阅读说明：本技术 一种航空发动机用高强度β锻钛合金锻件组织控制方法 (High-strength beta forging titanium alloy forging structure control method for aircraft engine ) 是由 邓雨亭 李四清 王旭 黄旭 王周田 李晓强 于 2021-07-30 设计创作，主要内容包括：本发明涉及一种航空发动机用高强度β锻钛合金锻件组织控制方法,包括以下步骤：将钛合金棒坯加热到相变点以上20℃～50℃；将棒坯锻造成锻件毛坯,各部位变形量均达到40％以上；将锻件毛坯水冷至室温；对锻件毛坯进行退火热处理；对锻件毛坯进行固溶和时效热处理。本发明在β锻造工艺中采用了锻后水冷的技术路线,通过在固溶和时效热处理前增加一次退火热处理,解决了锻后水冷表面急冷层组织不均匀和拉伸塑性低的问题,显著提升了锻件心部强度和整体强度的均匀性。(The invention relates to a high-strength beta forging titanium alloy forging structure control method for an aircraft engine, which comprises the following steps: heating the titanium alloy bar billet to 20-50 ℃ above the phase transformation point; forging the bar blank into a forging blank, wherein the deformation of each part reaches more than 40%; cooling the forging blank to room temperature by water; annealing heat treatment is carried out on the forging blank; and carrying out solid solution and aging heat treatment on the forging blank. The invention adopts the technical route of water cooling after forging in the beta forging process, solves the problems of uneven structure and low tensile plasticity of a quenching layer on the water-cooled surface after forging by adding one annealing heat treatment before the solid solution and aging heat treatment, and obviously improves the uniformity of the core strength and the overall strength of the forged piece.)

1. A high-strength beta forging titanium alloy forging structure control method for an aircraft engine comprises the following steps:

heating the titanium alloy bar billet to 20-50 ℃ above the phase transformation point;

forging the bar blank into a forging blank, wherein the deformation of each part reaches more than 40%;

cooling the forging blank to room temperature by water;

annealing heat treatment is carried out on the forging blank;

and carrying out solid solution and aging heat treatment on the forging blank.

2. The method of claim 1, wherein the heat treatment schedule for annealing the forging blank is: keeping the temperature of T to (T +100) DEG C for H to (H +3) hours, and cooling the titanium alloy to room temperature in air, wherein T is the optimal transition temperature of the alpha sheet layer of the titanium alloy, and H is the transition finishing time at the optimal transition temperature of the alpha sheet layer in unit hour.

3. The method according to claim 2, wherein the optimum transition temperature and the transition end time are obtained by looking up or plotting an isothermal transition curve of the titanium alloy used.

4. The method of claim 1, whereinControlling the strain rate to be 0.001s when the bar stock is forged into a forging blank^-1～0.05s^-1。

5. The method of claim 1 wherein said water cooling the forging blank to room temperature is performed by rapidly transferring the forging blank to a water tank having a circulating water function.

6. The method of claim 1, wherein the titanium alloy is TC17 titanium alloy.

7. The method according to claim 6, wherein the heat treatment schedule of the solution and aging heat treatment is 780 to 830 ℃ for 3 to 6 hours, water cooling to room temperature and 590 to 650 ℃ for 8 hours, and air cooling to room temperature.

8. The method of claim 1, wherein the titanium alloy is TC19 titanium alloy.

9. The method according to claim 8, wherein the heat treatment schedule of the solid solution and aging heat treatment is 915-965 ℃ for 1-4 hours, air-cooled to room temperature and 535-680 ℃ for 8 hours, and air-cooled to room temperature.

Technical Field

The invention belongs to the technical field of titanium alloy structure control, and particularly relates to a structure control method of a high-strength beta forging titanium alloy forging for an aircraft engine.

Background

The beta forging is the forging of heating the blank to a temperature above the beta transformation point, and the forge piece can obtain a fully woven basket structure, has good fracture toughness and creep property, and is widely used for manufacturing aviation engine fans and air compressors. Titanium alloys (titanium alloys with domestic designations TC17 and TC 19) adopting a beta forging process are usually rich in more beta stable elements, metastable beta phases can be obtained by rapid cooling, metastable phases are converted into secondary alpha phases by low-temperature aging treatment, and the properties of forging structures, strength and the like can be adjusted by adjusting a heat treatment system. However, with the requirement of an aero-engine on high thrust-weight ratio, the size of the forged piece is continuously increased, the shape of the forged piece is more complex, the limitation of the hardenability of the alloy leads the core strength of the obtained forged piece to be incapable of meeting the design requirement and have large strength property dispersity if the forged piece is subjected to air cooling or air cooling, and the window for regulating and controlling the structure property of the forged piece through subsequent heat treatment is very narrow.

The cooling speed after forging determines the width of an alpha lamella and the thickness of a crystal boundary alpha phase, and the 2 parameters are reduced along with the increase of the cooling speed, so that the core strength of the forging can be obviously improved by obtaining the fine lamella alpha phase through water cooling after forging. However, after forging, water cooling easily forms a quenching layer on the surface of the forging, the forging state macrostructure is uneven, the forging state microstructure is that intermittent crystal boundary alpha phase and a few alpha sheet layers near the crystal boundary are separated out on the original beta crystal boundary, the microstructure after solid solution and aging heat treatment is that short and fine alpha sheet layers are separated out in the crystal grains, the alpha sheet layers are poor in weaving state and have the length and width less than 10:1, the alpha sheet layers are unqualified structures, and the drawing plasticity of the forging is seriously reduced.

The Chinese patent 'a beta forging and heat treatment method of TC4 titanium alloy disc forgings (CN 109482796B)', discloses a method that 400KJ is adopted to stamp a hammer, the forging is carried out in a beta phase region at the temperature of 30-40 ℃ above a transformation point by heating, the deformation reaches 40%, air cooling is carried out for 5-6 minutes after the forging, then water cooling is carried out, a fine and uniform forged basket structure is obtained, the heat treatment after the forging adopts solid solution at the temperature of 30-40 ℃ below the transformation point, water cooling is carried out, then heat treatment for aging at the temperature of 620-630 ℃ is carried out, a fine and stable basket structure is obtained, and the performance has high strength and certain plasticity. The technology that air cooling is carried out after forging and then water cooling is carried out is adopted only for TC4 titanium alloy beta forged pieces, fine and uniform forged mesh basket structures are obtained, multiple factors influence the time required by air cooling in the first stage, the technology cannot be popularized to titanium alloy forged pieces of other sizes or other types within 5-6 minutes, the effect of improving strength cannot be achieved if the time is too long, alpha sheets with the sizes meeting the requirements cannot be separated out if the time is too short and most titanium alloys rich in beta stable elements are rich, and the rapid cooling layer structures are still formed to remarkably reduce plasticity.

Disclosure of Invention

In view of the above situation in the prior art, the invention aims to provide a method for controlling the structure of a high-strength beta forging titanium alloy forging for an aeroengine, which solves the problems of nonuniform structure and low tensile plasticity of a quenching layer on a water-cooled surface after forging, remarkably improves the uniformity of the core strength and the overall strength of the forging, and realizes the regulation and control of the structure and the performance of the quenching layer on the surface of the water-cooled forging after forging.

The above object of the present invention is achieved by the following technical solutions:

a high-strength beta forging titanium alloy forging structure control method for an aircraft engine comprises the following steps:

heating the titanium alloy bar billet to 20-50 ℃ above the phase transformation point;

forging the bar blank into a forging blank, wherein the deformation of each part reaches more than 40%;

cooling the forging blank to room temperature by water;

annealing heat treatment is carried out on the forging blank;

and carrying out solid solution and aging heat treatment on the forging blank.

Further, the heat treatment system for annealing heat treatment of the forging blank is as follows: keeping the temperature of T to (T +100) DEG C for H to (H +3) hours, and cooling the titanium alloy to room temperature in air, wherein T is the optimal transition temperature of the alpha sheet layer of the titanium alloy (namely the temperature point of the nose tip), and H is the transition finish time at the optimal transition temperature of the alpha sheet layer in unit hour. The TTT curve shows that the annealing treatment can obtain thick widmannstatten alpha lamella, the annealing temperature and the heat preservation time are selected to pre-separate out the alpha lamella of the quenching layer on the surface of the forging with high efficiency, and the thickness of the alpha lamella in the core of the forging is not remarkably coarsened.

Wherein the optimum transition temperature and the transition end time are obtained by inquiring or plotting an isothermal transition (TTT) curve of the titanium alloy used.

Wherein the strain rate is controlled to 0.001s when forging the bar into a forging blank^-1～0.05s^-1. And the water cooling of the forging blank to room temperature is carried out by quickly transferring the forging blank to a water tank with a circulating water function.

The method of the invention applies the technical route of water cooling after forging, annealing heat treatment, solid solution and aging heat treatment to the beta forging process, fully utilizes the advantage of water cooling after forging to improve the overall strength of the forging, adds one annealing heat treatment before the solid solution and aging heat treatment, selects the optimal transition temperature of the alpha lamella and the transition finish time at the temperature to formulate an annealing heat treatment system, so that the alpha phase of the lamella is pre-precipitated on the surface of the forging in the solid solution and aging heat treatment without obviously coarsening the thickness of the alpha lamella in the core of the forging. The structure of a quenching layer on the surface of the forging is obviously improved, alpha sheet layers from the surface to the core of the forging are well woven, and the length-width ratio is lower than 10: 1. The strength of the core of the large-size forge piece (the section size is more than or equal to 150mm) can be obviously improved, the design requirement is met, the process window of solid solution and aging heat treatment can be expanded for the medium-size forge piece and the small-size forge piece (the section size is less than 150mm), and the forge piece with high strength and excellent comprehensive performance is obtained.

Drawings

FIG. 1 shows a beta forged TC17 titanium alloy forging macrostructure.

FIG. 2 shows a forged quenching layer structure of a beta forged TC17 titanium alloy forging.

FIG. 3 is the surface structure of a beta forged TC17 titanium alloy forging after solution and aging heat treatment.

Fig. 4 is the TTT curve for TC17 titanium alloy.

FIG. 5 is the surface structure of a beta forged TC17 titanium alloy forging after annealing plus solution and aging heat treatment.

FIG. 6 is a beta forged TC19 titanium alloy forging macrostructure.

FIG. 7 is a surface microstructure of a beta forged TC19 titanium alloy forging after solution and aging heat treatment.

FIG. 8 is a TTT curve for TC19 titanium alloy.

FIG. 9 is a surface microstructure of a beta forged TC19 titanium alloy forging after annealing + solution and aging heat treatment.

Detailed Description

For a clearer understanding of the objects, technical solutions and advantages of the present invention, the present invention will be described in further detail below with reference to the accompanying drawings and embodiments.

The invention discloses a high-strength beta forging titanium alloy forging structure control method for an aircraft engine, which needs to provide equipment such as a titanium alloy bar blank, a blank heating furnace, a hydraulic machine, a manipulator, a water tank, a heat treatment furnace and the like. The specific process steps are as follows: 1. heating the titanium alloy bar blank to be 20-50 ℃ above the phase transformation point; 2. forging the bar blank into a forging blank, wherein the deformation of each part reaches more than 40 percent, and the strain rate is controlled to be 0.001s^-1～0.05s^-1(ii) a 3. Cooling the forging blank to room temperature by water; 4. annealing heat treatment is carried out on the forging blank; 5. and carrying out solid solution and aging heat treatment on the forging blank.

Example 1

The raw material of the bar billet is titanium alloy with Chinese material mark TC 17.

Step 1: the phase transition point temperature of the used phi 500mm TC17 titanium alloy bar billet is 900 ℃ measured by HB 6623.2.

Step 2: the titanium alloy bar billet is heated to 30 ℃ above the transformation point.

And step 3: forging the bar blank in the step 2 into a forging blank, wherein the deformation of each part is more than 40%, and the strain rate is controlled to be 0.01s^-1。

And 4, step 4: and (3) quickly transferring the forging blank in the step (3) to a water tank with a circulating water function, cooling to room temperature to obtain the macrostructure of the forging blank as shown in figure 1, wherein a bright band with the thickness of about 15mm exists on a quenching layer on the surface of the forging, and the macrostructure is uneven. As shown in figure 2, the forged microstructure only precipitates discontinuous grain boundary alpha phase and a small part of alpha sheet layer near the grain boundary on the original beta grain boundary, the inside of the grain is supercooled metastable beta phase, the microstructure after only solution treatment and aging heat treatment is shown in figure 3, short and fine alpha sheet layer is precipitated inside the grain, the alpha sheet layer has poor weaving state and the length and width of less than 10:1, and is a defective structure, the room-temperature tensile strength of the surface of the forged piece is up to 1220MPa, but the elongation is only 4.6%.

And 5: the TTT (isothermal transformation) curve of the TC17 titanium alloy was examined, as shown in fig. 4, to obtain an optimum transformation temperature of the α -sheet of about 600 c and an end time of transformation of about 0.3 hours at that temperature.

Step 6: and (4) annealing and heat treating the forging blank in the step (4), wherein the heat treatment system is as follows: keeping the temperature at 650 ℃ for 2 hours, and cooling to room temperature in air.

And 7: and (5) carrying out solid solution and aging heat treatment on the forging blank in the step 6. The common heat treatment system is to keep the temperature at 780-830 ℃ for 3-6 hours, cool the water to room temperature and keep the temperature at 590-650 ℃ for 8 hours, and cool the air to room temperature. The heat treatment system in this example was: keeping the temperature at 805 ℃ for 4 hours, cooling to room temperature by water, keeping the temperature at 620 ℃ for 8 hours, and cooling to room temperature by air.

The method is adopted to regulate and control the forging size of TC17 titanium alloy to be phi 1020mm multiplied by 327mm, the section size to be 170mm and the forging blank weight to be 570 Kg. The primary annealing heat treatment is added before the solid solution and aging heat treatment, the obtained microstructure is shown in figure 5, the alpha phase of the sheet layer can be pre-precipitated by the annealing heat treatment, compared with the method of directly carrying out high-temperature solid solution treatment, the alpha sheet layer is good in weaving, the length and the width reach 10:1, and the internal stress generated by water cooling after forging can be eliminated by the annealing treatment. The overall room-temperature tensile property of the final forging is remarkably improved: the room-temperature tensile strength of the surface before annealing treatment is not increased to 1220MPa, but the elongation is only 4.6 percent and is far lower than 12.2 percent of the core of the forging, and the core strength can reach 1165 MPa; the room-temperature tensile strength of the surface after annealing heat treatment is increased and reduced to 1180MPa, the elongation is increased to 10.4 percent, the elongation is equivalent to 14.1 percent of the core elongation of the forged piece, the core strength is not obviously reduced and can reach 1150MPa, the design requirements (the tensile strength is more than or equal to 1120MPa and the elongation is more than or equal to 6.5 percent) are met, and a large margin exists.

Example 2

The raw material of the bar billet is titanium alloy with Chinese material mark TC 19.

Step 1: measuring the phase transition point temperature of the used phi 180mm TC19 titanium alloy bar blank by adopting HB 6623.2 to be 965 ℃;

step 2: the titanium alloy bar billet is heated to 20 ℃ above the transformation point.

And step 3: forging the bar blank in the step 2 into a forging blank, wherein the deformation of each part is more than 40%, and the strain rate is controlled to be 0.04s^-1。

And 4, step 4: and (3) quickly transferring the forging blank in the step (3) to a water tank with a circulating water function, and cooling to room temperature to obtain the macrostructure of the forging blank as shown in figure 6, wherein the macrostructure of the quenching layer on the surface of the forging is uneven. As shown in FIG. 7, the microstructure after only solution heat treatment and aging heat treatment is short and fine in alpha phase of the braided sheet, which is a defective structure, and the surface tensile strength of the forged piece at room temperature is as high as 1280MPa, but the elongation is only 4.1%.

And 5: the TTT curve of the TC19 titanium alloy was examined, as shown in fig. 8, to obtain an optimum transition temperature of the alpha sheet of about 700 c and a transition completion time at that temperature of about 0.2 hours.

Step 6: and (4) annealing and heat treating the forging blank in the step (4), wherein the heat treatment system is as follows: keeping the temperature at 750 ℃ for 1.5 hours, and cooling to room temperature in air.

And 7: and (5) carrying out solid solution and aging heat treatment on the forging blank in the step 6. The common heat treatment system is heat preservation for 1-4 hours at 915-965 ℃, air cooling to room temperature, heat preservation for 8 hours at 535-680 ℃, and air cooling to room temperature. The heat treatment system in this example was: keeping the temperature at 935 ℃ for 2 hours, cooling to room temperature by air, keeping the temperature at 595 ℃ for 8 hours, and cooling to room temperature by air.

The TC19 titanium alloy forging regulated by the method has the size of phi 460mm multiplied by 80mm, the maximum section size of 80mm and the forging blank weight of 40 Kg. The obtained microstructure is shown in fig. 9, the lamellar alpha phase can be pre-precipitated through annealing heat treatment, the morphology of the lamellar alpha phase on the surface of the forge piece is well controlled on the premise of remarkably improving the overall strength of the forge piece, and the internal stress generated by water cooling after forging can be eliminated through the annealing treatment. The room temperature stretchability of the final forging is significantly improved: the tensile strength of the surface of the forging at room temperature before annealing treatment is not increased to 1280MPa, but the elongation is only 4.1%, the core strength can reach 1240MPa, and the elongation can reach 8.6%; the room-temperature tensile strength of the surface after annealing heat treatment is increased and reduced to 1230MPa, the elongation is increased to 8.9%, and the core strength is reduced to 1200MPa in a small range. The tensile strength is far higher than the design requirement (the tensile strength is more than or equal to 1089MPa and the elongation is more than or equal to 4 percent), the process window of solid solution and aging heat treatment is remarkably expanded, and the heat treatment system can be adjusted according to the performance requirement in actual production.