JPS6111311B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to water equipment with excellent cavitation and erosion resistance, and a method for manufacturing the same. 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. Furthermore, 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 increasingly higher in head and head. I'm here. Conventional water equipment, such as the main body of a water wheel runner, is made of martensitic material containing 3 to 5% Ni.
13% Cr stainless steel cast steel is used,
Cavitation and
Erosion has been accelerated, and there is a demand for materials with even better cavitation and erosion resistance. One way to improve the cavitation and erosion resistance of water turbine runners and other materials is to use austenitic stainless steel as the material for water turbine runners and other materials. Generally austenitic stainless steel
The cavitation and erosion resistance of stainless steel is better than that of martensitic 13% Cr stainless cast steel, but because this material has low yield strength, the manufacturing process is extremely complicated when used in the main body of a water turbine runner. There's a problem. For this reason, austenitic stainless steel is mainly used by overlay welding in areas where cavitation/erosion wear is significant, such as water turbine runner blades. However, as heads and heads become higher, there is a demand for overlay welded water turbine runners that have even better cavitation and erosion resistance. In view of these points, the present invention provides a water turbine runner, a guide vane, a stay vane, a marine propeller, and a water turbine runner with excellent cavitation and erosion resistance.
The purpose is to provide water equipment such as various pump parts and high-speed water flow parts, and methods for manufacturing the same. The present invention relates to water turbine runners, guide vanes, stay vanes, marine propellers, various pump parts,
A predetermined amount of Mn is contained in Cr-Ni stainless steel as the surface layer of at least cavitation/erosion wear parts of water equipment such as high-speed water flow components, and a ferrite phase (hereinafter referred to as α phase) is formed in the structure. epsilon phase (hereafter ε
phase) or austenite phase (hereinafter referred to as γ phase) to improve cavitation and erosion resistance. i.e. 10-20% Cr, 0.5-10% Ni, by weight percentage
The main component is more than 4% Mn and less than 20%, carbon is less than 0.2%, silicon is less than 2%, and the remainder of Mo is substantially Fe, and contains no α phase but ε phase or γ phase. The present invention is a water device in which a surface layer of at least a portion of cavitation/erosion wear is made of steel mainly consisting of phase, and in which the surface layer is a weld layer for overlay welding. In addition, by overlay welding on at least cavitation/erosion damage parts of water equipment,
Carbon below 0.2%, Silicon below 2%, 10-20%
of chromium, 0.5-10% nickel, over 4%20
% or less of manganese, molybdenum of 2% or less, and the remainder substantially consists of iron, and is characterized by forming a surface layer consisting of steel mainly consisting of epsilon phase or austenite phase without substantially containing ferrite phase. This is a method for manufacturing water equipment. The reasons for limiting the composition of the steel used in the water equipment of the present invention will be described below. Structure: The cavitation and erosion resistance of steel having the composition described in the claims is significantly effective when the steel is mainly composed of ε phase or γ phase. In this case, if α phase coexists in the structure, the cavitation and erosion resistance will be significantly deteriorated, so it is necessary that the structure does not contain α phase. In the present invention, only the surface of the main body, which is mainly composed of the ε phase and γ phase, which have excellent toughness, undergoes a phase transformation to the martensitic phase due to the impact force applied when the cavity collapses, thereby achieving excellent cavitation and erosion resistance properties. play. However, since phase transformation does not occur inside the steel, the toughness necessary for material properties is not impaired, and the steel as a whole has high toughness.
In other words, the steel itself is a self-repairing alloy that exhibits a protective effect depending on the external environment. Therefore, it has the toughness required for the material and has excellent cavitation and erosion resistance properties. When conventional martensitic steel is used, it is practically tempered due to its poor toughness.
However, when such a tempering treatment is performed, the cavitation and erosion resistance properties deteriorate. In the present invention, since the main body has excellent toughness, it is not necessary to perform such a treatment. Carbon (C): Carbon is an element necessary to form ε and γ phases and improve cavitation and erosion resistance, but excessive addition can lead to poor toughness and
Since it impairs corrosion resistance, the upper limit is set at 0.2%, but in practice it is desirable to set it at 0.03 to 0.15%. Silicon (Si): Silicon is necessary to improve the flowability and weldability of steel during melting, but excessive addition impairs toughness, so the upper limit is set at 2.
%, but in practice it is preferably 0.2 to 1.0%. Chromium (Cr): It is necessary to add 10% or more of chromium to improve corrosion resistance, but the upper limit must be set because excessive addition will generate α phase in the weld layer and reduce cavitation and erosion resistance. It is set at 20%, but in practical terms it is more desirable to set it at 11% to 15%. Nickel (Ni): Nickel combines with manganese to change the structure of steel to ε and γ, causing cavity impact〓〓〓〓〓
It is necessary to facilitate phase transformation of the steel surface due to force and to improve cavitation/erosion resistance, and it is necessary to add 0.5% or more to improve cavitation/erosion resistance and toughness. Even if added in a large amount, the effect is not great, and it actually inhibits phase transformation, reduces cavitation and erosion resistance, and increases cost. % is desirable. Manganese (Mn): Manganese works together with nickel to change the structure of steel to ε and γ, making it easier for the steel surface to undergo phase transformation due to the impact force of the cavity, and is particularly important for improving cavitation resistance, erosion resistance, and toughness. Although it is an element, if it is less than 4%, its effect is not sufficient, and it is necessary to add more than 4%. However, excessive addition will actually inhibit phase transformation, reduce cavitation and erosion resistance, and impair flowability, so the upper limit must be set.
It is set at 20%, but in practice it is more desirable to set it at 4% to 15%. 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%, but in practice it is 0.5-1.5%.
It is desirable to do so. By the way, one of the properties required of overlay welded materials is low residual strain due to thermal contraction after welding. If the coefficients of thermal expansion of the base metal and the weld layer are different, stress will be generated at the interface between the base metal and the weld layer during thermal contraction after welding, and this will become residual strain and cause cracking and deformation. This tendency is remarkable when martensitic stainless steel is used as the base material, and large strains occur during martensitic transformation. One method for alleviating this strain is to lower the yield strength of the weld layer and alleviate the generated stress through plastic deformation of the weld layer. According to this method, the lower the yield strength of the welded layer, the more effective it is in alleviating strain, and is therefore advantageous in preventing cracking and deformation after welding. In addition, as another method, stress can be alleviated by multilayer overlay welding. The steel for water equipment of the present invention improves cavitation and erosion resistance by forming ε phase and γ phase in the structure, and at the same time has a yield strength of usually 20 kg/mm ²
The following are austenitic stainless steels:
It is lower than SUS304 and has excellent resistance to cracking and deformation, making it particularly suitable for use as a weld layer in overlay welding. As described above, the water equipment of the present invention has excellent cavitation and erosion resistance, and has little cracking or deformation due to overlay welding, and has extremely excellent characteristics as equipment for high head and high head hydroelectric power generation, for example. ing. The water equipment of the present invention is provided with the steel at least in cavitation/erosion wear areas. For example, in the pump-turbine runner perspectively shown in FIG. 1, as shown in the hatched area in FIG. This is mainly done on the blade surface on the water inlet side when the turbine is operating (when generating electricity), or on the blade surface on the water inlet side (water outlet side when the turbine is operating) when the pump is operating (pumping water), and the guide vane 5 and stay vane. In 6,
This is mainly done on the outer corner surface of the vane. In addition, overlay welding of the steel to water equipment is performed using a film arc. It can be easily performed using normal welding methods such as TIG and MIG welding. The water equipment of the present invention will be described in detail below with reference to Examples. 13% Cr - 3.5%, which is the current integral water turbine runner material
Ni (Comparative Example 2) A water turbine runner blade model was cast using martensitic stainless steel.
After normalizing at ℃ for 4 hours and tempering at 650℃ for 3 hours, the 10 steel types shown in Table 1 (Examples 1 to 8, Comparative Examples 1 and 2) were applied to the surface. Approximately 5mm thick, overlay welded using TIG welding. A cavitation/erosion test piece was taken from the overlay weld, and the frequency was measured by electrostrictive vibration.
A cavitation/erosion test was conducted for 3 hours in pure water at 6.5 KHz and an amplitude of 100 μm at 25°C, and the cavitation/erosion index (CEI) was determined using the following formula to evaluate the cavitation/erosion resistance. CEI = cavitation/erosion weight loss (g) / test time (min) x specific gravity (g/cm ³ ) x ¹⁰ We melted 2.5Kg of
By remelting, casting, and air cooling in the atmosphere,
After applying a thermal history equivalent to that during welding, a tensile test piece was prepared.
Manufactured. In addition, Comparative Example 2 uses the above 13%Cr-3.5%Ni cast steel.
After tempering at 650°C, cavitation/erosion test pieces were prepared. Furthermore, after overlay welding, the main phase of each weld layer was determined using an optical microscope and X-ray diffraction.

【table】

【table】

[Table] Table 2 shows the cavitation/erosion index (CEI) of various overlay welding samples and their main phases. The structures of Examples 1 to 17 are mainly composed of ε phase or γ phase, and the CEI is composed of the integral water turbine runner material (Comparative Example 2) and the austenitic system, which is conventionally considered to have excellent cavitation and erosion resistance. Stainless steel SUS304
(Comparative Example 1) It is found that the water equipment according to the present invention has excellent cavitation and erosion resistance. Table 3 shows the yield strength of seven types of invented steels and one comparative steel that have a thermal history equivalent to that of overlay welding. The weldability was lower than that of SUS304. Examples may also include a small amount of α' phase. As described above, in the present invention, if the steel having the composition as claimed in the claims is overlay welded and the welding process mainly contains the ε phase and γ phase without containing the α phase, excellent cavitation and welding can be achieved. Shows erosion property. As explained above, since the water equipment of the present invention has excellent cavitation and erosion resistance, it can be said to be extremely useful in practice.

[Brief explanation of the drawing]

Figure 1 is a perspective view of the pump-turbine runner, Figure 2
is a sectional view of a pump-turbine runner. 1...Runner cone, 2...Crown, 3...Runner blade, 4...Schulland, 5...Guide vane, 6
…Stay Vane. 〓〓〓〓〓

Claims (1)

[Scope of Claims] 1. At least the surface layer of the cavitation/erosion wear area has a weight percentage of carbon of 0.2% or less, silicon of 2% or less, and chromium of 10 to 20%,
0.5 to 10% nickel, more than 4% but less than 20% manganese, less than 2% molybdenum, and the remainder is substantially iron, and is mainly composed of epsilon phase or austenite phase without substantially containing ferrite phase. Water equipment characterized by being made of steel. 2. By overlay welding on at least cavitation/erosion damage parts of water equipment,
Carbon below 0.2%, Silicon below 2%, 10-20%
of chromium, 0.5-10% nickel, over 4%20
% or less of manganese, molybdenum of 2% or less, and the remainder substantially consists of iron, and is characterized by forming a surface layer consisting of steel mainly consisting of epsilon phase or austenite phase without substantially containing ferrite phase. A manufacturing method for water equipment.