SU1163973A1 - Inoculating flux for alloy cast iron - Google Patents

Abstract

MODIFIED FLUX FOR DURABLE IRON, including crushed cryolite and ferroalloy, characterized in that, in order to reduce churned in cast iron and chromium-doped castings, the flux as a ferroalloy contains FS-75 ferrosilicon and, in addition, a nonmagnetic fraction of cast iron and a cast iron. , wt.%; 27-35 Cryolite Non-magnetic fraction of iron 3–5 shavings Ferrosilicon ko Else FS-75

Description

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The invention relates to foundry and can be used mainly in the centrifugal casting of blanks of alloyed iron in the chill mold, lined with bulk insulating materials.

The purpose of the invention is to reduce chill off in cast iron and chromium alloy castings.

6 batches of 50 castings were cast, each cylinder liner D-240, weight. castings 12kg. Cast iron contains chromium 0.4 and copper 0.5%. The first three batches were cast using the well-known G 31 flux (without the non-magnetic fraction of iron shavings), three subsequent batches using the new flux containing cryolite, FS-75 ferrosilicon, and the non-magnetic fraction of the iron chips in quantities corresponding to the average boundary and close boundary values.

The flux was dosed onto a stream of metal in the amount of 0.5% by weight of the metal being poured. The pilot billets were cast on a 20-position casting ring conveyor in molds lined with bulk heat insulating materials (ferrochromic core - 0.7 mm thick layer and cast iron chips with 5% nitrate - 1.2 mm layer). Dosing of liquid iron was made from magnetodynamic pumps. The metal pouring temperature is 1350-1370 ° С.

The compositions of the fluxes and the results of research on the quality of the experimental castings are given in Table. one.

It can be seen that the use of a known flux leads to scrap casting for bleaching (4-6%), while a flux containing a non-magnetic fraction of iron shavings completely eliminates this type of scrap.

The non-magnetic fraction is obtained by grinding iron castings in a ball mill to fractions of 0.05-0.60 mm, followed by separation on an electromagnetic separator. Before preparing the flux, all its components are melted at 120-150 ° C for 0.5 h, then they are loaded into a mixer of the SGU-400 type in a proportioned ratio and mixed for 3-5 minutes. During this time, the cryolite and non-magnetic fraction are evenly distributed in the volume of ferrosilicon.

The prepared flux is loaded into a special dispenser, which provides it to the metal stream when the rotational shape is filled with an alloy. The optimal amount of flux ranges from 0.4 to 0.6%. When you enter the flux in the metal in-quantity. less than 0.4%, its incomplete modification takes place; in the structure of the metal, cementite is observed in the amount of 2-3% of the ground area, which contributes to the bleaching of castings.

When you enter the flux in the metal in quantities of more than 0.6%. an increase in ferrite content is observed in the cast structure. It is known that cementite and ferrite adversely affect the wear resistance and other operational characteristics of castings.

When dispensing a flux of metal to be poured, falling into a rotating form, it is emulsified by centrifugal forces in the metal, as a result of which the surface of the interaction of the metal with the flux increases.

The nonmetallic component of the flux, cryolite, protects the cast alloy and modifiers from oxidation, refines the metal from harmful impurities and nonmetallic inclusions, and also insulates the free surface of the metal, creating the most favorable conditions for its direction from the external surface to internal solidification.

Ferrosilicon, which is part of the flux, is the main modifying additive that promotes the formation of the pearlite structure of the cast metal.

In the flux composition, the nonmagnetic fraction of the iron chips serves as a stabilizer of the metal structure, contributes to the formation of the casting structure without chill and reduces thermal stresses in the workpiece.

Ferromanganese, which is included in the composition of the non-magnetic fraction, is a dopant, dissolves in the liquid metal and crushes the metal grain, helping to increase the durability of the product. Other impurities, which are part of the non-magnetic fraction, predispose themselves (naturally, oxides of iron, silicon, manganese and other

elements that make up the pig iron are dissolved in liquid cryolite, facilitating the process of refining the liquid metal from harmful impurities and gases.

The quantitative optimal composition of the proposed flux has been tested experimentally, the results of experiments with fluxes of various compositions are given in Table. 2

The optimal amount of cryolite varies between 27-35% and depends on its modulus. With the cryolite module 1.7, it is necessary to introduce it into the composition of the flux in the amount of 27-30%, and with the module 1.5 it is necessary to increase it to 31-35%

With the introduction of cryolite in the composition. less than 27% of the flux, ferrosilicon increases, which contributes to the chipping of the ends of the casting, and with the introduction of more than 35%, fluxing of the lining of casting devices is observed, which reduces their durability.

The amount of ferrosilicon used depends on the fraction of its grinding and ranges from 60-70%. After grinding-ferrosilica in a ball mill using a set of sieves, it is established the particle size distribution. The maximum permissible particle size of ferrosilicon is 0.05-2 mm. When the content of the fraction is 0.05, -0.1 mm more than 10%, 60-65% ferrosilicon must be added to the flux composition, and when the content of this fraction is 5-9%, the content of ferrosilicon must be increased to 66-70%. With the introduction of ferrosilicon less than 60%, an increase in the content of cementite is observed, and with the introduction of more than 70%, an increase in the content of ferrite in the cast metal structure is observed. Both cementite and ferrite adversely affect the durability of cast iron products.

The amount of non-magnetic fraction in the composition of the flux also depends on the particle size distribution of ferrosilicon.

With a content of the fraction of 0.050, 1 mm over 10%, a 3% non-magnetic fraction is used, and with a content of 5-9% it is increased to 4-5%.

When using non-magnetic fraction in the composition of the modifying flux

less than 3%, the formation of cementite is observed in the structure of the metallic cast iron base, and when using more than 15%, an increase in the size of graphite inclusions in the microstructure of cast iron is observed. Both cementite and magnification of the size of graphite inclusions adversely affect the wear resistance of cast iron products.

Stable results on the structure of castings and the quality of finished products are provided by using a non-magnetic fraction of cast iron chips made of cast iron of the grade СЧ 36 and СЧ 40, which contain a limited number of carbide-forming alloying elements, such as manganese and chromium, which contribute to the formation of chill bleach.

In tab. Figure 3 shows the effect of the composition of the non-magnetic fraction with the indication of the boundary and average values of its components on the quality of the casting of cylinder liners obtained using a modified flux of the following composition, wt.%: Cryolite 31, FS-75 65 ferrosilicon, non-magnetic fraction 4 (the number of castings in each batch of 100 pieces).

From tab. 3, it can be seen that the use of a non-magnetic fraction of iron shavings with a content of components within the specified limits ensures the production of castings of cylinder liners of the required structure (without bleaching). When the content of manganese over 16%, the formation of chill on the ends of the casting is possible. Other impurities, which are mainly oxides of the metals that make up the chips, do not have a significant effect on the quality of the casting, since they are converted to the flux when the alloy is modified. The boundary content of ferrosilicon, ferromanganese, and carbon in the non-magnetic fraction depends on the content of these elements in the iron shavings, which is determined by the specifications for this material.

According to preliminary calculations, the expected economic effect from the introduction of the proposed composition by reducing rejects for bleaching and cracks will be 2-3 rubles. per ton of good to pour.

Table 1

0

Metal oxides 17, ferrosilicochrome-55, cryolite-28

Also

0

0

26

70

55

41

60

36

2 3

Cryolite 27

Ferrosilicon 70 is missing in the casting. Non-magnetic fraction 3

Cryolite 31

The same Ferrosilicium 65 Non-magnetic fraction 4

Cryolite 35 Ferrosilicon 60 Non-magnetic fraction 5

table 2

Increased chill chill formation

The required cast metal structure is provided.

Reduced durability of casting devices

Chances of churning castings increase

The required structure of the cast metal is provided.

65 70

31 26 21

75

65

33 32

6.5

27

f3

Continued table. 2

Reduced wear resistance

products

Reduced wear resistance

products

The required metal structure is ensured.

Table E

53.5

An alarming metal structure is provided.

Claims (1)

MODIFICATION FLUX FOR ALLOY IRONED IRON, including crushed cryolite and ferroalloy, characterized in that, in order to reduce bleached in castings made of copper and chromium cast iron, the flux contains ferrosilicon FS-75 as a ferroalloy and additionally a non-magnetic fraction of the cast iron chips with the following ingredients , wt.%: Cryolite 27-35 Non-magnetic fraction of cast iron shavings 3-5 Ferrosilicon FS-75 Else 1 163973