JP2009293077A - Heat resistant stainless steel wire, heat resistant spring and method for producing heat resistant spring - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a heat resistant stainless steel wire having high heat resistance and having excellent settling resistance in a high temperature region, to provide a heat resistant spring, and to provide a method for producing the same. <P>SOLUTION: The heat resistant stainless steel wire and heat resistant spring comprise, by mass, 0.04 to 0.08% C, 0.60 to 1.40% Si, 0.5 to 3.0% Mn, 16 to 20% Cr, 7.0 to 10.5% Ni and 0.16 to 0.25% N, and the balance Fe with inevitable impurities, and in which the average crystal grain size in the transverse section is 8 to 20 μm. Further, in the method for producing a heat resistant spring, the resistant stainless steel wire is subjected to spring working, and is thereafter subjected to low temperature annealing at 500 to 650°C for 1 min to <1 hr. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a heat-resistant stainless steel wire used as a part that requires heat resistance, such as an exhaust system part of an automobile engine, mainly as a spring material. In particular, the present invention relates to a heat resistant stainless steel wire for a heat resistant spring having excellent sag resistance in a high temperature range of 400 ° C. to 550 ° C.

  An exhaust system device for purifying exhaust gas is attached to an automobile engine. For example, a spring is used as a part of a joint portion of the exhaust system device. Conventionally, austenitic stainless steel wires such as SUS304 and SUS316 have been widely used as the spring material used in the exhaust system parts. In general, a stainless steel wire is manufactured by melting and casting stainless steel, performing forging and hot rolling to obtain a wire, and then repeating solution heat treatment and wire drawing.

  In recent years, exhaust gas regulations for automobiles are being strengthened as countermeasures for environmental problems, and in order to increase the efficiency of engines and exhaust gas purification catalysts, it is desired to increase the operating temperature of the exhaust system. However, stainless steel wire springs such as SUS304 and SUS316 are not suitable for use because they are insufficient in terms of heat resistance and sag resistance in a high temperature environment of 350 ° C. or higher. Therefore, in order to meet such a demand, it is necessary to improve the heat resistance and the sag resistance in a high temperature range of a stainless steel wire used as a spring material used for exhaust system parts.

  For example, Patent Documents 1 to 4 disclose techniques for improving the heat resistance of stainless steel wires and the sag resistance at high temperatures.

  Patent Document 1 discloses a reinforced stainless steel wire for springs in which C and N are increased and solid solution strengthened based on SUS316. Patent Document 1 describes that after coiling a stainless steel wire for a spring, it is annealed at a low temperature under conditions of about 500 ° C. × 30 minutes or more.

  Patent Document 2 discloses a stainless steel wire for heat-resistant springs containing C: 0.08 to 0.15% and N: 0.25 to 0.40% by mass%. C and N which are intrusion-type solid solution elements are disclosed. It is described that sag resistance is improved by positive addition.

  Patent Document 3 discloses a stainless steel wire for heat-resistant springs containing N and having an average crystal grain size in a cross section of the steel wire of less than 5 μm. By reducing the crystal grain size as much as possible, tensile strength is disclosed. Increasing the thickness and thus improving the sag resistance is described. Furthermore, Patent Document 4 describes that by setting the maximum crystal grain size in the cross section of the steel wire to less than 12 μm, coarse crystals that are likely to concentrate stress are eliminated, and sag resistance is improved. Patent Documents 3 and 4 describe that solid solution strengthening is performed by adding ferrite-forming elements such as W, Mo, Nb, and Si.

JP 2000-297327 A (paragraph 0006, FIG. 3) Japanese Patent Laying-Open No. 2005-325381 (paragraph 0026, FIG. 3) JP 2000-239804 A (paragraph 0018) JP 2004-197205 A (paragraph 0019)

  Recently, in order to further increase the efficiency, it has been studied to increase the operating temperature of the exhaust system, and attempts have been made to raise the maximum operating temperature to about 550 ° C. However, conventional heat-resistant stainless steel wires do not exhibit excellent sag resistance at such a high temperature range and are not suitable for use.

  As is clear from the description of the embodiments of each document, the heat-resistant stainless steel wires described in Patent Documents 1 to 4 have an assumed use temperature of 300 ° C. to 400 ° C., particularly a high temperature range of 400 ° C. to 550 ° C. No consideration has been given to sag resistance at high temperatures above 450 ° C.

  Moreover, since the heat-resistant stainless steel wire of Patent Document 1 contains 10% by mass or more of Ni and 2% by mass or more of Mo, the raw material cost is increased.

  The heat-resistant stainless steel wire of Patent Document 2 contains 0.25% or more of N, but this is a content that cannot be taken in by casting of stainless steel in the atmosphere. Therefore, in order to manufacture the heat-resistant stainless steel wire of Patent Document 2, special equipment for adding N excessively to the stainless steel is necessary, resulting in an increase in manufacturing cost.

  The heat resistant stainless steel wires of Patent Documents 3 and 4 are intended to make the crystal grain size as small as possible. However, excessive refinement of crystal grains is not necessarily effective in improving the mechanical properties at high temperatures. Is not limited.

  The present invention has been made in view of the above circumstances, and one of its purposes is to provide a heat-resistant stainless steel wire for a heat-resistant spring that has excellent sag resistance in a high temperature range.

  Another object of the present invention is to provide a heat-resistant spring excellent in sag resistance in a high temperature range and a method for producing the same.

  Usually, in order to improve the spring characteristics, in steel wires such as stainless steel wires, as shown in Patent Documents 3 and 4, it is a technical problem how to reduce the crystal grain size of the steel wire as a material. In the field of heat-resistant stainless steel wires, technology development to improve sag resistance is being advanced based on this concept.

  Here, “sag” means that when stress is applied above a certain temperature, dislocations existing in the structure of the steel wire move / disappear on the surface of the steel wire or grain boundaries, resulting in plastic deformation. It is a phenomenon that appears. Usually, dislocations in the structure of a steel wire are introduced by wire drawing, and distortion occurs around the dislocations, thereby improving the strength and hardness of the steel wire. Further, as the area reduction rate of the drawing process increases, the crystal grain size decreases and more dislocations are introduced, and the strain tends to increase. For this reason, by reducing the crystal grain size and increasing the strain, the elastic limit of the steel wire is increased, and plastic deformation hardly occurs even when a high load is applied. .

  However, as a result of diligent research by the present inventors, dislocation movement due to stress is likely to occur in a high-temperature environment that has not been assumed in the past such that the maximum use temperature reaches 550 ° C. It was found that no positive correlation was observed between the amount of (strain) introduced and sag resistance, and rather when more dislocations (strain) were introduced into the structure, the sag resistance decreased. The present inventors have obtained knowledge that it is useful to increase the average crystal grain size of the heat-resistant stainless steel wire beyond a certain level.

  The present invention has been made based on the above findings. The present invention will be described in detail below.

[Heat resistant stainless steel wire]
The heat-resistant stainless steel wire of the present invention is, in mass%, C: 0.04 to 0.08%, Si: 0.60 to 1.40%, Mn: 0.5 to 3.0%, Cr: 16 to 20%, Ni: 7.0 to 10.5, and N: It contains 0.16 to 0.25%, the balance is made of Fe and inevitable impurities, and the average crystal grain size in the cross section is 8 μm or more and 20 μm or less.

  The heat resistant stainless steel wire of the present invention is an austenitic stainless steel wire. Intrusion-type solid solution elements such as C and N dissolve in the base austenite phase (γ phase), and in addition to solid solution strengthening, which generates and strengthens strain in the crystal lattice, anchors dislocations in the structure. And an effect of improving strength (Cottrel effect) can be expected. Moreover, the effect of improving heat resistance can be expected when a ferrite-forming element such as Si is dissolved.

  Moreover, by setting the average crystal grain size in the cross section of the steel wire to 8 μm or more and 20 μm or less, a heat resistant stainless steel wire having excellent sag resistance in a high temperature range can be obtained. By setting the average crystal grain size to 8 μm or more, it is possible to suppress dislocations from moving to and disappearing from the crystal grain boundaries as much as the distance of dislocations increases, thereby improving sag resistance at high temperatures. In addition, as the crystal grain size increases, dislocation migration and annihilation can be suppressed, so that improvement in sag resistance can be expected at high temperatures. However, in the case of an exhaust system device attached to an automobile engine, for example, the operating temperature is low at the start of the engine, and the spring used in such a device is stressed even in a normal temperature environment. To sag resistance at high temperatures. Usually, when the crystal grain size is increased, sufficient strain is not introduced, and mechanical properties such as tensile strength near room temperature are lowered, so that sufficient sag resistance cannot be exhibited at room temperature. Therefore, the upper limit of the average crystal grain size is set to 20 μm. A more preferable upper limit of the average crystal grain size is 16 μm.

  In addition, in this invention, a cross section is a cross section cut | disconnected in the direction orthogonal to the longitudinal direction of a steel wire. The average crystal grain size is a value obtained by observing a cross-sectional structure with an optical microscope, obtaining a length between intersections with a crystal grain boundary on a straight line in an arbitrary visual field, and averaging the lengths.

<Chemical component>
The heat-resistant stainless steel wire of the present invention contains C, Si, Mn, Cr, Ni and N as chemical components, with the balance being Fe and inevitable impurities. The reasons for limiting each chemical component will be described below.

  C has the effect of increasing the strength by forming interstitial solid solution in the crystal lattice and generating strain. C also has the effect of forming a Cottrell atmosphere and fixing dislocations in the structure. Furthermore, it combines with Cr and the like contained in the steel wire to form carbides, thereby increasing the high temperature strength. However, if Cr carbide is excessively present in the grain boundary, the Cr diffusion rate in the γ phase is slow, so a Cr-deficient layer is formed in the vicinity of the grain boundary, resulting in a decrease in toughness and corrosion resistance. Therefore, the effective content is defined as 0.04 to 0.08 mass%. In order to obtain a tensile strength that improves the spring load characteristics, it is preferable that the amount be 0.06 to 0.07% by mass or more.

  Si has the effect of improving heat resistance by being dissolved. In addition, Si functions as a deoxidizer during melting and refining of steel, and is required to be 0.60% by mass or more in order to obtain an effect of improving heat resistance by solid solution strengthening. However, it is 1.40% by mass or less because it causes toughness deterioration.

  Mn functions as a deoxidizer during steel melting and refining. Mn is also effective for stabilizing the γ phase and can be an expensive alternative element for Ni. Furthermore, there is an effect of increasing the solid solubility limit of N in the γ phase. However, in order to cause deterioration of oxidation resistance at high temperatures, the content was set to 0.5 to 3.0% by mass. In particular, when emphasizing corrosion resistance, the Mn content is preferably 0.5 to 2.0 mass%. On the other hand, when increasing the solid solubility limit of N, that is, in order to reduce the number of micro blowholes of N as much as possible, when the Mn content is set to 2.0 to 3.0% by mass, the intended effect can be easily obtained. However, in this case, since the corrosion resistance is slightly affected, the content of Mn may be adjusted according to the purpose and application.

  Cr is a main additive element of stainless steel, and is effective in improving corrosion resistance, heat resistance and oxidation resistance. Therefore, Ni equivalent and Cr equivalent are calculated from other chemical components of the steel wire, and in order to obtain necessary heat resistance in consideration of the stability of the γ phase, it is set to 16% by mass or more. However, to cause deterioration of toughness, the content was set to 20% by mass or less.

  Ni is a main additive element of austenitic stainless steel effective for stabilizing the γ phase. However, when the N content is 0.2% by mass or more, a large amount of Ni causes blowholes. In this case, addition of Mn having a high affinity for N is effective, and in order to suppress the generation of blowholes as much as possible, it is necessary to adjust the Ni content in consideration of the Mn content. Therefore, it is set to 7.0% by mass or more for stabilizing the γ phase, and 10.5% by mass or less for suppressing blowhole generation and cost increase. The Ni content is preferably 7.0 to 10.5% by mass, but if it is less than 10.0% by mass, N can be easily dissolved in the melting / casting process. It is advantageous.

  N, like C, is an interstitial solid solution element and a Cottrell atmosphere forming element, and contributes to solid solution strengthening and strengthening by the Cottrell effect. N also has the effect of increasing the high-temperature strength by combining with Cr or the like contained in the steel wire to form a nitride. However, there is a limit (solid solubility limit) for solid solution in the γ phase, and addition of a large amount (0.2% by mass or more) of N causes blowholes during melting and casting. Blowholes can be controlled to some extent by increasing the solid solubility limit by adding elements with high affinity for N, such as Cr and Mn, but adding a large amount (over 0.25 mass%) of N Since it is necessary to strictly control the temperature and atmosphere at the time of melting, the manufacturing cost increases. Therefore, the effective content is defined as 0.16 to 0.25% by mass.

  Furthermore, the heat resistant stainless steel wire of the present invention preferably contains 0.4 to 2.0 mass% of Mo.

  Mo can be expected to have an effect of improving heat resistance by dissolving in the same manner as Si. Mo is a substitutional solid solution in the γ phase, and greatly contributes to the improvement of high-temperature tensile strength and sag resistance. Therefore, in order to obtain the effect of improving sag resistance, the content is set to 0.4% by mass or more. However, addition of a large amount causes deterioration of spring workability and an increase in raw material cost, so it was made 2.0% by mass or less.

<Production conditions>
In order to obtain a heat-resistant stainless steel wire having an average crystal grain size of 8 μm or more and 20 μm or less as defined in the present invention, for example, it can be realized by controlling (1) drawing process conditions and (2) solution heat treatment conditions. Specifically, in order to increase the average grain size of crystal grains to a certain level or more, the area reduction rate in the drawing process is lowered, the heating temperature in the solution heat treatment is increased, or the holding time is lengthened. Can be mentioned.

(1) Drawing process conditions The final area reduction rate in the drawing process (total area reduction ratio when the wire rod is drawn once or more to make a steel wire) is preferably 20 to 60%, more preferably 30 to 50%. When the area reduction rate is within the above range, it is easy to control the average crystal grain size defined in the present invention. However, even when the area reduction rate is out of the above range, the average crystal grain size defined in the present invention can be controlled depending on the solution heat treatment conditions described later.

  In addition, since the size of the wire before the drawing process is industrially standardized, if the surface reduction rate of the drawing process is reduced, the crystal grain size in the steel wire tends to increase as a result.

(2) Solution heat treatment conditions The heating temperature in the solution heat treatment is preferably 950 to 1200 ° C, particularly preferably 1000 to 1150 ° C. As the heating means, for example, atmospheric heating or high-frequency heating can be used. Moreover, it is preferable to set suitably holding time according to the wire diameter of a steel wire, and 0.5-10 minutes are preferable in the case of high frequency heating. Usually, the higher the heating temperature or the longer the holding time, the more crystal grains grow and the crystal grains become coarser. Therefore, it is preferable that the holding time is 1 minute or more when the heating temperature is less than 1000 ° C., and the holding time is 5 minutes or less when the heating temperature exceeds 1150 ° C. Of course, depending on the drawing process conditions described above, the heating temperature can be lowered within the above range.

By the way, when the crystal grain size is controlled by the drawing process conditions or the solution heat treatment conditions, it is considered that the mechanical properties such as tensile strength are affected. Therefore, the steel wire of the present invention, in consideration of the workability of the spring, the tensile strength is preferably satisfies the 1000 N / mm ² or more 1600 N / mm ² or less. Here, the tensile strength is the tensile strength at room temperature of the steel wire after the solution heat treatment and the drawing process and before the spring process or annealing process.

[Heat resistant spring]
The heat-resistant spring of the present invention is produced using the above-described heat-resistant stainless steel wire of the present invention, and has excellent sag resistance in a high temperature range. Further, after the spring processing, heat treatment such as strain relief annealing or nitriding treatment may be performed as necessary.

[Method of manufacturing heat-resistant spring]
The heat-resistant spring manufacturing method of the present invention is characterized in that after the above-described heat-resistant stainless steel wire of the present invention is spring-processed, low-temperature annealing is performed for 1 minute to less than 1 hour under conditions of 500 ° C. or higher and 650 ° C. or lower.

  By carrying out the low temperature annealing under the above conditions after the spring processing, the sag resistance in the high temperature region can be further improved. The annealing temperature is preferably set to a temperature equal to or higher than the operating temperature range (maximum operating temperature). This is because dislocations are more likely to move when stress is applied in a high-temperature environment. Therefore, annealing above the operating temperature range is performed in advance to promote the movement and disappearance of dislocations. This is to make it difficult to occur. On the other hand, when the annealing temperature is higher than 650 ° C., the introduced strain is released too much, and the sag resistance decreases from room temperature to high temperature range. Therefore, the annealing temperature was set to 500 ° C. or higher and 650 ° C. or lower. In consideration of the effect of improving sag resistance by annealing and the productivity of springs, the annealing time was set to 1 minute or more and less than 1 hour.

  The heat resistant stainless steel wire and heat resistant spring of the present invention have an average crystal grain size of 8 μm or more and 20 μm or less in the cross section, and are excellent in sag resistance in a high temperature range. In particular, it can exhibit excellent sag resistance even at high temperatures of 450 ° C or higher. The heat-resistant spring manufacturing method of the present invention can manufacture a heat-resistant spring having excellent sag resistance.

(Example 1)
Various stainless steels having chemical components shown in Table 1 were melted and cast, subjected to forging and hot rolling, and processed into wires. Thereafter, solution heat treatment and wire drawing were repeatedly performed on the wire, and processed into a heat-resistant stainless steel wire having a wire diameter of 3.0 mm to prepare various stainless steel test pieces. Here, the drawing process conditions [area reduction: 40%] and the solution heat treatment conditions [heating temperature: 1100 ° C., holding time: 1 minute] were used.

  About each produced test piece, the average crystal grain diameter and the tensile strength were measured. The results are shown in Table 2. In addition, the measuring method of an average crystal grain diameter and tensile strength is as follows.

  The average crystal grain size is measured from a photomicrograph taken at 1000 × magnification after electrolytic etching of the cross section of the test piece cut in the direction perpendicular to the longitudinal direction. Specifically, in a field of view of 60 mm × 80 mm on the photograph, vertical, horizontal, and two diagonal straight lines are drawn so as to pass through the center. And the length between the intersections of a straight line and a grain boundary is calculated | required in each straight line, the average is calculated, and the total average in all the straight lines is calculated. This is the average crystal grain size in this cross section. Here, measurement is performed on three cross sections, and the average of all three cross sections is defined as the average crystal grain size of each test piece.

  Tensile strength is measured at room temperature after leaving the specimen at room temperature (25 ° C) for 15 minutes or longer. The tensile strength is measured before and after low-temperature annealing of the test piece [annealing temperature: 500 ° C., annealing time: 20 minutes].

  Next, each test piece (not annealed) was subjected to spring processing to obtain a compression coil spring having the specifications shown in Table 3, and then the spring was subjected to low temperature annealing to obtain a sample. Here, low-temperature annealing conditions were set [annealing temperature: 500 ° C., annealing time: 20 minutes].

  Each sample subjected to low temperature annealing was evaluated for sag resistance. In addition, the evaluation method of sag resistance evaluates by calculating | requiring the residual shear strain in a high temperature range (400-550 degreeC). Here, as shown in FIG. 1, the residual shear strain is a constant load applied to the sample S (see FIG. 1A) at room temperature (load shear stress: 500 MPa). The test is held for 24 hours at each test temperature of 400 ° C, 450 ° C, 500 ° C and 550 ° C (see (B)). Then, release the load (strain) at room temperature (see (C)), and calculate from the amount of spring sag. The results are shown in Table 4.

Specifically, the residual shear strain (%) is obtained by the following equation.
(Formula) ... residual shear strain (%) = 8 / π × (P1-P2) × D / (G × d 3) × 100
However,
d (mm): Wire diameter
D (mm): Average coil diameter
P1 (N): Load equivalent to a stress of 500 MPa
P2 (N): Load when compressing to displacement a (mm) after the test (see Fig. 1 (D))
a (mm): Displacement when P1 is loaded before the test (see Fig. 1 (B))
G: Lateral elastic modulus (Here, the value of 6.9 × 10 ⁴ for a general stainless steel wire for springs is used)
P1 and P2 are both measured at room temperature.

  Moreover, when the average crystal grain size was measured for each sample, it was confirmed that the average crystal grain size was almost the same as that of each test piece before spring processing.

  From the results of Table 4, it can be seen that Samples 1-1 and 1-2 have small residual shear strain (%) and excellent sag resistance at each test temperature of 400 to 550 ° C. In particular, it exhibits excellent sag resistance even in a high temperature range of 450 ° C. or higher, and is considered to be sufficiently usable even in a high temperature environment reaching 550 ° C. It can also be seen that by adding Mo, the sag resistance can be improved.

  Moreover, when each sample was evaluated for sag resistance at room temperature, it was confirmed that each sample had sufficient sag resistance.

(Example 2)
Various test pieces having different average crystal grain sizes were produced mainly by changing the solution heat treatment conditions of Example 1. Here, in the same manner as in Example 1, after steel A and B in Table 1 were processed into wire rods, solution heat treatment and wire drawing were repeated under the wire drawing conditions and solution heat treatment conditions shown in Table 5, A test piece was prepared.

  About each produced test piece, it carried out similarly to Example 1, and measured the average crystal grain diameter and the tensile strength. The results are shown in Table 6.

  Moreover, after producing the compression coil spring of each test piece and carrying out low temperature annealing similarly to Example 1, the sag-proof property of each sample was evaluated. The results are shown in Table 7.

  From the results in Table 6, it can be seen that the tensile strength tends to increase as the average crystal grain size decreases. However, from the results of Table 7, it can be seen that samples satisfying an average crystal grain size of 8 to 20 μm have high sag resistance in a high temperature range of 450 to 550 ° C. and excellent sag resistance. In contrast, a sample having an average crystal grain size of less than 8 μm has high tensile strength, but has a high degree of sag in a high temperature range of 450 ° C. or higher. On the other hand, a sample having an average crystal grain size of more than 20 μm has low sag resistance at each test temperature and does not have sufficient sag resistance at high temperatures. For example, regarding Steel A in Table 7, Samples 2-3A and 2-4A having an average crystal grain size of 8 to 20 μm have a residual shear strain (%) of 0.6 or less at each test temperature of 400 to 550 ° C. It can be seen that compared to other samples, it is difficult to sag particularly in a high temperature range of 450 ° C. or higher. Regarding steel B, samples 2-2B, 2-3B, and 2-4B with an average crystal grain size of 8 to 20 μm have a residual shear strain (%) of 0.55 or less at each test temperature of 400 to 550 ° C. It can be seen that compared to other samples, it is difficult to sag particularly in a high temperature range of 450 ° C. or higher.

  Each sample was evaluated for sag resistance at room temperature. Samples 2-5A, 2-6A, 2-5B, and 2-6B with an average crystal grain size of more than 20 μm had sufficient sag resistance. It was confirmed that it does not have.

(Example 3)
Various test pieces having different average crystal grain sizes were produced mainly by changing the drawing process conditions of Example 1. Here, in the same manner as in Example 1, after steel B in Table 1 was processed into a wire rod, solution heat treatment and wire drawing were repeatedly performed under the wire drawing conditions and solution heat treatment conditions shown in Table 8, and various test pieces were obtained. Was made.

  About each produced test piece, it carried out similarly to Example 1, and measured the average crystal grain diameter. The results are shown in Table 9. Moreover, after producing the compression coil spring of each test piece and carrying out low temperature annealing similarly to Example 1, the sag-proof property of each sample was evaluated. The results are also shown in Table 9.

  From the results of Table 9, it can be seen that the average crystal grain size of the steel wire can be controlled even if the drawing condition (area reduction ratio) is changed. Even in this case, the sample with an average crystal grain size of 8 to 20 μm has higher sag resistance at high temperatures (500 ° C.) than the sample with an average crystal grain size of less than 8 μm. It can be seen that it has excellent sag resistance.

Example 4
In order to investigate the influence of the low-temperature annealing conditions, a compression coil spring of a test piece having an average grain size of 12 μm using the steel B of Table 1 as a material was prepared in the same manner as in Example 1, and then shown in Table 10. Various samples were prepared by low-temperature annealing at each annealing temperature. About each produced sample, it carried out similarly to Example 1, and evaluated sag-proof property. The results are also shown in Table 10. The annealing time was 20 minutes in all cases.

  From the results in Table 10, it can be seen that when the test temperature is 500 ° C., a large effect of improving sag resistance is obtained when the annealing temperature is set to 500 ° C. or higher and 650 ° C. or lower. In particular, when the annealing temperature is 600 ° C., the effect of improving sag resistance is large. Further, even when the test temperature was 400 to 550 ° C, the same tendency as when the test temperature was 500 ° C was observed. On the other hand, when the annealing temperature was higher than 650 ° C., it was confirmed that the sag resistance decreased from room temperature to a high temperature range, and the effect of improving the sag resistance could not be sufficiently obtained.

  From the above results, it can be seen that the heat-resistant stainless steel wire and heat-resistant spring of the present invention have high heat resistance, and are excellent in sag resistance from room temperature to high temperature. In particular, it exhibits excellent sag resistance even in a high temperature range of 450 ° C. or higher, and can be used sufficiently even in a high temperature environment reaching 550 ° C. Moreover, according to the manufacturing method of the heat-resistant spring of this invention, it turns out that the big improvement effect of sag resistance is acquired.

  Note that the present invention is not limited to the above-described embodiment, and can be modified as appropriate without departing from the gist of the present invention. For example, the chemical composition of the steel wire may be changed as appropriate, or the drawing process conditions and the solution heat treatment conditions may be changed as appropriate.

  The heat-resistant stainless steel wire, heat-resistant spring and manufacturing method thereof of the present invention can be suitably used for spring parts that require heat resistance, for example, exhaust parts for automobile engines, as well as electrical equipment parts (such as springs for breakers).

It is a figure for demonstrating the evaluation method of sag resistance.

Explanation of symbols

S sample (compression coil spring)

Claims (4)

Containing 0.04 to 0.08% by mass, Si: 0.60 to 1.40%, Mn: 0.5 to 3.0%, Cr: 16 to 20%, Ni: 7.0 to 10.5, and N: 0.16 to 0.25%, the balance Consists of Fe and inevitable impurities,
A heat-resistant stainless steel wire having an average crystal grain size in a cross section of 8 μm to 20 μm.   Furthermore, Mo: 0.4-2.0% is contained by the mass%, The heat-resistant stainless steel wire of Claim 1 characterized by the above-mentioned.   A heat-resistant spring manufactured using the heat-resistant stainless steel wire according to claim 1.   A method for producing a heat-resistant spring, comprising: heat-treating the heat-resistant stainless steel wire according to claim 1 or 2;

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