A method for achieving ultrafine grains in the inner wall of hollow components

Abstract

This invention discloses a method for achieving ultrafine grains on the inner wall of a hollow component. This method achieves fine grain strengthening of the inner wall of the spherical component through an internal thermal explosion reaction combined with external airflow disturbance. In this fine grain strengthening process, only internally pre-placed steel balls, Ti powder, Al powder, and Fe powder, and external helium gas are used. The weight and quantity of steel balls, Ti powder, Al powder, and Fe powder can be adjusted according to the volume of the spherical component, providing a large range of process adjustments. The entire process is simple in principle, has a high material utilization rate for the spherical component, and a low strengthening process cost.

Description

Background Technology

[0001] Hollow spherical components are generally used to manufacture integral components for deep-sea submarines. However, it is difficult to obtain a fine-grained microstructure through casting. To ensure a fine-grained microstructure, it is necessary to forge the sheet metal, then machine it, and finally weld and rivet it into a sphere. This method leads to a reduction in the surface integrity of the sphere, and excessive welds are potential failure points. Summary of the Invention

[0002] The present invention addresses the problems existing in the above-mentioned existing processes by providing a method for achieving ultrafine crystals in the inner wall of hollow components. Its purpose is to provide a plastic treatment method for the inner wall of hollow components to manufacture hollow components with an ultrafine crystal inner wall structure.

[0003] The objective of this invention is achieved through the following technical solution:

[0004] The steps of the method for achieving ultrafine grains on the inner wall of a hollow component according to the present invention are as follows:

[0005] Step 1: Preparation of hollow components

[0006] The hollow component is a hollow sphere cast from a nickel-based high-temperature alloy. Two through holes penetrating the sphere wall are machined on the surface of the hollow sphere, and the centers of the two through holes are perpendicular to the center of the hollow sphere.

[0007] In implementation, in step one, the wall thickness of the hollow sphere is 15-20mm.

[0008] In implementation, in step one, the diameter of the two through holes is 3-5mm.

[0009] The casting structure of the hollow sphere is relatively coarse and contains dendritic crystals. The two through holes on both sides serve two purposes: one is the casting process requirement, and the other is to ensure that helium can enter the spherical component through multiple channels, so that the steel ball can move more randomly inside it.

[0010] Step 2: Preparation of powder inside hollow components

[0011] Ti powder, Al powder, Fe powder, and steel balls of different diameters are poured into the hollow sphere through the above-mentioned through holes. The mass ratio of Ti powder to Al powder is consistent with the atomic mass ratio of Ti atoms to Al atoms. The total mass of Ti powder and Al powder is 1:1 with the mass ratio of Fe powder.

[0012] In implementation, in step two, the purity of the Ti powder, Al powder, and Fe powder is 99.99%, and the particle size is 300-350 mesh.

[0013] In implementation, in step two, the diameter of the steel ball is 1-3mm;

[0014] Step 3: Sealing the hollow components

[0015] A hollow sphere containing metal powder and steel balls is placed in a closed operating box and filled with air at 1 atmosphere. Then, the two through holes on the hollow sphere are sealed by welding, and the pressure threshold of the sealed weld is 1.5-2 atmospheres.

[0016] In steps two and three, the role of Ti powder, Al powder, and Fe powder is to rapidly increase the internal pressure of the hollow sphere by means of its thermal explosion reaction when the spherical component is heated. This prepares the hollow sphere for the helium gas from the outside to enter the interior of the hollow sphere in terms of pressure. The pressure must be greater than the atmospheric pressure that the two through-hole sealing joints can withstand.

[0017] The steel balls have diameters ranging from 1 to 3 mm, varying in size. When the hollow sphere is heated, the steel balls are also heated. However, when helium enters the hollow sphere, the smaller diameter steel balls cool down first, resulting in a greater impact force on the inner wall of the hollow sphere. The larger diameter steel balls cool down later, resulting in an increasing impact force on the inner wall of the hollow sphere. This is mainly because the inner and outer walls of the hollow sphere need time to cool down after the helium enters. If a steel ball with a large diameter collides directly with the inner wall with a large impact force, it can easily cause the hollow sphere to deform.

[0018] A certain amount of gas is injected into the hollow sphere beforehand to maintain its internal positive pressure and prevent helium from entering the hollow sphere prematurely. In addition, it is to increase the effect of the thermal explosion reaction and increase the explosion pressure inside the hollow sphere. The pressure that the two through-hole sealing points can withstand is greater than the original initial pressure inside the spherical component, which is also to ensure that the pressure is large enough when it is punctured.

[0019] Step 4: Refining the inner wall of the hollow component

[0020] One atmosphere of helium gas is introduced into a closed operating chamber, and the hollow sphere inside is heated to 1100-1400℃. The temperature is maintained until the sealed weld of the hollow sphere is destroyed by the internal gas pressure. At this point, the helium pressure is rapidly increased to 2-4 atmospheres, allowing the helium gas in the closed operating chamber to rush into the hollow sphere and blow the steel ball into random motion, causing the steel ball to collide with the inner wall of the hollow sphere. This collision results in the ultra-fine crystallization treatment of the inner wall of the hollow sphere. Afterward, the hollow sphere is air-cooled to room temperature, and the metal powder and steel ball inside the hollow sphere are poured out.

[0021] During implementation, in step four, when the sealed weld of the hollow sphere is destroyed by the internal air pressure, the heating of the hollow sphere is stopped;

[0022] During implementation, in step four, the collision time between the steel ball and the inner wall of the hollow sphere lasts for 1-3 minutes;

[0023] When the hollow sphere is heated, the Ti powder, Al powder, and Fe powder reach the temperature required for the thermal explosion reaction and undergo a chemical reaction. Since the reaction is exothermic, the pressure and temperature inside the hollow sphere rise rapidly, even exceeding the heating temperature of 1100-1400℃. When the pressure inside the hollow sphere exceeds the pressure that the weld joint can withstand, the weld joint will crack outward because the helium pressure outside the hollow sphere is lower than the pressure inside the hollow sphere.

[0024] At the moment the weld breaks, the external helium pressure is increased to 2-4 atmospheres. At this point, the helium pressure is greater than the internal pressure of the hollow sphere, causing helium to rapidly enter the hollow sphere through the two through holes. Simultaneously, the heating of the hollow sphere is stopped. Under the action of the helium, the hollow sphere and the steel ball inside begin to cool. Under the action of the airflow, the steel ball moves randomly inside the hollow sphere, colliding with the inner wall of the hollow sphere, achieving a fine-grain strengthening effect. This process can last for 1-3 minutes.

[0025] The beneficial effects of the technical solution of this invention are:

[0026] I. The present invention addresses the technical requirement of fine-grained strengthening of the inner wall of an integrally formed spherical component. It adopts a novel technical approach, which achieves fine-grained strengthening of the inner wall of the spherical component through internal thermal explosion reaction and external airflow disturbance. The whole process is simple in principle and has a high material utilization rate of the spherical component.

[0027] Second, in the process of fine-grained strengthening of the inner wall of the spherical component, only the internally pre-placed steel balls, Ti powder, Al powder, Fe powder and external helium gas are used. After the strengthening is completed, the steel balls can be reused. Ti powder, Al powder and Fe powder are conventional materials, and the strengthening process cost is low.

[0028] Third, by using the present invention, the weight and quantity of steel balls, Ti powder, Al powder, and Fe powder can be adjusted according to the volume of the spherical component, providing a large range of process adjustments. Detailed Implementation

[0029] The technical solution of the present invention will be further described in detail below with reference to the embodiments:

[0030] This embodiment describes the use of the method of the present invention to perform ultrafine grain treatment on the inner wall of a hollow sphere cast from a nickel-based superalloy. The steps of this method are as follows:

[0031] Step 1: Preparation of hollow components

[0032] The hollow sphere is cast from a nickel-based high-temperature alloy. The wall thickness of the hollow sphere is 15-20mm. Two through holes penetrating the sphere wall are machined on the surface of the hollow sphere. The diameter of the two through holes is 3-5mm. The centers of the two through holes are perpendicular to the center of the hollow sphere.

[0033] Step 2: Preparation of powder inside hollow components

[0034] Ti powder, Al powder, Fe powder, and steel balls of different diameters are poured into the hollow sphere through the aforementioned through-hole. The purity of the Ti powder, Al powder, and Fe powder is 99.99%, and the particle size is 300-350 mesh. The diameter of the steel balls is 1-3 mm. The mass ratio of Ti powder to Al powder is consistent with the atomic mass ratio of Ti atoms to Al atoms. The total mass of Ti powder and Al powder is 1:1 with the mass ratio of Fe powder.

[0035] Step 3: Sealing the hollow components

[0036] A hollow sphere containing metal powder and steel balls is placed in a closed operating box and filled with air at 1 atmosphere. Then, the two through holes on the hollow sphere are sealed by welding, and the pressure threshold of the sealed weld is 1.5-2 atmospheres.

[0037] Step 4: Refining the inner wall of the hollow component

[0038] One atmosphere of helium is introduced into a sealed operating chamber, and the hollow sphere inside is heated to 1100-1400℃. The temperature is maintained until the sealed weld of the hollow sphere is destroyed by the internal gas pressure. At this point, the heating of the hollow sphere is stopped, and the helium pressure is rapidly increased to 2-4 atmospheres, allowing the helium in the sealed operating chamber to rush into the hollow sphere and blow the steel ball into random motion for 1-3 minutes. This causes the steel ball to collide with the inner wall of the hollow sphere, resulting in ultra-fine crystallization treatment of the inner wall of the hollow sphere. Afterward, the hollow sphere is air-cooled to room temperature, and the metal powder and steel ball inside the hollow sphere are poured out.

Claims

1. A method for achieving ultrafine grains in the inner wall of a hollow component, characterized in that, The steps of this method are as follows: Step 1: Preparation of hollow components The hollow component is a hollow sphere cast from a nickel-based high-temperature alloy. Two through holes penetrating the sphere wall are machined on the surface of the hollow sphere, and the centers of the two through holes are perpendicular to the center of the hollow sphere. Step 2: Preparation of powder inside hollow components Ti powder, Al powder, Fe powder, and steel balls of different diameters are poured into the hollow sphere through the above-mentioned through holes. The mass ratio of Ti powder to Al powder is consistent with the atomic mass ratio of Ti atoms to Al atoms. The total mass of Ti powder and Al powder is 1:1 with the mass ratio of Fe powder. Step 3: Sealing the hollow components A hollow sphere containing metal powder and steel balls is placed in a closed operating box, and air at 1 atmosphere is introduced into the closed operating box. Then, the two through holes on the hollow sphere are sealed by welding, and the pressure threshold of the sealed weld is 1.5-2 atmospheres. Step 4: Refining the inner wall of the hollow component One atmosphere of helium gas is introduced into a closed operating chamber, and the hollow sphere inside the chamber is heated to 1100-1400℃. The temperature is maintained until the sealed weld of the hollow sphere is destroyed by the internal gas pressure. At this point, the helium pressure is rapidly increased to 2-4 atmospheres, allowing the helium gas in the closed operating chamber to rush into the hollow sphere and blow the steel ball into random motion, causing the steel ball to collide with the inner wall of the hollow sphere. This collision results in the ultra-fine crystallization treatment of the inner wall of the hollow sphere.

2. The method for achieving ultrafine grains in the inner wall of a hollow component according to claim 1, characterized in that, In step one, the wall thickness of the hollow sphere is 15-20 mm.

3. The method for achieving ultrafine grains in the inner wall of a hollow component according to claim 1, characterized in that, In step one, the diameter of the two through holes is 3-5mm.

4. The method for achieving ultrafine grains on the inner wall of a hollow component according to claim 1, characterized in that, In step two, the purity of the Ti powder, Al powder, and Fe powder is 99.99%, and the particle size is 300-350 mesh.

5. The method for achieving ultrafine grains in the inner wall of a hollow component according to claim 1, characterized in that, In step two, the diameter of the steel ball is 1-3 mm.

6. The method for achieving ultrafine grains in the inner wall of a hollow component according to claim 1, characterized in that, In step four, when the sealed weld of the hollow sphere is destroyed by the internal air pressure, the heating of the hollow sphere is stopped.

7. The method for achieving ultrafine grains in the inner wall of a hollow component according to claim 1, characterized in that, In step four, the collision between the steel ball and the inner wall of the hollow sphere lasts for 3-5 minutes.

8. The method for achieving ultrafine grains in the inner wall of a hollow component according to claim 1, characterized in that, After completing step four, the hollow sphere is air-cooled to room temperature, and the metal powder and steel ball inside the hollow sphere are poured out.