Method for improving mechanical property of smelted high-rhenium molybdenum-rhenium alloy

Abstract

The invention discloses a method for improving the mechanical property of a smelted high-rhenium molybdenum-rhenium alloy. The method comprises the steps that firstly, molybdenum powder and rhenium powder are mixed and then pressed and sintered in sequence, and a molybdenum-rhenium alloy blank is obtained; secondly, the molybdenum-rhenium alloy blank is sequentially subjected to electric arc melting and electron beam melting, and a molybdenum-rhenium alloy cast ingot is obtained; thirdly, the molybdenum-rhenium alloy cast ingot is subjected to hot extrusion and rolling in sequence, and a molybdenum-rhenium alloy forged rod in a rolling state is obtained; and 4, carrying out vacuum heat treatment to obtain the recrystallized molybdenum-rhenium alloy. The molybdenum-rhenium alloy in the rolling state is obtained through the processes of pressing sintering, smelting, hot extrusion and rolling in sequence, then vacuum heat treatment is conducted, the molybdenum-rhenium alloy is recrystallized, fine and dispersed second-phase particles are separated out, continuous growth of molybdenum crystal grains is limited, and therefore reduction of the strength of the molybdenum-rhenium alloy is restrained; and meanwhile, the second-phase particles play an obvious strengthening role, the room-temperature strength of the molybdenum-rhenium alloy is effectively improved, and the process is simple, convenient, easy to operate and suitable for popularization.

Description

Technical Field

[0001] The invention belongs to the technical field of molybdenum-rhenium alloy microstructure and mechanical property design and optimization, and specifically relates to a method for improving the mechanical properties of a smelted high-rhenium molybdenum-rhenium alloy. Background Art

[0002] Molybdenum-rhenium alloy is an ideal nuclear reactor core material with good comprehensive mechanical properties. In order to improve the purity and welding performance of the alloy, nuclear molybdenum-rhenium alloys are mostly prepared by vacuum melting, among which electron beam melting is a necessary process for preparing high-purity molybdenum-rhenium alloy ingots. The grains in the ingot after electron beam melting are very coarse, even at the centimeter level, resulting in poor mechanical properties. Therefore, it is necessary to use thermomechanical processing to break the grains to achieve the required shape and grain size of the product. After thermomechanical processing, the coarse equiaxed grains in the cast state are elongated into slender columnar crystals, and the grain size is greatly reduced. The disadvantage brought about by this is poor room temperature ductility, so subsequent heat treatment must be performed to achieve the purpose of toughening. The recrystallized high-rhenium molybdenum-rhenium alloy has good room temperature ductility, but its yield strength is significantly reduced. Therefore, while improving ductility, maintaining the strength of the molybdenum-rhenium alloy as much as possible has become a hot topic of research. Summary of the invention

[0003] The technical problem to be solved by the present invention is to provide a method for improving the mechanical properties of smelted high-rhenium molybdenum-rhenium alloy in view of the deficiencies of the above-mentioned prior art. The method sequentially adopts pressing sintering, smelting, hot extrusion and rolling processes, and designs each process to obtain a rolled molybdenum-rhenium alloy, and then performs vacuum heat treatment, so that the molybdenum-rhenium alloy undergoes recrystallization and precipitates fine dispersed second-phase particles, which limits the continued growth of molybdenum grains, thereby inhibiting the reduction of the strength of the molybdenum-rhenium alloy and increasing the thermal stability of the molybdenum-rhenium alloy. At the same time, the second-phase particles play a significant strengthening role, effectively improving the room temperature strength of the molybdenum-rhenium alloy, and solving the problem of reduced strength of the molybdenum-rhenium alloy after conventional heat treatment.

[0004] In order to solve the above technical problems, the technical solution adopted by the present invention is: a method for improving the mechanical properties of smelting high-rhenium molybdenum-rhenium alloy, characterized in that the method comprises the following steps:

[0005] Step 1: mixing molybdenum powder and rhenium powder, pressing and sintering them in sequence to obtain a molybdenum-rhenium alloy billet;

[0006] Step 2: arc melting and electron beam melting are performed on the molybdenum-rhenium alloy billet obtained in step 1 to obtain a molybdenum-rhenium alloy ingot;

[0007] Step 3, hot extruding and rolling the molybdenum-rhenium alloy ingot obtained in step 2 in sequence to obtain a rolled molybdenum-rhenium alloy forged rod;

[0008] Step 4: subjecting the rolled molybdenum-rhenium alloy forging rod obtained in step 3 to vacuum heat treatment to obtain a recrystallized molybdenum-rhenium alloy.

[0009] The above-mentioned method for improving the mechanical properties of smelting high-rhenium molybdenum-rhenium alloy is characterized in that the atomic ratio of molybdenum in the molybdenum-rhenium alloy billet in step 1 is 67% to 70%, and the remainder is rhenium, recorded as Mo 70 Re 30 .

[0010] The above-mentioned method for improving the mechanical properties of smelting high-rhenium molybdenum-rhenium alloy is characterized in that the mass purity of the molybdenum powder and the rhenium powder in step one is both above 99.97%, and the Fisher particle size is 2.5μm to 5.0μm; the rotation speed used for mixing is 80r / min to 90r / min, and the time is 6h.

[0011] The above-mentioned method for improving the mechanical properties of smelted high-rhenium molybdenum-rhenium alloy is characterized in that the pressing in step one adopts cold isostatic pressing processing, the pressure is 180MPa~200MPa, and the holding time is 60min~70min.

[0012] The above-mentioned method for improving the mechanical properties of smelting high-rhenium molybdenum-rhenium alloy is characterized in that the sintering in step one is protected by a hydrogen atmosphere, and the sintering temperature is 2100°C to 2250°C, and the holding time is 5 hours.

[0013] The above-mentioned method for improving the mechanical properties of high-rhenium molybdenum-rhenium alloy is characterized in that during the arc melting process in step 2, the vacuum degree in the melting furnace is 1.2×10 -2 Pa~1.6×10 -2 Pa, the current of the DC arc is 3900A-3980A, the voltage is 35V-40V, an external magnetic field is applied for stirring, and the diameter of the ingot obtained by arc melting is 80mm-82mm; during the electron beam melting process, the vacuum degree of the molten pool area is 6.0×10 -3 Pa~7.6×10 -3 Pa, the electron beam current is 6A-6.5A, the acceleration voltage is 23kV-24kV, the electron beam power is 138kW-156kW, and the diameter of the molybdenum-rhenium alloy ingot is 78mm-80mm.

[0014] The above-mentioned method for improving the mechanical properties of smelting high-rhenium molybdenum-rhenium alloy is characterized in that the heating temperature of the hot extrusion in step three is 1450°C to 1550°C, the holding time is 10min to 15min, and the extrusion ratio is 4; the heating temperature of the rolling is 1450°C to 1550°C, the holding time is 10min to 15min, and the deformation rate is 10% to 15%.

[0015] The above-mentioned method for improving the mechanical properties of smelting high-rhenium molybdenum-rhenium alloy is characterized in that the temperature of the vacuum heat treatment in step 4 is 1600°C ± 15°C, the heating rate is 30°C / min, the holding time is 100h, and the furnace is cooled after the insulation is completed. The present invention controls the temperature of the vacuum heat treatment above the recrystallization temperature to ensure that complete recrystallization occurs in the rolled molybdenum-rhenium alloy forging rod, thereby completely eliminating the metastable structure caused by processing, controlling the heating rate to reach the set temperature as soon as possible to avoid the appearance of low-temperature stable phases, and controlling the holding time to obtain a uniform precipitation phase. Thus, the present invention controls the temperature and time of the vacuum heat treatment to ensure the precipitation of the second phase, thereby controlling the molybdenum grain size, improving the room temperature plasticity of the molybdenum-rhenium alloy, and effectively exerting the strengthening effect of the second phase particles, thereby achieving precise regulation of the mechanical properties of the molybdenum-rhenium alloy.

[0016] Compared with the prior art, the present invention has the following advantages:

[0017] 1. The present invention sequentially adopts pressing sintering, smelting, hot extrusion and rolling processes, and designs each process to obtain a rolled molybdenum-rhenium alloy, and then performs vacuum heat treatment and adjusts the vacuum heat treatment process, so that the molybdenum-rhenium alloy undergoes recrystallization and precipitates fine dispersed second phase particles, which limits the continued growth of molybdenum grains, thereby inhibiting the reduction of the strength of the molybdenum-rhenium alloy and increasing the thermal stability of the molybdenum-rhenium alloy. At the same time, the second phase particles play a significant strengthening role, effectively improving the room temperature strength of the molybdenum-rhenium alloy.

[0018] 2. The present invention can achieve regulation of the second phase particles of the molybdenum-rhenium alloy by controlling the temperature and time of vacuum heat treatment, effectively improving the microstructure and room temperature mechanical properties of the molybdenum-rhenium alloy. The process is simple and easy to operate, and is suitable for promotion.

[0019] The technical solution of the present invention is further described in detail below through the accompanying drawings and embodiments. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 This is a comparison diagram of the cross-sectional band of the rolled molybdenum-rhenium alloy prepared in Example 1 of the present invention.

[0021] Figure 2 This is a comparison diagram of the longitudinal cross-section of the rolled molybdenum-rhenium alloy forged rod prepared in Example 1 of the present invention.

[0022] Figure 3 This is a longitudinal cross-sectional phase composition diagram of the rolled molybdenum-rhenium alloy forging rod prepared in Example 1 of the present invention.

[0023] Figure 4 This is a grain size distribution diagram of the rolled molybdenum-rhenium alloy forging rod prepared in Example 1 of the present invention.

[0024] Figure 5This is a room temperature tensile curve of the rolled molybdenum-rhenium alloy forging rod prepared in Example 1 of the present invention.

[0025] Figure 6 This is a comparison diagram of the cross-sectional bands of the recrystallized molybdenum-rhenium alloy prepared in Example 1 of the present invention.

[0026] Figure 7 This is a comparison diagram of the longitudinal cross-section of the recrystallized molybdenum-rhenium alloy prepared in Example 1 of the present invention.

[0027] Figure 8 This is a longitudinal cross-sectional phase composition diagram of the recrystallized molybdenum-rhenium alloy prepared in Example 1 of the present invention.

[0028] Fig. 9 This is a grain size distribution diagram of the recrystallized molybdenum-rhenium alloy prepared in Example 1 of the present invention.

[0029] Fig.10 This is a room temperature tensile curve of the recrystallized molybdenum-rhenium alloy prepared in Example 1 of the present invention.

[0030] Fig.11 This is a comparison diagram of the cross-sectional bands of the recrystallized molybdenum-rhenium alloy prepared in Comparative Example 1 of the present invention.

[0031] Fig.12 This is a comparison diagram of the longitudinal cross-section of the recrystallized molybdenum-rhenium alloy prepared in Comparative Example 1 of the present invention.

[0032] Fig.13 This is a longitudinal cross-sectional phase composition diagram of the recrystallized molybdenum-rhenium alloy prepared in Comparative Example 1 of the present invention.

[0033] Fig.14 This is a grain size distribution diagram of the recrystallized molybdenum-rhenium alloy prepared in Comparative Example 1 of the present invention.

[0034] Fig.15 This is a room temperature tensile curve of the recrystallized molybdenum-rhenium alloy prepared in Comparative Example 1 of the present invention. DETAILED DESCRIPTION

[0035] Example 1

[0036] This embodiment includes the following steps:

[0037] Step 1: Mix molybdenum powder and rhenium powder, press and sinter them in sequence to obtain a molybdenum-rhenium alloy billet; the atomic ratio of molybdenum in the molybdenum-rhenium alloy billet is 70%, and the remainder is rhenium, recorded as Mo 70 Re 30The purity of the molybdenum powder and the rhenium powder is above 99.97%, and the Fisher particle size is 2.5 μm to 5.0 μm; the mixing speed is 80 r / min to 90 r / min, and the time is 6 hours; the pressing adopts cold isostatic pressing, the pressure is 180 MPa to 200 MPa, and the holding time is 60 minutes; the sintering adopts hydrogen atmosphere protection, and the sintering temperature is 2100°C to 2250°C, and the holding time is 5 hours;

[0038] Step 2: arc melting and electron beam melting are performed on the molybdenum-rhenium alloy billet obtained in step 1 to obtain a molybdenum-rhenium alloy ingot; during the arc melting process, the vacuum degree in the melting furnace is 1.2×10 -2 Pa~1.6×10 -2 Pa, the current of the DC arc is 3900A-3980A, the voltage is 35V-40V, an external magnetic field is applied for stirring, and the diameter of the ingot obtained by arc melting is 80mm-82mm; during the electron beam melting process, the vacuum degree of the molten pool area is 6.0×10 -3 Pa~7.6×10 -3 Pa, the electron beam current is 6A-6.5A, the acceleration voltage is 23kV-24kV, the electron beam power is 138kW-156kW, and the diameter of the molybdenum-rhenium alloy ingot is 78mm-80mm, wherein the head diameter is 80mm and the tail diameter is 78mm;

[0039] Step 3, hot extruding and rolling the molybdenum-rhenium alloy ingot obtained in step 2 in sequence to obtain a rolled molybdenum-rhenium alloy forged rod; the heating temperature of the hot extrusion is 1450°C to 1550°C, the holding time is 10 minutes, and the extrusion ratio is 4; the heating temperature of the rolling is 1450°C to 1550°C, the holding time is 10 minutes, and the deformation rate is 10% to 15%;

[0040] Step 4: subject the rolled molybdenum-rhenium alloy forging rod obtained in step 3 to vacuum heat treatment at a temperature of 1600°C ± 15°C, a heating rate of 30°C / min, and a holding time of 100h. After the holding is completed, the rod is cooled in the furnace to obtain a recrystallized molybdenum-rhenium alloy.

[0041] Figure 1 The cross-sectional band comparison diagram of the rolled molybdenum-rhenium alloy prepared in this embodiment is shown in FIG. Figure 1 It can be seen that the grains of the rolled molybdenum-rhenium alloy are fine and the processing stress is large.

[0042] Figure 2 This is a comparison diagram of the longitudinal cross-section of the rolled molybdenum-rhenium alloy forged rod prepared in this embodiment. Figure 2It can be seen that the grains on the longitudinal section (parallel to the extrusion direction) of the rolled molybdenum-rhenium alloy are distributed in strips (columnar crystals).

[0043] Figure 3 The longitudinal section phase composition diagram of the rolled molybdenum-rhenium alloy forging rod prepared in this embodiment is shown in FIG. Figure 3 It can be seen that the phase composition of the rolled molybdenum-rhenium alloy is a single-phase BCC structure, and rhenium is dissolved in molybdenum to form a solid solution.

[0044] Figure 4 This is the grain size distribution diagram of the rolled molybdenum-rhenium alloy forging rod prepared in this embodiment. Figure 4 It can be seen that in the rolled molybdenum-rhenium alloy forging rod, by volume fraction, 75% of the grain size is less than 5μm, 15% of the grain size is greater than 5μm and less than 10μm, about 5% of the grain size is between 15μm and 20μm, and only about 5% of the grain size is greater than 20μm.

[0045] Figure 5 The room temperature tensile curve of the rolled molybdenum-rhenium alloy forged rod prepared in this embodiment is shown in FIG. Figure 5 It can be seen that the room temperature yield strength of the rolled molybdenum-rhenium alloy reaches 850 MPa, but the room temperature ductility is very poor (<5%).

[0046] Figure 6 This is a cross-sectional comparison of the recrystallized molybdenum-rhenium alloy prepared in this embodiment. Figure 6 It can be seen that a large number of black particles are dispersed on the grain boundaries of the recrystallized molybdenum-rhenium alloy, showing a different contrast with the matrix.

[0047] Figure 7 This is a longitudinal cross-sectional comparison of the recrystallized molybdenum-rhenium alloy prepared in this embodiment. Figure 7 It can be seen that Figure 6 Similarly, a large number of black particles are dispersed on the grain boundaries of the recrystallized Mo-R alloy.

[0048] Figure 8 This is a longitudinal cross-sectional phase composition diagram of the recrystallized molybdenum-rhenium alloy prepared in this embodiment. Figure 8 It can be seen that the blue area is the BCC phase, corresponding to the matrix of the molybdenum-rhenium alloy, and the red area is the precipitation phase of MoRe2, corresponding to the black particles precipitated on the grain boundary.

[0049] Fig. 9 This is the grain size distribution diagram of the recrystallized molybdenum-rhenium alloy prepared in this embodiment. Fig. 9 It can be seen that most of the grains in the recrystallized molybdenum-rhenium alloy are distributed in the range of 10 μm to 50 μm.

[0050] Fig.10The room temperature tensile curve of the recrystallized molybdenum-rhenium alloy prepared in this embodiment is shown in FIG. Fig.10 It can be seen that the room temperature yield strength of the recrystallized molybdenum-rhenium alloy reaches 600 MPa, the elongation is greater than 20%, and it has good comprehensive mechanical properties.

[0051] Comparative Example 1

[0052] The difference between this comparative example and Example 1 is that the holding time of the vacuum heat treatment in step 4 is 120 minutes.

[0053] Fig.11 This is a cross-sectional comparison diagram of the recrystallized molybdenum-rhenium alloy prepared in Comparative Example 1 of the present invention. Fig.11 It can be seen that obvious recrystallization occurs in the recrystallized molybdenum-rhenium alloy. Most of the grains are less than 100 μm in size, and some grains grow significantly, reaching a grain size of 200 μm to 300 μm.

[0054] Fig.12 This is a longitudinal cross-sectional comparison diagram of the recrystallized molybdenum-rhenium alloy prepared in Comparative Example 1 of the present invention. Fig.12 It can be seen that the grains of the recrystallized molybdenum-rhenium alloy have been arranged in an equiaxed shape, and the grains on the cross section and the longitudinal section have grown into a spherical shape.

[0055] Fig.13 The longitudinal section phase composition diagram of the recrystallized molybdenum-rhenium alloy prepared in Comparative Example 1 of the present invention is shown in FIG. Fig.13 It can be seen that the growth rate of the grains on the longitudinal section of the recrystallized molybdenum-rhenium alloy is greater than that of the grains on the cross section.

[0056] Fig.14 This is a grain size distribution diagram of the recrystallized molybdenum-rhenium alloy prepared in Comparative Example 1 of the present invention. Fig.14 It can be seen that most of the grains in the recrystallized molybdenum-rhenium alloy are distributed in the range of 10 μm to 50 μm.

[0057] Fig.15 The room temperature tensile curve of the recrystallized molybdenum-rhenium alloy prepared in Comparative Example 1 of the present invention is shown in FIG. Fig.15 It can be seen that the room temperature yield strength of the recrystallized molybdenum-rhenium alloy drops to 400 MPa, but the ductility reaches about 30%.

[0058] from Figure 11 to Figure 15 It can be seen that the short vacuum heat treatment annealing process used in Comparative Example 1 cannot precipitate the second phase in the recrystallized molybdenum-rhenium alloy, resulting in an increase in the ductility, i.e., plasticity, of the recrystallized molybdenum-rhenium alloy, but a decrease in strength performance, and it is impossible to achieve a simultaneous improvement in the strength and plasticity of the molybdenum-rhenium alloy at room temperature.

[0059] The Figure 1 to Figure 5and Figure 6 to Figure 10 Compared with Comparative Example 1 Figure 11 to Figure 15 By comparison, it can be seen that the present invention successfully achieves the precipitation of the second phase by performing vacuum heat treatment annealing on the rolled molybdenum-rhenium alloy and extending the vacuum heat treatment annealing time to 100 hours, and the grain size remains almost unchanged, that is, significantly extending the annealing time does not cause rapid growth of the grains, thereby increasing the thermal stability of the recrystallized molybdenum-rhenium alloy, thereby maintaining the room temperature strength of the molybdenum-rhenium alloy as much as possible while significantly improving the room temperature plasticity of the molybdenum-rhenium alloy.

[0060] Example 2

[0061] The difference between this embodiment and embodiment 1 is that the heating temperature of hot extrusion and rolling in step 3 is both 1650° C., and the holding time is both 15 minutes.

[0062] Example 3

[0063] The difference between this embodiment and embodiment 1 is that the rolling deformation rate in step 3 is 15% to 20%.

[0064] 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 improving the mechanical properties of smelting high-rhenium molybdenum-rhenium alloy, characterized in that: The method comprises the following steps: Step 1: mixing molybdenum powder and rhenium powder, pressing and sintering them in sequence to obtain a molybdenum-rhenium alloy billet; Step 2: arc melting and electron beam melting are performed on the molybdenum-rhenium alloy billet obtained in step 1 to obtain a molybdenum-rhenium alloy ingot; Step 3: hot extruding and rolling the molybdenum-rhenium alloy ingot obtained in step 2 in sequence to obtain a rolled molybdenum-rhenium alloy forged rod; Step 4: subjecting the rolled molybdenum-rhenium alloy forging rod obtained in step 3 to vacuum heat treatment to obtain a recrystallized molybdenum-rhenium alloy.

2. A method for improving the mechanical properties of smelting high-rhenium molybdenum-rhenium alloy according to claim 1, characterized in that: The atomic ratio of molybdenum in the molybdenum-rhenium alloy billet in step 1 is 67% to 70%, and the remainder is rhenium, which is recorded as Mo. 70 Re 30 .

3. A method for improving the mechanical properties of smelting high-rhenium molybdenum-rhenium alloy according to claim 1, characterized in that: The mass purity of the molybdenum powder and the rhenium powder in step 1 are both above 99.97%, and the Fisher particle size is 2.5μm to 5.0μm; the rotation speed used for mixing is 80r / min to 90r / min, and the time is 6h.

4. A method for improving the mechanical properties of smelting high-rhenium molybdenum-rhenium alloy according to claim 1, characterized in that: The pressing in step 1 is performed by cold isostatic pressing, the pressure is 180 MPa to 200 MPa, and the holding time is 60 min to 70 min.

5. A method for improving the mechanical properties of smelting high-rhenium molybdenum-rhenium alloy according to claim 1, characterized in that: The sintering in step 1 is protected by a hydrogen atmosphere, and the sintering temperature is 2100° C. to 2250° C., and the holding time is 5 hours.

6. A method for improving the mechanical properties of smelting high-rhenium molybdenum-rhenium alloy according to claim 1, characterized in that: During the arc melting process in step 2, the vacuum degree in the melting furnace is 1.2×10 -2 Pa~1.6×10 -2 Pa, the current of the DC arc is 3900A-3980A, the voltage is 35V-40V, an external magnetic field is applied for stirring, and the diameter of the ingot obtained by arc melting is 80mm-82mm; during the electron beam melting process, the vacuum degree of the molten pool area is 6.0×10 -3 Pa~7.6×10 - 3 Pa, the electron beam current is 6A-6.5A, the acceleration voltage is 23kV-24kV, the electron beam power is 138kW-156kW, and the diameter of the molybdenum-rhenium alloy ingot is 78mm-80mm.

7. A method for improving the mechanical properties of smelting high-rhenium molybdenum-rhenium alloy according to claim 1, characterized in that: The heating temperature of the hot extrusion in step three is 1450°C to 1550°C, the holding time is 10min to 15min, and the extrusion ratio is 4; the heating temperature of the rolling is 1450°C to 1550°C, the holding time is 10min to 15min, and the deformation rate is 10% to 15%.

8. A method for improving the mechanical properties of smelting high-rhenium molybdenum-rhenium alloy according to claim 1, characterized in that: The temperature of the vacuum heat treatment in step 4 is 1600°C ± 15°C, the heating rate is 30°C / min, the insulation time is 100h, and the furnace is cooled after the insulation is completed.

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