RU71574U1 - BILL FOR PRODUCTION OF RENT - Google Patents

Abstract

The utility model relates to the field of metallurgy and can be used in the manufacture of sheet, long products, pipes and special profiles. The billet for the production of rolled products, cast from black or non-ferrous alloy, is made with dimensions within a slab or bloom or with dimensions of their cross section, chemically homogeneous from a liquid-solid melt, with equal primary grain of its material, with crystallization under pressure, ensuring the porosity of the billet. It is cast either by a method of squeezing with crystallization under pressure, (LVKD), or by a method of squeezing the melt into a mold from a melting-distributing furnace (ladle) through a metal wire with crystallization under pressure (LVKD), or by continuous casting using a movable mold with high-speed extraction of the ingot (NLPK). The blank for the production of rolled products can be cast from ductile iron, incl. made of nodular cast iron. Using the utility model allows to improve the quality of rolled stocks and, accordingly, the rental itself, to reduce the cost of rental and reduce energy costs for its production.

Description

The utility model relates to the field of metallurgy and can be used in the manufacture of sheet and long products, pipes and special profiles.

Known billets for the production of rolled products, made either by continuous casting, or in the form of slabs and blooms obtained on slabs and blooms from a previously cast ingot (V.M. Klimenko, A.N. Anishchenko, A.A. Minaev, V.S. Gorelik, Rolling production technology, Kiev, the head publishing house of the Vyshcha Shkola Publishing Association, 1989, pp. 4, 16, 37).

A disadvantage of the known billets for the production of rolled products is that its material is chemically heterogeneous and defects that occur in ingots and in the continuously cast billet are transferred to the rolled products. In ingots, zonal and dendritic segregation occurs. For example, in ingots of boiling steel, the segregation of sulfur and phosphorus in some of its sections reaches 500-700% of their average content in steel. With continuous casting of steel, zonal segregation acquires a special character. The liquid melt enriched with carbon, sulfur, phosphorus and other impurities is pushed out by the front of growing crested grains into a narrow zone along the axis of the workpiece. In this zone, under the influence of hydrostatic pressure of the melt, significant movements of the melt enriched in impurities occur. Shrink pores and cracks are filled with liquids, along the axis of the workpiece are areas with positive and negative segregation. Most often, there are two types of axial segregation: V-shaped and string. Deformation of the workpiece in the support system of the continuous casting machine (CCM) is accompanied by an increase in the cross section of the workpiece (bloating). During bloating, melt mixing inside the billet and axial segregation are enhanced. In continuously cast billets of boiling steel, gas segregation develops. It consists in filling cell bubbles from the inside with liquids that penetrate there

under the influence of hydrostatic pressure. Bubble liquids arrive intermittently, so their chemical composition varies.

Zonal segregation of ingots during rolling is not eliminated; in rolled steel, segregation of the following types is observed: segregation square (circle) - segregation zone, the contour of which repeats the shape of the cross section of the ingot, spot and spotted segregation, shrink segregation. As a rule, the content of oxides, sulfides and nitrides is increased in segregation zones.

Many ingot defects are not eliminated by pressure processing and are inherited by rolled or forged steel. By location in the metal, defects are divided into internal and surface. The causes of the formation of internal defects are metal shrinkage, segregation, redox reaction of liquid steel, gas saturation of the steel. Surface defects appear due to oxidation and contamination, gas evolution in the surface layers of the crystallizing ingot, mechanical stress and damage.

The main types of surface defects of the ingot are subcortical bubbles, inversions of the crust, pollution, and cracks. If the ingots arrive at the cold redistribution, part of the surface defects are eliminated during stripping, the red ingots redistribution increases the number of surface defects, because only a small part of the defects of the ingot is destroyed during the formation of scale. During hot deformation, voids and pores with an unoxidized surface are welded: gas bubbles in ingots of boiling steel, axial porosity and friability in ingots of mild steel, small internal cracks. Hot cracks with an unoxidized surface, as well as oxidized shrink shells and voids, are not welded and breaks and discontinuities appear in them in rolled steel. A variety of surface defects of rolled steel appear in connection with defects of the ingot, its deformation processes and finishing operations. The most characteristic defects are:

longitudinal cracks due to unbroken subcortical bubbles located at the surface of the rolled metal at a depth of 10 mm; rolled peeling (captivity) of a tongue-shaped form; hair - chains of nearby particles of inclusions along the rolling direction.

The hairs are more characteristic of alloyed structural steels.

Common defects in workpieces are internal and surface cracks. The reasons for the appearance of crystallization cracks are mechanical stresses and reduced metal strength in certain temperature ranges. Low strength has steel with a structure in which the interdendritic spaces are filled with the melt. The rupture of the liquid sections creates hot cracks between the axes of the dendrites. Under the influence of hydrostatic pressure of the melt, these cracks are filled partially or completely with liquor enriched with impurities. Thus, segregation occurs. Internal cracks when rolling blanks are welded, segregation is preserved and manifests itself in the form of spots and stripes. Crystallization cracks occur when the cross-sectional shape of the workpiece is distorted, for example, the formation of a rhombus instead of a square.

All types of surface cracks cause the formation of captures and bands of chemical heterogeneity in the rolled blanks. Captions appear already during the rolling of subcortical bubbles in rolled billets of steel of all grades.

The axial porosity during rolling is completely welded, and the axial segregation is converted into segregation strips. The largest and longest strips lead to the delamination of sheets, pipes and other products. Liquidation strips have different microstructures and properties: segregation of phosphorus (and arsenic) promotes the formation of ferrite bands with sulfide inclusions, carbon segregation - the formation of strips with perlite structure; joint segregation of carbon and alloying elements

- formation of ferrite bands (Encyclopedia in forty volumes, section II, Materials of mechanical engineering, volumes II-2, steel - cast irons. Edited by E.T.Dolbenko, M., "Mechanical Engineering 2001", pp. 11-15) . Similar defects exist in non-ferrous alloy preforms and in rolled products obtained from them.

If it is necessary to improve the quality of the metal, refining ingots are used, which significantly increase the cost of rolling.

In the manufacture of ingots, for example, of steel, it is necessary to use cast-iron molds, in which the resistance is low, only up to 30 bulk. The resulting ingots are processed into slabs and blooms using metal-intensive slabs and blooms. In this case, 10-25% of the metal is lost to the edge. Ingots, slabs and blooms are additionally heated before deformation. The production scheme for the manufacture of rolled products, for example, from a steel ingot, is complex and involves large labor and energy costs. It includes: blast furnace production of cast iron; oxygen-converter steel production; production of steel ingots by casting into cast-iron molds; production of slabs and blooms on slabs and blooms; Production of rolled products (high-quality, sheet, etc.).

The purpose of this utility model is to eliminate the noted drawbacks, namely:

- improving the quality of rental,

- reduction of its cost

- reduction of energy consumption for heating.

This goal is achieved by the fact that the billet for the production of rolled products, made of ferrous alloys, is cast with dimensions within the slab or bloom of a liquid-solid melt chemically homogeneous, with equiaxed primary grain of its material. The liquid-solid state of the melt is achieved in the following ways: by cooling the melt in the furnace below the liquidus line to the crystallization temperature range or by introducing micro-refrigerators into the melt, or by introducing nano particles of refractory compounds into the melt, or by using all of the above methods.

To obtain a workpiece with the indicated characteristics, constant and one-time casting formulas are used, and the manufacturing method is mainly used for displacing (squeezing) the melt into a mold from a melting-transfer furnace (ladle) through a metal pipe with crystallization under pressure (LVPCD, Russian application No. 2006128002/02822018/02 "Method for the manufacture of castings", declared 1.08.2006, a positive decision of FIPS dated 04.24.2007 on the grant of a patent [1]; Russian patent No. 63270B22D 18/00 "Device for producing castings with crystallization under pressure, publ. 27.05. 2007 Bull. No. 15 [2] ").

Pressure (especially in the manufacture of billets from deoxidized, mild steel or cast iron) helps to reduce the size of the critical nucleus, increase the number of crystallization centers and eliminate micropores.

The material of the proposed billet for the production of rolled products is chemically homogeneous with small equivalent primary grains, which is achieved by manufacturing it from a liquid-hard alloy with ready crystallization centers, and solidification of the melt under pressure ensures its porosity. This allows you to eliminate the dendritic structure of the cast billet, grind the grain due to the ready crystallization centers in the molten metal cast into the form, improve the chemical uniformity of the billet metal, eliminate the dendritic and zonal segregation and, accordingly, all defects of the billets inherent in obtaining them from the overheated melt over the liquidus line with crystallization under atmospheric pressure. The proposed blank, in comparison with the known, is characterized by improved quality:

- fixed dendritic structure;

- there is equiaxed grain due to ready crystallization centers;

If the blank for receiving the rental does not have defects, then the rental obtained from it will also not have them.

The proposed preform hardens predominantly in volume and the criterion for its hardening is

Δt _kp / δt≥1, where

Δt _kp is the value of the crystallization temperature range,

δt is the temperature difference in the casting section.

With volumetric solidification, the temperature difference in the cross section of the cast billet is negligible. As a result, over the entire casting volume, immediately after filling the mold, there are already ready crystallization centers, which ensures uniform fine primary grain, chemical uniformity of the cast metal. Rolled products obtained from the proposed billet have no defects inherent in the known billet. Hardening of the workpiece under pressure ensures the elimination of microporosity - suppression of the gas forming micropores is suppressed, and shrinkage porosity is eliminated. In this case, the amount of liquid filtered through the two-phase state zone is determined according to Darcy's law

Q = k (F / L) Δ _p ,

where k is the coefficient of permeability of the semi-hardened alloy frame,

F is the cross-sectional area of the casting,

L is the length of the zone two-phase state of the alloy.

Pressure, along with the prevention of microporosity, allows you to: reduce the size of the critical crystallization nucleus and increase the number of crystallization centers; reduce the diffusion coefficient of impurities and reduce the speed of separation diffusion during crystallization of alloys; to improve the conditions for the impregnation of the solid-liquid zone and, therefore, to densify the structure; reduce the temperature of the start of casting shrinkage and reduce shrinkage in the effective range of crystallization; reduce casting shrinkage, grind grain, which leads to an increase in the plasticity reserve in the solid-liquid state, and thereby reduce the tendency to crack formation. When using the proposed blanks for the production of rolled metal, there is no need to use

the production cycle of metal-intensive slabs and blooms, eliminates the energy consumption for heating ingots, slabs and blooms, because the proposed workpiece is removed from the mold for subsequent rolling at the required (set) temperature. The manufacturing operations of ingots and molds for their manufacture disappear. The production scheme is simplified. It includes: blast furnace production of cast iron; oxygen-converter steel production; the manufacture of cast steel billets of the "slab" or "bloom" type from a liquid-solid melt with crystallization under pressure; production of rolled products (high-quality, sheet, etc.).

Metal waste to trimmings is reduced to 5% instead of 25% when manufacturing existing workpieces.

Billets are cast using both permanent forms (for example graphite blocks) and one-time (for example, from HTS). Burnout in cast billets is prevented by low pouring temperatures and gas back pressure.

Workpieces from liquid-solid melt with crystallization under pressure can also be obtained by continuous casting in a movable mold with accelerated drawing of the workpiece.

In the manufacture of billets by continuous casting, the melt enters the mold in a liquid-solid state from an intermediate ladle. A movable mold is used, providing high speeds for drawing the workpiece (2 m / s or more). The height of the liquid core is about 4 meters and the pressure in its lower part is determined as P = γH, where γ is the specific gravity of the material, in g / cm ³ ,

H - the height of the liquid column of metal, in cm

For steel, H = 400 cm, γ = 7.6 g / cm ³ , with P = 0.3 MPa. Under this pressure, the workpiece (ingot) hardens during continuous casting.

Another difference of the proposed workpiece is that it is made of ductile iron. The metal of the proposed workpiece has

increased ductility. Using VCh35 cast iron as a material (tensile strength δ _in when rolling> 350 MPa, δ>22; mechanical properties during rolling increase: strength not less than 10%, and ductility 2 or more times) it is possible to obtain rolled products with properties similar to those of steel sheet rental. The scheme for the production of rolled metal using high-strength cast iron is even more simplified: blast furnace production of cast iron; production of cast billets of the "slab" or "bloom" type from high-strength cast iron with spherical graphite; production of rolled products (high-quality, sheet, etc.).

In this case, the oxygen-converter process of steel is excluded from the production cycle, environmental pollution is reduced and the environment is improved, the cost of rolled products is reduced, and energy costs are reduced. The porosity of cast iron blanks obtained under pressure is reduced by 3 times, plastic properties increase by 2 times, and strength by 10%.

For example, railway rails made of high-strength bainitic cast iron of the ADI-3 grade (DIS standard) will have δ _in = 1200MPa and δ = 4%, and if K-1203 bainitic cast iron is used (the standard of the Mekhenait Metal Corp. farm), _in the delta = 1200-1500MPa at δ = 3-5%, which fully comply with the requirements of the steel rails P75, P60, P50, with the best results in toughness, especially in sub-zero temperatures.

The next difference of the proposed workpiece is that it is cast from aluminum cast iron with spherical graphite. For example, with the following chem. composition: C = 3.2-3.7%, Si = 2.3-2.7%, Al = 1.4-1.5%. The tensile strength of cast iron _in δ = 1100 MPa, δ = 5% (Engineering. Encyclopedia in 40 volumes. CATEGORY P. materials in mechanical engineering. T. II-2. Steel. Irons. Tob. Ed. E.T.Dolbenko. M ., Engineering, 2001, p. 646). The indicated mechanical properties are cast iron obtained from superheated melt with crystallization under atmospheric pressure, and according to the data,

shown on page 542 of the above source, the mechanical properties increase with decreasing porosity: tensile strength by 10%, and elongation by 2 times, which means that the workpiece will have δ _in = 1200 MPa, δ = 10%. Rolled products made from such a billet will have the same properties, which fully meets the requirements for steel rails.

Figure 1 shows the proposed blank hire of the Blum type with dimensions of 250 × 300 × 4000 mm. The billet consists of a thin fine-grained layer 1 and, basically, of equiaxed grains 2, smaller than in a conventional ingot, the remainder of the rod 3, through which gas pressure is transmitted during solidification of the cast billet in the mold, gas shrink shell 4. The dashed line indicates the location of the segments arrived.

The billet of rolled products is cast from 45L steel by displacing a liquid-solid melt from a melting-distributing furnace (ladle) according to the modes of the HPLC method [1], from the melt cooled in the furnace below the liquidus line. When the temperature of the steel entering the form is 1480 ° С (the liquidus temperature of this steel is 1490 ° С, the solidus temperature is 1415 ° С), the steel is forced into the mold. By pouring the liquid-solid phase into the form, the grain of the workpiece is crushed (in the presence of ready crystallization centers in the liquid-solid melt), the dendritic structure is eliminated, because dendrite growth conditions are eliminated, while the workpiece becomes chemically homogeneous. Crystallization of the melt in the mold under pressure of 0.4-0.6 MPA (according to the HPLC method) eliminates microporosity in the cast billet.

Since in the proposed workpiece there are no defects inherent in the known, the rolled products made from it are also devoid of these disadvantages.

If the workpiece is made of ductile iron with spherical graphite of the VCh60 grade (80% perlite), then the railway rails obtained from it (when machining for bainite) will have δ _in ≥1250 MPa, δ ₀₂ ≥980 MPa, δ≥4.2%, which fully meets the requirements for the mechanical properties of metal for steel rails.

Using the utility model allows to improve the quality of rolled stocks and, accordingly, the rental itself, to reduce the cost of rental and reduce energy costs for its production.

Claims (4)

1. Billet for the production of rolled metal made of ferrous alloys, characterized in that it is cast with dimensions within the slab or bloom of a liquid-solid melt chemically homogeneous with equiaxed primary grain of its material. 2. A billet for the production of rolled metal according to claim 1, characterized in that it is molded mainly by displacing (squeezing) the melt into a mold from a melting-distributing furnace (ladle) through a pressure-crystallized metal wire (LVPCD). 3. A billet for the production of rolled metal according to claim 1 or 2, characterized in that it is cast from ductile iron. 4. A billet for the production of steel according to claim 1 or 2, characterized in that it is cast from aluminum cast iron with spherical graphite.