Welding process for overlay welding of erosion-resistant metal material and turbine blade

Abstract

Welding method for the surfacing of erosion-resistant metal material, which is a method of welding erosion-resistant metal material onto a base element (1) of a turbine blade leading edge section, wherein the method comprises the steps: Providing a front end section (2A) of a recess (2) with a corner which is formed in a cross-sectional arc shape with a radius (R) greater than the thickness of the base element (1), wherein the recess (2) is designed such that no area of ​​reduced hardness occurs on any surface of the layer, and the depth (D) of the rear end section (2B) of the recess (2) is equally suitable for the erosion-resistant metal material to be filled in a single layer; and Welding the erosion-resistant metal material onto the flow edge section.

Description

Field of the invention

[0001] The present invention relates to a welding method for overlaying erosion-resistant metal material and a turbine blade. Technical background of the invention

[0002] A steam turbine blade is subject to wear and tear due to the impact of fine, solid particles, mainly composed of condensed water droplets and iron oxide in the steam. Therefore, an erosion-resistant layer is sometimes formed on a leading edge portion of the steam turbine blade (an upstream side of the steam flow). As a result, erosion of the steam turbine blade is reduced.

[0003] JP S61-12082 B2 discloses a technique for reducing erosion-induced wear by bonding an erosion shield to a base member of a steam turbine blade, the erosion shield having a boronized layer on its surface. Additionally, JP 4 901 413 B2 describes a leading edge portion as part of a blade shape of a turbine rotor blade, which is cut and in which an erosion prevention portion is restored in the leading edge portion of the blade using laser build-up welding.

[0004] US 2009 / 0162207 A1 discloses a method for producing an erosion protection layer made of steel by laser deposition welding onto the leading edge of rotating turbine blades. A material with a high chromium content is welded to the metallic substrate by laser deposition welding. A recess is created in the metallic substrate, and the recess is filled with the erosion protection layer.

[0005] JP 2008 / 128147 A describes a repair process for the high-temperature part of a turbine blade in which overlapping weld layers are arranged next to each other.

[0006] DE 43 10 896 C1 also describes a method for producing wear-resistant edges on turbine blades, wherein, before applying the edge protection, a recess is made at the corresponding point on the blade and a layer of powder is introduced into the recess by low-pressure plasma spraying or by means of capsule technology, which layer is then compacted by hot isostatic pressing.

[0007] JP H01-182 504 A proposes to improve the erosion resistance of a turbine blade by forming a recess on a steam inlet part of a turbine blade made of a titanium alloy and thermally spraying a heat-treatable titanium alloy onto the recess, then heating and melting the thermally sprayed part and performing a heat-treatment treatment. Description of the inventionTechnical problem

[0008] For an erosion-resistant layer bonded to a base member of a steam turbine blade, for example, a cobalt-based alloy with high wear resistance, such as Stellite (registered trademark), which consists of cobalt as a main component, or the like, is used. When bonding the cobalt-based alloy or the like to the base member, hardfacing is performed by brazing or TIG welding. Unfortunately, if a joint is formed using brazing, defects such as joint failure are likely to occur, and deterioration of the steam turbine blade is likely to occur due to repeated heating for post-processing.If the joining is performed using TIG welding, there is an additional problem in that the base material is mixed with the deposited metal, which is, for example, a cobalt-based alloy, which dilutes the deposited metal. As a result, the hardness of the erosion-resistant layer decreases, thus deteriorating the erosion resistance of the cobalt-based alloy or the like.

[0009] In a technique described in JP 4 901 413 B2, as in Fig. 1(c) of JP 4 901 413 B2, after a blade leading edge portion of a turbine rotor blade is cut along a longitudinal direction of the blade such that a band-shaped plane is formed, multiple layers are formed on the plane to form an erosion-preventing portion made of hard material. Fig. Fig. 16 is a cross-sectional view illustrating a base member 1 of a leading edge portion 1A of a conventional steam turbine blade and welding beads constituting an erosion prevention portion, wherein two-point chain lines in Fig. 16 illustrates a predetermined finished surface S of the erosion prevention portion. Since the hard material is brittle compared to the material of the blade body portion, the erosion prevention portion may detach or break away from the blade body portion if the entire blade leading edge portion is replaced as described in JP 4 901 413 B2.

[0010] The present invention has been made in view of the circumstances described above, and it is an object of the present invention to provide a method of welding erosion-resistant metal materials and a turbine blade capable of restraining deterioration of the hardness of an erosion-resistant layer at a blade leading edge portion. Solution to the problem

[0011] This object is achieved by a welding method for the build-up welding of erosion-resistant metal material having the features of claim 1 or 2 and / or by a turbine blade having the features of claim 9. Further embodiments emerge from the dependent claims.

[0012] According to the present invention, it is possible to reduce the degradation of the hardness of an erosion-resistant layer in a blade leading edge portion. Short description of the drawings Fig. 1 is a cross-sectional view illustrating a base member of a leading edge portion of the steam turbine blade according to an embodiment of the present invention. Fig. 2 is a cross-sectional view illustrating a base member of a leading edge portion of a steam turbine blade according to an embodiment of the present invention. Fig. 3 is a cross-sectional view illustrating a base member and weld beads of a leading edge portion of a steam turbine blade according to an embodiment of the present invention. Fig. 4 is a cross-sectional view illustrating a base member and weld beads of a leading edge portion of a steam turbine blade according to an embodiment of the present invention. Fig. 5 is a cross-sectional view illustrating a base member and weld beads of a leading edge portion of a steam turbine blade according to an embodiment of the present invention. Fig. 6 is a cross-sectional view illustrating a base member and weld beads of a leading edge portion of a steam turbine blade according to an embodiment of the present invention. Fig. 7 is a cross-sectional view illustrating a first example of a leading edge portion of a steam turbine blade according to an embodiment of the present invention. Fig. 8 is a cross-sectional view illustrating a second example of a leading edge portion of a steam turbine blade according to an embodiment of the present invention. Fig. 9 is a cross-sectional view showing a result of hardness measurement of the Fig. 7 shown leading edge section. Fig. 10 is a cross-sectional view showing a result of hardness measurement of a Fig. 7 shown leading edge section. Fig. 11 is a side view showing a steam turbine blade. Fig. 12 is a cross-sectional view illustrating a basic element of a leading edge portion of a conventional steam turbine blade. Fig. 13 is a perspective view showing a steam turbine blade. Fig. Figure 14 is a diagram showing a relationship between the laser energy density distribution and a fusion zone when there is no high-speed reciprocating motion of the laser. Fig. Figure 15 is a diagram showing a relationship between the laser energy density distribution and a fusion zone when high-speed reciprocating laser motion occurs. Fig. 16 is a cross-sectional view illustrating a base member and weld beads of the leading edge portion of the conventional steam turbine blade. Detailed description of preferred embodiments of the invention

[0013] Hereinafter, the embodiments according to the present invention will be described with reference to the accompanying drawings.

[0014] First, a structure of the leading edge portion 1A of the steam turbine blade 10 will be described. Fig. 11 is a side view showing the steam turbine blade 10.

[0015] The leading edge portion 1A of the steam turbine blade 10 is formed by bonding an erosion-resistant layer 3 to a base member 1. The erosion-resistant layer 3 is formed of a cobalt-based alloy consisting of cobalt as a main component. The erosion-resistant layer 3 is disposed in the leading edge portion 1A on an upstream side of the steam flow on the steam turbine blade 10 when the steam flow enters due to rotation of the steam turbine blade 10. Accordingly, it is possible to reduce the erosion of the leading edge portion 1A of the steam turbine blade 10.

[0016] The base element 1 (base material) is, for example, a chromium-based alloy and has, before the erosion-resistant layer 3 is formed, a Fig. 1 shown cross-sectional shape. Fig. 1 is a cross-sectional view taken along a direction vertical to a longitudinal direction of the steam turbine blade 10, illustrating the base member 1 for forming the leading edge portion 1A of the steam turbine blade 10. Two-dot chain lines show Fig. 1 the predetermined finished surface S of the erosion-resistant layer 3.

[0017] Before the erosion-resistant layer 3 is formed thereon, the base member 1 is provided with a recess 2 having a shape such that it is recessed into the base member 1 with respect to the predetermined finished surface S. The recess 2 has: a front end portion 2A located on an upstream side of the steam flow when the steam turbine blade 10 is rotated, and a rear end portion 2B located on a downstream side of the steam flow.

[0018] The front end portion 2A of the recess 2 has a corner formed in a cross-sectional shape, for example, in an arc shape. The radius R of the corner is, for example, larger than the thickness t of the base member 1. Therefore, when the erosion-resistant layer 3 is formed by a welding method described later, it is possible to reduce heat accumulation in the base member 1. The cross-sectional shape of the corner of the front end portion 2A is not limited to an arc shape, and other shapes can be adopted as long as heat can be easily dissipated from the base member 1 and a blade tip portion can be formed into a smoothly curved surface.

[0019] It is preferable that a depth D of the recess 2 in the rear end portion 2B with respect to the predetermined finished surface S only allows the deposited metal to be filled in one layer (that is, the depth does not allow multiple layers to be built up by welding), and at the same time, it is formed as deep as possible so that no reduced hardness region occurs on the surface. The depth D of the recess that can be filled by one layer is, for example, 2 mm or less. The reduced hardness region is a region where the base material is mixed into the cobalt-based alloy (which is the deposited metal by welding), and where the erosion resistance imparted by the cobalt-based alloy is deteriorated.

[0020] The erosion-resistant layer 3 formed in the recess 2 is formed by a plurality of passes in such a way that a layer is formed by welding, and has a thickness of 2 mm or less in a state before finishing (see Fig. 7 and Fig. 8). It is preferable that the thinning caused in the erosion-resistant layer 3 by the base material is 10% or less. In order to prevent the base material from melting into the deposited metal, it is additionally preferable that a tip portion 2C of the recess 2, as shown in Fig. 1, instead of being in a pointed shape, it is formed in the form of a plane.

[0021] The erosion-resistant layer 3 is formed of the cobalt-based alloy, which, for example, consists of cobalt as a main component. In the present embodiments, Stellite (registered trademark), for example, can be used as the cobalt-based alloy. The erosion-resistant layer 3 is formed such that weld beads that are adjacent to each other overlap with each other. Each weld bead has a portion that is in contact with the base material and a portion that is in contact with an adjacent weld bead. It is preferable to reduce the portion that is in contact with the base material and to increase the portion that is in contact with the adjacent weld bead (see beads). <3> until <7> in Fig. 7 and bulges <3> until <8> in Fig. 8). The erosion-resistant layer 3 is formed by several passes. After the weld beads have been formed as shown in Fig. 7 and Fig. 8, the leading edge portion 1A is machined to correspond to the predetermined finished surface S as shown in Fig. 1 is represented by a two-point chain line.

[0022] The leading edge section 1A is not coated as a whole with the erosion-resistant metal material (see JP 4 901 413 B2 or Fig. 16), but only a surface layer with a uniform thickness along a shape of the base member 1 is formed from the erosion-resistant metal material. As a result, it is possible to prevent damage to the erosion-resistant layer 3, which is formed from the erosion-resistant metal material, which exhibits brittle behavior compared to the base material 1.

[0023] Next, a method of forming a leading edge portion 1A of the steam turbine blade 10 according to the present embodiments, and more particularly, a method of bonding the erosion-resistant layer 3 to the base material will be described.

[0024] First, the recess 2 is formed in the base element 1 of the steam turbine blade 10, for example in the Fig. 1. That is, the front end portion 2A of the recess 2 is provided with a corner formed into an arcuate cross-sectional shape with a radius R greater than a thickness of the base member 1. In addition, the recess 2 is formed such that no area of reduced hardness occurs on a surface of the layer, and the depth D of the rear end portion 2B of the recess 2 is equally suitable for filling the deposited metal in only one layer.

[0025] Next, a build-up welding is carried out by laser welding on the base element 1 having a shape as described above, so that the erosion-resistant layer 3 is formed layer by layer. The build-up welding is carried out in multiple passes, as indicated by the reference numerals in angle brackets in Fig. 7 or Fig. 8. Each of the Fig. 7 or Fig. 8 shows an example in which a method of executing the passes is different.

[0026] It is possible to reduce the amount of base material mixed into the cobalt-based alloy of the overlay metal by increasing the overlap amount of each welding pass. Increasing the overlap amount reduces the portion of a weld bead that is in contact with the base material. The overlap amount is adjusted, for example, by using a laser target angle and the amount of movement between passes.

[0027] In the case of laser welding, automation is possible, which allows suitable welding to be carried out in each condition by generating a program before welding in such a way that a welding device is able to execute the program.

[0028] For laser welding, ordinary welding equipment is available, and in the present embodiments, laser welding is applied under the following conditions. Specifically, a positioning camera and a height adjustment jig with a height sensor are used. The welding position is always facing downward, and the movement between passes is performed while rotating the base member 1. In a program, a target position of each pass is input as a teaching point by teaching. In addition, a deformed shape of the base member 1 due to the influence of heat during welding is anticipated by setting the passes so that the passes are guided along the deformed shape of the base member 1 in advance.Furthermore, it is possible to implement welding while avoiding the occurrence of positional deviation when feedback is performed using the positioning camera.

[0029] An aiming direction of the laser is approximately 90° with respect to a plane of the base material or approximately 90° with respect to a tangent connecting projections. If the most forward section 11 of the laser is as shown in Fig. 2 shown near a shroud section 12 (see Fig. 13) and the like, a welding program is generated such that the laser aiming direction is set such that the most forward section 11 of the laser is prevented from interacting with a shroud section 12, and that it is nevertheless close to 90° with respect to a tangent connecting two projections in a fusion section. With respect to a flat surface opposite an R-surface, the laser aiming direction is as shown in Fig. 2 also 90°. If as in Fig. 3 and Fig. 4, the laser aiming direction is 90° with respect to a tangent connecting a projection of a bead and a projection of a base material. In addition, the laser aiming direction with respect to a tip portion of the base member 1 is as shown in Fig. 5 parallel to the flat surface. If two beads have already been formed, the laser aiming direction is relative to a tangent connecting a projection of one bead and a projection of the other bead as shown in Fig. 6 is shown at 90°. The determination of a laser targeting direction described above allows for the reduction of the melting error and also prevents the base material from being mixed into the deposited metal.

[0030] During laser welding, oscillations can be applied to a molten section. Consequently, it is possible to reduce welding defects. One method of welding while applying oscillations is as follows.

[0031] While erosion-resistant metal material in powder form is supplied to a melting section in a strip form, the laser is reciprocated in a width direction at high speed at the melting section to form the erosion-resistant layer 3, or the laser is reciprocated in the width direction at high speeds at the welding sections while the erosion-resistant metal material is supplied to the melting section in a strip form with a fixed thickness to form the erosion-resistant layer 3.

[0032] In addition, a layer of erosion-resistant metal material may be formed in advance by thermal spraying or cold spraying in an entire portion where the erosion-resistant layer 3 is to be formed, and then the laser is oscillated at high speed in the width direction at the welded portion to form the erosion-resistant layer 3. This allows for a larger oscillation range of the laser compared to the case where the erosion-resistant metal material is supplied in powder or strip form, and there is no overlapping portion of material. As a result, a defect is unlikely to occur.

[0033] Here, the width direction is transverse to the welding direction of the laser. In addition, the high speed allows the laser energy density distribution at the melting portion to assume a rectangular shape instead of a peak shape, which makes a thinning portion where the base material is mixed flatter. While weaving welding is normally carried out at frequencies of a few Hertz, weaving welding in the present embodiments is carried out at a frequency within the range of a few tens of Hertz to a few hundred Hertz. That is, if the laser is not oscillated back and forth at high speed, the energy density distribution develops as in Fig. 14 into a peak shape, so that a fusion zone is deeper. In contrast, if the laser is oscillated back and forth at high speed, it is possible to obtain the energy density distribution as shown in Fig. 15. As a result, it is possible to make the fusion zone flat and wide.

[0034] As described above, the method of the present embodiments allows the number of passes in deposition welding to be reduced, which reduces the number of defects. As a result, it is also possible to improve work efficiency. Furthermore, since the laser energy density distribution is flattened, the thinning of the erosion-resistant layer 3 by the base material is reduced. Furthermore, since the thinning by the base material can be reduced, it is possible to form the erosion-resistant layer 3 to a minimum thickness required for erosion resistance and high quality.

[0035] According to the method of forming the leading edge portion 1A of the steam turbine blade 10 in accordance with the above present embodiments, the following operational effects can be obtained.

[0036] First, a corner to be formed in the leading end portion 2A of the recess 2 of the base member 1 of the steam turbine blade 10 is formed into an arc shape having a radius R in cross section that is larger than a thickness of the base member 1, so that it is possible to reduce heat accumulation at the corner during welding. Conventionally, the corner was formed into an arc shape in cross section having a radius R0 shorter than the thickness of the base member 1, and such a cross-sectional shape of the above base member 1 does not allow the heat accumulated by receiving deposited metal to be easily dissipated. On the other hand, if an arc shape of the corner is formed smoothly in cross section as in the present embodiments, heat is dissipated from the base member 1, allowing local temperature increases to be reduced.As a result, it is possible to reduce the dilution of the deposit metal caused by mixing the base material into the deposit metal to reduce the reduction of hardness in the erosion-resistant layer 3.

[0037] In addition, the rear end portion 2B of the recess 2 on the base member 1 of the steam turbine blade 10 is formed to be as deep as possible with respect to the predetermined finished surface S of the erosion-resistant layer 3, so that it is possible to arrange a thinning region where the base material is mixed into the deposited metal inside the steam turbine blade 10 rather than on the surface side of the steam turbine blade 10. As a result, the thinning region where the hardness is reduced by the mixing of the base material into the deposited metal hardly occurs on the surface of the steam turbine blade 10, so that it is possible to provide a steam turbine blade 10 provided with an erosion-resistant layer 3 in which the hardness is ensured.

[0038] If the recess 2 is flat, a thinning area with low hardness as in Fig. 12, arranged near the predetermined finished surface S of the erosion-resistant layer 3. Therefore, the erosion resistance may be reduced.

[0039] Since the depth of the recess 2 is suitable for the deposited metal to be filled in a single layer, it is also possible to reduce the temperature rise of the base material, as would occur in multi-layer welding. As a result, it is possible to reduce the dilution rate of the deposited metal.

[0040] Furthermore, it is possible to reduce the dilution of the deposit metal caused by mixing the base material into the deposit metal to reduce the reduction in hardness in the erosion-resistant layer 3 by increasing the overlap amount of each pass in welding to reduce a portion of a weld bead in contact with the base material.

[0041] Furthermore, the application of laser welding allows the welding process to be automated to ensure proper weld formation and also allows the dilution rate of the deposited metal to be reduced by reducing the heat input into the base material.

[0042] In the welding method described above, the erosion-resistant layer 3 formed in the recess 2 consists of a layer formed by welding such that the dilution of the base material is 10% or less.

[0043] Each of the Fig. 7 and Fig. 8 shows an example of a cross section of a leading edge portion of a steam turbine blade when laser welding is performed under the following conditions: a thickness of the base member 1 is 4.6 mm; a radius of the corner is 7.8 mm; a depth of the recess is 0.8 mm; and the overlap amount of each welding pass is 3.2 mm. The reference numerals in the angle brackets indicate the order of the passes.

[0044] Fig. 9 and Fig. 10 show results of a Vickers hardness measurement test of the erosion-resistant layers 3, which were deposited by build-up welding in the Fig. 7 and Fig.8. The unit of the numerical values in the angle brackets is the hardness Hv. Each of the measurement points corresponds to the predetermined finished surface S of the erosion-resistant layer 3. From the measurement results, it can be seen that values exceeding the hardness Hv 400 are found on the predetermined finished surface S. This verifies that it is possible to form the erosion-resistant layer 3 with a hardness of Hv 400 or more.

[0045] Although in the present embodiments, a case of joining the erosion-resistant layer 3 by laser welding has been described, the invention is not limited to this example, and even if another welding method such as TIG welding is used, it is possible to obtain an operative effect as in the above-described embodiments by forming the shape of the base material and the erosion-resistant layer 3 as described above.

[0046] Although a cobalt-based alloy such as Stellite (registered trademark) was exemplified as the erosion-resistant metal material of the erosion-resistant layer in the present embodiments, a metal material other than the one described above can also be used as the erosion-resistant metal material depending on the base material and the application environment. Any materials expected to exhibit some erosion-resistant effects, such as materials that are harder than the base material, can be used as the erosion-resistant metal material. List of reference symbols 1 basic element 2 recess 3 erosion-resistant layer 10 steam turbine blades 11 most upstream section of the laser 12 shroud section S predetermined finished surface

Claims

[1] A welding method for overlaying erosion-resistant metal material, which is a method of welding erosion-resistant metal material to a base member (1) of a turbine blade leading edge portion, the method comprising the steps of: Providing a front end portion (2A) of a recess (2) with a corner formed into an arcuate shape in cross section with the radius (R) that is greater than a thickness of the base member (1), wherein the recess (2) is formed such that no area of reduced hardness occurs on a surface of the layer, and the depth (D) of the rear end portion (2B) of the recess (2) is equally suitable for the erosion-resistant metal material to be filled in only one layer; and Welding the erosion-resistant metal material onto the leading edge section. [2] A welding method for overlaying erosion-resistant metal material, which is a method of welding erosion-resistant metal material to a base member (1) of a turbine blade leading edge portion, the method comprising the steps of: Forming a recess (2) in the base element (1) into which erosion-resistant metal material is applied, depending on the thickness of a predetermined finished surface (S) of an erosion-resistant layer (3) and the erosion-resistant layer (3) such that the erosion-resistant metal material is filled in one layer; and Welding the erosion-resistant metal material to the recess (2); wherein the recess (2) has a depth (D) such that a region in which the base member (1) is mixed into the erosion-resistant metal material by welding does not appear on the finished surface, and wherein the dilution produced in the erosion-resistant layer (3) by the base member (1) is 10% or less. [3] A welding method for surfacing erosion-resistant metal material according to claim 2, wherein a depth (D) of the recess (2) with respect to the predetermined finished surface is 2 mm or less. [4] A welding method for surfacing erosion-resistant metal material according to any one of claims 1 to 3, wherein the overlap amount of each pass in welding is set such that a contact portion between a newly formed bead and an existing bead is wider than a contact portion between the newly formed bead and the base member (1). [5] A welding method for overlaying erosion-resistant metal material according to any one of claims 1 to 4, wherein the dilution of the welded erosion-resistant metal material by material of the base member (1) is 10% or less. [6] A welding method for surfacing erosion-resistant metal material according to any one of claims 1 to 5, wherein the erosion-resistant layer (3) formed by welding the erosion-resistant metal material before finishing consists of one layer and is 2 mm or less in thickness. [7] A welding method for surfacing erosion-resistant metal material according to any one of claims 1 to 6, wherein the step of welding the erosion-resistant metal material has a feature of oscillating a laser transversely to a welding direction to flatten the distribution of energy density. [8] A welding method for depositing erosion-resistant metal material according to claim 7, wherein the erosion-resistant metal material is welded while being supplied in powder form or in tape form, or is welded after the erosion-resistant metal material is deposited on a welding portion in advance by thermal spraying or cold spraying. [9] Turbine blade (10) with: a leading edge section; and an erosion-resistant layer (3) formed in the leading edge portion by the welding method for overlaying erosion-resistant metal material according to one of claims 1 to 8.

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