Method for strengthening zirconium and zirconium alloy through combination of thermal hydrogen treatment and vacuum hot pressing

Abstract

The invention relates to a method for strengthening zirconium and zirconium alloy, in particular to a method for strengthening zirconium and zirconium alloy through combination of thermal hydrogen treatment and vacuum hot pressing. The problem that existing zirconium and zirconium alloy are low in strength is solved. According to the invention, hydrogen is placed in zirconium or a zirconium alloy to realize hydrogenation by utilizing a thermal hydrogen treatment technology, and the hydrogen can reduce the phase transition temperature of the zirconium or the zirconium alloy. And then vacuum hot pressing is conducted on the zirconium or the zirconium alloy, large-scale recrystallization and recrystallization occur in the zirconium or the zirconium alloy under the combined action of temperature and pressure, crystal grains are refined to a certain degree, and the effect of fine grain strengthening is achieved. According to the vacuum hot pressing process, the zirconium or the zirconium alloy subjected to hot hydrogen treatment can release a large amount of hydrogen, hydrogen embrittlement of the zirconium or the zirconium alloy is avoided, other elements cannot be introduced into the zirconium or the zirconium alloy, and the corrosion resistance and other performance of the zirconium or the zirconium alloy cannot be affected. Meanwhile, the vacuum hot pressing also enables the zirconium or the zirconium alloy to generate work hardening, so that the strength is further improved, and the plasticity of the material is basically unchanged and even slightly improved.

Description

Technical Field

[0001] The present invention relates to a method for strengthening zirconium and zirconium alloys. Background Art

[0002] Zirconium and its alloys are widely used in nuclear engineering due to their low thermal neutron cross-sectional absorption rate, low density and thermal expansion coefficient, and excellent mechanical properties and corrosion resistance in harsh environments of high temperature and pressure. In recent years, as stainless steel and nickel-based alloy structural components used in traditional petroleum, chemical, and medical industries no longer fully meet the demands of these harsh working conditions, zirconium and its alloys are playing an increasingly important role in the chemical, pharmaceutical, and other fields, thanks to their excellent corrosion resistance and mechanical properties. Pure zirconium has a tensile strength of less than 300 MPa, making it difficult to use as a structural material.

[0003] The most common method of strengthening pure metals is metal alloying, also known as solid solution strengthening. However, there is currently a lack of mature theories for zirconium alloying. In addition to strengthening pure zirconium, the purpose of zirconium alloying is to suppress the harmful effects of other impurity elements and improve corrosion resistance. In theory, alloying with zirconium's congener elements is most beneficial for improving zirconium's corrosion resistance. Currently, the main zirconium and evolutionary elements used are: Sn, Cr, Fe, and Nb, and their usage is relatively limited. Among them, the usage of Nb can be slightly higher, but the Zr-Nb alloy mainly exhibits excellent plasticity, and its strength is not significantly improved.

[0004] Currently, the more mature zirconium alloys include Zr-2 and Zr-4 (Zr-Sn-Fe-Cr series), E110 (Zr-Nb series), and Zirlo (Zr-SnNb series). These alloys are nuclear-grade zirconium and have been successfully used as structural materials and cladding materials in nuclear reactors. However, due to the low addition of alloying elements, the strength of these zirconium alloys is still slightly insufficient as structural materials. Therefore, it is very difficult to strengthen zirconium and zirconium alloys without changing the elemental composition of the zirconium alloy, thereby not affecting its corrosion resistance, and at the same time without adversely affecting its excellent plasticity. Summary of the Invention

[0005] In order to solve the problem of low strength of existing zirconium and zirconium alloys, the present invention proposes a method for strengthening zirconium and zirconium alloys by combining thermal hydrogen treatment with vacuum hot pressing.

[0006] The method of the present invention for strengthening zirconium and zirconium alloys by combining thermal hydrogen treatment with vacuum hot pressing is carried out in the following steps:

[0007] Step 1: Grind and clean the zirconium or zirconium alloy to be strengthened;

[0008] Step 2: Place the zirconium or zirconium alloy treated in step 1 in a vacuum heat treatment furnace and evacuate the furnace at room temperature until the vacuum degree in the furnace is lower than 5×10 -3 Pa and then heating begins; hydrogen is added after the furnace temperature reaches 680-720℃, and the hydrogen pressure in the furnace is higher than 1×10 5 After the temperature reaches Pa, the temperature is kept at 40 to 90 minutes. After the temperature is kept at 40°C, the heating furnace is turned off, and the zirconium or zirconium alloy is cooled to room temperature along with the furnace, and then excess hydrogen is released, thereby completing the thermal hydrogen treatment of the zirconium or zirconium alloy to obtain hydrogenated zirconium or hydrogenated zirconium alloy.

[0009] Step 3: placing the hydrogenated zirconium or hydrogenated zirconium alloy processed in step 2 in a vacuum hot pressing furnace, fixing it, and performing hot pressing treatment;

[0010] The process of the hot pressing treatment is as follows: the vacuum degree in the furnace is adjusted to less than 5×10 -3 Pa starts heating, and when the temperature in the furnace reaches 350-450°C, a mechanical pressure of 25-35 MPa is applied to the zirconium or zirconium alloy; then the temperature in the furnace is heated to 680-700°C and kept at this temperature for 30-45 minutes. After the holding period is completed, the heating is turned off, and the zirconium or zirconium alloy is taken out after cooling to room temperature with the furnace;

[0011] In step 3, the heating rate used for heating to 350-450° C. is 5-15° C. / min; the heating rate used for heating to 680-700° C. is 5-15° C. / min.

[0012] The principles and beneficial effects of the present invention are:

[0013] 1. This invention utilizes thermal hydrogen treatment technology to introduce hydrogen into the zirconium or zirconium alloy to achieve hydrogenation. Hydrogen can lower the phase transition temperature of the zirconium or zirconium alloy. Subsequently, vacuum hot pressing is performed. Under the combined effects of temperature and pressure, large-scale recrystallization and recrystallization occur within the zirconium or zirconium alloy, resulting in a certain degree of grain refinement and achieving grain refinement strengthening.

[0014] 2. The vacuum hot pressing process of the present invention allows the zirconium or zirconium alloy to release a large amount of hydrogen after the thermal hydrogen treatment, thus preventing hydrogen embrittlement in the zirconium or zirconium alloy. It also prevents the introduction of other elements into the zirconium or zirconium alloy, thereby not affecting the corrosion resistance and other properties of the zirconium or zirconium alloy. Furthermore, the vacuum hot pressing process also causes work hardening of the zirconium or zirconium alloy, further increasing its strength.

[0015] 3. The zirconium and zirconium or zirconium alloy prepared by the method of thermal hydrogen treatment combined with vacuum hot pressing of the present invention has an increase in shear strength of 15-25%, and the plasticity of the material remains basically unchanged or even slightly improved. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Figure 1The existing rolled annealed Zr-4 alloy grain distribution image and the corresponding grain size statistics;

[0017] Figure 2 The grain distribution image and corresponding grain size statistics of the Zr-4 alloy after thermal hydrogen treatment combined with vacuum hot pressing strengthening in Example 1;

[0018] Figure 3 is a tensile curve diagram of the Zr-4 alloy in Example 1;

[0019] Figure 4 This is the shear curve diagram of the Zr-4 alloy in Example 2. DETAILED DESCRIPTION

[0020] The technical solution of the present invention is not limited to the specific implementation methods listed below, but also includes any reasonable combination of the specific implementation methods.

[0021] Specific embodiment 1: The method of combining thermal hydrogen treatment with vacuum hot pressing to strengthen zirconium and zirconium alloys in this embodiment is carried out in the following steps:

[0022] Step 1: Grind and clean the zirconium or zirconium alloy to be strengthened;

[0023] Step 2: Place the zirconium or zirconium alloy treated in step 1 in a vacuum heat treatment furnace and evacuate the furnace at room temperature until the vacuum degree in the furnace is lower than 5×10 -3 Pa and then heating begins; hydrogen is added after the furnace temperature reaches 680-720℃, and the hydrogen pressure in the furnace is higher than 1×10 5 After the temperature reaches Pa, the temperature is kept at 40 to 90 minutes. After the temperature is kept at 40°C, the heating furnace is turned off, and the zirconium or zirconium alloy is cooled to room temperature along with the furnace, and then excess hydrogen is released, thereby completing the thermal hydrogen treatment of the zirconium or zirconium alloy to obtain hydrogenated zirconium or hydrogenated zirconium alloy.

[0024] Step 3: placing the hydrogenated zirconium or hydrogenated zirconium alloy processed in step 2 in a vacuum hot pressing furnace, fixing it, and performing hot pressing treatment;

[0025] The process of the hot pressing treatment is as follows: the vacuum degree in the furnace is adjusted to less than 5×10 -3 Pa starts heating, and when the temperature in the furnace reaches 350-450°C, a mechanical pressure of 25-35 MPa is applied to the zirconium or zirconium alloy; then the temperature in the furnace is heated to 680-700°C and kept at this temperature for 30-45 minutes. After the holding period is completed, the heating is turned off, and the zirconium or zirconium alloy is taken out after cooling to room temperature with the furnace;

[0026] In step 3, the heating rate used for heating to 350-450° C. is 5-15° C. / min; the heating rate used for heating to 680-700° C. is 5-15° C. / min.

[0027] This embodiment has the following beneficial effects:

[0028] 1. This embodiment utilizes thermal hydrogen treatment technology to introduce hydrogen into the zirconium or zirconium alloy to achieve hydrogenation. Hydrogen can lower the phase transition temperature of the zirconium or zirconium alloy. Subsequently, vacuum hot pressing is performed. Under the combined effects of temperature and pressure, large-scale recrystallization and recrystallization occur within the zirconium or zirconium alloy, resulting in a certain degree of grain refinement and achieving grain refinement strengthening.

[0029] 2. The vacuum hot pressing process of this embodiment allows the zirconium or zirconium alloy to release a large amount of hydrogen after the thermal hydrogen treatment, thus preventing hydrogen embrittlement in the zirconium or zirconium alloy. It also prevents the introduction of other elements into the zirconium or zirconium alloy, thereby not affecting the corrosion resistance and other properties of the zirconium or zirconium alloy. Furthermore, the vacuum hot pressing process also causes work hardening of the zirconium or zirconium alloy, further increasing its strength.

[0030] 3. The shear strength of zirconium and zirconium or zirconium alloy prepared by the method of thermal hydrogen treatment combined with vacuum hot pressing in this embodiment increases by 15-25%, and the plasticity of the material remains basically unchanged or even slightly improved.

[0031] Specific embodiment 2: The difference between this embodiment and specific embodiment 1 is that: the polishing in step 1 uses 400# to 600# sandpaper to remove the surface oxide scale.

[0032] Specific embodiment three: This embodiment differs from specific embodiment one or two in that: the cleaning in step one adopts ultrasonic cleaning with anhydrous ethanol for 5 to 20 minutes.

[0033] Specific embodiment 4: This embodiment differs from any one of specific embodiments 1 to 3 in that: the zirconium alloy in step 1 is Zr-2, Zr-4 or Zr-2.5Nb.

[0034] Specific embodiment 5: This embodiment differs from any one of specific embodiments 1 to 4 in that the heating rate during the heating in step 2 is 5 to 10° C. / min.

[0035] Specific embodiment 6: This embodiment differs from any one of specific embodiments 1 to 5 in that: the hydrogen in step 2 is high-purity hydrogen with a purity of 99.999%.

[0036] Specific embodiment 7: This embodiment differs from any one of specific embodiments 1 to 6 in that: in step 2, the zirconium alloy treated in step 1 is placed in a vacuum heat treatment furnace, vacuumed at room temperature, and the vacuum degree in the furnace is lower than 5×10 - 3 Pa and then heating begins; hydrogen is added after the furnace temperature reaches 700 °C, and the hydrogen pressure in the furnace is higher than 1×10 5After the temperature reaches 90°C, heat preservation is continued for 90 minutes. After the heat preservation is completed, the heating furnace is turned off, and the zirconium alloy is cooled to room temperature with the furnace, and excess hydrogen is released, completing the thermal hydrogen treatment of the zirconium alloy to obtain hydrogenated zirconium hydride alloy.

[0037] Specific embodiment eight: This embodiment differs from any one of specific embodiments one to seven in that: in step two, the zirconium treated in step one is placed in a vacuum heat treatment furnace, vacuumed at room temperature, and the vacuum in the furnace is lower than 5×10 -3 Pa and then heating begins; hydrogen is added after the furnace temperature reaches 720°C, and the hydrogen pressure in the furnace is higher than 1×10 5 After the temperature reaches 1000 Pa, the temperature is kept at 4000 K for 75 minutes. After the temperature is kept at 4000 K, the heating furnace is turned off. After the zirconium cools down to room temperature with the furnace, the excess hydrogen is released, and the zirconium thermal hydrogen treatment is completed to obtain hydrogenated zirconium.

[0038] Specific embodiment 9: This embodiment differs from specific embodiments 1 to 8 in that: the process of hot pressing treatment in step 3 is to adjust the vacuum degree in the furnace to less than 5×10 -3 Pa starts heating, and when the temperature in the furnace reaches 450°C, a mechanical pressure of 35MPa is applied to the zirconium alloy; then the temperature in the furnace is heated to 690°C and kept warm for 30 to 45 minutes. After the insulation is completed, the heating is turned off, and the zirconium alloy is taken out after cooling to room temperature with the furnace; the heating rate used for heating to 450°C in step three is 10°C / min; the heating rate used for heating to 690°C is 10°C / min.

[0039] Specific embodiment 10: The difference between this embodiment and the specific embodiments 1 to 9 is that the process of hot pressing treatment in step 3 is to adjust the vacuum degree in the furnace to less than 5×10 -3 Pa starts heating, and when the temperature in the furnace reaches 450°C, a mechanical pressure of 30 MPa is applied to the zirconium; then the temperature in the furnace is heated to 700°C and kept warm for 30 minutes. After the insulation is completed, the heating is turned off, and the zirconium is taken out after cooling to room temperature with the furnace; the heating rate used for heating to 450°C in step three is 15°C / min; the heating rate used for heating to 700°C is 10°C / min.

[0040] Example 1

[0041] The method of the present invention for strengthening zirconium and zirconium alloys by combining thermal hydrogen treatment with vacuum hot pressing is carried out in the following steps:

[0042] Step 1: Grinding and cleaning the zirconium alloy to be strengthened (existing rolled annealed Zr-4 alloy);

[0043] The grinding was done with 400# sandpaper to remove the surface oxide scale;

[0044] The cleaning is performed by ultrasonic cleaning with anhydrous ethanol for 20 minutes;

[0045] The zirconium alloy is Zr-4;

[0046] Step 2: Place the zirconium alloy treated in step 1 in a vacuum heat treatment furnace and evacuate the furnace at room temperature until the vacuum degree in the furnace is lower than 5×10 -3 Pa and then heating begins; hydrogen is added after the furnace temperature reaches 700 °C, and the hydrogen pressure in the furnace is higher than 1×10 5 After the heat preservation is completed, the heating furnace is turned off, and the zirconium alloy is cooled to room temperature with the furnace, and the excess hydrogen is released, completing the thermal hydrogen treatment of the zirconium alloy to obtain a hydrogenated zirconium hydride alloy;

[0047] The heating rate during heating is 10°C / min;

[0048] The hydrogen is high-purity hydrogen with a purity of 99.999%;

[0049] Step 3: placing the zirconium hydride alloy processed in step 2 in a vacuum hot pressing furnace, fixing it, and performing hot pressing treatment;

[0050] The process of the hot pressing treatment is as follows: the vacuum degree in the furnace is adjusted to less than 5×10 -3 Pa starts heating, and when the temperature in the furnace reaches 450℃, a mechanical pressure of 35MPa is applied to the zirconium alloy; then the temperature in the furnace is heated to 690℃ and kept warm for 30-45min. After the holding period, the heating is turned off, and the zirconium alloy is taken out after cooling to room temperature with the furnace;

[0051] In step 3, the heating rate used for heating to 450°C is 10°C / min; the heating rate used for heating to 690°C is 10°C / min.

[0052] Figure 1 The existing rolled annealed Zr-4 alloy grain distribution image and the corresponding grain size statistics; Figure 2 The grain distribution image and corresponding grain size statistics of the Zr-4 alloy after thermal hydrogen treatment combined with vacuum hot pressing strengthening in Example 1; Figure 3 This is the tensile curve of the Zr-4 alloy in Example 1; the average grain size (equivalent circle diameter) of the existing rolled annealed Zr-4 alloy is 5.6μm, the shear strength is 395MPa, and the shear elongation is 28%; the average grain size of the strengthened Zr-4 alloy obtained in this example is only 1.28μm, the shear strength can reach 475MPa, and the shear elongation reaches 29%. Without deteriorating the plasticity, the shear strength is increased by 20%.

[0053] Example 2

[0054] The method of strengthening zirconium by combining thermal hydrogen treatment with vacuum hot pressing of the present invention is carried out in the following steps:

[0055] Step 1: Polish and clean the pure zirconium to be strengthened;

[0056] The grinding was done with 400# sandpaper to remove the surface oxide scale;

[0057] The cleaning is performed by ultrasonic cleaning with anhydrous ethanol for 20 minutes;

[0058] Step 2: Place the zirconium treated in step 1 in a vacuum heat treatment furnace and evacuate the furnace at room temperature until the vacuum degree in the furnace is lower than 5×10 -3 Pa and then heating begins; hydrogen is added after the furnace temperature reaches 720°C, and the hydrogen pressure in the furnace is higher than 1×10 5 After the temperature is maintained at Pa for 75 minutes, the heating furnace is turned off after the temperature is maintained, and the zirconium is cooled to room temperature with the furnace, and the excess hydrogen is released, completing the zirconium thermal hydrogen treatment to obtain hydrogenated zirconium;

[0059] The heating rate during heating is 10°C / min;

[0060] The hydrogen is high-purity hydrogen with a purity of 99.999%;

[0061] Step 3: placing the hydrogenated zirconium processed in step 2 in a vacuum hot pressing furnace, fixing it, and performing hot pressing treatment;

[0062] The process of the hot pressing treatment is as follows: the vacuum degree in the furnace is adjusted to less than 5×10 -3 Pa starts heating, and when the temperature in the furnace reaches 450℃, a mechanical pressure of 30MPa is applied to the zirconium; then the temperature in the furnace is heated to 700℃ and kept at this temperature for 30min. After the holding period, the heating is turned off, and the zirconium is taken out after cooling to room temperature with the furnace;

[0063] In step 3, the heating rate used for heating to 450°C is 15°C / min; the heating rate used for heating to 700°C is 10°C / min.

[0064] The tensile strength of pure Zr is 375MPa and the tensile elongation is 35%. The tensile strength of the reinforced pure Zr obtained in this example can reach 450MPa and the tensile elongation can reach 35%. Without deteriorating the plasticity, the shear strength is increased by 20% ( Figure 4 ).

Claims

1. A method for strengthening zirconium and zirconium alloys by thermal hydrogen treatment combined with vacuum hot pressing, characterized in that: The method of thermal hydrogen treatment combined with vacuum hot pressing to strengthen zirconium and zirconium alloys is carried out in the following steps: Step 1: Grind and clean the zirconium or zirconium alloy to be strengthened; Step 2: Place the zirconium or zirconium alloy treated in step 1 in a vacuum heat treatment furnace and evacuate the furnace at room temperature until the vacuum degree in the furnace is lower than 5×10 -3 Pa and then heating begins; hydrogen is added after the furnace temperature reaches 680~720℃, and the hydrogen pressure in the furnace is higher than 1×10 5 After the temperature reaches Pa, the temperature is kept at 40-90 minutes. After the temperature is kept at 40°C, the heating furnace is turned off, and the zirconium or zirconium alloy is cooled to room temperature along with the furnace, and then excess hydrogen is released, thereby completing the thermal hydrogen treatment of the zirconium or zirconium alloy to obtain hydrogenated zirconium or hydrogenated zirconium alloy. Step 3: placing the hydrogenated zirconium or hydrogenated zirconium alloy processed in step 2 in a vacuum hot pressing furnace, fixing it, and performing hot pressing treatment; The process of the hot pressing treatment is as follows: the vacuum degree in the furnace is adjusted to less than 5×10 -3 Pa starts heating, and when the temperature in the furnace reaches 350~450℃, a mechanical pressure of 25~35 MPa is applied to the zirconium or zirconium alloy; then the temperature in the furnace is heated to 680~700℃ and kept at this temperature for 30~45 minutes. After the holding period is completed, the heating is turned off, and the zirconium or zirconium alloy is taken out after cooling to room temperature with the furnace; In step 3, the heating rate used for heating to 350-450°C is 5-15°C / min; the heating rate used for heating to 680-700°C is 5-15°C / min.

2. The method for strengthening zirconium and zirconium alloys by thermal hydrogen treatment combined with vacuum hot pressing according to claim 1, characterized in that: The polishing described in step 1 uses 400#~600# sandpaper to remove the surface oxide scale.

3. The method for strengthening zirconium and zirconium alloys by thermal hydrogen treatment combined with vacuum hot pressing according to claim 1, characterized in that: The cleaning in step 1 is performed by ultrasonic cleaning with anhydrous ethanol for 5 to 20 minutes.

4. The method for strengthening zirconium and zirconium alloys by thermal hydrogen treatment combined with vacuum hot pressing according to claim 1, characterized in that: The zirconium alloy in step 1 is Zr-2, Zr-4 or Zr-2.5Nb.

5. The method for strengthening zirconium and zirconium alloys by thermal hydrogen treatment combined with vacuum hot pressing according to claim 1, characterized in that: The heating rate during step 2 is 5-10°C / min.

6. The method for strengthening zirconium and zirconium alloys by thermal hydrogen treatment combined with vacuum hot pressing according to claim 1, characterized in that: The hydrogen in step 2 is high-purity hydrogen with a purity of 99.999%.

7. The method for strengthening zirconium and zirconium alloys by thermal hydrogen treatment combined with vacuum hot pressing according to claim 1, characterized in that: In step 2, the zirconium alloy treated in step 1 is placed in a vacuum heat treatment furnace and vacuumed at room temperature until the vacuum degree in the furnace is lower than 5×10 -3 Pa and then heating begins; hydrogen is added after the furnace temperature reaches 700 °C, and the hydrogen pressure in the furnace is higher than 1×10 5 After the temperature reaches 90°C, heat preservation is performed for 90 minutes. After the heat preservation is completed, the heating furnace is turned off, and the zirconium alloy is cooled to room temperature with the furnace, and excess hydrogen is released, completing the thermal hydrogen treatment of the zirconium alloy to obtain hydrogenated zirconium hydride alloy.

8. The method for strengthening zirconium and zirconium alloys by thermal hydrogen treatment combined with vacuum hot pressing according to claim 1, characterized in that: In step 2, the zirconium treated in step 1 is placed in a vacuum heat treatment furnace and vacuumed at room temperature until the vacuum degree in the furnace is lower than 5×10 -3 Pa and then heating begins; hydrogen is added after the furnace temperature reaches 720°C, and the hydrogen pressure in the furnace is higher than 1×10 5 After the temperature reaches 1000 Pa, the temperature is kept at 4000 K for 75 minutes. After the temperature is kept at 4000 K, the heating furnace is turned off. After the zirconium cools down to room temperature with the furnace, the excess hydrogen is released, and the zirconium thermal hydrogen treatment is completed to obtain hydrogenated zirconium.

9. The method for strengthening zirconium and zirconium alloys by thermal hydrogen treatment combined with vacuum hot pressing according to claim 1, characterized in that: The process of hot pressing treatment in step 3 is as follows: the vacuum degree in the furnace is adjusted to less than 5×10 -3 Pa starts heating, and when the temperature in the furnace reaches 450°C, a mechanical pressure of 35 MPa is applied to the zirconium alloy; then the temperature in the furnace is heated to 690°C and kept warm for 30-45 minutes. After the insulation is completed, the heating is turned off, and the zirconium alloy is taken out after cooling to room temperature with the furnace; the heating rate used for heating to 450°C in step three is 10°C / min; the heating rate used for heating to 690°C is 10°C / min.

10. The method for strengthening zirconium and zirconium alloys by thermal hydrogen treatment combined with vacuum hot pressing according to claim 1, characterized in that: The process of hot pressing treatment in step 3 is as follows: the vacuum degree in the furnace is adjusted to less than 5×10 -3 Pa starts heating, and when the temperature in the furnace reaches 450°C, a mechanical pressure of 30 MPa is applied to the zirconium; then the temperature in the furnace is heated to 700°C and kept warm for 30 minutes. After the insulation is completed, the heating is turned off, and the zirconium is taken out after cooling to room temperature with the furnace; the heating rate used for heating to 450°C in step three is 15°C / min; the heating rate used for heating to 700°C is 10°C / min.

Images