RU1786088C - Process for alloying hot iron with nitrogen - Google Patents

Abstract

Usage: obtaining high-frequency cast iron castings. SUMMARY OF THE INVENTION: Urea is heated to 600-850 ° C before being fed into the molten iron. The proposed method allows to reduce the reagent consumption by more than two times and to improve the working conditions of foundry workers by providing a more smooth assimilation of the reagent and the absence of pyroeffect. 1 tab.

Description

g The invention relates to ferrous metallurgy and can be used in iron foundries of engineering plants.

A known method of modifying and alloying cast iron with nitrogen, in which nitrogen-containing substances are introduced with blast air into a smelting furnace.

The disadvantage of this method is the loss of nitrogen-containing substances due to oxidation by blast air.

There is also a known method of alloying cast iron with nitrogen by introducing into the melt a porous refractory impregnated with urea (urea).

The disadvantage of this method is that it is not suitable for the continuous processing of large quantities of cast iron under conditions of mass production. In addition, it is associated with a significant consumption of refractory bricks.

The closest technical solution to the invention is a method in which a nitrogen-containing substance (urea) is introduced into the cast iron by blowing through a refractory tube immersed in the metal. The disadvantage of this, as well as other known methods of alloying cast iron with nitrogen using solid carbamide, is that solid carbamide comes into direct contact with molten cast iron. Since the temperature of molten iron (1400-1450 ° C) is significantly higher than the temperature of intense gas evolution during thermal decomposition of urea (150-200 ° C), the interaction process becomes explosive. As a result, a significant part of the products of incomplete decomposition of urea is carried out on the metal surface and is not involved in the saturation of cast iron with nitrogen, and the decomposed part of urea does not have time to be completely absorbed by the metal due to the short duration of the processing process. All this leads to increased urea consumption and insufficient stability of the cast iron processing process.

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The purpose of the invention is to reduce reagent consumption and to ensure the stability of the assimilation process.

The goal is achieved in that the urea is preheated without access of air to 600-850 ° C.

The choice of a predetermined heating mode is explained by the following features of the thermal conversion of urea: when heated without air access to 120 ° C, the urea melts and ammonia begins to separate from it, and with a further increase in heating to 200 ° C, the gas evolution intensifies sharply. Upon completion of the evolution of ammonia, a solid residue forms, which at 600 ° C also passes into a gaseous state, but already quite calmly. The final thermal decomposition products of urea at 600-850 ° C are nitrogen, hydrogen and carbon monoxide.

Heating of urea above 850 ° C accelerates the reaction of its thermal decomposition, as a result of which the absorption of urea is impaired and its consumption is increased, and the stability of the cast iron processing process is impaired.

When heated with air, the urea ignites and completely burns out already at 400 ° C.

Known methods for alloying cast iron with nitrogen do not use carbamide preheating. Thus, the claimed technical solution satisfies the criterion of novelty.

The use of preheating of urea to a temperature lower than the temperature of the cast iron can significantly slow down the thermal decomposition process. In this case, the assimilation of gaseous products formed in cast iron is improved, and the losses of urea occurring in known methods are eliminated. with direct contact of carbamide with molten iron. The process of melt processing becomes calm, adjustable and proceeds stably with much less sparging and no pyroeffect. This allows us to conclude that the proposed method of alloying cast iron with nitrogen meets the criterion of significant differences.

Example. Cast iron was smelted in an induction furnace with a capacity of 30 kg and overheated

up to 1360 ° С according to the optical pyrometer without correction. The composition of the charge: 69.5% of cast iron of the LZ brand, 22% of the limit cast iron of the PVKZ brand, 8% of steel, 0.25% of ferromanganese and 0.25% of sulfur pyrite. Modifier - 0.4% FS75 ferrosilicon.

Carbamide in the form of briquettes weighing 1.3 g was introduced into the melt using a device consisting of a briquette dispenser, a sealed reaction chamber and a ceramic tube connected to it, immersed in the melt. The reaction chamber was heated by radiation from the surface of the molten iron in the furnace to 600-700 ° C.

For comparison, cast iron was also smelted using the same device, but with the reaction chamber turned off. In this case, the urea briquettes did not pre-heat, but fell from the batcher directly into a ceramic tube immersed in the molten iron.

In both melts, urea briquettes were fed into the device at a frequency necessary to maintain continuous bubbling of the molten metal.

During the experimental melts, samples for mechanical testing 30x300 were poured, the processing time and urea consumption were recorded. The metal was taken for pouring samples before the melt was treated with carbamide and after 100 and 200 s. after starting this processing.

The results of observations and analysis of experimental swimming trunks are given in the table.

The use of the proposed method for alloying cast iron with nitrogen makes it possible to reduce urea consumption by more than 2 times in comparison with known methods and ensures the stability of the process of assimilation of the reagent in the absence of pyroeffect.

Claims (1)

The claims A method of alloying cast iron with nitrogen, including treating its melt with carbamide, which is explained by the fact that, in order to reduce the reagent consumption and ensure the stability of the assimilation process, the carbamide is preheated without access of air to 600-850 ° C.