Method for adding rare earth elements into high-temperature niobium alloy

Abstract

The invention provides a method for adding rare earth elements in a high-temperature niobium alloy. The method comprises the steps of raw material preparation, vacuum suspension smelting, in-furnace welding, auxiliary electrode welding and two times of vacuum smelting. According to the scheme, raw materials needed for ingot casting are divided into a plurality of parts, each part is subjected to vacuum suspension smelting to obtain small ingot castings, then the small ingot castings are welded pairwise in a suspension smelting furnace to obtain welded ingot castings, the welded ingot castings are welded with an auxiliary electrode to form ingot castings capable of being smelted in a VAR furnace, and then the ingot castings are subjected to two times of vacuum consumable smelting to obtain the VAR ingot casting. And the niobium-based niobium alloy ingot with rare earth elements uniformly added is obtained.

Description

Technical Field

[0001] The invention relates to the technical field of high-temperature niobium alloy smelting, and in particular to a method for adding rare earth elements into a high-temperature niobium alloy. Background Art

[0002] Niobium metal has a relatively low density (8.57 g / cm 3 ), high melting point (2741K), high plasticity, good corrosion resistance and low vapor pressure, and high-temperature niobium alloy has high high-temperature (600-1600℃) specific strength and good hot and cold processing performance. It can be used to make parts with complex shapes and is one of the important materials for aerospace structural parts. It can be used to manufacture key components of rocket engines, space-to-earth shuttles, hypersonic aircraft, satellites, missiles and nuclear reactors. Rare earth as a microalloying element (such as Y, Sc, Sm) added to high-temperature niobium alloy can play the role of fine grain strengthening, solid solution strengthening, precipitation strengthening and aging strengthening, further improving the high-temperature oxidation resistance, corrosion resistance and high-temperature mechanical properties of the alloy.

[0003] The melting point and boiling point of rare earth elements are lower than those of high-temperature niobium alloys. In the prior art, rare earth elements are added to high-temperature niobium alloys using electron beam melting technology and vacuum melting technology. Under high vacuum conditions, rare earth elements are easy to volatilize, resulting in technical difficulties in controlling the uniformity of the composition and the content.

[0004] element density Melting point Nb 8.27 2741 Sm 7.54 1345 Y 5.01 2401 Sc 2.985 1814 Summary of the invention

[0005] In view of the above defects, the present invention proposes a method for adding rare earth elements to high temperature niobium alloys, comprising the following steps:

[0006] Raw material preparation: The ingredients are prepared according to the mass ratio. The niobium base is made of pure niobium blocks or niobium alloy blocks, the alloying elements are made of multi-element alloys or pure metal blocks, and the rare earth elements are made of pure metal particles. The raw materials are prepared in several portions;

[0007] Vacuum suspension melting: put one portion of the above raw materials into a crucible, evacuate to below 0.01Pa, adjust the current, voltage, and oscillating current, and after all the raw materials are melted, observe that the solution is suspended in the crucible, mix evenly, and then cool and take out of the furnace. Repeat the suspension melting at least three times to obtain a small ingot; repeat the operation, add several portions of raw materials into the crucible one by one for suspension melting, and obtain several small ingots;

[0008] In-furnace welding: put the two small ingots obtained by the above smelting into the suspension smelting furnace again with their heads and tails touching, evacuate, adjust the current and voltage, slowly increase the oscillating current, observe the connection between the two ingots in the crucible, turn off the power and cool after melting to form a welded ingot; put the single small ingots into the crucible in turn, contact them with the tail of the welded ingot, turn on the power, so that the contact position of the two adjacent small ingots is melted and connected to form a welded ingot.

[0009] Auxiliary electrode welding: The welding electrode and the auxiliary electrode are welded by tungsten inert gas arc welding outside the furnace to form a consumable electrode;

[0010] Two vacuum melting: Put the consumable electrode into the VAR furnace, perform two vacuum consumable melting, adjust the first melting current to 2.9-3.1kA, voltage to 32-33V, arc stabilization current DC 5-6A, adjust the second melting current to 4.5-4.8kA, voltage to 33-35V, arc stabilization current AC 5-6A15s; obtain the melted ingot;

[0011] Ingot surface treatment: Use lathe to peel the smelted ingot, and there are no large-area pores and defects on the surface;

[0012] Ingot inspection: Take samples from the ingot and test the element content.

[0013] Further, the following steps are included:

[0014] In the raw material preparation step: the rare earth element is selected from one of Y, Sc and Sm.

[0015] Further, the method comprises the following steps: the vacuum suspension melting current is 50±2A, the voltage is 530±5V, and the oscillation current is 150±3A.

[0016] Further, the method comprises the following steps: the welding current in the furnace is about 50±2A, the voltage is 530±5V, and the oscillating current does not exceed 150A.

[0017] In this scheme, the raw materials required for ingot casting are first divided into several portions, each of which is first subjected to vacuum suspension smelting to obtain a small ingot, and then several small ingots are welded in pairs in a suspension smelting furnace to obtain welded ingots, which are then welded with auxiliary electrodes to form ingots that can be smelted in a VAR furnace, and then subjected to two vacuum consumable smeltings to obtain niobium-based niobium alloy ingots with rare earth elements uniformly added. In this scheme, the raw materials are first divided into several portions, each of which has a small mass, which is suitable for suspension smelting, and the suspension smelting solution has good magnetic field stirring uniformity. It is only necessary to make each raw material uniform when mixing. The single smelting mass of suspension smelting is less, the mixing uniformity is better, and the magnetic field stirring has no great relationship with the element density. Therefore, the uniformity of a single small ingot is better after smelting. Each small ingot is smelted by the same method, and the uniformity between several small ingots is almost the same.

[0018] This scheme is to first use suspension smelting to form a small ingot with uniform composition, then weld in the furnace to form an auxiliary electrode to prepare for consumable smelting, and then use VAR consumable smelting to form a large ingot. Through the combination of single suspension smelting of small ingots and consumable smelting of welded ingots, the problems of poor material quality and solution fluidity, large segregation and uneven composition caused by direct electron beam smelting and VAR smelting are avoided, and the defect that only suspension smelting is only suitable for smelting ingots with small smelting quality and small batches is solved. In addition, during consumable smelting, when spot welding is used between the original single-section electrodes to form a longer consumable electrode, the welding strength is insufficient, resulting in block falling during consumable smelting and uneven smelting. Moreover, for niobium alloys, when several short ingots are spot welded to form a longer ingot, if external argon arc welding is used, there is an increase in the brittleness and stress of the welding point, and serious cracks will occur at the welding mouth. After entering the VAR furnace, after power is turned on, the welding point is very easy to break due to the spot welding method, resulting in block falling and incomplete smelting. This scheme places two adjacent small ingots in a suspension smelting furnace and uses the current adjustment method (the welding current is different from the smelting current) to melt the surface of the two small ingots at the joint to complete the welding. This welding process is different from spot welding. Due to the use of induction heating, the skin effect of the current causes the surface of the small ingot to melt in advance. In addition, there is a gap and a large resistance at the joint of the two small ingots. At the joint, due to the large resistance, the heat is more serious and the temperature is higher than other positions inside the ingot, so this position melts quickly to achieve welding connection; at the same time, when the coil is induced, the current tends to flow on the surface of the ingot, so a strong current is formed at the circumference of the outer wall of the joint of the two small ingots, so that a circle of melting layer and welding layer is formed in advance on the outer wall of the joint of the two small ingots. At the same time, the personnel observed that when the connection layer is formed at the joint of the two small ingots, the welding is completed, and the application of current and voltage is stopped, thus completing the welding connection of the two small ingots. Compared with spot welding, the welding of this scheme forms a circular ring-shaped welding layer at the head and tail of the two small ingots. The connection strength is much greater than spot welding. During welding, the small ingots are all in the smelting furnace, and current flows on the surface of the ingot in the length direction. The temperature difference between the welding point and other positions of the ingot is small, there is no local stress, there is no crack after welding, and the strength is greater.

[0019] The electron beam melting technology is only suitable for one-time melting of large-capacity and large-mass ingots (that is, after all the raw materials are mixed, they are placed in the electron beam furnace for high-temperature melting. Although the melting temperature can meet the requirements, due to the large amount of raw materials, the solution fluidity is poor due to the differences in specific gravity and density during the melting process, and rare earth elements and niobium are easily segregated). The vacuum consumable melting technology is also suitable for larger ingot capacity, but it depends entirely on the uniformity of the raw material mixing. The consumable melting solution gradually melts from bottom to top, and the liquid fluidity and uniformity are poor. If the mixing is uneven, segregation is easily caused. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 This is a schematic diagram of 7 small ingots after welding.

[0021] Figure 2 This is a schematic diagram of the weld layer formed after welding two small ingots.

[0022] Figure 3 This is a picture of the ingot's microstructure and crystal phase. DETAILED DESCRIPTION

[0023] Embodiment 1:

[0024] The Nb1Zr0.3Y alloy formula of this embodiment is: Zr: 1.1%, Y: 0.3%, the balance is Nb and inevitable impurities, the raw materials are pure niobium blocks, pure zirconium sheets and pure yttrium particles, the ingredients are prepared according to the above weight percentages, the total weight of a single portion is 900g, and there are 7 portions in total.

[0025] (1) Vacuum suspension smelting: Nb1Zr0.3Y small ingots were prepared by vacuum suspension smelting, and a total of 7 small ingots were obtained. First, a single portion of raw material was loaded into a φ50×150mm crucible, and the air was evacuated to below 0.01Pa, with a current of 50A, a voltage of 530V, and an oscillating current of 150A. According to the actual smelting situation, the smelting current was gradually increased to 500A. After all the materials were melted, the oscillating current was adjusted to 630A and the smelting power was about 270kw to suspend the solution in the crucible. After mixing, the power was turned off and cooled. After the ingot is taken out of the furnace, it is inverted in the crucible and the above process is repeated for smelting. Each small ingot is smelted for no less than three times. Three small ingots were randomly selected for sampling and component testing.

[0026]

[0027] The data in the table show that when three small ingots are randomly selected, the content of each element in the head and tail of each small ingot is relatively uniform, and there is no segregation of element content between any two small ingots. It can be seen that suspension smelting has better smelting uniformity for small ingots with smaller single element mass.

[0028] (2) Vacuum suspension melting and welding: Use vacuum suspension welding technology to prepare vacuum consumable melting electrodes, and weld every 7 small ingots into one electrode. Place two small ingots in a crucible, evacuate to below 0.01Pa, and start the arc after filling with argon. The current is about 50A, the voltage is about 530V, and the oscillating current is about 150A. Slowly increase the melting current to about 150A, observe the connection between the two ingots in the crucible, turn off the power and cool after melting and connection, and repeat the above welding operations in sequence. Weld every two sections, and the ingot after welding is considered as one section, and it is placed on top when loading the furnace. Figure 1 Schematic diagram showing a large welded ingot formed by welding 7 small ingots. Figure 2 It is a schematic diagram of a circle of molten layer and welding layer formed between two adjacent small ingots after welding.

[0029] (3) Welding consumable electrode: The suspension smelting welding electrode and the vacuum consumable smelting auxiliary electrode are welded by tungsten inert gas arc welding outside the furnace.

[0030] (4) Primary vacuum smelting: The φ115mm primary Nb1Zr0.3Y alloy ingot is smelted by vacuum consumable smelting method. Before smelting, the inner wall of the water-cooled copper crucible must be cleaned, and the welded electrodes must be loaded into the furnace. The furnace vacuum degree before smelting is ≤0.6Pa, and the leakage rate is ≤0.5Pa / min; in the stable smelting stage, the smelting current is 2.9~3.1kA, the voltage is 32~33V, and the arc stabilization current is DC5-6A.

[0031] (5) Secondary vacuum smelting: The φ165mm secondary Nb1Zr0.3Y alloy ingot is smelted by vacuum consumable smelting method. Before smelting, the inner wall of the water-cooled copper crucible must be cleaned first, and the primary niobium alloy ingot is placed upside down in the furnace. The auxiliary electrode is welded in the furnace. The vacuum degree of the furnace body before smelting is ≤0.6Pa, and the leakage rate is ≤0.5Pa / min; in the stable smelting stage, the smelting current is 4.5~4.8kA, the voltage is 33~35V, and the arc stabilization current is AC 5-6A 15s.

[0032] (6) Ingot peeling: The secondary smelting ingot is peeled using a lathe, and there are no large areas of pores or defects on the surface.

[0033] (7) Ingot inspection: The content of each alloy and interstitial gas element is tested on the test sample; non-destructive ultrasonic flaw detector is used to detect internal defects of the ingot and determine the position of the riser.

[0034] The three positions of the ingot after consumable smelting were tested, respectively. Figure 1 The end ingot, the tail ingot, and the middle ingot in the middle (due to welding, the 7 small ingots are Figure 1 After welding, the electrode enters the consumable melting furnace, and the tail ingot of the welded electrode slowly melts from bottom to top, and gradually melts upward. Due to the consumable melting, the fluidity of the solution is poor, so Figure 1 The positions of the end ingot, tail ingot and middle ingot during welding are basically unchanged), and the content of each element is as follows:

[0035]

[0036] The test data in the table show that the content of each element in the samples of the three parts is basically uniform, there is no problem of high local content, and there is no segregation problem after smelting. Figure 3As for the ingot, it is well known to the people in the art that the ingot has coarse and uneven grains because it has not undergone subsequent finishing (such as forging, upsetting, and heat treatment). The ingot is the basic material for finishing. Although the organizational structure of the ingot cannot reach the level of finishing, the excellent organizational structure of the ingot itself lays the foundation for subsequent finishing. Having a uniform organizational structure without segregation is also generally pursued by people in the art. Figure 3 It can be seen that the size of the ingot casting structure is uniform and evenly distributed, without obvious segregation and inclusions. Figure 3 The structure in is very excellent, which cannot be achieved by directly using vacuum consumable melting.

[0037] The embodiments of the present invention are described in detail above in conjunction with the accompanying drawings, but the present invention is not limited to the above embodiments. Various changes can be made within the knowledge scope of ordinary technicians in the relevant technical field without departing from the purpose of this patent.

Claims

1. A method for adding rare earth elements to high temperature niobium alloys, characterized in that The following steps are involved: Raw material preparation: The ingredients are prepared according to the mass ratio. The niobium base is made of pure niobium blocks or niobium alloy blocks, the alloying elements are made of multi-element alloys or pure metal blocks, and the rare earth elements are made of pure metal particles. The raw materials are prepared in several portions; Vacuum suspension melting: put one portion of the above raw materials into a crucible, evacuate to below 0.01Pa, adjust the current, voltage, and oscillating current, and after all the raw materials are melted, observe that the solution is suspended in the crucible, mix evenly, and then cool and take out of the furnace. Repeat the suspension melting at least three times to obtain a small ingot; repeat the operation, add several portions of raw materials into the crucible one by one for suspension melting, and obtain several small ingots; In-furnace welding: the two small ingots obtained by the above smelting are placed in the suspension smelting furnace again with their heads and tails in contact, vacuumed, the current and voltage are adjusted, the oscillating current is slowly increased, the connection between the two ingots in the crucible is observed, and the power is turned off and cooled after melting to form a welded ingot; the single small ingots are placed in the crucible in sequence, contacted with the tail of the welded ingot, and electricity is applied to melt and connect the contact positions of the two adjacent small ingots to form a welded ingot; Auxiliary electrode welding: The welding electrode and the auxiliary electrode are welded by tungsten inert gas arc welding outside the furnace to form a consumable electrode; Two vacuum melting: Put the consumable electrode into the VAR furnace, perform two vacuum consumable melting, adjust the first melting current to 2.9-3.1kA, voltage to 32-33V, arc stabilization current DC 5-6A, adjust the second melting current to 4.5-4.8kA, voltage to 33-35V, arc stabilization current AC 5-6A 15s; obtain the melted ingot; Ingot surface treatment: Use lathe to peel the smelted ingot, and there are no large-area pores and defects on the surface; Ingot inspection: Take samples from the ingot and test the element content.

2. The method for adding rare earth elements to high temperature niobium alloy according to claim 1, characterized in that The following steps are involved: In the raw material preparation step: the rare earth element is selected from one of Y, Sc and Sm.

3. The method for adding rare earth elements to high temperature niobium alloy according to claim 1, characterized in that The following steps are involved: The vacuum suspension melting current is 500±5A, the voltage is 530±5V, and the oscillation current is 630±5A.

4. The method for adding rare earth elements to high temperature niobium alloy according to claim 1, characterized in that The following steps are involved: The welding current in the furnace is about 150±2A, the voltage is 530±5V, and the oscillating current does not exceed 150A.

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