Low-cost high-toughness invar alloy and preparation method thereof

Abstract

The invention discloses a low-cost high-toughness invar alloy and a preparation method thereof, and belongs to the field of material processing. The component of the alloy is Fe50. 9Ni34Cr6Al6Ti3-xNbxB 0.1, x is larger than or equal to 3 and larger than or equal to 0, the atomic ratio of Fe to Ni to Cr to Al to Ti to Nb to B is 50.9: 34: 6: 6: 3-x: x: 0.1, and the microstructure of the alloy is of an isometric crystal structure. The low-cost and high-toughness invar alloy is prepared by adding trace Cr, Al, Ti, Nb and other alloy elements and matching with a reasonable thermal mechanical treatment process. Nano coherent and semi-coherent precipitation strengthening is achieved, the mechanical property of the invar alloy is improved, the yield strength of the invar alloy reaches 700-800 MPa, 26-35% of plasticity is maintained at the same time, and a low thermal expansion coefficient is maintained; and the application range of the invar alloy is greatly expanded.

Description

Technical Field

[0001] The invention relates to a low-cost, high-strength and tough Invar-like alloy and a preparation method thereof, and belongs to the field of material processing. Background Art

[0002] Invar alloy is famous for its extremely low thermal expansion coefficient, which makes its size almost unchanged when the temperature changes. This feature makes Invar alloy indispensable in many high-precision occasions, such as precision instruments, watches and clocks, and aerospace. Invar alloys generally include conventional Fe-Ni Invar alloys, super Invar alloys with further reduced thermal expansion coefficients by adding Co, stainless Invar alloys with improved corrosion resistance by adding Cr, and non-magnetic Invar alloys with reduced Fe content so that they do not exhibit magnetism in magnetic fields. Currently, the most commonly used ones are Fe-Ni Invar alloys and Fe-Co-Ni super Invar alloys. The low thermal expansion characteristics of Invar alloys are derived from their unique crystal structure and alloy composition. However, since the composition of Invar alloys is basically only iron and nickel, the choice of alloying is limited and may not meet specific needs. Moreover, the strength and hardness of Invar alloys are generally not high, with a yield strength of about 276 MPa and a Vickers hardness of about 160 HV. The safety factor is not high, which brings great difficulties to industrial production and practical applications. Therefore, the research and development of high-strength Invar alloys is imminent.

[0003] As an alloy material with a single austenite structure, Invar alloy is prone to form a coarse solidification structure during solidification, resulting in serious structural segregation, causing serious thermal cracks in subsequent processing, affecting the yield rate, and ordinary deformation and heat treatment processes do not significantly improve its strength. At present, the research on high-strength Invar alloy mainly focuses on deformation strengthening, second phase strengthening and fine grain strengthening. Deformation strengthening is the most effective means to improve the strength of metal materials. It mainly increases the dislocation density of the matrix through deformation, makes it interact, hinders the movement of dislocations, and thus improves the strength of the material. Yuan Junping et al. (Yuan Junping, Yi Danqing, Yu Zhiming, et al. Effect of deformation and heat treatment on the structure and properties of Invar alloy [J]. Metal Heat Treatment, 2005, (02): 50-53.) found that the mechanical properties of Invar alloy were improved after 800℃+23% cold rolling and 500℃ secondary annealing. The researchers (Sakaguchi N, Ohno H, Nakada N. Strengthening of Super Invar Cast Steel by Precipitation of Intermetallic Compounds. IsijInternational. 2022;62:1532-9) also added alloying elements such as Al, Ti, and Nb to the matrix and performed aging treatment to form intermetallic compounds to further improve the strength of Invar alloy. At the same time, the addition of Nb will cause a large number of fine Ni 3 Nb, as a site for heterogeneous nucleation, effectively prevents the growth of Invar alloy grains, thereby significantly improving its strength (Yang Xiaohua, Chen Weiqing, Yuan Shouqian. Effect of Nb modifier on the solidification structure of Fe-Ni expansion alloy [J]. Journal of Xi'an University of Architecture and Technology (Natural Science Edition), 2009, 41(01): 136-140). However, the precipitation of intermetallic compounds will lead to a significant decrease in the Ni content in the alloy, affecting its low expansion performance. Therefore, when aging treatment is required, the Ni content in the alloy should be increased, which will increase the alloy cost.

[0004] The performance improvement that can be achieved by thermomechanical treatment alone is limited, so we propose a nano-coherent precipitation strengthening, which is a strategy that can greatly improve strength without losing plasticity. The precipitated phase attached to the grain boundary can also inhibit grain growth. Based on the thermodynamic calculation of the phase diagram, the present invention intends to improve the strength while improving the antioxidant performance by adding trace amounts of alloying elements such as Cr, Al, Ti, Nb and matching a reasonable thermomechanical treatment process, so as to adapt to more complex service environments and expand the scope of application. Summary of the invention

[0005] In view of the problems of high cost, low strength and limited application of traditional Invar alloys, the present invention provides a low-cost, high-strength and tough Invar alloy and a preparation method thereof. By optimizing the alloy ratio and adding elements with precipitation strengthening, as well as combining a reasonable thermomechanical treatment process, the invention aims to reduce the alloy cost, improve the strength and broaden the application scope of Invar alloys.

[0006] The present invention discloses a low-cost, high-strength and tough Invar alloy and a preparation method thereof. The present invention firstly adjusts the composition by phase diagram calculation to design the low-cost, high-strength Invar alloy, and further optimizes the heat treatment process of the alloy. The yield strength of the alloys of this invention is much higher than that of the traditional Invar alloy. The Fe alloy with the lowest yield strength among the three components has a higher yield strength than the Fe alloy. 50.9 Ni 34 Cr 6 Al 6 Ti 1 Nb 2 B 0.1 can reach 700 MPa, the highest Fe 50.9 Ni 34 Cr 6 Al 6 Ti 3 B 0.1 It can reach 800 MPa, and its plasticity is basically the same as that of traditional Invar alloy. In addition, corrosion-resistant and oxidation-resistant elements are added, which improves the reliability of service in complex environments to a certain extent. The Invar alloy designed this time can have a broader application space. In the present invention, Cr is introduced into the Invar alloy as an economical and efficient alloying element to improve its mechanical strength. Cold rolling + secondary annealing refines the grain size, and the formation of intermetallic compounds during the aging process can further improve the strength and plasticity. At the same time, the addition of B improves the thermoplasticity of the alloy to a certain extent, thereby meeting the requirements of hot processing.

[0007] The present invention provides a low-cost, high-strength and tough Invar alloy, the composition of which is Fe 50.9 Ni 34 Cr 6 Al 6 Ti 3- x Nb x B 0.1 , 3 ≥ x ≥ 0, the atomic ratio of each element Fe, Ni, Cr, Al, Ti, Nb and B is 50.9:34:6:6:3-x:x:0.1, and the alloy microstructure is an equiaxed crystal structure.

[0008] The purity of the Fe, Ni, Cr, Al, Ti, Nb and B smelting raw materials used in the alloy is not less than 99.9%.

[0009] The present invention provides a method for preparing the above-mentioned low-cost, high-strength and tough Invar-like alloy, comprising the following steps: preparing an alloy ingot by smelting raw materials of Fe, Ni, Cr, Al, Ti, Nb and B; performing a homogenization heat treatment on the alloy ingot at 1000-1200°C for 2 h, and then sequentially performing cold rolling with a total deformation of 60-65%, a recrystallization heat treatment at 1000-1200°C for 0.5-2 min, and an aging heat treatment at 700°C for 4-8 h to prepare the above-mentioned alloy.

[0010] The method for preparing the low-cost, high-strength and tough Invar alloy comprises the following steps: Step 1: Weighing: First, raw material particles of Fe, Ni, Cr, Al, Ti, Nb and B with a purity of ≥99.9 wt.% were ultrasonically cleaned with anhydrous ethanol for ten minutes and then dried to remove surface impurities, and then weighed with an electronic balance with an accuracy of 0.0001g according to an atomic ratio of 50.9:34:6:6:3-x:x:0.1; Step 2: Melting: Use a vacuum arc melting furnace. Place element B at the bottom before melting to prevent it from being sucked away during vacuuming. Then add other elements in order from low to high melting points to ensure that all elements can be completely melted. Place the weighed Fe 50.9 Ni 34 Cr 6 Al 6 Ti 3-x Nb x B 0.1 The alloy mixed particles are first melted into ingots, and the ingots are repeatedly turned over and melted more than 5 times to ensure uniform distribution of alloy elements; Step 3: Casting: Place the smelted alloy ingot on a water-cooled crucible with a mold, heat the ingot to a molten state, make it completely melt and flow into a 5 mm × 10 mm × 40 mm water-cooled copper mold, and take out the sample after the plate cools down; Step 4: Thermomechanical treatment: The cast sample is subjected to homogenization heat treatment at 1000-1200 °C for 0.5-2 h, followed by cold rolling with a reduction of 60-65%. The cold rolled sample is further recrystallized at 1000-1200 °C for 0.5-2 min, and finally aged at 700 °C for 4-8 h, thereby preparing a multi-component alloy with high strength, good plasticity, corrosion resistance, oxidation resistance and potential low thermal expansion coefficient.

[0011] Beneficial effects of the present invention: (1) Fe designed by the present invention 50.9 Ni 34 Cr 6 Al 6 Ti3-x Nb x B 0.1 , 3 ≥ x ≥ 0, the microstructure is an equiaxed crystal structure. By adding trace amounts of alloying elements such as Cr, Al, Ti, Nb and matching reasonable thermomechanical treatment processes, nano-coherent and semi-coherent precipitation strengthening is achieved, the mechanical properties of Invar alloy are improved, and the yield strength reaches 700-800 MPa while maintaining 26-35% plasticity and a low thermal expansion coefficient.

[0012] (2) By adding Cr, Al, Ti, Nb and B elements to the traditional Invar alloy, alloying can meet the needs of certain special service environments, such as the chemical and petroleum industries, lightweight design and mold manufacturing, greatly expanding the scope of application. BRIEF DESCRIPTION OF THE DRAWINGS

[0013] Figure 1 Example 1 Preparation of Fe 50.9 Ni 34 Cr 6 Al 6 Ti 3 B 0.1 Phase diagram of alloys; Figure 2 Example 1 Preparation of Fe 50.9 Ni 34 Cr 6 Al 6 Ti 3 B 0.1 XRD pattern of the alloy; Figure 3 Example 1 Preparation of Fe 50.9 Ni 34 Cr 6 Al 6 Ti 3 B 0.1 Engineering stress-strain curves of alloys; Figure 4 Example 1 Preparation of Fe 50.9 Ni 34 Cr 6 Al 6 Ti 3 B 0.1 SEM images of the alloy; Figure 5 Example 2 Preparation of Fe 50.9 Ni 34 Cr 6 Al 6 Ti 1 Nb 2 B 0.1 Phase diagram of alloys; Figure 6 Example 2 Preparation of Fe 50.9 Ni 34 Cr 6 Al 6 Ti 1 Nb 2 B 0.1 XRD pattern of the alloy; Figure 7 Example 2 Preparation of Fe 50.9 Ni 34 Cr 6 Al 6 Ti 1 Nb 2 B 0.1 Engineering stress-strain curves of alloys; Figure 8 Example 2 Preparation of Fe 50.9 Ni 34 Cr 6 Al 6 Ti 1 Nb 2 B 0.1 SEM images of the alloy; Fig. 9 Example 3 Preparation of Fe 50.9 Ni 34 Cr 6 Al 6 Nb 3 B 0.1 Phase diagram of alloys; Fig.10 Example 3 Preparation of Fe 50.9 Ni 34 Cr 6 Al 6 Nb 3 B 0.1 XRD pattern of the alloy; Fig.11 Example 3 Preparation of Fe 50.9 Ni 34 Cr 6 Al 6 Nb 3 B 0.1 Engineering stress-strain curves of alloys; Fig.12 Example 3 Preparation of Fe 50.9 Ni 34 Cr 6 Al 6 Nb 3 B 0.1 SEM images of the alloy. DETAILED DESCRIPTION

[0014] In order to make the preparation method, process route and advantages of the present invention more clearly understood, the present invention is further described below by way of examples. It should be understood that the specific examples described herein are only used to explain the present invention and are not intended to limit the present invention. Example 1

[0015] This embodiment provides a low-cost, high-strength, Invar-like multi-component alloy, the composition of which is Fe 50.9 Ni 34 Cr 6 Al 6 Ti 3 B 0.1 The atomic ratio of the elements Fe, Ni, Cr, Al, Ti and B is 50.9:34:6:6:3:0.1.

[0016] The detailed preparation method is as follows: Step 1: Weighing: First, the raw material particles of Fe, Ni, Cr, Al, Ti, Nb and B with a purity of ≥99.9 wt.% were ultrasonically cleaned with anhydrous ethanol for about ten minutes and then dried to remove surface impurities. Then, an electronic balance with an accuracy of 0.0001g was used to weigh and proportion them according to the molar ratio of 50.9:34:6:6:3:0.1 to obtain a nominal composition of Fe 50.9 Ni 34 Cr 6 Al 6 Ti 3 B 0.1 Alloy mixed particles; Step 2: Melting: Use WK-II vacuum arc furnace to melt the weighed Fe 50.9 Ni 34 Cr 6 Al 6 Ti 3 B 0.1 The alloy mixed particles are first melted into an ingot weighing 35g. Before melting, B is placed at the bottom to prevent it from being sucked away during vacuuming. The ingot is repeatedly turned over and melted for more than 5 times to ensure uniform distribution of alloy elements. Step 3: Casting: Place the smelted alloy ingot on a water-cooled crucible with a mold, first heat the ingot to a molten state with a small current, then increase the current to make it completely melt and flow into a 5mm×10mm×40mm water-cooled copper mold. After the plate cools down, take out the sample; Step 4: Thermomechanical treatment: The cast sample is subjected to homogenization heat treatment at 1150 °C for 2 h, and then cold rolled with a 60% reduction. The cold rolled sample is further recrystallized at 1150 °C for 2 min, and finally aged at 700 °C for 4 h to prepare an alloy with high strength, good plasticity and low thermal expansion coefficient.

[0017] Figure 1 and Figure 2 They are respectively Fe prepared in Example 1 50.9 Ni 34 Cr 6 Al 6 Ti 3 B 0.1 Phase diagram and XRD spectrum of the alloy. It can be seen from the figure that the alloy has a single-phase FCC structure. Figure 3 The Fe prepared in Example 1 50.9 Ni 34 Cr 6 Al 6 Ti 3 B 0.1 The engineering stress-strain curve of the alloy shows that the alloy has a yield strength of 800 MPa and a high room temperature ductility of 31 %. Figure 4 Example 1 Preparation of Fe 50.9 Ni 34 Cr 6 Al 6 Ti 3 B 0.1 The SEM image of the alloy shows that the alloy has an equiaxed crystal structure. Example 2

[0018] This embodiment provides a low-cost, high-strength, Invar-like multi-component alloy, the composition of which is Fe 50.9 Ni 34 Cr 6 Al 6 Ti 1 Nb 2 B 0.1 The molar ratio of each element Fe, Ni, Cr, Al, Ti, Nb and B is 50.9:34:6:6:1:2:0.1.

[0019] The detailed preparation method is as follows: Step 1: Weighing: First, the raw material particles of Fe, Ni, Cr, Al, Ti, Nb and B with a purity of ≥99.9 wt.% were ultrasonically cleaned with anhydrous ethanol for about ten minutes and then dried to remove surface impurities. Then, an electronic balance with an accuracy of 0.0001g was used to weigh and proportion them according to the atomic ratio of 50.9:34:6:6:1:2:0.1 to obtain a nominal composition of Fe 50.9 Ni 34 Cr 6 Al 6 Ti 1 Nb 2 B 0.1 Alloy mixed particles; Step 2: Melting: Use WK-II vacuum arc furnace to melt the weighed Fe 50.9 Ni 34 Cr 6 Al 6 Ti 1 Nb 2 B 0.1 The alloy mixed particles are first melted into an ingot weighing 35g. Before melting, B is placed at the bottom to prevent it from being sucked away during vacuuming; Nb with a high melting point is placed at the top to melt it completely. The ingot is repeatedly turned over and melted for more than 5 times to ensure uniform distribution of the alloy elements. Step 3: Casting: Place the smelted alloy ingot on a water-cooled crucible with a mold, first heat the ingot to a molten state with a small current, then increase the current to make it completely melt and flow into a 5mm×10mm×40mm water-cooled copper mold. After the plate cools down, take out the sample; Step 4: Thermomechanical treatment: The cast sample is subjected to homogenization heat treatment at 1150 °C for 2 h, and then cold rolled with a 60% reduction. The cold rolled sample is further recrystallized at 1150 °C for 2 min, and finally aged at 700 °C for 4 h to prepare an alloy with high strength, good plasticity and low thermal expansion coefficient.

[0020] Figure 5 and Figure 6 The Fe prepared in Example 2 are 50.9 Ni 34 Cr 6 Al 6 Ti 1 Nb 2 B 0.1 Phase diagram and XRD spectrum of the alloy. It can be seen from the figure that the alloy has a single-phase FCC structure. Figure 7 The Fe prepared in Example 2 50.9 Ni 34 Cr 6 Al 6 Ti1 Nb 2 B 0.1 The engineering stress-strain curve of the alloy shows that the alloy has a yield strength of 710 MPa and a high room temperature ductility of 31 %. Figure 8 Example 2 Preparation of Fe 50.9 Ni 34 Cr 6 Al 6 Ti 1 Nb 2 B 0.1 The SEM image of the alloy shows that the alloy has an equiaxed crystal structure, and some grains are refined due to the addition of Nb element. Example 3

[0021] This embodiment provides a low-cost, high-strength, Invar-like multi-component alloy, the composition of which is Fe 50.9 Ni 34 Cr 6 Al 6 Nb 3 B 0.1 The molar ratio of each element Fe, Ni, Cr, Al, Nb and B is 50.9:34:6:6:3:0.1.

[0022] The detailed preparation method is as follows: Step 1: Weighing: First, the raw material particles of Fe, Ni, Cr, Al, Nb and B with a purity of ≥99.9 wt.% were ultrasonically cleaned with anhydrous ethanol for about ten minutes and then dried to remove surface impurities. Then, an electronic balance with an accuracy of 0.0001g was used to weigh and proportion them according to the molar ratio of 50.9:34:6:6:3:0.1 to obtain a nominal composition of Fe 50.9 Ni 34 Cr 6 Al 6 Nb 3 B 0.1 Alloy mixed particles; Step 2: Melting: Use WK-II vacuum arc furnace to melt the weighed Fe 50.9 Ni 34 Cr 6 Al 6 Nb 3 B 0.1 The alloy mixed particles are first melted into an ingot weighing 35g. Before melting, B is placed at the bottom to prevent it from being sucked away during vacuuming; Nb with a high melting point is placed at the top to melt it completely. The ingot is repeatedly turned over and melted for more than 5 times to ensure uniform distribution of the alloy elements. Step 3: Casting: Place the melted alloy ingot on a water-cooled crucible with a mold, first heat the ingot to a molten state with a small current, then increase the current to make it completely melt and flow into a 5 mm×10 mm×40 mm water-cooled copper mold. After the plate cools down, take out the sample; Step 4: Thermomechanical treatment: The cast sample is subjected to homogenization heat treatment at 1150 °C for 2 h, and then cold rolled with a 60% reduction. The cold rolled sample is further recrystallized at 1150 °C for 2 min, and finally aged at 700 °C for 4 h to prepare an alloy with high strength, good plasticity and low thermal expansion coefficient.

[0023] Fig. 9 and Fig.10 The Fe prepared in Example 3 are 50.9 Ni 34 Cr 6 Al 6 Nb 3 B 0.1 Phase diagram and XRD spectrum of the alloy. It can be seen from the figure that the alloy has a single-phase FCC structure. Fig.11 The Fe prepared in Example 3 50.9 Ni 34 Cr 6 Al 6 Nb 3 B 0.1 Engineering stress-strain curve of the alloy, the alloy has a yield strength of 800 MPa and a high room temperature ductility of 29%. Fig.12 Example 3 Preparation of Fe 50.9 Ni 34 Cr 6 Al 6 Nb 3 B 0.1 The SEM image of the alloy shows that the alloy has an equiaxed crystal structure, and the addition of Nb element further refines the grains.

Claims

1. A low-cost, high-strength and tough Invar alloy, characterized by: The alloy composition is Fe 50.9 Ni 34 Cr6Al6Ti 3- x Nb x B 0.1 , 3 ≥ x ≥ 0, the atomic ratio of each element Fe, Ni, Cr, Al, Ti, Nb and B is 50.9:34:6:6:3-x:x:0.1, and the alloy microstructure is an equiaxed crystal structure.

2. The low-cost, high-strength and tough Invar-like alloy according to claim 1, characterized in that: The purity of the Fe, Ni, Cr, Al, Ti, Nb and B smelting raw materials used in the alloy is not less than 99.9%.

3. A method for preparing a low-cost, high-strength and tough Invar-like alloy as claimed in claim 1 or 2, characterized in that The method comprises the following steps: preparing alloy ingots by smelting raw materials of Fe, Ni, Cr, Al, Ti, Nb and B; performing homogenization heat treatment on the alloy ingots at 1000°C-1200°C for 0.5h-2h, and then sequentially performing cold rolling with a total deformation of 60%-65%, recrystallization heat treatment at 1000°C-1200°C for 0.5min-2min, and aging heat treatment at 700°C for 4h-8h, so as to prepare low-cost and high-strength and toughness Invar alloy.

4. The method for preparing the low-cost, high-strength and tough Invar-like alloy according to claim 3, characterized in that The specific steps include: Step 1: Weighing: First, the raw material particles of Fe, Ni, Cr, Al, Ti, Nb and B with a purity of ≥99.9 wt.% are ultrasonically cleaned with anhydrous ethanol for ten minutes and then dried to remove surface impurities, and then weighed with an electronic balance with an accuracy of 0.0001g according to the atomic ratio of 50.9:34:6:6:3-x:x:0.1, 0≤x≤3; Step 2: Melting: Use a vacuum arc melting furnace. Place element B at the bottom before melting to prevent it from being sucked away during vacuuming. Then add other elements in order from low to high melting points to ensure that all elements can be completely melted. Place the weighed Fe 50.9 Ni 34 Cr6Al6Ti 3-x Nb x B 0.1 The alloy mixed particles are first melted into ingots, and the ingots are repeatedly turned over and melted more than 5 times to ensure uniform distribution of alloy elements; Step 3: Casting: Place the smelted alloy ingot on a water-cooled crucible with a mold, heat the ingot to a molten state, make it completely melt and flow into a water-cooled copper mold, and take out the sample after the plate cools down; Step 4: Thermomechanical treatment: The cast samples are subjected to homogenization heat treatment at 1000℃~1200℃ for 0.5h~2h, followed by cold rolling with a reduction of 60%-65%. The cold rolled samples are further recrystallized at 1000℃~1200℃ for 0.5min~2min, and finally aged at 700℃ for 4h~8h to prepare a multi-component alloy with high strength, good plasticity, corrosion resistance, oxidation resistance and potential low thermal expansion coefficient.

5. The method for preparing the low-cost, high-strength and tough Invar-like alloy according to claim 4, characterized in that: The yield strength of the low-cost, high-strength and tough Invar alloy produced reaches 700-800 MPa and the plasticity is 26-35%.

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