A method for controlling the microstructure and properties of stepped TC32 titanium alloy free forgings

Abstract

This invention belongs to the field of forging hot working and relates to a method for controlling the microstructure and properties of stepped TC32 titanium alloy free forgings. The method includes: forging: using a high-speed forging machine or free forging hammer for two-phase forging as needed, upsetting or drawing and shaping the bar stock, and performing single or multiple drawing operations according to the forging dimensions to obtain the final forging; heat treatment: performing quasi-β annealing or double annealing according to the microstructure requirements of the forging, and using air cooling or wind cooling as the cooling method.

Description

Technical Field

[0001] This invention belongs to the field of forging hot working and relates to a method for controlling the microstructure and properties of stepped TC32 titanium alloy free forgings. Background Technology

[0002] TC32 titanium alloy possesses comprehensive high-performance characteristics such as medium-to-high strength, high plasticity, high toughness, fatigue resistance, and damage tolerance. It also boasts low cost and simple processing, gradually becoming a new mainstay material for aircraft structural components. The main challenges are as follows: 1. As a new mainstay material, there is insufficient experience in controlling and understanding the microstructure and properties of TC32 titanium alloy forgings, requiring further exploration. 2. The forging heating temperature and time, deformation amount, and other process parameters for TC32 stepped forgings need further quantification and strict control. 3. The heating temperature and time, cooling method, and other process parameters for quasi-β annealing and double annealing heat treatment of TC32 stepped forgings need specific quantification and strict control to improve the forging yield. Summary of the Invention

[0003] The technical problem to be solved by this invention is to propose process parameters for forging, rough machining, and heat treatment of TC32 titanium alloy stepped forgings in the two-phase region, and to solve the matching problem between specific control points such as forging temperature, forging holding coefficient, forging method, forging deformation amount, forging deformation process control, rough machining equivalent thickness requirements, quasi-β annealing and double annealing heat treatment regimes, and heat treatment cooling method and the microstructure and properties of the forgings, so as to achieve batch-quality and stable delivery of forgings.

[0004] Technical solution:

[0005] A method for controlling the microstructure and properties of stepped TC32 titanium alloy free forgings is provided, including:

[0006] Forging: Two-phase forging is carried out using a high-speed forging machine or free forging hammer as needed. The bar stock is upsetting or drawing and shaping. Depending on the size of the forging, it is drawn in one or more passes to obtain the final forging.

[0007] Heat treatment: Quasi-β annealing or double annealing is performed according to the microstructure requirements of the forging, and air cooling or wind cooling is adopted.

[0008] Furthermore, for forgings with complex structures, the method further includes the following steps before heat treatment:

[0009] Rough machining: Based on the part dimensions, the forging is rough machined while ensuring the machining allowance and forging standard requirements to obtain a rough machined part, thereby reducing the equivalent thickness of the forging; the equivalent thickness of the forging after rough machining must meet the requirement of 50mm to 200mm.

[0010] Furthermore, the forging temperature is selected at (30-50)℃ below the phase transformation point. The heat preservation coefficient for cold material heating is calculated at 0.8 min / mm, and the heat preservation coefficient for hot material return to the furnace is calculated at 0.5 min / mm. Hot material return to the furnace is preferred for heating between forging cycles. Cold material heating is adopted when grinding and removing damage is required depending on the damage to the forging. Air cooling is adopted after forging.

[0011] Furthermore, multi-stage material drawing and elongation includes:

[0012] The first heat uses bar stock for upsetting or drawing and shaping. The width and thickness of the square billet obtained after shaping meet the maximum cross-sectional dimensions of the forging. Subsequent heats involve one or more heats of material drawing.

[0013] The maximum deformation per single firing is ≤35%. During drawing, the feed amount per hammer is 1 / 3 to 1 / 2 of the thickness to be pressed, and the deformation per hammer is 10% to 15%.

[0014] Furthermore, the specific heat treatment process for quasi-β annealing is as follows:

[0015] The first stage of quasi-β annealing: The furnace is heated to 35°C below the β phase transformation point and held for ≥10 min. The forgings are then loaded into the furnace and heated to 35°C below the β phase transformation point again, held for 150±15 min, and then heated to 15°C above the phase transformation point in 40-50 min increments. The heating coefficient is 0.35 min / mm. After being removed from the furnace, the forgings are air-cooled. The forgings are placed upright on their sides during loading and cooling, with a spacing of ≥100 mm between them. Thermocouples are used to monitor the temperature at the largest and smallest cross-sections of the forgings throughout the entire first stage of quasi-β annealing.

[0016] Second stage of quasi-β annealing: Load the furnace at the set temperature, then raise the temperature to 565℃, hold for 360±15min, and then air-cool after removing from the furnace.

[0017] Furthermore, the specific heat treatment process for double annealing is as follows:

[0018] First annealing: Preheat furnace, heat to 875℃, heating coefficient is 0.6~0.8min / mm, then air cool or wind cool.

[0019] Secondary annealing: Load the furnace at the specified temperature, raise the temperature to 550℃, hold for 6 hours, and then air-cool or blow-cool.

[0020] Furthermore, when the equivalent thickness of the double-annealed forging is ≥125mm, air cooling is required to improve the microstructure and properties of the forging. When air cooling is used, the spacing between the forgings should be ≥500mm, and the distance from the fan should be 800mm~1500mm.

[0021] Furthermore, for double-annealed forgings with an equivalent thickness of <125mm, air cooling is used; for quasi-β-annealed forgings, air cooling is used.

[0022] Beneficial effects: This study proposes process parameters for forging, rough machining, and heat treatment of TC32 titanium alloy stepped forgings in the two-phase region. It solves the matching problem between specific control points such as forging temperature, forging holding coefficient, forging method, forging deformation amount, forging deformation process control, rough machining equivalent thickness requirements, quasi-β annealing and double annealing heat treatment regimes, and heat treatment cooling methods and the microstructure and properties of forgings, so as to achieve batch-wise qualified and stable delivery of forgings. Attached Figure Description

[0023] Figure 1a This is a simplified structural diagram of a forging in a quasi-β-annealed heat-treated state according to an embodiment of the present invention.

[0024] Figure 1b This is a simplified structural diagram of a forging in a double-annealed heat-treated state according to an embodiment of the present invention.

[0025] Figure 2 This is a simplified diagram of the forging deformation process of the present invention.

[0026] Figure 3 This is a simplified diagram of the roughing process of the present invention.

[0027] Figure 4 This is a simplified diagram of the loading and cooling process for the quasi-β annealing heat treatment of the forgings according to the present invention.

[0028] Figure 5 This is a simplified diagram of the cooling process after double annealing heat treatment of the forgings according to the present invention. Detailed Implementation

[0029] This invention proposes process parameters for forging, rough machining, and heat treatment of TC32 titanium alloy stepped forgings in the two-phase region, solving the problem of matching process parameters, control points, and the microstructure and properties of forgings. The specific steps are as follows.

[0030] Example 1

[0031] This invention provides a method for controlling the microstructure and properties of stepped TC32 titanium alloy free forgings, forging as follows: Figure 3 The process for the forging shown is as follows: Figure 2 As shown, the method includes:

[0032] Step 1: Forging

[0033] Two-phase forging is performed using a high-speed forging mill or free forging hammer. The forging temperature is (30-50)℃ below the phase transformation point. The holding coefficient for cold material heating is calculated as 0.8 min / mm, and the holding coefficient for hot material reheating is calculated as 0.5 min / mm. Hot material reheating is preferred between forging passes. Cold material heating is used when grinding and removing defects are required due to the forging's damage. The first forging pass uses bar stock for upsetting or drawing and shaping. After shaping, the width and thickness dimensions meet the maximum cross-sectional dimensions of the forging. Subsequent passes involve multi-pass drawing and shaping. The maximum deformation per forging pass is ≤35%. During drawing, the feed per hammer is 1 / 3 to 1 / 2 of the thickness to be pressed, and the deformation per hammer is 10% to 15%. After forging, air cooling is used to obtain the final forging. Figure 1a ).

[0034] Step 2: Rough machining

[0035] Based on the part dimensions, and while ensuring machining allowance and forging standard requirements, the forging is rough-machined to obtain a rough-machined part, thereby reducing the equivalent thickness of the forging.

[0036] Preferably, the equivalent thickness of the forging after rough machining should meet the requirement of 50mm to 200mm. Figure 3 ).

[0037] Step 3: Heat treatment

[0038] Pre-β annealing, followed by air cooling after annealing.

[0039] The specific heat treatment process for quasi-β annealing is as follows:

[0040] The first stage of quasi-β annealing: Heat the furnace in an empty oven to 35°C below the β phase transformation point, hold for ≥10 min, load the forging, then heat again to 35°C below the β phase transformation point, hold for 150±15 min, then heat to 15°C above the phase transformation point in 40-50 min increments (heating coefficient 0.35 min / mm), and air cool after removal from the furnace. Figure 4 );

[0041] Pre-β annealing stage 2: Load the furnace at the set temperature, then raise the temperature to 565℃, hold for 360±15 min, and air cool after removing from the furnace. Figure 4 ).

[0042] Preferably, the forgings are placed upright during loading into the furnace and cooling, with a spacing of ≥100mm between forgings. During the entire first stage of quasi-β annealing, thermocouples are used to monitor the temperature at the maximum and minimum cross-sections of the forgings.

[0043] Example 2

[0044] This invention provides a method for controlling the microstructure and properties of stepped TC32 titanium alloy free forgings. The forging method includes:

[0045] Step 1: Forging

[0046] Two-phase forging is performed using a high-speed forging mill or free forging hammer. The forging temperature is (30-50)℃ below the phase transformation point. The holding coefficient for cold material heating is calculated as 0.8 min / mm, and the holding coefficient for hot material reheating is calculated as 0.5 min / mm. Hot material reheating is preferred between forging passes. Cold material heating is used when grinding and removing defects are necessary due to the forging's damage. The first forging pass uses bar stock for upsetting or drawing and shaping. After shaping, the width and thickness dimensions meet the maximum cross-sectional dimensions of the forging. Subsequent forging passes involve one-pass drawing of the material. The maximum deformation per forging pass is ≤35%. During drawing, the feed per hammer is 1 / 3 to 1 / 2 of the thickness to be pressed, and the deformation per hammer is 10% to 15%. After forging, air cooling is used to obtain the final forging. Figure 1b ).

[0047] Step 2: Heat treatment

[0048] Double annealing

[0049] The specific heat treatment process for double annealing is as follows:

[0050] First annealing: Preheat furnace, heat to 875℃, heating coefficient is 0.6~0.8min / mm, then air cool or wind cool.

[0051] Secondary annealing: Load the furnace at the specified temperature, raise the temperature to 550℃, hold for 6 hours, and then air-cool or blow-cool.

[0052] Preferably, when the equivalent thickness of the double-annealed forging is ≥125mm, air cooling should be used to improve the microstructure and properties of the forging. During air cooling, the spacing between forgings should be ≥500mm, and the distance from the fan should be 800mm~1500mm. For specific placement methods, see [link to relevant documentation]. Figure 5 .

[0053] Example 3

[0054] Free forgings for a certain type of machine beam, such as Figure 1a As shown, the bar material is TC32, and the specifications are... The forging outline dimensions are 1350×435×310 mm. The design methods for forging, rough machining, and heat treatment are as follows.

[0055] Step 1: Forging

[0056] The forging process involves heating at a phase transformation point of (30–50)℃ and performing 4–6 forging passes. The deformation amount in each pass ranges from 15% to 35%. During the drawing process, the feed amount per hammer is 1 / 3 to 1 / 2 of the thickness to be pressed, and the deformation amount per hammer is 10% to 15%. The cooling method after forging is air cooling.

[0057] Step 2: Rough machining

[0058] The forging is rough-machined according to the part size and forging standard requirements to obtain a rough-machined part with an equivalent thickness of ~125mm.

[0059] Step 3: Heat treatment

[0060] Quasi-β annealing is adopted, and the specific heat treatment process is as follows:

[0061] First stage of quasi-β annealing: Heat the furnace in an empty furnace to 35°C below the β phase transformation point, hold for ≥10 min, load the forging, heat again to 35°C below the β phase transformation point, hold for 150±15 min, then heat to 13°C above the phase transformation point in 40 min, and hold. After baking, spread them out to cool in the air.

[0062] Second stage of quasi-β annealing: Load the furnace at the set temperature, then raise the temperature to 565℃, hold for 360±15min, and then air-cool after removing from the furnace.

[0063] After implementation, this invention proposes process parameters for forging, rough machining, and heat treatment of TC32 titanium alloy stepped forgings in the two-phase region. It solves the matching problem between specific control points such as forging temperature, forging holding coefficient, forging method, forging deformation amount, forging deformation process control, rough machining equivalent thickness requirements, quasi-β annealing and double annealing heat treatment regimes, and heat treatment cooling methods and the microstructure and properties of forgings, so as to achieve batch-wise qualified and stable delivery of forgings.

Claims

1. A method for controlling the microstructure and properties of stepped TC32 titanium alloy free forgings, characterized in that, include: Forging: Two-phase forging is carried out using a high-speed forging machine or free forging hammer as needed. The bar stock is upsetting or drawing and shaping. Depending on the size of the forging, it is drawn in one or more passes to obtain the final forging. Rough machining: Based on the part dimensions, the forging is rough machined while ensuring machining allowance and forging standard requirements to obtain a rough-machined part, thereby reducing the equivalent thickness of the forging; the equivalent thickness of the forging after rough machining must meet the requirement of 50mm to 200mm. Heat treatment: Quasi-β annealing is performed according to the microstructure requirements of the forging, and air cooling is adopted. The specific heat treatment process for quasi-β annealing is as follows: The first stage of quasi-β annealing: The furnace is heated to 35°C below the β phase transformation point and held for ≥10 min. The forgings are then loaded into the furnace and heated to 35°C below the β phase transformation point again, held for 150±15 min, and then heated to 15°C above the phase transformation point in 40-50 min increments. The heating coefficient is 0.35 min / mm. After being removed from the furnace, the forgings are air-cooled. The forgings are placed upright on their sides during loading and cooling, with a spacing of ≥100 mm between them. Thermocouples are used to monitor the temperature at the largest and smallest cross-sections of the forgings throughout the entire first stage of quasi-β annealing. Second stage of quasi-β annealing: Load the furnace at the set temperature, then raise the temperature to 565℃, hold for 360±15min, and then air-cool after removing from the furnace.

2. The method according to claim 1, characterized in that, The forging temperature is selected as 30-50℃ below the phase transformation point. The heat preservation coefficient for cold material heating is calculated as 0.8 min / mm, and the heat preservation coefficient for hot material return to the furnace is calculated as 0.5 min / mm. Hot material return to the furnace is preferred for heating between forging cycles. Cold material heating is used when grinding is required to remove damage to the forging. Air cooling is used after forging.

3. The method according to claim 2, characterized in that, Multi-stage, multi-stage material drawing and elongation includes: The first heat is performed by upsetting or drawing and shaping of bar stock. The width and thickness of the square billet obtained after shaping meet the maximum cross-sectional dimensions of the forging. Subsequent heats are performed by drawing the material in one or more heats. The maximum deformation in a single heat is ≤35%. During drawing, the feed amount per hammer is 1 / 3 to 1 / 2 of the thickness to be pressed, and the deformation per hammer is 10% to 15%.

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