阅读说明：本技术 3d打印制造梯度管材及微观组织调控的方法 (Method for manufacturing gradient pipe through 3D printing and regulating and controlling microstructure ) 是由 孙中刚 朱朝阳 唱丽丽 楼玉民 鲍听 嵇书伟 于 2019-03-05 设计创作，主要内容包括：本发明公开了一种3D打印制造梯度管材及微观组织调控的方法,属于增材制造技术领域。在打印过程中,使用两种合金粉末制备梯度合金复合管材,后经过多道次扩孔热轧工艺,通过将粗大柱状/等轴晶进行破碎、再结晶以细化晶粒,调控梯度复合管材微观组织。同时,扩孔轧制工艺还扩大了梯度复合管材孔径尺寸,摆脱金属3D打印设备尺寸的限制,以适应更大的市场需求。(The invention discloses a method for manufacturing a gradient pipe by 3D printing and regulating and controlling a microstructure, and belongs to the technical field of additive manufacturing. In the printing process, the two alloy powders are used for preparing the gradient alloy composite pipe, and then the coarse columnar/isometric crystals are crushed and recrystallized to refine grains through a multi-pass reaming hot rolling process, so that the microstructure of the gradient composite pipe is regulated and controlled. Meanwhile, the hole expanding and rolling process also enlarges the aperture size of the gradient composite pipe, and gets rid of the size limitation of metal 3D printing equipment so as to adapt to larger market demands.)

1. A3D printing method for manufacturing a gradient pipe and regulating and controlling a microstructure is characterized by comprising the following steps:

step 1, printing a gradient pipe by adopting an additive manufacturing technology, wherein a first section and a second section of the gradient pipe are respectively printed by alloy powder A and alloy powder B which are different in material, an intermediate section is printed by mixed powder of the alloy powder A and the alloy powder B, the mass content of the alloy powder A in the mixed powder is gradually reduced from the joint of the first section and the intermediate section to the joint of the second section and the intermediate section, the mass content of the alloy powder B is gradually increased, and the selection of the alloy powder A and the alloy powder B meets the requirement of the rolling temperature T of the alloy powder A_AAnd rolling temperature T of alloy powder B_BHave an intersection between them, let the intersection be T_A∩T_B；

Step 2, confirming the rolling temperature of the gradient pipe, wherein the rolling temperature T is T ═ T_A∩T_BRolling temperature T_kSelecting an upper limit value T of the rolling temperature T_{On the upper part}+/-3 ℃ and finishing temperature T_zSelecting a lower limit value T of the rolling temperature T_{Lower part}+5～10℃；

Step 3, heating the gradient pipe to the initial rolling temperature T_kAt the initial rolling temperature, the gradient tube is rapidly subjected to broaching rolling processThe material is subjected to multi-pass rough rolling and multi-pass finish rolling, the compression ratio of each pass during rough rolling is 30-50%, the total compression ratio of finish rolling is 20-50%, and the final rolling temperature T is ensured_zAnd then carrying out final finish rolling for the last time.

2. The method of claim 1, wherein alloy powder a and alloy powder B are a combination of steel and steel, steel and titanium, copper and titanium, steel and superalloy, titanium and superalloy.

3. The method of claim 1, wherein in step 1, the gradient tubing is printed in a co-axial powder feed manner using a 3D printing apparatus using additive manufacturing techniques.

4. The method according to claim 1, wherein in step 1, the gradient tube has a minimum pore diameter of 5mm, a maximum outer diameter of 500mm, and a printing height of 2000 mm.

5. The method according to claim 1, wherein in step 3, the time interval of each rolling pass is 10 s.

6. The method according to claim 1, wherein in the step 3, the multi-pass rough rolling adopts 2-4 passes of rough rolling.

7. The method according to claim 1, wherein in the step 3, 3 to 9 finish passes are adopted for the multiple finish passes.

8. The method according to claim 1, wherein in step 3, the reduction rate of each pass in rough rolling is 30-40%.

9. The method according to claim 1, wherein in the step 3, the total reduction rate of the finish rolling is 20% to 40%.

10. The method of claim 1, wherein in step 3, the reaming is performed using a 20mm radius reaming tube.

Technical Field

The invention relates to the field of additive manufacturing, in particular to a method for manufacturing a gradient pipe through 3D printing and regulating and controlling a microstructure.

Background

The use of the metal gradient composite material and the advanced material preparation technology enable the internal structure and the composition in the middle to present gradient change, and obvious interface change does not exist, namely, the material components are subjected to gradient change in a certain direction. Therefore, the performance index of the material is greatly improved, the material of each component can exert the maximum effect, the precious metal material is saved, and the performance requirement which can not be met by single metal is realized. At present, in many occasions with strict requirements on materials, such as corrosion resistance, high temperature resistance, wear resistance and gradient materials, the gradient materials are considered to have wider prospects. For example, the elimination of thermal stress of a material is related to the improvement of the phase structure distribution inside the material, and the relaxation of the thermal stress by a gradient material can prove the development prospect of the gradient material.

The general rolling processing method is divided into cold rolling and hot rolling by taking temperature as a standard. The cold rolling production efficiency is high, the processing precision is high, and in recent years, the cold rolling is widely applied to various industries such as aviation, automobiles and ships, and the like, so that parts with high precision can be obtained by using less resources. The hot hole expanding belongs to one kind of hot rolling, and is characterized by that the pipe blank heated to high temp. is passed through the hole-expanding head to make the internal hole diameter of pipe blank be changed from small to large, and the hole of the pipe blank after hole expansion is matched with male die. After reaming and rolling, the pipe is deformed, the internal metallographic structure is changed, the crystal grains are refined, and the strength of the pipe is increased macroscopically.

Disclosure of Invention

The invention aims to provide a method for manufacturing a gradient pipe by 3D printing and regulating and controlling microstructure, and aims to produce the gradient pipe with excellent microstructure and mechanical property by a 3D printing and hot rolling hole expanding mode.

The basic concept of the invention is to prepare two gradient composite alloy pipe joints by a metal 3D printer, wherein the pipe joints are respectively formed by mixing two alloy powders in equal gradient and are uniformly mixed. At the moment, the crystal grains in the composite pipe joint are relatively large, and the high performance requirement on engineering cannot be met. Then, the aims of refining grains, regulating and controlling microstructures and optimizing the mechanical property of the pipe are achieved by adopting a multi-pass hot rolling hole expanding mode; meanwhile, the diameter size of the pipe can be enlarged by a hot rolling hole expanding mode, so that the method is suitable for larger market demands.

The above object of the invention is achieved by the features of the independent claims, the dependent claims developing the features of the independent claims in alternative or advantageous ways.

In order to achieve the above object, the present invention provides a method for 3D printing and manufacturing a gradient tube and regulating microstructure thereof, comprising:

step 1, adopting an additive manufacturing technology to coaxially send alloy powder A and alloy powder B with different materials to print the alloy powder A and the alloy powder B into a gradient composite alloy pipe, wherein a first section and a second section of the gradient pipe are respectively printed by the alloy powder A and the alloy powder B, a middle section is printed by mixed powder of the alloy powder A and the alloy powder B, the mass content of the alloy powder A in the mixed powder is gradually reduced from 99% to 1% and the mass content of the alloy powder B is gradually increased from 1% to 99% from the joint of the first section and the middle section to the joint of the second section and the middle section, wherein the selection of the alloy powder A and the alloy powder B needs to meet the rolling temperature range T of the alloy powder A_AAnd the rolling temperature range T of the alloy powder B_BHave an intersection between them, let the intersection be T_A∩T_B；

Step 2, confirming reaming rolling of gradient composite alloy pipeTemperature, wherein rolling temperature T ═ T_A∩T_BRolling temperature T_kSelecting the upper limit value T of the rolling temperature T_{On the upper part}At +/-3 ℃ namely T_A∩T_BUpper limit value of +/-3 ℃, and finishing temperature T_zLower limit value T of selective rolling temperature T_{Lower part}+5 to 10 ℃ being T_A∩T_BThe lower limit value of + 5-10 ℃;

step 3, heating the gradient composite alloy pipe to the initial rolling temperature T_kAt the start rolling temperature T_kThen, a broaching rolling mode is adopted to rapidly carry out multi-pass rough rolling and multi-pass finish rolling on the gradient composite alloy pipe, the reduction rate of each pass during rough rolling is 30-50%, the total reduction rate of finish rolling is 20-50%, so as to achieve the purposes of crushing crystal grains, recrystallizing and enlarging the size of the plate, and ensure the finishing rolling temperature T_zThe finish rolling of the last pass is performed as the final rolling.

Further, in the step 3, the optimal selection of the multi-pass rough rolling is 2-4 passes of rough rolling.

Furthermore, in the step 3, the multi-pass finish rolling is preferably performed by 3 to 9 passes.

Further, in step 3, a reaming pipe with the radius of 20mm is adopted for reaming.

The method for manufacturing the gradient pipe and regulating and controlling the microstructure by 3D printing has the remarkable advantages that: and preparing the gradient composite alloy functional pipe by combining additive manufacturing and hot rolling hole expanding. The printed composite gradient pipe is manufactured in an additive mode, two kinds of alloy powder are uniformly mixed according to two gradients in two directions, so that the defects of the pipe are reduced, and the process is simple. By matching with a proper hot rolling hole expanding process, coarse grains in the gradient composite pipe can be effectively refined and recrystallized to generate equiaxed grains with fine size and uniform distribution, so that the microstructure of the gradient composite pipe is improved, and the mechanical property of the gradient composite pipe is optimized. Meanwhile, the hot rolling reaming process also enlarges the diameter of the pipe, increases the available flow and effectively gets rid of the limitation of metal 3D printing equipment on the size of the workpiece. The method for preparing the functional composite gradient pipe can meet the requirements of one or more special properties such as corrosion resistance, friction resistance, high temperature resistance, impact resistance, pressure resistance, creep resistance and the like.

It should be understood that all combinations of the foregoing concepts and additional concepts described in greater detail below can be considered as part of the inventive subject matter of this disclosure unless such concepts are mutually inconsistent. In addition, all combinations of claimed subject matter are considered a part of the presently disclosed subject matter.

The foregoing and other aspects, embodiments and features of the present teachings can be more fully understood from the following description taken in conjunction with the accompanying drawings. Additional aspects of the present invention, such as features and/or advantages of exemplary embodiments, will be apparent from the description which follows, or may be learned by practice of specific embodiments in accordance with the teachings of the present invention.

Drawings

The drawings are not intended to be drawn to scale.

FIG. 1 is a schematic structural distribution diagram of a gradient tube material manufactured by 3D printing.

FIG. 2 is a schematic view of the microstructure of the gradient alloy functional composite pipe manufactured by 3D printing in reaming hot rolling. In the figure: 1 represents a microstructure after broaching rolling, 2 represents a microstructure during broaching rolling, and 3 represents a microstructure before broaching rolling.

Detailed Description

In order to better understand the technical content of the present invention, specific embodiments are described below with reference to the accompanying drawings.

In this disclosure, aspects of the present invention are described with reference to the accompanying drawings, in which a number of illustrative embodiments are shown. Embodiments of the present disclosure are not necessarily intended to include all aspects of the invention. It should be appreciated that the various concepts and embodiments described above, as well as those described in greater detail below, may be implemented in any of numerous ways, as the disclosed concepts and embodiments are not limited to any one implementation. In addition, some aspects of the present disclosure may be used alone, or in any suitable combination with other aspects of the present disclosure.

According to the disclosure of the invention, a 3D printing method for manufacturing a gradient pipe and regulating and controlling microstructure thereof is provided, as shown in figure 1, a bidirectional alloy pipe with 99% -1% of uniform components gradually decreased is prepared by a 3D printing technology, alloy powder A and alloy powder B of the gradient pipe can be respectively steel and steel, steel and titanium, steel and superalloy, titanium and superalloy, and are not limited to the four materials listed above in matching, but the alloy powder A and the alloy powder B are selected to meet the rolling temperature T of the alloy powder A_AAnd rolling temperature T of alloy powder B_BThere is an intersection between them, and therefore two alloy powders for which there is no intersection in the rolling temperature range, which is the range in which there is no intersection, are not suitable for use in the present invention. For example: the melting point of the aluminum alloy is about 660 ℃, which is far lower than the final rolling temperature of the titanium alloy, so that the titanium alloy and the aluminum alloy do not have rolling temperature intersection and are not suitable for the method.

And then combining a hot rolling hole expanding process to carry out hot processing treatment on the composite pipe. And refining and recrystallizing the coarse grains after 3D printing through multi-pass reaming rolling to generate fine equiaxed grains as shown in figure 2, so that various comprehensive properties of the composite gradient pipe are improved.

To facilitate better understanding, the invention is further illustrated below with specific reference to the following 5 additive examples, in which paired gradient alloy powders were selected, such as: q235 and 316 stainless steel (steel and steel), 316 and TC4 (steel and titanium), 316 and IN625 alloy (steel and superalloy), TC4 and IN625 alloy (titanium and superalloy), and TC4 and IN718 alloy (titanium and superalloy), among others. However, the types of the alloy powders are not limited to the alloy compositions listed in the examples, and the present disclosure includes, but is not limited to, the material combinations in the examples.

[ EXAMPLES one ]

The two gradient alloy powders are exemplified by Q235 steel and 316 stainless steel, wherein Q235 has excellent comprehensive mechanical properties, and 316 stainless steel has excellent corrosion resistance and high temperature resistance. The composite gradient pipe material composed of Q235 and 316 stainless steel has excellent mechanical property, corrosion resistance and high temperature resistance, and has a great application value in the engineering field. Wherein the rolling temperature range of Q235 is 910-1213 ℃, the rolling temperature range of 316 stainless steel is 900-1230 ℃, and the intersection T of the rolling temperature ranges of the two alloys is TA and TB is 910-1213 ℃. In the embodiment, 1213 +/-3 ℃ is selected as the initial rolling temperature, and 915-920 ℃ is selected as the final rolling temperature.

(1) And (3) adopting metal 3D printing equipment to coaxially send powder to print the gradient pipe by two kinds of alloy powder Q235 and 316 stainless steel, wherein the printing wall thickness is 20mm, the printing height is 2000mm, and finishing the preparation.

(2) Heating the Q235/316 composite gradient pipe prepared by 3D printing to 1213 +/-3 ℃, then adopting a continuous rolling and reaming process, rapidly reaming and rolling the pipe by using a reaming pipe with the radius of 20mm, and carrying out 2-pass rough rolling and 4-pass single-pass finish rolling during rolling. The wall of the 1 st pass rough rolling pipe is pressed to be 13.00mm thick, and the compression ratio is 35%; the wall of the rough rolling pipe in the 2 nd pass is 9.10mm thick, and the compression ratio is about 30 percent. The length of the pipe is prolonged to 3580.96mm in the rough rolling process, then finish rolling is carried out, the pipe with the thickness of 9.10mm is rolled to be 6.66mm in 4 passes, and the total reduction rate of the finish rolling is 21.5%. The time interval and the temperature between each pass of rough rolling and finish rolling are accurately controlled, and the 4 th pass of finish rolling is ensured to be used as final rolling at 935-940 ℃.

(3) The size of the gradient tube after final reaming is 6.66mm in wall thickness and 5.12m in tube length.

The specific technological parameters of the implementation can also adopt corresponding technological parameters according to different alloy types.

[ example two ]

The two kinds of gradient alloy powder are 316 stainless steel and TC4 (steel and titanium) as examples, wherein the 316 stainless steel has high mechanical property and good corrosion resistance and high temperature resistance; compared with 316 stainless steel, TC4 has more excellent corrosion resistance, mechanical property and high-temperature property; compared with 316 stainless steel, TC4 has more excellent mechanical property and corrosion resistance. The composite gradient pipe material composed of 316 stainless steel and TC4 has excellent mechanical property, corrosion resistance and high temperature resistance, and can adapt to more severe service environments, such as: corrosion resistant vessel in the oceanPieces, etc. Has great application value in the field of ocean engineering. Wherein the rolling temperature range of 316 stainless steel is 900-1230 ℃, the rolling temperature range of TC4 titanium alloy is 700-1050 ℃, and the intersection T-T of the rolling temperature ranges of the two alloys_A∩T_BAnd (4) 900-1050 ℃. In this embodiment, 1050 + -3 ℃ is selected as the initial rolling temperature, and 905-910 ℃ is selected as the final rolling temperature.

(1) And (3) adopting metal 3D printing equipment to coaxially send powder to print the gradient pipe by using two kinds of alloy powder 316 stainless steel and TC4, wherein the printing wall thickness is 20mm, the printing height is 2000mm, and finishing the preparation.

(2) Heating the 316/TC4 composite gradient pipe prepared by 3D printing to 1050 +/-3 ℃, then adopting a continuous rolling and reaming process, rapidly reaming and rolling the pipe by using a reaming pipe with the radius of 20mm, and adopting 2-pass rough rolling and 4-pass finish rolling during reaming and rolling. The wall of the 1 st pass rough rolling pipe is pressed to be 13.00mm thick, and the compression ratio is 35%; the wall of the 2 nd pass rough rolling pipe is pressed to be 9.10mm thick, and the compression ratio is about 30%. The length of the pipe is prolonged to 3580.96mm in the rough rolling process, then finish rolling is carried out, the pipe with the thickness of 9.10mm is rolled to be 6.67mm in 4 passes of finish rolling, and the total reduction rate of the finish rolling is 26.7%. The time interval and the temperature between each pass of the rough rolling and the finish rolling are accurately controlled, and the 4 th pass of the finish rolling is ensured to be used as the final rolling at 915-920 ℃.

(3) The size of the final reamed gradient tube is 6.67mm in wall thickness and 5.11m in tube length.

The specific technological parameters of the implementation can also adopt corresponding technological parameters according to different alloy types.

[ EXAMPLE III ]

The two gradient alloy powders are 316 stainless steel and IN625 (steel and high temperature alloy) as examples, wherein the 316 stainless steel has high mechanical property and good corrosion resistance and high temperature resistance; IN625 has more excellent high temperature resistance than 316 stainless steel. The composite gradient pipe material composed of 316 stainless steel and IN625 has excellent mechanical property, corrosion resistance and high temperature resistance, and can adapt to more severe service environments, such as: corrosion resistant devices in the ocean, etc. Has great application value in the field of ocean engineering. WhereinThe rolling temperature range of 316 stainless steel is 900-1230 ℃, the rolling temperature range of IN625 high-temperature alloy is 930-1200 ℃, and the intersection T-T of the rolling temperature ranges of the two alloys_A∩T_B930-1200 ℃. In the embodiment, 1200 +/-3 ℃ is selected as the initial rolling temperature, and 935-940 ℃ is selected as the final rolling temperature.

(1) And (3) adopting metal 3D printing equipment to coaxially send powder to print the gradient pipe by using two kinds of alloy powder 316 stainless steel and IN625, wherein the printing wall thickness is 20mm, the printing height is 2000mm, and finishing the preparation.

(2) Heating the 316/IN625 composite gradient pipe prepared by 3D printing to 1200 +/-3 ℃, then adopting a continuous rolling and reaming process, quickly carrying out reaming rolling on the pipe by using a reaming pipe with the radius of 20mm, and adopting 2-pass rough rolling and 4-pass finish rolling during reaming rolling. The wall of the 1 st pass rough rolling pipe is pressed to be 13.00mm thick, and the compression ratio is 35%; the wall of the 2 nd pass rough rolling pipe is pressed to be 9.10mm thick, and the compression ratio is about 30%. The length of the pipe is prolonged to 3580.96mm in the rough rolling process, then finish rolling is carried out, the pipe with the thickness of 9.10mm is rolled to be 7.14mm in 4 passes of finish rolling, and the total reduction rate of the finish rolling is 21.5%. The time interval and the temperature between each pass of rough rolling and finish rolling are accurately controlled, and the 4 th pass of finish rolling is ensured to be used as final rolling at 935-940 ℃.

(3) The size of the final reamed gradient tubing is 7.14mm in wall thickness and 4.76m in length.

The specific technological parameters of the implementation can also adopt corresponding technological parameters according to different alloy types.

[ EXAMPLE IV ]

The two kinds of gradient alloy powder take TC4 titanium alloy and IN625 (titanium and high temperature alloy) as examples, wherein TC4 has high mechanical property and good corrosion resistance; and the IN625 has more excellent high-temperature resistance compared with the TC4 titanium alloy. The composite gradient pipe composed of TC4 and IN625 has excellent mechanical property, corrosion resistance and high temperature resistance, and can adapt to more severe service environments, such as: corrosion resistant devices in the ocean, etc. Has great application value in the field of ocean engineering. Wherein the rolling temperature range of the TC4 titanium alloy is 700-1050 ℃, and the rolling temperature range of the IN625 high-temperature alloy isThe temperature of 930-1200 ℃, and the intersection T of the rolling temperature ranges of the two alloys is T_A∩T_B930-1050 ℃. In the embodiment, 1050 +/-3 ℃ is selected as the initial rolling temperature, and 935-940 ℃ is selected as the final rolling temperature.

(1) And (3) adopting metal 3D printing equipment to coaxially send powder to print the gradient pipe by using two kinds of alloy powder TC4 and IN625, wherein the printing wall thickness is 20mm, the printing height is 2000mm, and finishing the preparation.

(2) Heating the TC4/IN625 composite gradient pipe prepared by 3D printing to 1050 +/-3 ℃, then adopting a continuous rolling and reaming process, quickly reaming and rolling the pipe by using a reaming pipe with the radius of 20mm, and adopting 2-pass rough rolling and 4-pass finish rolling during reaming and rolling. The wall of the 1 st pass rough rolling pipe is pressed to be 13.00mm thick, and the compression ratio is 35%; the wall of the 2 nd pass rough rolling pipe is pressed to be 9.10mm thick, and the compression ratio is about 30%. The length of the pipe is prolonged to 3580.96mm in the rough rolling process, then finish rolling is carried out, the pipe with the thickness of 9.10mm is rolled to be 6.67mm in 4 passes of finish rolling, and the total reduction rate of the finish rolling is 26.7%. The time interval and the temperature between each pass of rough rolling and finish rolling are accurately controlled, and the 4 th pass of finish rolling is ensured to be used as final rolling at 935-940 ℃.

(3) The size of the final reamed gradient tube is 6.67mm in wall thickness and 5.11m in tube length.

The specific technological parameters of the implementation can also adopt corresponding technological parameters according to different alloy types.

[ EXAMPLE V ]

The two kinds of gradient alloy powder take TC4 titanium alloy and IN718 (titanium and high temperature alloy) as examples, wherein TC4 has high mechanical property and good corrosion resistance; and the IN625 has more excellent high-temperature resistance compared with the TC4 titanium alloy. The composite gradient pipe composed of TC4 and IN625 has excellent mechanical property, corrosion resistance and high temperature resistance, and can adapt to more severe service environments, such as: corrosion resistant devices in the ocean, etc. Has great application value in the field of ocean engineering. The rolling temperature range of the TC4 titanium alloy is 700-1050 ℃, the rolling temperature range of the IN718 high-temperature alloy is 930-1200 ℃, and the intersection T-T of the rolling temperature ranges of the two alloys_A∩T_B＝930～1050℃. In the embodiment, 1050 +/-3 ℃ is selected as the initial rolling temperature, and 935-940 ℃ is selected as the final rolling temperature.

(1) And (3) adopting metal 3D printing equipment to coaxially send powder to print the gradient pipe by using two kinds of alloy powder TC4 and IN718, wherein the printing wall thickness is 20mm, the printing height is 2000mm, and finishing the preparation.

(2) Heating the TC4/IN718 composite gradient pipe prepared by 3D printing to 1050 +/-3 ℃, then adopting a continuous rolling and hole expanding process, quickly carrying out hole expanding rolling on the pipe by using a hole expanding pipe with the radius of 20mm, and adopting 2-pass rough rolling and 4-pass finish rolling during the hole expanding rolling. The wall of the 1 st pass rough rolling pipe is pressed to be 13.00mm thick, and the compression ratio is 35%; the wall of the 2 nd pass rough rolling pipe is pressed to be 9.10mm thick, and the compression ratio is about 30%. The length of the pipe is prolonged to 3580.96mm in the rough rolling process, then finish rolling is carried out, the pipe with the thickness of 9.10mm is rolled to be 6.00mm in 4 passes of finish rolling, and the total reduction rate of the finish rolling is 34.1%. The time interval and the temperature between each pass of rough rolling and finish rolling are accurately controlled, and the 4 th pass of finish rolling is ensured to be used as final rolling at 935-940 ℃.

(3) The size of the gradient tube after final reaming is 6.00mm of wall thickness and 6.31m of tube length.

The specific technological parameters of the implementation can also adopt corresponding technological parameters according to different alloy types.

In the field of additive manufacturing, the formation of columnar crystals and coarse primary grains is rooted in the thermodynamic dynamic problem of a metallurgical process, the supernormal metallurgical conditions and the cyclic deposition in a micro molten pool in the additive manufacturing process cause insufficient supercooling of temperature and components, and the non-spontaneous nucleation particle reduction is a core problem. According to the method, the columnar crystals and the coarse original grains which are manufactured in an additive mode are crushed and recrystallized by using a hole expanding hot rolling process, and the equiaxial grains with fine and small sizes are generated, so that the accurate control of the microstructure in the gradient pipe manufactured in the additive mode is achieved.

The grain size and mechanical properties of the gradient tube material of each example are shown in the comparison table 1 before and after hot rolling.

TABLE 1 comparison of grain size of various gradient pipes with mechanical properties before and after hot rolling

Because the relationship between the strength of the alloy material and the grain size conforms to the Hall-Petch relationship, the finer the grain is, the higher the strength of the alloy is; and only by grain refinement, the strength and the plasticity of the material can be improved simultaneously. In the embodiment of the invention, the post-treatment-hot rolling process can effectively refine grains, improve the structure and improve the material performance.

Although the present invention has been described with reference to the preferred embodiments, it is not intended to be limited thereto. Those skilled in the art can make various changes and modifications without departing from the spirit and scope of the invention. Therefore, the protection scope of the present invention should be determined by the appended claims.