A process method for ensuring the tissue uniformity of forgings with high drop cross-sections

Abstract

The present invention belongs to the technical field of hot processing of materials, and particularly relates to a process method for ensuring the tissue uniformity of forgings with high-drop cross-sections. When producing the rough blank, a transition inclined plane is reserved during the drawing out of the slab billet to avoid stress concentration caused by a large drop at the transition part between the thick plate and the thin plate. During the production of the intermediate blank, a forging roughing die and a limiting plate are borrowed to finally obtain a rough shape similar to the shape and volume of the die forging. Borrowing the die makes the operation of the forging roughing process simple, the production process easy to control, and the size of the rough shape stable, ensuring the consistency of the same batch state of the forging rough shape and also improving the material utilization rate.

Description

Technical Field

[0001] The present invention belongs to the technical field of hot processing of materials, and particularly relates to a process method for ensuring the tissue uniformity of forgings with high-drop cross-sections. Background Art

[0002] Due to its low density, high specific strength, and good corrosion resistance, titanium alloy has become one of the important materials in the research and development of the aviation industry. In recent years, with the requirements of long-life and damage tolerance durability design for new-generation aircraft at home and abroad, β heat treatment forgings have gradually emerged and have been successfully used in key components such as aircraft connecting plates, landing gears, and wing joints. The structure of the forgings with high-drop cross-sections mentioned in the present invention is as Figure 1 shown. In its longitudinal section, the thickness drop is greater than 130 mm. For such forgings, the traditional forging method is to first forge a bar into a slab according to the maximum cross-section, and then divide the slab according to the volume required for the thin plate part. After thinning and stretching one end of the thin plate to the required thickness of the rough blank, the rough blank is placed in a mold for forging to obtain the required die forging. In the traditional forming method of such forgings, during the blank-making process, since one end of the thin plate needs to be thinned and stretched while the other end remains unchanged, it will cause the non-pressed end to be in an idle burning state for multiple heating times. Moreover, due to the small material consumption required for the thin plate part and the small contact area between the hammer head and the blank, it is difficult for workers to divide the material during production, and the difficulty of forging the rough blank is large. Also, using the traditional forging method, the cross-section height drop at the transition part between the thick plate end and the thin plate end is relatively large, making it difficult to control the dimensional accuracy during production, resulting in poor batch consistency of the rough shape. At the same time, during the deformation process of the blank, stress concentration is likely to occur in the transition area between the thick and thin plates, accelerating the deformation texture process and forming a strong texture. After β heat treatment, the grains in this area will grow abnormally, resulting in non-uniform tissue and inability to meet the product standard requirements, causing product rejection. Summary of the Invention

[0003] Object of the Invention: To provide a process method for ensuring the tissue uniformity of forgings with high-drop cross-sections and improving the tissue uniformity of forgings with high-drop cross-sections.

[0004] Technical Solution:

[0005] A process method for ensuring the tissue uniformity of forgings with high-drop cross-sections includes:

[0006] Step 1: Determine the rough shape. The rough shape is an L-shaped plate, which includes a longitudinal surface and a height surface. The longitudinal surface and the height surface are smoothly transitioned. The area of the longitudinal surface is smaller than the longitudinal area of the forging, and the thickness of the longitudinal surface is greater than the thickness of the longitudinal surface of the forging; the area of the height surface is smaller than the height surface area of the forging, and the thickness of the height surface is greater than the thickness of the height surface of the forging;

[0007] The bar stock cut to the specified size is heated in an electric furnace to the forging temperature and then flattened and shaped along the length direction on a free forging hammer to form a slab; the thickness of the slab is close to half of the sum of the thickness at the largest cross-section in the longitudinal direction of the rough shape and the thickness at the smallest cross-section in the longitudinal direction, and the width of the slab is 70% - 90% of the transverse dimension of the longitudinal surface of the final rough shape.

[0008] Step 2: After heating the slab in an electric furnace, the slab is divided into parts and then elongated to form a stepped blank.

[0009] Step 3: After heating the blank in an electric furnace, it is erected and placed in a special die, and eccentric pressing is carried out for 2 - 6 blows to obtain the first intermediate blank; the contour of the die cavity is the same as the contour of the rough shape.

[0010] Step 4: Place the limit plate on the upper end face of the die, and the upper hammer presses the first intermediate blank as a whole until the upper hammer is in full contact with the limit plate to obtain the second intermediate blank; the thickness of the limit plate is 20 mm.

[0011] Step 5: After heating the second intermediate blank in an electric furnace, without using the limit plate, the second intermediate blank is pressed as a whole, and the second intermediate blank is completely pressed into the die to obtain the rough shape.

[0012] Step 6: Finish forging. After heating the rough shape in an electric furnace, it is placed in the cavity of the finish forging die to be formed, and a forging with a high drop section of the final shape is obtained.

[0013] Step 7: β heat treatment. The finally formed die forging is placed in an electric furnace for heating, the heating temperature is 20 - 50 °C above the phase transformation point, the holding time is 40 - 60 min, and it is air-cooled to room temperature after being spread out.

[0014] Furthermore, in Step 1, the forging temperature is 30 - 50 °C below the phase transformation point.

[0015] Flattening and shaping along the length direction on a free forging hammer to form a slab specifically includes: flattening and shaping are carried out in two heating passes, and the deformation amount per heating pass during flattening is controlled between 5% - 25%, and it needs to be carried out in 2 - 3 passes.

[0016] Furthermore, in Step 2, after dividing the slab into parts and elongating it to form a stepped blank, it specifically includes:

[0017] During dividing the parts and elongating, the deformation amount of the deformed part is controlled between 5% - 25%, and it needs to be carried out in 2 - 3 passes and pressed to the specified size.

[0018] Furthermore, in Step 2, during the process of dividing the parts, it is ensured that the volume of the elongated part is larger than the volume of the longitudinal surface of the rough shape.

[0019] Furthermore, in Step 3, eccentric pressing is carried out for 2 - 6 blows to obtain the first intermediate blank, which specifically includes:

[0020] When pressing the first hammer, first press the suspended part of the blank, and the contact area of the upper hammer head does not exceed 1 / 2 of the cross-section to be pressed; when pressing the second hammer on the non-suspended part, the amount of each hammer pressing down is 1 / 3 - 2 / 5 of the height of the blank higher than the height of the die.

[0021] Furthermore, in step four, the limit plate is in a semi-surrounding structure. The limit plate not only limits the total pressing-down size of this heat, but also ensures the deformation amount of the rough shape in the final heat.

[0022] Furthermore, in step five, when pressing the second intermediate blank as a whole, slow pressing is required, and the pressing speed is controlled within the range of 3 - 10 mm / s.

[0023] Furthermore, in step six, the final forging is carried out in multiple heats, and the deformation amount of each heat is controlled between 5% and 25%.

[0024] Furthermore, the deformation amounts in step one, step two, and step six show a downward trend.

[0025] Beneficial effects:

[0026] The method for ensuring the uniform structure of forgings with high-drop cross-sections proposed by the present invention, using this process method, when producing rough blanks, by reserving a transition inclined plane during the slab splitting and drawing out process, stress concentration caused by a large drop at the transition part between thick plates and thin plates is avoided. When producing intermediate blanks, by borrowing the forging rough die and the limit plate, a rough shape similar to the shape and volume of the die forging is finally obtained. Borrowing the die makes the forging rough process easy to operate, the production process easy to control, and the rough shape size stable, ensuring the consistency of the same batch state of the forging rough shape, and also improving the material utilization rate. The finally produced die forgings, after β heat treatment, obtain a uniform structure, no abnormal grain growth occurs, and the grain size meets the standard requirements. Description of the drawings

[0027] Figure 1 It is a schematic diagram of a forging.

[0028] Figure 2 It is a schematic diagram of a rough shape.

[0029] Figure 3 It is a schematic diagram of a preform before entering the die.

[0030] Figure 4 It is a schematic diagram of placing the material in the die.

[0031] Figure 5 It is a schematic diagram of the limit plate. Specific implementation manners

[0032] A process method for ensuring the tissue uniformity of forgings with high drop sections, comprising: Step 1: Determine the rough shape. The rough shape is an L-shaped plate, which includes a longitudinal surface and a height surface. There is a smooth transition between the longitudinal surface and the height surface. The area of the longitudinal surface is smaller than the longitudinal area of the forging, and the thickness of the longitudinal surface is greater than the thickness of the longitudinal surface of the forging; the area of the height surface is smaller than the height surface area of the forging, and the thickness of the height surface is greater than the thickness of the height surface of the forging; when designing the blank, a transition area is reserved at the transition part between the thick plate and the thin plate of the slab to avoid a large drop in the height direction at the transition part between the thick plate and the thin plate, resulting in stress concentration and affecting the transformation of the material structure. The length of the transition area is determined according to the longitudinal dimension of the slab.

[0033] Heat the bar cut according to the specifications in an electric furnace to the forging temperature, and flatten and shape it along the length direction on a free forging hammer to form a slab; the thickness of the slab is close to one-half of the sum of the thickness at the largest cross-section in the longitudinal direction of the rough shape and the thickness at the smallest cross-section in the longitudinal direction, and the width of the slab is 70% - 90% of the transverse dimension of the longitudinal surface of the final rough shape;

[0034] Step 2: After heating the slab in an electric furnace, divide the slab and stretch it to form a stepped blank; when stretching the thin plate end of the divided slab, press the reserved transition area into a transition slope from the thick plate to the thin plate. This method can avoid stress concentration when there is a drop in the height direction at the transition part between the thick plate and the thin plate, exacerbating the tissue deformation texture and forming a strong texture. During the β heat treatment process of titanium alloy, the "strong texture" tissue will show abnormal grain growth or uneven tissue after nucleation and growth.

[0035] Step 3: After heating the blank in an electric furnace, place it vertically into a special forging roughing die and eccentrically press it 2 - 6 times to obtain the first intermediate blank; during production, with the help of the special forging roughing die, the contour of the die cavity is the same as the contour of the rough shape. Using the eccentric pressing method, press the blank into an intermediate blank with a volume similar to that of the die forging. Using this method, the operation is simple, the production process is easy to control, the size of the produced intermediate blank is stable, greatly improving the dimensional consistency of the same batch of rough shapes of the product, and at the same time improving the material utilization rate.

[0036] Step 4: Place the limit plate on the upper end face of the die, and the upper hammer head presses the first intermediate blank as a whole until the upper hammer head is in full contact with the limit plate to obtain the second intermediate blank; during the production of the second intermediate blank, strictly control the deformation amount with the help of the limit plate to avoid the problem of excessive core temperature rise caused by excessive deformation amount, and at the same time reserve sufficient deformation amount for the final heat treatment of the rough shape. The thickness of the limit plate is 20mm, and it is in a semi-surrounding structure. When pressing, use the method of pressing as a whole to ensure that all parts of the blank participate in the deformation. At the same time, with the help of the limit plate, the consistency of the blank deformation can also be ensured, providing an intermediate blank with as consistent a state as possible for the subsequent processes.

[0037] Step Five: After heating the second intermediate blank in an electric furnace, without using a limiting plate, the second intermediate blank is pressed as a whole, and the second intermediate blank is completely pressed into the matrix die to obtain a rough shape; the limiting plate is removed, and the first intermediate blank is pressed as a whole into the matrix die until the upper hammer head contacts the upper end face of the matrix die, and after holding pressure for about 10 s, demolding is carried out to obtain a rough shape similar to the shape and volume of the final forging.

[0038] Step Six: Finish forging. After heating the rough shape in an electric furnace, it is placed in the cavity of the finish forging die to be formed, and a forging with a high-drop cross-section of the final shape is obtained;

[0039] Step Seven: β heat treatment. The finally formed die forging is placed in an electric furnace for heating, the heating temperature is 20 - 50 °C above the phase transformation point, the heat preservation time is 40 - 60 min, and after taking it out of the furnace, it is scattered and air-cooled to room temperature.

[0040] In Step One, the forging temperature is 30 - 50 °C below the phase transformation point; it is flattened and shaped along the length direction on a free forging hammer to a slab, specifically including: flattening and shaping are carried out in two heating passes, and the deformation amount per heating pass during flattening is controlled between 5% and 25%, and it needs to be divided into 2 - 3 passes.

[0041] In Step Two, after dividing the slab, it is drawn out to form a stepped blank, specifically including: when drawing out the divided slab, a transition area connecting the thick plate and the thin plate needs to be reserved. When drawing out one end of the thin plate, the reserved transition area is pressed into a transition inclined plane, and the included angle between the transition inclined plane and the longitudinal plane is 20° - 40°, and at the same time, the deformation amount of the deformed part is controlled between 5% and 25%, and the pressing is carried out in 2 - 3 passes to the specified size.

[0042] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are some, but not all, of the embodiments of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without making creative efforts belong to the scope of protection of the present invention.

[0043] The features of each aspect of the embodiments of the present invention will be described in detail below. In the following detailed description, many specific details are put forward to provide a comprehensive understanding of the present invention. However, it is obvious to those of ordinary skill in the art that the present invention can also be implemented without these specific details. The following description of the embodiments is only for a better understanding of the present invention by showing examples of the present invention. The present invention is not limited to any specific settings and methods provided below, but covers any improvements, substitutions, etc. of all product structures and methods without departing from the spirit of the present invention.

[0044] Provide a reasonable, controllable and easy-to-operate forming method for forging parts with a thickness drop of more than 130 mm in the forming section, and obtain a uniform structure with grain size meeting the standard requirements.

[0045] A process method for ensuring the tissue uniformity of forgings with a high-drop cross-section includes the following steps:

[0046] Step 1:

[0047] The present invention will be further described in detail through specific embodiments below

[0048] A certain part of a connecting plate of a certain type of aircraft uses Ti-6Al-4V titanium alloy material. The required forging of this part has a final cross-section thickness drop of 200 mm, a thickness of 240 mm at the large cross-section, and a thickness of only 40 mm at the web part. It belongs to a forging with a high-drop cross-section, as Figure 1 shown. This high-drop cross-section forging has a relatively complex shape and high requirements for tissue uniformity. Therefore, the distribution of the rough shape size is crucial. Usually, based on the dimensions of the thickest and widest parts of the delivery drawing, it is first forged into a slab, and then shaped by material division and drawing. However, after die forging, the rough shape produced by this method has poor tissue uniformity, a high product rejection rate, and low material utilization rate. After multiple simulation verifications, the rough shape is optimized, and finally as Figure 2 shown.

[0049] Process method:

[0050] 1. Forging the slab:

[0051] a. Billet heating: Heat at 30 - 50 °C below the phase transition point and hold for heat preservation at a coefficient of 0.6 - 1.0 mm / min.

[0052] b. Tooling preheating: The parts of the hammer anvil and tooling in contact with the billet should be preheated; the preheating temperature is 200 - 300 °C;

[0053] c. Forging dimensions:

[0054] A bar with a diameter of ψ250×370 is forged in two heating times to a size of 150 mm×390 mm×315 mm. The 315 mm dimension is the streamline direction dimension of the plate, the 390 mm is the width direction dimension of the plate, and the 150 mm is the thickness direction dimension of the plate.

[0055] d. Cooling method: Air cooling.

[0056] 2. Divide the material and draw the thin plate part:

[0057] a. Billet heating: After the billet is air-cooled for 10 - 20 minutes, it is returned to the furnace and held for heat preservation at a coefficient of 0.6 - 1.0 mm / min.

[0058] b. Tooling preheating: The parts of the anvil and tooling that contact the blank should be preheated; the preheating temperature is 200 - 300 °C;

[0059] c. Forging dimensions: Stretch the thin plate part in two heating passes to Figure 3 as shown.

[0060] d. Cooling method: Air cooling.

[0061] 3. Open-die forging:

[0062] a. Blank heating: After the blank is air cooled for 10 - 20 min, it is returned to the furnace and heat-preserved at a coefficient of 0.6 - 1.0 mm / min.

[0063] b. Tooling preheating: The parts of the anvil and tooling that contact the blank should be preheated; the preheating temperature is 200 - 300 °C;

[0064] c. Forging dimensions:

[0065] First heating pass: Place the rough shape vertically into the special open-die, as Figure 4 shown, and then perform eccentric pressing. Place a limiting plate with a semi-surrounding structure and a thickness of 20 mm on the upper end face of the open-die to limit the total reduction dimension of this heating pass, and at the same time ensure the deformation amount of the final heating pass of the rough shape. The schematic diagram of the limiting plate is as Figure 5 .

[0066] Second heating pass: Continue to place the rough shape vertically into the special open-die, and press the blank completely into the open-die at a speed of 5 - 12 mm / s so that the blank fills the cavity of the open-die.

[0067] d. Cooling method: Air cooling.

[0068] 4. Die forging forming:

[0069] a. Blank heating: Heat at 30 - 50 °C below the phase transformation point and heat-preserve at a coefficient of 0.6 - 1.0 mm / min.

[0070] b. Tooling preheating: The parts of the tooling that contact the blank should be preheated; the preheating temperature is 200 - 300 °C; the preheating temperature of the die is 250 - 350 °C.

[0071] c. Forging dimensions: Press the blank in three heating passes to the final forming dimensions.

[0072] d. Cooling method: Air cooling.

[0073] 5. β heat treatment:

[0074] Heat treatment system: 30 °C above the phase transformation point, heat preservation for 50 min.

[0075] Cooling method: Spread out for air cooling

[0076] The forgings produced by this processing method have uniform structures, without the phenomenon of abnormal grain growth. The grain size meets the requirements specified by the standard. This processing method effectively ensures the uniformity of the product structure, improves the product qualification rate, saves costs, shortens the production cycle, wins the market, and is suitable for popularization.

Claims

1. A process method for ensuring the tissue uniformity of forgings with high drop sections, characterized in that, Including: Step 1: Determine the rough form. The rough form is an L-shaped plate. The rough form includes a longitudinal surface and a height surface. There is a smooth transition between the longitudinal surface and the height surface. The area of the longitudinal surface is smaller than the longitudinal area of the forging, and the thickness of the longitudinal surface is greater than the thickness of the longitudinal surface of the forging; the area of the height surface is smaller than the height area of the forging, and the thickness of the height surface is greater than the thickness of the height surface of the forging; Heat the bar cut to the specified size in an electric furnace to the forging temperature, and flatten and shape it along the length direction on a free forging hammer to obtain a slab. The thickness of the slab is close to half of the sum of the thickness at the largest cross-section in the longitudinal direction of the rough form and the thickness at the smallest cross-section in the longitudinal direction. The width of the slab is 70% - 90% of the transverse dimension of the longitudinal surface of the final rough form; Step 2: After heating the slab in an electric furnace, divide the slab and draw it out to form a stepped blank. When dividing and drawing out, the deformation amount of the deformed part is controlled between 5% and 25%, and it needs to be divided into 2 - 3 passes and pressed to the specified size; Step 3: After heating the blank in an electric furnace, stand it up and place it in a special die. Press it eccentrically for 2 - 6 hammers to obtain the first intermediate blank. When pressing the first hammer, first press the suspended part of the blank, and the contact area of the upper hammer head does not exceed 1 / 2 of the cross-section to be pressed; the second hammer presses the non-suspended part. When pressing, the amount of depression per hammer is 1 / 3 - 2 / 5 of the height of the blank above the die cavity. The contour of the die cavity is the same as the contour of the rough form; Step 4: Place the limit plate on the upper end face of the die. The upper hammer head presses the first intermediate blank as a whole until the upper hammer head is in full contact with the limit plate to obtain the second intermediate blank. The thickness of the limit plate is 20 mm, and the limit plate is in a semi-surrounding structure; Step 5: After heating the second intermediate blank in an electric furnace, without using the limit plate, press the second intermediate blank as a whole and press the second intermediate blank completely into the die to obtain the rough form; Step 6: Finish forging. After heating the rough form in an electric furnace, place it in the cavity of the finish forging die to form and obtain the forging with a high-drop cross-section that is finally formed; Step 7: β heat treatment. Place the finally formed die forging in an electric furnace for heating. The heating temperature is 20 - 50 °C above the phase transformation point, the holding time is 40 - 60 min, and it is air-cooled to room temperature after spreading out; 2. The process method for ensuring the tissue uniformity of forgings with high drop sections according to claim 1, characterized in that, In Step 1, the forging temperature is 30 - 50 °C below the phase transformation point; Flatten and shape it along the length direction on a free forging hammer to obtain a slab, specifically including: flattening and shaping are carried out in two heating times. When flattening, the deformation amount per heating time is controlled between 5% and 25%, and it needs to be divided into 2 - 3 passes.

3. The process method for ensuring the tissue uniformity of forgings with high drop sections according to claim 1, characterized in that, In Step 2, during the dividing process, ensure that the volume of the drawn-out part is greater than the volume of the longitudinal surface of the rough form.

4. The process method for ensuring the tissue uniformity of forgings with high drop sections according to claim 1, characterized in that, In Step 5, when pressing the second intermediate blank as a whole, it needs to be pressed slowly, and the pressing speed is controlled within the range of 3 - 10 mm / s.

5. The process method for ensuring the tissue uniformity of forgings with high drop sections according to claim 1, characterized in that, In Step 6, finish forging is carried out in multiple heating times, and the deformation amount per heating time is controlled between 5% and 25%.

6. The process method for ensuring the tissue uniformity of forgings with high drop sections according to claim 1, characterized in that, The deformation amounts in Step 1, Step 2, and Step 6 show a downward trend.

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