JPH0512420B2 - - Google Patents

Description

[Detailed description of the invention]

[Industrial Application Field] The present invention relates to a metal-ceramic composite material that is useful as a material for water turbine parts, pump parts, etc. and has excellent cavitation resistance and earth and sand abrasion resistance. [Prior Art] Water turbines operated by falling water in pumped storage power plants, pumps for the purpose of pumping water, or pump water turbines that function as both a water wheel and a pump are subject to cavitation erosion and erosion due to abrasion of earth and sand after long-term use. Cavitation erosion is caused by pressure changes associated with velocity changes in a water stream. That is,
When the local pressure of a fluid decreases below the vapor pressure at the fluid temperature, cavities (bubbles) are formed.
Next, when the pressure rises to vapor pressure, the cavity begins to collapse, and a shock wave is generated when the cavity collapses. Cavitation erosion is the destruction of a member due to repeated pressure changes. On the other hand, sediment abrasion erosion occurs when sediment is mixed in water.
The earth and sand collide with and come into contact with the surface of the component along with the water, and this repetition causes wear on the component. A description will be given of water turbine parts in which cavitation erosion and soil abrasion erosion are particularly problematic, using a Francis water turbine as an example. Figure 1 shows a cross section of the main part of a Francis turbine passing through its axis. 1 is a casing, 3 is a blade, and 5 is a runner. Pressure water flows from the casing 1 to the blade 3 from the inlet side 4 of the blade 3 of the runner via the gade pen 2, and applies hydraulic power to the water turbine runner 5 to perform work. After being transmitted, it flows out from the outlet side 6 of the blade 3. The water wheel runner 5 rotates due to the work of this water power. FIG. 2 is an explanatory cross-sectional view of the vicinity of the runner 5 for explaining the portion where erosion occurs, and FIGS. 3 and 4 respectively show a view in the direction of the P arrow and a view in the direction of the Q arrow in FIG. 2. In the diagram, 7 is the blade 3
a positive pressure surface directly hit by pressure water on the inlet side 6 of the
is the negative pressure side of the blade 3 opposite to the positive pressure side. The locations where cavitation erosion is likely to occur are locations where pressure changes occur due to changes in flowing water velocity as described above, and are the areas A indicated by diagonal lines in the figure, that is, the runner band 10 on the suction surface 8 side of the runner blade 3.
It is the base of the. In addition, the areas where the water turbine parts are likely to undergo earth and sand abrasion erosion are almost the same as the areas where the cavitation erosion is likely to occur. If a water turbine runner is subjected to cavitation erosion or sediment abrasion erosion, it will no longer be able to maintain its initial efficiency, and its lifespan will be greatly affected by erosion and erosion. It must be of excellent quality. It is known that the material and the shape of the blades have the greatest influence on erosion of a water turbine runner, but the shape of the blades also has a relationship with the efficiency of the original design, so it is important to prevent corrosion. It is not possible to unilaterally change the shape solely from a viewpoint. For this reason,
Corrosion prevention is generally considered from the perspective of materials, and stainless steel cast steels such as 13Cr-3.8Ni cast steel (A6NM) have been widely used from the viewpoint of cavitation corrosion resistance and soil abrasion erosion resistance. It is used. [Problems to be solved by the invention] Stainless steel casting products are superior to other materials as materials for water turbine parts, pump parts, etc., but their cavitation erosion resistance and sediment abrasion and erosion resistance are not necessarily sufficient. In many cases, the efficiency of water turbine runners decreases significantly after several years of use. In view of the above, it is an object of the present invention to provide a new material for improving the cavitation erosion resistance and soil abrasion erosion resistance of water turbine parts, pump parts, etc. [Means and effects for solving the problems] The anti-cavitation and anti-sediment wear material of the present invention is made of a metal having a composite structure consisting of a metal base and ceramic particles mixed as a dispersed phase in the metal base. - A ceramic composite material, wherein the metal base comprises Co: 50 to 65% and Cr: 10 to 40%.
%, W: 5 to 15%, Fe: 4.5% or less, and inevitable impurities, and the ceramic particles are carbide-based ceramic particles and account for 5 to 30% by weight in the composite structure. It is characterized by being Cavitation erosion that occurs in water turbine parts, etc.
As mentioned above, this is a type of impact fatigue due to repeated impact pressure when the cavity collapses, so by improving the strength, toughness and work hardening ability of the component material,
It becomes possible to strengthen its cavitation resistance.
Furthermore, among similar materials, those with higher hardness tend to have better cavitation resistance. The present invention enhances the resistance to cavitation erosion and improves the resistance to earth and sand abrasion erosion by selecting the material of the base metal and forming a composite structure with ceramic particles. That is,
The cobalt-based alloy, which is the base metal in the composite material of the present invention, is itself a metal material that has better strength, toughness, and work hardening ability in terms of cavitation resistance than other metal materials, On the other hand, ceramic particles also have high strength and are extremely hard particles, so they can be dispersed in the base metal to greatly increase the strength and hardness of the base, and the dispersion-strengthening mechanism of the particles can effectively prevent the movement of dislocations. As a result, it achieves outstanding cavitation and erosion resistance that cannot be obtained with conventional metal materials. Furthermore, as a result of the high hardness imparted by the dispersion effect of the ceramic particles in the matrix, excellent resistance to earth and sand abrasion and erosion is ensured, which cannot be obtained with conventional metal materials. The ceramic particles mixed in the base metal as a dispersed phase should preferably have high strength, high toughness, and high hardness as described above, and should also have good wettability with the base metal and be firmly bonded at the interface. is necessary. From this point of view, carbide ceramics, especially chromium carbide (Cr ₃ C ₂ ), silicon carbide (SiC),
Tungsten carbide (WC) or the like is preferably used. Although the particle size is not particularly limited, from the viewpoint of uniformity in the composite structure and dislocation prevention effect,
A range of 0.1 to 10 μm is suitable. The amount (wt%) of ceramic particles mixed in the composite structure [ceramic particles/(base metal + ceramic particles) x 100] is 5 to 60 wt%. The amount of ceramic particles mixed in is determined based on a comprehensive evaluation of cavitation erosion resistance and earth and sand abrasion erosion resistance. This is because it is difficult to ensure sufficient erosion resistance and soil abrasion and erosion resistance.On the other hand, the reason why the upper limit is 60% by weight is that if it exceeds 60%, the toughness of the composite material deteriorates, and the cavitation erosion resistance deteriorates. This is because you see. The reasons for limiting the components of the cobalt-based alloy constituting the base of the composite material of the present invention are as follows. Co: 50-65% Co is the basic component of the base metal. Co is an essential element for ensuring strength and corrosion resistance, and also has a strong effect on stabilizing austenite. It is also effective in improving cavitation erosion resistance. To ensure these characteristics, at least
Must be 50% or more. Cr: 10-40% Cr has a great effect on improving corrosion resistance, especially intergranular corrosion resistance, and is effective in improving stress corrosion cracking resistance. It also has the effect of stabilizing the structure and improving strength. However, since Cr is a strong ferrite-forming element, the quantitative balance with the austenite-forming elements (Co, Mn, etc.) should be considered in order to secure the austenite region, and addition of a large amount may affect the toughness. This results in a rapid decline. From these points, 10~
It shall be 40%. W: 5 to 15% W has a remarkable effect on improving strength, and is effective in enhancing resistance to earth and sand abrasion and cavitation erosion resistance. For this purpose, it is necessary to add at least 5%, but adding a large amount causes deterioration of toughness, so the upper limit is set at 15%. Fe: 4.5% or less Fe is a normal impurity that inevitably accompanies cobalt alloys. If the amount exceeds 4.5%,
Since corrosion resistance is significantly impaired, the upper limit is set at 4.5%. The base metal has the above-mentioned Co, Cr, W, and Fe as essential elements, and if desired, a part of Co is 0.5 to 5% Al, 0.5
It may be substituted with one or more elements such as ~2% Nb, 0.5~2% Ti, and 0.5~2% Cu. Note that the base metal may include C, Si, Mn, P, S, and the like. For example, C is 1.5% or less, Si
is 1.5% or less, Mn is 1.5% or less, P is 0.3% or less,
Even if 0.3% or less of S is mixed, the purpose of the present invention will not be impaired. The composite material of the present invention can be applied to water turbine parts, pump parts, etc. by casting, sintering, welding, or the like. According to the casting method, ceramic powder is added to and mixed with the molten base metal, and the desired part can be cast as a uniform solid-liquid mixture, and according to the sintering method, the base metal powder and ceramic powder are mixed together. A uniform powder mixture of is used as the sintering material,
The desired member can be obtained through pressure molding and sintering steps. In addition, when using the welding method,
A powder mixture of base metal powder and ceramic powder is used as a welding material, and a build-up layer with a composite structure is formed on the surface of the component by, for example, tungsten inert gas arc welding (TIG welding) or plasma powder welding (PAT welding). can do. In particular, when using the welding method, it is possible to selectively form a build-up layer not only on the entire surface of the member, but also only on a part of it.
As shown in Figures 2 to 4, if only the areas where anti-cavitation erosion and soil abrasion erosion are likely to occur (area A) are covered with a built-up layer, it is most efficient in terms of design and cost. It is possible to protect components and improve durability. The build-up layer formed by the welding method is sufficiently fused to the surface of the component by the welding heat input and has high bonding strength, so it functions as a protective layer for a long time without any problem of peeling. In addition,
When applying the welding method, etc., the raw powder mixture is used as granulated powder (preferably φ100 to 200 μm) that is granulated to an appropriate particle size from the viewpoint of handling properties and uniformity of the resulting composite structure. It's good to do that. [Example] A powder mixture consisting of metal and carbide ceramic particles or a single metal powder is used as a welding overlay material,
A built-up layer with a thickness of 3 to 4 mm was formed on the surface of a 13Cr-3.8Ni cast steel plate (10 ^W x 200 ^L x 50 ^t , mm) by TIG welding. Specimens were cut from these test materials and subjected to cavitation erosion tests and earth and sand abrasion tests. Table 1 shows the test materials and their test results. In the table, No. 1 to 12 are invention examples,
Nos. 11 to 14 are comparative examples. Among Comparative Examples No. 1 to 14, No. 11 is an example that does not contain ceramic particles, and No. 12 is an example that does not contain ceramic particles.
contains an appropriate amount of ceramic particles, but the base metal deviates from the specified composition of the present invention, No. 13 is an example in which the amount of ceramic particles deviates from the upper limit specified by the present invention, No. 14 is a cast material of 13Cr-3.8Ni cast steel (A6NM), which is commonly used as a conventional water turbine runner material. In the table, "Comprehensive evaluation"
In the column, "◎" indicates a significant effect, "○" indicates an effect, "△" indicates a small effect, and "x" indicates no effect. [I] Cavitation erosion test Measure the erosion loss (mg/15Hr) of the specimen under the following conditions using the vibration erosion test method. Frequency: 19.0KHz, Environment: Underwater (22±1℃),
Maximum displacement amplitude: 30μm, time: 15Hr [] Earth and sand abrasion test See Figure 1. A sample (TP) is fixed on the side of a container (inner diameter: φ220) (a), and the acid aqueous solution containing soil and sand (PH4, 66% by weight of soil) (b) is rotated at high speed (1700 rpm) by a blade (c). Stir by to form a high-velocity flow, 50
Measure the abrasion loss of the specimen after a certain period of time. In the table, "earth and sand abrasion corrosion ratio" is for conventional water turbine runner material.
It represents the wear loss ratio of the test piece, assuming that the wear loss of 13Cr-3.8Ni cast steel is 1. As shown in Table 1, compared to the conventional material No. 14 (13Cr-3.8Ni cast steel), the invention example has a significantly smaller amount of cavitation erosion and a significant reduction in the amount of earth and sand abrasion, resulting in improved cavitation resistance. It has excellent durability and soil abrasion resistance. In addition, regarding the other comparative examples Nos. 11 to 13, all of them are inferior to the material of the invention example in the comprehensive evaluation of both cavitation erosion resistance and earth and sand abrasion resistance properties.

〔Effect of the invention〕

The composite material of the present invention has excellent cavitation erosion resistance and soil abrasion erosion resistance.
For example, by applying it to water turbine parts and pump parts, cavitation erosion and soil abrasion erosion of these parts can be effectively suppressed, allowing stable use over a long period of time.

[Brief explanation of the drawing]

Fig. 1 is a sectional view of the main part of the water turbine, Fig. 2 is an explanatory diagram of the erosion-generated part of the water turbine, Fig. 3 is a view in the direction of the P arrow in Fig. 2, Fig. 4 is a view in the direction of the Q arrow in Fig. 2, FIG. 5 is an explanatory diagram of soil abrasion test procedures. 1...Casing, 2...Guide valve, 3...Blade, 5...Water wheel runner.

Claims (1)

[Claims] 1 It has a composite structure consisting of a metal base and ceramic particles mixed as a dispersed phase in the metal base, and the metal base has Co: 50 to 65%, Cr: 10 to
40%, W: 5 to 15%, Fe: 4.5% or less, and inevitable impurities.The ceramic particles are carbide ceramic particles, and the proportion of the composite structure is 5 to 60% by weight % cavitation-resistant and earth-and-sand wear-resistant composite material.