RU2113504C1 - Method for production of rail steel in electric furnaces - Google Patents

Abstract

FIELD: ferrous metallurgy; may be used in steel making for railroad rails in electric arc steel melting furnaces. SUBSTANCE: method includes melting of burden, and heat is subjected to oxidation and reduction. During reduction period, slag is deoxidized down to iron oxide content less than 3% with total amount of slag less than 2% of heat weight with basicity over 2.0. Melt is blown with nitrogen during reduction period. EFFECT: increased content of nitrogen in steel. 2 tbl

Description

 The invention relates to ferrous metallurgy and is intended for use in steelmaking in the smelting of steel for railway rails in electric arc furnace.

 A known method of production of nitrogen-containing steel in electric furnaces, selected as a prototype, is known, which involves loading charge materials, melting, oxidizing impurities, downloading oxidative slag, and then conducting a recovery period. An increase in the nitrogen content in the steel is carried out by blowing the melt into the oxidation period with nitrogen.

 There is also known a method of smelting rail steel in open-hearth furnaces using nitrided ferroalloys.

 It is also known that for the production of rails of low temperature reliability [2], an additive of nitrided ferroalloys is necessary to ensure the required nitrogen content.

 A significant disadvantage of this prototype is that to ensure the required nitrogen content, purging is carried out in the oxidation period under slags that impede the saturation of the steel with nitrogen. In this regard, it is not always possible to achieve the required nitrogen content in steel and the introduction of scarce and expensive nitrided ferroalloys is necessary.

 The essence of the patent is the production of low-temperature reliability rail steel in electric arc furnace without the use of nitrided ferroalloys.

 To achieve this, in the production of rail steel in electric furnaces to increase the nitrogen content in steel during the recovery period, slag is deoxidized to an iron oxide content of slag of less than 3% with a total amount of slag of less than 2% of the weight of the smelter with a basicity of more than 2.0, while purging metal with nitrogen.

An iron oxide content of more than 3% leads to a decrease in the nitrogen content in the steel due to the fact that oxygen cations prevent the penetration of nitrogen into the steel. An amount of slag of more than 2% leads to a decrease in the rate of nitrogen diffusion in the slag and, as a result, the absorption of the latter by steel decreases. The decrease in slag basicity (CaO / SiO ₂ ratio less than 2) leads to a decrease in the nitrogen content in steel, since the bond of nitrogen with silicon-oxygen ions is much weaker than with calcium ions, which, in turn, leads to a decrease in nitrogen in the slag and, as a consequence, in steel. The presence of oxygen in the metal melt slows down the dissolution of nitrogen, in connection with this, the purge is carried out on pre-deoxidized steel. The purge of steel with nitrogen during the recovery period increases the nitrogen content, firstly, due to the ionization of nitrogen atoms and the introduction of the latter into the melt, and secondly, due to the exposure of the metal from slag. Nitrogen purging of the steel allows increasing the nitrogen content in the steel to the required upper limits (0.012-0.020%). The complex of these measures allows to obtain the required nitrogen content in steel (0.008 - 0.020%) without the use of nitrided ferroalloys.

The proposed method was implemented in the smelting of NE76V rail steel of low temperature reliability in 100-ton electric arc furnace DSP-100I7. The metal was smelted according to the current TI 103-ES-388-91 with the following changes. After melting, the maximum possible amount of oxidizing slag was lowered from the furnace through the threshold of the working window and a new one was induced with a basicity of more than 2.0 in the amount of 2% of the weight of the heat. The slag was deoxidized in the furnace by additives of coke powder, crushed ferrosilicon of the FS75 grade and granular aluminum of the AB-88 grade in the amount of 0.8 - 1.2 kg / t of steel each, while the FeO content in the slag was less than 3%. The metal was deoxidized in the furnace using silicomanganese and ferrosilicon, and in the ladle, by silicocalcium and ferrovanadium. Nitrogen was blown into the furnace through tubes at a pressure of 5–7 atm and with a flow rate of up to 100 nm ³ / h; the blowing was carried out with partial exposure of metal from slag at the slag – metal interface in the arc zone.

 The data of some experimental swimming trunks with boundary, foreign and declared values are given in table. 1. In the swimming trunks carried out according to the inventive technology, the required nitrogen content is achieved. For comparison, the average data of 58 open-hearth rail melts melted using nitrided ferroalloys is given. The metal is poured into ingots of 8.5 tons and rolled onto P65 rails. The properties of steel smelted using the inventive technology and open-hearth steel smelted using nitrided ferrovanadium are given in Table 2.

Claims (1)

 A method of producing rail steel in electric furnaces, including melting the charge, maintaining oxidation and reduction periods, using nitrogen blown through the melt to increase the nitrogen content in steel, characterized in that during the recovery period, slag is deoxidized to an iron oxide content of less than 3% with a total amount of slag less than 2% of the weight of the heat, with a basicity of more than 2.0, moreover, the melt is purged with nitrogen during the recovery period.

Images