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
  • C21C5/00—Manufacture of carbon-steel, e.g. plain mild steel, medium carbon steel or cast steel or stainless steel
  • C21C5/28—Manufacture of steel in the converter
  • C21C5/30—Regulating or controlling the blowing
  • C21C5/32—Blowing from above

Definitions

• chromium containing deep drawing steels from chromium containing pig iron according to the oxygen top-blowing method.
• 5 to 50 kg of solid chromiumsidei es eey t a analysis of and a grain size of 3 to 20 mm, are added to the pig iron per metric ton of metallic input, whereupon within the period of 5 to 20 percent of the total blowing period an amount of CaO is added into the converter as is necessary for reducing to slag any accompanying elements of the pig iron and for adjusting a desired degree of slag basicity.
• the formation of liquid reactive slag is achieved more rapidly and the time for servicing the blowing lance is reduced. Yield losses are prevented and the life of the refractory lining of the converter is prolonged.
• the invention relates to a process for producing steels according to the oxygen top-blowing method, in particular for producing soft, rimming, chromium containing deep drawing steels from chromium containing pig iron, wherein basic slag formers and, if desired, fluxes are added for the formation of a fluid, reactive slag.
• a pig iron In the production of steel according to the oxygen top-blowing method difiiculties arise when a pig iron is refined that contains accompanying elements which are slagged to oxides that melt only with difficulty, whereby the formation of a fluid, reactive slag is delayed.
• a pig iron is for example a chromium containing steel pig iron containing about 4 percent C, 0.5 to 0.8 percent Si, 1.4 percent Mn, up to 0.2 percent P, up to 0.04 percent S and 0.9 to 1.2 percent Cr.
• This liquid end slag as a rule contains a high amount of CaO so that it is used for the next charge also in order to save lime.
• Working with retaining the final slag or part thereof leads to difficulties when the liquid pig iron of the following charge is filled into the converter because strong, even explosion-like reactions may occur between the carbon of the pig iron and the iron oxide of the slag.
• a further disadvantage lies in that the weight and the composition of the final slag does not remain constant so that disturbances may arise in the course of the process of the following melt and faulty analyses may be obtained.
• the temperature of the end slag and its viscosity may be very different at the beginning of blowing of the subsequent m'elt so that great delays may occur with regard to the period when a reactive slag starts to be formed.
• this process in which the final slag is used again for the following melt, cannot be used in refining pig iron sorts containing about 1 percent chromium, because they are refined in a one-step process so that the end slag contains the overall amount of the chromium reduced to slag as Cr O and thus cannot be used again.
• 1,608,310 suggests the use of synthetic slag formers instead of powderized lime or pieces of lime or limestone; these slag formers are to be produced from a mixture of a calcium oxide with powderized, partly or completely sintered iron ore.
• the production of synthetic slags necessitates certain raw materials and is expensive so that its use has not been justified on a large industrial scale.
• synthetic slag produced from red mud obtained from aluminum industry, from dolomite, lime and bauxite is used in an oxygen top blowing converter in order to increase the life of the refractory lining by providing for a rapid formation of a fluid slag.
• the invention is aimed at creating an inexpensive process that may easily be carried out, with which the formation of skulls at the blowing lance and losses of yields by spraying of the metal at the onset of blowing are prevented and with which also the life of the refractory lining of the converter is to be improved.
• the invention resides in that to the pig iron before or at the onset of blowing per metric ton of metallic input 5 to 50 kg, preferably 20 to 30 kg, of solid chromium oxide free slag having an analysis of Fe -20% si02 8-! 5% Mn 4- i 0% CaO 45-5 5% MgO 1-5 7.
• ALO, l-5% 150 14% and a grain size of 3 to mm, preferably 3 to 8 mm, are added, whereupon within a period of 5 to 20 percent of the total blowing period, calculated from the onset of blowing, an amount of CaO in the form of burnt lime is added into the converter as is necessary for reducing to slag any accompanying elements of the pigiron and for adjusting a desired degree of slag basicity.
• a slag is used whose pyrometric cone fall point (Seger) lies between l,300 and l,370C and whose flow point lies below l,380C.
• Such slags are obtained when chromium free steel pig iron sorts of customary composition are refined; since these slags are inexpensive, only the costs for their pulverisation have to be calculated for their use according to the invention.
• a mill product may be used that is already present and need not be produced synthetically; in the scope of the process according to the invention it is its main task to form a slag protective layer preventing spraying at the onset of blowing so that the blowing lance is protected.
• the solid chromium oxide free steel work slag may also be added already into the pig iron charge ladle so that it is preheated at the beginning of blowing and is liquefied yet more quickly.
• blowing chromium containing pig iron sorts it has been possible by this method to reduce the time for the formation of a liquid reactive slag by at least 2 minutes; the slag formation thus may be ended within a period of about 40 percent of the overall blowing time. While customarily ore is added at the beginning of blowing to provide for a more rapid liquefaction of the slag this is no longer necessary and results in an increase of the scrap amount and thus in a reduction of the input costs. Also the addition of fluxes, which are always unfavourable for the refractory lining, may be reduced when a solid slag is used. Finally the reduction of the time necessary for servicing, i.e., for removing skull formations at the lance, is expressed in a considerable increase in efficiency.
• ferro-manganese into the casting ladle in the production of rimming deep drawing steels with 0.2 to 0.4 percent chromium may be lowered, because, when solid slag is used for the formation of a protective layer for the pig iron bath, the
• a method for producing steel from pig-iron containing chromium by a single continuous oxygen topblowing process carried out in a converter comprising the steps of:

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• Engineering & Computer Science (AREA)
• Chemical & Material Sciences (AREA)
• Manufacturing & Machinery (AREA)
• Materials Engineering (AREA)
• Metallurgy (AREA)
• Organic Chemistry (AREA)
• Carbon Steel Or Casting Steel Manufacturing (AREA)

Applications Claiming Priority (1)

Publications (1)

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ID=3519368

Family Applications (1)

Country Status (9)

Cited By (5)

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• 1971
  • 1971-03-01 AT AT171371A patent/AT319298B/de not_active IP Right Cessation
• 1972
  • 1972-02-17 US US00227304A patent/US3802866A/en not_active Expired - Lifetime
  • 1972-02-17 IT IT20690/72A patent/IT947654B/it active
  • 1972-02-18 LU LU64807D patent/LU64807A1/xx unknown
  • 1972-02-22 DE DE19722208355 patent/DE2208355A1/de active Pending
  • 1972-02-22 NL NL7202308A patent/NL7202308A/xx unknown
  • 1972-02-24 GB GB868072A patent/GB1358326A/en not_active Expired
  • 1972-02-29 BE BE780017A patent/BE780017A/xx unknown
  • 1972-03-01 FR FR7207111A patent/FR2128488B1/fr not_active Expired

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