CN1159472C - Quasi-β Forging Process of Titanium Alloy - Google Patents

Abstract

The invention relates to a titanium alloy quasi-beta forging process for obtaining a high-plasticity basket structure, belonging to the technical field of material science. The process solves the technical key of low plasticity of the basket structure. The blank is at the beta transformation point _β) At a temperature of 20 to 40 ℃ below, namely T_βPreheating at the temperature of 20-40 ℃ below zero, and then rapidly heating to T along with the furnace_β-10℃～T_βAnd (3) forging, die forging or rolling after short-time heating at the temperature of +20 ℃, and rapidly cooling by water or air after forging. When the forging is carried out by more than the second fire, the heating temperature is T_β- (20 to 40) DEG C, and rapidly cooling in water or air after forging. The process is applicableThe obtained net basket structure primary alpha phase content is not more than 15% in the near alpha type, alpha-beta type and near beta type titanium alloys, the plasticity is the same as that of the binary structure, the fracture toughness, creep resistance and the like are obviously higher than those of the binary structure, and semi-finished products such as structural members, disc members, forging stocks, bars and the like can be manufactured.

Description

Quasi-β Forging Process of Titanium Alloy

The invention relates to a titanium alloy quasi-beta forging process for obtaining a highly plastic basket structure, which belongs to the field of material science and technology.

Near α-type and α-β-type titanium alloys can obtain four types of microstructures due to different hot deformation processes, among which the most practically used forgings are dual-state structures, that is, primary α+β transformation structures. Compared with the two-state structure, the basket structure has better comprehensive performance, and its fracture toughness, fatigue crack growth resistance, fatigue strength and creep resistance are high, which greatly improves the service life of the component and is very attractive to designers. However, the basket structure has not been accepted by users of forgings for a long time, because if the process control is not good, the plasticity of forgings will be significantly reduced. Solving the plasticity of the basket structure has always been a major problem in titanium alloy forging.

Titanium alloy forging is usually heated in the α+β two-phase region, that is, heated at 25~50°C below the β transformation point (T _β ). In order to increase the forging temperature and improve the formability, Chinese Patent No. 1048994 "Large Steam Turbine Titanium Alloy Long Blade Precision Forging Process and Device" adopts near-β forging heated at T _β -20°C. Near-β forging stipulates in the Chinese aviation industry standard HB/Z199-91 "Titanium Alloy Forging Process" that the heating temperature is T _β -(10～15)℃, which is the highest heating temperature for α+β forging. Since the primary α-phase content in the microstructure obtained by this process is significantly reduced, compared with the usual α+β forging structure, the fracture toughness and creep resistance of this structure are improved to a certain extent. However, this process has special requirements for the heating furnace, which needs to meet the requirements of Class II furnaces, that is, the maximum temperature deviation in the effective working area is not greater than ±5°C, which obviously cannot be met in general factories and cannot be industrialized.

Another forging process developed is called β forging, that is, forging after heating in the β zone. There have been experimental studies including, for Ti-6Al-2Sn-4Zr-6Mo titanium alloy using β forging at T _β + (20 ~ 75) ℃, for Ti-6Al-2Sn-4Zr-2Mo-0.1Si titanium Alloy proposed the best β forging heating temperature range is T _β + (10 ~ 65) ℃. Sub-beta forging heated at T _β + (10-40)°C is also specified in the navigation mark HB/Z 199-91.

A basket structure is obtained by the above-mentioned β forging and sub-β forging. According to the traditional concept, the basket structure is composed of the original β grain boundary α phase and the bundled flaky α phase within the grain that is basket-woven, that is to say, the basket structure does not contain the primary α phase. This concept makes the heating temperature of β forging higher than T _β +10℃. In addition, because the thermal conductivity of titanium alloy is relatively low, it is 1/3 of steel. Therefore, the specified heating time is relatively long. Even if it is heated in the β zone, the heating coefficient η, that is, the ratio of the heating time t (min) to the maximum section thickness δ _max (mm) of the billet, is generally above 0.7.

Studies have shown that the decisive influence on the kinetics of β grain growth is the heating temperature. The higher the heating temperature, the more intense the grain growth. In addition to heating temperature, long heating time can also promote the growth of β grains. In previous studies, it was precisely because of the high heating temperature and long holding time in the β zone that the low-magnification structure of coarse grains was produced, especially in the small deformation zone or the deformation "dead zone". Because the degree of undercooling is small during the deformation process, the α phase at the β grain boundary is not easy to precipitate. And when the α phase precipitates at the grain boundary, the deformation has basically ended. Even if a small part of α phase is precipitated during the deformation process, it is not easily broken due to the small amount of deformation. Its microstructure features are that the original β grains are relatively large, and the β grain boundary α is relatively straight, and the fracture is not enough. This is the fundamental reason why the usual basket organization is less plastic than the two-state organization. Table 1 lists the comparison of the mechanical properties of the two types of tissues.

Table 1 Mechanical properties of Ti-6Al-2.5Mo-1.5Cr-0.5Fe-0.3Si titanium alloy compressor discs Die forging process Heat treatment system organization type Sampling direction 20°C 400℃creep σ＝490MPat＝100h σ _b MPa σ _0.2 MPa δ ₅ % ψ% ε _p % T _β +10℃ sub-β forging isothermal annealing basket organization Chord direction 105310541077 988986988 14.015.114.2 24.421.920.6 0.1030.1040.086 T _β -30℃α+β forging isothermal annealing two-state organization Chord direction 101610551048 9829971009 16.517.717.0 45.741.242.4 0.1140.1200.156

It can be imagined that if a process can be designed to obtain neither primary α phase nor β grain boundary α phase, but only the basket structure of clustered flaky α phase of basket weaving, this will be an ideal network structure. basket organization. That is to control a state, the moment when the primary α phase has just dissolved and the β grains have not yet formed. This ideal state may exist in a small area, but it is impossible to make the entire forging have this state. However, as an engineering application, a transition zone can be found, that is, the primary α phase is limited to a certain proportion, such as 15%, and the β grain boundary α phase is partially generated, which is the area near the β phase transition point, that is, In the transition zone from T _β -10°C to T _β +10°C, which has not been studied by anyone. When heating in this area, due to the temperature drop of the billet after it comes out of the furnace, the deformation of the forging is actually carried out in the α + β area. During the deformation process, the α phase is first precipitated at the β grain boundary, which is deformed and broken. Continuous, straight grain boundary α will not be produced, and finally a basket-weave clustered sheet-like α phase will be formed in the grain. Such a basket organization has high plasticity.

The previous β forging and sub-β forging used the method of heating the billet directly in the β area, so the heating coefficient η is generally required to be above 0.7. If the method of segmental heating is adopted, that is, preheating in the α+β area first, and then The heating time in the β zone can be greatly shortened by rapidly heating up with the furnace to the β zone. Studies have shown that the time to heat up from the α + β zone to the β zone is about 8-10 minutes. During this heating process, the primary α phase is continuously dissolved, and the 100mm thick billet only needs to be kept in the β zone for 20-25 minutes (η = 0.2-0.25 ) can make the center and outer structure of the billet uniform, and the higher the heating temperature in the β zone, the shorter the holding time required.

The present invention utilizes heating in the vicinity of the β phase transition point, and adopts a segmented heating method to control the dissolution of the primary α phase, and designs a quasi-β forging process.

The purpose of this invention is to design a forging process to obtain a high-plasticity basket structure, that is, the basket structure has the same good plasticity as the two-state structure, and at the same time has the inherent excellent characteristics of the basket structure, thereby greatly improving the use of components life.

The technical solution of the present invention is to use nearly α-type, α-β-type and near-β-type titanium alloy billets, and heat them in a Class III furnace, that is, a resistance furnace with a maximum temperature deviation in the effective working area not greater than ±10°C. This condition is generally available in factories, and the temperature is controlled by silicon controlled silicon, and the temperature fluctuation is ±2°C. After the furnace temperature reaches the preheating temperature, the billet is loaded into the furnace and placed in the effective working area. First preheat at T _β -(20～40)℃, calculate the holding time after the furnace reaches the preheating temperature, holding time t(min)=η×δ _max , δ _max (mm) is the maximum section thickness of the billet, η is Heating coefficient, the value of the preheating heating coefficient η of the billet is 0.4~0.7, and then the temperature is rapidly raised to T _β -10℃～T _β +20℃ with the furnace to calculate the holding time. The calculation formula of the holding time t(min) is the same as The above are the same, but the value of the heating coefficient η is 0.1~0.5; in addition, the billet can also be directly placed in the resistance furnace to directly heat up to T _β -10℃～T _β +20 without the above-mentioned preheating and heat preservation steps. Calculate the holding time after ℃, the calculation formula of the holding time t(min) is the same as above, but the value of the heating coefficient η is ≥0.6; forging, die forging or rolling after heating, rapid water cooling or air cooling after forging; need to carry out the second step When forging over two fires, the heating temperature is T _β -(20～40)℃, and water or air cooling is performed quickly after forging. The research of 9 front shoulder shaft die forgings with two heat numbers by choosing different process parameters shows that in the second heating or direct heating to the processing temperature step, T _β ~ T _β +10°C is the optimum heating temperature range. In addition, before quasi-β forging, the heating temperature of blank forging is T _β -(20~40)℃,

Air cooling after forging. The processed parts are heat treated according to the technical requirements.

The invention has the advantages of higher heating temperature for quasi-β forging than conventional α+β forging, small deformation resistance, easy forming, and high yield; the thickness of the obtained basket structure α sheet is controlled in the range of 2 to 4 μm, and has a finer Low grain size, has the same good plasticity as the two-state structure, and has the inherent excellent characteristics of the basket structure, that is, high fracture toughness and fatigue crack growth resistance as well as high fatigue strength and creep resistance, which can be greatly improved. Improve the service life of components. Table 2 lists the performance comparison of die forgings.

Table 2 Mechanical properties of Ti-6Al-2.5Mo-1.5Cr-0.5Fe-0.3Si titanium alloy front shoulder shaft die forgings at room temperature Die forging process Heat treatment system organization type Sampling direction σ _b MPa σ _0.2 MPa δ ₅ % ψ% K _1C MPam ^1/2 quasi-beta forging 800℃, 2h, air cooling basket organization portrait 10551045 1010995 15.516.0 41.544.5 -- Horizontal (TL) 11101095 10701060 15.016.0 39.036.0 87 α+β forging 800℃, 2h, air cooling two-state organization portrait 10801105 10351055 17.017.0 43.045.0 -- Horizontal (TL) 11151105 10401030 14.515.0 36.537.0 63

Below in conjunction with embodiment technical solution of the present invention will be described in further detail:

The titanium alloy types applicable to the technical solution of the present invention are near-α-type titanium alloys, α-β-type titanium alloys and near-β-type titanium alloys, and a large number of experimental studies have been carried out on various alloy types. Among them, for near-α-type titanium alloys The alloy mainly includes, according to its nominal composition and weight percentage, there are TA11, Ti-8Al-1Mo-1V; TA 12, Ti-5.5Al-4Sn-2Zr-1Mo-0.25Si-1Nd; TA14, Ti-11Sn-5Zr-2.3 Al-1Mo-0.2Si; TA15, Ti-6.5Al-2Zr-1Mo-1V; TA19, Ti-6Al-2Sn-4Zr-2Mo-0.1Si. For α-β-type titanium alloys, it mainly includes TC4, Ti-6Al-4V by weight percentage according to its nominal composition; TC6, Ti-6Al-2.5Mo-1.5Cr-0.5Fe-0.3Si; TC11, Ti-6.5Al -1.5Zr-3.5Mo-0.3Si; TC16, Ti-3Al-5Mo-4.5V; TC17, Ti-5Al-2Sn-2Zr-4Mo-4Cr; TC18, Ti-5Al-4.75Mo-4.75V-1Cr-1Fe ; TC19, Ti-6Al-2Sn-4Zr-6Mo; TC20, Ti-6Al-7Nb; Ti-6Al-2Sn-2Zr-2Mo-2Cr-0.23Si. For near-β-type titanium alloys, it mainly includes TB6, Ti-10V-2Fe-3Al and metastable β-type titanium alloys, and its nominal components include TB8, Ti-15Mo-3Al-2.7 by weight percentage. Nb-0.2Si.

List some specific examples below

Example 1: Ti-6Al-2.5Mo-1.5Cr-0.5Fe-0.3Si titanium alloy Φ120mm bar was used, and the measured _Tβ was 983°C. First, heat the forging waste in a resistance furnace with an effective working area of 900mm×1600mm×300mm and a maximum temperature deviation of ±10°C, and use silicon controlled rectifiers and Eurotherm meters to control the temperature. The temperature fluctuation is ±1°C, and the heating temperature is 943°C. The finished blank weighs 14kg and has a maximum section thickness of 100mm. The second step is to die forge the front shoulder shaft on a 10t die forging hammer. First, preheat at 953°C for 50 minutes, then rapidly raise the temperature to 983°C with the furnace, hold for 40 minutes and then die forge. The forging is quickly water-cooled after trimming. The heating temperature of the second fire die forging is 943°C, and the water is cooled rapidly after forging. Die forgings are air-cooled and annealed at 800°C for 2 hours.

Example 2: Using the same rod as in Example 1, under the same conditions as in Example 1, the die forging heating was first preheated at 953°C for 50 minutes, and the temperature was rapidly raised to 985°C with the furnace, and after holding for 25 minutes, die forging, forging Then quickly water-cooled. The second fire forging and heat treatment are the same as in Example 1.

Example 3: Using the same rod as in Example 1, under the same conditions as in Example 1, the die forging heating was first preheated at 953°C for 50 minutes, and the temperature was rapidly raised to 998°C with the furnace, and after holding for 25 minutes, die forging, forging Then quickly water-cooled. The second fire forging and heat treatment are the same as in Example 1.

Example 4: Using the same rod as in Example 1, under the same conditions as in Example 1, the die forging heating was first preheated at 953°C for 50 minutes, and the temperature was rapidly raised to 973°C with the furnace, and after holding for 20 minutes, die forging, forging Then quickly water-cooled. The second fire forging and heat treatment are the same as in Example 1.

In view of the fact that the key to assessing the structure of the basket is the plasticity of the small deformation zone, for the front shoulder shafts die-forged in the above four examples, the tensile samples were cut from the ribs in the small deformation zones, and the impact samples were cut at the same time. Fracture toughness samples.

Table 3 lists the room temperature mechanical properties of the examples. example TT _β ℃ tmm Sampling direction σ _b MPa σ _0.2 MPa δ ₅ % ψ% akJ/ ^cm2 K _1C MPam ^1/2 1 0 40 portrait 10591035 1029994 19.016.4 47.044.3 47.442.1 -- 2 2 25 Longitudinal (TL) 10951080 10501025 20.020.0 47.039.0 58.552.0 74.9 3 15 25 portrait 10411056 988998 15.418.0 33.336.5 -- 4 -10 20 portrait 10461036 10101000 19.319.6 53.051.4 -- technical indicators - - Longitudinal (TL) 980～1180 - ≥10 ≥25 ≥29.5 ≥44

Claims (5)

1. titanium alloy quasi-beta forging process, the titanium alloy type that it was suitable for are nearly alpha titanium alloy, alpha-beta Type Titanium Alloy and nearly beta titanium alloy, it is characterized in that this technology comprises following each step:

(1) preheating insulation of titanium alloy blank is placed on preheating in the resistance furnace with titanium alloy blank, and preheating temperature is beta transformation point (T _β) following 20～40 ℃, i.e. T _β-(20～40) ℃, stove calculates soaking time, soaking time t (min)=η * δ after arriving preheating temperature _Max, δ _Max(mm) be the maximum cross-section thickness of blank, η is a heating coefficient, and the value of the preheating heating coefficient η of blank is 0.4～0.7;

(2) will be warming up to T with stove through the blank behind step (1) preheating insulation _β-10 ℃～T _βCalculate soaking time after+20 ℃, the unanimity of the same step of calculation formula (1) of soaking time t (min), but the value of heating coefficient η is 0.1～0.5;

(3) with above-mentioned in preset temperature heating and the blank after reaching predetermined soaking time forges, die forging or rolling, forge back water-cooled or air cooling rapidly.

2. titanium alloy quasi-beta forging process according to claim 1 is characterized in that: in the resistance furnace effectively the maximum temperature deviation of workspace be not more than ± 10 ℃, blank shove charge after furnace temperature arrives preheating temperature is placed in effective workspace.

3. titanium alloy quasi-beta forging process according to claim 1 is characterized in that: the Heating temperature in the above-mentioned steps (2) is T _β～T _β+ 10 ℃.

4. titanium alloy quasi-beta forging process, the titanium alloy type that it was suitable for are nearly alpha titanium alloy, alpha-beta Type Titanium Alloy and nearly beta titanium alloy, it is characterized in that this technology comprises following each step:

(1) blank is placed directly in the resistance furnace and directly is warming up to T with stove without preheating insulation _β-10 ℃～T _βCalculate soaking time after+20 ℃, the calculation formula of soaking time t (min) and aforesaid right require consistent in 1 the step (1), but the value of heating coefficient η is 〉=0.6;

(2) with above-mentioned in preset temperature heating and the blank after reaching predetermined soaking time forges, die forging or rolling, forge back water-cooled or air cooling rapidly.

5. titanium alloy quasi-beta forging process according to claim 4 is characterized in that: the Heating temperature in the above-mentioned steps (1) is T _β～T _β+ 10 ℃.