A preparation method of a fine-grained titanium alloy bar

Abstract

The present application provides a method for preparing a fine-grained titanium alloy bar, comprising: subjecting a titanium alloy ingot to multi-pass continuous rolling to obtain a rolled blank; subjecting the rolled blank to a first rolling to obtain a round blank, performing supplementary heating on the round blank, and subjecting the round blank after supplementary heating to a second rolling; subjecting the round blank after the second rolling to sizing rolling to obtain an ultrafine-grained titanium alloy bar. The present invention adopts a technical route different from the traditional method for preparing titanium alloys, that is: directly subjecting the ingot to large deformation rolling. This processing method uses rolling to break the billet instead of the traditional forging to break the billet, avoiding the problem of uneven coarse grains in the cross-section structure of the forged billet prepared by forging to break the billet. Moreover, after the ingot is subjected to large deformation rolling to break the billet, a uniform elongated α structure morphology is obtained. This structure morphology is beneficial to the preparation of ultrafine grains during subsequent large deformation finish rolling.

Description

Technical Field

[0001] The present invention relates to the technical field of titanium alloy bar processing, and particularly to a method for preparing a fine-grained titanium alloy bar. Background Art

[0002] Small-sized titanium alloy bars are mainly applied to the field of fasteners, which have extremely high requirements for the mechanical properties of materials. This fastener titanium alloy bar should have the technical characteristics of high strength, high toughness and fine grains.

[0003] The traditional method for preparing small-sized titanium alloy bars is as follows: alloy ingots are forged through multiple heating passes, and then subjected to one-pass large-deformation rolling or multiple-pass hot rolling to obtain straight bars and coiled rolled bars. The number of forging and rolling passes is large, the processing route is complex, and the manufacturing cycle is long and the cost is high.

[0004] Patent CN105750328B, a continuous rolling processing method for small-sized titanium and titanium alloy bars, uses 120-square billets for large-deformation rolling to obtain rolled bars (strips) of different diameters. However, the 120-square billets of the rolling billets still need to be formed by multiple forging passes, and the as-forged structure obtained after forging has an uneven morphological distribution in the cross-section.

[0005] Therefore, in the prior art, when processing by directly rolling the forged billet, the uneven structure of the forged billet will still show unevenness in the structure of the rolled billet after rolling, and the coarse, broken and elongated structure formed by forging is not conducive to the refinement of α grains during the rolling process. Summary of the Invention

[0006] The present invention provides a method for preparing a fine-grained titanium alloy bar to solve the technical problems that in the prior art, when processing by directly rolling the forged billet, the uneven structure of the forged billet will still show unevenness in the structure of the rolled billet after rolling, and the coarse, broken and elongated structure formed by forging is not conducive to the refinement of α grains during the rolling process.

[0007] To achieve the above object, the present invention is realized by the following technical solutions:

[0008] The present application provides a method for preparing a fine-grained titanium alloy bar, including:

[0009] Performing multi-pass continuous rolling on a titanium alloy ingot to obtain a rolled billet;

[0010] Performing one-pass rolling on the rolled billet to obtain a round billet, performing supplementary heating on the round billet, and performing second-pass rolling on the round billet after supplementary heating;

[0011] Performing sizing rolling on the round billet after second-pass rolling to obtain an ultrafine-grained titanium alloy bar.

[0012] Optionally, before the step of subjecting the titanium alloy ingot to multi-pass continuous rolling to obtain a rolled blank, the method further includes:

[0013] Subject the titanium alloy ingot to heat preservation heating, wherein the heating temperature range is: 1150 - 1170 °C, and keep warm for 5 - 7 h.

[0014] Optionally, the step of subjecting the titanium alloy ingot to multi-pass continuous rolling to obtain a rolled blank includes:

[0015] Use a large horizontal rolling mill to subject the ingot to multi-pass continuous rolling to obtain an intermediate blank with a diameter of Φ220 mm, then transfer it to an intermediate-temperature electric furnace and keep it warm at 960 - 980 °C for 2 h, and use a large horizontal rolling mill to subject it to multi-pass continuous rolling to obtain a rolled blank with a diameter of Φ90 - 110 mm.

[0016] Optionally, before the step of subjecting the rolled blank to a single rolling pass, the method further includes:

[0017] After subjecting the rolled blank with a diameter of Φ90 - 110 mm to surface peeling, saw it into single-piece blanks, and subject the single-piece blanks to heat preservation heating in a walking-beam intermediate-temperature electric furnace, wherein the heat preservation temperature range is: 940 - 950 °C, and the heat preservation duration is: 1 - 1.5 h.

[0018] Optionally, the single weight of the single-piece blank is 150 - 200 kg.

[0019] Optionally, the step of subjecting the rolled blank to a single rolling pass to obtain a round blank includes:

[0020] Roll the rolled blank with a diameter of Φ90 - 110 mm into a round blank with a diameter of Φ40 - 45 mm through a horizontal rolling mill.

[0021] Optionally, the step of replenishing the temperature of the round blank includes:

[0022] Use a line induction heating coil device to perform induction heating on the surface of the round blank with a diameter of Φ40 - 45 mm to replenish the surface temperature.

[0023] Optionally, the step of subjecting the round blank after temperature replenishment to a second rolling pass includes:

[0024] Use a large vertical rolling mill to perform a set of 6-pass vertical continuous rolling on the round blank after temperature replenishment.

[0025] Optionally, the step of subjecting the round blank after the second rolling pass to sizing rolling to obtain an ultrafine-grained titanium alloy bar includes:

[0026] Complete the sizing rolling through Kocks sizing and precision rolling forming, online straight bar fixed-length cutting, and cooling and shaping on a cooling bed to obtain an ultrafine-grained titanium alloy bar.

[0027] Optionally, the ultrafine-grained titanium alloy bar is a rolled bar with a diameter of Φ(13 - 17) mm.

[0028] The present application provides a method for preparing a fine-grained titanium alloy bar, comprising: performing multi-pass continuous rolling on a titanium alloy ingot to obtain a rolled billet; performing primary rolling on the rolled billet to obtain a round billet, performing supplementary heating on the round billet, and performing secondary rolling on the round billet after supplementary heating; performing sizing rolling on the round billet after secondary rolling to obtain an ultrafine-grained titanium alloy bar. The present invention adopts a technical route different from the traditional method for preparing titanium alloys, that is: directly performing large deformation rolling on the ingot. This processing method uses rolling to form the initial billet instead of traditional forging to form the initial billet, avoiding the problem of uneven coarse grains in the cross-sectional structure of the forged billet prepared by forging to form the initial billet. Moreover, after the large deformation rolling of the ingot to form the initial billet, a uniform elongated α tissue morphology is obtained. This tissue morphology is conducive to the preparation of ultrafine grains during subsequent large deformation finish rolling. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Figure 1 Figure 8 shows the high-magnification microstructural morphology of the cross-section of a Φ100mm round bar billet prepared by directly performing large deformation rolling on a Ti6Al4V alloy ingot.

[0030] Figure 2 Figure 12 shows the high-magnification microstructural morphology of the cross-section of a Φ15mm finished rolled bar of Ti6Al4V alloy prepared by the traditional preparation process.

[0031] Figure 3 Figure 16 shows the high-magnification microstructural morphology of the cross-section of a Φ15mm finished rolled bar of Ti6Al4V alloy prepared by the process of the present application. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0032] The following further describes the present invention in detail Figure 1 - with reference to the Figure 3 drawings.

[0033] In order to significantly improve the degree of grain refinement of the rolled bar and meet the requirements of high performance and material consistency, the present invention adopts a technical route different from the traditional method for preparing titanium alloys, that is: directly performing large deformation rolling on the ingot. This processing method uses rolling to form the initial billet instead of traditional forging to form the initial billet, avoiding the problem of uneven coarse grains in the cross-sectional structure of the forged billet prepared by forging to form the initial billet. Moreover, after the large deformation rolling of the ingot to form the initial billet, a uniform elongated α tissue morphology is obtained. This tissue morphology is conducive to the preparation of ultrafine grains during subsequent large deformation finish rolling. On this basis, the technical solution of the present application is proposed:

[0034] The present invention provides a method for preparing a fine-grained titanium alloy bar, comprising: step S110 - step S130.

[0035] Step S110. Perform multi-pass continuous rolling on a titanium alloy ingot to obtain a rolled billet.

[0036] In this embodiment, an ingot of Φ(500 - 700)mm Ti6Al4V titanium alloy is held at 1150 - 1170°C for 5 - 7 h in a high-temperature electric furnace, and a Φ220mm intermediate blank is obtained through multi-pass continuous rolling using a large-scale horizontal rolling mill. Then, it is transferred to a medium-temperature electric furnace and held at 960 - 980°C for 2 h, and a Φ(90 - 110)mm rolled blank is obtained through multi-pass continuous rolling using a large-scale horizontal rolling mill. As Figure 1 shown, Figure 1 Figure Figure 1 shows the high-magnification microstructure morphology of the cross-section of a Φ100mm round bar blank prepared by direct blooming rolling of a Ti6Al4V alloy ingot. It can be seen that the rolling method of the present application can effectively improve the cross-sectional tissue uniformity of the rolled blank obtained by rolling.

[0037] The present invention abandons the traditional process of forging and blanking of titanium alloys, and uses direct large-deformation rolling of ingots to blank. The as-cast structure is broken under high-temperature large deformation to obtain a rolled blank with a uniform fine-grained structure. This uniform elongated α tissue morphology is very conducive to further breaking into fine equiaxed grains during subsequent large-deformation continuous rolling. As Figure 1 shown in the metallographic structure diagram, the rolled blank processed by the process of the present application has good cross-sectional tissue uniformity. On this basis, step S120 is executed.

[0038] Step S120: Perform primary rolling on the rolled blank to obtain a round blank, perform supplementary heating on the round blank, and perform secondary rolling on the round blank after supplementary heating.

[0039] In this embodiment, in step S110, a Φ(90 - 110)mm rolled blank is obtained. Before performing primary rolling on the rolled blank, the Φ(90 - 110)mm rolled blank is surface peeled and then sawed into single-piece blanks with a single weight of 150 - 200 kg, and held at 940 - 950°C for 1 - 1.5 h in a walking-beam medium-temperature electric furnace.

[0040] In this embodiment, the finish rolling is carried out in a temperature range (940 - 950°C) close to the alloy phase transformation point. This temperature range is different from the traditional low-temperature range (900 - 910°C) rolling. The material undergoes hot rolling plastic deformation with a large deformation amount at a relatively high two-phase region temperature, which is conducive to the full and uniform breaking of the elongated α in the original rolled blank and its evolution from the elongated form to the equiaxed form, avoiding the induction of adiabatic shear bands, that is, non-uniform tissue bands, under low-temperature high-rate deformation.

[0041] Afterwards, the insulated billet is subjected to continuous large deformation rolling. The rolling mechanism used in this application is divided into two units, the first unit is a horizontal rolling mill, and the second unit is a 6-pass vertical rolling mill; during the rolling process, the Φ (90-110) mm billet is first rolled into Φ (40-45) mm by a horizontal rolling mill, and then passes through an online induction heating coil device for temperature supplementation, and then undergoes a group of 6-pass vertical rolling mill continuous rolling, and then is formed by kocks sizing and finishing rolling.

[0042] In this embodiment, the finished product is rolled in two stages: in the first stage, the Φ (90-110) mm billet is rolled into Φ (40-45) mm, and the billet is rolled into a round billet instead of the square billet reported in previous literature. Because when the square billet is switched to a round shape, the alloy will exhibit uneven deformation flow in the cross section, resulting in uneven cross-sectional structure. Therefore, the use of rolled round billets can ensure that the billet structure is uniform across the entire cross section under large deformation rolling. In the second stage, the Φ(40-45)mm billet is rolled into Φ(13-17)mm. After the first stage of rolling, the surface of the Φ(40-45)mm bar billet shows a temperature drop. Continuous large deformation rolling will cause cracking on the alloy surface. The surface of the Φ(40-45)mm titanium alloy billet is induction heated to replenish the surface temperature without affecting the internal temperature of the bar billet. After replenishing the temperature, the temperature of the entire bar cross section reaches the same level. Then, large deformation longitudinal rolling is continued. The entire cross section of the alloy is in a uniform temperature field, and the deformation resistance is also consistent. This is very beneficial for the α grains to continue to be refined, spheroidized, and equiaxed under large plastic rolling deformation, so that the finished rolled bar obtains uniform ultrafine grains. Figure 2 As shown: Figure 2 The grain morphology of the Φ15mm rolled rod prepared by the present invention is shown. Compared with the finished rolled rod of the same specification prepared by the traditional process, the difference between the two is almost one order of magnitude.

[0043] Step S130: performing sizing rolling on the round billet after the secondary rolling to produce an ultrafine-grained titanium alloy rod.

[0044] In this embodiment, the finished rolled bar material obtained in step S120 is cut into straight strips and shaped on a cooling bed to prepare a rolled bar with a diameter of Φ (13-17) mm.

[0045] The present invention adopts titanium alloy ingot direct blank rolling and finished product rolling. This full-process rolling process has high processing efficiency and greatly improves the processing yield rate. Except for heating fire loss, there is no invisible loss caused by forging billet grinding, and the overall cost is low. It is an efficient and low-cost titanium alloy bar preparation technology, which will replace the traditional forging and rolling combined preparation technology and is a technical optimization choice and development direction for commercial applications.

[0046] This specific embodiment is only an interpretation of the invention and not a limitation thereof. After reading this specification, those skilled in the art may make modifications to this embodiment that do not contribute creatively, but as long as they are within the protection scope of the present invention, they are protected by the Patent Law.

Claims

1. A method for preparing a fine-grained titanium alloy bar, characterized in that, Including: Conduct multi-pass continuous rolling on a titanium alloy ingot to obtain a rolled billet; After skinning the surface of the rolled billet, saw it into single-piece billets, and heat-insulate and heat the single-piece billets in a walking-beam medium-temperature electric furnace. Among them, the heat-insulation temperature range is: 940 - 950 °C, and the heat-insulation duration is: 1 - 1.5 h; Conduct primary rolling on the single-piece billet to obtain a round billet, replenish the temperature of the round billet, and conduct secondary rolling on the round billet after temperature replenishment; The step of conducting primary rolling on the rolled billet to obtain a round billet includes: rolling a rolled billet with a diameter of Φ90 - 110 mm into a round billet with a diameter of Φ40 - 45 mm through a horizontal tandem mill; The step of replenishing the temperature of the round billet includes: using a line induction heating coil device to conduct induction heating on the surface of the round billet with a diameter of Φ40 - 45 mm to replenish the surface temperature; The step of conducting secondary rolling on the round billet after temperature replenishment includes: using a large-scale vertical tandem mill to conduct a set of 6-pass vertical tandem continuous rolling on the round billet after temperature replenishment; Conduct sizing rolling on the round billet after secondary rolling to obtain a fine-grained titanium alloy bar; The step of conducting sizing rolling on the round billet after secondary rolling to obtain a fine-grained titanium alloy bar includes: forming through Kocks sizing and precision rolling, cutting off under online straight bar fixed length, and cooling and shaping on a cooling bed to complete the sizing rolling and obtain a fine-grained titanium alloy bar.

2. The preparation method of the fine-grained titanium alloy bar according to claim 1, wherein, Before the step of conducting multi-pass continuous rolling on a titanium alloy ingot to obtain a rolled billet, it further includes: Heat-insulate and heat the titanium alloy ingot, among which, the heating temperature range is: 1150 - 1170 °C, and keep warm for 5 - 7 h.

3. The preparation method of the fine-grained titanium alloy bar according to claim 1, characterized in that, The step of conducting multi-pass continuous rolling on a titanium alloy ingot to obtain a rolled billet includes: Using a large-scale horizontal tandem mill, conduct multi-pass continuous rolling to obtain an intermediate billet with a diameter of Φ220 mm, then transfer it to a medium-temperature electric furnace and keep warm at 960 - 980 °C for 2 h, and use a large-scale horizontal tandem mill to conduct multi-pass continuous rolling to obtain a rolled billet with a diameter of Φ90 - 110 mm.

4. The preparation method of the fine-grained titanium alloy bar according to claim 1, characterized in that, The single weight of the single-piece billet is 150 - 200 kg.

5. The preparation method of the fine-grained titanium alloy bar according to claim 1, characterized in that, The fine-grained titanium alloy bar is a rolled bar with a diameter of Φ13 - 17 mm.

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