Forging process of stainless steel high-complexity-coefficient forge piece

Abstract

The invention belongs to the technical field of forge piece machining, and particularly relates to a forging process of a stainless steel high-complexity-coefficient forge piece, which comprises the following working procedures of blanking, heating, upsetting, pre-forging, finish forging, punching and trimming, heat treatment, shot blasting, flaw detection, surface treatment, inspection and warehousing, the temperature of the blank is controlled to be 1100-1150 DEG C; the upsetting procedure comprises pre-upsetting and secondary upsetting, in the pre-upsetting procedure, part of blanks are accumulated at the bottom, and part of cavities of the blanks which do not need to be upset are arranged on an upper die; in the pre-forging process, the draft angle of a pre-forging die is increased to 8-10 degrees, and the fillet radius is increased to 15-20 mm; in the finish forging process, a composite release agent of plant ash and nano silicon dioxide is spread on the surface of the forge piece before finish forging, the problems of insufficient mold filling, mold sticking scrapping, out-of-tolerance deformation and the like in traditional forging are solved, the qualified rate of finished products is greatly increased, and the method is suitable for large-scale production of the high-complexity-coefficient stainless steel forge piece.

Description

Technical Field

[0001] This invention belongs to the field of forging processing technology, specifically relating to a forging process for stainless steel forgings with high complexity coefficients. Background Technology

[0002] 316L stainless steel is widely used in high-end equipment manufacturing due to its excellent corrosion resistance. However, this material has poor high-temperature plasticity, making it prone to incomplete filling during forging. For forgings with complex shapes, such as... Figure 1 , Figure 2 As shown, this forging has a shape complexity coefficient of S3 and weighs 17.5 kg. Its complex structure, with a short and long front end and a heavy rear end, makes material flow distribution during billet preparation difficult. Manual operation can easily lead to excessively rapid temperature drop in the billet, resulting in filling defects and making forging extremely challenging. Furthermore, stainless steel has poor high-temperature plasticity, and the high shape complexity necessitates strict control of heating and final forging temperatures to ensure complete filling. Additionally, 316L stainless steel exhibits strong adhesion to the mold at high temperatures, easily sticking to the die; sticking results in the forging being scrapped. Moreover, the thin and light front end of the forging is prone to plastic deformation during punching and trimming, leading to dimensional deviations. Existing forging processes cannot simultaneously address these issues, resulting in a finished product qualification rate of less than 60%, hindering the industrial production of highly complex stainless steel forgings.

[0003] Therefore, the above-mentioned problems should be considered and solved during the forging process of stainless steel forgings with high complexity coefficients. Summary of the Invention

[0004] To address the above problems, the present invention aims to provide a forging process for stainless steel forgings with high complexity coefficients, suitable for precision forging of stainless steel forgings with a shape complexity coefficient of S3 and large weight. The specific technical solution is as follows: This invention provides a forging process for stainless steel forgings with high complexity coefficients, specifically including the following steps: blanking -- heating -- upsetting -- pre-forging -- final forging -- punching and trimming -- heat treatment -- shot blasting -- flaw detection -- surface treatment -- inspection -- warehousing. The key feature is that: in the heating step, the billet temperature is controlled at 1100-1150℃; the upsetting step includes pre-upsetting and secondary upsetting, wherein in the pre-upsetting step, a portion of the billet is accumulated at the bottom. The blank cavity that does not require upsetting is placed in the upper die; in the pre-forging process, the draft angle of the pre-forging die is increased to 8-10° and the fillet radius is increased to 15-20mm; in the final forging process, a composite release agent of plant ash and nano silica is sprinkled on the surface of the forging before final forging, and the temperature of the forging is controlled above 900℃ after final forging to ensure the plasticity conditions for subsequent punching and trimming; punching and trimming are combined with a cavity-limiting trimming die to achieve hot punching and trimming using the residual heat after forging.

[0005] A further improvement of the present invention is that: in the heating process, a medium-frequency induction heating furnace is used to heat the billet, and the axial temperature difference is ≤±5℃, so as to avoid uneven plasticity caused by excessive local temperature drop.

[0006] A further improvement of the present invention is that: in the upsetting process, the pre-upsetting equipment is a 400T punch press, the secondary upsetting adopts a 6T programmable electro-hydraulic hammer, the pre-forging cavity is set close to the upsetting cavity, and the temperature drop of the billet from the upsetting station to the pre-forging station is ≤20℃.

[0007] A further improvement of the present invention is that: in the pre-forging process, a nano-ceramic coating is prepared on the surface of the pre-forging mold cavity, with a coating thickness of 50-80μm, which not only improves the wear resistance of the mold, but also reduces the adhesion between the billet and the mold.

[0008] A further improvement of the present invention is that: in the punching and trimming process, a 250T punch press is used, and the inner wall of the trimming die is coated with a polytetrafluoroethylene wear-resistant layer.

[0009] A further improvement of the present invention is that: in the heat treatment process, a solution treatment + water cooling method is adopted, the solution temperature is 1050-1100℃, the temperature is held for 2 hours and then water cooled to room temperature, the water cooling rate is ≥80℃ / min, to eliminate forging stress and ensure the corrosion resistance of stainless steel.

[0010] A further improvement of the present invention is that: the shot blasting process uses alloy steel shot with a shot diameter of 0.8-1.2 mm and a shot blasting intensity of 0.2-0.3A, and the oxide scale removal rate of the forging surface after shot blasting is ≥99%.

[0011] A further improvement of the present invention is that the flaw detection process is 100% dye penetrant testing, the flaw detection agent is a penetrant dye, and the development time is 5-8 minutes, ensuring that the forging is 100% free of cracks and folds.

[0012] A further improvement of the present invention is that: in the surface treatment process, a composite process of pickling and passivation + electropolishing is adopted, the pickling and passivation solution is composed of 10% nitric acid + 5% hydrofluoric acid, the electropolishing voltage is 12-15V, and the time is 3-5min, thereby improving the surface quality.

[0013] Compared with existing technologies, this invention achieves the following technical effects: The invention employs a segmented forming process of "two upsetting processes + pre-forging - final forging," with temperature control throughout the process enhancing the plasticity of 316L stainless steel, reducing forging resistance, and minimizing the risk of forging cracking. Combined with the design of placing the non-upsetting portion of the billet cavity in the upper die, it effectively avoids defects such as folding and insufficient filling in the forging, ensuring precise forming of complex shapes. Sprinkling a composite release agent of wood ash and nano-silica before final forging prevents the forging from sticking to the die and also assists in heat preservation. Utilizing the residual heat after forging for hot punching and trimming eliminates the need for secondary heating, saving energy and avoiding forging deformation caused by cold working. This solves problems such as insufficient filling, die sticking and scrapping, and excessive deformation in traditional forging, significantly improving the finished product qualification rate and making it suitable for the large-scale production of highly complex stainless steel forgings. Attached Figure Description

[0014] The accompanying drawings, which are included to provide a further understanding of the invention and form part of this invention, illustrate exemplary embodiments of the invention and are used to explain the invention, but do not constitute an undue limitation of the invention. In the drawings: Figure 1 , Figure 2 This is a schematic diagram of the product in this invention; Figure 3 This is a schematic diagram of the upsetting cavity in this embodiment; Figure 4 This is a schematic diagram of the lower molding die in this embodiment; Figure 5 This is a schematic diagram of the molding upper mold in this embodiment; Figure 6 This is a schematic diagram of the cutting die in the embodiment; Detailed Implementation

[0015] The following will describe in detail the implementation of the present invention with reference to the accompanying drawings and embodiments, so as to fully understand how the present invention uses technical means to solve technical problems and achieve technical effects and to implement it accordingly.

[0016] This embodiment provides a forging process for stainless steel forgings with high complexity coefficients, which specifically includes the following steps: (1) Blanking: Select φ90mm 316L stainless steel bars and cut them to 24kg / piece using a CNC saw; (2) Heating: The billet is heated to 1120℃ by a medium-frequency induction heating furnace, with an axial temperature difference of ±3℃. (3) Pre-upsetting: Upsetting is performed using a 400T punch press. The blank part that does not need to be upset is placed in the upper die, and the material flow accumulates at the bottom. (4) Secondary upsetting: Upsetting is carried out using a 6T programmable electro-hydraulic hammer. The pre-forging cavity is set up close to the upsetting cavity. The temperature drop of the billet when it is transferred from the upsetting station to the pre-forging station is 15℃. (5) Pre-forging: 6T programmable electro-hydraulic hammer is used for pre-forging, with a draft angle of 9°, a fillet radius of 18mm, and a nano-ceramic coating thickness of 60μm; (6) Final forging: Before final forging, a composite release agent of wood ash and nano silica is sprinkled on the surface of the forging. The temperature after final forging is 920℃. (7) Punching and trimming: The forging is hot punched and trimmed using a 250T punch press with a deformation of 0.3mm. The punch of the punching die is made of cemented carbide with a hardness ≥ HRC60. (8) Heat treatment: The combination of solution treatment and water cooling is adopted. The solution is held at 1080℃ for 2 hours and the water cooling rate is 90℃ / min. The residual stress of the forging at room temperature after water cooling is ≤150MPa. (9) Shot blasting and flaw detection: Alloy steel shot is used with a shot diameter of 0.8-1.2 mm and a shot blasting intensity of 0.2-0.3A. After shot blasting, the oxide scale removal rate of the forging surface is ≥99%. The flaw detection agent is a penetrating colorant with a development time of 5-8 min. After flaw detection, it is confirmed that the forging has no defects such as cracks, folds, or inclusions. (10) Surface treatment: A composite process of pickling and passivation + electropolishing is adopted. The pickling and passivation solution consists of 10% nitric acid and 5% hydrofluoric acid by mass. The passivation time is 25 min. Electropolishing is performed at 14V for 4 min. After polishing, the surface roughness Ra of the forging is ≤0.8μm. (11) Inspection: The inspection shall be carried out in accordance with the GB2828.1-2003 Normal Class II Inspection Standard, with an Acceptable Quality Limit (AQL) of 2.5. Dimensional inspection shall be carried out using a coordinate measuring machine with a measurement accuracy of ≤0.02mm.

[0017] In this embodiment, φ90mm 316L stainless steel bars are selected for blanking, and the blanks are cut using a CNC saw, with a single weight controlled at 24kg to ensure sufficient material flow distribution during the billet preparation stage. A medium-frequency induction heating furnace is used to heat the billet, with the heating temperature precisely controlled between 1100-1150℃. An in-furnace temperature compensation device ensures that the axial temperature difference of the billet is ≤±5℃, preventing uneven plasticity caused by excessively rapid local temperature drops. Because stainless steel has poor high-temperature plasticity, it cannot be upset completely in one pass (a single upset would result in bending and scrapping of the billet). Therefore, pre-upsetting is necessary to accumulate a portion of the material at the bottom for secondary upsetting. The portion of the billet that does not require upsetting is placed in the upper die to reduce the contact time between the billet and the die, keeping the temperature drop below 30℃. During secondary upsetting, the pre-forging cavity is positioned adjacent to the upsetting cavity, and the billet is laid flat. The workpiece then proceeds directly to the pre-forging process to reduce temperature drop during billet transfer. The draft angle of the pre-forging die is increased to 8-10° and the fillet radius is increased to 15-20mm to reduce billet filling resistance. A 50-80μm nano-ceramic coating is prepared on the die cavity surface to improve die wear resistance and reduce the adhesion between the billet and the die. Before final forging, a composite release agent of wood ash and nano-silica is sprinkled on the surface of the forging to further reduce the risk of sticking. After final forging, the forging temperature is controlled above 900℃ to ensure the plasticity conditions for subsequent punching and trimming. A 250T punch press is used with a cavity-limiting trimming die to perform hot punching and trimming using the residual heat after forging. The inner wall of the trimming die is sprayed with a polytetrafluoroethylene wear-resistant layer to reduce trimming resistance and prevent forging deformation through cavity limiting, with the deformation controlled within 0.5mm.

[0018] This embodiment employs a double upsetting process, which solves the problem of insufficient filling caused by the poor high-temperature plasticity of 316L stainless steel, significantly improving the filling qualification rate of forgings. Through the dual anti-sticking design of the mold nano-ceramic coating and composite release agent, the sticking scrap rate is reduced from 30% to less than 1%. By utilizing the hot punching and trimming of residual heat after forging, plus cavity limiting tooling, the deformation of the forging is controlled within 0.5mm, achieving precision-level dimensional accuracy. The complete process route covers the entire process from forming to inspection and warehousing, with parameters of each process matching each other, laying a good foundation for subsequent heat treatment, shot blasting, flaw detection, and other processes. Ultimately, 316L stainless steel forgings with high dimensional accuracy and stable internal quality can be obtained.

[0019] The foregoing description illustrates and describes several preferred embodiments of the present invention. However, as previously stated, it should be understood that the present invention is not limited to the forms disclosed herein and should not be construed as excluding other embodiments. It can be used in various other combinations, modifications, and environments, and can be altered within the scope of the inventive concept described herein through the foregoing teachings or techniques or knowledge in related fields. Any modifications and variations made by those skilled in the art that do not depart from the spirit and scope of the present invention should be within the protection scope of the appended claims.

Claims

1. A forging process for stainless steel forgings with high complexity coefficients, specifically comprising the following steps: blanking -- heating -- upsetting -- pre-forging -- final forging -- punching and trimming -- heat treatment -- shot blasting -- flaw detection -- surface treatment -- inspection -- warehousing, characterized in that: In the heating process, the billet temperature is controlled at 1100-1150℃; the upsetting process includes pre-upsetting and secondary upsetting. In the pre-upsetting process, part of the billet is accumulated at the bottom, and the part of the billet that does not need upsetting is placed in the upper die; in the pre-forging process, the draft angle of the pre-forging die is increased to 8-10°, and the fillet radius is increased to 15-20mm; in the final forging process, a composite release agent of wood ash and nano-silica is sprinkled on the surface of the forging before final forging, and the temperature of the forging is controlled above 900℃ after final forging; the punching and trimming process is combined with a cavity-limiting trimming die, and the residual heat after forging is used to achieve hot punching and trimming.

2. The forging process for a high-complexity stainless steel forging according to claim 1, characterized in that: In the heating process, a medium-frequency induction heating furnace is used to heat the billet, and the axial temperature difference is ≤ ±5℃.

3. The forging process for a high-complexity stainless steel forging according to claim 1, characterized in that: In the upsetting process, the pre-upsetting equipment is a 400T punch press, the secondary upsetting uses a 6T programmable electro-hydraulic hammer, the pre-forging cavity is set up close to the upsetting cavity, and the temperature drop of the billet from the upsetting station to the pre-forging station is ≤20℃.

4. The forging process for a high-complexity stainless steel forging according to claim 1, characterized in that: In the pre-forging process, a nano-ceramic coating is prepared on the surface of the pre-forging die cavity, with a coating thickness of 50-80μm.

5. The forging process for a high-complexity stainless steel forging according to claim 1, characterized in that: In the punching and trimming process, a 250T punch press is used, and the inner wall of the trimming die is coated with a polytetrafluoroethylene wear-resistant layer.

6. The forging process for a high-complexity stainless steel forging according to claim 1, characterized in that: In the heat treatment process, a solution treatment + water cooling method is adopted. The solution temperature is 1050-1100℃, and after holding at the temperature for 2 hours, it is cooled to room temperature by water with a water cooling rate ≥80℃ / min.

7. The forging process for a high-complexity stainless steel forging according to claim 1, characterized in that: The shot blasting process uses alloy steel shot with a shot diameter of 0.8-1.2 mm and a shot blasting intensity of 0.2-0.3A. After shot blasting, the oxide scale removal rate of the forging surface is ≥99%.

8. The forging process for a high-complexity stainless steel forging according to claim 1, characterized in that: The flaw detection process is 100% dye penetrant testing, using penetrating dye as the testing agent, with a development time of 5-8 minutes, to ensure that the forgings are 100% free of cracks and folds.

9. The forging process for a high-complexity stainless steel forging according to claim 1, characterized in that: In the surface treatment process, a composite process of pickling and passivation + electropolishing is adopted. The pickling and passivation solution is composed of 10% nitric acid + 5% hydrofluoric acid, and the electropolishing voltage is 12-15V, and the time is 3-5min.

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