Classifications

• • C—CHEMISTRY; METALLURGY
  • C21—METALLURGY OF IRON
  • C21C—PROCESSING OF PIG-IRON, e.g. REFINING, MANUFACTURE OF WROUGHT-IRON OR STEEL; TREATMENT IN MOLTEN STATE OF FERROUS ALLOYS
  • C21C1/00—Refining of pig-iron; Cast iron
  • C21C1/02—Dephosphorising or desulfurising
  • C21C1/025—Agents used for dephosphorising or desulfurising

Definitions

• the invention relates to means and methods for the desulfurization of molten iron, in particular pig iron and cast iron melts.
• the fine-grained, magnesium-containing desulfurization mixture is packaged in a metal jacket and conveyed into the iron melt in the form of a so-called sheath wire, which ensures a very uniform introduction of the agent into the melt. This procedure is only used in special cases and for small batches of a few tons.
• the magnesium has a so-called post-desulfurization property. After the desulfurization treatment with conventional mixtures has ended, magnesium-sulfur particles can still be excreted, which further change the final sulfur value of the melt.
• the invention has for its object to provide an improved desulfurization agent for the desulfurization of pig iron and cast iron melts, which does not have the disadvantages of the prior art.
• the desulfurization agent according to the invention contains at least one naturally occurring silicate mineral with a ribbon, leaf or spatial network structure.
• Montmorillonite such as e.g. Perlite (band structure), kaolinite (leaf structure) or those from the feldspar group (spatial network structure), such as albite (sodium feldspar), potassium feldspar or anorthite (lime feldspar) or syenite (with contents of alkali feldspar) or rhyolite with snap-in rings of plagioglass and biotite as well as nepheline ( a sodium aluminum silicate) is used.
• Perlite band structure
• kaolinite leaf structure
• feldspar group patial network structure
• albite sodium feldspar
• potassium feldspar or anorthite lime feldspar
• syenite with contents of alkali feldspar
• nepheline a sodium aluminum silicate
• the desulfurization agent consists of a mixture of magnesium, silicate mineral and optionally calcium carbide and / or calcium oxide.
• the magnesium is coated with the silicate minerals and the other components. This is done by a normal circulation process in a suitable mixer, provided that the silicate minerals are brought to approximately the same grain size have been like the magnesium. Under this condition, the silicate minerals envelop the fine-grained magnesium in a bowl shape.
• the other components such as calcium carbide and / or calcium oxide, can now be built into this shell at the same time. However, these components can also be applied to the silicate casing in an additional shell.
• Such a desulfurization agent therefore consists of: 5 to 92 wt% magnesium 3 to 90% by weight feldspar, nepheline syenite or rhyolite or montmorillonite 5 to 92% by weight calcium carbide and / or calcium oxide.
• This coating which is optionally applied to the magnesium with the aid of a conventional anhydrous binder, gives the magnesium grain approximately the same flowability as the mineral constituents of the desulfurization agent. In this way, a pneumatically easily conveyable agent is obtained which can be introduced into the molten iron evenly in the previously calculated amount over the entire blowing period.
• the magnesium also loses its metallic surface due to this coating, which not only reduces its tendency to segregate during transport and handling, but practically avoids it.
• the technologically complex blowing technique of co-injection can be avoided with such desulfurization mixtures according to the invention.
• the silicates with their alkali contents such as especially the nepheline, but also the potash and soda feldspars themselves contribute to the desulfurization by forming alkali sulfides by splitting off their alkali portion, which are separated in the slag.
• these feldspar together with the alkali-sulfur compounds and other additives of the desulfurizing agent, liquefy the slag and thereby reduce its absorption capacity for iron granules.
• the silicates used according to the invention have a particularly advantageous effect with regard to the slag properties. It has been found, quite surprisingly, that when the silicates are used, the iron content in the slag is significantly lower than in the case of slags which result from the use of previously known desulfurization mixtures. A lower iron content in the slag is of course synonymous with a higher iron yield and favors the economy of the process. At the same time, the slag can be easily and completely removed from the iron bath by conventional measures.
• the silicates used according to the invention influence the components contained in the mixture as diluents in that they liquefy them (or at least convert them to a viscous state), which favors the uptake of sulfidic products and improves their separation behavior.
• the desulfurization agent has a proportion of 3 to 95% by weight of feldspar or nepheline syenite in addition to magnesium as a further desulfurizing component. Furthermore, a proportion of a mixture consisting of 5 to 50% by weight rhyolite / montmorillonite can be added to the magnesium as a further desulfurizing component.
• the desulfurization agents proposed according to the invention generally do not require the addition of flow aids. Should such an addition e.g. prove necessary due to the technical design of the injection system, these do not affect the effectiveness of the desulfurization agent.
• the mean of eleven melts showed an initial sulfur content of 0.046% and a final sulfur content of less than 0.006%.
• the desulfurization agent requirement per ton of pig iron melt was 1.08 kg, which 0.54 kg of magnesium consumption per ton of pig iron.
• the slag was easy to remove. Above all, the iron granules content was low at 16% by weight.
• the mean of nine treatments with an average melt weight of 115 t resulted in an initial sulfur content of 0.038% by weight and after the treatment a final sulfur content of 0.004% by weight.
• the injection quantity was 1.46 kg of desulfurizing agent per ton, which results in a magnesium consumption of 0.36 kg per ton.
• the blowing time was about 7 minutes.
• All of the slags in the melts treated with the agent according to the invention had low iron contents in the form of granules in the range from 10 to 20% by weight, the slag being able to be removed very well without the iron melt moving along or being drawn along.
• a granulated mixture consisting of 25% by weight of magnesium, 45% by weight of calcium oxide and 30% by weight of feldspar was used with nine melts of approx. 115 t.
• the initial sulfur content was approximately 0.040% by weight and the final sulfur content after the treatment was less than 0.005% by weight.
• the injection quantity 1.55 kg mixture / t iron. This results in a magnesium consumption of 0.39 kg Mg / t.
• the blowing time was about 7 minutes.
• the slag contained granules in the range of 10-20% by weight. It could be removed very well without the iron melt moving along with it.
• the fine-grained magnesium component (0.2-0.9 mm) was mixed with 20% by weight of rhyolite; the calcium carbide component was mixed with 40% by weight of feldspar.
• the ratio of the two co-injection components was approximately 3.5: 1.
• a magnesium requirement of 0.35 kg / t was determined, compared to a magnesium requirement of 0.47 kg / t using a state-of-the-art method.
• a low iron granule content of less than 15% by weight was found to be particularly noteworthy.
• the slag ran perfectly out of the torpedo pan even after a long period of treatment.

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• Chemical & Material Sciences (AREA)
• Engineering & Computer Science (AREA)
• Materials Engineering (AREA)
• Metallurgy (AREA)
• Organic Chemistry (AREA)
• Refinement Of Pig-Iron, Manufacture Of Cast Iron, And Steel Manufacture Other Than In Revolving Furnaces (AREA)

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Citations (7)

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• 1992
  • 1992-08-13 DE DE4226833A patent/DE4226833A1/de not_active Withdrawn
• 1993
  • 1993-08-05 DE DE59308374T patent/DE59308374D1/de not_active Expired - Fee Related
  • 1993-08-05 EP EP93112545A patent/EP0582970B1/fr not_active Expired - Lifetime
  • 1993-08-05 AT AT93112545T patent/ATE164887T1/de active
  • 1993-08-12 US US08/105,751 patent/US5336293A/en not_active Expired - Fee Related

Patent Citations (8)

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