RU2277589C2 - Modifying master alloy for cast iron producing method - Google Patents

Abstract

FIELD: metallurgy, namely foundry, particularly processes for obtaining magnesium-containing modifying agents used for producing cast iron with spheroidal graphite.

SUBSTANCE: method comprises steps of preparing, heating, pouring and crystallizing melt under protective flux. Melt is heated till temperature higher than liquidus temperature t1 by 10 - 99°C; pressure value is in range 10^-3 - 0.9 x 10^-1 MPa. Invention allows prepare modifying master alloy with easy-to-melt magnesium-containing component, with high density and uniform distribution of properties in the whole volume.

EFFECT: improved properties of master alloy at minimum consumption of materials.

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Description

The invention relates to the field of foundry, in particular to methods for producing modifiers used to produce spheroidal cast iron.

In foundry, they are widely used as additives for the main melt of the ligature, including ferroalloys. These ligatures are used either to introduce useful alloying elements, or to remove or bind harmful elements, or to introduce components that have a modifying effect.

Fused modifiers for the formation of spherical graphite in cast irons usually consist of a base (most often ferrosilicon or ferronickel), which contains active elements (most often magnesium or magnesium together with rare-earth metals).

For example, a method for producing a complex modifier in an induction crucible furnace is known, including preparing the furnace, loading ferrosilicon and silicocalcium, melting and removing slag, pouring it into a weighing bucket, pouring granulated magnesium into the ladle reactor and casting it into the molds. Moreover, the preparation of the melting furnace includes repeated operations of draining and penetration of materials (RF Patent No. 2058397, IPC C 21 C 1/00, publication 04/20/1996).

The multioperability and complexity of this method makes it non-technological, unstable in relation to the quality of the resulting modifier, which prevents its wide industrial application.

There is also a method of producing a modifier of cast iron based on ferrosilicon. The method includes obtaining a base alloy, which additionally contains cerium, magnesium and aluminum, while oxygen is added to the base alloy in the form of one or more metal oxides and sulfur in the form of one or more metal sulfides (RF Patent No. 2172782, IPC С 21 С 1 / 10, published on August 27, 2001). The invention allows to increase the number of crystallization centers formed by adding a modifier to cast iron, as well as to improve reproducibility with respect to the formation of crystallization centers.

However, the modifiers obtained by this method are also characterized by great heterogeneity in quality, in particular in chemical composition, especially during long-term storage and transportation.

The closest technical solution is a method of producing a ligature, including melting the mixture, heating the melt above the melting temperature by 100-400 °, pouring and crystallization under a pressure of 0.1-200 MPa with a cooling rate of 10-10 ⁴ ° C / s, while the alloying components are introduced in an amount exceeding the calculated concentration by 1.2-2 times, the melt is held at elevated temperature with stirring for 3-5 minutes, then the concentration of alloying elements is reduced to the calculated one with a simultaneous decrease in the temperature melt is determined by the formula; crystallization of the melt is carried out in a force field of an unevenly distributed pressure of centrifugal forces (RF Patent 2111276, IPC С 22 С 1/02, publication of 05.20.1998 Bull. No. 14).

The method provides a high degree of grinding of intermetallic phases, increasing productivity and reducing the cost of the process.

The reasons limiting the widespread use of the method in the production of modifying ligatures with a low-melting Mg-containing component are high magnesium waste, the complexity and high cost of equipment for safe and reliable operation at high pressures, and the unstable quality of the surface layers of the ligature, especially ferronickel-based modifiers.

An object of the invention is to provide a method for the production of Mg-containing modifying ligatures, eliminating these disadvantages and providing simplicity and reliability of manufacture, reducing the cost of the product by reducing material consumption while maintaining stability and uniformity of the obtained properties.

The technical result from the implementation of the invention is to obtain a modifying ligature with a high density and uniform distribution of properties by volume at minimum cost, which provides an increase in the percentage of yield of the product.

The specified technical result is ensured by the fact that in the method of producing the modifying ligature, including the preparation, heating, pouring and crystallization of the melt under pressure in the field of centrifugal forces, all operations are carried out under a protective flux, while the melt is heated 10-99 ° C above temperature t ₁ , and the pressure is 10 ⁻³ −0.9 · 10 ⁻¹ MPa.

Carrying out the processes of preparation, heating, pouring and crystallization under flux allows you to reduce the evaporation and fumes of magnesium, due to which - to reduce its consumption and reduce the pyroelectric effect of these operations, reduce the cost of cleaning furnace gases production.

Submerged crystallization, in addition, allows you to create the necessary pressure in the surface layers on the inner diameter of the centrifugal casting of the ligature, thereby ensuring the necessary purity, increasing the uniformity of the density of the casting in thickness and increasing the yield of the product.

Heating the melt above a temperature of t ₁ above 99 ° C does not allow processes to be carried out without significant evaporation and fumes of magnesium and pyroelectric effect. Heating the melt above a temperature of t ₁ less than 10 ° C leads to the formation of crusts on the crucible, complicates the process, reduces the yield of the product.

Crystallization of the alloy under pressure below 10 ^-3 MPa does not provide uniform density across the thickness of the casting. Crystallization of the alloy under pressure above 0.9 · 10 ^-1 MPa is not advisable, since the increase in the uniformity of the density of the casting in the thickness is not significant, and the equipment to achieve such pressures is significantly complicated.

Example 1. The melt of the modifying ligature composition: 5% Mg, 45% Ni, 1% REM, 2% C, 1% Si, 0.3% P, the rest Fe, having t ₁ ≈ 1170 ° C, t _s ≈1060 ° C, prepared in an induction furnace IST-0.16 with a graphite crucible. Preparation, heating and crystallization of the melt was carried out under a flux layer of MHZ (chloride-containing flux produced by the Mendeleev Chemical Plant) with various heating and crystallization parameters.

For comparison, melting was carried out according to the known method with preliminary preparation of the melt composition; 7.5% Mg, 67.5% Ni, 1.5% REM, 1.3% C, 0.7% Si, 0.2% P, the rest Fe, with melt overheating above t ₁ at 200 ° C ( 1370 ° C), followed by dilution and cooling with cast iron to obtain a melt with a calculated content of elements corresponding to the base.

Casting according to all options was carried out at a temperature of 1225 ° C by centrifugal casting.

The results obtained with various options for the manufacture of ligatures are presented in table 1.

Table 1 The method of obtaining the ligature No. var. ΔT heating above t ₁ , ° C The pressure on the outer diameter of the ligature casting, MPa Pressure on the inner diameter of the ligature cast, MPa Magnesium Fume,% Product Yield,% Proposed one 10 0,047 0.001 7 94.1 2 55 0,075 0.007 9 95.3 3 99 0,090 0.001 13 94.7 Famous four 200 0.17 - 25 92.2

Claims (1)

A method of producing a magnesium-containing modifying ligature for cast iron, including the preparation, heating, pouring and crystallization of a melt under pressure in a centrifugal force field, characterized in that the preparation, heating, pouring and crystallization of the melt is carried out under a protective flux, while the melt is heated for 10-99 ° C above the liquidus temperature t ₁ , and the pressure value is 10 ^-3 ÷ 0.9 · 10 ^-1 MPA.