JPS61229481A - High temperature and high pressure steam turbine and welding method - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Application of the Invention] The present invention is applicable to a temperature of 600 to 650° C. and a pressure of 50 Q.
The present invention relates to a high-temperature, high-pressure turbine that uses steam of 550 kg and 7 cm, and a new welding method that is particularly suitable for forming welds therein.

[Background of the invention]

Traditionally, main steam at 538°C is used in the steam turbine, and
-MQ-V cast steel, 2-C! r-IMo steel, also Ha27Or
-The casing and main steam pipe were made of Mo-V steel. However, in response to demands for improved efficiency of power plants, high-temperature, high-pressure power plants in which the main steam temperature is, for example, 600° C. or higher are being considered.

Figure 1 shows steam temperature of 600 to 650℃ and pressure of 300 to 5℃.
50 kL4/cm" steam turbine; FIG.

In FIG. 1, numeral 1 is a live steam pipe, 2 is a telescopic tube, 5 is a blade, 4 is a rotor shaft, 5 is an internal casing,
6 means the outer casing, 7 means a dissimilar material welding part, and 8 means a same material welding part.

In FIG. 1, main steam at, for example, 650° C. passes through a main steam pipe 1 and an expansion pipe 2, hits a blade 3, and rotates a rotor shaft 4. External casing 6FX550 at that time
Melt in °C.

Austenitic stainless steel (for example, 8U8516) is used for the main steam pipe 1, internal casing 5, valve casing, etc. from the viewpoint of high temperature strength and oxidation resistance.

On the other hand, for the outer casing 6, considering its low temperature of about 550° C., creep strength, and economical efficiency, it is promising to use low-alloy cast steel, which is ferritic cast steel (or forged steel).

Therefore, welding of austenitic cast steels (main steam pipe welding, main stop valve and control valve welding, etc.) for welding austenitic cast steels and welding of austenitic cast steels and low alloy cast steels for 650°C, 352 Y/m steam turbines is recommended. There is welding.

However, as is generally stated, in austenitic cast steel, the austenite structure after solidification does not undergo structural transformation even when it reaches room temperature, and the significantly grown dendrite structure remains as it is [References, for example, the Japan Society for the Promotion of Science, 125th Committee on Research on Heat-Resistant Metallic Materials, Research Report 33
Volume 15, No. 2, pp. 79-91 (1972)].

This extremely coarse structure will not recrystallize and become finer even if it is subjected to solution heat treatment to a high temperature of 1000-1200°C.

However, the larger the crystal grain size, the greater the amount of low melting point impurities (such as P and S) segregated into the crystal boundaries. Therefore, such materials are extremely susceptible to weld hot cracking due to grain boundary segregation of low melting point impurities. Therefore, in order to prevent hot cracking in general austenitic cast stainless steel, the chemical composition is such that it contains more than 10 grams of delta ferrite. However, even if high-temperature cracking can be prevented during the welding process, a material containing several tens of delta ferrites will precipitate a sigma phase and become brittle if heated at 600° C. or higher for a long period of time. Therefore, it cannot be applied to high-temperature, high-pressure steam turbines.

A welding method that can form a welded part with high resistance to hot cracking has not been developed so far.

[Purpose of the invention]

The purpose of the present invention is to maintain main steam at 600 to 650°C and a pressure of 500°C.
An object of the present invention is to provide a steam turbine that can use high-temperature, high-pressure steam of ~s s oh/l-.

Another object of the present invention is to provide a welding method that can form a welded part with high strength without causing hot cracking.

[Summary of the invention]

To summarize the present invention, the first invention of the present invention relates to a high-temperature and high-pressure steam turbine, which comprises a rotor, an inner casing, an outer casing, and a main steam pipe, and the inner casing and the main steam pipe are made of austenite. In a high-temperature, high-pressure steam turbine constructed of stainless steel cast steel,
The structure of the weld heat affected zone in a joint weld and/or repair weld of the same or different materials, at least one of which is austenitic stainless steel cast steel, is characterized by a fine recrystallized structure.

A second invention of the present invention relates to a welding method, which includes a step of cold plastic working a welding groove surface of the welding groove surface, and a step of cold plastic working the weld groove surface, in the method of welding workpieces, at least one of which is austenitic stainless steel cast steel. It is characterized in that it includes each step of the process of performing post-welding.

The present inventors have discovered that the structure of austenitic cast stainless steel is significantly coarsened, and that delta ferrite is about 50-
Finding 9 from all experiments shows that high temperature cracking can be prevented even under the following conditions.

That is, in the present invention, a mechanical impact is applied in advance to the weld groove surface where austenitic stainless steel cast steel is to be welded, thereby plastically deforming the groove surface. However,
By applying plastic deformation to the groove surface, during subsequent welding, the plastic deformation portion recrystallizes due to the welding heat, resulting in a significant increase in microstructure and preventing hot cracking.

As for the depth, it is effective to set the welding boundary to α05- or more.

Cold plastic working can be applied to any method that leaves plastic deformation on the weld groove surface. In particular, chisel peening using an air hammer is simple and highly effective.

FIG. 2 is a micrograph of the metal structure of an example of the IW liquid contacting part of the present invention. In other words, as shown in the second diagram, after the welding groove surface of austenitic stainless cast steel (8US 516) is peened with an air hammer, 8U8516
Fig. 3 is a microscopic photograph of the metal structure of a welded part welded using a coated arc welding rod sound system, and shows the microscopic structure of the welded part after welding without peening treatment using the conventional method.

As is clear from comparing the two, the structure of the weld heat affected zone of the present invention shown in FIG. 2, in which the weld groove surface was peened before welding, exhibits a slight llB recrystallized structure. Of course, high temperature cracking is also not recognized. On the other hand,
In the structure of the heat-affected zone of the conventional welding method shown in FIG. 3, the L5 microstructure shown in FIG. 2 is not recognized. Furthermore, in Fig. 3, hot cracking occurs in the weld heat affected zone and the weld metal.

Next, we applied the welding method of the present invention to high-temperature (temperature 600~
650, pressure 500 to 350 hours f/-) The welding structure and welding construction of the steam turbine casing will be explained.

Since the main steam pipe is made of austenitic cast stainless steel, the main steam pipe is welded with austenitic cast stainless steel. The main steam pipe is 0 (105% 11%, 8i
a b -1,5'In, Mn 1-2%, Ni11-
16%, 0r14~20%, MO2~5% and the rest?・
, or this with T1α1-114chi, Nl) α05-cL
5%, B IQ ~60 ppm.

It is preferable to include 1 s or more of 1 s or more of ICLO 10 to α 06%. In this welding process, the entire surface of the groove, to which welding heat is applied, is first subjected to plastic processing. The plastic working is preferably performed using a chisel peening method using compressed air. Shot peening is also preferred.

Next, after performing plastic working on the groove surface, approximately 2 to 5 layers of overlay welding are performed on the groove portion. The overlay welding process is carried out in advance to inspect for defects such as cracks near the weld boundary.
This is the ninth point that makes inspection easier. After groove overlay welding, perform joint welding.

FIG. 4 is a schematic diagram showing an example of a welded joint structure according to the method of the present invention. Here, the reference numeral 20 means the material to be welded, 9 means the overlay welding part, and 10 means the joint welding part.

It is preferable to use an austenitic stainless steel welding rod containing several pieces of tubolite. It is preferable that the meat l & weld and the weld 41N for joint welding be the same.

Preferably, no preheating is performed. Welding bath temperature 1lc
The temperature is preferably 150°C or lower. After welding, it is preferable to perform stress relief annealing treatment at 600-650°C.

Next, welding between the outer casing and the main steam pipe will be explained.

FIG. 5 is a schematic diagram showing an example of a welded joint structure to which the welding method of the present invention is applied. In Figure 5, symbols 1 and 6
It has the same meaning as in FIG. 1, and 11 means a built-up weld on the groove surface of the main steam pipe 1, 12 means a texture weld on the groove surface of the outer casing 6, and 13 means a joint weld.

The main steam pipe 1 has the nine chemical components mentioned above. The outer casing 6 is Oα08S1116%, 811, 11% or less, Mn (15 to 1.5%, N115% or less crα8) by weight.
~1.8%, MO18~1.5%, 711~13%, other Ajα01% or less, T1α001~α02% and 1
5 to 10 ppm' (contains 1 and the remainder is preferably F'e.Ou is included as an impurity, but α4% or less is preferable.

Furthermore, the welded joint structure of the present invention has a nickel-based overlay weld 12 on the groove surface of the outer casing 6, a nickel-based overlay weld 11 on the groove surface of the main steam pipe 1, and further An N1 base joint weld 13 is provided between the overlay welds 12 and 11.

The reason why N1-based overlay welding 127 is performed on the groove surface of the outer casing is that the stability of carbides is particularly excellent among austenitic stainless steel welding rods, and even when welding to ferritic steel, the weld boundary No decarburized or carburized layer is formed in this area.

Next, a welding method for the welded joint structure of the present invention will be explained below.

First, overlay welds 11 and 12 are applied to the groove surfaces of the live steam pipe 1 and the outer casing 6. When overlaying the groove 11 of the live steam pipe 1, as described above, plastic working is applied to the entire surface of the groove in advance to prevent weld cracking. Chisel peening is preferable for plastic working. After the peening process, sensuous welding 11 is performed using an RZ nickel-based welding rod. On the other hand, for the overlay welding 12 on the outer casing side, the preheating and inter-bath temperatures are preferably 100 to 200°C.

After the above-mentioned welding, stress relief zone smoothing treatment is performed to eliminate residual stress and improve the toughness of the weld heat affected zone. Note that the temperature before the stress relief portion annealing treatment is preferably 100° C. or higher. It is also possible to perform dehydrogenation treatment at 400°C for 30 minutes before annealing the stress relief part. The stress relief part annealing treatment is preferably performed at 650 to 700°C for 1 hour or more. After the above overlay welds 11 and 12 are completed, joint welding 13 is performed. The same welding rod used in overlay welding 11 and 12, which is joint welding, is preferable. Preheating is not required, and the inter-bath temperature is preferably 150°C or less.

Next, welding repair of casting defects in the main steam pipe will be explained. Casting defects may develop into cracks during actual machine operation, so they must be thoroughly inspected and removed. FIG. 6 is a schematic diagram showing an example of a repair welding structure for a defective part by the welding method of the present invention.

I! In Fig. 6, the reference numeral 1 indicates the main steam pipe, and 1-4 indicates the repair welded portion.

In the repair welding of the present invention, the shape of the test piece used for the welding heat experiment was 100111 m in thickness, 150 mm in width,
It is 400m long. Welding was performed by two-layer overlay welding after chisel peening the entire surface of the test piece at full atmospheric pressure. In addition,
Preheating is not performed, and the interpass temperature is 100° C. or less.

Figure 7 shows peening time (sec/-1 horizontal axis) and pressure (I
Q/3", vertical axis) and weld hot cracking. Even if the peening time was as high as 5 IQ/cm", hot cracking occurred when the peening time was CL5 seconds and 75 m. As shown in Figure 3, hot cracking occurred between the weld metal and the base metal.On the other hand, if the peening time was α5 seconds or longer, no hot cracking was observed. The structure is shown in FIG. 2, and it is clear that the weld heat affected zone undergoes plastic deformation due to the peening treatment and is recrystallized by the subsequent welding heat.

From the above results, it is clear that according to the present invention, weld cracking can be prevented if the peening time is applied to both the 8UB316L and N1-based connecting rods for a length of L5 seconds/cm'' or more.

l! FIG. 8 is a graph showing the relationship between the recrystallization depth (vertical axis) and peening time (seconds/38, horizontal axis) and cracking caused by peening.

As a result, cracks do not occur if the recrystallization depth is 10 5 square meters or more. That is, it is clear that in order to prevent weld cracking according to the present invention, it is sufficient to plastically work the groove surface of the welded material so that the recrystallization depth of the weld heat-affected zone is greater than or equal to yaos-.

Real A visit 2 Next, a 1r joint strength test of the joint welded portion of the present invention was conducted.

The test material was +3U851 with the chemical composition shown in Part 1.
No. 6 cast steel and ar-M□-v cast steel having the chemical composition shown in No. 5 were used.

The shape of the welded joint test piece was 50 m thick, 100 mm wide, and 500 mm long. The groove shape was 45-.

As for the welding method, S/I physical feel welding was first performed using the cr-u□-v cast steel groove trap shown in Part 3 and the N1 group welding rod shown in Part 2. The preheating and pass temperature at that time is 15
It's 0℃. Stress-relief annealing treatment was performed at the weld radius at 690°C for 8 hours.

On the other hand, the method of welding the groove surface of RUB 516 cast steel in Table 1 involves first applying chisel peening to the entire surface of the weld groove, and then performing 5-layer overlay welding using an N1 welding rod. went. Peening was carried out under the conditions of pressure crab 5 K9/an'' and peening time 3 seconds/field 2. Overlay welding was carried out at an interpass temperature of 100° C. or lower without preheating.

Next, after overlaying both parts, joint welding is performed.9. The welding rod used for joint welding is the same N1 as used for overlay welding above.
It is a brown welding rod. The welding work was carried out without preheating and at a bath temperature of 150°C or less.

From the above welded test pieces, test pieces for joint weld cross-sectional inspection were taken and examined under a microscope for the presence or absence of L cracks. As a result, the welded joint of the present invention had no cracks and was found to be in good condition.

Next, a joint weld creep test was conducted on the joint weld.

The diameter of the parallel part of the test piece is 10φ and the length is 50mm.
], parallel part K Or-Mo-7 cast steel, welded metal and 8
It was designed to accommodate tJ8516 cast steel.

As a result of the creep rupture test, all fracture positions were Or-MO-
The base material was V-cast steel. 5 soc, 10 minutes 9 Ja creep rupture stress was 1α5 dark/-.

The temperature near the welded joint of Or-Mo-V cast steel in the actual machine is 55
0℃, and the design creep rupture stress at that point is 550℃.
, 100,000 hours and 1 o deception/kasumi.

This result satisfies the design stress.

As a result of the above, dissimilar metal welding structure and joining method 1 of the present invention; J
It is clear that the BUB516 series steel steam pipe material is suitable for welding the Or-Mo-V cast steel outer casing. t
In addition, according to the present invention, the operating source of the steam turbine has a temperature of 6
It is clear that a high temperature steam turbine trap with a C1 pressure of 552 q/cm'' is suitable.

Incidentally, a method of subjecting a high-temperature member to peening treatment has already been disclosed in Japanese Patent Laid-Open No. 148602/1983. However, this method involves peening the inside of the keyway of the Or-Mo-V copper rotor material to generate compressive residual stress on different surfaces to prevent stress corrosion cracking. This is fundamentally different from the method of peening the weld groove surface to create a recrystallized structure in the weld heat-affected zone to prevent hot cracking.

Example 3 Next, an experiment was conducted on the main steam pipe joint welding structure of the present invention. The joint welding base material is a joint of 808516 series steel shown in Table 1.
S, I used a commercially available 8118316L welding rod for the welding rod. The shape of the test piece is the same as in the previous example. One of the welding methods is commonly used welding,
80B directly! 116 cast steel is welded with an 8tr8516L welding rod. The other is the welded structure of the present invention, which was carried out under the conditions of the invention that can prevent weld cracking as in Example 1. That is, in the embodiment of the present invention, chisel peening is performed to apply plastic deformation to the welding groove surface to which welding heat is applied, and then five layers of overlay welding are performed on both welding groove surfaces, and then joint welding is performed. Nineteen. The peening conditions were: pressure crab 3K97cm'', time = 3 seconds/cm''. Overlay welding and joint welding do not require preheating, and the interpass temperature is 150°C.
I did the following. The above welding test pieces and test pieces for joint weld joint surface inspection were taken and examined under a microscope for the presence or absence of F cracks. As a result, no weld cracking was observed in the welds of the present invention. However, cracks were observed in the welded material compared to the present invention at the weld boundary.

Next, a creep rupture test was conducted on the welded joint. In addition,
A joint creep test piece was taken from a position where there was no weld cracking in the welded material for comparison with the present invention. Table 4 shows the results of the creep rupture test.

Table 4 As a result, the creep rupture strength of the present invention at 650°C for 105 hours is 1 (L8 / Shizuka).
The design requirement for creep rupture strength for 108 hours at ℃ is 10
kg/'s++" or more. The welded joint structure of the present invention satisfies this. On the other hand, the soft material of the present invention has a specific softness of 7.5 Y/-, which does not satisfy the design requirement. The fracture position of the inventive material was from the welded metal, whereas the comparative material was from the welded boundary.9 The reason why the fractured position of the invented material was not from the welded boundary is that the welded metal was It is presumed that by adding plastic working to the groove by peening, the heat-affected zone becomes a fine recrystallized structure due to the subsequent welding heat, which strengthens the weld boundary.

As described above, it is clear that the welded joint of the present invention is free from weld cracking and has extremely high creep rupture strength, so it is highly reliable and suitable for application to actual machines.

〔Effect of the invention〕

According to the present invention, welding cracks do not occur and the steam temperature is 600.
In steam turbines exposed to high temperatures and pressures of ~650°C and pressures of 500-552 kl//cIn'', the excellent effects of stable weld structure and high strength are exhibited.

Furthermore, in the method of applying plastic working to the caulking groove in order to prevent weld cracking of austenitic stainless steel cast steel according to the present invention, the welded structure of the steam turbine is not made of oak, but is made of nuclear power, hydraulic power, etc. if necessary. There is no problem when used in welded structures of chemical equipment.

[Brief explanation of the drawing]

Figure 1 shows steam temperature of 600-650℃ and pressure of 500-55℃.
0 IC9/cm'' steam turbine, Figure 2 is a microscopic photograph of each metal structure of each welded part 01 of the present invention, Figure 3 is a conventional method, and Figures 4 and 5 are of this invention. A schematic diagram showing an example of a welded joint structure to which the welding method of the invention is applied, FIG.
A schematic diagram showing an example, and FIGS. 7 and 8 are graphs showing the results of hot cracking tests of welded parts of the present invention and comparative examples. 1: Live steam pipe, 2: Telescopic pipe, 3 Ni blades, 4: Rotor shaft, 5: Internal casing, 6: External casing,
7: Welded parts of different materials, 8: Welded parts of same materials, 9.11 and 12:
Overlay welding part, 10 and 13: Joint welding part, 14: Repair welding part, 20: Material to be welded

Claims (1)

[Claims] 1. A high-temperature, high-pressure steam turbine comprising a rotor, an inner casing, an outer casing, and a main steam pipe, the inner casing and the main steam pipe being made of austenitic stainless steel cast steel, at least one of which is made of austenitic stainless steel. A high-temperature, high-pressure steam turbine characterized in that the structure of a weld heat-affected zone in a joint weld and/or repair weld of cast steel of the same or different materials is a fine recrystallized structure. 2. A method for welding materials to be welded, at least one of which is made of austenitic stainless steel cast steel, characterized by including the steps of cold plastic working the weld groove surface, and performing welding after said working. welding method. 3. The welding method according to claim 2, wherein the welding step includes a step of providing an overlay weld layer on the plastically worked weld groove surface, and then welding with a welding material. 4. The welding method according to claim 2 or 3, wherein the plastic working is peening. 5. The peening process is performed at a rate of 0 per unit area of the weld groove surface.
．． The welding method according to claim 4, wherein peening is performed at a rate of 5 seconds/cm^2.