RU2494152C2 - Method of iron carbonisation by means of nano-structured carboniser - Google Patents

Abstract

FIELD: metallurgy.

SUBSTANCE: proposed method comprises smelting of iron initial melt in the furnace, injecting carboniser and discharge of metal melt. Note here that iron initial melt is smelt in arc induction furnaces. Besides, gas cupola furnaces with fore hearth are used to overheat said melt at the temperature higher than that of liquidus by 10-400°C as well as carbonizer with nano-structured graphite particles sized to 0.00001…0.01 mcm in amount of 0.0001 - 0.01% for formation of preset concentration of graphite phase formation centers.

EFFECT: iron-carbon alloy with high mechanical properties and carbonisation, no pyro-effects, better environmental conditions of ironmaking.

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Description

The invention relates to metallurgy and foundry, in particular to methods for producing cast iron with a high carbon content in electric arc, induction furnaces and gas cupolas with a piggy bank.

There are various methods for carburizing alloys.

Known, for example, a method of carburizing cast iron (patent RU 2191832 s21c 1/08), with the aim of maximum contact of the molten metal with particles of the carburetor.

Closest to the claimed technical solution for the dimension of the carburizing component is the "Method for producing an alloy with free and bound carbon", patent RU 2196187. This method includes the smelting of low-carbon intermediate, overheating it above liquidus temperature by 20-70 °, the release of the melt, carbonization with soot with particle size 10 ⁵ -10 ⁷ cm, added to the melt in an amount of 0.01-2.14%, with the release and / or debugging, and / or casting, deoxidation elements, finishing, crystallization and alloy processing pressure and cooling blotched va lead during casting and crystallization to 1147 ° C at a rate greater than 10 degrees per minute.

The disadvantages of this method are the complexity of the process and the high cost of execution. The problem is the introduction into the melt of dispersed soot, easily sublimated by hot air currents, with a fraction of 10 ^-5 -10 ^-7 cm. The laboriousness of introducing soot into the melt does not ensure the stability of the entire technological process of carburizing the alloy.

The claimed invention is aimed at creating a sustainable method for carburizing iron-carbon alloys with nanostructured carburizers, at increasing the physicomechanical properties of alloys.

To solve the problem in a method for carburizing cast iron using a nanostructured carburizer, including smelting the cast iron, injection of the carburizer and the release of the melt, smelting the initial molten iron in electric arc induction furnaces in gas cupolas with a piggy bank melt overheats at a temperature above the liquidus temperature above 10 ... 400 ° C and use a carburizer with nanostructured graphite particles located on its surface with a size of 0.00 001 ... 0.01 μm and in an amount of 0.0001-0.01%, ensuring the formation of a given concentration of centers of nucleation of the graphite phase.

The method of carburization of iron-carbon alloys is based on the use of a nanostructured carburizer and consists of the following operations.

1. Smelting of the initial melt in electric arc, induction furnaces and gas cupolas with a piggy bank.

2. Overheating at a temperature above the liquidus temperature by 10 ... 400 ° C.

3. Injection input of a nanostructured carburizer with nanostructured graphite particles located on its surface with a size of 0.00001 ... 0.01 μm and in an amount of 0.0001-0.01%.

4. Subsequent release of metal.

After these operations, an exposure is transferred to the oven, fine-tuning by temperature and chemical composition, release of metal into the casting ladle, and pouring metal into casting molds.

Overheating of the alloy below 10 ° C above the liquidus line does not allow for the homogeneity of the liquid state of the melt when the carburizer is introduced, which reduces the carburization efficiency.

Overheating of the alloy above 400 ° C over the liquidus line increases the carbon monoxide burn and reduces the efficiency of the process.

The introduction of nanostructured particles into the iron-carbon alloy in an amount of 0.0001-0.01% ensures stable assimilation of carbon.

The introduction of nanostructured carburizer particles in an amount less than 0.0001% does not provide the possibility of the formation of the required number of centers of nucleation of the graphite phase, thereby the effect of carbonization of the iron-carbon alloy is insufficient.

The introduction of nanostructured carburizer particles in an amount greater than 0.01% causes an excessive concentration of the graphite phase in the iron-carbon alloy, which negatively affects the technological properties (fluidity), physical and mechanical properties (hardness, tensile strength).

Nanoparticles with sizes up to 0.00001 μm do not significantly increase the graphitizing effect in cast irons and the formation of an insufficient number of nucleation centers of the graphite phase is observed. Nanoparticles larger than 0.01 μm extend beyond the boundaries of the nanoparticles and over this size the graphitizing effect is reduced and there is no increase in the formation of centers of nucleation of the graphite phase.

The mechanism of action of a nanostructured carburizer is that when a particle of a carburizer enters a molten iron, the nanostructured elements are separated from the surface of the carburizer by thermal stresses and form a nucleus of graphite inclusion in a liquid metal. In this case, there is a cluster mechanism of nucleation and growth of small graphite crystals from the melt. The basis of this mechanism is bicluster reactions during crystallization:

$$\begin{array}{l}{\alpha }_{\text{n}}\text{+}{\alpha }_{\text{n}}\to \text{2}{\alpha }_{\text{n}}\\ {\alpha }_{\text{n}}\text{+2}{\alpha }_{\text{n}}\to \text{3}{\alpha }_{\text{n}}\\ {\alpha }_{\text{n}}\text{+3}{\alpha }_{\text{n}}\to \text{four}{\alpha }_{\text{n}}\\ ........................\\ {\alpha }_{\text{n}}\text{+ i}{\alpha }_{\text{n}}\to \text{(i + 1)}{\alpha }_{\text{n}}\end{array}$$

Where

α _n is a cluster in the liquid phase;

2α _n is an elementary crystal obtained by the fusion of two clusters;

iα _n is an intergrowth crystal;

i is the number of clusters.

The crystal growth mechanism due to the attachment of small crystals to larger crystals is characteristic of slow growth conditions in the presence of small supercooling and a solid-liquid zone in castings, which is most typical for alloys crystallizing under conditions of mass nucleation of crystallization centers, it is the competitive growth mechanism that is responsible for their intergrowth and enlargement of the primary crystalline structure of castings.

A balanced amount of nanostructured particles leads to the formation of a uniform structure of the iron-carbon alloy (graphite phase + metal matrix), which provides the conditions for achieving high physical and mechanical properties in cast iron.

The proposed method of carburization provides a high degree of assimilation of carbon in the alloy in a wide temperature range (1350-1650 ° C) and allows you to stably achieve the duration of the carburization effect (over two hours).

In this process, the pyroeffect and sublimation of finely dispersed particles of the carburizer above the metal mirror are absent, which improves the environmental conditions of carburization of the iron-carbon alloy.

The proposed method for carburizing cast iron using a nanostructured carburizer was subjected to comparative tests with the known method (patent RU 2196187) based on the initial melts prepared in electric arc, induction furnaces, as well as in a gas cupola with a piggy bank.

The results of comparative tests are shown in table 1.

The results of comparative tests show that the inventive method of carburization allows for more efficient technological increase in carbon content, to increase the retention time of the carburization effect, which is especially important in the production of high-quality castings without additional operations - pressure alloy processing, forced cooling (to provide an increased crystallization rate), and also the proposed method ensures the environmental applicability of the process without dust and grap suspended suspension in the air of the working area.

The inventive method of carburizing cast iron using a nanostructured carburizer

- provides cast iron with high physical and mechanical properties (tensile strength, relative elongation) due to the high degree of carburization;

- it is stable due to the long-term effect of maintaining the degree of carburization and the absence of pyroeffect;

- does not involve additional pressure treatment, since no regulation is required to control the cooling rate and subsequent crystallization of the iron-carbon alloy;

- improves the environmental conditions of the carburization process.

Claims (1)

A method of carburizing cast iron using a nanostructured carburizer, including smelting the initial cast iron melt, injecting the carburizer and releasing the metal melt, characterized in that when the initial molten iron is melted in electric arc, induction furnaces or gas cupolas with a piggy bank, the melt is overheated at a temperature above the liquidus temperature at 10-400 ° C and use a carburizer with nanostructured graphite particles located on its surface with size m 0.00001-0.01 microns and in an amount of 0.0001-0.01%, ensuring the formation of a given concentration of centers of nucleation of the graphite phase.