Cogging method of vanadium alloy cast ingot

Abstract

The invention provides a cogging method of a vanadium alloy cast ingot, which comprises the following steps of: selecting a high-strength graphite die as a cogging die, uniformly coating Y2O3 on the high-strength graphite die and the vanadium alloy cast ingot respectively as an isolating layer, filling the die in a hot-pressing sintering furnace, and carrying out cogging by a vacuum isothermal cogging method. According to the method, the defects that the utilization rate of materials is low, the step of removing the sheath is complex, the period is long, and the sheath cannot be repeatedly used due to cracking of the edge of the blank caused by low cogging temperature (1250 DEG C) due to the fact that the vanadium alloy adopts a low-melting-point stainless steel sheath (melting is started at 1300 DEG C) can be overcome. At 1350-1600 DEG C, the vacuum degree is less than or equal to 5 * 10 <-3 > Pa, and the strain rate is lt; and cogging is conducted under the condition of 0.05 s <-1 >, the edge cracking phenomenon is avoided, and the one-time cogging deformation can reach 90%. Oxidation of the vanadium alloy at high temperature is avoided through vacuum isothermal cogging, the defects that the vanadium alloy is high in high-temperature deformation resistance and prone to edge cracking are effectively overcome, the step of removing a sheath is omitted, and the method has the advantages of being high in material utilization rate, short in cogging period and the like.

Description

Technical Field

[0001] The invention belongs to the technical field of alloy hot processing, and in particular relates to a method for opening a vanadium alloy ingot. Background Art

[0002] Vanadium metal is a typical refractory metal, but the strength of pure metal is low and it is difficult to meet the needs of future engineering. By adding alloying elements such as Cr, Ti, Y, W and other elements, the strength of the alloy can be improved, the hydrogen embrittlement characteristics and high temperature oxidation resistance of the alloy can be changed, and the vanadium alloy after adding elements has good high temperature strength and plasticity, low radiation activation, high thermal conductivity, low thermal expansion coefficient, high creep strength and good resistance to radiation swelling. Therefore, it is selected as a candidate first wall structural material for fusion energy. Usually, vanadium alloys are made by vacuum consumable arc melting or electron beam melting, but the vanadium alloys prepared by the above melting methods have coarse grains and the grains at the edge of the ingot have the characteristics of directional growth. Such coarse grains lead to poor mechanical properties of the alloy, which cannot meet the needs of the first wall structural material of fusion energy. Vanadium alloys belong to single-phase solid solution strengthened metals. The mechanical properties of such alloys are mainly improved by refining the grains through pressure processing to obtain satisfactory organization and performance to meet the needs of the first wall structural material of fusion energy. Vanadium alloys begin to oxidize at temperatures above 450°C, and cannot form a dense oxide film to prevent further oxidation of the alloy, resulting in catastrophic oxidation. Therefore, the alloy is usually opened in an atmospheric environment with a stainless steel sheath during high-temperature opening. Due to the low melting point of stainless steel (melting begins at 1300°C), the opening is usually performed at temperatures below 1250°C, and this opening is performed in an air environment, and the entire billet is naturally air-cooled. When the upsetting opening begins, the surface temperature of the billet may be below 1100°C, and the deformation rate is difficult to control. At this time, the alloy is very likely to crack during the deformation process, so in practice, the vanadium alloy sheath is very likely to produce edge cracks after upsetting. In addition, this sheath opening method has many steps, a long cycle, and low material utilization. In addition, the removal of the sheath is difficult due to cracking, and the construction period is extremely long. In addition, the material of the stainless steel sheath cannot be reused, resulting in material waste. At present, there is no report on an efficient, short-cycle, and high-material utilization opening method for vanadium alloys in existing literature. Summary of the invention

[0003] The technical problem to be solved by the present invention is to provide a method for opening a vanadium alloy ingot in view of the shortcomings of the above-mentioned existing opening technology, through which the opening of vanadium alloy and other similar high-temperature easily oxidized, high-temperature strong and easy to crack alloy billets is guided.

[0004] The present invention selects high-strength graphite as the pressing die at both ends of the blank when opening the blank, and adopts Y 2 O 3As an isolation layer to prevent the graphite and vanadium alloy from reacting at high temperatures, and carbon from penetrating into the V-5Cr-5Ti alloy matrix at high temperatures. This technology uses vacuum isothermal blanking technology to replace the original stainless steel sheathing technology in view of the characteristics of V-Cr-Ti alloys that are easy to oxidize at high temperatures, have high deformation resistance, and are easy to crack at the edges, so as to shorten the blanking cycle and improve material utilization. At a temperature of 1350-1600℃, the vacuum degree is ≤5×10 -3 Pa high vacuum, using <0.05s -1 The strain rate of the vanadium alloy ingot is controlled by free upsetting. The combination of appropriate temperature and strain rate can effectively avoid cracking of the alloy edge. High vacuum can effectively prevent the vanadium alloy from oxidation at high temperature, which leads to the deterioration of alloy performance. This technology can effectively overcome the shortcomings of vanadium alloy ingots such as high resistance to high temperature deformation, easy edge cracking, and easy oxidation. Compared with conventional canned blank forging, it has obvious advantages, reduces many unnecessary steps (canned removal, especially when the vanadium alloy cracks at the edge, the canned removal cycle is very long), and improves material utilization (the original canned method has a vanadium alloy utilization rate of only about 30% due to the cracking of the vanadium alloy edge), thereby achieving the purpose of shortening the processing cycle and improving material utilization.

[0005] The technical solution adopted by the present invention is: a method for forming a vanadium alloy ingot, characterized in that the method comprises:

[0006] S1. Mixing the auxiliary elements of the vanadium alloy and the electrolytic dendrite vanadium uniformly, and then melting them by vacuum arc or electron beam to obtain a vanadium alloy ingot, and cutting it to obtain a vanadium alloy blank to be cut;

[0007] S2, select high-strength graphite as the blanking mold, and evenly coat Y on the surface of the high-strength graphite mold and the outer surface of the vanadium alloy blank to be blanked obtained in S1. 2 O 3 As an isolation layer;

[0008] S3, the coating Y obtained in S2 2 O 3 The vanadium alloy to be cut into billets is loaded into the coated Y 2 O 3 The graphite mold is opened in a vacuum hot pressing sintering furnace by a vacuum isothermal opening method, and then naturally cooled to room temperature to obtain a blank after opening; the conditions of the vacuum isothermal opening method are: the opening temperature is 1350° C. to 1600° C., and the strain rate is less than 0.05s -1 , vacuum degree in furnace ≤5×10 -3 Pa;

[0009] After loading the furnace, close the furnace door and start setting the corresponding program, then start vacuuming at room temperature until the vacuum reaches 5×10 - 3After Pa, the temperature starts to rise to the set temperature. After reaching the set temperature, the insulation time is set according to the following rules:

[0010] When the radius of the billet is smaller than the height of the billet, the holding time is the value of the billet radius:

[0011] T = R / min;

[0012] When the billet radius is greater than the billet thickness, the holding time is equal to the billet height:

[0013] T = H / min;

[0014] When the holding time reaches the set value, the billet is opened and the pressure loading rate is based on the pre-set strain rate. After the billet size is converted, the pressure loading curve is programmed for real-time loading. After the rated deformation is reached, the pressurization is stopped. After constant temperature insulation for 0.2h to 0.5h, the vacuum is stopped when the furnace is cooled to 400℃.

[0015] Preferably, the electrolytic dendrite vanadium in S1 has a purity of ≥99.95% and a length of greater than 3 mm.

[0016] Preferably, the auxiliary elements of the vanadium alloy in S1 include titanium and chromium; the purity of the auxiliary elements of the vanadium alloy is not less than 99.2%.

[0017] Preferably, the deformation amount in S3 is 70-90%.

[0018] Compared with the prior art, the present invention has the following advantages:

[0019] 1. In the present invention, a high-strength graphite mold is selected for the blanking mold. The strength of graphite increases with increasing temperature, and it has the characteristics of high high-temperature strength and good inertness. Therefore, graphite is selected as the blanking mold. This blanking method can overcome the disadvantages of using conventional stainless steel sheathing, which has too low melting point, resulting in low blanking temperature, uncontrollable deformation speed, severe edge cracking, and long unpacking time.

[0020] 2. The present invention adopts vacuum isothermal cogging method, and the cogging temperature is 1350℃~1600℃. Cogging at this temperature can effectively reduce edge cracks and improve material utilization. After cogging at this temperature, the grains are coarse and equiaxed, which is beneficial to the next step of rolling. The strain rate is <0.05s -1 , lower strain rate is conducive to dislocation coordination, reducing grain boundary stress and cracking. Vacuum degree in the furnace ≤5×10 -3 Pa; the pressure loading rate is calculated through the strain rate and the geometric dimensions of the blank. After the rated deformation is reached, the pressurization is stopped. After the constant temperature is maintained for 0.2h to 0.5h, the vacuum is stopped when the furnace is cooled to 400℃.

[0021] At vacuum degree ≤5×10 -3 Pa high vacuum, using <0.05s -1 The vanadium alloy ingot is freely upset at a strain rate. The lower strain rate can avoid the occurrence of cracking during the upsetting process. Temperature and strain rate are the two factors that have the greatest impact on cracking. The new blanking method has high blanking temperature and low strain rate. This deformation condition can greatly reduce the deformation resistance. The high temperature makes it easy to coordinate dislocations and grain boundaries, and the low deformation rate allows sufficient time for dynamic recovery and dynamic recrystallization, which greatly improves the deformation capacity of the material. Under this condition, the vanadium alloy blanking will not produce edge cracks. Finally, it is only necessary to simply remove the surface carbide skin. Compared with the process of removing the sleeve for blanking, the blanking cycle is greatly shortened.

[0022] 3. The alloy billet after blanking of the present invention has coarse equiaxed grains, and due to the slow cooling rate in the furnace, there is almost no residual stress in the billet. In addition, according to the principle of material plastic deformation, large-sized equiaxed grains are conducive to material deformation. The above two reasons will bring favorable conditions for the rolling of alloy plates, making the rolling deformation of alloy plates larger, and making the vanadium alloy grains finer after annealing, so that the strength and plasticity of the alloy plates are better.

[0023] The present invention is further described in detail below with reference to the accompanying drawings and embodiments. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 This is a photo of the vanadium alloy arc ingot according to Example 1 of the present invention.

[0025] Figure 2 This is a photo of the vanadium alloy arc ingot after cutting in Example 1 of the present invention.

[0026] Figure 3 This is a photo of the vanadium alloy arc ingot after charging in Example 1 of the present invention.

[0027] Figure 4 This is a photo of the vanadium alloy after billeting in Example 1 of the present invention.

[0028] Figure 5 This is a photo of the V-5Cr-5Ti alloy grains after blanking in Example 1 of the present invention. DETAILED DESCRIPTION

[0029] Example 1

[0030] This embodiment is to solve the problem of the method for opening a vanadium alloy by taking the method for opening a V-5Cr-5Ti alloy ingot as an example. The method is as follows:

[0031] S1. Mix vanadium, titanium and chromium raw materials evenly and then smelt them by vacuum arc or electron beam to obtain V-5Cr-5Ti alloy ingots, and cut them into blanks of certain sizes according to the size of the plate to be prepared; the vanadium is electrolytic dendrite vanadium with a purity of 99.95% and a length greater than 3 mm, the titanium is sponge titanium with a purity of 99.7% and a particle size of 3 mm to 5 mm, and the chromium is chromium sheets with a purity of 99.9% and a diameter greater than 8 mm;

[0032] S2, select a high-strength graphite mold as a blanking mold, and evenly coat Y on the surface of the high-strength graphite mold and the outer surface of the V-5Cr-5Ti alloy blank to be blanked obtained in S1 2 O 3 As an isolation layer;

[0033] V, Cr and Ti in the V-5Cr-5Ti alloy ingot are highly active and expensive, and are very easy to react with impurity elements such as O, H, and C at high temperatures, thereby affecting the purity and performance of the processed V-5Cr-5Ti alloy sheet; 2 O 3 The isolation coating is in powder form and is made of alcohol as a solvent. Before heating, the alcohol evaporates quickly, leaving an isolation layer that can prevent carbon from reacting with the V-5Cr-5Ti alloy ingot at high temperatures and prevent carbon from penetrating into the V-5Cr-5Ti alloy ingot matrix; and Y 2 O 3 The melting point is 2410℃. It will not melt during the process of V-5Cr-5Ti alloy billeting. Therefore, it can effectively prevent carbon from reacting with V-5Cr-5Ti alloy ingot at high temperature as an isolation layer, and effectively prevent carbon from penetrating into the V-5Cr-5Ti alloy matrix and causing alloy performance deterioration. In addition, Y 2 O 3 It does not react with V-5Cr-5Ti alloy and carbon, which can ensure that no additional impurities are introduced into the V-5Cr-5Ti alloy ingot during the billeting process. In addition, the literature reports that Y 2 O 3 The affinity of Y to oxygen is higher than that of V. This has been reported in some literatures. In the V-Cr-Ti system, Y can combine with O in V grains to form Y 2 O 3 Strengthening alloy, while other high temperature isolating agents are either not stable enough or will react with V at this temperature, making it difficult to achieve the purpose of isolation, so Y is selected 2 O 3 As a release agent, after the blanking is completed, Y 2 O 3 It will mix with graphite and adhere to the upper and lower surfaces of the vanadium alloy, and the surface layer will be removed by turning.

[0034] The strength of graphite increases with the increase of temperature, which makes it have a high-temperature strength higher than most refractory metals and their alloys. In addition, graphite has good inertness under vacuum; therefore, graphite is selected as the pressure head of the vacuum blanking material. Therefore, the use of vacuum isothermal blanking can overcome the shortcomings of conventional stainless steel sheath blanking, such as too low blanking temperature, easy edge cracking, complicated removal of the sheath, and inability to be reused;

[0035] S3, apply Y 2 O 3 The V-5Cr-5Ti alloy blank to be cut is coated with Y 2 O 3 Post-loading coating Y 2 O 3 The graphite mold is placed in a semi-solid furnace and the blank is opened by a vacuum isothermal blank opening method. When the set deformation amount is reached, the pressurization is stopped. After the deformation temperature is kept for 0.5h, the vacuum is stopped when the furnace is cooled to 400°C. After cooling to room temperature, the furnace is opened to take out the blank to obtain the slab to be rolled. The conditions of the vacuum isothermal blank opening method are as follows: the blank opening temperature is 1550°C. The blank opening at this temperature can effectively reduce edge cracks and improve material utilization. After the blank is opened at this temperature, the grains are coarse and all are equiaxed grains, which is beneficial to the next step of rolling. The strain rate is <0.05s -1 , lower strain rate is conducive to dislocation coordination, reducing grain boundary stress and cracking. Vacuum degree in the furnace ≤5×10 - 3 Pa;

[0036] After loading the furnace, close the furnace door and start setting the corresponding program, then start vacuuming at room temperature until the vacuum reaches 5×10 - 3 After Pa, the temperature starts to rise to the set temperature. After reaching the set temperature, the insulation time is set according to the following rules:

[0037] When the radius of the billet is smaller than the height of the billet, the holding time is the value of the billet radius:

[0038] T = R / min;

[0039] When the billet radius is greater than the billet thickness, the holding time is equal to the billet height:

[0040] T = H / min;

[0041] When the holding time reaches the set value, the billet is opened and the pressure loading rate is based on the pre-set strain rate. After the billet size is converted, the pressure loading curve is programmed for real-time loading. After the rated deformation (90%) is reached, the pressurization is stopped. After constant temperature insulation for 0.5h, the vacuum is stopped when the furnace is cooled to 400℃.

[0042] At vacuum degree ≤5×10 -3 Pa high vacuum, using <0.05s -1 The V-5Cr-5Ti alloy ingot is freely upset at a strain rate of 1.50. The lower strain rate can avoid the occurrence of cracking during the upsetting process. Temperature and strain rate are the two factors that have the greatest impact on cracking. With the increase of temperature and the decrease of deformation rate, the deformation resistance of the material decreases significantly, thereby reducing the requirements for the tonnage of the equipment. The conventional upsetting method uses a stainless steel sheath, which has a low initial heating degree. In addition, since the blank is opened in the air, the heat is lost quickly during the transportation process from the heating furnace to the press, so that the temperature of the blank has basically dropped to 1100℃ when it reaches the press anvil. In addition, the temperature of the press anvil is at room temperature, and the blank will drop sharply after contact, making the actual blank opening temperature of the blank lower than 1000℃, so only a faster blank opening speed can be used. Previous studies by the inventors have shown that after the temperature is lower than 1000°C, the alloy will have serious edge cracks. In order to prevent the vanadium alloy from causing more serious cracking due to the decrease in temperature, a faster strain rate must be used for blanking, and a faster strain rate will also cause serious edge cracks in the blank. This blanking method has the disadvantages of low temperature, uncontrollable deformation speed, rapid deformation, severe edge cracks, and long time to remove the sheath. The inventors' previous studies found that lower temperatures and faster strain rates are the main causes of edge cracks in vanadium alloys. The new blanking method has the characteristics of high blanking temperature, blanking in the isothermal section, controllable deformation speed, no edge cracks, etc., and finally only needs to simply remove the surface carburized skin, and its blanking cycle is greatly shortened. Stopping vacuuming when the temperature drops to 400°C can overcome the disadvantage of easy oxidation of vanadium alloy ingots under high temperature conditions (above 450°C), and the reduction in strain rate can overcome the disadvantage of high resistance to high temperature deformation of vanadium alloy ingots. Compared with conventional blanking forging, it has obvious advantages, especially eliminating the step of removing the sheath, which significantly shortens its processing cycle.

[0043] The deformation amount of the blank can reach 70% to 90% in one blank opening by using the method.

[0044] Figure 1 This is a photo of a vanadium alloy arc ingot (without the outer surface skin). Figure 2 This is a photo of the vanadium alloy arc ingot after cutting (skinned and cut into pieces, ready to be billeted). Figure 3 This is a photo of the vanadium alloy arc ingot after loading into the furnace. Figure 4 This is a photo of vanadium alloy after billeting. Figure 5 This is a photo of the V-5Cr-5Ti alloy grains after billeting.

[0045] The above is only a preferred embodiment of the present invention and does not limit the present invention in any way. Any simple modification, change and equivalent change made to the above embodiment according to the technical essence of the invention still falls within the protection scope of the technical solution of the present invention.

Claims

1. A method for forming a vanadium alloy ingot, characterized in that: The method is: S1. Mixing the auxiliary elements of the vanadium alloy and the electrolytic dendrite vanadium uniformly, and then melting them by vacuum arc or electron beam to obtain a vanadium alloy ingot, and cutting it to obtain a vanadium alloy blank to be cut; S2, select high-strength graphite as a blanking mold, and evenly coat Y2O3 as an isolation layer on the surface of the high-strength graphite mold and the outer surface of the vanadium alloy blank to be blanked obtained in S1; S3, the Y2O3 coated vanadium alloy blank to be blanked obtained in S2 is placed in a Y2O3 coated graphite mold, blanked by a vacuum isothermal blanking method in a vacuum hot pressing sintering furnace, and then naturally cooled to room temperature to obtain a blank after blanking; the conditions of the vacuum isothermal blanking method are: the blanking temperature is 1350°C to 1600°C, the strain rate is <0.05s -1 , vacuum degree in furnace ≤5×10 - 3 Pa; After loading the furnace, close the furnace door and start setting the corresponding program, then start vacuuming at room temperature until the vacuum reaches 5×10 -3 After Pa, the temperature starts to rise to the set temperature. After reaching the set temperature, the insulation time is set according to the following rules: When the radius of the billet is smaller than the height of the billet, the holding time is the value of the billet radius: T = R / min; When the billet radius is greater than the billet thickness, the holding time is equal to the billet height: T = H / min; When the holding time reaches the set value, the billet is opened and the pressure loading rate is based on the pre-set strain rate. After the billet size is converted, the pressure loading curve is programmed for real-time loading. After the rated deformation is reached, the pressurization is stopped. After constant temperature insulation for 0.2h to 0.5h, the vacuum is stopped when the furnace is cooled to 400℃.

2. A method for forming a vanadium alloy according to claim 1, characterized in that: The length of the electrolytic vanadium dendrite described in S1 is greater than 3 mm.

3. The method for forming a vanadium alloy according to claim 1, characterized in that: The auxiliary elements of the vanadium alloy in S1 include titanium and chromium.

Images