JPS5968571A - Manufacture of guide vane - Google Patents

Abstract

PURPOSE:To enable to improve the reliability against fracture by a method wherein a weld zone is constituted by two or more kinds of welding metals, the thermal expansion coefficients of which are different from each other, and the joining is performed by applying stress relief annealing treatment to the weld zone. CONSTITUTION:A welded joint consisting of austenitic stainless steel welding metal 10, the thermal expansion coefficient of which is larger, and martensitic stainless steel welding metals 11 and 12, the thermal expansion coefficient of which is smaller, is treated by stress relief annealing at or just below the temperature, at which the alpha gamma transformation of steel occurs, after welded. As a result, compression stress remains exceptionally on the surface of the weld metal of the first martensitic stainless steel welding metals 11 and 12, resulting in improving the reliability against fracture.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for manufacturing a guide vane, and more particularly to a method for manufacturing a guide vane that has a welded structure to reduce manufacturing costs and improve quality, and has improved brittle fracture strength and fatigue fracture strength.

Conventionally, guide vanes have been manufactured by integral casting, but cast products have the drawback of being prone to defects such as component segregation and shrinkage cavities during the casting process, which has led to problems with fatigue strength. Therefore, monolithic welding using electroslag melting has been adopted in order to improve quality and reduce costs. However, when melting guide vanes for pump water turbines, etc., the vane part is generally 1000 m long, and the shaft part is 3000 m+ long, so it takes a lot of time to melt, and water cooling is required during the welding process. The copper plate was also complicated and had drawbacks such as poor workability.

Therefore, the present inventors locally press-shaped the shaft material,
We tried a unique method of manufacturing the vane by electroslag melting on the shaped part. However, the shape of the water-cooled copper plate required during melting is complicated, and complete melting is difficult, resulting in a decrease in work efficiency. Therefore, in order to further improve the above-mentioned drawbacks, as shown in FIG. We attempted to manufacture a guide vane with a welded structure that connects to the shaft part. This simple method made it possible to significantly improve work efficiency. However, even with this method, even after the stress relief annealing treatment on the surfaces of the welds 8 and 9, the stress is usually less than about 10 Kgf/m'', which is desirable for brittle fracture, fatigue fracture, stress corrosion cracking, etc. The problem of uneven distribution of tensile residual stress was rare.
In FIG. 1, 1 indicates the upper axis of the guide vane, 2 indicates the lower axis of the guide vane, 3 indicates the upper edge of the guide vane, 4 indicates the upper edge of the guide vane, and 7 indicates the center portion of the kite vane. ) The purpose of the present invention is to solve the above-mentioned problems, improve the workability of welding work, and improve brittleness resistance.

It is an object of the present invention to provide a method for manufacturing a kite vane with improved reliability against fracture such as fatigue or stress corrosion cracking strength.

The present invention relates to a guide vane characterized in that the welded part is composed of two or more welded metals having different coefficients of thermal expansion, and the members are joined by applying stress-relieving annealing treatment after welding. The gist is the manufacturing method.

The present invention will be described in detail below with reference to FIGS. 2 to 5, which show one embodiment of the present invention, regarding the manufacture of a guide vane for a water turbine.

The method for manufacturing a guide vane of the present invention includes forming a welded part by overlaying or sequentially welding weld metals having different coefficients of thermal expansion, and after welding to this welded part, a stress relief annealing treatment is performed. In particular, compressive residual stress can be generated on the surface of the weld.

The theoretical background of the present invention will be explained with reference to a schematic cross-sectional view of a welded portion in FIG. 2, which illustrates the connection between the guide vane head 5 and the guide vane central portion. A second weld metal with a large coefficient of thermal expansion, for example, austenitic stainless steel weld metal 1
0 and a first hot liquid metal with a small thermal expansion coefficient, such as martensitic stainless steel weld metals 11 and 12, after welding, the temperature at which α#γ transformation of the steel occurs or just below that temperature (preferably 600-650'C
) is subjected to stress relief annealing treatment. During this heating, the second austenitic stainless steel weld metal 10 having a large coefficient of thermal expansion expands more than the first martensitic stainless steel weld metals 11 and 12 having a small coefficient of thermal expansion.

As a result, compressive stress is generated in the second austenitic stainless steel welded metalwork 0, and compressive plastic strain and creep strain are induced by f. On the other hand, tensile stress is generated in the first martensitic stainless steel weld metals 11 and 12, and tensile plastic strain and creep strain are induced after f. Conversely, during cooling, the second austenitic stainless steel weld metal 10 having a large coefficient of thermal expansion is
The martensitic stainless steel weld metal tries to shrink more. As a result, the strength of the weld metal increases as the temperature decreases, and tensile stress is generated in the second austenitic stainless steel weld metal, and compressive stress is generated in the first martensitic stainless steel weld metal. do. Furthermore, the plastic strain and creep strain induced in each weld metal during heating act to promote compressive stress generated in the first martensitic stainless steel weld metals 11 and 12 during cooling. As a result of the above,
First martensitic thread austenitic steel weld metal 11
Compressive stress remains on the weld metal surface of 12 and 12. It is considered that the magnitude of this compressive stress is influenced by the difference in the coefficient of thermal expansion, the ratio of the amount of welding, the lamination method, etc. The coefficient of thermal expansion varies depending on the components, but martensitic stainless steel has a coefficient of thermal expansion of 11 to 13 Xl0-'/C.

Austenitic stainless steel has a diameter of about 16 to 19X11π.

Generally, martensitic stainless steel is used as a constituent material for guide vane members for water turbines, and its composition is C: 0.03 to 0.15% by weight, s
*: 0.02-1.5%, Mn: 0.3-1.5%
, Ni: 6% or less, Cr: 10.0-14.0%
as the main component, and as necessary MO=2.5%
Contains 0.5% or less of each of Nb and V, with the balance F
Examples include those consisting of e and impurities. The weld metal of the weld zone is preferably a combination of austenitic stainless steel and martensitic stainless steel, and the composition of the austenitic stainless steel weld metal is C: 0.02 to 0.07% by weight, Si≦0 .6%, Mn
≦2.5%.

P≦0.03%, S≦0.02%+N': 1o, o~1
4.0%, Cr: 20.0-24.0%, MO≦
3.0%, the remainder consists of Fe and impurities, and
Composition of martensitic stainless steel weld metal is weight%
and C≦0.08%, B+≦0.5%, Mn≦0.7%,
P≦0.03%, S≦0.02%, N+≦7.0%, C
Preferably, it contains r: 11.0 to 14.0%, with the remainder consisting of Fe and impurities.

Next, the present invention will be explained in more detail with reference to Examples, but the present invention is not limited to the following Examples unless it exceeds the gist thereof.

Example 1 The head portion 5 and tail portion 6 of a full-sized guide vane as shown in FIG. 3 were each welded to the central portion 7 by the method of the present invention.

In addition, in FIG. 3, 1 to 4 refer to the same ones as in FIG. 1, respectively.

In this example, each member was joined by covered arc welding, and it was confirmed that the residual stress on the surface of the welded portion turned into compressive stress after stress relief annealing. As shown in FIG. 4, the joint has a K-shaped groove and is made of a first marten-length stainless steel welding material 15 having a small thermal expansion coefficient symmetrically in the plate thickness direction.

Then, a second austenitic stainless steel welding material 16.17 having a large coefficient of thermal expansion was welded by an amount h2. Finally, the first marten-length stainless steel welding material 18.19 was welded. The ratio of h, /h is 1
The target was 0%. Measurement of residual stress is 650Cx after welding.
strain gauge after stress relief annealing. Also,
Welding between the tail portion 6 and the center portion 7 was performed in the same manner.

The chemical compositions of the test kite vane and welding material are shown in Table 1 below. Further, the mechanical properties of each are shown in Table 2.

The measured residual stress in Table 1 and Table 2 is -4Ktjf/tone 2 at measurement point 13 in Figure 3 (point A in Figure 5), and -5Kgf/bleach 2 at measurement point 14 (Figure 5B). points). These compressive stresses improve the brittleness, fracture, fatigue, or stress corrosion strength of the guide vane.

In Fig. 5, the dotted line indicates a small test piece (length: 250+
++m, width: 250mm, thickness: 50m (a joint made by butt welding two plates with a mold groove in the same manner as above), and from this, the degree of compressive stress generated is It is clear that the compressive stress tends to increase as the ratio of the depth of the austenitic stainless steel weld metal to the thickness of the base metal increases.

According to the present invention, compressive stress can be applied to the surface of the welded part, and reliability against fracture such as brittleness resistance, fatigue resistance, stress cracking strength, etc. of the welded part is improved, and welding workability is also improved.

[Brief explanation of the drawing]

Figures 1 and 3 are views showing the external appearance of a welded guide vane for a water turbine, Figure 2 is a sectional view illustrating a welded part according to the method of the present invention, and Figure 4 is a method according to Example 1. FIG. 5 is a cross-sectional view illustrating a welded part, and FIG. 5 is a graph showing the relationship between residual stress and the proportion of austenitic stainless steel in the welded part. 1... Guide vane upper shaft, 2... Guide vane lower shaft, 3... Guide vane upper collar, 4... Guide vane upper collar, 5... Guide vane head, 6... Kite vane Tail part, 7... Central part of kite vane, 8, 9...
Welding part, lO...first weld metal, 11.12...
Second weld metal, 13.14...Residual stress measurement point, 1
5,18゜19...Marten length stainless steel! M
L16゜th l concave 6th 2nd trouble 4th country 5th

Claims (1)

[Scope of Claims] 1. The welded part is composed of two or more types of weld metals with different coefficients of thermal expansion, and stress-relieving annealing treatment is performed after welding.
A method for manufacturing a guide vane, which comprises joining members. 2. The method for manufacturing a guide vane according to claim 1, wherein the guide vane is made of martensitic stainless steel. 3. The guide vane contains C0.03 to 0.15% by weight,
Martensitic stainless steel containing s+o, o2 to 1.5% by weight, Mn 0.3 to 1.5% by weight, Ni 6% by weight or less, and Cr 10.0 to 14.0% by weight, with the balance consisting of Fe and impurities. A method for manufacturing a guide vane according to claim 2, characterized in that the guide vane is manufactured by: 4. The guide vane contains CO, 03 to 0.15% by weight, 8
10.02-1.5% by weight, Mn 0.3-1.5% by weight
, Ni 6% by weight or less, cr 10. [Characterized by being made of martensitic stainless steel containing 1 to 14.0% by weight, MO2, 5% by weight or less, Nb 0.5% by weight or less, and 7005% by weight or less, the balance being Fe and impurities. A method for manufacturing a guide vane according to claim 2. 5. Claims 1 to 4, characterized in that the welded portion is composed of two types of weld metals: a weld metal with a large coefficient of thermal expansion and a weld metal with a small coefficient of thermal expansion.
1. The method for manufacturing a guide vane according to item 1. 6. The method for manufacturing a guide vane according to claim 5, wherein the welded portion is configured such that the weld metal having a small coefficient of thermal expansion is located on the outer periphery of the bath contact portion. . 7. The method for manufacturing a kite vane according to claim 5, wherein the welded portion is composed of martensitic stainless steel weld metal and austenitic stainless steel weld metal. 8. The method for manufacturing a guide vane according to claim 7, wherein the welded portion is configured such that the martensitic stainless steel weld metal is located on the outer periphery of the welded portion. 9. The marten-length stainless V steel weld metal is c
o, o S weight% or less, S+O, S weight% or less, Mn
0.7% by weight or less, P O, 03% by weight or less, 80.0
2% by weight or less, Ni7.0% by weight or less and Cr11.0
9. The method for manufacturing a guide vane according to claim 7 or 8, wherein the guide vane contains Fe and impurities in an amount of 14.0% by weight. 10. The austenitic stainless steel weld metal has C
O, 02-0.07% by weight, sio, 6% by weight or less, M
n 2.5% by weight or less, P O, 03% by weight or less, 80.
02% by weight or less, Ni 10.0-14.0% by weight, Cr
The method for producing a guide vane according to claim 7 or 8, characterized in that the guide vane contains 0 to 24.0% by weight of 2O and 3.0% by weight or less of Mn, and consists of residual iFe and impurities. . 11. The method for manufacturing a guide vane according to any one of claims 1 to 10, wherein the guide vane is a guide vane for a water turbine. 12. The guide vane according to any one of claims 1 to 11, wherein the stress-relieving annealing treatment is for applying compressive stress to the surface of the welded part. manufacturing method. 13. The welding part builds up the weld metal, 1
The method for manufacturing a guide vane according to any one of claims 1 to 12, characterized in that: 14. The method for manufacturing a guide vane according to any one of Items 1 to 12 of Patent No. 6, wherein the welded portion is constructed by welding the weld metal.