JP2019005784A - High-temperature slide member and steam turbine - Google Patents

Abstract

To provide a high-temperature slide member that prevents abnormal hardening from occurring in a padding weld part due to high temperature during use, and that can prevent cracking from occurring in the padding weld part due to reduction in toughness accompanying abnormal hardening, without causing increase in cost or work period problems in manufacturing the high-temperature slide member.SOLUTION: A high-temperature slide member comprises a base material part made of an iron based material, and a padding weld part formed on a surface of the base material part using a Co-Cr based heat-resistant alloy. In the high-temperature slide member, a dilution rate with a base material component falls into a range of 10-30%, in a region within a range of 0.2 mm-0.8 mm from a boundary surface of the base material part in a thickness direction of the padding weld part.SELECTED DRAWING: Figure 2

Description

  The present invention relates to a sliding member and a steam turbine used at high temperatures.

  For example, valve bodies and valve seats in steam valves of steam turbines have thermal shock resistance and corrosion resistance to prevent wear, cracks and damage due to thermal shock, erosion, corrosion, etc. Conventionally, overlay welding a heat-resistant alloy including a Co-Cr heat-resistant alloy having a hardness higher than that of a base material made of an iron-based material, that is, an alloy known as a trade name "Stellite", to a portion in contact with a counterpart material It is made from.

  Techniques for improving the performance of this type of Co-Cr heat resistant alloy build-up welded part (contact part with the mating material), particularly attempts to suppress the occurrence of cracks in the build-up welded part have been hitherto. Has been made.

  For example, in Patent Document 1, as a steam valve used in a steam turbine or the like, slit portions are formed at intervals in the circumferential direction of the stellite build-up portion, and the linear expansion coefficient of an embedded member, preferably a valve base material, is formed in the slit portion. A steam valve provided with an embedded member having a linear expansion coefficient intermediate to that of stellite has been proposed. According to this proposal, it is said that the residual stress in the circumferential direction of the stellite build-up portion is relieved, and the occurrence of cracks in the build-up portion can be relieved.

  Patent Document 2 shows that, as a high-temperature sliding member such as a steam turbine valve, a Ni-based alloy having a large ductility is formed on the surface of the base material before stellite build-up, and stellite build-up is performed thereon. Has been. According to the technique of this patent document 2, it is supposed that the generation of cracks mainly due to thermal stress can be prevented.

JP 2010-236385 A JP-A-8-215842

  A valve body and a valve seat of a steam valve used in a steam turbine or the like are exposed to a high temperature of, for example, about 500 to 700 ° C. by high-temperature steam during use. However, with conventional conventional valve bodies and valve seats that have been subjected to stellite overlaying on the surface of the base material made of iron-based material, the hardness of the overlay welded part is abnormal during operation at high temperatures during overlay welding. It may increase and the toughness may decrease. Therefore, a crack may occur in the build-up weld due to an impact or thermal stress caused by a valve opening / closing operation during use.

However, in the technique of Patent Document 1, it is inevitable that abnormal hardening occurs at a high temperature during operation as described above, and it is difficult to reliably avoid the problem of cracking due to opening / closing impacts and the like due to the abnormal hardening. is there.
Moreover, in the technique of patent document 2, since Ni-based alloy is built up prior to stellite build-up, the production cost is inevitably increased, and there is a problem in terms of construction period.

  The present invention has been made against the background described above, and as a high-temperature sliding member that comes into contact with a mating material at high temperatures, it prevents abnormal hardening from occurring in the weld overlay due to high temperatures during use, and is accompanied by abnormal hardening. A high-temperature sliding member that can prevent cracks in the weld overlay due to a decrease in toughness, and that does not cause high cost or construction problems in its production, and It is an object to provide a steam turbine using this.

  The present inventors have conducted extensive experiments and studies in order to solve the above-mentioned problems. As a result, the state and extent of the dissolution (dilution) of the base material component in the overlay metal is abnormally hardened due to use at a high temperature. It has been newly found that it greatly affects the occurrence of And it discovered that the said subject could be solved by managing appropriately the dilution by a base material component, and came to make this invention.

  Specifically, the high-temperature sliding member of the basic aspect (first aspect) of the present invention is formed on the surface of the base material part by a base material part made of an iron-based material and a Co—Cr heat resistant alloy. The dilution ratio by the base material component is 10 in the region within the range of 0.2 mm to 0.8 mm from the interface with the base material part in the thickness direction of the buildup weld part. It is characterized by being in the range of ˜30%.

  Here, in forming the build-up weld on the surface of the base material portion, the base material component dissolves into the weld metal, and the component of the build-up material (the filler material) is diluted by the base material component. According to the knowledge of the present inventors, when a large amount of Fe, which is the main component of the base material, is melted into the overlay weld made of the Co—Cr heat resistant alloy, the temperature is about 500 ° C. to 700 ° C. During use, it has been found that σ phase, which is an Fe—Cr intermetallic compound, precipitates in the weld overlay due to thermal aging. Since the σ phase is extremely hard, if a large amount of σ phase precipitates, the weld overlay will be abnormally hardened and the toughness will be reduced. It tends to occur.

  However, according to said 1st aspect, the dilution rate by a base material component in the area | region in the range of 0.2 mm-0.8 mm from the interface with a base material part in the thickness direction of a build-up weld part is 30. By controlling to less than%, the generation of σ phase due to thermal aging during use at high temperatures is suppressed, thereby avoiding abnormal hardening and minimizing the risk of cracking in overlay welds. It becomes possible to limit to the limit. Further, by setting the dilution rate to 10% or more, it is possible to avoid the occurrence of poor fusion at the interface between the build-up weld and the base material. Moreover, since it is not necessary to build up the Ni-based alloy prior to the build-up of stellite (Co—Cr heat-resistant alloy), such as the technique shown in Patent Document 2, there is little increase in cost in the production, Moreover, productivity is not inhibited.

  The high temperature sliding member according to the second aspect of the present invention is characterized in that, in the high temperature sliding member according to the first aspect, the dilution ratio is in a range of 12 to 28%. To do.

  Moreover, the high temperature sliding member of the third aspect of the present invention is the high temperature sliding member of the first aspect or the second aspect, wherein the dilution rate is the Fe concentration in the region of the build-up weld. The Co concentration is a value calculated from one of the concentrations, or an average value of a value calculated from the Fe concentration and a value calculated from the Co concentration.

  The high temperature sliding member according to the fourth aspect of the present invention is the high temperature sliding member according to any one of the first to third aspects, wherein the Co—Cr heat-resistant alloy is contained in mass% and Cr: 24 to 32%, W: 0 to 20%, C: 0.2 to 3.5%, Mo: 0 to 6%, Ni: 0 to 25%, Fe 3% or less, the balance being made of Co and impurities It is characterized by.

  Moreover, the high temperature sliding member according to the fifth aspect of the present invention is the high temperature sliding member according to any one of the first to fourth aspects, wherein the iron base material constituting the base material portion contains Fe of 75 mass% or more. It is characterized by being heat-resistant steel.

  A high temperature sliding member according to a sixth aspect of the present invention is the high temperature sliding member according to any one of the first to fifth aspects, wherein the high temperature sliding member is a valve body or valve of a steam valve in a steam turbine. It is a seat.

  A steam turbine according to a seventh aspect of the present invention is characterized in that the high temperature sliding member according to any one of the first to fifth aspects is used for a valve body or a valve seat of a steam valve.

  According to the high temperature sliding member of one aspect of the present invention, abnormal hardening is prevented from occurring in the build-up weld due to high temperature during use, and cracks occur in the build-up weld due to a decrease in toughness associated with abnormal hardening. This can be prevented, and there is no problem of cost increase or construction period in the production.

It is a longitudinal cross-sectional view which shows an example of the valve body used for the steam valve of a steam turbine as a high temperature sliding member of one Embodiment of this invention. It is an enlarged view of the circled part II in FIG. It is a graph which shows the relationship between the heating time and Vickers hardness in various dilution rates at the time of heating to 600 degreeC about the member which carried out the overlay welding of the Co-Cr type heat-resistant alloy to the base material which consists of iron base materials. . It is a graph which shows the relationship between the dilution rate of a build-up weld part, and the Vickers hardness of the build-up weld part after a driving | operation in a real steam turbine. It is a graph which shows the relationship between the dilution rate of a build-up weld part, and a fusion defect generation | occurrence | production probability.

  The high temperature sliding member of one embodiment of the present invention will be described below. In addition, the following embodiment shows as an example applied to the valve body of the steam valve of a steam turbine.

<Overall configuration of valve body>
In FIG. 1, the whole shape of the valve body 1 of the steam valve as a high temperature sliding member is shown.
In FIG. 1, the overall shape of the valve body 1 may be the same as that of the steam valve of the steam turbine. This valve body 1 has a portion of the base material portion 2 made of an iron-based material that contacts the valve seat portion of a valve seat (not shown) that is a counterpart material, that is, a Co- The build-up weld 3 is formed by overlay welding of a Cr-based heat resistant alloy. This build-up weld 3 is enlarged and shown in FIG.

  In the overlay welding part 3, as already described, as a result of melting the base material surface part at the time of overlay welding, the base material component melts, and the Co—Cr heat-resistant alloy as the overlay material becomes the base material. Diluted by the ingredients. The situation in which the component of the base material part 2 is dissolved in the build-up weld 3 is schematically represented by dots in FIG.

In this embodiment, the degree of dilution of the weld metal by the base material component is generally referred to as a dilution rate. However, in the present embodiment, in the build-up weld portion 3, the base material is arranged in the thickness direction as will be described later. The dilution rate Pz by the base material component in the region Z within the range of 0.2 mm to 0.8 mm from the interface 4 with the part is defined. That is, the dilution rate in the region Z is in the range of 10 to 30%, preferably in the range of 12 to 28%.
The thickness of the build-up weld 3 (thickness of the cross-section of the build-up weld in the direction perpendicular to the surface of the base metal part) is not particularly limited, but the valve body and valve seat of a steam valve of a general steam turbine are not limited. In this case, it is about 2 to 5 mm.

<Material of base material>
The iron base material that is the material of the base material (base material) is preferably an Fe-based heat-resistant material conventionally used for a valve body or valve seat of a steam valve, that is, a material called heat-resistant steel. Although not limited to this, for example, a heat resistant steel containing 75 mass% or more of Fe and containing one or more alloy elements for improving heat resistance such as Cr, Mo, V, W, and Nb is preferable. The steel type and steel component of the heat-resistant steel are not particularly limited, but typical examples include Cr steel such as 9Cr steel and 12Cr steel, Cr—Mo steel, Cr—Mo—V steel, and the like. Specifically, for example, SUH1, SUH3, SUH4, SUH11, SUH600, SUH616, or similar heat resistant steels defined in JIS G 4311 may be used.

<Building material>
As a build-up material (melting material) added at the time of build-up welding, a Co—Cr heat resistant alloy known as a trade name “Stellite” or a Co—Cr heat resistant alloy similar to Stellite is used. The component composition of this Co—Cr heat-resistant alloy is, for example, mass%, Cr: 24-32%, W: 0-20%, C: 0.2-3.5%, Mo: 0-6%, Preferably, Ni is 0 to 25%, Fe is 3% or less, and the balance is Co and impurities.

<Dilution ratio>
In general, the dilution ratio due to the base metal component in the overlay weld is the average dilution ratio P ₀ of the entire overlay weld as viewed in a cross section perpendicular to the base metal surface. If the cross-sectional area of A is A and the cross-sectional area of the base material portion melted during overlay welding is B, the following equation (1):
P ₀ (%) = (B / A) × 100 (1)
Usually, it is prescribed | regulated by.

However, in a built-up weld with a certain thickness, such as a valve body or valve seat of a steam valve, the amount of the base material component is large in the vicinity of the interface with the base material, and on the surface of the build-up weld, The amount of melted is small or zero. In general, in overlay welding of actual valve bodies and valve seats, it is common to repeat a plurality of build-up welding passes and to have a structure in which multiple layers of beads are laminated. In the bead part by the first pass on the base material side, the amount of the base material component is larger, and the upper part bead part is the smaller the amount of the base material component.
As a result, the amount of σ phase generated due to heat aging due to the melting of Fe, which is the main component of the base material, also increases in the vicinity of the interface with the base material, and there is a risk of cracking due to the accompanying increase in hardness. It grows near the interface.

Therefore, in the present embodiment, the dilution rate Pz in the region of 0.2 mm to _0.8 mm is defined from the interface in the thickness direction of the buildup weld, not the average dilution rate P0 of the entire buildup weld. Yes.
Specifically, the component amount (concentration) of the specific component of the analyzed weld metal in the region Z (the metal in the weld zone after build-up welding) is Q1, the overlay material supplied for overlay welding If the component amount (concentration) of the same specific component of (filler material) is Q2, and the component amount (concentration) of the same specific component of the base material is Q3,
Dilution rate Pz (%) = {(Q1-Q2) / (Q3-Q2)} × 100 (2)
Thus, the dilution rate Pz (%) in the region Z can be calculated.

  Here, the base material contains Fe as a main component, while the build-up material does not contain Fe or is contained in a trace amount, so Fe is used as the specific component, and depending on the amount of Fe It is preferable to calculate the above equation (2).

  On the other hand, the base material contains little or no Co, and the build-up material contains a large amount of Co. The degree to which the amount of Co is reduced by diluting the overlay metal can also be regarded as the dilution rate. Therefore, Co can be used as the specific component, and the above equation (2) can be calculated based on the amount of Co.

  Here, since the value of the dilution rate Pz calculated with Fe as the specific element is the same as the value of the dilution rate Pz calculated with Co as the specific element, the dilution rate Pz (%) is calculated by the above equation (2). In the calculation, either Fe or Co may be used as the specific element.

  However, there may be a difference between the value of the dilution rate Pz calculated using the specific element as Fe and the value of the dilution rate Pz calculated using the specific element as Co due to variations in the distribution of dilution components, analysis errors, and the like. Therefore, when such a situation is a concern, the dilution rate Pz of the formula (2) is calculated by Fe, the dilution rate Pz of the formula (2) is calculated by Co, and the average value thereof is used as the final value. It is desirable to set the dilution ratio to be constant.

  In addition, although the measuring method of the component amount (concentration) of the specific component in the weld metal in Formula (2) is not specifically limited, For example, the semi-quantitative value measured with the electron beam microanalyzer can be used.

  Further, the dilution rate Pz in the region of 0.2 mm to 0.8 mm in the thickness direction of the weld overlay from the interface is measured at five locations at equal intervals in the thickness direction of 0.2 mm to 0.8 mm. Means the average value.

<Reason for limiting dilution: Upper limit>
Here, if the dilution rate Pz in the above-mentioned region Z exceeds 30%, the σ phase is likely to precipitate rapidly when heated to a temperature of about 500 to 700 ° C., and the hardness due to σ phase precipitation in a short time. An increase occurs and the possibility of cracking increases. Such a relationship between the dilution rate and the hardness is a novel finding of the present inventors.

  That is, first, the present inventors performed stress removal annealing (SR) at 700 ° C. for 3 hours on an overlay welded test piece with various dilution ratios Pz, and then simulated the use environment at a high temperature. FIG. 3 shows the results of examining the relationship between the heating time and the Vickers hardness of the overlay weld when heated to 600 ° C. for various times as heating. In this experiment, 12Cr steel was used as a base material, and Co: -Cr heat resistant alloy as a build-up material was Cr: 24.0-32.0%, C: 0.2-3.5%, Fe <3. Overlay welding was performed by plasma powder overlay welding using an alloy consisting of 0.0% and the balance Co and impurities.

  As shown in FIG. 3, it can be seen that when the dilution rate Pz is 52.0%, the hardness suddenly increases from the vicinity where the heating time at 600 ° C. exceeds 1000 hours, and abnormal hardening occurs. On the other hand, it can be seen that when the dilution rate Pz is 30% or less, the hardness hardly increases even when the time exceeds 1000 hours, and abnormal hardening does not occur.

Based on the experimental results shown in FIG. 3, the present inventors further described, as a lot of actual machine data about the valve body of the steam valve in the steam turbine, the Vickers of the overlay weld after being exposed to high-temperature steam at 500 ° C. or higher. The results of examining the relationship with hardness are shown in FIG.
In addition, the valve body of this actual machine data uses 12Cr steel and 2.25CrMo steel as a base material, and Co: Cr heat-resistant alloy of overlay material: Cr: 24.0 to 32.0%, C: 0.2 Overlay welding was performed by plasma powder overlay welding using an alloy consisting of ~ 3.5%, Fe <3.0%, the balance being Co and impurities.

  It can be seen from FIG. 4 that the higher the dilution rate, the higher the hardness, and in particular, the hardness increases rapidly when the dilution rate is around 30%. It has been found that if the dilution rate is 30% or less, the hardness does not increase, and particularly if it is 28% or less, the hardness can be maintained at a stable level. Therefore, the upper limit of the dilution rate Pz is set to 30%, preferably 28%.

<Reason for limiting dilution rate: Lower limit>
On the other hand, if the dilution rate Pz is less than 10%, poor fusion between the build-up weld and the base material tends to occur. That is, the interface between the base metal and the weld metal is not sufficiently fused, and there is a greater risk that cracks will occur from the boundary.

That is, the present inventors have found from a large number of actual machine data about the valve body of the steam valve in the actual steam turbine that the dilution rate and the probability of occurrence of poor fusion have a relationship as shown in FIG. Yes.
In addition, the actual valve body made into object here uses 12Cr steel and 2.25CrMo steel as a base material, Cr: 24.0 to 32.0%, C: 0 as a Co—Cr heat-resistant alloy as a build-up material .2 to 3.5%, Fe <3.0%, the balance welding was performed by the plasma powder overlay welding method using an alloy composed of Co and impurities.

  From FIG. 5, it can be seen that the lower the dilution rate, the more likely the fusion failure occurs. In particular, when the dilution rate is less than 10%, the fusion failure is likely to occur. When the dilution rate is 10% or more, the tendency of occurrence of poor fusion is saturated, and particularly when the dilution rate is 12% or more, the tendency of poor fusion is hardly changed. Therefore, the lower limit of the dilution rate Pz is set to 10%, preferably 12%.

<Dilution ratio adjustment method>
Although the method for controlling the dilution rate Pz to 10 to 30%, preferably 12 to 28% is not particularly limited, for example, at the time of overlay welding, the supply speed of the overlay material (in powder overlay welding) The dilution rate can be adjusted by controlling the supply amount of the powder per unit time) and the build-up welding speed (bead progression speed). For example, if the supply speed or welding speed of the build-up material is increased, the penetration of the base material component into the build-up weld is reduced, and the dilution rate is reduced. Therefore, the relationship between the supply rate of the overlaying material, the welding speed and the dilution is obtained by experiments and actual data, and based on this, the supply rate of the overlaying material and the welding are adjusted so that the dilution rate is within the above range. What is necessary is just to perform overlay welding by setting a speed | rate appropriately.

  The build-up welding method is not particularly limited, but the plasma powder build-up welding method is suitable for the valve body and valve seat of the steam valve of the steam turbine. In addition, the TIG welding method, the laser welding method, and the like are also applicable. .

  The high-temperature sliding member of the present invention is optimal for a valve body or a valve seat of a steam valve of a steam turbine, but can also be applied to a valve for other uses, for example, a valve body or a valve seat of an engine valve. Can also be applied to sliding parts used at high temperatures other than valves, such as bushes.

  Although the preferred embodiment of the present invention has been described above, this embodiment is merely an example within the scope of the gist of the present invention, and additions and omissions of configurations are within the scope not departing from the gist of the present invention. , Substitutions, and other changes are possible. That is, the present invention is not limited by the above description, is limited only by the scope of the appended claims, and can be appropriately changed within the scope.

DESCRIPTION OF SYMBOLS 1 ... Valve body 2 as a high temperature sliding member ... Base material part 3 ... Overlay welding part 4 ... Interface Z ... Area | region

Claims (7)

A base metal part made of an iron-based material, and a weld overlay formed on the surface of the base metal part by a Co-Cr heat-resistant alloy,
That the dilution ratio by the base material component is in the range of 10 to 30% in the region within the range of 0.2 mm to 0.8 mm from the interface with the base material part in the thickness direction of the build-up weld. High temperature sliding member characterized.   The high-temperature sliding member according to claim 1, wherein the dilution rate is in a range of 12 to 28%.   The dilution rate is a value calculated from one of the Fe concentration and the Co concentration, or an average value of a value calculated from the Fe concentration and a value calculated from the Co concentration. The high temperature sliding member according to any one of claims 1 and 2.   The Co—Cr heat resistant alloy is in mass%, Cr: 24 to 32%, W: 0 to 20%, C: 0.2 to 3.5%, Mo: 0 to 6%, Ni: 0 to 25 The high-temperature sliding member according to any one of claims 1 to 3, wherein the high-temperature sliding member contains Co and impurities.   The high-temperature sliding member according to any one of claims 1 to 4, wherein the iron-based material is heat resistant steel containing 75 mass% or more of Fe.   The high temperature sliding member according to any one of claims 1 to 5, wherein the high temperature sliding member is a valve body or a valve seat of a steam valve in a steam turbine.   A steam turbine, wherein the high-temperature sliding member according to any one of claims 1 to 5 is used for a valve body or a valve seat of a steam valve.

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