Hot rolling preparation method for producing flat-bulb titanium and application

Abstract

The invention provides a hot rolling preparation method for producing flat-bulb titanium and application, the method comprises the steps that S1, a square blank is preheated to T1 and then subjected to heat preservation for 1-2 h, the phase transformation point of the square blank is T2, T1 = T2-delta T, and delta T ranges from 20 DEG C to 30 DEG C; s2, rough rolling is conducted at the speed of 4.5 m / s to 5.5 m / s, a groove is formed, the blank temperature after rough rolling is larger than or equal to 880 DEG C, finish rolling is conducted in a continuous passing mode to conduct arc shaping on the blank, the symmetrical flat-bulb titanium profile with bulbs at the two ends and a web in the middle is obtained, the blank temperature after finish rolling is larger than or equal to 850 DEG C, and the total rolling deformation ranges from 75% to 85%; s3, the profile is conveyed to a line roller type tension straightening machine through a roller way to be subjected to tension straightening treatment, the speed is 0.4-0.6 m / s, and the temperature of the straightened profile is larger than or equal to 700 DEG C; and S4, air cooling treatment is carried out, then tongue-shaped parts at the head and the tail are cut off, oxide skin on the surface layer is cleaned, and two flat-bulb titanium profiles with the same specification are obtained through water cutting symmetric segmentation in the rolling direction. According to the method, the temperature difference between the head and the tail can be reduced, the structure property uniformity and the batch stability are improved, and the minimum length of the prepared flat-bulb titanium profile can reach 12-15 m.

Description

A hot rolling preparation method for producing spherical flat titanium and its application Technical Field

[0001] This invention relates to the field of metallic materials technology, and more specifically, to a hot rolling preparation method and application for producing spherical flat titanium. Background Technology

[0002] With the increasing demand for structural strength and lightweight in marine equipment, spherical flat titanium is an asymmetrical profile made of titanium alloy and consisting of a flat web and a spherical panel. As an important near-net-shape semi-finished component, it has advantages such as small machining allowance, high structural efficiency, and obvious comprehensive performance advantages. In the shipbuilding field, it can be processed into secondary load-bearing structural components such as ship bulkheads, which have significant weight reduction effects and can significantly improve the ship's loading capacity.

[0003] To produce high-quality spherical flat titanium profiles, welding, extrusion molding, and rolling processes have been developed. For example, Chinese patent application number 202310714987.2 discloses an extrusion process for pure titanium spherical flat profiles. This process involves mixing water glass and water with glass powder and pressing it into a glass pad. The pure titanium billet is placed in an electric furnace heated to 650–800°C and held for 20–120 minutes, then heated to 800–920°C and held again. The extrusion cylinder, extrusion die, and glass pad are preheated. The glass pad is placed inside the extrusion cylinder, which has a lubricant coating on its inner wall. After the billet is removed from the furnace and coated with powder, it is placed back into the extrusion cylinder for extrusion to obtain the pure titanium spherical flat profile. This method achieves high-quality extrusion molding by adding glass lubricant to reduce extrusion deformation resistance. However, it places high demands on the power, load pressure, and die type of the extrusion equipment, and results in poor metal flowability after extrusion, leading to easy twisting of the finished product. This results in a single spherical flat alloy profile being only 3–4 meters long, with a yield of less than 50%.

[0004] To address this, Chinese Patent Application No. 202311183912.2 discloses a method for producing spherical flat titanium alloy profiles. This method employs a continuous through-rolling process using a 9-unit tandem rolling mill, uniquely utilizing a two-sided symmetrical die production method. While this approach yields spherical flat alloy profiles up to 6m in length, limitations stem from inherent titanium alloy characteristics such as close-packed hexagonal crystal structure and high deformation resistance. Further increasing the length leads to poor microstructure uniformity and significant differences in macroscopic properties, hindering large-scale continuous production.

[0005] In view of this, the present invention is hereby proposed. Summary of the Invention

[0006] The problem solved by this invention is that, due to the inherent characteristics of titanium alloys, spherical flat titanium alloys, once they exceed a certain length, exhibit shortcomings such as poor uniformity of microstructure and large differences in macroscopic properties, which are not conducive to batch continuous production.

[0007] To address the aforementioned problems, this invention provides a hot-rolling preparation method for producing spherical flat titanium, comprising: S1, preheating a square billet to T1 and holding it at that temperature for 1-2 hours, wherein the phase transformation point of the square billet is T2 and T1 = T2 - ΔT, where ΔT is 20℃-30℃; S2, rough rolling at a speed of 4.5-5.5 m / s to form grooves, wherein the billet temperature after rough rolling is ≥880℃, and finishing rolling is performed continuously to shape the billet into an arc shape, thereby obtaining a spherical flat titanium. Symmetrical spherical flat titanium profiles with spherical ends and a middle web are rolled to a billet temperature ≥850℃ with a total rolling deformation of 75%~85%; S3, the profiles are conveyed to a linear tension straightener via roller conveyor for tension straightening at a speed of 0.4-0.6m / s, and the temperature of the straightened profiles is ≥700℃; S4, the profiles are air-cooled, the "tongue"-shaped parts at both ends are removed, the surface oxide scale is cleaned, and the profiles are symmetrically divided along the rolling direction using water jet cutting to obtain two spherical flat titanium profiles of the same specifications.

[0008] Preferably, the length of a single spherical flat titanium profile prepared in step S4 is 12.0~15.0m.

[0009] Preferably, in step S1, the oxide scale on the surface of the square billet is removed and the defects are cleaned by grinding before rolling, and the square billet is preheated to 910-930℃.

[0010] Preferably, the square billet is a TA24 (Ti75) alloy with a nominal composition of Ti-3Al-2Mo-2Zr. As an example of the present invention, the billet specifications are: thickness (δ): 150 × width (H): 150 × ≥ length (L) mm. Priority should be given to ensuring the thickness and width of the billet, while the length can be determined according to specific circumstances. Surface oxide scale and defects should be cleaned by grinding.

[0011] Preferably, step S2 includes: rough rolling at a speed of 4.8-5.2 m / s to form a groove, the billet temperature after rough rolling is 883-890℃, and finish rolling in a continuous pass to shape the billet into an arc and obtain a symmetrical spherical flat titanium profile with two spherical ends and a middle web, the billet temperature after finish rolling is 855-865℃, and the total rolling deformation is 78%~82%.

[0012] Preferably, step S3 uses a Φ365 tandem 7-stand rolling mill for continuous through rolling. After rough rolling, the dimensions of the billet are: thickness δ = 30mm, width H = 120mm, and length determined by the initial length. After rough rolling, the dimensions of the billet are: thickness δ = 6mm, width H = 60mm.

[0013] Preferably, in step S4, a through-type sandblasting machine is used for cleaning.

[0014] This invention also discloses the application of the above-mentioned hot rolling preparation method for producing spherical flat titanium in the field of marine engineering equipment.

[0015] Compared with the prior art, the hot rolling preparation method and application for producing spherical flat titanium described in this invention have the following beneficial effects:

[0016] 1) This invention ensures that the billet can be quickly and accurately formed into the required size and shape through multi-pass rolling and straightening, reducing the temperature difference between the beginning and end, improving the uniformity of microstructure and batch stability. The strength and toughness of the ball head or web of the hot-rolled spherical flat titanium profile are similar to the performance values ​​of titanium alloy plates of similar specifications specified in GJB / 944A-2018 standard, effectively meeting the construction and use requirements of complex structures in marine engineering. 2) It can effectively solve the problems of large number of welds, large residual stress, poor microstructure uniformity and low yield of hot-extruded spherical flat titanium profiles. 3) It increases the yield to ≥80%-93%, and the cost of mass production can be reduced by more than 40% compared with the extrusion process. Attached Figure Description

[0017] Figure 1 is a schematic diagram of the key processes of the hot-rolled spherical flat titanium profile of the present invention;

[0018] Figure 2 is a morphological diagram of the spherical flat titanium profile described in Embodiment 1 of the present invention;

[0019] Figure 3 shows the metallographic morphology of the spherical flat titanium profile described in Embodiment 1 of the present invention;

[0020] Figure 4 is a morphological diagram of the spherical flat titanium profile described in Comparative Example 1 of the present invention.

[0021] Figure 5 shows the metallographic morphology of the spherical flat titanium profile described in Comparative Example 1 of the present invention at the head position;

[0022] Figure 6 shows the metallographic morphology of the spherical flat titanium profile described in Comparative Example 1 of the present invention at the middle position;

[0023] Figure 7 shows the metallographic morphology of the spherical flat titanium profile described in Comparative Example 1 of the present invention at the tail position. Detailed Implementation

[0024] To make the above-mentioned objects, features, and advantages of the present invention more apparent and understandable, specific embodiments of the present invention will be described in detail below with reference to the accompanying drawings. Without conflict, the technical features of the embodiments of the present invention can be combined with each other.

[0025] In recent years, with the rapid development of marine engineering equipment and the maritime industry, the demand for asymmetric spherical flat titanium has been strong. However, due to the inherent properties of titanium alloys, the forming process of spherical flat titanium is greatly limited. For example, when preparing spherical flat titanium by extrusion molding, there are problems such as complex lubricant usage and immature extrusion technology, which lead to easy surface cracking and insufficient end filling, resulting in a maximum effective length of only 3-4m. When preparing spherical flat titanium by rolling, the maximum effective length can reach 6m, but the maximum length cannot be further increased due to the inherent properties of titanium alloys, which is not conducive to achieving continuous mass production. Therefore, the applicant proposes the following technical solution:

[0026] It should be noted that:

[0027] The structure of the marine-grade 6# spherical flat titanium profile is shown in Figure 1. The parameters of the finished spherical flat titanium profile are as follows: h - height; b - width; t - web thickness; r1 - radius of the fillet between the spherical top and the web, radius of the fillet at the spherical end; r2 - radius of the fillet at the shoulder of the spherical head; r - radius of the fillet at the end of the web; dx - distance from the center of gravity; 1 - longitudinal impact of the spherical head; 2 - longitudinal tension of the spherical head; 3 - longitudinal bending of the web. The engineering dimensions and allowable deviations of the spherical flat titanium profile are shown in Table 1.

[0028] Table 1. Specific models and permissible deviations of the No. 6 spherical flat titanium profile of this invention.

[0029] Example 1

[0030] A hot-rolling preparation method for producing spherical flat titanium includes:

[0031] S1. Raw Material Selection

[0032] Take a square TA24 (Ti75) alloy with dimensions of ~150×150×≥1200mm (independently developed in my country and of α type, with a near-nominal composition of Ti-3Al-2Mo-2Zr and an actual phase transformation temperature of 930℃), remove the surface oxide scale and clean the defects by grinding.

[0033] S2, Preheating and Rolling Forming

[0034] The square spherical flat titanium profile billet was preheated in a box-type resistance furnace at 910℃, which is 20℃ below the phase transformation temperature, and held for 2 hours. Then, the preheated billet was manually placed in a continuous Φ365 tandem 7-strand rolling mill for roughing and finishing in one pass, with process temperatures of 886℃ and 860℃, respectively. The total deformation of roughing and finishing was controlled at 80%. The effective size of the rough-rolled spherical flat titanium profile was δ30×120×≥6000mm, and the effective size of the finishing spherical flat titanium profile was δ6×60×≥12000~15000mm. The mill speed was maintained at 5.0m / s throughout the process to obtain the No. 6 spherical flat titanium profile, the appearance of which is shown in Figure 2.

[0035] S3, Straightening treatment

[0036] After rolling, the No. 6 spherical flat titanium profile is conveyed to the linear roller tension straightener via a roller conveyor. The residual heat after rolling is used to perform tension straightening on the No. 6 spherical flat titanium profile. The straightener is kept at a working speed of 0.5 m / s. After straightening, the lowest surface temperature of the No. 6 spherical flat titanium profile in all positions is 713℃.

[0037] S4. Cooling and cutting to length

[0038] The straightened 6# spherical flat titanium profile was air-cooled, and then the first and last "tongue"-shaped parts in Figure 2 were cut off by band sawing. The surface oxide scale was removed by sandblasting with a through-type sandblasting machine. The 6# spherical flat titanium profile met the Class A requirements by ultrasonic flaw detection, that is, the surface of the rolled profile was glossy, without cracks, without inclusions, with uniform structure and no segregation. This shows that the 6# spherical flat titanium profile rolled by the hot rolling preparation method for producing spherical flat titanium described in this application is a qualified spherical flat titanium profile.

[0039] The thickness tolerance of the spherical flat titanium profile was tested and mechanical properties were tested by simultaneous sampling. The sampling diagram is shown in Figure 1. Longitudinal tensile and longitudinal impact specimens were taken from the ball head of the spherical flat titanium profile. The V-notch direction was parallel to the web. Bending specimens were taken from the web. The room temperature tensile properties, impact properties and bending properties were tested according to GB / T 228.1-2021, GB / T 229-2020 and GB / T 232-2010 standards, respectively.

[0040] The results showed that the dimensions and thickness tolerances of the No. 6 spherical flat titanium profile met the requirements of Table 1, and the metallographic morphology at different magnifications is shown in Figure 3. Figure 3 reveals that the metallographic characteristics of the head, middle, and tail samples of the hot-rolled No. 6 spherical flat titanium profile mainly include equiaxed α phase, strip-shaped α phase, and transformed β structure. The equiaxed α phase grain size was assessed as grade 14.5, and no micropores, inclusions, or other defects were observed within the microstructure.

[0041] The longitudinal tensile properties of the No. 6 spherical flat titanium profile prepared by this invention at the head, middle, and tail spherical ends are all higher than the performance values ​​of rolled TA24 plates of similar specifications specified in GJB / 944A-2018. Specifically, the average tensile strength is ≥800MPa, the average yield strength is ≥660MPa, the average elongation after fracture is ≥18.0%, and the average impact energy and impact toughness are ≥60J and ≥765kJ / m, respectively. 2 The mechanical properties of a single profile were calculated to have a uniformity Cv value of ≤5%. No obvious cracks were observed on the original surface at the head, middle, and tail web positions of the single profile under the conditions of d=3t and α=80°. In other words, the hot-rolled 6# spherical flat titanium profile maintained a good strength-toughness match, achieving the target for controlled properties. Furthermore, calculations showed that the yield of a single spherical flat titanium profile was between 85-90%, effectively meeting the requirements of the marine environment for low-cost, high-performance spherical flat titanium profiles for key components.

[0042] Comparative Example 1

[0043] A hot-rolling preparation method for producing spherical flat titanium includes:

[0044] S1. Raw Material Selection

[0045] Take a square TA24 (Ti75) alloy with dimensions of ~150×150×≥1200mm (independently developed in my country and of α type, with a near-nominal composition of Ti-3Al-2Mo-2Zr and an actual phase transformation temperature of 930℃), remove the surface oxide scale and clean the defects by grinding.

[0046] S2, Preheating and Rolling Forming

[0047] The square spherical flat titanium profile billet was preheated in a box-type resistance furnace at 890℃, which is 40℃ below the phase transformation temperature, and held for 1 hour. Then, the preheated billet was manually placed in a continuous Φ365 tandem 7-roll mill for roughing and finishing in one pass, with process temperatures of 873℃ and 840℃, respectively. The total deformation of roughing and finishing was controlled at 80%. The effective size of the rough-rolled spherical flat titanium profile was δ30×120×≥6000mm, and the effective size of the finishing spherical flat titanium profile was δ6×60×≥14000mm. The mill speed was maintained at 5.0m / s throughout the process to obtain 6# spherical flat titanium profile, as shown in Figure 4, which also has a "tongue" shaped part.

[0048] S3, Straightening treatment

[0049] After rolling, the No. 6 spherical flat titanium profile is conveyed to the line roller tension straightener through the roller conveyor. The No. 6 spherical flat titanium profile is tension straightened by using the residual heat after rolling. The straightener is kept at a working speed of 0.5 m / s. After straightening, the lowest surface temperature of the No. 6 spherical flat titanium profile in all positions is 660℃.

[0050] S4. Cooling and cutting to length

[0051] The straightened 6# spherical flat titanium profile was air-cooled, and then the first and last "tongue" shaped parts in Figure 4 were cut off by band sawing. The surface oxide scale was removed by sandblasting with a through-type sandblasting machine. The 6# spherical flat titanium profile met the Class A requirements by ultrasonic flaw detection. The surface of the rolled profile was glossy, crack-free, inclusion-free, and the microstructure was uniform and without segregation. The dimensional and thickness tolerances of the prepared 6# spherical flat titanium profile met the allowable deviations specified in Table 1. The metallographic morphology at different magnifications is shown in Figures 5-7.

[0052] As shown in Figures 5-7, the metallographic characteristics of the head, middle, and tail samples of the hot-rolled 6# spherical flat titanium profile show significant differences. The head sample mainly consists of equiaxed α phase and transformed β phase, with some areas containing elongated α phase and lamellar α phase. The equiaxed α phase grain size is rated as grade 14, and no micropores, inclusions, or other defects are observed within the microstructure. The middle and tail samples mainly consist of equiaxed α phase and transformed β phase, with some areas containing lamellar α phase. The equiaxed α phase grain size is rated as grade 13.5. The uneven microstructure distribution of a single 6# spherical flat titanium profile indicates that there are temperature differences at different locations during the rolling process.

[0053] The longitudinal tensile properties of the hot-rolled single 6# spherical flat titanium profile prepared by this invention at the head, middle, and tail spherical head positions are all higher than the performance values ​​of similar rolled TA24 plates specified in GJB / 944A-2018. Specifically, the average tensile strength is ≥795MPa, the average yield strength is ≥662MPa, the average elongation after fracture is ≥13.0%, and the average impact energy and impact toughness are ≥53J and ≥694kJ / m, respectively. 2 The maximum Cv value for the uniformity of mechanical properties of a single profile was calculated to be 11%. Under the conditions of d=3t and α=80°, no obvious cracks were observed on the original surface of the bending properties at the head, middle and tail web positions of the single profile.

[0054] In summary, deviating from the core parameters, the hot-rolled 6# spherical flat titanium profile will exhibit poor uniformity in microstructure and properties, failing to effectively achieve a good balance between strength and toughness. It can be considered that while achieving shape control, the property control target was not achieved simultaneously. Calculations show that the yield of a single spherical flat titanium profile is between 78-85%, which does not effectively meet the requirements of the marine environment for low-cost, high-performance spherical flat titanium profiles for key components.

[0055] While the present invention has been disclosed above, it is not limited thereto. Any person skilled in the art can make various modifications and alterations without departing from the spirit and scope of the invention; therefore, the scope of protection of the present invention should be determined by the scope defined in the claims.

Claims

1. A hot-rolling preparation method for producing spherical flattened titanium, characterized in that, include: S1. Preheat the square billet to T1 and hold for 1-2 hours. The phase transformation point of the square billet is T2 and T1 = T2 - ΔT, where ΔT is 20℃-30℃. S2. Roughly roll the billet at a speed of 4.5-5.5 m / s to form a groove. The billet temperature after rough rolling is ≥880℃. Then, perform continuous through-rolling to shape the billet into an arc and obtain a symmetrical spherical flat titanium profile with two ball ends and a middle web. The billet temperature after finishing rolling is ≥850℃, and the total rolling deformation is 75%~85%. S3. Convey the profile to a linear tension straightener via a roller conveyor for tension straightening at a speed of 0.4-0.6 m / s. The profile temperature after straightening is ≥700℃. S4. Air cool the profile, then cut off the "tongue" shaped parts at both ends and clean the surface oxide scale. Use water jet cutting to symmetrically divide the profile along the rolling direction to obtain two spherical flat titanium profiles of the same specifications.

2. The hot-rolled preparation method for producing spherical flat titanium according to claim 1, characterized in that, The length of a single spherical flat titanium profile prepared in step S4 is 12.0~15.0m.

3. The hot-rolling preparation method for producing spherical flat titanium according to claim 1, characterized in that, In step S1, before rolling, the oxide scale on the surface of the square billet is removed and the defects are cleaned by grinding. The square billet is preheated to 910-930℃.

4. The hot-rolled preparation method for producing spherical flat titanium according to claim 3, characterized in that, The square billet is a TA24 (Ti75) alloy with a nominal composition of Ti-3Al-2Mo-2Zr.

5. The hot-rolled preparation method for producing spherical flat titanium according to claim 1, characterized in that, Step S2 includes: rough rolling at a speed of 4.8-5.2 m / s to form a groove, with the billet temperature after rough rolling being 883-890℃, and finishing rolling in a continuous pass to shape the billet into an arc and obtain a symmetrical spherical flat titanium profile with two spherical ends and a middle web, with the billet temperature after finishing rolling being 855-865℃ and the total rolling deformation being 78%~82%.

6. The hot-rolled preparation method for producing spherical flat titanium according to claim 5, characterized in that, Step S3 uses a Φ365 tandem 7-strand rolling mill for continuous through rolling.

7. The hot-rolled preparation method for producing spherical flat titanium according to claim 1, characterized in that, In step S4, a through-type sandblasting machine is used for cleaning.

8. The application of the hot rolling preparation method for producing spherical flat titanium according to any one of claims 1-7 in the field of marine engineering equipment.

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