Classifications

• • C—CHEMISTRY; METALLURGY
  • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
  • C22F—CHANGING THE PHYSICAL STRUCTURE OF NON-FERROUS METALS AND NON-FERROUS ALLOYS
  • C22F1/00—Changing the physical structure of non-ferrous metals or alloys by heat treatment or by hot or cold working
  • C22F1/10—Changing the physical structure of non-ferrous metals or alloys by heat treatment or by hot or cold working of nickel or cobalt or alloys based thereon
• • C—CHEMISTRY; METALLURGY
  • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
  • C22C—ALLOYS
  • C22C30/00—Alloys containing less than 50% by weight of each constituent
• • C—CHEMISTRY; METALLURGY
  • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
  • C22C—ALLOYS
  • C22C38/00—Ferrous alloys, e.g. steel alloys
  • C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
  • C22C38/40—Ferrous alloys, e.g. steel alloys containing chromium with nickel
• • C—CHEMISTRY; METALLURGY
  • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
  • C22C—ALLOYS
  • C22C38/00—Ferrous alloys, e.g. steel alloys
  • C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
  • C22C38/40—Ferrous alloys, e.g. steel alloys containing chromium with nickel
  • C22C38/44—Ferrous alloys, e.g. steel alloys containing chromium with nickel with molybdenum or tungsten
• • C—CHEMISTRY; METALLURGY
  • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
  • C22F—CHANGING THE PHYSICAL STRUCTURE OF NON-FERROUS METALS AND NON-FERROUS ALLOYS
  • C22F1/00—Changing the physical structure of non-ferrous metals or alloys by heat treatment or by hot or cold working
  • C22F1/002—Changing the physical structure of non-ferrous metals or alloys by heat treatment or by hot or cold working by rapid cooling or quenching; cooling agents used therefor
• • C—CHEMISTRY; METALLURGY
  • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
  • C22F—CHANGING THE PHYSICAL STRUCTURE OF NON-FERROUS METALS AND NON-FERROUS ALLOYS
  • C22F1/00—Changing the physical structure of non-ferrous metals or alloys by heat treatment or by hot or cold working
  • C22F1/02—Changing the physical structure of non-ferrous metals or alloys by heat treatment or by hot or cold working in inert or controlled atmosphere or vacuum
• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
  • G01N1/00—Sampling; Preparing specimens for investigation
• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
  • G01N2203/00—Investigating strength properties of solid materials by application of mechanical stress
  • G01N2203/0014—Type of force applied
  • G01N2203/0016—Tensile or compressive
  • G01N2203/0017—Tensile
• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
  • G01N2203/00—Investigating strength properties of solid materials by application of mechanical stress
  • G01N2203/0014—Type of force applied
  • G01N2203/0016—Tensile or compressive
  • G01N2203/0019—Compressive
• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
  • G01N2203/00—Investigating strength properties of solid materials by application of mechanical stress
  • G01N2203/02—Details not specific for a particular testing method
  • G01N2203/026—Specifications of the specimen
  • G01N2203/0262—Shape of the specimen
  • G01N2203/0274—Tubular or ring-shaped specimens

Definitions

• the present invention relates to Cr-Ni alloy tubes.
• oil wells oil and gas wells
• oil well tubular goods used in oil wells may be made of austenitic alloy pipes (hereinafter, also referred to as “Cr-Ni alloy pipes”) that contain Cr and Ni and have excellent corrosion resistance.
• OCTG In addition to excellent corrosion resistance, OCTG also requires high strength.
• the strength grade of OCTG is generally defined by the tensile yield stress in the axial direction of the tube. OCTG users determine the environment of the well to be drilled (geologic pressure, temperature and pressure of the production fluid) through exploratory drilling and geological surveys, and select OCTG with a strength grade that can withstand the conditions.
• the compressive yield strength in the axial direction is smaller than the tensile yield stress in the axial direction.
• the strength grade of OCTG is generally stressed at the tensile yield strength. Therefore, it is preferable that the difference between the compressive yield stress and the tensile yield stress is small.
• Patent Document 1 discloses an austenitic alloy tube that has small anisotropy in yield strength and can withstand stress distributions that vary depending on the usage environment.
• Cr-Ni alloy pipes used as oil well tubular goods are sometimes welded to other alloy pipes or steel pipes.
• the welded parts of the Cr-Ni alloy pipes soften due to the heat of welding. Therefore, it is necessary to select oil well tubular goods with a strength grade that can withstand the target oil well environment, taking into consideration the softening of the welded parts.
• the present invention aims to solve the above problems and provide a Cr-Ni alloy tube that has high strength while minimizing the difference between compressive yield stress and tensile yield stress.
• the tensile yield stress YS LT in the tube axial direction of the Cr-Ni alloy tube is 780 MPa or more;
• the chemical composition is, in mass%, W: 0.01-1.00%, Co: 0.01 to 1.00%, Sn: 0.001 to 0.010%, As: 0.001 to 0.010%, Zn: 0.001 to 0.010%, Pb: 0.0005 to 0.010%, Sb: 0.0005 to 0.010%, B: 0.0001 to 0.0050%, Ca: 0.0005-0.0200%, Mg: 0.0001 to 0.0200%, and REM: 0.001-0.100%, Contains one or more selected from The Cr-Ni alloy tube according to (3) above.
• the present invention makes it possible to obtain a Cr-Ni alloy tube with high strength while minimizing the difference between the compressive yield stress and the tensile yield stress.
• the Cr-Ni alloy tube according to this embodiment has mechanical properties that satisfy the following formulas (i) to (iii).
• the Cr-Ni alloy tube means an austenitic alloy tube containing 19.00 to 32.00% Cr and 29.50 to 55.00% Ni.
• the Cr-Ni alloy tube according to this embodiment has improved strength due to work hardening caused by cold working, but if it is subsequently subjected to heat treatment at high temperature, its strength decreases and it is not possible to maintain the strength required in the usage environment. That is, the Cr-Ni alloy tube according to this embodiment is in a state in which it is cold worked as is, or has been subjected to heat treatment at a low temperature after cold working. Therefore, the tensile yield stress in the tube axis direction of the Cr-Ni alloy tube is necessarily higher than the compressive yield stress in the tube axis direction.
• the compressive yield stress and the tensile yield stress in the axial direction must satisfy the following formula (i): 0.80 ⁇ YSLC / YSLT ⁇ 0.95...(i)
• the meanings of each symbol are as follows: YS LC : Compressive yield stress in the tube axial direction (MPa) YS LT : Tensile yield stress in the tube axial direction (MPa)
• YS LC /YS LT is preferably 0.82 or more, more preferably 0.84 or more, and even more preferably 0.86 or more.
• the value of YS LC /YS LT may be 0.94 or less.
• the Cr-Ni alloy tube according to the present embodiment is in a state in which it is cold worked or in a state in which it has been subjected to a low-temperature heat treatment after cold working, so that it is 780 MPa or more.
• the tensile yield stress YS LT in the tube axis direction is preferably 800 MPa or more, more preferably 820 MPa or more, even more preferably 840 MPa or more, and even more preferably 850 MPa or more.
• the compressive yield stress in the tube axial direction is determined by the following method.
• a compression test is performed according to the method of ASTM E9 (2019).
• a cylindrical test piece for compression testing is prepared from the center position of the wall thickness of the Cr-Ni alloy tube.
• the size of the cylindrical test piece is, for example, 4 mm in parallel diameter and 8 mm in length.
• the longitudinal direction of the cylindrical test piece is parallel to the tube axial direction of the Cr-Ni alloy tube.
• a compression test is performed using the cylindrical test piece in air at room temperature (25°C), and the obtained 0.2% offset yield strength is defined as the compressive yield stress YS LC (MPa) in the tube axial direction.
• the tensile yield stress in the tube axial direction is determined by the following method.
• a tensile test is performed according to the method of ASTM E8/E8M (2021).
• a round bar test piece for a tensile test is prepared from the center position of the wall thickness of the Cr-Ni alloy tube.
• the size of the round bar test piece is, for example, a parallel part diameter of 4 mm and a gauge length of 20 mm.
• the longitudinal direction of the round bar test piece is parallel to the tube axial direction of the Cr-Ni alloy tube.
• a tensile test is performed using the round bar test piece at room temperature (25°C) in the air, and the obtained 0.2% offset proof stress is defined as the tensile yield stress YS LT (MPa).
• ⁇ Base strength> As described above, the strength of a Cr-Ni alloy tube can be improved by cold working, but excessive working leads to an increase in anisotropy. Therefore, in order to avoid excessive working, it is necessary to sufficiently secure the strength before cold working, that is, the strength in a state without the effect of work hardening (hereinafter also referred to as "base strength"). As a result of the study by the present inventors, it was found that an index of the base strength can be obtained from the tensile yield stress of a test piece in which the effect of work hardening was eliminated by high-frequency induction heating and quenching, and the tensile yield stress in the tube axis direction of the Cr-Ni alloy tube.
• the base strength is sufficient for use as an oil country tubular good.
• the meanings of each symbol are as follows: YS LT : Tensile yield stress in the tube axial direction (MPa) YS HT : Tensile yield stress (MPa) of the test piece after high-frequency induction heating and quenching
• the cylindrical test piece is heated using a high-frequency induction heating device from room temperature to 1150°C at a heating rate of 100°C/s, and then to 1200°C at a heating rate of 25°C/s.
• the heating area by the high-frequency induction heating device is an area of 3.5 mm from the center of the test piece's length to both ends, and 7.0 mm in the longitudinal direction.
• the temperature of the test piece is measured using a thermocouple installed in the center of the test piece's length.
• the test piece is then held at 1200° C. for 180 s.
• Ar gas is sprayed onto the test piece to rapidly cool it to room temperature under conditions where the cooling rate in the temperature range from 1200° C. to 800° C. is 50° C./s.
• a tensile test is performed in air at room temperature (25° C.) in accordance with JIS Z 2241 (2011), and the obtained 0.2% offset proof stress is defined as the tensile yield stress YS HT (MPa) of the test piece after high-frequency induction heating and rapid cooling.
• the material has sufficient work hardening ability for use as an oil country tubular good.
• YS LT ⁇ 443 ⁇ YS LT /YS LC +2.28 ⁇ YS HT -350...(iii)
• YS LC Compressive yield stress in the tube axial direction
• YS LT Tensile yield stress in the tube axial direction
• YS HT Tensile yield stress (MPa) of the test piece after high-frequency induction heating and quenching
• the chemical composition of the Cr-Ni alloy tube according to this embodiment is not particularly limited as long as it contains a predetermined amount of Cr and Ni and has the above-mentioned mechanical properties.
• the Cr-Ni alloy tube according to this embodiment preferably has the chemical composition shown below. The reasons for limiting each element are as follows. In the following description, "%" for the content means “mass %”.
• Carbon (C) is an element that has the effect of increasing the strength of the alloy. However, if C is contained in excess, Cr carbides are formed at the grain boundaries. Cr carbides increase the stress corrosion cracking (SCC) susceptibility at the grain boundaries. Therefore, the C content is 0.030% or less.
• the preferred C content is less than 0.030%, more preferably 0.025%, and even more preferably 0.020% or less.
• the preferred lower limit of the C content is 0.001%, more preferably 0.003%, and even more preferably 0.005%.
• Si 0.50% or less Silicon (Si) is an element that has the effect of deoxidizing the alloy. However, if Si is contained in excess, the hot workability of the alloy decreases. Therefore, the Si content is 0.50% or less. The preferred Si content is less than 0.50%. The preferred upper limit of the Si content is 0.45%, more preferably 0.40%. The preferred lower limit of the Si content is 0.05%, more preferably 0.10%.
• Mn 1.00% or less
• Manganese (Mn) is an element that has the effect of deoxidizing the alloy. Mn is also an austenite forming element and stabilizes the austenite phase. However, if Mn is contained in excess, the hot workability of the alloy decreases. Therefore, the Mn content is 1.00% or less.
• the preferred Mn content is less than 1.00%.
• the preferred upper limit of the Mn content is 0.90%, more preferably 0.80%.
• the preferred lower limit of the Mn content is 0.10%, more preferably 0.30%.
• Phosphorus (P) is an impurity element. P increases the stress corrosion cracking susceptibility of the alloy in a hydrogen sulfide environment. Therefore, the P content is preferably small, and is 0.030% or less. The P content is preferably 0.025% or less, and more preferably 0.020% or less.
• S 0.0050% or less Sulfur (S) is an impurity element. S reduces the hot workability of the alloy. Therefore, the S content is preferably small, and is 0.0050% or less. The preferred S content is 0.0030% or less, and more preferably 0.0010% or less.
• Chromium (Cr) is an element that, in the presence of Ni, has the effect of increasing the stress corrosion cracking resistance (SCC resistance) of the alloy. Cr also increases the strength of the alloy by solid solution strengthening. If Cr is contained in excess, the effect of Cr becomes saturated and the hot workability of the alloy is deteriorated. Therefore, the Cr content is 19.00 to 32.00%. The upper limit of the Cr content is preferably 30.00%, more preferably 28.00%.
• Nickel (Ni) is an austenite forming element and has the effect of stabilizing the austenite phase. Ni also enhances SCC resistance. However, if Ni is contained in excess, the effect saturates. Therefore, the Ni content is 29.50 to 55.00%.
• the lower limit of the Ni content is preferably 34.00%, and more preferably 40.00%.
• the upper limit is 53.00%, more preferably 50.00%.
• Mo 2.50-12.00%
• Molybdenum (Mo) is an element that, in the presence of Cr and Ni, has the effect of increasing the SCC resistance of the alloy. Mo also increases the strength of the alloy by solid solution strengthening. However, when Mo is contained in excess, If the amount of Mo is increased beyond this range, the effect of the addition of Mo becomes saturated and the hot workability of the alloy deteriorates. Therefore, the Mo content is 2.50 to 12.00%.
• the preferred lower limit of the Mo content is 3.50%.
• the upper limit of the Mo content is preferably 10.00%, more preferably 8.00%.
• Vanadium (V) is an element that has the effect of increasing the strength of alloys by finely precipitating within grains as carbides, nitrides, or carbonitrides. It also has the effect of pinning grain boundaries, thereby forming grains. V also has the effect of making the grains finer. In addition, V increases the solubility of N in the alloy, which prevents pinholes from occurring near the surface when the N content is increased to increase the strength of the alloy. However, if V is contained in an excessive amount, the amount of precipitates becomes excessive, which not only reduces toughness but also increases the risk of weld cracking in the heat-affected zone.
• the lower limit of the V content is preferably 0.02%, and more preferably 0.03%.
• the upper limit of the V content is preferably 0.35%, and more preferably 0.50%. The preferred amount is 0.20%.
• Niobium (Nb) and titanium (Ti) are elements that have the effect of increasing the strength of the alloy by finely precipitating within the grains as carbides, nitrides, or carbonitrides. They also have the effect of pinning the grain boundaries. Nb and Ti also have the effect of refining the crystal grains by increasing the solubility of N in the alloy, which increases the amount of N near the surface when the N content is increased to increase the strength of the alloy. However, if Nb and/or Ti are contained in excess, the amount of precipitates becomes excessive, which not only reduces toughness but also increases the risk of weld cracks in the heat-affected zone.
• Nb and Ti are contained, and the total content thereof is 0.002 to 1.000%.
• the lower limit of the total content is preferably 0.010%, and more preferably,
• the upper limit of the total content is preferably 0.500%, and more preferably 0.300%.
• Al 0.001-0.500%
• Aluminum (Al) is an element that has the effect of deoxidizing the alloy. However, if Al is contained in excess, it impairs the cleanliness and deteriorates the workability and ductility. Therefore, the Al content is set to 0.
• the lower limit of the Al content is preferably 0.005%, and more preferably 0.010%.
• the upper limit of the Al content is preferably 0.300%. It is more preferably 0.100%.
• the Al content refers to the content of acid-soluble Al (so-called "sol. Al").
• N 0.005-0.400% Nitrogen (N) increases the strength of the alloy by solid solution strengthening. If N is added and solid solution heat treatment is performed, an alloy pipe with high strength can be obtained. If an alloy pipe with high strength is used, Even with low degree of cold working, the alloy pipe after cold working can have the desired strength. However, if N is contained in excess, pinholes will occur near the surface during solidification of the alloy. Furthermore, N reduces the hot workability of the alloy. Therefore, the N content is 0.005 to 0.400%. The preferred lower limit of the N content is 0.010%. The upper limit of the N content is preferably 0.350%, more preferably 0.300%.
• the Cr-Ni alloy tube according to this embodiment may further contain, in addition to the above elements, one or more elements selected from W, Co, Sn, As, Zn, Pb, Sb, B, Ca, Mg and REM. There is no need to set a lower limit for the content of any of the elements, and the content may be 0%.
• W 0 to 1.00% Tungsten (W) is an optional element. Therefore, W may not be contained. W has the effect of increasing SCC resistance, so it may be contained as necessary. However, if W is contained in excess, the effect is saturated and hot workability is further reduced. Therefore, the W content is 1.00% or less.
• the preferred W content is 0.50% or less, more preferably 0.30% or less.
• the preferred lower limit of the W content is 0.01%, more preferably 0.05%.
• Tin (Sn) is an optional element. Therefore, Sn does not have to be included. Sn has the effect of affecting the convection of the molten pool during welding, increasing the penetration depth, and improving weldability. However, if Sn is contained in an excessive amount, it not only increases the weld cracking susceptibility but also leads to a decrease in corrosion resistance. Therefore, the Sn content is set to 0.010% or less. The Sn content is preferably 0.008% or less, and more preferably 0.006% or less. The lower limit of the Sn content is preferably 0.001%, and more preferably 0.002%. %.
• Arsenic (As) is an optional element. Therefore, As does not have to be contained. As has the effect of affecting the convection of the molten pool during welding, increasing the penetration depth, and improving weldability. However, excessive As content not only increases weld cracking susceptibility but also leads to a decrease in corrosion resistance. Therefore, the As content should be 0.010% or less.
• the As content is preferably 0.008% or less, and more preferably 0.006% or less.
• the lower limit of the As content is preferably 0.001%, and more preferably 0.002% or less. %.
• Zinc (Zn) is an optional element. Therefore, Zn does not have to be included. Zn has the effect of affecting the convection of the molten pool during welding, increasing the penetration depth, and improving weldability. However, if Zn is contained in an excessive amount, it not only increases the weld cracking susceptibility but also leads to a decrease in corrosion resistance. Therefore, the Zn content is set to 0.010% or less. The Zn content is preferably 0.008% or less, and more preferably 0.006% or less. The lower limit of the Zn content is preferably 0.001%, and more preferably 0.002% or less. %.
• Pb 0-0.010%
• Lead (Pb) is an optional element. Therefore, Pb does not have to be contained. Pb has the effect of affecting the convection of the molten pool during welding, increasing the penetration depth, and improving weldability. However, excessive Pb content not only increases the weld cracking susceptibility but also reduces the corrosion resistance. Therefore, the Pb content is set to 0.010% or less.
• the Pb content is preferably 0.008% or less, and more preferably 0.006% or less.
• the lower limit of the Pb content is preferably 0.0005%, and more preferably 0.001%. %.
• Sb 0 to 0.010%
• Antimony (Sb) is an optional element. Therefore, Sb does not have to be contained. Sb has the effect of affecting the convection of the molten pool during welding, increasing the penetration depth, and improving weldability. However, if Sb is contained in excess, it not only increases the weld cracking susceptibility but also leads to a decrease in corrosion resistance. Therefore, the Sb content is set to 0.010% or less.
• the Sb content is preferably 0.008% or less, and more preferably 0.006% or less.
• the lower limit of the Sb content is preferably 0.0005%, and more preferably 0.001%. %.
• B 0-0.0050% Boron (B) is an optional element. Therefore, B does not have to be contained. B is an element that contributes to grain boundary strengthening and improves hot workability, so it may be contained as necessary. However, if B is contained in excess, the effect becomes saturated, and furthermore, liquation cracking occurs at the grain boundaries of the heat-affected zone during welding. Therefore, the B content is set to 0.0050% or less.
• the B content is preferably 0.0030% or less, and more preferably 0.0015% or less.
• the lower limit of the B content is preferably 0.0001%, and more preferably 0.0003%. be.
• Ca 0-0.0200% Calcium (Ca) is an optional element. Therefore, Ca does not have to be contained. Ca has the effect of fixing S as sulfide and improving the hot workability of the alloy, so it is preferable to add Ca as necessary. However, if Ca is contained in excess, coarse oxides are formed, which rather reduces the hot workability of the alloy. Therefore, the Ca content is 0.0200% or less.
• the Ca content is preferably 0.0100% or less, and more preferably 0.0050% or less.
• the lower limit of the Ca content is preferably 0.0005%, and more preferably 0.0010%. .
• Mg 0-0.0200%
• Magnesium (Mg) is an optional element. Therefore, Mg does not have to be contained. Like Ca, Mg has the effect of fixing S as sulfide and improving the hot workability of the alloy. Therefore, Mg may be added as necessary. However, if Mg is added in excess, coarse oxides are formed, which rather reduces the hot workability of the alloy. Therefore, the Mg content is set to 0.
• the Mg content is preferably 0.0100% or less, more preferably 0.0050% or less, and further preferably 0.0020% or less.
• the lower limit of the Mg content is preferably 0.0100% or less, more preferably 0.0050% or less, and further preferably 0.0020% or less. , 0.0001%, and more preferably 0.0005%.
• REM 0 ⁇ 0.100%
• Rare earth elements (REM) are optional elements. Therefore, REM may not be included.
• REM fixes S as sulfides to improve the hot workability of the alloy. However, if REM is contained in excess, coarse oxides are formed, which rather reduces the hot workability of the alloy.
• the REM content is preferably 0.050% or less, and more preferably 0.030% or less.
• the lower limit of the REM content is preferably 0.001%, and even more preferably 0.050% or less. Preferably, it is 0.005%.
• REM refers to Sc, Y, and lanthanides, a total of 17 elements
• REM content refers to the content of one type of REM when there is one type, and the total content when there are two or more types.
• REM is also generally supplied as misch metal, which is an alloy of multiple types of REM. For this reason, one or more individual elements may be added and contained, or they may be added in the form of misch metal, for example.
• the Cr-Ni alloy tube according to this embodiment contains the above-mentioned elements, with the remainder being Fe and impurities.
• impurities refers to components that are mixed in due to various factors in the raw materials, such as ores and scraps, and the manufacturing process when industrially producing alloy materials, and are acceptable within the range that does not adversely affect the present invention.
• the chemical composition of the Cr-Ni alloy tube according to this embodiment further satisfies the following formulas (iv) and (v). 9Mo+100N ⁇ 45.0...(iv) Ni+1.4Cu+Mo-0.9Cr-2Si-1.2Mn-5.7C+20N+90 (0.15Nb+0.27V+0.3Ti) ⁇ 42.0...(v)
• the element symbols indicate the content (mass%) of each element, and zero is substituted if the element is not contained.
• the inventors analyzed the relationship between the mechanical properties and chemical composition of various Cr-Ni alloy tubes, and found that in the above chemical composition, Mo and N contribute especially to the base strength. They also found that by satisfying the above formula (iv), a stable and high base strength can be obtained.
• the chemical composition of the Cr-Ni alloy tube according to the present embodiment preferably further satisfies the following formula (vi).
• the N content so as to satisfy the following formula (vi) in relation to the tensile yield stress in the tube axial direction of the Cr-Ni alloy tube, it becomes easier to suppress the increase in anisotropy even when the tube has a strength of 900 MPa or more.
• YS LC Compressive yield stress in the tube axial direction (MPa)
• N N content in alloy tube (mass%)
• an austenitic alloy is melted to produce a molten metal.
• the alloy can be melted in an electric furnace, an Ar- O2 mixed gas bottom blowing decarburization furnace (AOD furnace), a vacuum decarburization furnace (VOD furnace), or the like.
• the casting material may be, for example, an ingot, a slab, or a bloom. Specifically, an ingot is produced by an ingot casting method, or a slab or bloom is produced by a continuous casting method.
• the cast material is hot worked to produce a round billet.
• the hot working is, for example, hot rolling or hot forging.
• the produced round billet is then hot worked to produce a blank pipe.
• a blank pipe is produced from the round billet by an extrusion pipe-making process, such as the Ugine-Sejournet process.
• a blank pipe is produced from the round billet by the Mannesmann pipe-making process.
• Cold working is performed on the manufactured blank tube.
• Cold working includes cold drawing and cold rolling, typically Pilger rolling. Either cold drawing or cold rolling may be used in the present invention.
• Cold drawing imparts a larger tensile strain to the alloy tube in the axial direction than cold rolling.
• Cold rolling imparts a larger strain to the blank tube not only in the axial direction but also in the circumferential direction. Therefore, cold rolling imparts a larger compressive strain to the blank tube in the circumferential direction than cold drawing.
• the area reduction ratio during cold working is preferably 15% or more.
• the area reduction ratio is defined by the following formula (I).
• the lower limit of the area reduction ratio is preferably 20%.
• solution heat treatment may be performed on the hot-worked raw pipe.
• the raw pipe after solution heat treatment is descaled to remove the scale, and then cold working is performed.
• cold working may be performed multiple times. When cold working is performed multiple times, solution heat treatment may be performed as a softening heat treatment between cold working and the next cold working.
• straightening processing using an inclined roll straightener and/or low-temperature heat treatment may be performed. Either straightening processing or low-temperature heat treatment may be performed first. However, if the heat treatment temperature is too high, the yield stress will be excessively reduced and it will not be possible to maintain the strength required in the usage environment. Therefore, when performing low-temperature heat treatment, the heating temperature should be 300 to 550°C, and preferably 400 to 500°C.
• the wall thickness of the alloy pipe is preferably 4 mm or more, more preferably 6 mm or more, even more preferably 8 mm or more, and even more preferably 10 mm or more.
• An alloy having the chemical composition shown in Table 1 was melted and cast in a vacuum to obtain an ingot with an outer diameter of 120 mm and a weight of 30 kg. This ingot was hot forged to produce a material with a thickness of 50 mm. The temperature of the ingot before hot forging was 1200°C. Furthermore, hot rolling was performed on the material. At this time, in order to change the product strength, the cold working rate shown in Table 2 was applied, and the thickness of the intermediate alloy material (alloy plate) was determined by back-calculating so that the thickness after cold rolling was unified to 11.5 mm. Then, a softening heat treatment was performed by heat treatment for 10 minutes at the temperature shown in Table 2 and then water cooling.
• the compressive yield stress YS LC (MPa) and the tensile yield stress YS LT (MPa) in the tube axis direction were obtained by the above-mentioned method.
• a cylindrical test piece for the compression test and a round bar test piece for the tensile test were taken from the center position of the plate thickness of the alloy plate of each test number so that the longitudinal direction was parallel to the rolling direction.
• the cylindrical test piece had a parallel part diameter of 4 mm and a length of 8 mm.
• the round bar test piece had a parallel part diameter of 4 mm and a gauge length of 20 mm.
• a compression test was performed on the cylindrical test piece for the compression test in air at room temperature (25 ° C.) by a method conforming to ASTM E9 (2019).
• the 0.2% offset proof stress obtained by the compression test was taken as the compressive yield stress YS LC (MPa) in the tube axis direction.
• a tensile test was performed on the round bar test piece for the tensile test in air at room temperature (25 ° C.) by a method conforming to ASTM E8 / E8M (2013).
• the 0.2% offset yield strength obtained by the tensile test was taken as the tensile yield stress YS LT (MPa) in the axial direction of the tube.
• the tensile yield stress YS HT (MPa) of the test piece after high-frequency induction heating and quenching was obtained by the above-mentioned method. Specifically, a cylindrical test piece for high-frequency induction heating and quenching was taken from the center position of the plate thickness of the alloy plate of each test number so that the longitudinal direction was parallel to the rolling direction. The cylindrical test piece was prepared in accordance with ASTM E8/E8M (2021), had a diameter of 6 mm, and a gauge length of 30 mm. The cylindrical test piece for high-frequency induction heating and quenching was heated from room temperature to 1150 ° C.
• the heating area by the high-frequency induction heating device was set to a region of 3.5 mm from the center in the longitudinal direction of the test piece to both ends, and 7.0 mm in the longitudinal direction.
• the temperature of the test piece was measured using a thermocouple placed in the center of the test piece in the longitudinal direction.
• test piece was then held at 1200° C. for 180 s. Immediately after holding, Ar gas was sprayed onto the test piece, and the test piece was quenched to room temperature under conditions of a cooling rate of 50° C./s in the temperature range from 1200° C. to 800° C. Then, using the test piece after high-frequency induction heating and quenching, a tensile test was performed in air at room temperature (25° C.) in accordance with JIS Z 2241 (2011), and the obtained 0.2% offset proof stress was taken as the tensile yield stress YS HT (MPa) of the test piece after high-frequency induction heating and quenching.
• YS HT tensile yield stress
• an alloy material satisfying all of the requirements of the present invention has a high tensile yield stress of 780 MPa or more, and can achieve a YS LC /YS LT of 0.80 or more.
• the present invention it is possible to obtain a Cr-Ni alloy pipe having high strength while minimizing the difference between the compressive yield stress and the tensile yield stress. Therefore, by selecting the Cr-Ni alloy pipe according to the present invention as the material for oil well tubular goods, it is possible to obtain highly reliable oil well tubular goods that can maintain high strength even if softening occurs in the welded parts.

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• 2023
  • 2023-03-28 CN CN202380096513.4A patent/CN120936730A/zh active Pending
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