EP0066305B1 - Additive in wire form for treating molten metals - Google Patents

Description

The invention relates to a method for producing a wire-like means for treating cast iron melts.

As is well known, metal melts often receive post-treatment with a metallic or non-metallic treatment agent. The treatment agent can also be supplied to the melt in wire form in a known manner. In such a wire-like means for treating molten metals, reactive metal powder is coated with an iron metal.

When using wire-shaped treatment agents, there are certain difficulties in practice when an additive is introduced into the z. B. molten iron is easily volatile or evaporable and may also be present in relatively large amounts on average. There is thus the possibility that a component of the wire-shaped treatment agent such as magnesium, at a temperature below the melting point of a z. B. Cast iron quickly evaporates before the sheath wire is melted and absorbed by the melt. It is therefore known from DE-OS 25 31 573 to overcome such difficulties a wire-like agent for treating molten metal, in which between the outer jacket made of ferrous metal and core material made of relatively volatile metal, for. B. magnesium, an insulating material made of z. B. iron powder or magnesium-containing coke is arranged. With the previously known treatment agents, the core material should be added simultaneously with the melting of the casing material and premature melting and evaporation of the magnesium core should be prevented. The fine-particle treatment agents for molten iron known from US Pat. No. 4,152,150 are powdery inoculants which are enclosed in a wire-shaped metal jacket. The ferrosilicon or calcium silicon inoculant is coated with an iron sulfide or sodium sulfite inhibitor. The inhibitor is used to delay the reaction between the vaccine and the molten iron.

The additive known from DE-OS 22 56 381 for the treatment of iron and steel melts is based on powdered magnesium. The magnesium is embedded in a material that forms a coherent, stable, metal-permeable matrix at the temperature of the molten iron. The material of this matrix can be carbon-containing or metal oxide. The previously known additive can also contain iron powder. The known additive is mainly used in the form of briquettes or tablets.

According to the process known from DE-AS 26 03 412 for producing a wire-shaped composite additive for the treatment of iron or steel melts, the powdered calcium or magnesium-based filler material is extruded in an iron or steel strip serving as a sheath, with a dense overlap due to a special overlap Envelope and compression is achieved. The powdered filler material is protected against the effects of oxidative moisture and the treatment agent is therefore easy to store and handle. However, the problem of delaying the reaction of reactive mixtures has not been addressed.

To increase the reaction yield and to achieve a? According to the document EP - A2 - 030 043, a trouble-free, braked reaction sequence is provided in the form of a powdery mixture of at least one of the metals (A) magnesium, calcium and the rare earths and at least one of the metals (B) iron, nickel and manganese, which are provided with a shell is encased in ferrous metal.

The invention has for its object to provide a method for producing a wire-shaped agent for treating cast iron melts, with which the treatment process of the melt can be better controlled and varied within wide limits.

The invention solves the problem with a method for producing a wire-like agent for treating cast iron melts for producing spheroidal graphite iron, from a powdery mixture coated with iron metal, which contains at least one of the metals (A) magnesium, calcium and rare earths and at least one of the metals ( B) contains iron, nickel and manganese. The method of the aforementioned type is designed according to the invention in such a way that the metal powder (A) for the preparation of a reaction-delaying coating is first premixed with graphite or pearlite powder and then with component (B) and a reaction-inhibiting component C made of expandable silicates and / or graphite is combined to the final mixture, the grain size of the metal powder (A, B) and component (C) 0.02 to 2.0 mm and the composition of the powder mixture 30 to 80 wt .-% (A), 10 to 60% by weight (B), 1 to 15% by weight (C) and the amount of coating being contained in the amount of component (C).

Since both the layer thickness and particle size of the surface coating of the reactive metal (A) and the reaction-inhibiting component (C) can be varied widely in terms of type and amount, the treatment of a molten metal with wire-like treatment agent according to the method of the invention can be varied within wide limits.

Graphite or pearlite powder can be considered as a reaction-retarding or reaction-inhibiting coating for the reactive metal (A).

The coating can be achieved in a simple manner by dry mixing the materials, for example magnesium powder and graphite powder. However, it may also be expedient to provide a liquid, vaporizable medium in the mixing process, so that the coating is applied more firmly. The liquid medium can be, for example, water or an organic solvent. If appropriate, a small addition of about 2% of an organic or inorganic binder can also be expedient and bring about an adherent, tight coating. The particle size of the coating material is generally between 0.02 and 1.0 mm, a particle size of 0.05 to 0.25 mm being advantageous.

For the effectiveness of the wire-like treatment agent produced by the method of the invention, it is further important that the metal components of the powder mixture are of the same grain size. It has proven advantageous here to maintain a grain size of the metal powder of 0.02-2.0 mm. A preferred range is a grain size of 0.05 to 1.5 mm. The reactive metal component to be provided with the reaction-retardant coating is expediently in the form of granules with a particle size of 0.8 to 1.2 mm, in particular with a grain size of 1 mm.

According to a further embodiment of the present invention, the metal component (A) can also be used in the form of an alloy powder, for example Mg / Fe / Si alloys or Ca / Si / Mg alloys, which may also contain rare earth metals. The magnesium content of the alloys is generally between 3 and 50%.

The coated powder mixture of the treatment agent produced by the process according to the invention further contains a metallurgically neutral, reaction-inhibiting component (C). For the purposes of the invention, metallurgically neutral means that the substance is not absorbed into the melt. Suitable substances for this component are expandable silicates or carbon carriers or mixtures of these components. Quartz porphyry glasses, e.g.

Perlite, used, which expand to rock foam when heated to temperatures above 1200 ° C due to the escape of the enclosed water. Expandable sheet silicates, such as vermiculite, are also suitable. While the expandable silicates, due to their low thermal conductivity, produce the strongest reaction-inhibiting effect, if desired, by using coke or graphite alone or in a mixture with the expandable silicates as component (C), less reaction inhibition can be achieved and adapted to the respective local conditions of the treatment process.

Eine Zusammensetzung der Pulvermischung entsprechend

hat sich für die Behandlung von Gußeisenschmelzen zur Herstellung von Kugelgraphiteisen als besonders geeignet erwiesen.Although the composition of the powder mixture of the treatment wire produced by the method according to the invention can be varied in a wide range of amounts, it has generally proven to be expedient to provide a composition in preferably the following ranges:

A composition according to the powder mixture

has proven to be particularly suitable for the treatment of cast iron melts for the production of spheroidal graphite iron.

The casing made of ferrous metal enclosing the metal powder generally has a wall thickness of less than 1 mm and is preferably 0.15 to 0.5 mm. The treatment wire itself usually has a diameter of 2 - 6 mm. In some cases of melt treatments, much stronger, albeit less flexible, treatment wires up to 20mm in diameter may be required. Wires with a diameter of 2-6 mm are used in a method of treating the pouring stream of a molten metal, while wires with a diameter larger than 6 mm and up to 20 mm, preferably up to 15 mm, are used in the treatment of molten metals, such as cast iron, in the Pan can be used.

The treatment wire produced by the method according to the invention is flexible if the diameters are not too large and can be conveyed with very simple wire feeders. It can be used successfully if a feed speed of the wire drive of> 60 m / min is realized. However, speeds of 110 to about 200 m / min are preferably used in order to ensure that the wire is immersed deeply in the melt, so that optimum output is achieved. Depending on the amount of liquid metal to be treated, one or more wires can be coiled into the melt at the same time. The use of several wires advantageously results in shorter treatment times and lower temperature losses.

• a) Zwei Drähte mit Mg-Füllung gemäß vorliegender Erfindung;
• b) ein Draht als Legierungsdraht, auch als sogenannter "Monodraht" darstellbar, aus Elementen oder Legierungen der Elemente Cu, Al, Ni, Cr, Mg, Ti, Ce, Bi, Te, Sb, Nb;
• c) ein oder mehrere Drähte mit einer Füllung aus Impfmittel herkömmlicher Art, wie Ferrosilicium.

If several wires are used at the same time, they can either all be of the same nature or they can have different fillings, for example, can be used simultaneously for a metal melt treatment:

• a) Two wires with Mg filling according to the present invention;
• b) a wire as an alloy wire, also represented as a so-called "mono wire", made of elements or alloys of the elements Cu, Al, Ni, Cr, Mg, Ti, Ce, Bi, Te, Sb, Nb;
• c) one or more wires with a filling of conventional inoculant, such as ferrosilicon.

The treatment wire produced by the process according to the invention is usually wound into the static melt in my pan. The shape of the pan does not play a decisive role in contrast to conventional Mg treatment processes that do not use wires.

When using several treatment wires at the same time, it is advantageous not to immerse the wires in the melt at the same place. The usual size of the transport pan appears to be suitable for this method of Mg treatment.

In addition to inserting the wire into the ladle, the treatment wire can also be wound directly into the pouring stream, pouring basin or into the casting mold or immersed in a separate treatment vessel or channel between the furnace and the transport or pouring ladle.

• 1. Schritt: Entschwefeln und Desoxidieren mit einem nach dem erfindungsgemäßen Verfahren hergestellten Behandlungsdraht, enthaltend eine Pulvermischung der Zusammensetzung
  
• 2. Schritt: Modifizieren des Graphits mit einem Behandlungsdraht, entsprechend wie im 1. Schritt
• 3. Schritt: Legieren mit z.B. massivem Cu-Draht zur Einstellung einer gewünschten Matrix
• 4. Schritt: Impfen mit einem mit beispielsweise pulverförmigem Ferrosilicium gefüllten Draht als letzte metallurgische Behandlung vor dem Vergießen.

In the case of a greater variety of wires, these are preferably not immersed in the melt of the treatment vessel separately, but rather separately in individual process steps. For example, the treatment of a molten cast iron to produce spheroidal graphite cast iron can be carried out in the following manner:

• Step 1: Desulfurization and deoxidation using a treatment wire produced by the method according to the invention, containing a powder mixture of the composition
  
• Step 2: Modify the graphite with a treatment wire, as in step 1
• 3rd step: alloying with, for example, solid copper wire to set a desired matrix
• 4th step: Inoculation with a wire filled with, for example, powdered ferrosilicon as the last metallurgical treatment before casting.

The advantages of such a multi-stage procedure are that e.g. The various procedural steps can be carried out in quick succession at only one treatment station. There is no need to transfer the melt into other vessels. This saves time and avoids high temperature loss. It is also possible to work more precisely and easily.

The invention is explained in more detail and by way of example using an exemplary embodiment.

Example:

A wire-shaped treatment body was produced by deforming and compressing by means of a wire production machine. With an outer diameter of 5 mm of the wire, a sleeve made of mild steel tape (sheath thickness 0.35 mm) enclosed a core made of a metal powder mixture. The powder mixture consisted of 69% metallic magnesium powder, 26% iron powder, both with a particle size of 0.5 mm, and 5% graphite powder with a particle size <0.2 mm. Before the powder mixture was prepared, the magnesium metal powder was premixed with part of the graphite powder in order to ensure that the reaction-delaying coating was reliably formed on the magnesium surface. The magnesium content, based on the running meter of wire, was 10 g.

The treatment wire was introduced into cast iron melts by means of an automatic feed device. The cast iron melts were each in an open, so-called slim pan (capacity 1 to; ratio height: diameter = 2: 1). A cast iron melt of the following composition was treated in experiments 1 and II:

The further test conditions and the test results are listed in the table below:

The treatment of the cast iron melt proceeded smoothly and without ejection of melt components. The graphite was more than 90% spherical in cast samples.

The experiments show that even with an increased magnesium content in the treatment wire, the treatment proceeds smoothly and the magnesium is applied at a high rate of approximately 40%.

When using e.g. Perlite instead of graphite as a reaction-inhibiting component of the treatment wire produced by the method according to the invention, the treatment reaction also proceeds without eruptions. In addition, the silicate component in the treatment wire cleans the melt by binding the reaction products or slag particles dispersed in the melt.

If copper or nickel is used in powder form instead of iron powder in the treatment wire produced according to the method according to the invention, the iron melt can be alloyed with the magnesium treatment at the same time, which leads to an increased pearlite content in the basic structure.

Claims (4)

1. A process of producing an agent in the form of wire for treating moltan matarial for making nodular iron, from a powder mixture which is sheathad with farrous metal and contains at least one of tha metals (A) magnasium, calcium and rare earth elements, and at least one of tha metals (B) iron, nickel and manganese, characterized in that the metal powdar (A) is initially mixed with graphite powder or pearlita powder to form a reaction-retarding coating and is subsequently combined with component (B) and with a reaction-inhibiting component (C) of swellable silicates and/or coke and/or graphite to form the final mixture, wherein the metal powders (A, B) and component (C) hava particle sizes beteen 0.02 and 2.0 mm and tha powder mixture is composed of 30 to 80 wt.% (A), 10 to 60 wt.% (B) and 1 to 15 wt.% (C), the quantity of the coating being included in the quantity of component (C).

2. A process of producing an agant in the form of wire in accordance with claim 1, charactarized in that pearlite, vermiculite, coke, graphite or a mixture of said substances is used as component (C).

3. A process of producing an agent in the form of wire in accordance with claims 1 to 2, charictarized in that a powder mixture is used which is composed of

4. A procass of producing a agent in the form of wire in accordance with claims 1 to 3, charactarized in that a powder mixtura is used which is composed of