A process method for improving intergranular corrosion resistance of 800H alloy by combining grain boundary engineering and cold working deformation

Abstract

This invention relates to a process method for improving the intergranular corrosion resistance of 800H alloy by combining grain boundary engineering and cold working deformation. By obtaining a high proportion of low ΣCSL grain boundaries and then performing cold working deformation, the material's resistance to intergranular corrosion can be improved. Specifically, this method includes controlling the original microstructure to obtain a microstructure with uniform grain size and no obvious texture; controlling the amount of cold working deformation, heat treatment temperature, and cooling rate after annealing to obtain an 800H alloy with a low ΣCSL grain boundary ratio greater than 70%, achieving grain boundary engineering treatment; controlling the amount of cold working deformation to introduce a uniform strain distribution; and controlling the aging heat treatment temperature to repair chromium-depleted areas, further improving the resistance to intergranular corrosion. Compared with existing technologies, this invention improves the intergranular corrosion resistance of 800H alloy through the synergistic treatment of GBE, cold working deformation, and aging heat treatment.

Description

Technical Field

[0001] This invention relates to the field of deformation and heat treatment technology of metallic materials, and in particular to a process method that combines grain boundary engineering and cold working deformation to improve the intergranular corrosion resistance of 800H alloy. Background Technology

[0002] Due to its excellent high-temperature strength and creep resistance, 800H alloy is widely used in key components in petrochemical, nuclear, and aerospace industries, such as high-temperature pyrolysis furnace tubes, heat exchangers, and nuclear reactor structural materials. To meet the requirements of high-temperature service, the alloy is strengthened by inducing carbide precipitation through controlled carbon content (0.05wt%~0.10wt%) combined with solution treatment and aging. However, within the sensitization temperature range of 600°C to 800°C, continuous chromium carbides easily precipitate at grain boundaries, leading to "chromium-depleted zones" near the grain boundaries and subsequently causing severe intergranular corrosion (IGC). Intergranular corrosion failure has become a major cause of premature damage and shortened service life of 800H alloy structural components. Therefore, further improving the intergranular corrosion resistance of 800H alloy is a problem that needs to be solved.

[0003] Grain boundary engineering (GBE) based on annealed twins effectively improves the resistance to intergranular corrosion, stress corrosion cracking, and creep of low stacking fault energy face-centered cubic metals by forming annealed twins and multiple twins. Currently, scholars both domestically and internationally have conducted extensive research in this field and have derived some processing techniques to increase the proportion of low-Σ coincidence site lattice (CSL) grain boundaries. The Σ value represents the degree of coincidence of CSL positions; a low-Σ CSL grain boundary is defined as Σ≤29. The smaller the Σ value, the more atomic positions coincide in the lattice.

[0004] Although GBE treatment can improve the material's resistance to intergranular corrosion by increasing the proportion of low ΣCSL grain boundaries, chromium-rich carbides will still precipitate at the grain boundaries under high-temperature sensitization conditions of 600℃~800℃, thereby reducing the material's resistance to intergranular corrosion. Summary of the Invention

[0005] The purpose of this invention is to provide a process method that combines grain boundary engineering and cold working deformation to improve the intergranular corrosion resistance of 800H alloy. Without changing the composition of 800H alloy or significantly increasing production processes and costs, it can significantly improve the intergranular corrosion resistance of 800H alloy and has engineering application value.

[0006] The objective of this invention can be achieved through the following technical solutions: This invention provides a process method for improving the intergranular corrosion resistance of 800H alloy by combining grain boundary engineering and cold working deformation. The process method includes, in sequence, a grain boundary engineering treatment step, a cold working deformation step, and an aging heat treatment step. The grain boundary engineering treatment step further includes, in sequence, a step of controlling the original microstructure, a small-deformation cold working step, and a heat treatment step. The specific processes for each step are as follows: S1, controlling the original tissue: The 800H alloy was subjected to cold rolling and intermediate annealing, with the cold working deformation amount controlled at 30% to 80% and the intermediate annealing temperature at 1020℃ to 1250℃. The combination of the above-mentioned cold rolling and intermediate annealing process was repeated at least once to obtain an alloy microstructure with uniform grain size and no obvious texture. S2, small deformation cold working: The 800H alloy after step S1 is subjected to cold working deformation with a deformation amount of 3-20% to make the strain distribution inside the 800H alloy relatively uniform. S3, heat treatment: The 800H alloy after step S2 is subjected to heat treatment at a temperature of 1020℃~1250℃, and then rapidly cooled to room temperature at a cooling rate ≥0.2℃ / s to avoid the precipitation of a second phase during the cooling process. S4, cold working deformation: The 800H alloy after step S3 is subjected to cold working deformation with a deformation amount of 5-40% to make the strain distribution inside the 800H alloy uniform. S5, aging heat treatment: The 800H alloy after step S4 is subjected to aging heat treatment at a temperature of 800℃~1000℃.

[0007] Preferably, in step S1, the cold working deformation is 30-80%.

[0008] Preferably, in step S1, the intermediate annealing temperature is 1020–1250°C.

[0009] Preferably, in step S1, the combined process of cold rolling and intermediate annealing is repeated at least once.

[0010] Preferably, in step S2, the deformation amount of the cold working deformation is 3-20%.

[0011] Preferably, in step S3, the heat treatment time is at least 5 minutes and the cooling rate is ≥0.2 ℃ / s.

[0012] Preferably, the proportion of low Σ overlap lattice grain boundaries in the 800H alloy after heat treatment in step S3 is greater than or equal to 70%.

[0013] Preferably, in step S4, the deformation amount of the processing deformation is 5-40%.

[0014] Preferably, in step S5, the aging heat treatment temperature is 800℃~1000℃.

[0015] Preferably, the 800H alloy, by mass percentage, comprises: Ni: 30.0~35.0, Cr: 19.0~23.0, C: 0.05~0.10, Mn: ≤1.50, Si: ≤1.00, Cu: ≤0.75, Al: 0.15~0.60, Ti: 0.15~0.60, S: ≤0.015, P: ≤0.030, N: ≤0.03, H: ≤0.0005, Nb: ≤0.10, and Al+Ti: 0.85~1.20, with the balance being Fe.

[0016] In step S1, due to inclusions generated during the solidification process of the 800H alloy after melting, uneven grain size will occur in subsequent processing. Therefore, the material needs to undergo multiple cold rolling and intermediate annealing to form a microstructure with uniform grain size and no obvious texture. The 800H alloy exhibits numerous defects after cold rolling, necessitating intermediate annealing. It is important to note that annealing below 1020℃ will result in the precipitation of Ti-rich and Cr-rich carbides, affecting grain boundary migration during subsequent processing; annealing above 1250℃ will cause abnormal grain growth in the matrix, which is detrimental to increasing the proportion of special grain boundaries in subsequent processing. Therefore, the intermediate annealing temperature range is 1020–1250℃.

[0017] In step S2, the material undergoes cold working deformation with a deformation amount of 3% to 20%. If the deformation amount is less than 3%, the deformation energy stored in the material is insufficient; if the deformation amount is greater than 20%, the deformation energy stored in the material is excessive. Both of these are detrimental to the formation of a high proportion of special grain boundaries in the subsequent annealing process. Therefore, the cold deformation amount is controlled within the range of 3% to 20%.

[0018] In step S3, the cooling rate is preferably less than 0.2℃ / s. To avoid the precipitation of a second phase during cooling, the cooling rate needs to be ≥0.2℃ / s. Otherwise, during cooling, the precipitated second phase will pin the grain boundaries, affecting grain boundary migration and hindering the formation of a high proportion of special grain boundaries.

[0019] In step S4, the preferred cold working deformation amount is 5% to 40%. If the deformation amount is less than 5%, the dislocation density within the matrix is ​​insufficient to form sufficiently dense, heterogeneous nucleation sites, making it difficult to effectively induce carbide precipitation within the grains, thus limiting the anti-sensitization strengthening effect. Conversely, if the deformation amount is greater than 40%, the accumulated deformation energy in the material is too high, which can easily lead to local recrystallization during service, thereby reducing the material's performance. Therefore, the cold deformation amount is controlled within the range of 5% to 40%.

[0020] In step S5, the preferred aging heat treatment temperature is 800℃ to 1000℃. If the aging heat treatment temperature is below 800℃, a large amount of Cr-rich carbides will precipitate, forming chromium-depleted zones and exacerbating intergranular corrosion. Conversely, if the aging heat treatment temperature is above 1000℃, local recrystallization will occur in the cold-worked sample, thereby reducing the material's properties. Therefore, the aging heat treatment temperature is controlled within the range of 800℃ to 1000℃.

[0021] This invention primarily targets 800H alloy. Through the aforementioned third-step process control, according to the Palumbo Aust standard, a material with a low ΣCSL grain boundary ratio exceeding 70% can be obtained, while the low ΣCSL grain boundary ratio of materials processed by traditional methods is only 53%. Furthermore, through the aforementioned fourth-step process, cold working deformation introduces a uniform strain distribution, which reduces the precipitation of Cr-rich carbides on the grain boundaries during high-temperature service, thereby improving resistance to intergranular corrosion. Finally, through the aforementioned fifth-step process, aging heat treatment repairs the chromium-depleted areas, thereby further improving resistance to intergranular corrosion.

[0022] Compared with the prior art, the present invention has the following beneficial effects: (1) This invention provides a process method for improving the intergranular corrosion resistance of 800H alloy by combining grain boundary engineering and cold working deformation. The process method includes, in sequence, a grain boundary engineering treatment step, a cold working deformation step, and an aging heat treatment step. The grain boundary engineering treatment step includes, in sequence, a step of controlling the original microstructure, a small deformation cold working step, and a heat treatment step. Through the above process method, this invention can improve the intergranular corrosion resistance of 800H alloy without changing the composition of 800H alloy or increasing production processes and costs, and has engineering application value.

[0023] (2) This invention addresses the inclusions generated during the melting and solidification of 800H alloy, as well as the problems of uneven grain size and precipitation of the second phase that are prone to occur during processing. By performing multiple cold rolling and intermediate annealing synergistic treatments, the interference of inclusions and processing-induced second phase on the formation and evolution of special structural grain boundaries in grain boundary engineering is effectively reduced, thus providing a guarantee for the preparation of high-performance alloy structures.

[0024] (3) By controlling the grain boundary engineering process parameters, the intermediate annealing temperature is limited to 1020-1250℃, which avoids the precipitation of Ti-rich and Cr-rich carbides at low temperatures that hinder grain boundary migration, and also prevents abnormal grain growth at high temperatures. The small deformation cold working amount is controlled at 3-20%, matching the optimal deformation energy storage, and the cooling rate of ≥0.2℃ / s suppresses the precipitation of the second phase during the cooling process. According to the Palumbo-Aust standard, the proportion of low ΣCSL grain boundaries in 800H alloy can reach more than 70%, far exceeding the 53% of the traditional process, thus achieving the effective preparation of a high proportion of special grain boundaries.

[0025] (4) The present invention introduces a uniform strain distribution through cold working deformation of 5-40%, followed by aging heat treatment at 800℃-1000℃, which ensures the formation of sufficient non-uniform nucleation sites in the matrix and effectively induces the precipitation of carbides within the grains, while avoiding excessive deformation energy storage that could lead to local recrystallization during service. It also reduces the precipitation of Cr-rich carbides at grain boundaries during high-temperature service, improves the sensitization resistance of 800H alloy, and enhances its resistance to intergranular corrosion and service stability.

[0026] (5) The equipment required for the process of this invention are all conventional production equipment in metallurgical plants, and no special customized equipment is required. It has industrial production and promotion value. Attached Figure Description

[0027] Figure 1 The images show different types of grain boundary distribution maps (Palumbo Aust standard) obtained by EBSD for 800H alloy samples A, B, and C in Example 1; in the figures, a: sample A; b: sample B; c: sample C.

[0028] Figure 2 This is a statistical diagram showing the proportion of low ΣCSL grain boundaries in 800H alloy samples A, B, and C in Example 1.

[0029] Figure 3 The images show the local average orientation difference maps of 800H alloy samples A, B, and C obtained by EBSD in Example 1; in the figures, a: sample A; b: sample B; c: sample C.

[0030] Figure 4 These are scanning electron microscope (SEM) images of the carbide morphology on the same type of grain boundaries of 800H alloy samples B and C in Example 1 after sensitization at 700℃ for 4 hours. Figures (a) and (b) are SEM images of the carbide morphology on the grain boundaries of sample B at different magnifications, and Figures (c) and (d) are SEM images of the carbide morphology on the grain boundaries of sample C at different magnifications.

[0031] Figure 5The graphs are test curves obtained by testing 800H alloy samples A, B, C and D in Example 1 using the Double Loop Electrochemical Potentiokinetic Reactivation (DL-EPR) method.

[0032] Figure 6 The sensitization degree (DOS) is calculated by testing the 800H alloy samples A, B, C and D in Example 1 using the bicyclic electrochemical potentiodynamic reactivation method. Detailed Implementation

[0033] The present invention will now be described in detail with reference to the accompanying drawings and specific embodiments. These embodiments are based on the technical solution of the present invention and provide detailed implementation methods and specific operating procedures. However, the scope of protection of the present invention is not limited to the following embodiments.

[0034] Unless otherwise specified, the reagents, methods, instruments, and equipment used in this invention are conventional in the art. Unless otherwise specified, the reagents and materials used in the following examples are all commercially available.

[0035] The following examples show the 800H alloy composition by mass percentage as follows: 44.2 Fe, 21.5 Cr, 31.1 Ni, 0.6 Mn, 0.52 Ti, 0.4 Al, 0.062 Cu, 0.38 Si, 0.067 C, 0.011 N, 0.013 P, 0.001 S, 0.0005 H, and 0.01 Nb. The 800H alloy sample was cut to the target size using a DK7735 wire cutter, and the oxide scale left on the sample surface by wire cutting was removed using 400# metallographic sandpaper.

[0036] The above solution will be further described below with reference to specific embodiments. The preferred embodiments of the present invention are described in detail below: Example 1: In this embodiment, a process method for improving the intergranular corrosion resistance of 800H alloy by combining grain boundary engineering and cold working deformation includes five steps: controlling the original microstructure, small deformation cold working, heat treatment, cold working deformation, and aging heat treatment. The specific steps are as follows: The first step is to control the original tissue: A Y132S-4 type test rolling mill with a roll diameter of 130mm, dual-roll drive, and a rotation speed of 33r / min was used. In the first rolling, 800H alloy strips with dimensions of 70mm×20mm×7mm were fed into the rolls in multiple passes and rolled to a thickness of 3.5mm with a cross-sectional deformation of 50%, resulting in 800H alloy strips with dimensions of 153mm×22mm×3.5mm. The strips were then annealed in a KSY-12-16 type box muffle furnace at 1050℃ for 60min. The cold rolling and intermediate annealing process was repeated once, with the strips rolled to a thickness of 2.5mm in multiple passes with a cross-sectional deformation of 30%, resulting in 800H alloy strips with dimensions of 202mm×24mm×2.5mm. The strips were then annealed in an intermediate annealing process at 1050℃ for 30min to ensure that the 800H alloy strips had a uniform grain size and no obvious texture. The second step is cold working with minimal deformation: Using a DNS100 electro-hydraulic servo universal testing machine, the 800H alloy strip obtained in the first step was subjected to room temperature tensile deformation. A CSS 2210 extensometer was used to precisely control the tensile deformation of the strip. After inserting the positioning pin into the positioning hole, the upper and lower blades of the extensometer were fixed to the 800H alloy strip sample with rubber bands. The positioning pin was then removed to perform the tensile test. The tensile rate was 1 mm / min, and the tensile deformation was 6%. The third step, heat treatment: Using a KSY-12-16 type box-type muffle furnace, the heating rate is 0.5℃ / s. After annealing at 1150℃ for 60 minutes, the 800H alloy strip is taken out and cooled to room temperature by water quenching. Step 4, cold working deformation: Using a DNS100 electro-hydraulic servo universal testing machine, the 800H alloy strip obtained in the third step was subjected to room temperature tensile deformation. A CSS 2210 extensometer was used to precisely control the tensile deformation of the strip. After inserting the positioning pin into the positioning hole, the upper and lower blades of the extensometer were fixed to the 800H alloy strip sample with rubber bands. The positioning pin was then removed to perform the tensile test. The tensile rate was 1 mm / min, and the tensile deformation was 10%. Step 5, Aging heat treatment: The 800H alloy strips obtained in the fourth step were aged at 950℃ for 4 hours and 700℃ for 4 hours respectively using a KSY-12-16 box-type muffle furnace, and then cooled to room temperature by water quenching.

[0037] Sample A is an 800H alloy sheet that has not undergone the single-step controlled microstructure treatment of this embodiment (i.e., 800H alloy sheet treated using conventional processes). Sample B is an 800H alloy sheet that has undergone three steps of controlled microstructure, small deformation cold working, and heat treatment of this embodiment (i.e., grain boundary engineering treatment only according to the parameters in Example 1). Sample C is an 800H alloy sheet that has undergone five steps of controlled microstructure, small deformation cold working, heat treatment, cold working deformation, and aging treatment at 950℃ of this embodiment (this Example 1). Sample D is an 800H alloy sheet that has undergone five steps of controlled microstructure, small deformation cold working, heat treatment, cold working deformation, and aging treatment at 700℃ of this embodiment.

[0038] Experimental test analysis: The proportion of low-ΣCSL grain boundaries in each sample of this embodiment was determined using electron backscatter diffraction (EBSD) and analyzed using AZtecCrystal software according to the Palumbo Aust standard. The proportion of low-ΣCSL grain boundaries in sample A after conventional processing was 59.6%, in sample B after grain boundary engineering processing it was 76.7%, and in sample C after grain boundary engineering and cold working deformation processing in Example 1 it was 66.2%. Furthermore, the local orientation difference maps of samples A and B showed no obvious residual strain, while the local orientation difference map of sample C showed an orientation difference gradient, indicating that dislocations accumulated at high local orientation difference values. See also... Figure 1 , Figure 2 and Figure 3 .

[0039] Samples A and B were incubated at 700℃ for 4 hours and then cooled to room temperature in water. Samples A, B, C, and D were used for intergranular corrosion testing. All intergranular corrosion test samples were ground with 400# metallographic sandpaper to remove oxide scale. Residual sandpaper particles were wiped off the sample surface with cotton swabs under running water, followed by ultrasonic cleaning with alcohol and drying with a hair dryer. The double-ring electrochemical potentiodynamic reactivation intergranular corrosion test was performed according to standard GB_T29088-2012. Copper wires were first soldered to the back of the sample, then embedded in epoxy resin using a cold embedding method, leaving a 1 cm gap. 2The working surface was then subjected to sequential grinding with 400#, 600#, 800#, 1000#, 1500#, and 2000# metallographic sandpaper, followed by mechanical polishing with W2.5 and W0.5 diamond polishing paste. Residual polishing paste was first wiped off with cotton swabs under running water, then ultrasonically cleaned with alcohol, and finally dried with a hair dryer. Intergranular corrosion experiments were performed using a CorrTest CS150 electrochemical workstation with a standard three-electrode system: the sample as the working electrode, a platinum electrode as the auxiliary electrode, and a saturated calomel electrode as the reference electrode. The tests were conducted at room temperature in a 0.5 mol / L H2SO4 + 0.05 mol / L KSCN solution. Before the polarization scan began, the working electrode was immersed in the solution for 20 minutes to establish a stable open-circuit potential. Subsequently, the potential was scanned upwards from the open-circuit potential to 0.25 V (relative to the reference electrode) at a scan rate of 1.667 mV / s, and then scanned back to the open-circuit potential. This was achieved through the reactivation peak current (I0). r ) and activation peak current (I a The ratio of sensitization to intergranular corrosion is called the sensitization degree, which quantitatively characterizes the degree of sensitization. The smaller the ratio, the stronger the material's resistance to sensitization, and vice versa.

[0040] Figure 4 These are scanning electron microscope images of carbide morphology on the same type of grain boundaries after sensitization at 700℃ for 4 hours for samples B and C. As can be seen from the images, in sample B, continuous carbide chains are formed at the grain boundaries, while in sample C, not only is the amount of carbide precipitated at the grain boundaries reduced, but the grain boundary coverage is also lower, and the size is also smaller.

[0041] Based on the intergranular corrosion test results using the dual-ring electrochemical potentiodynamic reactivation method, it was found that sample C had the lowest peak value of the reactivation current curve, followed by sample D, while sample A had the highest peak value. The DOS value of sample C was 1.0%, that of sample D was 13.4%, that of sample B was 19.1%, and that of sample A was 28.4%. This indicates that sample C exhibits the best resistance to intergranular corrosion. (See also...) Figure 5 and Figure 6 .

[0042] Example 2: This embodiment is basically the same as the previous embodiments, except that: In this embodiment, a process method for improving the intergranular corrosion resistance of 800H alloy by combining grain boundary engineering and cold working deformation includes five steps: controlling the original microstructure, small deformation cold working, heat treatment, cold working deformation, and aging heat treatment. The specific steps are as follows: The first step is to control the original tissue: A Y132S-4 type test rolling mill with a roll diameter of 130mm, dual-roll drive, and a rotation speed of 33r / min was used. In the first rolling, 800H alloy strips with dimensions of 70mm×20mm×7mm were fed into the rolls in multiple passes and rolled to a thickness of 3.5mm with a cross-sectional deformation of 50%, resulting in 800H alloy strips with dimensions of 153mm×22mm×3.5mm. The strips were then annealed in a KSY-12-16 type box muffle furnace at 1050℃ for 60min. The cold rolling and intermediate annealing process was repeated once, with the strips rolled to a thickness of 2.5mm in multiple passes with a cross-sectional deformation of 30%, resulting in 800H alloy strips with dimensions of 202mm×24mm×2.5mm. The strips were then annealed in an intermediate annealing process at 1150℃ for 30min to ensure that the 800H alloy strips had a uniform grain size and no obvious texture. The second step is cold working with minimal deformation: Using a DNS100 electro-hydraulic servo universal testing machine, the 800H alloy strip obtained in the first step was subjected to room temperature tensile deformation. A CSS 2210 extensometer was used to precisely control the tensile deformation of the strip. After inserting the positioning pin into the positioning hole, the upper and lower blades of the extensometer were fixed to the 800H alloy strip sample with rubber bands. The positioning pin was then removed to perform the tensile test. The tensile rate was 1 mm / min, and the tensile deformation was 5%. The third step, heat treatment: Using a KSY-12-16 box-type muffle furnace, the heating rate was 0.5℃ / s. After annealing at 1050℃ for 60 minutes, the 800H alloy strip was removed and cooled to room temperature by water quenching.

[0043] Step 4, cold working deformation: Using a DNS100 electro-hydraulic servo universal testing machine, the 800H alloy strip obtained in the third step was subjected to room temperature tensile deformation. A CSS 2210 extensometer was used to precisely control the tensile deformation of the plate. After inserting the positioning pin into the positioning hole, the upper and lower blades of the extensometer were fixed to the 800H alloy strip sample with rubber bands. The positioning pin was removed and a tensile test was performed. The tensile rate was 1 mm / min and the tensile deformation was 12%.

[0044] Step 5, Aging heat treatment: The 800H alloy strips obtained in the fourth step were aged at 900℃ for 4 hours and at 650℃ for 4 hours respectively using a KSY-12-16 box-type muffle furnace, and then cooled to room temperature by water quenching.

[0045] Sample A is an 800H alloy sheet that has not undergone the single-step controlled microstructure treatment of this embodiment (i.e., 800H alloy sheet treated using conventional processes). Sample B is an 800H alloy sheet that has undergone three steps of controlled microstructure, small deformation cold working, and heat treatment of this embodiment (i.e., grain boundary engineering treatment only according to the parameters in Example 2). Sample C is an 800H alloy sheet that has undergone five steps of controlled microstructure, small deformation cold working, heat treatment, cold working deformation, and 900℃ aging heat treatment of this embodiment (this Example 2). Sample D is an 800H alloy sheet that has undergone five steps of controlled microstructure, small deformation cold working, heat treatment, cold working deformation, and 650℃ aging treatment of this embodiment.

[0046] The proportion of low-ΣCSL grain boundaries in each sample in this example was determined using electron backscatter diffraction (EBSD) and analyzed using AZtecCrystal software according to the Palumbo Aust standard. The proportion of low-ΣCSL grain boundaries in sample A (which underwent conventional processing without grain boundary engineering or cold working) was 57.1%, in sample B (which underwent grain boundary engineering) it was 79.3%, and in sample C (which underwent both grain boundary engineering and cold working) it was 67.1%. Through a double-ring electrochemical potentiodynamic reactivation intergranular corrosion experiment, the DOS values ​​were found to be 29.1% for sample A, 18.7% for sample B, 0.9% for sample C, and 12.7% for sample D.

[0047] Therefore, this embodiment utilizes a grain boundary engineering combined with cold working deformation process to achieve a high proportion of low ΣCSL grain boundaries while introducing a uniform strain distribution, thereby improving the material's resistance to intergranular corrosion. Specifically, this method includes controlling the original microstructure to obtain a microstructure with uniform grain size and no obvious texture; controlling the amount of small-deformation cold working, the heat treatment temperature, and the cooling rate after annealing to obtain an 800H alloy with a low ΣCSL grain boundary ratio greater than 70%, achieving GBE treatment; controlling the amount of cold working deformation to introduce a uniform strain distribution, thus improving resistance to intergranular corrosion; and controlling the aging heat treatment temperature to repair chromium-depleted areas, further improving resistance to intergranular corrosion.

[0048] Example 3: This embodiment is basically the same as the previous embodiments, except that: In this embodiment, a process method for improving the intergranular corrosion resistance of 800H alloy by combining grain boundary engineering and cold working deformation includes five steps: controlling the original microstructure, small deformation cold working, heat treatment, cold working deformation, and aging heat treatment. The specific steps are as follows: The first step is to control the original tissue: A Y132S-4 type test rolling mill with a roll diameter of 130mm, dual-roll drive, and a rotation speed of 33r / min was used. In the first rolling, 800H alloy strips with dimensions of 70mm×20mm×7mm were fed into the rolls in multiple passes and rolled to a thickness of 3.5mm with a cross-sectional deformation of 50%, resulting in 800H alloy strips with dimensions of 153mm×22mm×3.5mm. The strips were then annealed at 1100℃ for 60min using a KSY-12-16 type box muffle furnace. The cold rolling and intermediate annealing process was repeated once, with the strips rolled to a thickness of 2.5mm in multiple passes with a cross-sectional deformation of 30%, resulting in 800H alloy strips with dimensions of 202mm×24mm×2.5mm. The strips were then annealed at 1100℃ for 30min to give the 800H alloy strips a uniform grain size and no obvious texture. The second step is cold working with minimal deformation: Using a DNS100 electro-hydraulic servo universal testing machine, the 800H alloy strip obtained in the first step was subjected to room temperature tensile deformation. A CSS 2210 extensometer was used to precisely control the tensile deformation of the strip. After inserting the positioning pin into the positioning hole, the upper and lower blades of the extensometer were fixed to the 800H alloy strip sample with rubber bands. The positioning pin was then removed to perform the tensile test. The tensile rate was 1 mm / min, and the tensile deformation was 8%. The third step, heat treatment: Using a KSY-12-16 type box-type muffle furnace, the heating rate was 0.5℃ / s. After annealing at 1150℃ for 60 minutes, the 800H alloy strip was removed and cooled to room temperature by water quenching.

[0049] Step 4, cold working deformation: Using a DNS100 electro-hydraulic servo universal testing machine, the 800H alloy strip obtained in the third step was subjected to room temperature tensile deformation. A CSS 2210 extensometer was used to precisely control the tensile deformation of the strip. After inserting the positioning pin into the positioning hole, the upper and lower blades of the extensometer were fixed to the 800H alloy strip sample with rubber bands. The positioning pin was then removed to perform the tensile test. The tensile rate was 1 mm / min, and the tensile deformation was 8%. Step 5, Aging heat treatment: The 800H alloy strips obtained in the fourth step were aged at 1000℃ for 4 hours and at 600℃ for 4 hours respectively using a KSY-12-16 box-type muffle furnace, and then cooled to room temperature by water quenching.

[0050] Sample A is an 800H alloy sheet that has not undergone the single-step controlled microstructure treatment of this embodiment (i.e., 800H alloy sheet treated using conventional processes). Sample B is an 800H alloy sheet that has undergone three steps of controlled microstructure, small deformation cold working, and heat treatment of this embodiment (i.e., grain boundary engineering treatment only according to the parameters in Example 3). Sample C is an 800H alloy sheet that has undergone five steps of controlled microstructure, small deformation cold working, heat treatment, cold working deformation, and aging heat treatment at 1000℃ of this embodiment (this Example 3). Sample D is an 800H alloy sheet that has undergone five steps of controlled microstructure, small deformation cold working, heat treatment, cold working deformation, and aging treatment at 600℃ of this embodiment.

[0051] The proportion of low-ΣCSL grain boundaries in each sample was determined using electron backscatter diffraction (EBSD) and analyzed using AZtec Crystal software according to the Palumbo Aust standard. The proportion of low-ΣCSL grain boundaries in sample A (which underwent conventional processing without grain boundary engineering or cold working) was 55.9%, while that in sample B (which underwent grain boundary engineering) was 79.1%, and that in sample C (which underwent both grain boundary engineering and cold working) was 69.5%. Through a double-ring electrochemical potentiodynamic reactivation intergranular corrosion experiment, the DOS value was found to be 30.4% for sample A, 21.3% for sample B, 1.1% for sample C, and 15.3% for sample D.

[0052] Therefore, this embodiment, through a grain boundary engineering combined with cold working deformation process, can introduce a uniform strain distribution while obtaining a high proportion of low ΣCSL grain boundaries, thereby improving the material's resistance to intergranular corrosion. Specifically, this embodiment's method includes controlling the original microstructure to obtain a microstructure with uniform grain size and no obvious texture; controlling the amount of small-deformation cold working deformation, heat treatment temperature, and cooling rate after annealing to obtain an 800H alloy with a low ΣCSL grain boundary ratio greater than 70%, achieving GBE treatment; controlling the amount of cold working deformation to introduce a uniform strain distribution, thus improving the resistance to intergranular corrosion; and controlling the aging heat treatment temperature to repair chromium-depleted areas, further improving the resistance to intergranular corrosion.

[0053] The above description of the embodiments is provided to enable those skilled in the art to understand and use the invention. It will be apparent to those skilled in the art that various modifications can be made to these embodiments, and the general principles described herein can be applied to other embodiments without inventive effort. Therefore, the present invention is not limited to the above embodiments, and any improvements and modifications made by those skilled in the art based on the disclosure of the present invention without departing from the scope of the invention should be within the protection scope of the present invention.

Claims

1. A process method for improving the intergranular corrosion resistance of 800H alloy by combining grain boundary engineering and cold working deformation, characterized in that, The process method sequentially includes a grain boundary engineering treatment step, a cold working deformation step, and an aging heat treatment step. The grain boundary engineering treatment step sequentially includes a step of controlling the original microstructure, a small deformation cold working step, and a heat treatment step. The specific processes for each step are as follows: S1, controlling the original tissue: The 800H alloy was subjected to cold rolling and intermediate annealing, with the cold working deformation amount controlled at 30% to 80% and the intermediate annealing temperature at 1020℃ to 1250℃. The combination of the above-mentioned cold rolling and intermediate annealing process was repeated at least once to obtain an alloy microstructure with uniform grain size and no obvious texture. S2, small deformation cold working: The 800H alloy after step S1 is subjected to cold working deformation with a deformation amount of 3-20% to make the strain distribution inside the 800H alloy relatively uniform. S3, heat treatment: The 800H alloy after step S2 is subjected to heat treatment at a temperature of 1020℃~1250℃, and then rapidly cooled to room temperature at a cooling rate ≥0.2℃ / s. S4, cold working deformation: The 800H alloy after step S3 is subjected to cold working deformation with a deformation amount of 5-40% to make the strain distribution inside the 800H alloy uniform. S5, aging heat treatment: The 800H alloy after step S4 is subjected to aging heat treatment at a temperature of 800℃~1000℃.

2. The process method for improving the intergranular corrosion resistance of 800H alloy by combining grain boundary engineering and cold working deformation according to claim 1, characterized in that, In step S1, the cold working deformation is 30-80%.

3. The process method for improving the intergranular corrosion resistance of 800H alloy by combining grain boundary engineering and cold working deformation according to claim 1, characterized in that, In step S1, the intermediate annealing temperature is 1020–1250°C.

4. The process method for improving the intergranular corrosion resistance of 800H alloy by combining grain boundary engineering and cold working deformation according to claim 1, characterized in that, The combined process of cold rolling and intermediate annealing in step S1 is repeated at least once.

5. The process method for improving the intergranular corrosion resistance of 800H alloy by combining grain boundary engineering and cold working deformation according to claim 1, characterized in that, In step S2, the deformation amount of the cold working deformation is 3-20%.

6. The process method for improving the intergranular corrosion resistance of 800H alloy by combining grain boundary engineering and cold working deformation according to claim 1, characterized in that, In step S3, the heat treatment time is at least 5 minutes and the cooling rate is ≥0.2 ℃ / s.

7. The process method for improving the intergranular corrosion resistance of 800H alloy by combining grain boundary engineering and cold working deformation according to claim 1, characterized in that, The proportion of low-Σ overlap lattice grain boundaries in the 800H alloy after heat treatment in step S3 is ≥70%.

8. The process method for improving the intergranular corrosion resistance of 800H alloy by combining grain boundary engineering and cold working deformation according to claim 1, characterized in that, In step S4, the deformation amount of the processing deformation is 5-40%.

9. The process method for improving the intergranular corrosion resistance of 800H alloy by combining grain boundary engineering and cold working deformation according to claim 1, characterized in that, In step S5, the aging heat treatment temperature is 800℃~1000℃.

10. The process method for improving the intergranular corrosion resistance of 800H alloy by combining grain boundary engineering and cold working deformation according to claim 1, characterized in that, The 800H alloy, by mass percentage, comprises the following chemical composition: Ni: 30.0~35.0, Cr: 19.0~23.0, C: 0.05~0.10, Mn: ≤1.50, Si: ≤1.00, Cu: ≤0.75, Al: 0.15~0.60, Ti: 0.15~0.60, S: ≤0.015, P: ≤0.030, N: ≤0.03, H: ≤0.0005, Nb: ≤0.10, and Al+Ti: 0.85~1.20, with the balance being Fe.

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