CN108067596A - A kind of method that thin-belt casting rolling prepares TiAl alloy uniform formation slab - Google Patents

Abstract

The invention belongs to technical field of material metallurgy, and in particular to a kind of method that thin-belt casting rolling prepares TiAl alloy uniform formation slab.This method obtains TiAl alloy melt by vacuum induction melting; in the molten bath that the crystallization roll and side seal board that melt is reversely rotated through the inflow of chute passage by two form; working chamber, chute passage and sprue gate are carried out to continue atmosphere protection; it is 20~40 DEG C to control the molten bath upper surface alloy melt degree of superheat; 100~250mm of contact arc length of melt and crystallization roll roll surface; 0.3~0.4s of time of contact of melt and crystallization roll roll surface; make the crystallized roller solidification of melt and rolling deformation and export, obtain thin-belt casting rolling TiAl alloy sheet billet.Slab goes out carries out slow cooling processing immediately after roll, holding temperature is 800~1050 DEG C and cools to room temperature with the furnace, obtains the TiAl alloy slab with uniform equiaxed grain structure.The present invention realizes the high quality TiAl alloy slab with uniform tiny equiaxed structure, non-stop layer segregation by controlling the annealing process of casting-milling technology parameter and slab.

Description

A method for preparing TiAl alloy uniform structure slab by thin strip casting and rolling

Technical field:

The invention belongs to the technical field of material metallurgy, and in particular relates to a method for preparing a TiAl alloy uniform structure slab by thin strip casting and rolling.

Background technique:

TiAl alloy is a new type of light-weight high-temperature-resistant structural material, which has the advantages of low density, high-temperature strength, good oxidation resistance and high-temperature creep resistance, and is an ideal material for high-temperature structural components used in aerospace. However, TiAl alloys have low room temperature plasticity, difficult hot processing, and difficult preparation of large-size plates, which severely limit the development and application of this alloy. At present, TiAl alloy sheets are mainly prepared by sheathed hot rolling and isothermal rolling. The related methods can solve the problems of rapid heat dissipation at high temperature, crack initiation and expansion during thermal deformation of TiAl alloy sheets. However, limited by the structural stability of jacketed hot rolling and the complexity of the hot rolling process, the yield of the plate is low, and it is difficult to obtain industrial size plates. At the same time, the isothermal hot rolling equipment is expensive, and the prepared plates tend to have coarse lamellar structures, resulting in poor formability.

In addition, the twin-roll strip casting and rolling technology can effectively realize the preparation of large-scale TiAl alloy sheets. This technology is a new process of injecting liquid metal directly into the molten pool composed of two casting rolls and side sealing plates, and "casting and rolling" semi-finished billets or finished strips with the rotation of the casting rolls. Its near-net forming characteristics can realize the preparation of large-size plates of difficult-to-deform metals. At the same time, the process has the characteristics of sub-rapid solidification, which can significantly refine the as-cast structure and effectively improve the mechanical properties. However, in the process of preparing TiAl alloy slabs by twin-roll casting and rolling, its cooling characteristics easily lead to symmetrical growth of grains, and uneven distribution of columnar and equiaxed grains appears in the thickness direction of the slab. Row to the center of the sheet can easily lead to a central segregation zone. This inhomogeneous structure and segregation seriously reduces the mechanical properties and formability of the plate, and subsequent thermomechanical treatment of the slab is required, the process is complex and the structure and properties are difficult to control precisely. At the same time, the rapid cooling and uneven structure characteristics of thin strip casting and rolling can easily lead to large internal stress in the sheet, causing sheet cracking and internal defects, and seriously deteriorating the preparation and surface quality of TiAl alloy sheets. Therefore, how to obtain a uniform structure of TiAl alloy and control solute segregation through thin strip casting and rolling technology has become the key to high-quality slab preparation, and there is no related method to solve it.

Invention content:

Aiming at the problems of uneven structure and center segregation in twin-roll thin strip casting and rolling TiAl alloy slabs, the present invention provides a method for preparing TiAl alloy uniform structure slabs by thin strip casting and rolling. By controlling the casting and rolling process parameters and slab The slow cooling process achieves a high-quality TiAl alloy slab with uniform fine equiaxed structure and no center segregation.

Technical scheme of the present invention is as follows:

A method for preparing TiAl alloy uniform structure slabs by thin strip casting and rolling, the method obtains TiAl alloy melt through vacuum induction furnace melting, and the melt flows through the chute channel and consists of two counter-rotating crystallization rollers and side sealing plates In the melting pool, continuous atmosphere protection is carried out for the melting chamber, chute channel and pouring nozzle. The superheating degree of the alloy melt on the upper surface of the melting pool is controlled to be 20-40°C, and the contact arc length between the melt and the crystallization roller surface is 100-250mm. The contact time with the surface of the crystallization roll is 0.3-0.4s, so that the melt is solidified, rolled and deformed by the crystallization roll, and then exported to obtain a thin strip cast TiAl alloy thin slab; 800-1050°C and slow cooling to room temperature to finally obtain a TiAl alloy slab with a uniform equiaxed grain structure.

The method for preparing a TiAl alloy uniform structure slab by thin strip casting and rolling is carried out according to the following steps:

Step 1, obtaining a TiAl alloy melt by smelting in a vacuum induction furnace; wherein, the atomic percentage of the components in the TiAl alloy is: 44-48% Al, and the rest is Ti and unavoidable impurities;

Step 2, thin strip casting and rolling TiAl alloy slab preparation:

TiAl alloy slabs are prepared by a thin strip casting mill using beryllium copper rolls. The alloy melt flows into the molten pool formed by two counter-rotating crystallization rolls and side sealing plates through the chute channel, and the melting chamber, chute channel and pouring The nozzle is protected by continuous atmosphere, and the superheat of the alloy melt on the upper surface of the molten pool is controlled to be 20-40°C. The contact arc length between the melt and the surface of the crystallization roller is 100-250mm, and the contact time between the melt and the surface of the crystallization roller is 0.3-0.4s , so that the melt is solidified by crystallization rollers and rolled and deformed to form a TiAl alloy slab;

Step 3: Slowly cool the thin-strip cast-rolled slab immediately after it comes out of the roll. The holding temperature is 800-1050°C, and then slowly cool to room temperature to obtain a TiAl alloy slab with no obvious central segregation along the thickness direction and a uniform equiaxed grain structure. .

In the step 1, a calcium oxide crucible is used for melting in a vacuum induction furnace, and a TiAl alloy ingot is melted by a vacuum consumable arc as a base material.

In the step 2, the protective atmosphere used is argon.

In the step 2, the degree of superheat of the melt is controlled by the melt temperature of the TiAl alloy during the smelting process.

In the step 2, the diameter of the crystallization roller is 400-600mm, and the contact arc length between the melt in the molten pool and the surface of the crystallization roller is controlled by controlling the height of the liquid level in the molten pool, so that the titanium-aluminum alloy melt in the molten pool and the crystallization roller The contact arc length of the roller surface is 100-250mm.

In the step 2, the contact time between the TiAl alloy melt and the surface of the crystallization roller is controlled by adjusting the rotation speed of the crystallization roller, and the rotation speed of the crystallization roller is 0.25-0.6 m/s.

In the step 2, the chute channel and the casting nozzle are protected by atmosphere, and the protective atmosphere is introduced into the intermediate frequency vacuum induction furnace, so that the pressure in the melting furnace is normal pressure and there is protective atmosphere protection, and the plug-in valve is opened. After the melting crucible, chute channel and casting nozzle are poured, the casting and rolling plate is poured.

In step 3, the cast-rolled slab is quickly put into a pre-heated holding furnace after being removed from the casting roll to cool down with the furnace, or is covered and kept warm with heat-preserving asbestos.

In the method for preparing a TiAl alloy uniform structure slab by thin strip casting and rolling, the thickness of the TiAl alloy uniform structure slab is 2-5 mm, and the width is 100-200 mm.

Advantage of the present invention and beneficial effect are:

1. The present invention improves the solidification and plastic deformation conditions in the thin strip casting and rolling process, avoids the formation of inhomogeneous structures and promotes Solute diffusion provides favorable conditions for achieving uniform and fine equiaxed grain structure in the thickness direction and solute segregation control.

2. The production process of the present invention is simple and stable, and can be effectively used in the preparation of high-quality slabs of TiAl alloys cast by twin-roll strip continuous casting.

Description of drawings

Fig. 1 is a schematic diagram of the principle of twin-roll strip casting and rolling for TiAl alloy slab preparation in the present invention; wherein: 1: vacuum induction melting furnace; 2: argon protection device; 3: chute channel; 4: crystallization roll; 5: thin plate Blank.

Fig. 2 is a structure diagram of the TiAl alloy thin slab prepared in Example 1 of the present invention: (a) edge; (b) center.

Fig. 3 is a microstructure diagram of the TiAl alloy thin slab prepared in Example 2 of the present invention: (a) edge portion; (b) core portion.

Detailed ways

As shown in Figure 1, the present invention carries out the twin-roll strip casting and rolling structure of TiAl alloy slab preparation as follows: vacuum induction melting furnace 1 bottom opening communicates with chute passage 3, chute passage 3 top communicates with argon protection device 2, chute Crystallization rollers 4 are arranged on both sides of the outlet at the bottom of the channel 3 , and the TiAl alloy melt in the vacuum induction melting furnace 1 passes through the chute channel 3 and the crystallization rollers 4 to form a thin slab 5 .

In the specific implementation process, the method for preparing a TiAl alloy uniform structure slab by thin strip casting and rolling of the present invention, the specific steps are as follows:

In step 1, a TiAl alloy melt is obtained by smelting in a vacuum induction furnace; wherein, the atomic percentage of the TiAl alloy composition is: Al: 44-48%, and the rest is Ti and unavoidable impurities.

In step 1, a calcium oxide crucible is used for smelting in a vacuum induction furnace. The original TiAl alloy base metal ingot is obtained by vacuum consumable arc melting three times.

Step 2, preparation of cast-rolled TiAl alloy slab:

TiAl alloy slab preparation was performed on a strip caster with beryllium copper rolls. The alloy melt flows into the molten pool formed by two counter-rotating crystallization rollers and side sealing plates through the chute channel, and the melting chamber, the chute channel and the pouring nozzle are continuously protected by the atmosphere, and the superheat and melting of the alloy melt on the upper surface of the molten pool are controlled. The contact arc length between the body and the surface of the crystallization roller, and the contact time between the melt and the surface of the crystallization roller are three process parameters, so that the melt is solidified and exported by the crystallization roller to form a TiAl alloy thin strip. The process parameters are controlled as follows:

The superheating degree of the melt on the upper surface of the molten pool is 20-40°C;

The contact arc length between the melt in the molten pool and the surface of the crystallization roller is 100-250mm;

The contact time between the melt and the surface of the crystallization roller is 0.3-0.4s;

Process parameter control description is as follows:

(1) Melt superheat on the upper surface of the molten pool: The superheat of the melt on the upper surface of the molten pool is controlled by adjusting the temperature of the melt in the smelting furnace. Make the superheating degree of the melt on the upper surface of the molten pool reach 20-40°C. The relationship between the temperature of the melt flowing out of the smelting furnace and the superheat of the upper surface melt is:

ΔT = TT _r -T _s

Among them, ΔT is the degree of superheat, T is the melt outflow temperature, _Tr is the temperature drop during the melt outflow to the molten pool, _{and Ts} is the solidification temperature of the alloy, all in °C.

(2) The contact arc length between the melt in the molten pool and the surface of the crystallization roller

The diameter of the casting and rolling crystallization roll is 500 mm, and the length of the contact arc between the melt in the molten pool and the surface of the crystallization roll is controlled by adjusting the height of the molten pool, so that the length of the contact arc between the melt in the molten pool and the surface of the crystallization roll is 100-250 mm. The relationship between the molten pool height and the contact arc length is:

Among them, H is the height of the molten pool, r is the radius of the crystallization roller, L is the length of the contact arc, and the unit is m.

(3) The contact time between the melt in the molten pool and the surface of the crystallization roller is controlled by adjusting the rotation speed of the crystallization roller, so that the contact time between the melt and the surface of the crystallization roller is 03-04s. The data relationship between the rotational speed of the crystallization roll and the contact time between the melt and the surface of the crystallization roll is:

t=L/v

Among them, t is the contact time, in s; L is the contact arc length, in m; v is the crystallization roller speed, in m/s.

In step 2, the protective atmosphere is argon.

In step 2, the pouring process is as follows: protect the chute channel and the casting and rolling nozzle with atmosphere, and then pass the protective atmosphere into the intermediate frequency vacuum induction furnace, so that the pressure in the melting furnace is normal pressure and there is a protective atmosphere for protection, and open the inserting plate After the valve is connected to the smelting crucible, the chute channel and the casting nozzle, the casting and rolling plate is poured.

In step 2, the degree of superheat of the melt in the casting and rolling process is controlled by the melt temperature of the TiAl alloy in the smelting process. If the melt temperature is too high, there will be a melt leakage accident, and the slab cannot be formed. At the same time, under the condition of rapid solidification, columnar grain structure and center segregation will easily occur in the thickness direction. If the melt temperature is too low, insufficient flow and roll jam accidents will occur.

In step 2, the height of the liquid level in the molten pool directly affects the length of the contact arc between the melt and the surface of the crystallization roller, which in turn affects the internal structure of the sheet and the surface quality of the sheet.

In step 2, the contact time between the TiAl alloy melt and the surface of the crystallization roll can be controlled by adjusting the rotation speed of the crystallization roll. If the speed of the crystallization roll is too fast, the contact time between the melt and the surface of the crystallization roll will be too short, resulting in melt leakage accidents and insufficient rolling force; if the speed is too slow, the contact time between the melt and the surface of the crystallization roll will be too long Excessive rolling force and roll jam accidents.

Step 3, slow cooling treatment:

The thin-strip cast-rolled TiAl alloy slab is directly subjected to slow cooling treatment after exiting the roll, the holding temperature is 800-1050°C, and then slowly cooled to room temperature.

In step 3, after the cast-rolled slab is removed from the casting roll, it is quickly put into a pre-heated holding furnace and cooled with the furnace, or covered with heat-insulating asbestos to prevent crack defects in the plate, achieve uniform structure control and promote solute diffusion .

Below, the present invention is described in further detail through examples.

Example 1

In this embodiment, the method for preparing a TiAl alloy slab with a uniform structure by thin strip casting is as follows: a TiAl alloy melt is obtained by smelting in a vacuum induction furnace, wherein the alloy composition is Ti-44Al (atomic percentage). Introduce argon gas into the melting chamber to make it normal pressure, and provide continuous argon protection for the melting chamber, chute channel and casting nozzle. The alloy melt flows into the molten pool formed by two counter-rotating crystallization rollers and side sealing plates through the chute channel to control the superheat of the alloy melt on the upper surface of the molten pool, the contact arc length between the melt and the crystallization roller surface, and the The three process parameters of the contact time of the crystallization roller surface make the melt solidified and rolled deformed by the crystallization roller, and the process parameters are controlled as follows:

The superheat of the melt on the upper surface of the molten pool is 30°C;

The contact arc length between the melt in the molten pool and the surface of the crystallization roller is 100mm;

The contact time between the melt and the surface of the crystallization roller is 0.4s;

After the cast-rolled slab comes out of the roll, it is directly put into the heating furnace at a heating temperature of 800°C, and then slowly cooled to room temperature with the furnace.

The thickness of the TiAl alloy slab produced by twin-roll strip continuous casting produced by the invention is 3 mm, and the width is 200 mm.

The structure of the TiAl alloy thin slab prepared in the example of the present invention is shown in Figure 2: (a) edge structure; (b) core structure. It can be seen from Fig. 2 that the solidification structure of the TiAl alloy thin slab prepared by the present invention is a fine and uniform equiaxed grain structure without obvious central segregation.

Example 2

In this embodiment, the method for preparing a TiAl alloy slab with a uniform structure by thin strip casting and rolling is as follows: melting a TiAl alloy melt through vacuum induction furnace, wherein the alloy composition is Ti-46Al (atomic percentage). Introduce argon gas into the melting chamber to make it normal pressure, and provide continuous argon protection for the melting chamber, chute channel and casting nozzle. The alloy melt flows into the molten pool formed by two counter-rotating crystallization rollers and side sealing plates through the chute channel to control the superheat of the alloy melt on the upper surface of the molten pool, the contact arc length between the melt and the crystallization roller surface, and the The three process parameters of the contact time of the crystallization roller surface make the melt solidified and rolled deformed by the crystallization roller, and the process parameters are controlled as follows:

The superheat of the melt on the upper surface of the molten pool is 25°C;

The contact arc length between the melt in the molten pool and the surface of the crystallization roller is 120mm;

The contact time between the melt and the surface of the crystallization roller is 0.3s;

After the cast-rolled slab comes out of the roll, it is directly put into the heating furnace at a heating temperature of 1050°C, and then slowly cooled to room temperature with the furnace.

The thickness of the TiAl alloy slab produced by twin-roll strip continuous casting produced by the invention is 2.5 mm, and the width is 200 mm.

The structure of the TiAl alloy thin slab prepared in the example of the present invention is shown in Figure 3: (a) edge structure; (b) core structure. It can be seen from Fig. 3 that the solidification structure of the TiAl alloy thin slab prepared by the present invention is a fine and uniform full-lamellar equiaxed grain structure with a grain size of 30-60 μm.

Example 3

In this embodiment, the method for preparing a TiAl alloy slab with a uniform structure by thin strip casting is as follows: a TiAl alloy melt is obtained by smelting in a vacuum induction furnace, wherein the alloy composition is Ti-48Al (atomic percentage). Introduce argon gas into the melting chamber to make it normal pressure, and provide continuous argon protection for the melting chamber, chute channel and casting nozzle. The alloy melt flows into the molten pool formed by two counter-rotating crystallization rollers and side sealing plates through the chute channel to control the superheat of the alloy melt on the upper surface of the molten pool, the contact arc length between the melt and the crystallization roller surface, and the The three process parameters of the contact time of the crystallization roller surface make the melt solidified and rolled deformed by the crystallization roller, and the process parameters are controlled as follows:

The superheat of the melt on the upper surface of the molten pool is 30°C;

The contact arc length between the melt in the molten pool and the surface of the crystallization roller is 180mm;

The contact time between the melt and the surface of the crystallization roller is 0.4s;

After the cast-rolled slab leaves the roll, it is directly placed in asbestos for covering and heat preservation, and cooled to room temperature. The twin-roll thin strip continuous casting produced by the present invention produces a TiAl alloy full-lamellar equiaxed thin strip with a thickness of 2mm and a width of 100mm.

The results of the examples show that the method for preparing a TiAl alloy uniform structure slab by thin strip casting and rolling of the present invention can obtain uniform and fine equiaxed grain structure distribution along the thickness direction, reduce central segregation, reduce surface cracks and internal defects, and achieve high Preparation of quality TiAl alloy slabs.

Claims (10)

1. A method for thin strip casting and rolling to prepare TiAl alloy uniform structure slab, it is characterized in that, the method obtains TiAl alloy melt by vacuum induction furnace smelting, and melt flows into by two counter-rotating crystallization through chute channel In the melting pool composed of rollers and side sealing plates, continuous atmosphere protection is carried out for the melting chamber, chute channel and pouring nozzle, and the superheating degree of the alloy melt on the upper surface of the melting pool is controlled at 20-40°C, and the contact arc length between the melt and the surface of the crystallization roller 100-250mm, the contact time between the melt and the surface of the crystallization roll is 0.3-0.4s, so that the melt is solidified by the crystallization roll and deformed by rolling and then exported to obtain a thin strip cast TiAl alloy thin slab; immediately after the slab comes out of the roll Slow cooling treatment, the holding temperature is 800-1050° C. and slow cooling to room temperature, finally obtaining a TiAl alloy slab with uniform equiaxed grain structure. 2. thin strip casting according to claim 1 prepares the method for uniform structure slab of TiAl alloy, it is characterized in that, carry out according to the following steps: Step 1, obtaining a TiAl alloy melt by smelting in a vacuum induction furnace; wherein, the atomic percentage of the components in the TiAl alloy is: 44-48% Al, and the rest is Ti and unavoidable impurities; Step 2, thin strip casting and rolling TiAl alloy slab preparation: TiAl alloy slabs are prepared by a thin strip casting mill using beryllium copper rolls. The alloy melt flows into the molten pool formed by two counter-rotating crystallization rolls and side sealing plates through the chute channel, and the melting chamber, chute channel and pouring The nozzle is protected by continuous atmosphere, and the superheat of the alloy melt on the upper surface of the molten pool is controlled to be 20-40°C. The contact arc length between the melt and the surface of the crystallization roller is 100-250mm, and the contact time between the melt and the surface of the crystallization roller is 0.3-0.4s , so that the melt is solidified by crystallization rollers and rolled and deformed to form a TiAl alloy slab; Step 3: Slowly cool the thin-strip cast-rolled slab immediately after it comes out of the roll. The holding temperature is 800-1050°C, and then slowly cool to room temperature to obtain a TiAl alloy slab with no obvious central segregation along the thickness direction and a uniform equiaxed grain structure. . 3. The method for preparing a TiAl alloy uniform structure slab by thin strip casting according to claim 2, is characterized in that, in the described step 1, a calcium oxide crucible is used to smelt in a vacuum induction furnace, and a vacuum automatic Arc-melting TiAl alloy ingot was used as the base material. 4. The method for preparing a TiAl alloy slab with uniform structure by thin strip casting and rolling according to claim 2, characterized in that: in the step 2, the protective atmosphere used is argon. 5. the method for preparing TiAl alloy homogeneous structure slab by strip casting according to claim 2, is characterized in that, in described step 2, melt superheat is controlled by the melt temperature of TiAl alloy in smelting process . 6. The method for preparing a TiAl alloy uniform structure slab by thin strip casting and rolling according to claim 2, characterized in that: in the step 2, the diameter of the crystallization roll is 400-600mm, and the melt and crystallization in the molten pool The contact arc length of the roller surface is controlled by controlling the height of the liquid level in the molten pool, so that the contact arc length between the titanium-aluminum alloy melt in the molten pool and the roller surface of the crystallization roller is 100-250 mm. 7. The method for preparing a TiAl alloy uniform structure slab by thin strip casting according to claim 2, is characterized in that: in the described step 2, the contact time between the TiAl alloy melt and the surface of the crystallization roll is adjusted by crystallization The rotation speed of the roller is controlled, and the rotation speed of the crystallization roller is 0.25-0.6m/s. 8. The method for preparing a TiAl alloy uniform structure slab by thin strip casting and rolling according to claim 2, is characterized in that: in the described step 2, the chute channel and the casting and rolling nozzle are carried out atmosphere protection, and the intermediate frequency vacuum The protective atmosphere is introduced into the induction furnace so that the pressure in the melting furnace is normal pressure and protected by the protective atmosphere. After the gate valve is opened to connect the melting crucible, the chute channel and the casting nozzle, the casting and rolling plate is poured. 9. The method for preparing a TiAl alloy homogeneous structure slab by thin strip casting according to claim 2, is characterized in that: in the described step 3, the cast slab is quickly put into a preheated slab after the casting roll is removed. The heat preservation furnace is cooled with the furnace, or covered with heat preservation asbestos for heat preservation. 10. The method for preparing a TiAl alloy uniform structure slab by thin strip casting according to claim 1 or 2, characterized in that: the thickness of the TiAl alloy uniform structure slab is 2-5 mm, and the width is 100-200 mm.