Short process preparation method of titanium and titanium alloy round bar blank for hot continuous rolling

Abstract

The present application relates to the field of titanium alloy forming, and discloses a short-process preparation method for titanium and titanium alloy round bar blank for hot continuous rolling, comprising: S10, melting to obtain titanium and titanium alloy ingot; S20, heating the ingot; S30, first-stage rolling of the heated ingot to obtain a preliminary rolled piece; S40, second-stage rolling of the preliminary rolled piece to obtain a target round bar blank; wherein a plurality of passes of rolling are sequentially performed using a plurality of grooves of a preset groove system, the plurality of grooves comprising a plurality of elliptical grooves and a plurality of circular grooves arranged alternately; wherein step S40 comprises: S41, calculating the target size of the rolled piece after each pass of rolling according to the diameter of the target round bar blank and a preset linear coefficient; S42, determining the roll gap value of each pass according to the target size of each pass; and S43, performing rolling according to the roll gap value of each pass. The present application can realize short-process, multi-specification rolling of titanium and titanium alloy round bar blanks, and can effectively control the microstructure and properties.

Description

Technical Field

[0001] This invention relates to the field of titanium alloy forming technology, and specifically to a short-process preparation method for titanium and titanium alloy round bar billets for hot continuous rolling. Background Technology

[0002] Titanium and titanium alloys are widely used in aerospace, marine engineering, and medical fields due to their excellent specific strength, corrosion resistance, and biocompatibility. Large-diameter titanium alloy round bar billets are important intermediate billets for subsequent hot continuous rolling production of bars and wires, and their quality directly affects the performance of the final products.

[0003] Currently, the preparation of titanium alloy round bar billets mainly employs forging or rolling processes. Forging is a lengthy process with low yield and uneven microstructure; rolling often focuses on die design for single-specification products. When product specifications change, the entire set of rolls or rings must be replaced, leading to reduced production efficiency and increased equipment investment and costs. Furthermore, existing rolling processes struggle to effectively break up as-cast grains and refine the microstructure during the billet preparation process, resulting in uneven microstructure and coarse grains on the billet's core and surface, affecting the stability of subsequent hot continuous rolling and the final product quality.

[0004] Therefore, developing a direct rolling method for round bar billets that enables one-fire production, flexible manufacturing, and effective control of microstructure and properties has become an urgent need in the industry. Summary of the Invention

[0005] The main objective of this invention is to provide a short-process preparation method for titanium alloy round bar billets used in hot continuous rolling, so as to solve the technical problems of how to flexibly roll multi-specification products and effectively control the microstructure and properties of titanium alloys.

[0006] According to one aspect of the present invention, a short-process preparation method for titanium alloy round bar billets for hot continuous rolling is provided, comprising the following steps: S10, melting to obtain titanium and titanium alloy ingots; S20, heating the ingots; S30, performing a first-stage rolling on the heated ingots to obtain preliminary rolled pieces; wherein the total reduction rate is controlled to be not less than a preset value; S40, performing a second-stage rolling on the preliminary rolled pieces to obtain target round bar billets; wherein multiple passes are performed sequentially using multiple pass types of a preset pass system, the multiple pass types including multiple elliptical passes and multiple circular passes arranged alternately; wherein step S40 includes the following steps: S41, calculating the target size of the rolled piece after each pass based on the target round bar billet diameter and a preset linear coefficient; S42, determining the roll gap value for each pass based on the target size for each pass; S43, performing rolling based on the roll gap value for each pass.

[0007] According to one embodiment of the present invention, in step S40, a preset pass system is set on the same pair of rolls, and multiple passes are arranged along the length direction of the rolls; rolling is performed by reciprocating rolling.

[0008] According to an embodiment of the present invention, in step S41, the target dimensions include the target minor axis of the rolled piece after elliptical hole rolling and the target diameter of the rolled piece after circular hole rolling; the target minor axis is obtained by multiplying the target circular bar billet diameter by the corresponding preset linear coefficient, and the target diameter is obtained by multiplying the target circular bar billet diameter by the corresponding preset linear coefficient.

[0009] According to one embodiment of the present invention, the plurality of hole types include at least three elliptical holes and at least three circular holes arranged alternately; in step S41, the preset linear coefficient corresponding to the first elliptical hole is 1.25~1.35, the preset linear coefficient corresponding to the first circular hole is 1.55~1.65, the preset linear coefficient corresponding to the second elliptical hole is 1.05~1.15, the preset linear coefficient corresponding to the second circular hole is 1.20~1.30, the preset linear coefficient corresponding to the third elliptical hole is 0.85~0.95, and the preset linear coefficient corresponding to the third circular hole is 1.0.

[0010] According to one embodiment of the present invention, the ratio of the major axis to the minor axis of the first elliptical hole is 1.80 to 1.90, the ratio of the major axis to the minor axis of the second elliptical hole is 1.60 to 1.70, and the ratio of the major axis to the minor axis of the third elliptical hole is 1.30 to 1.40.

[0011] According to one embodiment of the present invention, step S40 further includes using a movable heat insulation cover to stabilize the final rolling temperature of the rolled piece at (T). β -30℃ to (T β Within the range of -80℃, where T β β is the β phase transformation temperature of titanium and titanium alloys.

[0012] According to one embodiment of the present invention, step S40 further includes: in the last 1 to 3 passes, fine-tuning the roll gap value according to the workpiece size detection value to ensure that the diameter tolerance of the final rolled workpiece is ≤ ±1.0 mm and the ellipticity is ≤ 1.5 mm; in step S40, after each rolling pass, the workpiece is flipped 90° and then sent to the next pass for rolling.

[0013] According to one embodiment of the present invention, in step S10, an electron beam cold hearth furnace is used for melting, and the vacuum degree is controlled to be ≤1×10⁻⁶. -2 Pa.

[0014] According to an embodiment of the present invention, in step S20, the heating is a stepped heating, including: a first stage, heating from room temperature to 820~850℃ at a heating rate of 50~80℃ / h, and holding for 3~5h; a second stage, heating to 80~150℃ above the β phase transition point and holding for 4~8h.

[0015] According to one embodiment of the present invention, step S30 includes: using flat rolls to perform the first pass of rolling, controlling the reduction rate of the first pass to be 15%~22%; using box-shaped holes to perform the second and third passes of rolling, controlling the total reduction rate of the second and third passes to be 25%~35%; and controlling the total reduction rate of the first stage of rolling to be not less than 35%.

[0016] In the technical solution of this invention, the target dimensions of the rolled pieces for each pass are calculated based on the diameter of the target round bar billet and a preset linear coefficient, and the roll gap value is adjusted accordingly, thereby achieving flexible production of round bar billets of different specifications on a set of fixed roll passes. In the first stage, large deformation rolling is performed with a total reduction rate greater than a preset value to rapidly break up the coarse as-cast grains of the titanium alloy ingot; then, in the second stage, multiple passes are performed using alternating elliptical and round roll passes to ensure sufficient deformation of the billet core, promoting dynamic recrystallization to refine the microstructure. Therefore, this invention enables flexible rolling of titanium and titanium alloy round bar billets of various specifications, effectively controls the microstructure and properties of titanium alloys, and allows for one-pass direct rolling, thus shortening the process. Attached Figure Description

[0017] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0018] Figure 1 A flowchart illustrating a short-process preparation method for hot-rolled titanium and titanium alloy round bar billets according to an embodiment of the present invention is shown. Figure 2 Another flowchart of a short-process preparation method for hot continuous rolling of titanium and titanium alloy round bar billets according to an embodiment of the present invention is shown. Figure 3 A cross-sectional schematic diagram of a preset hole pattern system according to an embodiment of the present invention is shown; Figure 4 The transverse and longitudinal metallographic structures of the TC4 round bar billet obtained according to an embodiment of the present invention are shown. Detailed Implementation

[0019] To make the objectives, technical solutions, and advantages of the present invention clearer, the embodiments of the present invention will be further described in detail below with reference to specific examples and the accompanying drawings.

[0020] In the description of this invention, it should be understood that the terms "center," "longitudinal," "lateral," "length," "width," "thickness," "upper," "lower," "front," "rear," "left," "right," "vertical," "horizontal," "top," "bottom," "inner," "outer," "clockwise," and "counterclockwise," etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are only for the convenience of describing this invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on this invention.

[0021] It should be noted that all uses of "first" and "second" in the embodiments of the present invention are for the purpose of distinguishing two entities or parameters with the same name but different names. It is clear that "first" and "second" are only for the convenience of expression and should not be construed as limiting the embodiments of the present invention. Subsequent embodiments will not explain this in detail.

[0022] The large-scale production of high-performance titanium and titanium alloy bars and wires relies on high-efficiency, high-precision hot continuous rolling technology. Hot continuous rolling equipment has strict requirements for the bar billets at the rolling inlet: first, strict dimensional tolerances and roundness to ensure stable bite in roughing; second, good surface quality to prevent defects from spreading during continuous deformation; and third, uniform and precise finishing rolling temperature to achieve a "seamless" connection of the rolling process.

[0023] As mentioned in the background section above, the inventors of this application recognize that existing processes for preparing titanium and titanium alloy round bar billets for hot rolling suffer from problems such as lengthy processes, difficulty in achieving multi-specification production, and difficulty in effectively controlling microstructure and properties. Currently, the supply of large-specification titanium alloy round bar billets for hot rolling mainly relies on two traditional paths: one is a long process of "vacuum self-consuming arc melting (VAR) + multi-fire forging + secondary heating rolling + cold grinding," which has inherent drawbacks such as long cycle time (several weeks), low yield (approximately 65-75%), huge energy consumption, and uneven microstructure between the billet head and tail and the core and surface. More importantly, the VAR process has limited ability to remove high / low density inclusions, which are the main risk source for fatigue failure of end products (such as aerospace fasteners). The second is ordinary rolling for billet preparation, which has large fluctuations in billet size and surface quality, and cannot meet the requirements of continuous and stable rolling. To solve the above-mentioned problems in the prior art, this invention proposes one or more embodiments as described below.

[0024] refer to Figure 1This invention proposes a short-process method for preparing titanium and titanium alloy round bar billets for hot continuous rolling, comprising the following steps: S10 is used for smelting to obtain titanium and titanium alloy ingots; S20, heating the ingot; S30 involves the first stage of rolling the heated ingot to obtain a preliminary rolled product; wherein the total reduction rate is controlled to be not less than a preset value. S40, the preliminary rolled piece is subjected to a second stage of rolling to obtain the target round bar billet; wherein multiple passes of a preset pass system are rolled in sequence, and the multiple passes include multiple elliptical passes and multiple round passes arranged alternately; Step S40 includes the following steps: S41, calculating the target size of the rolled piece after each pass based on the target round bar billet diameter and the preset linear coefficient; S42, determining the roll gap value for each pass based on the target size for each pass; S43, performing rolling based on the roll gap value for each pass.

[0025] In the technical solution of this invention, the target dimensions of each rolling pass are calculated based on the target round bar billet diameter and a preset linear coefficient, and the roll gap value is adjusted accordingly, thereby achieving flexible production of round bar billets of different specifications on a fixed die. In the first stage, large deformation rolling is performed with a total reduction rate greater than a preset value to rapidly break up the coarse as-cast grains of the titanium alloy ingot; then, in the second stage, multiple passes of rolling are performed using alternating elliptical and round holes, allowing the core of the billet to undergo sufficient deformation, promoting dynamic recrystallization to refine the microstructure. Therefore, this invention enables flexible rolling of titanium and titanium alloy round bar billets of various specifications, exhibiting good flexibility and adaptability. It solves the problems of low efficiency caused by frequent roll changes and multiple heating cycles in traditional processes; it enables one-fire production of titanium and titanium alloy round bar billets in a short-process billet opening, avoiding multiple heating cycles and secondary processing of intermediate billets, thereby shortening the production cycle and increasing the yield; and it can obtain high-quality round bar billets with uniform and refined microstructure through the synergistic effect of large deformation and alternating deformation.

[0026] It is understood that the numbering of each step in this invention is only for clarity of description and is not a strict limitation on the execution order. Without departing from the principle of this invention, the order of some steps can be adjusted. For example, steps S41 and S42 are process parameter setting steps (preparation steps), and their execution order can be before or in parallel with step S30.

[0027] refer to Figure 2In some embodiments, the short-process preparation method for titanium and titanium alloy round bar billets of the present invention may include the following steps: primary melting in an EB furnace (electron beam cold hearth furnace); peeling and chamfering of round ingots; multi-stage gradient heating; calling the corresponding pass pattern of the control system according to the target billet size D0; direct rolling after billet exiting the furnace; multi-pass turning and rolling; hot conveying of billets to subsequent hot continuous rolling mills.

[0028] In some embodiments, in step S10, an electron beam cold hearth furnace is used for melting, and the vacuum degree is controlled to be ≤1×10⁻⁶. - 2 Pa. Electron beam cold hearth furnaces can produce ingots with extremely high purity, fundamentally solving the problem of material purity. However, even with EB ingots, existing technologies still rely on traditional forging or fixed-pass rolling for subsequent billet preparation, failing to systematically integrate the material purity advantage with a flexible, precise, and short-process rolling technology to achieve a leapfrog improvement in billet quality and production efficiency. This invention proposes a short-process method that utilizes the advantages of EB ingots and can flexibly supply multi-specification continuously rolled billets. In step S10, raw material proportions (including sponge titanium and intermediate alloys, etc.) are made according to the composition of titanium and titanium alloys. After mixing, the raw materials are pressed into electrode blocks and smelted once in an electron beam cold hearth furnace at a purity of ≤1×10⁻⁶. -2 After being thoroughly refined in a cooling bed under high vacuum, it is cast into a cylindrical ingot of a specified diameter, thus eliminating high-density inclusions from the source.

[0029] After step S10, ingot preparation can be performed, including: CNC turning the outer diameter of the titanium and titanium alloy round ingot to remove the oxide scale and defect layer on the ingot surface, ensuring that the surface roughness Ra of the ingot after cleaning is ≤9.5μm; at the same time, the two ends of the ingot are flattened and chamfered to ensure that the two end faces of the ingot are perpendicular to the ingot axis, with a perpendicularity error ≤1mm / m, and the length of the right-angle side of the chamfer is ≥10mm and the chamfer angle is 45°~50°. In some embodiments, the diameter of the cylindrical ingot cross-section is φ550~750mm and the height is 2000~3000mm.

[0030] In some embodiments, step S20 involves stepped heating, comprising: a first stage, heating from room temperature to 820-850°C at a heating rate of 50-80°C / h, and holding at that temperature for 3-5 hours; and a second stage, heating to 80-150°C above the β phase transformation point and holding at that temperature for 4-8 hours. The purpose of the first stage is to promote the initial homogenization of the internal structure of the ingot; the purpose of the second stage is to ensure uniform temperature throughout the ingot.

[0031] In some embodiments, step S30 includes: performing a first pass of rolling using flat rolls, controlling the reduction rate of the first pass to be 15%~22% (relative to the original diameter of the ingot); performing a second and third pass of rolling using a box-shaped bore, controlling the total reduction rate of the second and third passes to be 25%~35%; and controlling the total reduction rate of the first stage of rolling to be not less than 35%. The first pass of rolling is used to rapidly break up the as-cast structure; the second and third passes of rolling utilize the constraint effect of the sidewalls of the box-shaped bore to roll the irregular cross-section after free expansion into a regular rectangular billet with precise dimensions and sharp edges. The heated ingot can be fed into a two-roll reversible mill for the first stage of rolling.

[0032] The rolled piece obtained after the first stage of rolling then enters a fixed die system consisting of multiple sets (e.g., at least three sets) of "elliptical-circular" die pairs for reciprocating rolling (second stage rolling). The rolled piece sequentially enters these pre-set, fixed slots to complete deformation. Different specifications of products are rolled by utilizing multiple slots on the rolls (along the length of the roll body) and adjusting the reduction (adjusting the roll gap). The die types used in this invention may include 1-2 box-shaped holes, at least 3 elliptical holes, and at least 3 circular holes.

[0033] refer to Figure 3 In some embodiments, in step S40, the preset pass system is set on the same pair of rolls, and multiple passes are arranged along the length of the rolls; accordingly, reciprocating rolling is used for rolling. In this invention, multiple passes for different rolling passes and capable of producing different specifications can be integrated into a single pair of rolls. This can be combined with a transverse guide device and the forward and reverse rotation of the rolls (reversible rolling) to sequentially call different passes to complete multiple rolling passes without changing the rolls. When switching product specifications, only the rolling schedule (such as guide position and roll gap value) needs to be adjusted, thereby significantly shortening the production line length, reducing equipment investment, and reducing roll change time, achieving flexibility, short-process, and efficient billet opening for titanium alloy ingots. In some embodiments, the box-shaped pass used in the first stage of rolling and the pass system used in the second stage of rolling can be integrated on the same pair of rolls.

[0034] In some embodiments, an elliptical hole may include two semi-elliptical grooves symmetrical about the major axis, and a circular hole may include two semi-circular grooves symmetrical about the diameter. This structural design facilitates changing the dimensions of the rolled piece by adjusting the roll gap value, and also ensures that the rolled piece is subjected to uniform stress and symmetrical deformation in the thickness direction.

[0035] In step S40, each pass of rolling is performed using different pass profiles. The target size of the rolled piece after each pass is determined based on the target round bar billet diameter and a predetermined linear coefficient. The target round bar billet diameter can be between 180 and 250 mm. In some embodiments, in step S41, the target size includes the target minor axis of the rolled piece after elliptical pass rolling and the target diameter of the rolled piece after circular pass rolling. The target minor axis is obtained by multiplying the target round bar billet diameter by the corresponding predetermined linear coefficient, and the target diameter is obtained by multiplying the target round bar billet diameter by the corresponding predetermined linear coefficient. The corresponding roll gap value can be determined based on the target size and the groove depth. For example, for an elliptical pass, the target minor axis can be subtracted from the sum of the depths of the two semi-elliptical grooves to obtain the corresponding roll gap value; for a circular pass, the target diameter can be subtracted from the sum of the depths of the two semi-circular grooves to obtain the corresponding roll gap value. Those skilled in the art can also make corrections based on actual conditions and in conjunction with compensation amounts, etc. This invention simplifies complex die design into linear proportional calculation. Based on the target round bar billet diameter and the corresponding linear coefficient, the target dimensions of different specifications of products in each pass can be generated quickly and accurately. Then, the roll gap value of each pass is adjusted according to these target dimensions, so that the same fixed die system can adapt to the production of round bar billets of different specifications without changing the rolls. This achieves flexible, parameterized, and efficient design of titanium alloy round bar billet blanking, significantly shortens the development cycle of new specifications, reduces reliance on operational experience, and ensures deformation coordination and product quality consistency.

[0036] In some embodiments, the plurality of hole types include at least three elliptical holes and at least three circular holes arranged alternately; in step S41, the preset linear coefficient corresponding to the first elliptical hole is 1.25~1.35, the preset linear coefficient corresponding to the first circular hole is 1.55~1.65, the preset linear coefficient corresponding to the second elliptical hole is 1.05~1.15, the preset linear coefficient corresponding to the second circular hole is 1.20~1.30, the preset linear coefficient corresponding to the third elliptical hole is 0.85~0.95, and the preset linear coefficient corresponding to the third circular hole is 1.0. These coefficients ensure that the deformation amount in each pass is reasonably distributed, and the elongation and width ratio are coordinated, ultimately obtaining a target round bar billet with accurate dimensions and uniform structure through a better deformation path.

[0037] In some embodiments, the ratio of the major and minor axes of the first elliptical hole (the ratio of the nominal dimensions of the major and minor axes, where the nominal dimension is the theoretical dimension when the roll gap value is 0) is 1.80~1.90, the ratio of the major and minor axes of the second elliptical hole is 1.60~1.70, and the ratio of the major and minor axes of the third elliptical hole is 1.30~1.40. Setting the ratio of the major and minor axes of the elliptical holes ensures a reasonable distribution of deformation in each pass, and coordinates the elongation and width ratios, ultimately obtaining a target round bar billet with accurate dimensions and good quality.

[0038] In some embodiments, in step S40, after each rolling pass, the rolled piece is flipped 90° before being fed into the next rolling pass to ensure uniform deformation, eliminate internal stress, and guarantee the roundness accuracy of the final product. In some embodiments, step S40 further includes using a movable heat insulation cover to stabilize the final rolling temperature of the rolled piece at (T). β -30℃ to (T β Within the range of -80℃, where T β This refers to the β-phase transformation point temperature of titanium and titanium alloys. Movable heat preservation covers can be installed between key passes on the rolling line as needed, and the final rolling temperature of the workpiece can be stabilized within the aforementioned range by adjusting the rolling rhythm. In some embodiments, step S40 further includes: in the last 1-3 passes, fine-tuning the roll gap value based on the workpiece size detection value to ensure that the diameter tolerance of the final rolled workpiece is ≤ ±1.0 mm and the ellipticity is ≤ 1.5 mm. In the last 2 finishing passes, an online laser diameter gauge, infrared thermometer, and surface inspection system can be used to measure the billet size and temperature in real time. By adjusting the roll gap and rolling rhythm, it can be ensured that the final rolled diameter tolerance of the billet is ≤ ±1.0 mm and the ellipticity is ≤ 1.5 mm, and that the final rolling temperature is stabilized within (T...). β -30℃ to (T β Within the temperature range of -80℃, the surface has no obvious defects such as cracks, folds, or pits.

[0039] In some embodiments, after step S40, hot delivery of billets can be carried out: after the qualified billets are hot-sawed to length by online inspection, they are directly sent to the downstream hot continuous rolling mill for subsequent wire rod rolling via insulated roller conveyor or special hot delivery car, or sent to the walking beam heating furnace for secondary heating and then rolling, to achieve "hot delivery and hot loading", reduce heat loss, reduce energy consumption costs and improve rolling efficiency.

[0040] Figure 4 This diagram shows a 1000x magnified transverse and longitudinal metallographic structure of the TC4 round bar billet obtained according to an embodiment of the present invention, with reference to... Figure 4 The TC4 round bar billet exhibits a uniform and fine bimodal microstructure in both the transverse and longitudinal directions, with no obvious grain coarsening or microstructure segregation. This indicates that the method described in this invention can effectively promote grain refinement and microstructure homogenization, thereby obtaining a high-quality round bar billet with good microstructure consistency across the entire cross-section.

[0041] The following description is based on specific embodiments.

[0042] Example 1 This embodiment produces Φ220mm TC4 ELI (Ti-6Al-4V ELI) titanium alloy hot-rolled round bar billets, whose β phase transformation point (T β The temperature is approximately 990℃. The production method includes the following steps: (1) Pure smelting: Electron beam cold hearth furnace is used for one-time smelting to produce ingots with specifications of Φ650mm×2000mm. The vacuum degree is maintained at ≤5×10 during the smelting process. -3 At 80 minutes, an electron beam thoroughly scans and agitates the molten pool within a cooling bed. The purified melt is then poured into a 650mm diameter circular water-cooled copper crystallizer to obtain a cylindrical ingot with a good surface finish.

[0043] (2) Ingot preparation: The EB round ingot is placed on a heavy-duty CNC lathe for overall machining of the outer diameter and end faces. The single-sided turning amount of the outer diameter is 3mm to completely remove the oxide scale and surface defect layer, so that the surface roughness Ra of the ingot reaches 6.5μm. At the same time, the two end faces are precision flat-faced to ensure that the perpendicularity error with the ingot axis is ≤0.8mm / m, and a chamfer of 12mm×45° is performed to facilitate subsequent rolling and prevent edge cracks.

[0044] (3) Gradient heating: The processed ingot is placed into a heating furnace and heated from room temperature to 830°C at a heating rate of 60°C / h, and then held at that temperature for 4 hours to fully reduce thermal stress and promote initial homogenization of the microstructure. Subsequently, heating is continued to the rolling temperature of 1070°C (i.e., T). β +80℃), and hold at this temperature for 8 hours to ensure uniform temperature of the ingot core surface.

[0045] (4) Rolling: The heated ingot is quickly transferred to a two-roll reversible rolling mill for rolling.

[0046] ① Large deformation blanking: Passes 1-3 (flat roll-box pass). In the first pass, the flat roll uses a large reduction of 100mm to form a flat cross-section rolled piece with a height of H1=550mm using free width expansion. After the rolled piece is flipped 90°, its width direction is changed to its height direction for the second pass of large reduction box pass rolling, which performs width compression and preliminary shaping, with an exit height of H2=480mm and an approximately rectangular cross-section. Subsequently, after flipping, it enters the third pass of box pass rolling to obtain a rectangular cross-section rolled piece of 380mm×440mm. The total reduction of area in this stage is 49.5%.

[0047] ②Parameterized roll pass sequence rolling: The rolled piece then enters a pre-set fixed "elliptical-circular" pass system for reciprocating rolling. After each pass, the rolled piece is transferred by the conveyor rollers to a side-mounted turning machine for a 90° turn before proceeding to the next pass. This system is designed with a target billet diameter D0 = 220 mm as the benchmark. The target dimensions of the rolled piece after each pass are calculated using pre-set coefficients. The deformation per pass is controlled within 30%, as detailed in Table 1. In the table, A4~A8 and B4~B8 represent the target major axis and target minor axis of the rolled piece after elliptical pass rolling, respectively, and D5~D9 represent the target diameter of the rolled piece after circular pass rolling. This invention primarily adjusts the roll gap value based on the target minor axis and target diameter. The target major axis is used to illustrate the proportional relationship of the pass design and is for reference only.

[0048] Table 1: Dimensional Design and Deformation Path of Each Pass for φ220mm Bar Billet

[0049] (5) Online finishing and temperature control: At the exit of the 8th pass (precision elliptical hole), the billet size and temperature are monitored in real time using an online laser diameter gauge and an infrared thermometer. The control system dynamically fine-tunes the roll gap of the final rolling pass (9th-10th passes) based on feedback to ensure the final rolled size Φ220.4±0.7mm and ellipticity ≤1.2mm; the final rolling temperature is 925±5℃ (i.e., T β -65℃), at (T β -30℃ to (T β The target temperature range is -80℃; online testing showed no surface defects such as cracks or folds.

[0050] (6) Hot delivery of billet: After qualified billet is hot-sawed to length, it is directly delivered to the subsequent hot rolling mill within 3 minutes through the heat-insulated roller conveyor to achieve "hot delivery and hot loading" with a delivery temperature of over 900℃.

[0051] Example 1 achieved high-precision one-fire billet preparation for large-size TC4 ELI round ingots, with a comprehensive yield of 91.5%. The cross-sectional microstructure was found to be uniform and fine α+β dual-state microstructure, verifying its excellent performance in preparing large-size, high-precision, and highly heat-transfer adaptable titanium alloy continuous rolling billets.

[0052] Example 2 This embodiment uses the same process principle and parametric design system as Embodiment 1 to produce Φ250mm TC4ELI titanium alloy round bar billets. The production method includes the following steps: (1) Pure smelting, (2) Ingot preparation, (3) Heating: The pure smelting (EB furnace one-time smelting), ingot specifications (Φ650mm), surface preparation and gradient heating system used in this embodiment are exactly the same as those in Embodiment 1.

[0053] (4) Rolling: The heated ingot is quickly transferred to a two-roll reversible rolling mill for rolling.

[0054] ① Large deformation blanking: The process steps and the purpose of this stage are completely the same as in Example 1. The same regular rectangular blank (380mm×440mm) is obtained at the exit, which serves as a stable feed material for the subsequent die system.

[0055] ②Parameterized roll pass sequence rolling: The rolled piece then enters a pre-set fixed "elliptical-circular" pass system for reciprocating rolling. After each pass, the rolled piece is transferred by the conveyor rollers to a side-mounted turning machine for a 90° turn before proceeding to the next pass. The system is designed with a target billet diameter D0 = 250 mm as the benchmark. The target dimensions of the rolled piece after each pass are calculated using preset coefficients, as detailed in Table 2.

[0056] Table 2: Dimensional Design and Deformation Path of Each Pass for φ250mm Bar Billet

[0057] (5) Online finishing and temperature control: The control logic is the same as in Example 1, ensuring the final rolled size Φ250.2±0.5mm and ellipticity ≤1.0mm; final rolling temperature: 925±5℃ (i.e., T β -65℃), at (T β -30℃ to (T β The target temperature range is -80℃; online testing showed no surface defects such as cracks or folds.

[0058] (6) Hot delivery of billet: After qualified billet is hot-sawed to length, it is directly delivered to the subsequent hot rolling mill within 3 minutes through the heat-insulated roller conveyor to achieve "hot delivery and hot loading" with a delivery temperature of over 900℃.

[0059] Example 2: Without changing any basic process steps or equipment, high-quality Φ250mm hot-rolled bar billets were successfully produced by adjusting only the target parameter D0. The cross-sectional microstructure was found to be a uniform and fine α+β bimodal microstructure with good microstructure properties.

[0060] Example 3 This embodiment uses the same process principle and parametric design system as Embodiment 1 to produce 200mm TC4ELI titanium alloy round bar billets. The process steps are basically the same as in Embodiment 1, only the parametric pass sequence rolling is changed. The system uses the target billet diameter D0=200mm as the design benchmark, and the target dimensions of the rolled piece after each rolling pass are calculated by preset coefficients. The specific procedures are shown in Table 3.

[0061] Table 3: Dimensional Design and Deformation Path of Each Pass for φ200mm Bar Billet

[0062] The hot-rolled bar billet with a diameter of φ200mm prepared in Example 3 has a diameter of Φ200.2±0.5mm and an ellipticity of ≤0.8mm; the final rolling temperature is 945±5℃ (i.e., T). β -45℃), at (T β -30℃ to (T β The target temperature range is -80℃. Online testing showed that the surface had no cracks, folds or other defects, and the cross-sectional structure was found to be a uniform and fine α+β bimodal structure with good microstructure properties.

[0063] In summary, this invention provides a short-process method integrating clean smelting and advanced rolling. Utilizing the high purity of EB furnace ingots, it employs an innovative parametric flexible direct rolling system to stably and efficiently produce large-diameter round bar billets with high dimensional accuracy, good surface quality, uniform microstructure, and precisely controllable final rolling temperature. These billets are directly hot-sent to downstream continuous rolling mills, achieving rapid production from ingots to continuously rolled billets. By changing the input parameters (target round bar billet diameter) and adjusting the corresponding pass schedule, this invention can flexibly produce billets of any size within a given range without changing the rolls.

[0064] Compared with existing continuous rolling billet preparation technologies, the present invention has the following significant advantages and beneficial effects: (1) The present invention uses EB furnace to melt and roll round ingots to prepare multi-specification titanium alloy continuous rolling billets, which eliminates the quality risks caused by inclusions from the source and provides a stable and high-quality source of billets for downstream processes.

[0065] (2) Parametric die design, combined with online finishing and temperature control system, enables the production of Φ180~250mm continuous rolling billet with one set of rolls. The obtained billet has a uniform fine grain structure throughout the cross section, with excellent microstructure and performance, excellent dimensional accuracy and surface quality, laying the foundation for stable continuous rolling production.

[0066] (3) The use of “one-fire direct rolling” instead of multi-fire forging has enabled the direct preparation of large-size round ingots into hot continuous rolled billets, avoiding multiple heating and secondary processing of intermediate billets. This shortens the billet preparation cycle from several weeks to several days, increases the yield from about 70% to more than 85%, and reduces the overall energy consumption by about 35-40%, resulting in significant economic benefits.

[0067] Those skilled in the art should understand that the discussion of any of the above embodiments is merely exemplary and is not intended to imply that the scope of the invention (including the claims) is limited to these examples. Within the framework of the invention, technical features of the above embodiments or different embodiments can be combined, and many other variations of the different aspects of the invention as described above exist, which are not provided in the details for the sake of brevity. Therefore, any omissions, modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the invention should be included within the protection scope of the invention.

Claims

1. A short-process method for preparing titanium and titanium alloy round bar billets for hot continuous rolling, characterized in that, Includes the following steps: S10 is used for smelting to obtain titanium and titanium alloy ingots; S20, the ingot is heated; S30, the heated ingot is subjected to a first-stage rolling process to obtain a preliminary rolled piece; The total reduction rate is controlled to be no less than a preset value; S40, the preliminary rolled piece is subjected to a second stage of rolling to obtain the target round bar billet; wherein multiple passes of a preset pass system are rolled in sequence, the multiple pass types including multiple elliptical holes and multiple round holes arranged alternately; Step S40 includes the following steps: S41, calculating the target size of the rolled piece after each rolling pass based on the target round bar billet diameter and the preset linear coefficient; S42, determine the roll gap value for each pass based on the target size for each pass; S43, perform rolling based on the roll gap value for each pass.

2. The method according to claim 1, characterized in that, In step S40, the preset pass system is set on the same pair of rolls, and the multiple passes are arranged along the length of the rolls; rolling is performed by reciprocating rolling.

3. The method according to claim 1, characterized in that, In step S41, the target dimensions include the target minor axis of the rolled piece after elliptical hole rolling and the target diameter of the rolled piece after circular hole rolling; the target minor axis is obtained by multiplying the target circular bar billet diameter by the corresponding preset linear coefficient, and the target diameter is obtained by multiplying the target circular bar billet diameter by the corresponding preset linear coefficient.

4. The method according to claim 3, characterized in that, The plurality of hole types include at least three elliptical holes and at least three circular holes arranged alternately; in step S41, the preset linear coefficient corresponding to the first elliptical hole is 1.25~1.35, the preset linear coefficient corresponding to the first circular hole is 1.55~1.65, the preset linear coefficient corresponding to the second elliptical hole is 1.05~1.15, the preset linear coefficient corresponding to the second circular hole is 1.20~1.30, the preset linear coefficient corresponding to the third elliptical hole is 0.85~0.95, and the preset linear coefficient corresponding to the third circular hole is 1.

0.

5. The method according to claim 4, characterized in that, The ratio of the major axis to the minor axis of the first elliptical hole is 1.80 to 1.90, the ratio of the major axis to the minor axis of the second elliptical hole is 1.60 to 1.70, and the ratio of the major axis to the minor axis of the third elliptical hole is 1.30 to 1.

40.

6. The method according to claim 1, characterized in that, Step S40 also includes using a movable heat insulation cover to stabilize the final rolling temperature of the rolled piece at (T). β -30℃ to (T β Within the range of -80℃, where T β β is the β phase transformation temperature of titanium and titanium alloys.

7. The method according to claim 1, characterized in that, Step S40 also includes: in the last 1 to 3 passes, fine-tuning the roll gap value according to the workpiece size detection value to ensure that the diameter tolerance of the final rolled workpiece is ≤ ±1.0 mm and the ovality is ≤ 1.5 mm; in step S40, after each rolling pass, the workpiece is flipped 90° and then sent to the next pass for rolling.

8. The method according to claim 1, characterized in that, In step S10, an electron beam cold hearth furnace is used for melting, and the vacuum degree is controlled to be ≤1×10⁻⁶. -2 Pa.

9. The method according to claim 1, characterized in that, In step S20, the heating is a stepped heating method, including: The first stage involves raising the temperature from room temperature to 820~850℃ at a rate of 50~80℃ / h and holding the temperature for 3~5h. In the second stage, heat to 80~150℃ above the β phase transition point and hold for 4~8 hours.

10. The method according to claim 1, characterized in that, Step S30 includes: using flat rolls for the first pass of rolling, controlling the reduction rate of the first pass to be 15%~22%; using box-shaped holes for the second and third passes of rolling, controlling the total reduction rate of the second and third passes to be 25%~35%; and controlling the total reduction rate of the first stage of rolling to be not less than 35%.

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