KR20010044765A - Production method of grain refinement of difficult-to-work materials using double equal channel angular processing - Google Patents

Abstract

PURPOSE: A crystal grain micronization method of difficult-to-work materials by double equal channel angular processing is provided to improve materialistic properties of a final product by applying to the improvement of plastic processability of a molding material such as aluminum, magnesium and titanium alloy, structure micronization of a structural material, softening of a brittle material and compaction of alloy powder. CONSTITUTION: The crystal grain micronization method of difficult-to-work materials by double equal channel angular processing comprises an extruding material supplying step (10) in which an extruding material is pushed into first channel by a main extruding plunger; first deformation step (20) in which the extruding material is shear deformed as transferring from the first channel to an intermediate channel inclined to an angle of 45 degrees; transferring step (30) of extruding and transferring the extruding material by the continuous operation of a main extruding plunger in the intermediate channel; second deformation step (40) in which the extruding material is shear deformed in the state that a back pressure is applied as transferring from the intermediate channel to a second channel inclined to an angle of 45 degrees; and discharging step (50) of extruding and discharging the extruding material by the continuous supply of the extruding material from the second channel.

Description

Production method of grain refinement of difficult-to-work materials using double equal channel angular processing}

The present invention relates to a method for extruding a hard workpiece. More specifically, the present invention relates to a method for producing grain refinement by a double constrained steel shear deformation method.

Conventional processing methods such as rolling and extrusion have been used to make structural changes while improving physical and mechanical properties of various materials. In particular, hot working has been used as a general method for increasing the elongation and strength and eliminating defects associated with casting ingots. Conventional metalworking methods such as forging, rolling and extrusion have also been used for the purpose of improving the mechanical properties of the desired material and removing defects. These processes reduce the original material by several times the original cross-sectional area. For example, in order to ensure the higher quality of aluminum alloys, the cross section reduction ratio between the initial ingot and the final product is more than 50: 1. In addition, conventional metalworking processes often cause serious organizational non-uniformity issues in the workpiece, resulting in a large amount of scrap from the workpiece.

Recently, the ECAP (equal channel angular processing), which is a method of extruding a desired material through a channel having a constant cross section area, has recently been developed in a pseudo-hydrostatic state. A new processing technology that improves the ductility and strength of materials by subjecting the material to severe shear deformation and then changing the crystal grain size of the material to less than microns through appropriate heat treatment. Since there is no reduction of the material, it is possible to process large-capacity materials.

However, in the ECAP technology, the material flow is not uniform due to the friction between the wall and the material and the curvature of the joint formed at 90 ° during the extrusion process using an L-shaped channel connected at 90 ° angles to maximize the strain. It is not. In other words, during the extrusion process, the material is deformed while the inner part of the L-shape is rotated by 90 °, but the shear curve is suppressed by the frictional force with the channel. P441-447, Shear Strain Characteristics in Constrained Shear Processing). In this case, the local strain difference may cause many problems such as difference in strength, microstructure, and elongation due to the nonuniformity of the material when the actual material is processed. In order to solve these various problems, the situation is being supplemented by changing the direction in units of 90 ° between repeated machining. The ECAP technique requires at least four passes to produce the desired microstructure. In addition, in the case of the L-shaped, the ECAP technology has a frictional resistance difference between the inner part and the outer part, so that the outer curved part has a high frictional resistance, so that the deformation of the material is difficult. This is easy. As a result, the front part of the extruded material is open without being constrained, so the outer curved part has a relatively high frictional force and the middle part has a relatively low frictional force. A protruding shape is achieved. 3 is a diagram of pure aluminum is analyzed using DEFORM, the world's most widely used software for forging analysis at room temperature, and in this figure, it can be seen that the front part of the extruded material protrudes. (4), p. 44-447, Journal of Metallurgical Society, Vol. This protruded front part has a problem because it is not subjected to a lot of shear deformation as shown in FIG. 3 and the strain is uneven, and because the cross-sectional area is not constant, it is often cut and removed, and the remaining material is changed by 90 ° again. There is a hassle to pass through the L-channel. In addition, the extrusion in the open state of the front part affects the shear extrusion process, especially in the case of flow softening such as titanium material, the shear deformation is continuously and locally generated, so that a shear band is generated. Shear fracture (Metallugical Transaction A 30A 1999 p2473-2481, Hot working of Ti-6Al-4V via equal channel angular extrusion). In order to prevent such a problem, using back pressure is one of the effective methods. In general, even if the hydrostatic pressure is very high, it is known that the hydrostatic pressure alone does not destroy the material. Therefore, the pseudo-hydrostatic state is applied to the extruded material during the back pressure operation when there is no back pressure, thereby preventing the fracture of the extruded material by shearing.

Accordingly, the present invention has been made to solve the above problems, an object of the present invention is to reduce the frictional force in the outer curved portion of the L-shaped channel to connect the two channels having the same cross-sectional area at 45 ° to the same material All microelements in the cross-sectional area cause shear deformation uniformly at the same time to 45 ° without changing the cross-sectional area. In addition, due to the difference in frictional force of the extruded part and the inconsistent state of the extruded material, a protruding problem of the front part of the extruded material and a shear band are generated, resulting in a local uneven microstructure. It is to provide a manufacturing method for greatly improving the mechanical properties, such as ductility and strength due to the miniaturization of.

In order to achieve the above object, the method for producing grain refinement by the double constrained steel shear deformation method of the present invention makes the material more uniform by continuous double constrained steel shear deformation of 45 ° angle in the hydrostatic pressure condition. It is characterized in that the material is refined by deformation.

Hereinafter, the specific configuration and operation of the present invention will be described in detail with reference to the accompanying drawings.

1 is a flow chart for the manufacturing method of the present invention,

2 is a block diagram of the present invention,

3 is a diagram showing a state of extrusion deformation using a numerical analysis for the existing invention,

4 is a detailed view showing the operation and effects of the present invention.

<Explanation of symbols for main parts of drawing>

1: Outer cylinder in which the first channel is installed 2: Outer cylinder in which the intermediate channel is installed

3: outer cylinder in which the second channel is installed 4: extruded material

5: main extrusion plunger 6: back pressure plunger

7: tapered channel inlet

1 is a flow chart of the manufacturing method of the present invention, Figure 2 is a block diagram of the present invention, Figure 3 is a diagram showing the extrusion deformation state using a numerical analysis for the existing invention, Figure 4 is a view of the present invention It is a detailed view which shows action and an effect.

As shown in Figs. 1, 2 and 4, the apparatus for producing grain refinement by the double constrained steel shear deformation method of a difficult-working material according to an embodiment of the present invention has an outer cylinder 1 provided with a first channel. ; An outer cylinder 2 in which an intermediate channel is installed; An outer cylinder 3 provided with a second channel; Extrusion material (4); A main extrusion plunger 5; A back pressure plunger 6; It consists of a tapered channel inlet 7.

The outer cylinder 1 in which the first channel is installed has a circular or square cross section of the first channel, and the channel inlet is tapered at an inlet of 5 to 10 ° to facilitate insertion of the extruded material 4. 7). The tapered channel inlet (7) is to facilitate the insertion of the extrusion material (4) through the second channel again without the grinding process of the end portion during the extrusion process.

The outer cylinder 2 in which the intermediate channel is installed is formed in the cross section of the same shape and dimensions as the first channel when the intermediate channel is viewed from the top, and is inclined at 45 ° with the first channel and the second channel. It is composed.

In the outer cylinder 3 in which the second channel is installed, the second channel is formed in the same cross section as the first channel and the intermediate channel. The first channel 1 and the second channel 3 are configured parallel to each other.

The main extrusion plunger 5 and the back pressure plunger 6 have the same cross-sectional shape as the cross-sectional shape of the channels, which can be changed according to the shape of the product.

The outer cylinder (1, 2, 3) is formed in a rectangular shape and can be integrally or separately assembled, and additionally may be extruded by applying a predetermined temperature by mounting a heater, wherein the temperature is depending on the material of the extrusion process Different. That is, the outer cylinders 1, 2 and 3 may be equipped with a heater inside or a chamber mounted outside to increase the temperature depending on the material so that the desired mechanical properties may be obtained. In general, it can be used as it is after passing a predetermined number of times depending on the material, or the structure can be refined by heat treatment, but appropriate heat treatment is also possible depending on the material after discharge by each extrusion. Lubricant is used for extrusion process using MoS2 or graphite system.

Next, a method for producing grain refinement by the double constrained steel shear deformation method of a hardworking material which is an embodiment of the present invention configured as described above comprises: an extrusion material supplying step 10; A first modification step 20; A moving step 30; A second modification step 40; The discharge step 50 is made and will be described in detail with reference to the operation below.

The extruded material supplying step 10 is a step in which the extruded material 4 is pushed into the first channel by the main extrusion plunger 5, inserting the extruded material 4 or a certain amount of mass into the first channel, An extruded plunger 5 is applied to the material to the desired depth to plastically deform the material and move it in the channel. The main extrusion plunger 5 is generally hydraulically operated, but can be operated in the form of pneumatic or screw jack depending on the material. The speed of the main extrusion plunger 5 does not significantly affect the strain of the extruded material 4 and depends on the discharge capacity of the cylinder pump connected to the main extrusion plunger 5.

The first deformation step 20 is a step of shear deformation by moving from the first channel to the intermediate channel inclined at 45 °. When the extruded material 4 is extruded from the first channel to the intermediate channel, the shear strain is reduced by simple shear. It is about 100%.

The moving step 30 is a step in which the extruded material 4 is extruded and moved without changing the strain rate by the continuous movement of the main extrusion plunger 5 in the intermediate channel.

The second deforming step 40 is a step of shear deformation by moving from the intermediate channel to the second channel inclined at 45 °. The extruded material 4 having passed through the intermediate channel once again enters the second channel and is about 100 again. A shear strain of% will occur. As the extruded material 4 passes through the inlet of the second channel, the back pressure plunger 6 applies back pressure to the extruded material 4 to suppress the protrusion of the front surface of the pressed steel material and to help uniform shear deformation in the remainder of the extruded material. .

The discharging step 50 is a step in which the extruded material 4 is extruded and discharged by a continuous supply of the extruded material 4 in the first channel.

The above process can be repeated continuously. When the first inserted extruded material (4) is finally passed through the second channel through the intermediate channel, the angle is rotated by 90 ° to be inserted again and repeated. Preferably, the direction should be equally deformed in units of 90 °, and the rotation angle can be changed depending on the material.

After the extruded material 4 passes through the second channel, the extruded material may be heat-treated according to the material, and the extrusion process may be repeated again, and a heat treatment process may be added to finally heat-treat after 2-3 extrusion.

As shown in FIG. 4, the shear strain that the material receives when passing through the intermediate channel in the first channel or from the intermediate channel to the second channel can be simply interpreted as follows.

Assuming that there is no surface frictional coefficient of incompressible material with each cross-sectional area of the channel being equal, if a certain amount of material consisting of the area ABCD is compressed to the same level by the main extrusion plunger 5 points A, B, C, D Will move to D, C, E, and F, respectively, so that all collinear particles will be deformed equally so that the shear strain becomes uniform throughout the process, thereby solving the problem of local non-uniform microstructure in the existing ECAP. In addition, because the angle of the two channels is 45 ° by the definition of the shear strain, DG = GF due to the angle 45 ° when passing through the connected intermediate channel at an inclination of 45 ° in the first channel, so that the shear strain becomes 1 as follows.

tan = tan 45 ° = 1 ( = GF / DG)

Shear strain 1 is the equivalent shear strain based on von Mises theory. In terms of to be. On the other hand, when the material passing through the intermediate channel passes through the second channel at a slope of 45 ° again, the shear strain is deformed to 100%, and passes through the first channel and through the final second channel. Effective strain corresponding to strain Occurs 115%.

The channel is made by connecting two channels having the same cross-sectional area at 45 °, thereby reducing the difference in frictional force between the local outer curved portion and the inner portion than the 90 ° connection of the conventional ECAP, thereby protruding the front part of the extruded material. Problems will also be reduced and shear bands will also be suppressed.

In addition, once the extruded material is passed once, the conventional ECAP is made once, but in the present invention, since the outer curved portion and the inner portion are each deformed twice, a homogeneous microstructure can be obtained.

In the present invention, in particular, by applying back pressure, it is possible to suppress the problem of protrusion of the front part of the extruded material and the generation of the shear band.

As a result, the entire cross section is homogeneous during the deformation process of the material. In other words, the uniformity of flow in the movement of the material due to plastic deformation from the first channel to the intermediate channel causes the same strain in the center and the surface of the workpiece. The only deformation is that the simple shear deformation along the transition plane that changes from the first channel to the intermediate channel can solve the problem of non-uniform microstructure in the existing ECAP. To ensure that a uniform strain is produced. In the present invention, it may be used for deformation of a workpiece having a very small cross-sectional area (diameter 10 mm) or a large cross-sectional area (250 mm diameter). It is also suitable for plastic working of brittle high strength aluminum and titanium alloys and magnesium alloys.

As described above, according to the method for producing grain refinement by the double equal channel angular processing of the workpiece of the present invention, a material such as the workpiece is formed at an angle of 45 ° in the hydrostatic pressure state. It is an excellent invention to improve the mechanical properties such as elongation and strength of hard cutting edge materials such as high strength brittle materials by making the microstructure more homogeneous by continuous shear deformation through the channel. In addition, the back pressure acts to solve the problem of shear failure due to the formation of shear bands in the existing ECAP and the problem of protrusion of the front surface of the extruded material, which is an excellent invention for obtaining a more homogeneous microstructure.

In the existing ECAP, in order to obtain a homogeneous microstructure, the extrusion material has to be extruded four times or more by inserting the extruded material by rotating it by 90 ° when inserting the extruded material after one pass and then inserting it. However, in the present invention, the same extrusion process as in the conventional ECAP, but the effect of redirection is doubled every one pass, after 4 times the strain is equivalent to 400%, but four times the reversal effect in the existing ECAP It is a very useful invention for the machine parts industry because it has an excellent effect of giving twice more than 8 times more homogeneous strain processing.

Claims (3)

An extruded material feeding step 10 in which the extruded material 4 is pushed into the first channel by the main extrusion plunger 5; A first deformation step 20 in which the extruded material 4 is sheared while moving from the first channel to the intermediate channel inclined at 45 °; A moving step 30 in which the extruded material 4 is extruded and moved under the action of the continuous main extrusion plunger 5 in the intermediate channel; A second deforming step (40) in which the extruded material (4) moves from the intermediate channel to the second channel inclined at 45 ° and shears while the back pressure is applied; Double equal channel angular of a hardworking material, characterized in that it consists of a discharge step 50 in which the extruded material 4 is extruded and discharged by the continuous supply of extruded material 4 in the second channel. Grain refinement method by processing). The cross section of the channel is a circle or square, the channel inlet is the outer cylinder (1) is provided with a first channel tapered in the range of 5 ~ 10 ° to facilitate the insertion of the extrusion material (4); An outer cylinder (2) formed in the same cross section as the first channel and provided with an intermediate channel configured to be inclined at 45 ° with the first channel and the second channel; An outer cylinder (3) in which the first channel and the intermediate channel are formed in the same shape and dimension on a plan view, and the first channel and the second channel are provided with a second channel configured to be parallel to each other; In the double equal channel angular processing of a hardworking material, characterized in that the cross-sectional shape is made up of the main extrusion plunger 5 and the back pressure plunger 6 formed in the same manner as the cross-sectional shape of the channel. Grain refinement manufacturing apparatus. The method of claim 1, wherein the extruded material (4) by a double equal channel angular processing of the workpiece, characterized in that for adding a heat treatment process that can be heat-treated after passing through the second channel. Grain refinement method.