JPH0146585B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a water turbine runner with excellent cavitation and erosion resistance. In recent years, the capacity of thermal and nuclear power plants has been increasing, but it is difficult for thermal and nuclear power plants with large capacities to handle instantaneous peak loads. As a measure against such peak loads, construction of hydroelectric power generation, especially pumped storage power plants, which can adjust power in a relatively short period of time, has become popular. The water turbine runner used in this pumped storage generator has the functions of both daytime power generation and nighttime water pumping. The water wheel is
There is a trend toward higher head, higher head, and larger capacity. Traditionally, 13 chromium steel has been mainly used as a material for water turbine runners, but with the trend toward higher heads, higher heads, and larger capacities, the conditions for use are becoming more severe. That is, as the water flow increases in speed, a cavity is generated on the surface of the blade 3 of the water turbine runner, as shown in perspective in Fig. 1 and cross-sectionally in Fig. 2, and when this cavity collapses, impact pressure is generated and the blade surface is Cavitation/erosion occurs, which causes wear and tear. In the figure, 1 is the runner cone, 2 is the crown, and 3 is the runner cone.
4 represents a shroud, 5 represents a guide vane, and 6 represents a stay vane. For this reason, with the trend towards higher heads, higher heads, and larger capacities in the future, it is desired to develop water turbine runners that have further improved mechanical strength and toughness, as well as particularly excellent cavitation and erosion resistance. The present invention was made in view of such demands,
It has high mechanical strength and toughness as a water turbine runner.
The object of the present invention is to provide a water turbine runner made of cast stainless steel having a martensitic phase that has particularly excellent cavitation and erosion resistance. That is, the present invention includes carbon of 0.1% or less, silicon of 1.0% or less, manganese of more than 2.0% and up to 9.0%, nickel of 0.5 to 8.0%, chromium of 11.0 to 14.0%,
Molybdenum 2.0% or less, balance substantially iron or even 0.01-0.1% niobium, 0.1-0.5% copper,
This water turbine runner is characterized in that it is made of stainless steel cast stainless steel containing 0.05 to 0.2% of one or more types of panadium and a martensitic phase containing 6% or more of Mn+Ni. The present invention will be explained in detail below. In the water turbine runner of the present invention, the reason for adding each component and the reason for limiting the components will be explained below. Carbon C functions to improve strength by converting the matrix into martensite through heat treatment. Note that since adding too much carbon significantly reduces toughness, the upper limit of the content was set at 0.1%. Silicon is added as a deoxidizing agent along with manganese during melting, and also has the effect of improving the flowability and toughness of cast steel.
Since excessive addition of silicon impairs toughness, the upper limit of silicon content was set at 1.0%. Manganese (Mn) is an element that plays a particularly important role in improving the cavitation and erosion resistance of the stainless steel cast steel of the present invention, and also acts as a deoxidizing agent. The reason for limiting the manganese content to more than 2.0% and up to 9.0% is that the effect is not significant below 2.0%, and
This is because if it exceeds 9.0%, epsilon phase and austenite phase will appear, resulting in a decrease in yield strength. Nickel Ni is an element that improves hardenability by forming a solid solution in the iron matrix, and also increases toughness. Increase the amount of nickel from 0.5 to 8.0%
The reason for this is that the effect of adding less than 0.5% is small.
Moreover, if it exceeds 8.0, the hardness increases, significantly worsening workability, and the amount of retained austenite increases, resulting in a decrease in yield strength. Chromium Cr is an element that improves corrosion resistance and improves the strength of cast steel when it coexists with nickel. Chromium content 11.0
The reason for limiting the range to ~14.0% is that if it is less than 11.0%, the addition effect will not be sufficient, and if it is added in excess of 14.0%, a large amount of delta ferrite will be generated in the matrix in relation to the amount of nickel added, which will prevent cavitation. - This is because it impairs erosion properties. Molybdenum Mo has a strong affinity with carbon, improves the strength of cast steel by forming hard carbides, and improves the hardenability of cast steel by solid solution in austenite.Moreover, it increases the temper softening resistance of martensite. This serves to prevent temper brittleness. This molybdenum content is
If it exceeds 2.0%, the impact value will decrease, so it is necessary to keep it below this value. Niobium Nb functions to improve yield strength by making crystal grains finer. If the niobium content is less than 0.01%, the addition effect will not be sufficient, and if it exceeds 0.1%, a large amount of ferrite will be produced in the matrix, impairing cavitation and erosion resistance, so the content range was limited to 0.01 to 0.1%. . Copper (Cu) functions to improve cavitation and erosion resistance. Copper 0.1%
If it is less than 0.5%, the addition effect will not be sufficient, and if it exceeds 0.5%, the toughness will deteriorate, so please limit the content range.
Limited to 0.1-0.5%. Panadium V functions to improve yield strength by making crystal grains finer. Panadium is
If it is less than 0.05%, the addition effect will not be sufficient, and
If it exceeds 0.2%, a large amount of ferrite will be generated in the matrix, impairing cavitation and erosion resistance, so the content range should be limited to 0.05 to 0.2%.
%. In addition, in the present invention, the Mn+Ni content is set to 6% or more because less than 6% provides sufficient cavitation resistance.
This is because erosion properties cannot be obtained. In addition, in the present invention, when elements such as V, Nb, and Cu are not included, it is desirable that the amount of Mn+Ni is 7% or more. Further, in addition to elements such as niobium Nb, copper Cu, and panadium V, the same effect can be obtained by adding elements such as hafnium Hf, tantalum Ta, zirconium Zr, and titanium Ti. Briefly explaining the method for manufacturing the water turbine runner of the present invention, the melting method may be high frequency melting, melting using an electric arc furnace, etc., and the casting may be carried out using a normal casting method such as sand mold casting or metal mold casting. can. After casting, it is preferable to cool at a rate that does not cause cracks, although it varies depending on the shape and size, and to perform quenching from 1000 to 1100°C and further tempering at 500 to 700°C. Next, examples of the present invention will be described, and in order to confirm the effects of the present invention, comparative examples will also be described. Example After melting a water turbine runner model with the composition shown in Table 1 No. 1 to No. 15 in a high-frequency induction melting furnace,
Equivalent to tempering after homogenization at 1050℃
Heat treatment was performed at 650℃. Test specimens were cut out from the water turbine runner model obtained in this way, and their tensile strength, yield strength, elongation, area of area, and impact value (shear value) were cut out.
2V, 0°C), Pickers hardness, and cavitation erosion index (CEI) were investigated. The results are shown in Table 2. The cavitation/erosion test was conducted using the electrostrictive vibration method, with a frequency of 6.5 KHz, an amplitude of 100 μm, and
The test was carried out in pure water at 25°C for 3 hours, and the cavitation/erosion index was determined using the following formula. CEI = cavitation erosion test weight loss (grams) / test time (minutes) x specific gravity x 10 ⁶ Comparative Example Using samples with the component compositions shown in No. 16 to No. 22 of Table 1, Melting, casting and heat treatment were carried out under the following conditions. The comparative samples thus obtained were also examined for various properties, and the results are also listed in Table 2.

【table】

【table】

【table】

[Table] As is clear from the above results, the example sample
The CEI is approximately 45 or less, which is smaller than the comparative example sample.
In particular, 13 chromium steel, which is commonly used in the past (comparative example)
No. 17) had a CEI of approximately 55 or higher, and it was confirmed that this material had significantly superior cavitation and erosion resistance. Furthermore, the example samples are also superior in mechanical strength and toughness compared to the comparative example samples. Furthermore, the example samples also had excellent weldability. Although Comparative Example Samples No. 19 and No. 21 have excellent cavitation and erosion resistance, their impact values are extremely low, making them unsuitable as materials for water turbine runners that require high toughness. As explained above, the water turbine runner according to the present invention is industrially easy to manufacture, does not require any special casting method, and has excellent cavitation resistance.
It can be said that it is a water turbine runner that not only has erosion resistance but also has excellent mechanical strength, toughness, and weldability.

[Brief explanation of drawings]

FIG. 1 is a perspective view of a pump-turbine runner, and FIG. 2 is a sectional view of the pump-turbine runner. 1...Rannacorn, 2...Crown, 3...
Runner blade, 4... Shroud, 5... Guide.
Vane, 6... Stay Vane.

Claims (1)

[Claims] 1. Carbon 0.1% or less, silicon 1.0% or less, manganese more than 2.0% up to 9.0%, nickel 0.5% by weight
~8.0%, chromium 11.0~14.0%, less than 2.0% molybdenum, and the balance consists essentially of iron, and Mn+
A water turbine runner characterized in that it is made of stainless cast steel consisting of a martensitic phase with a Ni content of 6% or more. 2 Weight ratio: carbon 0.1% or less, silicon 1.0% or less, manganese more than 2.0% up to 9.0%, Nickel 0.5
~8.0% chromium, 11.0-14.0% chromium, 2.0% or less molybdenum, and at least one of 0.01-0.1% niobium, 0.1-0.5% copper, 0.05-0.2% vanadium, with the balance being substantially consisting of iron and Mn
A water turbine runner characterized in that it is made of cast stainless steel consisting of a martensitic phase with a +Ni content of 6% or more.