A method for forming an oversized 35CrMo special-shaped spherical shell by die forging

Abstract

The present application relates to the technical field of forging, in particular to a method for super-large 35CrMo irregular shape spherical shell die forging forming. The method comprises the following steps: constructing a forging model of the super-large 35CrMo irregular shape spherical shell; inputting the forging model into DEFORM numerical simulation software to simulate the forging forming, and determining at least one key optimization area of the forging model; based on the Latin hypercube sampling algorithm, optimizing the structure of each key optimization area to obtain an optimized forging model. The die forging forming method solves the technical problem that the super-large 35CrMo irregular shape spherical shell die forging forming is prone to uneven structure and mechanical property fluctuation, improves the mechanical property uniformity and manufacturing stability of the super-large 35CrMo irregular shape spherical shell die forging forming, and thus improves the production efficiency.

Description

Technical Field

[0001] This invention relates to the field of forging technology, specifically to a method for die forging an ultra-large 35CrMo irregularly shaped spherical shell. Background Technology

[0002] 35CrMo steel, as a typical alloy structural steel, is widely used in the manufacture of main load-bearing structural components in aerospace, energy equipment and other fields due to its excellent comprehensive mechanical properties.

[0003] Currently, when using free forging and spin forming processes to process complex 35CrMo steel irregular spherical shell components, the following technical defects exist: 1. Due to the difficulty in controlling metal flow during forging, uneven microstructure and fluctuations in mechanical properties are easily generated during the die forging process, resulting in a generally low yield. 2. Although the design margin range of the 35CrMo steel irregular spherical shell was determined by comprehensively analyzing the relationship between the design margin, forming load and material utilization rate at the beginning of the structural design, the design margin range cannot be reasonably utilized, which will result in fluctuations in forming parameters and thus lead to material performance dispersion. The measured data shows that the impact toughness of the 35CrMo steel irregular spherical shell fluctuates in the range of 35-52J (43.5J±19.54%), which is much higher than the ±10% control range under ideal conditions.

[0004] In the existing technology, the technical solution of patent CN114260402A is based on a comprehensive analysis of the relationship between design margin, forming load, and material utilization rate to determine the range of design margin. However, it still suffers from problems of forming parameter fluctuations and material property dispersion.

[0005] The technical solution of patent CN110096741A achieves optimized design of the preforming die cavity for blade forging by defining design variables of the preforming die cavity, employing optimized Latin square experimental design, numerical simulation, radial basis function prediction model, and improved genetic algorithm, thereby improving deformation uniformity and reducing cracks. It is mainly applied to blade-type workpieces. However, its optimization effect is limited for large spherical shell forging with complex material properties (such as 35CrMo) and irregular shapes. Furthermore, it does not directly optimize the geometric features of the forging model itself, and cannot directly identify and eliminate defects such as localized stress concentration and cracks caused by abrupt changes in curvature or thickness in large, irregularly shaped workpieces (such as spherical shells).

[0006] In view of this, the above-mentioned technical defects have severely restricted the large-scale industrial production of high-reliability 35CrMo steel irregular spherical shells, and there is an urgent need to develop a new generation of die forging forming method that can achieve stable control of microstructure and properties. Summary of the Invention

[0007] This invention provides a method for die forging ultra-large 35CrMo irregularly shaped spherical shells, which solves the technical problem of uneven microstructure and fluctuations in mechanical properties of ultra-large 35CrMo irregularly shaped spherical shells during die forging. It improves the uniformity of mechanical properties and manufacturing stability of ultra-large 35CrMo irregularly shaped spherical shells during die forging, thereby improving production efficiency.

[0008] A method for die forging an ultra-large 35CrMo irregularly shaped spherical shell includes the following steps: 1) Construct a forging model of an ultra-large 35CrMo irregularly shaped spherical shell; 2) Input the forging model into numerical simulation software to perform forging forming simulation and determine at least one key optimization region of the forging model; the key optimization region is a transition zone located in the structural part of the forging model that has abrupt changes in curvature or thickness. 3) The structure of each key optimization region is optimized based on the Latin hypercube sampling algorithm and then retested to obtain the optimized forging model; 4) Determine the geometry of the mold cavity based on the geometry of the optimized forging model in step 3), and manufacture a forging mold with the geometry of the mold cavity; 5) The 35CrMo billet is first upset, and then die-forged in the forging die of step 4) to obtain a die-forged part. Finally, the die-forged part is heat-treated to obtain a large 35CrMo irregular spherical shell.

[0009] In one specific embodiment of the present invention, in step 3), the retest includes: The optimized forging model was input into the DEFORM numerical simulation software and retested, confirming that the optimized forging model had no critical optimization regions. If not, the key optimization region of the forging model after location optimization is located, and the key optimization region is re-optimized based on the Latin hypercube algorithm until the retest shows that there is no key optimization region.

[0010] In one specific embodiment of the present invention, the numerical simulation software is DEFORM numerical simulation software.

[0011] In one specific embodiment of the present invention, step 5), the upsetting is performed at 1100-1200℃ for 1-2 heat treatments.

[0012] In one specific embodiment of the present invention, step 5), the die forging is carried out in 1 to 2 forging cycles at a final forging temperature ≥850℃.

[0013] In one specific embodiment of the present invention, step 5) involves quenching and tempering the forging at 850±20℃ for 1 to 2 hours.

[0014] In one specific embodiment of the present invention, the tempering is performed at 550±10℃ for 5 to 7 hours.

[0015] The beneficial effects of this invention are: 1. The method of the present invention determines the key optimization area through forging simulation and optimizes the key optimization area through the Latin hypercube sampling algorithm. In actual forging, it can reduce the equivalent stress of the mold, improve the stress concentration of the forging and improve the uniformity of the forging deformation. 2. The method of the present invention, through optimization and retesting, can achieve evaluation and further optimization of key optimization areas; 3. The method of this invention improves the uniformity of forging properties and the stability of manufacturing. The microstructure and properties of the ultra-large 35CrMo irregularly shaped spherical shell formed by die forging meet the design requirements, and the production efficiency is high. Attached Figure Description

[0016] Figure 1 This is a schematic diagram of the machining allowance structure provided in an embodiment of the present invention; Figure 2 The optimized mold equivalent stress simulation diagram provided in the embodiments of the present invention; Figure 3 This is a simulation diagram of tissue deformation before optimization provided in an embodiment of the present invention; Figure 4 The optimized mold equivalent stress simulation diagram provided in the embodiment of the present invention; Figure 5 This is an optimized tissue deformation simulation diagram provided in an embodiment of the present invention.

[0017] Appendix Figure 1 The list of components represented by each number is as follows: 1. Transition fillet R1; 2. Transition fillet R2; 3. Slope 1; 4. Slope 2; 5. Key optimization area R10. Detailed Implementation

[0018] A method for die forging an ultra-large 35CrMo irregularly shaped spherical shell includes the following steps: 1) Construct a forging model of a large 35CrMo irregularly shaped spherical shell; 2) Input the forging model into numerical simulation software to perform forging forming simulation and determine at least one key optimization region of the forging model; the key optimization region is a transition zone located in the structural part of the forging model that has abrupt changes in curvature or thickness. 3) The structure of each key optimization region is optimized based on the Latin hypercube sampling algorithm and then retested to obtain the optimized forging model; 4) Determine the geometry of the mold cavity based on the geometry of the optimized forging model in step 3), and manufacture a forging mold with the geometry of the mold cavity; 5) The 35CrMo billet is first upset, and then die-forged in the forging die of step 4) to obtain a die-forged part. Finally, the die-forged part is heat-treated to obtain a large 35CrMo irregular spherical shell.

[0019] In some instances, step 3) involves retesting: The optimized forging model was input into the DEFORM numerical simulation software for retesting to confirm that there were no critical optimization regions in the optimized forging model. If not, then locate the key optimization region of the optimized forging model and re-optimize it based on the Latin hypercube algorithm until the retest shows that there is no key optimization region.

[0020] It should be noted that the Latin hypercube sampling algorithm optimizes the key optimization region within the design margin of the key optimization region.

[0021] In some instances, the numerical simulation software is DEFORM numerical simulation software.

[0022] In some instances, step 5), upsetting, involves upsetting a 35CrMo billet at 1100–1200°C for 1–2 passes.

[0023] In some instances, upsetting is achieved using a 45MN high-speed forging mill.

[0024] In some instances, before upsetting, the upper and lower anvils of the forging machine are preheated to ≥200℃ and held at that temperature for ≥2 hours.

[0025] In some cases, the amount of deformation under pressure during each upsetting process is controlled at 30-80%, and the pressing speed is controlled at 5-10 mm / s.

[0026] In some instances, after upsetting, the diameter of the upsetting billet is 0.7 to 1 times the diameter of the die cavity of the forging die; the thickness of the upsetting billet is 1 to 3 times the target design wall thickness of the ultra-large 35CrMo irregularly shaped spherical shell.

[0027] In some instances, after the upset billet meets the requirements for die forging, the upset billet is air-cooled.

[0028] In some instances, step 5), die forging is performed in 1 to 2 forging passes at a final forging temperature ≥850°C.

[0029] In some instances, before the first forging, a special anti-oxidant is applied to the surface of the upsetting billet, and then graphite fiber cloth is laid on the upper and lower surfaces of the upsetting billet; before each forging, graphite lubricant is applied to the cavity surface of the forging die.

[0030] In some instances, die forging is performed inside a large die forging press.

[0031] In some instances, the forging die is preheated to 250–350°C before the forging process begins.

[0032] In some instances, the deformation per forging pass is controlled at 30-80%, and the pressing speed is controlled at 5-10 mm / s.

[0033] In some instances, to eliminate internal stress in forgings and improve the toughness and plasticity of the material, step 5) involves heat treatment by holding the forging at 850±20℃ for 1 to 2 hours and then quenching it.

[0034] In some instances, the quenching transfer time is 10–60 seconds.

[0035] In some cases, tempering is performed at 550±10℃ for 5 to 7 hours; tempering is carried out after quenching.

[0036] The implementation method will be further described below with reference to specific embodiments.

[0037] Example

[0038] The material selected for the forging in this embodiment is 35CrMo.

[0039] The die forging method for the forging in this embodiment includes the following steps: 1. Based on the structural characteristics of the ultra-large 35CrMo irregularly shaped spherical shell forging, an optimized pre-forging model with a spherical shell section was constructed. A single-sided machining allowance of 100mm was added to the outer surface of the spherical shell section in the form of a flat parting die. As attached Figure 1 As shown, the machining allowance includes a transition fillet R1, a slope 1, a slope 2, and a transition fillet R2; 2. The equivalent stress simulation diagram of the die before optimization, obtained from the die forging simulation of the forging model in DEFORM numerical simulation software, is attached. Figure 2 As shown; the pre-optimization microstructure deformation simulation diagram obtained from the die forging simulation in DEFORM numerical simulation software is attached. Figure 3 As shown; See appendix Figure 1 and attached Figure 2The machining allowance designed for this spherical shell section is relatively high, the equivalent stress of the mold is relatively high, and the microstructure of the forging is relatively dispersed while the deformation is relatively concentrated; therefore, the machining allowance of this spherical shell section is considered a key optimization area. 3. The transition fillet R11, slope 13, slope 24 and transition fillet R22 of the key optimization region R105 are structurally optimized based on the Latin hypercube sampling algorithm; 4. The optimized forging model was then subjected to another die forging simulation in DEFORM numerical simulation software. The resulting optimized die equivalent stress simulation diagram is shown in the attached figure. Figure 4 As shown in the attached diagram; the optimized microstructure deformation simulation obtained from the die forging simulation. Figure 5 As shown.

[0040] See appendix Figure 4 and 5 After optimizing the key optimization areas, the equivalent stress of the mold was improved, the stress concentration of the forging was reduced, and the deformation uniformity of the forging was enhanced.

[0041] 5. Output the optimized forging model, determine the geometry of the mold cavity based on the geometry of the optimized forging model, and process and manufacture a forging mold with the geometry of the mold cavity.

[0042] 6. Forging of ultra-large 35CrMo irregularly shaped spherical shells: 6.1 Upsetting the billet using a 45MN high-speed forging mill: Before upsetting the billet, preheat the upper and lower anvils of the 45MN fast forging machine with natural gas for ≥2 hours and ≥200℃. A billet with dimensions of Φ775×180mm and a weight of 990kg is heated in an electric furnace and then subjected to upsetting forging at 1150℃ using a preheated 45MN high-speed forging machine. After air cooling, the upsetting billet is obtained. 6.2. Forging using an 800MN large die forging press: Preheat the forging die to 250–350°C; Before the upsetting billet is put into the furnace, its surface is coated with a special anti-oxidant; Before die forging, the cavity surface of the forging die is coated with graphite lubricant; Before the forging begins, graphite fiber cloth is laid on the upper and lower surfaces of the upsetting billet; The forgings are formed by one-pass die forging in an 800MN large die forging press. 6.3 Heat Treatment: The forging is heated to 850±20℃ and held for 1 to 2 hours, and then quenched. The quenching transfer time is controlled within 10 to 60 seconds. The quenching is then immediately tempered at 550±10℃ for 5 to 7 hours to obtain a large 35CrMo irregularly shaped spherical shell.

[0043] Performance characterization of ultra-large 35CrMo irregularly shaped spherical shells based on technical standards: Four samples were taken from the longitudinal and transverse directions of the shell section of a large 35CrMo irregularly shaped spherical shell forging, and the tensile strength R of the samples was tested. m Yield strength R p0.2 The ductility A5 and the section reduction rate Z; wherein, the sampling in the longitudinal direction is carried out on the surface of the curved spherical shell section above the transition fillet R2, the surface of slope 2, the surface of slope 1, and the surface of the curved spherical shell section below the transition fillet R1, and is recorded as longitudinal 1-1, longitudinal 1-2, longitudinal 1-3 and longitudinal 1-4 respectively; the sampling in the latitudinal direction is carried out at 90° intervals along the circular direction of the machining allowance, and is recorded as transverse 3-1, transverse 3-2, transverse 3-3 and transverse 3-4 respectively; Following the aforementioned sampling method, samples were taken from a large 35CrMo irregularly shaped spherical shell forging at different locations, and the impact absorption energy A was tested. KU2 Among them, samples taken along the meridian direction are designated as longitudinal 2-1, longitudinal 2-2, longitudinal 2-3 and longitudinal 2-4, and samples taken along the parallel direction are designated as transverse 4-1, transverse 4-2, transverse 4-3 and transverse 4-4.

[0044] The statistical results of the above samples are shown in Table 1.

[0045] Table 1. Statistical analysis of test results and technical standard requirements for each sample.

[0046] Note: In Table 1, "-" indicates none.

[0047] As shown in Table 1, the method of this invention can prepare ultra-large 35CrMo irregularly shaped spherical shell forgings that meet the technical standards. At the same time, the mechanical properties of the shell section fluctuate within ±10% in both the longitudinal and latitudinal directions. This indicates that optimizing the forging model of the ultra-large 35CrMo irregularly shaped spherical shell through the Latin hypercube sampling algorithm can improve the microstructure uniformity and performance stability of the large 35CrMo irregularly shaped spherical shell during the die forging process.

Claims

1. A method for die forging an ultra-large 35CrMo irregularly shaped spherical shell, characterized in that, Includes the following steps: 1) Construct a forging model of an ultra-large 35CrMo irregularly shaped spherical shell; 2) Input the forging model from step 1) into the numerical simulation software for forging simulation, and determine at least one key optimization region of the forging model; the key optimization region is a transition region located in the structural part of the forging model that has abrupt changes in curvature or thickness. 3) Based on the Latin hypercube sampling algorithm, structural optimization is performed on each key optimization region determined in step 2), and the results are retested to obtain the optimized forging model; 4) Determine the geometry of the mold cavity based on the geometry of the optimized forging model in step 3), and manufacture a forging mold with the geometry of the mold cavity; 5) The 35CrMo billet is first upset, and then die-forged in the forging die of step 4) to obtain a die-forged part. Finally, the die-forged part is heat-treated to obtain an ultra-large 35CrMo irregular spherical shell.

2. The method for forging ultra-large 35CrMo irregularly shaped spherical shells according to claim 1, characterized in that: Step 3), the retest includes: The optimized forging model was input into numerical simulation software and retested, confirming that the optimized forging model had no critical optimization areas. If not, the key optimization region of the forging model after location optimization is located, and the key optimization region is re-optimized based on the Latin hypercube algorithm until the retest shows that there is no key optimization region.

3. The method for forging ultra-large 35CrMo irregularly shaped spherical shells according to claim 1 or 2, characterized in that: The numerical simulation software is DEFORM numerical simulation software.

4. The method for forging ultra-large 35CrMo irregularly shaped spherical shells according to claim 1, characterized in that: Step 5), the upsetting is performed at 1100-1200℃ for 1-2 heat treatments.

5. The method for forging ultra-large 35CrMo irregularly shaped spherical shells according to claim 1, characterized in that: Step 5), the die forging process involves 1 to 2 forging passes at a final forging temperature ≥850℃.

6. The method for forging ultra-large 35CrMo irregularly shaped spherical shells according to claim 1, characterized in that: Step 5), the heat treatment is to quench and temper the forging after holding it at 850±20℃ for 1 to 2 hours.

7. The method for forging ultra-large 35CrMo irregularly shaped spherical shells according to claim 6, characterized in that: The tempering process involves holding the temperature at 550±10℃ for 5–7 hours.

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