SU933723A1 - Method for melting steels and alloys alloyed with nitrogen - Google Patents

Description

The invention relates to ferrous metallurgy, more specifically to the production of steel and alloys doped with nitrogen, in open electric furnaces. Known methods for smelting nitrogen-containing steels are: the fact that nitrided ferroalloys are used for nitriding metal, for example, ferrochrome j. The disadvantage of this method is the high cost of the steel produced due to the high cost of the nitrated ferroalloys and their increased consumption. The closest to the proposed software technical essence and the achieved result is a method of smelting steel and alloys doped with nitrogen, including melting the charge, deoxidation of the metal, blowing the melt with nitrogen for 2-20 minutes with an intensity of 0.5-10 m / min. metal, and then input, nitrogen-containing materials from the calculation of the melt doping with nitrogen at 10-50% mark content 2}. The disadvantage of this method is the substantial loss of nitrogen in the process of dissolving the alloy due to oversaturation of the metal layers with nitrogen with the fusible constituents (decoupling solution) Ligate nitrogenated swarm. As a result, absorption from the ligature decreases, and most importantly, becomes unstable, which makes it difficult to smelt metal with a given chemical composition. In addition, the lack of stirring of the melt during the period of dissolution of the ligature lengthens the duration of melting. The purpose of the invention is to increase the degree and stability of the assimilation of nitrogen by metal, saving nitrogen-containing materials and reducing the duration of smelting. This goal is achieved by the fact that according to the method of smelting steel and alloys doped with nitrogen, including 393, which melts the charge, deoxidation of the metal, the blowing of the melt with nitrogen and the introduction of nitrogen-containing materials into the metal, as well as its finishing, the blowing of the metal with nitrogen begins at 1 -5 min before the introduction of nitrogen-containing materials with an intensity (1.6-6.6 10 m / kg. S, after the introduction of nitrogen containing materials, the purge intensity is increased to (8.3-83) / kg. S, and after 5 10 min. Blowdown intensity is reduced to the initial level After the complete melting of nitrogen-containing additives, the use of short-term purging of the melt with nitrogen before the additive of nitrogen-containing materials allows the chemical composition and temperature of the liquid metal to be averaged before nitrating it by adding the appropriate ferroalloys to prepare the bath for dissolution. The ratio of the diameter of the bath to the depth, temperature and viscosity of the metal. It has been established experimentally that the 4th results on averaging the chemical composition of the metal and its temperature for furnaces of various capacities are determined by blowing intensity (1.6-6.6). C. If the blowing intensity is lower than the specified lower value, then sufficient uniformity is not achieved. mixing of the metal before its formation; In the case of blowing metal with intensity a; more than 6, m / kg-s, the effect of blowing on mixing quality is not detected, and, as a result, blowing leads to useless gas consumption. Similar results are found in case of deviation from the specified limits. the moment the purge began. If purging is started in less than 1 minute, the metal bath is unprepared to ensure a uniform flow of nitrogen throughout its volume when nitrogen-containing materials are introduced. If the purging starts more than 5 minutes before the addition of nitrogen-containing materials, this leads to a useless waste of nitrogen-containing gas and to the inhibition of smelting as a whole. An increase in the intensity of the purge after the addition of a nitrogen-containing ligature is necessary to block the process of transition of nitrogen dissolved in the metal into the gas phase due to supersaturation of the metal layers in contact with the nitrogen-containing ligature by nitrogen. The limits of the intensity of purging with nitrogen — during this period of melting (8.383) 10 m / KGS, were established experimentally and determined by the amount of nitrogen introduced into the composition of the ligature into the liquid metal, which, as is well known, depends on the chemical composition of the mark metal. It has been established that in the case of introducing a ligature at the rate of obtaining nitrogen in the metal in an amount below 0.05, the melt should be flushed with nitrogen with an intensity of 8.3-10 m. If the final nitrogen content in the steel grade produced is greater than 0.3, then the intensity of the blowing should be 83ICr M / Kr. with. When the intensity of the purge is higher than 83-10, an increase in the nitriding effect is not observed, as a result of which the nitrogen-containing gas is consumed uselessly. the duration of the purge intensity is determined by the number and size of the nitrogen-containing materials introduced. If the intensity of the purge is reduced earlier than 5 minutes after the introduction of these materials, the dissolution process does not have time to go into the stage of diffusion transfer, as a result of which the necessary effect on the nitriding of the metal bath is not reached. If intensive purging is carried out more than 10 min after the addition of nitrogen-containing materials, it does not lead to a further increase in the assimilation of nitrogen by the melt due to the completion of the transition of the dissolution process to the diffusion transfer stage of the PIMR. In a 20 t electric arc furnace, the production of nitrogen-containing steel grade 07x21 G7AN5 is produced. The filling of the metal charge with melting, oxidizing blowing and melting of the metal is carried out in a known manner. In the initial charge materials there are no waste nitrogen-containing steel grades. The purging of the metal with nitrogen begins 3 minutes before the introduction of nitrated

ferrochrome with an intensity of 3.5-4 / kg.

After the introduction of nitrided ferrochrome by 0.25 nitrogen (by calculation), the intensity of the pr-blowers is increased to 20--10 MVKr. At this level, the blast is maintained with nitrogen for 8 minutes, and then the intensity of the purge is reduced to 3 degrees.

The production and casting of steel is carried out according to conventional technology.

The nitrogen content of the marking sample is. Total melted 5 heats. To evaluate the results obtained by assimilation, the same number of heats are melted from the master alloy according to a known method.

The average nitrogen uptake is: on swimming trunks using this method, 89%; swimming trunks by known technology - B0%. The duration of melting by this method is, on average, 8 minutes less than the known.

The production of steels and alloys doped with nitrogen in this way reduces the consumption of ferroalloys doped with nitrogen, reduces the duration of smelting and increases the degree of stability of assimilation

nitrogen, which will be reflected in the reduction in the cost of steel.

Claims (2)

1. Himushin F, F. Stainless steel. M., Metallurgists, 1967, p. 699. 2. USSR author's certificate ff 538568, cl. C 21 C 5/52, 1975.