A method for inhibiting forging cracking of high-temperature titanium alloy by combining finite element simulation analysis

Abstract

This invention belongs to the field of materials science and plastic processing, specifically relating to a method for suppressing forging cracks in high-temperature titanium alloys using finite element simulation analysis. The method involves developing a corresponding simulation test plan based on the actual forging process of high-temperature titanium alloys; conducting numerical simulations to analyze and determine each pass of the initial forging and upsetting, identifying key areas prone to cracking and requiring optimization; developing simulation schemes for hammering with hammers of different surfaces based on the characteristics of different target areas, and conducting numerical simulations; comparing the simulation with the original process to evaluate whether surface hammering alleviates tensile stress or damage in the target area; iteratively simulating and optimizing the surface hammering process, and finally implementing the optimized scheme for hammering. This invention solves problems such as low yield due to easy surface cracking during the forging of difficult-to-deform materials like high-temperature titanium alloys, significantly extended processing cycles due to interruptions in the forging process caused by damage removal, and microstructural deterioration caused by changes in the hot working path.

Description

Technical Field

[0001] This invention belongs to the field of materials science and plastic processing, and specifically relates to a method for suppressing high-temperature titanium alloy forging cracks by combining finite element simulation analysis, particularly a process optimization method for titanium alloys and other forging processes with high crack sensitivity. Background Technology

[0002] Titanium alloys exhibit strong anisotropy, leading to problems such as a narrow forging temperature range, high susceptibility to cracking, and a tendency to develop surface cracks during high-temperature forging. This issue is particularly pronounced in difficult-to-deform alloys like high-temperature titanium alloys. These surface cracks caused by forging necessitate interrupting the forging process for surface cleaning in actual production. This additional cleaning step significantly prolongs production time due to prolonged cooling, grinding, and reheating of large ingots. Furthermore, the cleaning and finishing processes drastically reduce the yield of titanium alloy forging, often dropping to 70%–80%, and even as low as 50%–60% for new high-temperature titanium alloys. Simultaneously, the prolonged cooling and reheating significantly alter the alloy's thermal history, leading to microstructural deterioration and reduced overall uniformity of the billet structure. This negatively impacts the performance of the material in subsequent service, particularly critical properties such as high-temperature creep resistance, high-temperature durability, and fatigue resistance. Therefore, surface cracking in high-temperature titanium alloy forging remains a serious constraint on process design. To reduce surface cracking in titanium alloys, several different technical methods have been accumulated over the decades, mainly including: (1) methods such as covering the billet surface with insulating asbestos during alloy forging to reduce surface temperature drop; (2) methods such as coating the surface with glass lubricant to reduce friction between the billet and the mold, reduce direct contact heat transfer, and prevent oxidation; (3) adjusting the deformation process parameters based on the original process scheme in conjunction with finite element simulation analysis to reduce the tendency of surface cracking. The main causes of surface cracking in titanium alloy forging include strong anisotropy, poor plasticity, low thermal conductivity, and excessively rapid surface temperature drop, which leads to the formation of localized relatively high tensile stress areas or high damage areas. The above technical methods take into account some of the causes and solve the overall tendency of surface cracking in titanium alloys to a certain extent. However, surface cracking in actual alloy forging often has localized characteristics, and it is still necessary to stop the forging process for cleaning. Therefore, it is necessary to use appropriate methods to suppress localized cracking areas. To address the overall tendency and localized characteristics of surface cracking in high-temperature titanium alloy forging, this invention provides a method for suppressing forging cracks in high-temperature titanium alloys through hammering, based on finite element simulation and experimental analysis. Summary of the Invention

[0003] The purpose of this invention is to propose a method for suppressing forging cracks in high-temperature titanium alloys by combining finite element simulation analysis. This method combines finite element simulation and experimental analysis, and suppresses forging cracks in high-temperature titanium alloys by hammering. It can significantly reduce the overall tendency of surface cracking and the degree of local cracking in high-temperature titanium alloy forging, and greatly improve the hot working efficiency and yield.

[0004] To solve the ingot cracking problem in the titanium alloy forging process mentioned above, the technical solution of the present invention is as follows:

[0005] A method for suppressing forging cracks in high-temperature titanium alloys by combining finite element simulation analysis, which integrates actual high-temperature titanium alloy processes and numerical simulation predictions, involves selecting specific target areas and times during the forging process to perform surface hammering on the ingot, thereby suppressing surface cracking, and includes the following steps:

[0006] (1) Based on the actual forging process of high-temperature titanium alloy, formulate a corresponding simulation test plan;

[0007] (2) Conduct finite element numerical simulation to analyze and determine the target area that needs to be optimized after each upsetting pass;

[0008] (3) Based on the characteristics of different target areas, formulate different surface hammering simulation schemes and carry out numerical simulations;

[0009] (4) Compare with the original process simulation to evaluate whether pressure is introduced into the target area or the damage is alleviated after surface hammering;

[0010] (5) The surface hammering simulation scheme was optimized through multiple iterations to confirm the optimized process scheme.

[0011] The method for suppressing high-temperature titanium alloy forging cracks by combining finite element simulation analysis, in step (1), the actual forging process of high-temperature titanium alloy includes billet opening, upsetting, drawing out of the square and drawing out of the octagon; the simulation test scheme tries to restore the specific parameters in the actual process as much as possible, including: deformation temperature, deformation speed, deformation amount, each drawing out pass, drawing out hammer spacing and billet flipping form.

[0012] The method for suppressing high-temperature titanium alloy forging cracking by combining finite element simulation analysis, in step (2), the finite element numerical simulation based on the original process mainly selects the target area containing the surface high damage or tensile stress characteristics, and determines the key time period for the formation of the target area.

[0013] The method for suppressing forging cracks in high-temperature titanium alloys by combining finite element simulation analysis employs an alloy constitutive model optimized by temperature and friction corrections in the finite element numerical simulation.

[0014] The method for suppressing high-temperature titanium alloy forging cracks by combining finite element simulation analysis, in step (3), according to the common target areas and formation time periods in the upsetting and drawing process, the surface hammering simulation scheme mainly includes: (1) after upsetting, the middle of the side surface is slightly rolled; (2) in the four-sided and eight-sided drawing passes, according to the simulation results, after 1 to 3 passes, the high tensile stress area of ​​the side surface is hammered; (3) after the drawing is completed, the local high tensile stress area is hammered first, then the side surface is slightly rolled to flatten the surface, and finally the axial micro-upsetting is performed.

[0015] In the method of suppressing high-temperature titanium alloy forging cracks by combining finite element simulation analysis, step (4) involves comparing and analyzing whether the surface hammering simulation schemes selected for different target areas and formation times reduce tensile stress or damage value.

[0016] In the method of suppressing high-temperature titanium alloy forging cracks by combining finite element simulation analysis, step (5) involves selecting a combination of surface hammering simulation schemes for various target areas and fine-tuning the parameters according to the actual process window and key pass requirements of the alloy, iteratively optimizing the feasibility scheme, and conducting verification and evaluation.

[0017] The design concept of this invention is:

[0018] Compared to other materials, titanium alloys are prone to surface cracking during forging, especially high-temperature titanium alloys and other difficult-to-deform alloys. The direct causes are generally attributed to their poor plasticity, low thermal conductivity, and rapid surface temperature drop. From the perspective of plastic processing mechanics, the stress characteristics of surface cracking are the formation of high localized tensile stress concentrations or large cumulative plastic damage values. In other industrial production processes, common surface cracking occurs after casting, heat treatment, and plastic processing. To avoid these cracks, practical methods include rational casting system design and improved hot working and heat treatment processes. Regarding fatigue cracking during service, other industrial methods for improving the service performance of alloy surfaces commonly include surface modification methods such as shot peening, sandblasting, and ultrasonic rolling. These methods strengthen the surface and convert the original tensile stress into compressive stress, typically at a depth of micrometers to millimeters, thereby suppressing surface cracking during service. In actual high-temperature titanium alloy forging processes, the forging process window is very narrow, and surface cracking exhibits localized characteristics. Commonly used methods such as surface heat preservation and simulation-based process optimization do not address the localized surface cracking characteristics by transforming the stress characteristics. Therefore, this proposed method is highly original compared to traditional methods for suppressing forging cracks in titanium alloys. Based on simulation and experimental analysis, it specifically suppresses surface cracking through precisely controlled surface hammering.

[0019] The advantages and beneficial effects of this invention are:

[0020] The present invention proposes a method for suppressing cracking in high-temperature titanium alloy forging by combining finite element simulation and experimental analysis. Based on the basic process information and actual cracking conditions provided by experiments, comparative finite element simulation analysis is carried out to determine the target feature area and surface hammering modification method. This method can provide a technical path for suppressing the overall and local tendency of surface cracking in titanium alloy forging, which can help to significantly improve the yield of titanium alloy forging, reduce the processing cycle, and improve the overall microstructure and properties of the billet. Attached Figure Description

[0021] Figure 1 This is a schematic diagram of the high-temperature forging process for alloys.

[0022] Figure 2 The image shows a crack after the end of a high-temperature titanium alloy was forged and cut off. The remaining crack is still up to 5 centimeters deep.

[0023] Figure 3 This is a stress and damage cloud diagram during the alloy forging process. Among them, (a1,b1,c1,d1) is the maximum principal stress, (a2,b2,c2,d2) is the damage factor, (a1,a2) is the β phase region after blanking and forging, (b1,b2) is after upsetting, (c1,c2) ​​is after tetragonal drawing, and (d1,d2) is after octagonal drawing.

[0024] Figure 4 This is a stress cloud diagram of the alloy surface after the improved hammering process, obtained from finite element simulation. Among them, (a1,b1,c1) represents the whole, (a2,b2,c2) represents the cross section, (a1,a2) represents the original forging process after upsetting, (b1,b2) represents the first surface hammering improvement, and (c1,c2) ​​represents the optimized hammering process improvement. It can be seen that the local stress is significantly reduced. Detailed Implementation

[0025] In its specific implementation, this invention proposes a method for suppressing cracking during high-temperature titanium alloy forging, based on finite element simulation and experimental analysis. This method includes the following steps: developing a corresponding simulation test plan according to the actual forging process of high-temperature titanium alloys; conducting numerical simulations to analyze and determine the target areas that need optimization after each upsetting and drawing pass; developing different surface hammering simulation schemes based on the characteristics of different target areas and conducting numerical simulations; comparing the simulation with the original process to evaluate whether surface hammering introduces pressure or alleviates damage in the target area; and iteratively optimizing the surface hammering simulation scheme multiple times to confirm the optimized process scheme.

[0026] The present invention will now be described in further detail with reference to the accompanying drawings and embodiments:

[0027] Example 1

[0028] In this embodiment, forging optimization of a certain type of near-α high-temperature titanium alloy is performed. Based on finite element simulation analysis, target areas containing high surface damage or tensile stress characteristics are selected, and surface hammering is carried out to suppress forging cracking of the high-temperature titanium alloy. The method includes the following steps:

[0029] (1) As Figure 1 As shown, according to the actual forging process of high-titanium alloys, it includes common processes such as billet forging, upsetting, four-sided drawing, and eight-sided drawing. In the entire forging process, it generally includes high-temperature forging in the β phase region, multiple forgings in the upper two-phase region, and final forging in the lower two-phase region. In this embodiment, specific process parameters from the actual process are used, including: deformation temperature, deformation speed, deformation amount, each drawing pass, and drawing hammer spacing. The simulation uses high-temperature flow stress data (JMST, 1039, 35, 2019) that has been corrected for temperature and friction, as proposed by the research group in the early stage.

[0030] (2) In actual high-temperature titanium alloy forging processes, surface cracking can occur in various stages such as billet preparation, upsetting, and drawing. For example... Figure 2 As shown, a crack remains after the end of a high-temperature titanium alloy forging is cut off, and its depth is still more than 5 cm. The grinding work involved in the defect removal process is extremely large. For ton-sized high-temperature titanium alloy ingots, this single process often adds one or two weeks to the production time. To address this process, large-scale finite element simulations of the initial billet preparation and different hot working passes were conducted. The results are shown in [Figure number missing]. Figure 3 .like Figure 3 As shown in (a1,a2), the cloud maps of maximum principal stress and damage factor after billet forging show that high tensile stress is mainly concentrated at the end, while high damage areas are concentrated in the middle part of the billet side surface. The key time periods for the formation of areas with high surface damage or tensile stress characteristics are analyzed sequentially after upsetting, after the first square drawing, and after the octagonal drawing. Figure 3 As shown in (b1,b2), the high-damage area after upsetting is concentrated in the middle bulge area, and the damage varies greatly, with high lateral tensile stress on the end face; as Figure 3 As shown in (c1, c2), after a single square elongation, the high tensile stress is distributed on the two end faces and a pair of side surfaces. The damaged side surfaces are higher than the end faces, but the difference is reduced relative to the upsetting process. Figure 3 As shown in (d1,d2), after octagonal elongation, the high tensile stress region extends from the end face to a local area on the side surface. Furthermore, the high tensile stress characteristic of the end face is significantly higher and more distinct compared to upset and octagonal methods. This is related to... Figure 2 The significant crack formation at the end shown is consistent with the pattern, while the high tensile stress damage area exhibits a strip-like distribution on the side surface of the billet. All of these simulation steps are based on numerical simulations conducted using actual processes, obtaining the key pass characteristics and distribution features of the formation of high damage or tensile stress target characteristic areas.

[0031] (3) Based on the high damage or tensile stress characteristic areas obtained from the finite element simulation in step 2, and according to the actual process window characteristics, the stress or damage generated can be suppressed by surface hammering modification. Depending on the stress concentration and damage generated under the specific process parameters of each pass, various other stress or damage suppression methods can also be adopted, such as micro-rolling of the middle bulge of the side surface after upsetting; hammering the two end faces first after one square drawing to reduce the circumferential tensile stress of the end faces; hammering the local high tensile stress area of ​​the side surface first after eight-sided drawing, then flattening the surface, and finally axial micro-upsetting, with a radial deformation of 0.05% to 1.0% and a deformation rate of 0.005s. -1 ~1.0s -1 .

[0032] (4) Figure 2 As shown, one of the end-face cracking problems found in actual processes is the finite element analysis of the above steps. Considering the short actual processing time window of the alloy, a simulation of surface hammering modification after upsetting is prioritized. Rapid hammering is performed on the bulging area along the side surface of the alloy after upsetting. The results are shown in […]. Figure 4 .like Figure 4 As shown in (b1, b2), the maximum principal stress distribution is obtained after the first surface hammering. The surface hammering process parameters are radial deformation of ~0.5% and deformation rate of 0.1 s. -1 Above, the side surface rotation angle is 22.5°, and the total surface hammering time should be controlled within 30 seconds. (Comparison) Figure 4 (a1, a2) The surface and internal stress distribution characteristics after the original upsetting process show that after implementing the surface hammering scheme, the tensile stress on the bulging side surface is converted into a smaller compressive stress characteristic, which relaxes the uneven distribution of tensile and compressive stress in the billet as a whole. In particular, it significantly reduces the easily cracked areas at both ends and the annular high tensile stress area into some crescent-shaped small areas. Therefore, it can be predicted that the surface hammering scheme can effectively suppress the occurrence of surface cracking.

[0033] (5) Simulations show that while the side surface hammering reduces the surface tensile stress, a certain area of ​​tensile stress often accompanies the hammering area. This tensile stress, combined with the original tensile stress, may cause further surface damage. Furthermore, the hammering time of 30 seconds is still relatively long. To shorten the window time for subsequent surface hammering processes, the parameters of this hammering scheme were adjusted multiple times. The optimized surface hammering results are shown in [see figure]. Figure 4 (c1,c2), the surface hammering process parameters are: radial deformation 0.2%, deformation rate 0.01s. -1With a side surface rotation angle of 22.5°, the surface hammering process can be controlled within 10 seconds. Compared with the results of the first surface hammering, this method yields a smaller area of ​​converted compressive stress on the side surface, a reduced area of ​​associated tensile stress, and further improved uniformity of stress distribution on the surface and inside the billet. The high tensile stress in the easily cracked areas at both ends further degenerates from a crescent-shaped area to a tiny area, and the maximum pressure value is significantly reduced. Therefore, this optimized surface hammering process provides a more sufficient time window for subsequent processing schemes, and the overall stress distribution characteristics of the billet are significantly improved, effectively suppressing the occurrence of surface cracks.

[0034] The results show that the method proposed in this invention, which combines actual working conditions and finite element simulation analysis to suppress forging cracks in high-temperature titanium alloys, provides a new technical approach combining simulation and experimentation to address issues such as low yield due to surface cracking during the forging process of difficult-to-deform materials like high-temperature titanium alloys, significant extension of processing cycle due to interruption of the forging process caused by damage removal, and microstructure deterioration caused by changes in the hot working path.

Claims

1. A method for suppressing forging cracks in high-temperature titanium alloys by combining finite element simulation analysis, characterized in that, Combining actual high-temperature titanium alloy processing technology and numerical simulation predictions, a target area and time are selected during the forging process to perform surface hammering on the ingot, which inhibits surface cracking, and includes the following steps: (1) Based on the actual forging process of high-temperature titanium alloy, formulate a corresponding simulation test plan; (2) Conduct finite element numerical simulation to analyze and determine the target area that needs to be optimized after each upsetting pass; (3) Based on the characteristics of different target areas, formulate different surface hammering simulation schemes and carry out numerical simulations; (4) Compare with the original process simulation to evaluate whether pressure is introduced into the target area or the damage is alleviated after surface hammering; (5) Iterate and optimize the surface hammering simulation scheme multiple times to confirm the optimized process scheme; In step (2), the finite element numerical simulation based on the original process mainly selects the target area containing areas with high surface damage or tensile stress characteristics, and determines the key time period for the formation of the target area; In step (3), based on the common target areas and formation time periods in the upsetting and drawing process, the surface hammering simulation scheme mainly includes: (1) after upsetting, the middle of the side surface is slightly rolled; (2) in the four-sided and eight-sided drawing passes, according to the simulation results, after 1 to 3 passes, the high tensile stress area of ​​the side surface is hammered; (3) after the drawing is completed, the local high tensile stress area is hammered first, then the side surface is slightly rolled to flatten the surface, and finally the axial micro-upsetting is performed.

2. The method for suppressing forging cracks in high-temperature titanium alloys by combining finite element simulation analysis as described in claim 1, characterized in that, In step (1), the actual forging process of high-temperature titanium alloy includes billet opening, upsetting, drawing out of the square and drawing out of the octagon; the simulation test scheme restores the specific parameters in the actual process, including: deformation temperature, deformation speed, deformation amount, each drawing pass, drawing hammer spacing and billet flipping form.

3. The method for suppressing forging cracks in high-temperature titanium alloys by combining finite element simulation analysis as described in claim 1, characterized in that, In the finite element numerical simulation, an alloy constitutive model optimized by temperature and friction correction is adopted.

4. The method for suppressing forging cracks in high-temperature titanium alloys by combining finite element simulation analysis as described in claim 1, characterized in that, In step (4), the surface hammering simulation schemes selected for different target areas and formation times are compared and analyzed to see whether they reduce tensile stress or damage value.

5. The method for suppressing forging cracks in high-temperature titanium alloys by combining finite element simulation analysis as described in claim 1, characterized in that, In step (5), based on the actual process window and key pass requirements of the alloy, the combination of surface hammering simulation schemes for various target areas is selected and the parameters are fine-tuned. Feasibility schemes are iteratively optimized and then verified and evaluated.

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