Aluminum-containing heat-resistant spheroidal graphite cast iron
Patent Information
- Authority / Receiving Office
- JP · JP
- Patent Type
- Patents
- Current Assignee / Owner
- DAKAN MFG CO LTD
- Filing Date
- 2022-07-27
- Publication Date
- 2026-05-27
AI Technical Summary
Existing methods of adding aluminum to spheroidal graphite cast iron to improve heat resistance face limitations in maintaining mechanical properties and molten metal fluidity, with excessive aluminum leading to graphite spheroidization decrease and brittleness, while insufficient aluminum offers limited heat resistance improvement.
The addition of 0.3% to 0.4% aluminum by mass in high-silicon spheroidal graphite cast iron containing 4% silicon and 0.6% molybdenum maintains mechanical elongation and improves heat resistance without significant deterioration in fluidity.
This approach enhances heat resistance and mechanical properties, particularly elongation, while maintaining adequate molten metal flowability, suitable for manufacturing automotive and incinerator equipment parts.
Smart Images
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Abstract
Description
Technical Field
[0001] The present invention relates to a cast iron product with improved heat resistance by adding Al (aluminum) to spheroidal graphite cast iron.
Background Art
[0002] In Patent Document 1, Al (aluminum) is added in an amount less than 0.3% by mass to spheroidal graphite cast iron containing 4% by mass of Si (silicon) and 0.6% by mass of Mo (molybdenum) to improve heat resistance without degrading mechanical properties and the fluidity of the molten metal. In Patent Document 2, 0.5 - 2.0% by mass of Al (aluminum) is contained when Si (silicon) is 4 - 5% by mass. 0.05 - 0.2% by mass of a rare earth element is also added. It is said to have the function of preventing a decrease in the graphite spheroidization rate.
Prior Art Documents
Patent Documents
[0003]
Patent Document 1
【Patent Document %]] Japanese Unexamined Patent Application Publication No. 2002 - 088438
Summary of the Invention
Problems to be Solved by the Invention
[0004] When Al (aluminum) is added to spheroidal graphite cast iron, although heat resistance is improved, the spheroidization of graphite decreases, resulting in a decrease in mechanical properties and a deterioration in the fluidity of the molten metal. Patent Document 1 describes a heat-resistant cast iron made of high silicon spheroidal graphite containing 4 ± 0.1 mass% silicon and 0.6 ± 0.05 mass% molybdenum, with less than 0.3 mass% aluminum. Since the purpose is to manufacture turbine housings and other automotive parts, mechanical properties (especially elongation in tensile tests), molten metal flowability, and heat resistance are required. However, there are limits to the aluminum content that can be used to ensure these mechanical properties and flowability. Therefore, there are limitations to the improvement in heat resistance with an aluminum content of less than 0.3 mass%. Patent document 2 describes a method for manufacturing turbine housings for automotive parts, in which 4-5% by mass of silicon (Si) is present, along with 0.5-2.0% by mass of aluminum (Al). It states that below 0.5% by mass, no significant improvement in heat resistance or oxidation resistance can be expected. On the other hand, above 2.0% by mass, casting defects due to aluminum oxide dross become serious, and the material also becomes brittle. It claims that rare earth elements prevent the decrease in graphite spheroidization rate caused by the addition of aluminum (Al). However, no data to support these claims is provided. The effects of rare earth elements are also not documented with data. In this patent, experiments were conducted on adding Al to improve heat resistance. In experiments with Al (aluminum) content of 0.6, 1.0, and 2.0 mass%, the elongation of the mechanical properties was only 2%. Even with improved heat resistance, the low mechanical properties (elongation in tensile tests) make it impossible to use in the products targeted by Patent Document 2. [Means for solving the problem]
[0005] In a high-silicon spheroidal graphite cast iron containing 4 ± 0.1 mass% of silicon (Si) and 0.6 ± 0.05 mass% of molybdenum (Mo), we were able to develop a spheroidal graphite cast iron with high heat resistance and maintained mechanical elongation by adding less than 0.3 mass% to 0.4 mass% of aluminum (Al). [Effects of the Invention]
[0006] By adding 0.3% to less than 0.4% by mass of Al (aluminum), the heat resistance was improved compared to Patent Document 1, and the mechanical properties (elongation in tensile tests) were improved compared to Patent Document 2. [Brief explanation of the drawing]
[0007] [Figure 1] Experimental method [Figure 2] Chemical components [Figure 3] Heat resistance test results [Figure 4] Mechanical properties (tensile strength) [Figure 5] Mechanical properties (elongation) [Figure 6] Results of the swirling water flow test [Figure 7] Diagram showing the relationship between heat resistance and elongation. [Modes for carrying out the invention]
[0008] Figure 1 shows the experimental method. Three tons of high-Si molten metal 2 were melted in a high-frequency induction melting furnace 1. Next, a magnesium alloy (Mg) was placed at the bottom of a 300 kg ladle 4, and graphite spheroidization treatment was performed by pouring molten metal from the melting furnace into the ladle. At that time, a predetermined amount of Al was added to the pouring flow 3 for the graphite spheroidization treatment. Molten metal 5 was poured from the ladle into a molten metal flow test 6, a Y block 7, and a product 8 to prepare samples. The Y block conformed to JIS standards, and test pieces for mechanical properties were taken from the Y block. The product was a turbine housing.
[0009] Figure 2 shows the chemical composition of the molten metal used. The added aluminum (Al) was of nine different concentrations: 0, 0.05, 0.1, 0.2, 0.3, 0.4, 0.6, 1.0, and 2.0% by mass.
[0010] Figure 3 shows the results of a high-temperature oxidation test, i.e., a heat resistance test, when the casting was held at a temperature of 1073K (800℃) in an electric furnace under an atmospheric environment for 24 hours. When held at high temperatures, the surface of the casting is oxidized by oxygen in the atmosphere, generating iron oxide (Fe2O3, etc.) and increasing in weight. This weight increase was used as a measure of heat resistance. In this experiment, a high-temperature oxidation test was performed using a cast product.
[0011] In Figure 3, the oxidation increase on the vertical axis is shown as a weight increase (g) as shown in equation (1). Since the products made with each Al (aluminum) content were castings made from the same mold, the oxidation increase, which is the weight difference before and after heating, was calculated as shown in equation (1) and used as a measure of heat resistance. Oxidation increase (g) = Product weight after heating - Product weight before heating ... (1) At 1073K (800℃), the oxidation weight increase decreased with increasing Al (aluminum), meaning that the heat resistance improved. As the amount of Al (aluminum) added increased, the oxidation weight increase decreased, and thus the heat resistance improved, but the heat resistance improved significantly at an Al (aluminum) addition amount of 0.3 mass%. The direction of the magnitude of heat resistance is indicated on the right axis of Figure 3.
[0012] Figure 4 shows the tensile strength of the mechanical properties. The tensile strength remains almost unchanged, unaffected by the increase in Al (aluminum). The direction of magnitude of the tensile strength is indicated on the right axis of Figure 4.
[0013] Figure 5 shows the change in mechanical elongation. With 0% mass Al (aluminum), the elongation is 20%, but by adding 0.2 mass% Al (aluminum), it decreases to 16% (80% of 0% Al). With 0.3 mass% Al (aluminum), it decreases to 12.6% (63% of 0% Al), but still maintains a value close to 0.2 mass%. With 0.4 mass% Al (aluminum), it decreases further to 10.2% (51% of 0% Al), and with 0.6-2 mass% Al (aluminum), it decreases drastically to 2% (10% of 0% Al). Therefore, from the perspective of mechanical elongation (from the perspective of elongation in industrial products, it is considered necessary for the elongation to be 50% or more compared to 0% Al), the limit amount of Al (aluminum) was set to less than 0.4 mass%. The direction of magnitude of elongation is indicated on the right axis of Figure 5.
[0014] Figure 6 shows the results of the spiral flowability test. The flow length on the vertical axis is a measure of the ease of flow, and a longer flow length indicates better melt flowability. If the melt flowability is poor, the molten metal does not flow well in the sand mold, and the product is likely to be defective. In Figure 6, the flow length does not decrease until the Al (aluminum) content reaches 0.2 mass%. From 0.3 mass% to 2 mass%, the flow length decreases slightly, but it is considered that this does not affect product manufacturing. The right axis in Figure 6 indicates the direction of good melt flowability.
[0015] Figure 7 combines Figure 3 showing the oxidation increase, i.e., heat resistance, and Figure 5 showing the elongation of mechanical properties. Here, for heat resistance, as shown in Equation (2), it is indicated by the difference in oxidation increase from the oxidation increase at 0% mass Al (aluminum) for each Al content. Heat resistance (g) = Oxidation increase at 0 mass% Al (9 g) - Oxidation increase at each mass% Al ······ (2) When calculating the heat resistance from Equation (2), the following table is obtained. The heat resistance graph in Figure 7 was created based on the following table.
[0016] TIFF0007866161000001.tif21170
[0017] According to Figure 7, the optimal Al (aluminum) addition amount with the best balance between heat resistance and elongation is from 0.3 mass% Al to less than 0.4 mass% Al. When the Al (aluminum) content is less than 0.3%, the heat resistance decreases. When the addition amount is 0.4 mass% Al or more, although the heat resistance improves, the elongation, i.e., toughness, decreases, making it difficult to apply not only automotive parts with movement but also heat-resistant parts without movement (e.g., incinerator equipment parts).
[0018] In this patent, considering incinerator equipment parts (such as fire grates) as industrially usable parts, the optimal spheroidal graphite cast iron with a balance between elongation and heat resistance is obtained with 0.3 mass% Al (aluminum) to less than 0.4 mass% Al (aluminum).
Explanation of Reference Signs
[0019] 1 High-frequency induction melting furnace 2 High-Si cast iron melt 3. Add Al to the pouring stream. 4 ladle 5 Pouring 6. Hot water flow test 7 Y Block 8 products [Industrial applicability]
[0020] Suitable for use in heat-resistant spheroidal graphite cast iron for incineration equipment components (e.g., incinerator grates).
Claims
[Claim 1] A heat-resistant spheroidal graphite cast iron containing 3.9-4.1% by mass of Si, 0.55-0.65% by mass of Mo, 3.3% by mass of C, 0.3% by mass of Mn, 0.04% by mass of Mg, and less than 0.3% by mass of Al, with the remainder being Fe and unavoidable impurities.