JP5291479B2 - Duplex stainless steel and steel and steel products using the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a duplex stainless steel including a ferritic phase and a martensitic phase which can exhibit satisfactory corrosion resistance and strength while achieving the reduction of cost, and to provide a steel material and a steel product using the same. <P>SOLUTION: The duplex stainless steel has a composition containing, by mass, 0.080 to 0.120% C, 0.20 to 1.00% Si, 1.00 to 3.00% Mn, more than 1.00 to 3.00% Cu, 20.0 to 23.0% Cr, 0.50 to 1.00% Ni and at most 0.030% N, and in which [A] expressed by formula (1) satisfies 0.15&le;[A]&le;0.30, and also contains a ferritic phase and a martensitic phase, and in which the area ratio of the martensitic phase in the cross-sectional structure is 10 to 60%; wherein formula (1) is [A]=(1.4[Mn]+[Cu])/[Cr]. <P>COPYRIGHT: (C)2010,JPO&amp;INPIT

Description

  The present invention relates to a duplex stainless steel and a steel product and a steel product using the duplex stainless steel, and more particularly, a duplex stainless steel including a ferrite phase and a martensite phase, which has improved corrosion resistance and strength and has achieved cost reduction, and It relates to steel materials and steel products using the same.

  Ferritic stainless steel is generally inferior in corrosion resistance and strength to austenitic stainless steel. Therefore, in order to improve the corrosion resistance, a steel type with an increased amount of Cr has been developed. As such a steel type with an increased amount of Cr, for example, in Patent Document 1, by weight percent, Si: 0.05 to 3.0%, Mn: 0.1 to 2.0%, P: 0.04% Hereinafter, a ferritic stainless steel wire containing S: 0.01% or less, Cr: 14.0 to 24.0%, C + N: 0.005 to 0.15%, with the balance being Fe and inevitable impurities. It is disclosed.

  In addition, as a steel type used for applications requiring high strength and flatness such as a leaf spring, a flapper valve, and a metal gasket, Patent Document 2 discloses C: 0.10 to 0.20 mass%, Si: 2.0 mass% or less, Mn: 2.0 mass% or less, P: 0.040 mass% or less, S: 0.010 mass% or less, Ni: 0.50 to 4.0 mass%, Cr: 10. 0 to 20.0% by mass, N: 0.10% by mass or less, B: 0 to 0.015% by mass, with the balance having substantially the composition of Fe, and heating in the two-phase region (ferrite + austenite) The Vickers hardness is HV400 or more and has a small hardness fluctuation, characterized by a multiphase structure of ferrite and martensite formed by the martensitic transformation of the austenite phase during the cooling process. Stainless steel There has been disclosed.

  Furthermore, in Patent Document 3, as a steel type suitable for providing a high-strength stainless steel plate material as a steel strip, C: 0.10% or less, Si: 2.0% or less, Mn: 4. 0% or less, P: 0.040% or less, S: 0.010% or less, Ni: 4.0% or less, Cr: 10.0-20.0%, N: 0.12% or less, B: 0 More than .0050 to 0.0300%, O: 0.02% or less, Cu: 4.0% or less, and 0.01% ≦ C + N ≦ 0.20%, 0.20% ≦ Ni + (Mn + Cu ) /3≦5.0% so as to satisfy the relationship, with the balance being Fe and inevitable impurities, 20 vol. % To 95 vol. % High-strength, high-ductility, multi-phase stainless steel having a multiphase structure consisting of a martensite phase having an average particle size of 10 μm or less and a balance substantially consisting of a ferrite phase and a hardness of HV200 or more. It is disclosed.

JP2007-77444 JP 2002-105601 A JP 7-138704 A

  However, the ferritic stainless steel wire of Patent Document 1 does not reach the austenitic stainless steel, and the strength is not improved even if the amount of Cr is increased. Furthermore, the stainless steel made of the ferrite phase and martensite of Patent Documents 2 to 3 has a double phase structure and improves manufacturability, but the strength is not sufficient. Therefore, a duplex stainless steel containing a ferrite phase and a martensite phase excellent in both strength and corrosion resistance is required.

  On the other hand, SUS304, which is a general austenitic stainless steel, and SUSXM7, which is particularly used for screws and the like, have a problem that the cost is high because Ni contains about 8 to 10%. Therefore, a low-cost steel type is required while having corrosion resistance equivalent to that of SUS304, SUSXM7, or the like.

  The present invention has been made in view of the above circumstances, and the present invention provides a duplex stainless steel including a ferrite phase and a martensite phase that can exhibit good corrosion resistance and strength while reducing costs, and the same. It aims at providing the steel materials and steel products which used the.

  In order to solve the above problems, the present inventors can improve the corrosion resistance by increasing the amount of Cr even when Ni is reduced, and generate martensite by increasing the amount of austenite-forming elements such as Mn and Cu to form a two-phase structure. As a result, we obtained the knowledge that high strength can be achieved. The present invention has been made based on such knowledge.

The duplex stainless steel according to the present invention is
0.080 ≦ C ≦ 0.120 mass%, 0.20 ≦ Si ≦ 1.00 mass%, 1.00 ≦ Mn ≦ 3.00 mass%, 1.00 <Cu ≦ 3.00 mass%, 20. 0 ≦ Cr ≦ 23.0 mass%, 0.50 ≦ Ni ≦ 1.00 mass%, N ≦ 0.030 mass%,
[A] represented by the following formula (1) is 0.15 ≦ [A] ≦ 0.30, and
The gist is that the martensite phase of the cross-sectional structure including the ferrite phase and the martensite phase is 10% or more and 60% or less in terms of area ratio.
However, [A] = (1.4 [Mn] + [Cu]) / [ Cr] ... Formula (1)

In this case,
You may contain 0.10 <= Mo <= 1.00 mass%.
Furthermore,
0.0005 ≦ B ≦ 0.0050 mass%, and / or
You may contain 0.20 <= Al <= 0.80 mass%.
Furthermore,
You may contain O <= 0.030 mass%.
Furthermore,
One or more selected from the group consisting of Nb, Ti, V, W, Ta and Hf may be contained in a total amount of 0.01% by mass or more and 0.60% by mass or less.
Furthermore,
You may contain 0.01 <= Co <= 0.60 mass%.
Furthermore,
One or more selected from the group consisting of Ca, Mg and REM may be contained in a total amount of 0.0005 mass% or more and 0.0100 mass% or less.
And it is preferable that the Rockwell hardness is 85 HRB or more and 100 HRB or less.

  The gist of the steel material and the steel product according to the present invention is the duplex stainless steel according to the present invention. Here, the “steel material” includes, for example, a steel bar for billets, a shape material and a wire material obtained by hot rolling the steel bar, and a plate material and a steel wire (wire) obtained by processing these shape material and wire material, As the steel wire, for example, a steel wire that is cold drawn at a processing rate of 90% or less and thinned, and a hard or soft material that is further solution-treated at a temperature of 700 to 1000 ° C. are suitable. In particular, a solution-treated soft material and a material subjected to cold drawing at 30% or less after that are preferable because of good workability. “Steel products” means electronic equipment, office equipment, telecommunications equipment, vehicles, food equipment, chemical equipment, kitchen kitchen equipment, kitchen kitchen miscellaneous electronic machine parts, machine structural parts, building structural strength members, vehicles Parts, shafts, springs, wire mesh, nails, screws, bolts, wire ropes, cable wires, concrete reinforced steel wires, and kitchen utensils.

  The duplex stainless steel according to the present invention and the steel material and steel product using the same have the above component composition, satisfy the above formula (1), and include a ferrite phase and a martensite phase, and the martensite phase is predetermined. Since it is an area ratio, corrosion resistance is improved and it has favorable strength. This is due to the effect of improving the corrosion resistance by increasing the amount of Cr and the phase balance effect by adjusting the amount of Mn and the amount of Cu relative to the amount of Cr. Further, since the amount of Ni is suppressed, the cost can be reduced. Furthermore, according to the present invention, the composition has the above component composition, satisfies the above formula (1), and includes a ferrite phase and a martensite phase, and the martensite phase has a predetermined area ratio. Aperture is obtained.

It is a microscope picture of the cross-sectional structure of invention steel 1 (100 times).

Below, the duplex stainless steel containing the ferrite phase and martensite phase which concern on one Embodiment of this invention is demonstrated.
(Component composition, structure, characteristics, etc. of duplex stainless steel including ferrite phase and martensite phase, and reasons for limitation)
(1) C: 0.080 ≦ C ≦ 0.120 mass%
C is an essential element and is an important element for obtaining high strength. If the amount of C is less than 0.080% by mass, sufficient matrix strength cannot be obtained, so 0.080% by mass was made the lower limit. On the other hand, if the amount of C exceeds 0.120% by mass, the amount of carbide increases and the corrosion resistance deteriorates, so 0.120% by mass was made the upper limit. A more preferable amount of C is 0.080% by mass or more and 0.100% by mass or less at which sufficient matrix strength is obtained and corrosion resistance is good.

(2) Si: 0.20 ≦ Si ≦ 1.00 mass%
Si is an essential element and is a deoxidizer for steel. Therefore, the lower limit of Si content is 0.20% by mass. On the other hand, if the amount of Si is too large, the toughness is lowered and the hot workability of the steel is deteriorated, so the upper limit is made 1.00% by mass. In the case where the cold workability is particularly important, the upper limit of the Si amount is 0.50% by mass.

(3) 1.00 ≦ Mn ≦ 3.00 mass%
Mn is an essential element and is an element necessary for generating a martensite phase that contributes to an increase in strength. Therefore, the amount of Mn is made 1.00 mass% as a lower limit in order to secure a sufficient martensite phase. On the other hand, when Mn is added excessively, the work hardening ability is increased and the cold workability is hindered. Therefore, the upper limit of the amount of Mn is 3.00% by mass. A more preferable amount of Mn is 1.50% by mass or more and 2.50% by mass or less.

(4) 1.00 <Cu ≦ 3.00 mass%
Cu is an essential element and is an important element in the present invention, and is effective for improving corrosion resistance, particularly corrosion resistance in a reducing acid environment, and is necessary for securing a martensite phase. Increase strength by increasing the site phase. Cu further reduces work hardening ability, improves cold workability, and improves antibacterial properties when subjected to heat treatment or the like. Thus, Cu can improve both strength and corrosion resistance. Therefore, the lower limit of the amount of Cu is more than 1.00% by mass. On the other hand, since excessive addition of Cu deteriorates hot workability, the upper limit of the amount of Cu is 3.00% by mass. A more preferable amount of Cu is 1.50% by mass or more and 3.00% by mass or less.

(5) 20.0 ≦ Cr ≦ 23.0 mass%
Cr is an essential element, and is an essential element for ensuring corrosion resistance. Therefore, the lower limit of Cr content is 20% by mass. On the other hand, when Cr is excessively contained, hot workability is impaired and toughness is reduced due to σ phase precipitation. Therefore, the upper limit of Cr content is 23.0% by mass. A more preferable Cr amount is 20.5% by mass or more and 22.0% by mass or less, in which corrosion resistance can be sufficiently secured and toughness deterioration is small.

(6) 0.5 ≦ Ni ≦ 1.0 mass%
Ni is an essential element and is effective in improving the corrosion resistance, particularly the corrosion resistance in a reducing acid environment. Therefore, the lower limit of the Ni amount is 0.5% by mass. On the other hand, if Ni is excessively contained, the manufacturing cost increases. Therefore, the upper limit of the Ni amount is 1.0% by mass. A more preferable amount of Ni is 0.5% by mass or more and 0.7% by mass or less.

(7) N ≦ 0.030 mass%
N is an unavoidable impurity and is an element that should be suppressed as low as possible because it forms a nitride that degrades cold workability and machinability. Therefore, the N amount is 0.030% by mass or less. A more preferable N amount is 0.020% by mass or less from the viewpoint of manufacturing cost, and a further preferable N amount is 0.015% by mass or less.

(8) [A] represented by the following formula (1) is 0.15 ≦ [A] ≦ 0.30. However, [A] = (1.4 [Mn] + [Cu]) / [C r] (1).
[A] is concerned with both corrosion resistance and strength, and Mn and Cu are necessary for securing martensite. However, if the addition amount is large with respect to Cr, [A] 0.30 is the upper limit. On the other hand, when [A] is less than 0.15, martensite is reduced and the strength cannot be ensured, so [A] has a lower limit of 0.15. [A] is more preferably 0.20 or more and 0.25.

(9) The martensite phase of the cross-sectional structure is 10% or more and 60% or less by area ratio.
This is because the two-phase structure improves the corrosion resistance and strength. The reason why the lower limit of the area ratio of the cross-sectional structure of the martensite phase is set to 10% is that if it is less than this, the martensite is too small and the strength is lowered. Further, the reason why the upper limit of the area ratio of the cross-sectional structure of the martensite phase is set to 60% is that if it exceeds this, the martensite becomes excessive, and the drawing and the corrosion resistance deteriorate. The area ratio of the martensite phase is more preferably 15% to 40%, and still more preferably 20% to 35%.

(10) 0.10 ≦ Mo ≦ 1.00% by mass
Mo is an optional element and can improve the corrosion resistance without lowering the strength. Therefore, it can be contained if necessary. Therefore, the lower limit of the amount of Mo is 0.10% by mass. On the other hand, when Mo is excessively contained, hot workability is lowered and manufacturing cost is increased. Therefore, the upper limit of the Mo amount is 1.00% by mass. A more preferable amount of Mo is 0.20% by mass or more and 0.50% by mass or less.

(11) 0.0005 ≦ B ≦ 0.0050 mass%
B is an optional element. B increases the grain boundary strength and improves the hot workability of the steel. Therefore, the B amount is set to 0.0005 mass% or more. However, excessive addition forms a boride that impairs hot workability, so the upper limit of B content is 0.0050% by mass. A more preferable amount of B is 0.0005 mass% or more and 0.0030 mass% or less, and a more preferable amount of B is 0.0005 mass% or more and 0.0020 mass% or less.
(12) 0.20 ≦ Al ≦ 0.80 mass%
Al is an optional element. Al is a strong deoxidizer for steel, and is added as necessary to reduce O as much as possible or to improve oxidation resistance. The lower limit of the amount of Al is 0.20 mass% at which the effect can be confirmed. When Al is contained excessively, hot workability is deteriorated, so the upper limit of the amount of Al is 0.80% by mass. A more preferable Al amount is 0.50% by mass or less.

(13) O ≦ 0.030 mass%
O is an optional element and should be suppressed as low as possible because it forms an oxide harmful to cold workability and machinability. Therefore, the O amount is 0.030% by mass or less. A more preferable amount of O is 0.015% by mass or less, more preferably 0.010% by mass or less, in consideration of the manufacturing cost.

(14) The total amount of one or more selected from the group consisting of Nb, Ti, V, W, Ta and Hf and Co is 0.01% by mass or more and 0.60% by mass or less Nb, Ti, V, W , Ta and Hf are optional elements, and have the effect of forming C and carbides, or N, C and carbonitrides to refine the crystal grains of steel and increase 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 0.60% by mass or less. From the viewpoint of suppressing the manufacturing cost, the total amount of any one or more of these is more preferably 0.30% by mass or less.
(15) 0.01 ≦ Co ≦ 0.60 mass%
Co is an arbitrary element, and since high strength can be achieved by solid solution strengthening, the lower limit of the amount of Co is 0.01% by mass at which the effect becomes clear. However, if Co is excessively contained, the cost is significantly increased. Therefore, the upper limit of Co is 0.60% by mass, and 0.30% by mass or less is more preferable.

(16) One or two or more selected from the group consisting of Ca, Mg, and REM in a total amount of 0.0005 mass% to 0.0100 mass% Ca, Mg, and REM (Rare Eatrh Metal) are optional elements. Yes, it is an effective element for improving the hot workability of steel. Therefore, any one or more of these may be contained in a total amount of 0.0005% by mass or more. However, when these are contained excessively, the effect is saturated, and conversely, hot workability is lowered. 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.

(17) Rockwell hardness 85HRB or more and 100HRB or less The reason why Rockwell hardness is 85HRB or more and 100HRB or less is that sufficient strength cannot be obtained when the hardness is less than 85HRB, and the workability is deteriorated when the hardness exceeds 100HRB. . More preferable Rockwell hardness is 88HRB or more and 98HRB or less. Moreover, in order to ensure the intensity | strength which can be used as an austenitic stainless steel alternative use, and sufficient workability, it is good to make a proof stress ratio 65% or more and 80% or less. If the aperture is secured at 55% or more, the workability is further improved.

In addition, P is an inevitable impurity, segregates at the grain boundary, increases the intergranular corrosion susceptibility, and lowers the toughness. Therefore, it is desirable that the content is low. Invite the rise. Therefore, the amount of P is desirably set to 0.040% by mass or less. A more preferable amount of P is 0.030% by mass or less.
Moreover, S is an unavoidable impurity and reduces hot workability. Therefore, the amount of S is desirably 0.010% by mass or less. A more preferable amount of S is 0.005% by mass or less in view of the manufacturing cost.

(Method for producing duplex stainless steel including ferrite phase and martensite phase)
(1) First, a steel ingot containing the predetermined component is melted, cooled to form an ingot, and steel of a predetermined size is produced by hot forging.
(2) Next, this steel is air-cooled (annealed) after heat treatment at 700 to 1000 ° C. (preferably 750 to 950 ° C.) for about 1 to 24 hours (preferably about 1 to 8 hours) (cooling during air cooling) The speed is 15 to 250 ° C./min).
The steel having the predetermined component obtained through the steps (1) to (2) includes a ferrite phase and a martensite phase, and the martensite phase of the cross-sectional structure is 10% to 60% in area ratio. , Yield ratio 65% to 80%, aperture 55% or more, Rockwell hardness 85HRB to 100HRB.

(Example A)
(Production of test materials)
Invention steels and comparative steels shown in Table 1 were produced as follows. That is, 50 kg of each steel ingot having the component composition shown in Table 1 (the balance consisting of Fe and inevitable impurities) was melted in a high frequency induction furnace and cooled to prepare an ingot. Next, each ingot was heated to 1000 to 1200 ° C. and processed into a round bar having a diameter of 20 mm by hot forging.
Each round bar is further heated at 800 ° C. for 4 hours, and then air-cooled (annealed) at a cooling rate of 50 ° C./min to 100 ° C./min. The obtained inventive steels and comparative steels are used as test materials. did. Table 1 summarizes the component composition, [A] in the above formula (1), and the area ratio (%) of martensite. The area ratio of martensite will be described later.

(Various tests)
Next, using the obtained test material, the martensite area ratio (%), tensile strength (MPa), 0.2 proof stress (MPa), proof stress ratio (%), drawing (%), Rockwell Hardness and corrosion resistance were examined. Hereinafter, these tests will be described.

(Area ratio)
A test piece having a size of 10 mm × 10 mm × 10 mm was prepared from about 1 / 2R of the test material, and this was embedded and polished in a resin so that the longitudinal section could be observed. Villera (mixed solution of ethanol, hydrochloric acid and picric acid) ) Was used for etching. Black and white photographs were taken of the microstructure after etching at a magnification of 100 times, the color changed by etching corrosion was extracted as a martensite phase by image analysis processing, the area ratio per field of view was measured, and the average value of 30 fields of view Was defined as the area ratio. FIG. 1 shows a photograph of invention steel 1. As shown in the figure, it can be seen that a martensite phase is generated. The measurement results of the area ratio of each invention steel and each comparative steel are shown in Table 1.

(Tensile strength (MPa), 0.2 yield strength (MPa), yield strength ratio (%), drawing (%))
A JIS No. 4 test piece was prepared from the above test material, and a tensile test was performed based on JIS Z 2241. The maximum stress measured in the tensile test was taken as the tensile strength. And 0.2% yield strength was calculated | required by the offset method, and yield strength ratio (%) was calculated | required by following Formula (2).
Yield ratio (%) = 0.2% Yield strength (MPa) / Tensile strength (MPa) × 100 (2)
The restriction is the ratio of the difference between the minimum cross-sectional area after fracture of the specimen by the tensile test and the original cross-sectional area before the test to the original cross-sectional area. These results are shown in Table 2.

(Rockwell hardness)
The Rockwell hardness was determined by measuring the hardness based on JIS Z 2245. The results are shown in Table 2.

(Corrosion resistance)
Corrosion resistance was evaluated by performing a salt spray test based on JIS Z 2371. A test piece having a size of φ10 mm × 50 mm was prepared from the above-mentioned test material, a cylindrical test piece having a surface polished to # 400 was prepared, and exposure was performed for 96 hours in a 35 ° C., 5% sodium chloride aqueous solution spraying environment. A test was conducted. In this exposure test, the corrosion resistance was evaluated from the sprinkled area generated on the test surface. The firing rank is: A: No full-scale occurrence (cannot be confirmed visually), B: Partial occurrence can be confirmed, less than 50% area, C: More than half area (50% or more 75) Less than%)), D: The entire surface was found (75% or more). The results are shown in Table 2.

(Evaluation)
Inventive steels 1 to 21 all satisfied the required characteristics. In order to satisfy the above formula (1), the inventive steels 1 to 21 contain a predetermined amount of the components specified in Table 1 and include a ferrite phase and a martensite phase. This is probably because the site phase was 10% or more and 60% or less in area ratio and had both strength and corrosion resistance.

On the other hand, Comparative Steels 1 to 3 are all ferritic stainless steels, and have low strength and poor corrosion resistance.
The comparative steels 4 and 5 are for confirming the influence of the C amount, and even if other component compositions satisfy the predetermined conditions, the strength is lowered when the C amount is low as in the comparative steel 4. It was found that when the amount of C was large as in comparative steel 5, the corrosion resistance was poor.
The comparative steels 6 and 7 are for confirming the influence of the Cr amount. Even if the other component compositions satisfy the predetermined conditions, the corrosion resistance is deteriorated when the Cr amount is low, and the Cr amount is large. It was found that the strength was lowered.

The comparative steels 8 and 9 are for confirming the influence of the component balance of the Cr amount, the Cu amount, and the Mn amount, and the Cu amount and the Mn amount are not limited even if other component compositions satisfy the predetermined conditions. It was found that when both are low, the strength is low even if the corrosion resistance is good, and when both the amount of Cu and the amount of Mn are large, constriction and corrosion resistance are low even if the strength is good.
The comparative steels 10 and 11 are for confirming the influence of the [A] value. According to the comparative steel 10, even if the amount of Mn, the amount of Cu, and the amount of Cr are within the predetermined ranges, if the amount of Mn and the amount of Cu are too large relative to the amount of Cr, martensite is generated too much, and the area ratio is excessive. As a result, the phase balance deteriorated, resulting in insufficient drawing and corrosion resistance. On the other hand, according to the comparative steel 11, even if the amount of Mn, the amount of Cu and the amount of Cr are within a predetermined range, if the amount of Mn and the amount of Cu are too small relative to the amount of Cr, the martensite is small and the area ratio is too small. As a result, the phase balance deteriorated and the strength was insufficient.

  From these facts, the inventive steels 1 to 21 contain a predetermined amount of the components specified in Table 1 and satisfy the above formula (1), so that they include a ferrite phase and a martensite phase, It was confirmed that the martensite phase of the structure was 10% or more and 58% or less in area ratio, and had both strength and corrosion resistance.

(Example B)
(Production of test pieces and various tests)
Each steel ingot of 50 kg having the composition of the inventive steels 1 to 4 and the comparative steels 1 to 3 in Table 1 was melted in a high frequency induction furnace and cooled to prepare an ingot. Next, each ingot was heated to 1000 to 1200 ° C., processed into a round bar having a diameter of 5.5 mm by hot rolling, and further cold-drawn to a diameter of 4.0 mm. Then, the area ratio (%) of martensite was measured by the same method as in Example A. Furthermore, an annealing treatment was performed at 800 ° C. for 4 hours in an atmospheric heat treatment furnace, and after the surface was polished to # 800, a tensile test was performed based on JIS Z 2241. Further, a salt spray test was performed based on JIS Z 2371 using a similarly finished steel wire. The results are shown in Table 3.

(Evaluation)
Steel wires obtained by drawing the inventive steels 1 to 4 exhibit excellent properties in terms of tensile strength (MPa), 0.2 yield strength (MPa), yield strength ratio (%), drawing (%), and corrosion resistance. However, the steel wires obtained by drawing the comparative steels 1 to 3 did not satisfy the required characteristics except for drawing. From this, it has been confirmed that the inventive steels 1 to 4 have both strength and corrosion resistance even if they are drawn. Therefore, even if it wire-draws to the other invention steels 5-21, it can be said that it combines strength and corrosion resistance like the invention steels 1-4. In addition, in the cross-sectional structure of the steel wire (wire) obtained by the above cold wire drawing, a ferrite phase and a martensite phase exist, and the area ratio of the martensite phase was 30 to 35%. This area ratio was the same as the area ratio in the material state (the state when the area ratio was measured in Example A).

  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.

Since the duplex stainless steel including a ferrite phase and a martensite phase and a steel material using the same according to the present invention have high corrosion resistance and strength, they are electronic equipment, office equipment, telecommunications equipment, vehicles, food equipment, chemical equipment, kitchens. Used for machine structural parts such as kitchen equipment, kitchen kitchen miscellaneous goods, strength members for building structures, parts for vehicles, shafts, springs, nails, machine screws, wire ropes, cable wires, concrete reinforced steel wires, kitchen utensils, etc. Since it is suitable for steel and steel materials, it has high industrial utility value for steel material manufacturers.
Since the steel products according to the present invention have high corrosion resistance and strength, they are used industrially from manufacturers such as electronic equipment, office equipment, telecommunication equipment, vehicles, food equipment, chemical equipment, kitchen kitchen equipment to end users. High value.

Claims (10)

0.080 ≦ C ≦ 0.120 mass%,
0.20 ≦ Si ≦ 1.00% by mass,
1.00 ≦ Mn ≦ 3.00 mass%,
1.00 <Cu ≦ 3.00 mass%,
20.0 ≦ Cr ≦ 23.0% by mass,
0.50 ≦ Ni ≦ 1.00% by mass,
N ≦ 0.030 mass%,
[A] represented by the following formula (1) is 0.15 ≦ [A] ≦ 0.30, and
A duplex stainless steel characterized in that the martensite phase of the cross-sectional structure including the ferrite phase and martensite phase is 10% or more and 60% or less in terms of area ratio.
However, [A] = (1.4 [Mn] + [Cu]) / [ Cr] ... Formula (1) Furthermore,
The duplex stainless steel according to claim 1, which contains 0.10 ≦ Mo ≦ 1.00 mass%. Furthermore,
0.0005 ≦ B ≦ 0.0050 mass%, and / or
The duplex stainless steel according to claim 1, wherein the duplex stainless steel contains 0.20 ≦ Al ≦ 0.80 mass%. Furthermore,
The duplex stainless steel according to any one of claims 1 to 3, comprising O ≤ 0.030 mass%. Furthermore,
5. The composition contains one or more selected from the group consisting of Nb, Ti, V, W, Ta, and Hf in a total amount of 0.01% by mass to 0.60% by mass. The duplex stainless steel according to any one of the above. Furthermore,
The duplex stainless steel according to any one of claims 1 to 5, characterized by containing 0.01≤Co≤0.60 mass%. Furthermore,
It contains 0.0005 mass% or more and 0.0100 mass% or less of 1 type, or 2 or more types chosen from the group which consists of Ca, Mg, and REM in a total amount, It is any one of Claim 1 to 6 characterized by the above-mentioned. Duplex stainless steel.   The duplex stainless steel according to any one of claims 1 to 7, wherein the Rockwell hardness is 85HRB or more and 100HRB or less.   A steel material comprising the duplex stainless steel according to any one of claims 1 to 8.   A steel product comprising the duplex stainless steel according to any one of claims 1 to 8.

Images