Stainless steel material

Abstract

To provide stainless steel materials suitable for casting and molding. [Solution] The stainless steel material is applied to marine propellers and contains 14.6 to 16.1 wt% chromium (Cr), 5.4 to 6.2 wt% nickel (Ni), 1.52 to 2.2 wt% silicon (Si), 0.001 to 0.05 wt% carbon (C), 0.3 to 0.8 wt% manganese (Mn), 2.5 to 3.2 wt% copper (Cu), 1.2 to 2.0 wt% cobalt (Co), and 0.2 to 0.3 wt% niobium (Nb), as well as (Fe) and unavoidable impurities. In the casting process, the stainless steel material exhibits good fluidity, making it advantageous for forming thin-walled castings. Furthermore, the yield strength can be adjusted according to the actual conditions to facilitate the shaping process, while simultaneously maintaining tensile strength and impact resistance, resulting in a fracture strength far exceeding that of conventional duplex stainless steel materials.

Description

Technical Field

[0001] The present invention relates to a stainless steel material, particularly a stainless steel material suitable for casting and molding. Specifically, the stainless steel material is formulated with each material in a specific ratio, and by improving the moldability of thin-walled castings such as propellers and golf club heads, the casting can meet the required appearance and specifications.

Background Art

[0002] The shipbuilding industry includes not only shipyards responsible for hull manufacturing but also many related manufacturers, such as ship propeller manufacturers, ship hardware manufacturers, ship information equipment manufacturers, ship fitting manufacturers, etc. Propellers are installed on large container ships, cruise ships, warships, as well as small and medium-sized fishing boats, yachts, jet skis, etc. They rotate by the driving force of the motor while advancing the hull. When manufacturing ship propellers, plastic materials or metal materials can be adopted. Since propellers used by being immersed in water for a long time require good corrosion resistance and impact resistance, materials with high strength and corrosion resistance are generally adopted. On the other hand, 17-4PH (stainless steel) disclosed by Patent Document 1 and 15-5PH (stainless steel) disclosed by Patent Document 2 are classified as precipitation hardening stainless steels and are widely used in various industries such as aerospace, golf supplies, ship parts, and industrial parts. However, they have the disadvantages that the fluidity during casting is poor, Chrome Pitting is prominent, so it is easy to fail in work due to defects on the molding surface, and the manufacturing cost increases accordingly.

[0003] To maintain good fluidity during manufacturing, stainless steel with a high silicon content, as presented in Patent Document 3, can achieve higher tensile strength, but impact resistance cannot be ensured. Therefore, when used in the manufacture of marine propellers or golf club heads, the risk of propeller and golf club head breakage increases. In addition, during the casting process, shrinkage stress is generated due to the cooling rates of different parts, promoting deformation of the casting. Since the deformed casting does not conform to specifications, adjustment is necessary. However, since castings with high yield strength are difficult to mold, appropriately adjusting the yield strength is advantageous for molding.

[0004] Therefore, the objective of the present invention is to provide a stainless steel material that not only maintains good fluidity during casting and facilitates molding, thereby reducing the rate of defects on the molded surface and allowing for size adjustment according to specifications, but also possesses superior fracture toughness compared to conventional 15-5PH (stainless steel) and superior yield strength and tensile strength compared to conventional duplex stainless steel. [Prior art documents] [Patent Documents]

[0005] [Patent Document 1] Chinese Patent Application Publication No. 103643160 Specification [Patent Document 2] Chinese Patent Application Publication No. 116426725 Specification [Patent Document 3] U.S. Patent Application Publication No. 2004 / 0042926 [Overview of the project] [Problems that the invention aims to solve]

[0006] The present invention aims to provide a stainless steel material suitable for casting and molding, taking into consideration the shortcomings of conventional stainless steel materials. A stainless steel material suitable for casting and molding is composed by adding chromium (Cr), nickel (Ni), cobalt (Co), silicon (Si), etc., in appropriate proportions, and is not only highly fluid and easy to mold, but also possesses corrosion resistance, impact resistance, and high tensile strength. [Means for solving the problem]

[0007] To address the aforementioned challenges, stainless steel is used for marine propellers and contains 14.6 to 16.1 wt% chromium (Cr), 5.4 to 6.2 wt% nickel (Ni), 1.52 to 2.2 wt% silicon (Si), 0.001 to 0.05 wt% carbon (C), 0.3 to 0.8 wt% manganese (Mn), 2.5 to 3.2 wt% copper (Cu), 1.2 to 2.0 wt% cobalt (Co), and 0.2 to 0.3 wt% niobium (Nb), as well as iron (Fe) and unavoidable impurities.

[0008] In the technical features described above, stainless steel is advantageous for propeller molding in the manufacturing process of marine propellers because its fluidity can be significantly improved by the appropriate amount of silicon (Si). In particular, in the case of stainless steel with a relatively high chromium (Cr) content, the occurrence of chromium pitting on the molded surface can be suppressed, improving the yield of the finished product. Furthermore, since excessive fluidity reduces fracture toughness, the mechanical properties of stainless steel are maintained by limiting the content of chromium (Cr), nickel (Ni), cobalt (Co), and silicon (Si) within specific ranges.

[0009] In relatively preferable cases, 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. Subsequently, the molten metal is transferred to a ceramic shell mold at 1100°C to 1150°C and allowed to cool. After cooling, the ceramic shell 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 form the stainless steel material. Tests and comparisons of the stainless steel material of the present invention produced by the above method with conventional 17-4PH and 15-5PH (stainless steel) and duplex stainless steel materials revealed that the mechanical properties of the present invention are relatively good.

[0010] In relatively favorable cases, stainless steel materials contain an additional 0.01 to 0.3 wt% molybdenum (Mo). More specifically, molybdenum (Mo) can combine with carbon (C) to precipitate carbides, thereby increasing the hardness and corrosion resistance of stainless steel materials, but the molybdenum (Mo) content is limited to 0.3 wt% or less in order to maintain a certain level of impact resistance.

[0011] In relatively favorable cases, stainless steel materials contain an additional 0.01 to 0.05 wt% vanadium (V). More specifically, vanadium (V) can combine with carbon (C) to precipitate carbides, thereby increasing the hardness of the stainless steel material. However, to maintain a certain level of impact resistance, the vanadium (V) content is limited to 0.05 wt% or less.

[0012] In relatively favorable cases, stainless steel materials contain an additional 0.01 to 0.06 wt% nitrogen (N). More specifically, while nitrogen (N) can increase the strength of stainless steel materials, the nitrogen (N) content is limited to 0.06 wt% or less in order to maintain a constant impact resistance and suppress porosity defects caused by excessive nitrogen.

[0013] In relatively favorable cases, stainless steel materials contain an additional 0.01 to 0.04 wt% of phosphorus (P). More specifically, phosphorus (P) is an impurity in stainless steel materials, and it is preferable to reduce its content as much as possible. Considering the refining and refining costs, it is more economical to limit the phosphorus (P) content to 0.04 wt% or less.

[0014] In relatively preferable cases, stainless steel materials contain an additional 0.001 to 0.03 wt% of sulfur (S). More specifically, sulfur (S) is an impurity in stainless steel materials, and it is preferable to reduce its content as much as possible. To maintain good mechanical properties, the sulfur (S) content is limited to 0.03 wt% or less.

[0015] In relatively favorable cases, the silicon (Si) content of stainless steel is between 1.52 and 1.98 wt%. Therefore, stainless steel manufactured with the appropriate proportions mentioned above will have the best mechanical properties.

[0016] The detailed structure, characteristics, assembly, or use of the stainless steel material according to the present invention will be clarified through the detailed description of the embodiments below. Furthermore, it should be understood by anyone with common sense in the field of the present invention that the following detailed description and the embodiments presented herein are merely examples for illustrating the present invention and do not limit the scope of the claims of the present invention. [Brief explanation of the drawing]

[0017] [Figure 1] This is an organizational chart of Schaeffler showing one embodiment of the present invention and other stainless steel materials. [Modes for carrying out the invention]

[0018] (One embodiment) The composition of the stainless steel material according to an embodiment of the present invention includes iron (Fe) and inevitable impurities in addition to 14.6 to 16.1 wt% of chromium (Cr), 5.4 to 6.2 wt% of nickel (Ni), 1.52 to 2.2 wt% of silicon (Si), 0.001 to 0.05 wt% of carbon (C), 0.3 to 0.8 wt% of manganese (Mn), 2.5 to 3.2 wt% of copper (Cu), 1.2 to 2.0 wt% of cobalt (Co), and 0.2 to 0.3 wt% of niobium (Nb).

[0019] The stainless steel material according to an embodiment of the present invention is applied to a ship propeller. In order to clarify the mechanical properties of the stainless steel material, a tester for mechanical property testing is manufactured from the stainless steel material according to an embodiment of the present invention, and experiments are conducted. The tester for mechanical property testing is manufactured based on the G5121 standard regarding stainless steel castings of Japanese Industrial Standards (JIS).

[0020] First, in the step of separately manufacturing the molds for the ship propeller and the tester for mechanical property testing, after molding the wax pattern of the mold, the processes of dipping, stuccoing, and drying are repeated 5 times, and then the wax is removed by steam dewax to form a ceramic shell mold.

[0021] Proceed to the next step. Heat chromium (Cr), nickel (Ni), silicon (Si), carbon (C), manganese (Mn), copper (Cu), cobalt (Co), niobium (Nb), iron, etc. up to 1620 °C to generate molten metal, and then heat the mold up to 1150 °C. Subsequently, proceed to the pouring process, pour the molten metal into the mold and let it cool. After the mold has cooled, proceed to the de-shell process, remove the ingate part, and then proceed to the sand blasting treatment to form a prototype casting.

[0022] Subsequently, proceed to the step of improving properties such as hardness, strength, toughness, and corrosion resistance through heat treatment. Transfer the prototype casting to a vacuum furnace and conduct a solution heat treatment at 1050°C for one and a half hours. Subsequently, perform H1100 precipitation hardening on some mechanical property testers, and at the same time, shape and process the ship propeller manufactured according to the product specifications. Then, enhance the flatness, roughness, and gloss of the product through surface treatment.

[0023] In this embodiment, the prototypes of multiple mechanical property testers are molded at different ratios, and then tensile test bars are manufactured in accordance with the metal tensile test standard E8 / E8M of the American Society for Testing and Materials (ASTM). At the same time, metal material impact test specimens are manufactured in accordance with the impact test standard Z2202 for metal materials of the Japanese Industrial Standards (JIS). Subsequently, test the mechanical properties of the stainless steel material using the tensile test bars and metal material impact test specimens. First, explain the components and tests of the stainless steel material by citing Examples X804-1, X804-2, and X804-3.

[0024]

Table 1

[0025] The components of Examples X804-1, X804-2, and X804-3 are shown in Table 1. ​​​​​​Conventional 15-5PH or 17-4PH (stainless steel) has a silicon (Si) content of 1 wt% or less. In contrast, as shown in Table 1, the present invention increases the silicon (Si) content from 1.52 to 2.2 wt%. A silicon (Si) content of 1.5 wt% or more improves the fluidity of the molten metal during casting, which is advantageous not only for forming propellers or thin-walled castings but also reduces the occurrence of chromium pitting on the surface of propellers and thin-walled castings. Furthermore, to suppress the reduction in impact resistance caused by excessive silicon (Si), the silicon (Si) content is limited to 2.2 wt% or less. In particular, an optimal balance between fluidity and impact resistance can be achieved when the silicon (Si) content is between 1.52 and 1.98 wt%.

[0028] Carbon (C) is a component 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 the stainless steel with other elements.

[0029] Cobalt (Co) and niobium (Nb) can improve the stability of stainless steel materials at high temperatures and enhance their impact resistance.

[0030] Molybdenum (Mo) and vanadium (V) can combine with carbon (C) to precipitate carbides, thereby increasing the hardness of stainless steel materials. In particular, molybdenum (Mo) can repair the chromium oxide film, improve its stability, and maintain the corrosion resistance of stainless steel materials. Furthermore, to maintain a constant impact resistance, it is most preferable to limit the molybdenum (Mo) content to 0.01 to 0.3 wt% and the vanadium (V) content to 0.01 to 0.05 wt%. Molybdenum (Mo) and vanadium (V) are not limited to those described above and may not be added to the embodiments.

[0031] Phosphorus (P) and sulfur (S), which are not shown in Table 1, are impurities in stainless steel. While the presence of sulfur (S) makes stainless steel easier to process, it degrades its mechanical properties, so the sulfur (S) content is limited to 0.001 to 0.03 wt%. Phosphorus (P) is limited to 0.01 to 0.04 wt%. More specifically, when employing a method of generating molten metal by heat treatment, as in this embodiment, excluding relatively expensive refining methods, the lower the phosphorus (P) content, the better.

[0032] Nitrogen (N) increases the strength of stainless steel but reduces its impact resistance. Excessive nitrogen (N) can cause porosity defects, so the nitrogen (N) content is limited to 0.01 to 0.06 wt%.

[0033] [Table 2]

[0034] Ni equivalent=Ni+Co+0.5(Mn)+0.3(Cu)+25(N)+30(C)

[0035] Cr equivalent = Cr + 2(Si) + 1.5(Mo) + 5(V) + 5.5(Al) + 1.75(Nb) + 1.5(Titanium) + 0.75(W)

[0036] The Ni and Cr equivalents for Examples X804-1, X804-2, and X804-3 are shown in Table 2. Figure 1 is a Schaeffler microstructure diagram of conventional 15-5PH and 17-4PH (stainless steel) and Examples X804-1, X804-2, and X804-3.

[0037] Examples X804-1, X804-2, and X804-3 were found to belong to duplex stainless steel materials consisting of austenite and ferrite phases, based on their distribution in the Schaeffler microstructure diagram in Figure 1, and were found to exhibit a bias towards the austenite microstructure.

[0038] 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 0.8 wt% manganese (Mn) to the example can reduce the occurrence of hot cracking (hot tearing). However, if the manganese (Mn) content exceeds 0.8 wt%, the hardness of the stainless steel material will be significantly reduced.

[0039] [Table 3]

[0040] [Table 4]

[0041] [Table 5]

[0042] Tensile and impact tests were performed on Examples X804-1, X804-2, and X804-3 under casting, solid solution, and aging conditions. Test results under casting conditions are shown in Table 3. Test results under solid solution conditions are shown in Table 4. Test results under aging conditions are shown in Table 5.

[0043] In Tables 3, 4, and 5, YS indicates the yield strength, TS indicates the tensile strength, and EL indicates the elongation.

[0044] The mechanical properties of Examples X804-1, X804-2, and X804-3 after testing revealed that, regardless of whether they were cast, solid solution, or precipitated, increasing the Cr equivalent clearly reduced the yield strength. In other words, a predetermined yield strength can be obtained by appropriately adjusting the Cr equivalent. The tensile strength was found to be between 1000 and 1100 MPa, i.e., with little variation, and the fracture toughness was found to be able to maintain above 45 J. In contrast, conventional 15-5PH and 17-4PH (stainless steel) have fracture toughness between 10 and 30 J or less. In other words, the stainless steel material according to the present invention was found to have superior fracture toughness compared to conventional stainless steel materials.

[0045] Duplex stainless steel for casting conforming to the ASTM A890 standard has a yield strength of 415 to 485 MPa and a tensile strength of 620 to 690 MPa. In contrast, Examples X804-1, X804-2, and X804-3 have a yield strength of 302 to 586 MPa and a tensile strength of 647 to 1083 MPa. In other words, Examples X804-1, X804-2, and X804-3 have superior strength compared to conventional duplex stainless steel for casting.

[0046] To prevent the deterioration of mechanical properties caused by excessive chromium (Cr), it is preferable to limit the chromium (Cr) content to 14.6 to 15.2 wt%. The chromium (Cr) content may be limited to 15.3 to 16.1 wt% depending on the difficulty of shaping. In contrast, to maintain a constant strength and deformation resistance of the stainless steel material and to maintain good impact resistance, it is necessary to limit the nickel (Ni) content to 5.4 to 6.2 wt% and the cobalt (Co) content to 1.2 to 2.0 wt%.

[0047] To summarize the above, the stainless steel material according to the present invention has the following advantages over the conventional technology.

[0048] The stainless steel material according to the present invention enhances fluidity during casting by adjusting the silicon (Si) content, making it advantageous for forming marine propellers or other thin-walled castings during the casting process. Furthermore, it reduces defects caused by chromium pitting on the surface, improves the yield of thin-walled castings, and effectively reduces manufacturing costs.

[0049] The stainless steel material according to the present invention possesses properties such as corrosion resistance, impact resistance, and high strength due to the appropriate amounts of chromium (Cr), nickel (Ni), and cobalt (Co). Furthermore, the stainless steel material according to the present invention exhibits superior fracture toughness after testing compared to conventional 15-5PH and 17-4PH (stainless steel), and superior strength compared to conventional duplex stainless steel materials.

[0050] 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. A stainless steel material for use in marine propellers, characterized by containing 14.6 to 16.1 wt% chromium (Cr), 5.4 to 6.2 wt% nickel (Ni), 1.52 to 2.2 wt% silicon (Si), 0.001 to 0.05 wt% carbon (C), 0.3 to 0.8 wt% manganese (Mn), 2.5 to 3.2 wt% copper (Cu), 1.2 to 2.0 wt% cobalt (Co), 0.2 to 0.3 wt% niobium (Nb), iron (Fe), and unavoidable impurities.

2. The stainless steel material according to claim 1, characterized in that 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 shell mold at 1100°C to 1150°C and cooled, the ceramic shell mold is then removed and a solution heat treatment at 1050°C to 1100°C is carried out for one and a half hours, followed by molding by H1100 precipitation hardening.

3. Furthermore, the stainless steel material according to claim 1 is characterized by containing 0.01 to 0.3 wt% molybdenum (Mo).

4. Furthermore, the stainless steel material according to claim 1 is characterized by containing 0.01 to 0.05 wt% of vanadium (V).

5. Furthermore, the stainless steel material according to claim 1 is characterized by containing 0.01 to 0.06 wt% nitrogen (N).

6. Furthermore, the stainless steel material according to claim 1 is characterized by containing 0.01 to 0.04 wt% phosphorus (P).

7. Furthermore, the stainless steel material according to claim 1 is characterized by containing 0.001 to 0.03 wt% of sulfur (S).

8. The stainless steel material according to claim 1, characterized in that the silicon (Si) content is 1.52 to 1.98 wt%.

Images