FR2671563A1 - Process for metallurgical treatments - Google Patents

Abstract

Induction furnace of the kind including a crucible (1) elongate in the vertical direction, surrounded by inductive electrical windings (3) and incorporating a pedestal of refractory bricks (2), characterised by a tuyere-block (14-15) fitted through a passage (1) passing through the pedestal and the bottom (2) of the crucible, held in a position of leakproof clamping against the said passage wall by an external support means (18) fastened to the external shielding (4) of the furnace, the said tuyere (14-15) emerging towards the outside via an axial conduit for injecting gas (14). By virtue of this arrangement it is possible to carry out any metallurgical treatment, especially by injection of active gases such as CO2, O2, H2 and/or an inert gas such as Ar and/or N2.

Description

 The invention relates to metallurgical treatments using gas which, as is well known, is carried out in a conventional manner in receptacles of the converter type which they are equipped for this purpose with porous plugs for the injection of neutral gases such as argon or nitrogen, and / or nozzle block for the injection of gas or active gas mixtures such as oxygen, methane, if necessary hydrogen. Such converters are suitable for handling large loads of the order of tens of tonnes of metal; however, they are quite incapable of processing small quantities of metal in the range of 100 to 2000 kg, because this low metallic charge undergoes unacceptable cooling, especially at the end of treatment and does not allow the metal to be poured under good conditions.

 The present invention seen a metallurgical treatment process using gas on small quantities this metal, of the order of 100 to 2000 kg, with a particularly satisfactory course of thermal reactions thanks to correct regulation of the temperature of the metal and this objective of the invention is achieved in that a small quantity of metal is placed in a melting furnace of the induction type, the bottom of which is equipped with at least one gas-blowing nozzle chosen from one or more gases active ingredients such as oxygen, methane, hydrogen, if necessary in a mixture, if necessary in cooperation with a neutral gas such as argon or nitrogen and in that the metallurgical treatment proper is carried out with the required temperature, which is maintained and / or regulated throughout dhl said treatment by adjusting the electrical supply of the furnace inductors and in that the insufflation of an inert gas such as argon is maintained in any case outside the treatment period with active gas, as long as liquid metal remains in the crucible of the induction furnace.

 Despite the drawback of having to maintain a constant flow of injection gas as long as there is liquid metal in the furnace crucible, and this in order to avoid blockage of one or nozzles, the process according to the invention is particularly advantageous by the perfect control of the temperature of the metal both during the treatment and during the casting operation, even in the case of very low loads which can be as low as 100 kg.

It should be noted that once the metal has been put to the correct shade, it can either be poured directly into molds without transfer to an intermediate bag, or it can be transferred to molds in a perfectly insulated bag preheated to very high temperature.

 The invention also relates to a cowprenant induction furnace ~ a crucible elongated in the vertical direction surrounded by inductive electric windings and incorporating a base of refractory bricks, which is characterized by a nozzle block mounted through a passage of base and crucible bottom, which is held in position by an external support means removably attached to the furnace shield, allowing at least one axial gas duct to pass.

According to a more elaborate form of the invention, the axial duct of the nozzle block is located inside a second duct defining an annular duct for the passage of gas. In this way, it is easy to inject a gas, for example oxygen, through the central duct and a second gas, for example methane, through the annular duct.

 Several embodiments of an induction furnace according to the invention are now described with reference to the accompanying drawings - Figure 1 is a vertical sectional view of an oven according to the invention - Figures 2 and 3 are partial views of two other variant embodiments.

 Referring to Figure 1, an induction furnace is essentially formed of a crucible 1 of elongated shape along the vertical and having a spout 5 and a bottom of the crucible 6. The crucible 1 is surrounded on its outside by windings electric inductors 3, the whole being placed on a base of refractory bricks 2 and enveloped by a shield 4. The base 2 and the crucible bottom 6 are perforated so as to create a through passage 11 having a lower part 11a of cylindrical shape , an upper part llb of frustoconical shape converging upwards.

 Inside the passage 11 is engaged a nozzle block 13 formed of an axial metallic conduit 14 embedded in a refractory cement 15 all engaged in a receiving seat 16 secured to the crucible bottom 6 and the base 2. The block -Removable nozzle consisting of the conduit 14 and the refractory 15 with a bottom plate 17 is held in the clamped position in the refractory seat 15 by a support plate 18 securely anchored to the shield 4 by various lag bolts 19. m.

understands that in the induction furnace which has just been described, it is possible to inject through the conduit 14 different gases and in particular an active gas such as oxygen, if necessary in mixture with other active gases or not and / or an inert gas.

 In case of wear of the nozzle block 14-15, it is easily retractable by dismantling the support plate 18 in order to install a new or renovated nozzle block.

 According to FIG. 2, the nozzle block here consists of a simple conduit 24 embedded in a refractory coating 25 directly held in place by a support plate 27.

 According to FIG. 3 which represents a support block of the type described in FIG. 2, a central duct 34 opening out to the outside at 35 is here surrounded at a distance by a second duct 34 'supported in a base sleeve 36 and opening out at the outside by an eccentric pipe 37. Oh understands that in this embodiment, one can inject a gas for example oxygen through the axial pipe 35 and a second gas for example methane in the interstitial pipe 38 between the conduits 34 and 34 '.

 In all cases, due to the gas blowing which can be quite intense, a superficial bubbling of the liquid metal takes place, so that it is necessary, for existing ovens, either to reduce the metal load in the induction furnace compared to that for which it was designed without insufflation, or else to provide an extension in the form of an annular ring fixed in leaktight manner on the upper contour of the furnace crucible.

 Thanks to the arrangements described, it is possible to implement the precision of the temperature control of the liquid metal that is allowed by induction furnaces by simply applying to the inductors a relatively low electrical power which exactly compensates for the heat losses through the walls and the subsequent cooling to the presence of injected neutral gas. For example, for a metallic load of 800 kg in an oven with a nominal capacity of 1000 kg, and during an injection of argon of the order of 20 l / nn, the electrical power necessary to maintain the temperature at 16000C is approximately 100 Bqh.

 According to the invention, it is possible to inject different gases which are active, for example oxidizing gases such as oxygen and carbon dioxide, or reducing gases such as methane or hydrogen, or inert gases such as argon or neutral such as nitrogen, the injection can be carried out if necessary in the form of a mixture, and during the process it is possible to modify the flow injected while preserving if necessary the proportion of the required mixtures.

 For example, an appropriate o2 / CO2 / Ar mixture can be injected through a single nozzle as shown in Figures 1 and 2, using the endothermic cracking reaction of the OG2 molecule to cool the nose of the nozzle.

 In general, during the entire fusion, a neutral gas (nitrogen or argon) passes through the single or double nozzle to prevent any infiltration of liquid metal therein. The gas flow is between 1 and 1.5 M3 / h, so as to generate in mee tenps a slight stirring which accelerates the fusion by increasing the heat exchange between liquid metal and unfused blocks.

 When the liquid metal is at the required temperature, the metallurgical treatment itself can be undertaken and the various gas injections are carried out at suitable rates and proportions. This operation can advantageously be programmed and controlled by computer by referring to a few preliminary test flows. All additions of corrections are then made in general with a gas flow rate slightly higher than the minimum flow rate of clogging of the nozzle.

The main interest of the process is to be able to perfectly control the temperature of the liquid metal, a decisive factor with regard to the chemical reactions involved, play during the development, and fundamental parameter with regard to the final temperature or casting temperature, and this advantage is all the more accentuated when the capacities are low, generally between 100 and 1500 kg in particular
In steel foundries, it is possible to envisage direct casting of the furnace into molds, without transfer to an intermediate pocket, thus avoiding cooling and additional pollution of the metal.

 By way of example, a few metallurgical treatments are described below.

- Decarburization and controlled oxidation
From 600 kg of an iron and carbon alloy at 1.5%, treated in an oven of nominal capacity of one form, 1 injection of pure oxygen (and natural gas to cool the nozzle nose ) at a flow rate of 15 Ni3 / h achieves 0.2% carbon in about 30 minutes.

The oxygen yield is 90% in this decarburization phase with a metal height of 55 years. The dissolved oxygen content is 50 ppm.

The dilution of oxygen with argon and the substitution of natural gas with argon then begin, the amount of argon in the mixture being inversely proportional to the carbon content of the metal according to the following relationship
% Ar x 100 = - 20 (% C) 2 + 0.8
In about 20 minutes, 0.05% C is reached and a dissolved oxygen content of less than 200 ppm. At the end of the refining, the oxygen is completely cut off and the flow of argon rusts at 5 Nhl3 / h to carry out the desired nuance.

- Decarburization of steel at the chrane
The same technique can be used for the treatment of certain alloy steels such as Cr steels.

Starting from 600 kg of alloy with a composition close to 0.5% carbon and 22,90 of chrame, brought to 1550cl, decarburization begins with the blowing of 10 to 15 n3 / h of a gas mixture consisting of 15 % neutral gas (Ar or N2) and 85% oxygen.

 During decarburization, the mixture is gradually enriched in neutral gas. Up to 0.2 90 C, part of the argon or nitrogen can be replaced by CO2.

At the end of ripening, the mixture used comprises 85 90 of argon.

The total duration of the treatment which leads to a carbon content of 0.05% is of the order of 30 minutes, after which the flow of oxygen is stopped, and a low flow of argon is only maintained (5 Nm3 / h) to favor the reduction, the titration and the settling of inclusions.

- dephosphorization using lime powder introduced into the bath, at a relatively low temperature, either by the central nozzle with oxygen, or with a lance - desulphurization, at a higher temperature, the lime being conveyed in the central nozzle with argon or nitrogen.

- the deoxidation and degassing treatment of high purity copper by injecting hydrogen and nitrogen at the start of the operation, then only nitrogen at the end to obtain solid metal, after well inerted casting, oxygen content of the order of 10 ppr and a density of 8.96.

 The fields of application of the invention are defined by the two constraints inherent in this technique (guard height which limits the minimum capacity of the ovens and permanent gas injection as long as there is liquid metal in the oven) which are more than offset by the advantage of perfect control of the casting temperature, even in the case of low and very low capacities. 1000 to 100 kg.

 This precisely covers the range inaccessible to the range converter which, for reasons of heat loss, begins below 1000 ss 1500 kg.

 The invention also applies to the foundry of very elaborate steels and small parts.

Claims (6)

 1. A method of metallurgical treatments on small quantities of metal, of the order of 100 to 1,500 kg, characterized in that such a quantity of metal is melted in an induction type oven, the bottom of which is equipped with '' at least one gas-blowing nozzle for at least one active gas such as oxygen, methane, hydrogen, where appropriate in a mixture, optionally for a neutral gas such as argon and / or nitrogen, and in that 'the actual metallurgical treatment is carried out at the correct temperature which is maintained and / or regulated throughout said metallurgical treatment by adjusting the electrical supply of the furnace inductors, the insufflation being however maintained with an inert gas such as argon outside the metallurgical treatment period as long as liquid metal remains in the furnace crucible.  2. A steel casting process using the metallurgical treatment process according to claim 1, characterized in that once the metal has been put to the correct shade, it is poured directly into molds without transfer to an intermediate pocket.  3. A steel casting process using the metallurgical treatment process according to claim 1, characterized in that once the metal has been put to the correct shade, it is transferred to molds in a perfectly insulated pocket and preheated to very high temperature.  4. Induction furnace of the kind comprising an elongated crucible (1) in the vertical direction surrounded by inductive electrical windings (3) and incorporating a base of refractory bricks (2), characterized by a mounted nozzle block (14-15) through a through passage (1) of the base and of the crucible bottom (2), held in tight sealing position against said passage wall by an external support means (18) fixed to the external shielding (4) of furnace, said nozzle (14-15) opening outwardly through an axial gas injection duct (14).  5. Induction furnace according to claim 4, characterized in that the axial duct is located inside a second axial duct defining an annular gas passage duct.  6. Induction furnace according to claim 4 or 5, characterized in that it is associated with an extension or annular guard mounted in a sealed manner on the upper periphery of the furnace crucible.