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

• Desulfurizing agents for pig iron and steel melts have already been proposed in the previously published EP-A1-0019087, these agents being obtained by preheating to temperatures up to 2000 ° C. in an existing calcium carbide melt which has a calcium oxide content of up to 45% by weight , finely divided calcium oxide in an excess of 3 to 15 wt .-%, based on that in the end product. desired amount of CaO of more than 45 to 80 wt .-%, enters.
• the mixture obtained is then solidified to temperatures of 350 to 450 ° C and at these temperatures to grain. sizes smaller than 15 0 mm pre-broken, an inevitably occurring grain fraction smaller than 4 mm is then separated from the remaining product and the latter is crushed to exclude moisture by breaking and grinding to grain sizes smaller than 10 mm.
• Desulphurization agents based on CaC 2 ⁇ CaO are known in general and those which may additionally contain fluorspar (DE-C3-2 037 758). It is also state of the art to melt metal with technical carbide (approx. 80% by weight CaC 2 , remainder CaO) or also mixtures of such carbide with additives such as lime, coke, gas-releasing substances, e.g. B. CaC0 3 , CaNC 2 , Ca (OH 2 ) to desulfurize (DE-B2-2252795).
• the known desulfurization agents especially 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 in terms of both manufacture and use. Despite the fine grinding, in order to achieve the desired degree of desulfurization, relatively large amounts of. Desulfurizing agents can be added.
• part of the CaO in the crystal mixture is hydrated to Ca (OH) z .
• This is based on crystal mixtures with a proportion of 40 to 65% by weight CaO (corresponding to 35 to 60% by weight CaC 2 ).
• the agent according to the invention is furthermore preferably characterized in that the CaO in the crystal mixture 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, is hydrated.
• CaO and CaC 2 crystallize as a crystal mixture, in that the CaC 2 and CaO crystals are intertwined, specifically at the CaC 2 / CaO quantitative ratio given, with an undereutectic lying in the area of the eutectic or shifted to the lime side Composition.
• H 2 0 is added, part of the CaO 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 CaO 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 lime, which is highly reactive in statu nascendi, and with enlargement of the CaO-CaC 2 crystal surfaces grown together in the grain. With an almost eutectic crystal structure, there is an ideally large reaction surface.
• the released reducing gases offer ideal conditions for the implementation of the CaO 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 between the desulfurization agent exiting the melt and rising 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 CaO and the resulting enlargement of the crystal surfaces are more effective. The gas evolution is much more uniform and less violent than with known desulfurization agents, e.g. B. according to DE-B2-2 252 795, 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. Because of the higher reactivity of the desulfurization agent according to the invention as a result of the enlargement of the crystal surfaces when the grinding grain bursts in the melt the material can be used coarser, so that expensive fine grinding can be omitted.
• 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.
• a process for producing an agent for desulfurizing metal melts, in particular pig iron and steel melts, based on CaC 2 -CaO mixtures obtained in the melt flow which is characterized in that for the production of an end product which comprises 20 to Contains 55% by weight calcium carbide, more than 45 to 80% by weight calcium oxide and water bound to calcium oxide, in a present and customarily produced calcium carbide melt which already has a calcium oxide content of up to 45% by weight, enters finely divided calcium oxide, in an excess of 3 to 15% by weight, based on the amount desired in the end product, the mixture obtained then cools to temperatures of 350 to 450 ° C., solidifies at these temperatures to grain sizes smaller than 150 mm, which inevitably resulting grain fraction smaller than 4 mm is separated from the remaining product and the latter in the presence of air or nitrogen with e moisture content of 5 to 20 g / m 3 (at 1.013 bar and 273.15 K) by breaking and grinding at temperatures below 100 ° C., preferably
• 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 into the melt hot at these temperatures, it is possible to determine the CaO content in the carbide to increase to 80 wt .-%, the preheating is chosen higher, the higher the desired proportion of additionally dissolved calcium oxide should be between 45 and 80 wt .-%. 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 which have been screened off after the preliminary crushing essentially consist of CaO and can be returned to the process as finely divided calcium oxide, where they serve as the starting product together with fresh CaO. It was not foreseeable for the person skilled in the art that the portions which have less than 4 mm after the preliminary breaking are removed from the product by screening off those portions which have no or only a slight desulfurization effect, and thus the effectiveness of the end product is considerably 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 e.g. B. produced electrothermally, the lime-coke mixture in the Möller is set to a weight ratio of 100:40, which corresponds to a carbide with a CaO content of about 40 wt .-%.
• CaO 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 speed and entered in such quantities that, until the crucible is filled, there is a total CaC 2 : CaO weight ratio of 43:57, which is one.
• the fractions less 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 represents a crystal mixture of 50 wt.% CaC 2 and 50 wt Passing 1500 m 3 / h of air with a moisture content of 10 g / m 3 (at 15 ° C) is ground in a rotary mill with a throughput of 500 kg / h at 50 ° C to grain sizes less than 0.1 mm.
• the screened grain fraction smaller than 4 mm is used together with fresh lime (CaO) as a 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 CaO is preheated to a temperature of about 1100 ° C. and the amount of CaO is increased so that a total CaO content of 62.5 wt .-%, which corresponds to an excess of 4 wt .-%, based on the desired content in the finished end product of 60 wt .-% CaO.
• 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)

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• 1980
  • 1980-12-12 ES ES497686A patent/ES8200147A1/es not_active Expired
  • 1980-12-18 DE DE8080108013T patent/DE3069681D1/de not_active Expired
  • 1980-12-18 EP EP80108013A patent/EP0031552B1/de not_active Expired
  • 1980-12-22 US US06/218,731 patent/US4358312A/en not_active Expired - Fee Related
  • 1980-12-23 BR BR8008513A patent/BR8008513A/pt unknown
  • 1980-12-23 PL PL1980228753A patent/PL125943B1/pl unknown
  • 1980-12-23 NO NO803923A patent/NO153499C/no unknown
  • 1980-12-23 DK DK550980A patent/DK151570C/da not_active IP Right Cessation
  • 1980-12-24 CA CA000367572A patent/CA1154596A/en 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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