JP2003231951A - High-strength precipitation-hardening stainless steel, stainless steel wire and high-strength fastening member using this steel wire - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a high-strength precipitation-hardening stainless steel, a stainless steel wire and a high-strength fastening member using this steel wire. <P>SOLUTION: The high-strength precipitation-hardening semi-austenitic stainless steel showing an excellent cold workability contains at least 0.01-0.1 mass% C, ≤2 mass% Si, 2-4 mass% Mn, 4-8 mass% Ni, 12-18 mass% Cr, ≤2 mass% Mo, 1.5-4 mass% Cu, ≤0.5 mass% Nb and 0.05-0.25 mass% N, wherein C/N is ≤1, Ni-bal calculated by the formula: Ni-bal=Ni+27C+23N+0.1Mn+0.3 Cu-1.2(Cr+Mo)-0.5Si+10 is ≥-2, Ms (°C) calculated by the formula: Ms=1684-60.8Cr-89.2Ni-48.7Mn-40.6Si-2433(C+N) is ≤-100°C, Md<SB>30</SB>(°C) calculated by the formula: Md<SB>30</SB>=551-462(C+N)-9.2Si-8.1Mn-13.7Cr-29(Ni+ Cu)-18.5Mo-68Nb is ≥-30°C, and the amount of austenite after a solution treatment is ≥80 vol.%. <P>COPYRIGHT: (C)2003,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a precipitation hardening type which can be used as various fastening parts such as self-drilling screws, tapping screws, nails and pins by high-strength forging parts by cold working and age hardening. The present invention relates to stainless steel, stainless steel wire, and high-strength parts for fastening with the steel wire.

[0002]

2. Description of the Related Art Conventionally, forgings made of stainless steel such as screws and bolts produced by forging are manufactured according to JIS, for example.
As specified in G 4314, in addition to austenitic stainless steels such as SUS304, SUS316, and SUSXM7, chromium-based stainless steels such as SUS410 and SUS430 are also used. Which material is selected depends on the purpose of use and It is selected according to finishing dimensions. In addition, recently, high-strength fastening components such as self-drilling screws and tapping screws that have a drilling function have been used in order to shorten the installation process, and as a material therefor, for example, quenching and tempering treatment Chromium-based stainless steel such as SUS410, which enables predetermined high strength properties by cold working, is generally used.

However, the material of stainless steel having such high strength characteristics is limited to chromium-based stainless steel which can be heat treated such as quenching, so that it is inferior in corrosion resistance, and also in terms of strength. Since this is not the case, surface treatment such as plating and nitriding is required, which is one of the causes of co-stop due to the increase in processes. To deal with such a problem, for example, JP-A-6-2
In Japanese Patent No. 64194, martensitic stainless steel is used, and in Japanese Patent Laid-Open No. 2001-107192, formation of work-induced martensite is performed by adding 0.10 to 0.20% C and 2 to 5% Si. Methods for facilitating and hardening the austenite phase have been proposed.

[0004]

However, these conventional stainless steels cannot be said to be sufficient in view of the molding process for making the final product and the uses thereof,
It is necessary to provide surface treatment and application restrictions. That is, since the wire according to Japanese Patent Laid-Open No. 6-264194 is a martensitic stainless steel containing Cr: 12 to 16% and Ni: 1 to 2.5%, it takes a long time to perform heat treatment during intermediate processing and finishing. However, it is difficult to obtain a brilliant surface state because the finished state has a problem such as having oxide scale on the surface. Moreover, the mechanical properties of the obtained wire are also very high with a tensile strength of 800 to 1200 N / mm ^2, and the product yield is poor for a forged product that requires severe header processing, It has a problem in productivity.

On the other hand, in the stainless steel according to Japanese Patent Laid-Open No. 2001-107192, since Si is increased to 2 to 5%, the hardness in the solution heat treatment state is high and the cold workability is impaired. There is. Also, for example, SU
Martensitic precipitation hardening stainless steels such as S630 harden by precipitating a Cu phase by age hardening in cooled martensite, but in cold workability, corrosion resistance, hydrogen embrittlement resistance, toughness, etc. It was inferior. Therefore, it has been pointed out that such a material causes a large amount of head jump during header processing and during use.

[0006]

In order to solve the above-mentioned problems, the inventors of the present invention have made earnest developments, and as a result, in the present invention, the structure before processing (solution heat treatment) is substantially austenite phase. By adjusting the C / N ratio, Ms, Md ₃₀ and other component ratios, it is possible to increase the curing rate in the aging treatment after the molding process, while providing good cold workability. A high-strength precipitation hardening stainless steel is provided.

The gist of the invention is as follows: (1)% by mass, C: 0.01 to 0.1%, Si: 2%
Hereinafter, Mn: 2 to 4%, Ni: 4 to 8%, Cr: 12 to 12
18%, Mo: 2% or less, Cu: 1.5 to 4%, Nb:
0.5% or less, N: 0.05 to 0.25% at least, and C / N: 1 or less, the following formula Ni-bal:-
High strength precipitation hardening type stainless steel characterized by improving cold workability by adjusting to 2 or more, Ms: -100 ° C or less, and Md ₃₀ : -30 ° C or more. Ni-bal = Ni + 27C + 23N + 0.1Mn +
0.3Cu-1.2 (Cr + Mo) -0.5Si + 10 Ms (° C) = 1684-60.8Cr-89.2Ni-
48.7Mn-40.6Si-2433 (C + N) Md 30 (℃) = 551-462 (C + N) -9.2Si
-8.1Mn-13.7Cr-29 (Ni + Cu) -1
8.5Mo-68Nb

(2) Further, any one or more of Ti, Zr, V and Ta is added in a total amount of 0.002 to 0.5.
% High-strength precipitation hardening stainless steel as described in (1) above. (3) The stainless steel is the high-strength precipitation hardening stainless steel according to (1) or (2) above, in which one or two of Ca and Mg are added in a total amount of 0.001 to 0.1%.

(4) C: 0.01 to 0.1 by mass%
%, Si: 2% or less, Mn: 2 to 4%, Ni: 4 to 8
%, Cr: 12 to 18%, Mo: 2% or less, Cu: 1.
5-4%, Nb: 0.5% or less, N: 0.05-0.2
5% at least and C / N: 1 or less, the following formula Ni-bal: -2 or more, Ms: -100 ° C or less, Md
₃₀ : A high-strength precipitation hardening stainless steel wire characterized by being adjusted to -30 ° C or higher and having an austenite amount of 80% by volume or more by solution heat treatment or skin pass working subsequent to the heat treatment. Ni-bal = Ni + 27C + 23N + 0.1Mn +
0.3Cu-1.2 (Cr + Mo) -0.5Si + 10 Ms (° C) = 1684-60.8Cr-89.2Ni-
48.7Mn-40.6Si-2433 (C + N) Md 30 (℃) = 551-462 (C + N) -9.2Si
-8.1Mn-13.7Cr-29 (Ni + Cu) -1
8.5Mo-68Nb

(5) The steel wire is the stainless steel wire according to (4), the surface of which is coated with a lubricating film. (6) The stainless steel wire according to (4) or (5), which has a tensile strength of 500 to 850 N / mm ² and an elongation property of 20 to 50%. (7) The stainless steel wire according to any one of (4) to (6) is formed into a predetermined shape by forging, and at least a part of the Hv hardness is set to 500 or more by aging treatment. It is a characteristic high-strength component for fastening.

As mentioned above, the present invention is directed to stainless steel.
The basic composition as described above and, if necessary, some third element
And adjust the compounding balance of each element.
By improving the moldability by
By improving the curing rate in the precipitation hardening treatment of
It should be possible to efficiently manufacture high-strength fastening parts.
It In the present invention, C / N and Ni are used as the component balance.
-Bal, Ms, Md ₃₀So that each value of
Is adjusted to. In the present invention, "stainless steel wire"
Is a stainless steel bar or wire drawn
Or by further forming processing such as forging as it is
Finished so that the required fasteners can be manufactured
Of. For example, the stainless steel is drawn to a predetermined wire diameter.
After processing, solution heat treated or lighter
Degree skin pass processing (for example, processing rate of about 3-10%)
Corresponding to those that have been subjected to the
Is preferred.

According to the present invention, the amount of austenite (γ amount) in the material is 80% by volume or more, preferably 90 to 99.5%, and the tensile strength is 500 to 850 N / mm ² by such treatment. In addition, it is assumed that the material has an elongation property of 20 to 50%. Regarding the amount of austenite, it is desirable to directly measure the surface or cross section of the wire by, for example, an X-ray analyzer, but when it is difficult, the amount of martensite or the amount of ferrite of the material can be measured by a known arbitrary method. It may be determined by an indirect method in which the remaining amount obtained by subtracting the total amount is regarded as the amount of austenite, and may be indicated by the average value of several measured values as necessary.
Further, it is preferable to apply a lubricant such as copper, nickel, or other inorganic material to the surface of the stainless steel wire. Since it is shown in the literature, it is not specified.

On the other hand, the fastening parts, which can be used in the above-mentioned products, are particularly effective for self-drilling screws and tapping screws which are required to have self-piercing properties. A known method such as rolling is performed. Further, since stainless steel is subjected to an aging treatment or a precipitation hardening heat treatment at a relatively low temperature for the purpose of enhancing mechanical properties after processing, even in the present invention, such a heat treatment (for example, 350 to 500 ° C. × 5 min. Two
Time). By this process, the hardness of the fastening component is further increased.

[0014]

BEST MODE FOR CARRYING OUT THE INVENTION The reasons for limiting the composition of each component in the present invention will be described below. C: 0.01 to 0.1% C is a basic element that enhances the strength, and if it is less than 0.01%, the austenite phase and the work-induced martensite phase cannot be said to be sufficiently hardened, and moreover, due to NbC. Insufficient curing. On the other hand, addition of more than 0.1% is inferior in corrosion resistance and molding processability. Therefore, the range is 0.01 to
0.1%, but more preferably 0.02 to 0.08
%.

Si: 2% or less Si is a deoxidizing agent and is an element that imparts strength, but if it exceeds 2%, the cold workability deteriorates, so the upper limit is made 2%. It is preferably 1% or less. Mn: 2 to 4% Mn, like Si, is a deoxidizing agent and an element that stabilizes austenite. In order to exert its action, 2% or more is necessary, but if it exceeds 4%, work hardening becomes difficult and high hardness does not appear, so the upper limit was made 4%. It is preferably set to 2.2 to 3.8%.

Ni: 4-8% Ni is an element that stabilizes the austenite structure in stainless steel, contributes to the improvement of toughness and corrosion resistance, and is required to be at least 4% or more. Also, 4
If it is less than%, there is also a problem that N blowholes are generated during the ingot making. However, if added in excess of 8%, work hardening becomes difficult and high hardness cannot be achieved. Therefore, the range is set to 4 to 8%, preferably 4.5 to 7%.

Cr: 12-18% Cr is an element which improves the corrosion resistance. Therefore, 12% or more is required to improve the corrosion resistance. However, addition of more than 18% results in the formation of δ-ferrite, resulting in deterioration of moldability. Therefore, the range is set to 12 to 18%, preferably 14 to 17%. Mo: 2% or less Mo is an element that improves corrosion resistance. However, if it exceeds 2%, cold workability deteriorates due to the formation of δ ferrite. Therefore, the upper limit is set to 2%, preferably 1%.

Cu: 1.5 to 4% Cu is an element which is necessary for age hardening and reduces the work hardening rate during cold working to improve workability. However, if it is less than 1.5%, the material curing rate after the aging heat treatment is small, which is not preferable. On the other hand, if it exceeds 4%, work hardening becomes difficult, and high hardness cannot be obtained. Therefore, the range is 1.
5 to 4%. It is preferably set to 2.1 to 2.9%.

Nb: 0.5% or less Nb acts to form NbC and improve hardness. However, if it exceeds 0.5%, coarse carbonitrides are formed and δ-ferrite is liable to be formed, so that cold workability is deteriorated. Therefore, the upper limit is set to 0.5%. However, if it is less than 0.1%, the curing by NbC will be insufficient, so 0.1 to 0.3% is desirable.

N: 0.05 to 0.25% N is an element necessary for imparting strength by hardening austenite. However, if it is less than 0.05%, the austenite is not sufficiently hardened, while if it exceeds 0.25%, N blowholes are generated during the ingot making and the cold workability is deteriorated. Therefore, the range is 0.05
~ 0.25%. Desirably 0.06 to 0.2%,
More preferably, it is 0.06 to 0.15%.

The stainless steel and the stainless steel wire of the present invention contain at least such a composition, and can further contain a slight amount of a third element, if necessary, with the balance Fe and inevitable impurities. It is supposed to consist of. Examples of the third element include Ti and Z
Besides r, V, Ta, etc., Ca, Mg, etc. are used. In particular, the former Ti, Zr, V, and Ta all have the function of improving the age hardenability, but if they are contained in a large amount, the cold workability deteriorates. To 0.5%, and even when two or more of them are used in combination, the total content is 0.5%.
The following is recommended.

The latter Ca and Mg both have the function of improving the hot workability, but if the content exceeds 0.1%, the effect will be saturated, so in the case of each element alone. Is preferably 0.001 to 0.1%, and even when both are used in combination, the upper limit is 0.1%.
The following is recommended. On the other hand, as unavoidable impurities in the present invention, for example, P, S, Al, etc. are assumed, and P
For S and S, the toughness of the material is deteriorated, so it is not preferable to add a large amount.
%, Preferably 0.05% or less, and S is also 0.03% or less, preferably 0.02% or less.

Further, Al is used as a deoxidizing agent in the stage of producing stainless steel, but if its content exceeds 0.1%, coarse nitrides will be formed, and cold workability will be caused. Is deteriorated, the upper limit is 0.1
%, Preferably 0.05% or less.
In order to improve cold workability and age-hardenability together with such a composition, the present invention provides C / N: 1 or less, Ni-bal: -2 or more as a component amount balance between the compositions.
The requirements for Ms: −100 ° C. or lower and Md ₃₀ : −30 ° C. or higher are also set, and the calculation thereof can be obtained from the above-described formula.

C / N: 1 or less C / N is the most important parameter in the present invention. C / N is a regulation value for imparting strength by hardening of the austenite phase, and it has been found that N is more effective than the C for hardening the austenite phase because it works-hardens the austenite phase. Also, from the viewpoint of corrosion resistance, it is more advantageous to add N than C. In addition,
In the present invention, C is added in an amount of 0.01% or more in order to secure the age hardenability of NbC,
Even in that case, if the C / N exceeds 1, the hardening of the austenite phase will be insufficient. Therefore, the upper limit is set to 1, preferably 0.8.

FIG. 1 is a diagram showing the influence of C / N on the cold work hardness, and FIG. 2 is the C / N on the aging hardness.
Shows the effect of. As shown in FIGS. 1 and 2, the cold working hardness and the aging hardness are also affected by Md ₃₀ , but the C / N becomes higher as the C / N becomes smaller, and the C / N becomes smaller. It is understood that high hardness is obtained by this. Ni-bal: -2 or more Ni-bal is N for suppressing the formation of δ ferrite.
i balance is regulated, and if this value is less than −2, δ ferrite is formed and cold workability is deteriorated. Therefore, the lower limit is set to -2.

Ms: -100.degree. C. or less Ms is a temperature for controlling the amount of austenite, and if it has a small amount of austenite phase (large amount of martensite phase) before working (solution heat treatment), it is worked by cold working. Since it is difficult to harden, the amount of austenite after solution heat treatment is set to 80% by volume or more by setting Ms to −100 ° C. or less, and high hardness is obtained after cold working and age hardening. However, −
If it exceeds 100 ° C, the amount of austenite becomes less than 80% by volume, and the hardness after cold working or age hardening becomes insufficient, so the upper limit was made -100 ° C. Md ₃₀ : −30 ° C. or higher Md ₃₀ is a regulation temperature for work-hardening property and age-hardening property, and if the value is less than −30 ° C., work-hardening property and age-hardening property decrease, so the lower limit value is −. 30 ° C
And

FIG. 3 is a diagram showing the influence of Cu on the age hardening degree ΔHa (aging hardness-working hardness). As shown in this figure, it is understood that the age hardening degree is maximum in the vicinity of Cu 2.5%. It is speculated that the reason why a sufficient age hardening degree cannot be obtained when the amount of Cu is small is that the precipitation of the Cu phase contributing to age hardening is small. On the contrary, it is considered that when the Cu content is too large, the work hardening rate of the matrix is reduced and a sufficient age hardening degree cannot be obtained.

[0028]

Example 1 100 kg of stainless steel having the chemical composition shown in Table 1 was melted in a vacuum melting furnace, cast into an ingot, heated to 1150 ° C., forged into a φ20 material and heated to 1025 ° C. After holding for 30 minutes, water-cooled solution heat treatment was performed, and then the test piece was processed and tested. Table 2 shows the test results. The amount of retained austenite (γ) after solution heat treatment (ST) was measured by X-ray diffraction, and the Hv hardness was also measured. Further, in order to evaluate the cold workability, the critical upsetting rate after solution heat treatment was measured (φ14 × 21L, 1
No. Restraint type test piece, Cold Forging Subcommittee of Japan Society for Plastic Processing),
Further, in order to evaluate the work hardening property and the age hardening property, the Hv hardness after cold working (50% upsetting) was measured, and after the cold working, an aging treatment (440 ° C., holding for 30 minutes, air cooling) was performed. After that, the Hv hardness was measured. Also, 50% cold working and 4
Corrosion resistance after aging treatment at 40 ° C (JISZ 237
1 salt spray test, 50 ° C., 24 h spray) was evaluated. The evaluation criteria were ◯: no rusting, and Δ: rusting. Further, Table 3 shows that some steels are 50% cold worked, 440 ° C, 30
The results of measuring the Charpy impact value after aging treatment of holding for minutes and air cooling (normal temperature, U-notch test piece) are shown. In addition, the results of measuring the amount of austenite after cold working and aging treatment using X-ray diffraction are also shown.

[0029]

[Table 1]

[0030]

[Table 2]

[0031]

[Table 3]

Nos. Shown in Tables 1-2. Nos. 1 to 18 are examples of the present invention, and the γ amount after ST is 80 vol% or more, the hardness after ST is 200 Hv or less, the critical upsetting ratio is 50% or more, the cold work hardness is 400 Hv or more, and after aging. The hardness is 450 Hv or more, the corrosion resistance after aging is all good, and excellent properties are exhibited. On the other hand, No. 19 to 33 are comparative examples. Comparative Example No. 19, 22, and 23 have large C / N and low cold work hardness and aging hardness. Comparative Example No. 20, 21, 2
2, 26 have low Md _{30 and} low cold work hardness and aging hardness.

Comparative Example No. 23 has a high C and cold workability,
Corrosion resistance is poor. Comparative Example No. 24 has high N and poor cold workability. Comparative Example No. Inventive Example No. 25, in which Ms is high, Ms is high, cold workability is poor, and γ amount after ST is small, so that Md ₃₀ is equivalent. Cold working hardness and aging hardness are lower than those of 2.
Comparative Example No. In No. 27, since Si is high, cold workability is poor,
Corrosion resistance is also poor. Comparative Example No. No. 28 has a low Ni-bal and is poor in cold workability and corrosion resistance. Comparative Example No. 29 is A
1 is high and cold workability is poor.

FIG. 4 is a diagram showing the influence of C / N on the toughness. As shown in FIG. 4, the invention example No. 1 having a C / N of 0.71. No. 11 has the composition other than C and N of the present invention example No. 11 and C / N is 1.
Comparative example No. 40 which is 40. Despite having a higher hardness than No. 22, it exhibits high toughness due to the large amount of retained austenite (γ). Further, it exhibits excellent toughness as compared with the conventional steel, martensitic SUS630.
Therefore, by setting C / N to 1 or less,
It can be seen that even if the amount of retained austenite is large, high hardness is obtained and the obtained toughness is obtained.

(Embodiment 2) In Embodiment 1, No. 1 in Table 1. 3 and No. For 15 stainless steels, 4.0 mmφ
After cold-drawing to the wire diameter of, the solution annealing bright heat treatment is further carried out in the continuous annealing furnace, the surface is coated with oxalic acid lubricating film, and the skin pass processing with a processing rate of 6% is performed. Got a steel wire. The solution heat treatment in this case can be performed, for example, under the conditions of a temperature of 900 to 1200 ° C. and a time of 10 seconds to 30 minutes, but in the present embodiment, a temperature of 1150 ° C. and a time of 100 seconds are selected, and argon gas or the like is selected. Performed in an inert atmosphere. Further, as a comparative material for comparing the effects of the present invention, No. 29
And No. 32 was used and the same treatment as above was performed. Table 4 shows the mechanical properties of the obtained steel wire.
It can be seen that all of the stainless steel wires according to the present invention are in a soft state with a tensile strength of 690 to 730 N / mm ^{2, and} are softer and have superior characteristics to the comparative material. Further, as a reference, the change in tensile strength with cold drawing ratio of these materials is shown in FIG. 5 as work hardening characteristics. From these results, the steel wire of the present invention has sufficient cold workability and workability. It can be seen that it has curability.

[0036]

[Table 4]

Example 3 Next, for each stainless steel wire (No. 3 and No. 15) obtained in Example 2, a drilling tapping screw shown in FIG. , Cold forgeability and tool life were evaluated, and the screw products obtained were further tested at temperatures of 420-48.
The Hv hardness at the tip of the cutting edge was measured after aging treatment at 0 ° C. for 30 min in an inert atmosphere. The results are shown in Table 5. SUS304 was used as a comparative material.
The stainless steel wire according to the present invention had stable press workability and tool life, and could be stably operated. As an example of the fastening component according to the present invention described above, a drilling tapping screw is shown in FIG. 6, and a cutting tooth portion A for self-drilling is provided at the tip. In such screw parts, the tip incisor A
The mechanical characteristics of (1) are directly required for product quality, and are achieved by molding and precipitation hardening treatment (aging treatment) so that the retained hardness has high strength characteristics of Hv500 or higher.

[0038]

[Table 5]

FIG. 7 shows the change in Hv hardness of the tip of the tooth tip at each aging treatment temperature, and it can be seen that the characteristics at the temperature of 460 ° C. or less are the best. In particular, the material N
o. In 3, the stainless steel wire of the present invention exhibits characteristics close to Hv600, and the stainless steel wire of the present invention is soft in the solution heat treatment state and easy to be processed, while the aging treatment after forming has extremely hard characteristics. It turns out that this is a large material.

[0040]

As described above, in addition to hardening by forming work-induced martensite by cold working and hardening by aging treatment according to the present invention, addition of appropriate amounts of C and N and C
According to the regulation of / N, a high strength precipitation hardening type stainless steel excellent in cold workability which hardens the austenite phase remaining after cold working can be obtained, and an extremely excellent effect is exhibited.

[Brief description of drawings]

FIG. 1 is a diagram showing the influence of C / N on work hardness.

FIG. 2 is a diagram showing the effect of C / N on aging hardness.

FIG. 3 is a diagram showing an influence of Cu on an age hardening degree ΔHa (aging hardness-working hardness).

FIG. 4 is a diagram showing the effect of C / N on toughness.

FIG. 5 is a work hardening curve showing a change in tensile strength with a working rate of cold drawing.

FIG. 6 is a front view of a drilling tapping screw.

FIG. 7 is a diagram showing a relationship between an aging treatment temperature and an Hv hardness of a screw product.

[Explanation of symbols]

A Tip incisor

Continued front page    (72) Inventor Takanori Kazunari             No. 3007 Nakajima-Character Nakashima, Himeji City, Hyogo Prefecture               Sanyo Special Steel Co., Ltd. (72) Inventor Tatsuro Isomoto             No. 3007 Nakajima-Character Nakashima, Himeji City, Hyogo Prefecture               Sanyo Special Steel Co., Ltd. (72) Inventor Yoshinori Tanimoto             4-17-1, Ikenomiya, Hirakata-shi, Osaka Japan             Seisen Co., Ltd. (72) Inventor Tamotsu Kariki             4-17-1, Ikenomiya, Hirakata-shi, Osaka Japan             Seisen Co., Ltd. (72) Inventor Yoichi Suzuki             4-17-1, Ikenomiya, Hirakata-shi, Osaka Japan             Seisen Co., Ltd.

Claims (7)

[Claims] 1. In mass%, C: 0.01 to 0.1%, Si: 2% or less, Mn: 2 to 4%, Ni: 4 to 8%, Cr: 12 to 18%, Mo: 2 % Or less, Cu: 1.5 to 4%, Nb: 0.5% or less, N: 0.05 to 0.25% at least, and C / N: 1 or less, the following formula Ni
−bal: −2 or more, Ms: −100 ° C. or less, Md ₃₀ :
A high-strength precipitation hardening stainless steel characterized by having improved cold workability by being adjusted to -30 ° C or higher. Ni-bal = Ni + 27C + 23N + 0.1Mn +
0.3Cu-1.2 (Cr + Mo) -0.5Si + 10 Ms (° C) = 1684-60.8Cr-89.2Ni-
48.7Mn-40.6Si-2433 (C + N) Md 30 (℃) = 551-462 (C + N) -9.2Si
-8.1Mn-13.7Cr-29 (Ni + Cu) -1
8.5Mo-68Nb 2. The high-strength precipitation hardening stainless steel according to claim 1, further containing one or more of Ti, Zr, V, and Ta in a total amount of 0.002 to 0.5%. 3. The high-strength precipitation hardening stainless steel according to claim 1, wherein the stainless steel contains 0.001 to 0.1% in total of one or two of Ca and Mg. 4. In mass%, C: 0.01 to 0.1%, Si: 2% or less, Mn: 2 to 4%, Ni: 4 to 8%, Cr: 12 to 18%, Mo: 2 % Or less, Cu: 1.5 to 4%, Nb: 0.5% or less, N: 0.05 to 0.25% at least, and C / N: 1 or less, the following formula Ni
−bal: −2 or more, Ms: −100 ° C. or less, Md ₃₀ :
A high-strength precipitation hardening stainless steel wire, which is adjusted to -30 ° C or higher, and whose austenite amount is set to 80% by volume or more by solution heat treatment or further skin pass working subsequent to the heat treatment. Ni-bal = Ni + 27C + 23N + 0.1Mn +
0.3Cu-1.2 (Cr + Mo) -0.5Si + 10 Ms (° C) = 1684-60.8Cr-89.2Ni-
48.7Mn-40.6Si-2433 (C + N) Md 30 (℃) = 551-462 (C + N) -9.2Si
-8.1Mn-13.7Cr-29 (Ni + Cu) -1
8.5Mo-68Nb 5. The stainless steel wire according to claim 4, wherein the surface of the steel wire is covered with a lubricating film. 6. A tensile strength of 500 to 850 N / mm ² ,
6. An elongation characteristic having a characteristic of 20 to 50%.
Stainless steel wire described in. 7. The stainless steel wire according to any one of claims 4 to 6 is formed into a predetermined shape by forging forming, and at least a part of the Hv hardness is set to 500 or more by aging treatment. High strength parts for fastening.