JPS633947B2 - - Google Patents

Description

[Detailed description of the invention]

[Object of the invention] (Industrial application field) The present invention is directed to anti-cavitation materials used in water turbine runners for hydroelectric power generation, guide vanes, stay vanes, marine propellers, various pumps, etc.
Concerning steel with excellent erosion properties. (Prior Art) In recent years, from the standpoint of effective energy use, construction of hydroelectric power plants whose output can be adjusted in a relatively short period of time, particularly pumped storage power plants that can effectively utilize surplus power at night, has been popular. Moreover, 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 high in head and head. . However, the increase in head, which leads to an increase in head and flow velocity, has caused problems in that cavitation increases and cavitation and erosion of the turbine runner is accelerated. Further, as ships become larger and faster, propellers are also becoming larger and faster, but this increased speed is accelerating cavitation and erosion of marine propellers. Conventionally, martensitic 13% Cr stainless steel cast steel containing a relatively large amount of Ni has been used for water turbine runner materials, guides, vane materials, stay vane materials, etc. However, due to higher head and head, cavitation and Erosion has been accelerated, and there is a demand for materials with even better cavitation and erosion resistance. Additionally, as propellers for ships become larger and faster, the propeller material is shifting from copper alloy to 13% Cr stainless cast steel, which can be lighter. There is a demand for a material with excellent erosion properties. The cavitation and erosion resistance of martensitic 13% Cr stainless steel cast steel has a Ni content of 9.
It is known that the cavitation resistance of cast steel containing about 9% Ni improves as the amount of Ni increases.
Erosion resistance is comparable to that of SUS304, an austenitic stainless steel. In general, the cavitation and erosion resistance of austenitic stainless steel is superior to that of martensitic 13% Cr cast stainless steel.
Because this material has low yield strength, it is used by overlay welding on parts of water turbine runners and other areas where cavitation/erosion wear is significant. (Problem to be solved by the invention) As the usage conditions of materials for hydroelectric power generation, marine propulsors, various pumps, etc. become more severe, materials with better cavitation and erosion resistance than conventional materials are being developed. It has been requested. In view of these points, an object of the present invention is to provide a steel with excellent cavitation and erosion resistance, which is superior to SUS304. [Structure of the invention] (Means for solving the problems) The present invention provides a method for adding a predetermined amount of Mn to Cr-Ni stainless steel.
Cavitation resistance is achieved by containing substantially no ferrite phase in the matrix, making the epsilon phase essential, and mainly consisting of the epsilon phase (hereinafter referred to as ε phase) or the austenite phase (hereinafter referred to as γ phase). - Improves erosion properties. i.e. in weight percent
0.20% or less C, 0.2-1.0% Si, 11-15% Cr,
0.5-10% Ni, more than 4% but less than 15% Mn, 2.0
% or less of Mo, the substrate must have an epsilon phase (ε phase), and an epsilon phase (ε phase)
Or, the cavitation and erosion resistance of steel mainly composed of austenite phase (γ phase)
It was discovered 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, the composition range (hereinafter referred to as the optimum composition range) necessary for forming the ε phase or γ phase exhibiting excellent cavitation and erosion resistance can be expanded by increasing the amount of C. That is, when the C content of martensitic stainless steel within the claimed composition range is increased, ε phase and γ phase are formed in the base composition, and the cavitation and erosion resistance is significantly improved. Furthermore, by adding Mo, the cavitation and erosion resistance is further improved. (Operation) Below, the reasons for limiting the scope of claims related to the present invention will be described. Composition: The cavitation and erosion resistance of the steel having the composition described in the claims is particularly effective when the steel has an ε phase as an essential component and is mainly composed of an ε phase or a γ phase. In this case, if a ferrite phase is mixed in the composition, the cavitation and erosion resistance will be significantly deteriorated, so it is necessary that the composition does not contain a ferrite 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): 0.2% or more of silicon is necessary to improve the flowability and weldability of steel during melting, but since excessive addition impairs toughness, the upper limit is set at 1%. However, in practice, it is desirable to set it to 0.2 to 0.8%. Chromium (Cr): It is necessary to add 11% or more of chromium to improve corrosion resistance, but the upper limit must be set because excessive addition will generate a ferrite layer in the weld layer and reduce cavitation and erosion resistance. It is set at 15%, but in practical terms it is set at 12%.
It is desirable to set it to 15%. Nickel (Ni): Nickel is necessary to combine with manganese to change the composition 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 improving cavitation and erosion resistance.・Addition of 0.5% or more is necessary to improve erosion properties and toughness. Even if added in large amounts, the effect is not great, and it actually inhibits phase transformation, lowers cavitation and erosion resistance, and increases costs. Therefore, the upper limit is set at 10%, but in practice it is 2%.
to 8%, more preferably more than 4.5% to 8%.
% or less. Manganese (Mn): Manganese combines with nickel to change the composition 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 15%, but in practical terms it is more desirable to set it at 4.5 to 10%. Molybdenum (Mo): Molybdenum improves cavitation and erosion resistance, but excessive addition impairs toughness, so the upper limit is set at 2%. 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 hydroelectric power generation equipment such as water turbine runners, guide vanes, stay vanes, etc., marine propellers, various pumps, etc., and can also be used as overlay welding materials for areas where cavitation/erosion occurs in hydroelectric power generation equipment such as water turbine runners, guide vanes, and stay vanes. It is a corrosion-resistant material that can be widely used in pipes and other areas where erosion resistance is required. (Example) The steel of the present invention will be explained in detail with reference to Examples below. Samples having the compositions shown in Table 1 were melted using a vacuum high-frequency induction melting furnace. The samples of Examples 1 to 6 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. Furthermore, in Comparative Examples 2 to 4, the materials were subjected to solution treatment at 1100°C for 2 hours, which corresponds to the heat treatment conventionally applied to runner materials, and then tempered at 650°C for 2 hours. It is.

【table】

[Table] The cavitation/erosion test was conducted using the electrostrictive vibration method at a frequency of 6.5 KHz, an amplitude of 100 μm, and a temperature of 25°C.
The cavitation erosion index (CEI) was calculated using the following formula. CEI = cavitation erosion weight loss (g)
/Test time (minutes) x specific gravity x 10 ⁶ In addition, the dominant phase of each sample was determined by optical microscopic observation, thermal expansion measurement, and X-ray diffraction. Examples 1 to 6 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 compositions of Examples 1 to 6 essentially contain ε phase and ε phase or γ phase, and their CEI was compared to SUS304 (Comparative Example 1), which is considered to have excellent cavitation and erosion resistance. ), which shows that the corrosion-resistant material according to the present invention has excellent cavitation and erosion resistance. Although the compositions of Examples 1 and 2 may contain some α' phase (martensite phase), they exhibit excellent cavitation and erosion resistance due to the presence of the ε phase. In addition, the compositions of Examples 3, 4, and 5 are mainly composed of γ phase, but always contain ε phase. As described above, the cavitation/erosion resistant material according to the present invention exhibits excellent cavitation/erosion resistance if it does not contain a ferrite phase but has an ε phase as its essential phase, and if the ε phase and γ phase are the main phases. [Effects of the Invention] As explained above, the steel according to the present invention has excellent cavitation and erosion resistance, and is suitable for use in water turbine runners for hydroelectric power generation, guide vanes, stay vane marine propellers, and various pumps. This can be said to be applied as a member that requires cavitation/erosion properties.

Claims (1)

[Claims] 1 Carbon not more than 0.20% by weight, 0.2~
1.0% silicon, 11-15% chromium, 0.5-10% nickel, more than 4% and less than 15% manganese, 2.0
% or less of molybdenum, the remainder being substantially iron, and having essentially an epsilon phase without substantially containing a ferrite phase, and mainly consisting of an epsilon phase or an austenite phase. Superior steel.