Process for improving low-temperature impact performance of petrochemical forge piece

Abstract

The invention discloses a process for improving the low-temperature impact performance of a petrochemical forge piece. According to the process, the low-temperature impact performance of the petrochemical forge piece is improved by adopting twice subcritical quenching. The method adopts twice subcritical quenching to improve the low-temperature impact performance of the petrochemical forge piece, and comprises the following steps: S1, primary subcritical quenching and tempering: the quenching temperature of the primary subcritical quenching is 910-930 DEG C, then primary quenching water cooling is carried out, then primary tempering is carried out, the temperature of the primary tempering is 690-710 DEG C, and then air cooling is carried out; s2, secondary subcritical quenching and tempering operation are conducted, after the surface temperature of a forging workpiece is smaller than or equal to 50 DEG C, the forging is subjected to secondary subcritical quenching, the temperature of secondary subcritical quenching is 840-870 DEG C, then secondary quenching water cooling is conducted, then secondary tempering is conducted, the temperature of secondary tempering is 640-690 DEG C, precipitation of brittle phases is reduced by reducing the tempering temperature, and then water cooling is conducted; and precipitation of a brittle phase on a grain boundary is reduced.

Description

Technical Field

[0001] The present invention relates to the technical field of petrochemical forging processing, and specifically to a process for improving the low-temperature impact performance of petrochemical forgings. Background Art

[0002] With the development of the domestic and foreign petrochemical industries, large forgings that meet the requirements for low-temperature impact energy absorption have become the core components of pressure vessels, which is of great strategic significance for the service life and safe operation of large pressure vessel equipment. With the large-scale development of domestic and foreign pressure vessel equipment, pressure vessel steel forgings have the characteristics of large cross-sectional dimensions, heavy mass, high technical requirements, and great difficulty in production and manufacturing. Moreover, the larger the workpiece, the greater the brittleness. Traditional process methods have been difficult to meet the technical and quality requirements of forgings, which has become an important factor restricting the development of the petrochemical industry. Therefore, it has become an urgent task to develop and produce large pressure vessel steel forgings that meet the requirements for low-temperature impact energy absorption.

[0003] The grade is SA182F11CL2, and its chemical composition meets the requirements of SA182F11CL2 (see Table 1)

[0004]

[0005] Table 1 Chemical Composition Requirements (W%)

[0006] For the petrochemical forgings made therefrom, the low-temperature impact energy absorption kv2 should meet the NB / T47008-2017 standard (see Table 2)

[0007]

[0008]

[0009] Table 2 Mechanical Property Requirements (NB / T47008-2017)

[0010] However, during actual testing, due to the high silicon content in SA336F11CL2, a large amount of scrap steel added in the raw materials, segregation of impurity elements, uniformity of chemical composition, and mixed crystals, etc., great problems are brought to the low-temperature impact energy absorption. When post-forging heat treatment is carried out according to the existing technology using a single subcritical quenching process, its low-temperature impact performance often fails to meet the requirements. Therefore, it is urgent to develop a process that can improve the low-temperature impact performance of petrochemical forgings. Summary of the Invention

[0011] In view of the above problems, the present invention provides a process for improving the low-temperature impact performance of petrochemical forgings, which uses double subcritical quenching to improve the low-temperature impact performance of petrochemical forgings.

[0012] A process for improving the low-temperature impact performance of petrochemical forgings, characterized in that it uses two subcritical quenches to improve the low-temperature impact performance of petrochemical forgings, and it includes the following steps:

[0013] S1. First subcritical quench and temper. The quenching temperature of the first subcritical quench is 910°C - 930°C. Then, the first quenching water cooling is carried out. After that, the first tempering is carried out. The temperature of the first tempering is 690°C - 710°C. Then, air cooling is carried out;

[0014] S2. Second subcritical quench and tempering operation. After waiting for the surface temperature of the forging workpiece to be ≤ 50°C, the forging is subjected to a second subcritical quench. The temperature of the second subcritical quench is 840°C - 870°C. Then, the second quenching water cooling is carried out. After that, the second tempering is carried out. The temperature of the second tempering is 640°C - 690°C. By reducing the tempering temperature, the precipitation of brittle phases is reduced. Then, water cooling is carried out to reduce the precipitation of brittle phases at the grain boundaries.

[0015] It is further characterized in that:

[0016] In step S1, the holding time of the first subcritical quench is 5h - 12h, and the time of the first quenching water cooling is 0.5h - 3h. Ensure that the surface temperature of the workpiece is ≦ 50°C, and then carry out the first tempering;

[0017] In step S2, the holding time of the second subcritical quench is 5h - 12h, and the time between the second quenching water coolings is 0.5h - 3h. During the second quenching water cooling, the water is strongly stirred so that the surface of the workpiece is fully water cooled to obtain a good structure, and ensure that the surface temperature of the workpiece is ≦ 50°C, and then carry out the second tempering;

[0018] In step S2, to ensure the effect of the second subcritical quench, when loading the furnace, the left and right gaps between forgings are not less than 150mm, and the stacking method is not allowed;

[0019] The holding time of the second tempering is 7h - 16h, which is 20% - 30% shorter than the existing holding time of tempering after quenching. Appropriately shorten the tempering holding time after the second subcritical quench to reduce the precipitation of brittle phases at the grain boundaries;

[0020] In step S2, the water cooling time is 1 - 3min.

[0021] It is still further characterized in that:

[0022] The chemical composition should not only meet the requirements of SA336F11CL2, but also comply with the following regulations:

[0023] a. J coefficient = (Si + Mn) × (P + Sn) × 10 4 ≦ 120, where the elements are substituted by percentage contents;

[0024] b. X coefficient = (10P + 5Sb + 4Sn + As) × 10 -2 ≤ 15, where the elements are substituted by ppm content;

[0025] c. Si + Mn ≤ 1.20, where the elements in the formula are percentage contents;

[0026] d. (Cu + Sn + As) ≤ 10 -2 , where the elements in the formula are percentage contents;

[0027] The chemical composition should, in addition to meeting the requirements of SA336F11CL2, also include inclusion requirements:

[0028] For the forgings, the inclusions of types A, B, C, D, and DS shall not be greater than grade 1.5; and the sum of type A and type C shall not be greater than grade 2.0; the sum of type B and type D and type DS shall not be greater than grade 2.5; the sum of types A, B, C, D, and DS shall not be greater than grade 4.0.

[0029] After adopting the present invention, after the forged workpiece undergoes one subcritical quenching and tempering, and then waits until the surface temperature of the forged workpiece ≤ 50°C, the forging is subjected to a second subcritical quenching and tempering, and the temperatures of the second subcritical quenching and tempering are relatively low. By adjusting the process temperature of the subcritical quenching and the tempering temperature, appropriately shortening the tempering holding time, and strengthening the cooling, a scientific and reasonable two-step subcritical quenching process is designed, thereby improving the low-temperature impact performance of petrochemical forgings. Specific embodiments

[0030] A process for improving the low-temperature impact performance of petrochemical forgings, characterized in that it adopts two-step subcritical quenching to improve the low-temperature impact performance of petrochemical forgings, and it includes the following steps:

[0031] S1. First subcritical quenching and tempering. The quenching temperature of the first subcritical quenching is 910°C - 930°C, the holding time is 5h - 12h, then the first quenching water cooling is carried out, and the first quenching water cooling time is 0.5h - 3h to ensure that the surface temperature of the workpiece ≤ 50°C, then the first tempering is carried out, the first tempering temperature is 690°C - 710°C, and then air cooling is carried out;

[0032] S2. Secondary subcritical quenching and tempering operations. After waiting for the surface temperature of the forging workpiece to be ≤50°C, the forging is subjected to secondary subcritical quenching with a holding time of 5h - 12h and a subcritical quenching temperature of 840°C - 870°C. Then, the second quenching is followed by water cooling, with the interval between the second quenching and water cooling being 0.5h - 3h. During the second quenching water cooling, the water is vigorously stirred to ensure that the surface of the workpiece is fully water-cooled to obtain a good microstructure, and the surface temperature of the workpiece is ensured to be ≦50°C. Then, the second tempering is carried out at a temperature of 640°C - 690°C. By reducing the tempering temperature, the precipitation of brittle phases is reduced. After that, water cooling is carried out for 1 - 3 minutes to reduce the precipitation of brittle phases at the grain boundaries.

[0033] During specific implementation, in step S2, to ensure the effect of secondary subcritical quenching, when loading the furnace, the left and right gaps between forgings should be not less than 150mm, and the stacking method is not allowed.

[0034] The holding time of the second tempering is 7h - 16h, which is 20% - 30% shorter than the existing holding time after quenching and tempering. Appropriately shortening the tempering holding time after secondary subcritical quenching can reduce the precipitation of brittle phases at the grain boundaries.

[0035] During specific implementation, the chemical composition of the forging raw material should not only meet the requirements of SA336F11CL2 but also comply with the following regulations:

[0036] a. J coefficient = (Si + Mn) × (P + Sn) × 10 4 ≦120, where the elements are substituted with percentage contents;

[0037] b. X coefficient = (10P + 5Sb + 4Sn + As) × 10 -2 ≦15, where the elements are substituted with ppm contents;

[0038] c. Si + Mn ≦ 1.20, where each element in the formula is in percentage content;

[0039] d. (Cu + Sn + As) ≦ 10 -2 , where each element in the formula is in percentage content;

[0040] Inclusion requirements:

[0041] For the forging, the inclusions of types A, B, C, D, and DS should not be greater than grade 1.5; and the sum of type A and type C should not be greater than grade 2.0; the sum of type B, type D, and type DS should not be greater than grade 2.5; the sum of types A, B, C, D, and DS should not be greater than grade 4.0.

[0042] After the forging processed by the process of the present invention is subjected to new technology specification tests, the test process and results are as follows:

[0043] After heat treatment of the forging, samples are taken from the body, and the sample position is T*1 / 4T; then the samples are subjected to minimum simulated post-weld heat treatment and maximum simulated post-weld heat treatment; the samples subjected to minimum simulated post-weld heat treatment and maximum simulated post-weld heat treatment are subjected to tensile tests at room temperature and high temperature and low temperature impact tests.

[0044] Simulated post-weld heat treatment

[0045] ① Simulated maximum post-weld heat treatment (Max.PWTH)

[0046] The heating rate ≤ 70°C / h, 690 ± 14°C × 26h, furnace cooling to ≤ 300°C and then discharging from the furnace.

[0047] ② Simulated minimum post-weld heat treatment (Min.PWHT)

[0048] The heating rate ≤ 70°C / h, 690 ± 14°C * 8h, furnace cooling to ≤ 300°C and then discharging from the furnace.

[0049] The mechanical properties of the forging corresponding to the samples are shown in Table 3

[0050]

[0051] Table 3 The qualified indexes of high-temperature yield strength of the forging mechanical property samples at the test temperature are shown in Table 4

[0052] T / ℃ 350 400 450 500 Rp0.2 (MPa) 210 200 190 175

[0053] Table 4 The qualified indexes of high-temperature yield strength at the test temperature

[0054] After adopting the present invention, reasonable chemical compositions of the ingot raw materials are designed and formulated, harmful elements in the steel are reduced, the purity of the material is improved, the adverse factors affecting low-temperature impact are reduced, and after the forged workpiece is subjected to one subcritical quenching and tempering, and then waiting until the surface temperature of the forging workpiece ≤ 50°C, the forging is subjected to secondary subcritical quenching and tempering, and the temperatures of the secondary subcritical quenching and tempering are relatively low. By adjusting the process temperature and tempering temperature of the subcritical quenching, appropriately shortening the tempering holding time, strengthening the cooling, a scientific and reasonable two-stage subcritical quenching process is designed, thereby improving the low-temperature impact performance of the petrochemical forging. In addition, the forging is tested according to the new technical specifications and meets the standards.

[0055] For those skilled in the art, it is obvious that the present invention is not limited to the details of the above-described exemplary embodiments, and without departing from the spirit or basic characteristics of the present invention, the present invention can be implemented in other specific forms. Therefore, from any point of view, the embodiments should be regarded as exemplary and non-limiting. The scope of the present invention is defined by the appended claims rather than the above description. Therefore, it is intended to embrace all changes within the meaning and scope of the equivalent elements of the claims in the present invention.

[0056] In addition, it should be understood that although this specification is described according to embodiments, not every embodiment only contains an independent technical solution. This narrative way of the specification is only for clarity. Those skilled in the art should regard the specification as a whole, and the technical solutions in each embodiment can also be appropriately combined to form other embodiments that can be understood by those skilled in the art.

Claims

1. A process for improving the low-temperature impact performance of petrochemical forgings, characterized in that, It adopts double subcritical quenching to improve the low-temperature impact performance of petrochemical forgings, and it includes the following steps: S1. First subcritical quenching and tempering. The quenching temperature of the first subcritical quenching is 910°C to 930°C. Then, the first quenching water cooling is carried out. After that, the first tempering is carried out. The temperature of the first tempering is 690°C to 710°C. Then, air cooling is carried out. S2. Second subcritical quenching and tempering operation. After waiting for the surface temperature of the forging workpiece to be ≤50°C, the forging is subjected to second subcritical quenching. The temperature of the second subcritical quenching is 840°C to 870°C. Then, the second quenching water cooling is carried out. After that, the second tempering is carried out. The temperature of the second tempering is 640°C to 690°C. By reducing the tempering temperature, the precipitation of brittle phases is reduced. Then, water cooling is carried out to reduce the precipitation of brittle phases at the grain boundaries.

2. The process for improving the low-temperature impact performance of petrochemical forgings according to claim 1, characterized in that, In step S1, the holding time of the first subcritical quenching is 5h to 12h, and the time of the first quenching water cooling is 0.5h to 3h. Ensure that the surface temperature of the workpiece is ≦50°C, and then carry out the first tempering.

3. A process for improving the low-temperature impact performance of petrochemical forgings according to claim 2, characterized in that: In step S2, the holding time of the second subcritical quenching is 5h to 12h, and the time between the second quenching water coolings is 0.5h to 3h. During the second quenching water cooling, the water is strongly stirred to make the surface of the workpiece fully cooled by water and obtain a good structure. Ensure that the surface temperature of the workpiece is ≦50°C, and then carry out the second tempering.

4. A process for improving the low-temperature impact performance of petrochemical forgings according to claim 3, characterized in that: In step S2, to ensure the effect of the second subcritical quenching, when loading the furnace, the left and right gaps between the forgings shall not be less than 150mm, and the stacking method is not allowed.

5. A process for improving the low-temperature impact performance of petrochemical forgings according to claim 4, characterized in that: The holding time of the second tempering is 7h to 16h, which is 20% to 30% shorter than the existing holding time of tempering after quenching. Appropriately shorten the tempering holding time after the second subcritical quenching to reduce the precipitation of brittle phases at the grain boundaries.

6. A process for improving the low-temperature impact performance of petrochemical forgings according to claim 4, characterized in that, The chemical composition should not only meet the requirements of SA336F11CL2, but also comply with the following regulations: a. J coefficient = (Si + Mn) × (P + Sn) × 10 4 ≤ 120, where the elements are substituted by their percentage contents; b, X coefficient = (10P + 5Sb + 4Sn + As) × 10 -2 ≤ 15, where the elements are substituted with ppm contents; c. Si + Mn ≦ 1.20, where each element is in percentage content; d, (Cu + Sn + As) ≤ 10 -2 , where each element is the percentage content.

7. A process for improving the low-temperature impact performance of petrochemical forgings according to claim 6, characterized in that, The chemical composition should not only meet the requirements of SA336F11CL2, but also include inclusion requirements: For inclusions of types A, B, C, D, and DS in the forging, they shall not be greater than grade 1.5; and the sum of types A and C shall not be greater than grade 2.0; the sum of types B and D and type DS shall not be greater than grade 2.5; the sum of types A, B, C, D, and DS shall not be greater than grade 4.0.

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