RU2237561C1 - Process for dressing tubes of different type steels for diffusion welding - Google Patents

Abstract

FIELD: preparation of tube ends for welding, namely dressing tube butts for diffusion welding.

SUBSTANCE: on edges of tube end of steel with less value of heat resistance tapered portions are formed. Between said tapered portions flat ring is formed. Mean line of flat ring is arranged lower than mean line of tube wall. Centering annular step is formed on end of tube made of steel with higher degree of heat resistance. It is possible to weld different type steels at keeping linear size of joined blanks.

EFFECT: enhanced quality of welded joints due to providing high stability of strength properties and coaxial position of welded tube blanks.

4 cl, 2 dwg, 1 ex

Description

The invention relates to the field of preparation of pipe ends for welding, and more particularly to diffusion butt welding of mainly short thick-walled pipes made of dissimilar metals, for example, austenitic and ferritic steels. Such designs are widely used in industry, for example, in cases of stepper motors, in which the case is made in the form of a set of alternating rings of non-magnetic (austenitic) and magnetic (ferritic) steels interconnected by welding. Welded structures of stepper motors must have extremely narrow transition zones between rings of dissimilar steels. At the same time, high demands are made on the accuracy of the axial dimensions of the connected rings.

The most acceptable method of welding these structures from dissimilar steels is welding in the solid phase, since it allows you to get structures with a minimally narrow transition zone between the welded workpieces and with the most accurate dimensions along their axes.

A known design of a permanent connection made using diffusion welding in vacuum with induction heating. This design is a set of a number of blanks from magnetic steels - grade 25Х17М4Г5АФ2 and non-magnetic - grade 0Х20Н4АГЮ (Kazakov NF. Diffusion welding of materials. M .: Mashinostroenie, 1976, p. 135). Billets of magnetic and non-magnetic steels contact each other at the ends, and the cutting of the edges is the surface of the end, perpendicular to the axis of rotation of the pipes.

When connecting pipes with the indicated grooving by diffusion welding with induction heating, it is difficult to ensure their regulated deformation, since billets are heated unevenly - magnetic (ferritic) steel is heated intensively by induction currents, while non-magnetic (austenitic) steel is heated less intensively and mainly due to heat transfer along the connected ends of the billets. Ferritic steel has less heat resistance than austenitic steel, and therefore it creeps intensively at the welding temperature and welding pressure, whereas austenitic steel is slightly deformed. In addition, using an inductor, it is difficult to provide local heating of the welding site of small rings along the length. In the process of compression, in this case, neighboring rings are subjected to deformation, which is unacceptable. Therefore, it is practically impossible to make a stepper motor case consisting of a set of narrow rings of dissimilar steels by diffusion welding with induction heating.

Known for electron-beam heating of billets during diffusion welding (Kazakov NF Diffusion welding of materials. M: Mechanical Engineering, 1976, p. 100). Electron beam heating provides more uniform heating of the workpieces at the welding site. Closest to the claimed invention in its essential features and purpose is the design of cutting the edges of the pipe joints made using diffusion welding in vacuum (Kazakov NF Diffusion welding of materials. M .: Mechanical Engineering, 1976, p. 283). The cutting of the edges of this design is the end surface perpendicular to the axis of rotation of the welding pipes. Due to the large difference in plastic properties at the welding temperature and a significant mass of deformed metal at the welded ends, this shape of the ends limits the possibility of obtaining welded blanks from heterogeneous rings with limited dimensions along their length. In this case, the specific compressive force of the workpieces is usually about 1.5 kgf / mm ² . The specified shape of the ends for welded joints of dissimilar steels limits the activation of the surface, which negatively affects the stability of the properties of the joints. To obtain coaxial joints with this shape of the ends, a special device is required that centers the workpieces. This is also a disadvantage of joining flat pipe ends.

The objective of the invention is to create a design for joining thick-walled pipes for diffusion butt welding of dissimilar steels, which allows to obtain welded joints while maintaining the linear dimensions of the joined workpieces and high stability of strength properties, as well as ensuring the alignment of the welded workpieces.

The technical result obtained by the implementation of the claimed invention is that the specified design of the pipe connection allows you to heat a narrow zone at the end of the pipe made of less heat-resistant steel, including by heating a small volume of metal, which provides local dosed deformation of the welded workpieces, and allows you to activate diffusion processes due to increased near-surface deformation of the edge of the workpiece from less heat-resistant steel.

The specified technical result is achieved by the fact that the cutting of tubes of dissimilar steels for diffusion welding with electron beam heating involves making bevels along the edges of the end of the pipe from less heat-resistant steel to form a flat ring between them, the middle line of which is below the middle line of the pipe wall, and the end of the pipe is made of more heat-resistant steel an annular centering step;

- in addition, the flat ring is made at least 1 mm wide;

- in addition, the gaps formed by bevels on the pipe of less heat-resistant steel and the end of the pipe of more heat-resistant steel are made not wider than 4 mm;

- in addition, the height of the annular centering step is made not lower than 0.1 mm

The invention is illustrated by drawings, where figure 1 shows the connection of pipes with wall thickness S, figure 2 shows a diagram of the welding of rings of dissimilar steels.

At the end of the pipe 1, bevels made of less heat-resistant steel are made on the outside and inside of the pipe. The bevels form a flat ring h through which contact is made with the end face of a workpiece made of more heat-resistant steel 2. A centering step of height d is made at the end of the pipe made of more heat-resistant steel. The bevels form a gap a and f between the pipes to be welded along their cylindrical surfaces, respectively, from the outside and from the inside. The middle line of the flat ring is located below the middle line of the pipe by a value of k, which is dictated by the conditions of heating and deformation of the pipe end of less heat-resistant steel. So, when the electron beam 3 acts on the surface of the outer bevel, the outer surface of the pipe is heated to a greater extent and, therefore, most of the metal will flow to its outer surface during deformation. In addition, the cylindrical geometry of the welded workpieces also contributes to the flow of metal outward when squeezing the workpieces. The bevel allows you to effectively activate the connected surface, since the electron beam directly affects them. The protrusion formed by bevels and a flat ring, during diffusion welding, provides significant surface deformation of less heat-resistant steel without noticeable deformation of the rest of it and the workpiece of more heat-resistant steel, which provides a connection with the planned overall linear dimensions of the welded workpieces. The specific compressive force of the workpieces is approximately 0.8 kgf / mm ² , i.e. almost 2 times lower than in connection with the cutting edges indicated in the prototype. The optimal dimensions of a flat ring are as follows: its height is at least 1 mm, the middle line of blunting is located below the middle line of the pipe wall. The bevels at the end of the pipe are made in such a way that the gaps between the pipes to be welded along their cylindrical surfaces have a value not exceeding 4 mm. These gaps and determine the angles of the bevel end. At the end of the pipe made of more heat-resistant steel, a centering step is made, which allows, without a special device, to center the pipes during assembly for welding. The optimum height of the indicated step is not less than 0.1 mm.

Before welding, all rings are processed to the required size, taking into account the allowance for subsequent deformation during welding. The allowance is determined previously on technological samples. The joint of the rings is carried out on an annular centering step. Rings are collected on a mandrel. Welding is carried out in a chamber in which a vacuum of ~ 10 ^-4 mm is created. Hg. pillar. The electron beam of the gun is sent to the cutting and give the mode of heating. In this case, the mandrel rotates. Significant rotation speed of the welded rings allows you to evenly heat the workpiece at the junction. In the process of heating, the rings are constantly tightened with the welding force R. As the plastic state is reached, the welded rings come together mainly due to the deformation of less heat-resistant steel. The movement of the workpieces is limited by the stopper and is carried out until the gap between the rings with a certain margin is completely selected.

The diffusion welding technology described above allows one to obtain welded billets from a set of rings with ensuring their exact axial dimensions, since the connection of the pipe ends with the above parameters makes it possible to have a stable uniform movement of the rings during welding, and hence a stable uniform deformation allowance.

Usage example.

The case of the stepper motor was welded from a set of rings of steel 09X17T and 08X18H10T. Case dimensions: outer diameter 110 mm, wall thickness 15 mm. The number of rings 13. The end rings were made of austenitic steel. The cutting parameters are as follows: the width of the flat ring h = 4 mm, the middle line of the flat ring is located at a distance k = 5 mm from the middle line of the wall of the ring, the gap between the welded rings along their cylindrical surfaces a and f was 4 and 3 mm, respectively, the height of the ring centering steps equal to 0.5 mm.

This cutting of edges provided an optimal mode of heating and deformation of the rings when squeezing the workpieces with a minimum specific force, which made it possible to weld the stepper motor case with the required axial dimensions of the rings of dissimilar steels with the necessary mechanical properties. Mechanical testing of test specimens showed satisfactory quality of welded joints. The samples were destroyed with a tensile strength of 39-40 kgf / mm ² .

Claims (4)

1. Cutting pipes of dissimilar steels for diffusion welding with electron beam heating, characterized in that the bevels are made on the edges of the pipe end face from less heat-resistant steel to form a flat ring between them, the middle line of which is located below the middle line of the pipe wall, and at the end pipes made of more heat-resistant steel have an annular centering step. 2. Cutting pipes for diffusion welding according to claim 1, characterized in that the flat ring is made at least 1 mm wide. 3. Cutting pipes for diffusion welding according to claim 1, characterized in that the gaps formed by bevels on the pipe of less heat-resistant steel and the end of the pipe of more heat-resistant steel are made not wider than 4 mm. 4. Cutting pipes for diffusion welding according to any one of claims 1 and 2, characterized in that the height of the annular centering step is made not lower than 0.1 mm.

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