JP5154122B2 - High strength stainless steel and high strength stainless steel wire using the same - Google Patents

Description

  The present invention relates to a high-strength stainless steel and a high-strength stainless steel wire using the same, and more specifically, a wire rod that requires high corrosion resistance, high strength, high rigidity, high elastic modulus, and high twisting characteristics, for example, The present invention relates to a high-strength stainless steel suitable as a hard wire such as a spring, a wire rope, a cable wire, and a concrete reinforced steel wire, and a high-strength stainless steel wire using the same.

  For wire rods used in office equipment, telecommunications equipment, mechanical structural parts, building structural strength members, vehicle parts, food equipment, chemical equipment springs, wire ropes, cable wires, concrete reinforced steel wires, etc. Since stress acts, it is required to have high strength, rigidity, elastic modulus and twisting characteristics, and high resistance to fatigue and creep (sag resistance).

Traditionally, this type of application
(1) Austenitic stainless steel (for example, SUS300, SUS300 series stainless steel such as SUS301, 302, 304, 304N1, 304N2, 316, etc.) after solution treatment, and then a stainless steel wire obtained by cold drawing.
(2) A piano wire obtained by patenting a carbon steel containing 0.60 to 0.95% C and cold-drawing,
(3) A hard steel wire obtained by subjecting a carbon steel in the vicinity of the eutectoid composition (0.24-0.86% C) to a patenting treatment and cold drawing,
(4) Especially for bridge main cables that require corrosion resistance, the surface of hard steel wire or piano wire is galvanized steel wire, etc.
Is used.

Furthermore, various techniques for increasing the strength, elastic modulus, rigidity, and the like have been proposed along with the expansion of applications of austenitic stainless steel and improvement of required characteristics. For example, the austenitic stainless steel disclosed in Patent Document 1 is intended to drastically improve its rigidity and obtain a rigidity comparable to that of a piano wire. 03 to 0.14%, Si: 0.1 to 4.0%, Mn: 0.1 to 8.0%, Ni: 1.0 to 8.0%, Cr: 13.0 to 19.0% , N: 0.005 to 0.30%, the balance is made of Fe and inevitable components, and the Md30 value is 0 to 150 (° C). Heating to a warm region, the total area reduction: 20-95% wire drawing, followed by a total area reduction: 10-70% wire drawing in a low temperature region of 100 ° C. or lower, It is obtained by applying low temperature aging in the range of 150 to 600 ° C.
JP-A-2005-290538

  Among the various uses described above, office equipment, telecommunications equipment, and the like are required to be smaller and lighter and to have higher functions year after year. Therefore, the spring material used in these applications is light and thin while maintaining strength, rigidity, elastic modulus, twisting characteristics, sag resistance, etc. (reducing the spring molding size, reducing the number of turns, etc.) ) It is required to be possible. However, when used as a spring material, the conventional various steel wires described above are intended to maintain or improve strength, rigidity, elastic modulus, twisting characteristics, sag resistance, etc., while reducing the thickness and thickness of the steel wire. There was a limit. For example, SUS301 and SUS304 have poor twisting characteristics, SUS316 has low tensile strength, and the high-strength stainless steel wire of Patent Document 1 has room for improvement in terms of rigidity and tensile strength.

  Moreover, the galvanized steel wire used for the main cable for bridges which requires corrosion resistance has a problem that it takes time for the plating process and causes an increase in cost. If stainless steel has superior strength, rigidity, elastic modulus, torsional characteristics, and sag resistance compared to conventional ones, and also has excellent corrosion resistance, a plating step is not necessary.

The present invention has been made in view of the above circumstances, and the purpose thereof is high strength stainless steel having high strength, rigidity, elastic modulus, twisting characteristics, and high sag resistance, and high strength stainless steel using the same. To provide steel wire. As a result, it is intended to cope with the reduction in size and weight and increase in functionality of office equipment and telecommunications equipment.
Another object of the present invention is to provide high strength stainless steel having high corrosion resistance in addition to high strength, rigidity, elastic modulus, twisting characteristics, and high sag resistance, and high strength using the same. To provide stainless steel wire. This eliminates the need for a plating process in applications that require corrosion resistance, thereby improving production cost and production efficiency.

  (Delete)

In order to solve the above problems, a high strength stainless steel Ru engaged to the invention, 0.05 ≦ C ≦ 0.12 wt%, 0.10 ≦ Si ≦ 3.0 wt%, 0.50 ≦ Mn ≦ 1 .50 mass%, 6.1 ≦ Ni ≦ 7.9 mass%, 16.0 ≦ Cr ≦ 22.0 mass%, and 0.5 ≦ Co ≦ 2.0 mass%,
Furthermore,
Cu ≦ 0.50 mass%, and
Mo ≦ 2.0 mass%,
Containing at least one selected from
An austenite-ferrite two-phase high-strength stainless steel, the balance of which is Fe and inevitable impurities, and containing 0.05-20.0% by volume of ferrite in the steel matrix,
Md30 represented by the following formula (1) is −20 ≦ Md30 ≦ 100 ° C.,
[Ni] represented by the following formula (2) is 10.0 ≦ [Ni] ≦ 14.0,
It is a summary. In this case, it is desirable that [Cr] represented by the following formula (3) is 20.0 ≦ [Cr] ≦ 24.0.
However,
Md30 = 551-462 * (C + N) -9.2 * Si-8.1 * Mn-13.7 * Cr-18.5 * Mo-29 * (Ni + Cu) ... Formula (1),
[Ni] = Ni + 0.5Mn + 0.3Cu + 25N + 30C ... Formula (2),
[Cr] = Cr + 1.5Mo + 2Si + 1.5Ti + 5V + 5.5Al + 1.75Nb + 0.75W Formula (3).
For elements that do not contain the elements necessary for the calculation of the above formulas (1) to (3) or whose contents are unknown, these expressions should be set to “0”. Shall be substituted.

High-strength stainless steel according to the present onset Ming, In any of the above cases, further, Nb, V, W, Ta, and 0.01 mass in a total amount of at least one kind or two or more selected from Hf % Or more and 2.0% by mass or less.
In any of the above cases, the high-strength stainless steel according to the present invention further comprises at least one or more selected from Ca, Mg, B and REM in a total amount of 0.0001% by mass or more 0 You may contain 0.0100 mass% or less.
In any of the above cases, the high-strength stainless steel according to the present invention may further contain 0.001 ≦ Al ≦ 0.10 mass%.

  In order to solve the above problems, a high-strength stainless steel wire according to the present invention can be obtained by subjecting the high-strength stainless steel according to any one of the above to wire drawing or wire drawing and aging treatment. This is the gist. The obtained high-strength stainless steel has a three-phase composite structure of an austenite phase, a ferrite phase, and a work-induced martensite phase due to transformation of the austenite phase, a tensile strength of 2300 MPa or more, and an elastic modulus. Is preferably 185 GPa or more and the rigidity is 75 GPa or more.

The high-strength stainless steel according to the present invention contains the above-described components, and has been optimized Md30 and [Ni] and [Cr], so that strength, rigidity, elastic modulus, twisting characteristics, There is an effect that mechanical properties such as sag resistance and corrosion resistance are high.
Another high-strength stainless steel according to the present invention is an austenite-ferrite two-phase high-strength stainless steel that contains the above components, and optimizes Md30 and optimizes [Ni]. Therefore, mechanical properties such as strength, rigidity, elastic modulus, twisting characteristics, and sag resistance are high, and there is an effect that high temperature strength and magnetism can be imparted.
These high-strength stainless steels according to the present invention can be processed into steel to obtain steel processed products with improved strength, rigidity, elastic modulus, twisting characteristics, sag resistance, and corrosion resistance. There is an effect that it is.
Since the high-strength stainless steel wire according to the present invention uses the high-strength stainless steel wire according to the present invention, the same effect as this can be obtained.

  The high-strength stainless steel according to one embodiment of the present invention will be described below.

(Configuration of high-strength stainless steel)
(1) The high-strength stainless steel according to the present embodiment contains C, Si, Mn, Ni, Cr, and Co as essential elements. In addition, the high-strength stainless steel according to the present embodiment is optionally at least one selected from Cu and Mo, at least one selected from Nb, V, W, Ta, and Hf, or You may contain 2 or more types, at least any 1 type or 2 or more types chosen from Ca, Mg, B, and REM, and / or Al. Moreover, as for the high strength stainless steel which concerns on this embodiment, the remainder consists of Fe and an unavoidable impurity. Inevitable impurities include, for example, P, S, O, and N.

(2) The high-strength stainless steel according to the present embodiment containing such a component composition satisfies either or both of the following conditions A and B.
Condition A:
Md30 represented by the following formula (1) is −20 ≦ Md30 ≦ 100 ° C.,
[Ni] represented by the following formula (2) is 10.0 ≦ [Ni] ≦ 14.0,
[Cr] represented by the following formula (3) is 20.0 ≦ [Cr] ≦ 24.0.
However,
Md30 = 551-462 * (C + N) -9.2 * Si-8.1 * Mn-13.7 * Cr-18.5 * Mo-29 * (Ni + Cu) ... Formula (1),
[Ni] = Ni + 0.5Mn + 0.3Cu + 25N + 30C ... Formula (2),
[Cr] = Cr + 1.5Mo + 2Si + 1.5Ti + 5V + 5.5Al + 1.75Nb + 0.75W Formula (3).
For elements that do not contain the elements necessary for the calculation of the above formulas (1) to (3) or whose contents are unknown, these expressions should be set to “0”. Shall be substituted.

Condition B:
An austenite-ferrite two-phase high-strength stainless steel containing 0.05-20.0 vol% ferrite in a steel matrix,
Md30 represented by the above formula (1) is −20 ≦ Md30 ≦ 100 ° C.
[Ni] represented by the above formula (2) is 10.0 ≦ [Ni] ≦ 14.0.

(Component composition of high-strength stainless steel and reasons for limitation)
As described above, the essential elements are C, Si, Mn, Ni, Cr, and Co, and their contents and reasons for limitation are as follows.
(1) 0.05 ≦ C ≦ 0.12% by mass
C is indispensable as an austenite forming element and improves the work hardening rate. Therefore, C content shall be 0.05 mass% or more. On the other hand, when C is contained excessively, coarse carbides are crystallized and workability is deteriorated. Therefore, C content shall be 0.12 mass% or less. More preferable C content is 0.08 mass% or more and 0.11 mass% or less.

(2) 0.10 ≦ Si ≦ 3.0 mass%
Si is a deoxidizer for steel. Therefore, Si content shall be 0.10 mass% or more. On the other hand, if the content of Si becomes excessive, the hardness of the steel after solution treatment is hardened, adversely affects its cold workability, and decreases its hot workability. Then, Si content shall be 3.0 mass% or less. A more preferable Si content when strength is particularly emphasized is 0.8 ≦ Si ≦ 2.0 mass%.

(3) 0.50 ≦ Mn ≦ 1.50 mass%
Mn acts as a deoxidizer for steel. Then, Mn content shall be 0.50 mass% or more. On the other hand, when Mn is contained excessively, corrosion resistance is deteriorated. Then, Mn content shall be 1.50 mass% or less. A more preferable Mn content is 1.0% by mass or less.

(4) 6.1 ≦ Ni ≦ 7.9 mass%
Ni is effective for improving the corrosion resistance, particularly the corrosion resistance in a reducing acid environment. Therefore, the Ni content is set to 6.1% by mass or more. On the other hand, if Ni is excessively contained, the manufacturing cost increases. Therefore, the Ni content is 7.9% by mass or less. A more preferable Ni content is 7.0% by mass or less.

(5) 16.0 ≦ Cr ≦ 22.0 mass%
Cr is an essential element for ensuring corrosion resistance. Then, Cr content shall be 16.0 mass% or more. On the other hand, when Cr is excessively contained, hot workability is impaired and toughness is reduced. Then, Cr content shall be 22.0 mass% or less. A more preferable Cr content is 19.1% by mass or more and 21.0% by mass or less, and a still more preferable Cr content is 19.1% by mass or more and 20.0% by mass or less.

(6) 0.5 ≦ Co ≦ 2.0 mass%
When Co is contained, high strength can be achieved by solid solution strengthening. Co contributes to an improvement in elastic modulus and rigidity. Therefore, the Co content is set to 0.5% by mass or more so that the effect becomes clear. On the other hand, when Co is excessively contained, the manufacturing cost is significantly increased. Therefore, the Co content is set to 2.0 mass% or less. More preferable Co content is 0.8 mass% or more and 1.5 mass% or less.
Further, the Co content is 0.5% by mass or more and 2.0% by mass or less, but in order to improve the twisting property, the content is further related to the Si content so that Co / Si is less than It is preferable that it is 0.75 or more and 1.80 or less.

Moreover, as above-mentioned, an unavoidable impurity is P, S, O, and N, for example, The content and the reason for limitation are as follows.
(7) P ≦ 0.080 mass%
P is segregated at the grain boundaries to increase the intergranular corrosion susceptibility and causes a decrease in toughness. Therefore, a lower content is desirable, but an excessive reduction in the content causes an increase in production cost. Therefore, the P content is set to 0.080 mass% or less. A more preferable P content is 0.030% by mass or less.

(8) S ≦ 0.020 mass%
S decreases hot workability. Then, S content shall be 0.020 mass% or less. A more preferable S content is 0.010% by mass or less, more preferably 0.005% by mass or less, in consideration of the manufacturing cost.

(9) O ≦ 0.015 mass%
O is an element to be suppressed as low as possible because it forms an oxide harmful to cold workability and twisting characteristics. Therefore, the O content is set to 0.015% by mass or less. A more preferable O content is 0.010% by mass or less, more preferably 0.005% by mass or less, in consideration of the manufacturing cost.

(10) N ≦ 0.050 mass%
N is an element that should be suppressed as low as possible because it forms nitrides harmful to cold workability and twisting characteristics. Then, N content shall be 0.050 mass% or less. More preferable N content is 0.030 mass% or less from the balance with manufacturing cost.

Furthermore, the element (optional element) that can optionally be contained as described above is at least one selected from Cu and Mo, and at least any selected from Nb, V, W, Ta, and Hf. Or at least one selected from Ca, Mg, B, and REM, and / or Al, and the allowable content and the reasons for the limitation are as follows: It is as follows.
(11) Cu ≦ 0.50 mass%
Cu is effective for improving the corrosion resistance, particularly the corrosion resistance in a reducing acid environment, lowering the work hardening ability, improving the cold workability, and antibacterial by applying heat treatment. In order to improve, it can contain as needed. On the other hand, when Cu is contained excessively, hot workability is reduced. Then, Cu content shall be 0.50 mass% or less.

(12) Mo ≦ 2.0 mass%
Mo is necessary for obtaining the desired corrosion resistance and can improve the strength, so that it can be contained as necessary. On the other hand, when Mo is excessively contained, hot workability is lowered and manufacturing cost is increased. Then, Mo content shall be 2.0 mass% or less. A more preferable Mo content is 1.0% by mass or less.

(13) One or more of Nb, V, W, Ta, and Hf in a total amount of 0.01% by mass to 2.0% by mass. Nb, V, W, Ta, and Hf are C and carbide. Alternatively, N, C and carbonitrides are formed, and the steel crystal grains are refined to increase the toughness. Therefore, any one or two or more of these may be contained in a total amount of 0.01% by mass or more and 2.0% by mass or less. On the other hand, when these are contained excessively, the manufacturing cost rises. Therefore, the total amount of any one or more of these is 1.0% by mass or less. A more preferable total amount of these is 0.5% by mass or less.

(14) One or more of Ca, Mg, B, and REM in a total amount of 0.0001 mass% to 0.0100 mass% Ca, Mg, B, and REM (Rare Eatrh Metal) are made of steel. It is an effective element for improving hot workability. Therefore, any one or more of these may be contained in a total amount of 0.0001% by mass or more. On the other hand, when these are contained excessively, the effect is saturated and conversely, hot workability is reduced. Therefore, the total amount of one or more of them is set to 0.0100% by mass or less. The total amount of these is more preferably 0.0050% by mass or less. Note that REM is made of Ce, La, or an alloy thereof.

(15) 0.001 ≦ Al ≦ 0.10 mass%
Al is a strong deoxidizer for steel and has the effect of reducing O as much as possible. Therefore, Al is contained as necessary. Then, Al content shall be 0.001 mass% or more which can confirm the effect. On the other hand, excessive addition of Al reduces hot workability. Then, Al content shall be 0.10 mass% or less.

(Condition A, Condition B and reasons for limitation)
Next, the conditions A and B of the high-strength stainless steel according to the present embodiment and the reasons for limitation will be described.

(16) -20 ≦ Md30 ≦ 100 ° C.
“Md30” is represented by the following formula (1) (same as the above formula (1)).
Md30 (° C.) = 551-462 × (C + N) −9.2 × Si−8.1 × Mn−13.7 × Cr−18.5 × Mo−29 × (Ni + Cu) (1)
Since the high-strength stainless steel according to this embodiment has Md30 adjusted to a range of −20 to 100 ° C., the processing (drawing process or the like) in this temperature range results in an austenite structure (50% to 80%). ) Can be transformed into martensite. Martensite has higher strength and elastic modulus than austenite, and ferrite has higher elastic modulus than austenite. Therefore, the high-strength stainless steel according to the present embodiment can obtain higher strength and elastic modulus than the case of the austenite single phase by performing wire drawing or the like.
The reason why Md30 is set to −20 ° C. or higher is that when Md30 is lower than −20 ° C., austenite is excessively stabilized and it becomes difficult to generate martensite, and work hardening is small and the required strength cannot be obtained. On the other hand, the reason why Md30 is set to 100 ° C. or lower is that when Md30 exceeds 100 ° C., the amount of martensite generated is too large during processing, and breakage such as disconnection and vertical cracking occurs.

(17) 10.0 ≦ [Ni] ≦ 14.0
[Ni] is represented by the following formula (2) (same as the above formula (2)), and indicates the sum of the austenite stabilizing elements.
[Ni] = Ni + 0.5Mn + 0.3Cu + 25N + 30C Formula (2)
[Ni] is set to 10.0 or more in order to stabilize austenite (see FIG. 1). On the other hand, when [Ni] is too large, the hot workability is lowered and the production cost is increased. Therefore, [Ni] is set to 14.0 or less (see FIG. 1).

Here, in the case of the above condition A, in addition to the above formulas (1) and (2), [Cr] represented by the following formula (3) (same as the above formula (3)) should be in the following range. Is preferred.
(18) 20.0 ≦ [Cr] ≦ 24.0
[Cr] is represented by the following formula (3), and indicates the sum of ferrite stabilizing elements.
[Cr] = Cr + 1.5Mo + 2Si + 1.5Ti + 5V + 5.5Al + 1.75Nb + 0.75W Formula (3)
[Cr] is set to 20.0 or more in order to generate ferrite or work-induced martensite (see FIG. 1). On the other hand, when [Cr] is too large, the hot workability is lowered due to the formation of the σ phase. Therefore, [Cr] is set to 24.0 or less (see FIG. 1). By adjusting [Cr], ferrite can be generated, so that the elastic modulus and twisting characteristics can be improved.

Moreover, in the case of the said condition B, it is preferable to make ferrite content into the following ranges in addition to said Formula (1) (2).
(19) 0.05 vol% ≦ ferrite content ≦ 20.0 vol%
The ferrite content (here, ferrite is the δ phase) is in this range because when the ferrite content is less than 0.05% by volume, a sufficient elastic modulus / rigidity cannot be obtained and it exceeds 20.0% by volume. This is because the strength is low. A more preferable amount of ferrite is 0.05 volume% or more and 5.0 volume% or less. The high-strength stainless steel according to the present embodiment has an effect that the ferrite can prevent, for example, high-temperature cracking, expand applications by increasing magnetism, increase strength, or improve intergranular corrosion and stress corrosion cracking properties. In addition, the amount of ferrite is intended for the amount in the heat treatment state, and the measurement can be calculated from, for example, a Schaeffler state diagram based on component elements in addition to a ferrite indicator, a ferrite scope, and the unit is volume%. Indicated by

FIG. 1 shows the phase structure during casting solidification of the high-strength stainless steel according to this embodiment in relation to [Ni] and [Cr] and the amount of ferrite. The hatched portion in the figure indicates the phase structure during casting solidification when [Ni] and [Cr] are within the predetermined range.
As indicated by the hatched portion in the figure, the high-strength stainless steel according to the present embodiment has a ferrite content of 20.0% by volume or less, 10.0 ≦ [Ni] ≦ 14.0, and 20.0 ≦ [ [Cr] ≦ 24.0 is preferable, and the metal structure is a two-phase state of austenite and ferrite.
Therefore, the high-strength stainless steel according to this embodiment is
(1) By adjusting the components of [Ni] and [Cr] to the predetermined range, or
(2) By adjusting the component of [Ni] to the predetermined range and including the ferrite phase in the predetermined range,
Hard martensite is not generated during casting and solidification, and ferrite that solidly dissolves impurities S, P and the like that impair hot workability is present appropriately, and therefore workability is good.

And if the high strength stainless steel which concerns on this embodiment is given the process (drawing process etc.) which gives a distortion, a part of austenite will transform into a hard martensite, and it will become a steel wire by processing. Is a three-phase state of austenite, ferrite and martensite. Therefore, the strength and elastic modulus of the high-strength stainless steel according to the present embodiment is increased when processing such as wire drawing is performed. In particular, in the high-strength stainless steel according to this embodiment including a predetermined amount of ferrite phase, the ferrite phase is ferromagnetic, and thus the magnetism is further increased by the ferrite and martensite.
Of the high-strength stainless steel according to the present embodiment, the austenite single-phase one at the time of casting and solidification (the upper left part in the hatched portion in the figure) is also austenite after being subjected to straining (such as wire drawing). In addition, it has high strength and high elasticity in the two-phase state of martensite, and as described above, the three-phase state of austenite, ferrite and martensite is more preferable.

(20) P.I. I ≧ 18
P. I (pitting index) is an index of pitting corrosion resistance and is expressed by the following equation (4). P. I indicates that the larger the value, the better the pitting corrosion resistance, and preferably 19 or more and 23 or less.
P. I = Cr + 3.3Mo + 16N ... Formula (4)

(High strength stainless steel wire and its manufacturing method)
Next, the stainless steel wire and its manufacturing method according to the present embodiment will be described. (1) First, a steel ingot containing the predetermined component is melted, and after forging, a wire (high-strength stainless steel) having an appropriate diameter is produced by hot rolling.
Since the wire thus obtained has the predetermined component, the structure is basically in a two-phase state of austenite and ferrite as shown in FIG. Therefore, since ferrite is present, the elastic modulus and rigidity are good.

(2) Next, solution treatment and wire drawing are repeatedly performed on the obtained wire (high-strength stainless steel) as necessary to reduce the diameter of the wire. Thereby, the finally obtained wire has desired characteristics. In this case, the solution treatment is performed by holding at 1050 to 1150 ° C. for 1 to 60 minutes and rapidly cooling. In addition, the wire drawing is usually performed by cold drawing at a drawing rate (50 to 95%). However, in particular, when toughness is required, for example, temperature is used instead of cold drawing. You may perform the warm wire drawing which makes a diameter narrow, heating at the low temperature of about 200 degrees C or less. In addition, after these wire drawing processes, it is also preferable to further improve the properties by performing an aging heat treatment at about 300 to 500 ° C. for about 30 minutes.

  In cold wire drawing, a part of austenite is transformed into martensite, and the resulting wire has, for example, a three-phase state of austenite, ferrite and martensite, and by work-induced martensite generated by work hardening, For example, a high strength characteristic with a tensile strength of 2300 MPa or more is obtained, and an elastic characteristic with an elastic modulus of 185 GPa or more and a rigidity of 75 GPa or more is provided. Therefore, the high-strength stainless steel wire according to an embodiment of the present invention is suitable for applications that require high strength and high elastic properties such as springs and wire ropes. For example, in the case of a spring product, an aging treatment is performed after molding (for example, coiling) or thereafter. By this aging treatment, for example, a fine intermetallic compound corresponding to the amount and type of the additive element is formed, and the twisting property and the strength can be improved.

(Production of invention steel and comparative steel)
Each steel ingot of 50 kg having the composition shown in Tables 1 and 2 (the balance is composed of Fe and inevitable impurities) is melted in a high-frequency induction furnace, hot forged after forging, and the diameter of each steel ingot is measured. 12.5 mm wire was produced (Invention steels 1 to 26, Comparative steels 1 to 3). The comparative steels 1 and 2 used SUS304, and the comparative steel 3 used SUS316. Table 3 shows Md30 (° C.), [Ni], [Cr], and P.I. I is shown.

(Test pieces and tests for evaluating ferrite content, tensile strength, elastic modulus, rigidity, twist value, magnetism)
(Test pieces)
Next, a solution treatment at 1050 to 1150 ° C. for each wire rod having a diameter of 12.5 mm (invention steels 1 to 26 and comparative steels 1 to 3) (the measurement of the amount of ferrite described later is performed first solution treatment). (The sample taken from the sample was used as a measurement sample) and the wire was drawn repeatedly to reduce the diameter, followed by cold drawing with a final processing rate of 95%, and a stainless steel wire with a wire diameter of 2.0 mm. Got. The obtained stainless steel wires were obtained by using the inventive steels 1 to 26, and those using the inventive wires 1 to 26 and the comparative steels 1 to 3, respectively, as comparative wires 1 to 3, respectively. And in order to evaluate the aging characteristics of Invention Wires 1 to 26 and Comparative Steels 1 to 3, aging treatment is performed at 300 to 500 ° C. for 30 minutes, tensile strength, elastic modulus, rigidity, twist value, and A test piece for measuring magnetism was used.

(Tensile strength and elastic modulus)
The tensile strength and elastic modulus were measured by applying a tensile load to the tip of the test piece based on JIS-Z2201. And the breaking stress at this time was made into tensile strength, and the inclination in an elastic region was made into the elasticity modulus. In addition, about the tensile strength, the thing before an aging treatment was also measured.
(Rigidity)
The rigidity was calculated from the relationship between the torsion angle and the torsional strength in a minute region by a torsion test of a steel wire.
(Twist value)
The twist value was obtained by fixing one end of the test piece so that the gauge distance was 100 times the wire diameter, and rotating the other end at a constant speed of 2 times / min until the test piece broke. . The number of twists when the test piece broke was taken as the twist value.
(Amount of ferrite)
The amount of ferrite was calculated with a ferrite meter by taking a measurement sample (taken from the sample after the first solution treatment as described above).
(Magnetic)
The magnetism was measured using a permeability meter. As a result, each of the inventive wires 1 to 26 had a magnetization characteristic with a relative permeability of 10 or more.

(Test specimen and test for corrosion resistance evaluation)
(Test pieces)
Each wire (invention steel 1 to 26 and comparative steels 1 to 26) having a diameter of 12.5 mm is straightened and subjected to a solution treatment under the same conditions as in the preparation of a test piece for measuring tensile strength and the like. A circular test piece (φ10 × 50 mm) whose surface was finished to # 400 was manufactured. This was used to test the corrosion resistance.
(Corrosion resistance)
Corrosion resistance was evaluated by performing a salt spray test based on JIS-Z2371. The salt spray test was conducted by exposing the test piece to a 35 ° C., 5% sodium chloride aqueous solution spray environment for 96 hours. The presence / absence of rust and its properties were confirmed visually. As a result, “A” indicates that no rusting was observed, and “B” indicates that spotted spots and red rust were observed.

(Test pieces and tests for evaluation of coiling workability and sag resistance)
(Coiling workability and test piece)
Next, coiling was performed on the inventive wires 1 to 26 and the comparative wires 1 to 3, and a compression coil spring having an average spring diameter of 20 mm, a free length of 50 mm, a total number of turns of 6.5, and an effective number of turns of 4.5 was formed. . These were formed under the conditions of a coil average diameter D / wire diameter d ratio of 10 and a coiling speed of 60 pieces / min. Thereby, it became clear that the coiling workability of the cold-drawn stainless steel wires (invention wires 1 to 26, comparative wires 1 to 3) was good.

(Sag resistance)
The springs obtained by processing the inventive wires 1 to 26 and the springs obtained by processing the comparative wires 1 to 26 were set in a star coil spring fatigue tester “Tokai Test Machine Manufacturing: TSC-16B type” and tested. A continuous 96-hour fatigue test was performed under the conditions (average stress: 500 N / mm ² , stress amplitude: 250 N / mm ² , speed: 20 Hz). The value indicating the sag resistance was calculated by the following equation (5) by measuring the load loss ΔP before and after the fatigue test.
Value indicating sag resistance = (8D · ΔP) / (πGd ³ ) × 100 (5)
Where D: average diameter of spring, d: wire diameter of steel wire, G: transverse elastic modulus of steel wire, ΔP: load loss.
When the value obtained by the above formula (5) is 0.05% or less, it is judged that the sag resistance is good, and it is indicated by “◯” in Table 4, and the value is 0.10% or more. Judgment was poor and the result was indicated by “x” in the table, and the value between them was judged as slightly good and the result was indicated by “Δ” in the same table.

Table 4 shows the corrosion resistance, ferrite content, tensile strength, elastic modulus, rigidity, twist value, and sag resistance as test results.

(Evaluation)
Invention wires 1 to 26 (invention steels 1 to 26) all satisfied the required characteristics. This is presumably because the inventive steels 1 to 26 contain a predetermined amount of the components specified in Table 1, and the Md30 is optimized and [Ni] and [Cr] are optimized. The strength was high because the austenite was transformed into martensite because the test piece having Md30 of −20 to 100 ° C. was drawn. The reason why the elastic modulus was high is considered to be that ferrite was generated because [Cr] and [Ni] were adjusted to the predetermined range in addition to the optimization of Md30. The reason why the twisting property is good is considered to be due to the aging treatment.
Table 4 also shows the tensile strength before the aging heat treatment, but the inventive wire rods 1 to 26 were good results with a large increase in tensile strength compared to the comparative wire rods 1 to 3. Furthermore, regarding the sag resistance, the sag rate of the springs obtained by processing the inventive wires 1 to 26 is 0.04% or less, and the sag of the springs obtained by processing the comparative steels 1 to 3 It was good compared to the rate.
In Table 4, only the values after the aging treatment are shown for the elastic modulus and the rigidity, but these values are compared with the elastic modulus and the rigidity before the aging treatment, that is, in the wire drawing state. About 2 to 3%. Therefore, the inventive wires 1 to 26 have an elastic modulus of 185 GPa or more and a rigidity of 75 GPa or more in any state regardless of before or after the aging treatment.

  The comparative wire 1 had a relatively high tensile strength, but had a low elastic modulus, rigidity, and twist value. This is probably because Comparative Steel 1 has a low [Cr], so that almost no ferrite can be generated during casting and solidification, and a sufficient amount of martensite has not been generated after wire drawing. Moreover, it is considered that an oxide harmful to the twisting property was formed because the content of O was large.

  The comparative wire 2 had low tensile strength, elastic modulus, rigidity, and twist value. This is because the comparative steel 2 has a slightly low [Cr], so it cannot sufficiently generate ferrite during casting solidification, and since the Md30 is low, austenite becomes too stable and it becomes difficult to generate martensite. This is probably because the strength was not obtained. Moreover, it is considered that an oxide harmful to the twisting property was formed because the content of O was large. Since Comparative Steels 2 and 3 did not contain Co and Md30 was lower than −20 ° C., the sag resistance of the spring obtained by processing them was as large as 0.12%. It has been found that wires 2 and 3 are not suitable for springs.

  The comparative wire 3 had a relatively high twist value, but had low tensile strength, elastic modulus, and rigidity. This is presumably because the comparative steel 3 had a very low Md30 value, so that austenite was so stabilized that it was difficult to produce work-induced martensite and the required strength could not be obtained. Moreover, it is considered that an oxide harmful to the twisting property was formed because the content of O was large.

  As mentioned above, although one Embodiment of this invention was described, the said embodiment is only an example and does not limit this invention. That is, the above embodiment can be variously modified without departing from the gist of the present invention.

  High-strength stainless steel according to the present invention includes office equipment, telecommunications equipment, machine structural parts, building structural strength members, vehicle parts, food equipment, chemical equipment springs, wire ropes, cable wires, concrete reinforced steel. Since it is suitable for a wire used for a wire or the like, it has high industrial utility value for a steel manufacturer. High-strength stainless steel wire has high industrial utility value from manufacturers of office equipment to end users.

It is the relationship figure which showed the phase structure at the time of the casting solidification of the high strength stainless steel which concerns on one Embodiment of this invention by the relationship with [Ni] and [Cr], and the ferrite content.

Claims (10)

0.05 ≦ C ≦ 0.12 mass%,
0.10 ≦ Si ≦ 3.0 mass%,
0.50 ≦ Mn ≦ 1.50 mass%,
6.1 ≦ Ni ≦ 7.9% by mass,
16.0 ≦ Cr ≦ 22.0 mass%, and
0.5 ≦ Co ≦ 2.0% by mass,
Furthermore,
Cu ≦ 0.50 mass%, and
Mo ≦ 2.0 mass%,
Containing at least one selected from
An austenite-ferrite two-phase high-strength stainless steel, the balance of which is Fe and inevitable impurities, and containing 0.05-20.0% by volume of ferrite in the steel matrix,
Md30 represented by the following formula (1) is −20 ≦ Md30 ≦ 100 ° C.,
[Ni] represented by the following formula (2) is 10.0 ≦ [Ni] ≦ 14.0,
High-strength stainless steel characterized by
However,
Md30 = 551-462 * (C + N) -9.2 * Si-8.1 * Mn-13.7 * Cr-18.5 * Mo-29 * (Ni + Cu) ... Formula (1),
[Ni] = Ni + 0.5Mn + 0.3Cu + 25N + 30C Formula (2). Furthermore,
The high-strength stainless steel according to claim 1 , wherein [Cr] represented by the following formula (3) satisfies 20.0 ≦ [Cr] ≦ 24.0.
However,
[Cr] = Cr + 1.5Mo + 2Si + 1.5Ti + 5V + 5.5Al + 1.75Nb + 0.75W Formula (3). Furthermore, according to claim 1, wherein Nb, V, W, Ta, and, by containing at least one kind or 2.0 wt% 0.01 wt% of two or more thereof in a total amount less selected from Hf Or the high-strength stainless steel according to 2. Furthermore, Ca, Mg, B, and, from claim 1, characterized in that it contains at least one kind or 0.0100 wt% 0.0001 wt% or more of two or more thereof in a total amount less selected from REM 3 High-strength stainless steel according to any one of the above. Furthermore, 0.001 <= Al <= 0.10 mass% is contained, The high strength stainless steel in any one of Claim 1 to 4 characterized by the above-mentioned. A high-strength stainless steel wire obtained by subjecting the high-strength stainless steel according to any one of claims 1 to 5 to wire drawing, wherein the tensile strength is 2300 MPa or more. Stainless steel wire. A high-strength stainless steel wire obtained by subjecting the high-strength stainless steel according to any one of claims 1 to 5 to wire drawing and aging treatment, wherein the tensile strength is 2300 MPa or more. High strength stainless steel wire. Metal structure, austenite phase and a ferrite phase, and, according to claim 6 or 7 a portion of the austenite phase, characterized in that it is a shall which have a composite structure of three phases including transformation was induced martensitic phase High strength stainless steel wire as described in. The high-strength stainless steel wire according to any one of claims 6 to 8 , wherein an elastic modulus is 185 GPa or more. The high-strength stainless steel wire according to any one of claims 6 to 9 , wherein the rigidity is 75 GPa or more.

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