A forging method for large-size irregular-shaped tee forgings of high-performance austenitic stainless steel for nuclear power applications

Abstract

This invention discloses a forging method for large-size irregular-shaped tee forgings made of high-performance austenitic stainless steel for nuclear power applications. The technical solution includes step S1, raw material preparation; and step S2, forging, comprising the following steps: Step 1: Upsetting the forging billet, followed by elongation of the forging billet, with the forging ratio controlled within 2.5-3.5, and finally reheating in the furnace at a temperature range of 1150℃-1200℃; Step 2: Upsetting the forging billet, followed by punching the forging billet, with the forging ratio controlled within 2.5-3.5, and finally reheating in the furnace at a temperature range of 1150℃. -1200℃; Step 3: Expand the hole of the forging billet with a forging ratio controlled within 2.5-3.5, and finally put it back into the furnace for heat preservation, with a heat preservation temperature range of 1150℃-1200℃; Step 4: Insert a mandrel into the inner hole of the forging billet for drawing, and then put it back into the furnace for heat preservation, with a heat preservation temperature range of 1000℃-1100℃; Step 5: Divide the forging billet according to the marking, draw it out and trim it to the target size; Step S3, trimming: put it back into the furnace for heat preservation after deformation is completed; Step S4, cooling: immerse the forging in water for cooling. The present invention aims to improve the deformation force and grain size of the alloy.

Description

Technical Field

[0001] This invention relates to the field of austenitic stainless steel forging, and in particular to a forging method for large-sized irregular tee forgings of high-performance austenitic stainless steel for nuclear power. Background Technology

[0002] With the continuous development of nuclear energy technology, the operating conditions of nuclear power plant main equipment are becoming increasingly demanding. The nuclear power pressure vessel is the most important main equipment in the nuclear island, operating in the harshest environment. Due to long-term neutron radiation, it must possess extremely high stability. Therefore, the quality of nuclear power plant forgings is closely related to the quality of piping connections in the primary loop main equipment of the nuclear reactor, such as pressure vessels, evaporators, and pressurizers.

[0003] Currently, these forgings are generally made of austenitic steel. The traditional manufacturing process involves forging the cylinder and the connecting pipe separately, and then welding them together using a saddle-shaped weld. The following difficulties exist in the manufacturing process:

[0004] 1. Austenitic stainless steel is a single-phase structure at room temperature and does not undergo structural transformation. This means that austenitic stainless steel has greater resistance to deformation and poorer plasticity, which increases the difficulty of forging, makes it impossible to deeply crush the coarse-grained structure, affects the overall uniformity of the structure, and fails to achieve the required grain size refinement.

[0005] 2. Austenitic stainless steel is very sensitive to impurities. If the coarse grains are not crushed evenly during the forging process, it is easy to cause excessive local impurity content and excessive original ferrite content. In addition, when the deformation resistance is high, defects such as cracks will occur, affecting the quality of the forging. Summary of the Invention

[0006] In view of the shortcomings of the prior art, the purpose of this invention is to provide a forging method for large-size irregular tee forgings of high-performance austenitic stainless steel for nuclear power, which has the advantages of improving the deformation force and grain size of the alloy, which is beneficial to the forming of parts and improves the quality of the formed parts.

[0007] The above-mentioned technical objective of the present invention is achieved through the following technical solution:

[0008] A forging method for large-sized irregular-shaped tee forgings of high-performance austenitic stainless steel for nuclear power applications, characterized by the following steps:

[0009] Step S1: Raw material preparation;

[0010] Step S2, forging, includes the following steps:

[0011] Step 1: Upsetting the billet, then drawing the billet, controlling the forging ratio within 2.5-3.5, and finally heat-keeping it in the furnace, with a holding temperature range of 1186℃-1214℃;

[0012] Step 2: Upsetting the forging billet, then punching the forging billet, controlling the forging ratio within 2.5-3.0, and finally heat-keeping in the furnace, with a heat-keeping temperature range of 1150℃-1200℃;

[0013] Step 3: Expand the hole of the forging billet lever, control the forging ratio within 2.5-2.5, and finally put it back into the furnace for heat preservation, with a heat preservation temperature range of 1150℃-1200℃;

[0014] Step 4: Insert a mandrel into the inner hole of the forging billet for drawing, and then return it to the furnace for heat preservation, with a heat preservation temperature range of 1000℃-1100℃;

[0015] Step 5: Mark the forging billet number, divide it into portions, and trim it to the target size;

[0016] Step S3, Finishing: After the main deformation of the forging billet is completed, it is returned to the furnace for heat preservation;

[0017] Step S4, Cooling: Immerse the forging in water for cooling.

[0018] Furthermore, in step S1, the tail removal rate of raw materials is ≥5%, and the head removal rate of raw materials is ≥3%.

[0019] Furthermore, in step 1 of step S2, a two-stage heating process is adopted: after the forging billet is put into the furnace, it is heated to 750℃-850℃, held for 10-12 hours, and then heated to 1186℃-1214℃.

[0020] Furthermore, in step 1 of step S2, during the process of heating to 750℃-850℃, the heating rate is not higher than 75℃ / h; during the process of heating to 1186℃-1214℃, the heating rate is not higher than 100℃ / h.

[0021] Furthermore, in step 2 of step S2, the heated steel ingot is quickly transferred to the material table, and a upset plate is used for center compaction and upset upsetting to control the forging deformation rate ≤10mm / s; after upset to the predetermined height, upper and lower narrow anvils are used for rapid elongation.

[0022] Furthermore, in step 2 of step S2, the rapid elongation process involves: anvil advance of 400mm, anvil connection of 100mm, and single downward pressure controlled at 40-70mm.

[0023] Furthermore, in step 2 of step S2, after forging is completed, the steel ingot is reheated in the furnace for 240-400 minutes.

[0024] Furthermore, in step 3 of step S2, after the steel ingot is enlarged, it is trimmed, and then the steel ingot is returned to the furnace for reheating for 90-150 minutes.

[0025] Furthermore, a mandrel is inserted into the steel ingot for drawing. After drawing to the target size, a triangular knife is used to divide the material and pre-draw it to the intermediate size.

[0026] Furthermore, in step S3, the reflow temperature ranges from 1050 to 1100°C.

[0027] In summary, the present invention has the following beneficial effects:

[0028] 1. A small forging ratio for austenitic stainless steel may not reach the critical deformation level for recrystallization, while an excessively large forging ratio may lead to coarse grains, thus affecting the steel's corrosion resistance. Therefore, forging below the critical deformation zone should be avoided, and the forging ratio per forging pass should be controlled at 2.5-3.5 to obtain a more uniform grain structure.

[0029] 2. Setting the forging heating temperature: Under the premise of generating harmful phases, the forging heating temperature is increased. However, if the temperature is too high, the grain size will grow rapidly and high-temperature ferrite will be generated. Heating for a long time at 1000℃-1100℃ will not result in obvious grain size growth, which is conducive to grain refinement and reduces the resistance to forging deformation.

[0030] 3. During the forging heating process and at the center, the forging should not stay in the high-temperature zone for too long, otherwise it will easily cause severe over-oxidation, element depletion and grain coarsening.

[0031] 4. The forging deformation adopts a near-net-shape forming method, and the billet size is as close as possible to the finished product size to reduce the material input weight. Attached Figure Description

[0032] Figure 1 This is a schematic diagram of the deformation of the forging billet in step 4.

[0033] Figure 2 This is a schematic diagram of the deformation of the forging billet in step 5.

[0034] Figure 3 This is a schematic diagram of the structure of the forged part after repair.

[0035] Figure 4 This is a grain size detection diagram taken from the large end of the forging at 0° in Example 1.

[0036] Figure 5 This is a grain size detection diagram taken from the large end of the forging at 0° in Example 2.

[0037] Figure 6 This is a grain size detection diagram taken from the large end of the forging in Example 1 at 90°.

[0038] Figure 7 This is a grain size detection diagram taken from the large end of the forging in Example 2 at 90°.

[0039] Figure 8 This is a grain size detection diagram of the branch nozzle sample of the forging in Example 1.

[0040] Figure 9 This is a grain size detection diagram of the branch nozzle sample of the forging in Example 2. Detailed Implementation

[0041] Example 1:

[0042] Step S1: Raw material preparation. The raw material is austenitic stainless steel. The austenitic stainless steel forging billet is smelted in an electric furnace, then refined outside the furnace, and finally obtained by electroslag remelting. The raw material is then shaped, with a tail removal rate ≥5% and a head removal rate ≥3%. In this embodiment, the forging billet weighs 13000 kg. Figure 1 As shown, the original dimensions of the forging billet are: height H = 1260 mm, inner diameter φ1170 mm, and outer diameter φ1815 mm.

[0043] Step S2, forging, includes the following steps:

[0044] Step 1: Upsetting the billet, followed by drawing the billet. The dimensions of the billet are as follows: Calculations show that the forging ratio for step 1 is 3.4. The forged billet is then returned to the furnace for heat treatment at 1200℃.

[0045] Step 2: Upsetting the billet, followed by drawing the billet. The dimensions of the billet are as follows: Calculations show that the forging ratio for step 1 is 2.5. The forged billet is then returned to the furnace and held at 1180℃.

[0046] Step 3: Expand the hole of the forging billet lever. The dimensions of the forging billet are as follows: The forging ratio is 2.5, and the final furnace is used for heat preservation, with a heat preservation temperature range of 1180℃.

[0047] Step 4: As Figure 1 As shown, a mandrel is inserted into the inner hole of the forging billet for drawing. The mandrel diameter is Φ1180mm, and the size of the forging billet is φ1815mm. Then it is put back into the furnace for heat preservation at a temperature of 1000℃.

[0048] Step 5: As Figure 2 As shown, the marked material is drawn and trimmed to the size of the forging billet, which is φ1800mm.

[0049] Step S3, Trimming: such as Figure 3 As shown, after the main deformation of the forging billet is completed, it is returned to the furnace for heat preservation at 1100℃.

[0050] Step S4, Cooling: Immerse the forging in water for cooling.

[0051] Example 2:

[0052] The difference from Example 1 is:

[0053] Step S2, forging, includes the following steps:

[0054] Step 1: Upsetting the forging billet, then returning the forging billet to the furnace for heat preservation at a temperature of 1150℃.

[0055] Step 2: Upsetting the billet, then drawing the billet, and then returning the billet to the furnace for holding at 1170℃.

[0056] Step 3: Expand the hole of the forged billet lever, and finally put it back into the furnace for heat preservation, with a heat preservation temperature range of 1150℃.

[0057] Step 4: Insert a mandrel into the inner hole of the forging billet for drawing, and then return it to the furnace for heat preservation at a temperature of 1050℃.

[0058] Step 5: The material is cut and trimmed to the size of the forging billet.

[0059] Forging inspection:

[0060] Sampling standards: The inspection surface is a cross-section perpendicular to the axis of the forging, and the radial dimension is at least the distance from the inner surface of the forging to 1 / 2 the wall thickness. Samples are taken from the large end of the forging at 0° and 90°, as well as from the tee branch nozzle of the forging.

[0061] Example 2:

[0062] The difference from Example 1 is:

[0063] Step S2, forging, includes the following steps:

[0064] Step 1: Upsetting the forging billet, then returning the forging billet to the furnace for heat preservation at a temperature of 1150℃.

[0065] Step 2: Upsetting the billet, then drawing the billet, and then returning the billet to the furnace for holding at 1170℃.

[0066] Step 3: Expand the hole of the forged billet lever, and finally put it back into the furnace for heat preservation, with a heat preservation temperature range of 1150℃.

[0067] Step 4: Insert a mandrel into the inner hole of the forging billet for drawing, and then return it to the furnace for heat preservation at a temperature of 1050℃.

[0068] Step 5: The material is cut and trimmed to the size of the forging billet.

[0069] Example 3:

[0070] The difference from Example 1 is:

[0071] Step S2, forging, includes the following steps:

[0072] Step 1: Upsetting the billet, then returning the billet to the furnace for heat preservation at a temperature of 1130℃.

[0073] Step 2: Upsetting the billet, then drawing the billet, and then returning the billet to the furnace for holding at 1150℃.

[0074] Step 3: Expand the hole of the forged billet lever, and finally put it back into the furnace for heat preservation, with a heat preservation temperature range of 1170℃.

[0075] Step 4: Insert a mandrel into the inner hole of the forging billet for drawing, and then return it to the furnace for heat preservation at a temperature of 1000℃.

[0076] Step 5: The material is cut and trimmed to the size of the forging billet.

[0077] Forging inspection:

[0078] Sampling standards: The inspection surface is a cross-section perpendicular to the axis of the forging, and the radial dimension is at least the distance from the inner surface of the forging to 1 / 2 the wall thickness. Samples are taken from the large end of the forging at 0° and 90°, as well as from the tee branch nozzle of the forging.

[0079] Ferrite content assessment requirements:

[0080] Ferrite content analysis samples were taken from the extended portion of the forgings in the delivery condition. The inspection surface was a cross-section perpendicular to the forging axis, with a circumferential dimension of 15–20 mm and a radial dimension of at least the distance from the inner surface of the forging to half the wall thickness. One sample was taken from each batch of tee-type forgings at both the 0° and 90° directions, at the end with the greater nominal thickness. Following the area method specified in GB / T 13305-2008, the field of view with the highest ferrite phase area content on the inspection surface was selected. The ferrite content of the heat-treated forgings in the delivery condition must be less than 1%. The microscope magnification was 300x, and the actual field of view diameter was 0.267 mm.

[0081] Test results:

[0082] Grain size detection results at 0° large end sampling: (e.g.) Figure 4 and Figure 5 As shown.

[0083] Grain size detection results at 90° sampling at the large end: (e.g.) Figure 6 and Figure 7 As shown.

[0084] Branch nozzle grain size testing results: such as Figure 8 and Figure 9 As shown.

[0085] Results analysis:

[0086] The large end of the tee forging has a grain size of grade 5.0, with no ferrite observed, and the overall grain is relatively uniform, meeting the assessment requirements.

[0087] Grain size analysis was performed on samples taken from the branch nozzle location. The grain size was grade 5.0, and no ferrite was observed. The forging is generally uniform, meeting the process design objectives.

[0088] The technical features of the above embodiments can be combined in any way. For the sake of brevity, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0089] The embodiments described above are merely illustrative of several implementations of the present invention, and while the descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the invention patent. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the present invention, and these all fall within the protection scope of the present invention. Therefore, the protection scope of this invention patent should be determined by the appended claims.

Claims

1. A forging method for large-sized irregular-shaped tee forgings of high-performance austenitic stainless steel for nuclear power plants, characterized in that, Includes the following steps: Step S1: Raw material preparation; Step S2, forging, includes the following steps: Step 1: Upsetting the billet, then drawing the billet, controlling the forging ratio within 2.5-3.5, and finally heat-keeping it in the furnace, with a heat-keeping temperature range of 1186℃-1214℃; Step 2: Upsetting the forging billet, then punching the forging billet, controlling the forging ratio within 2.5-3.0, and finally heat-keeping in the furnace, with a heat-keeping temperature range of 1150℃-1200℃; Step 3: Expand the hole of the forging billet lever, with a forging ratio of 2.5, and finally put it back into the furnace for heat preservation, with a heat preservation temperature range of 1150℃-1200℃; Step 4: Insert a mandrel into the inner hole of the forging billet and draw it out, then return it to the furnace for heat preservation, with a heat preservation temperature range of 1000℃-1100℃; Step 5: Forging billet is marked with a number, then drawn and trimmed to the target size; Step S3, Finishing: After the main deformation of the forging billet is completed, it is returned to the furnace for heat preservation; Step S4, Cooling: Immerse the forging in water for cooling; In step S2, step 1 involves a two-stage heating process: after the forging billet is placed in the furnace, it is heated to 750℃-850℃ and held for 10-12 hours, and then the temperature is increased to 1186℃-1214℃. In step 1 of step S2, during the process of heating to 750℃-850℃, the heating rate shall not exceed 75℃ / h; during the process of heating to 1186℃-1214℃, the heating rate shall not exceed 100℃ / h. In step 2 of step S2, the heated steel ingot is quickly transferred to the material table, and upsetting is performed by center compaction using an upsetting plate, controlling the forging deformation rate to ≤10mm / s; after upsetting to the predetermined height, it is quickly drawn out using upper and lower narrow anvils; In step 2 of step S2, the rapid elongation process is as follows: the anvil advance is 400mm, the anvil connection is 100mm, and the single downward pressure is controlled between 40-70mm. In step S3, the reflow temperature range is 1050~1100℃.

2. The forging method for large-size irregular-shaped tee forgings of high-performance austenitic stainless steel for nuclear power plants according to claim 1, characterized in that: In step S1, the tail removal rate of raw materials is ≥5%, and the head removal rate of raw materials is ≥3%.

3. The forging method for large-size irregular-shaped tee forgings of high-performance austenitic stainless steel for nuclear power plants according to claim 1, characterized in that: In step 2 of step S2, after forging is completed, the steel ingot is reheated in the furnace for 240-400 minutes.

4. The forging method for large-size irregular-shaped tee forgings of high-performance austenitic stainless steel for nuclear power plants according to claim 1, characterized in that: In step 3 of step S2, after the steel ingot is enlarged, it is trimmed and then returned to the furnace for reheating for 90-150 minutes.

5. The forging method for large-size irregular-shaped tee forgings of high-performance austenitic stainless steel for nuclear power plants according to claim 1, characterized in that: In step 4 of step S2, a mandrel is inserted into the steel ingot for drawing. After drawing to the target size, a triangular knife is used to divide the material and pre-draw it to the intermediate size.

Images