RU2489219C1 - Method of rolling billets with fine-grained structure - Google Patents

Abstract

FIELD: process engineering.

SUBSTANCE: proposed method comprises straining the billet outside of the main rolls in gap between adjacent lengthwise rolling stands whereat said strain allows billet layers stretch, contraction and shear. For this, billet is subjected to continuous alternate flexure through angles approximating to 90 degrees with minimum possible flexure radius. Note here that flexing is performed by drawing by, at least, three additional rolls staggered on billet both sides to displace vertically thereabout. Diameter of said additional rolls is, preferably, commensurable with billet thickness. Distance between said additional rolls in working position equal the billet thickness. Said additional rolls in working position are aligned with axes of the stand bottom main rolls. Note here that said additional rolls are riffled in lengthwise direction.

EFFECT: expanded means for making specified structure including microcrystalline in flat billets and sheets.

6 cl, 2 dwg, 8 ex

Description

The present invention relates to the field of metallurgy, and in particular to the section of changing the physical structure of metals and alloys by hot plastic processing, leading to grain refinement, to obtain high technological and operational characteristics of flat billets.

A known method of equal-channel angular pressing (CGS), including multiple forcing a cylindrical workpiece through several channels of the same cross section, intersecting at a certain angle, mainly close to or equal to 90 °. After each pass, the workpiece can be rotated around its longitudinal axis by an angle of 90 ° or 180 °. (Valiev R.Z., Aleksandrov I.V. Nanostructured materials obtained by intense plastic deformation, M .: Logos, 2000, p. 13). The disadvantage of this method is the complexity and inability to use it for flat workpieces.

A known method of processing billets of metals and alloys (patent RU 2203975 C2, IPC C22F 1/18, published 10.05.03), which consists in obtaining a microstructure with the required grain size through plastic deformation, carried out in one or more stages, based on grain sizes in source blank. The temperature and speed conditions at the stage are chosen to ensure the transformation of the structure in the process of dynamic recrystallization. In addition, the stage is carried out in several transitions for the most complete transformation of the structure in the volume of the workpiece. When processing an axisymmetric workpiece at the transitions, workpiece-regulated layers of the workpiece are worked out using complex loading, including at least at the first transition of the first stage, torsion as the sole or predominant component, and compression or tension at the subsequent transitions, or a combination of compression or tension with torsion. Processing is carried out in isothermal or quasi-isothermal conditions. The method allows to obtain a fine-grained structure in axisymmetric blanks. However, the disadvantage of this method is the significant complexity in the processing of small flat plates and the inability to process extended plates.

A known method of straightening plate products from high-strength low-alloy strip steel (patent RU 2432221 C1, B21D 1/05, published October 27, 2011), including alternating elastoplastic bending of rolled products in a sheet straightening machine between two rows of rollers at a regulated temperature at which the maximum bending value is set from the ratio of the thickness of the rental and the distance between the axes of the lower and upper rollers. The disadvantage of this method is the impossibility of significant grinding of metal grains, since the dressing process is carried out under deformation conditions that do not provide adequate accumulation of deformations during processing, and can only be used for low alloy steels at low temperatures.

As a prototype, a method for producing billets with a fine-grained structure of combined helical and longitudinal rolling was selected (Patent RU 2347631 C1, B21B 19/02, published February 27, 2009), including deformation of the workpiece outside the main rolls by twisting in the gap between adjacent helical and longitudinal rolling stands . The treatment is started by longitudinal rolling, after which cross-helical rolling is carried out with circular compression and rotation of the workpiece, ensuring that the workpiece is subjected to compressive stress by back-up force due to the difference in the flow rates of the metal during longitudinal and helical rolling.

The advantage of this method is the use of the gap between adjacent stands for deformation of the workpiece by compressive stresses. The disadvantage of this method is the use of screw rolling for these purposes, since it is only possible to process axisymmetric billets to obtain fine grain.

The objective of the invention is to expand the arsenal of means of obtaining a regulated structure, including microcrystalline, in flat blanks and sheets during rolling.

The solution to this problem is achieved by the fact that, similar to the prototype, the method of producing billets with a fine-grained structure during rolling involves deformation of the billet outside the main rolls in the gap between adjacent stands of longitudinal rolling. In contrast to the prototype, a deformation is created that provides tension, compression and shear of the workpiece layers, for which continuous dynamic alternating bending of the workpiece is carried out at angles approaching 90 ° with the smallest possible bending radius.

In the particular case of the implementation of the method, the bending is carried out by a broach between at least three additional rolls located staggered on both sides of the workpiece with the possibility of vertical movement.

In the particular case of the method, the bending is carried out using additional rolls, the diameter of which is mainly comparable with the thickness of the workpiece.

In the particular case of the method, the distance between the additional rolls in working condition is equal to the thickness of the workpiece.

In the particular case of the implementation of the method, the additional rolls in working condition are located mainly coaxially with the axes of the lower main rolls of the stands.

In the particular case of the method, additional rolls are made with longitudinal corrugation. The use of additional rolls with longitudinal corrugation will reduce the formation of textured grains in the surface layers of the workpiece.

The physical essence of the method consists in increasing the accumulated deformation by the workpiece during processing. The development of the process of plastic deformation during continuous dynamic bending of the workpiece is carried out under alternating tension and compression, as well as shear, which stimulates the formation of stable dislocation clusters in the material and allows you to create significant accumulated deformation.

Dynamic bending of the workpiece at angles approaching 90 ° with the smallest possible bending radius brings the deformation conditions closer to the conditions carried out in the known method of equal channel angular pressing. In angular pressing, a change in the direction of movement of the compact by 90 ° gives the maximum grinding effect due to hydrostatic compression, tension and shear of the compact layers (Valiev R.Z., Alexandrov I.V. Nanostructured materials obtained by intense plastic deformation. M .: Logos, 2000 , p. 13).

In the proposed method, bending the workpiece at angles approaching 90 ° with the smallest possible bending radius also gives the maximum effect of grinding grain. The bending radius corresponds to the radius of the additional roll, the minimum value of which is limited by the complexity of the technical implementation, for example, due to the possibility of bending with a significant length of the roll. It was experimentally established that the bending radius, which is comparable with half the thickness of the workpiece, is optimal. The bending radius of more than two, three values of the thickness of the workpiece leads to such an insignificant treatment effect, which makes the application of this method impractical.

The implementation of the method, including in combination with subsequent heat treatment, ensures the formation of new grains due to the development of dynamic or static recrystallization. In the particular case of applying the method to steels, due to the combination with phase transformations of the eutectoid type in the iron-carbon system, the transformation of a coarse-grained or coarse lamellar microstructure into a globular one is accelerated.

To achieve bending at angles close to 90 °, the distance between the additional rolls in working condition should be equal to the thickness of the workpiece, the rolls themselves should have a diameter predominantly comparable to the thickness of the workpiece and are located mainly coaxially with the axes of the lower main rolls of the stands.

A more significant effect of the accumulation of deformation will be realized in the case of an increase in the number of passes through additional rolls, for which you can increase the number of additional rolls or repeat the processing.

Additional rolls in working condition should be located mainly coaxially with the axes of the lower main rolls of the stands, since an increase in the bias of the workpiece relative to the rolling axis can increase the pulling force and cause the workpiece to break.

Application of the proposed method in the field of dynamic recrystallization or the intercritical region for alloys with polymorphic transformations can lead to the formation of a stable nanostructure up to the level of 40-50 nm.

The possibility of implementing the proposed method is illustrated by graphic materials.

Figure 1 shows the arrangement of additional rolls in the gap between adjacent stands of longitudinal rolling at the initial moment of processing the workpiece, where 1 is the workpiece, 2 and 3 are adjacent stands of longitudinal rolling, 4 and 5 are the upper additional rolls, 6 - lower additional roll , 7 and 8 - the upper and lower bed.

Figure 2 presents a diagram of a process for processing flat billets.

In the particular case of the implementation of the proposed method, a device can be used (Fig. 1), including additional rolls 4, 5, mounted on the bed 7 and the roll 6, mounted on the bed 8, staggered at a distance equal to the thickness of the workpiece 1. The diameter of the additional rolls 4-6 is equal to the thickness of the workpiece 1.

The method is as follows. The workpiece 1 is heated to the temperature necessary for processing, and rolling is started in the first stand 2, and then in the second stand 3. Then lower the frame 7 with the upper additional rolls 4, 5, which are aligned with the lower main rolls of the working stand 2, 3 (FIG. 2), thereby providing a dynamic continuous alternating bending of the workpiece 1 at angles approaching 90 ° with the minimum possible bending radius, determined by the diameter of the additional rolls. At the same time, in sections of the workpiece located in the gap between the roll of stand 2 and roll 4, rolls 4-6 and 6-5, roll 5 and roll of stand 3, layer-by-layer compression, tension, and shear deformation are carried out, which, as the workpiece 1 is drawn between additional rolls 4, 5, 6 change their sign and lead to a significant accumulation of deformation and, consequently, grain refinement. Grain grinding can be regulated by changing the processing conditions, for example, the distance between the rollers, the bending angle, etc.

Example 1

A billet in the form of a bar of annealed industrial copper 10 mm wide and 8 mm thick with a grain size of 95 μm was heated to 700 ° C and rolled using two stands 2, 3 of the laboratory mill located at a distance of 84 mm from each other to a thickness of 6 mm, compression was carried out by 25%. The diameter of the additional rollers 4-6 was 20 mm, the distance between the upper additional rollers 4 and 5-32 mm, between the upper and lower rollers 4-6 and 6-5 at the time of drawing, was 6 mm. The upper rolls 4, 5 with the help of a hydraulic jack were lowered to a level that ensures their alignment with the lower axes of the rolls of the working stands 2, 3.

Metallographic analysis of the samples after processing showed an average grain size of about 2 μm. Thus, the resulting structure has a significantly smaller grain size than in the initial state.

Example 2

Processed the same as in example 1, a copper billet in the same conditions. Rolling was carried out only through the first stand without broaching through additional rolls that remained in the initial position. The grain size was 40 microns.

Thus, conventional rolling does not significantly reduce the grain size of the metal.

Example 3

The copper billet was processed under the same conditions as in example 1. The processing was carried out twice. The grain size was 0.9 μm.

Thus, an increase in the number of bending cycles further reduced grain size.

Example 4

We processed the same copper billet as in Example 1 under the same conditions, but the distance between the two stands of the laboratory mill was 140 mm, the distance between the upper additional rollers was 60 mm, and between the upper and lower rollers at the time of drawing it was 20 mm.

Metallographic analysis of the samples after processing showed an average grain size of about 8 μm, that is, there is a smaller degree of grain refinement than in example 1.

Example 5

We processed the same as in example 1, the copper billet under the same conditions, but the distance between the two stands of the laboratory mill is 144 mm, the distance between the upper additional rolls is 52 mm, between the upper and lower rolls at the time of drawing, 6 mm, the diameter of the additional rolls - 40 mm.

The grain size was 25 microns, that is, the grinding of grain is negligible. The increase in roll diameter, i.e. bending radius leads to a significantly smaller treatment effect.

Example 6

We processed the same as in example 1, the copper billet under the same conditions, but additional rolls were lowered down to a distance not reaching 15 mm to the axis of the lower rolls of the working stands.

The grain size was 25 μm, since the workpiece was not bent to angles close to 90 °, which did not allow to obtain the desired result.

Example 7

A workpiece similar to that described in example 1 was processed under the same conditions, but the additional rolls had longitudinal corrugation.

The grain size after processing was 2 μm, and the grain shape was close to equiaxial, i.e. longitudinal corrugation of the rolls further reduces texturing and thereby improves the quality of the metal.

Example 8

A blank of aluminum alloy D16 in the form of a bar 10 mm wide and 8 mm thick, with a grain size of 103 μm was heated to 400 ° C and processed further under conditions similar to example 1.

The grain size after processing was 3.5 μm, which indicates the effectiveness of the processing used for aluminum billets.

Thus, the proposed method expands the arsenal of means for obtaining a regulated structure, including microcrystalline, by continuous dynamic alternating bending when rolling a flat workpiece at angles approaching 90 ° with the smallest possible bending radius.

Claims (6)

1. A method of producing billets with a fine-grained structure during rolling, including deformation of the billet outside the main rolls in the gap between adjacent stands of longitudinal rolling, characterized in that the deformation of the billet, providing tension, compression and shear of the billet layers, is created by means of continuous dynamic alternating bending of the billet with the smallest possible bending radius at angles close to 90 °. 2. The method according to claim 1, characterized in that the bending of the workpiece is carried out by pulling at least three additional rolls located between adjacent stands in a checkerboard pattern on both sides of the workpiece with the possibility of vertical movement. 3. The method according to claim 2, characterized in that the bending of the workpiece is carried out using additional rolls, the diameter of which is mainly comparable with the thickness of the workpiece. 4. The method according to claim 2 or 3, characterized in that the distance between the additional rolls in the working state is set equal to the thickness of the workpiece. 5. The method according to claim 2, characterized in that the additional rolls perform with the possibility of their location in working condition coaxially with the axes of the lower main rolls of the stands. 6. The method according to claim 2, characterized in that the additional rolls are performed with longitudinal corrugation.

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