A method for preparing a Ti80 titanium alloy plate with a thickness of ≥50 mm and high impact toughness

Abstract

The present invention discloses a Ti80 titanium alloy plate with a thickness of ≥50 mm and high impact toughness and a preparation method thereof, comprising: S1) selecting a Ti80 slab with a thickness of 200-500 mm; S2) rolling the slab, heating the slab and then rolling it through 1-2 heats to obtain a plate with a thickness of 50-180 mm, with a total rolling deformation of 60-90%, and a final rolling temperature ≥T β -250°C, S3) plate straightening. This invention achieves micro-hardening of the surface of thick, sized intermediate slabs through intermittent cooling. Simultaneously, by controlling the amount of rolling deformation and its distribution, the deformation is more readily penetrated into the "softened" core, refining the core structure and improving its toughness. This solves the problem of inconsistent structure between the surface and core of Ti80 titanium alloy thick plates (thickness ≥ 50mm) and insufficient core impact toughness. The resulting Ti80 thick plates can meet the demand for thick plates in marine engineering equipment.

Description

Technical Field

[0001] The invention belongs to the technical field of titanium alloy hot processing, and particularly relates to a method for preparing a high-impact-toughness Ti80 titanium alloy plate with a thickness of 50 mm or more. Background Art

[0002] Ti80 titanium alloy, a near-α-type titanium alloy independently developed in my country, boasts excellent comprehensive properties and is currently widely used in marine engineering equipment such as ships and submersible pressure hulls. Its primary form is plate. In recent years, with the upgrading of marine engineering equipment, the thickness of Ti80 plate has gradually increased from under 25 mm to 50-180 mm.

[0003] Regarding relatively thin medium and thick plates, Chinese patent CN109504876 discloses a Ti80 medium and thick plate with high impact toughness, its preparation method, and application. The prepared slab has a thickness of 10-24mm, and the core is easily rolled through during the rolling process, with minimal differences in microstructure and performance between the surface and core. However, for Ti80 titanium alloy plates with a thickness of 50mm or more, the corresponding increase in slab thickness makes rolling more difficult, and rolling deformation has difficulty penetrating into the core of the hot-rolled plate, resulting in serious inconsistencies in the surface and core microstructures. This makes it difficult to control the microstructure during subsequent heat treatment. In terms of performance, this is reflected in the low impact toughness at half the thickness of plates with a thickness of 50mm or more, and may even fail to meet design standards.

[0004] In addition to the difficulty of the rolling process, the existing titanium processing plant rolling mills also have shortcomings. When rolling plates with a thickness of more than 50mm, the following problems are common:

[0005] (1) The mill opening is small and the slab thickness is limited, resulting in a small total deformation of the plate along the thickness direction;

[0006] (2) The rolling force and torque are small. For titanium alloys with high deformation resistance such as Ti80, the deformation during the rolling process is small and the deformation is difficult to penetrate into the core.

[0007] (3) The degree of automation of the rolling mill is low, and the process repeatability and product quality stability are insufficient.

[0008] Modern steel mills have large rolling mills with large rolling force and torque, large opening, and high degree of process automation, which are particularly suitable for batch rolling of wide and thick plates. Summary of the Invention

[0009] The object of the present invention is to provide a method for preparing a Ti80 titanium alloy plate with a thickness of ≥50 mm and high impact toughness, improve the uniformity of the surface and core structure of the Ti80 titanium alloy plate with a thickness of more than 50 mm, and enhance the impact toughness of the core of the plate. The obtained titanium alloy plate has a tensile strength of ≥840 MPa at each position, a yield strength of ≥740 MPa, an elongation after fracture A ≥12%, a cross-sectional reduction rate Z ≥39%, and an impact toughness KV2>50J.

[0010] To achieve the above objectives, the technical solutions of the present invention are as follows:

[0011] A method for preparing a Ti80 titanium alloy plate with a thickness of 50 mm or more and high impact toughness, comprising the following steps:

[0012] S1) Slab

[0013] Select Ti80 titanium alloy slab with a thickness of 200~500mm;

[0014] S2) Slab rolling

[0015] The heated slab is rolled 1-2 times to obtain a plate with a thickness of 50-180 mm. The heating temperature is T β - (10~80) ℃; total rolling deformation 60~90%, 1-pass rolling is divided into two stages, the second stage rolling temperature is 20~40 ℃ lower than the first stage temperature; 2-pass rolling, the second pass rolling temperature is 30~50 ℃ lower than the first pass temperature, the final rolling temperature ≥T β -250℃, where T β represents the β phase transition temperature of the titanium alloy slab, in °C;

[0016] S3) Plate straightening

[0017] After straightening, the plates are air-cooled to room temperature.

[0018] Preferably, the upper and lower surfaces of the Ti80 titanium alloy slab are respectively composited with pure titanium plates with a thickness of 1.5 to 3 mm, and the surfaces of the pure titanium plates not in contact with the titanium alloy slab are coated with anti-oxidation and heat-insulating coatings.

[0019] Preferably, the mass percentage of each component in the Ti80 titanium alloy slab is: 5.8%≤Al≤6.2%, 2.8%≤Nb≤3.2%, 1.8%≤Zr≤2.2%, 0.9%≤Mo≤1.5%, 0<Si≤0.15%, 0<Fe≤0.25%, 0<C≤0.10%, 0<N≤0.05%, 0<H≤0.010%, 0.06%≤O≤0.12%, the remainder is Ti and unavoidable impurities, and the slab microstructure is a two-phase deformation structure.

[0020] Preferably, in step S2), the temperature uniformity of the heating furnace used for heating and insulating the slab is within ±10°C.

[0021] Preferably, in step S2), the specific control of rolling fire number 1 is as follows:

[0022] S21) Slab heating

[0023] Heating temperature T β - (10~80)℃, holding time t= (1.2~3.0) × H, where t is in min and H is the slab thickness in mm;

[0024] S22) First stage rolling

[0025] The total rolling deformation is controlled at 20~35%, the first pass deformation is 2~3%, and the remaining passes deformation is 4~8%; the surface temperature of the slab after rolling is T1;

[0026] S23) Second stage rolling

[0027] When the surface temperature of the slab drops to 20~40℃ below T1, the second stage of rolling begins. The rolling adopts low speed and high reduction, and the total deformation is 30~50%; the deformation of the first pass is 5~7%, and the deformation of the remaining passes is 9~17%.

[0028] Preferably, in step S2), the specific control of rolling fire number 2 is as follows:

[0029] S21) Slab heating

[0030] The heating temperature is T β - (10~80)℃, holding time t= (1.2~3.0) × H, where t is in min and H is the slab thickness in mm;

[0031] S22) 1st hot rolling

[0032] The total rolling deformation is controlled at 20~35% to obtain the rolled billet; the deformation of the first pass is 2~3%, and the deformation of the remaining passes is 4~8%;

[0033] S23) Reheating

[0034] The slab is returned to the furnace for heating at a temperature 10-20°C lower than the first hot slab heating temperature. The holding time is t = (0.8-1.5) × h, where t is in min and h is the slab thickness in mm.

[0035] S24) Second hot rolling

[0036] After the billet is taken out of the furnace, rolling begins when the surface temperature drops by 20~30℃. The total rolling deformation is 30~50%; the deformation of the first pass is 5~7%, and the deformation of the remaining passes is 9~17%.

[0037] Preferably, in step S2), the rolling speed is controlled at 1.2-2.5 m / s.

[0038] Preferably, in the step S3);

[0039] Plate thickness ≥90mm, use rolling mill for leveling; leveling passes 2~3 times, single pass reduction 0.5~1.0mm;

[0040] The plate thickness is less than 90mm, and it is leveled by a straightening machine with 1 to 3 straightening passes and a straightening speed of 0.5 to 1.0 m / s.

[0041] The titanium alloy plate obtained by the present invention has a uniform dual-state microstructure after annealing, the primary α phase is equiaxed, the average grain size is 12-25 μm, and the primary α phase content is 20-30%; the tensile strength at each position of the titanium alloy plate is ≥840 MPa, the yield strength is ≥740 MPa, the elongation after fracture A is ≥12%, the cross-sectional shrinkage Z is ≥39%, and the impact toughness KV2 is greater than 50 J.

[0042] In the manufacturing method of the present invention:

[0043] During the slab rolling process, the present invention controls the total rolling deformation to be between 60% and 90%, so as to ensure that the slab undergoes sufficient recrystallization during rolling and subsequent heat treatment, thereby obtaining a uniform and refined structure.

[0044] Control the final rolling temperature ≥T β -250℃ to ensure surface quality. At the same time, rolling at too low a temperature will easily produce adiabatic shear bands, affecting the organization and performance.

[0045] In the rolling process of the present invention, the plate rolling scheme can be 1-2 heat rolling.

[0046] During the rolling process, the slab has a cooling process (intermittent cooling), which causes the temperature of the slab surface to drop. The rolling of the first fire is divided into two stages, and the rolling temperature of the second stage is 20~40℃ lower than that of the first stage; during the second fire rolling, the rolling temperature of the second fire is 30~50℃ lower than that of the first fire. During the 1st or 2nd fire rolling, there will be a cooling process, which causes a certain temperature drop on the slab surface. The purpose is to achieve micro-hardening of the intermediate slab surface, so that deformation can easily penetrate into the "softened" core of the titanium alloy plate, refine the core structure, and improve the toughness of the core.

[0047] Furthermore, the slab heating temperature and time are controlled.

[0048] If the billet heating temperature is too low, the surface of the plate is prone to cracking during the rolling process; if it is too high, the billet enters the single-phase region or the deformation heat during the rolling process causes the core of the billet to enter the single-phase region, affecting the microstructure and properties of the final plate. The holding time is based on the burn-through time. If the time is too long, the grains will grow, affecting the final microstructure. Preferably, electric furnace heating is used, and the heating and holding temperature is T β - (10~80)℃, holding time t = (1.2~3.0) × H, where t is in min and H is the slab thickness in mm.

[0049] Furthermore, for the first heat rolling, it can be divided into three stages:

[0050] The first stage is at a higher temperature T β Rolling deformation at - (10 ~ 80) ℃ refines the surface structure and improves plasticity to prevent surface cracking during subsequent low-temperature rolling.

[0051] In the second stage, the slab temperature is controlled to achieve micro-hardening of the intermediate slab surface. Temperature control ends when the slab surface temperature is 20-40°C lower than the temperature at the end of the first stage. If the temperature is too low, the subsequent rolling deformation resistance will be too high, increasing equipment stress and the risk of surface cracking.

[0052] The third stage adopts a large deformation rolling process, and the total deformation is controlled at 30~50%, so that the deformation can penetrate into the "softened" core of the titanium alloy plate, refine the core structure, and improve the core toughness.

[0053] Furthermore, for the 2-pass rolling, the 1st pass rolling is the same as the 1st pass rolling scheme, at a higher temperature T β - Rolling deformation at -(10~80)℃ refines the surface structure and improves plasticity to prevent surface cracking during subsequent low-temperature rolling;

[0054] The second heat rolling heating temperature is 10-20℃ lower than the first heat temperature. On the one hand, it prevents the growth of a grains, and on the other hand, it ensures that the core temperature is sufficient for subsequent rolling. After the billet is taken out of the furnace, the surface temperature is reduced by 20-30℃ before rolling begins. The purpose is to achieve micro-hardening of the intermediate state slab surface and allow the deformation to penetrate into the "softened" core of the titanium alloy plate.

[0055] During the first stage rolling in a 1-pass rolling plan or the first pass rolling in a 2-pass rolling plan, the billet is relatively thick. Considering the limitations of the equipment's rolling force and torque, the deformation in the first pass is controlled at 2-3%, and the deformation in the remaining passes is controlled at 4-8%.

[0056] During the second stage of rolling in a 1-pass rolling scheme or the second pass of rolling in a 2-pass rolling scheme, the billet has been thinned. In order to fully deform the core, the deformation amount of each pass should be appropriately increased. The deformation amount of the first pass should be controlled at 5-7%, and the deformation amount of subsequent passes should be controlled at 9-17%.

[0057] The rolling speed is controlled between 1.2 and 2.5 m / s, taking into account both the billet rolling time and the steel casting time. If the rolling speed is too slow, the surface temperature drop will be large, increasing the risk of surface cracking. If the rolling speed is too fast, the steel casting distance will be long, increasing the time it takes for the slab to re-engage the rollers. Furthermore, a large amount of deformation heat will be generated in a short period of time, causing uneven microstructure.

[0058] Compared with the prior art, the present invention has the following beneficial effects:

[0059] (1) The present invention adopts 1-2 hot rolling to obtain thick specification plates of 50-180 mm. During the rolling process, the slab has a cooling process (intermittent cooling) to make the surface temperature of the slab drop. That is, during the 1-hot rolling, the slab is stopped in the middle to make the surface temperature of the slab drop by 20-40 ° C, or during the 2-hot rolling, the rolling is started after the slab temperature drops by 20-30 ° C before the second hot rolling, so as to achieve micro-hardening of the surface of the thick specification intermediate state slab. At the same time, by controlling the rolling deformation and the distribution of the deformation, the deformation is more likely to penetrate into the "softened" core, refine the core structure, thereby making the microstructure of the surface layer and core of the slab uniform and fine, and improving the toughness of the core; it can solve the technical problem that the surface and core structure of the 50-180 mm thick Ti80 titanium alloy plate are seriously inconsistent, resulting in insufficient impact toughness of the core of the titanium alloy plate (thickness ≥ 50 mm). The rolling method in the prior art does not have the step of cooling during rolling.

[0060] (2) After annealing treatment, the Ti80 titanium alloy thick plate produced by the method of the present invention has good microstructure uniformity in the surface and core, the primary α phase is equiaxed, the grain size is 12~25μm, the primary α phase content is 20~30%, the surface and core tensile strength is ≥840MPa, the yield strength is ≥740MPa, the elongation after fracture A is ≥12%, the cross-sectional shrinkage Z is ≥39%, and the impact toughness KV2 is greater than 50J.

[0061] (3) In view of the problems existing in the rolling mills of existing titanium processing plants, the present invention adopts a 1-2 fire rolling process, which can directly use the advanced rolling production line of the steel plant to roll titanium alloys. The rolling line has a high degree of automation and the rolling parameters are accurately controlled to ensure the uniformity of the plate structure and performance. BRIEF DESCRIPTION OF THE DRAWINGS

[0062] Figure 1 This is the appearance of the plate prepared in Example 1 of the present invention;

[0063] Figure 2 This is a microstructure picture of the plate after annealing treatment in Example 1 of the present invention;

[0064] Figure 3 This is the appearance of the plate prepared in Example 2 of the present invention;

[0065] Figure 4 This is a microstructure picture of the plate after annealing in Example 2 of the present invention;

[0066] Figure 5 This is a microstructure picture of the plate after annealing in the comparative example. DETAILED DESCRIPTION

[0067] The present invention will be further described below with reference to the embodiments and accompanying drawings. Example 1

[0068] The manufacturing method of Ti80 titanium alloy plate with a specification of 125×214×4550mm includes the following steps:

[0069] S1) Composite slab

[0070] The upper and lower surfaces of the titanium alloy slab are explosively bonded with 2mm thick pure titanium plates, and then coated with anti-oxidation and heat-insulating coatings to obtain a composite slab with a size of 380×1500×2200mm.

[0071] S2) Slab rolling (1st heat)

[0072] S21) heating the composite slab at 980° C. for 600 min using an electric furnace, and then removing the composite slab from the furnace for the first stage of rolling;

[0073] S22) First stage rolling

[0074] The total rolling deformation is controlled at 30.5%, the first pass deformation is 2.9%, and the remaining passes deformation is 4-8%. The surface temperature of the slab after rolling is 940℃.

[0075] S23) Second stage rolling

[0076] When the slab temperature drops to 900°C, the second stage of rolling begins. The total deformation of the rolling process is controlled at 36.6%, with the first pass deformation of 5.7% and the remaining passes deformation of 9-17%. The final rolling temperature is 810°C. The specifications of the rolled plate are 125×214×4550mm.

[0077] S3) Plate straightening

[0078] The steel was straightened and leveled in three passes with reductions of 1 mm, 0.8 mm and 0.5 mm respectively.

[0079] Figure 1 The appearance of the plate prepared in Example 1 of the present invention is as follows: Figure 1 It can be seen that the appearance of the board is in good shape and there is no obvious cracking on the surface.

[0080] Figure 2 The microstructure of the plate after annealing in Example 1 of the present invention, left: surface layer; right: thickness / 2, from Figure 2 It can be seen that both the surface and core of the plate have a dual-state (α+β) structure, and the primary α phase grain size is 18~22μm; the primary α phase content in the surface is 25%, and the primary α phase content in the core is 30%. Example 2

[0081] The manufacturing method of Ti80 titanium alloy plate with a specification of 65×2150×7400mm includes the following steps:

[0082] S1) Composite slab

[0083] The upper and lower surfaces of the titanium alloy slab are respectively composited with 2.5mm thick pure titanium plates by explosion, and then coated with anti-oxidation and heat-insulating coatings to obtain composite slabs with specifications of 200×1600×3200mm;

[0084] S2) Slab rolling (1st heat)

[0085] S21) heating the composite slab at 970° C. for 250 min using an electric furnace, and then removing the composite slab from the furnace for first-pass rolling;

[0086] S22) First stage rolling

[0087] The total rolling deformation is controlled at 25%, the first pass deformation is 3.0%, and the remaining passes deformation is 4~8%. The surface temperature of the slab after rolling is 940;

[0088] S23) Second stage rolling

[0089] When the slab surface temperature drops to less than 920℃, the second stage of rolling begins. The rolling deformation is 42.5%, the first pass deformation is 6.7%, and the remaining passes deformation is 9-17%. The final rolling temperature is 800℃. The plate specifications after rolling are 65×2150×7400mm.

[0090] S3) Plate straightening

[0091] Use straightening machine to straighten for 3 times, and the outlet gap is 65mm.

[0092] The microstructure of the plate after annealing is a dual-state (α+β) structure, and the primary α phase grain size is 18~22μm; the primary α phase content in the surface layer is 20%, and the primary α phase content in the core is 27%. Example 3

[0093] The manufacturing method of Ti80 titanium alloy plate with a specification of 55×2250×14000mm includes the following steps:

[0094] S1) Composite slab

[0095] The upper and lower surfaces of the titanium alloy slab are explosively bonded with 2mm thick pure titanium plates, and then coated with anti-oxidation and heat-insulating coatings to obtain composite slabs with specifications of 400×1600×2700mm.

[0096] S2) Slab rolling (2 passes)

[0097] S21) The composite slab is heated in a heating furnace at 965°C for 700 minutes and then taken out of the furnace for second-pass rolling;

[0098] S22) 1st hot rolling

[0099] The width is expanded to 2240mm in the transverse direction. The deformation of this rolling process is 20%, the deformation of the first pass is 2.5%, and the deformation of the remaining passes is 4~8%, resulting in a slab thickness of 280mm.

[0100] S23) Slab reheating

[0101] The rolled slab is returned to the furnace for heating at a temperature of 945°C and a holding time of 300 minutes.

[0102] S24) Second hot rolling

[0103] When the surface temperature of the rolled slab drops to 920°C, rolling begins. The total deformation during rolling is 40%, with the first pass deformation being 5.4% and the remaining passes deformations ranging from 9 to 17%. The final rolling temperature is 810°C, and the specifications of the rolled plate are 55×2250×14000mm.

[0104] S3) Plate straightening

[0105] Use straightening machine to straighten for 3 times, and the outlet gap is 55mm.

[0106] Figure 3 The appearance of the plate prepared in Example 3 of the present invention is as follows: Figure 3 It can be seen that the appearance of the board is in good shape and there is no obvious cracking on the surface.

[0107] Figure 4 This is a microstructure picture of the plate after annealing in Example 3 of the present invention. Figure 4 It can be seen that both the surface and core of the plate have a dual-state (α+β) structure, and the primary α phase grain size is 18~22μm; the primary α phase content in the surface is 20%, and the primary α phase content in the core is 27%. Example 4

[0108] The manufacturing method of Ti80 titanium alloy plate with a specification of 55×2250×14000mm includes the following steps:

[0109] S1) Composite slab

[0110] The upper and lower surfaces of the titanium alloy slab are explosively bonded with 2mm thick pure titanium plates, and then coated with anti-oxidation and heat-insulating coatings to obtain composite slabs with specifications of 400×1600×2700mm.

[0111] S2) Slab rolling (2 passes)

[0112] S21) The composite slab is heated at 965°C for 700 minutes using an electric furnace, and then taken out of the furnace for second-pass rolling;

[0113] S22) 1st hot rolling

[0114] The width is expanded to 2240mm in the transverse direction. The deformation of this rolling process is 28%, the deformation of the first pass is 2.0%, and the deformation of the remaining passes is 4~8%, resulting in a slab thickness of 280mm.

[0115] S23) Slab reheating

[0116] The rolled slab is returned to the furnace for heating at a temperature of 950°C and a holding time of 400 minutes.

[0117] S24) Second hot rolling

[0118] When the surface temperature of the rolled billet drops to 920℃, rolling begins. The total deformation of the rolling process is 50%, the deformation of the first pass is 5.6%, and the deformation of the remaining passes is 9-17%. The final rolling temperature is 820℃. The specifications of the rolled plate are 180×2200×5400mm.

[0119] S3) Plate straightening

[0120] The steel was straightened and leveled in three passes with reductions of 1 mm, 0.8 mm and 0.5 mm respectively.

[0121] After annealing, the microstructure of the black skin plate is a dual-state (α+β) structure, and the primary α phase grain size is 18~25μm; the primary α phase content in the surface layer is 21%, and the primary α phase content in the core is 26%. Comparative Example 1

[0122] The manufacturing method of Ti80 titanium alloy plate with a specification of 134×2130×3750mm includes the following steps:

[0123] S1) Composite slab

[0124] The upper and lower surfaces of the titanium alloy slab are respectively composited with 2mm thick pure titanium plates by explosion, and then coated with anti-oxidation and heat-insulating coatings to obtain composite slabs with specifications of 240×1500×3000mm;

[0125] S2) Slab rolling (1st heat)

[0126] The composite slab was heated in an electric furnace at 970°C for 400 minutes, then removed from the furnace for single-pass rolling. The first 10 passes were for widening rolling, and the last 6 passes were for lengthening rolling. The final rolling temperature was 820°C. The plate specifications after rolling were 134×2130×3750mm, with a total deformation of 46%.

[0127] S3) Plate straightening

[0128] The steel was straightened and leveled in three passes with reductions of 1 mm, 0.8 mm and 0.5 mm respectively. Comparative Example 2

[0129] The manufacturing method of Ti80 titanium alloy plate with a specification of 160×2150×5000mm includes the following steps:

[0130] S1) Composite slab

[0131] The upper and lower surfaces of the titanium alloy slab are respectively composited with 2mm thick pure titanium plates by explosion, and then coated with anti-oxidation and heat-insulating coatings to obtain composite slabs with specifications of 450×1500×2600mm;

[0132] S2) Slab rolling (2 passes)

[0133] S21) The composite slab is heated at 970°C for 1000 min using an electric furnace, and then taken out of the furnace for second-pass rolling;

[0134] S22) 1st hot rolling

[0135] It is widened to 2150mm in the transverse direction and then longitudinally rolled to a thickness of 189mm. The deformation of this rolling process is 58%, the deformation of the first pass is 10%, and the deformation of the remaining passes is 4-8% to obtain a rolled billet.

[0136] S23) Slab reheating

[0137] The rolled slab is returned to the furnace for heating at a temperature of 950°C and a holding time of 220 minutes.

[0138] S24) Second hot rolling

[0139] When the surface temperature of the rolling slab drops to 930℃, rolling begins. The total rolling deformation is 15%, the final rolling temperature is 840℃, and the thickness of the rolled plate is 160mm.

[0140] S3) Plate straightening

[0141] The steel was straightened and leveled in three passes with reductions of 1 mm, 0.8 mm and 0.5 mm respectively.

[0142] Figure 5 The microstructure of the plate obtained in Comparative Example 1 after annealing is shown in FIG. Figure 5 As can be seen from the figure, both the surface and the core are dual-state structures, but the core structure is coarse and the primary α phase strips still exist, showing an orientation distribution along the rolling direction. The core microstructure of the plate obtained in Comparative Example 2 after annealing also has incompletely broken primary α phase strips.

[0143] Compared to the examples, the total rolling reduction in Comparative Example 1 was small, and there was no intermittent cooling during the rolling process, making it difficult for deformation to penetrate the "softened" core. In Comparative Example 2, the total rolling deformation was 66%, of which 58% was in the first heat, 10% in the first pass, and 18% in the second heat. This unreasonable deformation distribution resulted in too little deformation in the plate after surface hardening, which was not conducive to deformation penetrating into the core.

[0144] The chemical compositions of the materials in Examples 1-4 and Comparative Examples 1-2, as well as the tensile mechanical properties of the surface and core of the resulting plates, are shown in Tables 1 and 2. The strength and impact toughness of the materials in the Examples met the design requirements. The strength of the plates obtained in Comparative Examples 1-2 met the design requirements, but the core impact toughness KV2 did not meet the requirements.

[0145] The embodiments described above are merely descriptions of preferred implementations of the present invention and are not intended to limit the scope of the present invention. Without departing from the spirit of the present invention, various modifications and improvements made to the technical solutions of the present invention by ordinary technicians in this field should fall within the scope of protection determined by the claims of the present invention.

[0146]

[0147]

Claims

1. A method for preparing a Ti80 titanium alloy plate with a thickness of ≥50 mm and high impact toughness, characterized in that: The steps include: S1) Slab Select Ti80 titanium alloy slab with a thickness of 200~500mm; S2) Slab rolling After the slab is heated, it is rolled through 1 to 2 heats to obtain a plate with a thickness of 50 to 180 mm. Finishing rolling temperature ≥T β -250℃, where T β represents the β phase transition temperature of the titanium alloy slab, in °C; The specific control of rolling fire number 1 is as follows: S21) Slab heating Heating temperature T β -(10~80)℃, holding time t=(1.2~3.0)×H, where t is in min and H is the slab thickness in mm; S22) First stage rolling The total rolling deformation is controlled at 20~35%, the first pass deformation is 2~3%, and the remaining passes deformation is 4~8%; the surface temperature of the slab after rolling is T1; S23) Second stage rolling When the slab surface temperature drops to 20-40°C below T1, the second stage of rolling begins. The rolling adopts low speed and high reduction, and the total deformation is 30-50%. The deformation of the first pass is 5-7%, and the deformation of the remaining passes is 9-17%. The specific control of rolling fire number 2 is as follows: S21) Slab heating The heating temperature is T β -(10~80)℃, holding time t=(1.2~3.0)×H, where t is in min and H is the slab thickness in mm; S22) 1st hot rolling The total rolling deformation is controlled at 20~35% to obtain the rolled billet; the deformation of the first pass is 2~3%, and the deformation of the remaining passes is 4~8%; S23) Furnace heating The slab is returned to the furnace for heating at a temperature 10-20°C lower than the first hot slab heating temperature. The holding time is t=(0.8-1.5)×h, where t is in min and h is the slab thickness in mm. S24) Second hot rolling After the slab comes out of the furnace, rolling begins when the surface temperature drops by 20~30℃. The total deformation of rolling is 30~50%; the deformation of the first pass is 5~7%, and the deformation of the remaining passes is 9~17%. S3) Plate straightening After straightening, the plates are air-cooled to room temperature.

2. The method for preparing a high impact toughness Ti80 titanium alloy plate with a thickness of ≥50 mm as claimed in claim 1, characterized in that: The upper surface and the lower surface of the Ti80 titanium alloy slab are respectively composited with pure titanium plates with a thickness of 1.5 to 3 mm, and the surfaces of the pure titanium plates not in contact with the titanium alloy slab are coated with anti-oxidation and heat-insulating coatings.

3. The method for preparing a high impact toughness Ti80 titanium alloy plate with a thickness of ≥50 mm as claimed in claim 1 or 2, characterized in that: The mass percentages of the components of the Ti80 titanium alloy slab are: 5.8%≤Al≤6.2%, 2.8%≤Nb≤3.2%, 1.8%≤Zr≤2.2%, 0.9%≤Mo≤1.5%, 0<Si≤0.15%, 0<Fe≤0.25%, 0<C≤0.10%, 0<N≤0.05%, 0<H≤0.010%, 0.06%≤O≤0.12%, and the remainder is Ti and unavoidable impurities. The microstructure of the slab is a two-phase deformation structure.

4. The method for preparing a high impact toughness Ti80 titanium alloy plate with a thickness of ≥50 mm as claimed in claim 1, characterized in that: In step S2), the temperature uniformity of the heating furnace used for heating and keeping the slab warm is within ±10°C.

5. The method for preparing a high impact toughness Ti80 titanium alloy plate with a thickness of ≥50 mm as claimed in claim 1, characterized in that: In step S2), the rolling speed is controlled at 1.2-2.5 m / s.

6. The method for preparing a high impact toughness Ti80 titanium alloy plate with a thickness of ≥50 mm as claimed in claim 1, characterized in that: In the step S3), Plate thickness ≥90mm, use rolling mill for leveling; leveling passes 2~3 times, single pass reduction 0.5~1.0mm; The plate thickness is less than 90mm, and it is leveled by a straightening machine with 1 to 3 straightening passes and a straightening speed of 0.5 to 1.0 m / s.

7. A Ti80 titanium alloy plate prepared by the method according to any one of claims 1 to 6, characterized in that: The microstructure of the titanium alloy plate after annealing is a uniform dual-state structure, the primary α phase is equiaxed, the grain size is 12-25 μm, and the primary α phase content is 20-30%; The tensile strength of the titanium alloy plate at each position is ≥840 MPa, the yield strength is ≥740 MPa, the elongation after fracture A is ≥12%, the cross-sectional shrinkage Z is ≥39%, and the impact toughness KV2 is greater than 50J.

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