WO2022038956A1 - 継目無鋼管およびその製造方法 - Google Patents
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- WO2022038956A1 WO2022038956A1 PCT/JP2021/027349 JP2021027349W WO2022038956A1 WO 2022038956 A1 WO2022038956 A1 WO 2022038956A1 JP 2021027349 W JP2021027349 W JP 2021027349W WO 2022038956 A1 WO2022038956 A1 WO 2022038956A1
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- steel pipe
- seamless steel
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- outer diameter
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- 229910000831 Steel Inorganic materials 0.000 title claims abstract description 166
- 239000010959 steel Substances 0.000 title claims abstract description 166
- 238000000034 method Methods 0.000 title claims abstract description 37
- 238000004519 manufacturing process Methods 0.000 title claims abstract description 24
- 238000005096 rolling process Methods 0.000 claims description 139
- 239000013078 crystal Substances 0.000 claims description 33
- 229910001566 austenite Inorganic materials 0.000 claims description 31
- 238000010438 heat treatment Methods 0.000 claims description 22
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- 238000010622 cold drawing Methods 0.000 abstract description 12
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Images
Classifications
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- C—CHEMISTRY; METALLURGY
- C21—METALLURGY OF IRON
- C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
- 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
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- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F16—ENGINEERING ELEMENTS AND UNITS; GENERAL MEASURES FOR PRODUCING AND MAINTAINING EFFECTIVE FUNCTIONING OF MACHINES OR INSTALLATIONS; THERMAL INSULATION IN GENERAL
- F16L—PIPES; JOINTS OR FITTINGS FOR PIPES; SUPPORTS FOR PIPES, CABLES OR PROTECTIVE TUBING; MEANS FOR THERMAL INSULATION IN GENERAL
- F16L9/00—Rigid pipes
- F16L9/02—Rigid pipes of metal
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B21—MECHANICAL METAL-WORKING WITHOUT ESSENTIALLY REMOVING MATERIAL; PUNCHING METAL
- B21B—ROLLING OF METAL
- B21B19/00—Tube-rolling by rollers arranged outside the work and having their axes not perpendicular to the axis of the work
- B21B19/02—Tube-rolling by rollers arranged outside the work and having their axes not perpendicular to the axis of the work the axes of the rollers being arranged essentially diagonally to the axis of the work, e.g. "cross" tube-rolling ; Diescher mills, Stiefel disc piercers or Stiefel rotary piercers
- B21B19/04—Rolling basic material of solid, i.e. non-hollow, structure; Piercing, e.g. rotary piercing mills
-
- C—CHEMISTRY; METALLURGY
- C21—METALLURGY OF IRON
- C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
- C21D1/00—General methods or devices for heat treatment, e.g. annealing, hardening, quenching or tempering
- C21D1/26—Methods of annealing
-
- C—CHEMISTRY; METALLURGY
- C21—METALLURGY OF IRON
- C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
- C21D1/00—General methods or devices for heat treatment, e.g. annealing, hardening, quenching or tempering
- C21D1/26—Methods of annealing
- C21D1/28—Normalising
-
- C—CHEMISTRY; METALLURGY
- C21—METALLURGY OF IRON
- C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
- C21D6/00—Heat treatment of ferrous alloys
- C21D6/002—Heat treatment of ferrous alloys containing Cr
-
- C—CHEMISTRY; METALLURGY
- C21—METALLURGY OF IRON
- C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
- C21D9/00—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor
- C21D9/08—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor for tubular bodies or pipes
-
- 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
- C22C38/001—Ferrous alloys, e.g. steel alloys containing N
-
- 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
- C22C38/02—Ferrous alloys, e.g. steel alloys containing silicon
-
- 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
- C22C38/04—Ferrous alloys, e.g. steel alloys containing manganese
-
- 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
-
- 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
- C22C38/22—Ferrous alloys, e.g. steel alloys containing chromium with molybdenum or tungsten
-
- 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
- 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
- C22C38/54—Ferrous alloys, e.g. steel alloys containing chromium with nickel with boron
Definitions
- the present invention relates to a seamless steel pipe and a method for manufacturing the same.
- seamless steel pipes drilling rolling to make holes in solid materials, thinning / stretching rolling to make the wall thickness the product size, and finally standard rolling (outer diameter reduction rolling) to make the outer diameter the product size. It is manufactured by doing.
- Seamless steel pipes are more reliable than welded steel pipes, which are welded by bending a plate, because the material of the peripheral cross section can be made uniform. Further, since the seamless steel pipe can easily form a product shape having a thick wall thickness with respect to the outer diameter, a high geometrical moment of inertia can be obtained. Therefore, seamless steel pipes are often used for parts for automobiles and heat-resistant steel pipes for boilers in power plants.
- Patent Document 1 discloses a method for manufacturing a small-diameter seamless steel pipe having a small diameter and a thick wall, such as cold drawing a small-diameter seamless steel pipe such as various shafts of an automobile.
- Patent Document 2 discloses a small-diameter seamless steel pipe having excellent heat resistance by containing Cr up to 25.0%.
- the main purpose of drilling rolling and wall reduction / stretching rolling is to make holes in the material hot and reduce the wall thickness of the steel pipe, so there is no function to make the outer diameter thinner. Therefore, the seamless steel pipe obtains a predetermined dimension by standard rolling (outer diameter reduced diameter rolling) using a standard rolling mill. Since the inner diameter is smaller in the outer diameter reduced diameter rolling, a tool cannot be used on the inner surface, and the inner surface of the steel pipe is freely deformed. In such a case, the material on the inner surface of the steel pipe is not restrained or straightened, so that the wall thickness changes, or the uneven thickness generated by drilling rolling or thinning / stretching rolling remains in the product without being straightened. do.
- the seamless steel pipe after regular rolling becomes a product as it is or after further cold working (cold drawing) if necessary. If there is uneven thickness in the seamless steel pipe after regular rolling, various problems will occur. For example, the product strength characteristics are lowest in the portion where the wall thickness is uneven and the wall thickness is thin. Since the product characteristics are guaranteed at the portion with the lowest strength characteristics, the product strength characteristics deteriorate if there is a thin portion due to uneven thickness. Further, when the pipes are joined by welding at the end portion in the longitudinal direction, the wall thickness of the joined portion does not match, so that the joining becomes poor. Therefore, strict control standards are set for the external dimensions and uneven thickness of steel pipes. Since the uneven thickness of the seamless steel pipe remains even after the cold drawing process, it is necessary to obtain a steel pipe without the uneven thickness before the cold processing.
- the minute defects referred to here are defects that remain on the inner and outer surfaces of the steel pipe and are not detected as harmful by inspection, that is, a collection of fine defects such that the depth of the flaw is 10% or less with respect to the wall thickness. .. It has not been fully elucidated that seamless steel pipes, which have many such fine depth flaws or even fine flaws and are distributed in the circumferential direction of the inner surface of the steel pipe, cause various problems. rice field.
- the present invention has been made in view of the above circumstances, and the fatigue life is improved, and even when cold working (cold drawing) is performed, troubles during cold working are suppressed and the yield is improved. It is an object of the present invention to provide a seamless steel pipe that can be used and a method for manufacturing the same.
- the shape is designed so that the product life is satisfied based on the fatigue characteristics of the material and the cross-sectional shape including the uneven thickness of the steel pipe.
- the depth is equal to or greater than a certain depth of fine flaws, or if many fine flaws are distributed on the inner surface in the circumferential direction. It was found that the life was reduced when a longer fatigue life was required. In other words, if minute flaws can be suppressed, the wall thickness required for improving fatigue life can be reduced, and weight reduction and material cost can be reduced.
- a seamless steel pipe having a steel pipe outer diameter Dout (mm) and a wall thickness t (mm) of t / Dout 0.05 to 0.40.
- the maximum depth dmax (mm) of the flaw on the inner surface of the steel pipe having a cross section perpendicular to the pipe axis direction is dmax ⁇ 0.350.
- the average flaw depth dave (mm) of a flaw having a depth of 0.050 mm or more on the inner surface of the steel pipe is dave ⁇ 0.200.
- a seamless steel pipe having a depth of 0.050 mm or more on the inner surface of the steel pipe and having 30 or less per 1 mm inner peripheral length in the circumferential direction.
- the seamless steel pipe has a chemical composition of% by mass.
- the seamless steel pipe according to [1] which contains C: 0.05 to 0.45%, Si: 0.05 to 0.45%, and Mn: 0.05 to 1.2%.
- [7] The method for manufacturing a seamless steel pipe according to any one of [1] to [6].
- the fatigue life is improved, and even when cold working (cold drawing) is performed, troubles during cold working can be suppressed and the yield can be improved.
- FIG. 1 is a manufacturing process for manufacturing a seamless steel pipe.
- FIG. 2 shows the form of fine scratches generated on the inner surface of a seamless steel pipe.
- FIG. 3 is a test piece shape for investigating the relationship between the standard rolling conditions and the crystal grain size.
- FIG. 1 is a diagram showing a manufacturing process for manufacturing a seamless steel pipe.
- the drilling and rolling method used in the manufacturing process of the present invention can be either a hot extrusion method effective for hot forming of difficult-to-process materials such as high alloys or a Mannesmann method suitable for mass production. Thinning and stretching rolling can be performed by any of the elongator, plug mill, mandrel mill, and push bench method. Fixed-form rolling is targeted for outer-diameter reduced-diameter rolling using hole-shaped rolls typified by sizers and reducers. That is, in the standard rolling, the outer diameter of the raw pipe after rolling is smaller than the outer diameter of the raw pipe before rolling because the standard rolling is performed while reducing the outer diameter of the pipe by using the hole type roll.
- the present inventors have discovered that the compression strain in the circumferential direction of the pipe generated during this outer diameter reduction rolling and the thickening strain at that time are the causes of fine flaws. Furthermore, the present inventors have also found that, in addition to this strain form, the structure of the material undergoing outer diameter reduction rolling affects the generation of fine flaws.
- FIG. 2 shows the morphology of fine flaws generated on the inner surface of the seamless steel pipe.
- the present inventors have a maximum depth dmax (mm) of a flaw on the inner surface of a steel pipe having a cross section perpendicular to the pipe axis direction dmax ⁇ 0.350, and an average flaw of a flaw having a depth of 0.050 mm or more on the inner surface of the steel pipe. If the depth dave (mm) is dave ⁇ 0.200 and the number of flaws with a depth of 0.050 mm or more on the inner surface of the steel pipe per 1 mm of the inner peripheral length in the pipe circumferential direction is 30 or less, the fatigue life is improved. , It was found that even when performing secondary processing (cold drawing), troubles during secondary processing can be suppressed and yield can be improved.
- the maximum depth dmax (mm) of the flaw on the inner surface of the steel pipe having a cross section perpendicular to the pipe axis direction which is a fine flaw (hereinafter, may be simply referred to as a fine flaw)
- a fine flaw which is a fine flaw (hereinafter, may be simply referred to as a fine flaw).
- the mechanical properties and heat resistance of the product deteriorate.
- the average flaw depth dave (mm) of a flaw having a depth of 0.050 mm or more on the inner surface of the steel pipe exceeds 0.200 mm, the mechanical properties and heat resistance of the product are similarly deteriorated, and cold working is performed. This will damage the tool surface and shorten the tool life.
- the mechanical properties and heat resistance of the product are similarly deteriorated, and the coldness is also deteriorated. It damages the tool surface when machining and shortens the tool life.
- the depth of the flaw on the inner surface of the steel pipe means the flaw in the direction (depth direction) from the inner surface of the steel pipe to the outer surface.
- the depth and distribution of the flaws may be observed by cutting out a round section of the steel pipe.
- the portion to be sliced can be confirmed, for example, by cutting out a cross section of the sliced portion in the vicinity of the central portion in the longitudinal direction of the steel pipe, polishing the surface, and then observing with a microscope. If cutting the central part in the longitudinal direction of the steel pipe causes a problem in the product, the front and rear ends of the steel pipe may be similarly cut out and observed.
- the tension at the rear end of the rolling tip is different from that at the stationary portion, so that fine flaws are likely to occur excessively. Therefore, when investigating fine flaws using the front and rear ends, when the outer diameter of the steel pipe rolled by the standard rolling mill is Dout, secure a distance of 10 Dout or more from the front and rear ends and collect the round slice cross section. It is preferable to investigate. Further, the observation range of the round sliced cross section may be the entire inner surface of the steel pipe (range of 0 to 360 ° in the circumferential direction of the steel pipe cross section).
- the depth of the flaw refers to the flaw in the direction from the inner surface of the steel pipe to the outer surface (depth direction) as described above, but as shown in dmax in FIG. 2, the arc formed by the outer surface of the steel pipe A flaw in the normal direction (depth in the direction perpendicular to the outer surface of the steel pipe).
- the seamless steel pipe in the present invention preferably has a small outer diameter of 57.2 mm or less.
- the average crystal grain size of ferrite grains is preferably 15 ⁇ m or less.
- the reason is to improve mechanical properties such as strength and toughness.
- the lower limit of the particle size is not particularly limited, but if the particle size is too fine, the strength becomes too high due to the fine particle size effect, and the subsequent moldability deteriorates. Therefore, the lower limit of the particle size is preferably 0.5 ⁇ m.
- the average crystal grain size of the old austenite grains is preferably 15 ⁇ m or more.
- the heat resistance performance of the steel pipe is improved.
- the quenchability austenite does not become ferrite but becomes martensite by cooling from hot
- the structure differs depending on the amount of Cr.
- the amount of Cr is less than 4.5%, the ferrite grain size is measured in the case of ferrite grains, and when the amount of Cr is 4.5% or more, it is hot austenite.
- the old austenite particle size in martensite which is the particle size of the part, is measured.
- the old austenite particle size can be measured using an optical microscope after the old austenite particles are corroded. Alternatively, it can be determined by performing crystal orientation analysis.
- the upper limit of the average crystal grain size of the old austenite grains is not particularly limited, but if the grain size becomes too large, the mechanical properties deteriorate. Therefore, the upper limit is preferably 300 ⁇ m.
- the seamless steel pipe of the present invention preferably has the following composition. Further, the% indication of the component composition means mass% unless otherwise specified.
- C 0.05 to 0.45% C is an important element that affects the strength characteristics of steel pipe products. In order to obtain good strength characteristics, it is preferably contained in an amount of 0.05% or more, whereby high strength can be obtained. Increasing the content is preferable because the strength is improved. On the other hand, if the content is excessive, cold workability and weldability are impaired. Therefore, it is preferably 0.45% or less. In order to satisfy the strength, cold workability and weldability, 0.08 to 0.38% is a preferable range.
- Si 0.05-0.45% Si is effective in increasing the strength of steel.
- the content is preferably 0.05% or more.
- it is preferably 0.45% or less.
- the range of 0.10 to 0.30% is suitable for achieving both strength and workability.
- Mn 0.05-1.2% Mn is effective in increasing the strength. In order to obtain the effect, 0.05% or more is preferable. On the other hand, if it is contained in a large amount, the ferrite phase at room temperature becomes unstable, residual austenite remains, and the fatigue strength decreases. Therefore, it is preferably 1.2% or less. The range of 0.15 to 0.80% is suitable for achieving both strength and fatigue characteristics.
- Cr may be further contained.
- Cr 4.5-9.5%
- Cr is an element that improves the hardenability of steel and improves high-temperature strength and high-temperature oxidation resistance, and is useful for stably obtaining strength characteristics, high-temperature strength, and high-temperature oxidation resistance. Therefore, it is preferable to contain 4.5% or more of a material that requires mechanical properties, high temperature strength, and high temperature oxidation resistance. When the addition amount is reduced, the quenchability, high temperature strength and high temperature oxidation resistance are lowered, so that the addition amount can be appropriately adjusted according to the high temperature strength and high temperature oxidation resistance required for the application. Cr is more preferably contained in an amount of 5.0% or more in applications where heat resistance and fatigue life are required.
- the upper limit is not particularly limited, but if the content increases, it becomes difficult to miniaturize the crystal grain size during hot rolling, and fine flaws occur during standard rolling. It will be easier to do. Therefore, it is preferably 9.5% or less. Further, in order to achieve both fine scratches and characteristics, the ratio is more preferably 7.5 to 9.0%.
- any one or more of Ni, Mo, W, N, and B may be contained as a component other than the above. The reason for the limitation is described below.
- Ni is effective for toughness.
- toughness it is preferably added in the range of 0.5% or less. A more preferable range is 0.10 to 0.30%.
- Mo is effective for heat treatment characteristics and heat resistance, and is preferably added in the range of 1.5% or less. More preferably, it is in the range of 0.3 to 1.3%.
- W is effective for heat resistance and is preferably added in an amount of 2.5% or less. More preferably, it is in the range of 1.0 to 2.0%.
- N is effective in improving the strength, and it is preferable that N is added in an amount of 0.10% or less. More preferably, it is in the range of 0.01 to 0.08%.
- B is effective in improving heat resistance and hot workability, and is preferably added at 0.010% or less. More preferably, it is in the range of 0.0005 to 0.005%.
- the rest is Fe and unavoidable impurities.
- the unavoidable impurities for example, P: 0.030% or less and S: 0.008% or less are acceptable.
- the steel pipe outer diameter Dout (mm) and the wall thickness t 0 (mm) before standard rolling are characterized by satisfying the following formula (1). (D ini- D out ) 2 x t 0 2 x GD 2 ⁇ 9980 (1)
- D ini- D out 2 x t 0 2 x GD 2 ⁇ 9980
- the inventors conducted various studies to clarify the mechanism of the occurrence of fine flaws.
- the inventors investigated in detail the form of strain on the inner surface of the steel pipe caused by standard rolling. As a result, in regular rolling, a large compressive strain is generated in the circumferential direction of the pipe and the outer diameter is reduced, but at the same time, a strain in the thickness direction is also generated on the inner surface that can be freely deformed, and the inner surface of the steel pipe is thickened. It was found that deformation occurred. The inventors considered that this special strain change caused fine scratches on the inner surface of the steel pipe.
- FIG. 3 shows the shape of a standard rolling simulated test piece for investigating the effects of the diameter reduction amount of a steel pipe and the crystal grain size on the generation of fine flaws in the present invention.
- a general-purpose uniaxial compression tester (Thermec Master or Gleeble tester) can be used.
- general-purpose test devices equipped with a resistance heating device using a direct current and an IH heating device using a coil are commercially available, and the temperature history generated by hot working can be easily simulated.
- the upper figure of FIG. 3 is a view of the test piece from the Lt direction (L: length of the test piece, t: wall thickness of the test piece), and the lower figure is a view from the Lw direction. There is (w: width of the test piece). Both ends of the test piece may have a round bar or plate shape that can be appropriately changed according to the connection with the compression device.
- an evaluation surface located in the axial half portion when a compression displacement is applied in the axial direction R1: R1 in FIG. 3 is an evaluation surface and simulates the inner surface of a steel pipe during standard rolling.
- a large compressive strain is generated in the part to be used.
- R1 forming the evaluation surface and R2 of the surface located on the opposite side of the evaluation surface are set to the radius of curvature of R1> the radius of curvature of R2, the compression displacement in the axial direction increases and the evaluation surface is bent. Bending on the inner surface occurs, which causes high thickening strain in the center of the evaluation surface.
- the balance and magnitude of the compressive strain and the thickening strain can be easily controlled by the compressive displacement amount and R1 / R2, and the outer diameter reduced diameter rolling by any standard rolling can be accurately simulated.
- w can be any length, but the longer w is, the more stable the stress state of the evaluation surface is, so it may be longer if there is no interference with the device.
- the lower limit of w is preferably the same as or longer than the compression stroke length of the test piece. Since the size of the test piece in FIG. 3 is not limited and can be manufactured even in a small size, for example, a steel ingot having a small product component is cast and the ingot is subjected to arbitrary hot rolling or heat treatment to change the structure morphology. Then, if a fixed-form rolling simulated test piece is cut out from the test piece and tested, evaluation can be easily performed. In addition, it is better to collect the material before standard rolling, cut it out from it, and test it. In this mock test, for example, the difference in crystal grain size, the influence of the rolled texture on the compression direction of the test piece, and the influence of temperature and strain can be evaluated.
- the inventors have simulated the circumferential compression strain generated on the inner surface of the steel pipe in the standard rolling, that is, the compression stroke amount in FIG. .
- the particle size before deformation is measured in advance by microscopic observation, the average particle size is obtained by the cutting method, the relationship between the size of the particle size before deformation and the fine flaws is investigated, and the processing conditions and structure given to the fine flaws ( We were able to obtain information on the effect of the average crystal grain size before deformation).
- the obtained tube end was subjected to intergranular corrosion of the former austenite at the center of the wall thickness and the inner surface surface layer, observed with an optical microscope, and the average particle size was measured by a cutting method.
- the problem due to fine flaws can be overcome by satisfying the equation (1). (D ini- D out ) 2 x t 0 2 x GD 2 ⁇ 9980 (1) If this formula is satisfied, fine scratches generated on the inner surface of the steel pipe can be suppressed, the fatigue life of the product can be improved, and a seamless steel pipe having excellent cold pullability can be provided.
- the steel pipe outer diameter Dout after regular rolling is the same as the steel pipe outer diameter Dout of the product.
- the austenite crystal grain size GD For the structure after thinning / stretching rolling and before standard rolling, the smaller the austenite crystal grain size GD is, the better.
- the chemical composition of the material such as the addition of a pinning element that suppresses grain growth during heating may be changed, but recrystallization or recrystallization may occur after thinning / stretching rolling and before standard rolling.
- a method using reverse transformation is good. Recrystallization can be carried out by increasing the reduction rate, and the crystal grain size is refined by recrystallization. Further, in order to suppress grain growth after recrystallization, it is preferable to increase the rolling reduction in the wall thinning / stretching step immediately before the standard rolling.
- the reverse transformation is a process in which the austenite phase is cooled to a ferrite transformation point or lower existing at 300 ° C. or lower after thinning / stretching rolling and before standard rolling, and then heated again to cause an austenite phase transformation.
- the standard rolling can be performed in a state where the austenite crystal grain size after reheating is refined.
- the cooling at this time is more effective when it is performed from the state of the austenite phase while it is hot, so a cooling start temperature of 650 ° C. or higher is preferable.
- the austenite crystal grain size becomes finer by increasing the average cooling rate before the reverse transformation and the average heating rate of the reverse transformation, it is preferable to set each to 1.0 ° C./s or more.
- the average cooling rate particularly affects the particle size, a larger effect can be obtained by preferably setting it at 5.0 ° C./or or higher.
- Both the average cooling rate and the average heating rate are preferably 20 ° C./s or less because cracks may occur due to thermal stress if they are too fast. If recrystallization and reverse transformation are performed together, the effect will be further enhanced. Therefore, if it is desired to suppress fine flaws, both should be performed.
- the reverse transformation there is no particular limitation on the reduction rate, but since the thickness is always reduced in the thinning step, the reduction is usually performed at 50% or less.
- the product after regular rolling may be heat-treated.
- the subsequent heat treatment does not affect the quality of the inner surface of the steel pipe.
- a good balance of strength and toughness can be obtained by heat treatment after regular rolling.
- the heating temperature of the product after regular rolling is 850 to 1150 ° C. and the soaking time is 10 minutes or more.
- Cr is contained in an amount of 4.5% or more, it is preferable to heat at 950 to 1150 ° C. for 15 minutes or more and slowly cool at 1 ° C./s or less because excellent heat resistance can be obtained.
- the present invention can be carried out as a method for manufacturing a seamless steel pipe. Specifically, after drilling rolling, thinning and stretching rolling, and before standard rolling, raw pipes (recrystallized and / or reverse transformation / recrystallization after recrystallization and before standard rolling). The tube end of the tube) is cut, the average crystal grain size GD (mm) of austenite is measured using the cooled sample, and it is inspected whether the following formula (1) is satisfied.
- the manufacturing conditions for drilling rolling and wall thinning / stretching rolling are not particularly limited, and as described above, the drilling rolling method is a hot extrusion effective for hot forming of difficult-to-process materials such as high alloys. Either the method or the Mannesmann method suitable for mass production is possible. Thinning and stretching rolling can be performed by any of the elongator, plug mill, mandrel mill, and push bench method.
- the method of changing the austenite crystal grain size was recrystallization, reverse transformation, or both.
- the reduction ratio was changed by thinning rolling performed in the range of 850 to 1150 ° C. before standard rolling, and the reduction was accumulated between 1.0 and 9.5 s.
- the cumulative reduction rate was the value shown in the table.
- reverse transformation after thinning and stretching and rolling, the mixture was cooled to 300 ° C. or lower to normal temperature at various average cooling rates shown in the table, and then reheated to 850 ° C. or higher.
- the reheating was atmospheric heating, and the average heating rate was 0.5 to 5.0 ° C / s depending on the wall thickness.
- the pipe end of the raw tube (the raw tube after recrystallization and / or recrystallization treatment and before standard rolling) is cut before standard rolling.
- the old austenite particle size GD was observed and measured using the sample after cooling.
- the value of the formula (1) was calculated from the old austenite particle size GD.
- the average value was calculated by observing three different fields of view of the same test piece with an optical microscope or a scanning electron microscope (SEM) at a magnification of 400 to 2000 times.
- the central part in the length direction of the steel pipe was sliced, and the cross section of the inner surface of the steel pipe was mirror-polished and then fine flaws were observed.
- the observation range was set to the range of 0 ° to 360 ° of the cross section of the inner surface of the steel pipe.
- fine flaws the maximum depth dmax of the flaw on the inner surface of the steel pipe, the average flaw depth dave of the flaw depth of 0.050 mm or more on the inner surface of the steel pipe, and the number of flaws of 0.050 mm or more on the inner surface of the steel pipe. I asked for each.
- Some seamless steel pipes with a Cr content of less than 4.5% were subjected to quenching (quenching temperature Q) and tempering (tempering temperature) T at the temperatures shown in Table 2 as heat treatment.
- some seamless steel pipes having a Cr content of 4.5% or more were annealed as a heat treatment by holding them at the annealing temperature N shown in Table 2 for 15 minutes and slowly cooling them at an average cooling rate of 1 ° C./s.
- ferrite average crystal grain size is used for materials with Cr less than 4.5%, and old austenite is used for Cr amount of 4.5% or more.
- the average crystal grain size was measured.
- the particle size was measured using a cutting method and used as the average crystal particle size.
- Fatigue life was evaluated using seamless steel pipes obtained after regular rolling or heat treatment.
- the method for evaluating fatigue life is to compress a seamless steel pipe sliced to 1/2 the outer diameter with a flat plate at the position facing the outer peripheral surface of the pipe, and generate the same stress as the yield strength of the steel pipe measured in advance according to JIS Z 2241. The number of stress loads until fatigue fracture was obtained when stress was repeatedly applied at 2 Hz.
- Fatigue life and tool life were calculated and evaluated as relative values when the comparative example of seamless steel pipes with the same composition, the same outer diameter, and the same wall thickness was set to 1.
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Abstract
Description
[1]鋼管外径Dout(mm)と肉厚t(mm)がt/Dout=0.05~0.40である継目無鋼管で、
管軸方向に垂直な断面の鋼管内表面における疵の最大深さdmax(mm)がdmax≦0.350で、
前記鋼管内表面における深さ0.050mm以上の疵の平均疵深さdave(mm)がdave≦0.200で、
前記鋼管内表面における深さ0.050mm以上の疵の管周方向内周長1mmあたりの個数が30個以下である継目無鋼管。
[2]前記継目無鋼管は、フェライト粒の平均結晶粒径が15μm以下、または、旧オーステナイト粒の平均結晶粒径が15μm以上である[1]に記載の継目無鋼管。
[3]前記継目無鋼管は、化学成分として、質量%で、
C:0.05~0.45%、Si:0.05~0.45%、Mn:0.05~1.2%を含有する[1]に記載の継目無鋼管。
[4]前記継目無鋼管は、化学成分として、さらに、質量%で、Cr:4.5%未満を含有し、フェライト粒の平均結晶粒径が15μm以下である[3]に記載の継目無鋼管。
[5]前記継目無鋼管は、化学成分として、さらに、質量%で、Cr:4.5~9.5%を含有し、旧オーステナイト粒の平均結晶粒径が15μm以上である[3]に記載の継目無鋼管。
[6]前記継目無鋼管は、化学成分として、さらに、質量%で、Ni:0.5%以下、Mo:1.5%以下、W:2.5%以下、N:0.10%以下、B:0.010%以下から選ばれる1種以上を含有する[3]~[5]のいずれかに記載の継目無鋼管。
[7][1]~[6]のいずれかに記載の継目無鋼管の製造方法であって、
穿孔圧延し、次いで減肉・延伸圧延した後、定形圧延するに際し、定形圧延前のオーステナイトの平均結晶粒径GD(mm)と定形圧延前の鋼管外径Dini(mm)と定形圧延後の鋼管外径Dout(mm)、定形圧延前の肉厚t0(mm)について、下記式(1)を満たす継目無鋼管の製造方法。
(Dini-Dout)2×t0 2×GD2≦9980 (1)
[8][7]に記載の継目無鋼管の製造方法であって、前記定形圧延後、加熱温度850~1150℃で均熱保持時間が10分以上の熱処理を行う継目無鋼管の製造方法。
Cは鋼管製品の強度特性に影響を与える重要な元素である。良好な強度特性を得るには0.05%以上含有することが好ましく、これにより高強度が得られる。含有量を増加させると強度が向上するため好ましい。一方で含有量が過大になると冷間加工性や溶接性を損なう。そのため、0.45%以下とすることが好ましい。強度と冷間加工性、溶接性を満足するためには、0.08~0.38%が好ましい範囲となる。
Siは鋼の強度を高めるのに有効である。その効果を得るには0.05%以上の含有が好ましい。一方で、多量に含有すると熱間加工中の脆化を招く。そのため、0.45%以下とすることが好ましい。強度と加工性を両立するには0.10~0.30%の範囲が好適である。
Mnは強度を高めるのに有効である。その効果を得るには0.05%以上が好ましい。一方で、多量に含有すると常温でのフェライト相を不安定にし、残留オーステナイトが残存して疲労強度が低下する。そのため1.2%以下とすることが好ましい。強度と疲労特性を両立するには0.15~0.80%の範囲が好適である。
Crは鋼の焼き入れ性の改善や高温強度、耐高温酸化特性を向上する元素であり、強度特性や高温強度、耐高温酸化特性を安定的に得るのに役立つ。そのため、機械的特性や高温強度、耐高温酸化特性が必要な材料については4.5%以上含有することが好ましい。添加量が低減すると焼き入れ性や高温強度や耐高温酸化性能が低下するため、用途に必要な高温強度や耐高温酸化性能に応じて添加量を適宜調整できる。Crは耐熱性能と疲労寿命が求められる用途では5.0%以上の含有がより好ましい。また、より高温度域で使用するためには7.5%以上がさらに好ましい。耐高温酸化性能は含有量の増加に伴い向上するので上限は特に限定がないが、含有量が増えると、熱間圧延中の結晶粒径の微細化が難しくなり、定形圧延時に微細疵が発生しやすくなる。そのため、9.5%以下とすることが好ましい。また、微細疵と特性を良好に両立させるには7.5~9.0%とすることがより好ましい。
(Dini-Dout)2×t0 2×GD2≦9980 (1)
以下、式(1)に到った経緯について説明する。
(Dini-Dout)2×t0 2×GD2≦9980 (1)
この式を満たせば鋼管内表面に発生する微細疵を抑制し、製品の疲労寿命を向上させることができ、冷間引き抜き性に優れた継目無鋼管を提供することが可能となる。なお、定形圧延後の鋼管外径Doutは、製品の鋼管外径Doutと同じである。
(Dini-Dout)2×t0 2×GD2≦9980 (1)
定形圧延前の鋼管外径Dini(mm)、定形圧延後の鋼管外径Dout(mm)、定形圧延前の肉厚t0(mm)
上記検査工程は、製品となったときの継目無鋼管のサイズ、および強度グレードが同一の材料に対し、一回以上実施する。式(1)を満たした減肉および延伸圧延後の素管を合格とし、合格となった素管と同一サイズ、および強度グレードが同一の素管を、定形圧延して継目無鋼管を製造する。
なお、継目無鋼管の外径は24.5~57.2mmとして製造した。
R2 R1と対向する面
W 試験片の幅
Claims (8)
- 鋼管外径Dout(mm)と肉厚t(mm)がt/Dout=0.05~0.40である継目無鋼管で、
管軸方向に垂直な断面の鋼管内表面における疵の最大深さdmax(mm)がdmax≦0.350で、
前記鋼管内表面における深さ0.050mm以上の疵の平均疵深さdave(mm)がdave≦0.200で、
前記鋼管内表面における深さ0.050mm以上の疵の管周方向内周長1mmあたりの個数が30個以下である継目無鋼管。 - 前記継目無鋼管は、フェライト粒の平均結晶粒径が15μm以下、または、旧オーステナイト粒の平均結晶粒径が15μm以上である請求項1に記載の継目無鋼管。
- 前記継目無鋼管は、化学成分として、質量%で、
C:0.05~0.45%、Si:0.05~0.45%、Mn:0.05~1.2%を含有する請求項1に記載の継目無鋼管。 - 前記継目無鋼管は、化学成分として、さらに、質量%で、Cr:4.5%未満を含有し、フェライト粒の平均結晶粒径が15μm以下である請求項3に記載の継目無鋼管。
- 前記継目無鋼管は、化学成分として、さらに、質量%で、Cr:4.5~9.5%を含有し、旧オーステナイト粒の平均結晶粒径が15μm以上である請求項3に記載の継目無鋼管。
- 前記継目無鋼管は、化学成分として、さらに、質量%で、Ni:0.5%以下、Mo:1.5%以下、W:2.5%以下、N:0.10%以下、B:0.010%以下から選ばれる1種以上を含有する請求項3~5のいずれかに記載の継目無鋼管。
- 請求項1~6のいずれかに記載の継目無鋼管の製造方法であって、
穿孔圧延し、次いで減肉および延伸圧延した後、定形圧延するに際し、定形圧延前のオーステナイトの平均結晶粒径GD(mm)と定形圧延前の鋼管外径Dini(mm)と定形圧延後の鋼管外径Dout(mm)、定形圧延前の肉厚t0(mm)について、下記式(1)を満たす継目無鋼管の製造方法。
(Dini-Dout)2×t0 2×GD2≦9980 (1) - 請求項7に記載の継目無鋼管の製造方法であって、前記定形圧延後、加熱温度850~1150℃で均熱保持時間が10分以上の熱処理を行う継目無鋼管の製造方法。
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BR112023002327A BR112023002327A2 (pt) | 2020-08-19 | 2021-07-21 | Tubo de aço sem costuras e método para fabricação deste |
JP2021562012A JP7239019B2 (ja) | 2020-08-19 | 2021-07-21 | 継目無鋼管およびその製造方法 |
US18/020,458 US20230265947A1 (en) | 2020-08-19 | 2021-07-21 | Seamless steel pipe and method of manufacture thereof |
EP21858105.6A EP4169634A4 (en) | 2020-08-19 | 2021-07-21 | SEAMLESS STEEL PIPE AND METHOD FOR MANUFACTURING SAME |
MX2023001817A MX2023001817A (es) | 2020-08-19 | 2021-07-21 | Tubo de acero sin soldadura y metodo de fabricacion del mismo. |
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CN115156307A (zh) * | 2022-07-29 | 2022-10-11 | 无锡华贝钢管制造有限公司 | 适用于无缝钢管的数据处理方法及系统 |
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