WO2024087681A1

WO2024087681A1 - Method for improving flattening performance of titanium alloy seamless tube

Info

Publication number: WO2024087681A1
Application number: PCT/CN2023/102287
Authority: WO
Inventors: 江健
Original assignee: 成都先进金属材料产业技术研究院股份有限公司
Priority date: 2022-10-25
Filing date: 2023-06-26
Publication date: 2024-05-02
Also published as: CN115647107A; CN115647107B

Abstract

Provided in the present invention is a method for improving the flattening performance of a titanium alloy seamless tube. The method comprises the following steps: performing VAR smelting three times to obtain a titanium alloy ingot; preparing the titanium alloy ingot into a titanium alloy round bar; pressing the titanium alloy round bar into a hollow tube blank, and subjecting the interior of the hollow tube blank to wet sand blasting, external grinding and acid pickling to prepare a hollow tube blank; rolling the hollow tube blank into a finished titanium alloy seamless tube; sampling the finished titanium alloy seamless tube, and measuring the maximum depth h1 of a micro-pit in the inner surface and the maximum extension depth h2 of a micro-crack formed by the extension of the micro-pit; subjecting the inner surface of the finished titanium alloy seamless tube to wet sand blasting so as to remove a wall thickness of h1 + 0.02 mm, and subjecting the inner surface of the finished titanium alloy seamless tube to flow acid cleaning so as to remove a wall thickness of h2 + 0.02 mm; and subjecting the finished titanium alloy seamless tube in step 6 to vacuum annealing and straightening to obtain a finished tube. In the present invention, proper grain orientation is regulated by means of composition design and optimization, a thermal deformation process and a cold rolling process; and a better inner surface treatment method is used to completely eliminate micro-crack defects on the inner surface of the titanium alloy tube.

Description

A method for improving the flattening performance of titanium alloy seamless pipe

Technical Field

The invention relates to the technical field of nonferrous metal seamless pipes, in particular to a method for improving the flattening performance of titanium alloy seamless pipes.

Background technique

Flattening performance is an important indicator to measure the quality of titanium alloy tube products, and is generally tested according to GB/T246-2017 standard. For example, the distance between the flat plates of TA18 titanium alloy tubes for aviation is required to be less than 10 times the wall thickness after flattening, that is, the distance between the flat plates of 20*1mm after flattening must be less than or equal to 10mm to be qualified. The existing cold rolling, heat treatment process, and internal surface treatment process are not optimized for the flattening performance of titanium alloy tubes, resulting in unqualified flattening performance of TA18 titanium alloy tubes.

The failure form of the flattening performance of titanium alloy tubes is cracking on the inner surface of the flattened specimen. There are two reasons for the unsatisfactory flattening performance. One is the unreasonable design of the titanium alloy composition and the unreasonable grain orientation distribution of the tube. The other is the unsatisfactory flattening performance caused by the defects on the inner surface of the titanium alloy tube. The microcrack defect on the inner surface is in the form of tiny pits plus microcracks.

Summary of the invention

According to the above technical problems, a method for improving the flattening performance of titanium alloy seamless tube is provided. The present invention mainly solves the first reason mentioned above by optimizing the composition design, regulating the appropriate grain orientation and the appropriate strength-plasticity matching by the hot deformation process and the cold rolling process; and solves the second reason mentioned above by using a better inner surface treatment method to completely remove the microcrack defects on the inner surface of the titanium alloy tube.

The technical means adopted by the present invention are as follows:

A method for improving the flattening performance of a titanium alloy seamless tube comprises the following steps:

Step 1: three times of VAR smelting to obtain a titanium alloy ingot, and the oxygen content of the titanium alloy ingot is controlled to be ≤0.07%;

Step 2: The titanium alloy ingot is made into titanium alloy round bars by free forging with 4 fires, 3-stump and 3-drawing, and radial forging with 2 fires. The flaw detection round bars meet the AA grade of GB/T5193 standard;

Step 3: The titanium alloy round rod is extruded into a hollow tube blank, and the inside of the hollow tube blank is wet-sandblasted, the outside is ground, and the pickling is performed to form a hollow tube blank with no defects on the inner and outer surfaces; the sandblasting uses 100-mesh green silicon carbide particles and water mixed in a weight ratio of 1:2, and the grain orientation type of the hollow tube blank is α phase <11-20>//tube blank radial direction, <10-10>//tube blank axial direction;

Step 4: The hollow tube billet is cold rolled 3 to 4 times on a two-roll cold rolling mill to form a titanium alloy finished seamless tube. Vacuum annealing is performed after each cold rolling. The cold rolling process design ensures that the K value of each cold rolling pass is ≥1, and the deformation rate ε and K value of each cold rolling pass are larger than those of the previous pass. The grain orientation type of the titanium alloy finished seamless tube is α phase <0001>//pipe radial direction, <10-10>//pipe axial direction; the hollow tube billet with an outer diameter of D1 and a wall thickness of S1 is cold rolled once to form a hollow tube billet with an outer diameter of D2 and a wall thickness of S2. The deformation rate ε of this cold rolling pass is calculated as follows:
ε＝((D1-S1)×S1-(D2-S2)×S2)/((D1-S1)×S1);

The calculation formula of K value of this cold rolling pass is: K = (S1-S2) × D1/(D1-D2) × S1;

Step 5: Take multiple groups (preferably 10 groups) of transverse and longitudinal metallographic structure samples from the titanium alloy finished seamless tube in step 4, observe the metallographic structure samples to measure the maximum depth h1 of the micro-pits on the inner surface of the titanium alloy tube, and the maximum extension depth h2 of the micro-cracks extending from the micro-pits on the inner surface;

Step 6: wet-blast the inner surface of the titanium alloy finished seamless tube obtained in step 4 to remove the wall thickness of h1+0.02 mm, cover the outer surface of the titanium alloy tube with a plastic bag after sandblasting, and perform flow pickling on the inner surface of the titanium alloy finished seamless tube to remove the wall thickness of h2+0.02 mm;

Sandblasting uses 100-mesh green silicon carbide particles and water mixed in a weight ratio of 1:2 to remove h1+0.02mm wall thickness. After sandblasting, the outer surface of the titanium alloy tube is covered with a plastic bag. The inner surface of the titanium alloy finished seamless tube is flow pickled. The pickling liquid uses HF acid: the pickling liquid uses HF acid: HNO ₃ acid: water mixed in a weight ratio of 5:20:75, and flows through the inner surface of the titanium alloy tube at a speed greater than or equal to 2 meters/minute;

Step 7: The titanium alloy finished seamless pipe in step 6 is vacuum annealed, straightened and flaw detected. The flaw depth of the flaw detection sample pipe is 0.04mm, the width is 0.10mm and the length is 1.52mm. After the flaw detection is qualified, the sample is taken for tensile performance and flattening performance test to obtain a qualified finished pipe.

Compared with the prior art, the present invention has the following advantages:

The three-step VAR smelting of the present invention ensures uniform composition of the titanium alloy; controls the oxygen content ≤0.07%, which improves the flattening performance of titanium alloy finished tubes; the combination of hot deformation processes of three-pier three-drawing billet opening and radial forging ensures that the titanium alloy round bar has uniform structure and performance, and the flaw detection can reach the AA level of GB/T5193 standard; the extrusion billet process improves the flattening performance of titanium alloy finished tubes by adjusting the tube billet grain orientation type to α phase <11-20>//tube billet radial direction, <10-10>//tube billet axial direction; the process combination of internal sandblasting, external grinding and pickling completely eliminates the defects on the inner and outer surfaces of the hollow tube billet to avoid greater defects in the cold rolling process caused by tube billet defects; the combination of deformation rate ε and K value of the cold rolling process ensures that the grain orientation of the titanium alloy finished seamless tube is reasonable and the structure is fine and uniform. The grain orientation type of the titanium alloy finished seamless tube is α phase <0001>//tube radial direction, <10-10>//tube axial direction, which ensures the flattening performance of the titanium alloy finished tube; Phase observation confirmed the maximum depth h1 of the micro-pits 2 on the inner surface of the titanium alloy tube, and the maximum extension depth h2 of the micro-cracks 3 extended from the micro-pits on the inner surface; a corresponding defect elimination process was formulated according to the defect morphology of the inner surface of the titanium alloy tube, that is, wet sandblasting was first used to remove the micro-pits on the inner surface of the titanium alloy tube (sandblasting rubs the inner wall of the titanium tube and causes the temperature to rise, which affects the microstructure and properties of the titanium tube. Wet sandblasting can cool down and avoid this damage because of water cooling), and then flow pickling was used to remove the micro-cracks on the inner surface of the titanium alloy tube, and 0.02mm was removed to ensure that the defects were completely removed. The combined treatment process of the inner surface of the titanium alloy tube completely eliminated the influence of the inner surface defects of the titanium alloy tube on the flattening performance of the titanium alloy tube; the scratch depth of 0.04mm is the shallowest scratch that can be carved at present. The defect removal effect was confirmed by ultrasonic flaw detection on the entire length of each titanium alloy finished seamless tube, and samples were taken for tensile and flattening performance tests to obtain finished pipes.

Based on the above reasons, the present invention can be widely promoted in the fields of titanium alloy seamless pipes and the like.

BRIEF DESCRIPTION OF THE DRAWINGS

In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

FIG1 is a schematic diagram of micro-pits and micro-cracks on the inner surface of a titanium alloy finished seamless tube in a specific embodiment of the present invention.

Detailed ways

It should be noted that, in the absence of conflict, the embodiments of the present invention and the features in the embodiments can be combined with each other. The present invention will be described in detail below with reference to the accompanying drawings and in combination with the embodiments.

To make the purpose, technical solutions and advantages of the embodiments of the present invention clearer, the following will be combined with the present invention to The accompanying drawings in the embodiments of the present invention clearly and completely describe the technical solutions in 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. The following description of at least one exemplary embodiment is actually only illustrative and is by no means a limitation on the present invention and its application or use. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative work are within the scope of protection of the present invention.

It should be noted that the terms used herein are only for describing specific embodiments and are not intended to limit exemplary embodiments according to the present invention. As used herein, unless the context clearly indicates otherwise, the singular form is also intended to include the plural form. In addition, it should be understood that when the terms "comprising" and/or "including" are used in this specification, it indicates the presence of features, steps, operations, devices, components and/or combinations thereof.

Unless otherwise specifically stated, the relative arrangement, numerical expressions and numerical values of the parts and steps set forth in these embodiments do not limit the scope of the present invention. Meanwhile, it should be clear that, for ease of description, the sizes of the various parts shown in the accompanying drawings are not drawn according to the actual proportional relationship. The technology, method and equipment known to those of ordinary skill in the relevant art may not be discussed in detail, but in appropriate cases, the technology, method and equipment should be considered as a part of the specification. In all examples shown and discussed here, any specific value should be interpreted as being merely exemplary, rather than as a limitation. Therefore, other examples of exemplary embodiments may have different values. It should be noted that similar reference numerals and letters represent similar items in the following drawings, and therefore, once a certain item is defined in an accompanying drawing, it does not need to be further discussed in subsequent drawings.

In the description of the present invention, it is necessary to understand that the directions or positional relationships indicated by directional words such as "front, back, up, down, left, right", "lateral, vertical, perpendicular, horizontal" and "top, bottom" are usually based on the directions or positional relationships shown in the drawings. They are only for the convenience of describing the present invention and simplifying the description. Unless otherwise specified, these directional words do not indicate or imply that the device or element referred to must have a specific direction or be constructed and operated in a specific direction. Therefore, they cannot be understood as limiting the scope of protection of the present invention: the directional words "inside and outside" refer to the inside and outside relative to the contours of each component itself.

For the convenience of description, spatially relative terms such as "on...", "above...", "on the upper surface of...", "upper", etc. may be used herein to describe the structure shown in the figure. The spatial positional relationship of a device or feature shown in the figure with other devices or features. It should be understood that spatially relative terms are intended to include different orientations of the device in use or operation in addition to the orientation described in the figure. For example, if the device in the figure is inverted, the device described as "above other devices or structures" or "on top of other devices or structures" will be positioned as "below other devices or structures" or "below their position devices or structures". Thus, the exemplary term "above..." can include both "above..." and "below..." orientations. The device may also be positioned in other different ways (rotated 90 degrees or in other orientations), and the spatially relative descriptions used here are interpreted accordingly.

In addition, it should be noted that the use of terms such as "first" and "second" to limit components is only for the convenience of distinguishing the corresponding components. Unless otherwise stated, the above terms have no special meaning and therefore cannot be understood as limiting the scope of protection of the present invention.

Step 5: Take 10 groups of transverse and longitudinal metallographic structure samples from the titanium alloy finished seamless tube in step 4, observe the metallographic structure samples to measure the maximum depth h1 of the micro-pits on the inner surface of the titanium alloy tube, and the maximum extension depth h2 of the micro-cracks extending from the micro-pits on the inner surface (as shown in FIG. 1 );

Example 1

The production specification is TA16 titanium alloy seamless pipe with Φ14×0.8mm.

The production process adopted is as follows: sponge titanium and alloy components are subjected to three vacuum self-consumption processes to form Φ490 round TA16 titanium alloy ingots with an oxygen content of 0.059-0.065% → free forging into Φ170 round bars by hydraulic press with 4 fires, three piers and three draws → forging into Φ70 black skin round bars by 2 fires → extrusion, internal sandblasting, external lathe machining and internal and external pickling to form Φ54*5 hollow tube billets → cold rolling into Φ33×3 titanium tubes (ε is 63.3%, K value is 1.03) by LG30 two-roller cold rolling mill → vacuum annealing at 740° for 1h → cold rolling into Φ21×1.7 titanium tubes (ε is 63.5%, K value is 1.19) by LG15 two-roller cold rolling mill → vacuum annealing at 740° for 1h → cold rolling into Φ14×0.8 titanium tube (ε is 67.8%, K value is 1.59) → 750° insulation for 1h vacuum annealing and straightening → Φ14×0.8 titanium tube takes 10 groups of transverse and longitudinal metallographic structure samples, observes the metallographic structure samples and measures the maximum depth of the micro-pits on the inner surface of the titanium alloy tube to be 0.02mm, and the maximum extension depth of the micro-cracks extending from the micro-pits on the inner surface is 0.02mm → Φ14×0.8 titanium tube inner surface sandblasting, remove wall thickness 0.04mm → Φ14×0.8 titanium tube inner surface flow pickling, remove wall thickness 0.04mm → Φ14×0.8 titanium tube full length ultra-detection (the flaw detection sample tube has a flaw depth of 0.04mm, a width of 0.10mm, and a length of 1.52mm) → sampling to check the tensile and flattening properties → packaging.

The TA16 titanium alloy seamless tube with a specification of Φ14×0.8 mm produced in this embodiment has a yield strength of 470 MPa, a tensile strength of 590 MPa, and an elongation of 25%. The sample does not crack when the pressure plate spacing is 6 mm.

Example 2

The production specification is TA18 titanium alloy seamless pipe with Φ15×1mm.

The production process adopted is as follows: sponge titanium and alloy components are subjected to three vacuum self-consumptions to form Φ490 round TA18 titanium alloy ingots with an oxygen content of 0.059-0.068% → 4-fire three-drill three-draw free forging on a hydraulic press to form Φ170 round bars → 2-fire diameter forging to form Φ70 black skin round bars → extrusion, internal sandblasting, external lathe processing and internal and external pickling to form Φ50*5.5 hollow tube billets → LG30 two-roller cold rolling tube mill to cold-roll into Φ32×3.4 titanium tubes (ε is 60.3%, K value is 1.06) → 700° insulation for 1h vacuum annealing → LG15 two-roller cold rolling tube mill to cold-roll into Φ21×2 titanium tubes (ε is 60.9%, K value is 1.20) → 700° insulation for 1h vacuum annealing → LG15 two-roller cold rolling tube mill to cold-roll into Φ21×2 titanium tubes (ε is 60.9%, K value is 1.20) The tube mill is cold rolled into Φ15×1 titanium tube (ε is 63.2%, K value is 1.75) → 720° insulation for 1h vacuum annealing and straightening → 10 groups of transverse and longitudinal metallographic structure samples are taken from the Φ15×1 titanium tube, and the maximum depth of the micro-pits on the inner surface of the titanium alloy tube is 0.03mm, and the maximum extension depth of the micro-cracks extending from the micro-pits on the inner surface is 0.03mm → Sandblasting the inner surface of the Φ15×1 titanium tube to remove 0.05mm of wall thickness → Flow pickling on the inner surface of the Φ15×1 titanium tube to remove 0.05mm of wall thickness → Full-length ultra-detection of each Φ15×1 titanium tube (the flaw depth of the flaw detection sample tube is 0.04mm, the width is 0.10mm, and the length is 1.52mm) → Sampling to check the tensile and flattening properties → Packaging.

The TA18 titanium alloy seamless tube with a specification of Φ15×1mm produced in this embodiment has a yield strength of 540Mpa, a tensile strength of 650Mpa, and an elongation of 20%. The sample does not crack when the pressure plate spacing is 9mm.

Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or replace some or all of the technical features therein by equivalents. However, these modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

A method for improving the flattening performance of a titanium alloy seamless tube, characterized in that it comprises the following steps:

Step 1: three VAR smeltings to obtain a titanium alloy ingot, wherein the oxygen content of the titanium alloy ingot is ≤0.07%;

Step 2: The titanium alloy ingot is subjected to 4-times three-plunge three-draw free forging and 2-times radial forging to form a titanium alloy round bar;

Step 3: The titanium alloy round rod is extruded into a hollow tube blank, and the inside of the hollow tube blank is wet-sandblasted, the outside is ground, and the hollow tube blank is pickled to form a hollow tube blank with no defects on the inner and outer surfaces;

Step 4: The hollow tube billet is cold rolled 3-4 times on a two-roller cold rolling mill to form a titanium alloy finished seamless tube. Vacuum annealing is performed after each cold rolling. The cold rolling process design ensures that the K value of each cold rolling pass is ≥1, and the deformation rate ε and K value of each cold rolling pass are greater than those of the previous pass.

A hollow tube with an outer diameter of D1 and a wall thickness of S1 is cold rolled in one pass to form a hollow tube with an outer diameter of D2 and a wall thickness of S2. The calculation formula for the deformation rate ε of this cold rolling pass is:
ε＝((D1-S1)×S1-(D2-S2)×S2)/((D1-S1)×S1);

The calculation formula of K value of this cold rolling pass is: K = (S1-S2) × D1/(D1-D2) × S1;

Step 5: Take multiple groups of transverse and longitudinal metallographic structure samples from the titanium alloy finished seamless tube in step 4, observe the metallographic structure samples to measure the maximum depth h1 of the micro-pits on the inner surface of the titanium alloy tube, and the maximum extension depth h2 of the micro-cracks extending from the micro-pits on the inner surface;

Step 6: wet-blast the inner surface of the titanium alloy finished seamless tube obtained in step 4 to remove the wall thickness of h1+0.02 mm, coat the outer surface of the titanium alloy tube after sandblasting, and perform flow pickling on the inner surface of the titanium alloy finished seamless tube to remove the wall thickness of h2+0.02 mm;

Step 7: The titanium alloy finished seamless pipe obtained in step 6 is subjected to vacuum annealing and straightening to obtain a finished pipe.
The method for improving the flattening performance of titanium alloy seamless tubes according to claim 1 is characterized in that the titanium alloy round bar obtained in step 2 is flaw-detected and reaches AA grade according to GB/T5193 standard.
The method for improving the flattening performance of a titanium alloy seamless tube according to claim 1 is characterized in that in step three and step six, sandblasting is performed by mixing 100-mesh green silicon carbide particles and water in a weight ratio of 1:2.
The method for improving the flattening performance of titanium alloy seamless tubes according to claim 1 is characterized in that the grain orientation type of the hollow tube obtained in step 3 is α phase <11-20>//tube radial direction, <10-10>//tube axial direction.
The method for improving the flattening performance of titanium alloy seamless tubes according to claim 4 is characterized in that the grain orientation type of the titanium alloy finished seamless tube obtained in step 4 is α phase <0001>//tube radial direction, <10-10>//tube axial direction.
The method for improving the flattening performance of a titanium alloy seamless tube according to claim 1 is characterized in that, in step six, the pickling liquid is a mixture of HF acid: HNO3 acid: water in a weight ratio of 5:20:75, and flows through the inner surface of the titanium alloy tube at a speed greater than or equal to 2 m/min.