EP0546351B1 - Cored wire containing a passivated pyrophoric metal and its application - Google Patents

Abstract

The invention concerns a cored wire comprising a metal tube and a filling of magnesium or other pyrophoric metals passivated with from 0.5 to 5% by weight of organic nitrogen compounds. As the passivating agent, compounds from the series of the s-triazine and/or guanidine derivatives, preferably from 2 to 5% by weight of dicyandiamide, applied by means of an adhesion promoter, are preferred. The wires used in accordance with the invention serve to produce cast iron with spheroidal and vermicular graphite, to desulphurize pig iron melts or to produce metal alloys.

Description

The present invention relates to a cored wire for the treatment of molten metals and the use thereof.

Pyrophoric metals such as magnesium, calcium, aluminum and corresponding alloys thereof, in particular in finely divided form, pose particular problems in their handling and use. The metals are used in the finely divided form for treatment, such as for the deoxidation of iron and steel melts, for the desulphurization of pig iron melts, for the production of certain alloys and others.

It is already known from US Pat. No. 4,209,325 or US Pat. No. 3,998,625 to dilute pyrophoric metals by adding 10 to 50% by weight of lime, aluminum oxide, SiO ₂ dusts or metallurgical slags in order to make them flammable Reduce.

When coating the pyrophoric metals with molten salts, predominantly alkali metal or alkaline earth metal chlorides are used (US Pat. No. 3,881,913, US Pat. No. 4,186,000 or US Pat. No. 4,279,641), the chlorine-containing salts require special measures for protecting the plant parts and the environment.

Finally, DE 39 08 815 A1 and the corresponding EP-A-0 388 816 describe a process for passivating pyrophoric metals, in particular magnesium, with 0.5 to 5% by weight of an s-triazine and / or guanidine Derivatives described as passivating agents, based on the weight of the metal. Such passivated fine-particle metals are characterized by their favorable burning behavior and are therefore particularly suitable as treatment agents for metallurgical melts, e.g. in the desulfurization of pig iron. DE 39 08 815 is hereby incorporated by reference into the present disclosure.

For the treatment of molten iron, e.g. In foundries, the treatment of melts with cored wire with a filling of the corresponding components has been introduced in recent years, and this has now largely become established.

For example, patent specification DE 39 24 558 C1 describes an agent in the form of a cored wire and a method for its production, the use of which consists in treating cast iron melts with a magnesium-containing silicon alloy. The advantage of the flux cored wire described can be seen in the shifting of the excretion form of the cast iron carbon in the direction of spheroidal graphite by adding 5-30% by weight of pure magnesium and 0.1-5% by weight of rare earth metals, as well as in the reduction of the process steps desulfurization, magnesium treatment and Inoculating cast iron melts on a single treatment measure to be carried out simultaneously.

EP-A-0 066 305 describes the use of passivated magnesium or calcium as a wire filling. The passivation of these metals is achieved with a surface coating that consists essentially of Aluminum oxide, magnesium oxide, finely divided silica, graphite or coke powder.

Due to the reaction-delaying effect of the coating, the premature reaction of the reactive agent is suppressed only during the treatment process, e.g. the premature melting and evaporation of the magnesium core is to be overcome. However, the process has serious disadvantages, such as afterglow or afterburning of the wire, and the release of harmful metal oxides during and after the treatment.

The present invention was based on the object of providing a cored wire with improved internal forces for the treatment of molten metals.

Further objects of the invention are evident from the description below.

The object is achieved according to the features of claim 1. Particular embodiments of the invention result from claims 2 to 6.

According to the invention, use is made of a finely divided pyrophoric metal, namely magnesium, which has been coated with a passivating agent based on organic nitrogen compounds, preferably organic NCN compounds from the series of the s-triazines and / or guanidine derivatives. For passivation of the pyrophoric magnesium, melamine or melamine cyanurate, guanylurea or guanylurea phosphate is preferably used. Cyanoguanidine (dicyandiamide) is particularly preferably used as a passivating agent.

The passivating agent is used in an amount of 0.5 to 5% by weight, preferably 3% by weight, based on the weight of the pyrophoric metal, namely magnesium, and is applied to the metal with the aid of an adhesion promoter. Viscous mineral oils, vegetable oils or preferably silicone oils are used as adhesion promoters. Adhesion promoters of this type are generally used in an amount of 0.1 to 0.5% by weight, based on the metal to be coated (see published patent application DE 39 08 815 A1). The particle size of the passivating agent is 5 to 60 μm, preferably less than 10 μm.

The inventors noted that the addition of reactive metals, such as magnesium, to molten iron in the form of a cored wire had the disadvantage that it continued to burn a considerable distance after the winding process had ended before it extinguished. This had a negative effect on the yield of treatment agent and resulted in mistreatment and rejects. In addition, these wires have given rise to accidents and considerable exposure to metal oxides in the workplace.

The use according to the invention of wires filled with the passivated metal particles described above has the advantage over the wires filled with non-passivated pyrophoric metals that the yield of reactive component is higher and incorrect treatment and rejects are excluded. Such cored wires also contribute to operational and occupational safety and environmental protection, since after the winding process has ended they neither glow nor burn and do not release any, possibly harmful, metal oxides into the environment.

The cored wire according to the invention also contains 60 to 40% by weight of ferrosilicon. Furthermore, additional components in the form of ferrosilicon containing rare earth metals can be added to the passivated pyrophoric metal, namely magnesium. A preferred wire filling, which in addition to passivated magnesium contains further treatment agents for the purpose of desulfurization and inoculation, is, for example, a mixture of 40 to 60% by weight of passivated magnesium with 60 to 40% by weight of ferrosilicon, with a content of 0.3 to 1.3% by weight of rare earth metals. Particularly preferably, such a wire filling consists of 49% by weight of magnesium and 51% by weight of ferrosilicon, optionally with a content of 0.5 to 1% by weight, preferably 0.9%. %, Rare earth metal.

A cored wire, which also alloys the treated metal, contains, in addition to the desulfurizing and inoculating components, alloying elements such as copper, manganese or tin in appropriate proportions.

In addition to the metallic components to be used, the wire filling can also contain non-metallic components, e.g. Calcium carbide, carbon or silicon dioxide. These components are used for desulfurization, carburization or as a filler to dampen the reaction. Their amount generally depends on the sulfur content of the base iron, the amount of carbon required or the intended degree of reaction damping.

The simultaneous presence of such treatment components allows the use of the cored wire to e.g. adjust the cast iron to the desired structure or composition in one operation.

The particle size of the passivated pyrophoric metal is preferably between 0.1 to 2 mm and is particularly preferably 0.2 to about 0.7 mm. The additional components are in a particle size of preferably 0.05 to 2.0 mm, particularly preferably 0.1 to 1.6 mm.

A typical cored wire sheathing consists of folded steel, rare copper tape, the wall of which is a thickness of 0.25 or 0.4 mm; Such cored wires with a total diameter of 5.9 and 13 mm are used.

The cored wire used according to the invention is characterized by a safe application, a high yield of the reactive component and by being environmentally friendly. Due to the constant burn-up conditions and the good reproducibility of the reactive component, there is a significant quality improvement in the treated metal melts. For example, in the production of spheroidal graphite cast iron using a cored wire filled with passivated magnesium particles, this has less oxidized magnesium on the bath surface after the treatment has ended. As a result, the reject rate caused by surface defects (Dross) is significantly reduced.

The following example is intended to explain the invention in more detail.

example 1

Magnesium powder (99.8% Mg) with a particle size of 0.2 to 0.7 mm was mixed with 0.3% by weight of silicone oil and passivated with 3% by weight of dicyandiamide with a particle size of 98% <10 µm by coating.

Then 40 parts by weight of the passivated magnesium were mixed with 51 parts by weight of ferrosilicon (75% Si) with a particle size of 0.2 to 0.7 mm and 9 parts by weight with rare earth metal-containing ferrosilicon (FeSiSE 36) with a particle size of 0 , 01 to 1 mm mixed and packed in a cored wire that has the following characteristics: Wire diameter 9 mm Wire weight 206 g / m Filling weight 94 g / m Fill factor 46% Magnesium content 36 g / m Silicon content 30 g / m SE content 3 g / m

Pre-desulfurized cupola furnace with the following analysis: 3.80 Wt% carbon 2.25 % By weight silicon 0.50 % By weight of manganese 0.04 % By weight phosphorus 0.012 % By weight of sulfur was treated by winding 31 m of the aforementioned wire. The results obtained are summarized in Table 1. Table 1 Treatment no. 1 2nd 3rd 4th Base iron (kg) 1000 1000 1000 1000 Amount of wire (m) 31 31 31 31 Winding speed (m / min) 28 28 28 28 Melt temperature (C) 1478 1485 1484 1480 Sulfur content after treatment (% S) 0.009 0.008 0.008 0.008 Magnesium introduced (% Mg) 0.112 0.112 0.112 0.112 Residual magnesium (%) 0.044 0.046 0.046 0.045 Magnesium yield (%) 39 41 41 40 Spherical graphite content (%) > 90 > 90 > 90 > 90 Spherolite per mm ² (Y2) 250 250 250 250

The precipitated graphite showed a proportion of> 90% in spherical form in a cast Y2 sample (25 mm). The number of Spärolites of 250 balls / mm ² corresponded to the inoculation power of this type of wire.

Claims (6)

1. Filler wire for the treatment of metal smelts comprising a filling material and a metallic casing enveloping the latter, the filling material containing 40-60 wt% of magnesium, which is passivated with 0.5 to 5 wt% with respect to the magnesium of an organic nitrogen compound based on a sym-triazine and/or guanidine derivative, and 60 to 40 wt% of ferrosilicon.
2. Filler wire according to Claim 1, characterised in that the ferrosilicon contains 0.3 to 1.3 wt% of rare earth metal.
3. Filler wire according to Claims 1 or 2, characterised in that its filling material consists of a mixture of 49 wt% of passivated magnesium and 51 wt% of ferrosilicon, the ferrosilicon containing if need be 0.5 to 1.0 wt% of rare earth metal.
4. Use of the filler wire according to Claims 1 to 3 for the production of cast iron with nodular graphite and cast iron with compacted graphite.
5. Use of the filler wire according to Claims 1 to 3, for the desulphurisation of pig iron smelts.
6. Use of the filler wire according to Claims 1 to 3 for the alloying of metal smelts with magnesium.