Stainless steel material for marine propellers 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 a ship propeller constituted by blending various materials in specific proportions. Specifically, when the stainless steel material is applied to a propeller, it generates good fluidity, is not only advantageous for the molding of the propeller, but also has excellent impact resistance compared to conventional stainless steel materials. That is, it can meet the conditions for a ship propeller that can withstand the impact of seawater for a long time.

Background Art

[0002] Taiwan is surrounded by sea and has many small islands around it. Taking advantage of this geographical location, it has developed regional commercial trade, tourism and leisure industries centered around the sea. In economic development, the import and export of many goods have to rely on maritime transportation. Large cruise ships carry tourists between different regions, and many coastal tourist destinations also focus on various water sports, so the demand for various ships is very high. Therefore, many large, medium and small ship hulls are established in places close to the port.

[0003] The shipbuilding industry includes not only shipyards responsible for hull construction, but also many related manufacturers, such as ship propeller manufacturers, ship hardware manufacturers, ship information equipment manufacturers, and ship outfitting manufacturers. Propellers are installed on large container ships, cruise ships, warships, as well as small and medium-sized fishing boats, yachts, and jet skis, and propel the ship forward by rotating under the power of a motor. When manufacturing ship propellers, plastic or metal materials can be used. For propellers used submerged in water for long periods, good corrosion resistance and impact resistance are required, so materials with high strength and corrosion resistance are generally used. In contrast, 17-4PH (stainless steel) listed in Patent Document 1 and 15-5PH (stainless steel) listed in Patent Document 2 are classified as precipitation-hardening stainless steels and are widely used in various industries such as aerospace, golf equipment, ship parts, and industrial parts. However, they have the disadvantage of poor fluidity during casting and noticeable chrome pitting, which makes them prone to failure due to defects in the molded surface, thus increasing manufacturing costs.

[0004] While stainless steel with a high silicon content, as described in Patent Document 3, can achieve higher tensile strength in order to maintain good fluidity during manufacturing, it cannot ensure impact resistance, thus increasing the risk of propeller breakage when used in the manufacture of marine propellers. In contrast, the object of the present invention is to provide a material for marine propellers that can maintain good fluidity during casting, reduce the occurrence rate of defects on the molded surface, and possess good impact resistance.

[0005] Therefore, in light of the many shortcomings of existing stainless steel materials used in marine propellers, the inventor created this invention by relying on extensive expertise and many years of practical experience to make improvements. [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 [Overview of the project] [Problems that the invention aims to solve]

[0007] The primary objective of this invention is to provide a stainless steel material for marine propellers. This stainless steel material for marine propellers is composed by adding silicon (Si) and cobalt (Co) in appropriate proportions and adjusting the proportions of other materials, resulting in a stainless steel material with corrosion resistance, impact resistance, and high strength. In the manufacturing process of marine propellers, it is possible to suppress the occurrence of chromium pitting on the molded surface, improve the yield of finished products, and thus reduce manufacturing costs. [Means for solving the problem]

[0008] To address the aforementioned challenges, the composition of stainless steel material 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. These other components consist of 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 molten metal. Subsequently, the molten metal is transferred to a ceramic mold heated to 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 molding of stainless steel material by H1100 precipitation hardening.

[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 drawing]

[0015] [Figure 1] This is an organizational chart of Schaeffler for one embodiment of the present invention and other stainless steel materials. [Modes for carrying out the invention]

[0016] (One embodiment) According to one embodiment of the present invention, the composition of the stainless steel material for a marine propeller is 14.0 to 14.8 wt% chromium (Cr) and 5.4 to 6.0 wt% nickel. The elements are (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), 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 Standard (JIS) G5121 standard for stainless steel castings. First, in the step of manufacturing the mold for the marine propeller, a wax pattern is formed for the mold, followed by repeating the processes of dipping, stuccoing, and drying five times, and then the wax is removed by steam dewaxing to form a mold from ceramic material.

[0018] Proceed to the next step, 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 up to 1620 °C to generate molten metal, then proceed to the pouring step, pour the molten metal into a mold and let it cool. After the mold has cooled, proceed to the de-shell step, remove the mold, and then proceed to the sand blasting treatment to shape the prototype casting. Subsequently, proceed to the step of improving properties such as hardness, strength, toughness and corrosion resistance by heat treatment, transfer the prototype casting to a vacuum furnace, and carry out a solution heat treatment at 1050 °C for one and a half hours. Subsequently, form the ship propeller of the present invention by Hxxx precipitation hardening treatment. Subsequently, enhance the flatness, roughness and gloss of the product by surface treatment.

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

[0020] (Table 1) TIFF0007900459000001.tif63167

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

[0022] Carbon (C) is a component that increases the hardness of stainless steel. If the carbon content is too high, excessive carbides will precipitate, reducing the fracture toughness and affecting the corrosion resistance. Therefore, it is preferable to limit the carbon (C) content to 0.001 to 0.05 wt% and increase the hardness of the stainless steel by other elements.

[0023] Molybdenum (Mo) and vanadium (V) can combine with carbon (c) to precipitate carbides and increase the hardness of the stainless steel material. Molybdenum (Mo) can enhance the corrosion resistance of the stainless steel material. 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 as described above and may not be added in the embodiments.

[0024] Phosphorus (P) and sulfur (S) were not shown in Table 1. Adding sulfur (S) facilitates the processing of stainless steel, but it reduces the mechanical properties. Therefore, it is preferable to limit the sulfur (S) content to 0.03 wt% or less. The lower the phosphorus (P) content, the more preferable. Considering the cost, phosphorus (P) is generally limited to 0.04 wt% or less. Nitrogen (N) increases the strength of stainless steel but reduces the impact resistance. If the nitrogen content is too high, pore defects will occur. Therefore, the nitrogen (N) content is limited to 0.05 wt% or less.

[0025] (Table 2) TIFF0007900459000002.tif52170

[0026] Table 1 shows the proportions of the components disclosed in the embodiments. Table 2 shows the Ni equivalent and Gr equivalent of the examples disclosed in Table 1 and the conventional 15-5PH and 17-4PH (stainless steel). Figure 1 is the Schaeffler structure diagram of the examples disclosed in Table 1 and the conventional 15-5PH and 17-4PH (stainless steel).

[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(Titanium) + 0.75(W)

[0029] As shown in Figure 1, Examples X71, X72, X81, and X82 belong to the category of three-phase stainless steel materials consisting of an austenite phase, a martensite phase, and a ferrite phase, and were found to be biased towards the austenite microstructure, i.e., possessing good fracture toughness.

[0030] In stainless steel materials, manganese (Mn) and sulfur (S) react chemically to form manganese sulfide (MnS), which suppresses the formation of ferrous sulfide (FeS). Therefore, adding 0.3 to 0.7 wt% of manganese (Mn) to the material can reduce the occurrence of hot cracking (hot tearing). However, adding more than 0.7 wt% of manganese (Mn) causes the microstructure of the stainless steel material to lean towards austenitic-ferritic stainless steel, thus reducing its hardness.

[0031] (Table 3) TIFF0007900459000003.tif156170

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

[0033] In Table 3, YS indicates the yield strength, TS indicates the tensile strength, and EL indicates the elongation.

[0034] Conventional 15-5PH (stainless steel) or 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 increases from 1.52 to 1.98 wt%, thereby increasing the fluidity of the molten metal during casting. Increased fluidity of the molten metal is advantageous for propeller molding and can reduce the occurrence of chromium pitting on the propeller surface.

[0035] To suppress the degradation of mechanical properties caused by excessive chromium (Cr), this invention limits the chromium (Cr) content to 14.0 to 14.8 wt% and the nickel (Ni) content to 5.4 to 6.0 wt%. Furthermore, the impact strength of the stainless steel is increased by adding 0.01 to 1.0 wt% cobalt (Co). 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 were found to have average fracture toughness significantly exceeding that of 15-5PH and 17-4PH (stainless steel), reaching 45.3 J. The differences in yield strength and tensile strength between Examples X71, X72, X81, X82, and conventional 15-5PH and 17-4PH (stainless steel) are not very 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 exhibit resistance to deformation. To put it another way, the stainless steel material according to the present invention is not only suitable for marine propeller elements, but also possesses sufficient strength to withstand the impact of seawater over long periods, thereby extending its service life.

[0036] The above is a description of this embodiment. Compared to the conventional technology, 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 improved fluidity during casting by adjusting the silicon (Si) content. This is advantageous not only for forming the propeller during the casting process, but also for reducing surface chromium pitting defects, improving the yield of marine propellers, and effectively reducing manufacturing costs.

[0038] The stainless steel material for ship propellers according to the present invention has superior fracture toughness compared to conventional stainless steel materials because its impact resistance is enhanced by the addition of an appropriate amount of cobalt (Co). In other words, it can be used for the manufacture of ship propellers.

[0039] In other words, the stainless steel material for ship propellers according to the present invention can achieve the expected effects of use by the embodiments described above.

[0040] The present invention is not limited in any way to the embodiments described above, and can be implemented in various forms without departing from the spirit of the invention.

Claims

1. Used in the manufacture of marine propellers, The main components are 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), 0.01 to 0.3 wt% molybdenum (Mo), 0.01 to 0.05 wt% vanadium (V), and 0.005 to 0.05 wt% nitrogen (N), with the remaining portion being iron (Fe) and unavoidable impurities. Stainless steel material for marine propellers, characterized by being a three-phase stainless steel material consisting of an austenite phase, a martensite phase, and a ferrite phase.

2. The stainless steel material for a ship's propeller according to claim 1, further characterized by containing 0.04 wt% or less of phosphorus (P).

3. The stainless steel material for a ship's propeller according to claim 1, further characterized by containing 0.03 wt% or less of sulfur (S).

4. A method for producing stainless steel material for a ship's 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), molybdenum (Mo), vanadium (V), nitrogen (N), and iron (Fe) is heated to 1600°C to 1700°C to produce molten metal, the molten metal is then transferred to a ceramic mold at 1100°C to 1150°C and cooled, the ceramic mold is then removed and a solution heat treatment is carried out at 1050°C to 1100°C for 1.5 hours, followed by molding by H1100 precipitation hardening to obtain a three-phase stainless steel material consisting of an austenite phase, a martensite phase, and a ferrite phase.

Images