SU1640176A1 - Process for melting alloyed steels and alloys - Google Patents

Description

one

(21) 4642447/02

(22) 12/15/88

(46) 04/07/91. Bup. № 13

(71) Scientific and Production Association for Machine-Building Technology TSNIITMASH

(72) V.G.Dyubanov, I.A.Svitenko, Ya.N.Kunakov, O.V. Ivanova, S.A.Iodkovsky, V.S. Dub,

| V.R.Sul gin, V.I. Aleksandrovich, M.Yu.Sobolev and V.P.Rukavets

(53) 669.0465 (088.8)

(56) USSR Author's Certificate No. 621735, cl. C 21 C 5/52, 1976.

USSR author's certificate number 768821, cl. C 21 C 5/52, 1978.

(54) METHOD FOR MELTING ALLOYED STEEL AND ALLOYS

(57) The invention relates to metallurgy, in particular to the smelting of steels and alloys in arc furnaces. The aim of the invention is to stabilize the desired chemical composition of the nitrogen-containing steel. After melting the mixture and heating the melt at 300-500 ° C above the liquidus temperature, it is cooled to a temperature of 50-150 ° C above the liquidus temperature in steps with an interval of 50 + 5 ° C with a mixture of nitrated and low-carbon ferrochrome at a ratio of 0.5- 1.2 in the amount of Q T (4000-1 2000) 3-M, where L T is the temperature of the metal above the liquidus temperature, ° C, 4000-12000 are the coefficients established experimentally, M is the amount of the metal being smelted, t. Duration the shutter speeds at each cooling stage are t 15 - (0.7-1.5) Q, min, gd S.Q - the total amount of mixture introduced in the previous stages of the cooling, t, 0.7-1.5 and 15 - the coefficients established experimentally. As a result, the content of nitrogen in the metal is stabilized while maintaining plasticity. 2 tab.

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The invention relates to metallurgy, in particular to the smelting of steels and alloys in arc furnaces, and can be used in the smelting of nitrogen-containing high-alloyed chromium-nickel-manganese steels.

The aim of the invention is to stabilize the desired chemical composition of the nitrogen-containing steel.

In the process after melting the charge, the heating is carried out.

melt 300-500 ° C above the liquidus temperature and then cooling to a temperature of 50-150 ° C above the liquidus temperature release into the ladle and casting the molds.

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Step-by-step cooling of the melt to the specified temperature after every mixture of nitrated and low-carbon ferrochromes, taken in a ratio of 0.5-1.2 in an amount numerically equal to

3 AT

1640176

4000 - 12000

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and with the upgrade at each stage, numerically with a grind of t 15 - (0.7-1.5) - -,

ensures the optimal solubility of nitrogen in the melt at the temperature of each step, which ultimately ensures the production of the required grade of nitrogen in the finished metal.

When the metal is cooled with a step of less than 50.5 ° C, the solubility of nitrogen increases slightly and the conditions for nitrogen absorption by the melt do not improve. Cooling of the metal with a step size of more than 50i5 ° C leads to a local significant overcooling of the melt at the point of entry of the ferrochromic mixture due to the limited thermal conductivity of the liquid metal. Local overcooling slows down the diffusion processes in the distribution of nitrogen throughout the melt and, as a result, its losses into the furnace atmosphere as a result of local exceedances of the nitrogen solubility limits, which does not provide the specified nitrogen content in the metal.

The use of a mixture of nitrated and low-carbon ferrochromes with a ratio of less than 0.5 is not rational, since it leads to a delay in the process of saturating the melt with nitrogen to a given chemical composition for this element. This leads to uncontrolled losses of nitrogen into the atmosphere of the furnace and to non-occurrence of nitrogen in the required chemical composition of the metal.

The use of a mixture with a ratio of components greater than 1.2 does not improve the assimilation of nitrogen by the melt, since in the dissolution zone of ferroalloys there is not created sufficient supersaturation over chromium to facilitate the transition of nitrogen from ferroalloy to metal.

The ratio determining the exposure time was established experimentally. At a coefficient less than 0.7, the metal exposure is too long, which results in nitrogen not falling into the given steel chemical composition due to the uncontrolled loss of nitrogen from the metal, especially in the electric arc burning zone, Where

there is significant (up to 3500 K) local overheating of the metal. At this temperature, the solubility of nitrogen in the high-chromium melt tends to zero, which is why it is removed from the steel.

With a coefficient of more than 1.5, the exposure time is inefficient from the point of view of removing nonmetallic inclusions, since the oxides formed as a result of the additive in the metal of the mixture due to the interaction of chromium and oxygen dissolved in the metal do not have time to float and emulsify with slag. This leads to a decrease in the technological plasticity of the metal.

The ratio for determining the amount of ferroalloy introduced into the melt has also been established experimentally. At a ratio of less than 4000, an excess amount of ferroalloys is introduced into the steel, leading to the creation of large temperature gradients in the metal, causing an uneven distribution of nitrogen throughout the melt, resulting in the formation of cracks during pressure treatment. When the coefficient is greater than 12,000, the additive is ineffective from the point of view of metal doping with nitrogen, i.e. The required nitrogen metal composition is not provided.

A mixture of nitrated and low-grade ferrochrome has room temperature. Nitrided materials are not calcined to avoid uncontrolled nitrogen losses in them. In order to ensure the stability of nitrogen absorption by steel, the temperature of the mixture materials is maintained within 50-350 ° C. At the specified temperatures of the mixture of ferroalloys, the loss of nitrogen from it is insignificant, which contributes to the achievement of the goal - to obtain nitrided steel of a given composition.

An example proposed by the proposed method is to produce steel grade 05X16NUAHMB in a 5-ton electric arc furnace. Steel contains 0.25-0.20% nitrogen. The grading, the preparation of materials, the filling and melting of the metal are carried out according to the current technology. After adjusting the refining slag and its deoxidation with aluminum and ferrosilicon powders, the metal is heated to 1700 ° C (Tlicr 1400 ° C, i.e., melting point by 300 ° C).

Then, step-by-step cooling is started, for which a mixture of nitrided ferrochrome PCHN600L with low carbon ferrochrome PCX002 is introduced in the ratio 0.8 in an amount determined from the above ratio, Q 0.150 m (the amount of the metal being smelted is 5 tons).

After cooling the metal to 1650 + 5 ° C, a delay is carried out, the duration of which is determined from the above ratio, t 8.33 minutes.

The temperature of the mixture used in this example is 20 ° C.

The necessary temperature drops in the actual course of smelting at a specific steelmaking unit are easily achieved by the indicated amount of the ferroalloy mixture (taking into account, if necessary, temperature adjustments due to the electric mode). The calculations carried out are estimated; their accuracy is ± 5 ° С.

A decrease in the temperature of the metal with a mixture of ferroalloys during the holding due to cooling does not exceed the specified interval of + 5 ° C. If the temperature exceeds the permissible values, it is corrected by introducing electric power.

The heat of chemical reactions (dissolution reactions of ferroalloys in the metal) is taken into account in the total heat loss during experimental melting.

In the smelting of alloyed nitrided steels with a nitrogen content of from 0.05 to 0.20%, nitrided ferrochrome with a nitrogen content of from 4 to 6% is used. Nitrided ferrochrome with a nitrogen content of 6–8.5% is used in steel production with a high nitrogen content. The uptake of nitrogen is included in the quality indicators given in table. one.

The temperature change is equal to 50 + 5 ° С, chosen so that when a mixture of nitrated and low carbon ferrochrome (0.5-1.2) is introduced, the chromium content and the temperature obtained at each step does not exceed the limit of nitrogen solubility, which contributes most full absorption of the injected nitrogen and the achievement of the goal.

Then the next portion of the mixture is introduced in the amount Q

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0

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0

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0

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 0.125 tons. After cooling the metal to 1600 + 5 ° C, the exposure is carried out, the duration of which is t 11.36 mN.

Similarly, the method is carried out further. A portion of the mixture in the amount of Q 0.100 tons is introduced and when the metal is cooled to 1550+ 5 ° C, the shutter speed t is 12.33 minutes.

Then, the next portion of the mixture Q is 0.075 tons and, when the metal is cooled to 1500 ° C (i.e., 100 ° C above the liquidus temperature), the exposure t is 12.78 minutes.

After this exposure, the metal is released into the ladle and poured into molds.

In addition, steel production is also carried out at the boundary values of the proposed parameters with the introduction of a mixture of nitrated ferrochrome with low carbon ferrochrome in the ratio of 0.5 and 1.2. In all the cases described, no metal defects were detected.

The proposed method is also carried out beyond the proposed quantitative characteristics, and the required nitrogen content is not provided in the metal. The results of the study of the metal are given in Table. 1 and 2. Technological plasticity of the metal is estimated by the coefficient of ductility (Ksch).

According to this criterion, when Kc is less than 0.1, the steel is not hammered, when Ku is 0.1-3, ductility is low, and at K, 3.1-8.0, malleability is% satisfactory (Kw -.- ;-).

T) KGS / MM2

Analysis of the results shows the advantage of the proposed technology for smelting a corrosion-resistant nitrogen-containing high-alloyed metal in comparison with the known one: the required content of nitrogen in the metal is maintained while maintaining satisfactory ductility (%

The malleability rate is about 4,).

ICG / mm2

Claims (1)

Invention Formula The method of melting alloyed steels and alloys, including melting the mixture and heating the melt at 300– 500 ° C above the liquidus temperature and cooling it, including ferroalloys, to a temperature of 50–150 ° C above the liquidus temperature, holding and releasing the metal from the furnace, characterized by that, in order to stabilize a given chemical composition of nitrogen-containing steel, cooling is carried out in steps with an interval of (50 + 5) ° C with a mixture of nitrated and low-carbon ferrochrome with their ratio 0.5-1.2 in the amount Q, determined by the formula Q LT (4000-12000) 3M, where dt - the temperature of the metal exceeds the liquidus temperature, X Famous Welcome 42,8 107.2 8 9 10 11 12 13 14 15 16 17 18 nineteen 20 21 22 23 2 /, five 0 4000-12000 - the coefficients established experimentally M is the amount of metal produced, m, the duration t of the exposure at each cooling stage is determined by the following relationship: t 15 - (0.7-1.5) J-, where 2J) is the total amount of the mixture introduced in the previous stages of cooling, t, 15 and 0.7-1.5 - the coefficients established experimentally. Table 1 ,four 150 The required nitrogen content in the metal is not ensured (N-O, IX, Ku 5.0) The required nitrogen content in the metal (N -0.150; Ku - 4.5) No defects detected (N 0.37.1 К ... 4.0) The required content in the metal is not ensured (N 0.152; Kts, - 4.5) The required nitrogen content in the metal is not ensured (N e 0.0812, K - 4.5) No defects were detected (K - 0.35%, l ((/ 3.7) The required nitrogen content in the metal (N  o, a; KV 4.0) The required nitrogen content in the metal is not provided (N  oh p; KV 4, g) No defects detected (N 0.29 К 3.9) lit provides arrestable nitrogen in the metal (N a -0.132; Kv 4.1) Me provides the required nitrogen concentration in the metal (N e -0.15%; K - 4.3) No effects detected (And 0.37  V 3.8) Ik provides the required nitrogen concentration in the metal (N B - 0.09Г, KV - 5.2) 1 a b l and u a