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
  • C21C7/00—Treating molten ferrous alloys, e.g. steel, not covered by groups C21C1/00 - C21C5/00
  • C21C7/04—Removing impurities by adding a treating agent
  • C21C7/064—Dephosphorising; Desulfurising
  • C21C7/0645—Agents used for dephosphorising or desulfurising
• • 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
• • 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
  • C21C1/10—Making spheroidal graphite cast-iron

Definitions

• the technical field of the invention is that of desulfurization of cast irons, whether they are refining, that is to say intended for the manufacture of steel, or molding, intended in particular for the manufacture of parts. in spheroidal graphite cast iron.
• the sulfur content In the first case, for reasons of mechanical characteristics, the sulfur content must be reduced to 0.005-0.010%; in the second case, spheroidization is only possible for sulfur contents below 0.010%.
• Most desulphurizing agents are based on two alkaline earths: magnesium and calcium which combine easily with sulfur to give sulphides, forming insoluble slag in the iron.
• the excess magnesium and calcium are eliminated from the because of their high vapor pressure at the processing temperature, the excess calcium carbide, in the form of slag, is thus used, separately or in combination, metallic magnesium, calcium carbonate, lime, lime diamide (mixture of Ca carbonate and carbon) and calcium carbide, optionally added with products intended to improve the flowability of the mixture or to release gases allowing a good distribution of the desulfurizer in the liquid iron.
• These desulphurizers are, most often, injected using a lance, suspended in an inert carrier gas.
• Simultaneous injection of calcium carbide and magnesium for desulfurization can be done in two ways: either by co-injection of two components stored separately, the mixture taking place in the lance, either by injecting a premix of the two components.
• the invention relates to a new desulfurizing product which is a premix based on calcium carbide and magnesium.
• German utility model GBM 88 16 829.8 (SKW TROSTBERG AG) describes a desulfurizing premix based on calcium and magnesium carbide in which the apparent densities and grain sizes of the carbide and magnesium are in the same field.
• German patent DE 3,831,831 (SKW TROSTBERG AG) describes a desulfurizing premix based on calcium and magnesium carbide in which the particles of the two constituents are both coated with a layer of a product such as diatom or bentonite, containing silica, bound using an oil, vegetable or silicone.
• the object of the invention is to reconcile these requirements Apparently contradictory. It concerns a new product for desulfurization of cast iron, consisting of a premix of two constituents, one based on calcium carbide, the other based on magnesium.
• the inventors started from two observations: The first is that when a powder of homogeneous composition but of fairly large particle size is stored in a container and subjected to vibrations such as those which occur during transport, a spontaneous segregation: the largest particles migrate to the top of the container, the finest to the bottom.
• the second observation is that when a powder of two constituents of different densities, but of the same particle size is stored in a container and subjected to vibrations, there is again spontaneous segregation: the least dense particles migrate upwards. container, the densest down.
• Such a coated magnesium grain affects the approximate shape of a sphere of diameter D1 coated with an outer layer of thickness e.
• the average size of the magnesium grains is 630 micrometers.
• the thickness of the coating, consisting of a single layer of slag grains is 100 micrometers.
• the magnesium has the same particle size as in the previous example, the coating layer has the same thickness.
• Example 2 above makes it possible to understand the entire scope of the invention.
• what the client generally wants is a certain weight ratio between magnesium and calcium carbide. comes in two forms: calcium carbide in separate grains and coated calcium carbide.
• the percentage of magnesium in the coated magnesium grain is 37.7%. If this percentage is suitable, it is then unnecessary to mix with calcium carbide and the product obtained, composed only of coated magnesium grains then conforms to one of the desulphurizing products described in French patent application No. 90 14092. In the general case, on the contrary, a weight percentage of magnesium less than 38% is desired , of the order of 20%, for example. We are therefore led to add to the grains coated with magnesium grains of calcium carbide and the calculation shows that, in order to avoid, according to the invention, the segregation of the two types of grains , the calcium carbide grains must have an average dimension of 920 micrometers.
• the binder which can be used both for coating magnesium with calcium carbide or another mineral substance and for agglomerating calcium carbide can be an organic, animal, vegetable or mineral oil or fat (silicone ).
• the choice of the coating and agglomeration binder is therefore essential.
• a product composed almost exclusively or at least 85% of a single chemical species such as a saturated fatty ester, obtained for example by catalytic hydrogenation of an unsaturated oil (process of hardening of oils). Its molar mass should be high enough to obtain a sufficiently high melting point.
• binders can be used in place of hydrogenated castor oil, in particular hard coal pitches.
• each of the two components, magnesium base and carbide base is done in a mixer or a grinder, into which the solid products are introduced which are brought to a temperature slightly higher than that of the binder melting, so that this binder melts and can thus perfectly coat the grains.
• the quantity of binder can vary in fairly large proportions: between 0.2 to 10% of the weight of the solid product with a preferred value close to 1%.
• the product is optionally sieved at the outlet, after cooling to remove the finest and coarsest fractions. It is also possible, in the context of this invention, to add carbon products (coal, smoke black, etc.) to the calcium carbide and to the binder in a proportion of 4 to 10% of the weight of carbide.
• Example 2 shows that the coated magnesium grains covered with a monolayer of carbide particles will have a diameter of 830 micrometers and that, in order to respect the proportionality of the particle sizes to the densities, the carbide particles must have a diameter of 920 micrometers.
• coated magnesium contains 37.7% magnesium and 62.3% carbide.
• the carbide is agglomerated under the same conditions with the addition of hydrogenated castor oil in a mixer containing the carbide powder. It may be useful, at the outlet of the mixer, to sieve the product to obtain a particle size centered on 920 micrometers , for example from 700 to 1050 micrometers, the finest particles and, after rough grinding, the coarsest being recycled in the mixer.
• Example 3 We want, as in Example 3, to make a non-segregating desulfurizing mixture containing by weight 80% calcium carbide and 20% magnesium.
• the coated magnesium will consist of 375 micrometers average diameter magnesium grains surrounded by an average layer of carbide of 40 micrometers.
• the composite grains will therefore have an external diameter of 455 micrometers on average. According to formula (4), they will contain 49.7% magnesium and 50.3% carbide. As we want to obtain a mixture of 20% magnesium, it will consist of 40.2% coated magnesium and 59.8% agglomerated carbide.
• Example 2 Using the conditions of Example 1, we want to obtain a desulfurizing mixture in which the weight proportion of calcium carbide is 4 times the proportion of magnesium.
• the average size of the magnesium grains is 630 micrometers.
• the thickness of the coating, consisting of a single layer of slag grains is 100 micrometers.
• the average size of the coated magnesium grains is therefore 830 micrometers.

Landscapes

• 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)
• Mold Materials And Core Materials (AREA)

Applications Claiming Priority (2)

Publications (2)

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Family Applications (1)

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Cited By (3)

Citations (3)

Family Cites Families (2)

• 1991
  • 1991-05-16 FR FR9106612A patent/FR2676457B1/fr not_active Expired - Fee Related
• 1992
  • 1992-05-11 EP EP19920420150 patent/EP0514294B1/de not_active Expired - Lifetime
  • 1992-05-11 DE DE1992613550 patent/DE69213550T2/de not_active Expired - Fee Related
  • 1992-05-11 ES ES92420150T patent/ES2091431T3/es not_active Expired - Lifetime

Patent Citations (3)

Non-Patent Citations (2)

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