JP6858931B2 - Stainless steel wire and its manufacturing method, and spring parts - Google Patents

Description

The present invention relates to a wire rod for a stainless steel wire, a stainless steel wire and a method for manufacturing the same, and a spring component.

Conventionally, high-strength stainless steel products such as coil springs have been processed and molded using austenitic stainless steel wire rods and steel wires represented by SUS304 and SUS316 as materials. However, the strength characteristics and delamination resistance characteristics of stainless steel products processed and manufactured from the above-mentioned austenitic stainless steel wire rods cannot sufficiently correspond to precision parts, and have a drawback that their applications are limited.

With respect to the above problems, techniques utilizing reinforcement by processing-induced martensite (hereinafter, may be referred to as processing-induced martensite in the present specification) have been studied (for example, Patent Documents 1, 2, and 3).

Japanese Unexamined Patent Publication No. 2001-262281 Japanese Unexamined Patent Publication No. 2005-290538 Japanese Unexamined Patent Publication No. 2005-29893

The invention of Patent Document 1 aims to provide a high-strength semi-stable stainless steel having excellent cold workability, and the inventions of Patent Documents 2 and 3 aim to provide a high-strength stainless steel wire having excellent rigidity. In these inventions, vertical cracking (aging cracking) during cold wire drawing is studied. In Patent Document 3, processing-induced martensite and temperature-controlled wire drawing are combined to improve the wire drawing resistance in vertical cracking, but such a method increases the manufacturing cost.

Here, the stainless steel wire is required to have a property of being hard to peel off when various forces are applied, that is, a delamination resistance property. In particular, automobile parts such as spring parts are required to have excellent characteristics against delamination occurring in the vicinity of the torsional yield point. However, in the inventions of Patent Documents 1 to 3 described above, the delamination resistance property has not been studied at all.

An object of the present invention is to provide a high-strength stainless steel wire having excellent delamination resistance and a method for manufacturing the same.

In order to solve the above problems, the present inventors have repeated studies focusing on the helical dislocation fraction of the austenite phase at a position 200 μm from the surface layer of the stainless steel wire. The spiral dislocation fraction is measured by X-ray diffraction using CuKα rays at a position 200 μm from the surface layer of the steel wire in the L cross section of the steel wire, and is measured (111), (200), (220) (311). ) Is measured, and it can be obtained from the obtained data by using the modified Williamson-Hall equation.

Then, the present inventors have found that excellent delamination resistance characteristics can be obtained when the spiral dislocation fraction is 0.9 or less. As a result of examining the wire drawing conditions for obtaining a steel wire having a spiral dislocation fraction of 0.9 or less, the present inventors have appropriately determined the total surface reduction rate, the number of passes, and the surface reduction rate in the final pass. We found that it was especially important to manage it.
The gist of the present invention is as follows.

(1) By mass%
C: 0.005 to 0.15%,
Si: 0.1-4.0%,
Mn: 0.1 to 8.0%,
Ni: 1.0 to 10.0%,
Cr: 13.0 to 20.0%,
Mo: 0.01 to 3.00%,
Cu: Over 0.80% to 4.00%,
N: 0.005 to 0.20%,
V: 0-2.5%,
B: 0 to 0.012%,
Al: 0-2.0%,
W: 0-2.5%,
Ga: 0-0.0500%,
Co: 0-2.5%,
Sn: 0-2.5%,
Ti: 0-1.0%,
Nb: 0-2.5%,
Ta: 0-2.5%,
Ca: 0-0.012%,
Mg: 0 to 0.012%,
Zr: 0-0.012%,
REM: 0-0.05%,
The rest consists of Fe and unavoidable impurities,
Md30 represented by the following formula (a) is -20 to 40.
Wire rod for stainless steel wire.
Md30 = 551-462 (C + N) -9.2Si-8.1Mn-29 (Ni + Cu) -13.7Cr-18.5Mo ... (a)
However, the element symbol in the formula (a) means the content (mass%) of the element in steel. When the content of the element in the formula (a) is 0%, "0" is substituted for the corresponding symbol and calculated.

(2) By mass%
C: 0.005 to 0.15%,
Si: 0.1-4.0%,
Mn: 0.1 to 8.0%,
Ni: 1.0 to 10.0%,
Cr: 13.0 to 20.0%,
Mo: 0.01 to 3.00%,
Cu: Over 0.80% to 4.00%,
N: 0.005 to 0.20%,
V: 0-2.5%,
B: 0 to 0.012%,
Al: 0-2.0%,
W: 0-2.5%,
Ga: 0-0.0500%,
Co: 0-2.5%,
Sn: 0-2.5%,
Ti: 0-1.0%,
Nb: 0-2.5%,
Ta: 0-2.5%,
Ca: 0-0.012%,
Mg: 0.012%,
Zr: 0-0.012%,
REM: 0-0.05%,
The rest consists of Fe and unavoidable impurities,
Md30 represented by the following formula (a) is -20 to 40.
The process-induced martensite phase is 20 to 95 vol. Has a metallographic structure that is%
The helical dislocation fraction of the austenite phase at a position 200 μm from the surface layer of the steel wire is 0.9 or less.
Stainless steel wire.
Md30 = 551-462 (C + N) -9.2Si-8.1Mn-29 (Ni + Cu) -13.7Cr-18.5Mo ... (a)
However, the element symbol in the formula (a) means the content (mass%) of the element in steel. When the content of the element in the formula (a) is 0%, "0" is substituted for the corresponding symbol and calculated.

In the stainless steel wire of (2) above, it is preferable that the metal structure contains an austenite phase. Further, the stainless steel wire of the above (2) preferably has a tensile strength of 1600 MPa or more and a shear strain rate of generating delamination of 3.0 × 10 ^-4 / s or more.

(3) A method for producing the stainless steel wire of the above (2) by drawing the wire of the above (1).
A method for manufacturing a stainless steel wire, wherein the wire drawing process is performed under the conditions of a total surface reduction rate of 40 to 90%, a number of passes: 7 times or more, and a surface reduction rate of the final pass: 0.5 to 25%.

(4) Spring parts using the stainless steel wire of (2) above.

According to the present invention, it is possible to provide a high-strength stainless steel wire having excellent delamination resistance.

1. 1. Wire rod for stainless steel wire First, the chemical composition of the wire rod for stainless steel wire will be described. In the following description, (%) is mass (%) unless otherwise specified.

C: 0.005 to 0.15%
C is contained in an amount of 0.005% or more in order to obtain high strength after wire drawing. However, if C is excessively contained, vertical cracks occur during wire drawing, and the delamination resistance is deteriorated. Therefore, the C content is set to 0.15% or less. The preferred lower limit is 0.06% and the preferred upper limit is 0.13%.

Si: 0.1-4.0%
Si is contained in an amount of 0.1% or more in order to obtain high strength after wire drawing. However, if Si is excessively contained, the wire drawing workability is deteriorated and the delamination resistance is deteriorated. Therefore, the content thereof is set to 4.0% or less. It is preferably 1.0% or less.

Mn: 0.1 to 8.0%
Mn is an effective alternative element to expensive Ni, and is an element effective for obtaining high strength after wire drawing. Therefore, Mn is contained in an amount of 0.1% or more. However, if Mn is excessively contained, the delamination resistance property of the steel wire is deteriorated, so the content thereof is limited to 8.0% or less. It is preferably 3.0% or less.

Ni: 1.0 to 10.0%
Ni is contained in an amount of 1.0% or more in order to secure delamination resistance. Preferably, the amount of Ni is 4.0% or more. However, if it is excessively contained, the Md30 value in γ becomes low and the production of processing-induced α'effective for strength is suppressed, so that the content is set to 10.0% or less. Preferably, it is 9.0% or less.

Cr: 13.0 to 20.0%
Cr is contained in an amount of 13.0% or more in order to ensure corrosion resistance. The amount of Cr is preferably 15.0% or more. However, if Cr is excessively contained, the delamination resistance property of the steel wire is deteriorated, so that the content is set to 20.0% or less. Preferably, it is 19.0% or less.

Mo: 0.01 to 3.00%
Mo is contained in an amount of 0.01% or more in order to obtain corrosion resistance and delamination resistance. However, if Mo is contained in an excessive amount, the effect is saturated and the delamination resistance property is deteriorated. Therefore, the upper limit is set to 3.00% or less. It is preferably 1.00% or less.

Cu: Over 0.80% to 4.00%
Cu has an effect of lowering the spiral dislocation fraction of the steel wire, and is contained in excess of 0.80%. However, if Cu is excessively contained, the hot workability is deteriorated and the strength is lowered. Therefore, the content thereof is set to 4.00% or less. It is preferably 3.00% or less, more preferably 2.00% or less, still more preferably 1.50% or less.

N: 0.005 to 0.20%
N is contained in an amount of 0.005% or more in order to obtain high strength after wire drawing. However, if N is excessively contained, vertical cracks occur during wire drawing and the delamination resistance is lowered, so the amount of N is set to 0.20% or less. It is preferably 0.10% or less. The amount of N is preferably 0.02 or more.

V: 0 to 2.5%
V may be contained in order to form a carbonitride to make the crystal grain size finer and improve the strength and wire drawing workability of the wire rod and the steel wire. However, if V is excessively contained, coarse inclusions are generated and the wire drawing workability and delamination resistance are deteriorated. Therefore, the upper limit of the content is set to 2.5%. The preferred range is 1.0% or less, and the more preferable range is 0.5% or less. In order to exhibit the above effect, the amount of V is preferably 0.001% or more.

B: 0 to 0.012%
B may be contained because it is effective in improving the grain boundary strength and the strength of the wire rod and the steel wire. However, if B is contained in an excessive amount, the wire drawing workability and the delamination resistance are deteriorated due to the formation of coarse boride. Therefore, the upper limit of the content is set to 0.012%. It is preferably 0.005% or less. In order to exhibit the above effect, the amount of B is preferably 0.001% or more.

Al: 0-2.0%
Al may be included to promote deoxidation and improve inclusion cleanliness levels. However, if Al is excessively contained, the effect is saturated and the strength and delamination resistance characteristics of the material itself are deteriorated. Therefore, the upper limit of the content is set to 2.0%. It is preferably 1.0% or less, and more preferably 0.3% or less. In order to exhibit the above effect, the amount of Al is preferably 0.001% or more.

W: 0-2.5%
Since W is an element effective for improving corrosion resistance, it may be contained. However, if W is excessively contained, the effect is saturated, and on the contrary, the delamination resistance property may be deteriorated. Therefore, the upper limit when it is contained is set to 2.5%. More preferably, it is 2.0% or less, and further preferably 1.5% or less. In order to exert the above effect, the amount of W is preferably 0.05% or more. More preferably, it is 0.10% or more.

Ga: 0-0.0500%
Since Ga is an element effective for improving corrosion resistance, it may be contained. However, if Ga is excessively contained, the hot workability is lowered. Therefore, the upper limit when it is contained is set to 0.0500%. In order to exhibit the above effect, the amount of Ga is preferably 0.0004% or more.

Co: 0-2.5%
Co may be contained because it has an effect of improving the strength of the steel wire. However, if Co is excessively contained, the effect is saturated, and on the contrary, the delamination resistance property of the steel wire may be deteriorated. Therefore, the upper limit when it is contained is set to 2.5%. More preferably, it is 1.0% or less, and further preferably 0.8% or less. In order to exhibit the above effect, the amount of Co is preferably 0.05% or more, and more preferably 0.10% or more.

Sn: 0-2.5%
Since Sn is an element effective for improving corrosion resistance, it may be contained. However, if Sn is contained in an excessive amount, the effect is saturated, and conversely, the delamination resistance property may be deteriorated. Therefore, the upper limit when it is contained is set to 2.5%. More preferably, it is 1.0% or less, and further preferably 0.2% or less. In order to exert the above effect, the Sn amount is preferably 0.01% or more. More preferably, it is 0.05% or more.

Ti: 0-1.0%
Nb: 0-2.5%
Ta: 0-2.5%
Ti, Nb, and Ta may be contained in order to form a carbonitride to make the crystal grain size finer and improve the strength and delamination resistance of the steel wire. However, if each of these elements is excessively contained, coarse inclusions may be formed and the delamination resistance property of the steel wire may be deteriorated. Therefore, the upper limit of the content is 1.0% for Ti, 2.5% for Nb, and 2.5% for Ta. Ti is preferably 0.7% or less, and more preferably 0.5% or less. Nb is preferably 1.5% or less, and more preferably 0.9% or less. Ta is preferably 1.5% or less, and more preferably 0.9% or less. In order to exhibit the above effect, it is preferable that Ti is contained in an amount of 0.01% or more, Nb is contained in an amount of 0.01% or more, and Ta is contained in an amount of 0.01% or more. Ti is preferably 0.03% or more, and more preferably 0.05% or more. Nb is preferably 0.04% or more, and more preferably 0.08% or more. Ta is preferably 0.04% or more, and more preferably 0.08% or more.

Ca: 0 to 0.012%
Mg: 0 to 0.012%
Zr: 0-0.012%
REM: 0-0.05%
Ca, Mg, Zr, and REM may be contained, if necessary, for deoxidation. However, there is a risk that coarse inclusions will be generated and the delamination resistance and wire drawing workability of the steel wire will deteriorate. Therefore, the upper limit of the content is 0.012% for Ca, 0.012% for Mg, 0.012% for Zr, and 0.05% for REM. Ca is preferably 0.010% or less, and more preferably 0.005% or less. The Mg content is preferably 0.010% or less, more preferably 0.005% or less. Zr is preferably 0.010% or less, and more preferably 0.005% or less. The REM is preferably 0.05% or less. In order to exhibit the above effects, it is preferable that Ca is contained in an amount of 0.0002% or more, Mg is contained in an amount of 0.0002% or more, Zr is contained in an amount of 0.0002% or more, and REM is contained in an amount of 0.0002% or more. Ca is preferably 0.0004% or more, and more preferably 0.001% or more. Mg is preferably 0.0004% or more, and more preferably 0.001% or more. Zr is preferably 0.0004% or more, and more preferably 0.001% or more. The REM is preferably 0.0004% or more, and more preferably 0.001% or more.

The chemical composition of the wire rod for stainless steel wire contains each of the above elements, and the balance consists of Fe and unavoidable impurities. Typical unavoidable impurities include O, S, P and the like, which are usually mixed in the range of 0.0001 to 0.1% as unavoidable impurities in the steel manufacturing process.

In addition to the elements described above, they can be contained within a range that does not impair the effects of the present invention. Although other components are not particularly specified in the present invention, it is preferable to reduce P, S, Zn, Bi, Pb, Se, Sb, H and the like, which are general impurity elements, as much as possible. The content ratio of these elements is controlled to the extent that the problem of the present invention is solved, and if necessary, P ≦ 400 ppm, S ≦ 100 ppm, Zn ≦ 100 ppm, Bi ≦ 100 ppm, Pb ≦ 100 ppm, Se ≦ 100 ppm. , Sb ≦ 500 ppm, H ≦ 100 ppm.

Md30 value: -20 to 40
The Md30 value is an index obtained by investigating the relationship between the volume fraction and the composition of the processing-induced martensite after wire drawing, and stably secures high strength and warm relaxation characteristics of the steel wire. Need to be controlled.

The Md30 value is a value obtained from the following formula (a), and when this value in the austenite phase is less than -20, it becomes difficult to generate work-induced α'and the strength characteristics become inferior. On the other hand, when the Md30 value exceeds 40, the austenite phase becomes unstable, and the work-induced martensite phase initially generated in the wire drawing process deteriorates the wire drawing workability and the delamination resistance. Therefore, the Md30 value is limited to -20 or more and 40 or less. Preferably, the lower limit of the Md30 value is 0. The upper limit is 20.
Md30 = 551-462 (C + N) -9.2Si-8.1Mn-29 (Ni + Cu) -13.7Cr-18.5Mo ... (a)
However, the element symbol in the formula (a) means the content (mass%) of the element in steel. When the content of the element in the formula (a) is 0%, "0" is substituted for the corresponding symbol and calculated.

The wire rod according to the present embodiment has the above-mentioned chemical composition and has an Md30 value of -20 to 40. Therefore, when a stainless steel wire is manufactured using the wire rod, the volume fraction of the work-induced martensite phase of the stainless steel wire is 20 to 95 vol. %, Which makes it easier to obtain high-strength stainless steel wire with excellent delamination resistance.

2. Stainless Steel Wire The chemical composition and Md30 value of the stainless steel wire according to the present embodiment are the same as the chemical composition and Md30 value of the wire rod, and thus the description thereof will be omitted.

Process-induced martensite phase: 20-95 vol. %
Regarding the volume fraction of the processing-induced α'of steel wire, 20 vol. If it is less than%, strength characteristics cannot be obtained. Therefore, the machining-induced α'fraction of the steel wire of the present invention is 20 vol. % Or more. On the other hand, the volume fraction of the processing-induced α'is 95 vol. If it exceeds%, the upper limit is set to 95 vol. In order to reduce the wire drawing workability and delamination resistance. % Or less. Preferably, 30 vol. % Or more. Further, preferably, 70 vol. % Or less.

Since the process-induced martensite phase has ferromagnetism and the austenite phase is paramagnetic, an electromagnetic measurement method is used to measure the phase ratio, and the process-induced martensite phase is referred to as vol. Can be calculated in%. Even if the unavoidable precipitate phase is present, 1.0 vol. % Or less, very small compared to the process-induced martensite and austenite phases. Therefore, 1.0 vol. Of the unavoidable impurity phase. Since% can be ignored, the vol% of the austenite phase can be changed from 100% to the vol. Of the process-induced martensite phase. The value is obtained by subtracting%.

Spiral dislocation fraction of the austenite phase at a position 200 μm from the surface layer of the steel wire: 0.9 or less The spiral dislocation fraction of the austenite phase at a position 200 μm from the surface layer of the steel wire contributes to the delamination resistance. If the spiral dislocation fraction becomes excessively high, it becomes difficult to deform and the delamination resistance characteristics deteriorate. Therefore, the upper limit is set to 0.9 or less. It is preferably 0.8 or less, more preferably 0.7 or less, still more preferably 0.6 or less. It is not necessary to set the lower limit of the spiral dislocation fraction, but if it is too low, the strength may deteriorate. Therefore, the spiral dislocation fraction is preferably 0.001 or more. The preferred lower limit is 0.01 and the more preferred lower limit is 0.05.

Tensile strength: If the tensile strength of the steel wire is 1600 MPa or more and less than 1600 MPa, the strength deteriorates and the effect of the present invention does not appear. Therefore, the lower limit of the tensile strength is set to 1600 MPa or more. It is preferably 1700 MPa or more, more preferably 1800 MPa or more, still more preferably 1900 MPa or more.

Shear strain rate that causes delamination: 3.0 × 10 ^-4 / s or more Next, if the shear strain rate that causes delamination of steel wire is ^{less than 3.0 × 10 -4} / s, delamination resistance Since the characteristics are low, the effect of the present invention is not exhibited. Therefore, the lower limit is set to 3.0 × 10 ^-4 / s or more. It is preferably 7.0 × 10 ^-4 / s or more, more preferably 2.0 × 10 ^-3 / s or more, and further preferably 3.5 × 10 ^-3 / s or more.

The steel wire according to the present embodiment has the same chemical composition as the above-mentioned wire rod according to the present invention, and has an Md30 value of -20 to 40. Further, the volume fraction of the processing-induced α'is 20 to 95 vol. %, And the spiral dislocation fraction of the austenite phase at a position 200 μm from the surface layer of the steel wire is 0.9 or less, so that the high-strength stainless steel wire having excellent delamination resistance is obtained. In addition, the steel wire has a tensile strength of 1600 or more and a shear strain rate of 3.0 × 10 ^-4 / s or more that causes delamination.

3. 3. Method for Manufacturing Stainless Steel Wire Next, a method for manufacturing a high-strength stainless steel wire and wire rod according to the present embodiment will be described. Needless to say, the method for manufacturing the high-strength stainless steel wire and the wire rod of the present invention is not limited to the conditions described below.

Steel having the above composition is melted, cast into a slab having a predetermined diameter, and then hot wire rolling is performed on the slab. After that, if necessary, solution treatment and pickling are performed to obtain a wire rod.

The stainless steel wire according to the present embodiment can be obtained by cold drawing the above-mentioned wire rod. Specifically, a steel wire or a steel wire is drawn under the following conditions to manufacture a stainless steel wire.

Total reduction rate: 40-90%
The total surface reduction rate in wire drawing is set to 40% or more in order to secure the amount of machining-induced α'and increase the strength. On the other hand, if the total surface reduction rate becomes too large, the amount of work-induced α'increases too much and the delamination resistance characteristics deteriorate. Therefore, the upper limit of the total surface reduction rate is set to 90%. The lower limit of the total surface reduction rate is preferably 50%, and the upper limit is preferably 80%.

Number of passes: 7 times or more The wire drawing process is performed by multi-pass wire drawing with 7 or more passes. The number of passes means the number of times a work such as a wire rod passes through a die. If the number of passes is too small, the spiral dislocation fraction of the austenite phase at a position 200 μm from the surface layer of the steel wire is increased and the delamination resistance is deteriorated. Therefore, the number of passes is set to 7 or more. It is preferably 15 times or more, and more preferably 21 times or more.

Final pass reduction rate: 0.5 to 25%
In order to improve the delamination resistance characteristics, it is important to reduce the surface reduction rate of the final pass within a predetermined range. That is, if the surface reduction rate of the final pass is too large, the spiral dislocation fraction of the austenite phase at a position 200 μm from the surface layer of the steel wire is increased and the delamination resistance is deteriorated. Therefore, the surface reduction rate is set to 25% or less. It is preferably 20% or less, more preferably 10% or less, still more preferably 5% or less. On the other hand, if the surface reduction rate of the final pass is less than 0.5%, the spiral dislocation fraction of the austenite phase at a position 200 μm from the surface layer of the steel wire increases, and the improvement of the delamination resistance characteristics becomes insufficient. Is 0.5% or more.

By the above manufacturing method, a high-strength stainless steel wire having excellent delamination resistance according to the present embodiment can be obtained.

Examples of the present invention will be described below, but the conditions in the examples are one condition example adopted for confirming the feasibility and effect of the present invention, and the present invention is used in the following examples. It is not limited to the conditions that existed. The present invention can adopt various conditions as long as the gist of the present invention is not deviated and the object of the present invention is achieved.

Tables 1 and 2 show the chemical composition of the steels of Examples (steel grades A to AR) and the Md30 value in the austenite (γ) phase. The underlined lines in Table 2 indicate those outside the scope of the present invention.

Steels having these chemical compositions were melted in a 100 kg vacuum melting furnace and cast into slabs having a diameter of 180 mm, assuming AOD melting, which is an inexpensive melting process for stainless steel. After heating the obtained slab at 1100 ° C. for 200 minutes, hot wire rod rolling (surface reduction rate: 99.9%) was performed to φ5.5 mm, and hot rolling was completed at 1050 ° C. Immediately after that, in-line heat treatment at 1050 ° C. for 3 minutes was continuously performed as a solution treatment, water-cooled, and pickled to obtain a wire rod. Then, the wire was drawn cold to φ4.0 mm. The obtained stainless steel wire having a diameter of 4.0 mm was annealed with an intermediate strand at 1050 ° C. for 3 minutes, and then coldly drawn to a diameter of 2.0 mm to obtain a high-strength stainless steel wire. At that time, the total surface reduction rate was 75%, the number of passes was 7, and the surface reduction rate of the final pass was 10%.

Then, for the steel wire produced by the above method, according to the following method, the processing-induced martensite fraction (α'parts), the spiral dislocation fraction of the austenite phase at a position 200 μm from the surface layer of the steel wire, the tensile strength, The shear strain rate of delamination was evaluated.

[Processing-induced martensite fraction (processing-induced α'fraction)]
Deformation-induced alpha 'fraction of the steel wire, as "steel wire", "of the steel wire 1050 ° C. × 3 min heat-treated material" when imparted with a magnetic field of 1.0 × 10 4 ^Oe at DC magnetic flux meter The saturation magnetization value was measured and calculated by the following formula (B). A DC magnetization characteristic test device (manufactured by Metron Giken Co., Ltd.) was used to measure the saturation magnetization value.
α'partition (vol.%) = {(Σ _{s −σ 1050} ) / σ _s (bcc)} × 100 ・ ・ ・ (B)
Here, σ _s is the saturation magnetization value (T) _{of the product, σ 1050} is the saturation magnetization value (T) of the material obtained by heat-treating the product at 1050 ° C. × 3 minutes, and σ _s (bcc) is 100% martensite (γ). α') The saturation magnetization value at the time of transformation (calculated value represented by the following formula (C)) is shown. Creq in the following formula (C) is represented by the following formula (D).
σ _s (bcc) = 2.14-0.030 × Creq ・ ・ ・ (C)
Creq = Cr + 1.8 x Si + Mo + 0.5 x Ni + 0.9 x Mn + 3.6 (C + N) + 1.25 x P + 2.91 x S ... (D)

[Spiral dislocation fraction of the austenite phase at a position 200 μm from the surface layer of the steel wire]
The helical dislocation fraction of the austenite phase at a position 200 μm from the surface layer of the steel wire was measured by X-ray line profile analysis. In the L cross section of the steel wire, at a position 200 μm from the surface layer of the steel wire, measurement is performed using CuKα rays by X-ray diffraction, and the half-value widths of (111), (200), (220) and (311) are measured. Then, the obtained half price range is substituted into the following modified Williamson-Hall equation (E).
ΔK = 0.9 / D + √ ((πM ² b ² ρ) / 2) KC ^1/2 + O (K ² C) ・ ・ ・ (E)

In the formula (E), D is the crystallite size (nm), ρ is the dislocation density (m- ² ), b is the size of the Burgers vector (nm), and M is the dislocation density ρ and the dislocation interaction distance Re. It is a constant with respect to (nm), and C is the average contrast factor of dislocations. Further, K and ΔK are as follows.
K = 2sinθ / λ,
ΔK = 2βcosθ / λ

In the above equation, β, θ and λ are the full width at half maximum (rad), Bragg reflection angle (rad) and X-ray wavelength (CuKα = 0.15405 nm) of each diffraction line, respectively.
Here, if both sides of the equation (E) are squared, the higher-order term O (K ² C) is ignored, and α = (0.9 / D) ² and γ = πM ² b ² ρ / 2 , Equation (F) is obtained.
[(ΔK) ^2- α] / K ² = γC ・ ・ ・ (F)

In the above ^formula, a ^{C = C h00 (1-qH} 2). And q is a parameter including the type of dislocation and its ratio, and H (= (h ² k ² + h ² l ² + k ² l ² ) / (h ² + k ² + l ² ) ² ) is the index h of the diffraction line. It is a function of, k, l. _Ch00 is a constant obtained from the elastic constant.
The above q value is measured, and the spiral dislocation fraction S of austenite can be calculated from the following formula (G).
S = (q-q ^e ) / (q ^s- q ^e ) ... (G)

In the above equation, q ^e and q ^s are q values in the case of 100% blade dislocations and spiral dislocations, respectively, and are constants determined by elastic constants.

[Tensile strength]
The tensile strength of the steel wire was evaluated by the tensile strength in the tensile test of JIS Z 2241.

[Shear strain rate of delamination]
The shear strain rate of steel wire delamination was evaluated by a twist test. In the twist test, the wire diameter d of the steel wire is 2.0 mm, the distance between chucks L is 150 mm, the rotation speed R (rpm) is changed, and the shear strain rate γ'(/ s) of the outermost layer is controlled. A twist test was performed. At various shear strain rates, the torque reduction after 0.3% proof stress was defined as the occurrence of delamination, and the shear strain rate at which the delamination occurred was used as an index of the delamination resistance characteristics.

The evaluation results are shown in Tables 3 and 4.

As shown in Table 3, in the steel wires of Examples 1 to 33 of the present invention, the work-induced α'partition was 20 to 90 vol. %, The tensile strength was 1600 MPa or more, and the helical dislocation fraction of the austenite phase at a position 200 μm from the surface layer of the steel wire was 0.9 or less. Further, the shear strain rate at which delamination occurred in Examples 1 to 33 of the present invention was 3.0 × 10 ^-4 / s or more. On the other hand, the steel wires of Comparative Examples 34 to 48 had deteriorated in either the tensile strength and the delamination resistance. In addition, Comparative Example No. In No. 41, since the corrosion resistance was poor, the tensile strength and the delamination were not evaluated.

Next, the influence of manufacturing conditions was investigated.

Using the steel type R shown in Table 1, stainless steel wires having various diameters produced by the same method as described above are drawn under the wire drawing conditions shown in Table 5 to obtain a steel wire having a diameter of 2.0 mm. Made. In each example, the steel wire diameter to be subjected to wire drawing and the steel wire diameter before the final pass were adjusted so that the final wire diameter of the steel wire was φ2.0 mm. Then, for the obtained steel wire, the volume fraction of the work-induced martensite (α'), the spiral dislocation fraction of the austenite phase at a position 200 μm from the surface layer of the steel wire, the tensile strength and the delamination are carried out in the same manner as described above. The generated shear strain rate was measured and evaluated. The evaluation results are shown in Tables 5 and 6.

Test No. The steel wires of the examples of the present invention shown in 45 to 53 have a work-induced α'partition of 20 to 90 vol. %, The spiral dislocation fraction of the austenite phase at a position 200 μm from the surface layer of the steel wire is 0.9 or less, the tensile strength is 1600 MPa or more, and the shear strain rate at which delamination occurs is 3.0 × 10 ^-4. It was / s or more. On the other hand, the steel wires of Comparative Examples 54 to 58 in which the wire drawing process was not performed under appropriate conditions had deteriorated in either the tensile strength and the delamination resistance.

According to the present invention, it is possible to provide a high-strength stainless steel wire having excellent delamination resistance, which is extremely useful in industry. By applying this stainless steel wire to a spring part or the like, it is possible to provide a spring part or the like having excellent delamination resistance. The spring parts mean springs for automobiles, springs for industrial machines, springs for home appliances, and the like.

Claims (6)

By mass%
C: 0.005 to 0.15%,
Si: 0.1-4.0%,
Mn: 0.1 to 8.0%,
Ni: 1.0 to 10.0%,
Cr: 13.0 to 20.0%,
Mo: 0.01 to 3.00%,
Cu: Over 0.80% to 4.00%,
N: 0.005 to 0.20%,
V: 0-2.5%,
B: 0 to 0.012%,
Al: 0-2.0%,
W: 0-2.5%,
Ga: 0-0.0500%,
Co: 0-2.5%,
Sn: 0-2.5%,
Ti: 0-1.0%,
Nb: 0-2.5%,
Ta: 0-2.5%,
Ca: 0-0.012%,
Mg: 0 to 0.012%,
Zr: 0-0.012%,
REM: 0-0.05%,
The rest consists of Fe and unavoidable impurities,
Md30 represented by the following formula (a) is -20 to 40.
The process-induced martensite phase is 20 to 95 vol. Has a metallographic structure that is%
The helical dislocation fraction of the austenite phase at a position 200 μm from the surface layer of the steel wire is 0.9 or less.
Stainless steel wire.
Md30 = 551-462 (C + N) -9.2Si-8.1Mn-29 (Ni + Cu) -13.7Cr-18.5Mo ... (a)
However, the element symbol in the formula (a) means the content (mass%) of the element in steel. When the content of the element in the formula (a) is 0%, "0" is substituted for the corresponding symbol and calculated. Furthermore, in% by mass,
V: 0.001 to 2.5%,
B: 0.001 to 0.012%,
Al: 0.001 to 2.0%,
W: 0.05-2.5%,
Ga: 0.0004-0.0500%,
Co: 0.05-2.5%,
Sn: 0.01-2.5%,
Ti: 0.01-1.0%,
Nb: 0.01-2.5%,
Ta: 0.01-2.5%,
Ca: 0.0002 to 0.012%,
Mg: 0.0002 to 0.012%,
Contains one or more selected from Zr: 0.0002 to 0.012% and REM: 0.0002 to 0.05%.
The stainless steel wire according to claim 1. The metallographic structure contains an austenite phase.
The stainless steel wire according to claim 1 or 2. The tensile strength is 1600 MPa or more, and the shear strain rate at which delamination occurs is 3.0 × 10 ^-4 / s or more.
The stainless steel wire according to any one of claims 1 to 3. By mass%
C: 0.005 to 0.15%,
Si: 0.1-4.0%,
Mn: 0.1 to 8.0%,
Ni: 1.0 to 10.0%,
Cr: 13.0 to 20.0%,
Mo: 0.01 to 3.00%,
Cu: Over 0.80% to 4.00%,
N: 0.005 to 0.20%,
V: 0-2.5%,
B: 0 to 0.012%,
Al: 0-2.0%,
W: 0-2.5%,
Ga: 0-0.0500%,
Co: 0-2.5%,
Sn: 0-2.5%,
Ti: 0-1.0%,
Nb: 0-2.5%,
Ta: 0-2.5%,
Ca: 0-0.012%,
Mg: 0 to 0.012%,
Zr: 0-0.012%,
REM: 0-0.05%,
The rest consists of Fe and unavoidable impurities,
The method for producing a stainless steel wire according to any one of claims 1 to 4 , wherein a wire rod having an Md 30 of -20 to 40 represented by the following formula (a) is drawn.
A method for manufacturing a stainless steel wire, wherein the wire drawing process is performed under the conditions of a total surface reduction rate of 40 to 90%, a number of passes: 7 times or more, and a surface reduction rate of the final pass: 0.5 to 25%.
Md30 = 551-462 (C + N) -9.2Si-8.1Mn-29 (Ni + Cu) -13.7Cr-18.5Mo ... (a)
However, the element symbol in the formula (a) means the content (mass%) of the element in steel. When the content of the element in the formula (a) is 0%, "0" is substituted for the corresponding symbol and calculated. A spring component using the stainless steel wire according to any one of claims 1 to 4.