RU2541250C1 - Method of production of cast iron casting - Google Patents

Abstract

FIELD: metallurgy.

SUBSTANCE: method includes cast iron casting, pouring in ladder, to which preliminary pre-spheroidising, spheroidising and graphitising conditioning agents are added in quantity 0.2-0.3, 0.4-0.5, 0.4-0.5 wt % of liquid cast iron in ladder, respectively. After averaging of the chemical analysis the cast iron is poured in the mould, in which the chiller with applied on it layer of casting paint of graphite base with minimum thickness 0.3 mm is installed. Ratio of weight of the chiller and casting is 1:4. During cooling in the mould for at least 60 minutes till shake-out the casting self-tempering is performed. The casting has gradient structure. The work layer contains nodular graphite, the intermediate layer contains vermiculite graphite, and external layer has flaked graphite.

EFFECT: parts made out of cast iron have high service durability.

2 cl, 2 dwg, 5 tbl, 1 ex

Description

The invention relates to foundry and can be used for the manufacture of iron castings with high performance properties.

Among the majority of works dealing with the manufacture of castings of glass molds from cast iron, methods and processes related to changing the chemical compositions of such cast irons, their modification at the stage of casting molten iron from the furnace, or at the stage of casting it into a casting mold and its casting technology are considered.

A known method of producing castings of alloyed cast iron with spherical graphite [1], which consists in smelting cast iron, graphitizing its modification with ferrosilicon at a temperature of 1440-1460 ° C, spheroidizing modification with magnesium and cerium at 1420-1440 ° C. Get the cast iron of the following chemical composition (in wt.%): Carbon 2.2-4.0; silicon 0.5-3.5; manganese 0.2-3.0; chrome 3.0-10.0; nickel 2.0-5.5; boron 0.2-0.4; vanadium 0.2-1.0; copper 0.2-0.8; aluminum 0.1-0.4; cerium 0.03-0.2; magnesium 0.02-0.1; calcium 0.05-0.2; iron is the rest. Mold filling is carried out at a temperature of 1310-1360 ° C, knocking out is carried out at a temperature of 750-550 ° C. The castings are cooled to ambient temperature in air. The method provides castings with high values of hardness, wear resistance and impact resistance in the molten state.

The disadvantages of this method of producing cast iron are: the inability to control the number and size of the structural components of cast iron (ferrite, graphite, cementite) in order to control the operational stability of parts; a high proportion of alloying additives, significantly increasing the cost of manufactured products and creating an increased number of complex alloyed carbides in the casting structure and, as a result, insufficient operational stability.

Closest to the proposed method for the manufacture of castings from cast iron is the method [2], including smelting, casting in a ladle, modification, casting and heat treatment of cast iron of chemical composition (in wt.%): Carbon 3.0-3.5, silicon 4.0-5.0, manganese - up to 0.9%, chromium - up to 0.6%, sulfur - up to 0.025%, phosphorus - up to 0.15%, iron - the rest. Heat treatment of castings - annealing for 2-3 hours at 650 ° C. Cast iron after heat treatment has the structure of ferrite + perlite with spherical graphite.

The disadvantages of this method are the large number of carbide-forming elements - manganese and chromium, as well as the production of metal grains of ferrite and graphite inclusions of large sizes (Fig. 1), which reduce the performance (the number of heat exchanges) obtained from such cast iron parts.

The present invention solves the problem of increasing operational stability, resource parts - the number of withstand heat transfer.

The problem is solved by achieving the following technical result: in the resulting casting, the inner (working) layer contains spherical graphite, the intermediate one is vermicular, and the outer one is lamellar. This arrangement of the carbon phase allows high heat resistance of the internal (working) surfaces of the part (due to the production of spherical graphite), increased strength and thermal conductivity in the intermediate layer, and the highest thermal conductivity in the outer layer with a plate-like graphite form.

This technical result is achieved by the fact that in the method of manufacturing castings from cast iron, including its smelting, casting into a ladle, modifying, pouring into molds and heat treatment, pre-spheroidizing, spheroidizing and graphitizing modifiers are introduced into the ladle in an amount of 0.2-0.3, respectively , 0.4-0.5, 0.4-0.5 by weight of molten iron in the ladle, and a metal refrigerator is placed in the mold before pouring in a ratio of 1: 4 to the weight of the casting with a graphite-based foundry paint layer applied on it with a thickness not less than 0.3 mm. Heat treatment of the castings is carried out by self-annealing from the foundry heating for at least 60 minutes before knocking out.

The chemical composition of cast iron is selected in such a way that there is a stable maximum ferritization of the structure of cast iron with a minimum tendency to bleach it (reducing the proportion of carbide-stabilizing elements).

From the point of view of increasing the share of ferrite and the hardness of the casting, the best silicon content is in the range of 4.0-5.0%. In order to avoid a sharp decrease in toughness and heat resistance, its content should not exceed a threshold of 5.0%, to obtain castings with a ferrite-pearlite structure (with a ferrite fraction of at least 80%), its content should be at least 4.0%.

Manganese and chromium have a negative effect on the ferritization of cast iron, so their content should not exceed 0.4% and 0.1%, respectively.

Additionally, 0.1% of aluminum was introduced into the composition of cast iron. Together with silicon, aluminum increases the scale resistance of the metal base with an increase in its thermal conductivity.

The content of magnesium introduced in the modifiers is recommended in the range of 0.015-0.03%. An increase in the magnesium content contributes to an increase in the share of spherical graphite and a decrease in the thermal conductivity of the part as a whole. If the residual magnesium content is less than 0.015%, the modification results are unstable and there will be no spherical graphite in the working (inner) layer near the metal refrigerator and the vermicular layer in the intermediate layer.

To obtain cast iron castings with a residual magnesium content of 0.015-0.03%, the calculated amount of the spheroidizing modifier (FSMg5) introduced into the bucket is 0.4-0.5% of the ladle metal consumption.

Cast iron is smelted in a crucible furnace, which provides effective remelting and overheating of the melt before exhaustion to a temperature of 1540-1550 ° C. Then the molten metal is fed into the casting ladle, where there are pre-spheroidizing (CK20), graphitizing (FS75) and spheroidizing (FSMg5) modifiers. After this, the metal is mixed and averaged over the chemical composition and temperature. Further, at a temperature of 1380-1440 ° C, molds are filled with metal refrigerators previously placed in them.

The use of metal refrigerators in the form allows to obtain spherical shape of graphite in the working (inner) layer of the casting to a depth of 10-15 mm with a ratio of the casting mass and the mass of the metal refrigerator used 4: 1 (var. 2, Table 1). A large mass of a metal refrigerator increases the amount of cementite and ledeburite cementite in the structure, which negatively affects the operational stability of parts (var. 3, 4, Table 1), a smaller mass does not provide high hardness to the internal (working) surfaces of the part and increases the ferritic value grains and graphite inclusions (var. 1, table 1).

The use of 0.3 mm thick graphite-based foundry paint favorably affects the ferritisation of castings with a slight increase in the average size of graphite inclusions (from 8 μm to 13) (var. 3, Table 2). A smaller layer of paint does not contribute to the complete course of the process of ferritization of castings (var. 1, 2, table 2). A larger layer of paint has no effect on the structure of cast iron (var. 4, table 2).

The use of modifiers for various purposes (pre-spheroidizing, spheroidizing, graphitizing) provides the necessary number of graphite inclusions of the minimum size in the mass of the casting (var. 2, Table 3). The low content of modifiers does not allow to obtain a gradient casting structure (a structure characterized by the presence of several layers with different shapes of graphite for each layer) (var. 1, Table 3). The high content of modifiers forms exclusively spherical graphite in the entire casting volume (var. 3, 4, table 3).

The resulting cast iron provides the necessary properties of cast iron after self-annealing of castings. Self-annealing - cooling of castings in sand form for at least 60 minutes before knocking out in order to improve the structure of cast iron (var. 3, table 4). A shorter exposure time of the castings in the mold does not allow the ferritization of the castings to proceed fully (var. 2, Table 4). A higher exposure of castings in the mold does not affect the structure of cast iron (var. 4, table 4).

An example of the method

In the induction furnace, cast iron of the following composition is smelted (% wt.): Carbon 3.2, silicon 4.25%, manganese 0.4%, chromium 0.05%, sulfur 0.01%, phosphorus 0.05%, iron - rest. Pour into a bucket at a temperature of 1540 ° C. Modification is carried out by the following modifiers (in mass%): SK20 - 0.3, FSM5 - 0.45, FS75 - 0.45. After modification, cast iron is poured into prepared forms, where metal refrigerators made of gray cast iron are preliminarily placed, while the mass of the refrigerator and the mass of the casting are in a ratio of 1: 4.

Glass mold castings were obtained in which the most optimal combination of microstructural parameters (amount of ferrite and cementite, grain size of ferrite, size of graphite inclusions) is:

- the amount of ferrite is not less than 80% of the mass .;

- the average grain size of ferrite is not more than 20 microns;

- the amount of cementite and cementite ledeburite in the surface layer is not more than 1% of the mass .;

- the average grain size of graphite in the working layer is not more than 10-15 microns.

In other examples, the composition of cast iron and the cooking conditions were changed as described above.

The test results are shown in tables 1-5 and in FIG. 1 and 2, from which you can see the confirmation given in the justification of the technical result of the data.

Studies show that the proposed solution meets the criterion of "novelty", the technical result obtained indicates an inventive step, and the tests confirm industrial applicability.

Table 1 The mass of the metal refrigerator Option Casting weight with profit, kg Mass is metal. refrigerator, kg Cast mass / mass metal. the refrigerator Hardness at a depth of 40 mm, HRC The amount of ferrite according to GOST 3443 The amount of ledeburite according to GOST 3443 The average grain size of ferrite, microns Cast condition one 41 4.1 1:10 28 F80 one 35 2 10.25 1: 4 32 F55 four twenty 3 16,4 1: 2.5 39 FZO twenty 16 four 20.5 1: 2 44 F15 60 12.5 Condition after self-annealing 5 41 10.25 1: 4 29th F80 four twenty

table 2 Paint Thickness Option Mass is metal. the refrigerator The thickness of the paint layer, mm The amount of ferrite according to GOST 3443,% The average grain size of graphite, microns The amount of cementite according to GOST 3443,% one 10.25 0 F55 8 four 2 0.1 F80 10 2 3 0.3 F80 13 one four 0.4 F80 13 one

Table 3 Modifier Content Option The applied modifiers,% The structure of cast iron in the layers SK20 FSMg5 FS75 interior intermediate Outer one 0.1-0.2 0.3-0.4 0.3-0.4 Vermiculite graphite perlite cast iron Lamellar graphite perlite cast iron Lamellar graphite perlite cast iron 2 0.2-0.3 0.4-0.5 0.4-0.5 Nodular Ferrite Pearlitic Iron Ferrite-pearlitic iron with vermicular graphite Lamellar graphite ferrite 3 0.3-0.4 0.5-0.6 0.4-0.6 Nodular Ferrite Pearlitic Iron Nodular Ferrite Pearlitic Iron Ferrite-pearlitic iron with vermicular graphite four 0.4-0.6 0.6-0.8 0.6-0.8 Nodular Ferrite Pearlitic Iron Nodular Ferrite Pearlitic Iron Nodular Ferrite Pearlitic Iron

Table 4 Heat treatment of castings Option Way Type of heat treatment Time h The value of graphite inclusions, microns Metal base one Prototype Exposure at 650 ° C 2-3 30-60 F80 2 Proposed Self-annealing 0.5 12-14 F55 3 one F80 four 1,5 F80

Table 5 Durability of finished parts No. p / p Ways The durability of parts on the production line, thousand heat exchange one Prototype 550-650 2 Proposed 700-1000

Information sources

1. RF patent No. 2395366, C22C 37/00, publ. 07/27/2010.

2. Averchenko P.A. Cast iron for glass forms // P.A. Averchenko, B.C. Kravchenko / Foundry. - 1970. - No. 8. - S. 39.

Claims (2)

1. A method of manufacturing castings from cast iron, including smelting cast iron, casting into a ladle, modifying cast iron, pouring into molds and heat treatment of the casting, characterized in that pre-spheroidizing, spheroidizing and graphitizing modifiers are introduced into the ladle in an amount of 0.2-0.3, respectively , 0.4-0.5 and 0.4-0.5, by weight of molten iron in the ladle, a metal refrigerator is placed in the mold before pouring at a ratio of its mass to the mass of the casting 1: 4, and the heat treatment of the castings is carried out by self-annealing in the mold for at least 60 minutes before beatings. 2. The method according to claim 1, characterized in that a layer of casting paint on a graphite base 0.3 mm thick is applied to the metal refrigerator.

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