral surface of the seamless spring steel pipe 47 during extrusion is very small, such as 50 μm or less from the surface (inner peripheral surface and outer peripheral surface) of the steel pipe. Therefore, it is possible to implement a seamless steel pipe that has few points that are likely to be the starting point of breakage or the like even when it is continuously expanded and contracted.

  On the other hand, when the depth of the continuous wrinkles exceeds 50 μm from the outer peripheral surface and the inner peripheral surface, it is not preferable because the continuous wrinkles may be broken or cracked when continuously extended.

  Further, when the hot isostatic pressing device 29 is used, the surface roughness of the outer peripheral surface and the inner peripheral surface of the seamless spring steel pipe 47 can be lowered so that the average roughness Ra = 12.5 μm or less. is there.

When the average roughness Ra exceeds 12.5 μm or less, the skin is so rough that many points that are likely to be the starting points of breakage and cracking are included when the stretching operation is continued. . In addition, it is so preferable that average roughness Ra is low. The average roughness Ra is, for example, preferably Ra = 12 μm or less, more preferably 10 μm or less, further preferably 8 μm or less, and even more preferably 4 μm or less, but there is no lower limit. .
As described above, the seamless spring steel pipe 47 of the present embodiment has an average roughness Ra of 12.5 μm or less on the inner and outer peripheral surfaces thereof, which is very smooth. However, it is possible to further eliminate a portion that is likely to be a starting point of destruction or the like.

  The surface roughness is preferably specified by measuring the roughness in the tube axis direction on the inner and outer peripheral surfaces of the seamless spring steel pipe 47.

  The hot isostatic extrusion apparatus 29 includes a container 35 having a die 31 provided at the front thereof via an indicator member 33, a seal piston 37 disposed in the container 35, and a stem that presses the seal piston 37. 39 and a mandrel 43 that penetrates the seal piston 37 and the stem 39 and forms the inner diameter of the seamless steel pipe intermediate body 41.

  This hot isostatic pressing device 29 is arranged in a container 35 with a billet 27 that has been heated and softened in advance to a high temperature (for example, 1050 ° C. or higher and lower than 1300 ° C.), The billet 27 is pressed. By this pressing, the billet 27 is discharged from between the die 31 and the mandrel 43 to produce the seamless steel pipe intermediate body 41.

  Specifically, for example, a billet 2 made of a hollow spring steel material having an inner diameter of 50 to 60 mm and an outer diameter of 140 to 160 mm is hot isostatically extruded using the hot isostatic extrusion apparatus 29. By this processing, for example, a seamless spring steel pipe 47 having an outer diameter of 30 to 60 mm and a thickness of 4 to 7 mm can be easily manufactured.

  Needless to say, the inner diameter and outer diameter of the billet 2 and the outer diameter and wall thickness of the seamless spring steel pipe 47 can be changed as appropriate, and are not limited to the above ranges.

  Here, as a spring steel material used in order to manufacture the seamless spring steel pipe 47 of a present Example, SiCrV steel stronger than SiCr steel or CrV steel can be used, for example. Specifically, JIS G3560, JIS G3561, etc. can be used suitably, More specifically, KHV12N, KHV10N, KHV6N, KHV7, CRV, HRS6, SRS600, UHS1900, UHS2000 manufactured by Kobe Steel, Ltd. Etc. can be used particularly preferably.

    As such a steel material, the composition thereof is C: 0.3 to 1.0 mass%, more preferably 0.5 to less than 0.7 mass%, Si: 0.1 to 3.0 mass%, and more. Preferably 1.0 to 3.0 mass%, Mn: 0.05 to 1.5 mass%, more preferably 0.5 to 1.5 mass%, Ni: 0 to 2.5 mass%, more preferably 0.05 to 0.5% by mass, Cr: 0 to 2.0% by mass, more preferably 0.05 to 1.5% by mass, Mo: 0 to 0.8% by mass, V: 0 to 0.8% Preferably containing 0.05% by mass, more preferably 0.05-0.3% by mass, Ti, Nb, Co, W: 0-0.5% by mass with the balance being Fe and inevitable impurities Can do.

(C: 0.3-1.0% by mass)
C is an element useful for increasing the tensile strength of a wire drawing material, that is, a seamless spring steel pipe (including a seamless steel pipe), and ensuring fatigue characteristics and sag resistance.

  If the C content exceeds 1.0% by mass, the susceptibility to defects is increased, cracks from surface defects and non-metallic inclusions are generated, and the fatigue life is deteriorated.

  However, when the C content is less than 0.3% by mass, not only the tensile strength necessary for a high stress spring can be secured, but also the amount of proeutectoid ferrite that promotes the occurrence of fatigue cracks increases and the fatigue characteristics deteriorate. .

  Therefore, the C content in the present invention is defined as 0.3 to 1.0 mass%. In addition, as more preferable content, it is less than 0.5-0.7 mass%.

(Si: 0.1-3.0% by mass)
Si is an element that contributes to improving fatigue characteristics and sag resistance by increasing the tensile strength of seamless steel pipes by solid solution strengthening.

  When the Si content is less than 0.1% by mass, the above-described effects cannot be obtained.

  However, if the Si content exceeds 3.0% by mass, surface deoxidation, wrinkles, and the like increase, resulting in poor fatigue resistance.

  Therefore, the Si content in the present invention is defined as 0.1 to 3.0% by mass. In addition, more preferable content is 1.0-3.0 mass%.

  In addition, it is necessary to contain Si as much as the C content is lowered.

(Mn: 0.05 to 1.5% by mass)
Mn is an element that contributes to the improvement of fatigue properties by densifying and ordering the pearlite structure.

  If the Mn content is less than 0.05% by mass, the effects described above cannot be obtained.

  However, if the Mn content exceeds 1.5% by mass, a bainite structure is likely to be formed during hot isostatic pressing and the fatigue characteristics are deteriorated.

  Therefore, the Mn content in the present invention is specified to be 0.05 to 1.5 mass%. In addition, more preferable content is 0.5-1.5 mass%.

(Ni: 0 to 2.5% by mass)
Ni may not be contained, but it is preferable to contain Ni because it has the effect of reducing notch sensitivity and increasing toughness. In addition, Ni has an effect of suppressing breakage trouble and improving the fatigue life when, for example, spring winding is performed.

  In order to acquire such an effect, it is good to contain 0.05 mass% or more of Ni.

  However, if the Ni content exceeds 2.5% by mass and becomes excessive, a bainite structure is likely to be formed at the time of hot isostatic pressing or the like, which is counterproductive.

  Therefore, the content of Ni in the present invention is defined as 0 to 2.5% by mass. In addition, More preferably, it is 0.05-0.5 mass%.

(Cr: 0 to 2.0% by mass)
Cr may not be included, but the pearlite lamella spacing is reduced to increase the strength after hot isostatic pressing or heat treatment and improve sag resistance. Is preferred.

  In order to acquire such an effect, it is good to contain 0.05 mass% or more of Cr.

  However, if the Cr content exceeds 2.0% by mass, the patenting time becomes too long, and the toughness and ductility deteriorate.

  Therefore, the Cr content in the present invention is defined as 0 to 2.0 mass%. In addition, More preferably, it is 0.05-1.5 mass%.

(Mo: 0 to 0.8 mass% or less)
Mo may not be contained, but may be contained because it contributes to increasing the strength of the spring steel by increasing the hardenability.

  In order to acquire such an effect, it is good to contain 0.2 mass% or more of Mo.

  However, if the Mo content is too large, the toughness is extremely deteriorated, so it is necessary to keep the content to 0.8% by mass or less.

  Therefore, the Mo content in the present invention is specified to be 0 to 0.8% by mass or less.

(V: 0 to 0.8% by mass)
V can be excluded, but it is useful to improve the workability of the seamless steel pipe by making the pearlite nodule size fine, so it is preferable to contain V. Further, V is useful for improving the toughness and sag resistance of the spring material, for example, when the spring material is used.

  In order to acquire such an effect, it is preferable to contain V 0.05 mass% or more.

  If the V content exceeds 0.8% by mass and excessively contained, a bainite structure is likely to be formed during hot isostatic pressing, and the fatigue life is deteriorated.

  Therefore, the content of V in the present invention is defined as 0 to 0.8 mass%. In addition, More preferably, it is 0.05-0.3 mass%.

(Inevitable impurities)
The basic component composition in the seamless steel pipe of the present invention is as described above, and the balance is substantially made of Fe, but does not hinder the characteristics of the seamless steel pipe using the steel material other than the various components described above. The seamless steel pipe containing a trace component is also included in the scope of the present invention. Examples of the trace component include impurities, particularly unavoidable impurities such as P, S, As, Sb, and Sn.

  Thus, since the seamless steel pipe 1 of the present invention is manufactured using spring steel having high hardness, even if it is a hollow material, it is used for general structural rolled steel (JIS G 3101) or mechanical structure as in the conventional product. Hardness comparable to that of a solid material manufactured using carbon steel (JIS G 4051) or the like can be provided.

  Moreover, despite using such a hard steel material, it can be manufactured into a seamless steel pipe intermediate by hot isostatic pressing, to produce a seamless steel pipe, that is, without being drilled, etc. Easy to manufacture and inexpensive to manufacture. It is also possible to provide further desired properties by performing appropriate cold working, heat treatment, etc. after hot isostatic pressing.

  Therefore, the seamless spring steel pipe 47 of the present invention can be provided with a high hardness that could not be achieved conventionally, such as a Vickers hardness of Hv500 or higher. Needless to say, the seamless spring steel pipe 47 of the present embodiment can have a higher hardness than this, for example, a Vickers hardness of Hv550 or higher, or a higher hardness of Hv600 or higher, even higher. The hardness can be Hv650 or higher.

And the seamless spring steel pipe 47 of a present Example contains a nonmetallic inclusion in metal structure. Non-metallic inclusions refer to glass-like inclusions such as CaO.SiO ₂ .Al ₂ O ₃ system, for example. The maximum thickness of the nonmetallic inclusions in the direction orthogonal to the tube axis of the seamless spring steel tube 47 is preferably 50 μm or less. In addition, in a member that requires a life exceeding 10 million times (stretching operation), the non-metallic inclusions contained therein have a maximum thickness in the direction perpendicular to the tube axis of the seamless steel pipe of less than 30 μm, and More preferably, the number per 100 mm ² is less than 30.

  If the maximum thickness of the nonmetallic inclusions in the direction perpendicular to the tube axis exceeds 50 μm, for example, in repeated fatigue parts, stress concentration may occur and fatigue failure may occur, which is not preferable. On the other hand, since it is preferable not to contain nonmetallic inclusions from the viewpoint of improving durability, there is no lower limit.

The maximum thickness of non-metallic inclusions and the number per 100 mm ² can be measured by a conventionally known means such as observing the cross section with a scanning electron microscope.

  As described above, the seamless spring steel pipe 47 of the present invention has the depth of the continuous flaw, the maximum length of the non-metallic inclusions contained in the metal structure, the maximum thickness, the number per unit area, and the range of composition components. And by appropriately controlling the average roughness Ra between the inner peripheral surface and the outer peripheral surface, even if the expansion and contraction operation is continued, there is no breakage, so that the durability is excellent. Moreover, the seamless spring steel pipe 47 of the present invention can have a higher hardness than a conventional seamless steel pipe.

Moreover, since it is a hollow material, 30-40% of weight reduction can be achieved compared with a solid material. This realizes a weight reduction substantially equal to that of a β-titanium alloy when used as a vehicle part.
[Inner shot]
FIG. 8 is a conceptual diagram showing the inner surface shot. As shown in FIG. 8, shot peening is performed by directing a shot nozzle 55 of a shot peening machine using air pressure toward the hole 53 of the one end 51 of the coiled hollow body 49. Thereafter, this shot peening is also performed from another terminal of the hollow body 49. By making the diameter of the shot grains 1/3 or less of the diameter of the hole 53, the hole 53 can be surely imparted with residual stress.
Further, when an ultrasonic wave is applied in a state in which shot grains are put in the hole portion, a similar shot peening effect can be obtained on the inner surface portion.
[Material cleanliness and surface properties]
Table 1 shows the relationship between the implementation of hot isostatic pressing and inclusions. When the heating temperature (extrusion temperature) of the spring steel material in the hot isostatic pressing step 7 was 950 ° C., the extrusion resistance was so strong that extrusion could not be performed. At an extrusion temperature of 1000 ° C., the maximum thickness of the non-metallic inclusions in the seamless spring steel pipe was as large as 52 μm, and the number was as large as 32/100 mm ² . When the extrusion temperature was 1300 ° C. or higher, the maximum thickness of the non-metallic inclusions in the seamless spring steel pipe was as large as 58 μm or more, and the number was as large as 42 pieces / 100 mm ² or more. On the other hand, when the extrusion temperature was 1050 ° C. or higher and lower than 1300 ° C., the maximum thickness of the nonmetallic inclusions was as small as 38 μm or less, and the number was as small as 20/100 mm ² or less. Further, the rough surface of the seamless spring steel pipe did not occur at a temperature lower than 1300 ° C., whereas the rough surface was observed at a temperature of 1300 ° C. or higher.
Therefore, in order to improve the material cleanliness and the surface properties, it is preferable to set the extrusion temperature of the spring steel material in the hot isostatic extrusion process 7 to 1050 ° C. or more and less than 1300 ° C. From the viewpoint of the number and size of non-metallic inclusions in the steel that affect the durability of the spring, it is preferable to more reliably set the extrusion temperature to 1050 ° C. to 1250 ° C. Considering the damage of the tool, it is advantageous to perform extrusion molding on the low temperature side, and the extrusion temperature should be set at 1050 ° C. or more and less than 1200 ° C. If quality is important, 1100 ° C. or more and 1200 ° C. It is recommended to set to less than.
By setting such an extrusion temperature, the material cleanliness and surface properties of the seamless spring steel pipe 47 can be increased.
[Lightening effect]
FIG. 10 is a chart showing a comparison of the effect of reducing the weight of the coil spring. In FIG. 10, a coil inner diameter: φ = 45 mm, a maximum use load: 2750 N, a coil spring using a solid material of SiCr steel (solid material), a conventional hollow coil spring using S45C, etc. (conventional hollow material) The hollow coil springs of the examples using SiCr steel and high-strength SiCrV steel were compared.
As shown in FIG. 10, the conventional hollow coil spring is made of low carbon steel as a material, has a hardness after quenching of Hv 440 and a tensile strength (TS) of 1480 MPa, and is coiled on the outer surface side (outer side) of the cross section. When the inner diameter side stress of the diameter is 716 MPa and the TS ratio is set to 48%, the mass is 439 g.
On the other hand, in the case of an example product using SiCr steel, the hardness is Hv 545, the tensile strength (TS) is 1850 MPa, and in the case of an example product using high strength SiCrV steel, the hardness is Hv 580, tensile. When the strength (TS) is 2020 MPa and the TS ratio is set to 48%, the masses are 298 g and 255 g, respectively, the number of turns can be reduced, and a more compact and lightweight hollow coil spring can be obtained.
This performance is not inferior to that of a solid material as shown in FIG.
Therefore, in the hollow coil spring of the present embodiment, the effect of reducing the weight can be surely obtained, and the natural frequency can be increased as shown in the chart of FIG.
[Chemical composition of high strength SiCrV steel]
FIG. 11 is a chart showing an example of chemical components of high-strength SiCrV steel. Both steel A and steel B were developed as other than JIS standard SiCr steel, and vanadium V or the like can be added to reliably obtain the above-described lightening effect as high-strength SiCrV steel.
[durability]
FIGS. 12 to 16 relate to the durability of the hollow coil spring, FIG. 12 is a chart of durability test data with respect to the extrusion temperature of the suspension spring of the automobile suspension, and FIG. 13 is an durability test with respect to the extrusion temperature of the valve spring of the automobile engine. Data chart, FIG. 14 is a chart of endurance test data against hardness after heat treatment of suspension springs of automobile suspension, FIG. 15 is a graph plotting the results of FIG. 14, and FIG. It is a chart of the endurance test data to the compressive residual stress of the surface. 12, 2, 3, 4,... Correspond to Table 1, and the extrusion conditions A, B, C, D,.

  The test material used for the hollow coil spring is shown in FIG. 9 with the seamless spring steel pipe 47 used as the material of the A spring and the valve spring of FIG. 11 in the state where the seamless spring steel pipe 47 used as the material of the suspension spring is shown in Table 1. It is B steel of FIG. 11 in a state (high purity).

  In the case of the suspension spring of FIG. 12, the test was performed under the conditions of wire diameter: φ10.0 mm, hole diameter: φ5.0 mm (wall thickness: 2.5 mm), outer maximum shear stress: 1,100 MPa, hardness after heat treatment: Hv620. . Extrusion conditions 2, 3, 4, 5, and 6 all had 500,000 cycles of durability and no breakage, significantly exceeding the required durability of the suspension springs of 200 to 300,000.

  In the case of the valve spring of FIG. 13, the test was performed under the conditions of wire diameter: φ5.6 mm, hole diameter: φ2.8 mm (wall thickness: 1.4 mm), outer maximum shear stress: 950 MPa, and hardness after heat treatment: Hv620. Extrusion conditions A, B, and C all had 30 million cycles of durability and no breakage, significantly exceeding the required 10 million cycles of valve springs.

  In the case of the suspension spring of FIG. 14, the hardness was changed by heat treatment after processing, and the wire diameter was φ10.0 mm, the hole diameter was φ5.0 mm (thickness 2.5 mm), and the outer maximum shear stress was: 1,100 MPa, extrusion temperature: E in FIG.

  With Hv620 or more, there was no breakage after durability of 500,000 times. In Hv480, breakage was observed on the outer surface at the first 14,500 times and the second 18,800 times. In Hv505, breakage was observed on the outer surface in the first 198,000 times and the second 215,000 times. With Hv535, breakage was observed on the outer surface after the first 252,000 times and the second 286,000 times. With Hv580, breakage was observed on the hole side surface at the first 407,000 times and the second 472,000 times. When this is plotted as shown in FIG. 15, an inflection point exists in Hv500, and the hardness after heat treatment should be Hv500 or more.

  In the case of the suspension spring of FIG. 16, the wire diameter: φ10.0 mm, hole diameter: φ5.0 mm (wall thickness: 2.5 mm), outer maximum shear stress: 1,100 MPa, hardness after heat treatment: Hv580 . In the case of Base in which compressive residual stress was not applied to the inner surface of the hole portion of the hollow coil spring, breakage was observed on the inner surface in the first 407,000 times and the second 472,000 times. On the other hand, when compressive residual stress is applied to the inner surface of the hole by nitriding, carburizing and quenching, or shot (inner surface shot), the durability is 500,000 times and there is no breakage, and the required durability of the suspension spring The number was significantly higher than the 200,000 to 300,000 times.

[Concrete example]
Next, the seamless spring steel pipe 47 and its manufacturing method used in this embodiment will be described by comparing a specific example that satisfies the requirements of this embodiment with a comparative example that does not satisfy the requirements of this embodiment.

  First, using a steel material for high strength spring shown as steel B in FIG. Cylindrical billets according to 1 to 9 were produced. These billets were prepared to have an outer diameter of 143 mm and an inner diameter of 52 mm. And these billets were heated at each temperature of 950-1400 degreeC as shown in Table 1. And the heated test No. The billet of 1-9 was hot isostatically extruded by the hot isostatic extrusion apparatus at each temperature (extrusion temperature), and the seamless steel pipe was manufactured. Thereafter, test no. The seamless steel pipes 1 to 9 were subjected to spheroidizing annealing treatment at 680 ° C. for 16 hours, followed by pilger mill rolling and drawing to extend to an outer diameter of 10.6 mm and an inner diameter of 5.9 mm. And test no. After the seamless steel pipes 1 to 9 were heated at 700 ° C. for 0.5 hours, they were pickled and tested. It was set as the seamless steel pipe of 1-9.

  In addition, as a pressure medium at the time of hot isostatic extrusion, a pressure medium in which graphite was mixed with a lubricating oil containing molybdenum disulfide and a synthetic oil as a matrix was used.

Test no. For the seamless steel pipes 1 to 9, the maximum thickness (μm) of nonmetallic inclusions and the number per unit area (number / 100 mm ² ) were measured, and the extrudability and rough skin were evaluated.

The maximum thickness (μm) of non-metallic inclusions and the number per unit area (number / 100 mm ² ) were measured by observing the cross section with a scanning electron microscope.

  The evaluation of extrudability was evaluated as “possible” when the hot isostatic extrusion process was performed without problems, and the hot isostatic extrusion process was smoothed because the extrusion resistance was too strong. Those that could not be carried out were evaluated as “NG”.

  The evaluation of rough skin was conducted according to Test No. 1 to 9 seamless steel pipes were visually inspected. Those without rough skin were evaluated as “None”, and those with rough skin were evaluated as “Generated”.

Table 1 shows heating temperature conditions, measurement results, and evaluation results.

  As shown in Table 1, test no. When it was 1 (950 ° C.), the extrusion resistance was strong, and hot isostatic extrusion could not be performed (NG).

Test No. 2 (1000 ° C.), the maximum thickness of the non-metallic inclusions in the seamless steel pipe was as large as 52 μm, and the number was as large as 32 pieces / 100 mm ² .

On the other hand, test No. whose extrusion temperature is 1300 degreeC or more is shown. In Nos. 7 to 9, the maximum thickness of the non-metallic inclusions in the seamless steel pipe was as large as 58 μm or more, or the number of non-metallic inclusions was as large as 42 or more / 100 mm ² . Moreover, rough skin was also generated. Test No. 1, test no. 2 and test no. 7 to 9 were comparative examples.

On the other hand, test No. which is extrusion temperature 1050 degreeC or more and less than 1300 degreeC. In 3-6, the maximum thickness of the nonmetallic inclusions was as small as 38 μm or less, and the number was as small as 20 or less / 100 mm ² . Moreover, rough skin was not generated. Test No. 3 to 6 were examples.

  Therefore, in order to improve the smoothness of the surface, it has been found that the extrusion temperature of the billet in the hot isostatic extrusion process described above should be set to 1050 ° C. or higher and lower than 1300 ° C. In particular, for example, in the case of a coil spring, the extrusion temperature is more preferably 1050 to 1250 ° C. from the viewpoint of the number and size of non-metallic inclusions in the metal structure that affect the durability of the coil spring. It was found that it is preferable to set to. Further, considering the damage of jigs and tools, it is advantageous to extrude on the low temperature side, and the extrusion temperature should be set at 1050 ° C. or more and less than 1200 ° C. If the quality is more important. It was found that the temperature is preferably set to 1100 ° C. or higher and lower than 1200 ° C.

  By setting such an extrusion temperature, the surface of the seamless steel pipe can be smoothed.

[Effect of Example]
As described above, the hollow coil spring 1 of the present embodiment is formed into a coiled hollow body using the seamless spring steel pipe 47 in which a heated spring steel material is extruded by liquid pressure to improve the material cleanliness and the surface properties. Since the surface treatment that applies compressive residual stress is applied, it is easy to apply compressive residual stress uniformly, the material strength of the hollow spring is high, and spring sag (permanent deformation) and breakage are suppressed even at high stress, so design stress Therefore, it is possible to achieve both a light weight reduction effect and an increase in fatigue strength.
The seamless spring steel pipe 47 heats and softens the spring steel material processed into the hollow billet as described above, performs hot isostatic pressing to produce a seamless pipe, and the seamless pipe has a predetermined diameter. Perform surface reduction.
That is, if hot isostatic pressing is performed, the spring steel material is formed in a fluid state, and thus, for example, a seamless pipe having an outer diameter of 30 to 60 mm is manufactured directly from a hollow billet having an outer diameter of 300 mm or more. Is possible.
The spring steel material is preferably subjected to hot isostatic pressing while being heated to 1050 ° C. or higher and lower than 1300 ° C. As a result, the spring steel material is not melted but is in a softened state, and fluidity is ensured under ultrahigh pressure.
Here, as the spring steel material, for example, when used for a valve spring, it is preferable to use steel A shown in FIG. The state of non-metallic inclusions in this case is shown in the chart of FIG.
The spring steel material processed into a hollow billet is heated and softened, and a seamless tube is manufactured by hot isostatic pressing, so a seamless tube with a small diameter (for example, 30-60 mm) is manufactured from a hollow billet with a large diameter. Furthermore, the seamless pipe can be reduced to a predetermined size (for example, pilger mill, drawing, drawing). In addition, the seamless tube manufactured by the above-described manufacturing method is beautiful and the surface crystal grains are fine because of the hydrostatic pressure extrusion process with little friction with the tool unlike rolling.
Therefore, the manufacturing process of the seamless spring steel pipe 47 is simplified as a whole, it can be manufactured at a higher quality and at a lower cost, and a tubular spring can actually be used in a vehicle.
As described above, the seamless spring steel pipe 47 manufactured in this way is expected to be 30% to 40% lighter than a normal wire rod, and can be reduced in weight substantially equivalent to a β titanium alloy when used as a vehicle part. .
The effects when applied to several automotive parts are described below.
First, in order to improve the engine performance, the output characteristics and the like are improved by a method such as increasing the engine speed limit to improve the output or improving the shape of the intake / exhaust port. Among them, the movement of the valve train is a major limiting factor as a factor that determines the engine speed limit. The rotational movement of the crankshaft transmitted via the cam leads to the vertical movement of the valve, and the valve spring serves to press and push back the valve that moves up and down. Therefore, the time when the vertical movement of the valve spring itself cannot follow the rotational movement of the cam is the engine limit speed. Therefore, in order to improve performance, it is indispensable to increase the spring load or reduce the inertia weight of a reciprocating part such as a valve including the spring. In order to satisfy the above, it is desirable to reduce the weight of the spring itself, reduce the size, and maintain and improve the spring load at the same time (for example, as the natural frequency of the valve spring increases due to weight reduction) Increase in engine speed limit).
The fuel efficiency improvement effect by reducing the inertia weight of the valve spring is large. Generally, the fuel efficiency can be improved by about 0.5 to 1.0% with respect to the 20% reduction of the spring weight, and a great effect can be expected.
Next, the suspension spring of automobile suspension has a great influence on driving performance such as ride comfort and cornering, and is a major factor in determining the merchandise of the car. This suspension performance depends largely on the characteristics of the suspension itself including the suspension spring and the unsprung weight of the tire portion in addition to the basic structure of the vehicle. Suspension springs used for suspension support high loads because they support the entire weight of the vehicle, and the weight is therefore increased. Therefore, if the same parts can be reduced in weight as in the case of engine valve springs, the unsprung weight can be reduced. For example, the lightening effect of the unsprung load can be obtained 10 times as much as the body lightening effect. It also leads to downsizing of the entire structure, improving not only the ride comfort but also the product power of adopting a new structure.
Finally, current motor sports are positioned as a powerful tool for improving the brands of automobile companies, and building a major position there is an important strategy for automobile companies. In particular, marketing technology used in motorsports will lead to significant added value for automobiles and increase merchantability. At present, WRC or JGTC, which is the top brand of motor sports, requires that important parts such as springs should be made of the same material as mass-produced commercial vehicles. For this reason, hollow springs and the like whose functions can be improved by changing the structure are very easy to understand and have high value.

  FIG. 17 is a cross-sectional view of a hollow coil spring according to the second embodiment of the present invention.

  In the hollow coil spring 1A of the present embodiment, the relative position of the cross-sectional inner shape 6 with respect to the cross-sectional outer shape 5 is eccentric to the outside in the coil radial direction of the hollow body constituting the hollow coil spring 1A. Accordingly, the thickness t1 on the inner diameter side of the hollow coil spring 1A is relatively thick with reference to the thickness t2 on the outer diameter side.

  The relative positions of the cross-sectional outer shape 5 and the cross-sectional inner shape 6 of the hollow coil spring 1A were ensured by the setting of the coil diameter and material hardness of the hollow body constituting the hollow coil spring 1A and the relative position in the material state.

  Therefore, in the present embodiment, in addition to the effects of the first embodiment, the strength on the inner diameter side on which relatively higher stress is exerted than the outer diameter side of the hollow coil spring 1A can be further increased, and the durability can be improved. Can do.

  FIG. 18 is a cross-sectional view of a hollow coil spring according to a third embodiment of the present invention.

  In the hollow coil spring 1B of the present embodiment, the cross-sectional outer shape 5 and the cross-sectional inner shape 6 are both elliptical, and the cross-section is flat in the coil axial direction of the hollow body constituting the hollow coil spring 1B. . The ellipses of the cross-sectional outer shape 5 and the cross-sectional inner shape 6 are concentric.

  The relative positions of the cross-sectional outer shape 5 and the cross-sectional inner shape 6 of the hollow coil spring 1B were secured by setting the coil diameter and material hardness of the hollow body. The flat cross-sectional shape was realized by rolling the seamless spring steel pipe 47.

  Therefore, in the present embodiment, in addition to the effects of the first embodiment, the height of the hollow coil spring 1B can be lowered, and the stress on the inner diameter side and the outer diameter side can be equalized.

  FIG. 19 shows other modified examples, and (a), (b), and (c) are cross-sectional views of main parts of the modified examples.

  FIG. 9A shows a hollow coil spring 1C having a cross-sectional outer shape 5 having an elliptical flat shape and a cross-sectional inner shape 6 having a perfect circular shape.

  FIG. 9B shows a hollow coil spring 1D having a cross-sectional outer shape 5 having an oval shape with a smaller radius of curvature on the coil inner diameter side, and a cross-sectional inner shape 6 having a perfect circle shape.

  FIG. 9C shows that the cross-sectional outer shape 5 of the hollow coil spring 1E has an elliptical shape (or a true circular shape) as a basic shape, and both sides in the coil axial direction are formed flat, and the inner cross-sectional shape 6 is an elliptical shape (or egg shape). It is what. The cross-sectional outline 5 can also be formed in a rectangular shape.

  In this embodiment, in any case, at least the cross-sectional outer shape of the hollow body constituting the hollow coil springs 1B, 1C, 1D, 1E is formed in a non-circular shape.

  The present invention can also be applied to a hollow stabilizer that is a rod-shaped hollow body having a bent portion. The hollow stabilizer has arms at both ends of a rod-shaped main body, and has a bent portion between the main body and the arm. The forming of the hollow stabilizer is a step of forming an arm instead of the coil forming step 13 of the first embodiment. The cross-sectional shape of the bent portion of the hollow stabilizer is set in the same manner as the hollow coil springs 1, 1A, 1B, and the thickness is adjusted in the direction of the radius of curvature of the bent portion. The flat cross section may be the entire hollow stabilizer.

  FIG. 20 is a chart of endurance test data of the hollow stabilizer. Wire diameter: φ25.0 mm, hole diameter: φ12.5 mm (thickness 6.25 mm), outer maximum principal stress: ± 700 MPa, hole side maximum principal stress: ± 450 MPa.

  The conventional hollow stabilizer using S40C had a hardness of Hv420, and the outer surface was broken in the first 85,000 times and the second 95,000 times. In the hollow stabilizer of the embodiment of the present invention, the hardness was Hv515, and the inner surface (hole surface) of the hole portion was broken in the first 246,000 times and the second time 313,000 times. In contrast, about three times the life could be achieved. Further, the hardnesses of Hv550 and 590 were durable for 500,000 times and there was no breakage.

  Therefore, also in the case of a hollow stabilizer, the same effect as Example 1 can be produced.

  Moreover, as a rod-shaped spring, it can also be comprised as a torsion bar which does not have a bending part.

(Example 1) which is sectional drawing of a hollow coil spring. 6 is a chart showing a relationship between t / D and a weight reduction rate (Example 1). It is a graph which shows the relationship between t / D, a weight reduction rate, and a hole stress (Example 1). It is a graph which shows the relationship between t / D, contact | adhesion height increase rate, and a hole part stress (Example 1). It is a block diagram which shows the manufacturing process of a hollow coil spring (Example 1). It is process drawing of a hot isostatic-pressure extrusion process (Example 1). It is sectional drawing of a hot isostatic-pressure extrusion processing apparatus (Example 1). It is a conceptual diagram which shows an inner surface shot (Example 1). It is a chart which shows the relationship between implementation of hot isostatic pressing, and inclusions (Example 1). It is a graph which shows the comparison of the weight reduction effect of a coil spring (Example 1). It is a graph which shows an example of the chemical component of high strength SiCrV steel (Example 1). It is a table | surface of the durability test data with respect to the extrusion temperature of the suspension spring of a motor vehicle suspension (Example 1). It is a table | surface of the durability test data with respect to the extrusion temperature of the valve spring of a motor vehicle engine (Example 1). It is a chart of the durability test data with respect to the hardness after heat processing of the suspension spring of a motor vehicle suspension (Example 2). It is the graph which plotted the result of FIG. 14 (Example 1). It is a chart of the endurance test data to the compressive residual stress of the inner surface of the suspension spring of an automobile suspension (Example 1). (Example 2) which is sectional drawing of a hollow coil spring. (Example 3) which is sectional drawing of a hollow coil spring. (A), (b), (c) is principal part sectional drawing of each modification (Example 3). It is a table | surface of the durability test data of a hollow stabilizer (Example 4).

Explanation of symbols

1, 1A, 1B Hollow coil spring 3 Hole 5 Cross-sectional outer shape 6 Cross-sectional inner shape 47 Seamless spring steel pipe

Claims (14)

A compressed spring residue is formed in a hollow body that is formed into a coil shape, a rod shape, or a rod shape having a bent portion using a seamless spring steel pipe extruded from a heated hollow spring steel material by hydraulic pressure in order to enhance material cleanliness and surface properties. A hollow spring characterized by a surface treatment for applying stress. The hollow spring according to claim 1,
The hollow spring according to claim 1, wherein the heating of the spring steel material is performed at 1050 ° C. or higher and lower than 1300 ° C. so as not to cause roughening by the extrusion process. The hollow spring according to claim 1 or 2,
The hollow spring according to claim 1, wherein the hydraulic pressure is a hydrostatic pressure. The hollow spring according to claim 3,
A hollow spring characterized by using a lubricant in which graphite is added to an oil and fat system during the extrusion process. A hollow spring according to any one of claims 1 to 4,
A hollow spring characterized in that the ratio of the thickness t and the outer diameter D of the cross-section of the coil-shaped, rod-shaped or rod-shaped hollow body having a bent portion is set to t / D = 0.10 to 0.35. A hollow spring according to any one of claims 1 to 5,
A hollow spring having a hardness of H _V = 500 or more. A hollow spring according to any one of claims 1 to 6,
A hollow spring characterized in that at least an outer surface of the seamless spring steel pipe is ground. A hollow spring according to any one of claims 1 to 7,
The hollow spring according to claim 1, wherein the surface treatment is performed on an outer surface and an inner surface of the hollow body. A hollow spring according to any one of claims 1 to 8,
A hollow spring characterized in that the cross-sectional outer shape and inner cross-sectional shape of the coil-shaped hollow body or the relative positions of the cross-sectional outer shape and inner cross-sectional shape at the bent portion of the rod-shaped hollow body are circular concentric. A hollow spring according to any one of claims 1 to 8,
The hollow spring characterized in that the relative positions of the cross-sectional outer shape and the inner cross-sectional shape of the coil-shaped hollow body or the cross-sectional outer shape and the inner cross-sectional shape of the bent portion of the rod-shaped hollow body are eccentric. A hollow spring according to any one of claims 1 to 8,
A hollow spring, wherein at least a cross-sectional outer shape of the hollow body is a non-circular shape. The hollow spring according to any one of claims 1 to 11,
A hollow spring, wherein a depth of a continuous rod formed on at least one of an inner peripheral surface or an outer peripheral surface of the seamless spring steel pipe is 50 μm or less from the inner peripheral surface or the outer peripheral surface. The hollow spring according to any one of claims 1 to 11,
The seamless spring steel pipe contains non-metallic inclusions in the metal structure,
A hollow spring, wherein the maximum thickness of the non-metallic inclusions in a direction perpendicular to the tube axis is 50 μm or less. A hollow spring according to any one of claims 1 to 13,
The hollow spring characterized in that the surface roughness of at least one of the inner peripheral surface or the outer peripheral surface of the seamless spring steel pipe is an average roughness Ra = 12.5 μm or less.

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