JP2014001702A - Steam valve device and manufacturing method of the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a steam valve device in which a lower padding layer is formed on a base material by means of build-up welding and which is capable of preventing occurrence of a crack when a surface hardened layer is formed by means of build-up welding.SOLUTION: According to an embodiment, a steam valve device is provided in a flow channel for high-temperature steam and has a weld zone formed on a base material 1. The weld zone has a lower padding layer 2 made from Ni group alloy and formed by means of build-up welding on the base material 1 made from ferrite heat-resistant steel, and a surface hardened layer 3 made from hard alloy and formed by means of build-up welding on the lower padding layer 2.

Description

  Embodiments described herein relate generally to a steam valve device and a method for manufacturing the same.

  A steam turbine power generation facility of a thermal power plant is provided with a steam valve device having a steam flow rate control function. Examples of the main steam valve device include a main steam stop valve, a steam control valve, a reheat steam stop valve, and an intercept valve.

  For example, a steam control valve adjusts the steam flow rate by moving a valve stem and a valve body linked to the valve stem in the axial direction of the valve stem to change the opening of the valve. In a series of flow rate adjusting operations, the valve rod moves using a bush installed inside the valve stand, and the valve element moves using a sleeve as a guide. Since the valve stem and the valve body are not fixed in a direction orthogonal to the axial direction, the sliding with respect to the bush and the sleeve is repeated by vibration due to the steam pressure.

  The steam valve device under steam conditions (538 ° C or 566 ° C) of conventional steam turbine power generation equipment is resistant to oxidation (suppression of oxide scale generation) and wear resistance (improvement of high temperature hardness) ) Processing is being considered.

  The gaps in the sliding parts such as the valve body and the sleeve, the valve stem and the bush are very small in order to prevent steam leakage and vibration due to steam pressure. When high-temperature steam flows into this gap, an oxide scale is generated. This oxide scale becomes a factor of a so-called stick phenomenon in which the valve sticks as it accumulates on the sliding portion over time. In order to suppress this sticking phenomenon, in the conventional steam valve device, build-up welding of stellite (trade name), which is a Co-based hard alloy, is performed on the sliding surface of the sliding portion.

  In addition, in conventional steam valve devices, thermal shock due to inflow or outflow of high-temperature and high-pressure superheated steam, damage to the seat of the valve seat or valve body due to impact load at the time of rapid closing of the steam valve, erosion due to steam flow (erosion) It is necessary to prevent damage due to wear such as corrosion. Therefore, in the conventional steam valve device, the seat portion of the valve seat and the valve body is subjected to overlay welding of stellite having thermal shock resistance and oxidation resistance and higher hardness than the valve base material.

  Thus, the high temperature member of the equipment used at high temperature is required to be excellent in wear resistance and oxidation resistance at high temperature. As a matter of course, the structural member on which the stress acts needs to satisfy the required high temperature strength.

  The above-mentioned stellite is a Co-based hard alloy containing Co as a main component and containing approximately 30% Cr and 4-15% tungsten, and is known as a material excellent in wear resistance.

  Further, this stellite has a small decrease in hardness even at a high temperature and is excellent in oxidation resistance because it contains a large amount of Cr and Co. However, since stellite itself has poor toughness, if the cooling rate after welding is high, cracks may occur in the welded portion of stellite due to thermal stress. For this reason, it is important that stellite is sufficiently controlled for preheating, interlayer temperature, post-heat treatment, and the like when performing welding.

  Further, depending on the properties of the base material to be overlay welded, the base material itself may be cracked. In a conventional steam valve device, a general method is that a SUS309 welding material (austenitic stainless steel) is welded on a base metal and stellite is overlay welded thereon.

  As a technique for preventing such a welded portion of stellite and cracking of the base material, there is one disclosed in Patent Document 1, for example. In this technique, a method of overlaying stellite on the upper surface of a base material by changing the overlay welding material to a base material from a SUS309 welding material (austenitic stainless steel) to a Ni-based alloy having ductility is disclosed.

JP-A-8-215842

  In the technique disclosed in the above-mentioned Patent Document 1, although improvement is achieved by changing the base welding material to a Ni-based alloy, martensite containing about 9 to 13% of Cr in the base material for the base welding is performed. A heat resistant steel is used. Since this martensitic heat resistant steel has a high quenching hardenability, microcracks are generated at the time of underlay welding, and the cracking problem of the base metal itself has not been solved.

  The embodiment of the present invention has been made in consideration of such circumstances, and cracks are generated in the base material when the overlay layer is welded on the base material and the surface hardened layer is welded on the base material. It is an object of the present invention to provide a steam valve device capable of preventing the above and a manufacturing method thereof.

  In order to achieve the above object, a steam valve device according to an embodiment of the present invention is a steam valve device provided in a flow path of high-temperature steam and having a welded portion formed on a base material, the welded portion comprising a ferrite A Ni-base alloy underlayer formed by underlay welding on a base heat-resistant steel base material, and a hard alloy surface hardened layer formed by overlay welding on the underlay layer. And

  A method for manufacturing a steam valve device according to an embodiment of the present invention is a method for manufacturing a steam valve device that is provided in a flow path for high-temperature steam and forms a weld in a base material, and is a base material made of ferritic heat resistant steel Forming an underlayer of Ni-based alloy by underlay welding, and forming a hardened surface layer of hard alloy on the underlay layer by overlay welding; and It is characterized by having.

  According to the embodiment of the present invention, it is possible to prevent the occurrence of cracks when the overlay layer is overlay welded to the base material and the surface hardened layer is overlay welded.

In one Embodiment of the manufacturing method of the steam valve apparatus which concerns on this invention, it is an expanded sectional view which shows the example which formed the welding part in the groove | channel of a cross-section inverted trapezoid shape. In one Embodiment, it is an expanded sectional view which shows the modification which formed the welding part in the groove | channel of circular arc cross section. In one Embodiment, it is an expanded sectional view which shows the modification which formed the welding part in the bush which is a cylindrical-shaped base material. It is a longitudinal cross-sectional view which shows the structure of the valve body periphery part of the steam control valve to which the manufacturing method of the steam valve apparatus which concerns on one Embodiment of this invention was applied. It is a longitudinal cross-sectional view which shows the structure of the valve body periphery part of the combination reheat valve to which the manufacturing method of the steam valve apparatus which concerns on one Embodiment of this invention was applied.

  Embodiments and examples of a steam valve device and a method for manufacturing the same according to the present invention will be described below with reference to the drawings.

(Embodiment)
FIG. 1 is an enlarged cross-sectional view showing an example in which a welded portion is formed on a groove having an inverted trapezoidal cross section in one embodiment of a method for manufacturing a steam valve device according to the present invention. In addition, the welding part of this embodiment is formed in the sliding part of a steam valve apparatus, a valve seat, or the seat part of a valve body, for example on high temperature steam conditions (steam temperature of 600 degreeC or more).

  As shown in FIG. 1, in this embodiment, a groove portion 1 a having an inverted trapezoidal cross section is formed in advance on a base material 1 for overlaying. A bottom layer 2 is formed on the groove portion 1a by bottom welding. A surface hardened layer 3 is formed on the underlying layer 2 by overlay welding.

  The base material 1 is formed of ferritic heat-resistant steel containing, for example, about 9% Cr. As the material for the underlayer 2, a Ni-based alloy having a high ductility is used. As the material of the surface hardened layer 3, stellite, which is a Co-based hard alloy, is used.

  In the present embodiment, when the surface hardened layer 3 is formed by overlay welding of stellite, the material of the base material 1 is not a martensitic heat-resistant steel containing about 9 to 13% of Cr as in the prior art, but carbon. Ferritic heat-resistant steel containing about 9% Cr, for example, having a small solid solution amount and good weldability is used.

  Further, in the present embodiment, prior to the overlay welding of stellite which is the surface hardened layer 3 to the base material 1, the base layer 2 is formed by overlay welding a Ni-based alloy having high ductility to the base material 1. ing. Thereafter, the stellite which is the surface hardened layer 3 is build-up welded on the underlying layer 2 by PTA welding (Plasma Transferred Arc) in which the welding speed, the temperature at the time of welding, and the like are controlled.

  Next, the operation of this embodiment will be described.

  In recent years, a thermal power plant having a steam temperature of 600 ° C. or more has been operated for the purpose of improving the efficiency of the steam turbine. The material of the steam valve device suitable for increasing the steam temperature is higher in strength and oxidation resistance than martensitic heat-resistant steel containing about 9 to 13% of Cr used as a conventional heat-resistant alloy steel. For improvement, ferritic heat resistant steels such as 9Cr steel containing 9% Cr and 12Cr steel containing 12% Cr are suitable.

  Therefore, as the sliding member and the valve seat portion in the steam valve device according to the present embodiment, an optimum one as a high temperature member used at a high temperature is selected. For example, when forming the surface hardened layer 3 of stellite using a ferritic heat-resistant steel containing about 9% of Cr as a base material 1, a Ni-base alloy having a large ductility and having a thermal expansion coefficient comparable to that of stellite The hardened surface layer 3 is formed by overlaying stellite by PTA welding in which the welding speed and the temperature during welding are controlled.

  Thus, according to this embodiment, by forming the Ni-based alloy as the underlayer 2, the difference in thermal expansion coefficient from the ferritic heat resistant steel of the base material 1 is small, and stellite is a thermal expansion coefficient. Therefore, the generation of thermal reaction force associated with the heat cycle of heating and cooling can be reduced. Furthermore, since the Ni-based alloy of the underlayer 2 has a high ductility, it becomes a buffer material against cracks in the stellite and the base material 1, so that the occurrence of cracks in the welded portion can be prevented in advance.

  Furthermore, according to the present embodiment, the generation of thermal stress is small even during use at high temperatures, and the reliability is improved against thermal fatigue and creep damage. In addition, since the Ni-based alloy of the underlay layer 2 has a small amount of carbon solid solution, it has an effect of preventing carbon migration at the weld boundary on the base material 1 side and reducing strength reduction due to decarburization phenomenon.

  As described above, according to the steam valve device having the sliding portion, the valve seat portion, and the like using the present embodiment, the member can be manufactured with a high yield and the high temperature steam higher than the conventional temperature can be manufactured. Under the conditions, effective properties can be obtained with respect to oxidation resistance and high temperature hardness. As a result, the generation of oxide scale can be prevented, the amount of wear due to sliding can be reduced, the malfunction of the steam valve can be prevented, and there is little deterioration damage during use, increasing the reliability as a steam valve device. be able to.

  FIG. 2 is an enlarged cross-sectional view showing a modification in which a weld is formed in a groove having an arcuate cross section in one embodiment. In this modification, a groove portion 1b having a circular arc cross section is formed on the base material 1 for overlaying. A bottom layer 2 is formed on the groove portion 1b by bottom welding. A surface hardened layer 3 is formed on the underlying layer 2 by overlay welding.

  Moreover, the base material 1, the underlaying layer 2, and the surface hardened layer 3 are made of the same material as in the above embodiment. Other functions and effects are the same as those of the above-described embodiment, and thus description thereof is omitted.

  FIG. 3 is an enlarged cross-sectional view showing a modification in which a weld portion is formed on a bush that is a cylindrical base material in one embodiment. In this modification, the underlayer 2 is formed by underlay welding on the outer peripheral surface 1c of the bush, which is the cylindrical base material 1. A surface hardened layer 3 is formed on the underlying layer 2 by overlay welding.

  Moreover, the outer peripheral surface 1c of the bush which is the base material 1, the underlaying layer 2 and the surface hardened layer 3 are made of the same material as in the above embodiment. Other functions and effects are the same as those of the above-described embodiment, and thus description thereof is omitted.

(Example)
FIG. 4 is a longitudinal sectional view showing the structure of the periphery of the valve body of the steam control valve to which the method for manufacturing the steam valve device according to one embodiment of the present invention is applied.

  The steam control valve shown in FIG. 4 adjusts the steam flow rate by moving the valve stem 4 and the valve body 6 linked to the valve stem 4 in the axial direction to change the opening of the valve.

  In a series of flow rate adjusting operations, the valve rod 4 moves with the bush 5 installed inside the valve stand 11 and the valve body 6 moves with the sleeve 7 as a guide. Since the valve stem 4 and the valve body 6 are not fixed in a direction perpendicular to the axial direction, the valve rod 4 and the valve body 6 are repeatedly slid by vibration due to steam pressure.

  FIG. 5 is a longitudinal sectional view showing the structure of the periphery of the valve body of the combined reheat valve to which the method for manufacturing the steam valve device according to one embodiment of the present invention is applied.

  As in the case of the steam control valve shown in FIG. 4, the combined reheat valve shown in FIG. 5 moves the valve stem 4 and the valve body 6 linked to the valve stem 4 in the axial direction, thereby changing the opening of the valve. The steam flow is adjusted.

  In a series of flow rate adjusting operations, the valve rod 4 of the combined reheat valve shown in FIG. 5 has the bush 5 and the guide bush 9 installed inside the upper lid 12 and the guide piece 13, and the valve body 6 has the sleeve 7. , Each move as a guide. Since the valve stem 4 and the valve body 6 are not fixed in a direction perpendicular to the axial direction, the valve rod 4 and the valve body 6 are repeatedly slid by vibration due to steam pressure.

  As shown in FIG. 4 and FIG. 5, the portion where the stellite is build-up welded to form the surface hardened layer includes the outer peripheral surface of the valve stem 4 that contacts the bush 5, the inner peripheral surface of the bush 5 that guides the valve stem 4, The inner peripheral surface of the sleeve 7 that guides the valve body 6, the outer peripheral surface of the valve body 6 that contacts the inner peripheral surface of the sleeve 7, the valve seat portion 10 of the valve body 6, and the valve seat portion 10 of the valve seat 8.

  The surface on which the stellite is overlay welded is very hard and has poor workability, so only the valve rod 4, bush 5, sleeve 7 and valve body 6 sliding surface and valve seat portion 10 are processed. To do.

As a base material for overlay welding, for example, in Bush 5, ASTM (American Society for Testing and Materials) A182 Grade F91 (9% Cr-1% Mo—) of ferritic heat-resistant steel containing about 9% Cr 0.25V steel), the inner peripheral surface of the bush 5 is subjected to machining before overlay welding, and as a main component under the following welding conditions, for example,
Underlay welding was performed with a welding rod made of a Ni-based alloy containing 18 to 22% Cr− ≦ 0.75% Ti− ≦ 1.5% Fe−2 to 3% (Nb + Ta) under the following conditions.

  FIG. 3 shows a cross section of the hardened surface layer 3 subjected to underlay welding using a Ni-based alloy and overlaid welding of stellite. In FIG. 3, the code | symbol 2 has shown the underlaying layer.

  Preheating: 300 to 350 ° C., welding: TIG (Tungsten Inert Gas) welding Ar gas, post-heat treatment: 740 ° C. × 1 hr / 1 inch (air cooling).

  Next, overlay welding of stellite was performed by PTA (Plasma Transferred Arc) welding of automatic welding in which the welding speed was stable. Also, thorough temperature control of preheating, interlayer, and post-heat treatment during welding was performed.

  The build-up material is cobalt substrate alloy powder and uses AWS A5, 13 RCoCr-A equivalent material stellite (American Welding Association standard, main component: Cr 28% -4% W-1% C-balance Co), Overlay molding was performed by PTA welding under the welding conditions described above.

  Preheating: 300 to 350 ° C., welding: PTA welding Ar gas, welding speed: 50 to 70 mm / min, weaving width: 10 to 15 mm, post heat treatment: 740 ° C. × 1 hr / 1 inch (air cooling).

  The inner surface of the bush 5 was subjected to machining finishing after overlay welding of stellite, and finished to a predetermined shape, size and surface roughness.

  In this way, no crack was observed in the stellite overlay of the bush 5 manufactured by the manufacturing method of the present embodiment, and it was confirmed that the quality was highly reliable.

  In this example, the case where the ASTM A182 Grade F91 material was used as the alloy base material was explained. However, the Ni-based alloy according to this example is similarly applied to the ferritic heat-resistant steel containing 3% or less of Cr. Underlay welding and then overlay welding of stellite were confirmed, and the effect was confirmed.

  Next, the operation and effect of an embodiment of the steam valve device according to the present invention will be described.

The thermal expansion coefficient in the above-described conventional material structure is about 12.0 × 10 ⁻⁶ / ° C. for the 9 to 13 Cr martensitic heat resistant steel which is the base material, and about austenitic stainless steel which is the overlay welding material is about 19.0 × 10 ⁻⁶ / ° C., and stellite was about 15.0 × 10 ⁻⁶ / ° C.

On the other hand, the thermal expansion coefficient in one embodiment of the present invention is about 13.0 × 10 ⁻⁶ / ° C. for the 9Cr ferritic heat resistant steel which is the base material 1, and the Ni-based alloy steel which is the overlay layer 2 is , About 15.0 × 10 ⁻⁶ / ° C., and the stellite which is the surface hardened layer 3 is about 15.0 × 10 ⁻⁶ / ° C.

That is, as the underlaying layer 2 directly deposited on the base material 1, by using a Ni-based alloy having a thermal expansion coefficient similar to that of stellite, a small amount of solid solution of carbon, and a large ductility,
(1) Since the difference in thermal expansion coefficient with the base material 1 is small, the generated thermal stress is small.

  (2) Since the stellite and the Ni-based alloy have the same thermal expansion coefficient, there is little generation of thermal stress.

  (3) By making the underlayer 2 an Ni-based alloy, the amount of solid solution of carbon is small, carbon migration from the base material 1 side at the weld boundary can be prevented, and generation of a decarburized layer is prevented. , Prevent strength reduction.

  (4) Therefore, by using a Ni-based alloy having high ductility as the underlay layer 2, it becomes a buffer material for cracking, and it becomes possible to prevent cracking of the stellite and the base material 1.

  The Ni-base alloy satisfying the above requirements (1) to (4) has a main component of Cr18-22% -Ti≤0.75% -Fe≤1.5%-(Nb + Ta) 2-3% -Ni balance. Alloy steel such as JIS NCF625, which is composed of 1% alloy steel and Cr21.5% -Mo9% -Fe2.5%-(Nb + Ta) 3.7% -Ni61%, and further contains the following composition: Is preferred.

  Specifically, the Ni-based alloy has a Cr of 18 to 22%, more preferably 20 to 22%, a Ti of 0.75% or less, more preferably 0.2 to 0.6%, and a Fe of 3% or less. More preferably, it is 1-2%, most preferably 1.4%, Nb + Ta is 2-3%, and Ni is the balance.

  Moreover, the ferritic heat resistant steel containing about 9% of Cr used as the base material 1 in this example is typically represented by ASTM A182 Grade F91 (9% Cr-1% Mo-0.25V steel), for example. It is preferable to use one having the composition:

  Specifically, C is 0.08 to 0.12%, Cr is 8 to 9.5%, Mo is 0.85 to 1.05%, V is 0.18 to 0.25%, and Mn is 0. 0.3 to 0.6%, Ni is ≦ 0.4%, Nb is 0.06 to 0.10%, N is 0.03 to 0.07%, and Fe is the balance.

  Here, when C is less than 0.08%, the weldability is improved, but the strength is lowered. On the other hand, when C exceeds 0.12%, the weldability is lowered although the strength is improved. Therefore, when C contains the range of 0.08 to 0.12% as described above, both weldability and strength are improved.

  As described above, the embodiments and examples of the present invention have been described. However, these embodiments and examples are presented merely as examples, and are not intended to limit the scope of the invention. These novel embodiments and examples can be implemented in various other forms, and various omissions, replacements, and changes can be made without departing from the spirit of the invention. These embodiments, examples, and modifications thereof are included in the scope and gist of the invention, and are included in the invention described in the claims and the equivalents thereof.

  In the above embodiment, the material of the base material 1 is not limited to the above-mentioned ASTM A182 Grade F91 as long as it is a ferritic heat resistant alloy steel with a small amount of carbon solid solution and good weldability. Even if new materials are developed as the steam conditions increase, they can be applied without departing from the essence of the present invention.

  Further, in one embodiment of the present invention, the surface hardened layer 3 is formed by overlay welding of stellite on the Ni-based alloy that has been welded under welding, but other than stellite, for example, it is a Co-based hard alloy. Trivalloy (trade name) material, or Kolmonoy (trade name) material and Clervalloy (trade name) which are Ni-based hard alloys are also applicable.

  Furthermore, even if a new material is developed with further increase in steam conditions in the future, any material that has thermal shock resistance and oxidation resistance and has higher hardness than the base material can be applied.

DESCRIPTION OF SYMBOLS 1 ... Base material 1a ... Groove part 1b ... Groove part 1c ... Outer peripheral surface 2 ... Bottom layer 3 ... Surface hardening layer 4 ... Valve rod 5 ... Bushing 6 ... Valve body 7 ... Sleeve 8 ... Valve seat 9 ... Guide bush DESCRIPTION OF SYMBOLS 10 ... Valve seat part 11 ... Valve stand 12 ... Upper lid 13 ... Guide piece

Claims (7)

A steam valve device provided in a flow path for high-temperature steam and having a weld formed on a base material,
The welded portion is a Ni-based alloy underlayer formed by underlay welding on a base material made of ferritic heat-resistant steel,
A hardened surface layer made of hard alloy formed by overlay welding on the underlying layer,
A steam valve device comprising:   The steam valve device according to claim 1, wherein the base material ferritic heat-resistant steel contains C in a range of 0.08 to 0.12%.   The base material is formed with a welded portion including an inner surface of a bush that guides the valve stem, an outer surface of the valve rod that contacts the inner surface of the bush, an inner surface of a sleeve that guides the valve body, and the valve body that contacts the inner surface of the sleeve. The steam valve device according to claim 1, wherein the steam valve device is any one of an outer surface, the valve body, and a valve seat portion of the valve seat.   The steam valve device according to claim 3, wherein a portion where a weld is formed on the base material is formed at least in part.   The steam valve device according to claim 1, wherein the hardened surface layer is a hard alloy of a Co-based hard alloy or a Ni-based hard alloy. A method of manufacturing a steam valve device that is provided in a flow path of high-temperature steam and forms a weld in a base material,
An underlay layer forming step of forming an underlay layer made of a Ni-based alloy on a base material made of ferritic heat resistant steel by underlay welding;
A surface hardened layer forming step of forming a hardened surface hardened layer on the underlayer by overlay welding;
A method for manufacturing a steam valve device.   The method for manufacturing a steam valve device according to claim 6, wherein the surface hardened layer forming step performs build-up molding by PTA welding.

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