A method for evaluating the compositional uniformity of titanium alloy ingots

Abstract

This invention relates to the field of titanium alloy testing technology, and discloses a method for evaluating the compositional uniformity of titanium alloy ingots, comprising the following steps: Step 1, high-temperature solution treatment in the single-phase region, heating the ingot riser to T... β + (10~300)℃, hold at the temperature and then rapidly cool; Step 2, first stage low temperature aging, place the ingot riser cooled in Step 1 at T β Keep warm below 200-400°C, then raise the temperature to T. β -30~60℃, hold at that temperature and then cool; Step 3, β-spot heat treatment, place the riser of the ingot cooled in Step 2 at T β The process involves holding the ingot at -25°C and then cooling it. Step four, the second stage of low-temperature aging, involves holding the water-cooled ingot riser from step three at 600–650°C and then cooling it. Step five, high and low magnification microstructure detection. This invention patent solves the problems of complex detection processes, poor accuracy, and high evaluation costs in the existing technology for detecting the uniformity of titanium alloy ingot composition.

Description

Technical Field

[0001] This invention relates to the field of titanium alloy testing technology, and specifically to a method for evaluating the compositional uniformity of titanium alloy ingots. Background Technology

[0002] Titanium alloys possess high specific strength, good ductility, and excellent fracture toughness, leading to their increasing market share in the aerospace field. Among them, near-β and β-type titanium alloys, due to their high strength and toughness, are widely used in the manufacture of critical load-bearing components such as aircraft landing gear, main beams, and shafts. However, the strengthening effect of these titanium alloys largely depends on the alloying effects of elements such as Cr, Fe, and Mo. Common examples of such titanium alloys include TC17 (Ti-5Al-4Mo-4Cr-2Zr-2Sn), TB6 (Ti-10Al-2Fe-3V), and Ti-55531 (Ti-5Al-5Mo-5V-3Cr-1Zr). Most of the aforementioned alloying elements are β-stabilizing elements. In the production process of these types of titanium alloys, the poor solubility of the solid / liquid phases leads to macroscopic and microscopic segregation problems. The increased local element content caused by microscopic segregation significantly lowers the local phase transformation point T. β Titanium alloys are typically in (T β Forging is carried out within a narrow range of -50℃ to (Tβ+30℃), therefore, when T β Changes in these elements can significantly affect the microstructure and properties of titanium alloys. Therefore, assessing the microsegregation levels of elements such as Cr, Fe, and Mo is crucial for the production and application of these titanium alloys.

[0003] Since microscopic segregation is typically on the millimeter scale and lacks obvious distinguishing features, it is impossible to assess the level of microscopic segregation by detecting chemical composition. Therefore, existing technologies usually use the detection of α-phase content to evaluate the local phase transformation point of titanium alloys. The specific principle is that the content of α-phase decreases as it approaches the phase transformation point. Therefore, when the α-phase content is normal in most locations of a titanium alloy product, but the α-phase content is very low or close to 0 in some areas, it indicates that the local phase transformation point is low, meaning that elements such as Cr, Fe, and Mo accumulate in these areas. At the same time, they appear as bright spots on the low-magnification microstructure. This detection method is known in the industry as "β-spot inspection". However, in actual testing, since the α phase is absent in the microstructure of titanium alloy ingots, β spots cannot be directly inspected. In the testing process, multiple forging processes are generally required to obtain the α phase before testing, which increases the testing procedures and costs. Furthermore, the microstructure may deteriorate during the forging process, affecting the accuracy of the test. Alternatively, testing can be performed on the finished bar stock. However, if the test assessment reveals poor uniformity of the ingot composition, it will result in material scrapping and waste of the cost of forging the finished bar stock. Summary of the Invention

[0004] The present invention aims to provide a method for evaluating the compositional uniformity of titanium alloy ingots, so as to solve the problems of complex detection process, poor accuracy and high evaluation cost in the existing technology for detecting the compositional uniformity of titanium alloy ingots.

[0005] To solve the above problems, the present invention adopts the following technical solution: a method for evaluating the compositional uniformity of titanium alloy ingots, comprising the following steps:

[0006] Step 1: High-temperature solution treatment in the single-phase region, heating the ingot riser to T β + (10~300)℃, hold for heat and then rapidly cool;

[0007] Step 2, First Stage Low Temperature Aging: The ingot riser cooled in Step 1 is subjected to T... β - Keep warm below 200-400°C, then raise the temperature to T. β - (30~60)℃, keep warm and then cool;

[0008] Step 3: β-spot heat treatment. The riser of the ingot cooled in Step 2 is then subjected to T... β The temperature was kept at -25℃, and then cooled.

[0009] Step 4, the second stage of low-temperature aging, involves holding the water-cooled ingot riser from Step 3 at 600-650℃, and then cooling it.

[0010] Step 5: High and low magnification tissue analysis.

[0011] The principle of this scheme is as follows: In step one, the ingot riser is rapidly cooled after solid solution treatment in the single-phase region, causing the ingot riser structure to become a supersaturated solid solution. During the heating process after the first stage of low-temperature aging in step two, the driving force for the nucleation of new phases increases significantly due to the large free energy difference. The interface of the new phase changes from a semi-coherent interface to an incoherent interface with higher interfacial energy. The α phase with the incoherent interface will spontaneously geomorphize, forming an equiaxed or short rod-shaped α phase, which makes the ingot riser have the basic conditions for β spot detection. Then, the β spot heat treatment in step three and the second stage of low-temperature aging in step four make the ingot riser form a detectable α phase state. Finally, the equiaxed or short rod-shaped α phase can be conveniently and clearly detected and observed in the high and low magnification structure detection in step five, thereby accurately evaluating the compositional uniformity of the ingot.

[0012] The beneficial effects of this plan are:

[0013] 1. High accuracy in ingot composition uniformity assessment: Compared to existing technologies that require multiple forging processes to obtain equiaxed or short-bar morphologies of the α phase for better observation and identification, this method is not only more complex but also deteriorates the internal structure of the titanium alloy during multiple forging processes, affecting the accuracy of ingot composition uniformity assessment. In this application, a high-temperature solid solution process in the single-phase region and a first-stage low-temperature aging process are used to form equiaxed or short-bar morphologies of the α phase at the ingot riser, effectively improving the visibility in subsequent α phase detection processes. This not only effectively reduces the difficulty of detection but also avoids the formation of lamellar α phases, improving the identification of the α phase. It is easily identifiable at both high and low magnification scales, thus enabling a more accurate assessment of the composition uniformity of the titanium alloy ingot.

[0014] 2. Higher process feasibility: Compared to existing detection methods, which require multiple forging processes, this approach is not only complex but also deteriorates the internal structure of the titanium alloy, affecting the accuracy of ingot composition uniformity assessment. The detection process in this application eliminates the need for multiple forging processes, enabling the ingot riser to form easily identifiable equiaxed or short-bar α-phase. This not only improves assessment accuracy but is also simpler, more feasible, and less costly.

[0015] 3. Efficient testing: In this application, since the ingot riser is treated by heat treatment, it is not necessary to spend a lot of time on forging, etc., which effectively improves the efficiency of evaluation and testing, helps to shorten the titanium alloy production cycle, and obtains better economic benefits.

[0016] 4. Good economic benefits: By directly detecting β spots on the ingot, the reliability of the smelting process and the level of product segregation can be quickly assessed. Compared with conventional finished bar testing, it effectively saves about 100,000 yuan per furnace forging cost and material loss, while avoiding the scrapping of ingots (the cost of each furnace of ingots is between 300,000 and 500,000 yuan).

[0017] Preferably, as an improvement, the ingot riser holding time in step one is T1 = D × (0.5~3.0) minutes, where D is the riser thickness in mm.

[0018] Preferably, as an improvement, in step two, the ingot riser is at T β The heat preservation time at (200~400)℃ is 1~8h.

[0019] Preferably, as an improvement, in step two, the ingot riser is heated to T... β - The heat preservation time after (30~60)℃ is T2 = D × (0.5~3.0) minutes, where D is the thickness of the riser in mm.

[0020] Preferably, as an improvement, in step three, the ingot riser is at Tβ The heat preservation time is 2 hours at -25℃.

[0021] Preferably, as an improvement, the ingot riser in step four is kept at a temperature of 600-650°C for 4-8 hours.

[0022] Preferably, as an improvement, the rapid cooling method in step one is water cooling.

[0023] Preferably, as an improvement, in step two, the ingot riser is heated to T... β - After heat preservation at (30~60)℃, the cooling method is air cooling.

[0024] Preferably, as an improvement, in step three, the ingot riser is at T β After being kept at -25℃, the cooling method is water cooling.

[0025] Preferably, as an improvement, the cooling method after the ingot riser is kept at 600-650℃ in step four is air cooling.

[0026] The beneficial effects of this plan are:

[0027] 1. In this scheme, the holding time for high-temperature solidification of the ingot riser in the single-phase region in step one and the temperature rise to T in step two are determined based on the thickness of the ingot riser. β The holding time after (30~60)℃ is conducive to the ingot riser completing the spheroidization transformation of the α phase more fully, and fully forming the α phase in the form of equiaxed or short rods, so as to facilitate convenient and accurate subsequent detection.

[0028] 2. Set the rapid cooling method in step one to water cooling, so that the riser of the ingot after high-temperature solidification is rapidly cooled, which facilitates the formation of supersaturated solid solution, greatly increases the driving force for the precipitation of α phase in step two, and changes the morphology of the precipitated phase.

[0029] 3. Since the phase transformation point of the titanium alloy was not detected before the uniformity of the ingot composition was evaluated, the β spot heat treatment temperature value in step three could not be accurately determined. Therefore, the empirical average phase transformation point of the corresponding type of titanium alloy was used to conduct trial treatment on the ingot riser, and the heat treatment temperature value of the β spot heat treatment in step three was adjusted according to the trial treatment results, so as to obtain β spot detection results with obvious characteristics. Attached Figure Description

[0030] Figure 1 This is a high-magnification tissue photograph taken after step two in Embodiment 1 of the present invention.

[0031] Figure 2 This is a high-magnification microstructure photograph of a conventional finished bar stock used in the comparative example of this invention.

[0032] Figure 3This is a low-magnification tissue photograph taken after step five in Embodiment 1 of the present invention.

[0033] Figure 4 This is a low-magnification tissue photograph (side view) taken after step five in Embodiment 1 of the present invention.

[0034] Figure 5 This is a low-magnification tissue photograph (frontal view) taken after step five in Embodiment 1 of the present invention.

[0035] Figure 6 This is a high-magnification tissue photograph of the normal area after step five in Embodiment 1 of the present invention.

[0036] Figure 7 This is a high-magnification tissue photograph of the bright spot area after step five in Embodiment 1 of the present invention. Detailed Implementation

[0037] The following detailed description illustrates the specific implementation method:

[0038] Example 1

[0039] Example 1: A method for evaluating the compositional uniformity of titanium alloy ingots, comprising the following steps:

[0040] Step 1: High-temperature solution treatment in the single-phase region, heating the ingot riser to T β + (10~300)℃, hold for a period of time and then rapidly cool down. The holding time is T1=D×(0.5~3.0) minutes, where D is the thickness of the riser in mm. In addition, the rapid cooling method in this step is water cooling, and the water cooling is brought to room temperature.

[0041] Step 2, First Stage Low-Temperature Aging: The riser of the ingot, which was water-cooled to room temperature in Step 1, is then subjected to T... β - Hold the ingot at a temperature below 200-400°C for 1-8 hours, then raise the temperature of the ingot riser to T. β - (30~60)℃, heat preservation followed by cooling, heat preservation time T2 = D×(0.5~3.0) minutes, where D is the thickness of the riser in mm, and the cooling method is air cooling.

[0042] Step 3: β-spot heat treatment. The riser of the ingot after air cooling in Step 2 is then subjected to T... β The temperature was kept at -25℃ for 2 hours, and then cooled by water cooling.

[0043] Step 4, the second stage of low-temperature aging, involves holding the water-cooled ingot riser from Step 3 at 600-650℃ for 4-8 hours, followed by air cooling.

[0044] Step 5: High and low magnification tissue analysis.

[0045] Specifically, this embodiment uses a typical TC17 titanium alloy as an example. The nominal composition of TC17 titanium alloy is Ti-5Al-4Mo-4Cr-2Sn-2Zr, and its empirical average β transformation temperature is 895℃ (i.e., T). β The value is 895℃), and the process steps are as follows:

[0046] Step 1: High-temperature solution treatment in the single-phase region. The ingot riser with dimensions Φ620×50mm (i.e., the diameter of the riser is 620mm and the thickness is 50mm) is heated to 930℃ (i.e., T). β (+35℃), keep warm for 120 minutes and then water cool.

[0047] Step 2, the first stage of low-temperature aging, involves aging the ingot riser, which was water-cooled to room temperature in Step 1, at 630℃ (i.e., T). β Aging at -295℃ for 2 hours, then raising the ingot riser temperature to 850℃ (i.e., T). β -45℃), keep warm for 120 minutes and then air cool.

[0048] Step 3: β-spot heat treatment. The riser of the ingot cooled in Step 2 is heated to 870℃ (i.e., T). β The sample was kept at a temperature of -25℃ for 2 hours, and then cooled with water.

[0049] Step 4, the second stage of low-temperature aging, involves aging the water-cooled ingot riser from Step 3 at 630℃ for 8 hours, followed by air cooling.

[0050] Step 5: High and low magnification tissue analysis.

[0051] Comparative example: Conventional finished bars were subjected to low-magnification and high-magnification testing, and the test results are as follows. Figure 4-Figure 6 As shown.

[0052] according to Figure 1 and Figure 2 As can be seen from the comparison, after steps one and two in this embodiment, equiaxed / short rod α phases with similar morphology to finished bars but smaller size have appeared in the original cast structure, which has the basic conditions for β spot detection.

[0053] Combination Figures 3-7 As can be seen from the low-magnification and high-magnification tissue photographs, Figure 6 The α phase content in the normal region is still 9.4%, while the bright spot region has no α phase present. Under normal circumstances, it can be judged as β spot. Therefore, it can be seen that the compositional uniformity of titanium alloy ingots can be easily determined.

[0054] In this embodiment, the composition of the ingot riser after step four is also tested. A three-dimensional atomic probe is used to analyze the composition of the normal area and the bright spot area. Two locations are taken from each of the normal area and the bright spot area for testing. The results of the analysis of each alloy element are shown in Table 1. According to the test results in Table 1, it can be seen that there is obvious Cr enrichment in the bright spot area, which confirms that the bright spot is caused by Cr segregation. This shows that the process can accurately detect the β spot of the ingot, which is convenient for assessing the compositional uniformity level of the ingot.

[0055] Element types Al Mo Cr Sn Zr Normal area 1 4.33 4.43 4.01 2.22 1.97 Normal area 2 4.43 4.16 4.18 2.34 1.88 Bright spot area 1 4.21 4.51 4.55 2.01 2.09 Bright spot area 2 4.27 4.22 4.72 2.26 2.01

[0056] Table 1 Elemental Analysis Results

[0057] The above descriptions are merely embodiments of the present invention, and common knowledge such as specific technical solutions and / or characteristics are not described in detail here. It should be noted that those skilled in the art can make various modifications and improvements without departing from the technical solutions of the present invention, and these should also be considered within the scope of protection of the present invention. These modifications and improvements will not affect the effectiveness of the implementation of the present invention or the practicality of the patent. The scope of protection claimed in this application should be determined by the content of its claims, and the specific embodiments described in the specification can be used to interpret the content of the claims.

Claims

1. A method for evaluating the compositional uniformity of titanium alloy ingots, comprising the following steps: Step 1: High-temperature solution treatment in the single-phase region, heating the ingot riser to T β + (10~300)℃, water cooling after heat preservation, heat preservation time T1=D×(0.5~3.0) minutes, where D is the thickness value of the ingot riser, in mm; Step 2, First Stage Low Temperature Aging: The ingot riser cooled in Step 1 is subjected to T... β - Keep warm at temperatures below 200-400°C for 1-8 hours, then raise the temperature to T. β - (30~60)℃, hold for a period of time, then cool. The holding time is T2 = D × (0.5~3.0) minutes, where D is the thickness of the ingot riser in mm. Step 3: β-spot heat treatment. The riser of the ingot cooled in Step 2 is then subjected to T... β The sample was kept at -25℃ for 2 hours, and then cooled. Step 4, the second stage of low-temperature aging, involves holding the water-cooled ingot riser from Step 3 at 600-650℃ for 4-8 hours, and then cooling it. Step 5: High and low magnification tissue analysis.

2. The method for evaluating the compositional uniformity of titanium alloy ingots according to claim 1, characterized in that: In step two, the ingot riser is heated to T. β - After heat preservation at (30~60)℃, the cooling method is air cooling.

3. The method for evaluating the compositional uniformity of titanium alloy ingots according to claim 1, characterized in that: In step three, the ingot riser is at T β After being kept at -25℃, the cooling method is water cooling.

4. The method for evaluating the compositional uniformity of titanium alloy ingots according to claim 1, characterized in that: In step four, the ingot riser is kept at 600-650℃ and then cooled by air cooling.

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