Heat treatment process for improving high-temperature strong plasticity of deformed nickel-iron-chromium-based high-temperature alloy

Abstract

The invention discloses a heat treatment process for improving high-temperature strength and plasticity of deformed nickel-iron-chromium-based high-temperature alloy, which belongs to the technical field of metal materials and comprises the following steps: 1) placing a cold-rolled nickel-iron-chromium-based high-temperature alloy pipe at the temperature 160-180 DEG C higher than the gamma'phase precipitation starting temperature; (2) the alloy pipe treated in the step (1) is subjected to aging treatment, and the intracrystalline and grain boundary strengthened precipitation strengthened nickel-iron-based high-temperature alloy is obtained; (3) aging treatment is conducted on the intracrystalline and grain boundary strengthened precipitation strengthened nickel-iron-based high-temperature alloy, and the precipitation strengthened nickel-iron-based high-temperature alloy with the grain boundary strength matched with the intracrystalline strength is obtained; the temperature of the aging treatment in the step 3) is lower than the temperature of the aging treatment in the step 2). Precipitation of harmful phases at the grain boundary is inhibited, the strength of the grain boundary is enhanced, good matching between the grain boundary strength and the intragranular strength of the alloy is achieved, and meanwhile the high-temperature tensile strength and plasticity of the alloy are improved.

Description

Technical Field

[0001] The invention belongs to the technical field of alloy materials, and in particular relates to a heat treatment process for improving the high-temperature strength and plasticity of a deformed nickel-iron-chromium-based high-temperature alloy. Background Art

[0002] Due to the abundant coal resources and special energy structure in China, coal-fired power accounts for an absolute share of power generation, and will continue to dominate for a long time in the future. In view of the urgent need for energy conservation and emission reduction at this stage, based on the existing energy structure, improving the steam temperature and pressure of ultra-supercritical units is the main direction of existing technology improvement, which puts extremely high performance requirements on the service materials of the units. The boiler superheater and reheater tubes are the parts with the worst external environment, and they are required to withstand multiple factors such as high-temperature creep, thermal fatigue, oxidation and high-temperature flue gas corrosion during service. The development of high-temperature alloy materials that can meet the performance requirements of superheater / reheater tubes of high-parameter units has become an urgent issue to be solved in the thermal power generation industry.

[0003] The final superheater / reheater of the ultra-supercritical thermal power unit boiler is a key component that converts the heat generated by coal into water vapor. The service environment is the most demanding, which requires that the precipitation-strengthened high-temperature alloy used for this component not only has high high-temperature strength, resistance to flue gas corrosion, and resistance to steam oxidation corrosion, but also has good high-temperature plasticity. If the heat-resistant alloy has high high-temperature tensile plasticity, the plastic damage area can be discovered in time during the daily maintenance of the unit and replaced to avoid sudden failure, resulting in loss of personnel and property, and improve the safety and economy of the operation of the thermal power unit.

[0004] For the final superheater tubes of high-parameter ultra-supercritical units, traditional ferrite heat-resistant steel and austenite heat-resistant steel can no longer meet the service performance requirements. At present, the candidate alloy materials at home and abroad are mainly precipitation-strengthened nickel-based, nickel-iron-based and iron-based high-temperature alloys. It is well known that precipitation-strengthened high-temperature alloys are mainly strengthened by γ′ phase particles, because these particles can hinder dislocation movement, thereby improving the strength of the alloy. Therefore, the size of γ′ phase particles is usually obtained by heat treatment to control the microstructure morphology, and the strength and plasticity show a trade-off relationship. For precipitation-strengthened high-temperature alloys, the size of the precipitation phase is closely related to the aging temperature. When the aging temperature is low, the precipitation size is small, and its strength is high but the plasticity is poor; when the aging temperature is high, the size of the precipitation phase is large, and the strength and plasticity are opposite, that is, the strength increases and the plasticity decreases, or the plasticity increases and the strength decreases. Summary of the invention

[0005] In order to solve the above technical problems, improve the high temperature strength and plasticity of high temperature alloys, and ensure that the boiler tubes for superheaters / reheaters of high-parameter ultra-supercritical boilers do not crack prematurely during service, the purpose of the present invention is to provide a heat treatment process for improving the high temperature strength and plasticity of deformed nickel-iron-chromium-based high temperature alloys. The process can change the morphology of grain boundary carbides, inhibit the precipitation of harmful phases at grain boundaries, regulate the distribution morphology of the main strengthening phases in the alloy, achieve a good match between grain boundary strength and intracrystalline strength, and improve the strength and plasticity of the alloy at high temperatures. At the same time, the process also has the advantages of simple process and low thermal sensitivity of the organization.

[0006] In order to achieve the above object, the present invention adopts the following technical solution:

[0007] A heat treatment process for improving the high temperature strength and plasticity of a deformed nickel-iron-chromium-based high temperature alloy comprises the following steps:

[0008] 1) Place the cold-rolled nickel-iron-chromium-based high-temperature alloy tube at 160-180°C above the γ′ phase precipitation starting temperature and keep it warm for 0.5-1h;

[0009] 2) subjecting the alloy tube treated in step 1) to aging treatment, and keeping the temperature for 0.5-1h to obtain a precipitation-strengthened nickel-iron-based high-temperature alloy with intragranular and grain boundary strengthening;

[0010] 3) performing aging treatment on the intragranular and grain boundary strengthened precipitation-strengthened nickel-iron-based high-temperature alloy to obtain a precipitation-strengthened nickel-iron-based high-temperature alloy having a matching grain boundary strength and intragranular strength; the aging treatment temperature in step 3) is lower than the aging treatment temperature in step 2).

[0011] Further, the temperature of the aging treatment in step 2) is M 23 The nose temperature of C6 type carbide is ±20℃.

[0012] Furthermore, in step 1), the mixture is kept warm and then air-cooled to room temperature.

[0013] Furthermore, in step 2), the mixture is kept warm and then cooled to room temperature with water.

[0014] Furthermore, in step 3), the aging treatment temperature is below the γ′ phase precipitation starting temperature of 200-323° C., and the time is 16-24 h.

[0015] Furthermore, in step 3), the aging treatment is followed by air cooling to room temperature.

[0016] Furthermore, the grain size of the precipitation-strengthened nickel-iron-based high-temperature alloy that matches the grain boundary strength and the intragranular strength is 90-125 μm.

[0017] Furthermore, the γ′ phase in the precipitation-strengthened nickel-iron-based high-temperature alloy with matched grain boundary strength and intragranular strength exhibits a bimodal distribution, wherein the average size of the coarse γ′ phase particles is no greater than 45 nm.

[0018] Furthermore, the precipitation-strengthened nickel-iron-based high-temperature alloy with matched grain boundary strength and intragranular strength has a tensile strength of more than 800 MPa at 700° C. and an elongation after fracture of more than 11.8%.

[0019] Compared with the prior art, the present invention has the following beneficial effects:

[0020] The present invention provides a heat treatment process for improving the high-temperature strength and plasticity of a deformed nickel-iron-chromium-based high-temperature alloy. By changing the high-temperature solution treatment cooling method and combining the high-temperature aging heat treatment process, the grain boundary stress state is changed, and the precipitation of harmful phases at the grain boundaries during the high-temperature aging process is suppressed, so that the alloy has excellent high-temperature and long-term performance. At the same time, the high-temperature aging treatment in step 2 combined with the low-temperature aging heat treatment in step 3 changes the size and distribution morphology of the main strengthening phase γ′ phase in the crystal, adjusts the deformation mechanism of the alloy in the crystal, achieves a good match between the alloy grain boundary strength and the intracrystalline strength, and improves the strength and plasticity of the alloy at high temperatures.

[0021] Furthermore, by 23 The C6 carbide is subjected to high temperature short time aging treatment at the nose temperature of ±20℃ to obtain high density grain boundary carbides, change the distribution morphology of the grain boundary precipitation phase, inhibit the precipitation of harmful phases at the grain boundary during the subsequent aging process, and strengthen the strength of the grain boundary.

[0022] Furthermore, after high temperature solution treatment, the alloy is air-cooled to room temperature to reduce the stress within the grain boundary and inhibit the precipitation of harmful phases at the grain boundary. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 The macrostructure of the nickel-iron-chromium-based high-temperature alloy obtained by using Example 1 of the present invention;

[0024] Figure 2 The nickel-iron-chromium-based high-temperature alloy grain boundary carbides are obtained by using Example 1 of the present invention;

[0025] Figure 3 The intragranular γ / γ′ microstructure of the nickel-iron-chromium-based high-temperature alloy obtained by using Example 1 of the present invention;

[0026] Figure 4 The macrostructure of the nickel-iron-chromium-based high-temperature alloy obtained by using Example 2 of the present invention;

[0027] Figure 5 The nickel-iron-chromium-based high-temperature alloy grain boundary carbides obtained by Example 2 of the present invention;

[0028] Figure 6 This is the intragranular γ / γ′ microstructure of the nickel-iron-chromium-based high-temperature alloy obtained by using Example 2 of the present invention. DETAILED DESCRIPTION

[0029] In order to facilitate the understanding of the present invention, the present invention will be described more fully below with reference to the relevant drawings. The preferred embodiments of the present invention are given in the drawings. However, the present invention can be implemented in many different forms and is not limited to the embodiments described herein. On the contrary, the purpose of providing these embodiments is to make the disclosure of the present invention more thoroughly and comprehensively understood.

[0030] The room temperature in the present invention is 25°C.

[0031] A heat treatment process for improving the high temperature strength and plasticity of a deformed nickel-iron-chromium-based high temperature alloy according to the present invention comprises the following steps:

[0032] 1) The present invention adopts the application number: 201210513438.0, and the name is: A high-strength and corrosion-resistant nickel-iron-chromium-based high-temperature alloy and a preparation method to make a cold-rolled nickel-iron-chromium-based high-temperature alloy tube for heat treatment.

[0033] 2) High temperature solution treatment: Place the cold-rolled nickel-iron-chromium-based high-temperature alloy tube in a heat treatment furnace at 160-180°C above the precipitation temperature of the γ′ phase, keep it warm for 0.5-1h, and then air-cool it to room temperature to reduce the stress in the grain boundary, so as to inhibit the precipitation of harmful phases at the grain boundary during the subsequent aging process;

[0034] 3) High temperature aging treatment: The alloy tube treated in step 2) is placed in M 23 The nose temperature of C6 type carbide is ±20℃, kept for 0.5-1h, and then water-cooled to room temperature to obtain a grain boundary strengthened nickel-iron-chromium based high temperature alloy;

[0035] After high-temperature aging treatment, the carbides in the obtained nickel-iron-chromium based high-temperature alloy are discontinuously precipitated in a "necklace" shape at the grain boundaries, which strengthens the grain boundary strength and further inhibits the precipitation of harmful phases at the grain boundaries.

[0036] 4) Perform low-temperature aging treatment: Place the grain boundary strengthened nickel-iron-chromium-based high-temperature alloy after step 3) in a 650-700°C heat treatment furnace for 16-24 hours, and then air cool to room temperature to obtain a nickel-iron-chromium-based high-temperature alloy with grain boundary strength matching the grain boundary strength.

[0037] The nickel-iron-chromium-based high-temperature alloy obtained by the present invention has a grain size of 90-125 μm, a strengthening phase inside the grain presents a bimodal distribution, and an average size of coarse γ′ particles is less than 45 nm.

[0038] Example 1

[0039] The precipitation temperature of the γ′ phase in the cold-rolled nickel-iron-chromium-based high-temperature alloy tube used in this embodiment is 973°C. 23 The nose temperature of C6 carbide is 920℃, and the equilibrium phase diagram M 23 The precipitation temperature of C6 carbide is 850℃.

[0040] After the cold-rolled nickel-iron-chromium-based high-temperature alloy tube is solid-solution treated at 1140℃ for 0.5h, it is air-cooled to room temperature to obtain an equiaxed crystal structure with a grain size of 90-125μm. Figure 1 As shown;

[0041] Then, the carbide structure was obtained by water quenching at 920℃ for 0.5h, and the densely distributed grain boundary carbides were obtained. Figure 2 As shown;

[0042] Finally, the sample was kept at 700 °C for 24 h to obtain a bimodal γ′ microstructure with an average size of 41 nm for coarse γ′ particles. Figure 3 shown.

[0043] Table 1 shows the tensile properties of the alloy at 700°C after the heat treatment in this example. From Table 1, it can be seen that the nickel-iron-chromium-based high-temperature alloy obtained a good strength-plasticity match after the heat treatment method of the present invention.

[0044] Table 1 Tensile properties of alloy of Example 1 at 700°C

[0045] Sample No. Tensile strength / MPa Elongation after break / % Example 1 820 12

[0046] Example 2

[0047] The precipitation temperature of the γ′ phase in the cold-rolled nickel-iron-chromium-based high-temperature alloy tube used in this embodiment is 973°C. 23 The nose temperature of C6 carbide is 920℃, and the M 23 The precipitation temperature of C6 carbide is 850℃.

[0048] After the cold-rolled nickel-iron-chromium-based high-temperature alloy tube is solid-solution treated at 1140°C for 30 minutes, it is air-cooled to room temperature to obtain an equiaxed crystal structure with a grain size of 90-125 μm. Figure 3 As shown;

[0049] Then, the carbide structure was obtained by water quenching after keeping at 910℃ for 1h, and the carbide structure with dense distribution at grain boundaries was obtained. Figure 4 As shown;

[0050] Finally, the sample was kept at 700℃ for 24h to obtain a bimodal γ′ microstructure with an average size of 38nm for the coarse γ′ particles. Figure 6 shown.

[0051] Table 2 shows the tensile properties of the alloy at 700°C after the heat treatment in this example. From Table 2, it can be seen that the nickel-iron-chromium-based high-temperature alloy obtained a good strength-plasticity match after the heat treatment method of the present invention.

[0052] Table 2 Tensile properties of alloy of Example 2 at 700°C

[0053] Sample No. Tensile strength / MPa Elongation after break / % Example 2 802 13

[0054] Example 3

[0055] The precipitation temperature of the γ′ phase in the cold-rolled nickel-iron-chromium-based high-temperature alloy tube used in this embodiment is 973°C. 23 The nose temperature of C6 carbide is 920℃, and the M 23 The precipitation temperature of C6 carbide is 850℃.

[0056] The cold-rolled nickel-iron-chromium-based high-temperature alloy tube was solution-treated at 1133°C for 0.8 h, air-cooled to room temperature, then kept at 920°C for 1 h, water-quenched, and finally kept at 680°C for 20 h.

[0057] Example 4

[0058] The precipitation temperature of the γ′ phase in the cold-rolled nickel-iron-chromium-based high-temperature alloy tube used in this embodiment is 973°C. 23 The nose temperature of C6 carbide is 920℃, and the M 23 The precipitation temperature of C6 carbide is 850℃.

[0059] The cold-rolled nickel-iron-chromium-based high-temperature alloy tube was solution-treated at 1153°C for 0.6 h, air-cooled to room temperature, then kept at 920°C for 0.5 h, water-quenched, and finally kept at 700°C for 16 h.

[0060] Comparative Example 1

[0061] The precipitation temperature of the γ′ phase in the cold-rolled nickel-iron-chromium-based high-temperature alloy tube used in this comparative example is 973°C. 23 The nose temperature of C6 carbide is 920℃, and the M 23 The precipitation temperature of C6 carbide is 850℃.

[0062] The heat treatment process adopts the heat treatment process in the patent application number: 201210513438.0, entitled A high-strength and corrosion-resistant nickel-iron-chromium-based high-temperature alloy and its preparation method, to heat treat the cold-rolled nickel-iron-chromium-based high-temperature alloy tube.

[0063] Table 3 shows the tensile properties of the alloy at 700°C after heat treatment using Comparative Example 1. From Table 3, it can be seen that the nickel-iron-chromium-based high-temperature alloy obtained after heat treatment using the heat treatment method in Comparative Example 1 has excellent tensile plasticity, but slightly lower tensile strength.

[0064] Table 3 Tensile properties of alloys obtained at 700°C using Comparative Example 1

[0065] Sample No. Tensile strength / MPa Elongation after break / % Comparative Example 1 788 14

[0066] Comparative Example 2

[0067] The precipitation temperature of the γ′ phase in the cold-rolled nickel-iron-chromium-based high-temperature alloy tube used in this comparative example is 973°C. 23 The nose temperature of C6 carbide is 920℃, and the M 23 The precipitation temperature of C6 carbide is 850℃.

[0068] The heat treatment process adopts the heat treatment process in the patent application number: 201710084310.X, named "A heat treatment process for obtaining bent serrated grain boundaries of nickel-iron-chromium-based deformed high-temperature alloy" to heat treat the cold-rolled nickel-iron-chromium-based high-temperature alloy tube.

[0069] Table 4 shows the tensile properties of the alloy after heat treatment in Comparative Example 2 at 700°C. From Table 4, it can be seen that the strength and plasticity of the nickel-iron-chromium-based high-temperature alloy after heat treatment in Comparative Example 2 are not as good as the tensile properties of the alloy after treatment in the present invention.

[0070] Table 4 Tensile properties of alloys obtained at 700°C using Comparative Example 2

[0071] Sample No. Tensile strength / MPa Elongation after break / % Comparative Example 2 797 8.8

[0072] Comparative Example 3

[0073] The precipitation temperature of the γ′ phase in the cold-rolled nickel-iron-chromium-based high-temperature alloy tube used in this comparative example is 973°C. 23 The nose temperature of C6 carbide is 920℃, and the M 23 The precipitation temperature of C6 carbide is 850℃.

[0074] The heat treatment process adopts the heat treatment process in the patent application number: 202111644906.3, entitled A heat treatment method for simultaneously improving the strength and plasticity of nickel-iron-based alloys, to heat treat the cold-rolled nickel-iron-chromium-based high-temperature alloy tube.

[0075] Table 5 shows the tensile properties of the alloy at 700°C after heat treatment using Comparative Example 3. It can be seen from Table 5 that the strength of the nickel-iron-chromium-based high-temperature alloy treated by the heat treatment method in Comparative Example 3 is equivalent to the strength of the alloy treated by the present invention, but the tensile plasticity of the alloy is only 60% of the tensile plasticity of the alloy treated by the present invention.

[0076] Table 5 Tensile properties of alloys obtained at 700°C using Comparative Example 3

[0077] Sample No. Tensile strength / Mpa Elongation after break / % Comparative Example 4 824 7.3

[0078] Comparative Example 4

[0079] The precipitation temperature of the γ′ phase in the cold-rolled nickel-iron-chromium-based high-temperature alloy tube used in this comparative example is 973°C. 23 The nose temperature of C6 precipitation is 910℃, and the equilibrium phase diagram M 23 The precipitation temperature of C6 carbide is 850℃.

[0080] The heat treatment process adopts the heat treatment process in the patent application number: 201410384335.8, entitled A heat treatment process for grain boundary strengthening of cold-rolled nickel-iron-based high-temperature alloy, to heat treat the cold-rolled nickel-iron-chromium-based high-temperature alloy tube.

[0081] Table 6 shows the tensile properties of the alloy at 700°C after heat treatment in Comparative Example 4. As can be seen from Table 6, the strength of the nickel-iron-chromium-based high-temperature alloy after heat treatment in Comparative Example 4 is 30MPa lower than that of the alloy after treatment in the present invention, but the tensile plasticity is only improved by about 5%.

[0082] Table 6 Tensile properties of alloys at 700°C obtained using Comparative Example 3

[0083] Sample No. Tensile strength / MPa Elongation after break / % Comparative Example 5 790 17

[0084] The above results show that the nickel-iron-chromium-based alloy treated by Example 1 has good comprehensive mechanical properties. It has the characteristics of high strength and high plasticity at the service temperature, and the quenching starting temperature is low, so it can effectively prevent the generation of internal stress and is suitable for large alloy parts.

[0085] The above description is only for the best embodiment of the present invention, but it should not be understood as limiting the claims. The present invention is not limited to the above embodiments, and its specific structure is allowed to be changed. However, all changes made within the protection scope of the independent claims of the present invention are within the protection scope of the present invention.

[0086] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as those commonly understood by those skilled in the art of the present invention. The terms used herein in the specification of the present invention are only for the purpose of describing specific embodiments and are not intended to limit the present invention. The term "and / or" used herein includes any and all combinations of one or more related listed items.

Claims

1. A heat treatment process for improving the high temperature strength and plasticity of a deformed nickel-iron-chromium-based high temperature alloy, characterized in that: The following steps are involved: 1) Place the cold-rolled nickel-iron-chromium-based high-temperature alloy tube at 160-180°C above the γ′ phase precipitation starting temperature and keep it warm for 0.5-1h; 2) subjecting the alloy tube treated in step 1) to aging treatment, and keeping the temperature for 0.5-1h to obtain a precipitation-strengthened nickel-iron-based high-temperature alloy with intragranular and grain boundary strengthening; 3) performing aging treatment on the intragranular and grain boundary strengthened precipitation-strengthened nickel-iron-based high-temperature alloy to obtain a precipitation-strengthened nickel-iron-based high-temperature alloy having a matching grain boundary strength and intragranular strength; the aging treatment temperature in step 3) is lower than the aging treatment temperature in step 2).

2. The heat treatment process for improving high temperature strength and plasticity of deformed nickel-iron-chromium-based high temperature alloy according to claim 1, characterized in that: The temperature of the aging treatment in step 2) is M 23 The nose temperature of C6 type carbide is ±20℃.

3. The heat treatment process for improving high temperature strength and plasticity of deformed nickel-iron-chromium-based high temperature alloy according to claim 1, characterized in that: In step 1), the mixture is kept warm and then air-cooled to room temperature.

4. The heat treatment process for improving high temperature strength and plasticity of deformed nickel-iron-chromium-based high temperature alloy according to claim 1, characterized in that: In step 2), the mixture is kept warm and then cooled to room temperature with water.

5. The heat treatment process for improving high temperature strength and plasticity of deformed nickel-iron-chromium-based high temperature alloy according to claim 1, characterized in that: The temperature of the aging treatment in step 3) is below the precipitation temperature of the γ′ phase, 200-323° C., and the time is 16-24 h.

6. The heat treatment process for improving high temperature strength and plasticity of deformed nickel-iron-chromium-based high temperature alloy according to claim 1, characterized in that: In step 3), after aging treatment, the mixture is air-cooled to room temperature.

7. The heat treatment process for improving high temperature strength and plasticity of deformed nickel-iron-chromium-based high temperature alloy according to claim 1, characterized in that: The grain size of the precipitation-strengthened nickel-iron-based high-temperature alloy that matches the grain boundary strength and intragranular strength is 90-125μm.

8. The heat treatment process for improving high temperature strength and plasticity of deformed nickel-iron-chromium-based high temperature alloy according to claim 1, characterized in that: The γ′ phase in the precipitation-strengthened nickel-iron-based high-temperature alloy with matched grain boundary strength and intragranular strength presents a bimodal distribution, in which the average size of the coarse γ′ phase particles is no more than 45 nm.

9. The heat treatment process for improving high temperature strength and plasticity of deformed nickel-iron-chromium-based high temperature alloy according to claim 1, characterized in that: The precipitation-strengthened nickel-iron-based high-temperature alloy with matched grain boundary strength and intragranular strength has a tensile strength of more than 800 MPa at 700° C. and an elongation after fracture of more than 11.8%.

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