Stainless steel material for marine propeller

Abstract

The invention relates to a stainless steel material for a marine propeller, which comprises the following components in percentage by weight: 14.0 to 14.8 percent of chromium (Cr), 5.4 to 6.0 percent of nickel (Ni), 1.52 to 1.98 percent of silicon (Si), 0.001 to 0.05 percent of carbon (C), 0.3 to 0.7 percent of manganese (Mn), 2.5 to 3.5 percent of copper (Cu), 0.01 to 1.0 percent of cobalt (Co), 0.2 to 0.3 percent of niobium (Nb) and the balance of iron (Fe) and inevitable impurities. When the stainless steel material is cast, good fluidity can be provided, forming of the marine propeller is facilitated, and the impact resistance is improved.

Description

Technical Field

[0001] This invention relates to a stainless steel material, and more particularly to a stainless steel material that can be used to manufacture ship propellers. By adjusting the specific proportions of each material, better fluidity can be obtained during propeller manufacturing, which is beneficial for shaping the propeller. Compared with traditional stainless steel materials, it has better impact resistance and is quite suitable for use in ship propellers that need to be subjected to seawater impact for a long time. Background Technology

[0002] Surrounded by the sea and dotted with numerous small islands, this region benefits from its advantageous topography, leading to a development of commerce, trade, and entertainment centered around the ocean. Economic development relies heavily on maritime transport for goods, and large cruise ships carry tourists to and from other regions. Many coastal tourist areas also feature a variety of water sports. This demonstrates a high demand for various types of vessels, resulting in numerous shipyards, including those for large and medium-sized vessels, established in areas near various ports.

[0003] The shipbuilding industry includes not only shipyards responsible for hull construction, but also many manufacturers of related components, such as propeller manufacturers, marine hardware manufacturers, marine information equipment manufacturers, and marine parts manufacturers. Propellers are used in everything from large container ships, cruise ships, and warships to small and medium-sized fishing boats, yachts, and jet skis. A motor drives the propeller to rotate, propelling the vessel forward. Materials used to manufacture marine propellers can be plastic or metal. Because propellers are immersed in water for extended periods, they require excellent corrosion resistance and impact resistance; therefore, high-strength and corrosion-resistant materials are typically chosen. Chinese patent publications CN103643160A and CN116426725A respectively disclose 17-4 and 15-5 stainless steel materials. 17-4 and 15-5 stainless steel are precipitation-hardening stainless steels, widely used in aerospace, golf equipment, ship parts, and industrial components. However, when used in casting, they exhibit poor fluidity and chromium pitting (chrome corrosion). Pitting has obvious drawbacks, which can easily lead to defects in the molding surface and result in failure, thereby increasing manufacturing costs.

[0004] To achieve good flowability during manufacturing, US Patent Publication No. 2004 / 0042926A1 provides a stainless steel material with high silicon content. While this material achieves high tensile strength, it sacrifices impact resistance, increasing the risk of propeller breakage if used in ship propeller manufacturing. Therefore, the inventor's inventive concept is to provide a material with excellent casting flowability to reduce the probability of surface defects during product forming, while also possessing good impact resistance. Summary of the Invention

[0005] In view of the fact that the existing stainless steel materials for marine propellers still have many shortcomings in actual use, this invention is derived by utilizing extensive professional knowledge and years of practical experience.

[0006] The main objective of this invention is to provide a stainless steel material for marine propellers. By adding appropriate proportions of silicon (Si) and cobalt (Co) and adjusting the composition ratio of other materials, a stainless steel material with corrosion resistance, impact resistance, and high strength is formed. Furthermore, during the manufacturing process of marine propellers, the occurrence of chromium pitting on the surface can be reduced, the manufacturing success rate of the product can be improved, and the manufacturing cost can be effectively reduced.

[0007] To achieve the above-mentioned objectives, the present invention provides a stainless steel material for a marine propeller, comprising 14.0-14.8 wt% chromium (Cr), 5.4-6.0 wt% nickel (Ni), 1.52-1.98 wt% silicon (Si), 0.001-0.05 wt% carbon (C), 0.3-0.7 wt% manganese (Mn), 2.5-3.5 wt% copper (Cu), 0.01-1.0 wt% cobalt (Co), and 0.2-0.3 wt% niobium (Nb), with the remainder comprising iron (Fe) and unavoidable impurities.

[0008] In one embodiment of the present invention, an alloy material containing chromium (Cr), nickel (Ni), silicon (Si), carbon (C), manganese (Mn), copper (Cu), cobalt (Co), niobium (Nb), and iron (Fe) is heated to a temperature of 1600℃-1700℃ and mixed into molten iron. The molten iron is then added to a ceramic mold at a temperature of 1100℃-1150℃. After cooling, the mold is removed, and a solution treatment is performed at a temperature of 1050℃-1100℃ for 1.5 hours. Then, H1100 precipitation hardening is performed to obtain stainless steel material.

[0009] In one embodiment of the present invention, the stainless steel material may further contain less than 0.3 wt% molybdenum (Mo).

[0010] In one embodiment of the present invention, the stainless steel material may further contain less than 0.05 wt% vanadium (V).

[0011] In one embodiment of the present invention, the stainless steel material may further contain less than 0.05 wt% nitrogen (N).

[0012] In one embodiment of the present invention, the stainless steel material may further contain less than 0.04 wt% phosphorus (P).

[0013] In one embodiment of the invention, the stainless steel material may further contain less than 0.03 wt% sulfur (S). Attached Figure Description

[0014] Figure 1 The Schaeffler diagrams of the preferred embodiments of the present invention and other stainless steel materials are shown. Detailed Implementation

[0015] The stainless steel material of the marine propeller of the present invention comprises 14.0-14.8 wt% chromium (Cr), 5.4-6.0 wt% nickel (Ni), 1.52-1.98 wt% silicon (Si), 0.001-0.05 wt% carbon (C), 0.3-0.7 wt% manganese (Mn), 0.01-0.3 wt% molybdenum (Mo), 0.01-0.05 wt% vanadium (V), 2.5-3.5 wt% copper (Cu), 0.01-1.0 wt% cobalt (Co), 0.2-0.3 wt% niobium (Nb), 0.005-0.05 wt% nitrogen (N), 0.01-0.04 wt% phosphorus (P), and 0.001-0.03 wt% sulfur (S), with the remainder being iron (Fe).

[0016] In implementing this invention, it is manufactured according to the G5121 standard of the Japanese Industrial Standards (JIS) for stainless steel castings. First, a mold for a ship's propeller is made. After creating a wax pattern for the mold, it undergoes five repeated processes of dipping, stuccoing, and drying. Finally, the wax is removed by steam dewaxing, resulting in a mold made of ceramic material.

[0017] The alloy material containing chromium, nickel, silicon, carbon, manganese, molybdenum, vanadium, copper, cobalt, niobium, nitrogen, phosphorus, sulfur, and iron is heated to 1620°C and mixed into molten iron. The mold is then heated to 1150°C, and the molten iron is poured into the mold. After cooling, the mold is removed through a de-shell process, and sandblasting is performed to obtain a rough blank. Heat treatment is then carried out to improve hardness, strength, toughness, and corrosion resistance. The product is placed in a vacuum furnace and subjected to solution treatment at 1050°C for 1.5 hours. Finally, H1100 precipitation hardening is performed to obtain the marine propeller of this invention. Further surface treatment can be performed to increase the smoothness, roughness, and gloss of the product surface.

[0018] In the embodiments, the present invention prepares multiple stainless steel materials in different proportions, and then processes them into tensile test bars conforming to the American Society for Testing and Materials (ASTM) standard E8 / E8M for tensile testing of metals and impact test pieces conforming to the Japanese Industrial Standard (JIS) standard Z2202 for impact testing of metallic materials, and compares their mechanical properties with those of traditional 15-5 stainless steel and 17-4 stainless steel.

[0019] The composition of embodiments X71, X72, X81 and X82 of the present invention is shown in Table 1.

[0020] Table 1:

[0021]

[0022] Carbon primarily enhances the hardness of stainless steel, but excessive carbon content can lead to the precipitation of too many carbides, which reduces impact toughness and affects corrosion resistance. Therefore, the carbon content is limited to 0.001-0.05 wt%, with other elements used to enhance the hardness of stainless steel.

[0023] Molybdenum and vanadium combine with carbon to precipitate carbides, increasing the hardness of stainless steel. Molybdenum also enhances the corrosion resistance of stainless steel. To maintain a certain impact resistance, the molybdenum content is limited to below 0.3 wt% and the vanadium content is limited to below 0.05 wt% to achieve the optimal ratio. However, in this invention, it is also possible to omit the addition of molybdenum and vanadium.

[0024] Table 1 does not show the composition of phosphorus and sulfur. Although sulfur can make stainless steel easier to process, it also means that the mechanical properties will decrease. Therefore, the sulfur content is limited to below 0.03 wt%. The phosphorus content is generally better the lower it is. Considering the cost of purification, it is usually limited to below 0.04 wt%. Furthermore, although nitrogen can improve the strength of stainless steel, it will also reduce the impact resistance. Excessive nitrogen content will form nitrogen porosity defects. Therefore, the nitrogen content is limited to below 0.05 wt%.

[0025] The composition ratios of the embodiments in Table 1, and the values ​​of their nickel equivalent (Nieq) and chromium equivalent (Creq) are shown in Table 2, which can also be consulted. Figure 1 The diagram shows the traditional 15-5 and 17-4 stainless steel materials and the Schaeffler diagram of the embodiments of the present invention.

[0026] Table 2:

[0027]

[0028] The formula for calculating the nickel equivalent is: Nieq = Ni + Co + 0.5 (manganese) + 0.3 (copper) + 25 (nitrogen) + 30 (carbon).

[0029] The formula for calculating chromium equivalent is: Creq = Cr + 2(silicon) + 1.5(molybdenum) + 5(vanadium) + 5.5(aluminum) + 1.75(niobium) + 1.5(titanium) + 0.75(tungsten).

[0030] Depend on Figure 1 As can be seen from the diagram, the positions of X71, X72, X81 and X82 in the Schaeffler diagram are basically stainless steel materials with a three-phase structure of Austenite + Martensite + Ferrite, but they are closer to the metallographic structure of Austenite, indicating better impact toughness.

[0031] In stainless steel, manganese and sulfur form manganese sulfide (MnS), which reduces the chance of ferrous sulfide (FeS) formation. Therefore, adding 0.3-0.7 wt% manganese in the examples can reduce hot tearing during casting. However, if too much manganese is added, the metallographic structure of the stainless steel will enter the ferroferroaluminate + ferroferroaluminate region, which will reduce the hardness.

[0032] Three samples of traditional stainless steel materials 15-5 and 17-4 and samples of Examples X71, X72, X81 and X82 were taken for tensile tests, and one sample of each was taken for impact tests. The test results are shown in Table 3.

[0033] Table 3:

[0034]

[0035] In Table 3, YS represents yield strength, TS represents tensile strength, and EL represents elongation.

[0036] Traditional stainless steel materials 15-5 or 17-4 typically contain less than 1 wt% silicon, while Table 1 shows that the silicon content of the present invention is increased to 1.52-1.98 wt%. This increases the fluidity of molten iron during casting, which is beneficial for the forming of the propeller shape and reduces the occurrence of chromium pitting on the propeller surface.

[0037] To prevent the mechanical properties from deteriorating due to excessively high chromium equivalent, the chromium content was controlled at 14.0-14.8 wt%, and the nickel content at 5.4-6.0 wt%. Furthermore, the impact resistance of the stainless steel was further improved by adding 0.01-1.0 wt% cobalt. As shown in Table 3, compared to traditional stainless steel materials 15-5 and 17-4, the average impact toughness of X71, X72, X81, and X82 in this embodiment reached 45.3 J, significantly higher than the impact toughness of 26.1 J and 9.9 J of 15-5 and 17-4 stainless steel, respectively. Furthermore, the yield strength and tensile strength of X71, X72, X81, and X82 in this embodiment are close to those of 15-5 and 17-4 stainless steel materials, indicating that the strength of this embodiment is not weaker than that of 15-5 and 17-4 stainless steel materials, and it also has good resistance to deformation. Therefore, the stainless steel material of this invention is more in line with the requirements of marine propellers, can be used in water for a long time, and provides sufficient impact resistance to extend service life.

[0038] As can be seen from the above description, compared with the prior art, the present invention has the following advantages:

[0039] 1. The stainless steel material of the marine propeller of the present invention, by adjusting the silicon content to increase the fluidity during casting, can help the propeller shape during casting, and also reduce the defects of chromium pitting on the surface, thereby improving the success rate of manufacturing marine propellers and effectively reducing manufacturing costs.

[0040] 2. The stainless steel material of the marine propeller of the present invention, by adding an appropriate amount of cobalt, can improve the impact resistance of the stainless steel material, and its impact toughness is significantly better than that of traditional stainless steel materials, making it more suitable for manufacturing ship propellers.

[0041] In summary, the stainless steel material of the marine propeller of the present invention can indeed achieve the expected performance through the above-disclosed embodiments; however, the above-disclosed drawings and descriptions are only preferred embodiments of the present invention, and the methods and constituent elements disclosed in the above embodiments are only illustrative examples and are not intended to limit the scope of the present invention. Substitutions or variations of other equivalent elements should also be covered by the claims of the present invention.

[0042] The specific embodiments described above should be interpreted as merely illustrative and not as limiting the remainder of the invention in any way.

Claims

1. A stainless steel material for a marine propeller, used to manufacture ship propellers, the stainless steel material comprising 14.0-14.8 wt% chromium (Cr), 5.4-6.0 wt% nickel (Ni), 1.52-1.98 wt% silicon (Si), 0.001-0.05 wt% carbon (C), 0.3-0.7 wt% manganese (Mn), 2.5-3.5 wt% copper (Cu), 0.01-1.1 wt% cobalt (Co), and 0.2-0.3 wt% niobium (Nb), the remainder comprising iron (Fe) and unavoidable impurities.

2. The stainless steel material for the marine propeller according to claim 1, characterized in that, The process involves heating an alloy containing chromium (Cr), nickel (Ni), silicon (Si), carbon (C), manganese (Mn), copper (Cu), cobalt (Co), niobium (Nb), and iron (Fe) to 1600℃-1700℃ to form molten iron. This molten iron is then poured into a ceramic mold at 1100℃-1150℃. After cooling, the mold is removed, and the mixture undergoes a solution treatment at 1050℃-1100℃ for 1.5 hours. Finally, H1100 precipitation hardening is performed to obtain the stainless steel material.

3. The stainless steel material for the marine propeller according to claim 1, characterized in that, The stainless steel material further contains less than 0.3 wt% molybdenum (Mo).

4. The stainless steel material for the marine propeller according to claim 1, characterized in that, The stainless steel material further contains less than 0.05 wt% vanadium (V).

5. The stainless steel material for the marine propeller according to claim 1, characterized in that, The stainless steel material further contains less than 0.06 wt% nitrogen (N).

6. The stainless steel material for the marine propeller according to claim 1, characterized in that, The stainless steel material further contains less than 0.04 wt% phosphorus (P).

7. The stainless steel material for the marine propeller according to claim 1, characterized in that, The stainless steel material further contains less than 0.03 wt% sulfur (S).

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