SU1749245A1 - Method of nickel-chrome alloys melt - Google Patents

Abstract

The charge is melted with the guidance of a finely clay-alumina-silica-slag with a basicity of 1.5-5; after reaching a temperature of 1360-1440 ° C, titanium is introduced in an amount of 0.015-0 045% of the mass of the charge 2 table 2

Description

The invention relates to metallurgy, in particular to the smelting of nickel-chromium alloys in electric furnaces.

The usual smelting of nickel alloys by the method of fusing alloyed waste, nickel and chromium in open electric arc furnaces is characterized by a low technological plasticity of individual heats and a high level of chromium. Under the same conditions of alloy smelting with deoxidation and modification, the reason for low ductility is the contamination of the metal with nitrides, which is caused by the relatively high solubility of nitrogen in nickel-chromium alloys at temperatures of steelmaking processes. The solubility of nitrogen in a nickel-chromium melt during electric arc smelting with an additive of chromium in the filling remains almost constant, and the contamination of the final metal with nitrides is estimated by the nature of the arrangement and the size of nitrides. Nitrides have a negative effect on the quality of nickel-chromium deformable alloys.

The closest to the invention is a method for producing steel with a low nitrogen content, including melting the base metal, oxidizing blowing with preliminary deoxidation with siliceous deoxidizing agents and doping with ferroalloys, followed by titanium additive, which is set on the basis of 0.05-0.20% by weight of the charge 10–30 min before release. At the same time, the removal of nitrogen is associated with the formation of solid titanium nitrides, followed by their precipitation on oxides, the flooding of such inclusions and their assimilation into slag.

However, the known method of removing nitrogen in the form of titanium nitrides in the smelting of nickel-chromium alloys is practically unrealizable, since with the introduction of titanium into the melt before discharging from the furnace, the solubility of nitrogen in the alloy increases and additional metal contamination with nitrogen occurs due to contact of the melt with the atmosphere during smelting. This is due to the lower coefficient of activity of titanium in nickel and nickel-chromium alloys compared to liquid iron and steel. Thus, the indicated concentrations of titanium in a known manner are not sufficient for the formation of nitrides in nickel alloys at the melting and outlet temperatures of the alloy from the furnace, this technology is not effective (L

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effective for de-nitration of nickel alloys and saving of alloying by their optimum ratio in the filling during smelting.

The purpose of the invention is to save alloying materials, reduce metal contamination with nitrides, and increase yield.

This goal is achieved by the fact that after the melting of the filling at 1360-1440 ° C and the basicity of lime-silica slag 1.5-5, titanium is placed in a bath (0.015-0.045)% by weight of the metal stock in the bath.

It is known that high-chromium nickel alloys with a content of 51 May. % chromium crystallizes at 1340 ° C, and alloys from 10–20 May. % chromium melts in a fairly narrow temperature range 40-50 ° C below the melting point of nickel. In fact, when smelting, the average melt temperature with an additive of titanium at 10-12 ° C is higher than the liquidus temperature of the calculated chemical composition of the melted nickel-chrome alloy. In the temperature range claimed, the rate of removal of nitrides from the metal to the slag is much higher than the rate of solution-1 nitrides in the melt, which allows nitrogen to be removed from the alloy by the nitride mechanism.

When titanium is introduced into the nickel-chrome melt at temperatures close to the temperature range of the two-phase region, titanium nitrides are formed, which are carried to the slag. Titanium nitride is well wetted with CaO-A120z-5U2 system slags with a basis of 1.5-5. The wetting angle of titanium nitride with slag varies from 0 to 20 °, and the adhesion of titanium nitride to slag is greater than that of nickel-chromium melt, and exceeds 1000 mJ / m (tab. 1).

If the slag basicity is less than 1.5, the nickel-chrome melt is contaminated during the smelting of silicon. This is unacceptable because it leads to the rejection of the metal by chemical composition. When the slag basicity is more than 5, the slag melting point is high compared to the melting point of the nickel-chrome alloy. The resulting heterogeneous slag practically does not assimilate titanium nitrides, which causes the contamination of the metallic melt with nitrogen and causes a sharp decrease in the technological plasticity of the alloy due to the presence of titanium nitrides in it. on.

The amount of addition of titanium into the bath for the metal deazotation by the nitride mechanism without contamination of the melt with titanium was experimentally established. For additives

titanium less than 0.015% of the mass of the filling in the temperature range 1360-1440 ° C. Titanium nitrides in the nickel-chromium melt are not formed due to the oxidation of titanium with dissolved oxygen. In this case, titanium works as a deoxidizing agent. If the amount of titanium exceeds 0.045% by weight of the charge, the melt is alloyed with titanium, which is undesirable for alloys without titanium. In addition, an increase in the titanium content is accompanied by an increase in the solubility of nitrogen in the final metal, and due to the secondary oxidation of titanium, the alloy is contaminated with oxides. In the amounts claimed, the titanium additive at the specified temperature and slag conditions binds nitrogen to nitrides without saturating the melt with titanium.

There is no information in the literature on the smelting of nickel-chromium alloys with the introduction of chromium together with nickel and alloyed waste into the filling, after melting of which the de-nitration of the melt is carried out by the nitride mechanism by giving titanium at a strictly defined temperature and slag basicity. Under the conditions of open electrofusion, this method has not been previously used to save alloying and increase the yield of nickel alloys in the production of nickel alloys.

Example. Using the proposed method in the smelting of nichrome X20H80 in a 5-ton electric arc furnace.

Metallic nickel, chromium, lumpy waste, sheet trimmings and nichrome chips are used in the filling. On the furnace hearth, before charging the charge, lime and fluorspar are given at the rate of obtaining the slag basicity after the charge is melted and during subsequent smelting equal to 3.2. After the melting of the charge at 1400 ± 40 ° C, metallic titanium is deposited in the metal in amounts corresponding to the required redistribution and beyond these limits. Then, at 1470 ° C, the melt is doped with metal manganese, and the slag is smelted with a mixture of powdered silicocalcium, lime, and the ductility of a square sample is checked, after which calcium metal is introduced into the melt in an amount up to 1 kg / t, samples are taken for chemical analysis and they grind under white slag, which is induced by a mixture of lime and silicocalcium in the furnace. Before release, calcium is injected into the metal at the rate of its production in the finished metal 0.03-0.06 May. %, square samples are cast and, at 1510 ° C, the metal is discharged from the furnace. Casting is carried out in the usual order into ungreased molds for ingots of mass (G 600 kg.

The ingots on the mill 600 are rolled into a billet of 125 mm according to a known technology. Based on the results of weighing the ingots and rolled products, the yield for the alloy redistribution is calculated.

The results of melting the melt according to the proposed technology are compared with melting of the alloy according to the known technology, by which, after deoxidation and alloying of the melt, 15 minutes before the metal is released from the furnace, it is placed at 0.05 May. % titanium in order to remove nitrogen from the alloy. The resulting ingots are similarly processed into a 125 mm billet.

In tab. 2 shows data on the effect of the method of smelting nichrome with melt processing by titanium under slag with a regulated basicity at 1,400 ± 40 ° С after melting the filling. After titanium was added to the melt, the nitrogen content in the X20H80 alloy melted according to the proposed technology with the optimal consumption of titanium in smelting, 2 times lower than the solubility limit of nitrogen for nichrome and there is no contamination of the alloy with titanium and nitrides. Compared with the known technology, the nitrogen content is reduced by 30 rel. %, which makes it possible to increase the yield when ingots are converted into a billet by 4 abs. % compared to metal

Claims (1)

known smelting technology The yield of suitable smelting options increases 70% which is possible due to the higher technological plasticity of the metal, in which there are no nitrides of 35-40 µm. In the alloy obtained by the known technology, there are stitches of nitrides elongated in the direction of rolling, as well as Large titanium nitrides, which caused a large number of coarse flaws and cracks. The alloy produced according to the proposed technology does not have these defects even with an elevated chromium content close to the upper limit of the grade composition. Formula of the invention The method of smelting nickel-chrome alloys, including charge melting, titanium introduction and metal release from the furnace, is different in that in order to save alloying, reduce metal contamination with nitrides and an increase in the yield of the useful during melting of the charge induce lime-alumina-silica slag with a basicity of 1.5-5.0, and titanium is introduced after p fusion filling a melt temperature of 1360-1440 ° C in an amount of 0,015-0 045% by weight of metal charge Mainness, (% CaO) B (% 510g) Slag melting point, ° C The ratio of T DD. slag square eutectic Ni-Cr The wetting angle of the slag titanium nitride, hail Note 1L 1,53,25,05,2 135013 & 01 301 | i + 01 50 1, 015 1, 1.075 1.052 ABOUT ABOUT ABOUT Low Slag wetting with titanium basic nitride; good slag contamination of the metal with silicon Nitride bad slag 1,53,25,05,2 ABOUT ABOUT Titanium nitride poorly moistened with slag Note. The filling weight is 5700 kg. Standard absorption of titanium.