JPH07324672A - Rolled steel plate for hydraulic turbine runner - Google Patents

Abstract

PURPOSE:To provide a rolled steel plate for a hydraulic turbine runner having properties of high strength and high tenacity, and by which the hydraulic turbine runner can be manufactured with less manhours. CONSTITUTION:A rolled steel plate to be used for a hydraulic turbine runner composed of a vane 1, a crown 2 and a band 3 is constituted as follows; 0.01 to 0.10 carbon, 0.10 to 1.0% silicon, 0.10 to 2.0% manganese, 2 to 7% nickel, 10 to 15% chromium and 0.10 to 3% molybdenum, and the remainder of Fe and unavoidable impurities. The metallic organization is of mixture of martensite and residual austenite, and the residual austenite amount is 10 to 35% by the volume ratio.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a rolled steel sheet for a water turbine runner, and more particularly to a rolled steel sheet for a water turbine runner having high strength and high toughness.

[0002]

2. Description of the Related Art In recent years, in order to improve power generation efficiency, there is a tendency toward high head and high head in hydraulic power generation. Along with this, a turbine wheel runner with high strength and high toughness is required. Conventionally, 13Cr steel, which is martensitic stainless steel excellent in cavitation resistance, has been used for a water turbine runner. This 13Cr steel did not contain Ni.
However, in response to a demand for increased output and improved efficiency of a single-machine turbine runner, 13Cr steel containing Ni and having excellent toughness has been developed, and a turbine runner in which this 13Cr steel is integrally cast or dividedly cast has been proposed (for example, Japanese Patent Publication No. 60-53
No. 737).

[0003]

However, the above conventional techniques have the following problems. Sufficient toughness cannot be obtained due to the occurrence of segregation and other defects specific to casting such as shrinkage cavities. Non-destructive inspection methods such as ultrasonic flaw detection and radiation inspection are used to detect defects, but a large number of man-hours are required to accurately inspect the entire three-dimensional water turbine runner.

Casting defects detected by non-destructive inspection are repair-welded by covered arc welding or the like. During this repair-welding work, 13Cr steel is prone to weld cracking.
Then, in order to avoid this welding crack, preheating, postheating, etc. are required, and a lot of man-hours are also required for repair work. A great deal of work is required to finish the casting surface of the turbine runner.

An object of the present invention is to provide a rolled steel sheet for a water turbine runner, which has characteristics of high strength and high toughness and can be manufactured with a small number of steps.

[0006]

In order to achieve the above object, the rolled steel sheet for a water turbine runner of the present invention has a weight ratio of C:
0.01 to 0.10%, Si: 0.10 to 1.0%, Mn:
0.1 to 2.0%, Ni: 2 to 7%, Cr: 10 to 15
%, Mo: 0.10 to 3%, balance Fe and unavoidable impurities, the metallic structure is a mixture of martensite and retained austenite, and the amount of retained austenite is 10 to 35% by volume. Is characterized by.

The rolled steel sheet for a water turbine runner of the present invention is
By weight, C: 0.01 to 0.10%, Si: 0.10 to 1.
0%, Mn: 0.10 to 2.0%, Ni: 2 to 7%, C
r: 10-15%, Mo: 0.10-3%, balance Fe and unavoidable impurities, and maximum oxygen content of 60 pp
m, nitrogen content is controlled to a maximum of 120 ppm, the metal structure is composed of a mixture of martensite and retained austenite, and the retained austenite content is 10 to 3 by volume ratio.
It is characterized in that a rolled steel plate of 5% is laminated on the surface of a mild steel material by welding to form a layered plate material.

[0008]

[Function] The main components such as Cr and Ni are necessary for imparting strength and cavitation resistance to the turbine runner,
It is essentially the same as the content in cast steel. But 13
In electron beam welding of high alloy steel such as Cr steel, it is necessary to control the oxygen and nitrogen contents in the steel in order to prevent the occurrence of welding defects and to secure the toughness, and the voids such as cavities in the meat quality of the base metal should be controlled. It is essential that there is no

Below, the reasons for limiting the chemical components in forming a steel sheet will be described. When C exceeds 0.10%, the weldability deteriorates, and the notch toughness deteriorates in contrast with the increase in strength. Further, if it is less than 0.01%, there is a problem in strength and dissolution. Si needs to be 0.1% or more as a deoxidizing agent during steel making, but if it exceeds 1%, it becomes hard and brittle, so 0.1% is required.
It is limited to 1 to 1.0%. Mn has a deoxidizing / desulfurizing action and contributes to toughness as an austenitizing element, but if it exceeds 2%, a problem of weld hardenability occurs.

Ni is an austenite-forming element, and in order to secure an effective residual austenite amount, it is 2 to 7%.
Although necessary, it is particularly preferably 4 to 6%. However, 7%
If it exceeds, the retained austenite increases and the strength decreases. Cr is a basic component for ensuring corrosion resistance, and it is necessary to be 10% or more for obtaining corrosion resistance in fresh water.
However, if Cr increases, δ ferrite increases and embrittles, so the upper limit is limited to 15%. Mo is also a carbide-forming element, is a component that is extremely effective in improving fatigue strength in water, and is also effective in preventing temper embrittlement. However, if it exceeds 3%, the effect is weakened, and on the contrary, the hardenability increases and the toughness decreases.

Oxygen is an element that lowers the toughness of the weld metal, but in electron beam welding in particular, it tends to cause internal defects such as blowholes, so its upper limit must be limited to 60 ppm. Nitrogen has a small amount of bonding with Al in the steel and has an effect as a nucleus for refining crystal grains, but if too much nitrogen segregates at austenite grain boundaries to deteriorate hardenability, Similarly, it is necessary to limit the upper limit to 120 ppm so that blowholes are easily generated.

The structure of the steel of the present invention is mainly a mixed state of martensite and retained austenite. The retained austenite amount is preferably 10% or more from the viewpoint of toughness and 35% or less from the viewpoint of strength.

The above-mentioned steel is rolled into a steel plate,
After being subjected to non-destructive inspection and visual inspection, it is cut into a predetermined size and used as a member of a water turbine runner. However, the inspection as a steel plate is not only very efficient, but also can improve accuracy. Actually, about 80 to 90% of the entire turbine runners have been inspected in this state. Then, the steel sheet is plastically worked in a mold having a three-dimensional curved surface, and then welded and assembled by electron beam welding or the like.

[0014]

EXAMPLES The present invention will be described in detail below with reference to examples. FIG. 1 is a perspective view of a Francis turbine runner to which the present invention is applied, and FIG. 2 is a view in which it is cut at the center. As shown in the figure, the vane 1 is provided between the crown 2 and the band 3. The central portion of the crown 2 is connected to a drive shaft (not shown).

Next, Table 1 shows the chemical composition of the test steel of the water turbine runner, and Table 2 shows its mechanical properties. In addition,
Table 2 also shows the results of the cavitation erosion test (abbreviated as CE test in the table) and the fracture toughness test.

In the cavitation erosion test, a magnetostrictive vibration type tester was used, and the test conditions were frequency: 6.5.
KHz, amplitude: 120 μm, test liquid: tap water, test liquid temperature: 25 ° C., test time: 2 hours, the difference in weight before and after the test was measured on the test surface having a diameter of 22 mm, and the amount of bite on the test surface was obtained. .

[0017]

[Table 1]

[0018]

[Table 2]

In the fracture toughness test, ASTM E813-
According to No. 81, the fracture toughness at 0 ° C. was obtained by the elasto-plastic fracture toughness test method using a compact tension test piece having a plate thickness of 12.7 mm.

Next, the test results will be described. Specimen No. 1 to No.
No. 3 is the steel of the present invention, and No. 4 to No. 6 are comparative steels.
Of these, No. 5 and No. 6 are cast steel products of the same quality as conventional turbine runners, and all others are rolled steel. 5 for each
Ni-13Cr was the main component, but the contents of oxygen and nitrogen gas in the steel were changed.

Although there is no difference in tensile strength and 0.2% proof stress between the cast steel and the rolled steel, it can be seen that the rolled steel is slightly larger and more ductile than the cast steel in terms of elongation and drawing. Further, regarding the properties required for preventing the structure from breaking, such as impact value or fracture toughness, the rolled steel was superior to the cast steel in particular, more than the difference in elongation in the above-mentioned tensile test. This was influenced by the difference in the amount of non-metallic inclusions contained in the steel, and the cleanliness (Totol) of both was 0.033 to 0.053 for the rolled steel and 0.111 to 0 for the cast steel. .1
4 and rolled steel were smaller than cast steel.

Next, the results of studying the electron beam weldability of 5Ni-13Cr steel will be described. The electron beam welding method has been applied to the field of large-scale thick structures such as carbon steel with the development of high-power equipment because it has the advantage that welding deformation is small and it can weld thick plates in one pass. It is being converted.

In practical application to a water turbine runner, points to be particularly considered are to examine porosity, presence of welding defects such as hot cracking, and mechanical properties of welds and fracture toughness performance. is important.

Table 3 shows the results of a study on the weldability of 5Ni-13Cr steel. The bead shape is shown in FIG. The test material was processed to a plate thickness of 80 mm, and I
Accelerating voltage of 90 KV, beam current of 300
~ 350mA, beam vibration 0.5mm diameter x 500H
Welding was performed at z and a focus position of 80 mm below the surface of the material to be welded. As a result, hot cracking did not occur in all the test materials, but in all of the test materials No. 4 to No. 6, porosity was observed near the center of the weld metal. As a result of various studies, it was found that this factor was due to the influence of oxygen and nitrogen gases contained in the steel. In the test materials No. 4 to No. 6, as shown in the table, the oxygen amount was 100 to 120 ppm and the nitrogen amount was 460 to 470 ppm.

[0025]

[Table 3]

Based on these findings, the relationship between the generation of porosity in 5Ni-13Cr steel and the relationship between oxygen and nitrogen was examined. As a result, by setting the oxygen content to 60 ppm and the nitrogen content to 120 ppm, defects such as high temperature cracks were, of course, generated. It turns out that porosity does not occur at all. It has been confirmed that such steel exhibits excellent properties not only in fracture toughness of the base material but also in weld metal.

Regarding the fracture toughness and the amount of cavitation corrosion of the electron beam weld metal, Table 4 shows the comparison results between the steel of the present invention and the comparative steel.

[0028]

[Table 4]

Although there is not much difference in cavitation characteristics between the two, the steel of the present invention is about 30% higher in fracture toughness than the comparative steel. This is apparently influenced by the cleanliness and oxygen content of the base material, as described above.

Regarding the tensile test of the electron beam welded joint,
Table 5 shows the test results of the steel of the present invention.

[0031]

[Table 5]

From the table, it is clear that the weld metal of electron beam welding has the same strength as the base metal without being softened. The table also shows the strength when the welding rod D309Mo is used, but the strength of the austenitic welding rod is considerably lower than that of electron beam welding.

As described above, it was found that the rolled steel used in this example is excellent in electron beam weldability and the notch toughness of the joint is superior to that of the cast material. Based on this result, an actual half size turbine runner was prototyped.

Next, the trial production of the turbine runner will be described. The size of the runner is length: 8000mm, maximum width: 17
The thickness was 00 mm and the plate thickness was 80 mm. Then, as shown in FIG. 4, the vane 1 is divided into three plate members 1A, 1B, 1C, and the plate members 1A, 1B, 1C are arranged so that the rolling directions of the plate members 1A, 1B, 1C coincide with the longitudinal direction of the vane 1. The board was removed. The plate materials 1A, 1B and 1C were hot and cold drawn using a press machine capable of multiaxial plastic working.

The press machine has a structure as shown in FIG. 5, and movable rods 13 each having a hemispherical movable head 12 are attached to an upper table 10 and a lower table 11 which are vertically opposed to each other. A mold 14 having a three-dimensional curved surface is fixed to the tip of the movable head 12, and both side ends of the mold 14 are supported by supporting side plates 15. Also,
A water conduit 16 is provided in the mold 14 so that the mold 14 can be cooled.

The plate materials 1A, 1B, 1 are processed by the above-mentioned press working machine.
When C is pressed into a three-dimensional curved surface, plate materials 1A, 1
After heating B and 1C to about 950 ° C. in advance, they were inserted between the upper and lower molds 14 and pressurized. Then, the plate materials 1A, 1B, and 1C were continuously pressed until the martensitic transformation was completed. This was to prevent the plate materials 1A, 1B and 1C from buckling or deforming due to the thermal expansion of the martensitic transformation if the pressure is released before the martensitic transformation is completed. .

The plate material 1 pressed in this way
A, 1B, and 1C were welded by a three-dimensional electron beam welding machine, joined to each other and integrated, and then a dimensional inspection and a nondestructive inspection were performed to form a vane.

The present invention can be applied not only to the vane 1 but also to the band 2 as a matter of course. In addition,
A flow chart showing the procedure until the turbine runner is created is as shown in FIG.

[0039]

As described above, according to the present invention,
Since it is possible to obtain a rolled steel plate for a water turbine runner that has high strength and high toughness and corrosion resistance, it is possible to improve reliability of fracture safety of the water turbine runner. Also,
Since the number of inspection steps and repair steps can be reduced, there are great economic advantages.

[Brief description of drawings]

FIG. 1 is a perspective view of a Francis turbine runner to which the present invention can be applied.

FIG. 2 is a sectional view when FIG. 1 is cut at the center.

FIG. 3 is a view showing a bead shape.

FIG. 4 is an assembly drawing of a runner.

FIG. 5 is a sectional view of a press machine.

FIG. 6 is a flowchart showing a procedure for manufacturing a runner.

[Explanation of symbols]

 1 vane 1A, 1B, 1C plate material 2 crown 3 band 10 upper table 11 lower table 12 movable head 13 movable rod 14 type 15 support side plate 16 water conduit

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Junzo Komatsu 3-1-1, Saiwaicho, Hitachi-shi, Ibaraki Hitachi Ltd. Hitachi factory (72) Inventor Masakazu Midorikawa 3-chome, Saiwaicho, Hitachi-shi, Ibaraki 1-1 Hitachi Stock Co., Ltd. Hitachi Factory (72) Inventor Tsuguo Yoshikawa 3-1-1 1-1 Saiwaicho, Hitachi City, Ibaraki Hitachi Co., Ltd. Hitachi Factory

Claims (2)

[Claims] 1. C: 0.01 to 0.10% by weight, S
i: 0.10 to 1.0%, Mn: 0.10 to 2.0%, N
i: 2 to 7%, Cr: 10 to 15%, Mo: 0.10 to 3
%, The balance Fe and unavoidable impurities, the metallic structure is a mixture of martensite and retained austenite, and the amount of retained austenite is 10 to 35 by volume.
% Rolled steel sheet for water turbine runners. 2. C: 0.01 to 0.10% by weight, S
i: 0.10 to 1.0%, Mn: 0.10 to 2.0%, N
i: 2 to 7%, Cr: 10 to 15%, Mo: 0.10 to 3
%, The balance Fe and unavoidable impurities, the oxygen content is controlled to a maximum of 60 ppm, the nitrogen content is controlled to a maximum of 120 ppm, and the metal structure is composed of a mixture of martensite and retained austenite, and the retained austenite amount. A rolled steel sheet for a water turbine runner, which is a layered sheet material obtained by welding a rolled steel sheet having a volume ratio of 10 to 35% to the surface of a mild steel material by welding.