A heat treatment method for ultra-high strength and toughness nickel-based corrosion-resistant alloy

Abstract

The present invention relates to a heat treatment method for an ultra-high-strength and tough nickel-based corrosion-resistant alloy. The main steps and parameters of this method are: deformation within a temperature range of 850-1180°C, with a deformation amount of 30-85% → controlled cooling to below 500°C → heating to 700-800°C and holding for 6-12 hours → controlled cooling to 600-660°C and holding for 10-20 hours → cooling to room temperature. The method refines the alloy's grain size, precipitates a large amount of γ′ and γ″ phases, and forms a double- or triple-layer "hamburger-like" structure. The alloy exhibits excellent mechanical properties, including a tensile strength of 1500 MPa or higher, a yield strength of 1400 MPa or higher, an elongation of 12% or higher, and a reduction of area of ​​20% or higher. The alloy is suitable for use in high-temperature and corrosive environments with high strength requirements.

Description

Technical Field

[0001] The present invention relates to a heat treatment method for a metal material, in particular to a heat treatment method for an ultra-high strength and toughness nickel-based corrosion-resistant alloy. Background Art

[0002] Nickel-based alloys can be divided into solid solution-strengthened nickel-based alloys and aging-strengthened nickel-based alloys according to the strengthening method. They have outstanding high temperature resistance, localized corrosion resistance and stress corrosion resistance, and are key materials used extensively in aviation, aerospace, chemical industry, oil and gas and other fields.

[0003] Heat treatment is one of the main methods to improve material properties. Solution + aging heat treatment is a commonly used heat treatment process for aging-strengthening nickel-based alloys. After solution + aging heat treatment, the tensile strength of Ni-Cr-Fe-Nb-Mo-Ti-Al nickel-based alloys can reach about 1400MPa and the yield strength can reach about 1200MPa. With the development of high-end equipment, some extreme application scenarios (such as scenarios where the structural size is limited and the load-bearing capacity cannot be increased by increasing the load-bearing area) have increasingly higher requirements on the strength and yield strength of materials, and further improvements in material formulation or heat treatment technology are needed.

[0004] The present invention discloses a heat treatment method suitable for aging-hardened nickel-based corrosion-resistant alloys. By regulating the microstructure through the heat treatment process, a good dispersion strengthening effect is achieved for second phases of different sizes, and a fine grain strengthening effect is superimposed, thereby significantly improving the yield strength of the Ni-Cr-Fe-Nb-Mo-Ti-Al series nickel-based alloy. Summary of the Invention

[0005] The purpose of the present invention is to provide a heat treatment method for an ultra-high-strength and tough nickel-based corrosion-resistant alloy. The alloy is a nickel-based corrosion-resistant alloy. The heat treatment process of the alloy is as follows: using the alloy formed by forging to perform thermomechanical treatment, the thermomechanical treatment process includes: deforming within a temperature range of 850-1180°C, with a deformation amount of 30-85% → controlled cooling to below 500°C → heating to 700-800°C and holding the temperature for 6-12 hours → controlled cooling to 600-660°C and holding the temperature for 10-20 hours → cooling to room temperature. The material prepared by the method of the present invention has a fine grain size, precipitates a large amount of γ′ phase and γ″ phase, forms a double-layer or triple-layer "hamburger-shaped" structure, has good mechanical properties, and has a tensile strength of ≥1500MPa, a yield strength of ≥1400MPa, an elongation of ≥12%, and a cross-sectional reduction rate of ≥20%. It is suitable for use in high-temperature environments and corrosive environments with high strength requirements.

[0006] The technical solution of the present invention is:

[0007] Thermomechanical treatment method for ultra-high strength and toughness nickel-based corrosion-resistant alloy, the alloy is subjected to thermomechanical treatment after vacuum induction melting → electroslag remelting / vacuum consumable remelting smelting → forging and blanking. The specific steps are as follows:

[0008] 1) Take the nickel-based corrosion-resistant alloy after forging and hot deformation, forging or hot rolling, with a total deformation of 30-85%, a pass deformation of no more than 15%, a heat preservation system of 1100-1180°C for 2-3 hours before forging / rolling, a deformation time of 2-10 minutes, a final forging / rolling temperature of 850-950°C, cooling at a rate of 60-300°C / h to ≤500°C after hot deformation, and air cooling to room temperature;

[0009] 2) then heating the temperature to 700-800°C at a rate of 100-200°C / h, holding the temperature for 6-12 hours, and cooling the furnace to the holding temperature of step 3) for a cooling time of ≤4 hours;

[0010] 3) maintaining the temperature at 600-660° C. for 10-20 hours, and air cooling to room temperature for 12 hours or less, to obtain an ultra-high strength and toughness nickel-based corrosion-resistant alloy, wherein the alloy has a grain size finer than level 6, a large amount of γ′ phase and γ″ phase precipitate, and a double-layer or triple-layer “hamburger-shaped” structure, a tensile strength of 1500 MPa or more, a yield strength of 1400 MPa or more, an elongation of 12% or more, and a reduction of area of ​​20% or more.

[0011] The alloy is of Ni-Cr-Fe-Nb-Mo-Ti-Al system, and the weight percentage of each component is: Cr: 20.0-22.0%, Mo: 2.5-6.0%, Nb: 5.3-7.5%, Al: 0.5-0.9%, Ti: 0.9-1.2%, Fe: 4.0-14.0%, the total content of trace elements and harmful elements such as C, Si, Mn, V, Zr, Mg, Ca, B, N, P, S, Pb, and Sn does not exceed 1%, and Ni is the balance.

[0012] The preferred process parameters of step 1) are: pre-forging / rolling holding temperature 1110-1130° C. for 2-3 hours, deformation time 3-5 minutes, final forging temperature 880-930° C., deformation time 3-5 minutes, and deformation amount of each pass below 950° C. ≤5%.

[0013] The total deformation amount in step 1) is 36-50%.

[0014] After the deformation in step 1) is completed, the temperature is cooled to ≤500°C at a rate of 60-150°C / h.

[0015] The preferred process parameters of step 2) are: heating to 770-800°C and keeping warm for 6-7 hours, cooling in the furnace to the temperature for the next holding step, and the cooling time is ≤2 hours.

[0016] In step 3), the temperature is kept at 600-620° C. for 15-20 hours, and the cooling time is ≤8 hours.

[0017] Step 3) The alloy is in the form of a rod with a diameter of 30 to 200 mm.

[0018] The alloy in step 3) has a tensile strength of 1580-1670 MPa, a yield strength of 1400-1520 MPa, an elongation of 13-17%, and a cross-sectional reduction rate of 25-32%.

[0019] The forged blank material can also be directly used for heat treatment.

[0020] The corrosion-resistant alloy rod obtained by the method of the present invention has a diameter of 30 to 200 mm, a grain size finer than level 6, and a multiphase structure composed of δ phase + γ″ and γ′ phases of various sizes, wherein the γ″ and γ′ phases account for a high proportion, and the double-layer or triple-layer "hamburger-shaped" structure composed of the γ′ phase and the γ″ phase accounts for more than 50%. The yield strength is increased by about 20% compared with the rod prepared by the conventional solid solution + aging process. The performance is as follows: tensile strength ≥1500 MPa, yield strength ≥1400 MPa, elongation ≥12%, and cross-sectional shrinkage rate ≥20%. It is suitable for use in high-temperature and corrosive environments where the structure size is limited and the force-bearing area cannot be increased, thus requiring high strength.

[0021] The design ideas and functions of the main steps and parameters of the heat treatment method of the present invention are as follows:

[0022] The heat treatment method of the present invention is used for nickel-based alloys with high contents of Nb, Ti, and Al. Due to the rich content of aging elements such as Nb, Ti, and Al, a large amount of second phases can be precipitated in the austenite matrix. Through the deformation heat treatment technology of the present invention, the microstructure is regulated to make the grains fine and precipitate a large amount of second phases of various sizes, resulting in a composite strengthening effect, thereby obtaining good mechanical properties.

[0023] Step 1) Thermal deformation adjusts the microstructure, refines the microstructure, ensures uniform microstructure, generates residual stress, stores energy in the microstructure, and precipitates a composite preparatory microstructure consisting of a larger δ phase + γ″ and γ′ phases of various sizes during cooling.

[0024] Step 2) Based on the composite preparatory structure, the ultrafine second phase is used as the nucleation core. Under the conditions of thermal deformation residual stress and tissue energy storage, a new fine second phase is precipitated, and the ultrafine second phase is grown to about 20 nm, while the residual stress and tissue energy storage are weakened.

[0025] Step 3) Based on the second step, another second phase is further precipitated to form a double-layer or triple-layer "hamburger-shaped" structure, and the proportion of fine second phase is further increased, and residual stress and tissue energy storage are weakened.

[0026] Through the above three steps, residual stress and tissue energy storage, as well as the small-sized second phase as the nucleation core, are utilized to promote the dispersion and precipitation of the fine second phase, and finally form a multiphase structure composed of δ phase + γ″ and γ′ phases of various sizes. Among them, the proportion of γ″ and γ′ phases is high, and the proportion of double-layer or triple-layer "hamburger-shaped" γ″ and γ′ phases reaches more than 50%, which can greatly increase the resistance to dislocation movement and thus improve the yield strength.

[0027] Beneficial effects of heat treatment of the ultra-high strength and toughness nickel-based corrosion-resistant alloy of the present invention:

[0028] (1) The corrosion-resistant alloy rod obtained by the heat treatment method of the present invention has good microstructural uniformity, fine grains (finer than level 6), and strong hindering effect of second relative dislocations of different sizes and high density, which can produce good strengthening effect.

[0029] (2) Under the premise of not significantly reducing the elongation and cross-sectional shrinkage, the present invention can increase the yield strength by about 20% compared with the conventional solution + aging heat treatment process.

[0030] (3) The method of the present invention can improve the strength while changing the shape and size of the material, and reduces the solid solution step compared to conventional heat treatment processes.

[0031] The applicant's experiments show that the high-strength and tough nickel-based corrosion-resistant alloy obtained by the heat treatment method of the present invention has a grain size of 6 to 8, a tensile strength of 1580 to 1670 MPa, a yield strength of 1430 to 1520 MPa, an elongation of 13 to 17%, and a cross-sectional shrinkage rate of 25 to 32%. It can be used in equipment manufacturing fields that have high requirements on material mechanical properties and corrosion resistance, and in complex working conditions such as high temperature, high pressure, corrosion, and wear.

[0032] The present invention will be further described below with reference to specific embodiments, but the present invention is not limited to the scope of the embodiments. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] Figure 1 This is the second phase morphology of ultra-high strength and toughness nickel-based corrosion-resistant alloy rod (bright field image);

[0034] Figure 2 、 Figure 3 、 Figure 4 for Figure 1 Dark field images of the same area and different directions;

[0035] Figure 5 、 Figure 6 This is a photo of the second phase micro-nanostructure of the ultra-high strength and toughness nickel-based corrosion-resistant alloy rod;

[0036] Figure 7This is the stress-strain curve of a typical ultra-high strength and toughness nickel-based corrosion-resistant alloy tensile test. DETAILED DESCRIPTION

[0037] Example 1:

[0038] The vacuum induction melting + electroslag remelting process is used for smelting. The weight percentage of the components of the electroslag ingot is as follows: C: 0.01%, Si: 0.06%, Mn: 0.19%, Cr: 22.1%, Mo: 5.9%, Nb: 5.7%, Al: 0.5%, Ti: 0.9%, Fe: 5.3%, V: 0.12%, Cu: 0.1%, Zr: 0.04%, Mg: 0.01%, B: 0.003%, and Ni is the balance. First, the blank is forged to 240mm in diameter, and then the thermomechanical treatment begins. The specific steps and parameters are as follows:

[0039] ①The first step: four-sided forging is used for deformation. The pre-forging holding system is 1130℃×2.5h. The pass reduction above 950℃ is 10-25mm. The pass reduction below 950℃ is 5-10mm. The deformation time is 3 minutes. The final forging temperature is 890℃. The size after forging is Ф130mm. Cool to 500℃ for 2h after forging, and then air cool to room temperature.

[0040] ②The second step: start heating from room temperature at a rate of 200℃ / h to 780℃ and keep warm for 8h. Cool in the furnace to the second stage heat treatment temperature and cool for 3h.

[0041] ③Step 3: Keep at 640℃ for 10h, then air cool to room temperature, cooling time is 8h.

[0042] The prepared Ф130mm ultra-high strength and toughness nickel-based corrosion-resistant alloy rod has a grain size of grade 6, a tensile strength of 1580MPa, a yield strength of 1430MPa, an elongation of 13%, and a cross-sectional shrinkage of 25%.

[0043] Example 2:

[0044] The vacuum induction melting + electroslag remelting process is used for smelting. The weight percentage of the components of the electroslag ingot is: C: 0.02%, Mn: 0.2%, Cr: 20.6%, Mo: 2.8%, Nb: 6.8%, Al: 0.6%, Ti: 0.9%, Fe: 11.7%, V: 0.1%, Zr: 0.04%, Mg: 0.01%, B: 0.004%, and Ni is the balance. First, the blank is forged to Ø100mm, and then the deformation heat treatment begins. The specific steps and parameters are as follows:

[0045] The first step: use electro-hydraulic hammer forging for deformation, the pre-forging insulation system is 1120℃×2h, the pass reduction above 950℃ is 5-15mm, the pass reduction below 950℃ is not more than 5mm, the deformation time is 3 minutes, the final forging temperature is 860℃, the size after forging is Ф60mm, and it is cooled to 450℃ for 2h after forging.

[0046] ②The second step: start heating from 200℃, heating rate 200℃ / h, heating to 750℃ and keeping warm for 8h, cooling in the furnace to the second stage heat treatment temperature, cooling time 2h.

[0047] ③Step 3: Keep at 630℃ for 12h, air cool to room temperature, cooling time 3h.

[0048] The second phase morphology of the prepared Ø60mm ultra-high strength and toughness nickel-based corrosion-resistant alloy rod can be found in Figure 1 、 Figure 2 、 Figure 3 、 Figure 4 , the second phase micro-nanostructure see Figure 5 (Double-layer "hamburger"), Figure 6 (three-layer "hamburger shape"), the obtained rod has a grain size of 7, a tensile strength of 1670MPa, a yield strength of 1520MPa, an elongation of 17%, a cross-sectional reduction of 32%, and a tensile stress-strain curve of Figure 7 .

[0049] Example 3:

[0050] The vacuum induction melting + electroslag remelting process is used for smelting. The weight percentage of the components of the electroslag ingot is: C: 0.02%, Mn: 0.2%, Cr: 22.1%, Mo: 6.0%, Nb: 6.0%, Al: 0.8%, Ti: 1.2%, Fe: 4.5%, V: 0.2%, Co: 0.2%, Zr: 0.01%, Mg: 0.03%, B: 0.003%, and Ni is the balance. First, the billet is forged to 90mm in diameter, and then the thermomechanical treatment begins. The specific steps and parameters are as follows:

[0051] Step 1: Deformation is carried out by hot rolling, with a pre-rolling insulation system of 1170℃×2h, a pass deformation of 4-15%, a deformation time of 2 minutes, a final rolling temperature of 860℃, a size of Ф40mm after forging, and cooling to 450℃ for 3h after forging.

[0052] ② Step 2: Start heating from room temperature at a rate of 150℃ / h to 730℃ and keep warm for 10h. Cool in the furnace to the second stage heat treatment temperature for 2h.

[0053] ③Step 3: Keep at 620℃ for 15h, air cool to room temperature, cooling time 3h.

[0054] The prepared Ф40mm ultra-high strength and toughness nickel-based corrosion-resistant alloy rod has a grain size of grade 8, a tensile strength of 1650MPa, a yield strength of 1440MPa, an elongation of 16%, and a cross-sectional shrinkage of 25%.

[0055] The ultra-high strength and toughness nickel-based corrosion-resistant alloy rod obtained in this embodiment can be used in complex working conditions such as high temperature, high pressure, corrosion, and wear.

[0056] The present invention is not limited to the above embodiments. The above embodiments and descriptions in the specification are only for illustrating the principles of the present invention. Without departing from the spirit and scope of the present invention, the present invention may have various changes and improvements, which all fall within the scope of protection claimed by the present invention.

Claims

1. A heat treatment method for an ultra-high strength and toughness nickel-based corrosion-resistant alloy, characterized in that: The alloy is smelted through vacuum induction melting → electroslag remelting / vacuum consumable remelting → forging and then heat treated. The specific steps are as follows: 1) Take the nickel-based corrosion-resistant alloy after forging and hot deformation, forging or hot rolling, the total deformation is 30-85%, the deformation per pass does not exceed 15%, the holding system before forging / rolling is 1100-1180℃×2-3h, the deformation time is 2-10 minutes, the final forging / rolling temperature is 850-950℃, after hot deformation, it is cooled at a speed of 60-300℃ / h to ≤500℃, and then air-cooled to room temperature; 2) Then, heat the furnace to 700-800°C at a rate of 100-200°C / h, hold the temperature for 6-12 hours, and cool the furnace to the holding temperature of step 3) for a cooling time of ≤4 hours; 3) maintaining the temperature at 600-660°C for 10-20 hours, and air cooling to room temperature for ≤12 hours to obtain an ultra-high strength and toughness nickel-based corrosion-resistant alloy, wherein the alloy has a grain size ≥6, a large amount of γ′ phase and γ″ phase precipitated, a double-layer or triple-layer "hamburger-shaped" structure composed of the γ′ phase and the γ″ phase, a tensile strength ≥1500 MPa, a yield strength ≥1400 MPa, an elongation ≥12%, and a reduction of area ≥20%; The alloy is of Ni-Cr-Fe-Nb-Mo-Ti-Al system, and the weight percentage of each component is: Cr: 20.0-22.0%, Mo: 2.5-6.0%, Nb: 5.3-7.5%, Al: 0.5-0.9%, Ti: 0.9-1.2%, Fe: 4.0-14.0%, the total content of trace elements and harmful elements such as C, Si, Mn, V, Zr, Mg, Ca, B, N, P, S, Pb, and Sn does not exceed 1%, and Ni is the balance.

2. The heat treatment method according to claim 1, wherein the heat preservation system before forging / rolling is 1110-1130°C for 2-3 hours, the deformation time is 3-5 minutes, the final forging temperature is 880-930°C, the deformation time is 3-5 minutes, and the deformation amount of each pass below 950°C is ≤5%.

3. The heat treatment method according to claim 1, wherein: The total deformation in step 1) is 36-50%.

4. The heat treatment method according to claim 1, wherein: After the deformation in step 1) is completed, the temperature is cooled to ≤500°C at a rate of 60-150°C / h.

5. The heat treatment method according to claim 1, wherein in step 2) the temperature is raised to 770-800°C and kept at this temperature for 6-7 hours, and then the furnace is cooled to the temperature for the next holding step, and the cooling time is ≤ 2 hours.

6. The heat treatment method according to claim 1, wherein: Step 3) Keep at 600-620℃ for 15-20h, cooling time ≤8h.

7. The heat treatment method according to claim 1, wherein: Step 3) The alloy is in the form of a rod with a diameter of 30 to 200 mm.

8. The heat treatment method according to claim 1, wherein: The alloy in step 3) has a tensile strength of 1580-1670 MPa, a yield strength of 1400-1520 MPa, an elongation of 13-17%, and a reduction of area of ​​25-32%.

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