JP5526809B2 - High corrosion resistance, high strength, non-magnetic stainless steel and high corrosion resistance, high strength, non magnetic stainless steel products and methods for producing the same - Google Patents

Description

  The present invention relates to a high corrosion resistance, high strength, nonmagnetic stainless steel and a high corrosion resistance, high strength, nonmagnetic stainless steel product and a method for producing the same, and more particularly, the influence of geomagnetism can be cut off and used particularly in petroleum well drilling. The present invention relates to a technique for producing a suitable nonmagnetic stainless steel without impairing characteristics (high corrosion resistance and high strength).

  Conventionally, when drilling oil wells using a drill, the position of the drill tip from the ground surface (for example, azimuth / inclination) is specified by magnetic sensing and the drill is controlled. Mounted on the drill collar. In this case, in order to measure the azimuth and inclination, it is necessary that the drill collar or the like is made of nonmagnetic steel in order to block the influence of geomagnetism. Conventionally, 13Cr-18Mn-0.5Mo-2Ni-0.3N, 13Cr-21Mn-0.3N, 16.5Cr-16Mn-1Mo-1.3Ni-0.5Cu-0. High Mn nonmagnetic stainless steel such as 4N has been used.

As this kind of well-known improvement technique, for example, a technique described in the following patent document has been proposed.
In Patent Document 1, C: 0.15% or less, Si: 0.1-2.0%, Mn: 7.0-18.0%, Ni for use in a centrifuge rotor or the like : 0.50 to 6.0%, Cr: 15.0 to less than 21.0%, Mo: 0.5 to 4.0%, N: 0.20 to 0.60%, the balance Fe and impurities A high strength austenitic stainless steel is disclosed.

  In Patent Document 2, C: 0.01 to 0.20 wt%, Si: 0.05 to 1.5 wt%, Mn: 16 to, for use as a superconducting electromagnet or a superconductor holding material. 27 wt%, Cr: 10 to 20 wt%, Cu: 0.1 to 4 wt%, N: 0.10 to 0.50 wt%, Al: 0.003 to 0.20 wt%, the balance being Fe and inevitable An extremely low temperature tough steel having excellent rust resistance composed of impurities is disclosed.

  In Patent Document 3, C: 0.15% or less, Si: 0.1 to 2.0%, Mn: 7.0 to 18.0%, Ni: 0.50 to 6.0%, Cr: 15 0.0-26.0%, Mo: 0.5-4.0%, N: 0.2-0.6%, the balance being substantially made of Fe and hot working with a reduction rate of 50% or more And a high-strength member for a submarine vessel equipped with an underwater search ship having a finishing temperature of 800 to 1000 ° C. is disclosed.

  In Patent Document 4, C: 0.20% or less, Si: 0.05 to 2.5%, Mn: 16 to 35%, for use as a superconducting electromagnet or a superconductor holding material, etc. Cr: 10 to 20%, Ni: 0.1 to 8.0%, N: 0.10 to 0.50%, Al: 0.001 to 0.20%, S: 0.003% or less In addition, a rust-resistant, high-manganese tough steel for cryogenic use whose balance is made of Fe and inevitable impurities is disclosed.

  In Patent Document 5, C: 0.20% or less, Si: 0.05 to 2.5%, for use in a structure or the like used in a nuclear fusion experimental reactor using a superconducting electromagnet, Mn: 9 to 35%, Cr: 10 to 20%, Ni: 0.1 to 8.0%, N: 0.001 to 0.50%, Al: 0.001 to 0.20%, Ca: 0 A high-manganese steel for cryogenic temperatures having excellent rust resistance, containing 0.001 to 0.020% and the balance being Fe and inevitable impurities is disclosed.

  In Patent Document 6, C: 0.01 to 0.15 wt%, Si: 0 for applications to precision instrument parts (micromotor shaft, magnetic tape guide, shaft, etc.) that need to avoid magnetism. 0.05 to 0.60 wt%, Mn: 16 to 25 wt%, S ≦ 0.010 wt%, Ni ≦ 4.0 wt%, Cr: 14 to 20 wt%, N: 0.3 to 0.6 wt%, O ≦ 0 .01 wt%, Al: 0.001 to 0.20 wt%, and in addition, the area ratio is non-metallic inclusions ≦ 0.10%, and the balance is excellent in weather resistance consisting of Fe and inevitable impurities A high strength non-magnetic steel is disclosed.

  In Patent Document 7, for use as an interdental brush wire, C ≦ 0.07%, Si ≦ 0.6%, Mn: 13-17%, Ni: 2.0-5. 0%, Cr: 16.0 to 20.0%, Mo: 0.4 to 2.0%, N: 0.3 to 0.60%, and Cu: 0.3 to 1.0% An interdental brush wire is disclosed.

  In Patent Document 8, C: 0.06% or less, Si: 0.40% or less, Mn: 15.5 to 17%, P: 0.040 for use as a drill collar for drilling oil wells. % Or less, S: 0.010% or less, Cu: 0.35 to 2.00%, Ni: 2.50 to 4.00%, Cr: 17.0 to 21.0%, Mo + W: 0.5 to 1.5%, N: 0.42 to 0.65%, O: 0.01% or less, sol-Al: 0.05% or less and B: 0.001 to 0.010%, the balance being Non-magnetic stainless steel that is substantially Fe is disclosed.

  Thus, many stainless steels excellent in properties such as corrosion resistance and non-magnetic properties have been proposed.

JP-A-53-117618 JP 59-104455 A JP 59-205452 A JP-A 61-143563 JP-A 61-170545 JP-A-61-238943 JP 2004-052097 A Japanese Patent Laid-Open No. 2004-156066

Recently, however, the drilling area for oil wells is also diverse, and there is a demand from the industry for further high corrosion resistance and high strength stainless steel premised on non-magnetism. Moreover, the various steels described in Patent Documents 1 to 8 have many problems to be improved. For example, the high-strength austenitic stainless steel of Patent Document 1 and the high-strength member for underwater search ship-mounted equipment of Patent Document 3 are concerned with deterioration of workability and corrosion resistance due to coarse carbide crystallization because C is excessive.
The extremely low temperature tough steel of Patent Document 2 and the rust-resistant high temperature tough steel for extremely low temperature of Patent Document 4 have a concern that it may not satisfy the required characteristics of nonmagnetic properties, high strength, and corrosion resistance because N is low. The extremely low temperature tough steel of Patent Document 2 is also concerned about deterioration of corrosion resistance due to excessive Mn.

The cryogenic high-manganese steel of Patent Document 5 has a low Cr content relative to Mn and a low N content, so there is a concern that it will not satisfy the required characteristics of nonmagnetic properties, high strength, and corrosion resistance.
The high-strength nonmagnetic steel of Patent Document 6 has less Ni and N, the interdental brush wire of Patent Document 7 has too little Mn and Ni, and the nonmagnetic stainless steel of Patent Document 8 has too little Ni and Mo. Therefore, there is a concern that the required properties of nonmagnetic properties, high strength, and corrosion resistance are not satisfied.
As described above, according to Patent Documents 1 to 8, stainless steel satisfying the required characteristics has not been obtained.

The present invention has been made in view of the above circumstances, and has high corrosion resistance, high strength, nonmagnetic stainless steel, high corrosion resistance, high strength, nonmagnetic stainless steel products and high corrosion resistance, high strength, nonmagnetic properties, and its An object is to provide a manufacturing method.
In particular, it can block the influence of geomagnetism when drilling oil wells and can be applied to petroleum well cutting products across a wide range of areas, as well as high corrosion resistance suitable as a material for various parts (various spring products, VTR guide pins, motor shafts) It is an object of the present invention to provide a high-strength non-magnetic stainless steel, a high corrosion resistance high-strength non-magnetic stainless steel product, and a method for producing the same.

In order to solve the above-mentioned problems, the present inventors have conducted extensive research focusing on the use of Cr and Mo, which are elements for improving corrosion resistance, in order to achieve high corrosion resistance. However, the increase in Cr and Mo is magnetic. Therefore, we faced the problem that “non-magnetism that can block the influence of geomagnetism” required for drill collars for oil well cutting and the like cannot be achieved. Therefore, as a result of further diligent research, the present inventors, as a result of using Cr and Mo to achieve high corrosion resistance, use N and Ni to adjust the composition balance to achieve stable nonmagnetic properties. It came to know that an austenite single phase structure was obtained.
The present invention has been made based on such knowledge.

In order to solve the above problems, the high corrosion resistance / high strength / nonmagnetic stainless steel according to the present invention is 0.01 ≦ C ≦ 0.05 mass%, 0.05 ≦ Si ≦ 0.50 mass%, 16. 0 <Mn ≦ 19.0 mass%, P ≦ 0.040 mass%, S ≦ 0.010 mass%, 0.50 ≦ Cu ≦ 0.80 mass%, 3.5 ≦ Ni ≦ 5.0 mass%, 17.0 ≦ Cr ≦ 21.0 mass%, 1.80 ≦ Mo ≦ 3.50 mass%, 0.0010 ≦ B ≦ 0.0050 mass%, O ≦ 0.010 mass%, and 0.45 ≦ N ≦ 0.65 mass%,
The following expressions (1) to (4) meet, the balance is summarized in that consisting of F e and unavoidable impurities.
P. I = [Cr] + 3.3 × [Mo] + 16 × [N] ≧ 30 Formula (1)
[Cr] / [C] ≧ 330 Formula (2)
[Cr] / [Mn]> 1.0 Formula (3)
([Ni] + 3 × [Cu]) / ([Cr] + [Mo])> 0.25 Formula (4) where [M] represents mass% of the component M.

High corrosion resistance, high strength, non-magnetic stainless steel according to the present invention is
Furthermore, any one or two or more of the group consisting of Ca, Mg, and REM may be contained in total, 0.0001 ≦ Ca + Mg + REM ≦ 0.0100 mass%,
Furthermore, any one or two or more of the group consisting of Nb, V, Ta, Hf may be contained in total, 0.1 ≦ Nb + V + Ta + Hf ≦ 2.0% by mass,
Furthermore, 0.001 ≦ Al ≦ 0.10% by mass may be contained,
Furthermore, you may contain 0.1 <= W + Co <= 3.0 mass% in any one or the 2 types or more in the group which consists of W and Co in total.

  The manufacturing method of the high corrosion resistance / high strength / non-magnetic stainless steel product according to the present invention is a reduction in area ratio under the temperature condition of 300 to 900 ° C. with respect to the high corrosion resistance / high strength / non-magnetic stainless steel according to the present invention. The gist is to perform 15 to 40% processing.

  The high corrosion resistance / high strength / non-magnetic stainless steel product according to the present invention has a surface area reduction rate of 15 to under a temperature condition of 300 to 900 ° C. compared to the high corrosion resistance / high strength / nonmagnetic stainless steel according to the present invention. The gist is obtained by performing 40% processing. Examples of the steel product to be obtained include oil well drilling products, spring products, VTR guide pins, motor shafts, and the like.

The high corrosion resistance / high strength / nonmagnetic stainless steel product and the high corrosion resistance / high strength / nonmagnetic stainless steel product according to the present invention have the above component composition and satisfy the above formulas (1) to (4). Corrosion resistance, high strength, non-magnetic. Therefore, it is possible to cut off the influence of geomagnetism when drilling oil wells, and to be applied to petroleum well cutting products across a wide range of areas, as well as suitable as a material for various parts (various spring products, VTR guide pins, motor shafts). There is.
According to the method for producing a high corrosion resistance / high strength / nonmagnetic stainless steel product according to the present invention, the obtained steel product can exhibit the same effects as described above.

A high corrosion resistance, high strength, nonmagnetic stainless steel according to an embodiment of the present invention will be described below.
The high corrosion resistance / high strength / nonmagnetic stainless steel according to the present embodiment contains the following essential elements and selective elements, with the balance being Fe and inevitable impurities, and the formulas (1) to (4) described below. Satisfies the relationship defined in.

(Composition composition of high corrosion resistance, high strength, non-magnetic stainless steel and reasons for limitation)
The high corrosion resistance / high strength / nonmagnetic stainless steel according to the present embodiment contains C, Si, Mn, Cu, Ni, Cr, Mo, B, and N as essential elements, with the balance being Fe and inevitable impurities. Consists of. Here, inevitable impurities include, for example, P, S, and O.

(1) 0.01 ≦ C ≦ 0.05 mass%
C is an essential element indispensable as an austenite-forming element and contributes to strength, so 0.01% by mass is set as the lower limit. Further, if C is added excessively, coarse carbides are crystallized to deteriorate workability and corrosion resistance, so 0.05 mass% is made the upper limit. The C content is more preferably 0.03 ≦ C ≦ 0.05 mass%.

(2) 0.05 ≦ Si ≦ 0.50 mass%
Since Si is an essential element to be added as a deoxidizer for steel, 0.05% by mass is set as the lower limit. However, if the content of Si is excessive, the toughness is lowered and the hot workability of the steel is deteriorated, so the upper limit is made 0.50% by mass. The Si content is more preferably 0.10 ≦ Si ≦ 0.30 mass%.

(3) 16.0 <Mn ≦ 19.0 mass%
Mn is an essential element that acts as a deoxidizer for steel, and in order to ensure N solid capacity, the lower limit is 16.0% by mass. On the other hand, since Mn deteriorates corrosion resistance, the upper limit is 19.0% by mass. The Mn content is more preferably 16.0 ≦ Mn ≦ 17.0% by mass.

(4) P ≦ 0.040 mass%
P is an unavoidable impurity, segregates at the grain boundary, increases the intergranular corrosion sensitivity, and lowers the toughness. % Or less. As for P content, 0.030 mass% or less is more preferable.

(5) S ≦ 0.010 mass%
S is an unavoidable impurity and lowers the hot workability, so 0.010% by mass is the upper limit. From the viewpoint of balance with the manufacturing cost, the S content is more preferably 0.005% by mass or less.

(6) 0.50 ≦ Cu ≦ 0.80 mass%
Cu is an essential element, and is effective for improving corrosion resistance, particularly corrosion resistance in a reducing acid environment, and is effective for obtaining an austenite single phase structure. The lower limit. On the other hand, since excessive addition of Cu deteriorates hot workability, the upper limit of the Cu content is 0.80% by mass.

(7) 3.5 ≦ Ni ≦ 5.0 mass%
Ni is an essential element and is effective in improving the corrosion resistance, in particular, the corrosion resistance in a reducing acid environment, and since an austenite single phase structure is obtained during the solution heat treatment, 3.5 mass. % Is the lower limit. On the other hand, excessive addition of Ni causes an increase in cost, so the upper limit is made 5.0 mass%. The Ni content is more preferably 3.5 ≦ Ni ≦ 4.5% by mass from the balance between characteristics and cost.

(8) 17.0 ≦ Cr ≦ 21.0% by mass
Cr is an essential element from the viewpoint of ensuring corrosion resistance, and in order to ensure the amount of N solid solution, the lower limit is 17.0% by mass. On the other hand, excessive addition of Cr impairs hot workability and causes a decrease in toughness, so the upper limit is 21.0% by mass. The Cr content is more preferably 18.0 ≦ Cr ≦ 19.5% by mass.

(9) 1.80 ≦ Mo ≦ 3.50 mass%
Mo is an essential element, and necessary corrosion resistance can be obtained and the strength can be further improved. Therefore, 1.80% by mass is set as the lower limit. On the other hand, excessive addition of Mo impairs hot workability and causes an increase in cost. Therefore, the upper limit is set to 3.50% by mass. The Mo content is more preferably 2.00 ≦ Mo ≦ 2.50 mass%.

(10) 0.0010 ≦ B ≦ 0.0050 mass%
B is an essential element effective for improving the hot workability of steel, so 0.0010% by mass is set as the lower limit. On the other hand, excessive addition of B forms nitrides such as BN and degrades workability, so 0.0050 mass% is made the upper limit. The B content is more preferably 0.0030% by mass or less.

(11) O ≦ 0.010 mass%
O is an unavoidable impurity and forms a harmful oxide that adversely affects cold workability, fatigue properties, and the like, so it should be suppressed as low as possible, and the upper limit is 0.010 mass%. From the viewpoint of balance with the manufacturing cost, the O content is more preferably 0.007% by mass or less, and further preferably 0.005% by mass or less.

(12) 0.45 ≦ N ≦ 0.65 mass%
N is an essential element necessary for obtaining nonmagnetic properties, high strength, and good corrosion resistance, and the lower limit is 0.45% by mass. On the other hand, excessive addition of N causes N blow, so the upper limit is 0.65% by mass. The N content is more preferably 0.50 ≦ N ≦ 0.60 mass%.

The high corrosion resistance / high strength / nonmagnetic stainless steel according to the present embodiment further includes the following selective elements, that is, a group consisting of “Ca, Mg, REM”, a group consisting of “Nb, V, Ta, Hf”, You may contain any 1 type (s) or 2 or more types of the element contained in the group which consists of Al and "W, Co".
(13) Any one or more of the group consisting of Ca, Mg and REM in total,
0.0001 ≦ Ca + Mg + REM ≦ 0.0100 mass%
Ca, Mg, and REM are selective elements, and since they are effective elements for improving the hot workability of steel, 0.0001 mass% in total may be added as a lower limit. However, these excessive additions saturate the effect and conversely reduce the hot workability, so the upper limit is 0.0100% by mass. As for these content, 0.0050 mass% or less is more preferable. In the present embodiment, REM refers to a material containing Ce, La, or an alloy thereof.

(14) Any one or two or more of the group consisting of Nb, V, Ta, and Hf in total, 0.1 ≦ Nb + V + Ta + Hf ≦ 2.0% by mass
Nb, V, Ta, and Hf are selective elements, and these have the effect of forming carbides or carbonitrides to refine the crystal grains of the steel and increase the toughness. Therefore, the total content of Nb, V, Ta, and Hf is 0.1% by mass as the lower limit. On the other hand, excessive addition of Nb, V, Ta, and Hf causes an increase in cost, so the upper limit is made 2.0 mass% in total. As for content of Nb, V, Ta, and Hf, 1.0 mass% or less is more preferable.

(15) 0.001 ≦ Al ≦ 0.10 mass%
Al is a strong deoxidizing element, and is an optional element added as necessary to reduce O as much as possible. The lower limit of the Al content is 0.001% by mass, the effect of which can be confirmed. On the other hand, excessive addition of Al deteriorates hot workability, so the upper limit is made 0.10% by mass. The Al content is more preferably 0.050% by mass or less, and further preferably 0.010% by mass or less.

(16) Any one or two or more of the group consisting of W and Co in total, 0.1 ≦ W + Co ≦ 3.0 mass%
W is an optional element and has the effect of improving corrosion resistance, forming carbides or carbonitrides to refine steel crystal grains and increasing toughness, so that 0.1 ≦ W ≦ 3.0 mass% You may add in the range. On the other hand, excessive addition of W causes an increase in cost, so the W content is more preferably 2.0% by mass or less.

  Co is a selective element, is effective for obtaining an austenite single phase structure, and can be added as necessary because high strength can be achieved by solid solution strengthening. However, excessive addition of Co causes a significant increase in cost, so the upper limit is 3.0% by mass. The Co content is more preferably 1.5% by mass or less.

(Relationship between high corrosion resistance, high strength, non-magnetic stainless steel and reasons for limitation)
The high corrosion resistance / high strength / nonmagnetic stainless steel according to the present embodiment satisfies the following formulas (1) to (4).
(17) P.I. I = [Cr] + 3.3 × [Mo] + 16 × [N] ≧ 30 Formula (1)
P. I (Pitting Index) is a value indicating corrosion resistance, and is defined by [Cr], [Mo], [N]. The larger the value, the better the corrosion resistance. In order to be able to be used even in a severe corrosive environment, the value of the formula (1) is more preferably 33 or more.

(18) [Cr] / [C] ≧ 330 Formula (2)
C combines with Cr to form a carbide, reduces the Cr content in the matrix, and causes deterioration in corrosion resistance. Therefore, Expression (2) is a relational expression that can be used as an index of corrosion resistance. Therefore, since the deterioration of the corrosion resistance can be suppressed as the Cr content increases with respect to the C content, the value of the formula (2) is set to 330 or more.

(19) [Cr] / [Mn]> 1.0 Formula (3)
Both Cr and Mn are added to sufficiently dissolve N, but since Mn deteriorates the corrosion resistance, it is necessary to balance with Cr, which is an element that improves the corrosion resistance. Therefore, in order to sufficiently maintain the corrosion resistance by supplementing with Cr to the extent that the corrosion resistance deteriorates due to the addition of Mn, the value of Equation (3) is set to more than 1.0.

(20) ([Ni] + 3 × [Cu]) / ([Cr] + [Mo])> 0.25 Formula (4)
Both Cr and Mo are added to ensure sufficient corrosion resistance, but the stability of the austenite single phase decreases accordingly. Therefore, in order to stabilize the austenite phase, a predetermined amount of Ni and Cu, which are austenite forming elements, are contained to suppress a decrease in stability of the austenite single phase. Moreover, since Cr increase and addition of Mo act in the direction which impairs nonmagnetism, nonmagnetism is maintained by Ni and Cu. In view of these circumstances, Equation (4) defines a quantitative relationship that Ni and Cu should satisfy with respect to Cr and Mo. Although the value of Formula (4) shall be over 0.25, 0.30 or more is more preferable.

(High corrosion resistance, high strength, non-magnetic stainless steel and steel product manufacturing method using the same)
High corrosion resistance, high strength, non-magnetic stainless steel according to this embodiment is
(1) melting a steel ingot containing a predetermined amount of the predetermined component so as to satisfy a predetermined relationship;
(2) After processing into an appropriate shape and size by hot processing,
(3) Obtained by subjecting to a solution treatment (1050-1150 ° C.),
High corrosion resistance, high strength, non-magnetic stainless steel products according to the present embodiment,
(4) It is obtained by performing warm processing (300 to 900 ° C., area reduction rate of 15 to 40%), and further cutting or the like may be performed as necessary. The lower limit temperature is set to 300 ° C. because the lower the processing temperature, the higher the strength, while the lower the elongation / drawing and the lower the processing.

(Production of invention steel and comparative steel)
A 50 kg steel ingot having the composition shown in Tables 1 and 2 (the balance is made of Fe and inevitable impurities) is melted in a high-frequency induction furnace, and a bar with a diameter of 20 mm is produced by hot forging. The solution treatment was performed at 1050 to 1150 ° C. Table 2 also shows the values of the above formulas (1) to (4). In Tables 1 and 2, the horizontal bar (-) indicates that the corresponding element is not added, or is inevitably included even if it is not added.

その後、表３及び表４に示す温度条件及び減面率で温間加工を実施し、供試材（加工材）を作製した。この供試材から各種試験片に加工を行った。
引張強さ、０．２％耐力、伸び（％）は、供試材からＪＩＳ４号試験片を作製し、ＪＩＳ Ｚ ２２４１に準拠して先端に引張荷重を加えた際の破断応力を測定することにより求めた。
透磁率は、外部磁界を２００Ｏｅとし、ＶＳＭ法に従って透磁率測定を行うことにより求めた。
耐食性は、６％塩化第二鉄試験（ＪＩＳ Ｇ ０５７８）、１０％蓚酸エッチ試験（ＪＩＳ Ｇ ０５７１）により評価した。
これらの試験結果を表３及び表４に併せて示す。

Then, warm processing was implemented on the temperature conditions and surface-reduction rate shown in Table 3 and Table 4, and the test material (processed material) was produced. Various test pieces were processed from this specimen.
Tensile strength, 0.2% proof stress, and elongation (%) are measured by measuring the rupture stress when a JIS No. 4 test piece is prepared from the specimen and a tensile load is applied to the tip in accordance with JIS Z 2241. Determined by
The magnetic permeability was determined by measuring the magnetic permeability according to the VSM method with an external magnetic field of 200 Oe.
The corrosion resistance was evaluated by a 6% ferric chloride test (JIS G 0578) and a 10% oxalic acid etch test (JIS G 0571).
These test results are also shown in Tables 3 and 4.

(Evaluation)
Inventive steels 1 to 26 have strength (tensile strength ≧ 1050 MPa, 0.2% yield strength ≧ 968 MPa), workability (elongation ≧ 25), nonmagnetic (permeability ≦ 1.010), corrosion resistance (ferric chloride corrosion) <0.5, 10% oxalic acid etch met the required properties for any of the steps). Inventive steels 1 to 26 contain a predetermined amount of the components specified in Tables 1 and 2 and satisfy the formulas (1) to (4) specified in Table 2, so that they have high corrosion resistance, high strength, and nonmagnetic properties. It is thought that it was achieved at the same time.
Therefore, invention steels 1 to 26 block the influence of geomagnetism during oil well drilling and can be applied to petroleum well cutting products across a wide range of areas, as well as various parts (various spring products, VTR guide pins, motor shafts) materials. It was also found to be suitable.

  On the other hand, the comparative steels 1 to 10 have the strength (tensile strength ≧ 1050 MPa, 0.2% proof stress ≧ 968 MPa), workability (elongation ≧ 25), nonmagnetic (permeability ≦ 1.010), corrosion resistance (salt chloride). Some ferric corrosion <0.5, 10% oxalic acid etches) did not meet the required properties. It is considered that Comparative Steels 1 to 10 did not contain a predetermined amount of the components specified in Tables 1 and 2 or did not satisfy any of Formulas (1) to (4) specified in Table 2.

For example, it is considered that the comparative steel 1 does not satisfy the formula (1) because Mo is small, and further does not satisfy the formula (2) because C is excessive, and the corrosion resistance is impaired even if the Mn is small. The comparative steel 1 did not satisfy the formula (4), but the magnetic permeability satisfied the required characteristics.
Even if the comparative steel 2 contains a predetermined amount of Cr that is essential for ensuring corrosion resistance, Mo and N are small, so the formula (1) is not satisfied and the corrosion resistance is considered to be impaired. Furthermore, it is thought that the reason why the permeability of the comparative steel 2 was high was that N was low.

Even if the comparative steel 3 contains a predetermined amount of Cr that is essential for ensuring corrosion resistance, Mo and N are small, so Formula (1) is not satisfied, and C is too large to satisfy Formula (2). Therefore, it is considered that the corrosion resistance is impaired.
Comparative steel 4 and comparative steel 5 are considered to have deteriorated corrosion resistance because they have too little Mo, too much Mn, and little Cr, so they do not satisfy formulas (1) and (3).
It is considered that the comparative steel 6 does not satisfy the formula (4) because Cu is too small, and the corrosion resistance is impaired.

In comparative steel 7, Cu, Ni, and Mo are outside the predetermined range, but satisfy the formulas (1) to (4) and satisfy the required characteristics of high corrosion resistance, non-magnetic property, and high strength. However, it was found that the comparative steel 7 had a low processing temperature and therefore had a low elongation and was difficult to process and not suitable for actual production.
It is considered that the comparative steel 8 has insufficient Cu and Mo, does not satisfy the formula (1), and has deteriorated the corrosion resistance. Further, in the comparative steel 8, the processing temperature was set to 950 ° C., but it was confirmed that even if the processing temperature was raised, the strength was not very effective.

  The comparative steel 9 and the comparative steel 10 are considered to have deteriorated corrosion resistance because Mo is insufficient, does not satisfy the formula (1), does not satisfy the formula (3) due to the component balance, and further, Cu is insufficient. It is done. Furthermore, all of these had high magnetic permeability. In addition, it is considered that the comparative steel 9 has a high elongation because it has a low area reduction rate of 10% even when the processing temperature is low, and the workability does not deteriorate due to work hardening. On the other hand, it was found that the comparative steel 10 had a low processing temperature and a high surface area reduction ratio of 50%, so that it became high strength by work hardening, but its elongation was low and difficult to process, making it unsuitable for actual production.

  As mentioned above, although one embodiment of the present invention has been described, the present invention is not limited to the above-described embodiment at all, and various modifications can be made based on the knowledge of those skilled in the art without departing from the spirit of the present invention. Such modifications are possible and are within the scope of the invention.

  The high corrosion resistance, high strength, non-magnetic stainless steel and steel product according to the present invention and the manufacturing method thereof have a predetermined component composition and the relationship between the predetermined components is adjusted. High value. The high corrosion resistance, high strength, nonmagnetic stainless steel according to the present invention is expected to be applied to steel products such as petroleum well cutting products, springs, shafts, bolts, screw products and the like.

Claims (7)

0.01 ≦ C ≦ 0.05% by mass,
0.05 ≦ Si ≦ 0.50 mass%,
16.0 <Mn ≦ 19.0% by mass,
P ≦ 0.040 mass%,
S ≦ 0.010 mass%,
0.50 ≦ Cu ≦ 0.80 mass%,
3.5 ≦ Ni ≦ 5.0 mass%,
17.0 ≦ Cr ≦ 21.0% by mass,
1.80 ≦ Mo ≦ 3.50 mass%,
0.0010 ≦ B ≦ 0.0050 mass%,
O ≦ 0.010 mass%, and
0.45 ≦ N ≦ 0.65 mass%,
The following formulas (1) to (4) meets the high corrosion-resistant, high-strength and non-magnetic stainless steel balance being composed of F e and unavoidable impurities.
P. I = [Cr] + 3.3 × [Mo] + 16 × [N] ≧ 30 Formula (1)
[Cr] / [C] ≧ 330 Formula (2)
[Cr] / [Mn]> 1.0 Formula (3)
([Ni] + 3 × [Cu]) / ([Cr] + [Mo])> 0.25 Formula (4) where [M] represents mass% of the component M. Furthermore,
Any one or more of the group consisting of Ca, Mg and REM in total,
0.0001 ≦ Ca + Mg + REM ≦ 0.0100 mass%,
The high corrosion resistance / high strength / nonmagnetic stainless steel according to claim 1, which is contained. Furthermore,
Any one or more of the group consisting of Nb, V, Ta, Hf in total,
0.1 ≦ Nb + V + Ta + Hf ≦ 2.0 mass%,
The high corrosion resistance / high strength / nonmagnetic stainless steel according to claim 1, which is contained. Furthermore,
0.001 ≦ Al ≦ 0.10 mass%,
The high corrosion resistance / high strength / nonmagnetic stainless steel according to claim 1, wherein the stainless steel is contained. Any one or more of the group consisting of W and Co in total,
0.1 ≦ W + Co ≦ 3.0% by mass,
5. The high corrosion resistance / high strength / nonmagnetic stainless steel according to any one of claims 1 to 4, which is contained.   The high corrosion resistance / high strength / nonmagnetic stainless steel according to any one of claims 1 to 5 is processed at a temperature reduction of 15 to 40% under a temperature condition of 300 to 900 ° C. Manufacturing method of high corrosion resistance, high strength, non-magnetic stainless steel products.   The high corrosion resistance, high strength, non-magnetic stainless steel according to any one of claims 1 to 5 can be obtained by performing processing with a surface reduction rate of 15 to 40% under a temperature condition of 300 to 900 ° C. High corrosion resistance, high strength, non-magnetic stainless steel products characterized by