Stainless steel material for marine propeller and method for manufacturing stainless steel material

Abstract

To provide a stainless steel material for a marine propeller.SOLUTION: The composition of the stainless-steel material for a marine propeller includes 14.0 to 14. 8wt% of chromium (Cr), 5.4 to 6. 0wt% of nickel (Ni), 1.52 to 1. 98wt% of silicon (Si), 0.001 to 0. 05wt% of C, 0.3 to 0. 7wt% of manganese (Mn), 2.5 to 3. 5wt% of copper (Cu), 0.01 to 1. 0wt% of cobalt (Co), 0.2 to 0. 3wt% of niobium (Nb), and a remainder. The remainder is iron (Fe) and unavoidable impurities. The above-mentioned proportions of the components can not only maintain good fluidity during casting, but also facilitate the molding of the marine propeller and increase the impact resistance.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a stainless steel material, particularly a stainless steel material for marine propellers, which is made by blending various materials in specific proportions. Specifically, when used in propellers, the stainless steel material not only exhibits good fluidity, which is advantageous for molding the propeller, but also has superior impact resistance compared to conventional stainless steel materials. In other words, it can meet the requirements for marine propellers that can withstand the impact of seawater over long periods of time. [Background technology]

[0002] Taiwan is surrounded by water and is surrounded by many small islands. Taking advantage of this geographical advantage, the country has developed its regional trade, tourism, and leisure industries, centered on the sea. As the economy develops, the import and export of much of its goods must rely on maritime transport. Large cruise ships transport tourists to and from other regions, and many coastal tourist destinations also place emphasis on various water sports, creating a high demand for a variety of vessels. Therefore, numerous large, medium, and small vessels have been established near ports.

[0003] The marine industry includes not only shipyards responsible for building ship hulls, but also many related manufacturers, such as marine propeller manufacturers, marine hardware manufacturers, marine information equipment manufacturers, and marine outfitting manufacturers. Propellers are attached to large container ships, cruise ships, and warships, as well as small and medium-sized fishing boats, yachts, and jet skis, and rotate using the driving force of a motor to propel the hull forward. Marine propellers can be manufactured using either plastic or metal materials. Propellers used for long periods of time underwater require good corrosion resistance and impact resistance, so materials with high strength and corrosion resistance are generally used. In contrast, 17-4PH (stainless steel) disclosed in Patent Document 1 and 15-5PH (stainless steel) disclosed in Patent Document 2 are classified as precipitation-hardened stainless steels and are widely used in various industries, including aerospace, golf equipment, marine parts, and industrial parts. However, they have disadvantages: poor fluidity during casting and noticeable chrome pitting, which makes them prone to failure due to defects on the molding surface, resulting in higher manufacturing costs.

[0004] The stainless steel with a high silicon content disclosed in Patent Document 3 maintains good fluidity during manufacturing, which allows it to achieve higher tensile strength, but it does not ensure impact resistance, so when used to manufacture marine propellers, there is a high risk of the propeller breaking. In response, the objective of the present invention is to provide a material for marine propellers that maintains good fluidity during casting, reduces the incidence of defects on the molding surface, and has good impact resistance.

[0005] Therefore, the inventor has considered the many shortcomings of the stainless steel materials currently used in marine propellers and has created the present invention by making improvements based on his extensive expertise and many years of practical experience. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] CN 103643160 A publication publication [Patent Document 2] CN 116426725 A publication publication [Patent Document 3] US 2004 / 0042926 A1 publication publication Summary of the Invention [Problem to be solved by the invention]

[0007] The main objective of this invention is to provide a stainless steel material for marine propellers. This stainless steel material for marine propellers is made by adding silicon (Si) and cobalt (Co) in appropriate proportions and adjusting the proportions of other materials, resulting in corrosion resistance, impact resistance, and high strength. This stainless steel material can suppress the occurrence of chrome pitting on the molding surface during the marine propeller manufacturing process, improve the yield of finished products, and reduce manufacturing costs. [Means for solving the problem]

[0008] To solve the above-mentioned problems, the composition of stainless steel materials for marine propellers includes 14.0 to 14.8 wt% chromium (Cr), 5.4 to 6.0 wt% nickel (Ni), 1.52 to 1.98 wt% silicon (Si), 0.001 to 0.05 wt% carbon (C), 0.3 to 0.7 wt% manganese (Mn), 2.5 to 3.5 wt% copper (Cu), 0.01 to 1.0 wt% cobalt (Co), 0.2 to 0.3 wt% niobium (Nb), and other components, the remaining components being iron (Fe) and unavoidable impurities.

[0009] In one embodiment of the present invention, an alloy material of chromium (Cr), nickel (Ni), silicon (Si), carbon (C), manganese (Mn), copper (Cu), cobalt (Co), niobium (Nb), and iron (Fe) is heated to 1600°C to 1700°C to produce a molten metal. The molten metal is then transferred to a ceramic mold at 1100°C to 1150°C and allowed to cool. After cooling, the mold is removed and a solution heat treatment is carried out at 1050°C to 1100°C for 1.5 hours, followed by H1100 precipitation hardening to produce a stainless steel material.

[0010] In one embodiment of the present invention, the stainless steel material further contains 0.3 wt% or less of molybdenum (Mo).

[0011] In one embodiment of the present invention, the stainless steel material further contains 0.05 wt% or less of vanadium (V).

[0012] In one embodiment of the present invention, the stainless steel material further contains 0.05 wt% or less of nitrogen (N).

[0013] In one embodiment of the present invention, the stainless steel material further contains 0.04 wt% or less of phosphorus (P).

[0014] In one embodiment of the present invention, the stainless steel material further contains 0.03 wt% or less of sulfur (S). [Brief explanation of the drawings]

[0015] [Figure 1] 1 is a Schaeffler structural diagram of an embodiment of the present invention and another stainless steel material. DETAILED DESCRIPTION OF THE INVENTION

[0016] (One embodiment) The stainless steel material of the marine propeller according to one embodiment of the present invention contains 14.0 to 14.8 wt% chromium (Cr), 5.4 to 6.0 wt% nickel. (Ni), 1.52 to 1.98 wt% silicon (Si), 0.001 to 0.05 wt% carbon (C), 0.3 to 0.7 wt% manganese (Mn), 0.01 to 0.3 wt% molybdenum (Mo), 0.01 to 0.05 wt% vanadium (V), 2.5 to 3.5 wt% copper (Cu), 0.01 to 1.0 wt% cobalt (Co), 0.2 to 0.3 wt% niobium (Nb), 0.005 to 0.05 wt% nitrogen (N), 0.01 to 0.04 wt% phosphorus (P), and 0.001 to 0.03 wt% sulfur (S) and iron (Fe).

[0017] As one embodiment of the present invention, a marine propeller is manufactured in accordance with the Japanese Industrial Standards (JIS) G5121 standard for stainless steel castings. First, in the step of manufacturing a mold for a marine propeller, a wax pattern for the mold is formed, and then the processes of dipping, stuccoing, and drying are repeated five times. After that, the wax is removed by steam dewaxing, and a ceramic mold is formed.

[0018] The next step is to heat an alloy of chromium (Cr), nickel (Ni), silicon (Si), carbon (C), manganese (Mn), molybdenum (Mo), vanadium (V), copper (Cu), cobalt (Co), niobium (Nb), nitrogen (N), phosphorus (P), sulfur (S), and iron to 1620°C to produce a molten metal. The molten metal then moves on to the pouring process, where it is poured into a mold and cooled. After the mold cools, the de-shelling process involves removing the mold, followed by sandblasting to create a prototype casting. The next step involves heat treatment to improve properties such as hardness, strength, toughness, and corrosion resistance. The prototype casting is then transferred to a vacuum furnace and subjected to solution heat treatment at 1050°C for an hour and a half. The marine propeller of the present invention is then molded by H1100 precipitation hardening, followed by surface treatment to improve the flatness, roughness and gloss of the product.

[0019] In this embodiment, multiple stainless steel materials are molded at different ratios, and then processed to produce tensile test bars in accordance with the American Society for Testing and Materials (ASTM) metal tensile testing standard E8 / E8M. At the same time, metallic material impact test pieces are produced in accordance with the Japanese Industrial Standards (JIS) metallic material impact test standard Z2202. Next, the mechanical properties of the tensile test bars, metallic material impact test pieces, conventional 15-5PH (stainless steel), and 17-4PH (stainless steel) are compared.

[0020] (Table 1) TIFF2026025804000002.tif63167

[0021] The components of Examples X71, X72, X81 and X82 of the present invention are shown in Table 1.

[0022] Carbon (C) is an element that increases the hardness of stainless steel. If the carbon content is too high, excess carbides will precipitate, reducing fracture toughness and affecting corrosion resistance. Therefore, it is preferable to limit the carbon (C) content to 0.001 to 0.05 wt% and increase the hardness of stainless steel with another element.

[0023] Molybdenum (Mo) and vanadium (V) combine with carbon (C) to precipitate carbides, increasing the hardness of stainless steel materials. Molybdenum (Mo) can improve the corrosion resistance of stainless steel materials. To maintain a constant impact resistance, it is most preferable to limit the molybdenum (Mo) content to 0.3 wt% or less and the vanadium (V) content to 0.05 wt% or less. Molybdenum (Mo) and vanadium (V) are not limited to the above and may not be added in some embodiments.

[0024] Phosphorus (P) and sulfur (S) are not listed in Table 1. Adding sulfur (S) makes stainless steel easier to process, but it also reduces its mechanical properties, so it is preferable to limit the sulfur (S) content to 0.03 wt% or less. The lower the phosphorus (P) content, the better. Considering cost, phosphorus (P) is generally limited to 0.04 wt% or less. Nitrogen (N) increases the strength of stainless steel, but reduces its impact resistance. Too much nitrogen can cause porosity defects, so the nitrogen (N) content is limited to 0.05 wt% or less.

[0025] (Table 2) TIFF2026025804000003.tif52170

[0026] Table 1 shows the proportions of the listed components according to the embodiment. Table 2 shows the Ni equivalent and Gr equivalent of the examples and conventional 15-5PH and 17-4PH (stainless steel) listed in Table 1. Figure 1 shows the Schaeffler structural diagram of the examples and conventional 15-5PH and 17-4PH (stainless steel) listed in Table 1.

[0027] Ni equivalent=Ni+Co+0.5(Mn)+0.3(Cu)+25(N)+30(C)

[0028] Cr equivalent = Cr + 2(Si) + 1.5(Mo) + 5(V) + 5.5(Al) + 1.75(Nb) + 1.5(Ti) + 0.75(W)

[0029] As shown in FIG. 1, Examples X71, X72, X81, and X82 belong to the triple-phase stainless steel material consisting of an austenite phase, a martensite phase, and a ferrite phase, and it was found that they have a metal structure biased toward austenite, i.e., good fracture toughness.

[0030] In stainless steel, manganese (Mn) and sulfur (S) chemically react to form manganese sulfide (MnS), which inhibits the formation of ferrous sulfide (FeS). Adding 0.3 to 0.7 wt% of manganese (Mn) to the steel can reduce the occurrence of hot tearing. However, adding more than 0.7 wt% of manganese (Mn) shifts the metal structure of the stainless steel toward austenitic-ferritic stainless steel, reducing hardness.

[0031] (Table 3) TIFF2026025804000004.tif156170

[0032] Next, three samples of the conventional 15-5PH and 17-4PH (stainless steel) and the examples X71, X72, X81, and X82 were subjected to tensile tests, and one sample of each was subjected to impact tests. The test results are shown in Table 3.

[0033] In Table 3, the notation YS indicates Yield Strength, the notation TS indicates Tensile Strength, and the notation EL indicates Elongation.

[0034] Conventional 15-5PH (stainless steel) and 17-4PH (stainless steel) have a silicon (Si) content of 1 wt% or less. In contrast, as shown in Table 1, the silicon (Si) content of the present invention is increased from 1.52 to 1.98 wt%, which increases the fluidity of the molten metal during casting. Increasing the fluidity of the molten metal is beneficial for propeller molding and reduces the occurrence of chrome pitting on the propeller surface.

[0035] To prevent the deterioration of mechanical properties due to excessive chromium (Cr), the present invention limits the chromium (Cr) content to 14.0 to 14.8 wt% and simultaneously limits the nickel (Ni) content to 5.4 to 6.0 wt%. Furthermore, the addition of 0.01 to 1.0 wt% cobalt (Co) increases the impact resistance of stainless steel materials. As shown in Table 3, 15-5PH (stainless steel) has an average fracture toughness of 26.1 J. 17-4PH (stainless steel) has an average fracture toughness of 9.9 J. In contrast, Examples X71, X72, X81, and X82 significantly exceed those of 15-5PH and 17-4PH (stainless steels), reaching an average fracture toughness of 45.3 J. Furthermore, the differences in yield strength and tensile strength between Examples X71, X72, X81, and X82 and the conventional 15-5PH and 17-4PH (stainless steels) are not significant. In other words, the strength of Examples X71, X72, X81, and X82 is comparable to that of conventional 15-5PH and 17-4PH (stainless steel), and they have the ability to resist deformation. In other words, the stainless steel material of the present invention is not only suitable for marine propeller components, but also has sufficient strength to withstand the impact of seawater for a long period of time, thereby extending its service life.

[0036] The above is a description of the present embodiment. Compared with the prior art, the features and advantages of the present invention are as follows:

[0037] The stainless steel material for marine propellers according to the present invention has an increased fluidity during casting due to the adjustment of the silicon (Si) content, which is not only advantageous for propeller molding during the casting process but also reduces surface chrome pitting defects, improves marine propeller yields, and effectively reduces manufacturing costs.

[0038] The stainless steel material for marine propellers according to the present invention has an improved impact resistance due to the addition of an appropriate amount of cobalt (Co), and therefore has superior fracture toughness to conventional stainless steel materials, making it suitable for the manufacture of marine propellers.

[0039] In other words, the stainless steel material of the marine propeller according to the present invention can achieve the expected usage effects of the above-mentioned embodiments.

[0040] As described above, the present invention is not limited to the above-described embodiment, and can be embodied in various forms without departing from the spirit of the invention.

Claims

1. Used in the manufacture of marine propellers, A stainless steel material for marine propellers characterized by its main components being 14.0 to 14.8 wt% chromium (Cr), 5.4 to 6.0 wt% nickel (Ni), 1.52 to 1.98 wt% silicon (Si), 0.001 to 0.05 wt% carbon (C), 0.3 to 0.7 wt% manganese (Mn), 2.5 to 3.5 wt% copper (Cu), 0.01 to 1.0 wt% cobalt (Co), and 0.2 to 0.3 wt% niobium (Nb), with the remainder being iron (Fe) and unavoidable impurities.

2. 2. The stainless steel material for a marine propeller according to claim 1, characterized in that 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 1600 to 1700°C to produce a molten metal, which is then transferred to a ceramic mold at 1100 to 1150°C and cooled, after which the ceramic mold is removed and the stainless steel is subjected to solution heat treatment at 1050 to 1100°C for one and a half hours, followed by H1100 precipitation hardening treatment to form the stainless steel.

3. 2. The stainless steel material for a marine propeller according to claim 1, further comprising 0.3 wt % or less of molybdenum (Mo).

4. 2. The stainless steel material for a marine propeller according to claim 1, further comprising 0.05 wt % or less of vanadium (V).

5. 2. The stainless steel material for a marine propeller according to claim 1, further containing 0.06 wt % or less of nitrogen (N).

6. 2. The stainless steel material for a marine propeller according to claim 1, further comprising 0.04 wt % or less of phosphorus (P).

7. 2. The stainless steel material for a marine propeller according to claim 1, further containing 0.03 wt % or less of sulfur (S).

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