RU2634103C1 - Cast iron modification method - Google Patents

Abstract

FIELD: metallurgy.

SUBSTANCE: method of cast iron modification includes introduction of magnesium oxide into composition of lining of casting ladle and its reduction by silicon of liquid cast iron poured into ladle. Silicon-calcium and nano-structured diamond powder are additionally introduced into the ladle lining composition, said ingredients and magnesium oxide are preliminarily mixed and exposed to the action of a silent discharge with a strength of 700…1100 v/m in a boiling layer of materials, and reduction of magnesium from its oxide is performed jointly with nanostructured diamond powder and silicon of liquid cast iron, poured into ladle at temperature 1360…1400°C.

EFFECT: invention makes it possible to modify the cast iron without a pyroeffect by reducing magnesium from its oxide, reduce temperature of cast iron overheating before modification while reducing consumption of spheroidizing mixture, improve physico-mechanical properties of cast iron due to production of spherical graphite and grinding of metal matrix.

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Description

The invention relates to ferrous metallurgy, namely to foundry, and can be used in the production of high-strength cast irons and castings from them for critical purposes.

The prior art method for smelting iron-carbon alloys in induction furnaces, including filling the metal part of the charge, melting and alloying the melt with a complex mixture containing silicon and carbon (Pat. RF No. 2395589, 07/27/2010. Method for smelting iron-carbon alloys in induction furnaces / A. D. Podolchuk, M.I. Gasik, V.V. Serbin and others). The known technical solution allows to improve the technological process for the production of castings from synthetic cast irons due to the simultaneous pre-carbonization and graphitizing modification. However, the analogue does not provide a spheroidizing modifying effect on the molten iron.

The main element for spheroidizing modification of cast iron is magnesium. The treatment of cast iron with magnesium is usually accompanied by the formation of vapors of high elasticity, which requires the creation of special devices or the use of low percent (for magnesium) alloys to avoid a large pyroelectric effect and splashes of metal. Entering magnesium into cast iron in the form of chemical compounds with reducing agents eliminates the boiling process of magnesium. Atomic magnesium released as a result of the reduction reaction is in a state of high chemical activity and intensively interacts with the components of cast iron without accumulating in an independent phase.

The closest in technical essence and the achieved result is a method of modifying cast iron, including the reduction of magnesium oxide with silicon contained in cast iron, at a temperature of 1380 ... 1480 ° C. The lining of the casting ladle or its separate parts serves as a source of magnesium oxide compounds (Pat. RF No. 2058396, 04/30/1996. Method for the modification of cast iron / T.A. Shakhnazarov, N.N. Alexandrov, E.V. Kovalevich, etc.) . In this case, the difficulties associated with the environment and the scarcity of materials are eliminated, the process is simplified and cheapened. As a magnesium compound, cheap, non-deficient and non-sublimable magnesium oxide is used, and as a reducing agent, silicon, which is part of the treated cast iron. However, the prototype has the following significant disadvantages:

- low rate of reduction of magnesium from its oxide;

- high temperature of overheating of cast iron for modification;

- increased consumption of a spheroidizing mixture;

- low adhesion of the spheroidizing mixture to the main lining mass of the bucket;

- low absorption coefficient of magnesium;

- the absence of grinding the metal matrix of cast iron;

- a slight increase in the physico-mechanical properties of cast iron.

The technical problem is the basis of the invention - the creation of a method for modifying cast iron without pyroeffect by reducing magnesium from its oxide, which would provide a high rate of magnesium reduction, lowering the temperature of cast iron overheating before modification, while reducing the consumption of a spheroidizing mixture and, as a result of such complex modification (production of spherical graphite and grinding a metal matrix), increasing the physicomechanical properties of cast iron and improving the quality of castings made from it responsible appointment.

This problem is solved in such a way that in the method of modifying cast iron, comprising introducing magnesium oxide into the lining of the casting ladle and reducing it with silicon, molten iron, according to the invention, silicocalcium and nanostructured diamond powder are additionally introduced into the ladle lining, wherein said ingredients and magnesium oxide are pre-mixed and subjected a silent discharge of 700 ... 1100 V / m in a fluidized bed of materials, and the reduction of magnesium from its oxide is carried out jointly by silicon m of molten iron and nanostructured diamond powder at temperatures of 1360 ... 1400 ° C.

The additional introduction of silicocalcium and nanostructured diamond powder into the lining of the casting ladle provides an increase in the adhesion of the spheroidizing mixture to it due to the use of materials with a high specific surface, as well as grinding of the metal matrix of cast iron under the action of nanostructured carbon from diamond powder.

Pretreatment of a spheroidizing mixture consisting of magnesium oxide, silicocalcium and nanostructured diamond powder with a quiet discharge increases the rate of reduction of magnesium from its oxide in molten iron by accelerating the interaction between the components of the spheroidizing mixture.

The quiet discharge intensity of 700 ... 1100 V / m is optimal for increasing the degree of absorption of magnesium in molten iron.

The reduction of magnesium with a nanostructured diamond powder at temperatures of 1360 ... 1400 ° C reduces the superheat temperature for modifying cast iron and ensures a reduction in the consumption of a spheroidizing mixture due to the acceleration of the reaction.

As a result of complex modification of cast iron (obtaining spherical graphite and grinding of a metal matrix), conditions are created to increase the physicomechanical properties and improve the quality of manufacturing of castings for critical purposes from high-strength cast iron.

The method of modifying cast iron is as follows. First, a mixture is prepared by mixing magnesium oxide, silicocalcium and nanostructured diamond powder in a ratio of 1: 2.5: 0.1 by volume. Then the prepared dried mixture is subjected to a quiet discharge with an intensity of 700 ... 1100 V / m in a "fluidized bed" of materials. At an intensity of less than 700 V / m, the rate of reduction of magnesium from its oxide under the action of a spheroidizing mixture in liquid iron is negligible. If the intensity of a quiet discharge is more than 1100 V / m, then the energy costs for preparing a spheroidizing mixture increase. The activated mixture is used for lining the casting ladle. Cast iron is melted in an induction furnace, it is poured into a ladle and spheroidizing modification is carried out in it at a temperature of 1360 ... 1400 ° C for 2 ... 5 minutes depending on the volume of the melt.

At a melt modification temperature of more than 1400 ° C, the fumes of elements and energy costs increase significantly. At a melt temperature in the ladle less than 1360 ° C, the effect of spheroidizing modification of cast iron is weakly expressed.

The proposed method for modifying cast iron is illustrated by the following examples.

Example 1. A spheroidizing mixture of magnesium oxide, silicocalcium and nanostructured diamond powder was prepared in a ratio of 1: 2.5: 0.1 by volume by mixing these materials in a fluidized bed with simultaneous exposure to a quiet discharge. Quiet discharge intensity varied 700; 900; 1100 V / m. Then the casting ladle was lined with the activated mixture using liquid glass as a binder. The ladle was dried and calcined at a temperature of 800 ... 850 ° C.

Cast iron was smelted in an induction melting furnace with an acid lining. Molten iron was poured from the furnace into the ladle. At a temperature of 1400 ° C, the cast iron was kept in the ladle for modification for 2 ... 3 minutes. Then, the processed melt was poured to obtain samples in molds that were made from a sand-clay mixture with a moisture content of 3.5%. Determined: chemical composition of cast iron (C = 3.5%; Si = 2.5%; Mn = 0.6%; P = 0.08%; S = 0.01%; Mg = 0.07%), form graphite is a globular, metal matrix is perlite-ferrite. According to GOST 3443-87 "Castings from cast iron with various forms of graphite. Methods for determining the structure "according to the form of inclusion of graphite correspond to SHGf5, according to the size of graphite SHGd15, the distribution of graphite SHGr1; structure of a metal matrix P80 (F20). To assess the structure and mechanical tests, cylindrical samples with a diameter of 30 mm and a length of 200 mm were obtained. Strength tests were carried out on an INSTRON tensile testing machine at a tensile speed of 2 mm / min. Whitening was determined by a wedge-shaped sample, fluidity - by a spiral test (GOST 16438-70). For comparison, iron was smelted in an induction furnace according to the prototype.

The influence of the considered methods of modification on the structure and properties of cast iron are presented in table 1.

Example 2. Modification of cast iron was carried out analogously to example 1, while the intensity of the quiet discharge during processing of the spheroidizing mixture was 800 V / m The temperature of the molten iron was varied upon modification of 1360; 1390; 1400 ° C. The influence of this parameter on the structure and properties of cast iron is presented in table 2.

Thus, the obtained results show that the developed method improves the physicomechanical and casting properties of cast iron by complex modification of cast iron (obtaining spherical graphite and grinding the metal matrix) with a spheroidizing mixture of magnesium oxide, silicocalcium and nanostructured diamond powder activated by a quiet discharge and introduced into the lining of the casting ladle, at a temperature of 1360 ... 1400 ° C.

Claims (1)

A method of modifying cast iron, comprising introducing magnesium oxide into the lining of the casting ladle and restoring it with silicon, liquid cast iron poured into the ladle, characterized in that silicocalcium and nanostructured diamond powder are additionally added to the lining of the ladle, said ingredients and magnesium oxide being pre-mixed and subjected to a quiet discharge of 700 ... 1100 V / m in a fluidized bed of materials, and the reduction of magnesium from its oxide is carried out jointly by nanostructured diamond powder and silicon cast iron, poured into the ladle at a temperature of 1360 ... 1400 ° C.