RU2630101C1 - Method for melting high-chromium steels and alloys in open induction furnaces - Google Patents

Abstract

FIELD: metallurgy.

SUBSTANCE: method includes pouring the charge, melting thereof, introducing slag-forming materials into the furnace, preliminary deoxidation, alloying the melt, absorption of alloying elements, final deoxidation, slag loading and casting into the ladle. At the end of alloying after absorption of alloying elements with melt temperature not higher than 1600°C, chromium and alloying elements that increase the solubility of nitrogen in iron are injected simultaneously, and after absorption, the final deoxidation, slag loading and casting into the ladle are carried out for 5-7 minutes. After the introduction of each portion, the slag-forming mixture is additionally fed in the melt in an amount of 1-3% of the portion weight.

EFFECT: invention allows to reduce nitrogen content in high-chromium steels and alloys melted in open induction furnaces.

4 cl, 1 tbl

Description

The invention relates to the field of metallurgy and can be used in the smelting in open induction furnaces of high-chromium heat-resistant steels with a low nitrogen content.

Known methods for smelting high-chromium steels and alloys in vacuum induction furnaces, which allow to obtain a metal with a low nitrogen content.

(RU 2373297, С22В 9/20, С22С 38/50, published November 20, 2009, RU 2469117, С22С 38/18, С22С 1/02, published December 10, 2012)

However, the cost of smelting in a vacuum induction furnace is several times higher than the cost of smelting in an open induction furnace. Moreover, the duration of vacuum smelting compared to the duration of smelting in an open induction is 2.5-3 times higher.

A known method of smelting high-chromium heat-resistant steel in an open induction furnace.

(RU 2579710, С22С 38/60, С22С 38/50, published on 04/10/2016)

However, the implementation of this method in an open induction furnace requires the use of only pure charge materials. At the same time, the use of metal, which was in operation and highly oxidized components, is unacceptable.

The closest in technical essence is a method of smelting high-chromium heat-resistant steel in an open induction furnace, including filling the mixture, melting it, introducing chromium at the end of melting of the mixture (after the mixture is sintered 0.5-0.7 in height of the crucible), melting, introducing slag-forming components, preliminary deoxidation, introduction of alloying components, their assimilation, final deoxidation, slag downloading and pouring into the ladle.

(Collection of technological instructions for the smelting and casting of heat-resistant, precision steels and alloys in an arc and induction furnace, Minchermet USSR, Dneprspetsstal plant, Zaporizhia, 1983, p. 99-105, p. 167-172)

A disadvantage of the known methods for smelting high-chromium steels and alloys in open induction furnaces is, even taking into account a fairly short smelting time, an increase in the concentration of nitrogen in the steel being smelted due to the absorption of nitrogen from the air. This leads to the precipitation of coarse particles of nitrides and carbides of the Me ₂₃ C _{6 type} along grain boundaries and the formation of united boundary zones, which reduces the strength characteristics of the metal, in particular, the time to failure of the metal under stress by more than an order of magnitude. Therefore, the nitrogen content in high-chromium heat-resistant steels should be limited to 0.02-0.025 wt. %

The objective and technical result of the invention is to reduce the nitrogen content in high-chromium steels and alloys smelted in open induction furnaces to a nitrogen content of 0.02-0.025% in the metal.

The technical result is achieved by the fact that the method of smelting high-chromium steels and alloys in open induction furnaces includes filling the charge, melting it, introducing slag-forming materials into the furnace, preliminary deoxidation, alloying of the melt, assimilation of alloying components, final deoxidation, downloading slag and pouring into the ladle, at the end of alloying after assimilation of the alloying components at a melt temperature of no higher than 1600 ° C, chrome and alloying components are added in portions to increase the solution Axle nitrogen in iron, and after digestion for no more than 5-7 minutes final deoxidation is performed, deslagging and pouring into the ladle, and after the introduction of each portion in the melt is additionally fed slagging mixture in an amount of 1-3% by weight of the portion.

The technical result is also achieved by the fact that as an alloying component that increases the solubility of nitrogen in iron, use vanadium, niobium and titanium; the nitrogen content in the charge materials is not more than 0.015 wt. %, and as a slag-forming mixture using a mixture of calcium oxide and fluoride in a ratio of 1: 1 or a mixture of aluminum powder, oxide and calcium fluoride in a ratio of 1: 1: 1 - 1: 1: 2. The invention can be illustrated by the following example.

Smelting of heat-resistant steel 08X14H4M2D was carried out on pure charge components. This steel may contain up to 0.12 wt. % nitrogen with a dense defect-free metal structure.

Materials with a low nitrogen content were used as charge components: ferrochrome carbon-free grade ФХ002; electrolytic nickel grade N-1; Iron type "Armco"; MShV brand molybdenum; NBS grade niobium; copper cathode; electrolytic manganese grade MPO; ferrosilicon FS 75; primary and rare-earth metals (REM) aluminum grade MTs 50ZhZ. You can use chrome instead of ferrochrome, such as X99, or X98.5, it is even cleaner and better, only much more expensive. The nitrogen content in nickel, copper, manganese, niobium, ferrosilicon, aluminum and rare-earth metals did not exceed 0.003% and in accordance with the requirements of GOST. The nitrogen content in the electrode battle did not exceed 0.05 wt. %, and the amount of nitrogen introduced by it is 0.006 g. The nitrogen content in iron did not exceed 0.015 wt. %

As the slag-forming materials used a mixture of calcium oxide and fluoride in a ratio of 1: 1. A similar result was achieved when using a mixture of aluminum powder, calcium oxide and calcium fluoride in a ratio of 1: 1: 1 as a slag-forming mixture.

Steel smelting in a known manner in a 12-kg open induction furnace was carried out in a hot run after washing smelting. Carbon, iron and nickel-containing charge materials were fed into the filling. After melting the filling, slag-forming materials and molybdenum were introduced into the furnace, and after melting of the charge materials and assimilation of molybdenum, ferrochrome was introduced.

As a slag-forming material, a mixture of calcium oxide and calcium fluoride in a ratio of 1: 1 was used. A similar result gives a mixture of powder of aluminum, oxide and calcium fluoride in a ratio of 1: 1: 1 - 1: 1: 2. Then, the melt was preliminarily deoxidized with silicon and alloying was carried out by introducing alloying components: manganese, copper, etc. After holding the melt for 5-6 minutes, the remaining alloying components, including vanadium, niobium and titanium in the form of ferroalloys and / or ligatures, were introduced to completely assimilate the components. After the melt was held in the furnace until all the components were fully assimilated, the melt in the furnace was finally deoxidized with aluminum. The temperature of the melt was about 1550 ° C. After that, the slag was downloaded and cast into the ladle. In the ladle, metal was deoxidized by rare-earth metals (rare-earth elements).

Then samples were taken for chemical and gas analysis and the metal was poured into the molds. The results of the study of the nitrogen content in the metal are presented in the table. From the data presented in the table, it follows that during the smelting process, steel adsorbed 0.04 wt. % nitrogen at a rate of 0.0025 wt. % per minute, and the concentration of nitrogen in the finished metal was 0.057 wt. %, which exceeded the specified nitrogen content by more than two times.

Steel smelting by the method according to the invention was carried out on the same charge materials in induction furnaces of various capacities: 12 kg, 50 kg and 150 kg with different ratios of the area of the mirror of the metal bath to the mass of the charge - K _{s / m} , respectively, equal to: 0.001; 0.0006 and 0.0004 m ² / kg. Carbon, iron and nickel-containing charge materials were fed into the filling. When filling was molten and a liquid metal mirror was formed, slag-forming materials and molybdenum were introduced. After the charge was melted, the melt was preliminarily deoxidized with silicon and alloying was carried out by introducing alloying components (manganese, copper, etc.), which were necessary in composition, in the form of ligatures and ferroalloys.

After their assimilation at the end of alloying at a melt temperature of no higher than 1600 ° C, chromium (in the form of pure metal or ferrochrome) and alloying components that increase the solubility of nitrogen in iron (vanadium, niobium and titanium) were introduced simultaneously in portions, and after each portion was introduced into the melt an additional slag-forming mixture was fed in an amount (by weight) of 1-3% by weight of a portion. As a slag-forming material used a mixture of aluminum powder, oxide and calcium fluoride in a ratio of 1: 1: 1. Then, after the assimilation of the indicated alloying components for a period of 5-7 minutes (no more), the final deoxidation with aluminum, downloading of slag and casting of metal into the ladle were carried out.

The process temperature was 1550-1570 ° C. In the ladle, metal was deoxidized by rare-earth metals, a sample was taken for chemical and gas analysis, poured into molds.

The results of the study of the nitrogen content in the metal are presented in the table. From the data presented in the table, it follows that the nitrogen content in steel 08Kh14N4M2D ranged from 0.016 to 0.018 wt. %

According to the proposed technology, a series of 50 heats was conducted at the Kirov Foundry and Mechanical Plant in a 450-kg induction furnace with a main lining. The nitrogen content in the metal of all pilot melts ranged from 0.014 to 0.022 wt. %

Thus, the nitrogen content in steel smelted according to the proposed technology is significantly lower than the nitrogen content in steel smelted in a known manner, and is at the level of nitrogen content in the metal smelted using vacuum arc furnaces.

Claims (4)

1. A method of smelting high-chromium steels and alloys in open induction furnaces, including filling the charge, melting it, introducing slag-forming materials into the furnace, preliminary deoxidation, alloying of the melt, assimilation of alloying components, final deoxidation, downloading slag and casting into a ladle, characterized in that at the end of alloying after assimilation of the alloying components at a melt temperature of no higher than 1600 ° C, chrome and alloying components are introduced in portions simultaneously, which increase the solubility of nitrogen in iron after their assimilation, the final deoxidation, slag downloading and pouring into the ladle are carried out over a period of 5-7 minutes, moreover, after introducing each portion into the melt, an additional slag-forming mixture is supplied in an amount of 1-3% of the portion weight. 2. The method according to p. 1, characterized in that as an alloying component that increases the solubility of nitrogen in iron, vanadium, niobium and titanium are used. 3. The method according to p. 1, characterized in that the nitrogen content in the charge materials set no more than 0.015 wt. % 4. The method according to p. 1, characterized in that as a slag-forming mixture using a mixture of calcium oxide and fluoride in a ratio of 1: 1 or a mixture of aluminum powder, oxide and calcium fluoride in a ratio of 1: 1: 1-1: 1: 2.