Forging process of high-strength stainless steel forge piece

Abstract

The invention discloses a high-strength stainless steel forge piece forging process. The process comprises the following steps of graded heating, wherein forging temperature parameters are set in a refined mode according to the mark and component characteristics of stainless steel; dynamic forging deformation control is conducted, specifically, staged rolling reduction gradient design is adopted, rolling reduction in the initial upsetting stage is distributed according to small, large and small, a radial upsetting and axial drawing composite technology is adopted in the drawing stage according to the length-diameter ratio, the forging ratio of the flange part is larger than or equal to 2.5, and the forging ratio of the rod part is larger than or equal to 2.0; carrying out fine forging post-treatment; and simulating and optimizing the digital twinning process. The method has the beneficial effects that through deep integration of simulation, monitoring and regulation, an industrial mass production solution is provided for the high-strength stainless steel forgings, and the method has remarkable technical innovation and industrial application value.

Description

Technical Field

[0001] This invention relates to the field of stainless steel forging technology, and in particular to a forging process for high-strength stainless steel forgings. Background Technology

[0002] High-strength stainless steel forgings are widely used in nuclear power, deep-sea equipment, high-end chemical industry and other fields due to their excellent mechanical properties and corrosion resistance. Their manufacturing process has strict requirements for the uniformity of structure, strength and corrosion resistance.

[0003] The existing forging process has the following defects:

[0004] The temperature control is crude: the heating parameters are not subdivided according to the stainless steel grade and composition. For example, the initial forging temperature of 1150℃ is uniformly used for austenitic stainless steel, which leads to the large deformation resistance of Mo-containing grades such as 316L due to insufficient temperature, and the grain coarsening of 310S due to overheating.

[0005] Fixed deformation parameters: Relying on manual experience to set the reduction amount, lacking dynamic adjustment, large forgings are prone to internal porosity due to uneven deformation;

[0006] Post-forging treatment is limited: natural air cooling or fixed annealing processes are used. Martensitic stainless steel exhibits residual stresses as high as 280 MPa, while duplex steel suffers from insufficient cooling rates leading to Cr... 23 C6 grain boundary precipitation reduces corrosion resistance by 40%;

[0007] Low level of digitalization: No process simulation optimization, relying on trial and error for development, long cycle, and batch pass rate of only 82%.

[0008] As high-end equipment develops towards larger scale and higher parameters, there is an urgent need for a forging process that integrates precise temperature control, dynamic deformation regulation and digital optimization to solve the problems of "poor temperature adaptability, insufficient microstructure uniformity and low performance stability" in traditional technologies, and to meet the high-performance manufacturing requirements of high-strength stainless steel forgings. Summary of the Invention

[0009] The main technical problem solved by this invention is to provide a forging process for high-strength stainless steel forgings, thereby solving one or more of the problems in the prior art.

[0010] To solve the above-mentioned technical problems, the present invention adopts a technical solution as follows: a forging process for high-strength stainless steel forgings, the innovation of which lies in the following steps:

[0011] (1) Graded heating: The forging temperature parameters are refined according to the grade and composition characteristics of the stainless steel, including:

[0012] a: Martensitic stainless steel is classified into low carbon (C≤0.15%) and high carbon (C≥0.4%) according to its carbon content. The final forging temperature of low carbon martensitic stainless steel is controlled at 800-850℃, and the final forging temperature of high carbon martensitic stainless steel is controlled at 850-900℃.

[0013] b: Austenitic stainless steel is graded according to the content of alloying elements (Cr, Ni, Mo). The initial forging temperature of grade 304 / 321 is 1150-1170℃, that of grade 316L is 1160-1180℃, and that of grade 310S is 1180-1200℃.

[0014] (2) Dynamic forging deformation control: A phased reduction gradient design is adopted. The reduction in the initial upsetting stage is distributed in the order of "small → large → small" (20% for the first time, 40% for the middle, and 30% for the last time). In the elongation stage, a composite process of "radial upsetting + axial elongation" is adopted according to the length-to-diameter ratio. The forging ratio of the flange part is ≥2.5, and the forging ratio of the rod part is ≥2.0.

[0015] (3) Refined post-forging treatment:

[0016] a: Martensitic stainless steel is annealed in a furnace within 8 hours after forging, with an annealing temperature of 680-720℃ and a holding time calculated based on the thickness of the forging (2-3 min / mm). After furnace cooling to 500℃, it is then air-cooled.

[0017] b: Ferritic-austenitic stainless steel is water-cooled rapidly after forging, with the cooling rate controlled at 30-50℃ / min, and then cooled to below 200℃ before being air-cooled out of the water.

[0018] c: Large forgings weighing >500kg undergo intermediate softening treatment at 700-750℃ for 1 hour after the 2nd-3rd heating.

[0019] (4) Digital twin process simulation optimization: Before step (1), the forging process is simulated by a digital twin model. The model includes the three-dimensional geometric parameters of the forging, the material constitutive equation and the equipment dynamics data. It simulates the stress distribution and deformation under different process parameters and outputs the optimized initial forging temperature, reduction and pass allocation scheme. The simulation error is ≤ ±3%.

[0020] In some implementations, in step (1), the graded heating is achieved through an AI temperature control system, which includes:

[0021] Distributed infrared temperature measurement array (≥3 sensors, sampling frequency 1Hz) to collect the surface temperature field of forgings in real time;

[0022] The data processing unit has a built-in stainless steel grade-temperature sensitivity model to dynamically calculate temperature deviation;

[0023] The heating control module adjusts the furnace temperature according to the deviation, so that the actual temperature fluctuates with the target temperature by ≤±5℃.

[0024] In some implementations, in step (2), online monitoring of microstructure is added after each forging pass: the surface grain size is detected by laser confocal microscopy. If the martensitic stainless steel grains are >30μm or the austenitic stainless steel grains are >50μm, the reduction rate of the next forging pass is increased by 10%-15% until the grain size is restored to within the threshold.

[0025] In some embodiments, in step (3), for forgings that are welded or forged in a high-hydrogen environment, a dehydrogenation-isothermal composite treatment is added before conventional annealing: first, dehydrogenation is carried out at 300-350℃ for 2 hours, then the temperature is raised to 680℃ and held isothermally for 1 hour, and then the furnace is cooled to 500℃ and air-cooled, with the residual hydrogen content controlled to ≤2ppm.

[0026] In some embodiments, in step (3), the rapid cooling process employs a gradient cooling medium: ferritic-austenitic stainless steel is first sprayed with 80°C hot water (cooling rate 50°C / min) to 600°C, then switched to 25°C cold water (cooling rate 30°C / min) to 200°C. This dual-medium synergistic control helps prevent Cr from accumulating. 23 C6 grain boundary precipitation.

[0027] In some implementations, in step (2), the "last heat deformation amount" meets the requirement of cumulative deformation amount ≥ 60%, and the single reduction rate is dynamically allocated according to "30%-40% in the high temperature stage and 25%-30% in the medium temperature stage", so as to break the casting structure while avoiding overheating and cracking.

[0028] The beneficial effects of this invention are: a comprehensive leap in performance: grain refinement by 30%-40%, tensile strength increase by 15%-39%, and corrosion resistance improvement by more than 60%;

[0029] Enhanced process stability: Temperature fluctuations decreased from ±20℃ to ±5℃, residual stress decreased by 50%-60%, and batch pass rate increased from 82% to 99%.

[0030] Leading level of intelligence: Digital twins and AI control enable unmanned operation throughout the entire process, which is suitable for the stringent requirements of forging consistency in high-end fields such as nuclear power and deep-sea equipment.

[0031] This invention provides an industrial mass production solution for high-strength stainless steel forgings through the deep integration of simulation, monitoring, and control, and has significant technological innovation and industrial application value. Attached Figure Description

[0032] To more clearly illustrate the technical solutions in the embodiments of the present invention, the accompanying drawings used in the description of the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort, wherein:

[0033] Figure 1 This is a flowchart of a high-strength stainless steel forging process according to the present invention. Detailed Implementation

[0034] The technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only a part of the embodiments of the present invention, and not all of them. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0035] like Figure 1 As shown, this invention solves the problems of poor temperature adaptability, rough deformation control, and insufficient quality stability in traditional processes through a complete process innovation involving digital simulation optimization, intelligent process control, and refined microstructure regulation. The core components and complete process steps are described in detail below:

[0036] 1. Essential Constituent Elements

[0037] (1) Digital Twin Simulation System

[0038] This system provides pre-optimization solutions for the forging process, and its core components include:

[0039] 3D geometric modeling module: Import CAD models of forgings (such as flanges, shafts and other complex structures), automatically generate meshes (mesh size ≤ 5mm) to accurately simulate deformation areas;

[0040] Material Constitutive Database: Built-in thermodynamic parameters (such as coefficient of thermal expansion and flow stress curves) for 200+ stainless steel grades, covering the influence of alloying elements such as Cr / Ni / Mo on plasticity;

[0041] Finite element analysis unit: developed based on the DEFORM-3D platform, coupled with equipment dynamic data (such as press tonnage and anvil speed), simulates stress distribution (error ≤ ±3%), strain path and grain growth trend under different process parameters, and outputs optimized initial forging temperature, reduction amount and pass allocation scheme.

[0042] (2) AI Temperature Control System

[0043] The precise dynamic control of forging temperature consists of the following components:

[0044] Distributed infrared temperature measurement array: contains ≥3 high-precision sensors (wavelength 8-14μm, temperature measurement range 500-1300℃), sampling frequency 1Hz, covering the upper / middle / lower regions of the forging, and constructing the surface temperature field distribution;

[0045] Data processing unit: Built-in "grade-temperature sensitivity model", such as the "carbon content-final forging temperature correction coefficient" algorithm for martensitic stainless steel, to calculate the deviation between the actual temperature and the target value in real time;

[0046] Heating control module: PID closed-loop control is adopted. By adjusting the gas flow or electric heating power, the furnace temperature fluctuation is kept ≤±5℃, ensuring that the initial forging temperature deviation of austenitic stainless steel does not exceed ±10℃.

[0047] (3) Microstructure Online Monitoring Unit

[0048] Real-time feedback of grain size during forging includes:

[0049] Laser confocal microscope: integrated into the forging production line, it performs non-destructive testing on the surface of forgings during the interval between passes (testing depth ≥200μm, resolution 0.1μm);

[0050] Grain identification algorithm: Automatically counts grain size distribution. When the grain size of martensitic stainless steel is >30μm or the grain size of austenitic stainless steel is >50μm, a reduction rate adjustment command is triggered.

[0051] Feedback control module: In conjunction with the forging equipment, it increases the reduction rate of the next forging pass by 10%-15% (e.g., from 30% to 45%) until the grain size returns to the target range.

[0052] (4) Composite forging post-processing device

[0053] Configurations are available to meet the specific requirements of different types of stainless steel:

[0054] Gradient cooling system: dual-medium storage tank (hot water 80±5℃ / cold water 25±2℃), spray zone switching via servo valve, cooling rate continuously adjustable (30-50℃ / min), equipped with cooling curve recorder (sampling interval 1s);

[0055] Dehydrogenation-isothermal annealing furnace: zoned temperature control (temperature difference ≤ ±5℃), supports stepped heating (e.g., 300→680℃), holding time is automatically calculated according to the thickness of the forging (2-3min / mm), built-in hydrogen detector (accuracy 0.1ppm);

[0056] Intermediate softening treatment module: For forgings weighing >500kg, perform annealing at 700-750℃ for 1h after the 2nd-3rd heat treatment, and control the hardness to ≤200HBW.

[0057] 2. Complete process steps

[0058] Step 1: Digital Twin Simulation Optimization

[0059] Input a 3D model of the forging (e.g.) Flange), material grade (e.g., 316L) and performance indicators (tensile strength ≥ 650 MPa, grain size ≥ grade 6);

[0060] The simulation model uses the constitutive equations of 316L (strain rate 0.1-10s). -1 The simulation was performed using flow stress data to simulate the deformation effect at initial forging temperatures of 1150℃ / 1180℃ and reduction rates of 30% / 40%. The optimal solution was output: initial forging temperature of 1170℃, upsetting reduction rate of 40%, drawing reduction rate of 35%, 3 passes, and simulation error ≤ ±3%.

[0061] Step 2: Staged heating and AI temperature control

[0062] Based on the simulation results, the AI ​​system starts the heating furnace: 316L austenitic stainless steel is heated to 1170℃ at a rate of 5℃ / min, and the temperature field is monitored in real time by a distributed infrared array.

[0063] If the local temperature deviation is >5℃ (e.g., 1160℃ at the edge / 1180℃ at the center), the PID module adjusts the furnace power and corrects the deviation to ≤±5℃ within 30 seconds.

[0064] Step 3: Dynamic Forging and Microscopic Feedback

[0065] First upsetting: reduction rate 40% (forging height reduced from 500mm to 300mm), laser confocal microscopy detection grain size 45μm (meets standard);

[0066] Second pass elongation: reduction rate 35%, grain size increased to 52μm (exceeding the limit), the system automatically increased the reduction rate of the third pass from 30% to 45%;

[0067] After final forging, the grain size recovered to 40μm, with a cumulative deformation of 65%.

[0068] Step 4: Post-forging treatment of composite forging

[0069] The forgings were transferred to a gradient cooling system, first cooled to 600°C by 80°C hot water spray (50°C / min), and then cooled to 200°C by 25°C cold water (30°C / min). The cooling curve was recorded throughout the process.

[0070] After cooling, dehydrogenation annealing was performed (320℃×2h) to reduce the residual hydrogen content to ≤2ppm.

[0071] Examples and Comparative Examples

[0072] The effectiveness of the present invention is verified through three examples (covering martensitic, austenitic, and duplex stainless steels) and one comparative example (traditional process). The testing standards are in accordance with GB / T 1220-2021 "Stainless Steel Bars".

[0073] 1. Example 1: Martensitic Stainless Steel Forgings

[0074] Process parameters:

[0075] Staged heating: initial forging 1080℃ (for high carbon martensite), final forging 880℃, AI temperature control fluctuation ±3℃;

[0076] Deformation control: 4 passes of digital twin, compression rate 20%→40%→35%→32%, cumulative deformation 68%;

[0077] Post-forging treatment: Dehydrogenation-isothermal composite treatment (320℃×2h+680℃×3h), followed by furnace cooling to 500℃ and air cooling.

[0078] Performance results: Grain size 25μm, hardness 210HBW, residual stress 120MPa, impact toughness 85J / cm 2 .

[0079] 2. Example 2: Austenitic stainless steel forgings

[0080] Process parameters:

[0081] Staged heating: initial forging 1170℃ (optimized temperature for 316L), final forging 950℃, with real-time monitoring via infrared array;

[0082] Deformation control: Microscopic feedback adjusts the reduction rate (45% correction), stabilizing the grain size at 40μm;

[0083] Post-forging treatment: gradient cooling (80℃ hot water → 25℃ cold water), cooling rate 40℃ / min.

[0084] Performance results: tensile strength 680MPa, yield strength 320MPa, salt spray corrosion resistance 0.012mm / year (ASTM B117 standard, 5000h), no cracks in intergranular corrosion test (ASTM A262 E method).

[0085] 3. Example 3: Duplex Stainless Steel Forgings

[0086] Process parameters:

[0087] Staged heating: initial forging 1150℃, final forging 900℃, with the AI ​​system dynamically adjusting the furnace temperature;

[0088] Deformation control: Intermediate softening treatment (720℃×1h), hardness reduced to 190HBW;

[0089] Post-forging treatment: rapid cooling (35℃ / min) + annealing (700℃×2h), ferrite / austenite ratio 50:50.

[0090] Performance results: tensile strength 820MPa, yield strength 650MPa, elongation 25%, pitting resistance equivalent (PREN=Cr+3.3Mo+16N) 35.

[0091] 4. Comparative Example

[0092] Process parameters:

[0093] Temperature control: Austenitic stainless steel is uniformly forged at 1150℃, without further subdivision;

[0094] Deformation control: Single compression rate 25%, no dynamic adjustment, cumulative deformation 45%;

[0095] Post-forging treatment: natural air cooling, annealing temperature 700℃ (holding time fixed at 2h).

[0096] Performance results: grain size 75μm, tensile strength 590MPa, residual stress 280MPa, salt spray corrosion resistance 0.035mm / year.

[0097] 5. Performance Comparison Table

[0098]

[0099] The principle of this technical solution is as follows:

[0100] Digital pre-optimization: By coupling material constitutive model and equipment dynamics through digital twin model, the traditional "trial and error method" is transformed into "data-driven design", shortening the process development cycle by 40%;

[0101] Temperature-tissue closed-loop control: The AI ​​temperature control system achieves temperature control with an accuracy of ±5℃, and dynamically adjusts the compression rate based on microscopic monitoring feedback, thus solving the black box problem of "macroscopic parameters - microscopic performance";

[0102] Multi-physics field coordinated regulation: Gradient cooling controls Cr through dual-medium coordinated regulation 23 C6 precipitation and dehydrogenation-isothermal treatment reduce residual hydrogen to ≤2ppm, simultaneously improving strength and corrosion resistance.

[0103] The advantages of this technical solution are:

[0104] Overall performance improvement: grain refinement by 30%-40%, tensile strength increase by 15%-39%, and corrosion resistance improvement by over 60%;

[0105] Enhanced process stability: Temperature fluctuations decreased from ±20℃ to ±5℃, residual stress decreased by 50%-60%, and batch pass rate increased from 82% to 99%.

[0106] Leading level of intelligence: Digital twins and AI control enable unmanned operation throughout the entire process, which is suitable for the stringent requirements of forging consistency in high-end fields such as nuclear power and deep-sea equipment.

[0107] This invention provides an industrial mass production solution for high-strength stainless steel forgings through the deep integration of simulation, monitoring, and control, and has significant technological innovation and industrial application value.

[0108] The above description is merely an embodiment of the present invention and does not limit the patent scope of the present invention. Any equivalent structural or procedural transformations made based on the content of the present invention specification, or direct or indirect applications in other related technical fields, are similarly included within the patent protection scope of the present invention.

Claims

1. A forging process for high-strength stainless steel forgings, characterized in that: Includes the following steps: (1) Graded heating: The forging temperature parameters are refined according to the grade and composition characteristics of the stainless steel, including: a: Martensitic stainless steel is divided into low carbon and high carbon according to carbon content. The final forging temperature of low carbon martensitic stainless steel is controlled at 800-850℃, and the final forging temperature of high carbon martensitic stainless steel is controlled at 850-900℃. b: Austenitic stainless steel is graded according to the content of alloying elements. The initial forging temperature of grade 304 / 321 is 1150-1170℃, that of grade 316L is 1160-1180℃, and that of grade 310S is 1180-1200℃. (2) Dynamic forging deformation control: A phased reduction gradient design is adopted. The initial upsetting stage reduction is distributed in small, large, and small. The elongation stage adopts a composite process of radial upsetting and axial elongation according to the length-to-diameter ratio. The forging ratio of the flange part is ≥2.5, and the forging ratio of the rod part is ≥2.

0. (3) Refined post-forging treatment: a: Martensitic stainless steel is annealed in a furnace within 8 hours after forging, with an annealing temperature of 680-720℃. The holding time is calculated based on the thickness of the forging. After furnace cooling to 500℃, it is air-cooled. b: Ferritic-austenitic stainless steel is water-cooled rapidly after forging, with the cooling rate controlled at 30-50℃ / min, and then cooled to below 200℃ before being air-cooled out of the water. c: Large forgings weighing >500kg undergo intermediate softening treatment at 700-750℃ for 1 hour after the 2nd-3rd heating. (4) Digital twin process simulation optimization: Before step (1), the forging process is simulated by a digital twin model. The model includes the three-dimensional geometric parameters of the forging, the material constitutive equation and the equipment dynamics data. It simulates the stress distribution and deformation under different process parameters and outputs the optimized initial forging temperature, reduction and pass allocation scheme. The simulation error is ≤ ±3%.

2. The forging process for high-strength stainless steel forgings according to claim 1, characterized in that: In step (1), the graded heating is achieved through an AI temperature control system, which includes: Distributed infrared temperature measurement array to collect the surface temperature field of forgings in real time; The data processing unit has a built-in stainless steel grade-temperature sensitivity model to dynamically calculate temperature deviation; The heating control module adjusts the furnace temperature according to the deviation, so that the actual temperature fluctuates with the target temperature by ≤±5℃.

3. The forging process for high-strength stainless steel forgings according to claim 1, characterized in that: In step (2), online monitoring of microstructure is added after each forging pass: the surface grain size is detected by laser confocal microscopy. If the martensitic stainless steel grains are >30μm or the austenitic stainless steel grains are >50μm, the reduction rate of the next forging pass is increased by 10%-15% until the grain size is restored to within the threshold.

4. The forging process for high-strength stainless steel forgings according to claim 1, characterized in that: In step (3), for forgings that are welded or forged in a high-hydrogen environment, a dehydrogenation-isothermal composite treatment is added before conventional annealing: first, dehydrogenation is carried out at 300-350℃ for 2 hours, then the temperature is raised to 680℃ and held isothermally for 1 hour, and then the furnace is cooled to 500℃ and air-cooled. The residual hydrogen content is controlled to be ≤2ppm.

5. The forging process for high-strength stainless steel forgings according to claim 1, characterized in that: In step (3), the rapid cooling process uses a gradient cooling medium: ferritic-austenitic stainless steel is first sprayed with 80℃ hot water (cooling rate 50℃ / min) to 600℃, and then switched to 25℃ cold water to 200℃. This dual-medium synergistic control prevents Cr from being discharged. 23 C6 grain boundary precipitation.

6. The forging process for high-strength stainless steel forgings according to claim 1, characterized in that: In step (2), the "last heat deformation amount" meets the requirement of cumulative deformation amount ≥ 60%, and the single reduction rate is dynamically distributed according to "30%-40% in the high temperature stage and 25%-30% in the medium temperature stage" to break the casting structure while avoiding overheating and cracking.

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