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

Abstract

The purpose of the present invention is to provide a stainless steel powder that can be used to produce a stainless steel member having high strength, excellent low-temperature toughness, and excellent corrosion resistance in a high-temperature, harsh corrosive environment including carbon dioxide (CO2) and chlorine ions (Cl-) or in an environment including hydrogen sulfide (H2S). The stainless steel powder has a specific composition, a D50 particle diameter, which is the median diameter located at the 50th percentile of the mass cumulative distribution, of 10-200 μm, 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 producing high-strength stainless steel couplings and accessories such as parts and fittings used in crude oil or natural gas oil wells and gas wells (hereinafter simply referred to as oil wells). The present invention also relates to a stainless steel member shaped using this stainless steel powder and a method for producing a stainless steel member. [Background technology]

[0002] In recent years, in light of the expected depletion of energy resources in the near future, development has been actively carried out in areas that were previously ignored, such as deep oil fields and oil and gas fields in sour environments containing carbon dioxide and hydrogen sulfide, which are highly corrosive. These oil and gas fields are generally located at extremely deep depths, and the atmosphere is hot and contains CO2, Cl, etc. - The environment is now severely corrosive, containing hydrogen sulfide and H2S. Oil well steel pipes used in such environments are required to have high strength and high corrosion resistance. Furthermore, with the increasing use of oil wells in cold regions and deep seas, low-temperature toughness is also required.

[0003] Recently, development of oil wells in corrosive environments with high temperatures up to 150°C has been progressing, and 13Cr-based stainless steels and 15Cr-based stainless steels are being used in such environments. For example, Patent Documents 1 to 8 describe 13Cr-based stainless steel pipes. Patent Document 9 describes a manufacturing method involving a rapid melting and rapid solidification process. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] International Publication No. 2008 / 023702 [Patent Document 2] Japanese Patent Application Publication No. 9-170019 [Patent Document 3] Japanese Patent Application Publication No. 7-166303 [Patent Document 4] Japanese Patent Application Laid-Open No. 2010-242163 [Patent Document 5] International Publication No. 2017 / 038178 [Patent Document 6] International Publication No. 2018 / 079111 [Patent Document 7] International Publication No. 2019 / 065115 [Patent Document 8] International Publication No. 2019 / 065116 [Patent Document 9] Japanese Patent Application Publication No. 2019-119913 Summary of the Invention [Problem to be solved by the invention]

[0005] In the techniques disclosed in the above Patent Documents 1 to 9, carbon dioxide (CO2) and chlorine ions (Cl - In recent years, these steels have been unable to withstand the increasingly harsh environments found in oil and gas field development, such as in severe corrosive environments at high temperatures containing sulfur dioxide (CO₂) and in environments containing hydrogen sulfide (H₂S).

[0006] Therefore, the present invention solves the problems of the prior art and is particularly concerned with the prevention of carbon dioxide (CO2) and chloride ions (Cl - The present invention aims to provide a stainless steel powder suitable for molding, which can be used to produce stainless steel members having high strength, excellent low-temperature toughness, and excellent corrosion resistance in high-temperature, severely corrosive environments containing hydrogen sulfide (H2S), environments containing hydrogen sulfide (HS), etc. Another object of the present invention is to provide a stainless steel member and a method for producing a stainless steel member that have high strength, excellent low-temperature toughness, and excellent corrosion resistance in the above-mentioned environments.

[0007] In the present invention, "high strength" refers to a yield strength of 655 MPa or more.

[0008] "Excellent low-temperature toughness" refers to the absorbed energy vE at a test temperature of -10°C in a Charpy impact test conducted on a V-notch test piece (10 mm thick) in accordance with the provisions of JIS Z 2242, with the test piece's longitudinal direction perpendicular to the build direction and the notch parallel to the build direction. -10 This refers to the case where the value is 40J or more.

[0009] Furthermore, "excellent corrosion resistance" refers to "excellent resistance to carbon dioxide corrosion" and "excellent resistance to sulfide stress corrosion cracking."

[0010] The above-mentioned "excellent carbon dioxide corrosion resistance" means, in the case where the Cr content in the steel is 14.0% or less, that the corrosion rate when a test piece is immersed in a test liquid: a 20 mass % NaCl aqueous solution (liquid temperature: 150°C, CO gas atmosphere at 10 atmospheres) held in an autoclave for 336 hours is 0.125 mm / y or less, and that the test piece after the corrosion test is observed for the presence or absence of pitting corrosion on the surface using a 10x magnifying glass, and no pitting corrosion with a diameter of 0.2 mm or more is found. If the Cr content in the steel exceeds 14.0%, the test piece is immersed in a test liquid (20 mass % NaCl aqueous solution, liquid temperature: 180°C, CO2 gas atmosphere at 10 atmospheres) held in an autoclave for 336 hours, and the corrosion rate is 0.125 mm / y or less. Furthermore, after the corrosion test, the test piece is inspected for the presence or absence of pitting corrosion on the surface using a 10x magnifying glass, and no pitting corrosion with a diameter of 0.2 mm or more is observed.

[0011] The above-mentioned "excellent resistance to sulfide stress corrosion cracking" refers to the case where a test piece is immersed in a test solution: a 5% by mass aqueous solution of NaCl (liquid temperature: 25°C, H2S: 0.1 atm, CO2: 0.9 atm) adjusted to a pH of 3.5 by adding acetic acid and sodium acetate; the immersion time is 720 hours; and a load stress of 90% of the yield stress is applied; and the test piece does not undergo cracking after the test. [Means for solving the problem]

[0012] To solve the above-mentioned problems, the inventors focused on additive manufacturing (AM), a method of producing three-dimensional objects using a 3D printer (3D printing). In AM, the raw material stainless steel powder is rapidly heated and cooled during fabrication, resulting in a significantly finer structure and a reduction or refinement of nonmetallic inclusions (hereinafter referred to as "inclusions"), which are known to cause deterioration in corrosion resistance. Therefore, extensive research was conducted into the various factors that affect the strength, corrosion resistance, and low-temperature toughness of stainless steel components fabricated by AM.

[0013] Specifically, an ingot produced by the melting and casting process was used as a master ingot, and then the master ingot was remelted and gas atomized to produce stainless steel powder. This stainless steel powder was then used to produce a 3D printed object, and the various factors mentioned above were investigated. As a result, it was found that in order to achieve the desired strength, corrosion resistance, and low-temperature toughness, the composition of the stainless steel powder, particle size (median diameter of mass cumulative distribution (mass basis)) D 50 It was found that the apparent density and the porosity must be within a desired range.

[0014] Furthermore, by subjecting the resulting shaped product to an appropriate heat treatment, it is possible to obtain a component having the steel structure necessary to satisfy the desired strength, corrosion resistance, and low-temperature toughness. This has enabled the achievement of the desired high strength, excellent low-temperature toughness, and excellent corrosion resistance (resistance to carbon dioxide corrosion and sulfide stress corrosion cracking) in any shape.

[0015] The present invention has been completed based on the above findings and further investigations. The gist of the present invention is as follows. [1] In mass %, C: 0.001 to 0.06%, Si: 0.01 to 1.0%, Mn: 0.01 to 2.0%, P: 0.05% or less, S: less than 0.005% Cr: over 11.0% and up to 15.0% Ni: 2.5 to 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 Contains The balance has a composition consisting of Fe and unavoidable impurities, Particle size D is the median diameter at 50% of the cumulative mass distribution 50 is 10 to 200 μm, Apparent density: 3.5 to 5.0 Mg / m 3 Stainless steel powder. [2] In addition to the above component composition, further, in mass%, Cu:3.5% or less, W: 3.0% or less, Nb: 0.5% or less, Ti: 0 to 0.30% B: 0~0.0050%, Zr: 0-0.2% Co: 0-1.0% Ta: 0 to 0.1%, Ca: 0 to 0.050%, REM: 0~0.1%, Mg: 0 to 0.01%, Sn: 0 to 0.5% The stainless steel powder according to [1], containing one or more selected from Sb: 0 to 0.5%. [3] In mass %, C: 0.001 to 0.06%, Si: 0.01 to 1.0%, Mn: 0.01 to 2.0%, P: 0.05% or less, S: less than 0.005% Cr: over 11.0% and up to 15.0% Ni: 2.5 to 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 Contains The balance has a composition consisting of Fe and unavoidable impurities, The steel has a steel structure having, by volume fraction, 45% or more of a tempered martensite phase, 0 to 40% of a ferrite phase, and 25% or less of a retained austenite phase; The yield strength is 655 MPa or more, and the absorbed energy vE at a test temperature of -10°C in the Charpy impact test -10 Stainless steel members with a strength of 40J or more. [4] In addition to the above component composition, further, in mass%, Cu:3.5% or less, W: 3.0% or less, Nb: 0.5% or less, Ti: 0 to 0.30% B: 0~0.0050%, Zr: 0-0.2% Co: 0-1.0% Ta: 0 to 0.1%, Ca: 0 to 0.050%, REM: 0~0.1%, Mg: 0 to 0.01%, Sn: 0 to 0.5% Sb: 0 to 0.5% The stainless steel member according to [3], containing one or more selected from the following: [5] The number of inclusions with a major axis of 2 μm or more is 10 / mm 2 The stainless steel member according to [3] or [4] below. [6] A stainless steel member according to any one of [3] to [5], wherein in the tempered martensite phase, among the crystal grains having an orientation difference of 5° or more with adjacent grains, the number of the crystal grains having a grain size of 5 μm or more is 10% or less of the total number of crystal grains. [7] A manufacturing process for forming a shaped object using the stainless steel powder according to [1] or [2]; a heat treatment process including, for the shaped object, one or more times of quenching treatment in which the shaped object is heated to a temperature range of 850 to 1150°C, and then cooled to a temperature range of 50°C or less at an average cooling rate faster than air cooling, and a tempering treatment in which the shaped object is heated to a temperature range of 500 to 650°C; A method for manufacturing a stainless steel member having the above structure. [8] The method for manufacturing a stainless steel member according to [7], wherein the manufacturing process is a process for forming a shaped object using an additive manufacturing method. [Effects of the Invention]

[0016] According to the present invention, it is possible to provide a stainless steel powder, a stainless steel member using the same, and a method for manufacturing a stainless steel member. In particular, the stainless steel powder is suitably used for manufacturing a stainless steel member by additive manufacturing.

[0017] Furthermore, the stainless steel member produced using the stainless steel powder of the present invention has high strength and excellent low-temperature toughness, and is resistant to high temperatures of 150°C or higher and to the effects of CO2, Cl2, and the like. - It has excellent corrosion resistance even in severe corrosive environments including hydrogen and hydrogen sulphide, and in environments containing hydrogen sulphide. DETAILED DESCRIPTION OF THE INVENTION

[0018] The present invention will be described in detail below.

[0019] The stainless steel powder of the present invention has the component composition described below and a particle size D controlled within an appropriate range. 50 and apparent density. The stainless steel member of the present invention is produced from this 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.

[0020] First, the component compositions of the stainless steel powder and stainless steel member of the present invention and the reasons for limiting them will be explained. Unless otherwise specified, % by mass will be simply referred to as "%".

[0021] C: 0.001 to 0.06% 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, if the C content exceeds 0.06%, 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.

[0022] Si: 0.01 to 1.0% Si is an element that acts as a deoxidizer, and to obtain this effect, it is necessary to contain 0.01% or more of 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, if the Si content exceeds 1.0%, 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. Even more preferably, the Si content is 0.4% or less.

[0023] Mn: 0.01 to 2.0% Mn is an element that increases the strength of martensitic stainless steel, and in order to ensure the desired strength, a Mn content of 0.01% or more is required. Therefore, the Mn content is set to 0.01% or more. Preferably, the Mn content is 0.1% or more. More preferably, the Mn content is 0.15% or more, and even more preferably, 0.25% or more. On the other hand, if the Mn content exceeds 2.0%, low-temperature toughness decreases. Therefore, the Mn content is set to 2.0% or less. Preferably, the Mn content is 1.0% or less. More preferably, the Mn content is 0.8% or less. Even more preferably, the Mn content is 0.6% or less.

[0024] P:0.05% or less P is an element that reduces corrosion resistance such as carbon dioxide corrosion resistance and sulfide stress corrosion cracking resistance, and is preferably reduced as much as possible in the present invention, but 0.05% or less is acceptable. Therefore, the P content is set to 0.05% or less. Preferably, the P content is 0.03% or less. More preferably, the P content is 0.02% or less. There is no particular restriction on the lower limit, but the P content is preferably 0.005% or more.

[0025] S: Less than 0.005% S is an element that reduces corrosion resistance, and it is preferable to reduce it as much as possible, but less than 0.005% is acceptable. For this reason, 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 restriction on the lower limit, but preferably, the S content is 0.0004% or more.

[0026] Cr: Over 11.0% and up to 15.0% Cr is an element that forms a protective film on the surface of a steel pipe and contributes to improving corrosion resistance. If the Cr content is 11.0% or less, the desired corrosion resistance cannot be ensured. Therefore, the Cr content is set to more than 11.0%. Preferably, the Cr content is 11.5% or more. More preferably, the Cr content is 12.0% or more. Even more preferably, the Cr content is 12.5% ​​or more. On the other hand, a Cr content of more than 15.0% is excessive for the purpose of obtaining the desired corrosion resistance and increases costs. Furthermore, it is disadvantageous in terms of low-temperature toughness. Therefore, the Cr content is set to 15.0% or less. Preferably, the Cr content is 14.5% or less. More preferably, the Cr content is 14.0% or less. Even more preferably, the Cr content is 13.5% or less.

[0027] Ni: 2.5 to 8.0% Ni is an element that strengthens the protective coating on the surface of a steel pipe and contributes to improving corrosion resistance. This effect becomes significant when the Ni content is 2.5% or more. For this reason, the Ni content is set to 2.5% or more. Preferably, the Ni content is 3.0% or more. More preferably, the Ni content is 3.5% or more. Even more preferably, the Ni content is 5.0% or more. On the other hand, a Ni content of more than 8.0% reduces the stability of the martensite phase and decreases strength. For this reason, the Ni content is set to 8.0% or less. Preferably, the Ni content is 7.5% or less. More preferably, the Ni content is 7.0% or less. Even more preferably, the Ni content is 6.5% or less.

[0028] V: 0.005 to 0.5% V is an element that contributes to improving strength through solid solution, and also contributes to improving yield strength by combining with C and N to precipitate as V carbonitrides (V precipitates). To achieve this effect, a V content of 0.005% or more is required. Therefore, the V content is set to 0.005% or more. Preferably, the V content is 0.01% or more. More preferably, the V content is 0.02% or more. Even more preferably, the V content is 0.03% or more. On the other hand, a V content exceeding 0.5% leads to a decrease in low-temperature toughness and sulfide stress corrosion cracking resistance. Therefore, the V content is set to 0.5% or less. Preferably, the V content is 0.3% or less. More preferably, the V content is 0.2% or less. Even more preferably, the V content is 0.1% or less.

[0029] Al: 0.1% or less Al is an element that acts as a deoxidizer. On the other hand, if the Al content exceeds 0.1%, the amount of oxides increases, the cleanliness decreases, and the low-temperature toughness and corrosion resistance decrease. For this reason, 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. There is no particular lower limit, and the Al content is desirably 0% or more. Preferably, the Al content is 0.01% or more. More preferably, the Al content is 0.02% or more.

[0030] N: 0.100% or less N is an element that improves pitting corrosion resistance. On the other hand, if the N content exceeds 0.100%, nitrides are formed, which reduces low-temperature toughness and corrosion resistance. For this reason, 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. Even more preferably, the N content is 0.060% or less. There is no particular lower limit, and the N content is desirably 0% or more. Preferably, the N content is 0.005% or more.

[0031] O: 0.3% or less O (oxygen) exists in the form of oxide in steel and has an adverse effect on various properties. For this reason, in the present invention, it is desirable to reduce the O content as much as possible. Although there is no particular lower limit, the O content is preferably 0.01% or more. In particular, if the O content exceeds 0.3%, corrosion resistance and low-temperature toughness decrease. For this reason, 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.

[0032] Mo: 3.5% or less Mo stabilizes the protective film on the steel pipe surface and prevents Cl - Mo is an element that increases resistance to pitting corrosion due to low pH or low temperature, thereby enhancing sulfide stress corrosion cracking resistance. Although there is no particular lower limit, the Mo content is preferably 0% or more. The Mo content is more preferably 0.4% or more, and even more preferably 1.0% or more. Most preferably, the Mo content is 1.8% or more. On the other hand, a Mo content exceeding 3.5% increases the ferrite fraction and decreases the tempered martensite fraction, thereby resulting in a decrease in sulfide stress corrosion cracking resistance. Furthermore, Mo is an expensive element, leading to an increase in material costs. For this reason, 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%. Even more preferably, the Mo content is 2.7% or less. Most preferably, the Mo content is 2.5% or less.

[0033] The balance other than the above components is Fe and unavoidable impurities.

[0034] In the present invention, the above-mentioned components are the basic component composition. The above-mentioned basic component composition can provide the properties desired in the present invention. In the present invention, the following components may be added as optional elements as needed to further improve strength, corrosion resistance, etc.

[0035] One or more selected from 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%

[0036] Cu:3.5% or less Cu increases the amount of retained austenite and forms precipitates, contributing to improved yield strength (YS), thereby enabling high strength to be obtained without reducing low-temperature toughness. It also strengthens the protective coating on the steel pipe surface, inhibiting hydrogen penetration into the steel and enhancing resistance to sulfide stress corrosion cracking. While there is no particular lower limit, when Cu is contained, the Cu content is preferably 0% or more. More preferably, the Cu content is 0.3% or more. Even more preferably, the Cu content is 0.5% or more. Most preferably, the Cu content is 1.0% or more. On the other hand, a Cu content exceeding 3.5% leads to coarse Cu precipitates, deteriorating resistance to sulfide stress corrosion cracking. Therefore, when Cu is contained, the Cu content is set to 3.5% or less. Preferably, the Cu content is 3.0% or less. More preferably, the Cu content is 2.0% or less. Even more preferably, the Cu content is 1.5% or less.

[0037] W: 3.0% or less W is an important element that contributes to improving the strength of steel and stabilizes the protective film on the steel pipe surface, thereby enhancing sulfide stress corrosion cracking resistance. When W is contained in combination with Mo, it significantly improves sulfide stress corrosion cracking resistance. While there is no particular lower limit, when W is contained, the W content is preferably greater than 0%. More preferably, the W content is 0.3% or more. Even more preferably, the W content is 0.5% or more. Most preferably, the W content is 0.8% or more. On the other hand, a W content exceeding 3.0% promotes the precipitation of intermetallic compounds and reduces corrosion resistance. 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. Even more preferably, the W content is 1.0% or less.

[0038] Nb: 0.5% or less Nb combines with C and N to precipitate as Nb carbonitrides (Nb precipitates), contributing to an improvement in yield strength. Although there is no particular lower limit, when Nb is contained, the Nb content is preferably 0% or more. More preferably, the Nb content is 0.01% or more. Even more preferably, the Nb content is 0.05% or more. On the other hand, an Nb content exceeding 0.5% leads to a decrease in low-temperature toughness and sulfide stress corrosion cracking resistance. 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. Even more preferably, the Nb content is 0.1% or less.

[0039] Ti, B, Zr, Co, and Ta are all elements that increase strength, and one or more of these elements can be selected and contained as necessary. In addition to the effects described above, Ti, B, Zr, Co, and Ta also have the effect of improving sulfide stress corrosion cracking resistance. In particular, Ta is an element that provides the same effect as Nb and can replace part of Nb. Note that Ti, B, Zr, Co, and Ta are optional elements and may not be contained, and their respective contents are preferably 0% or more. That is, when Ti is contained, the Ti content is preferably 0% or more, more preferably 0.01% or more. When B is contained, the B content is preferably 0% or more, more preferably 0.0001% or more. When Zr is contained, the Zr content is preferably 0% or more, more preferably 0.01% or more. When Co is contained, the Co content is preferably 0% or more, more preferably 0.01% or more. When Ta is contained, the Ta content is preferably 0% or more, more preferably 0.01% or more. On the other hand, if the content exceeds Ti: 0.30%, B: 0.0050%, Zr: 0.2%, Co: 1.0%, and Ta: 0.1%, low-temperature toughness decreases. Therefore, when Ti is contained, the Ti content is 0.30% or less, preferably 0.10% or less. When B is contained, the B content is 0.0050% or less, preferably 0.0030% or less. When Zr is contained, the Zr content is 0.2% or less, preferably 0.05% or less. When Co is contained, the Co content is 1.0% or less, preferably 0.4% or less. When Ta is contained, the Ta content is 0.1% or less, preferably 0.03% or less.

[0040] Both Ca and REM (rare earth metals) are elements that contribute to improving sulfide stress corrosion cracking resistance by controlling the morphology of sulfides. Ca and REM are optional elements and do not need to be contained, and their respective contents are preferably 0% or more. However, if they are contained to obtain the effects described above, it is preferable that Ca be contained in an amount of 0.0001% or more. The Ca content is more preferably 0.001% or more. If REM is contained, it is preferable that REM be contained in an amount of 0.001% or more. The REM content is more preferably 0.003% or more. On the other hand, if the Ca content exceeds 0.050% and the REM content exceeds 0.1%, the effect saturates and no effect commensurate with the content can be expected. Therefore, if Ca is contained, the Ca content is set to 0.050% or less. The Ca content is preferably 0.005% or less. If REM is contained, the REM content is set to 0.1% or less. The REM content is preferably 0.01% or less.

[0041] Mg, Sn, and Sb are all elements that improve corrosion resistance. Since Mg, Sn, and Sb are optional elements, they are not necessarily contained, and their respective contents are preferably 0% or more. However, when they are contained to obtain the above-described effects, it is preferable to contain 0.002% or more of Mg, 0.01% or more of Sn, and 0.01% or more of Sb. That is, when Mg is contained, the Mg content is preferably 0% or more, more preferably 0.002% or more. When Sn is contained, the Sn content is preferably 0% or more, more preferably 0.01% or more. When Sb is contained, the Sb content is preferably 0% or more, more preferably 0.01% or more. On the other hand, even if the contents exceed 0.01%, 0.5%, and 0.5%, respectively, the effects saturate, and it is no longer possible to expect effects commensurate with the contents. Therefore, when Mg is contained, the Mg content is set to 0.01% or less. When Sn is contained, the Sn content is set to 0.5% or less, and preferably to 0.2% or less. When Sb is contained, the Sb content is set to 0.5% or less, and more preferably to 0.2% or less.

[0042] Next, the particle size of the stainless steel powder of the present invention will be described.

[0043] The stainless steel powder of the present invention is D 50 The particle size defined by is 10 to 200 μm. 50 If the particle size D is too fine, the powder fluidity will decrease, resulting in uneven powder filling, which will cause defects such as voids to form during additive manufacturing. As a result, low-temperature toughness and corrosion resistance (pitting corrosion resistance and SSCC resistance) will be significantly reduced. 50 The above phenomenon occurs when the particle size D is less than 10 μm. 50 The particle size D must be 10 μm or more. 50 is preferably 15 μm or more, more preferably 20 μm or more, and even more preferably 30 μm or more. 50 If the grain size D is too coarse, it will cause defects during additive manufacturing. As a result, the low-temperature toughness and corrosion resistance (pitting corrosion resistance and SSCC resistance) will be significantly reduced due to the defects. 50 The above phenomenon occurs when the particle size D exceeds 200 μm. 50 The particle size D is 200 μm or less. 50 is preferably 175 μm or less, more preferably 150 μm or less, even more preferably 125 μm or less, and most preferably 100 μm or less.

[0044] The particle size of the stainless steel powder is shown as D 50 The median diameter 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 diameter. In the present invention, the particle diameter D of the stainless steel powder is measured by the method described below. 50 Measure.

[0045] Examples of laser diffraction particle size analyzers include the LA-950V2 manufactured by Horiba, Ltd. While other devices can be used, it is preferable to use one with a measurable particle size range of 0.1 μm or less and 45 μm or more for accurate measurements. In other words, it is preferable to use one that can measure a range of 0.1 to 45 μm. With this device, a laser beam is irradiated onto a solvent containing dispersed iron powder, 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 beam. Ethanol, which has good particle dispersibility and is easy to handle, is preferably used as the solvent for dispersing the iron powder. Using a solvent with high van der Waals forces and low dispersibility, such as water, is undesirable because it causes particles to aggregate during measurement, resulting in measurement results that are coarser than the actual average particle size. Therefore, it is preferable to perform an ultrasonic dispersion treatment on the ethanol solution containing the iron powder before measurement.

[0046] Since the appropriate dispersion treatment time varies depending on the powder being dispersed, the dispersion treatment time is varied between 0 and 60 minutes in seven steps at 10-minute intervals, and the average particle size of the iron powder is measured after each dispersion treatment. During each measurement, the solvent is stirred to prevent particle aggregation. The smallest particle size obtained from the seven measurements, which were performed with the dispersion treatment time varied at 10-minute intervals, is then taken as the particle size of the iron powder (particle size D 50 ) is used as

[0047] Particle size D 50 The above properties can be obtained by controlling both the apparent density and the apparent density. 3 If the density is less than 3.5Mg / m, the fluidity will decrease, causing defects during additive manufacturing. 3 More preferably, 3.7 Mg / m 3 More preferably, the apparent density is 4.0 Mg / m or more. 3 On the other hand, the apparent density is 5.0Mg / m or more. 3 If the apparent density exceeds 5.0 Mg / m, it becomes difficult to stably control the apparent density from an industrial point of view. 3 The density should be less than 4.8 Mg / m3 or less, more preferably 4.6 Mg / m 3 The following is the result.

[0048] The apparent density shall be the value measured using the test method specified in JIS Z 2504.

[0049] The alloy powder can be used as a stainless steel powder for molding, for example, for cladding, 3D printers, sintering, etc. It is particularly suitable as an alloy powder for 3D printers.

[0050] Next, the steel structure of the stainless steel member of the present invention and the reasons for its limitations will be explained.

[0051] The stainless steel member of the present invention is formed from the above-described stainless steel powder, has the above-described chemical composition, and has a steel structure consisting of, by volume, 45% or more of a tempered martensite phase, 0 to 40% of a ferrite phase, and 25% or less of a retained austenite phase.

[0052] In order to ensure the strength (yield strength) targeted by the present invention, the stainless steel member of the present invention has a tempered martensite phase as the main phase. Here, "main phase" refers to a structure that occupies 45% or more by volume of the steel member. If the tempered martensite phase is less than 45%, the desired strength cannot be obtained. For this reason, the tempered martensite phase is set to 45% or more. The tempered martensite phase is preferably set to 55% or more. The tempered martensite phase is more preferably set to 60% or more, and even more preferably set to 70% or more. The upper limit of the tempered martensite phase may be 100%.

[0053] The remainder other than the main phase is a ferrite phase, a retained austenite phase, or a combination of a ferrite phase and a retained austenite phase.

[0054] In order to ensure the strength and sulfide stress corrosion cracking resistance targeted in the present invention, the volume fraction of the ferrite phase is 40% or less. The volume fraction of the ferrite phase is preferably 20% or less, more preferably 10% or less, even more preferably 5% or less, and most preferably 3% or less. Since the stainless steel member of the present invention can achieve the above-mentioned effects even when it is a single tempered martensite phase, the volume fraction of the ferrite phase may be 0%.

[0055] As described above, the stainless steel member of the present invention can achieve the above-described effects even if it is composed of a single tempered martensite phase, so the austenite phase (residual austenite phase) may be 0%. However, since the presence of the retained austenite phase can improve ductility and low-temperature toughness, it is preferable to precipitate the austenite phase (residual austenite phase). Specifically, to achieve such improved ductility and low-temperature toughness, it is preferable that the retained austenite phase precipitate at a volume fraction of more than 10%. More preferably, the retained austenite phase is 13% or more, and even more preferably, 15% or more. On the other hand, precipitation of a large amount of retained austenite phase, exceeding 25% by volume, leads to a decrease in strength. For this reason, the retained austenite phase is set to a volume fraction of 25% or less. Preferably, the retained austenite phase is 23% or less, and even more preferably, the retained austenite phase is 20% or less.

[0056] The above-mentioned steel structure of the stainless steel member of the present invention can be measured by the following method. First, a test piece for microstructure observation is taken from a cross section perpendicular to the manufacturing direction of a material (steel member) manufactured by additive manufacturing or the like. The test piece for microstructure observation is corroded with Virrella's reagent (a mixture of picric acid, hydrochloric acid, and ethanol in proportions of 2 g, 10 ml, and 100 ml, respectively), and the microstructure is imaged using a scanning electron microscope (accelerating voltage: 15 kV, magnification: 1000x). The microstructure fraction (area fraction %) of the ferrite phase is calculated using an image analyzer, and this area fraction is taken as the volume fraction (%) of the ferrite phase.

[0057] The X-ray diffraction specimen is then ground and polished so that the cross section perpendicular to the manufacturing direction becomes the measurement surface, and the amount of retained austenite (γ) is measured using X-ray diffraction. The amount of retained austenite is determined by measuring the integrated intensity of the diffracted X-rays from the (220) plane of γ and the (211) plane of α, and converting it into a volume fraction using the following formula: γ(volume ratio)=100 / (1+(IαRγ / IγRα)) where Iα is the integrated intensity of α, Rα is the theoretically calculated value of α, Iγ is the integrated intensity of γ, and Rγ is the theoretically calculated value of γ.

[0058] The structural fraction (volume fraction %) of the tempered martensite phase is the remainder other than the ferrite phase and the retained austenite phase.

[0059] The steel structure of the stainless steel member of the present invention can be adjusted to fall within the ranges of the above-mentioned phases by appropriately controlling the heat treatment steps (quenching and tempering) described below.

[0060] 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 consist of, by volume, 45% or more of tempered martensite phase, 0 to 40% of ferrite phase, and 25% or less of retained austenite phase, thereby achieving the strength and properties (corrosion resistance and low-temperature toughness) targeted by the present invention.

[0061] In addition, the number of inclusions with a major axis of 2 μm or more is 10 / mm 2 The reasons why it is preferable to have the number of inclusions with a major diameter of 2 μm or more are the starting points for pitting corrosion when a sulfide stress corrosion cracking resistance test is conducted. Pitting corrosion is accompanied by stress concentration and hydrogen generation, which causes sulfide stress corrosion cracking. Therefore, in order to improve sulfide stress corrosion cracking resistance, it is preferable to reduce the number of inclusions with a major diameter of 2 μm or more. This effect is achieved when the number of inclusions with a major diameter of 2 μm or more is 10 / mm 2 Therefore, the number of inclusions with a major axis of 2 μm or more is 10 / mm 2 It is preferable to limit the number of inclusions with a major axis of 2 μm or more to 7 / mm 2It is more preferable that the thickness is 4 / mm or less. 2 The lower limit of the number of inclusions with a major axis of 2 μm or more is not particularly limited, and the number of inclusions with a major axis of 2 μm or more is preferably 0 / mm 2 The above is desirable.

[0062] The reason why it is preferable that the number of crystal grains with a grain size of 5 μm or more among those with a misorientation of 5° or more from adjacent grains be 10% or less of all crystal grains is as follows. Crystal grains with a grain size of 5 μm or more deteriorate low-temperature toughness and sulfide stress corrosion cracking resistance. Therefore, to improve low-temperature toughness and sulfide stress corrosion cracking resistance, it is preferable to reduce the grain size. This effect can be achieved by limiting the number of crystal grains with a grain size of 5 μm or more among those with a misorientation of 5° or more from adjacent grains to 10% or less of all crystal grains. Therefore, it is preferable that the number of crystal grains with a grain size of 5 μm or more among those with a misorientation of 5° or more from adjacent grains be 10% or less of all crystal grains. It is more preferable that the number of crystal grains with a grain size of 5 μm or more be 9% or less of all crystal grains, and even more preferable that it be 8% or less. There is no particular lower limit for the number of crystal grains with a grain size of 5 μm or more among those with a misorientation of 5° or more from adjacent grains, but it is preferably 0% or more.

[0063] The stainless steel member of the present invention has a yield strength of 655 MPa or more. Although there is no particular upper limit, it is preferably 900 MPa or less to prevent a decrease in low-temperature toughness. The absorbed energy vE at a test temperature of -10°C in a Charpy impact test -10 The upper limit is not particularly limited, but is preferably 300 J or less. Furthermore, the stainless steel member of the present invention also has excellent toughness in the Charpy impact test at a test temperature of -60°C, and the absorbed energy vE -60 The absorbed energy vE is preferably 40 J or more. -60 It is preferable that the load is 200 J or less.

[0064] Next, a preferred embodiment of the method for producing stainless steel powder of the present invention will be described.

[0065] The stainless steel powder of the present invention is provided in the final material form through the following series of manufacturing steps: for example, melting, forming an ingot, remelting the master ingot, and producing powder through an atomization process.

[0066] First, in the melting-ingot formation process, predetermined amounts of the above-mentioned elements are melted as materials in a high-frequency vacuum melting furnace, alloyed, and cast to produce an ingot (master ingot). In this process, melting is preferably performed under conditions of a reduced-pressure Ar atmosphere and a melting temperature of 1600°C or higher. The reason for these conditions is as follows: if the melting temperature is too low, the molten steel will solidify when dripping from the nozzle, causing the nozzle to clog. While there is no particular upper limit for the melting temperature, a melting temperature of 1700°C or lower is preferred. Furthermore, from the viewpoint of preventing oxidation of the molten steel, it is desirable to perform melting in a reduced-pressure Ar atmosphere. The melting furnace used in this process is not limited to a high-frequency vacuum melting furnace; other melting furnaces (e.g., direct-current heating melting furnaces) can also be used in the present invention.

[0067] Next, in the master ingot remelting-atomization process, the cast master ingot is used as the raw material and remelted in a melting furnace such as a high-frequency or induction furnace, and then a powder with a low oxygen content is obtained by gas atomization using an inert gas such as Ar or He.

[0068] These powders are then classified to particle sizes of 10 to 200 μm and used as the stainless steel powder of the present invention. Classification may be performed using a sieve or other methods such as air classification. Furthermore, water atomization may be used instead of gas atomization.

[0069] The apparent density is controlled by appropriately adjusting the gas pressure, gas flow rate, gas temperature, and focusing angle during gas atomization.

[0070] Next, one embodiment of the method for manufacturing a stainless steel member of the present invention will be described.

[0071] The method for producing a stainless steel member of the present invention includes a shaping step and a heat treatment step.

[0072] First, in the manufacturing process, the above-mentioned stainless steel powder is used to manufacture a stainless steel additive manufacturing object (three-dimensional structure) by, for example, an additive manufacturing method (metal powder additive manufacturing method).

[0073] As an additive manufacturing method, for example, a 3D printer method can be used. Here, a laser-type powder bed fusion 3D printer is used. No particular setting conditions for the 3D printer are specified. From the viewpoint of preventing excessive or insufficient melting, for example, it is preferable to set the laser output to 150 to 300 W and the scan speed to 700 to 1100 mm / s.

[0074] Next, in the heat treatment step, the shaped three-dimensional structure is subjected to quenching and tempering under predetermined conditions to obtain the stainless steel member of the present invention. In this heat treatment step, it is preferable to perform a quenching treatment in which the structure is heated to a temperature range of 850 to 1150°C, and then cooled at an average cooling rate faster than air cooling to a temperature range where the surface temperature is 50°C or less. It is then preferable to perform a tempering treatment in which the structure is heated to a temperature range of 500 to 650°C (tempering temperature). It is preferable to perform the above quenching and tempering treatments at least once each. Although there is no upper limit, it is preferable to perform the quenching and tempering treatments three or fewer times each.

[0075] Here, "an average cooling rate faster than air cooling" means 0.01°C / s or more. "An average cooling rate faster than water cooling" means 0.2°C / s or more.

[0076] [Quenching treatment] From the viewpoint of refining the martensite phase, the heating temperature in the quenching treatment (reheating temperature) is set to 850°C or higher, preferably 880°C or higher, and more preferably 900°C or higher. The heating temperature in the quenching treatment (reheating temperature) is set to 1150°C or lower, preferably 1050°C or lower, and more preferably 1000°C or lower.

[0077] From the viewpoint of uniform heating, it is preferable to hold the reheating temperature for 10 minutes or more. It is more preferable to hold the reheating temperature for 15 minutes or more. The holding time at the reheating temperature is preferably 60 minutes or less. It is more preferable to hold the reheating temperature for 30 minutes or less.

[0078] Furthermore, the cooling rate in the quenching treatment is air-cooled or faster in order to ensure the desired low-temperature toughness. Preferably, the average cooling rate is 0.01°C / s or faster. More preferably, the average cooling rate in the quenching treatment is 0.1°C / s or faster. Preferably, the average cooling rate in the quenching treatment is 200°C / s or slower. More preferably, the average cooling rate in the quenching treatment is 100°C / s or slower. Here, the average cooling rate refers to the average cooling rate from the start to the end of cooling. The cooling stop temperature is set to a temperature at which the surface temperature of the three-dimensional structure is 50°C or lower. Preferably, it is 40°C or lower, and more preferably, it is 30°C or lower. If the temperature exceeds 50°C, excessive residual austenite will precipitate, making it impossible to obtain the desired high strength. Although there is no particular lower limit, the cooling stop temperature is preferably 5°C or higher.

[0079] [Tempering treatment] If the tempering temperature (tempering temperature) exceeds 650°C, the austenite phase will precipitate excessively, making it impossible to obtain the desired high strength. Therefore, the tempering temperature (tempering temperature) is set to 650°C or lower. The tempering temperature (tempering temperature) is preferably set to 630°C or lower. On the other hand, if the tempering temperature is less than 500°C, the strength will be excessively high, making it impossible to obtain the desired low-temperature toughness. Therefore, the tempering temperature is set to 500°C or higher. The tempering temperature is preferably set to 525°C or higher.

[0080] From the viewpoint of uniform heating, the tempering temperature is preferably maintained for 10 minutes or longer, more preferably 20 minutes or longer. The tempering temperature is preferably maintained for 60 minutes or shorter, more preferably 40 minutes or shorter.

[0081] Furthermore, from the viewpoint of ensuring the desired low-temperature toughness, the cooling rate in the tempering treatment is preferably equal to or faster than air cooling. More preferably, the average cooling rate is 0.01°C / s or more. Even more preferably, the average cooling rate is 0.1°C / s or more. The cooling rate in the tempering treatment is preferably equal to or lower than 200°C / s. More preferably, the cooling rate in the tempering treatment is equal to or lower than 100°C / s.

[0082] In the method for producing a stainless steel member of the present invention, the three-dimensional structure may be further machined before or after the heat treatment step described above in order to form it into a desired shape.

[0083] As described above, the stainless steel member of the present invention manufactured from the stainless steel powder of the present invention has high strength, excellent corrosion resistance, and low-temperature toughness, and therefore can be suitably used as a structural material (e.g., sliding parts) for equipment such as compressors and pumps used in highly corrosive environments such as oil wells. It can also be used as a coupling or accessory for oil wells. Furthermore, the present invention makes it possible to reduce the manufacturing costs of special members with various shapes and also improve dimensional accuracy. [Example]

[0084] The present invention will be described below based on examples, but the present invention is not limited to the following examples.

[0085] The manufacturing method of the stainless steel powder (powder alloy) shown in Table 1 will be described in detail. First, the predetermined amounts of the component compositions shown in Table 1 were melted in a high-frequency vacuum melting furnace (in an Ar atmosphere under reduced pressure, at a melting temperature of 1600°C or higher) and cast to produce master ingots of these alloys. Next, the master ingots of the alloys were remelted in an Ar atmosphere and powdered by gas atomization to obtain powder alloys. Then, the particle size D was determined by classification. 50 The alloy powders (stainless steel powders) with different particle sizes were obtained. 50 The apparent density was measured by the above-mentioned method, and the values ​​are shown in Table 2.

[0086] Next, using a commercially available 3D printer (laser-type powder bed fusion method), three-dimensional structures measuring 50 mm x 80 mm x 12 mm (t: layer thickness) were produced from these powder alloys. The laser output was 250 W, the scan speed was 900 mm / s, and the layer thickness per layer was 40 μm. The produced three-dimensional structures were then subjected to a heat treatment process under the conditions shown in Table 2 to obtain stainless steel components.

[0087] Test pieces were taken from the obtained stainless steel members by the methods described below, and were subjected to microstructural observation, inclusion number measurement, particle size measurement, tensile test, Charpy impact test, and corrosion resistance test.

[0088] (1) Microstructure observation A specimen for microstructure observation was taken from the obtained stainless steel member so that the cross section perpendicular to the molding direction (perpendicular to the layering surface) served as the observation surface. The obtained specimen for microstructure observation was corroded with Vilela's reagent (a mixture of 2 g of picric acid, 10 ml of hydrochloric acid, and 100 ml of ethanol), and the structure was imaged using a scanning electron microscope (accelerating voltage: 15 kV, magnification: 1000x). The structure fraction (area fraction) of the ferrite phase was calculated using an image analyzer, and this was taken as the volume fraction (%) of the ferrite phase.

[0089] X-ray diffraction specimens were then taken from the stainless steel components and ground and polished so that the cross section perpendicular to the fabrication direction served as the measurement surface. The amount of retained austenite (γ) was then measured using X-ray diffraction. The amount of retained austenite was determined by measuring the integrated intensity of the diffracted X-rays from the (220) plane of γ and the (211) plane of α, and converting it to a volume fraction using the following formula: γ(volume ratio)=100 / (1+(IαRγ / IγRα)) where Iα is the integrated intensity of α, Rα is the theoretically calculated value of α, Iγ is the integrated intensity of γ, and Rγ is the theoretically calculated value of γ.

[0090] The structural fraction (vol %) of the tempered martensite phase was determined as the remainder other than the ferrite phase and the retained austenite phase.

[0091] (2) Measuring the number of inclusions The number of inclusions was measured by scanning electron microscope (SEM) specimens of cross sections perpendicular to the manufacturing direction, from half the thickness to 500 mm. 2 The area was sampled. For each sample, inclusions were identified by SEM observation, and the number of inclusions per unit area was calculated. Inclusions with a major axis of 2 μm or more were identified by binarizing the contrast in the backscattered electron image of the scanning electron microscope to define the periphery of the inclusion, and then measuring the major axis from the periphery of the inclusion.

[0092] (3) Particle size measurement The sample for measuring grain size was taken from a position halfway through the thickness of the cross section perpendicular to the manufacturing direction. After EBSD observation (accelerating voltage: 15 kV, step size: 0.5 μm) was performed on the sample in an area 300 μm in the width direction and 500 μm in the thickness direction, a crystal with an orientation difference of 5° or more was defined as one crystal, and the proportion of crystal grains with a grain size of 5 μm or more was measured using the intercept method.

[0093] (4) Tensile test JIS13B half test pieces (GL = 25 mm) were cut from the obtained stainless steel parts so that the tensile direction was perpendicular to the molding direction. Then, tensile tests were conducted in accordance with the JIS standard (Z2241:2011) to determine the yield strength YS and tensile strength TS as tensile properties. Here, a yield strength of 655 MPa or more was evaluated as high strength and passed. On the other hand, a yield strength of less than 655 MPa was rejected.

[0094] (5) Charpy impact test V-notch test pieces (10 mm thick) were taken from the obtained stainless steel parts so that the longitudinal direction of the test piece was perpendicular to the molding direction, and Charpy impact tests were carried out in accordance with the provisions of JIS Z 2242 (2018). The test temperature was -10°C, and the absorbed energy at -10°C, vE -10 The absorbed energy (J) of the stainless steel member was calculated by measuring the absorbed energy vE at -10°C. -10 Those with a vE of 40J or more were evaluated as having high toughness and were deemed to have passed. -10 The test was also conducted at a test temperature of -60°C, and the absorbed energy vE -60 Three test pieces were used for each test, and the arithmetic mean of the obtained values ​​was taken as the absorbed energy (J) of the stainless steel member.

[0095] (6) Corrosion resistance test As corrosion resistance tests, corrosion tests and sulfide stress corrosion cracking resistance tests (SSCC resistance tests) were conducted.

[0096] [Corrosion test] Corrosion test pieces measuring 3 mm thick x 30 mm wide x 40 mm long were machined from the obtained stainless steel members, and corrosion tests were carried out to evaluate the carbon dioxide corrosion resistance. For corrosion tests with a Cr content of 14% or less (Condition A), the corrosion test specimens were immersed in a test solution (a 20% by mass NaCl aqueous solution, liquid temperature: 150°C, CO gas atmosphere: 10 atm) held in an autoclave for 14 days (336 hours). The weight of the specimens after the corrosion test was measured, and the corrosion rate was calculated from the weight loss before and after the corrosion test. A corrosion rate of 0.125 mm / y or less was considered a pass, and a corrosion rate of more than 0.125 mm / y was considered a fail.

[0097] When the Cr content exceeded 14% (Condition B), the corrosion test specimens were immersed in a test liquid (20% by mass NaCl aqueous solution, liquid temperature: 180°C, 10 atm CO2 gas atmosphere) held in an autoclave for 14 days (336 hours). The weight of the specimens after the corrosion test was measured, and the corrosion rate was calculated from the weight loss before and after the corrosion test. A corrosion rate of 0.125 mm / y or less was considered a pass, and a corrosion rate of more than 0.125 mm / y was considered a fail.

[0098] After the corrosion test, the test pieces were inspected for the presence or absence of pitting corrosion on their surfaces using a 10x magnifying glass. The presence of pitting corrosion refers to the presence of pitting corrosion with a diameter of 0.2 mm or more. Test pieces without pitting corrosion were rated as pass, and those with pitting corrosion were rated as fail.

[0099] In this example, a material having a corrosion rate of 0.125 mm / y or less and no occurrence of pitting corrosion is evaluated as having excellent carbon dioxide gas corrosion resistance.

[0100] [SSCC resistance test] Round bar-shaped test pieces (diameter: 6.4 mmφ) were machined from the obtained stainless steel members so that the longitudinal direction of the test pieces was perpendicular to the manufacturing direction, and sulfide stress corrosion cracking resistance tests (SSCC resistance tests) were conducted in accordance with NACE (National Association of Corrosion and Engineering) TM0177 Method A. The SSCC resistance test was performed by immersing test specimens in a 5% by mass NaCl aqueous solution (liquid temperature: 25°C, H2S: 0.1 atm, CO2: 0.9 atm) adjusted to a pH of 3.5 by adding acetic acid and sodium acetate. The immersion time was 720 hours, and a load stress of 100% of the yield stress was applied. After the test, the test specimens were observed for cracks. Those without cracks were rated as passing, and those with cracks were rated as failing.

[0101] The results obtained are shown in Table 3.

[0102] [Table 1]

[0103] [Table 2]

[0104] [Table 3]

[0105] All of the examples of the present invention have the above-mentioned component composition and particle size D 50 The stainless steel powder had a specific surface area and an apparent density controlled within an appropriate range. The stainless steel parts manufactured from this steel powder have high strength and excellent low-temperature toughness in low-temperature environments, and are resistant to CO2, Cl2, and other chemicals. - It had excellent corrosion resistance in high-temperature, severely corrosive environments including hydrogen and H2S.

[0106] On the other hand, in the comparative examples outside the scope of the present invention, the stainless steel powder was not controlled within the appropriate range, and the stainless steel parts manufactured from these steel powders did not achieve the desired characteristic values ​​of at least one of yield strength, corrosion resistance, and low-temperature toughness of the present invention.

Claims

1. A stainless steel powder used for stainless steel members having a steel structure with, by volume, 45% or more of tempered martensite phase, 0-40% of ferrite phase, and 25% or less of retained austenite phase, the number of inclusions with a major axis of 2 μm or more being 10 pieces / mm 2 or less, a yield strength of 655 MPa or more, and an absorbed energy vE -10 of 40 J or more in a Charpy impact test at a test temperature of -10°C, 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 not more than 15.0%; 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, Contains The balance has a composition consisting of Fe and unavoidable impurities, Particle size D, which is the median diameter at 50% of the cumulative mass distribution ５０ is 10 to 200 μm, Apparent density of 3.5 to 5.0 Mg / m ３ Stainless steel powder.

2. In addition to the above component composition, the following is further added in mass%: 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: 0-0.1%, Ca: 0-0.050%, REM: 0-0.1%, Mg: 0 to 0.01%, Sn: 0 to 0.5%, 2. The stainless steel powder according to claim 1, further comprising one or more selected from the group consisting of Sb: 0 to 0.5%.

3. 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 not more than 15.0%; 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, Contains The balance has a composition consisting of Fe and unavoidable impurities, The steel has a steel structure having, by volume, 45% or more of a tempered martensite phase, 0 to 40% of a ferrite phase, and 25% or less of a retained austenite phase, and the number of inclusions having a major axis of 2 μm or more is 10 pieces / mm 2 or less, The yield strength is 655 MPa or more, and the absorbed energy vE at a test temperature of -10 ° C in the Charpy impact test －１０ A stainless steel member having a strength of 40J or more.

4. In addition to the above component composition, the following is further added in mass%: 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: 0-0.1%, Ca: 0-0.050%, REM: 0-0.1%, Mg: 0 to 0.01%, Sn: 0 to 0.5%, Sb: 0 to 0.5% The stainless steel member according to claim 3, containing one or more selected from the group consisting of:

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

6. 5. The stainless steel member according to claim 4, wherein, in the tempered martensite phase, among crystal grains having an orientation difference of 5° or more from adjacent grains, the number of crystal grains having a grain size of 5 μm or more is 10% or less of the total number of crystal grains.

7. A method for manufacturing a stainless steel member according to any one of claims 3 to 6, comprising: a molding step of forming a shaped object using the stainless steel powder according to claim 1 or 2; a heat treatment process including, for the shaped object, one or more times of a quenching treatment in which the shaped object is heated to a temperature range of 850 to 1150°C, and then cooled to a temperature range of 50°C or less at an average cooling rate faster than air cooling, and a tempering treatment in which the shaped object is heated to a temperature range of 500 to 650°C; A method for manufacturing a stainless steel member having the above structure.

8. The method for manufacturing a stainless steel member according to claim 7 , wherein the manufacturing step is a step of forming a shaped object using an additive manufacturing method.

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