KR101615844B1 - High-strength stainless steel wire having excellent heat deformation resistance, high-strength spring, and method for manufacturing same - Google Patents

Abstract

The high strength stainless steel wire is characterized in that it comprises 0.02 to 0.12% of C, 0.005 to 0.03% of N, 0.05 to 0.3% of C, 0.1 to 2.0% of Si, 0.1 to 2.0% of Mn, 6.8 to 9.0%, Cr: 12.0 to 14.4%, Mo: 1.0 to 3.0% and Al: 0.5 to 2.0%, the balance being Fe and inevitable impurities, the machined organic martensite- , The amount of the processed organic martensite is 80 to 99 vol%, and the tensile strength is 1800 to 2200 MPa. MdS = 551-462 (C + N) -9.2Si-8.1Mn-29 (Ni + Cu) -13.7Cr-18.5Mo

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a high-strength stainless steel wire, a high strength spring,

The present invention relates to a high-strength stainless steel wire used as a heat-resistant steel wire material for heat-resistant springs, heat-resisting ropes, and the like, as well as components that require high strength characteristics in addition to heat resistance of automobile engine exhaust system parts and electric parts. The present invention relates to a precipitation hardening type metastable austenitic high strength stainless steel wire having a metal structure on austenite (γ) phase + machined organic martensite (α '), which is obtained by adding Mo, Al, The fine precipitates are controlled by the above-mentioned method. Particularly, the present invention relates to a high-strength heat-resistant stainless steel wire, a high-strength spring using the same, and a method of manufacturing the same.

The present application claims priority based on Japanese Patent Application No. 2012-076870 filed on March 29, 2012 and Japanese Patent Application No. 2013-62817 filed in Japan on Mar. 25, 2013 And the contents are used here.

Conventionally, piano wires and high strength stainless steel wires such as SUS304 and SUS301 have been used as materials for high strength springs. However, conventional spring products have sufficient strength at room temperature. However, in the piano wire, for example, in the warm range of the environmental temperature of about 100 ° C to 300 ° C, the heat distortion resistance is rapidly lowered to 0.01% or more due to the residual shear deformation described later, and the application is limited. This tendency is also true in the case of a stainless steel wire, and therefore, an austenitic stainless steel wire containing, for example, Mo, Al, Ti or the like has been proposed (Patent Documents 1 and 2). By such composition adjustment, the heat resistance is improved. However, since the amount of the processed organic martensite is small and the tensile strength is less than 1800 MPa, the strength becomes insufficient, so that it is difficult to say that it is sufficient as a product for high strength springs.

Further, a martensitic stainless steel strength using precipitation hardening such as Mo and Al has been proposed (Patent Document 3). However, the stainless steel has a high C content and is already in the form of martensite after the heat treatment, so that the workability is poor and a large work hardening can not be expected, so that the strength of the high strength spring product is not sufficient.

Further, a precipitation hardening type austenitic steel having high strength using precipitation hardening such as Mo, Al, Cu and the like has been proposed (Patent Document 4). However, this stainless steel contains a large amount of Ni and Cu, so that the material cost is high. Further, this stainless steel suppresses the processed organic martensite, and it is difficult to satisfy the heat resistant deformation.

Thus, in the conventional stainless steel wire for high strength springs, strength and thermal deformation resistance can not be combined.

Japanese Patent No. 4163055 Japanese Unexamined Patent Application Publication No. 10-68050 Japanese Patent No. 3482053 Japanese Patent No. 4327601

It is an object of the present invention to provide a high-strength stainless steel wire having high strength characteristics and sufficient heat-resistant deformation even under the temperature environment, in particular, for a heat-resistant material widely used in the warm region, And a method of manufacturing the same.

As a result of various investigations to solve the above problems, it has been found that, in the precipitation hardening type metastable austenitic stainless steel wire, it is effective to significantly increase strength and heat resistance deformation by the following matters, The invention was obtained.

1) A large amount of the processed organic martensite (orthoformed martensite) structure is formed from the austenite main body by steel working such as cold drawing before controlling the austenite stability and forming by a spring shape or the like. Thus, strength is improved while maintaining ductility.

2) 0.05? (C + N)? 0.13, the ductility is secured while maintaining the strength.

3) Al and Mo are added, and Ni, Al, and Mo-based fine compounds are uniformly dispersed in the steel-processed processed organic martensite structure, particularly in the vicinity of the steel wire surface layer, by combination of the steelmaking process and aging heat treatment conditions.

That is, one aspect of the present invention has the following requirements.

(C + N)? 0.13%, Si: 0.1 to 2.0%, Mn: 0.1 to 2.0%, C: 0.02 to 0.12%, and N: 0.005 to 0.03% 6.8 to 9.0% of Ni, 12.0 to 14.4% of Cr, 1.0 to 3.0% of Mo and 0.5 to 2.0% of Al, the balance being Fe and inevitable impurities,

Wherein the processed martensite-forming index MdS value represented by the formula (1) is 15 to 60, the amount of the processed organic martensite in the matrix is 80 to 99 vol%, and the tensile strength is 1800 to 2200 MPa. Excellent high strength stainless steel wire.

However, the symbol of the element in the mathematical expression means the content (% by mass) of the element.

(2) A steel material which further contains at least one of V: 0.01 to 1.0%, Nb: 0.01 to 1.0%, Ti: 0.01 to 1.0%, W: 0.05 to 2.0% and Ta: 0.05 to 2.0% (1), wherein the heat-resistant stainless steel wire has excellent heat resistance and heat resistance.

(1) or (2), further comprising at least one of Cu: not more than 0.8%, Co: 0.1 to 2.0%, and B: 0.0005 to 0.015% High strength stainless steel wire with excellent deformability.

(1) to (3), further comprising at least one of Ca: 0.0005 to 0.01%, Mg: 0.0005 to 0.01%, and REM: 0.0005 to 0.1% A high strength stainless steel wire having excellent heat distortion resistance as described in item (1).

(5) When the above stainless steel wire is held between the gauge distances of 100 times the equivalent wire diameter and twisted at one end thereof is twisted, the twist rotation value leading to the break without longitudinal cracks is 5 times (1) to (4), wherein the high-strength stainless steel wire has high torsional rotation characteristics.

(6) The stainless steel wire subjected to the aging heat treatment, wherein the stainless steel wire satisfies the component composition, the amount of the processed organic martensite and the MdS value described in any one of (1) to (4) Strength stainless steel wire excellent in heat-resistant deformation.

(7) A proof stress ratio (σ _0.2 / σ _B ) × 100 of a tensile strength (σ _B ) and a 0.2% proof stress (σ _0.2 ) of 80 to 95% Resistant stainless steel wire according to any one of (1) to (6).

(8) A stainless steel wire according to any one of (1) to (7), characterized in that the residual shear strain epsilon represented by the formula (2) at an environmental temperature of 200 DEG C satisfies? High-strength spring with superior heat-resistant deformation.

(N / mm < 2 >), where D is the center diameter of the spring (mm), d is the equivalent wire diameter (mm)

(9) The high-strength spring according to (8), wherein the matrix of the steel wire has NiAl-based fine compound particles having a particle diameter of 50 nm or less.

(10) A process for producing a stainless steel wire according to any one of claims 1 to 7, wherein the stainless steel wire is produced by subjecting a predetermined equivalent wire diameter to a cold working of 60 to 90% at a total working ratio after the heat treatment for solidification, And a step of performing an age heat treatment at a temperature of 300 to 600 占 폚.

(11) The aging heat treatment is performed under the condition that the aging heat treatment factor of the following formula (3) is 100 to 10000, whereby NiAl-based fine compound particles having a particle diameter of 50 nm or less are precipitated in the matrix of the steel wire (10), which is excellent in thermal deformation resistance.

The high strength stainless steel wire of the precipitation hardening type excellent in thermal deformation resistance according to an embodiment of the present invention has a high amount of processed organic martensite (? ') And a predetermined tensile strength in the drawing step. Further, the high-strength stainless steel wire according to one embodiment of the present invention promotes the formation of a fine compound, particularly the precipitation of a fine compound uniformly dispersed in the surface layer of the steel wire, by subjecting it to a spring shape and then an aging heat treatment. As a result, it is possible to further impart high-strength, and particularly heat-resistant deformation in the warm region. Therefore, it is possible to provide a high-strength spring product having high strength and excellent heat-resistant deformation that has been difficult to achieve at the same time. Therefore, the high strength stainless steel wire according to one embodiment of the present invention is particularly suitable for high strength springs which require strict quality characteristics.

Further, according to the method of manufacturing a spring according to one aspect of the present invention, it can be carried out within the range of ordinary low-temperature heat treatment, and can be stably carried out without involving any special increase in cost due to serialization.

Fig. 1 is an enlarged view of a wavefront obtained by a twisting test. Fig. 1 (a) shows a good torsional wavefront, and Fig. 1 (b) shows a twisted wavefront.
Fig. 2 is an explanatory diagram for explaining a method of measuring a spring characteristic, in which (a) is a spring before a compression load is applied, (b) is a spring in a state in which a compression load is applied, State.
3 is a photomicrograph and an example of a molecular model of NiAl showing an example of the state of production of the precipitation compound by the aging heat treatment. (a) is a bright field image, (b) is a diffraction image field, (c) is a dark field image field, and (d) is a molecular model of NiAl with a B2 structure.
Fig. 4 is a diagram showing an example of the evaluation result, wherein (a) shows the relationship between the aging heat treatment temperature and the tensile strength, and (b) shows an example of the relationship between the aging heat treatment temperature and the residual shear strain characteristics.

The high-strength stainless steel wire excellent in thermal deformation resistance according to the present embodiment contains 0.02 to 0.12% C, 0.005 to 0.03% N, 0.05%? (C + N)? 0.13% 2.0 to 2.0% of Mn, 6.8 to 9.0% of Ni, 12.0 to 14.4% of Cr, 1.0 to 3.0% of Mo and 0.5 to 2.0% of Al, with the balance being Fe and inevitable impurities. (Hereinafter simply referred to as " production index ") MdS value of the processed organic martensite (? ') Production index expressed by the following formula (1) is 15 to 60.

The amount of the processed organic martensite (? ') In the matrix is 80 to 99 vol%, and the tensile strength is 1800 to 2200 MPa. The high-strength stainless steel wire of the present embodiment is a high-strength heat-resisting stainless steel wire, and is suitable, for example, as a wire rod for a spring, particularly as a wire rod to be used in a warm range at an environmental temperature of 100 to 300 占 폚.

[Equation 1]

However, the symbol of the element in the mathematical expression means the content (% by mass) of the element. In the case where an element necessary for calculation is not included or an element whose content is unclear is present, 0 shall be substituted as the content of the element.

The shape of the stainless steel wire is not particularly limited, and the stainless steel wire of the present embodiment may be a conventional wire, for example, a wire having a wire diameter of 6 mm or less, more specifically about 0.05 to 3 mm It is used for many purposes. The shape of the stainless steel wire of the present embodiment is not particularly limited, and the stainless steel wire of the present embodiment is used as a wire material having a non-circular shape such as a flat wire or a square wire in addition to a round wire. However, the present invention is not limited thereto, and can be applied in various forms. As described above, the shape of the stainless steel wire according to the present embodiment includes a wire having a non-circular cross-sectional shape, and the wire diameter is, for example, an equivalent wire diameter d calculated from an arbitrary cross- .

In the present embodiment, a description will be given centering on the case where the wire is manufactured by drafting. However, a composite process in which, for example, a rolling process and a drawing process are combined may be employed.

Further, the stainless steel wire has a precipitation hardening function, and fine compound particles are precipitated and distributed in the matrix by the aging heat treatment performed in the final stage. In the present embodiment, precipitation elements such as Al and Mo are added to the composition so that the precipitation hardening function is exhibited, and appropriate amounts of N and C are added. Then, NiAl and Mo-based compound particles are uniformly dispersed and precipitated on the machined organic martensite in the vicinity of the surface layer of the steel wire subjected to the steel drawing process under the drawing conditions such as cold drawing or cold rolling. As a result, it is possible to provide a heat resistant spring product having high strength and excellent heat distortion resistance.

It is generally known that austenitic stainless steels are hardened by cold working, and one of the factors is influenced by the processed organic martensite which is accompanied by the processing. However, the amount of organic generation (amount of produced organic martensite) varies greatly depending on the balance of the composition of each element constituting the organic martensite and the processing conditions thereof. For example, in the case of the stable SUS316 stainless steel, the amount of the processed organic martensite is only about several percent even when the ordinary processing is performed. On the other hand, in the present embodiment, the composition is adjusted so as to actively promote the production of machined organic martensite following cold working, and to increase the production amount to 80 to 99 vol%. As a result, the tensile strength of the steel wire itself is made high in the range of 1800 to 2200 MPa in a cold working state such as drawing, and this is one of the characteristics of the present embodiment.

As another means for improving the heat resistance of the spring product in addition to the high strength property, the composition is adjusted so that the machined organic martensite formation index MdS value is 15 to 60, and the stainless steel is subjected to a drawing process under specific processing conditions . As a result, the generation of the processed organic martensite serving as the precipitation nuclei of the fine precipitates is promoted. The generation index MdS value is a balance index of each component composition.

The MdS value means a temperature at which 50% of the structure is transformed into a martensite phase when a tensile strain of 30% is given to stainless steel, and the level of the amount of the processed organic martensite produced by the processing It is to grasp in relation.

As a result, the amount of the processed organic martensite at the time of drawing processing can be increased, contributing to the enhancement of the strength.

In the present embodiment, the reason why the MdS value is set in the above range is that if the MdS value is less than 15, the stabilization of the austenite phase is increased and the amount of the processed organic martensite after drawing is lowered to less than 80 vol%, making it difficult to increase the strength. Also, the precipitation strengthening amount accompanying the aging heat treatment at 300 to 600 占 폚 is also reduced, and the heat distortion resistance is also deteriorated. On the other hand, when the MdS value exceeds 60, a surplus processed organic martensite exceeding 99 vol% is produced in a predetermined drawing process, and the soft toughness after the drawing is lowered, resulting in poor productivity. More preferably, the range of the MdS value is 20 to 50.

By adjusting these components, the stainless steel wire of the present embodiment enables the amount of the processed organic martensite to be in the range of 80 to 99 vol%, thereby improving each characteristic. That is, when the amount of the processed organic? '(Martensite) in the matrix is less than 80 vol%, the required high strength characteristics can not be obtained even when aging heat treatment is performed on the spring product. On the contrary, when the content of the processed organic? '(Martensite) exceeds 99 vol%, the corrosion resistance and toughness are hardly satisfied due to the structural stability. It is also expected that the spring fatigue resistance is inferior. The amount of the processed organic martensite is preferably 83 vol% or more, more preferably 85 vol% or more. The amount of the processed organic martensite is preferably 95 vol% or less, more preferably 90 vol% or less.

[Measurement of martensite amount]

As a method for measuring the amount of martensite, various methods such as a ferrite-scoped method, a magnetic method, and an X-ray method can be employed, and measurement is performed on a test piece taken arbitrarily from a stainless steel wire. For example, the Japanese Iron and Steel Association "Iron and Steel" (81-S1163) and so on are described in detail.

In the present embodiment, the amount of machined organic martensite (? ') Was calculated by measuring the saturation magnetization value at 1.0 × 10 ⁴ Oe of the wire material in the direct current magnetic fluxmeter and using the following equations (4) to (6).

σ _{s is the} saturation magnetization value (T), σ _s (bcc) is the saturation magnetization value (calculated value) when 100% of the tissue is α 'transformed.

However, the symbol of the element in the mathematical expression means the content (% by mass) of the element.

Thus, the stainless steel wire has high strength characteristics with a tensile strength (σ _B ) in the cold drawn state of 1800 to 2200 MPa. The tensile strength can be measured by, for example, JIS-Z2241. When the tensile strength is less than 1800 MPa, it is impossible to expect a significant improvement in the strength characteristics even by the subsequent aging heat treatment. Further, when the tensile strength exceeds 2200 MPa, there is a problem in terms of quality, such as an increase in the deviation of the spring shape in the spring forming step and a tendency to cause brittle fracture. A more preferable tensile strength is 1900 to 2100 MPa.

On the other hand, when the cold drawn steel wire of the present embodiment is subjected to the age heat treatment, the strength characteristics are further improved remarkably. Depending on the conditions of the aging heat treatment, a preferable value of tensile strength of 2100 to 2600 MPa is obtained. Therefore, for example, in the application in which the spring-type product is used in a linear state such as a part for a micro-shaft, it is also possible to perform a calibration treatment subsequent to the above-described drawing and to continuously heat- In this respect, the mechanical properties in the wire state can be further increased. These processes can be performed continuously.

The present embodiment also includes stainless steel wires subjected to aging heat treatment after cold drawing as other forms. The tensile strength in the case of aging heat treatment is 2100 to 2600 MPa, more preferably, the lower limit of the tensile strength is 2200 MPa, and the more preferable upper limit is 2500 MPa. The conditions of the aging heat treatment on the steel wire can be appropriately set so that the tensile strength after the aging heat treatment falls within the above range. As an example, the condition of the aging heat treatment after the spring forming can be mentioned as will be described later.

Further, the obtained tensile strength (σ _B) and with a tensile strength (σ _B) and the 0.2% yield strength (σ _0.2) strength ratio _{{(σ 0.2 / σ B)} × 100} of. It is preferable that this proof stress ratio is 80 to 95%. Such a stainless steel wire is effective as a material for a heat-resisting spring for improving high strength and fatigue fracture. Further, when the proof stress ratio is less than 80%, a predetermined elastic property can not be obtained. When the proof stress ratio exceeds 95%, there is a fear that adverse effect is exerted on the yield in severe spring working. A more preferable lower limit of the proof stress ratio is 83%, and a more preferable upper limit is 91%.

[Twisting test 1]

Another characteristic for evaluating the spring workability is the torsional rotation characteristic measured by the following twist test. The torsional rotation characteristic is measured as follows. The test specimen taken from the stainless steel wire is twisted and rotated at one end side while being held between the gauge distances of 100 times the equivalent wire diameter. Then, measure the number of times of warping until the stainless steel wire is broken. The number of times this twist (twist rotation value) is the twist rotation characteristic. For example, cold-worked stainless steel wires can be widely used as various spring products when they have high torsional rotation characteristics of 5 or more times, for example, 5 to 10 times or more without longitudinal cracks.

In the stainless steel wire subjected to the aging heat treatment and the stainless steel wire having an electric strength ratio exceeding 95%, the twisting rotation characteristic is only about two or three times, or longitudinal cracks are likely to occur. As a result, for example, in the case of machining with a coil spring having a ratio D / d of the line diameter d to the average coil diameter D of not more than 4 times, in the case of spring working under severe conditions, There is a concern. That is, although the spring forming is possible irrespective of the twist rotation value, it is more preferable that the stainless steel wire showing the twist rotation value five times or more without vertical cracks is preferable for the spring forming, and the twisting rotation value is six times or more.

[Twisting test 2]

In the twisting test 2, for example, as described in JIS-G4314, the stainless steel wire is twisted and rotated until it is broken. Then, the toughness of the stainless steel wire is evaluated by observing the fracture surface.

Fig. 1 shows an example of a fractured section. Fig. 1 (a) shows a roughly uniform fracture surface. On the other hand, FIG. 1 (b) shows that a part of the cross section is twisted and broken, and the brittle is broken. In a stainless steel wire in which a good fracture surface such as electrons is obtained, the number of times of warping can be satisfied.

Next, the reasons for limiting each constituent element of the stainless steel wire to be subjected to the present embodiment will be described. Further, in the present embodiment, when there is no particular period, the content unit of the element is mass%.

C is added in an amount of 0.02% or more (hereinafter, all in mass%) in order to obtain high strength after drawing. However, when C is added in an amount exceeding 0.12%, it is sensitized and not only the corrosion resistance is deteriorated but also the composition is deteriorated. For this reason, the upper limit of the amount of C is set to 0.12%. The amount of C is preferably less than 0.10%, more preferably 0.04 to 0.09%.

N is an element contributing to strength and has the effect of forming a carbonitride and reducing the grain size of the material before cold working at the time of the solid solution heat treatment. Therefore, 0.005% or more of N is added. However, if N is added in an amount exceeding 0.03%, formation of coarse nitride such as AlN and deterioration of soft toughness are caused, and the composition is markedly deteriorated. Therefore, the upper limit of the amount of N is set to 0.03%. The preferred lower limit of the N content is 0.01%, and the preferable upper limit is 0.025%.

C and N are all intrinsic elements, which produce deformation and contribute to consolidation of solids which acts on consolidation. Further, C and N have the effect of forming a cotrel atmosphere and fine carbonitride and fixing the potential in the metal structure. In order to obtain these effects, C and N are added in a total amount (C + N) of 0.05% or more. However, when C and N are added in a total amount (C + N) of more than 0.13%, the soft toughness is deteriorated. As a result, the upper limit of C + N is set to 0.13%. The preferable range of C + N is 0.08 to 0.11%.

Si is added by 0.1% or more for deoxidation. However, when Si is added in an amount exceeding 2.0%, the effect is saturated and the upper limit of the amount of Si is set to 2.0% in view of deterioration of the composition. A preferable range of the amount of Si is 0.3 to 1.0%.

Mn is added by 0.1% or more for deoxidation. However, when Mn is added in an amount exceeding 2.0%, the corrosion resistance is deteriorated. In addition, the amount of the processed organic martensite (? ') Is lowered so that not only the strength is lowered but also the heat distortion resistance is deteriorated. For this reason, the upper limit of the amount of Mn is set to 2.0%. The preferable range of the Mn content is 0.5 to 1.5%.

Ni is added in an amount of 6.8% or more in order to ensure soft toughness of the material and obtain an appropriate amount of processed organic martensite by drawing. However, when Ni is added in an amount exceeding 9.0%, the MdS value is lowered, and the amount of the processed organic martensite is lowered, whereby the strength is lowered. Also, the heat resistant deformability is deteriorated. Therefore, the upper limit of the amount of Ni is set to 9.0%. The preferable range of the amount of Ni is more than 7.0% and not more than 8.5%, and more preferably 7.5 to 8.2%.

Cr is added in an amount of not less than 12.0% in order to ensure corrosion resistance and to obtain an appropriate amount of processed organic martensite. However, when Cr is added in an amount exceeding 14.4%, the MdS value is lowered and the amount of the processed organic martensite is lowered and the strength is lowered. Also, the heat resistant deformability is deteriorated. Therefore, the upper limit of the amount of Cr is set to 14.4%. The preferable range of Cr content is 13.0 to 14.0%.

Mo is dissolved in the austenite parent phase to increase the hardness of the parent phase and to relax the thermal deformation due to the temperature rise during use. Further, by the aging heat treatment at 300 to 600 占 폚 in the production of the spring, Mo causes fine Mo clusters of metal clusters to be precipitated in the processed organic martensite. As a result, the strength is increased and the thermal deformation resistance is improved. Therefore, Mo is an element effective for increasing the strength and improving the thermal deformation resistance, and 1.0% or more of Mo is added. However, when Mo is added in an amount exceeding 3.0%, the effect is saturated and the MdS value also decreases. As a result, the amount of the processed organic martensite is lowered, not only the strength is lowered but also the heat distortion resistance is deteriorated. Therefore, the upper limit of the amount of Mo is set to 3.0%. The preferred range of the amount of Mo is 1.5 to 2.6%, more preferably 1.7 to 2.3%.

Al finely precipitates a fine NiAl intermetallic compound in the processed organic martensite by aging heat treatment at, for example, 300 to 600 占 폚 when the spring is produced. As a result, the strength is increased and the thermal deformation resistance is improved. Therefore, Al is an element effective to increase the strength and improve the thermal deformation resistance, and it is added by 0.5% or more. However, even if Al is added in an amount exceeding 2.0%, the effect is saturated and the composition is deteriorated. Therefore, the upper limit of the amount of Al is set to 2.0%. The preferable range of the amount of Al is 0.7 to 1.5%, more preferably 0.9 to 1.2%.

The stainless steel wire contains these constituent elements and is subjected to component adjustment such that the MdS value is 15 to 60, with the balance being Fe and unavoidable impurities. The inevitable impurities include, for example, 0.001 to 0.01% of O, 0.001 to 0.01% of Zr, 0.001 to 0.1% of Sn, 0.00005 to 0.01% of Pb, 0.00005 to 0.01% of Bi, Zn: 0.0005 to 0.01%, substances contained in raw materials or refractories, etc., and a total amount of not more than 2.0% is allowed.

In addition to the above constituent elements, the present embodiment may further contain any one or more of the following elements.

The first group includes V, Nb, Ti, W, and Ta, and each of these elements forms fine carbonitride. As a result, these elements contribute to the enhancement of the thermal deformation resistance as well as the strengthening of the crystal grains by making them finer. The effect is preferably 0.01 to 1.0% (preferably 0.05 to 0.6%), Nb: 0.01 to 1.0% (preferably 0.05 to 0.4%), Ti: 0.01 to 1.0% (preferably 0.02 to 0.2% ), W: 0.05 to 2.0% (preferably 0.05 to 0.5%) and Ta: 0.05 to 2.0% (preferably 0.1 to 0.5%). However, when an amount exceeding each upper limit is added, the carbonitride coarsens and the composition is lowered. Therefore, it is more preferable to carry out the above-mentioned preferred range.

In the second group, there are the following elements, and these elements enhance the effect of side effects such as corrosion resistance, toughness and workability of the stainless steel wire. As a result, the addition of any one or more of the following elements is permitted, if necessary.

Cu is an element effective for improving the corrosion resistance and is added as needed. However, when Cu is added in an amount exceeding 0.8%, the work hardening is reduced to not only soften but also deteriorate the thermal deformation resistance. Therefore, the upper limit of the amount of Cu is set to 0.8% or less. The preferable range of the amount of Cu is 0.1 to 0.6%.

Co secures soft toughness and improves thermal deformation resistance, so if necessary, it is added by 0.1% or more. However, when Co is added in an amount exceeding 2.0%, the strength is lowered and thermal deformation resistance deteriorates, so the upper limit of the amount of Co is set to 2.0%. The preferred range of the amount of Co is 0.5% to 1.5%.

Further, B improves the hot workability and toughness of the stainless steel, so if necessary, B is added in an amount of 0.0005% or more. However, when boron is added in an amount exceeding 0.015%, boride is produced, and on the contrary, the soft toughness is lowered and the composition is deteriorated. Therefore, the upper limit of the amount of B is set to 0.015%. The preferable range of the amount of B is 0.001 to 0.01%.

As the third group, Ca, Mg, and REM are selected. These elements may be contained for deoxidation. If necessary, at least one of Ca: 0.0005 to 0.01%, Mg: 0.0005 to 0.01% and REM: 0.0005 to 0.1% is added. However, if it is added in excess of each upper limit, coarse inclusions are formed and the composition is lowered.

In this embodiment, it is also preferable to adjust P and S as other elements to a specific range from the viewpoint of hot workability and soft toughness. As the allowable range, P is 0.015 to 0.045%, and S is 0.0001 to 0.01%. The reduction more than necessary is rather a factor of cost increase. On the other hand, if it is contained in a large amount, nonmetallic inclusions may cause deterioration of quality. Of these groups, elements may be selected and added from a single group, but elements may be selected from any two or more groups.

The stainless steel wire of the present embodiment thus configured is manufactured, for example, by the following method. Casting and hot rolling are performed on the cast piece having the predetermined component composition to obtain a lot wire member. Subsequently, the lot wire rod is subjected to cold working while being repeatedly subjected to cold working. In addition, a solid solution heat treatment may be performed between cold working steps. By this triple curing, a stainless steel wire having a target wire diameter can be obtained. The cold working includes the above drawing or rolling, for example, continuous drawing using a draw die or roller dies, or rolling using a rolling roller. Particularly, in the cold working after the final heat treatment for solidification, the total machining ratio can be set to 60 to 90%. This makes it possible to realize the machined organic martensite (α ') amount and tensile strength in the matrix defined in the present embodiment, and to realize the twist rotation value and the proof stress ratio of the stainless steel wire similarly defined in the present embodiment. The final cold milling rate is preferably about 65 to 85%, more preferably 70 to 83%, and it is preferable to perform the final cold mill within a range in which the total machining rate is relatively suppressed.

As a more preferable form of these cold working, it is preferable to adjust the processing temperature so that the surface temperature of the final finishing die or the steel wire on the inlet side of the final roll becomes 70 占 폚 or less (preferably 10 to 50 占 폚) Do. In addition, it is preferable to carry out surface-uniform steel machining with a machining rate of 20% or less, preferably 10% or less, in the final finishing dies or final rolling. Thereby, the heat-resistant deformability can be further improved.

By controlling the surface temperature of the steel wire at the inlet side of the final finishing die and the machining rate at the final finishing die or final rolling, the heat resistant deformability is further improved. This mechanism is unclear at this point. The inventors of the present invention observed and compared the vicinity of the surface layer of the steel wire after the aging heat treatment after the steel wire in the case of controlling these conditions and the steel wire in the case of not controlling them. As a result, it was found that the fine compounds were uniformly distributed in the case where the above conditions were controlled. From this, it can be inferred that the more uniform precipitation of the fine compound in the vicinity of the surface layer of the steel wire affects the improvement of the further improvement of the thermal deformation resistance.

If necessary, it is also effective to increase the lubricity by applying Ni plating or the like to the surface of the stainless steel wire, thereby improving the yield.

The machining rate is expressed by the rate of change of the area of the cross section of the stainless steel wire following the machining, and is calculated by the following equation.

Processing rate (%) = {(cross sectional area before machining - cross sectional area after machining) / cross sectional area before machining} x 100

[Manufacturing method of spring product]

Next, the spring product of the present embodiment will be described. The spring product is made of the stainless steel wire of the present embodiment and is formed in various shapes such as a coil spring, a torsion spring, and a linear spring. Further, by performing the later-described aging heat treatment, the spring characteristics can be improved. In the present embodiment, the spring characteristic is set based on the environmental temperature of 200 占 폚, and the residual shear strain at that temperature is 0.008% or less, in view of the premise that it is used in the warm region.

The heat-resistant deformability of the spring characteristic may appear as a load loss. For example, a height corresponding to a certain stress (for example, 400 MPa) as shown in Fig. 2, and is heated under predetermined environmental test conditions while maintaining this state. Subsequently, the load loss is calculated by dividing the load difference of the load load corresponding to the spring height before and after the test by the load load before the test.

However, the load loss measured by this method depends on the shape of the spring, and is not necessarily standard. For this reason, in the present embodiment, the residual shear strain is used instead of the load loss. The environmental temperature is also set at 200 占 폚 as described above.

The residual shear strain epsilon is defined as follows. And applies a constant load or torque to the predetermined spring to deform it. Then, the load or torque is removed. The residual shear strain when the load or torque is removed is the residual shear strain epsilon, and is calculated, for example, by the following equation (7). That is, for example, in the case of a compression coil spring, a predetermined compressive load is applied to the coil spring as shown in FIG. 2, and the spring height is displaced from S to S1. While maintaining this state, the temperature is heated to 200 占 폚. Subsequently, it is cooled to room temperature to release the compression load. Then, the spring height when the compression load is released is S0, and the load loss? P is calculated by using the load when the spring height returns from S1 to S0. More specifically, the spring height S1 when the compression load shown in Fig. 2 (b) is loaded is set to a predetermined set height. Fig. 2 (c) shows a spring after being heated in a state where a predetermined compression load is applied, then cooled, and the compression load is released, and the spring height is S0. 2 (a) shows a spring before test in which a predetermined compressive load is applied, and a spring height is S. In Fig. For each of the springs of Figs. 2 (a) and 2 (c), the load necessary to displace the spring to the height of S1 is measured by a spring load tester. The difference between their required loads is calculated, and the value is defined as a load loss (DELTA P). Then, the residual shear strain epsilon is calculated from the following equation (7) using the load loss. The thermal deformation resistance can be evaluated from the residual shear strain epsilon.

P: Load loss (N)

D is the center diameter (mm) of the spring, and as shown in Fig. 2 (a), the distance between the center points of the opposing steel wires.

d: equivalent wire diameter of steel wire (mm)

G: Transverse elastic modulus of steel wire (N / mm 2), (MPa)

BACKGROUND ART [0002] Conventionally, in a spring product, for example, a heat setting process is performed in order to alleviate the deterioration of function in use. In a spring product having a residual shear strain of 0.008% or less and excellent thermal deformation resistance, there is an advantage that the heat setting treatment can be omitted. The more preferable residual shear strain is 0.005% or less.

In order to further improve such a spring characteristic, it is recommended to perform aging heat treatment, for example. Specifically, the spring product is heat-treated at a predetermined temperature in advance to uniformly deposit the fine compound particles in the structure of the stainless steel wire, particularly in the vicinity of the surface layer. In the aging heat treatment, a heating time of, for example, about 300 to 600 DEG C, preferably about 3 to 10 hours is set. As a result, for example, fine and hard compounds as shown in Fig. 3 can be formed and distributed. As a result, the residual shear deformation of the high-strength spring specified in the present embodiment can be realized. Particularly, it is desired to adjust the component in advance so that the stainless steel wire is subjected to a steel working so that the above-mentioned compound precipitates and becomes precipitation hardening type stainless steel.

More preferred conditions of the aging heat treatment are shown below. The shape and distribution state of the compound particles precipitated by the age heat treatment are affected by the volume and shape of the spring product. It is preferable to adjust the set temperature and the heating time in consideration of the volume and shape of the spring product. For example, it is preferable to adjust the set temperature and the heating time so that the aging heat treatment factor in the following formula (3) becomes 100 to 10000, preferably 150 to 3000.

&Quot; (3) "

The development path is the entire length of the stainless steel wire constituting the spring product.

By this aging heat treatment, the desired compound precipitates in the matrix, and the material properties are improved.

When the heating temperature of the aging heat treatment is less than 300 ° C, even if heated for a long time, no compound is formed sufficiently. When the heating temperature of the aging heat treatment exceeds 600 ° C, the stainless steel wire is softened and the strength tends to be lowered. The aging heat treatment is more preferably performed at about 400 to 580 캜. In addition, the state of formation and precipitation of the compound also depends on the heating time, and the particle diameter and density change. For this reason, it is preferable to perform heating for at least 3 minutes. And the appropriate range of heating temperature and time is set by the above-mentioned Equation (3). A more preferable suitable range of the heating temperature is 400 to 550 占 폚.

In addition, from the viewpoint of the extremely fine nature of the compound, it is difficult to specify the existence of the compound in most of the above-mentioned conditions of the aging heat treatment, but it can be confirmed by a three-dimensional atom probe or a transmission electron microscope. Particularly, since the temperature of the aging heat treatment is high and the heating time is long, the compound grows slowly, so that it becomes possible to confirm the presence of the compound by a transmission electron microscope under processing conditions near the upper limit.

For example, FIG. 3 (a) is a photograph showing a cross section of a stainless steel wire obtained by an aging heat treatment at 600 ° C. for 30 minutes at a high magnification. A fine compound of NiAl having an average particle diameter of 50 nm or less is precipitated at a high density in a matrix of martensite. 3 (b) is the electron diffraction pattern thereof, and it was confirmed that the compound had a B2 structure. The average particle diameter of the compound is represented by, for example, an average value of the particle diameters of the respective compound particles identified in an arbitrary observation field of the diffraction image, and the more optimal particle diameter is 20 nm or less.

FIG. 3 (a) is a bright field image of a transmission electron microscope of a thin film sample taken from a stainless steel wire, and shows an image of a processed organic martensite structure. 3B shows the diffraction image (Fourier transformed structure of the sample) of the region. In addition to the BCC structure of the processed organic martensite, the presence of NiAl having the B2 structure as shown in FIG. 3 (d) Can be confirmed. FIG. 3 (c) shows a dark field illuminated only by the NiAl precipitate of the B2 structure. Further, the compound particles tend to be more uniformly distributed by controlling the surface temperature of the steel wire on the inlet side of the final finishing die described above and the machining rate in the final finishing die or final rolling.

As described above, the form and the distribution state of the compound largely depend on the heating temperature, the heating conditions, the processing conditions of the steel wire, and the constituent elements. For example, when heated at high temperature or heated for a long time, the reaction is promoted, thereby increasing the particle diameter of the compound and increasing the density. Therefore, it is preferable to carry out a pretreatment so as to obtain the desired state of compound formation.

In other stainless steel wire and piano wire which have been used conventionally, preheating adjustment (heat setting) process is carried out before using the spring. On the other hand, the spring product obtained by this embodiment has high strength and excellent heat distortion resistance. Therefore, it is expected that cost reduction by omitting the preheating adjustment (heat setting) process is expected. As described above, in a spring product made of a piano wire, the property deteriorates in a warm region in a slightly heated state. On the other hand, the stainless steel wire of the present embodiment is suitable for a heat-resistant spring product in a warm area in a slightly heated state. Further, the stainless steel wire of the present embodiment is expected to be applied to heat resistance applications such as general high temperature environment applications of 400 DEG C or higher, and its application range is expanded.

Hereinafter, the embodiment of the present embodiment will be described further.

Example 1

"Manufacture of stainless steel wire"

Table 1 and Table 2 show the chemical composition of the stainless steel used as an example, and the comparative steels are also described. In Table 1 and Table 2, underlines are displayed in numerical values deviating from the range defined in the present embodiment.

These chemical components were dissolved in a vacuum melting furnace, cast into a casting piece having a diameter of 178 mm, and the cast piece was made into a rod steel having a diameter of 62 mm by hot forging. Subsequently, the sheet was heated to 1250 占 폚 using a hot extrusion simulator and extruded to obtain a wire having a diameter of 10.7 mm. Thereafter, solution treatment and pickling were carried out, and the product was fresh to φ5.5 mm, and was made into a wire.

Then, using this as a raw material, cold drawing and solidification heat treatment were repeatedly conducted to form a soft wire having a wire diameter of 2.2 mm. Subsequently, as a final cold drawing process, a hard fine wire having a diameter of 1.0 mm (fresh material) was obtained. In addition, final cold drawing processing was performed at a final total drawing processing rate of 80%. Further, the reduction ratio (processing rate) of the fresh die at the final finishing was adjusted to 8 to 25%, and the surface temperature of the steel wire at the inlet side of the die was adjusted to 0 to 80 캜. Then, a Ni plating layer having a thickness of 1.2 占 퐉 was formed on the surface of the processed steel wire (fresh material).

In the present invention according to the present embodiment, high-strength fine wires having a tensile strength of 1800 to 2200 MPa (N / mm < 2 >), a proof stress ratio of 80 to 95%, and a torsional rotation value of 5 or more were obtained . The amount of the processed organic martensite (? ') Was 80 to 95 vol%.

The tensile strength and the 0.2% proof stress were measured by JIS-Z2241. The amount of the treated organic martensite was measured by the magnetic method described in [Measurement of the amount of martensite]. The torsional rotation value was measured by the method described in [Torsion Test 1] and [Torsion Test 2] above. The results are shown in Tables 3 and 4.

Example 2

"Verification of aging characteristics"

Subsequently, each stainless steel wire (fresh material) after the final drawing process of Example 1 was cut into a length of 150 mm in order to evaluate the change of characteristics of each stainless steel wire (fresh material) by the aging heat treatment of the above- To obtain a sample. Then, the sample was subjected to an age heat treatment at 500 DEG C for 30 minutes. The aging heat treatment factor represented by the formula (3) was 612.

Then, the tensile strength, the proof stress, the proof stress ratio, the twist rotation value, and the stiffness of the stainless steel wire (fresh and aged heat treatment material) after the age heat treatment were evaluated. The results are shown in Table 5 and Table 6. The stiffness was evaluated by a twist pendulum method.

The aged heat treated steel wire of the present invention example according to the present embodiment had excellent strength properties with a tensile strength of 2100 to 2600 MPa, a proof stress ratio of 80 to 95%, and a stiffness of 77000 MPa or more. In addition, observation of any arbitrary cross section with a microscope revealed that the precipitation compound containing NiAl particles having an average particle diameter of about 3 to 10 nm could be confirmed as in Fig.

With regard to the twist rotation value, in the stainless steel wire subjected to the aging heat treatment, longitudinal cracks occurred at all five beating times.

Example 3

"Verification of Spring Products"

Then, in order to further verify the effect of Example 2, each stainless steel wire (fresh material) before the aging heat treatment was subjected to coiling processing, and the average coil diameter was 7 mm, the number of effective winding turns was 4.5, 25 mm, and a developing length of 100 mm. Subsequently, an aging heat treatment was performed at 500 캜 for 30 minutes. Then, the heat resistance of the actual spring product was evaluated. The heat-resistant deformation (residual shear strain) was measured by the method described in the above-mentioned [Method of Manufacturing Spring Products]. Specifically, while maintaining a state of applying a compressive stress of 600 MPa, it was held at 200 캜 for 96 hours. Then, the residual shear strain epsilon was calculated by Equation (7).

The obtained results are shown in Tables 5 and 6. All of the examples of the present invention were confirmed to have a residual shear strain of 0.008% or less, high strength and excellent heat distortion resistance. On the other hand, in the comparative example, all the specimens except for No. 51 were large in residual shear strain exceeding 0.008%. Therefore, the effect of the present embodiment has been recognized. Further, No. 51 had a small residual shear strain but was insufficient in strength.

The manufacturability was evaluated as inability to manufacture when cracking, breakage, or breakage occurred in wire rod steel rolling, drawing, or spring working. In the present invention, it was possible to manufacture spring products without any problems.

Example 4

"Effect of aging conditions"

Next, in order to evaluate the influence of the conditions of the aging heat treatment of the stainless steel wire and the spring material (compression coil spring) described above, AP steels of inventive steels A and D steels and comparative steels of Table 2 were prepared. Then, a cold-drawn stainless steel wire having a diameter of 1.0 mm was produced by the method described in " Production of stainless steel wire " In addition, a compression coil spring before the aging heat treatment was produced from a cold-drawn stainless steel wire by the method described in " Verification of Spring Product " Subsequently, the cold-drawn stainless steel wire and the compression coil spring were subjected to an age heat treatment at a temperature of 250 to 650 占 폚 for 2 minutes to 10 hours. Then, the tensile strength of the stainless steel wire after the aging heat treatment and the thermal deformation resistance of the compression coil spring were evaluated. The results of the part are shown in Table 7, Fig. 4 (a) and Fig. 4 (b).

The tensile strength showed a peak particularly near the temperature of 450 to 550 占 폚, and slightly softened at 600 占 폚. Similarly, with respect to the residual shear strain, all of the characteristics of about 0.008% or less were obtained, but it was found that the characteristics were slightly lowered in the temperature range up to about 600 캜. In addition, in the case where the aging heat treatment factor is about 150 to 825, the residual strain property is 0.005% or less, which is very preferable.

Example 5

Subsequently, the A and D steels shown in Table 1 were drawn by the method described in Example 1, and soft wires having a diameter of 1.8 mm were collected. A lubricant of a metal soap was applied to the surface of the soft wire, followed by a fine-diameter machining with a cold drawing device to obtain a hard fine wire having a wire diameter of 1.0 mm. Subsequently, the steel sheet was subjected to cold rolling by a multi-stage rolling apparatus, and finally pressed to a thickness of 0.2 mm to produce a hard flat wire. In this rolling process, an optimal cooling method was adopted so that the surface temperature of the steel wire at the entrance side of the rolling roll of the final finishing was 45 占 폚.

The total machining ratio after the heat treatment for solidification was 83%, and it was confirmed that the stainless steel wire had good workability because there was no trouble such as material cracking and disconnection accompanied by the above-mentioned multi-step cold rolling.

Then, in order to evaluate the characteristics when the flat wire was processed into a spring product, the surface adhesion lubricant was first removed with a solvent. Subsequently, an aging heat treatment was performed at 500 캜 for 30 minutes in the same manner as in Example 2, and the characteristics of the flat lines before and after the heat treatment were evaluated.

The results are shown in Table 8.

Here, the tensile strength was evaluated by a tensile test method in the same manner as in Example 1. The residual shear strain was evaluated as follows at a temperature of 200 ° C as in Example 3, as follows. Torsional stress was applied to both ends of the flat line having a predetermined length. The temperature was maintained at 200 캜 while maintaining this state. Subsequently, the torsional stress was released by cooling to room temperature, and the residual shear strain was evaluated by a change in the return angle at that time.

Specifically, in the same manner as in the case of the spring, the residual shear deformation of the flat line was calculated using the load loss, the elastic modulus and the cross sectional area. Also, in the case of the flat line, the load loss was measured as follows, which is different from that in the case of the spring. An arbitrary distance in the range of, for example, about 5 to 50 times the width dimension of the flat flat line was set as the gauge distance. A predetermined stress was applied to both ends of the flat line having the length of the gauge distance and twisted. The temperature was maintained at 200 캜 while maintaining this state. And then cooled to room temperature to release the stress. The load required to obtain the same twist angle was measured for each of the flat line after the series of operations and the flat line before the operation (initial test). The difference between these loads was calculated, and the value was used as a load loss (DELTA P).

As shown in this result, the flat line of the stainless steel has excellent mechanical properties which can be used, for example, as a spring material for a web spring. In addition, the surface property thereof was favorable because a bright surface excellent in smoothness was obtained along with the fine crystal grains.

As described above, the stainless steel wire according to the present embodiment has a tensile strength of 1800 to 2200 MPa in a state of being drawn. The amount of the processed organic martensite is 80 to 99 vol%. As a result, the spring characteristics are greatly improved by the subsequent aging heat treatment. In particular, high strength and excellent heat distortion resistance are obtained. Therefore, the stainless steel wire of the present embodiment is applied to various spring products such as compression coil springs, tension coil springs, torsion springs, and the like, and a spring product having high strength and excellent heat resistance can be obtained.

As a specific application, for example, it is suitable to be applied to a spring product used in a hot zone of a warm state such as an engine or an electric system of an automobile, and a heat resistant spring for use in household appliances. In addition to these, the present embodiment is also applicable to a linear product having various high strength and heat resistance such as heat-resistant high-strength ropes, heat-resistant shafts, and heat-resistant fins used in high temperature regions, and is industrially useful.

Claims (23)

(C + N)? 0.13%, Si: 0.1-2.0%, Mn: 0.1-2.0%, Ni: 6.8% , Cr: 12.0 to 14.4%, Mo: 1.0 to 3.0% and Al: 0.5 to 2.0%, the balance being Fe and inevitable impurities,
Characterized in that the processed organic martensite generation index MdS value represented by the formula (1) is 15 to 60, the amount of the processed organic martensite in the matrix is 80 to 99 vol%, and the tensile strength is 1800 to 2200 MPa. High strength stainless steel wire for excellent heat-resistant material.
[Equation 1]

However, the symbol of the element in the mathematical expression means the content (% by mass) of the element. Further, when Cu is not contained, Cu in the formula (1) is zero. The method according to claim 1,
A high strength stainless steel wire for a heat resistant material having excellent heat resistance and deformability, which further contains at least one selected from the following group A to C.
A: V: 0.01 to 1.0%, Nb: 0.01 to 1.0%, Ti: 0.01 to 1.0%, W: 0.05 to 2.0%, Ta: 0.05 to 2.0%
Group B: at most 0.8% of Cu, 0.1 to 2.0% of Co, and at least one of B and 0.0005 to 0.015%.
Group C: Ca: 0.0005 to 0.01%, Mg: 0.0005 to 0.01%, REM: 0.0005 to 0.1% of the total amount. 3. The method according to claim 1 or 2,
When the twist test in which the stainless steel wire is held between the gauge distances of 100 times the equivalent wire diameter and is twisted at one end thereof is performed, the twist rotation value leading to the break without vertical cracks is 5 or more Wherein the heat-resistant stainless steel wire has excellent heat resistance and rotational characteristics. Characterized in that the stainless steel wire is a stainless steel wire subjected to an age heat treatment and satisfies the component composition, the amount of processed organic martensite, and the MdS value described in the item 1 or 2, and the tensile strength is 2100 to 2600 MPa. High Strength Stainless Steel Wire for Heat-Resistant Material with Excellent Heat-Resistance Deformation. 3. The method according to claim 1 or 2,
, And a proof stress {(? _0.2 /? _B ) 占 100} of a tensile strength? _B and a 0.2% proof stress? (? _0.2 ) of 80 to 95% High Strength Stainless Steel Wire for Heat-Resisting Material with Excellent Deformability. The method of claim 3,
, And a proof stress {(? _0.2 /? _B ) 占 100} of a tensile strength? _B and a 0.2% proof stress? (? _0.2 ) of 80 to 95% High Strength Stainless Steel Wire for Heat-Resisting Material with Excellent Deformability. 5. The method of claim 4,
, And a proof stress {(? _0.2 /? _B ) 占 100} of a tensile strength? _B and a 0.2% proof stress? (? _0.2 ) of 80 to 95% High Strength Stainless Steel Wire for Heat-Resisting Material with Excellent Deformability. A stainless steel wire according to any one of claims 1 to 3, characterized in that a residual shear strain epsilon represented by the formula (2) at an environmental temperature of 200 DEG C is subjected to an age heat treatment and satisfies?? 0.008% , High strength spring with excellent heat distortion.
&Quot; (2) "

D: the center diameter of the spring (mm), d: the equivalent wire diameter (mm) of the steel wire, G: the load resistance of the steel wire, Transverse elastic modulus of steel wire (N / mm2) Characterized in that the stainless steel wire according to claim 3 is subjected to an age heat treatment and the residual shear strain ε expressed by the formula (2) at an environmental temperature of 200 ° C. satisfies ε ≦ 0.008% Excellent high strength spring.
&Quot; (2) "

D: the center diameter of the spring (mm), d: the equivalent wire diameter (mm) of the steel wire, G: the load resistance of the steel wire, Transverse elastic modulus of steel wire (N / mm2) Characterized in that the stainless steel wire according to claim 4 is subjected to the age heat treatment and the residual shear strain epsilon represented by the formula (2) at an environmental temperature of 200 DEG C satisfies?? 0.008% Excellent high strength spring.
&Quot; (2) "

D: the center diameter of the spring (mm), d: the equivalent wire diameter (mm) of the steel wire, G: the load resistance of the steel wire, Transverse elastic modulus of steel wire (N / mm2) Characterized in that the stainless steel wire according to claim 5 is subjected to an age heat treatment and the residual shear strain ε expressed by the formula (2) at an environmental temperature of 200 ° C. satisfies ε ≦ 0.008% Excellent high strength spring.
&Quot; (2) "

D: the center diameter of the spring (mm), d: the equivalent wire diameter (mm) of the steel wire, G: the load resistance of the steel wire, Transverse elastic modulus of steel wire (N / mm2) Characterized in that the stainless steel wire according to claim 6 is subjected to the age heat treatment and the residual shear strain ε expressed by the formula (2) at an environmental temperature of 200 ° C. satisfies ε ≦ 0.008% Excellent high strength spring.
&Quot; (2) "

D: the center diameter of the spring (mm), d: the equivalent wire diameter (mm) of the steel wire, G: the load resistance of the steel wire, Transverse elastic modulus of steel wire (N / mm2) Characterized in that the stainless steel wire according to claim 7 is subjected to aging heat treatment and the residual shear strain epsilon represented by the formula (2) at an environmental temperature of 200 DEG C satisfies?? 0.008% Excellent high strength spring.
&Quot; (2) "

D: the center diameter of the spring (mm), d: the equivalent wire diameter (mm) of the steel wire, G: the load resistance of the steel wire, Transverse elastic modulus of steel wire (N / mm2) 9. The method of claim 8,
A high-strength spring excellent in thermal deformation resistance, characterized by comprising NiAl-based fine compound particles having a particle diameter of 50 nm or less in a matrix of a steel wire. 10. The method of claim 9,
A high-strength spring excellent in thermal deformation resistance, characterized by comprising NiAl-based fine compound particles having a particle diameter of 50 nm or less in a matrix of a steel wire. 11. The method of claim 10,
A high-strength spring excellent in thermal deformation resistance, characterized by comprising NiAl-based fine compound particles having a particle diameter of 50 nm or less in a matrix of a steel wire. 12. The method of claim 11,
A high-strength spring excellent in thermal deformation resistance, characterized by comprising NiAl-based fine compound particles having a particle diameter of 50 nm or less in a matrix of a steel wire. 13. The method of claim 12,
A high-strength spring excellent in thermal deformation resistance, characterized by comprising NiAl-based fine compound particles having a particle diameter of 50 nm or less in a matrix of a steel wire. 14. The method of claim 13,
A high-strength spring excellent in thermal deformation resistance, characterized by comprising NiAl-based fine compound particles having a particle diameter of 50 nm or less in a matrix of a steel wire. Casting and hot rolling are performed on a cast piece having the composition described in claim 1 or 2 and satisfying the machined organic martensite generation index MdS value of 15 to 60 expressed by the following formula 1, ;
The cold working and the solid heat treatment are repeatedly performed on the lot wire material, and the total machining ratio in the cold working after the final solidification heat treatment is set to 60 to 90%, whereby the thinned stainless steel wire ;
A step of forming the stainless steel wire into a predetermined spring shape and subsequently carrying out aging heat treatment at a temperature of 300 to 600 占 폚,
A high-strength spring having excellent heat-resistant deformability is produced by these steps, wherein a high-strength spring having a residual shear strain ε expressed by the following formula (2) at an environmental temperature of 200 ° C. satisfies ε≤0.008%.
[Equation 1]

However, the symbol of the element in the mathematical expression means the content (% by mass) of the element. Further, when Cu is not contained, Cu in the formula (1) is zero.
&Quot; (2) "

D: the center diameter of the spring (mm), d: the equivalent wire diameter (mm) of the steel wire, G: the load resistance of the steel wire, Transverse elastic modulus of steel wire (N / mm2) delete 21. The method of claim 20,
Characterized in that NiAl-based fine compound particles having a particle diameter of 50 nm or less are precipitated in the matrix of the steel wire by performing the aging heat treatment under the condition that the aging heat treatment factor of the following formula (3) is 100 to 10000: A method of manufacturing a high strength spring having excellent deformability.
&Quot; (3) "

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