A 880MPa low anisotropy TC4ELI wide and thick plate and its preparation method

Abstract

The present invention relates to the technical field of TC4ELI alloy plates, and in particular to an 880MPa-grade low anisotropy TC4ELI wide and thick plate and a preparation method thereof. The wide and thick plate is prepared by the preparation method. The preparation method comprises: smelting TC4ELI alloy components according to a required ratio to obtain a TC4ELI alloy ingot; forging the TC4ELI alloy ingot into a TC4ELI alloy slab; processing the TC4ELI alloy slab into a composite slab; preheating the composite slab in a furnace at 800-900°C for 6-8h; and then heating the composite slab to T β ‑70~T β ‑20℃, keep warm for 1‑2h; then, quickly take out of the furnace and roll. During rolling, the ratio of transverse deformation to longitudinal deformation is controlled to be no less than 1:4; the rolled composite sheet is post-processed to obtain a finished sheet. The present invention solves the problems of low longitudinal strength and large difference in isotropic properties of TC4ELI alloy sheets in the prior art.

Description

Technical Field

[0001] The invention relates to the technical field of TC4ELI alloy plates, and in particular to an 880MPa-grade low-anisotropy TC4ELI wide and thick plate and a preparation method thereof. Background Art

[0002] In TC4ELI alloy plates, the alloy strength is low due to the low content of interstitial elements (such as Fe, O, C, N and H). Specifically, the national standard "GB / T 3620.1-2016 Titanium and Titanium Alloy Grades and Chemical Compositions" strictly stipulates that the mass percentage range of TC4ELI alloy components is: Al: 5.5%-6.5%, V: 3.5%-4.5%, Fe<0.25%, O<0.13%, C<0.08%, N<0.03%, H<0.012%, other single impurity element content <0.1%, and the total content of other impurity elements <0.3%. Therefore, it is difficult to improve its strength performance by significantly adjusting the content of alloy elements.

[0003] For TC4ELI alloy plates with a thickness of more than 50 mm, the national standard "GB / T 3621-2022 Titanium and Titanium Alloy Plates" requires a transverse tensile strength R m ≥895MPa, R p0.2 ≥795MPa, and the longitudinal strength of the plate may be lower, which will cause the plate performance to fail to meet the use requirements of certain high-strength scenarios, and will also increase the transverse and longitudinal performance differences of the plate (i.e., isotropic performance differences). Specifically, during the rolling of titanium alloy plates, due to the large deformation in the longitudinal direction, the performance after rolling will show that the transverse strength of the plate is higher than the longitudinal strength, that is, anisotropy exists. In addition, due to the limitation of the rolling mill width, it is difficult to reduce the anisotropy of the plate by increasing the width ratio (i.e., the rolling ratio before and after the cross-rolling reversal).

[0004] In summary, it is necessary to develop an 880MPa-grade low anisotropy TC4ELI wide and thick plate and a preparation method thereof to solve the problems of low longitudinal strength and large difference in anisotropic properties of TC4ELI alloy plates in the prior art. Summary of the invention

[0005] The object of the present invention is to provide a 880MPa low anisotropy TC4ELI wide and thick plate and a preparation method thereof. The specific technical scheme is as follows:

[0006] In a first aspect, the present invention provides a method for preparing a 880MPa low anisotropic TC4ELI wide and thick plate, comprising:

[0007] Step S1, adding TC4ELI alloy components into a smelting furnace according to a required ratio to obtain a TC4ELI alloy ingot; the mass percentage ratio of the TC4ELI alloy components is as follows:

[0008] 5.9% ~ 6.4%Al, 3.9% ~ 4.3%V, 0.17% ~ 0.20%Fe, 0.09% ~ 0.13%O, 0.03% ~0.05%C, 0.03% ~ 0.05%Si, the sum of other impurities is less than 0.1% and the balance is Ti;

[0009] Step S2, forging the TC4ELI alloy ingot into a TC4ELI alloy slab;

[0010] Step S3, after grinding and polishing the TC4ELI alloy slab, pure titanium plates are respectively bonded to the upper surface and the lower surface thereof to form a composite slab;

[0011] Step S4, preheating the composite slab in a furnace, the preheating temperature is 800 ~ 900 ° C, the preheating holding time is 6 ~ 8h; then, heating to Tβ-70 ~ Tβ-20 ° C, keeping warm for 1-2h; taking out of the furnace; Tβ is the β phase transition point temperature of the TC4ELI alloy ingot;

[0012] Step S5, rolling the composite slab after being taken out of the furnace, controlling the ratio of the transverse deformation to the longitudinal deformation to be not less than 1:4, to obtain a composite plate;

[0013] Step S6: post-process the rolled composite plate to obtain a finished plate, namely, TC4ELI wide and thick plate.

[0014] Optionally, in step S2, the thickness of the TC4ELI alloy slab is 100 to 330 mm.

[0015] Optionally, in step S2, the process conditions used for forging include a six-fire forging process with a gradually decreasing temperature; the six-fire forging process includes two-fire billet forging at a temperature of 1080 to 1150°C, two-fire β phase zone forging at a temperature of 1000 to 1050°C, and two-fire two-fire α+β forging at 920 to 960°C; wherein α+β forging means forging after heating at 20 to 50°C below the temperature Tβ, that is, conventional two-phase zone forging, to obtain a dual-state structure or an equiaxed structure.

[0016] Optionally, in step S3, the pure titanium plate with a thickness of 1 to 1.5 mm is explosively bonded to the upper surface and the lower surface of the TC4ELI alloy slab.

[0017] Optionally, in step S5, transverse rolling is performed first, and then vertical reversal is performed for longitudinal rolling; during the transverse rolling, the transverse rolling ratio is controlled to be 10% to 50%; during the longitudinal rolling, the longitudinal rolling ratio is controlled to be 30% to 85%.

[0018] Optionally, in step S6, the post-processing includes straightening treatment and annealing treatment performed sequentially; the straightening temperature used in the straightening treatment is 450 ~ 600 ° C; the annealing temperature used in the annealing treatment is 700 ~ 800 ° C, and the annealing time is 2 ~ 4h.

[0019] Optionally, in step S6, the post-processing further includes grinding, trimming and surface polishing, which are sequentially arranged after the annealing; the grinding includes using a grinder to remove the oxide layer on the pure titanium plate and the TC4ELI alloy slab.

[0020] Optionally, in step S6, the thickness of the finished plate is not less than 50 mm.

[0021] Optionally, in step S6, the overall transverse and longitudinal yield strength Rp0.2 of the finished plate is greater than 880 MPa, the tensile strength Rm is greater than 990 MPa, and the transverse and longitudinal strength difference is controlled within 30 MPa.

[0022] In a second aspect, the present invention provides an 880 MPa-level low anisotropy TC4ELI wide and thick plate, which is prepared by the preparation method of the 880 MPa-level low anisotropy TC4ELI wide and thick plate.

[0023] The application of the technical solution of the present invention has at least the following beneficial effects:

[0024] The present invention provides an 880MPa-grade low-anisotropy TC4ELI wide and thick plate and a preparation method thereof, which can prepare a finished plate with an overall transverse and longitudinal yield strength Rp0.2>880MPa, a tensile strength Rm>990MPa, and a transverse and longitudinal strength difference controlled within 30MPa, thereby solving the problems of low longitudinal strength and large anisotropic performance difference of TC4ELI alloy plates in the prior art. Specifically, in step S1 of the preparation method of the present invention, the TC4ELI alloy composition is controlled to add an appropriate amount of C element and Si element. On the one hand, grain refinement is beneficial to weakening texture and reducing anisotropy; on the other hand, the strength of the plate is improved by fine grain strengthening; at the same time, adding an appropriate amount of Si element can increase the fluidity of the alloy and reduce the deformation resistance of the alloy during hot working; in step S4, by optimizing the heating method before rolling in step S5, the composite slab presents a state of high surface temperature (Tβ-70 ~ Tβ-20℃, such as 950℃) and slightly low core temperature (such as 880℃) after insulation; then, through step S5, rapid large deformation rolling is performed to increase the core temperature, so that the surface temperature and the core temperature are balanced during rolling; in step S5, the ratio of transverse deformation to longitudinal deformation is controlled to be not less than 1:4, the anisotropy after rolling is weakened, thereby weakening the transverse and longitudinal performance differences of the finished plate. DETAILED DESCRIPTION

[0025] The technical solutions in the present invention will be described clearly and completely below in conjunction with the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. All other embodiments obtained by ordinary technicians in this field based on the embodiments of the present invention belong to the scope of protection of the present invention.

[0026] Embodiment 1:

[0027] A method for preparing 880MPa low anisotropy TC4ELI wide and thick plate, comprising:

[0028] Step S1, pressing the TC4ELI alloy components into electrodes according to the required proportions, and then smelting them in a VAR smelting furnace (i.e., vacuum consumable smelting furnace) to obtain a TC4ELI alloy ingot with a size of φ980*2750mm; the mass percentage proportions of the TC4ELI alloy components are as follows:

[0029] 6.1%Al, 4.2%V, 0.18%Fe, 0.13%O, 0.04%C, 0.04%Si, the sum of other impurities is less than 0.1% and the balance is Ti;

[0030] Step S2, forging the TC4ELI alloy ingot into a TC4ELI alloy slab with a size of 330 mm in thickness × 1600 mm in width × 3150 mm in length through six fires; the process conditions adopted for the forging include a six-fire forging process with a temperature gradually reduced; the six-fire forging process includes two-fire forging at a temperature of 1080-1150°C (such as 1100°C), two-fire β-phase forging at a temperature of 1000-1050°C (such as 1020°C), and two-fire α+β forging at 928-958°C (such as 940°C); wherein α+β forging means forging after heating at 20-50°C below the temperature Tβ, i.e. conventional two-phase forging, to obtain a dual-state structure or an equiaxed structure;

[0031] Step S3, after grinding and polishing the TC4ELI alloy slab, a pure titanium plate is respectively bonded on the upper surface and the lower surface thereof by explosion method to form a composite slab; the pure titanium plate is a TA1 titanium plate, and the size specification is 1.5 mm in thickness × 1600 mm in width × 3150 mm in length; the pure titanium plate is used to control the surface oxidation of the TC4ELI alloy slab and reduce the risk of rolling cracking after the surface of the TC4ELI alloy slab is cooled;

[0032] Step S4, preheating the composite slab in an electric heating furnace, the preheating temperature is 800°C, and the preheating holding time is 8h; then, heating to Tβ-43°C (i.e. 935°C), holding for 2h; taking out of the furnace; Tβ is the β phase transition point temperature of the TC4ELI alloy ingot, which is 978°C;

[0033] Step S5, rolling the composite slab after being taken out of the furnace without dephosphorization, controlling the ratio of the transverse deformation to the longitudinal deformation to be not less than 1:4, to obtain a composite plate; specifically, when the composite slab starts rolling, the surface temperature of the composite slab is measured by an infrared thermometer to be 915°C, and the rolling process table is shown in Table 1. After the fifth rolling pass is completed, the sixth pass is vertically reversed, and the final rolling temperature is measured by an infrared thermometer to be 850°C. The ratio of rolling deformation before and after reversing is 1:2.5 (30.5%:77.5%) (i.e., 231.5 mm thickness reversing, the rolling ratio before reversing is (333-231.5) / 333, and the rolling ratio after reversing is (231.5-52) / 231.5);

[0034] Step S6: The rolled composite plate is post-processed to obtain a finished plate, namely, a TC4ELI wide and thick plate, and the size of the finished plate is 51 mm in thickness×2100 mm in width×14000 mm in length.

[0035] In step S6, the post-treatment includes straightening treatment and annealing treatment performed in sequence; the straightening temperature used in the straightening treatment is 450°C, and then the composite plate is air-cooled to room temperature on a cooling bed to obtain a titanium alloy straightened plate; the annealing temperature used in the annealing treatment is 750°C, the annealing time is 3h, and the annealing is performed by entering the furnace (specifically a roller furnace) at a temperature, and air-cooling is performed after exiting the furnace.

[0036] In step S6, the post-processing also includes grinding, trimming and surface polishing, which are sequentially arranged after the annealing treatment; the grinding includes using a grinder to remove the oxide layer on the pure titanium plate and the TC4ELI alloy slab; the trimming is used to cut off the unevenly elongated parts of the head and tail and both sides of the long side of the TC4ELI alloy slab.

[0037] Table 1 Rolling parameters used in the rolling process of step S5 in Example 1

[0038]

[0039] Embodiment 2:

[0040] The difference from Example 1 is that in step S1, the mass percentage ratio of the TC4ELI alloy components is as follows:

[0041] 6.4%Al, 4.3%V, 0.20%Fe, 0.10%O, 0.03%C, 0.03%Si, the sum of other impurities is less than 0.1% and the balance is Ti; Tβ is 970℃;

[0042] In step S2, the size of the TC4ELI alloy slab is 325 mm thick × 1600 mm wide × 2700 mm long;

[0043] In step S3, the size of the pure titanium plate is 1 mm thick × 1600 mm wide × 2700 mm long;

[0044] In step S4, the composite slab is preheated in an electric heating furnace and then heated to Tβ-40°C (i.e., 930°C);

[0045] In step S5, when the composite slab starts rolling, the surface temperature of the composite slab is measured by an infrared thermometer to be 908°C, and the rolling process table is shown in Table 2. After the fifth rolling pass is completed, the sixth pass is vertically reversed, and the final rolling temperature is measured by an infrared thermometer to be 855°C. The ratio of rolling deformation before and after reversing is 1:2.1 (36.5%:75.5%) (i.e., 207.6 mm thickness reversing, the rolling ratio before reversing is (327-207.6) / 327, and the rolling ratio after reversing is (207.6-50.8) / 207.6);

[0046] In step S6, the finished plate has a size of 50 mm in thickness×2500 mm in width×11000 mm in length.

[0047] In step S6, the straightening temperature used in the straightening process is 500°C.

[0048] Table 2 Rolling parameters used in the rolling process of step S5 in Example 2

[0049]

[0050] Embodiment 3:

[0051] Different from Example 2, in step S1, the mass percentage ratio of the TC4ELI alloy components is as follows: 5.9% Al, 3.9% V, 0.17% Fe, 0.13% O, 0.05% C, 0.05% Si, the total content of other impurities is less than 0.1% and the balance is Ti; Tβ is 982°C.

[0052] Embodiment 4:

[0053] Different from Example 3, the thickness of the slab after coating with pure titanium plate is 325 mm. In step S5, the ratio of rolling deformation before and after reversing is 1:4 (20%:80%) (i.e., for 260 mm thickness reversal, the rolling ratio before reversing is (325-260) / 325, and the rolling ratio after reversing is (260-52) / 260).

[0054] Comparative Example 1:

[0055] Different from Example 1, in step S1, Si and C elements are not added to the TC4ELI alloy composition, and the mass percentage ratios used are as follows:

[0056] 6.2%Al, 4.0%V, 0.18%Fe, 0.10%O, the sum of other impurities is less than 0.1% and the balance is Ti; Tβ is 975℃;

[0057] No preheating is used in step S4;

[0058] In step S5, the rolling deformation ratio before and after the reversal is controlled to be 1:4.

[0059] Comparative Example 2:

[0060] Different from Example 1, in step S1, a low amount of Si element and C element are added to the TC4ELI alloy composition, and the mass percentage ratios thereof are as follows:

[0061] 6.2%Al, 4.0%V, 0.18%Fe, 0.10%O, 0.02%C, 0.02%Si, the sum of other impurities is less than 0.1% and the balance is Ti; Tβ is 976℃;

[0062] In step S5, the rolling deformation ratio before and after the reversal is controlled to be 1:2.9.

[0063] Comparative Example 3:

[0064] Different from Example 1, in step S1, excessive amounts of Si and C are added to the TC4ELI alloy composition, and the mass percentage ratios thereof are as follows:

[0065] 6.2%Al, 4.0%V, 0.20%Fe, 0.13%O, 0.07%C, 0.06%Si, the sum of other impurities is less than 0.1% and the balance is Ti; Tβ is 980℃;

[0066] In step S5, the rolling deformation ratio before and after the reversal is controlled to be 1:5.

[0067] Comparative Example 4:

[0068] Different from Example 1, in step S1, the mass percentage ratio of the TC4ELI alloy components is as follows:

[0069] 5.9%Al, 3.9%V, 0.17%Fe, 0.13%O, 0.05%C, 0.05%Si, the sum of other impurities is less than 0.1% and the balance is Ti; Tβ is 982℃;

[0070] In step S4, no preheating is used; the temperature is directly raised to 940°C and kept for 2 hours;

[0071] In step S5, the rolling deformation ratio before and after the reversal is controlled to be 1:3.8.

[0072] The finished plates prepared in Examples 1-4 and Comparative Examples 1-4 were sampled in the middle of the width for tensile mechanical property testing, and the test method was carried out in accordance with the national standard "GB / T 228.1-2021 Metallic Material Tensile Test Part 1: Room Temperature Test Method", and the test results are shown in Table 3. Among them, Rp0.2 is the yield strength, Rm is the tensile strength, A is the elongation after fracture, and Z is the cross-sectional shrinkage.

[0073] Table 3 Performance test of each finished board prepared in Examples 1-4 and Comparative Examples 1-4

[0074]

[0075] From the data in Table 3, it can be seen that the present invention uses Examples 1-4 to prepare finished plates with overall transverse and longitudinal yield strength Rp0.2>880MPa, tensile strength Rm>990MPa, and transverse and longitudinal strength difference controlled within 30MPa, which solves the problems of low longitudinal strength and large difference in anisotropic properties of TC4ELI alloy plates in the prior art.

[0076] In Comparative Example 1, Si and C elements were not added, and the longitudinal yield strength Rp0.2 and transverse yield strength Rp0.2 of the prepared finished plate were both insufficient; Comparative Example 1 did not use 800°C preheating, which resulted in a significant increase in the core temperature of the composite slab during the rolling process. On the one hand, the texture strength was increased, resulting in large transverse and longitudinal anisotropy. On the other hand, the excessively high core temperature also prolonged the cooling time of the plate after rolling, resulting in slightly insufficient alloy strength.

[0077] The contents of Si and C added in Comparative Example 2 are both lower than the lower limit, resulting in insufficient solid solution strength of the alloy, leading to insufficient longitudinal yield strength Rp0.2 and transverse yield strength Rp0.2.

[0078] The transverse and longitudinal rolling ratio used in Comparative Example 3 exceeds the standard, which increases the texture strength and makes the transverse and longitudinal anisotropy large; in addition, the added Si element and C element content exceed the upper limit, which easily produces brittle phases of titanium silicon compounds (such as Ti5Si3 and Ti3Si, etc.) or / and brittle phases of titanium carbide (such as TiC, etc.) during smelting or heat treatment, seriously reducing the elongation of the material.

[0079] In Comparative Example 4, 800°C preheating was not used, which resulted in a serious increase in the core temperature of the composite slab during rolling. On the one hand, this increased the texture strength, resulting in large transverse and longitudinal anisotropy. On the other hand, the excessively high core temperature also prolonged the cooling time of the plate after rolling, resulting in slightly insufficient alloy strength.

[0080] The edges of the finished plates prepared in Examples 1-4 were sampled for tensile mechanical property testing. The testing was carried out in accordance with the national standard GB / T 228.1-2021 Metal Material Tensile Test Part 1: Room Temperature Test Method. The test results were combined with the corresponding middle sampling performance data in Table 3 to form Table 4.

[0081] Table 4 Performance test of the middle and edge samples of each finished plate prepared in Examples 1-4

[0082]

[0083] It can be seen from the data in Table 4 that no matter whether it is the middle sampling test or the edge sampling test, the present invention can use Examples 1-4 to prepare finished plates with overall transverse and longitudinal yield strength Rp0.2>880MPa, tensile strength Rm>990MPa, and transverse and longitudinal strength difference controlled within 30MPa.

[0084] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. For those skilled in the art, the present invention may have various modifications and variations. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A method for preparing 880MPa low anisotropy TC4ELI wide and thick plate, characterized in that: include: Step S1, adding TC4ELI alloy components into a smelting furnace according to a required ratio to obtain a TC4ELI alloy ingot; the mass percentage ratio of the TC4ELI alloy components is as follows: 5.9% ~ 6.4%Al, 3.9% ~ 4.3%V, 0.17% ~ 0.20%Fe, 0.09% ~ 0.13%O, 0.03% ~ 0.05%C, 0.03% ~ 0.05%Si, the sum of other impurities is less than 0.1% and the balance is Ti; Step S2, forging the TC4ELI alloy ingot into a TC4ELI alloy slab; Step S3, after grinding and polishing the TC4ELI alloy slab, pure titanium plates are respectively attached to the upper surface and the lower surface thereof to form a composite slab; Step S4: preheat the composite slab in a furnace at a temperature of 800 to 900°C for 6 to 8 hours; then, heat the composite slab to T β -70 ~ T β -20℃, keep warm for 1 - 2h; remove from oven; the T β is the β phase transition point temperature of the TC4ELI alloy ingot; Step S5, rolling the composite slab after being taken out of the furnace, controlling the ratio of the transverse rolling deformation to the longitudinal rolling deformation to be not less than 1:4, to obtain a composite plate; Step S6: post-process the rolled composite plate to obtain a finished plate, namely, TC4ELI wide and thick plate.

2. The method for preparing the 880MPa low anisotropy TC4ELI wide and thick plate according to claim 1, characterized in that: In step S2, the thickness of the TC4ELI alloy slab is 100 to 330 mm.

3. The method for preparing the 880MPa low anisotropy TC4ELI wide and thick plate according to claim 1, characterized in that: In step S2, the process conditions used for forging include a six-fire forging process with a gradually decreasing temperature; the six-fire forging process includes two-fire forging at a temperature of 1080-1150°C, two-fire β-phase forging at a temperature of 1000-1050°C, and two-fire α+β forging at 920-960°C; wherein β-phase forging means forging at a temperature of T β After the above heating, forging is performed. α+β forging means that at temperature T β After heating at 20 ~ 50℃, forging is performed.

4. The method for preparing the 880MPa low anisotropy TC4ELI wide and thick plate according to claim 1, characterized in that: In step S3, the pure titanium plates with a thickness of 1 to 1.5 mm are bonded to the upper and lower surfaces of the TC4ELI alloy slab by explosion.

5. The method for preparing the 880MPa low anisotropy TC4ELI wide and thick plate according to claim 1, characterized in that: In step S5, transverse rolling is performed first, and then vertical reversal is performed for longitudinal rolling; during the transverse rolling, the transverse rolling ratio is controlled to be 10% to 50%; during the longitudinal rolling, the longitudinal rolling ratio is controlled to be 30% to 85%.

6. The method for preparing 880MPa low anisotropy TC4ELI wide and thick plates according to claim 1, characterized in that: In step S6, the post-treatment includes a straightening treatment and an annealing treatment performed in sequence; the straightening treatment adopts a straightening temperature of 450 to 600° C.; the annealing treatment adopts an annealing temperature of 700 to 800° C. and an annealing time of 2 to 4 hours.

7. The method for preparing 880MPa low anisotropy TC4ELI wide and thick plates according to claim 6, characterized in that: In step S6, the post-treatment further includes grinding treatment, edge trimming treatment and surface polishing treatment sequentially arranged after the annealing treatment; the grinding treatment includes using a grinder to remove the oxide layer on the pure titanium plate and the TC4ELI alloy slab.

8. The method for preparing 880MPa low anisotropy TC4ELI wide and thick plates according to claim 1, characterized in that: In step S6, the thickness of the finished plate is not less than 50 mm.

9. The method for preparing 880MPa low anisotropy TC4ELI wide and thick plates according to claim 1, characterized in that: In step S6, the transverse and longitudinal overall yield strength R of the finished plate p0.2 >880MPa, tensile strength R m >990MPa, the difference in transverse and longitudinal strength is controlled within 30MPa.

10. A 880MPa low anisotropy TC4ELI wide and thick plate, characterized in that: The plate is prepared by the method for preparing 880MPa-grade low anisotropy TC4ELI wide and thick plate as described in any one of claims 1 to 9.

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