Stainless steel material suitable for casting and shaping

Abstract

A stainless steel material includes 14.6 to 16.1 wt % of chromium (Cr), 5.4 to 6.2 wt % of nickel (Ni), 1.5 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), 0.2 to 0.3 wt % of niobium (Nb), and a remainder of iron (Fe) and impurities. This stainless steel material provides better fluidity during casting, which helps in the formation of thin castings. It also allows for a reduction in yield strength as needed, making shaping easier while maintaining high tensile strength and impact strength. Compared to traditional dual-phase stainless steel material, its fracture strength is significantly enhanced.

Description

BACKGROUND OF THE INVENTION1. Field of the Invention

[0001] The present invention relates to stainless steel materials and more particularly, to a stainless steel material that is suitable for casting and shaping. By adjusting the specific proportions of each material, this stainless steel material is ideal for manufacturing thin castings, such as propellers and golf club heads. This stainless steel material provides better formability and facilitates adjustments to ensure the casting's shape and specifications align accurately.2. Description of the Related Art

[0002] In the shipbuilding industry, there are not only shipyards responsible for hull construction but also many related manufacturers, such as propeller factories, hardware factories, marine equipment manufacturers, and ship outfitting factories. Various types of ships, from large container ships, cruise ships, and warships to medium and small fishing boats, yachts, and jet skis, all use propellers. The propeller is driven by a motor to rotate and propel the vessel forward. Materials used for manufacturing ship propellers can include plastic or metal materials. Since propellers are constantly immersed in water, they need to have good corrosion resistance and impact strength. Therefore, high-strength and corrosion-resistant materials are typically chosen. CN 103643160 A and CN 116426725 A provide stainless steel materials 17-4 and 15-5, respectively. These stainless steel materials are precipitation-hardened steels, widely used in aerospace, golf equipment, ship parts, and industrial components. However, when used in casting, they have the significant disadvantages of poor fluidity and noticeable chrome pitting, which leads to defects on the forming surface and result in failure.

[0003] This increases the manufacturing cost.

[0004] To achieve better fluidity during manufacturing, U.S. Patent Publication No. 20040042926A1 provides a stainless steel material with a high silicon content. Although this material can achieve higher tensile strength, it sacrifices impact resistance. If used to manufacture ship propellers or golf club heads, it would increase the risk of propeller and golf club head fracture. Additionally, during casting, the varying cooling rates across different regions can cause shrinkage stresses, leading to deformation of the casting shape. Deformed castings that do not meet specifications require reshaping adjustments. However, castings with high yield strength are more difficult to reshape, so appropriately controlling the yield strength is beneficial for easier shaping.

[0005] Therefore, the goal is to provide a stainless steel material that has excellent casting fluidity and is easy to shape, in order to reduce the likelihood of surface defects during product formation and to adjust the dimensions to meet specifications. This material should also offer superior impact toughness compared to traditional 15-5 stainless steel materials, while having a higher yield strength and tensile strength than conventional dual-phase steel materials. This is the direction envisioned by the inventor.SUMMARY OF THE INVENTION

[0006] It is a primary objective of the present invention to provide a stainless steel material suitable for casting and shaping, which has characteristics of high fluidity, ease of shaping, corrosion resistance, impact toughness, and high tensile strength by adding appropriate proportions of chromium (Cr), nickel (Ni), cobalt (Co), and silicon (Si).

[0007] To attain the above objective, the stainless steel material of the present invention is used for manufacturing a propeller of a ship, comprising 14.6 to 16.1 wt % of chromium (Cr), 5.4 to 6.2 wt % of nickel (Ni), 1.5 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), 0.2 to 0.3 wt % of niobium (Nb), and a remainder of iron (Fe) and impurities.

[0008] It can be seen from the above that the stainless steel material of the present invention have an appropriate content of silicon (Si), which can significantly improve the fluidity of the stainless steel material. During the manufacturing process of the propeller, it not only helps in the formation of the propeller, but also reduces the chrome pitting phenomenon on the surface of castings, especially in stainless steels with higher chromium (Cr) content. This enhancement increases the success rate of product manufacturing. Furthermore, excessively high fluidity in the stainless steel material leads to a reduction in impact toughness. Therefore, the content of chromium (Cr), nickel (Ni), cobalt (Co), and silicon (Si) in the stainless steel material is controlled within a specific range to achieve optimal mechanical properties.

[0009] Preferably, an alloy material containing the chromium (Cr), the nickel (Ni), the silicon (Si), the carbon (C), the manganese (Mn), the copper (Cu), the cobalt (Co), the niobium (Nb), and the iron (Fe) is heated to a temperature of 1600° C.-1700° C. and mixed into a molten iron mixture, and then the molten iron mixture is poured into a ceramic mold at a temperature of 1100° C.-1150° C. Thereafter, the mold is removed after cooling, and solidification treatment is performed at a temperature of 1050° C.-1100° C. for 1.5 hours, and a precipitation hardening treatment (H1100) is optionally performed to obtain the stainless steel material. In this way, after testing and comparing the stainless steel material of the present invention with traditional 17-4, 15-5 stainless steel materials and duplex steel, the present invention has better mechanical properties.

[0010] Preferably, the stainless steel material further contains 0.01-0.3 wt % of molybdenum (Mo). This allows molybdenum to combine with carbon to form carbides, increasing the hardness and corrosion resistance of the stainless steel material. However, to maintain a certain level of impact toughness, the molybdenum content is controlled to be below 0.3 wt %.

[0011] Preferably, the stainless steel material further includes 0.01-0.05 wt % of vanadium (V). This enables vanadium to combine with carbon to form carbides, increasing the hardness of the stainless steel. However, to preserve a certain level of impact toughness, the vanadium content is controlled to be below 0.05 wt %.

[0012] Preferably, the stainless steel material further includes 0.01-0.06 wt % of nitrogen (N). In this way, nitrogen is used to enhance the strength of the stainless steel material, but to maintain impact toughness and avoid defects such as nitrogen porosity, the nitrogen content is controlled to be below 0.06 wt %.

[0013] Preferably, the stainless steel material further contains 0.01-0.04 wt % of phosphorus (P). In this way, phosphorus is an impurity in stainless steel, and its content should be minimized. Based on the cost of refining and purification, the phosphorus content is controlled to be below 0.04 wt % for a more economically viable proportion.

[0014] Preferably, the stainless steel material further includes 0.001-0.03 wt % of sulfur(S). In this way, sulfur is an impurity in stainless steel, and its content should be minimized. To maintain better mechanical properties, the sulfur content is controlled to be below 0.03 wt %.

[0015] Preferably, the silicon (Si) content of the stainless steel material is 1.52-1.98 wt %. This proportion ensures the optimal mechanical properties of the final product.

[0016] Other advantages and features of the present invention will be fully understood by reference to the following specification in conjunction with the accompanying drawings, in which like reference signs denote like components of structure.BRIEF DESCRIPTION OF THE DRAWINGS

[0017] The sole FIGURE is a Schaeffler diagram, showing the metallographic structures of the present invention compared with other stainless steel materials.DETAILED DESCRIPTION OF THE INVENTION

[0018] The stainless steel material of the present invention comprises 14.6 to 16.1 wt % of chromium (Cr), 5.4 to 6.2 wt % of nickel (Ni), 1.5 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), 0.2 to 0.3 wt % of niobium (Nb), and a remainder of iron (Fe) and impurities.

[0019] The stainless steel material of the present invention is suitable for manufacturing a propeller of a ship. To test the characteristics of the stainless steel material, standard test specimens for mechanical properties are made by using this stainless steel material. These test specimens are prepared according to the Japanese Industrial Standard (JIS) G5121, which specifies the standards for stainless steel castings.

[0020] First, molds for the propeller and the standard test specimens for mechanical properties are separately made. After the wax patterns for the molds are created, they undergo a repeated process of dipping, stuccoing, and drying five times. Afterward, the wax is removed by using steam dewaxing, resulting in a ceramic shell mold.

[0021] The materials containing chromium, nickel, silicon, carbon, manganese, copper, cobalt, niobium, and iron are heated to a temperature of 1620° C. and mixed into a molten iron mixture. The mold is then heated to 1150° C., and the molten iron mixture is poured into the mold. After cooling, the ingate is removed through the de-shelling process, and sandblasting is performed to obtain a rough casting.

[0022] The rough casting is then subjected to heat treatment to enhance its strength and corrosion resistance. The product is placed in a vacuum furnace and treated at a temperature of 1050° C. for 1.5 hours for solid solution treatment. Some standard test specimens for mechanical properties undergo H1100 precipitation hardening treatment. The resulting propeller is further shaped and processed to meet the product specifications, followed by surface treatment to improve the smoothness, roughness, and gloss of the product's surface.

[0023] In this embodiment, multiple standard test specimens for the mechanical properties of the stainless steel materials are prepared in different proportions. These specimens are then processed into tensile test rods according to ASTM standard E8 / E8M for metal tensile testing, and processed into impact test specimens according to JIS standard Z2202 for metal material impact testing. These specimens are used to test the mechanical properties of the stainless steel material. The stainless steel material is explained and tested in the following three examples: X804-1, X804-2, and X804-3. The composition of X804-1, X804-2, and X804-3 are shown in Table 1.TABLE 1CrNiSiCMnMoVCuCoNbNX804-114.835.811.730.020.400.100.032.621.620.240.04X804-215.365.971.820.020.390.090.032.841.610.230.04X804-316.085.851.870.020.370.090.032.811.590.230.04

[0024] Chromium (Cr) can form a chromium oxide protective film on the surface of the stainless steel material, primarily to isolate external oxygen from coming into contact with iron, which makes the stainless steel material less prone to rusting. Therefore, adding a higher amount of chromium can enhance the rust resistance of the stainless steel material. Nickel (Ni) has excellent corrosion resistance, and when combined with chromium to produce the stainless steel material, it helps promote the formation of the chromium oxide protective film, thus maintaining the rust-resistant properties of the stainless steel material.

[0025] Traditional stainless steel material, such as 15-5 or 17-4, typically contains less than 1 wt % of silicon. However, as shown in Table 1, the silicon content in the present invention is increased to 1.5-2.2 wt %. Silicon content greater than 1.5 wt % improves the fluidity of the molten iron mixture during casting, which is beneficial for the formation of the propeller or the thin casting. This reduces the occurrence of chromium pitting on the surface of the propeller and the thin casting. To avoid the negative impact of excessive silicon on impact resistance, the silicon content is limited to be below 2.2 wt %. The optimal silicon content is between 1.52-1.98 wt % to achieve a balance between optimal fluidity and impact resistance.

[0026] Carbon (C) is primarily used to enhance the hardness of the stainless steel material. However, excessive carbon leads to the precipitation of too many carbides, which reduces impact toughness and affects corrosion resistance. Therefore, the carbon content is restricted to 0.001-0.05 wt %, with other elements used to increase the hardness of the stainless steel material.

[0027] Cobalt (Co) and niobium (Nb) can improve the high-temperature stability of the stainless steel material and provide good impact resistance to the stainless steel material.

[0028] Molybdenum (Mo) and vanadium (V) can combine with carbon (C) to form carbides, thereby increasing the hardness of the stainless steel material. Molybdenum (Mo) also helps repair the chromium oxide protective film and enhances its stability, maintaining the corrosion resistance of the stainless steel material. To maintain a certain level of impact resistance, the molybdenum content is limited to 0.01-0.3 wt %, and the vanadium content is limited to 0.01-0.05 wt %, achieving an optimal ratio. However, in the present invention, molybdenum (Mo) and vanadium (V) may also be excluded.

[0029] Phosphorus (P) and sulfur(S) are not specified in Table 1. Phosphorus (P) and sulfur(S) are considered impurities in the stainless steel material. While sulfur(S) makes the stainless steel material easier to process, it also causes a decline in mechanical properties. Therefore, the sulfur content is restricted to 0.001-0.03 wt %. As for phosphorus (P), the lower the content, the better. In addition to using a more costly refining method, the phosphorus content is usually limited to 0.01-0.04 wt % by simply heating to create a molten iron mixture.

[0030] Moreover, although nitrogen (N) can increase the strength of the stainless steel material, it also reduces impact resistance. Excessive nitrogen (N) leads to the formation of nitrogen gas void defects. Therefore, the nitrogen content is restricted to 0.01-0.06 wt %.

[0031] The values of Ni equivalent and Cr equivalent for X804-1, X804-2, and X804-3 are shown in Table 2, as well as comparing them to traditional 15-5 and 17-4 stainless steel materials on a Schaeffler diagram as shown in the sole FIGURE.TABLE 2Ni equivalentCr equivalent15-58.017.417-48.218.5X804-110.0219.01X804-210.2319.69X804-310.0720.51

[0032] The calculation formula of Ni equivalent is: Nieq=nickel+cobalt+0.5 (manganese)+0.3 (copper)+25 (nitrogen)+30 (carbon).

[0033] The calculation formula of Cr equivalent is: Creq=chromium+2 (silicon)+1.5 (molybdenumo)+5 (vanadium)+5.5 (aluminum)+1.75 (niobium)+1.5 (titanium)+0.75 (tungsten).

[0034] As shown in the sole FIGURE, it can be seen that X804-1, X804-2, and X804-3 are located in the Schaeffler diagram, where they generally belong to the stainless steel material with a dual-phase microstructure of Austenite+Ferrite. However, their microstructure is closer to that of Austenite.

[0035] In the stainless steel material, manganese (Mn) and sulfur(S) form manganese sulfide (MnS), which reduces the likelihood of iron sulfide (FeS) formation. Therefore, the stainless steel material with 0.3-0.8 wt % of Mn can reduce the occurrence of hot tearing during casting. However, if the manganese content exceeds 0.8 wt %, the hardness of the stainless steel material will significantly decrease.

[0036] X804-1, X804-2, and X804-3 are subjected to tensile tests and impact tests in casting, solid solution, and aging states. The test results for the casting state are shown in Table 3, for the solid solution state in Table 4, and for the aging state in Table 5.TABLE 3(casting state)YS(Mpa)TS(Mpa)EL(%)IT(J)X804-1469974453.2X804-2391832971.3X804-33026479169TABLE 4(solid solution state)sampleYS(Mpa)TS(Mpa)EL(%)IT(J)X804-1A56110351569.6B561103914C586102214average569103214X804-2A46110061970.5B464100914C457101216average461100916X804-3A3679461680.5B38697116C36895921average37495918TABLE 5(aging state)sampleYS(Mpa)TS(Mpa)EL(%)IT (J)X804-1A56110821964.6B579106217C574106917average571107118X804-2A50310831546B495106618C502106715average500107216X804-3A41210381659.3B407103015C402102319average407103017In Tables 3 to 5, YS represents Yield Strength, TS represents Tensile Strength, EL 5 represents Elongation, and IT represents Impact Toughness. The impact toughness indicates the impact resistance.Based on the mechanical properties of X804-1, X804-2, and X804-3 observed after testing, it is evident that as the Cr equivalent increases, the yield strength significantly decreases in the casting, solid solution, and aging states. Therefore, the yield strength can be adjusted by modifying the Cr equivalent. The tensile strength remains between 1000-1100 MPa, showing little variation. The impact toughness consistently performs above 45 J, whereas traditional 15-5 and 17-4 stainless steel materials exhibit impact toughness of only 10-30 J, and in some cases, even below 10 J. This indicates that the impact toughness of the stainless steel material in the present invention is significantly superior to that of traditional stainless steel material.

[0039] When compared to ASTM A890 specifications for cast duplex steel materials, which have a specified yield strength of 415-485 MPa and a tensile strength of 620-690 MPa, the yield strength of X804-1, X804-2, and X804-3 ranges from 302-586 MPa, with tensile strengths between 647-1083 MPa. This shows that X804-1, X804-2, and X804-3 outperform traditional cast duplex steels in terms of strength performance.

[0040] In addition, to prevent a decline in mechanical properties due to excessively high Cr equivalent, it is preferable to control the chromium content between 14.6-15.2 wt %. However, depending on the difficulty of shaping, the chromium content can be adjusted to 15.3-16.1 wt %. At the same time, the nickel content should be controlled between 5.4-6.2 wt %, and the cobalt content should be controlled between 1.2-2.0 wt % to maintain a certain level of strength and deformation resistance in the stainless steel material, while also ensuring good impact toughness.

[0041] As indicated above, compared to the existing technology, the stainless steel material provided by the present invention has at least the following advantages:

[0042] 1. The stainless steel material of the present invention improves fluidity during casting by adjusting the silicon content. This helps in shaping the outer profile of the ship propeller or other thin products during casting and reduces defects such as chromium pitting on the surface. This improvement increases the success rate of producing thin castings, effectively lowering manufacturing costs.

[0043] 2. Through the combination of appropriate amounts of chromium, nickel, cobalt, and other materials, the present invention forms a stainless steel material that possesses characteristics of corrosion resistance, impact resistance, and high strength. After testing, its impact toughness is significantly superior to that of traditional 15-5 and 17-4 stainless steel materials, and its strength also outperforms traditional duplex steels.

[0044] The invention being thus described, it will be obvious that the same may be varied in many ways. Such variations are not to be regarded as a departure from the spirit and scope of the invention, and all such modifications as would be obvious to one skilled in the art are intended to be included within the scope of the following claims.

Claims

1. A stainless steel material for manufacturing a propeller of a ship, the stainless steel material comprising 14.6 to 16.1 wt % of chromium (Cr), 5.4 to 6.2 wt % of nickel (Ni), 1.5 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), 0.2 to 0.3 wt % of niobium (Nb), and a remainder of iron (Fe) and impurities.

2. The stainless steel material as claimed in claim 1, wherein an alloy material containing the chromium (Cr), the nickel (Ni), the silicon (Si), the carbon (C), the manganese (Mn), the copper (Cu), the cobalt (Co), the niobium (Nb), and the iron (Fe) is heated to a temperature of 1600° C.-1700° C. and mixed into a molten iron mixture, and the molten iron mixture is poured into a ceramic mold at a temperature of 1100° C.-1150° C.; after cooling, the mold is removed, and solidification treatment is performed at a temperature of 1050° C.-1100° C. for 1.5 hours, and a precipitation hardening treatment (H1100) is performed to obtain the stainless steel material.

3. The stainless steel material as claimed in claim 1, further comprising 0.01 to 0.3 wt % of molybdenum (Mo).

4. The stainless steel material as claimed in claim 1, further comprising 0.01 to 0.05 wt % of vanadium (V).

5. The stainless steel material as claimed in claim 1, further comprising 0.01 to 0.06 wt % of nitrogen (N).

6. The stainless steel material as claimed in claim 1, further comprising 0.01 to 0.04 wt % of phosphorus (P).

7. The stainless steel material as claimed in claim 1, further comprising 0.001 to 0.03 5 wt % of sulfur(S).

8. The stainless steel material as claimed in claim 1, wherein the silicon (Si) is 1.52 to 1.98 wt %.

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