JP6434729B2 - Ni-based alloy tube manufacturing method, Ni-based alloy high-frequency heated bending tube manufacturing method, Ni-based alloy welded tube manufacturing method, and boiler steam tube manufacturing method - Google Patents

Description

The present invention relates to a method of manufacturing a tube made of a Ni- based alloy, a method of manufacturing a high-frequency heated bending tube of a Ni-based alloy, a method of manufacturing a welded joint tube of a Ni-based alloy, and a method of manufacturing a steam tube for a boiler . In particular, a method of manufacturing a tube made of a Ni-based alloy that can be suitably used for a main pipe of a boiler of a power plant having a steam temperature of around 700 ° C., a method of manufacturing a high-frequency heated bending tube of a Ni-based alloy, Ni The present invention relates to a method for manufacturing a welded joint pipe of a base alloy and a method for manufacturing a steam pipe for a boiler.

Many large heat transfer tubes and pipes are used in large boilers for power plants. Among these, 2.25 to 11% Cr ferritic heat resistant steel is conventionally used for thick and large-diameter pipes such as a high temperature header having a steam temperature of 500 ° C. or higher, a main steam pipe and a reheat steam pipe. It has been used for many years. In recent years, against the backdrop of carbon dioxide emission suppression, particularly in a coal-fired thermal power plant, the steam temperature is being improved to improve the plant efficiency. Currently, a plant with a main steam temperature of 600 ° C. is also operating.
On the other hand, the development of power plants with a main steam temperature of 700 ° C has been promoted mainly in Europe with the aim of further improving plant efficiency. In such a high temperature range, there are problems with high temperature strength and corrosion resistance. Application of ferritic heat-resistant steel becomes impossible.
For this reason, it is necessary to adopt a high-strength Ni-based alloy material (including a solid solution strengthened / precipitation strengthened Ni-based alloy or Fe—Ni-based alloy) for the piping in the high temperature part.

JP-A-53-114722 JP 54-138814 A JP-A-55-58329 JP 2005-265449 A JP2013-44252A

  When these high-strength Ni-based alloy materials are subjected to hot working such as hot extrusion or hot bending in the manufacturing process of pipes, coarse precipitates are formed in the metal structure, resulting in a decrease in strength. In order to cause a decrease in corrosion resistance, it is necessary to decompose and dissolve this to form a uniform structure to obtain a stable structure, strength and corrosion resistance. Therefore, the solution treatment is performed every hot working, but the solution treatment temperature Is very high at around 1200 ° C.

  Thin thin tubes with a wall thickness of less than 20 mm and an outer diameter (diameter) of less than 100 mm used for heat transfer tubes have a relatively short retention time of about 10 minutes or less at around 1200 ° C., resulting in coarse crystal grains. However, in the case of thick large-diameter pipes with a wall thickness of 20 mm or more and an outer diameter of 100 mm or more, especially heat treatment time of around 1200 ° C. is 1 to several in order to ensure a soaking time. Since the time is longer, the crystal grains of the entire pipe material are coarser than the small diameter pipe (for example, average crystal grain size: 200 μm or more). Furthermore, as a finishing process of the tube material, after improving the diffusion of precipitates by solution heat treatment in the previous step, the inner surface of the tube and the outer surface of the tube ( In the following, work hardening occurs by machining near the inner and outer surfaces, the ductility near the inner and outer surfaces decreases, and high-frequency bending, which is the next stage of machining, and tensile stress (bending moment) near the inner and outer surfaces during welding. And the shrinkage stress at the time of welding solidification, etc.), there is a problem that the susceptibility to microcracking is higher than that of conventional materials.

  More specifically, these high-strength Ni-based alloys (for example, Alloy617 (52Ni-22Cr-13Co-9Mo-Ti-1Al), HR6W (45Ni-23Cr-7W-NbTi), Alloy263 (50Ni-20Cr-20Co-) In 6Mo-2Ti-Al)), as described above, the structure near the inner and outer surfaces of the material for the header and the thick-walled large-diameter tube is coarsened, and work hardening occurs due to machining, resulting in reduced ductility near the surface. However, there is a problem in that the potential for microcracking in the vicinity of the surface during high-frequency bending or welding, which is the next stage of processing, is high.

FIG. 4 is an explanatory diagram of a thick-walled large-diameter pipe during machining in the prior art, FIG. 4A is an observation diagram of the microstructure of the material surface, and FIG. 4B is a hardness distribution in the thickness direction of the thick-walled large-diameter pipe. It is a graph.
FIG. 4 shows a representative example of the microstructure of the surface of a high-strength Ni-based header or thick-walled large-diameter pipe material whose surface is finished by machining according to the prior art and the hardness distribution in the thickness direction.
4A is a large-diameter tube having a diameter of 350 mm and a thickness of 40 mm made of HR6W as a high-strength Ni-based alloy. FIG. 4A is a photograph taken at 100 × with an optical microscope. The Vickers hardness from the outer surface to the inner surface of the cross section was measured by cutting the ring in the circumferential direction of the large diameter pipe.
As shown in FIG. 4A, in the conventional machining method, the microstructure is a coarse-grained structure, and as shown in FIG. 4B, the hardness protrudes and becomes high on the inner and outer surfaces.

5 is an explanatory view when the large-diameter pipe shown in FIG. 4 is machined. FIG. 5A is a side view of a machined portion during high-frequency bending, FIG. 5B is a cross-sectional view taken along the line VB-VB in FIG. 5A, and FIG. FIG. 5D is an enlarged view of a VC portion in FIG. 5B, FIG. 5D is an explanatory view at the time of welding, and FIG. 5E is a cross-sectional view taken along the line VE-VE in FIG.
FIG. 5 is an explanatory view of fine cracks in the vicinity of the surface generated in the processed part and the welded part when the high-strength Ni-based alloy large-diameter pipe is subjected to high-frequency induction heating bending and welding.
In FIG. 5, conventionally, in a high-strength Ni-based alloy material (for example, Alloy 617) finished to a final dimension by machining (cutting) after a solution treatment at a high temperature in the previous step, as shown in FIG. Since the inner and outer surfaces have a coarse-grained structure, when this is directly subjected to high-frequency induction heating bending (see FIGS. 5A to 5C) or welded (see FIGS. 5D and 5E), work hardening by machining is performed near the inner and outer surfaces. As a result, the ductility in the vicinity of the inner and outer surfaces is further lowered, so that the susceptibility to the occurrence of fine cracks in the vicinity of the inner and outer surfaces is relatively higher than that of the conventional material. In particular, as shown in FIGS. 5A to 5C, since tensile stress acts on the outside of the bend, generation and progress of fine cracks are likely to occur.

  In order to avoid such fine cracks in the vicinity of the surface, it is desirable to improve by reducing the crystal grain size of the entire header or thick-walled large-diameter pipe. Since the product size of the diameter pipe is long and thick, the structure is coarsened by solution heat treatment.

  As a conventional method, after solidifying austenitic stainless steel, cold processing such as shot peening, grinder processing and polishing is applied to the tube surface, and then again a solution treatment is performed. Have been proposed (for example, Patent Document 1 (Japanese Patent Laid-Open No. 53-114722), Patent Document 2 (Japanese Patent Laid-Open No. 54-138814), and Patent Document 3 (Japanese Patent Laid-Open No. 55-58329). ), Patent Document 4 (Japanese Patent Laid-Open No. 2005-265449). These methods all relate to austenitic stainless steel small-diameter pipes, and are subjected to a solution treatment at a high temperature in order to improve surface steam oxidation resistance.

  In the case of such a high temperature solution heat treatment, in the case of a Ni-based alloy, crystal grains are likely to grow more than conventional austenitic steel, so that the crystal grains are coarsened by the solution treatment, and the ductility near the surface is often not improved. . Further, the conventional invention is intended to suppress delamination of the scale, and is formed in a relatively shallow processed layer (up to several tens of μm) so that the crystal grain boundary and the crystal grain can be distinguished. Therefore, even if a fine-grained layer is formed, a sufficient thickness cannot be obtained, and in the case of thick and large-diameter pipes made of Ni-based alloys, fine cracks near the surface during pipe welding and bending It is difficult to prevent the occurrence.

    A technique is also known in which a solution treatment is performed after a friction stir processing method (FSP method) is performed on a welded surface after welding in a Ni-based alloy pipe or the like (for example, Patent Document 5). (JP 2013-44252 A). However, the application target of the technique described in Patent Document 5 is FSP rotation processing on the weld end face (plane) of the pipe, and cannot be applied to the pipe inner / outer face (curved surface) of the present invention. Further, since it takes a lot of processing time to perform the FSP processing, it is not suitable for processing from the surface to the deep, and is difficult to apply to a thick member.

  The present invention is a technology for suppressing the occurrence of surface cracks when welding or bending of a pipe material made of a high-strength Ni-based alloy that can be used in a facility having a main steam temperature of 700 ° C. As an objective.

In order to solve the technical problem, a manufacturing method of a Ni-based alloy pipe according to claim 1 includes a pipe-making process for manufacturing a pipe made of a Ni-based alloy, and a pipe-making process. A work hardening step in which work hardening by shot peening is performed on the surface of the pipe that has been subjected to shot particle irradiation at a pressure of 0.4 MPa for 1 minute, and the work hardened tube is made to have a 1/2 melting point of the material. And a recrystallization heat treatment step of heating in a recrystallization temperature region in which a thick internal crystal grain does not grow and is higher than the temperature and lower than the solution treatment temperature.

In order to solve the technical problem, a method for producing a high-frequency heated bending pipe of a Ni-based alloy according to claim 2 includes a pipe- making process for producing a pipe made of a Ni-based alloy, and the pipe-making process. The surface of the tube produced in the process is subjected to work hardening by shot peening for at least 1 minute at a shot particle irradiation pressure of 0.4 MPa, and the work hardened tube is made of 1 A recrystallization heat treatment step of heating in a recrystallization temperature region that is not lower than the melting point temperature and not higher than the solution treatment temperature and in which thick internal crystal grains do not grow, and a high-frequency wave using a tube subjected to the recrystallization heat treatment step And a step of bending by heating.

In order to solve the technical problem, a method for manufacturing a welded joint tube of a Ni-based alloy according to the invention described in claim 3 includes a pipe- making process for manufacturing a pipe made of a Ni-based alloy, and the pipe-making process. The work hardening step in which the work hardening by shot peening is performed at least at an irradiation pressure of the shot particles of 0.4 MPa for 1 minute on the surface of the pipe manufactured in step 1 and A recrystallization heat treatment step of heating in a recrystallization temperature region in which the melting point is not lower than 2 melting point and not higher than the solution treatment temperature and the thick internal crystal grains are not grown, and a step of welding pipes subjected to the recrystallization heat treatment step And .

In order to solve the technical problem, a method for producing a steam pipe for a boiler according to claim 4 includes a pipe making process for producing a pipe made of a Ni-based alloy, and pipe making in the pipe making process. A work hardening step in which work hardening by shot peening is performed on the surface of the finished tube at least at a shot particle irradiation pressure of 0.4 MPa for 1 minute; A boiler main steam pipe comprising the above-described recrystallization heat treatment step for heating in a recrystallization temperature region below the solution treatment temperature and in which thick internal crystal grains do not grow, and the tube subjected to the recrystallization heat treatment step Or a step of creating a reheat steam pipe.

According to the first aspect of the present invention, when a pipe made of a high-strength Ni-based alloy that can be used in a facility having a main steam temperature of 700 ° C. is welded or bent, surface cracks are caused. Occurrence can be suppressed.
According to the second aspect of the present invention, a high-frequency heated bending tube in which occurrence of cracks on the surface is suppressed can be obtained.
According to invention of Claim 3, the welded joint pipe by which generation | occurrence | production of the crack of the surface was suppressed is obtained.
According to invention of Claim 4, the steam for boilers which can obtain the main steam pipe and reheat steam pipe with which generation | occurrence | production of the crack of the surface was suppressed, and can be used for the power plant in which steam temperature becomes around 700 degreeC . A tube is obtained.

FIG. 1 is a drawing showing a schematic configuration in which shot processing and fine grain heat treatment are performed on the inner and outer surfaces of a Ni-based alloy thick-walled large-diameter tube as an example of a Ni-based alloy tube according to an embodiment of the present invention. is there. 2A and 2B are explanatory diagrams of a pipe manufactured by the manufacturing method of the pipe of Example 1, FIG. 2A is a cross-sectional microstructure, and FIG. 2B is an explanatory diagram of hardness distribution near the surface. 3 is an explanatory view when the large-diameter pipe shown in FIG. 2 is processed, FIG. 3A is a side view of a processing portion during high-frequency bending, FIG. 3B is a cross-sectional view taken along the line IIIB-IIIB in FIG. 3A, and FIG. FIG. 3D is an enlarged view of the IIIC portion of FIG. 3B, FIG. 3D is an explanatory view during welding, and FIG. 3E is a cross-sectional view taken along the line IIIE-IIIE of FIG. FIG. 4 is an explanatory diagram of a thick-walled large-diameter pipe during machining in the prior art, FIG. 4A is an observation diagram of the microstructure of the material surface, and FIG. 4B is a hardness distribution in the thickness direction of the thick-walled large-diameter pipe. It is a graph. 5 is an explanatory view when the large-diameter pipe shown in FIG. 4 is machined. FIG. 5A is a side view of a machined portion during high-frequency bending, FIG. 5B is a cross-sectional view taken along the line VB-VB in FIG. 5A, and FIG. FIG. 5D is an enlarged view of a VC portion in FIG. 5B, FIG. 5D is an explanatory view at the time of welding, and FIG. 5E is a cross-sectional view taken along the line VE-VE in FIG.

Next, specific examples of embodiments of the present invention (hereinafter referred to as examples) will be described with reference to the drawings, but the present invention is not limited to the following examples.
In the following description using the drawings, illustrations other than members necessary for the description are omitted as appropriate for easy understanding.

FIG. 1 shows a schematic configuration in which shot processing and fine grain heat treatment are performed on the inner and outer surfaces of a Ni-based alloy thick-walled large-diameter tube as an example of a Ni-based alloy tube according to an embodiment of the present invention. It is a drawing.
In the method for producing a Ni-based alloy pipe according to Example 1 of the present invention, the thick large-diameter pipe 1 is produced by hot extrusion or forging boring made of a Ni-based alloy.
Next, the tube 1 or the shot nozzle 2 is relatively moved in the longitudinal direction of the pipe 1 while the tube 1 or the shot nozzle 2 is relatively rotated in the thick large-diameter pipe 1 manufactured, and the inner and outer surfaces of the pipe 1 are moved. A high energy density processing layer 3 is formed in the vicinity of the inner and outer surfaces of the tube 1 by shot processing of the inner and outer surfaces of the tube by shot peening as an example of the curing process. That is, by the shot processing, a processed layer 3 in which dislocations (linear crystal defects) are distributed with high density is formed near the surface of the tube 1.
Next, recrystallization heat treatment is performed on the entire tube material.

  As long as the particles used for shot peening are hard and effective, the material and shape thereof are not limited, but the shot processing layer 3 is 0.5 mm or more and the depth from the surface of the tube 1 is 0.3 mm or more. In this range, it is preferable that the hardness is substantially constant and is uniformly formed on the entire inner and outer surfaces of the tube 1. As an example, when HR6W is used as a high-strength Ni-based alloy, when using Martensit MG-120 as the particles for shot, the irradiation time is 1 minute, and the irradiation pressure is 0.4 MPa, 0.5 mm or more, The hardness was almost constant in the range from the surface of the tube 1 to a depth of 0.3 mm or more, and was uniformly formed on the entire inner and outer surfaces of the tube 1.

  The temperature and time of the recrystallization heat treatment are set to a recrystallization temperature region in which each material has a melting point not lower than ½ melting point and not higher than the solution treatment temperature, and thick internal crystal grains do not grow. As an example, when HR6W is used as a high-strength Ni-based alloy, recrystallization with a 1/2 melting point temperature of 800 ° C. or higher, a solution treatment temperature of 1220 ° C. or lower, and a thick internal crystal grain does not grow. In order to satisfy the temperature range of 1050 ° C. to 1200 ° C., it is preferably 1100 to 1150 ° C. and 0.5 to 1 hour.

2A and 2B are explanatory diagrams of a pipe manufactured by the manufacturing method of the pipe of Example 1, FIG. 2A is a cross-sectional microstructure, and FIG. 2B is an explanatory diagram of hardness distribution near the surface.
Further, FIG. 2 shows the results of the cross-sectional microstructure and the near-surface hardness distribution of the Ni-based large-diameter tube 1 (for example, HR6W) after the shot processing and the recrystallization heat treatment, respectively.
2 is a large-diameter tube having a diameter of 350 mm and a thickness of 40 mm made of HR6W as a high-strength Ni-based alloy, as in FIG. 4, and FIG. 2A was photographed at 100 × with an optical microscope. FIG. 2B is a diagram in which the Vickers hardness from the outer surface to the inner surface of the cross section is measured by cutting a ring in the circumferential direction of the large diameter pipe.

  From this result, the surface of the Ni-based large-diameter tube 1 is equivalent to a fine-grained structure having a thickness of 0.3 mm or more and a wall thickness center by forming a shot processing layer 3 having a high energy density and subsequent recrystallization heat treatment The formation of the surface layer 4 having excellent hardness and excellent ductility was confirmed. In the mechanical finishing (work hardening by shot processing) in the conventional method, the hardness in the vicinity of the surface becomes hard and the particle size is large as shown in FIG. 4A, so the ductility is poor (becomes easy to break). . In the tube 1 of Example 1, the shot treatment and the recrystallization heat treatment were performed on the conventional Ni-based alloy large-diameter tube having a surface coarse grain structure with poor ductility. As shown in FIG. 2A, the particle size is fine in the vicinity of the surface and the ductility of the surface layer 4 is improved (it is difficult to break). Therefore, a Ni-based large-diameter tube 1 having a fine grain structure with excellent surface ductility can be produced.

3 is an explanatory view when the large-diameter pipe shown in FIG. 2 is processed, FIG. 3A is a side view of a processing portion during high-frequency bending, FIG. 3B is a cross-sectional view taken along the line IIIB-IIIB in FIG. 3A, and FIG. FIG. 3D is an enlarged view of the IIIC portion of FIG. 3B, FIG. 3D is an explanatory view during welding, and FIG. 3E is a cross-sectional view taken along the line IIIE-IIIE of FIG.
Therefore, in FIG. 3, when the Ni-based large-diameter pipe 1 having excellent surface ductility subjected to the shot processing and recrystallization heat treatment of Example 1 is used, high-frequency bending processing is performed as shown in FIGS. 3A to 3C. 3D and 3E, even if welding is performed, the surface layer 4 having excellent ductility can suppress the occurrence of surface microcracking as in the prior art, and bending or welding heated at high frequency. Can be easily performed.
In addition, after bending and welding, a high-frequency heating bent pipe or a welded joint pipe can be finally produced by performing a solution treatment to diffuse precipitates (aggregation).

  The pipe created by the above-described manufacturing method of the present invention can be suitably used for a main steam pipe and a reheat steam pipe of a boiler in a power plant having a main steam temperature of 700 ° C.

DESCRIPTION OF SYMBOLS 1 ... Tube 2 ... Shot nozzle 3 ... Processed layer 4 by shot processing ... Surface layer after recrystallization heat treatment

Claims (4)

A pipe making process for producing a pipe made of a Ni-based alloy;
A work hardening step of performing work hardening by shot peening for at least one shot particle irradiation pressure of 0.4 MPa on the surface of the pipe made in the pipe making step;
A recrystallization heat treatment step of heating the work-hardened tube in a recrystallization temperature region not lower than a melting point temperature of the material and not higher than a solution treatment temperature and in which a thick internal crystal grain does not grow;
A method for producing a Ni-based alloy tube, comprising: A pipe making process for producing a pipe made of a Ni-based alloy;
A work hardening step of performing work hardening by shot peening for at least one shot particle irradiation pressure of 0.4 MPa on the surface of the pipe made in the pipe making step;
A recrystallization heat treatment step of heating the work-hardened tube in a recrystallization temperature region not lower than a melting point temperature of the material and not higher than a solution treatment temperature and in which a thick internal crystal grain does not grow;
Heating by high frequency using the tube subjected to the recrystallization heat treatment step , and performing a bending process;
The manufacturing method of the high frequency heating bending pipe | tube of Ni-based alloy characterized by having provided . A pipe making process for producing a pipe made of a Ni-based alloy;
A work hardening step of performing work hardening by shot peening for at least one shot particle irradiation pressure of 0.4 MPa on the surface of the pipe made in the pipe making step;
A recrystallization heat treatment step of heating the work-hardened tube in a recrystallization temperature region not lower than a melting point temperature of the material and not higher than a solution treatment temperature and in which a thick internal crystal grain does not grow;
A step of welding the recrystallization heat treatment step to tubes each other,
A method for producing a welded joint tube of a Ni-based alloy, comprising : A pipe making process for producing a pipe made of a Ni-based alloy;
A work hardening step of performing work hardening by shot peening for at least one shot particle irradiation pressure of 0.4 MPa on the surface of the pipe made in the pipe making step;
A recrystallization heat treatment step of heating the work-hardened tube in a recrystallization temperature region not lower than a melting point temperature of the material and not higher than a solution treatment temperature and in which a thick internal crystal grain does not grow;
A step of creating a main steam pipe or a reheat steam pipe for a boiler comprising the pipe subjected to the recrystallization heat treatment process ;
A method for manufacturing a steam pipe for a boiler.

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