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

Definitions

• the invention relates to an agent for desulfurizing metal melts, in particular steel and pig iron melts, on the basis of CaC2-CaO crystal mixtures obtained in the melt flow, and to a method for producing the agent.
• Desulphurization agents based on CaC2-Ca0 and those which can additionally contain fluorspar are known (DE-PS 20 37 758). It is also state of the art to melt metal with technical carbide (approx. 80% by weight CaC 2 , rest Ca0) or also mixtures of such carbide with additives such as lime, coke, gas-releasing substances, e.g. CaCO 3 , CaCN 2 , Ca (OH ) To desulfurize 2 (DE-AS 22 52 795). In order to get a good degree of utilization, the known desulfurization agents, in particular for use by the immersion lance method, first had to be ground as finely as possible. According to this, these agents meet the requirements, but are expensive both in terms of manufacture and use. Despite the fine grinding, relatively large amounts of the desulfurizing agents had to be added to achieve the desired degree of desulfurization.
• part of the Ca0 in the crystal mixture is hydrated to Ca (OH) 2 .
• the agent according to the invention is furthermore preferably characterized in that Ca0 in the crystal mixture is hydrated with 1 to 6% by weight H 2 0, preferably 2.5 to 3.5% by weight H 2 0, based on the amount of CaC 2 -CaO.
• Ca0 and CaC 2 crystallize as a crystal mixture in which the CaC 2 and Ca0 crystals are intertwined, specifically at the CaC 2 / CaO quantitative ratio given, with a lying in the area of the eutectic or shifted to the lime side hypoeutectic composition.
• H 2 0 is added, part of the Ca0 in the crystal mixture reacts according to the equation without the CaC 2 grown together with the CaO crystals being substantially attacked by the H 2 0.
• the grinding grains which consist of CaO-CaC 2 crystal adhesions in which some of the Ca0 crystals are hydrated, disintegrate at the prevailing temperatures above 800 ° C according to the following reaction equation
• the grinding grain Because of the gas development at the reactive crystal interfaces, the grinding grain literally bursts with the release of in statu nascendi highly reactive lime and with enlargement of the overgrown CaO-CaC 2 crystal surfaces. With an almost eutectic crystal structure, there is an ideally large reaction surface.
• the released reducing gases offer ideal conditions for the implementation of Ca0 with the sulfur dissolved in the molten metal.
• Such a desulfurization agent is particularly suitable for desulfurization processes in which the time for the desulfurization agent to react with the sulfur is very short.
• This process includes the immersion lance process, in which the desulfurization agent should be converted as completely as possible by blowing desulfurization agents into a molten metal below its surface in the short time from the point at which the desulfurization agent emerges in the melt until it rises to the bath surface.
• the desulfurization agent according to the invention is superior to the best known carbide-based agents in the desulfurization effect. Because of the intergranular gas reaction in the grinding grain, the conversion of CaC 2 to Ca0 and the resulting enlargement of the crystal surfaces are more effective, the gas development is much more uniform and less violent than with known desulfurization agents, for example according to DE-AS 22 52 795, to which gas-releasing additives are mechanically mixed . Desulphurization therefore takes place more quietly and with less metal emissions, particularly in the open pan and the torpedo pan.
• the material can be used in a coarser size, so that expensive fine grinding can be dispensed with.
• the use of the desulfurization agent according to the invention enables greater accuracy with regard to the final content required in each case.
• the production costs for the agent according to the invention are considerably lower than for known agents based on carbide.
• the process can be characterized in that, for the production of the end product, which contains 2o to 55% by weight calcium carbide, more than 45 to 8o% by weight calcium oxide and water chemically bound to calcium oxide, calcium carbide melt which is present and produced in a customary manner and which Already has a calcium oxide content of up to 45% by weight, finely divided calcium oxide is introduced in an excess of 3 to 15% by weight, based on the amount desired in the end product, then the mixture obtained cools to temperatures of 35 ° to 450 ° C.
• the calcium oxide which is introduced into the melt, is preheated to temperatures up to 2000 ° C., preferably up to 1100 ° C., and is introduced hot into the melt at these temperatures, it is possible to determine the CaO content in the carbide to increase to 80% by weight, the higher the preheating chosen, the higher the desired proportion of additionally dissolved calcium oxide should be between 45 and 80% by weight. This enables use in low-carbon pig iron and steel melts and also increases the desulfurization yield, based on calcium carbide.
• the portions smaller than 4 mm that have been screened off after the preliminary crushing essentially consist of Ca0 and can be recycled back into the process as finely divided calcium oxide, where they serve as the starting product together with fresh Ca0. It was not foreseeable for the person skilled in the art that the sieving of the An parts smaller than 4 mm are removed from the product, the parts that have no or only a low desulfurization effect, and so the effectiveness of the end product is significantly increased.
• the product produced according to the invention can be ground much better than products obtained by known processes. This is particularly important because in some cases the product has to be used with a grain size of less than 0.1 mm.
• Calcium carbide for example electrothermally, is produced in a known manner from lime and coke, the lime-coke mixture in the Möller being adjusted to a weight ratio of 100:40, which corresponds to a carbide with a CaO content of approximately 40% by weight.
• Ca0 with a grain size of 3 to 8 mm and a Ca (OH) 2 - and CaC0 3 content of less than 1% by weight each is injected into the jet of the molten carbide, which has been tapped from the furnace into a crucible, at such a rate and in such a rate Amounts entered that, until the crucible is filled, there is a total CaC 2 : Ca0 weight ratio of 43:57, which corresponds to an excess of 14% by weight Ca0, based on the Ca0 content of 50% by weight desired in the end product. It is then cooled until the average temperature of the solidified carbide block is approximately 400 ° C., and the block is pre-broken to sizes smaller than 150 mm.
• the fractions smaller than 4 mm obtained during the preliminary crushing essentially contain the CaO used in excess, while the remaining product with grain sizes larger than 4 mm contains a crystal mixture of 50% by weight CaC 2 and 50% by weight Ca0 represents that then with passage of 1500 m 3 / h of air with a moisture content of 1o g / m 3 (at 15 ° C) in a rotary mill with a throughput of 5oo kg / h at 5o ° C to grain sizes less than 0.1 mm is ground.
• the screened grain fraction smaller than 4 mm is used together with fresh lime (Ca0) as the starting product.
• the product obtained contains 2.5% by weight of chemically bound water.
• Example 2 The procedure is as in Example 1, with the changes that the Ca0 is preheated to a temperature of about 1100 ° C. and the amount of Ca0 is increased so that a total Ca0 content of 62.5 wt % results, which corresponds to an excess of 4% by weight, based on the desired content of 60% by weight Ca0 in the finished end product.
• 1800 kg of the product worked up and ground according to the invention are used to desulfurize a 300 t steel melt with a sulfur content of 0.02% by weight at 1650 ° C.
• the sulfur content of the melt is reduced to less than 0.005% by weight.

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)
• Treatment Of Steel In Its Molten State (AREA)
• Lubricants (AREA)
• Solid-Sorbent Or Filter-Aiding Compositions (AREA)

Priority Applications (1)

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Publications (2)

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Cited By (3)

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Citations (1)

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• 1980
  • 1980-12-12 ES ES497686A patent/ES497686A0/es active Granted
  • 1980-12-18 DE DE8080108013T patent/DE3069681D1/de not_active Expired
  • 1980-12-18 EP EP80108013A patent/EP0031552B1/fr not_active Expired
  • 1980-12-22 US US06/218,731 patent/US4358312A/en not_active Expired - Fee Related
  • 1980-12-23 PL PL1980228753A patent/PL125943B1/pl unknown
  • 1980-12-23 BR BR8008513A patent/BR8008513A/pt unknown
  • 1980-12-23 DK DK550980A patent/DK151570C/da not_active IP Right Cessation
  • 1980-12-23 NO NO803923A patent/NO153499C/no unknown
  • 1980-12-24 CA CA000367572A patent/CA1154596A/fr not_active Expired
  • 1980-12-24 AU AU65853/80A patent/AU532988B2/en not_active Ceased
  • 1980-12-29 DD DD80226700A patent/DD155528A5/de not_active IP Right Cessation
• 1981
  • 1981-01-05 MX MX185476A patent/MX154953A/es unknown

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Non-Patent Citations (2)

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