WO2016038809A1 - 油井用高強度継目無鋼管およびその製造方法 - Google Patents
油井用高強度継目無鋼管およびその製造方法 Download PDFInfo
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- C21D1/00—General methods or devices for heat treatment, e.g. annealing, hardening, quenching or tempering
- C21D1/18—Hardening; Quenching with or without subsequent tempering
- C21D1/25—Hardening, combined with annealing between 300 degrees Celsius and 600 degrees Celsius, i.e. heat refining ("Vergüten")
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- C21D2211/008—Martensite
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- C21D8/00—Modifying the physical properties by deformation combined with, or followed by, heat treatment
- C21D8/10—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of tubular bodies
- C21D8/105—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of tubular bodies of ferrous alloys
Definitions
- the present invention relates to a seamless steel pipe suitable for use in oil well pipes and line pipes, and in particular, has high resistance to sulfide stress corrosion cracking (SSC resistance) in a wet hydrogen sulfide environment (sour environment).
- SSC resistance sulfide stress corrosion cracking
- the present invention relates to a strength seamless steel pipe and a manufacturing method thereof.
- Patent Document 1 In response to such a demand, for example, in Patent Document 1, C: 0.2 to 0.35%, Cr: 0.2 to 0.7%, Mo: 0.1 to 0.5%, V: 0.1 to 0.3%, and C, There has been proposed a method for producing oil-well steel in which low alloy steel containing Cr, Mo, and V is adjusted and quenched at an Ac 3 transformation point or higher and then tempered at 650 ° C. or more and an Ac 1 transformation point or less. According to the technique described in Patent Document 1, the total amount of precipitated carbide can be adjusted to 2 to 5% by weight, and the proportion of MC type carbide in the total amount of carbide can be adjusted to 8 to 40% by weight. It is said that oil well steel having excellent resistance to sulfide stress corrosion cracking can be obtained.
- Patent Document 2 discloses a low alloy containing, by mass, C: 0.15 to 0.3%, Cr: 0.2 to 1.5%, Mo: 0.1 to 1%, V: 0.05 to 0.3%, and Nb: 0.003 to 0.1%. After the steel is heated to 1150 ° C or higher, the hot working is finished at 1000 ° C or higher and subsequently quenched from 900 ° C or higher, then tempered at 550 ° C or higher and below the Ac 1 transformation point, and further 850-1000 ° C.
- a method for producing oil well steel with excellent toughness and sulfide stress corrosion cracking resistance has been proposed, in which the steel is reheated and quenched and subjected to quenching and tempering at least once at 650 ° C or higher and the Ac 1 transformation point or lower. Yes.
- the total amount of precipitated carbide is 1.5 to 4% by mass
- the proportion of MC type carbide in the total amount of carbide is 5 to 45% by mass.
- M 23 C 6 type carbide This ratio can be adjusted to 200 / t (t: wall thickness (mm)) mass% or less, and it is said that the oil well steel is excellent in toughness and resistance to sulfide stress corrosion cracking.
- Patent Document 3 describes, in mass%, C: 0.15-0.30%, Si: 0.05-1.0%, Mn: 0.10-1.0%, Cr: 0.1-1.5%, Mo: 0.1-1.0%, Al: 0.003. -0.08%, N: 0.008% or less, B: 0.0005-0.010%, Ca + O: 0.008% or less, Ti: 0.005-0.05%, Nb: 0.05% or less, Zr: 0.05% or less, V: 0.30% or less contain one or two or more of, is 80 ⁇ m or less than the maximum length of the non-metallic inclusions continuously by cross-section observation, the number of more than the particle size 20 ⁇ m of non-metallic inclusions by the cross section observation is 10/100 mm 2
- the following steel materials for oil wells have been proposed. Thereby, it is said that a low alloy steel material for oil wells having high strength required for oil wells and excellent SSC resistance commensurate with the strength is obtained.
- Patent Document 4 in mass%, C: 0.20 to 0.35%, Si: 0.05 to 0.5%, Mn: 0.05 to 0.6%, P %: 0.025% or less, S: 0.01% or less, Al: 0.005 to 0.100 %, Mo: 0.8 to 3.0%, V: 0.05 to 0.25%, B: 0.0001 to 0.005%, N: 0.01% or less, O: 0.01% or less and sulfide stress corrosion resistance satisfying 12V + 1-Mo ⁇ 0 Low alloy oil well pipe steels with excellent cracking properties have been proposed.
- Cr 0.6% or less may be contained so as to satisfy Mo ⁇ (Cr + Mn) ⁇ 0, and Nb: 0.1% or less, Ti : 0.1% or less, Zr: One or more of 0.1% or less may be contained, and Ca: 0.01% or less may be contained.
- the object of the present invention is to solve the problems of the prior art and to provide a high strength seamless steel pipe for oil wells excellent in sulfide stress corrosion cracking resistance (SSC resistance) and a method for producing the same.
- SSC resistance sulfide stress corrosion cracking resistance
- high strength refers to the case where the yield strength YS is 110 ksi or higher, that is, the yield strength YS is 758 MPa or higher.
- excellent in SSC resistance refers to the test method specified in NACE TM0177 Method A, and 0.5 mass% acetic acid + 5.0 mass% saline solution saturated with H 2 S (liquid temperature) : A constant load test is performed at 24 ° C), and the test material is subjected to a stress of 85% of the yield strength of the material under test.
- the present inventors need to achieve both desired high strength and excellent SSC resistance, and therefore earnestly research on various factors affecting strength and SSC resistance. did. As a result, it was discovered that it is important to strictly suppress center segregation and microsegregation in order to maintain excellent SSC resistance as a high-strength seamless steel pipe for oil wells.
- the inventors focused on the difference in the effect on SSC resistance when center segregation or microsegregation occurs for each alloy element, selected elements with a large influence, and considered the strength of the influence of each element.
- X M is the element M, a (segregation content (mass%)) / (average content (mass%)).
- M indicates each element of Si, Mn, Mo, and P.
- X M is a value obtained as follows.
- Step 1 with an electron beam microanalyzer (EPMA) that uses a beam with a diameter of 20 ⁇ m in a square area of 5mm x 5mm, with a piece centered at 1 / 4t position (t: tube thickness) from the inner surface of the seamless steel tube.
- EPMA electron beam microanalyzer
- the measurement values of all the measurement fields are collected and arranged in descending order of the concentration, and the number of measurement points x 0.0001th value (if this value is not an integer, the segregation part is larger than this value and the nearest integer value) It was set as content.
- the present invention has been completed based on such findings and further studies. That is, the gist of the present invention is as follows. (1) By mass%, C: 0.20 to 0.50%, Si: 0.05 to 0.40%, Mn: 0.3 to 0.9%, P: 0.015% or less, S: 0.005% or less, Al: 0.005 to 0.1%, N: 0.008 %: Cr: 0.6 to 1.7%, Mo: 0.4 to 1.0%, V: 0.01 to 0.30%, Nb: 0.01 to 0.06%, B: 0.0003 to 0.0030%, O (oxygen): 0.0030% or less,
- the composition comprising the balance Fe and inevitable impurities, the tempered martensite phase is 95% or more by volume, and the structure is that the prior austenite grains are 8.5 or more in grain size number, and is 1/4 t from the inner surface of the steel pipe.
- a method for producing a high-strength seamless steel pipe The heating temperature of the heating is a temperature in the range of 1050 to 1350 ° C., and the cooling after the hot working is cooling performed to a temperature at which the surface temperature becomes 200 ° C. or less at a cooling rate of air cooling or higher, and after the cooling, Re-heat to a temperature in the range of Ac 3 transformation point to 1000 ° C or less, and quenching is performed at least once to quench the surface temperature to 200 ° C or less. After the quenching treatment, the temperature is in the range of 600 to 740 ° C.
- a high strength seamless steel pipe for oil wells having a yield strength YS: 758 MPa or more and excellent resistance to sulfide stress corrosion cracking can be easily and inexpensively manufactured, and has a remarkable industrial effect. Play. Further, according to the present invention, it is possible to stably produce a high-strength seamless steel pipe that contains a proper amount of an appropriate alloy element and maintains desired high strength for oil wells together with excellent SSC resistance.
- C 0.20 to 0.50% C dissolves and contributes to increasing the strength of the steel, improves the hardenability of the steel, and contributes to the formation of a structure whose main phase is the martensite phase during quenching. In order to acquire such an effect, C needs to contain 0.20% or more. On the other hand, if the content of C exceeds 0.50%, cracking occurs during quenching, and the productivity is significantly reduced. For this reason, C is limited to the range of 0.20 to 0.50%. Preferably, C is 0.20 to 0.35%. More preferably, C is 0.22 to 0.32%.
- Si 0.05 to 0.40%
- Si is an element that acts as a deoxidizer, has a function of increasing the strength of the steel by solid solution in the steel, and further suppressing softening during tempering. In order to acquire such an effect, it is necessary to contain Si 0.05% or more.
- a large amount of Si exceeding 0.40% promotes the formation of a ferrite phase that is a softening phase, inhibits the desired high strength, and further promotes the formation of coarse oxide inclusions, Reduces SSC resistance and toughness.
- Si is an element that segregates and locally hardens the steel, and if a large amount is contained, a local hardened region is formed and the SSC resistance is adversely affected. Therefore, in the present invention, Si is limited to the range of 0.05 to 0.40%.
- Si is 0.05 to 0.30%. More preferably, Si is 0.20 to 0.30%.
- Mn 0.3-0.9%
- Mn is an element that improves the hardenability of steel and contributes to an increase in steel strength. In order to acquire such an effect, Mn needs to contain 0.3% or more.
- Mn is an element that segregates and locally hardens the steel, and the inclusion of a large amount of Mn has an adverse effect of forming a local hardening region and lowering the SSC resistance. Therefore, in the present invention, Mn is limited to a range of 0.3 to 0.9%. Preferably, Mn is 0.4 to 0.8%. More preferably, Mn is 0.5 to 0.8%.
- P 0.015% or less
- P is an element that not only segregates at grain boundaries to cause grain boundary embrittlement but also segregates and locally hardens steel.
- P is an inevitable impurity as much as possible. It is preferable to reduce it, but up to 0.015% is acceptable. For this reason, P was limited to 0.015% or less.
- P is 0.012% or less.
- S 0.005% or less S is an unavoidable impurity, most of which is present as sulfide inclusions in steel, and lowers ductility, toughness and SSC resistance. Up to 0.005% is acceptable. For this reason, S was limited to 0.005% or less. Preferably, S is 0.003% or less.
- Al acts as a deoxidizer and is added to deoxidize molten steel. In addition, it combines with N to form AlN, contributing to refinement of austenite grains during heating, and preventing solid solution B from combining with N, reducing the effect of improving the hardenability of B. Suppress. In order to acquire such an effect, Al needs to contain 0.005% or more. On the other hand, the content of Al exceeding 0.1% causes an increase in oxide inclusions, lowers the cleanliness of the steel, and leads to a decrease in ductility, toughness and SSC resistance. For this reason, Al is limited to the range of 0.005 to 0.1%. Preferably, Al is 0.01 to 0.08%. More preferably, Al is 0.02 to 0.05%.
- N 0.008% or less N is present in steel as an inevitable impurity, but forms AlN by combining with Al. If Ti is contained, TiN is formed to refine crystal grains and toughness. It has the effect
- Cr 0.6-1.7% Cr is an element that increases the strength of steel through the improvement of hardenability and improves the corrosion resistance.
- Cr is an element that combines with C during tempering to form carbides such as M 3 C, M 7 C 3 , and M 23 C 6 (M is a metal element) and improves temper softening resistance.
- M is a metal element
- M 3 C type carbide has a strong effect of improving the temper softening resistance.
- Cr needs to contain 0.6% or more.
- the Cr content exceeds 1.7%, a large amount of M 7 C 3 and M 23 C 6 is formed, which acts as a hydrogen trap site and lowers the SSC resistance.
- Cr is limited to the range of 0.6 to 1.7%.
- Cr is 0.8 to 1.5%. More preferably, Cr is 0.8 to 1.3%.
- Mo 0.4-1.0%
- Mo forms carbides and contributes to strengthening the steel by precipitation strengthening. In addition, it dissolves in steel and segregates at the prior austenite grain boundaries, contributing to the improvement of SSC resistance. Furthermore, Mo has an action of densifying the corrosion product and further suppressing the generation and growth of pits that are the starting points of cracks. In order to acquire such an effect, Mo needs to contain 0.4% or more.
- Mo is limited to the range of 0.4 to 1.0%.
- Mo is 0.6 to 1.0%. More preferably, Mo is 0.8 to 1.0%.
- V 0.01 to 0.30%
- V is an element that forms carbides and carbonitrides and contributes to the strengthening of steel. In order to acquire such an effect, V needs to contain 0.01% or more. On the other hand, even if it contains V exceeding 0.30%, the effect is saturated and an effect commensurate with the content cannot be expected, which is economically disadvantageous. For this reason, V is limited to the range of 0.01 to 0.30%. Preferably, V is 0.03 to 0.25%.
- Nb 0.01-0.06% Nb forms carbides and / or carbonitrides and contributes to strengthening of steel. These also contribute to the refinement of austenite grains. In order to acquire such an effect, Nb needs to contain 0.01% or more. On the other hand, when Nb is contained in a large amount exceeding 0.06%, coarse precipitates are formed, and the contribution to increasing the strength is small, and the SSC resistance is lowered. Therefore, Nb is limited to the range of 0.01 to 0.06%. More preferably, Nb is 0.02 to 0.05%.
- B 0.0003 to 0.0030% B segregates at the austenite grain boundaries and suppresses the ferrite transformation from the grain boundaries, thereby having the effect of enhancing the hardenability of the steel even when contained in a small amount. In order to acquire such an effect, B needs to contain 0.0003% or more. On the other hand, when B is contained in excess of 0.0030%, it precipitates as carbonitride and the like, the hardenability is lowered, and thus the toughness is lowered. For this reason, B is limited to the range of 0.0003 to 0.0030%. Preferably, B is 0.0005 to 0.0024%.
- O (oxygen) 0.0030% or less
- O (oxygen) exists as an oxide inclusion in steel as an inevitable impurity. Since these inclusions become the starting point of SSC generation and reduce SSC resistance, in the present invention, it is preferable to reduce O (oxygen) as much as possible. However, excessive reduction leads to higher refining costs, so up to 0.0030% is acceptable. For this reason, O (oxygen) was limited to 0.0030% or less. Preferably, O is 0.0020%.
- the above components are basic components.
- One or more selected from the following and / or Ca: 0.0005 to 0.005% can be contained.
- Ti 0.005-0.030% Ti combines with N during solidification of the molten steel and precipitates as fine TiN, which contributes to the refinement of austenite grains by its pinning effect. In order to acquire such an effect, Ti needs to contain 0.005% or more. The effect of Ti is small when the content is less than 0.005%. On the other hand, if Ti is contained in excess of 0.030%, TiN becomes coarse, and the pinning effect described above cannot be exhibited, but the toughness is reduced. In addition, the coarser TiN causes the SSC resistance to decrease. For these reasons, when Ti is contained, Ti is preferably limited to a range of 0.005 to 0.030%.
- Ti / N 2.0-5.0
- Ti / N which is the ratio of Ti content to N content
- Ti / N is larger than 5.0, the tendency of TiN to become coarse becomes remarkable, and toughness and SSC resistance are lowered.
- Ti / N is preferably limited to a range of 2.0 to 5.0. More preferably, Ti / N is 2.5 to 4.5.
- Cu is an element that contributes to increasing the strength of steel and has the effect of improving toughness and corrosion resistance. In particular, it is an extremely effective element for improving SSC resistance in severe corrosive environments.
- Cu When Cu is contained, a dense corrosion product is formed and the corrosion resistance is improved, and further, the generation and growth of pits as the starting point of cracking are suppressed.
- it is desirable to contain Cu 0.03% or more.
- Cu even if Cu is contained in an amount exceeding 1.0%, the effect is saturated, and an effect commensurate with the content cannot be expected, which is disadvantageous for economic efficiency. For this reason, when it contains Cu, it is preferable to limit Cu to 1.0% or less. More preferably, Cu is 0.05 to 0.6%.
- Ni is an element that contributes to increasing the strength of steel and further improves toughness and corrosion resistance. In order to acquire such an effect, it is desirable to contain Ni 0.03% or more. On the other hand, even if Ni is contained in an amount exceeding 1.0%, the effect is saturated, and an effect commensurate with the content cannot be expected, which is disadvantageous for economic efficiency. For this reason, when it contains Ni, it is preferable to limit Ni to 1.0% or less. More preferably, Ni is 0.05 to 0.6%.
- W is an element that forms carbides and contributes to increasing the strength of the steel by precipitation strengthening, and also dissolves and segregates at the prior austenite grain boundaries to contribute to the improvement of SSC resistance.
- W is preferably contained in an amount of 0.03% or more.
- W it is preferable to limit W to 2.0% or less. More preferably, W is 0.4 to 1.5%.
- Ca 0.0005 to 0.005%
- Ca is an element that combines with S to form CaS and effectively acts to control the morphology of sulfide inclusions, and improves toughness and SSC resistance through the morphology control of sulfide inclusions. Contribute. In order to acquire such an effect, Ca needs to contain at least 0.0005%. On the other hand, even if Ca is contained in excess of 0.005%, the effect is saturated and an effect commensurate with the content cannot be expected, which is disadvantageous in terms of economy. For this reason, when Ca is contained, Ca is preferably limited to a range of 0.0005 to 0.005%.
- the balance other than the above components is composed of Fe and inevitable impurities.
- unavoidable impurities Mg: 0.0008% or less, Co: 0.05% or less are acceptable.
- the high-strength seamless steel pipe of the present invention has the above-described composition, and further has a structure in which the tempered martensite phase is the main phase and the prior austenite grains are 8.5 or more in particle size number.
- Tempered martensite phase 95% or more
- the martensite phase is used to secure the high strength of YS: 110 ksi class or higher and to maintain the ductility and toughness required for the structure.
- the tempered martensite phase is the main phase.
- the term “main phase” refers to a single phase in which the volume is 100% by volume, or a second phase in which the volume ratio is within a range that does not affect the characteristics and the second phase is 5% or less. The case where it is more than%.
- examples of the second phase include a bainite phase, a retained austenite phase, pearlite, or a mixed phase thereof.
- the above structure of the high-strength seamless steel pipe of the present invention can be adjusted by appropriately selecting the heating temperature at the time of quenching according to the steel components and the cooling rate at the time of cooling.
- Particle size number of prior austenite grains 8.5 or more If the particle size number of prior austenite grains is less than 8.5, the substructure of the martensite phase produced becomes coarse and SSC resistance decreases. For this reason, the particle size number of the prior austenite grains is limited to 8.5 or more. As the particle number, a value measured in accordance with JIS G 0551 is used.
- the particle size number of the prior austenite grains can be adjusted by changing the heating rate, heating temperature and holding temperature in the quenching process, and the number of times of quenching process.
- the high-strength seamless steel pipe of the present invention is a segregation obtained by conducting an area analysis of each element by an electron beam microanalyzer (EPMA) centering on a 1/4 t position (t: pipe thickness) from the inner surface of the steel pipe.
- EPMA electron beam microanalyzer
- t pipe thickness
- Ps 8.1 (X Si + X Mn + X Mo ) + 1.2X P
- the segregation degree index Ps defined by (where X M : (Segregation part content (mass%) of element M) / (average content (mass%) of element M)) satisfies less than 65, seamless. It is a steel pipe.
- the above-described Ps is a value obtained by selecting an element having a large influence on SSC resistance when segregated, and is a value introduced to show the degree of decrease in SSC resistance due to segregation. If this value increases, the local hardening region increases and the SSC resistance decreases. If the Ps value is less than 65, the necessary SSC resistance can be obtained. Therefore, in the present invention, the Ps value is limited to less than 65. Preferably, the Ps value is less than 60. The smaller the Ps value, the smaller the adverse effect of segregation and the better the SSC resistance.
- X M is the ratio of (segregation part content) to (average content) for element M (segregation part content) / (average content), and is calculated as follows. Value.
- X M is the ratio between the segregation part content and the average content described above for element M, that is, (segregation part content) / (average content) of element M.
- Ps needs to be controlled in a continuous casting process. Specifically, it can be reduced by electromagnetic stirring with a mold and / or a strand.
- the steel pipe material having the above composition is heated, subjected to hot working, cooled to obtain a seamless steel pipe having a predetermined shape, and then to the obtained seamless steel pipe. Apply quenching and tempering treatment.
- the manufacturing method of the steel pipe material is not particularly limited, but the molten steel having the above composition is melted in a conventional melting furnace such as a converter, an electric furnace, a vacuum melting furnace, and the continuous casting method. It is desirable to use a steel pipe material such as a billet by such a method.
- the steel pipe material having the above composition is heated to a heating temperature in the range of 1050 to 1350 ° C.
- Heating temperature 1050-1350 ° C
- the heating temperature is less than 1050 ° C.
- the dissolution of carbides in the steel pipe material becomes insufficient.
- crystal grains become coarse, precipitates such as TiN precipitated during solidification become coarse, and cementite becomes coarse, so that the steel pipe toughness decreases.
- a thick scale layer is formed on the surface of the steel pipe material, causing surface defects during rolling. From this point of view and energy saving, the heating temperature is limited to the range of 1050 to 1350 ° C.
- the steel pipe material heated to the above temperature is then subjected to hot working to obtain a seamless steel pipe having a predetermined dimension and shape.
- Any hot working method using a conventional seamless steel pipe manufacturing facility can be applied to the hot working in the present invention.
- the conventional seamless steel pipe manufacturing equipment include Mannesmann-plug mill type or Mannesman-mandrel type seamless steel pipe manufacturing equipment.
- a hot extrusion facility using a press method can also be used.
- the hot working conditions are not particularly limited as long as the seamless steel pipe having a predetermined size and shape can be manufactured, and any conventional hot working conditions can be applied.
- Cooling after hot working to a surface temperature of 200 ° C or less at a cooling rate of air cooling or higher
- the surface temperature of the obtained seamless steel pipe is 200 ° C or lower at a cooling rate of air cooling or higher.
- a process of cooling to a temperature of In the composition range of the present invention if the cooling rate after hot working is equal to or higher than air cooling, the structure of the seamless steel pipe after cooling can be a structure having a martensite phase as a main phase, and the subsequent quenching treatment Can be omitted. In order to completely complete the martensitic transformation, it is necessary to cool the surface temperature to a temperature of 200 ° C. or lower at the above cooling rate. If the cooling stop temperature exceeds 200 ° C.
- the cooling after hot working is performed at a cooling rate equal to or higher than air cooling to a temperature at which the surface temperature becomes 200 ° C. or lower.
- the “cooling rate over air cooling” refers to 0.1 ° C./s or more. If it is less than 0.1 ° C./s, the metal structure after cooling becomes non-uniform, and the metal structure after the subsequent heat treatment becomes non-uniform.
- the above-described seamless steel pipe that has been cooled after hot working is then subjected to quenching and tempering.
- a structure having a martensite phase as a main phase may not be obtained, and in order to stabilize the material, quenching and tempering are performed.
- Reheating temperature for quenching Ac 3 transformation point to 1000 ° C
- the quenching process is a process of reheating to a temperature in the range of Ac 3 transformation point to 1000 ° C. and then rapidly cooling until the surface temperature becomes 200 ° C. or less.
- the reheating temperature for quenching is lower than the Ac 3 transformation temperature, the austenite single phase region is not heated, and therefore a structure mainly composed of martensite cannot be obtained after quenching.
- the reheating temperature is higher than 1000 ° C, the crystal grains become coarse and the toughness decreases, and the oxide scale layer on the surface becomes thick, causing them to peel and cause flaws on the surface of the steel pipe. There is.
- the reheating temperature for quenching is limited to a temperature in the range of Ac 3 transformation point to 1000 ° C.
- the cooling after reheating for quenching is rapid cooling, preferably the average temperature from 700 to 400 ° C at the calculated center temperature, with a cooling rate of 2 ° C / s or higher and a surface temperature of 200 ° C or lower, Preferably, the cooling is performed by water cooling until the temperature becomes 100 ° C. or lower.
- the quenching process may be performed twice.
- Ac 3 transformation point (° C) 937-476.5C + 56Si-19.7Mn-16.3Cu-4.9Cr-26.6Ni + 38.1Mo + 124.8V + 136.3Ti + 198Al + 3315B
- values calculated using C, Si, Mn, Cu, Cr, Ni, Mo, V, Ti, Al, and B are used.
- elements not included in the formula are calculated with the content of the element as “zero”.
- Tempering temperature 600-740 °C
- the tempering treatment is performed in order to reduce the dislocation density in the structure formed by the quenching treatment (including cooling after hot working) and to improve toughness and SSC resistance.
- the tempering treatment is performed by heating to a temperature (tempering temperature) in the range of 600 to 740 ° C. Moreover, it is preferable to perform the process of air-cooling after this heating.
- the tempering temperature is less than 600 ° C., the reduction of dislocation is insufficient, so that excellent SSC resistance cannot be ensured.
- the temperature exceeds 740 ° C., the tissue is remarkably softened and the desired high strength cannot be ensured.
- a correction process may be performed warm or cold as necessary to correct a defective shape of the steel pipe.
- Molten steel having the composition shown in Table 1 was melted in a converter and cast by a continuous casting method to form a slab, which was used as a steel pipe material.
- electromagnetic stirring was performed with a mold and a strand other than P steel.
- electromagnetic stirring was not performed between the mold and the strand.
- these steel pipe materials were charged into a heating furnace and heated to the heating temperatures shown in Table 2 and held (holding time: 2 hours).
- the heated steel pipe material was piped using the Mannesmann-plug mill method to obtain seamless steel pipes having the dimensions shown in Table 2 (outer diameter 178.0 to 244.5 mm ⁇ ⁇ thickness 15 to 30 mm).
- After hot working cooling was performed by air cooling to a temperature of 200 ° C. or less at the surface temperature shown in Table 2.
- the air-cooled seamless steel pipe was further tempered or re-heated and quenched and tempered under the conditions shown in Table 2. In addition, it air-cooled after the tempering process.
- Specimens were collected from the obtained seamless steel pipe and subjected to structure observation, tensile test and sulfide stress corrosion cracking test.
- the test method was as follows. (1) Microstructure observation From the obtained seamless steel pipe, the cross section (C cross section) orthogonal to the pipe axis direction, and the thickness 1 / 4t position (t: pipe thickness) from the pipe inner surface is the observation position. Observation specimens were collected. The specimen for tissue observation is polished, corroded with nital solution (nital (nitric acid-ethanol mixed solution)), and the tissue is examined using an optical microscope (magnification: 1000 times) and a scanning electron microscope (magnification: 2000 to 3000 times). Observed and imaged. Using the obtained tissue photograph, the tissue identification and the tissue fraction (volume%) were measured by image analysis.
- the collected specimens for tissue observation were polished and corroded with a picral solution (picral (picric acid-ethanol mixed solution)) to reveal the prior austenite grain boundaries, and using an optical microscope (magnification: 1000 times), 3
- the field of view was observed and imaged, and the particle size number was determined using a cutting method according to JIS G0551.
- an electron microanalyzer (beam diameter: 20 ⁇ m) in a 5 mm x 5 mm area centered on the 1/4 t thickness (t: tube thickness) from the inner surface of the tube.
- EPMA electron microanalyzer
- the surface analysis of each element of Si, Mn, Mo, and P was performed in at least three fields under the condition of 0.1 second per point of 20 ⁇ m step. From the obtained results, the cumulative frequency distribution of the content of each element in the measured region was determined for each element.
- the content at which the cumulative frequency becomes 0.0001 is determined for each element, and this is the segregated portion content (hereinafter, also referred to as (segregated portion content) M ). It was.
- the average content of each element in each seamless steel pipe (hereinafter, also referred to as (average content) M ) is obtained by referring to the composition analysis result (representative value) of each seamless steel pipe. .
- Tensile test pieces (bar-shaped test piece: parallel part diameter 12.5mm ⁇ , parallel part length: 60mm, GL: 50mm) are collected and subjected to tensile test, tensile properties (yield strength YS (0.5% yield strength)), tensile strength TS).
- Yield strength YS (0.5% yield strength
- tensile strength TS tensile strength TS.
- a piece (parallel part diameter 6.35 mm ⁇ ⁇ parallel part length 25.4 mm) was collected and subjected to a sulfide stress corrosion cracking test in accordance with NACE TM0177 Method A.
- test solution 0.5% by mass acetic acid + 5.0% by mass saline solution (liquid temperature: 24 ° C.) saturated with H 2 S was used.
- the test was a constant load test conducted up to 720 h in a state where a rod-shaped test piece was immersed in a test solution and a constant load (stress of 85% of yield strength) was applied.
- rupture by 720h was set as "(circle)" (pass), and the case where it fractured
- the sulfide stress corrosion cracking test was not performed for steel pipes that did not achieve the target yield strength (758 MPa).
- the yield strength YS retained at a high strength of 758 MPa or more, and yielded in a 0.5 mass% acetic acid + 5.0 mass% saline solution (liquid temperature: 24 ° C.) saturated with H 2 S. It is a high-strength seamless steel pipe with excellent sulfide stress corrosion cracking resistance that does not crack even if it exceeds 720h under a stress of 85% of its strength.
- the desired high strength cannot be ensured or the SSC resistance is lowered.
- Steel pipe No. 7 had a quenching temperature of over 1000 ° C., so the prior austenite grains were coarsened and the SSC resistance was reduced.
- Steel pipe No. 10 has a tempering temperature exceeding the upper limit of the range of the present invention, and a desired high strength cannot be ensured. Further, in Steel Pipe No. 11, the quenching cooling stop temperature exceeds the upper limit of the range of the present invention, a structure having a desired martensite phase as a main phase cannot be obtained, and a desired high strength cannot be ensured.
- Steel pipe No. 14 has a C content lower than the lower limit of the range of the present invention, and a desired high strength cannot be ensured.
- Steel pipe No. 15 has a C content exceeding the upper limit of the range of the present invention, and a Ps value of 65 or more, resulting in a decrease in SSC resistance.
- Steel pipe No. 16 has a Mo content lower than the lower limit of the range of the present invention, a Ps value of 65 or more, and the SSC resistance is reduced.
- Steel pipe No. 17 has a Cr content lower than the lower limit of the range of the present invention, and a Ps value of 65 or more, resulting in a decrease in SSC resistance.
- Steel pipe No. 18 has Ti / N exceeding the upper limit of the range of the present invention, and the Ps value is 65 or more, and the SSC resistance is lowered.
Abstract
Description
Ps=8.1(XSi+XMn+XMo)+1.2XP・・・(1)
(ここで、XM:元素Mの、(偏析部含有量(質量%))/(平均含有量(質量%))で定義される偏析指数Ps値を考案した。このPs値が大きくなるに伴い、局部的に硬さが高くなる局部的硬化領域が増加する。これら局部的硬化領域は、き裂の伝播を促進させ、耐SSC特性を低下させる。そこで、耐SSC性の向上には、このような局部的硬化領域の発生を抑制することが重要となる。そして、Ps値を65未満とすることにより、局部的硬化領域の発生が抑制されて耐SSC性が顕著に向上することを見出した。
(1)質量%で、C:0.20~0.50%、Si:0.05~0.40%、Mn:0.3~0.9%、P:0.015%以下、S:0.005%以下、Al:0.005~0.1%、N:0.008%以下、Cr:0.6~1.7%、Mo:0.4~1.0%、V:0.01~0.30%、Nb:0.01~0.06%、B:0.0003~0.0030%、O(酸素):0.0030%以下を含有し、残部Feおよび不可避的不純物からなる組成と、焼戻マルテンサイト相を体積率で95%以上とし、旧オーステナイト粒が粒度番号で8.5以上である組織と、を有し、鋼管の内面から1/4t位置(t:管厚)を中心に、電子線マイクロアナライザー(EPMA)による各元素の面分析を行って得られた偏析部含有量と平均含有量との比であるXMを用いて次(1)式
Ps=8.1(XSi+XMn+XMo)+1.2XP・・・(1)
(ここで、XM:(元素Mの偏析部含有量(質量%))/(元素Mの平均含有量(質量%))で定義される偏析度指数Psが65未満である降伏強さYS:758MPa以上である油井用高強度継目無鋼管。
(2)(1)において、前記組成に加えてさらに、質量%で、Ti:0.005~0.030%を、Ti含有量とN含有量との比であるTi/Nが2.0~5.0の範囲を満足するように、含む油井用高強度継目無鋼管。
(3)(1)または(2)において、前記組成に加えてさらに、質量%で、Cu:1.0%以下、Ni:1.0%以下、W:2.0%以下のうちから選ばれた1種または2種以上を含有する油井用高強度継目無鋼管。
(4)(1)ないし(3)のいずれかにおいて、前記組成に加えてさらに、質量%で、Ca:0.0005~0.005%を含有する油井用高強度継目無鋼管。
(5)鋼管素材を加熱し、熱間加工を施して所定形状の継目無鋼管とする油井用継目無鋼管の製造方法であって、(1)ないし(4)のいずれかに記載の油井用高強度継目無鋼管の製造方法であり、
前記加熱の加熱温度を、1050~1350℃の範囲の温度とし、前記熱間加工後の冷却を、空冷以上の冷却速度で表面温度が200℃以下となる温度まで行う冷却とし、該冷却後、Ac3変態点以上1000℃以下の範囲の温度に再加熱し、表面温度で200℃以下となる温度まで急冷する焼入れ処理を1回以上施し、前記焼入れ処理後600~740℃の範囲の温度に加熱する焼戻処理を施す油井用高強度継目無鋼管の製造方法。
Cは、固溶して鋼の強度増加に寄与するとともに、鋼の焼入性を向上させ、焼入れ時にマルテンサイト相を主相とする組織の形成に寄与する。このような効果を得るためには、Cは0.20%以上の含有を必要とする。一方、Cの0.50%を超える含有は、焼入れ時に割れを発生させ、製造性を著しく低下させる。このため、Cは0.20~0.50%の範囲に限定した。なお、好ましくは、Cは0.20~0.35%である。さらに好ましくは、Cは0.22~0.32%である。
Siは、脱酸剤として作用するとともに、鋼中に固溶して鋼の強度を増加させ、さらに焼戻時の軟化を抑制する作用を有する元素である。このような効果を得るためには、Siは0.05%以上含有する必要がある。一方、Siの0.40%を超える多量の含有は、軟化相であるフェライト相の生成を促進し、所望の高強度化を阻害したり、さらに粗大な酸化物系介在物の形成を促進して、耐SSC性や靭性を低下させる。また、Siは偏析して局部的に鋼を硬化させる元素であり、多量の含有は、局部的硬化領域を形成し、耐SSC性を低下させるという悪影響をおよぼす。このようなことから、本発明では、Siは0.05~0.40%の範囲に限定した。なお、好ましくは、Siは0.05~0.30%である。さらに好ましくは、Siは0.20~0.30%である。
Mnは、Cと同様に、鋼の焼入性を向上させ、鋼の強度増加に寄与する元素である。このような効果を得るためには、Mnは0.3%以上の含有を必要とする。一方、Mnは、偏析して局部的に鋼を硬化させる元素であり、多量のMnの含有は、局部的硬化領域を形成し、耐SSC性を低下させるという悪影響をおよぼす。このため、本発明では、Mnは0.3~0.9%の範囲に限定した。なお、好ましくは、Mnは0.4~0.8%である。さらに好ましくは、Mnは0.5~0.8%である。
Pは、粒界に偏析して粒界脆化を引き起こすだけでなく、偏析して局部的に鋼を硬化させる元素であり、本発明では、Pは不可避的不純物として、できるだけ低減することが好ましいが、0.015%までは許容できる。このため、Pは0.015%以下に限定した。なお、好ましくは、Pは0.012%以下である。
Sは、不可避的不純物として、鋼中ではそのほとんどが硫化物系介在物として存在し、延性、靭性、さらには耐SSC性を低下させるため、できるだけ低減することが好ましいが、0.005%までは許容できる。このため、Sは0.005%以下に限定した。なお、好ましくは、Sは0.003%以下である。
Alは、脱酸剤として作用し、溶鋼を脱酸するために添加される。また、Nと結合してAlNを形成して、加熱時のオーステナイト粒の微細化に寄与するととともに、固溶BがNと結合するのを防止して、Bの焼入性向上効果の低減を抑制する。このような効果を得るためには、Alは0.005%以上の含有を必要とする。一方、0.1%を超えるAlの含有は、酸化物系介在物の増加をもたらし、鋼の清浄度を低下させて、延性、靭性、さらには耐SSC性の低下を招く。このため、Alは0.005~0.1%の範囲に限定した。なお、好ましくは、Alは0.01~0.08%である。さらに好ましくは、Alは0.02~0.05%である。
Nは、不可避的不純物として鋼中に存在するが、Alと結合してAlNを形成し、また、Tiを含有する場合はTiNを形成して、結晶粒を微細化し、靭性を向上させる作用を有する。しかし、0.008%を超えるNの含有は、形成される窒化物が粗大化し、耐SSC性や靭性を著しく低下させる。このため、Nは0.008%以下に限定した。
Crは、焼入性の向上を介して鋼の強度を増加させるとともに、耐食性を向上させる元素である。また、Crは、焼戻処理時にCと結合し、M3C、M7C3、M23C6(Mは金属元素)などの炭化物を形成し、焼戻軟化抵抗を向上させる元素であり、とくに鋼管の高強度化に際しては必要な元素である。特にM3C型炭化物は、焼戻軟化抵抗を向上させる作用が強い。このような効果を得るためには、Crは0.6%以上の含有を必要とする。一方、1.7%を超えてCrを含有すると、多量のM7C3、M23C6を形成し、水素のトラップサイトとして作用して耐SSC性を低下させる。このようなことから、Crは、0.6~1.7%の範囲に限定した。なお、好ましくは、Crは0.8~1.5%である。さらに好ましくは、Crは0.8~1.3%である。
Moは、炭化物を形成し、析出強化により鋼の強化に寄与する。また、鋼中に固溶して、旧オーステナイト粒界に偏析して耐SSC性の向上に寄与する。さらに、Moは、腐食生成物を緻密化し、さらに割れの起点となるピットの生成および成長を抑制する作用を有する。このような効果を得るためには、Moは0.4%以上の含有を必要とする。一方、1.0%を超えるMoの含有は、針状のM2C析出物や、場合によってはLaves相(Fe2Mo)を形成し、耐SSC性を低下させる。このため、Moは0.4~1.0%の範囲に限定した。なお、好ましくは、Moは0.6~1.0%である。さらに好ましくは、Moは0.8~1.0%である。
Vは、炭化物や炭窒化物を形成し、鋼の強化に寄与する元素である。このような効果を得るためには、Vは0.01%以上の含有を必要とする。一方、0.30%を超えてVを含有しても、効果が飽和し、含有量に見合う効果を期待できなくなり、経済的に不利となる。このため、Vは0.01~0.30%の範囲に限定した。なお、好ましくは、Vは0.03~0.25%である。
Nbは、炭化物やあるいはさらに炭窒化物を形成し、鋼の強化に寄与する。また、これらはオーステナイト粒の微細化にも寄与する。このような効果を得るためには、Nbは0.01%以上の含有を必要とする。一方、Nbを0.06%を超えて多量に含有すると、粗大な析出物を形成し、高強度化への寄与が少なく、また、耐SSC性を低下させる。そのため、Nbは0.01~0.06%の範囲に限定した。さらに好ましくは、Nbは0.02~0.05%である。
Bは、オーステナイト粒界に偏析し、粒界からのフェライト変態を抑制することにより、微量の含有でも、鋼の焼入性を高める作用を有する。このような効果を得るためには、Bは0.0003%以上の含有を必要とする。一方、0.0030%超えてBを含有すると、炭窒化物等として析出し、焼入性が低下し、したがって靭性が低下する。このため、Bは0.0003~0.0030%の範囲に限定した。なお、好ましくは、Bは0.0005~0.0024%である。
O(酸素)は、不可避的不純物として、鋼中では酸化物系介在物として存在している。これら介在物は、SSCの発生起点となり、耐SSC性を低下させるため、本発明ではO(酸素)は、できるだけ低減することが好ましい。しかし、過剰な低減は精錬コストの高騰を招くため、0.0030%までは許容できる。このため、O(酸素)は0.0030%以下に限定した。なお、好ましくは、Oは0.0020%である。
Tiは、溶綱の凝固時にNと結合し微細なTiNとして析出し、そのピンニング効果により、オーステナイト粒の微細化に寄与する。このような効果を得るためには、Tiは0.005%以上の含有を必要とする。Tiは、0.005%未満の含有ではその効果が小さい。一方、Tiを0.030%を超えて含有すると、TiNが粗大化し、上記したピンニング効果が発揮できず、かえって靭性が低下する。また、さらに粗大なTiNが起因となり、耐SSC性が低下する。このようなことから、Tiを含有する場合には、Tiは0.005~0.030%の範囲に限定することが好ましい。
Tiを含有する場合には、Ti含有量とN含有量との比であるTi/Nが2.0~5.0の範囲を満足するように調整する。Ti/Nが2.0未満では、Nの固定が不十分となりBによる焼入性向上効果が低下する。一方、Ti/Nが5.0を超えて大きい場合には、TiNが粗大化する傾向が顕著になり、靭性や耐SSC性が低下する。このようなことから、Ti/Nは2.0~5.0の範囲に限定することが好ましい。なお、より好ましくは、Ti/Nは2.5~4.5である。
Cu、Ni、Wはいずれも、鋼の強度増加に寄与する元素であり、必要に応じて1種または2種以上を選択して含有できる。
Caは、Sと結合しCaSを形成して、硫化物系介在物の形態制御に有効に作用する元素であり、硫化物系介在物の形態制御を介して、靭性、耐SSC性の向上に寄与する。このような効果を得るためには、Caは少なくとも0.0005%の含有を必要とする。一方、Caを0.005%を超えて含有しても、その効果が飽和し、含有量に見合う効果が期待できなくなり、経済性に不利となる。このため、Caを含有する場合には、Caは0.0005~0.005%の範囲に限定することが好ましい。
本発明の高強度継目無鋼管では、YS:110ksi級以上の高強度を確保するためと構造物として必要な延性や靭性を保持するために、マルテンサイト相を焼戻した焼戻マルテンサイト相を主相とする。ここでいう「主相」とは、当該相が体積率で100%である単相、あるいは特性に影響しない程度の範囲である体積率で5%以下の第二相を含む、当該相が95%以上である場合をいう。なお、本発明では、第二相は、ベイナイト相、残留オーステナイト相、パーライトあるいはそれらの混合相が例示できる。
旧オーステナイト粒の粒度番号が8.5未満では、生成するマルテンサイト相の下部組織が粗大化し、耐SSC性が低下する。このため、旧オーステナイト粒の粒度番号を8.5以上に限定した。なお、粒度番号は、JIS G 0551の規定に準拠して測定した値を用いるものとする。
Ps=8.1(XSi+XMn+XMo)+1.2XP・・・(1)
(ここで、XM:(元素Mの偏析部含有量(質量%))/(元素Mの平均含有量(質量%))で定義される偏析度指数Psが65未満を満足する、継目無鋼管である。
加熱温度が1050℃未満では、鋼管素材中の炭化物の溶解が不十分となる。一方、1350℃を超えて加熱されると、結晶粒が粗大化するとともに、凝固時に析出したTiNなどの析出物が粗大化し、また、セメンタイトが粗大化するため、鋼管靭性が低下する。さらに、1350℃を超える高温に加熱すると、鋼管素材表面にスケール層が厚く生成し、圧延時に表面疵の発生原因になる。このようなことや、省エネルギーの観点から、加熱温度は1050~1350℃の範囲の温度に限定する。
本発明では、上記した熱間加工後、得られた継目無鋼管に、空冷以上の冷却速度で表面温度が200℃以下となる温度まで冷却する処理を施す。本発明の組成範囲では、熱間加工後の冷却速度が空冷以上であれば、冷却後の継目無鋼管の組織を、マルテンサイト相を主相とする組織とすることができ、その後の焼入れ処理を省略することも可能となる。なお、マルテンサイト変態を完全に完了させるために、表面温度で200℃以下の温度まで上記した冷却速度で冷却する必要がある。冷却の停止温度が表面温度で200℃超えでは、マルテンサイト変態が完全に完了していない場合がある。このため、熱間加工後の冷却は、空冷以上の冷却速度で表面温度が200℃以下となる温度まで冷却する。また、本発明において、「空冷以上の冷却速度」とは、0.1℃/s以上のことを指す。0.1℃/s未満であると、冷却後の金属組織が不均一になり、その後の熱処理後の金属組織が不均一となる。
焼入れ処理は、Ac3変態点以上1000℃以下の範囲の温度に再加熱したのち、表面温度が200℃以下となるまで急冷する処理とする。焼入れのための再加熱温度が、Ac3変態温度未満では、オーステナイト単相域に加熱されないため、焼入れ後に、マルテンサイトを主相とする組織が得られない。一方、この再加熱温度が1000℃を超える高温では、結晶粒が粗大化し靭性が低下するうえ、表面の酸化スケール層が厚くなり、それらが剥がれて、鋼管表面の疵の発生の原因となる場合がある。また、再加熱温度が1000℃を超えると、熱処理炉の負荷が増大するなどの悪影響があるうえ、再加熱のためのエネルギーが過大となり、省エネルギーの観点からも問題となる。そこで、本発明では、焼入れのための再加熱温度はAc3変態点~1000℃の範囲の温度に限定する。
(ここで、C、Si、Mn、Cu、Cr、Ni、Mo、V、Ti、Al、B:各元素の含有量(質量%))を用いて算出された値を用いるものとする。なお、上記した式を用いて、Ac3変態点を計算するに際し、式中に記載された元素のうち、含有しないものは、当該元素の含有量を「零」として計算するものとする。
焼戻処理は、焼入れ処理(熱間加工後の冷却を含む)で形成された組織における転位密度を減少させ、靭性および耐SSC性を向上させるために行う。本発明では焼戻処理は、600~740℃の範囲の温度(焼戻温度)に加熱する。また、この加熱ののち、空冷する処理を行うことが好ましい。
(1)組織観察
得られた継目無鋼管から、管軸方向に直交する断面(C断面)で、管内面から肉厚1/4t位置(t:管厚)が観察位置となるように、組織観察用試験片を採取した。組織観察用試験片を研磨、ナイタール液(nital(硝酸-エタノール混合液))腐食して、光学顕微鏡(倍率:1000倍)および走査型電子顕微鏡(倍率:2000~3000倍)を用いて組織を観察し、撮像した。得られた組織写真を用いて、画像解析により、組織の同定と、組織分率(体積%)を測定した。
Ps=8.1(XSi+XMn+XMo)+1.2XP・・・(1)
を用いて、各継目無鋼管のPs値を算出した。
(2)引張試験
得られた継目無鋼管の内面側1/4t位置(t:管厚)から、JIS Z 2241の規定に準拠して、引張方向が管軸方向となるように、JIS 10号引張試験片(棒状試験片:平行部径12.5mmφ、平行部長さ:60mm、GL:50mm)を採取し、引張試験を実施し、引張特性(降伏強さYS(0.5%耐力))、引張強さTS)を求めた。
(3)硫化物応力腐食割れ試験
得られた継目無鋼管から、管内面から肉厚1/4t位置(t:管厚)を中心として、管軸方向が試験片長手方向となるように棒状試験片(平行部径6.35mmφ×平行部長さ25.4mm)を採取し、NACE TM0177 Method Aに準拠して、硫化物応力腐食割れ試験を実施した。試験液は、H2Sが飽和した0.5質量%酢酸+5.0質量%食塩水溶液(液温:24℃)を用いた。試験は、棒状試験片を試験液に浸漬し、定荷重(降伏強さの85%の応力)を負荷した状態で720hまで行う定荷重試験とした。なお、720hまでに破断しなかった場合を「○」(合格)とし、720hまでに破断した場合を「×」(不合格)と評価した。なお、引張試験において、目標の降伏強さ(758MPa)が得られなかった鋼管については、硫化物応力腐食割れ試験を実施しなかった。
Claims (5)
- 質量%で、
C :0.20~0.50%、 Si:0.05~0.40%、
Mn:0.3~0.9%、 P :0.015%以下、
S :0.005%以下、 Al:0.005~0.1%、
N :0.008%以下、 Cr:0.6~1.7%、
Mo:0.4~1.0%、 V :0.01~0.30%、
Nb:0.01~0.06%、 B :0.0003~0.0030%、
O(酸素):0.0030%以下
を含有し、残部Feおよび不可避的不純物からなる組成を有し、焼戻マルテンサイト相を体積率で95%以上とし、旧オーステナイト粒が粒度番号で8.5以上である組織を有し、鋼管の内面から1/4t位置(t:管厚)を中心に、電子線マイクロアナライザー(EPMA)による各元素の面分析を行って得られた偏析部含有量と平均含有量との比であるXMを用いて下記(1)式で定義される偏析度指数Psが65未満であり、降伏強さYS:758MPa以上である油井用高強度継目無鋼管。
記
Ps=8.1(XSi+XMn+XMo)+1.2XP・・・(1)
ここで、XM:(元素Mの偏析部含有量(質量%))/(元素Mの平均含有量(質量%)) - 前記組成に加えてさらに、質量%で、Ti:0.005~0.030%を、Ti含有量とN含有量との比であるTi/Nが2.0~5.0の範囲を満足するように、含む請求項1に記載の油井用高強度継目無鋼管。
- 前記組成に加えてさらに、質量%で、Cu:1.0%以下、Ni:1.0%以下、W:2.0%以下のうちから選ばれた1種または2種以上を含有する請求項1または2に記載の油井用高強度継目無鋼管。
- 前記組成に加えてさらに、質量%で、Ca:0.0005~0.005%を含有する請求項1ないし3のいずれかに記載の油井用高強度継目無鋼管。
- 鋼管素材を加熱し、熱間加工を施して所定形状の継目無鋼管とする油井用継目無鋼管の製造方法であって、請求項1ないし4のいずれかに記載の油井用高強度継目無鋼管の製造方法であり、
前記加熱の加熱温度を、1050~1350℃の範囲の温度とし、前記熱間加工後の冷却を、空冷以上の冷却速度で表面温度が200℃以下となる温度まで行う冷却とし、該冷却後、Ac3変態点以上1000℃以下の範囲の温度に再加熱し、表面温度で200℃以下となる温度まで急冷する焼入れ処理を1回以上施し、前記焼入れ処理後600~740℃の範囲の温度に加熱する焼戻処理を施す油井用高強度継目無鋼管の製造方法。
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JPWO2016038809A1 (ja) | 2017-04-27 |
EP3192890B1 (en) | 2019-10-09 |
AR101760A1 (es) | 2017-01-11 |
BR112017004534B1 (pt) | 2021-05-04 |
MX2017002975A (es) | 2017-06-19 |
US20170275715A1 (en) | 2017-09-28 |
CN112877602A (zh) | 2021-06-01 |
CN106687613A (zh) | 2017-05-17 |
EP3192890A4 (en) | 2017-08-16 |
EP3192890A1 (en) | 2017-07-19 |
BR112017004534A2 (pt) | 2017-12-05 |
US10472690B2 (en) | 2019-11-12 |
JP5971435B1 (ja) | 2016-08-17 |
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