RU2495134C2 - Method for obtaining nanostructured recarburising agent for out-of-furnace treatment of high-strength cast-iron with ball-shaped and compacted graphite - Google Patents

Abstract

FIELD: metallurgy.

SUBSTANCE: method involves preparation of carbon-containing composition containing the following components, wt %: anthracite 50-85, graphite scrap 5-25, broken electrodes 5-25, graphite structure 5-15 that is crushed to the fraction of 0.1-3.2 mm, burnt at the temperature of 500-1500°C, graphite spheroids are formed in the material structure at high specific pressure of up to 20 GPa and subject to high-temperature exposure at 1800-2500°C in a reducing medium so that graphite nanostructures with the size of up to 100 nm are formed, which represent graphite nanoclusters with a hexagonal pattern.

EFFECT: production of casts of responsible purpose from high-strength cast-irons.

2 tbl, 1 dwg

Description

The invention relates to metallurgy, to foundry, in particular to methods for producing a nanostructured carburizer for the out-of-furnace treatment of high-strength cast iron with spherical and vermicular graphite, used to adjust the composition of cast iron and steel by the carbon content smelted in foundries and steelmaking.

No analogues were found close to the claimed technical solution.

The invention is aimed at ensuring the production of castings for critical purposes from high-strength cast irons with spherical and vermicular graphite during subsequent out-of-furnace modifying treatment.

To implement the method of obtaining a nanostructured carburizer for out-of-furnace treatment of high-strength cast iron with spherical and vermicular graphite, a carbon-containing composition is prepared containing, wt.%: Anthracite 50-85, graphite scrap 5-25, electrode fight 5-25, and graphite shavings 5-15, which is crushed to a fraction of 0.1-3.2 mm, calcined at a temperature of 500-1500 ° C, form graphite spheroids in the structure of the material at high specific pressure up to 20 GPa and subjected to high temperature exposure at 1800-2500 ° C in a reducing environment f with the formation of graphite nanostructures up to 100 nm, which are graphite nanoclusters with a hexagonal lattice

Figure 1 shows graphite nanoclusters with a hexagonal lattice.

Currently, in the smelting of pig iron, there is a need to increase the carbon content by introducing a carburizer into a liquid metal. For carburization of metal, graphite and compositions are used, consisting of wastes of carbon-containing materials, coke, charcoal, etc.

To implement the inventive method for producing a nanostructured carburizer for the out-of-furnace treatment of high-strength cast iron with spherical and vermicular graphite, a carbon-containing composition is prepared containing, wt%: anthracite 50-85, graphite scrap 5-25, electrode battle 5-25 and graphite shavings 5-15. The components of this composition together provide the required degree of carbon uptake in the iron-carbon alloy.

Anthracite, which is part of the composition, is one of the main components of the carburizer, which determine the functionality and technological value of the entire carbon-containing material. The introduction of less than 50% into the composition of anthracite entails a decrease in the efficiency of carburization of the iron-carbon alloy and an increase in the absorption temperature. The presence of anthracite over 85% in the carburizer cannot be obtained.

Graphite scrap is an important component of a carburizer. When less than 5% is introduced into the composition, graphite scrap is unpromising - it is too small to ensure a uniform distribution of graphite layers as substrates for the growth of the graphite phase. When the content of graphite scrap is more than 25%, a temperature increase is necessary to assimilate the carburizer, which is technologically unacceptable.

Electrode battle is an important element in reducing the cost of production of a carburizer. Its presence of less than 5% has practically no effect on cost reduction. The introduction of an electrode battle of more than 25% leads to an increase in the total consumption of the carburizer and, consequently, to an overall increase in the cost price with satisfactory technological and operational indicators.

Graphite shavings are a finely divided component of a carburizer. The content of graphite chips less than 5% impairs the ability of the carburizer in the formation of centers of crystallization of the graphite phase in cast irons. The introduction of more than 15% of graphite shavings into the composition provokes the formation of "graphite spell" in cast irons, which is unacceptable in the further production of high-strength cast irons.

The inventive method of producing a nanostructured carburizer for secondary furnace treatment of ductile iron with spherical and vermicular graphite is carried out by a three-stage process.

In the first stage, the components of the carburizer: anthracite, graphite scrap, electrode breakdown and graphite shavings are crushed to a fraction of 0.1-3.2 mm and calcined in rotary calciners or rotary kilns of drum type at temperatures of 500-1500 ° C. When using fractions less than 0.1 mm, significant dust formation occurs, due to which the material consumption increases. Fraction of more than 3.2 mm - reduces the degree of assimilation of carbon from the material, due to the fact that it partially goes into furnace slag. The temperature range of 500-1500 ° C during calcination in rotary calcining furnaces or rotary kilns of drum type at temperatures is optimal for removing moisture and volatile substances from the material, while also improving the physical and mechanical properties. At annealing temperature below 500 ° C, the removal of volatile substances will not occur, above 1500 ° C - intense carbon from the material will begin.

At the second stage, calcined carbon-containing material in special reactors form graphite spheroids in the structure of the material at high specific pressure up to 20 GPa. At lower pressure, the formation of graphite spheroids in the material structure will not be ensured. It is rather difficult and economically inefficient to provide more pressure.

In the third step the material is subjected to high temperature aging - 1800-2500 ° C in a reducing atmosphere to form a graphite nanostructures to 100 nm, representing nanoclusters geksonalnoy graphite lattice. At temperatures below 1800 ° C, there will be no neutralization of molecular gases and the production of "high" purity graphite; temperatures above 2500 ° C are impractical due to significant energy consumption. In these furnaces, under the influence of a high-temperature factor, the formation of graphite nanostructures with parameters up to 100 nm occurs, which are graphite nanoclusters with a hexagonal lattice. The indicated sizes and shape of graphite are optimal for the formation of nuclei of vermicular and spherical graphite in cast iron. In this case, the nanocluster particles of graphite are located on a carbon-graphite macrocarrier - carburizer particles with a fraction of 0.1-3.2 mm.

An electron-microscopic study was performed using a Quanta 3D FEG scanning electron microscope (FEI double-beam SDB setup) in the magnification range × 10000 - × 100000. Samples for research were provided by KAMA-Metallurgy OJSC. Two samples of carbon powder material were compared:

- sample No. 1 (control) - crushed, dried, not activated graphite powder;

- sample No. 2 - crushed, dried, activated by processing at high temperature (~ 2000 ° C) and high pressure (up to 20 hPa).

The preparations were prepared by applying powder to the stage in the initial state, without subsequent blowing.

According to the test results, it was revealed that sample No. 1, which was not subjected to high specific pressure and high-temperature processing, has a pronounced large-crystalline layered structure characteristic of graphite.

Sample №2, are at high specific pressures and a high temperature treatment, showed the presence of spheroids (individual particles and clusters), including nanoscale - 100 nm, usually associated with larger particles of graphite.

The test results are shown in table 1.

Table 1 Test samples Material processing Structure Sample No. 1 No high temperature and pressure treatment Coarse-grained layered structure characteristic of graphite Sample No. 2 High temperature treatment (1800-2500 ° C) and pressure treatment (up to 20 GPa) The layered structure of spherulites, on the surface of which there are particles (droplets) of size 100 nm or less

In the production of cast iron, OJSC "KAMA-Metallurgy" were subjected to comparative tests of 3 variants of the composition of the proposed method. The results of the comparative data are shown in table 2.

table 2 No. p / p Name of material Absorption temperature, ° C The presence of cementite The nitrogen content in the metal,% Assimilation of carbon by weight of material,% one Option No. 1 of the composition (lower level) 1450 no 0.005 97 2 Option number 2 composition (intermediate level) 1400 no 0.004 98 3 Option No. 3 of the composition (upper level) 1350 no 0.003 99

According to the table of comparative data, it is obvious that all options are characterized by a high degree of carbon assimilation in a liquid metal melt at all levels: 97-99% versus 80%, uniform nucleation of crystallization centers of graphite inclusions, the absence of harmful impurities and gases in the metal melt, as well as lower temperature of carburization of the melt 1350-1450 ° C against 1500 ° C.

The claimed invention provides for the production of castings for critical purposes from high-strength cast irons with spherical and vermicular graphite with subsequent out-of-furnace modifying treatment by creating more graphitization centers.

The claimed technical solution has the following advantages:

- a higher degree of absorption of carbon;

- lower melt temperatures of the processed material;

- nanocluster structure of graphite with a hexagonal lattice for producing cast iron with spherical and vermicular graphite.

Claims (1)

A method of obtaining a nanostructured carburizer for out-of-furnace treatment of ductile iron with spherical and vermicular graphite, characterized in that a carbon-containing composition is prepared containing, wt.%: Anthracite 50-85, graphite scrap 5-25, electrode battle 5-25, graphite shavings 5-25 15, crushed to a fraction of 0.1-3.2 mm, calcined at a temperature of 500-1500 ° C, form graphite spheroids in the material structure at high specific pressure up to 20 GPa and subjected to high-temperature exposure at 1800-2500 ° C in a reducing medium f to form graphite nanostructures to 100 nm, representing a graphite nanoclusters with a hexagonal lattice.

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