JPS6341981B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to corrosion-resistant materials used in water turbine runners for hydroelectric power generation, guide vanes, stay vanes, marine propellers, various pumps, and the like. In recent years, from the standpoint of effective energy use, construction of hydroelectric power plants that can adjust output in a relatively short period of time, especially pumped storage power plants that can effectively utilize surplus electricity at night, has been active. In addition, hydropower plants tend to have larger capacities due to limitations on construction sites, lower construction costs relative to single-unit capacity, and improved power generation efficiency, and pumped storage power generation is becoming higher in head and head. There is. Conventionally, martensitic 13% Cr stainless steel cast steel containing a relatively large amount of Ni has been used for water turbine runner materials, guide vane materials, stay vane materials, etc., but this leads to higher head and flow velocity. Higher head increases the occurrence of cavitation, causing problems such as accelerating cavitation and erosion of the water turbine runner. In addition, propeller materials for ships are shifting from copper alloys to 13% Cr stainless steel, which is lighter in weight. is being accelerated. It is known that the cavitation and erosion resistance of martenside type 13% Cr stainless steel cast steel improves as the Ni content increases up to about 9% Ni. Even with cast steel containing aluminum, its cavitation and erosion resistance is comparable to that of austenitic stainless steel. In general, the cavitation and erosion resistance of austenitic stainless steel is better than that of martensitic 13% Cr stainless steel cast steel, but this material has a low yield strength, which complicates the manufacturing process when applied to the turbine runner body. To achieve this, it is used by overlay welding on areas where cavitation/erosion wear is significant, such as the surfaces of water turbine runner blades. However, even better cavitation resistance is achieved in overlay welding materials.
Erosion properties are required. In this way, hydroelectric power generation materials can be used for marine propulsors,
As the usage conditions of various pumps and the like become more severe, there has been a demand for materials with even better cavitation and erosion resistance than conventional materials. In view of these points, an object of the present invention is to provide a corrosion-resistant material that has better cavitation and erosion resistance than austenitic stainless steel (SUS304). The present invention incorporates a predetermined amount of Mn into Cr-Ni stainless steel to form an epsilon phase (hereinafter referred to as ε phase) or an austenite phase (hereinafter referred to as γ phase) without containing a ferrite phase in the matrix. This improves cavitation and erosion resistance. i.e. 10 to 10% by weight
More than 2% in steel containing 20% Cr, 0.5-10% Ni
Cavitation and erosion resistance of steel containing 20% or less Mn and forming ε phase or γ phase without containing ferrite phase in the matrix
It was found that the cavitation and erosion resistance is superior to that of SUS304 austenitic stainless steel. In this case, if a ferrite phase coexists in the matrix, the cavitation and erosion resistance will be significantly deteriorated, so it is necessary that the matrix does not contain a ferrite phase. Further, C forms ε phase and γ phase together with Mn and Ni, thereby improving cavitation and erosion resistance. That is, when the C content of the martensitic stainless steel according to the present invention is increased, ε phase and γ phase are formed in the base structure, and the cavitation and erosion resistance is significantly improved. Furthermore, when Mo or Co is added to the steel, the cavitation and erosion resistance is further improved. The reasons for limiting the scope of the claims will be described below. Carbon (C): Carbon is a necessary element to form ε and γ phases and improve cavitation and erosion resistance, but excessive addition impairs corrosion resistance, so the upper limit is set at 0.2%. Silicon (Si): Silicon is necessary to improve the flowability and weldability of steel during melting, but since excessive addition impairs toughness, the upper limit must be set.
2.0%. Chromium (Cr): Chromium needs to be added in an amount of 10% or more to improve corrosion resistance, but excessive addition will cause ferrite to form in the base material and reduce cavitation and erosion resistance, so the upper limit is set at 20%. do. Nickel (Ni): Nickel is an element necessary to improve cavitation resistance, erosion resistance, and toughness, and it is necessary to add 0.5% or more, but even if added in large amounts, the effect will be greater and the cost will increase. The upper limit was set at 10%. Manganese (Mn): Manganese is a particularly important element for forming ε and γ phases and improving cavitation and erosion resistance, but if it is less than 2%, the effect is not sufficient, so it is not recommended to add more than 2.0%. is necessary. However, the upper limit is set at 20% because excessive addition impairs the flowability of the metal. Molybdenum (Mo): Molybdenum is necessary to improve cavitation/erosion resistance and corrosion resistance, but since excessive addition impairs toughness, the upper limit is set at 2.0%. Cobalt (Co): Cobalt needs to be added in an amount of 0.5% or more to improve cavitation and erosion resistance, but even if added in large amounts, the effect is not large and costs increase, so the upper limit has been set at 5.0%.
%. Structure: The cavitation and erosion resistance of steel having the composition described in the claims is significantly effective when the base material contains ε phase or γ phase. It is necessary to include In this case, if a ferrite phase coexists in the structure, the cavitation and erosion resistance will be significantly reduced, so it is necessary not to contain a ferrite phase. The present invention can be used as a cavitation/erosion resistant member that does not require high yield strength.
It can be used as a build-up welding material for cavitation/erosion areas of hydraulic power generation equipment such as water turbine runners, guide vanes, stay vanes, etc., marine propellers, various pumps, etc., and can also be used for overlay welding on areas where cavitation/erosion occurs in water turbine runners, guide vanes, stay vanes, etc., as well as for moisture separators, reheaters, etc. in power generation plants. It is a corrosion-resistant material that can be widely used in pipes and other areas where erosion resistance is required. The steel of the present invention will be explained below with reference to Examples. Samples having the chemical compositions shown in Table 1 were melted using a vacuum high-frequency induction melting furnace. The samples of Examples 1 to 3 were solution treated at 1100° C. for 2 hours and then cooled in air. In Comparative Example 1, commercially available SUS304 was used after being subjected to the same heat treatment as above. In addition, Comparative Examples 2 to 4 are
The heat history equivalent to the heat treatment conventionally applied to runner materials was solution treatment at 1100°C for 2 hours, followed by tempering at 650°C for 2 hours.

[Table] The cavitation/erosion test was conducted using the electrostrictive vibration method at a frequency of 65 KHz, an amplitude of 100 μm, and 180 minutes in pure water at 25°C, and the cavitation/erosion index (CEI) was determined using the following formula. CEI = cavitation erosion weight loss (g)
/test time (minutes) x specific gravity x 10 ⁶ The phase of each sample was also determined by optical microscopic observation, thermal expansion measurement, and X-ray diffraction. Examples 1 to 3 in Table 2 are corrosion-resistant materials according to the present invention, Comparative Example 1 is SUS304 austenitic stainless steel (γ phase) conventionally used as an overlay welding material, and Comparative Example 2 is a water turbine runner. This is a 13%Cr-3.5%Ni martensitic stainless steel (α' phase) used as a material.

[Table] The structures of Examples 1 to 3 contain ε phase or γ phase, and their CEI is conventionally considered to have excellent cavitation and erosion resistance.
It is significantly smaller than SUS304 (Comparative Example 1), indicating that the corrosion-resistant material according to the present invention has excellent cavitation and erosion resistance. By the way, the corrosion-resistant material according to the present invention not only has excellent cavitation and erosion resistance but also has low yield strength, and Example 1 has a yield strength of 11 kg/mm.
Since it is lower than SUS304, it is suitable as an overlay welding material. Although Examples 1 and 2 may contain some α' phase (martensite phase), they exhibit excellent corrosion resistance due to the presence of the ε phase. Furthermore, Example 3 may include an ε phase. As described above, in the present invention, it is sufficient to contain the ε phase and the γ phase without containing the ferrite phase, but in practice, the more the ε phase and the γ phase, the better the corrosion resistance. As explained above, the corrosion-resistant material according to the present invention has excellent cavitation and erosion resistance, and can be used in water turbine runners for hydroelectric power generation, guide vanes, stay vanes, marine propellers, various pumps, etc. It can be said that it is suitable as a material that requires

Claims (1)

[Claims] 1 Carbon not more than 0.20% by weight, 2.0%
Silicon below, 10-20% chromium, 0.1-10% nickel, more than 2% but less than 20% manganese, 2.0
% or less of molybdenum, the balance of 0.5 to 50% of cobalt is substantially iron, and the structure contains an epsilon phase or an austenite phase without containing a ferrite phase.