Stainless steel powder, stainless steel member, and method for producing stainless steel member

Abstract

The purpose of the present invention is to provide a stainless steel powder with which it is possible to produce a stainless steel member having high strength, excellent low-temperature toughness, and excellent corrosion resistance in a high-temperature harsh corrosive environment containing carbon dioxide (CO2) and chloride ions (Cl-), an environment containing hydrogen sulfide (H2S), or the like. A stainless steel powder having a specific composition, a particle diameter D50, which is a median diameter located at 50% of the mass cumulative distribution, of 10-200 [mu] m, and an apparent density of 3.5-5.0 Mg / m3.

Description

Technical Field

[0001] The present invention relates to a stainless steel powder suitable for manufacturing high-strength stainless steel couplings, parts, accessories and other parts used in oil wells and gas wells (hereinafter referred to as oil wells) of crude oil or natural gas, etc. In addition, the present invention relates to a stainless steel member molded using the stainless steel powder and a method for manufacturing the stainless steel member. Background Art

[0002] In recent years, from the perspective of predicting the depletion of energy resources in the near future, the development of previously undiscovered deep oil fields, oil fields and gas fields in a so-called acidic environment containing carbon dioxide, hydrogen sulfide, etc., has been actively carried out. In such oil fields and gas fields, the depth is usually very deep, and the atmosphere is also high temperature and contains CO2, Cl - The oil well steel pipe used in such an environment is required to have high strength and high corrosion resistance. In addition, low temperature toughness is also required as the development of cold regions and deep sea is in full swing.

[0003] Recently, oil wells are being developed in a high-temperature corrosive environment of up to 150°C. In such an environment, 13Cr stainless steel and 15Cr stainless steel are used. For example, as 13Cr stainless steel pipes, there are Patent Documents 1 to 8. In addition, as a molding method accompanied by a rapid melting and rapid solidification process, there is Patent Document 9.

[0004] Prior art literature

[0005] Patent Literature

[0006] Patent Document 1: International Publication No. 2008 / 023702

[0007] Patent Document 2: Japanese Patent Application Laid-Open No. 9-170019

[0008] Patent Document 3: Japanese Patent Application Laid-Open No. 7-166303

[0009] Patent Document 4: Japanese Patent Application Publication No. 2010-242163

[0010] Patent Document 5: International Publication No. 2017 / 038178

[0011] Patent Document 6: International Publication No. 2018 / 079111

[0012] Patent Document 7: International Publication No. 2019 / 065115

[0013] Patent Document 8: International Publication No. 2019 / 065116

[0014] Patent Document 9: Japanese Patent Application Publication No. 2019-119913 Summary of the invention

[0015] Problems to be solved by the invention

[0016] The technologies disclosed in Patent Documents 1 to 9 are particularly useful in the presence of carbon dioxide (CO2) and chloride ions (Cl - ) in severe corrosive environments with high temperatures or in environments containing hydrogen sulfide (H2S), and sometimes cannot withstand the harsher development environments of oil fields and gas fields in recent years.

[0017] Therefore, the object of the present invention is to solve the problems of the prior art and provide a stainless steel powder suitable for molding, which can be produced especially in the presence of carbon dioxide (CO2) and chloride ions (Cl - The present invention provides a stainless steel component having high strength, excellent low-temperature toughness and excellent corrosion resistance in a severe corrosive environment of high temperature such as 200°C or 250°C, an environment containing hydrogen sulfide (H2S), etc. In addition, an object of the present invention is to provide a stainless steel component having high strength, excellent low-temperature toughness and excellent corrosion resistance in the above-mentioned environment and a method for manufacturing the stainless steel component.

[0018] It should be noted that the "high strength" in the present invention refers to a case where the yield strength is 655 MPa or more.

[0019] In addition, "excellent low temperature toughness" means the following: According to the provisions of JIS Z 2242, a V-notch test piece (10 mm thick) is cut so that the length direction of the test piece is perpendicular to the shaping direction and the notch is parallel to the shaping direction, and the Charpy impact test is carried out. The test temperature in the Charpy impact test is: the absorbed energy vE at -10°C -10 More than 40J.

[0020] In addition, “excellent corrosion resistance” refers to the case of having “excellent carbon dioxide corrosion resistance” and “excellent sulfide stress corrosion cracking resistance”.

[0021] Regarding the above-mentioned "excellent carbon dioxide corrosion resistance", when the Cr content in the steel is 14.0% or less, it refers to the following situation: the test piece is immersed in a test liquid maintained in an autoclave: a 20 mass% NaCl aqueous solution (liquid temperature: 150°C, a CO2 gas atmosphere of 10 atmospheres), the immersion time is set to 336 hours and the corrosion rate during implementation is 0.125 mm / y or less, and for the test piece after the corrosion test, a magnifying glass with a magnification of 10 times is used to observe whether pitting occurs on the surface of the test piece, and no pitting with a diameter of 0.2 mm or more is generated. When the Cr content in the steel exceeds 14.0%, it refers to the following situation: the test piece is immersed in a test liquid: 20 mass % NaCl aqueous solution (liquid temperature: 180°C, CO2 gas atmosphere of 10 atmospheres) maintained in an autoclave, the immersion time is set to 336 hours and the corrosion rate during implementation is 0.125 mm / y or less, and for the test piece after the corrosion test, a magnifying glass with a magnification of 10 times is used to observe whether pitting corrosion occurs on the surface of the test piece, and no pitting corrosion with a diameter of 0.2 mm or more is generated.

[0022] In addition, the above-mentioned "excellent resistance to sulfide stress corrosion cracking" refers to the following situation: the test piece was immersed in an aqueous solution prepared by adding acetic acid + sodium acetate to the test liquid: 5% mass NaCl aqueous solution (liquid temperature: 25°C, H2S: 0.1atm, CO2: 0.9atm) and adjusting the pH to 3.5, the immersion time was set to 720 hours, 90% of the yield stress was loaded as the load stress, and no cracks were generated in the test piece after the test.

[0023] Methods used to solve problems

[0024] In order to solve the above problems, the inventors have focused on the stacking molding method, a method of manufacturing a three-dimensional object using a 3D printer (3D printing method). In the stacking molding method, the stainless steel powder used as the raw material during molding is quickly heated and cooled, so that the structure is significantly refined, and non-metallic inclusions (hereinafter referred to as inclusions) known to cause corrosion resistance degradation are reduced or refined. Therefore, various factors that affect the strength, corrosion resistance and low-temperature toughness of the component composition in the stainless steel member molded by the stacking molding method have been repeatedly studied.

[0025] Specifically, the ingot produced by the melting-casting process was used as a master ingot, and then the master ingot was remelted and gas atomized to produce stainless steel powder, and then the stainless steel powder was used to produce a model by so-called 3D printing, and the above-mentioned various factors were studied. As a result, it was found that in order to meet the desired strength, corrosion resistance and low-temperature toughness, the composition of the stainless steel powder, the particle size (median particle size of the mass cumulative distribution (mass basis)) D 50and the apparent density is within the desired range.

[0026] In addition, by subjecting the obtained shaped object to appropriate heat treatment, a member having a steel structure required to meet the desired strength, corrosion resistance and low-temperature toughness can be obtained. It is found that the desired high strength, excellent low-temperature toughness and excellent corrosion resistance (carbon dioxide corrosion resistance, sulfide stress corrosion cracking resistance) can be achieved in any shape.

[0027] The present invention has been completed through further research based on the above findings. The gist of the present invention is as follows.

[0028] [1] A stainless steel powder having a composition comprising, in mass%, 0.001 to 0.06% C, 0.01 to 1.0% Si, 0.01 to 2.0% Mn, 0.05% or less P, less than 0.005% S, more than 11.0% and less than 15.0% Cr, 2.5 to 8.0% Ni, 0.005 to 0.5%, less than 0.1% Al, less than 0.100% N, less than 0.3% O, less than 3.5% Mo, with the balance being Fe and unavoidable impurities,

[0029] The median particle size at 50% of the mass cumulative distribution is the particle size D 50 10~200μm,

[0030] Apparent density is 3.5~5.0Mg / m 3 .

[0031] [2] The stainless steel powder according to [1], which, in addition to the above component composition, further contains one or more selected from the group consisting of Cu: 3.5% or less, W: 3.0% or less, Nb: 0.5% or less, Ti: 0 to 0.30%, B: 0 to 0.0050%, Zr: 0 to 0.2%, Co: 0 to 1.0%, Ta: 0 to 0.1%, Ca: 0 to 0.050%, REM: 0 to 0.1%, Mg: 0 to 0.01%, Sn: 0 to 0.5%, and Sb: 0 to 0.5%, in terms of mass %.

[0032] [3] A stainless steel member having a composition comprising, in mass%, 0.001 to 0.06% C, 0.01 to 1.0% Si, 0.01 to 2.0% Mn, 0.05% or less P, less than 0.005% S, more than 11.0% and less than 15.0% Cr, 2.5 to 8.0% Ni, 0.005 to 0.5%, less than 0.1% Al, less than 0.100% N, less than 0.3% O, less than 3.5% Mo, with the balance being Fe and unavoidable impurities,

[0033] The steel structure has a tempered martensite phase of 45% or more, a ferrite phase of 0 to 40% and a retained austenite phase of 25% or less by volume.

[0034] The yield strength of the stainless steel component is 655 MPa or more, and the absorption energy vE at the test temperature of -10°C in the Charpy impact test is -10 More than 40J.

[0035] [4] The stainless steel component according to [3], which, in addition to the above-mentioned component composition, further contains one or more selected from the group consisting of Cu: 3.5% or less, W: 3.0% or less, Nb: 0.5% or less, Ti: 0 to 0.30%, B: 0 to 0.0050%, Zr: 0 to 0.2%, Co: 0 to 1.0%, Ta: 0 to 0.1%, Ca: 0 to 0.050%, REM: 0 to 0.1%, Mg: 0 to 0.01%, Sn: 0 to 0.5%, and Sb: 0 to 0.5%.

[0036] [5] The stainless steel member according to [3] or [4], wherein the number of inclusions having a major diameter of 2 μm or more is 10 / mm 2 the following.

[0037] [6] The stainless steel member according to any one of [3] to [5], wherein, in the tempered martensite phase, among the grains having an orientation difference of 5° or more with adjacent grains, the number of the grains having a grain size of 5 μm or more is less than 10% of the total number of grains.

[0038] [7] A method for manufacturing a stainless steel component, comprising:

[0039] A molding step, wherein a molded object is formed using the stainless steel powder described in [1] or [2]; and

[0040] The heat treatment process includes heating the above-mentioned shaped object to a temperature range of 850-1150°C, cooling it to a temperature range of 50°C or below at an average cooling rate higher than air cooling, and performing a quenching treatment by heating it in a temperature range of 500-650°C, one or more times.

[0041] [8] The method for manufacturing a stainless steel member according to [7], wherein the molding step is a step of forming a molded object using a layered molding method.

[0042] Effects of the Invention

[0043] According to the present invention, a stainless steel powder, a stainless steel member using the stainless steel powder, and a method for manufacturing the stainless steel member can be provided. In particular, the stainless steel powder is suitable for manufacturing the stainless steel member by lamination molding.

[0044] In addition, the stainless steel components manufactured using the stainless steel powder of the present invention have high strength and excellent low temperature toughness, and can withstand temperatures above 150°C and contain CO2, Cl - It also has excellent corrosion resistance in harsh corrosive environments and environments containing H2S. DETAILED DESCRIPTION

[0045] Hereinafter, the present invention will be described in detail.

[0046] The stainless steel powder of the present invention has the following composition and a particle size D controlled within an appropriate range. 50 The stainless steel component of the present invention is formed from the stainless steel powder and has the same component composition as the stainless steel powder described below and a steel structure controlled within an appropriate range.

[0047] First, the component compositions of the stainless steel powder and the stainless steel member of the present invention and the reasons for their limitation are described.

[0048] C: 0.001~0.06%

[0049] C is an important element that increases the strength of martensitic stainless steel. In the present invention, in order to ensure the desired high strength, it is necessary to contain 0.001% or more of C. Therefore, the C content is set to 0.001% or more. Preferably, the C content is 0.005% or more. More preferably, the C content is 0.015% or more. On the other hand, when more than 0.06% of C is contained, the SSCC resistance decreases. Therefore, the C content is set to 0.06% or less. Preferably, the C content is 0.04% or less, and more preferably, the C content is 0.03% or less.

[0050] Si: 0.01~1.0%

[0051] Si is an element that acts as a deoxidizer. In order to obtain such an effect, it is necessary to contain 0.01% or more Si. Therefore, the Si content is set to 0.01% or more. Preferably, the Si content is 0.1% or more. More preferably, the Si content is 0.15% or more. On the other hand, when more than 1.0% Si is contained, the low-temperature toughness decreases. Therefore, the Si content is set to 1.0% or less. Preferably, the Si content is 0.8% or less. More preferably, the Si content is 0.6% or less. It is further preferred that the Si content is 0.4% or less.

[0052] Mn: 0.01~2.0%

[0053] Mn is an element that increases the strength of martensitic stainless steel. In order to ensure the desired strength, it is necessary to contain more than 0.01% Mn. Therefore, the Mn content is set to more than 0.01%. Preferably, the Mn content is more than 0.1%. More preferably, the Mn content is more than 0.15%, and more preferably, more than 0.25%. On the other hand, when more than 2.0% of Mn is contained, the low-temperature toughness decreases. Therefore, the Mn content is set to less than 2.0%. Preferably, the Mn content is less than 1.0%. The Mn content is more preferably less than 0.8%. More preferably, the Mn content is less than 0.6%.

[0054] P: 0.05% or less

[0055] P is an element that reduces corrosion resistance such as carbon dioxide corrosion resistance and sulfide stress corrosion cracking resistance. In the present invention, it is preferably reduced as much as possible, but it is allowed to be 0.05% or less. Therefore, the P content is set to 0.05% or less. The P content is preferably 0.03% or less. The P content is more preferably 0.02% or less. There is no particular limitation on the lower limit, but the P content is preferably 0.005% or more.

[0056] S: less than 0.005%

[0057] S is an element that reduces corrosion resistance, and is preferably reduced as much as possible, but less than 0.005% is acceptable. Therefore, the S content is set to less than 0.005%. Preferably, the S content is 0.003% or less. More preferably, the S content is 0.002% or less. There is no particular limitation on the lower limit, but the S content is preferably 0.0004% or more.

[0058] Cr: more than 11.0% and less than 15.0%

[0059] Cr is an element that forms a protective film on the surface of the steel pipe and contributes to the improvement of corrosion resistance. When the Cr content is less than 11.0%, the desired corrosion resistance cannot be ensured. Therefore, it is set to contain more than 11.0% Cr. Preferably, the Cr content is 11.5% or more. More preferably, the Cr content is 12.0% or more. It is further preferred that the Cr content is 12.5% ​​or more. On the other hand, for the purpose of obtaining the desired corrosion resistance, containing more than 15.0% Cr is excessive and the cost increases. Furthermore, it is disadvantageous in terms of low-temperature toughness. Therefore, the Cr content is set to less than 15.0%. Preferably, the Cr content is less than 14.5%. More preferably, the Cr content is less than 14.0%. It is further preferred that the Cr content is less than 13.5%.

[0060] Ni: 2.5~8.0%

[0061] Ni is an element that makes the protective film on the surface of the steel pipe firm and helps improve the corrosion resistance. Such an effect becomes significant when containing more than 2.5% Ni. Therefore, the Ni content is set to more than 2.5%. Preferably, the Ni content is more than 3.0%. More preferably, the Ni content is more than 3.5%. It is further preferred that the Ni content is more than 5.0%. On the other hand, when containing more than 8.0% Ni, the stability of the martensite phase decreases and the strength decreases. Therefore, the Ni content is set to less than 8.0%. Preferably, the Ni content is less than 7.5%. More preferably, the Ni content is less than 7.0%. It is further preferred that the Ni content is less than 6.5%.

[0062] V: 0.005~0.5%

[0063] V is an element that, in addition to being dissolved in solid and contributing to the improvement of strength, combines with C and N and precipitates in the form of V carbonitride (V precipitate), thereby contributing to the improvement of yield strength. In order to obtain such an effect, it is necessary to contain more than 0.005% V. Therefore, the V content is set to more than 0.005%. Preferably, the V content is more than 0.01%. More preferably, the V content is more than 0.02%. It is further preferred that the V content is more than 0.03%. On the other hand, when more than 0.5% of V is contained, low-temperature toughness and resistance to sulfide stress corrosion cracking are reduced. Therefore, the V content is set to less than 0.5%. Preferably, the V content is less than 0.3%. More preferably, the V content is less than 0.2%. It is further preferred that the V content is less than 0.1%.

[0064] Al: 0.1% or less

[0065] Al is an element that acts as a deoxidizer. On the other hand, when containing more than 0.1% Al, the amount of oxide increases and the cleanliness decreases, and the low-temperature toughness and corrosion resistance decrease. Therefore, the Al content is set to 0.1% or less. Preferably, the Al content is 0.07% or less. More preferably, the Al content is 0.05% or less. The lower limit is not particularly limited, and the Al content is preferably 0% or more. Preferably, the Al content is 0.01% or more. More preferably, the Al content is 0.02% or more.

[0066] N: 0.100% or less

[0067] N is an element that improves pitting corrosion resistance. On the other hand, when containing more than 0.100% N, nitrides are formed to reduce low-temperature toughness and corrosion resistance. Therefore, the N content is set to 0.100% or less. Preferably, the N content is 0.080% or less. More preferably, the N content is 0.070% or less. Further preferably, the N content is 0.060% or less. The lower limit is not particularly limited, and the N content is preferably 0% or more. Preferably, the N content is 0.005% or more.

[0068] O: 0.3% or less

[0069] O (oxygen) exists in the form of oxides in steel, and therefore has adverse effects on various properties. Therefore, in the present invention, it is preferably reduced as much as possible. The lower limit is not particularly limited, but the O content is preferably set to 0.01% or more. In particular, when O exceeds 0.3%, corrosion resistance and low-temperature toughness decrease. Therefore, the O content is set to 0.3% or less. Preferably, the O content is 0.2% or less. More preferably, the O content is 0.1% or less.

[0070] Mo: 3.5% or less

[0071] Mo is used to stabilize the protective film on the surface of the steel pipe and to - , an element that increases resistance to pitting corrosion caused by low pH, thereby improving resistance to sulfide stress corrosion cracking. The lower limit is not particularly limited, but the Mo content is preferably set to 0% or more. The Mo content is more preferably 0.4% or more, and further preferably 1.0% or more. The most preferred Mo content is 1.8% or more. On the other hand, when more than 3.5% Mo is contained, the ferrite fraction is increased and the tempered martensite fraction is reduced, thereby reducing resistance to sulfide stress corrosion cracking. In addition, Mo is an expensive element, which leads to a rise in material costs. Therefore, the Mo content is set to 3.5% or less. Preferably, the Mo content is 3.2% or less. More preferably, the Mo content is less than 3.0%. More preferably, the Mo content is 2.7% or less. The most preferred Mo content is 2.5% or less.

[0072] The balance other than the above components is Fe and inevitable impurities.

[0073] In the present invention, the above components are set as the basic component composition. Through the above basic component composition, the properties targeted in the present invention can be obtained. In the present invention, for the purpose of further improving strength, corrosion resistance, etc., the following components can be further added as optional elements as needed.

[0074] One or more selected from the group consisting of Cu: 3.5% or less, W: 3.0% or less, Nb: 0.5% or less, Ti: 0-0.30%, B: 0-0.0050%, Zr: 0-0.2%, Co: 0-1.0%, Ta: 0-0.1%, Ca: 0-0.050%, REM: 0-0.1%, Mg: 0-0.01%, Sn: 0-0.5%, Sb: 0-0.5%

[0075] Cu: 3.5% or less

[0076] Cu increases the residual austenite phase and forms precipitates to contribute to the improvement of yield strength (YS), so high strength can be obtained without reducing low-temperature toughness. In addition, it also has the effect of making the protective film on the surface of the steel pipe firm and inhibiting the intrusion of hydrogen into the steel and improving the resistance to sulfide stress corrosion cracking. The lower limit is not particularly limited. In the case of containing Cu, the Cu content is preferably 0% or more. More preferably, the Cu content is 0.3% or more. It is further preferred that the Cu content is 0.5% or more. The most preferred Cu content is 1.0% or more. On the other hand, when containing more than 3.5% Cu, coarse Cu precipitation occurs, and the resistance to sulfide stress corrosion cracking deteriorates. Therefore, in the case of containing Cu, the Cu content is set to 3.5% or less. Preferably, the Cu content is 3.0% or less. It is more preferred that the Cu content is 2.0% or less. It is further preferred that the Cu content is 1.5% or less.

[0077] W: 3.0% or less

[0078] W is an important element that helps to improve the strength of steel and stabilizes the protective film on the surface of the steel pipe to improve the resistance to sulfide stress corrosion cracking. W is contained in combination with Mo, especially significantly improving the resistance to sulfide stress corrosion cracking. The lower limit is not particularly limited. When W is contained, the W content is preferably greater than 0%. More preferably, the W content is 0.3% or more. It is further preferred that the W content is 0.5% or more. The most preferred W content is 0.8% or more. On the other hand, when more than 3.0% W is contained, the precipitation of intermetallic compounds is promoted, and the corrosion resistance is reduced. Therefore, when W is contained, the W content is set to 3.0% or less. Preferably, the W content is 2.5% or less. More preferably, the W content is 2.0% or less. It is further preferred that the W content is 1.0% or less.

[0079] Nb: 0.5% or less

[0080] Nb combines with C and N to precipitate in the form of Nb carbonitride (Nb precipitate), which helps to improve the yield strength. The lower limit is not particularly limited. When Nb is contained, the Nb content is preferably 0% or more. More preferably, the Nb content is 0.01% or more. It is further preferred that the Nb content is 0.05% or more. On the other hand, containing more than 0.5% Nb leads to a decrease in low-temperature toughness and resistance to sulfide stress corrosion cracking. Therefore, when Nb is contained, the Nb content is set to 0.5% or less. Preferably, the Nb content is 0.3% or less. More preferably, the Nb content is 0.2% or less. It is further preferred that the Nb content is 0.1% or less.

[0081] Ti, B, Zr, Co and Ta are all elements that increase strength, and one or more selected from these elements can be contained as needed. In addition to the above effects, Ti, B, Zr, Co and Ta also have the effect of improving resistance to sulfide stress corrosion cracking. In particular, Ta is an element that brings the same effect as Nb, and a part of Nb can be replaced by Ta. It should be noted that Ti, B, Zr, Co and Ta are optional elements, so they may not be contained, and each content is preferably 0% or more. That is, in the case of containing Ti, the Ti content is preferably set to 0% or more, and more preferably set to 0.01% or more. In the case of containing B, the B content is preferably set to 0% or more, and more preferably set to 0.0001% or more. In the case of containing Zr, the Zr content is preferably set to 0% or more, and more preferably set to 0.01% or more. In the case of containing Co, the Co content is preferably set to 0% or more, and more preferably set to 0.01% or more. In the case of containing Ta, the Ta content is preferably set to 0% or more, and more preferably set to 0.01% or more. On the other hand, when the Ti content exceeds 0.30%, the B content exceeds 0.0050%, the Zr content exceeds 0.2%, the Co content exceeds 1.0%, and the Ta content exceeds 0.1%, the low temperature toughness decreases. Therefore, when Ti is contained, the Ti content is set to less than 0.30%, preferably less than 0.10%. When B is contained, the B content is set to less than 0.0050%, preferably less than 0.0030%. When Zr is contained, the Zr content is set to less than 0.2%, preferably less than 0.05%. When Co is contained, the Co content is set to less than 1.0%, preferably less than 0.4%. When Ta is contained, the Ta content is set to less than 0.1%, preferably less than 0.03%.

[0082] Both Ca and REM (rare earth metal) are elements that contribute to improving resistance to sulfide stress corrosion cracking through morphology control of sulfides. It should be noted that Ca and REM are optional elements, so they may not be contained, and their respective contents are preferably above 0%. However, in the case of containing in order to obtain the above-mentioned effect, it is preferred to contain 0.0001% or more of Ca. The Ca content is more preferably set to 0.001% or more. In the case of containing REM, it is preferred to contain 0.001% or more of REM. The REM content is more preferably set to 0.003% or more. On the other hand, even if the Ca content exceeds 0.050% and the REM content exceeds 0.1%, the effect is saturated, and the effect consistent with the content cannot be expected. Therefore, in the case of containing Ca, the Ca content is set to less than 0.050%. The Ca content is preferably set to less than 0.005%. In the case of containing REM, the REM content is set to less than 0.1%. The REM content is preferably set to less than 0.01%.

[0083] Mg, Sn and Sb are all elements that improve corrosion resistance. It should be noted that Mg, Sn and Sb are optional elements, so they may not be contained, and their respective contents are preferably 0% or more. However, in order to obtain the above-mentioned effects, it is preferred that the Mg content is 0.002% or more, the Sn content is 0.01% or more, and the Sb content is 0.01% or more. That is, in the case of containing Mg, the Mg content is preferably set to 0% or more, and more preferably 0.002% or more. In the case of containing Sn, the Sn content is preferably set to 0% or more, and more preferably 0.01% or more. In the case of containing Sb, the Sb content is preferably set to 0% or more, and more preferably 0.01% or more. On the other hand, even if the Mg content exceeds 0.01%, the Sn content exceeds 0.5%, and the Sb content exceeds 0.5%, the effect is saturated, and the effect consistent with the content cannot be expected. Therefore, in the case of containing Mg, the Mg content is set to 0.01% or less. In the case of containing Sn, the Sn content is set to 0.5% or less. The Sn content is preferably set to 0.2% or less. When Sb is contained, the Sb content is set to 0.5% or less. The Sb content is more preferably set to 0.2% or less.

[0084] Next, the particle size of the stainless steel powder of the present invention will be described.

[0085] The stainless steel powder of the present invention is D 50 The specified particle size is 10 to 200 μm. 50 When the particle size is too small, uneven filling of the powder occurs due to reduced fluidity of the powder, resulting in defects such as voids during lamination. As a result, low-temperature toughness and corrosion resistance (pitting resistance, SSCC resistance) are greatly reduced. 50 When the particle size is less than 10 μm, the above phenomenon occurs. 50 Set to 10 μm or more. Particle size D 50 It is preferably 15 μm or more, more preferably 20 μm or more, and even more preferably 30 μm or more. 50 If the particle size is too coarse, defects will be generated during lamination. As a result, the low-temperature toughness and corrosion resistance (pitting resistance, SSCC resistance) will be greatly reduced due to the defects. 50 When the particle size exceeds 200 μm, the above phenomenon occurs, so the particle size D 50 Set to 200 μm or less. Particle size D 50 It is preferably 175 μm or less, more preferably 150 μm or less, further preferably 125 μm or less, and most preferably 100 μm or less.

[0086] It should be noted that D, which represents the particle size of the stainless steel powder, 50The median particle size is the value at the 50% position of the cumulative mass distribution of the powder. A laser diffraction particle size measuring device can be used to measure the median particle size. In the present invention, in the method described below, the particle size D of the stainless steel powder is measured. 50 .

[0087] As a laser diffraction particle size measuring device, there is LA-950V2 manufactured by Horiba, Ltd., etc. Of course, other devices can also be used. In order to perform accurate measurements, it is preferred to use a laser diffraction particle size measuring device with a lower limit of a measurable particle size range of less than 0.1 μm and an upper limit of more than 45 μm. That is, it is preferred to use a laser diffraction particle size measuring device that can measure a range of 0.1 to 45 μm. In the above-mentioned device, a laser is irradiated on a solvent in which iron powder is dispersed, and the particle size distribution and average particle size of the iron powder are measured based on the diffraction and scattering intensity of the laser. As a solvent for dispersing the iron powder, it is preferred to use ethanol, which has excellent particle dispersibility and is easy to operate. If a solvent with high van der Waals force and low dispersibility such as water is used, the particles agglomerate during the measurement, and a measurement result coarser than the original average particle size is obtained, which is not preferred. Therefore, it is preferred to implement a dispersion treatment using ultrasound on the ethanol solution into which iron powder is added before the measurement.

[0088] It should be noted that the appropriate dispersion treatment time is different depending on the powder being the object. The above-mentioned dispersion treatment time is implemented in 7 stages with an interval of 10 minutes between 0 and 60 minutes, and the average particle size of the iron powder is measured after each dispersion treatment. In each measurement, in order to prevent agglomeration of particles, the measurement is performed while stirring the solvent. Moreover, among the particle sizes obtained in the 7 measurements performed by changing the dispersion treatment time at intervals of 10 minutes, the smallest value is used as the particle size of the iron powder (particle size D 50 ).

[0089] By controlling the particle size D 50 The above characteristics can be obtained by combining the apparent density with that of the carbon steel. The apparent density is less than 3.5Mg / m 3 When the fluidity is reduced, defects in stacking are generated. Therefore, the apparent density is set to 3.5Mg / m 3 More than 3.7Mg / m 3 More preferably, the apparent density is set to 4.0 Mg / m 3 On the other hand, the apparent density exceeds 5.0Mg / m 3 From an industrial point of view, it is difficult to stably control the apparent density, so the apparent density is set to 5.0Mg / m 3 Below. Preferably 4.8Mg / m 3 Below, more preferably 4.6Mg / m 3 the following.

[0090] In addition, the apparent density uses the value measured by the test method prescribed|regulated by JIS Z 2504.

[0091] It should be noted that the alloy powder can be used for modeling purposes, for example, stainless steel powder can be provided in the form of stainless steel powder for cladding, 3D printer, sintering, etc. In particular, the alloy powder is suitable for 3D printer use.

[0092] Next, the steel structure of the stainless steel member of the present invention and the reasons for its limitation will be described.

[0093] The stainless steel component of the present invention is formed from the above-mentioned stainless steel powder, has the above-mentioned component composition, and has a steel structure composed of more than 45% tempered martensite phase, 0-40% ferrite phase and less than 25% retained austenite phase by volume.

[0094] In order to ensure the strength (yield strength) targeted in the present invention, the stainless steel component of the present invention uses the tempered martensite phase as the main phase. Here, the "main phase" refers to a structure that accounts for more than 45% of the volume ratio relative to the steel component. When the tempered martensite phase is less than 45%, the desired strength cannot be obtained. Therefore, the tempered martensite phase is set to more than 45%. The tempered martensite phase is preferably set to more than 55%. The tempered martensite phase is more preferably set to more than 60%, and further preferably set to more than 70%. The upper limit of the tempered martensite phase can be 100%.

[0095] The balance other than the main phase is a ferrite phase, a retained austenite phase, or a ferrite phase and a retained austenite phase.

[0096] In order to ensure the strength and sulfide stress corrosion cracking resistance targeted in the present invention, the ferrite phase is set to 40% or less by volume. The ferrite phase is preferably 20% or less, more preferably 10% or less, further preferably 5% or less, and most preferably 3% or less. The stainless steel component of the present invention can obtain the above effect even if it is a tempered martensite phase single phase, so the ferrite phase can be 0%.

[0097] It should be noted that, similar to the above, the stainless steel component of the present invention can obtain the above effect even if it is a tempered martensite phase single phase, so the austenite phase (retained austenite phase) can be 0%. However, by the presence of the retained austenite phase, ductility and low-temperature toughness can be improved, so it is preferred that the austenite phase (retained austenite phase) is precipitated. Specifically, in order to obtain such ductility and low-temperature toughness improvement effect, the retained austenite phase is preferably precipitated more than 10% by volume. The more preferred retained austenite is more than 13% by volume, and more preferably more than 15%. On the other hand, the precipitation of a large amount of retained austenite phases exceeding 25% by volume leads to a reduction in strength. Therefore, the retained austenite phase is set to less than 25% by volume. The preferred retained austenite is less than 23% by volume. The further preferred retained austenite is less than 20% by volume.

[0098] Here, the above-mentioned steel structure of the stainless steel component of the present invention can be measured by the following method. First, a test piece for structure observation is cut from a cross section in a direction perpendicular to the molding direction of a material (steel component) molded by an additive manufacturing method or the like. The test piece for structure observation is corroded with a Vilella reagent (a reagent prepared by mixing picric acid, hydrochloric acid and ethanol in a ratio of 2 g, 10 ml and 100 ml, respectively), and then the structure is photographed with a scanning electron microscope (accelerating voltage: 15 kV, magnification: 1000 times), and the structure fraction (area ratio %) of the ferrite phase is calculated using an image analysis device, and the area ratio is used as the volume ratio (%) of the ferrite phase.

[0099] Then, the X-ray diffraction test piece was ground and polished in a manner that the cross section perpendicular to the molding direction was used as the measurement surface, and the amount of retained austenite (γ) was measured using the X-ray diffraction method. Regarding the amount of retained austenite, the integrated intensity of diffracted X-rays on the (220) plane of γ and the (211) plane of α was measured and converted into a volume fraction using the following formula.

[0100] γ(volume ratio)=100 / (1+(IαRγ / IγRα))

[0101] Among them, Iα: integrated intensity of α, Rα: value calculated by crystallographic theory of α, Iγ: integrated intensity of γ, Rγ: value calculated by crystallographic theory of γ.

[0102] In addition, the structure fraction (volume ratio %) of the tempered martensite phase is set as the balance other than the ferrite phase and the retained austenite phase.

[0103] It should be noted that the steel structure of the stainless steel member of the present invention can be adjusted to be within the range of the above-mentioned phases by appropriately controlling the heat treatment steps (quenching treatment and tempering treatment) described later.

[0104] As described above, the stainless steel member of the present invention has the above-mentioned specific component composition, and the steel structure is adjusted to contain 45% or more of a tempered martensite phase, 0 to 40% of a ferrite phase and 25% or less of a retained austenite phase by volume, so that the strength and characteristics (corrosion resistance, low temperature toughness) targeted in the present invention can be obtained.

[0105] In addition, the number of inclusions with a major diameter of 2 μm or more is preferably set to 10 / mm 2 The following reasons are explained. Inclusions with a long diameter of 2 μm or more become the starting point of pitting corrosion when conducting a sulfide stress corrosion cracking resistance test. Pitting corrosion is accompanied by stress concentration and the generation of hydrogen, which causes sulfide stress cracking. Therefore, in order to improve the resistance to sulfide stress corrosion cracking, it is preferred to reduce the number of inclusions with a long diameter of 2 μm or more. This effect is achieved when the number of inclusions with a long diameter of 2 μm or more is 10 / mm 2 Therefore, it is preferred to set the number of inclusions with a major diameter of 2 μm or more to 10 / mm. 2 More preferably, the number of inclusions with a major diameter of 2 μm or more is set to 7 / mm. 2 Below, it is further preferably set to 4 / mm 2 The lower limit of the number of inclusions with a major diameter of 2 μm or more is not particularly limited, but the number of inclusions with a major diameter of 2 μm or more is preferably 0 / mm. 2 above.

[0106] The following is an explanation of the reason why the number of grains with a grain size of 5 μm or more in the grains having an orientation difference of 5° or more with the adjacent grains is preferably set to less than 10% of the total grains. Grains with a grain size of 5 μm or more deteriorate low-temperature toughness and resistance to sulfide stress corrosion cracking. Therefore, in order to improve low-temperature toughness and resistance to sulfide stress corrosion cracking, it is preferred to reduce the grain size. Such an effect is obtained by setting the number of grains with a grain size of 5 μm or more in the grains with an orientation difference of 5° or more with the adjacent grains to less than 10% of the total grains. Therefore, in the grains with an orientation difference of 5° or more with the adjacent grains, the number of grains with a grain size of 5 μm or more is preferably set to less than 10% of the total number of grains. The number of grains with a grain size of 5 μm or more is more preferably set to less than 9% of the total number of grains, and further preferably set to less than 8%. The lower limit of the number of crystal grains having a grain size of 5 μm or more among crystal grains having an orientation difference of 5° or more from adjacent crystal grains is not particularly limited, but is preferably 0% or more.

[0107] The yield strength of the stainless steel member of the present invention is 655 MPa or more. The upper limit is not particularly limited, but is preferably 900 MPa or less to prevent a decrease in low-temperature toughness. Absorption energy vE at a test temperature of -10°C in a Charpy impact test -10The upper limit is not particularly limited, but is preferably 300 J or less.

[0108] Furthermore, the stainless steel member of the present invention has excellent toughness at a test temperature of -60°C in a Charpy impact test, and the absorbed energy vE -60 Preferably it is 40 J or more. -60 It is preferably 200 J or less.

[0109] Next, a preferred embodiment of the method for producing stainless steel powder of the present invention will be described.

[0110] The stainless steel powder of the present invention is provided as a final material form through the following series of manufacturing steps. For example, the stainless steel powder of the present invention is manufactured through the steps of melting - ingot formation - remelting of the mother ingot - atomization process to produce powder.

[0111] First, in the melting-ingot forming process, the specified amount of the above-mentioned elements is melted in a high-frequency vacuum melting furnace in the form of material, alloyed and cast to make an ingot (mother ingot). At this time, it is preferably melted under the conditions of Ar atmosphere under reduced pressure and melting temperature: above 1600°C. The reasons for setting this condition are as follows. When the melting temperature is too low, the molten steel solidifies and blocks the nozzle when dripping from the nozzle. The upper limit of the melting temperature is not particularly limited, and the melting temperature is preferably below 1700°C. In addition, from the viewpoint of preventing oxidation of the molten steel, it is preferably melted in an Ar atmosphere under reduced pressure. It should be noted that the melting furnace used in this process is not limited to a high-frequency vacuum melting furnace, and other melting furnaces (such as a directly electrically heated melting furnace) can also be used in the present invention.

[0112] Next, in the process of remelting-atomizing the mother ingot, the cast mother ingot is used as a raw material and is remelted in a melting furnace such as a high-frequency furnace or an induction furnace, and a low-oxygen powder is obtained by a gas atomization method using Ar or He as an inert gas.

[0113] Then, these powders are classified into particle sizes of 10 to 200 μm and provided as the stainless steel powder of the present invention. It should be noted that the classification can be performed using a sieve or other methods such as air flow classification. In addition, water atomization can be used instead of gas atomization.

[0114] The apparent density is controlled by appropriately adjusting the gas pressure, gas flow rate, gas temperature and beam angle during gas atomization.

[0115] Next, one embodiment of the method for producing a stainless steel member of the present invention will be described.

[0116] The method for manufacturing a stainless steel member of the present invention includes a molding step and a heat treatment step.

[0117] First, in a molding step, the stainless steel powder is used to mold a stainless steel laminated object (three-dimensional structure) by, for example, a laminated molding method (metal powder laminated molding method).

[0118] As a layered modeling method, for example, a 3D printing method can be used. Here, a 3D printer using a laser-type powder bed fusion method is used. There are no special regulations for the setting conditions of the 3D printer. From the perspective of preventing excessive melting or insufficient melting, for example, it is preferred that the laser power is set to 150 to 300 W and the scanning speed is set to 700 to 1100 mm / s.

[0119] Next, in the heat treatment process, the three-dimensional structure after shaping is subjected to quenching and tempering treatments under prescribed conditions to obtain the stainless steel component of the present invention. In the heat treatment process, the quenching treatment as described below is preferably performed: after heating to a temperature range of 850 to 1150°C, cooling to a temperature range of 50°C or less at an average cooling rate higher than air cooling. Then, a tempering treatment is preferably performed by heating to a temperature range of 500 to 650°C (tempering temperature). Preferably, the above-mentioned quenching treatment and tempering treatment are each performed at least once. There is no upper limit, and the quenching treatment and tempering treatment are preferably performed three times or less each.

[0120] Here, the "average cooling rate of air cooling or higher" is 0.01°C / s or higher. In the case of "average cooling rate of water cooling or higher", it is 0.2°C / s or higher.

[0121] [Quenching treatment]

[0122] From the viewpoint of refining the martensite phase, the heating temperature of the quenching treatment (the temperature of reheating) is set to 850°C or more. Preferably, it is set to 880°C or more. More preferably, it is set to 900°C or more. The heating temperature of the quenching treatment (the temperature of reheating) is set to 1150°C or less. Preferably, it is set to 1050°C or less. More preferably, it is set to 1000°C or less.

[0123] It should be noted that, from the viewpoint of thermal uniformity, it is preferred to maintain the above-mentioned reheating temperature for more than 10 minutes. It is more preferred to maintain the reheating temperature for more than 15 minutes. The holding time at the reheating temperature is preferably set to 60 minutes or less. The holding time at the reheating temperature is more preferably set to 30 minutes or less.

[0124] In addition, from the viewpoint of ensuring the desired low-temperature toughness, the cooling rate of the quenching treatment is set to be above air cooling. It is preferably set to 0.01°C / s or more in terms of the average cooling rate. The cooling rate of the quenching treatment is more preferably set to 0.1°C / s or more in terms of the average cooling rate. The cooling rate of the quenching treatment is preferably set to 200°C / s or less in terms of the average cooling rate. The cooling rate of the quenching treatment is more preferably set to 100°C / s or less in terms of the average cooling rate. Here, the average cooling rate refers to the average of the cooling rates from the start of cooling to the stop of cooling. The cooling stop temperature is set to a temperature of 50°C or less in terms of the surface temperature of the three-dimensional structure. It is preferably 40°C or less, and more preferably 30°C or less. When it exceeds 50°C, the retained austenite precipitates excessively, and the desired high strength cannot be obtained. The lower limit is not particularly limited, and the cooling stop temperature is preferably set to 5°C or more.

[0125] [Tempering treatment]

[0126] When the tempering temperature (tempering temperature) exceeds 650°C, the austenite phase precipitates excessively and the desired high strength cannot be obtained. Therefore, the tempering temperature (tempering temperature) is set to 650°C or less. The tempering temperature (tempering temperature) is preferably set to 630°C or less. On the other hand, when the tempering temperature is lower than 500°C, the strength becomes too high and the desired low-temperature toughness cannot be obtained. Therefore, the tempering temperature is set to 500°C or more. The tempering temperature is preferably set to 525°C or more.

[0127] It should be noted that, from the viewpoint of heat uniformity, it is preferred to maintain the above-mentioned tempering temperature for 10 minutes or more. It is more preferred to maintain it for 20 minutes or more. The holding time at the tempering temperature is preferably set to 60 minutes or less. The holding time at the tempering temperature is more preferably set to 40 minutes or less.

[0128] In addition, from the viewpoint of ensuring the desired low-temperature toughness, the cooling rate of the tempering treatment is preferably set to air cooling or more. It is more preferably set to 0.01°C / s or more as an average cooling rate. It is further preferably set to 0.1°C / s or more as an average cooling rate. The cooling rate of the tempering treatment is preferably set to 200°C / s or less as an average cooling rate. The cooling rate of the tempering treatment is more preferably set to 100°C / s or less as an average cooling rate.

[0129] In addition, in the method for manufacturing a stainless steel member of the present invention, in order to form a desired shape, the three-dimensional structure may be further subjected to mechanical processing before or after the above-mentioned heat treatment step.

[0130] As described above, the stainless steel component of the present invention formed by the stainless steel powder of the present invention has high strength, excellent corrosion resistance and low temperature toughness, and can be used as a constituent material (e.g., sliding part) of equipment such as compressors and pumps used in highly corrosive environments such as oil wells. In addition, it can also be used as a coupling or fitting for oil wells. Moreover, according to the present invention, the manufacturing cost of special components made into various shapes can be reduced, and the dimensional accuracy can also be improved.

[0131] Example

[0132] Hereinafter, the present invention will be described based on examples. It should be noted that the present invention is not limited to the following examples.

[0133] The method for producing the stainless steel powder (powder alloy) shown in Table 1 is described in detail. First, the specified amount of the component composition shown in Table 1 is melted and cast in a high-frequency vacuum melting furnace (Ar atmosphere under reduced pressure, melting temperature above 1600°C) to produce the master ingots of these alloys. Next, the master ingot of the alloy is re-melted in an Ar atmosphere and powdered by gas atomization to obtain a powder alloy. Then, the particle size D is obtained by classification. 50 Different alloy powders (stainless steel powder). Particle size D of stainless steel powder 50 , and apparent density were measured by the above-mentioned methods, and their values ​​are shown in Table 2.

[0134] Next, a commercially available 3D printer (laser-type powder bed fusion method) was used to make a three-dimensional structure of 50mm×80mm×12mmt (t: stacking thickness) from these powder alloys. The laser power at this time was 250W, the scanning speed was 900mm / s, and the stacking thickness of one layer was 40μm. Next, a heat treatment process was performed on the produced three-dimensional structure under the conditions shown in Table 2 to obtain a stainless steel component.

[0135] Test pieces were cut out from the obtained stainless steel members by the following method, and microstructure observation, inclusion count measurement, grain size measurement, tensile test, Charpy impact test, and corrosion resistance test were performed. The test method is as follows.

[0136] (1) Organizational Observation

[0137] A test piece for tissue observation was cut from the obtained stainless steel member in such a way that the cross section in the direction perpendicular to the molding direction (the direction perpendicular to the stacking surface) was used as the observation surface. The obtained test piece for tissue observation was corroded with Vilella reagent (a reagent prepared by mixing picric acid, hydrochloric acid and ethanol in a ratio of 2g, 10ml and 100ml respectively), and the structure was photographed with a scanning electron microscope (accelerating voltage: 15kv, magnification: 1000 times), and the structure fraction (area ratio) of the ferrite phase was calculated using an image analysis device, and it was used as the volume ratio (%) of the ferrite phase.

[0138] In addition, a test piece for X-ray diffraction was cut from the obtained stainless steel component, and the cross section in the direction orthogonal to the molding direction was ground and polished as the measurement surface. Then, the amount of retained austenite (γ) was measured using the X-ray diffraction method. Regarding the amount of retained austenite, the diffracted X-ray integrated intensity of the (220) plane of γ and the (211) plane of α was measured and converted into a volume fraction using the following formula.

[0139] γ(volume ratio)=100 / (1+(IαRγ / IγRα))

[0140] Among them, Iα: integrated intensity of α, Rα: value calculated by crystallographic theory of α, Iγ: integrated intensity of γ, Rγ: value calculated by crystallographic theory of γ.

[0141] Then, the structure fraction (volume %) of the tempered martensite phase was determined as the balance other than the ferrite phase and the retained austenite phase.

[0142] (2) Determination of the number of inclusions

[0143] Regarding the number of inclusions, a 500 mm section was cut from a position 1 / 2 of the wall thickness as a scanning electron microscope (SEM) sample of a cross section perpendicular to the molding direction. 2 For each sample cut out, inclusions were identified by SEM observation and the number of inclusions per unit area was calculated. Inclusions with a major diameter of 2 μm or more were identified by defining the periphery of the inclusions by binarizing the contrast of the reflected electron image of the scanning electron microscope and measuring the major diameter from the periphery of the inclusions.

[0144] (3) Particle size measurement

[0145] The sample for measuring the grain size was cut from the position of 1 / 2 of the wall thickness of the cross section perpendicular to the molding direction. For the cut sample, an area of ​​300 μm in the width direction and 500 μm in the wall thickness direction was observed by EBSD (accelerating voltage: 15 kV, step length: 0.5 μm), and the area with an orientation difference of 5° or more was defined as one crystal. The proportion of grains with a grain size of 5 μm or more was measured by the cutting method.

[0146] (4) Tensile test

[0147] A JIS13B half (GL=25mm) test piece is cut from the obtained stainless steel component in a tensile direction perpendicular to the molding direction. Then, a tensile test is performed according to the JIS standard (Z2241:2011) to obtain the yield strength YS and tensile strength TS as tensile properties. Here, the sample with a yield strength of 655MPa or more is evaluated as high strength and qualified. On the other hand, the sample with a yield strength less than 655MPa is deemed unqualified.

[0148] (5) Charpy impact test

[0149] V-notch test pieces (10 mm thick) were cut from the obtained stainless steel components in such a way that the length direction of the test piece was orthogonal to the molding direction, and Charpy impact tests were performed in accordance with the provisions of JIS Z 2242 (2018). The test temperature was set at -10°C, and the absorbed energy vE at -10°C was calculated. -10 , evaluate the low temperature toughness. It should be noted that the test pieces were set to 3 each, and the arithmetic average of the obtained values ​​was taken as the absorption energy (J) of the stainless steel member. Here, the absorption energy vE at -10°C is -10 The samples with a toughness of 40 J or more were evaluated as having high toughness and were considered acceptable. -10 Samples with less than 40 J were considered unqualified. In addition, the test was also conducted at a test temperature of -60°C to determine the absorption energy vE at -60°C. -60 In addition, three test pieces were prepared, and the arithmetic average of the obtained values ​​was defined as the absorbed energy (J) of the stainless steel member.

[0150] (6) Corrosion resistance test

[0151] As corrosion resistance tests, corrosion tests and sulfide stress corrosion cracking resistance tests (SSCC resistance tests) were performed.

[0152] [Corrosion test]

[0153] A corrosion test piece of 3 mm in thickness×30 mm in width×40 mm in length was prepared from the obtained stainless steel member by machining, and a corrosion test was carried out to evaluate the carbon dioxide corrosion resistance.

[0154] Regarding the corrosion test, when the Cr content is less than 14% (condition A), the above-mentioned corrosion test piece is immersed in the test liquid maintained in the autoclave: 20 mass% NaCl aqueous solution (liquid temperature: 150°C, 10atm CO2 gas atmosphere), and the immersion period is set to 14 days (336 hours). The weight of the test piece after the corrosion test is measured, and the corrosion rate is calculated based on the weight loss before and after the corrosion test. The sample with a corrosion rate of less than 0.125mm / y is qualified, and the sample exceeding 0.125mm / y is unqualified.

[0155] When the Cr content exceeds 14% (condition B), the corrosion test piece is immersed in a test liquid maintained in an autoclave: a 20 mass% NaCl aqueous solution (liquid temperature: 180°C, 10atm CO2 gas atmosphere), and the immersion period is set to 14 days (336 hours). The weight of the test piece after the corrosion test is measured, and the corrosion rate is calculated based on the weight loss before and after the corrosion test. The sample with a corrosion rate of 0.125mm / y or less is qualified, and the sample with a corrosion rate exceeding 0.125mm / y is unqualified.

[0156] In addition, for the test piece after the corrosion test, a magnifying glass with a magnification of 10 times was used to observe whether pitting occurred on the surface of the test piece. It should be noted that pitting refers to pitting with a diameter of 0.2 mm or more. Here, the sample without pitting was deemed qualified, and the sample with pitting was deemed unqualified.

[0157] In addition, in this Example, the sample in which the corrosion rate was 0.125 mm / y or less and the above-mentioned pitting corrosion did not occur was evaluated as having excellent carbon dioxide corrosion resistance.

[0158] [SSCC resistance test]

[0159] A round rod-shaped test piece (diameter: 6.4 mmφ) was made from the obtained stainless steel member by machining in such a way that the length direction of the test piece was orthogonal to the molding direction, and a sulfide stress corrosion cracking resistance test (SSCC (Sulfide Stress Corrosion Cracking) resistance test) was carried out according to NACE (National Association of Corrosion and Engineerings) TM0177 Method A.

[0160] For the SSCC resistance test, acetic acid + sodium acetate was added to the test solution: 5 mass% NaCl aqueous solution (liquid temperature: 25°C, H2S: 0.1atm, CO2: 0.9atm atmosphere) and the pH was adjusted to 3.5. The test piece was immersed in the aqueous solution, the immersion time was set to 720 hours, and 100% of the yield stress was set as the load stress. Then, the test piece after the test was observed for cracks. Here, the sample without cracks was qualified, and the sample with cracks was unqualified.

[0161] The obtained results are shown in Table 3.

[0162]

[0163]

[0164]

[0165] The examples of the present invention are all the above-mentioned composition, particle size D 50 The stainless steel powder with an apparent density controlled within an appropriate range. In addition, the stainless steel components molded from the steel powder are high-strength and have excellent low-temperature toughness in low-temperature environments. - It has excellent corrosion resistance in harsh corrosive environments with high temperatures and in environments containing H2S.

[0166] On the other hand, the stainless steel powder of the comparative example outside the scope of the present invention is not controlled within the appropriate range. Moreover, the yield strength, corrosion resistance, and low-temperature toughness of the stainless steel component molded from the steel powder cannot obtain the characteristic value targeted by the present invention.

Claims

1. A stainless steel powder having a composition comprising, by mass%, C: 0.001-0.06%, Si: 0.01-1.0%, Mn: 0.01-2.0%, P: 0.05% or less, S: less than 0.005%, Cr: more than 11.0% and 15.0% or less, Ni: 2.5-8.0%, V: 0.005-0.5%, Al: 0.1% or less, N: 0.100% or less, O: 0.3% or less, Mo: 3.5% or less, and the balance being Fe and inevitable impurities, The median particle size at 50% of the mass cumulative distribution is the particle size D 50 10~200μm, Apparent density is 3.5~5.0Mg / m 3 .

2. The stainless steel powder according to claim 1, wherein: In addition to the above-mentioned component composition, it also contains one or more selected from the group consisting of Cu: 3.5% or less, W: 3.0% or less, Nb: 0.5% or less, Ti: 0-0.30%, B: 0-0.0050%, Zr: 0-0.2%, Co: 0-1.0%, Ta: 0-0.1%, Ca: 0-0.050%, REM: 0-0.1%, Mg: 0-0.01%, Sn: 0-0.5%, and Sb: 0-0.5%, in terms of mass %.

3. A stainless steel member having a composition comprising, in mass %, C: 0.001-0.06%, Si: 0.01-1.0%, Mn: 0.01-2.0%, P: 0.05% or less, S: less than 0.005%, Cr: more than 11.0% and 15.0% or less, Ni: 2.5-8.0%, V: 0.005-0.5%, Al: 0.1% or less, N: 0.100% or less, O: 0.3% or less, Mo: 3.5% or less, and the balance being Fe and inevitable impurities, The steel structure has a tempered martensite phase of 45% or more, a ferrite phase of 0 to 40% and a retained austenite phase of 25% or less by volume. The yield strength of the stainless steel component is 655 MPa or more, and the absorbed energy vE at the test temperature of -10°C in the Charpy impact test is -10 More than 40J.

4. The stainless steel component according to claim 3, wherein: In addition to the above-mentioned component composition, it also contains one or more selected from the group consisting of Cu: 3.5% or less, W: 3.0% or less, Nb: 0.5% or less, Ti: 0-0.30%, B: 0-0.0050%, Zr: 0-0.2%, Co: 0-1.0%, Ta: 0-0.1%, Ca: 0-0.050%, REM: 0-0.1%, Mg: 0-0.01%, Sn: 0-0.5%, and Sb: 0-0.5%, in terms of mass %.

5. The stainless steel member according to claim 3 or 4, wherein: The number of inclusions with a major diameter of 2 μm or more is 10 / mm 2 the following.

6. The stainless steel member according to claim 3 or 4, wherein: In the tempered martensite phase, among the grains having an orientation difference of 5° or more with adjacent grains, the number of the grains having a grain size of 5 μm or more accounts for 10% or less of the total number of grains.

7. The stainless steel member according to claim 5, wherein: In the tempered martensite phase, among the grains having an orientation difference of 5° or more with adjacent grains, the number of the grains having a grain size of 5 μm or more accounts for 10% or less of the total number of grains.

8. A method for manufacturing a stainless steel component, comprising: Modeling process, including: Using the stainless steel powder according to claim 1 or 2 to form a shaped object; and The heat treatment process includes heating the shaped object to a temperature range of 850 to 1150°C and then cooling it to a temperature range of 50°C or below at an average cooling rate higher than air cooling, and a tempering treatment of heating it in a temperature range of 500 to 650°C, each for at least one time.

9. The method for manufacturing a stainless steel member according to claim 8, wherein: The molding step is a step of forming a molded object using a layered molding method.

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