JP2014028396A - Welding method for erosion resistant metallic material and turbine blade - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a welding method for an erosion resistant metallic material capable of suppressing a reduction in hardness of an erosion resistant layer in a blade front edge portion, and further to provide a turbine blade.SOLUTION: A welding method for an erosion resistant metallic material that is a method for welding the erosion resistant metallic material to a base body 1 in a turbine blade front edge portion 1A comprises the steps of: forming a groove to be applied with the erosion resistant metallic material on the base body 1 on the basis of a scheduled finish surface of an erosion resistant layer and a thickness of the erosion resistant layer such that the erosion resistant metallic material is embedded in the groove in one layer; and welding the erosion resistant metallic material to the groove.

Description

  The present invention relates to a method for welding an erosion resistant metal material and a turbine blade.

The steam turbine blade may be eroded by an impact effect received from fine solid particles mainly composed of condensed water droplets and iron oxide in the steam, and the surface may be worn. Therefore, an erosion-resistant (erosion) layer may be formed at the front edge portion that is in front of the steam turbine blade (upstream side of the steam flow), thereby suppressing the erosion of the steam turbine blade.
Patent Document 1 discloses a technique for reducing erosion wear by joining an erosion shield having a borated layer formed on a surface thereof to a base of a steam turbine blade. Patent Document 2 describes that a blade leading edge portion, which is a part of the blade shape of a turbine rotor blade, is cut out and the erosion preventing portion is reconstructed using overlay welding using a laser.

Japanese Examined Patent Publication No. 61-12082 Japanese Patent No. 4901413

  As the erosion-resistant layer to be joined to the base of the steam turbine blade, for example, a cobalt-based alloy having high wear resistance such as Stellite (registered trademark) whose main component is cobalt is used. When a cobalt base alloy or the like is joined to the substrate, overlay welding by brazing or TIG welding is performed. However, in the case of joining by brazing, problems such as poor joints are likely to occur, and the quality of the steam turbine blades is likely to deteriorate due to multiple heating by rework. In addition, in the case of joining by TIG welding, there is a problem that the base metal is mixed into a weld metal such as a cobalt-based alloy and the weld metal is diluted. As a result, the hardness of the erosion resistant layer is lowered, and the erosion resistance performance due to the cobalt-based alloy or the like is lowered.

  In the technique of Patent Document 2, as shown in FIG. 1C of Patent Document 2, the blade leading edge portion of the turbine rotor blade is cut along the blade length direction to form a belt-like plane, The erosion preventing portion made of a hard material is formed by stacking multiple layers. FIG. 16 is a cross-sectional view showing the base 1 of the front edge portion 1A of the conventional steam turbine blade and the weld bead constituting the erosion preventing portion, and the two-dot chain line in FIG. 16 is the expected finished surface of the erosion preventing portion. S is shown. Since the hard material is more fragile than the material of the wing body part, when the entire wing leading edge part is replaced as in Patent Document 2, the erosion preventing part is peeled or damaged from the wing body part.

  The present invention has been made in view of such circumstances, and provides a welding method for an erosion-resistant metal material and a turbine blade capable of suppressing a decrease in hardness of an erosion-resistant layer at a blade leading edge. The purpose is to do.

In order to solve the above problems, the erosion resistant metal material welding method and turbine blade of the present invention employ the following means.
That is, the erosion-resistant metal material welding method according to the reference example of the present invention is a erosion-resistant metal material welding method to the base at the turbine blade leading edge, and the erosion-resistant metal material is applied. Forming a radius of a curved surface at the front edge portion larger than a thickness of the base; and welding the erosion resistant metal material to the front edge portion.

  According to this reference example, the base body at the front edge portion has a shape that allows heat to escape easily, and when the erosion-resistant metal material is welded to the base body, heat accumulation in the base body can be suppressed. As a result, heat is dissipated from the substrate, and a local temperature rise can be suppressed. And the dilution of the erosion-resistant metal material by mixing of the base material into the erosion-resistant metal material can be reduced, and the decrease in the hardness of the erosion-resistant layer can be suppressed. The cross-sectional shape of the front end portion is not limited to the circular arc shape, and may be other shapes as long as the blade tip portion can be formed into a smooth curved surface.

  Further, the welding method of the erosion resistant metal material according to the present invention is a welding method of the erosion resistant metal material to the base at the turbine blade leading edge, so that the erosion resistant metal material is buried in one layer. Forming a groove on the substrate based on a predetermined finish surface of the erosion-resistant layer and a thickness of the erosion-resistant layer, and welding the erosion-resistant metal material to the groove; Steps.

  According to the present invention, the groove to which the erosion resistant metal material is applied is formed in the base based on the planned finish surface of the erosion resistant layer and the thickness of the erosion resistant layer. The erosion resistant metal material is, for example, a cobalt base alloy. The groove depth with respect to the planned finished surface is, for example, a depth at which the erosion-resistant metal material is buried in one layer, that is, a depth at which multi-layer welding is not performed, and as deep as possible so that a hardness reduction region does not appear on the surface. By being formed, deterioration of the erosion resistance can be prevented. A hardness reduction area | region is an area | region where a base material (base | substrate) mixes in a weld metal by welding.

  In the above invention, the depth of the groove is desirably 2 mm or less with respect to the planned finished surface. Thereby, the depth of the groove can be set to a depth at which the erosion-resistant metal material is buried in one layer, that is, a depth at which multilayer welding is not performed.

  In the above invention, the step of determining an overlap amount of each pass during welding so that a contact portion between a newly formed bead and an already formed bead is formed wider than a contact portion with the base. And a step of welding the erosion-resistant metal material to the base based on the amount of overlap.

  According to this invention, the overlap amount of each pass at the time of welding is increased, and the portion where the newly formed bead contacts the base body (base material) is less than the contact portion with the already formed bead. . As a result, dilution of the erosion-resistant metal material due to mixing of the base material into the erosion-resistant metal material (welding material) can be reduced, and a decrease in the hardness of the erosion-resistant layer can be suppressed.

  In the above invention, it is desirable that the welded erosion resistant metal material has a dilution with the base material of 10% or less. Thereby, dilution of the erosion-resistant metal material is reduced, and a decrease in the hardness of the erosion-resistant layer can be suppressed.

In the above invention, the erosion-resistant layer before finishing formed by welding the erosion-resistant metal material is desirably 2 mm or less per layer.
According to the present invention, since dilution by the base material can be reduced, a high-quality erosion-resistant layer having a minimum thickness necessary for erosion resistance can be formed.

In the above invention, the step of welding the erosion resistant metal material is characterized in that the laser is weaved in a direction transverse to the traveling direction so that the energy density distribution is flattened.
According to the present invention, the energy density distribution can be flattened, and the melted portion can be made shallower or wider.
The erosion-resistant metal material may be welded while being supplied in the form of a powder or a strip, or may be welded after the erosion-resistant metal material is previously applied to the welding site by thermal spraying or cold spraying.
According to the present invention, the number of passes can be reduced and the occurrence of defects can be suppressed.

  In the turbine blade according to the present invention, the erosion-resistant layer is formed on the front edge portion by the above-described erosion-resistant metal material welding method.

  According to the present invention, it is possible to suppress a decrease in the hardness of the erosion-resistant layer at the blade leading edge.

It is a cross-sectional view which shows the base | substrate of the steam turbine blade front edge part which concerns on one Embodiment of this invention. It is a cross-sectional view which shows the base | substrate of the steam turbine blade front edge part which concerns on one Embodiment of this invention. It is a cross-sectional view which shows the base | substrate and weld bead of the steam turbine blade front edge part which concerns on one Embodiment of this invention. It is a cross-sectional view which shows the base | substrate and weld bead of the steam turbine blade front edge part which concerns on one Embodiment of this invention. It is a cross-sectional view which shows the base | substrate and weld bead of the steam turbine blade front edge part which concerns on one Embodiment of this invention. It is a cross-sectional view which shows the base | substrate and weld bead of the steam turbine blade front edge part which concerns on one Embodiment of this invention. It is a transverse cross section showing the 1st example of the steam turbine blade front edge part concerning one embodiment of the present invention. It is a cross-sectional view which shows the 2nd example of the steam turbine blade front edge part which concerns on one Embodiment of this invention. It is a cross-sectional view showing the hardness measurement result of the front edge part of FIG. It is a cross-sectional view showing the hardness measurement result of the front edge part of FIG. It is a side view which shows a steam turbine blade. It is a cross-sectional view which shows the base | substrate of the conventional steam turbine blade front edge part. It is a perspective view which shows a steam turbine blade. It is the schematic which shows the relationship between the energy density distribution of the laser when not weaving a laser at high speed, and the molten part by welding. It is the schematic which shows the relationship between the energy density distribution of the laser in the case of weaving a laser at high speed, and the fusion | melting part by welding. It is a cross-sectional view which shows the base | substrate and welding bead of the conventional steam turbine blade front edge part.

Embodiments according to the present invention will be described below with reference to the drawings.
First, the configuration of the front edge portion 1A of the steam turbine blade 10 will be described. FIG. 11 is a side view showing the steam turbine blade 10.
A front edge 1 </ b> A of the steam turbine blade 10 is formed by bonding an erosion-resistant layer 3 made of a cobalt base alloy containing cobalt as a main component to the base 1. When the steam turbine blade 10 rotates and the steam flow flows, the erosion-resistant layer 3 is disposed on the front edge 1 </ b> A that is the upstream side of the steam flow in the steam turbine blade 10. Thereby, the erosion (erosion) of the front edge part 1A of the steam turbine blade 10 can be suppressed.

  The substrate 1 (base material) is, for example, a chromium-based alloy, and has a cross-sectional shape as shown in FIG. 1 before the erosion-resistant layer 3 is formed. FIG. 1 is a cross-sectional view showing a base body 1 for forming a front edge portion 1A of a steam turbine blade 10 and is a view cut in a direction perpendicular to the blade length direction of the steam turbine blade 10. A two-dot chain line in FIG. 1 indicates a planned finished surface S of the erosion-resistant layer 3.

  The base body 1 before the formation of the erosion-resistant layer 3 has a groove portion 2 having a shape recessed with respect to the planned finished surface S on the inner side of the base body 1. When the steam turbine blade 10 rotates, the front end 2A of the groove 2 is located on the upstream side of the steam flow, and the rear end 2B of the groove 2 is located on the downstream side of the steam flow.

  The front end portion 2A of the groove portion 2 has, for example, a corner portion whose cross-sectional surface has an arc shape. The radius R of the cross section of the corner is larger than the thickness t of the base 1, for example. Thereby, when forming the erosion-resistant layer 3 with the welding method mentioned later, the heat accumulation in the base | substrate 1 can be suppressed. The cross-sectional shape of the corner portion of the front end portion 2A is not limited to the circular arc shape, and may be any other shape as long as heat can be easily released from the base 1 and the blade tip can be formed into a smooth curved surface.

  The groove depth D with respect to the planned finished surface S at the rear end portion 2B of the groove portion 2 is a depth at which the weld metal is buried in one layer, that is, a depth at which multi-layer welding is not performed, and a reduced hardness region appears on the surface. It is desirable to form as deeply as possible. The groove depth D that can be welded in one layer is, for example, 2 mm or less. The hardness reduction region is a region where the base material is mixed into the cobalt base alloy of the weld metal by welding, and is a region where the erosion resistance performance that should be obtained by the cobalt base alloy is reduced.

  The erosion-resistant layer 3 formed in the groove portion 2 is formed from a plurality of passes, but is formed by one-layer overlay welding, and the thickness before finishing (see FIGS. 7 and 8) is 2 mm. It is as follows. The erosion resistant layer 3 is desirably diluted with a base material to 10% or less. The tip 2C of the groove 2 is preferably not a pointed shape but a flat surface as shown in FIG. 1 in order to prevent the base material from being melted into the weld metal.

  The erosion resistant layer 3 is, for example, a cobalt base alloy containing cobalt as a main component. In the present embodiment, for example, Stellite (registered trademark) can be applied as the cobalt-based alloy. The erosion resistant layer 3 is formed such that adjacent weld beads overlap each other. The weld bead has a part that contacts the base material and a part that contacts the adjacent weld bead that has already been formed, reduces the part that contacts the base material, and widens the part that contacts the adjacent weld bead. Is desirable (see beads <3> to <7> in FIG. 7 and beads <3> to <8> in FIG. 8). The erosion resistant layer 3 is formed by performing a plurality of passes. In addition, after the weld bead as shown in FIGS. 7 and 8 is formed, the front edge portion 1A is processed so as to have a planned finished surface S as shown by a two-dot chain line in FIG.

  The front edge portion 1A is not entirely replaced with an erosion-resistant metal material (see Patent Document 2 or FIG. 16), but only the erosion-resistant metal material having a uniform thickness along the shape of the substrate 1 Formed with. Therefore, damage to the erosion-resistant layer 3 of the erosion-resistant metal material having brittle properties compared to the substrate 1 can be suppressed.

  Next, a method for forming the front edge portion 1A of the steam turbine blade 10 according to the present embodiment, that is, a method for joining the erosion-resistant layer 3 to the base material will be described.

  First, the groove portion 2 is formed in the base 1 of the steam turbine blade 10 to have a shape as shown in FIG. That is, at the front end portion 2A of the groove portion 2, a corner portion having a radius R longer than the thickness of the base body 1 and having an arc-shaped cross section is formed. Further, the depth D of the rear end portion 2B of the groove portion 2 is formed to such a depth that the weld metal is buried in one layer and the hardness reduction region does not appear on the surface.

  Next, build-up welding by laser welding is performed on the base body 1 having the above-described shape to form the erosion-resistant layer 3 with one layer. In overlay welding, a plurality of passes are executed in the order shown by the numbers in <> in FIG. 7 or FIG. 8. FIG. 7 and FIG. 8 show examples of different path execution methods.

  At this time, by increasing the overlap amount of each pass during welding and reducing the portion where the weld bead contacts the base material, the amount of the base material mixed into the cobalt-based alloy of the weld metal can be reduced. The amount of overlap is adjusted by, for example, the laser target angle and the amount of movement between passes.

In the case of laser welding, automation is possible, and it is possible to execute appropriate welding according to each state by creating a program before welding and causing the welding apparatus to execute the program.
Laser welding can use a normal welding apparatus, and in this embodiment, the laser welding is performed under the following conditions. That is, a positioning camera and a height adjusting jig having a height sensor are used. The welding posture is always downward and moves between passes while rotating the base 1. The target position of each pass is input to the program as a teaching point by teaching. Further, the deformation shape of the base body 1 due to the influence of heat during welding is predicted, and the path is set in advance so as to follow the deformation shape of the base body 1. Furthermore, by using a positioning camera, it is possible to perform welding so as not to cause a positional shift while performing feedback.

  The aiming direction of the laser is about 90 ° with respect to the plane of the base material, or about 90 ° with respect to a tangent line connecting the convex portions. For example, as shown in FIG. 2, when the laser tip portion 11 is close to the shroud portion 12 (see FIG. 13) or the like, the laser aiming direction is that the laser tip portion 11 does not interfere with the shroud portion 12 and A welding program is created so as to be close to 90 ° with respect to a tangent line connecting the two convex portions. Further, as shown in FIG. 2, the laser target direction is 90 ° with respect to the flat plate surface on the side opposite to the R plane, and beads are already formed as shown in FIGS. If it is, it is 90 ° with respect to a tangent line connecting the convex portion of the bead and the convex portion of the base material. Further, as shown in FIG. 5, the laser target direction is parallel to the flat plate surface at the tip of the base 1, and when two beads are already formed as shown in FIG. , It is 90 ° with respect to a tangent line connecting the convex portion of one bead and the convex portion of another bead. Thus, by determining the laser aiming direction, it is possible to reduce welding defects and to suppress the base material from being mixed into the weld metal.

  Further, during laser welding, oscillation may be applied to the welding location. Thereby, poor welding can be reduced. As a method of welding while applying oscillation, there are methods as shown below.

  The erosion-resistant layer 3 is formed by weaving the laser at the welded portion at a high speed in the width direction while supplying the powdered erosion-resistant metal material in a band shape to the welded portion. Alternatively, the erosion-resistant layer 3 is formed by weaving a laser at the welded portion at a high speed in the width direction while supplying a strip-like erosion-resistant metal material having a certain thickness to the welded portion.

  Furthermore, a layer made of an erosion-resistant metal material is formed in advance on the entire portion where the erosion-resistant layer 3 is formed by spraying, cold spraying, or the like, and the laser at the welded portion is weaved at a high speed in the width direction, thereby The erosion layer 3 is formed. The vibration width of the laser at this time can be made wider than when supplying an erosion-resistant metal material in the form of powder or strip, and there is no overlapping portion of the material, so that defects are hardly generated. .

  Here, the width direction is a lateral direction with respect to the laser traveling direction. The high speed is a speed at which the energy density distribution of the laser at the welded portion is made rectangular instead of mountain-like, and the diluted portion mixed with the base material is made shallow. While normal weaving welding has a frequency of several Hz, in the present embodiment, the frequency is several tens Hz to several hundreds Hz. That is, when the laser is not weaved at a high speed, as shown in FIG. 14, the energy density distribution becomes a mountain shape and the melted portion becomes deep, but by weaving the laser at a high speed, as shown in FIG. The energy density distribution can be flattened, and the melted portion can be made shallower and wider.

  As described above, according to the method of the present embodiment, the number of passes during overlay welding can be reduced, the number of defects can be reduced, and work efficiency can be improved. Further, since the energy density distribution of the laser is flattened, the dilution of the erosion resistant layer 3 by the base material is suppressed. And since dilution by a base material can be reduced, it is possible to form a high-quality erosion-resistant layer 3 having a minimum thickness necessary for erosion resistance.

As described above, according to the method for forming the front edge portion 1A of the steam turbine blade 10 according to the present embodiment, the following operational effects are obtained.
First, the corner portion formed at the front end portion 2A of the groove portion 2 of the base body 1 of the steam turbine blade 10 is formed into an arc-shaped cross section having a radius R longer than the thickness of the base body 1, whereby the heat of the corner portion at the time of welding is obtained. You can relieve the masses. Conventionally, the corner portion has an arc-shaped cross section having a radius R ₀ shorter than the thickness of the base body 1. However, such a cross-sectional shape of the base body 1 is unlikely to dissipate heat accumulated from the weld metal. . On the other hand, by making the arc shape of the corner cross section gradual as in the present embodiment, heat is radiated from the base 1 and local temperature rise can be suppressed. As a result, the dilution of the weld metal due to the mixing of the base material into the weld metal can be reduced, and the decrease in the hardness of the erosion-resistant layer 3 can be suppressed.

Further, by making the rear end portion 2B of the groove portion 2 of the base body 1 of the steam turbine blade 10 as deep as possible from the planned finish surface S of the erosion-resistant layer 3, a dilution region where the base material is mixed with the weld metal is formed in the steam. It can be located not on the surface side of the turbine blade 10 but on the inner side. As a result, the diluted region whose hardness has been reduced due to the mixing of the base material into the weld metal is unlikely to appear on the surface, so that the steam turbine blade 10 having the erosion-resistant layer 3 whose hardness is ensured can be formed.
On the other hand, as shown in FIG. 12, when the depth of the groove 2 is shallow, the dilution region with low hardness is close to the planned finished surface S of the erosion-resistant layer 3, and the erosion-resistant performance may be reduced.

  Moreover, since the depth of the groove part 2 is a depth in which the weld metal is buried in one layer, an increase in the temperature of the base material in the case of multilayer welding can be suppressed, and the dilution rate of the weld metal can be reduced.

  In addition, by increasing the amount of overlap of each pass during welding and reducing the number of parts where the weld bead contacts the base metal, dilution of the weld metal due to the base metal mixed into the weld metal is reduced, and an erosion-resistant layer 3 can be suppressed.

Furthermore, by applying laser welding, the welding operation can be automated, the welded portion can be properly formed, and the amount of heat input to the base material can be suppressed to reduce the dilution rate of the deposited metal.
In the welding method described above, the erosion-resistant layer 3 formed in the groove 2 is formed by welding one layer so that the dilution with the base material is 10% or less.

  FIGS. 7 and 8 show that when the thickness of the substrate 1 is 4.6 mm, the radius of the corner is 7.8 mm, the groove depth is 0.8 mm, and the lap amount of each welding pass is 3.2 mm. It is an example of the cross section when performing. <> Indicates the order of the paths.

  9 and 10 show the results of the Vickers hardness measurement test when the erosion-resistant layer 3 is formed by overlay welding in the order of FIGS. 7 and 8, respectively. The unit of numerical values in <> is hardness Hv. The measurement point corresponds to the planned finished surface S of the erosion resistant layer 3. From the measurement results, it was found that the planned finished surface S had a value exceeding the hardness Hv400, and it was confirmed that the erosion-resistant layer 3 having a hardness of Hv400 or higher can be formed.

  In the present embodiment, the case of laser welding has been described for the joining of the erosion-resistant layer 3, but the present invention is not limited to this example, and even in the case of other welding methods such as TIG welding, By forming the shape and the erosion-resistant layer 3 in the same manner as described above, the same effects as those in the above-described embodiment can be obtained.

DESCRIPTION OF SYMBOLS 1 Base | substrate 2 Groove part 3 Erosion-resistant layer 10 Steam turbine blade 11 Laser tip part 12 Shroud part S Plane finish surface

Claims (8)

A method of welding an erosion resistant metal material to a base body at a leading edge of a turbine blade,
Forming a groove on the substrate based on a predetermined finish surface of the erosion-resistant layer and a thickness of the erosion-resistant layer so that the erosion-resistant metal material is filled in one layer. When,
Welding the erosion resistant metal material to the groove;
An erosion resistant metal material welding method comprising:   The erosion resistant metal material welding method according to claim 1, wherein a depth of the groove is 2 mm or less with respect to the planned finish surface. Determining the overlapping amount of each pass during welding so that a contact portion between a newly formed bead and an already formed bead is formed wider than a contact portion with the base body;
Welding the erosion resistant metal material to the substrate based on the amount of overlap;
The erosion resistant metal material welding method according to claim 1, further comprising:   4. The method for welding an erosion-resistant metal material according to claim 1, wherein the welded erosion-resistant metal material has a dilution with the base material of 10% or less. 5.   The erosion resistant metal material welding method according to any one of claims 1 to 4, wherein the erosion resistant layer before finishing formed by welding the erosion resistant metal material is 2 mm or less per layer. .   6. The welding according to claim 1, wherein the step of welding the erosion resistant metal material comprises weaving a laser in a direction transverse to a traveling direction so that an energy density distribution is flattened. Method for welding erosion resistant metal materials.   The erosion-resistant metal according to claim 6, wherein the erosion-resistant metal material is welded while being supplied in the form of a powder or a strip, or the erosion-resistant metal material is welded after previously being sprayed or cold sprayed on the welded portion. Material welding method.   A turbine blade in which an erosion-resistant layer is formed on a leading edge portion by the welding method for an erosion-resistant metal material according to any one of claims 1 to 7.

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