Low-expansion high-temperature alloy and manufacturing method thereof

Abstract

The invention discloses a low-expansion high-temperature alloy and a manufacturing method thereof. The low-expansion high-temperature alloy comprises the following chemical components in percentage by mass: less than or equal to 0.030% of C, 2.00-3.00% of Cr, 26.0-30.0% of Ni, 4.00-5.00% of Al, 0.50-1.50% of Ti, 25.0-28.0% of Fe, 3.50-4.20% of Nb, less than or equal to 0.012% of B, 0.50-1.50% of Si, less than or equal to 0.5% of Mn, less than or equal to 0.005% of S, less than or equal to 0.015% of P, less than or equal to 0.5% of Cu and the balance of Co and inevitable impurities. By designing alloy components and optimizing process parameters, the low-expansion high-temperature alloy with excellent high-temperature oxidation resistance is prepared, has excellent high-temperature mechanical property and low-expansion property at 700 DEG C or above, and can meet the requirements of materials for equipment in the fields of aviation, aerospace, energy industry and the like in China.

Description

Technical Field

[0001] The present invention relates to the field of low-expansion alloys, and particularly to a low-expansion superalloy and a manufacturing method thereof. The low-expansion superalloy has excellent high-temperature oxidation resistance at temperatures above 700 °C. Background Art

[0002] Low-expansion superalloys, due to their high strength and low expansion coefficient at high temperatures, are widely used in high-temperature resistant components in the fields of aviation, aerospace, and energy, and have good resistance to thermal cycling. In recent years, with the rapid development of China's modern aviation, aerospace, and energy industries, in order to further improve efficiency, reduce energy consumption, etc., the technical parameters of various equipment have been greatly improved and the operating conditions have become increasingly harsh. These have put forward higher requirements for the high-temperature oxidation resistance, high-temperature strength, and low expansion of materials at higher service temperatures.

[0003] GH2907 and GH2909 alloys are commonly used Fe-Ni-Co-based precipitation-hardening low-expansion superalloys, which are strengthened at high temperatures by adding elements such as niobium and titanium. They have good strength and thermal fatigue resistance below 650 °C. However, in order to achieve low expansion performance, the Cr content in these alloys is less than 1%, and they do not contain antioxidant elements such as aluminum. Therefore, their high-temperature oxidation resistance is poor, and the service temperature is severely limited. To ensure the high-temperature oxidation resistance of superalloys, iron-based, nickel-based, or cobalt-based superalloys often add a relatively high amount of Cr, and the Cr content is usually above 15%. According to data, the addition of Cr elements will reduce the average atomic magnetic moment of iron-nickel-cobalt-based alloys, directly leading to an increase in the thermal expansion coefficient. Therefore, developing a low-expansion superalloy with good high-temperature oxidation resistance is of great significance for meeting the demand for equipment materials in the fields of China's aviation, aerospace, and energy industries.

[0004] Chinese Patent Application No. CN201010568111.4 provides an antioxidant low-expansion superalloy, and its composition control is shown in Table 1. This technology reduces the expansion coefficient by reducing Cr on the basis of Thermo-Span alloy, improves the long-term aging stability by increasing Al, and simultaneously adds Zr and B to improve the grain boundary strength and eliminate notch sensitivity. This alloy has a low thermal expansion coefficient and long-term aging tissue stability, a long service life, and no notch sensitivity. However, its oxidation weight gain at 650 °C / 100 h is as high as 0.06 g / (m 2 .h), so it is difficult to meet the antioxidant requirements in a higher service temperature environment.

[0005] Chinese Patent Application No. CN201310397115.4 provides a low-cost low-expansion nickel-based alloy, and its composition control is shown in Table 1. This technology reduces costs and improves workability by reducing precious metals and increasing the Fe content, increases strength with Mo and W, improves oxidation resistance with a high Cr content, and adds rare earth elements to improve grain boundary strength. This alloy has a low cost, a low coefficient of thermal expansion, excellent high-temperature strength, hot working performance, and oxidation and corrosion resistance, but its coefficient of thermal expansion is relatively high, thus limiting the application fields of this alloy.

[0006] Table 1 Comparison Table of Alloy Chemical Compositions (wt%)

[0007]

[0008] In view of this, there is an urgent need to develop a new low-expansion alloy and its preparation method, which has excellent high-temperature oxidation resistance and can meet the demand for equipment materials in the fields of aviation, aerospace, and energy industries in China. Summary of the Invention

[0009] Aiming at the defects existing in the prior art, the object of the present invention is to provide a low-expansion high-temperature alloy and its manufacturing method. By designing the alloy composition and optimizing the process parameters, a low-expansion high-temperature alloy with excellent high-temperature oxidation resistance can be obtained, which has excellent high-temperature mechanical properties and low-expansion properties above 700 °C and can meet the demand for equipment materials in the fields of aviation, aerospace, and energy industries in China.

[0010] In order to achieve the above object, the present invention adopts the following technical solutions:

[0011] The first aspect of the present invention provides a low-expansion high-temperature alloy, including the following chemical components by mass percentage: C ≤ 0.030%, Cr: 2.00 - 3.00%, Ni: 26.0 - 30.0%, Al: 4.00 - 5.00%, Ti: 0.50 - 1.50%, Fe: 25.0 - 28.0%, Nb: 3.50 - 4.20%, B ≤ 0.012%, Si: 0.50 - 1.50%, Mn ≤ 0.5%, S ≤ 0.005%, P ≤ 0.015%, Cu ≤ 0.5%, and the rest is Co and inevitable impurities.

[0012] Preferably, the low-expansion high-temperature alloy has a coefficient of thermal expansion ≤ 13.5×10 -6 °C and an oxidation rate ≤ 0.050 g / (m 2 .h) after 100 h at 700 °C.

[0013] Preferably, the low-expansion high-temperature alloy has a tensile strength σ b ≥ 800 MPa and a yield strength σ 0.2≥650 MPa, elongation δ5≥25%.

[0014] The second aspect of the present invention provides a manufacturing method of a low-expansion superalloy, comprising the following steps:

[0015] (1) Vacuum induction melting: After proportioning the raw materials according to the composition of the low-expansion superalloy as described in the first aspect of the present invention, melt them, control the vacuum degree at ≤3.0 Pa, and add the main components Ni, Co, and Fe during the melting period; after the main components are melted clear, add the remaining raw materials including Al, Ti, Nb, Cr, and Si in batches, melt and refine; after the refining is completed, conduct a composition analysis. After the chemical composition of the molten steel meets the target requirements of the low-expansion superalloy, tap the molten steel and pour it into a vacuum induction electrode;

[0016] (2) Vacuum consumable remelting: Grind the surface of the vacuum induction electrode to the metal natural color and then conduct vacuum consumable remelting. After the vacuum consumable remelting is completed, cool in the mold for more than 90 min and then demold and air-cool to obtain a consumable ingot;

[0017] (3) Homogenization treatment: Control the homogenization temperature at 1150 - 1250 °C, and the homogenization time ≥48 h;

[0018] (4) Forging: Remove the surface scale of the consumable ingot after the homogenization treatment by grinding, heat it, and conduct multi-pass upsetting and drawing forging to obtain the low-expansion superalloy.

[0019] Preferably, in the vacuum induction melting, the power during the melting period is 300 - 2500 kw.

[0020] Preferably, in the vacuum induction melting, during the refining process, the power is controlled at 100 - 1000 kw, and the total refining time ≥45 min.

[0021] Preferably, in the vacuum induction melting, during the pouring process, the pouring temperature is 1450 - 1550 °C.

[0022] Preferably, during the vacuum consumable remelting process, the melting rate is set at 2.0 - 4.0 kg / min, the current is set at 2000 - 800 A, and the voltage is set at 20 - 30 V.

[0023] Preferably, in the forging process, the heating temperature is 1050 - 1150 °C, and the final forging temperature ≥850 °C.

[0024] Preferably, for the low-expansion superalloy at 700 °C, the thermal expansion coefficient ≤13.5×10 -6 °C, the oxidation rate after 100 h ≤0.050 g / (m 2 .h), the tensile strength σ b≥800 MPa, yield strength σ 0.2 ≥650 MPa, elongation δ5 ≥ 25%.

[0025] The principles for the composition design of the low-expansion superalloy of the present invention are as follows:

[0026] C: A strong austenite-forming element and also an essential element for carbide formation in superalloys, which is beneficial to improving the strength of the alloy and can play a role in deoxidation during vacuum induction melting. When the C content is too high, it will lead to a decrease in the plastic toughness of the alloy. Therefore, the C content is controlled at ≤ 0.030%.

[0027] Cr: An important element for improving corrosion resistance and can also improve the oxidation resistance of the alloy. However, considering the requirement of a low expansion coefficient comprehensively, the Cr content is controlled at 2.0 - 3.0%.

[0028] Ni: As an element that strongly forms and expands the austenite region, it can improve the stability of the austenite structure and the hot working performance. Excessive Ni will increase the expansion coefficient. Therefore, the preferred Ni content should be controlled between 26.00 - 30.00%.

[0029] Al: An element for forming high-temperature strengthening phases, which can form γ′ phases with Nb and Ti to improve the high-temperature strength and high-temperature stability of the alloy, and can also form intragranular and grain boundary strengthening phases in combination with Ni, enhancing the oxidation resistance of the alloy and improving the grain boundary oxidation brittleness. Excessive Al content will increase the difficulty of hot working of the alloy. Therefore, the Al content is controlled at 4.00 - 5.00%.

[0030] Ti: An element for forming high-temperature strengthening phases, which can effectively improve the high-temperature strength and high-temperature stability of the alloy. Excessive titanium content will generate harmful phases, resulting in poor plasticity of the alloy. Considering the requirement of a low expansion coefficient, the titanium content is controlled at 0.50 - 1.50%.

[0031] Fe: Can form an austenite matrix together with Ni and Co. An appropriate amount of iron can significantly reduce the alloy cost and ensure the alloy expansion coefficient. Excessive iron content will promote the precipitation of harmful phases, resulting in the deterioration of the alloy performance. Therefore, the iron content is controlled at 25.00 - 28.00%.

[0032] Nb: An element for forming high-temperature strengthening phases, which can effectively improve the high-temperature strength and high-temperature stability of the alloy. Excessive addition of niobium content is likely to form segregation and deteriorate the alloy performance. Therefore, the niobium content is controlled at 3.50 - 4.20%.

[0033] B: Trace B in superalloys can strengthen the grain boundary, improve the plasticity of the alloy, and enhance the high-temperature creep resistance of the alloy. Excessive B content will deteriorate the hot working performance of the alloy. Therefore, the B content is controlled at ≤ 0.012%.

[0034] Si: It is a ferrite-forming element, which can effectively act as a deoxidizer and is beneficial to the high-temperature oxidation resistance. However, if too much is added, the processing performance and toughness will deteriorate. Therefore, the addition of Si is controlled at 0.50 - 1.50%.

[0035] Mn: It is a weak austenite element and plays a role in stabilizing austenite. Excessive Mn will reduce the hot plasticity and oxidation resistance of the alloy. Therefore, the Mn content should be controlled at ≤0.50%.

[0036] S: It is an impurity element in steel. Considering the hot plasticity and corrosion resistance, the less content of this element, the better. Therefore, the sulfur content is controlled at ≤0.005%.

[0037] P: It is an impurity element in steel. Trace amounts of phosphorus can improve the high-temperature creep rupture properties and creep life of some superalloys. Excessive P content will exacerbate segregation and deteriorate the hot working performance of the alloy. Therefore, the P content is controlled at ≤0.015%.

[0038] Cu: It is an element that improves corrosion resistance, but it is a harmful element in some superalloys. Excessive Cu content is not conducive to improving the alloy strength and reducing the hot workability of the alloy. Therefore, the Cu content is controlled at ≤0.50%.

[0039] Co: It can form an austenite matrix with elements such as Ni and Fe, and can improve the hot strength, tissue stability and oxidation resistance of the alloy at high temperatures, and increase the Curie temperature of the alloy.

[0040] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0041] 1. The low-expansion superalloy and its manufacturing method of the present invention use Co to replace Fe and Ni. By increasing the Co content and appropriately reducing the Fe and Ni contents, the high-temperature oxidation resistance, high-temperature strength and thermal stability of the alloy are improved; by increasing the Cr and Si contents, the oxidation resistance of the alloy is enhanced; using Al to replace Nb and Ti, Al can form γ′ phase with Nb and Ti to improve the high-temperature strength of the alloy, and can also combine with Ni to form intragranular and grain boundary strengthening phases, enhancing the oxidation resistance of the alloy and improving the grain boundary oxidation brittleness; through the above alloy composition design, a low-expansion superalloy with good high-temperature oxidation resistance is obtained.

[0042] 2. The service temperature of the low-expansion superalloy prepared by the present invention is above 700°C. Its high-temperature oxidation resistance is significantly better than that of GH2909 alloy, and it has excellent high-temperature mechanical properties and low-expansion properties above 700°C, which can meet the requirements of the equipment in the fields of aviation, aerospace and energy industries in China for high-temperature oxidation-resistant and low-expansion alloy materials. Specific Embodiments

[0043] The present invention will be described in detail below in conjunction with specific embodiments. The following embodiments will help those skilled in the art to further understand the present invention, but do not limit the present invention in any form.

[0044] The low-expansion superalloy provided by the present invention includes the following chemical components by mass percentage: C≤0.030%, Cr: 2.00-3.00%, Ni: 26.0-30.0%, Al: 4.00-5.00%, Ti: 0.50-1.50%, Fe: 25.0-28.0%, Nb: 3.50-4.20%, B≤0.012%, Si: 0.50-1.50%, Mn≤0.5%, S≤0.005%, P≤0.015%, Cu≤0.5%, and the rest is Co and inevitable impurities.

[0045] The above low-expansion superalloy has a thermal expansion coefficient ≤13.5×10 -6 ℃ at 700 °C, and an oxidation rate ≤0.050 g / (m 2 .h) after 100 h, a tensile strength σ b ≥800 MPa, a yield strength σ 0.2 ≥650 MPa, and an elongation δ5≥25%.

[0046] The manufacturing method of the above low-expansion superalloy specifically includes the following steps:

[0047] (1) Vacuum induction melting: Charge the raw materials according to the composition of the above low-expansion superalloy, and the materials used should be clean; then carry out melting, and control the vacuum degree ≤3.0 Pa. First, add the main component Ni, Co, Fe, etc. during the melting period, and carry out high-vacuum and high-power smelting. The power during the melting period is controlled at 300-2500 kw. After the main component is melted, add the remaining raw materials including Al, Ti, Nb, Cr, Si in batches, melt and carry out refining, with the power controlled at 100-1000 kw, and the total refining time ≥45 min. After the refining is completed, take a finished product sample for composition analysis. After the chemical composition of the molten steel meets the control target requirements of the low-expansion superalloy, tap the molten steel and pour it into a vacuum induction electrode, and the pouring temperature is 1450-1550 °C.

[0048] (2) Vacuum consumable remelting: Grind the surface of the vacuum induction electrode until it shows the metal's natural color, and no oxide scale or other contaminants are allowed. Then carry out vacuum consumable remelting. After the vacuum consumable remelting is completed, cool in the mold for more than 90 min and then demold and air-cool to obtain a consumable ingot. In the vacuum consumable remelting, the melting rate is set at 2.0-4.0 kg / min, the current is set at 2000-800 A, and the voltage is set at 20-30 V.

[0049] (3) Homogenization treatment: the consumable ingot after demoulding is homogenized, the homogenization temperature is controlled at 1150-1250°C, and the homogenization time is ≥48h;

[0050] (4) Forging, grinding the homogenized consumable ingot to remove the surface oxide scale, heating it and performing multiple upsetting forging to obtain a low expansion high temperature alloy;

[0051] Specifically, the consumable ingot after homogenization treatment is ground to remove the surface oxide scale and heated to 1050-1150°C. The consumable ingot is upset and drawn on a forging machine for 2-3 times to break the cast structure and improve the thermoplasticity of the alloy. Finally, it is elongated and forged into low-expansion high-temperature alloy bars of different diameters for 3-5 times, and the final forging temperature is ≥850°C.

[0052] The low expansion high temperature alloy and the method for manufacturing the same of the present invention are further described below with reference to specific examples;

[0053] Examples 1 to 8

[0054] The specific preparation process of the low expansion high temperature alloy in Examples 1 to 8 is as follows:

[0055] (1) Vacuum induction smelting process: The materials are prepared according to the chemical composition described in Table 2, and the raw materials used should be clean. The vacuum degree of the smelting process is controlled at ≤3.0Pa, and the power is controlled at 300-2500kW. First, the main ingredients such as Ni, Co, and Fe are added during the melting period, and high vacuum and high power smelting is carried out. After the main ingredients are melted, they are refined, and the remaining raw materials including chemical components such as Al, Ti, Nb, Cr, and Si are added in batches, melted and refined, and the power is controlled at 100-1000KW. The total refining time is ≥45min; finally, the finished product sample is taken for component analysis. After the chemical composition of the molten steel meets the control target requirements, the vacuum induction electrode is cast, and the casting temperature of the vacuum induction electrode is controlled at 1450-1550℃.

[0056] (2) Vacuum consumable remelting smelting process: The surface of the vacuum induction electrode is ground clean to the original color of the metal, and no scale or other contaminants are allowed. The melting rate is set at 2.0-4.0 kg / min, the current is controlled at 2000-8000 A, and the voltage is 20-30 V. 90 minutes after the remelting is completed, the consumable ingot is demolded and air-cooled.

[0057] (3) Homogenization process: The consumable ingot after demoulding is subjected to homogenization treatment, the homogenization temperature is 1150-1250°C, and the homogenization time is ≥48h.

[0058] (4)Forging process: Grind the consumable ingot to remove the surface oxide scale. The forging heating temperature is 1050 - 1150 °C. The consumable ingot is upset and drawn on the forging machine for 2 - 3 heating times. The as-cast structure is broken by upsetting and drawing to improve the hot plasticity of the alloy. Finally, it is drawn and forged for 3 - 5 heating times to obtain low-expansion superalloy forged bars with different diameters. The finish-forging temperature is ≥850 °C.

[0059] Table 2 Chemical composition (wt.%) of the low-expansion superalloy in the examples

[0060]

[0061]

[0062] Table 3 Alloy properties

[0063]

[0064] The low-expansion superalloy bars obtained according to the chemical composition shown in Table 1 and the manufacturing process of the present invention in the above examples have the properties shown in Table 3. For the low-expansion superalloys in Examples 1 - 8, at 700 °C, the thermal expansion coefficient ≤ 12.45×10 -6 °C, the oxidation rate after 100 h ≤ 0.015 g / (m 2 .h), the tensile strength σ b ≥ 868 MPa, the yield strength σ 0.2 ≥ 730 MPa, and the elongation δ5 ≥ 39%. Thus, it can be seen that the low-expansion superalloys in the examples of the present invention have significantly better high-temperature oxidation resistance than GH2909 alloy at 700 °C, and have excellent high-temperature mechanical properties and low-expansion properties, which can meet the requirements of equipment in the fields of aviation, aerospace, and energy industries in China for high-temperature oxidation-resistant and low-expansion alloy materials.

[0065] It should be noted that the above examples are only used to illustrate the technical solutions of the present invention and are not restrictive. Although the present invention has been described in detail with reference to the preferred embodiments, those of ordinary skill in the art should understand that the technical solutions of the present invention can be modified or equivalently replaced without departing from the purpose and scope of the technical solutions of the present invention, and they should all be covered within the scope of the claims of the present invention.

Claims

1. A low-expansion superalloy, characterized in that, It includes the following chemical components by mass percentage: C ≤ 0.030%, Cr: 2.00 - 3.00%, Ni: 26.0 - 30.0%, Al: 4.00 - 5.00%, Ti: 0.50 - 1.50%, Fe: 25.0 - 28.0%, Nb: 3.50 - 4.20%, B ≤ 0.012%, Si: 0.50 - 1.50%, Mn ≤ 0.5%, S ≤ 0.005%, P ≤ 0.015%, Cu ≤ 0.5%, and the rest is Co and inevitable impurities.

2. The low-expansion superalloy according to claim 1, characterized in that, The low-expansion superalloy has a thermal expansion coefficient ≤ 13.5×10 -6 ℃ at 700℃ and an oxidation rate ≤ 0.050 g / (m 2 .h) after 100 h.

3. The low-expansion superalloy according to claim 1, characterized in that, The low-expansion superalloy has a tensile strength of σ b ≥ 800 MPa, a yield strength of σ 0.2 ≥ 650 MPa, and an elongation of δ5 ≥ 25% at 700 °C.

4. A manufacturing method of a low-expansion superalloy, characterized in that, It includes the following steps: (1) Vacuum induction melting: After proportioning the raw materials according to the composition of the low-expansion high-temperature alloy described in Claim 1, carry out melting, control the vacuum degree at ≤ 3.0 Pa, and add the main components Ni, Co, and Fe during the melting period; after the main components are melted clear, add the remaining raw materials including Al, Ti, Nb, Cr, and Si in batches, melt and carry out refining; after the refining is completed, conduct component analysis. After the chemical composition of the molten steel meets the target requirements of the low-expansion high-temperature alloy, tap the molten steel and pour it into the vacuum induction electrode. (2) Vacuum consumable remelting: Grind the surface of the vacuum induction electrode to the metal natural color and then carry out vacuum consumable remelting. After the vacuum consumable remelting is completed, cool in the mold for more than 90 minutes and then demold and air-cool to obtain a consumable ingot. (3) Homogenization treatment: Control the homogenization temperature at 1150 - 1250 °C and the homogenization time ≥ 48 h. (4) Forging: Grind the surface oxide scale of the consumable ingot after the homogenization treatment and then heat it and carry out multi-pass upsetting and drawing forging to obtain the low-expansion high-temperature alloy.

5. The manufacturing method of a low-expansion superalloy according to claim 4, characterized in that, In the vacuum induction melting, the power during the melting period is 300 - 2500 kw.

6. The manufacturing method of a low-expansion superalloy according to claim 4, characterized in that, In the vacuum induction melting, during the refining process, the power is controlled at 100 - 1000 kw and the total refining time ≥ 45 min.

7. The manufacturing method of a low-expansion superalloy according to claim 4, characterized in that, In the vacuum induction melting, during the pouring process, the pouring temperature is 1450 - 1550 °C.

8. The manufacturing method of a low-expansion superalloy according to claim 4, characterized in that, During the vacuum consumable remelting process, the melting rate is set at 2.0 - 4.0 kg / min, the current is set at 2000 - 800 A, and the voltage is set at 20 - 30 V.

9. The manufacturing method of a low-expansion superalloy according to claim 4, characterized in that, In the forging process, the heating temperature is 1050 - 1150 °C and the final forging temperature ≥ 850 °C.

10. The manufacturing method of a low-expansion superalloy according to claim 4, characterized in that, The low-expansion superalloy has a thermal expansion coefficient ≤ 13.5×10 -6 ℃ at 700℃, an oxidation rate ≤ 0.050 g / (m 2 .h) after 100 h, a tensile strength σ b ≥ 800 MPa, a yield strength σ 0.2 ≥ 650 MPa, and an elongation δ5 ≥ 25%.

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