RU2533521C2 - Production of nanostructured carburiser carburising of iron-carbon alloys - Google Patents

Abstract

FIELD: metallurgy.

SUBSTANCE: invention relates to metallurgy. Proposed method comprises the analysis of initial carbon-containing stock components for fraction and chemical composition, proportioning, flushing with water flow, drying and grinding to 0.1…30.0 mm fraction. Ground composition is subjected to high specific pressure of up to 20 GPa and heated to 500…1500°C in reducing medium for 5…20 minutes. Then, smooth cooling sizing to fractions are performed. Then, heating is performed to 1800…2500°C along with holding and forced cooling at the rate of 1.5…3.0°C/min to the room temperatures to produce graphite nanostructures of 100 nm on carburiser particles to be packed in watertight container.

EFFECT: better carbon assimilation and uniform distribution of graphite phase in cast iron matrix, higher mechanical properties.

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Description

The invention relates to metallurgy, to foundry, to the processing of cast iron, to the processing in the molten state of iron-carbon alloys, and in particular, to methods for the production of nanostructured carburizers of high-strength cast iron with spherical graphite in melting units.

There are a number of ways to produce carburizers for the steel industry.

A known method of preparing a carburizing reagent for steel production (patent RU No. 767216), including mixing in the drum of metal shavings and pyrocarbonate, forming particles with a size of 15 ... 20 mm, pelletizing the dispersed metal-containing component in a mixture with a carbon-containing component and a binder, for example liquid glass or starch . The ratio of specific gravities of metal and carbon components is 3 ... 10.

The disadvantages of this method are the low carbon content and low strength of the particles of the carburizer, designed for a one-time movement, when used in the filling composition of the charge. In addition, the inevitable repeated transport rashes when used for precise alloying in the process of after-furnace treatment lead to excessive grinding of particles and increased cooling of the melt.

Also known is a method of manufacturing a carburizer for alloying steel with carbon in vacuum plants (PL patent No. 76738), comprising feeding a powdery carbon material, 2% starch and 10% water into the mixer, mixing them, molding the carburizer particles by compressing the mixture into arbitrary-shaped granules with a diameter of 3 ... 10 mm and further drying.

The disadvantages of this method are the low absorption of carbon and the lack of accuracy of the processing, due to the poor mechanical strength of the granules during transportation and use, and therefore, the presence of difficult to account for losses of the carburizer.

Also known is a method of manufacturing a carburizer for alloy steel with carbon in vacuum installations (patent RU No. 2073728), comprising feeding a powdery carbon-containing material to the mixer simultaneously with starch and water in the form of a colloidal solution, continuously stirring the components of the mixture, molding the particles and drying them, while the resulting pasty mixture, the mass ratio of carbon-containing material, starch and water is (50-60) :( 4: 3) :( 46-37), respectively.

However, the use in this method of substances such as a colloidal solution based on starch emulsion in water and wood chips in the manufacture of a paste-like mixture with subsequent shaping in the form of half cylinders, allows the use of a carburizer only in vacuum plants, which significantly reduces the scope of carburizer.

Also known is a method of manufacturing a carburizer used by Desulco for foundries (Germany). The known method includes the following operations:

- testing of raw materials;

- splitting up;

- sieving with subsequent analysis for compliance with chemical composition, purity and fractional size;

- high temperature annealing at temperatures above 2300 ° C;

- carburizer packaging.

The disadvantage of this method is the high-temperature heating of the carburizer without temporary regulation and the speed of subsequent cooling of the material. Without the application of specific pressure on the carbon-containing material, the formation of nanostructured carbon particles is not ensured, which reduces the efficiency of carbonization of ductile iron with spherical graphite. For this reason, the use of carburizing material obtained in a known manner is less effective and limited for practical use.

The invention is aimed at obtaining a nanostructured carburizer that improves the physicomechanical properties of ductile iron with spherical graphite.

For this, in the production method of a nanostructured carburizer for carburizing high-strength cast iron with spherical graphite, the components of the initial carbon-containing raw material are analyzed by fractional and chemical composition, dosing, washing with a stream of water, drying, crushing to a fraction of 0.1 ... 30.0 mm, after crushing, carbon-containing components subjected to high specific pressure up to 20 GPa and carry out the first high-temperature heating in a reducing medium at a temperature of 500 ... 1500 ° C for 5 ... 20 minutes, then pl it is cooled explicitly, dispersed into fractions, and then subjected to a second high-temperature heating in a reducing medium at a temperature of 1800 ... 2500 ° C, followed by exposure and forced cooling at a speed of 1.5 ... 3.0 degrees per minute to room temperature with the formation of graphite nanostructures up to 100 nm on particles of a carburizer and its subsequent packaging in a moisture-proof container.

As raw materials in the inventive method for the production of a nanostructured carburizer for carburizing high-strength cast iron with spherical graphite, traditional materials are used: anthracite, graphite scrap, electrode fight, graphite shavings and other carbon-containing components.

Before raw materials enter production, an analysis of the chemical composition and friction size of each of the types of starting materials is carried out. Based on the analysis, a dosage of each material is compiled according to the available formulation, so that the total carbon content is at least 85%. Then the raw components are washed with a stream of water under high pressure to reduce the ash content and further remove moisture by drying in a tumble dryer at a temperature of 100 ... 120 ° C.

After preparing the raw materials, the materials are crushed using a hammer mill to a fraction of 0.1 ... 30.0 mm. With a fraction up to 0.1 mm in size, carburizer particles make it difficult to enter the melt further, and materials with a fraction in excess of 30.0 mm impair melt solubility.

Then, the feedstock passes through the conveyor through the reactor, undergoing high specific pressure up to 20 GPa. High specific pressure allows breaking weak van der Waals bonds between graphite plates and preparing materials for subsequent temperature treatments. At pressures below 20 GPa, Van der Waals bonds between graphite plates are not destroyed.

After the reactor, the carbon-containing material is subjected to the first stage of high-temperature heating in a reducing medium at a temperature of 500 ... 1500 ° C for 5 ... 20 minutes to remove various impurities and volatile substances. At temperatures below 500 ° C, complete removal of impurities and volatile substances does not occur; at temperatures above 1500 ° C thermal stresses occur that prevent the fixation of graphite nanostructures on the faces of the carburizer.

A heating time of less than 5 minutes is not enough to remove volatiles and impurities; over 20 minutes to heat is impractical, since the removal of volatile substances and impurities is completed.

Then there is a smooth cooling of the carbon-containing material and sieving by fractions.

The repeated sieving of the carbon-containing material in fractions between the first and second high-temperature heating is carried out in order to isolate the carburizer particles with a fraction of less than 0.1 mm, which can form after the first stage of high-temperature heating. As a result of re-sieving, the fraction above the upper limit is subjected to additional grinding and sieving, and the fraction below the lower level is collected separately and subjected to dry granulation within the required fractions for further use as high-strength cast iron carbonizer.

Next, the material is subjected to the second stage of high-temperature heating at a temperature of 1800 ... 2500 ° C in special furnace units in a reducing environment, followed by exposure and forced cooling at a speed of 1.5 ... 3.0 degrees per minute to room temperature.

At temperatures below 1800 ° C, the formation of graphite nanoclusters from individual nanostructures does not occur. It is not practical to heat above 2500 ° C due to high energy consumption.

A cooling rate of less than 1.5 degrees per minute reduces the performance of the process; more than 3.0 degrees per minute leads to stresses in the structure of the carburizer.

As a result, graphite nanostructures are formed with parameters up to 100 nm, which are graphite nanoclusters with a hexagonal lattice. In this case, the nanocluster particles of graphite are located on the carbon-graphite macrocarrier - carburizer particles. The quality of the carburizer is checked by the main parameters:

1. Appearance - granular material of black color, shiny, without lumps and foreign inclusions.

2. Screen (granulometric) composition.

3. The chemical composition.

4. The presence of nanostructured graphite (up to 100 nm).

In the production of cast iron, OJSC KAMA-Metallurgy, tests of carburizers were carried out by the claimed and known method, selected as a prototype.

The results of the comparative characteristics of carburizers are shown in table 1.

For comparative data table it is evident that recarburiser obtained by the claimed method, is distinguished by a high degree of assimilation of carbon in the liquid metal melt at all levels: 97-99% vs. 95%, a uniform nucleation nucleation of graphite inclusions in cast iron: 250-400 per mm ² versus 200, the absence of the introduction of harmful impurities and gases into the molten metal, a lower absorption temperature of 1350-1450 ° C against 1500 ° C, as well as the presence of nanostructures at all levels.

A method of manufacturing a nanostructured carburizer for carburizing ductile iron with nodular graphite provides for the production of a nanostructured carburizer with a high carbon content.

The claimed technical solution in comparison with the known provides

- a higher degree of assimilation of carbon and a uniform distribution of the graphite phase in the metal matrix of iron casting due to the presence of nanostructures of graphite;

- an increase in physical and mechanical properties (such as tensile strength, elongation and hardness) in high-strength cast iron obtained from the initial melt is also due to the presence of graphite nanostructures.

Claims (1)

A method of manufacturing a nanostructured carburizer for carburization of ductile iron with spherical graphite, characterized in that they analyze the components of the initial carbon-containing raw materials by fractional and chemical composition, dosing, washing with a stream of water, drying and crushing to a fraction of 0.1 ... 30.0 mm, after crushing carbon-containing components are subjected to high specific pressure up to 20 GPa and the first high-temperature heating in a reducing medium at a temperature of 500 ... 1500 ° C for 5 ... 20 minutes, d then it is cooled smoothly and dispersed into fractions, after which it is subjected to a second high-temperature heating in a reducing medium at a temperature of 1800 ... 2500 ° C, followed by exposure and forced cooling at a rate of 1.5 ... 3.0 degrees per minute to room temperature with the formation of graphite nanostructures up to 100 nm on particles of a carburizer, which is packaged in a waterproof container.