US3823042A - Process for the decarbonization of steel - Google Patents

Process for the decarbonization of steel Download PDF

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Publication number
US3823042A
US3823042A US00227921A US22792172A US3823042A US 3823042 A US3823042 A US 3823042A US 00227921 A US00227921 A US 00227921A US 22792172 A US22792172 A US 22792172A US 3823042 A US3823042 A US 3823042A
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United States
Prior art keywords
decarbonization
temperature
hydrogen
steel
heat treatment
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Expired - Lifetime
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US00227921A
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English (en)
Inventor
F Boelling
F Toussaint
A Mayer
M Parikh
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Thyssen AG
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August Thyssen Huette AG
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Publication date
Priority claimed from DE19712108242 external-priority patent/DE2108242C/de
Application filed by August Thyssen Huette AG filed Critical August Thyssen Huette AG
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    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D3/00—Diffusion processes for extraction of non-metals; Furnaces therefor
    • C21D3/02—Extraction of non-metals
    • C21D3/04—Decarburising
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/02—Ferrous alloys, e.g. steel alloys containing silicon

Definitions

  • This invention is directed to the decarbonization of electrical strip or cold-rolled sheet steel. More particularly, this invention is directed to the simultaneous decarbonization and the development of magnetic properties in electrical strip or sheet steel. This invention is also directed to such a decarbonization and development of magnetic properties in the development of a specific steel having a given silicon and carbon content.
  • the present-day, commonly practiced methods of finally annealing high-alloy, cold-rolled electrical strip or sheet steel are mostly characterized by a two-step procedure.
  • the material is decarbonized at a temperature of about 750 to 900 C., under a relatively moist, hydrogen-rich atmosphere, and highly annealed at a temperature of 1,000 to 1,200 C., under a relatively dry furnace atmosphere to improve its magnetic characteristics.
  • Typical examples of such methods are described in US. Pat. No. 2,599,340 and in German Auslegeschrift 1,182,276.
  • a moist atmosphere an atmosphere in which the ratio between the water vapor content and the hydrogen content amounts to more than 0.02, and as a rule to about 0.1-0.4.
  • the atmosphere can contain nitrogen or other components, for example, but the composition is usually such that the atmosphere is a reducing atmosphere for iron.
  • the water vapor content is substantially less than about 1 to 2% of the hydrogen content. Further information in this regard is contained in US Pat. No. 2,287,467 and German Auslegeschrift. 1,182,276.
  • German Auslegeschrift 1,259,923 also discloses a method in which a decarbonization reaction is performed in a higher temperature range of from 1,065 to 1,205" C. In this range, cold-rolled sheets are partially decarbonized in a moist, preferably oxidizing atmosphere, then pickled, and finally decarbonized to a final carbon content at 760 to 927 C. in an atmosphere that is reducing for iron.
  • a final heat treatment in the high temperature range to accomplish complete decarbonization is considered undesirable because in that case a silicon dioxide coating is left on the sheet surface. Such coating is difficult to pickle off and very greatly impairs the punchability of the material.
  • German Pat. No. 861,702 it is known to perform the decarbonization and at the same time develop the magnetic characteristics with a single heat treatment in a temperature range of 1,040 to l,175 C.
  • no guidance for moisture content of the atmosphere is given in the patent.
  • This process is applicable only to a sheet which, in contrast to the processes mentioned hitherto, is covered with scale on its surface.
  • the scale plays an important role in the decarbonization reaction in German Pat. No. 861,702.
  • the object of the invention is to provide a process of the kind initially described, by which an improved surface quality and improved magnetic properties can be achieved in the electrical strip or sheet steel in a simple and economical manner.
  • This invention contemplates the simultaneous decarbonization and development of magnetic properties in electrical strip or sheet steel by a process which comprises heat treating said steel at a temperature of at least 1,000- C. in an atmosphere in which the partial pressures of water vapor and hydrogen are especially controlled.
  • a cold-rolled electrical strip or sheet steel having electrical properties is subjected to a heat treatment of 1,000 C. in the presence of a mixture of hydrogen and water vapor such that the ratio of the partial pressure of the water vapor and hydrogen is in the range of 2 l0 to 3 l0- It should be understood that the present invention is carried out with a mixture of water vapor and hydrogen. The ratio of these partial pressures varies inversely with the temperature employed.
  • the ratio of the partial pressure of water vapor to the partial pressure of hydrogen is between '2X10- to 10-
  • An especially desirable va is 5X10- to 2x10
  • a suitable ratio for these partial pressures is 5X10" to 2X10.
  • the present in vention contemplates the decarbonization and development of magnetic properties in electrical strip or sheet steel, which steel has a silicon content of between 2 and 6 weight percent and preferably between 2 and 4 weight percent, of which no more than 2% and preferably no more than 0.5% of said silicon can be replaced by aluminium and no more than 0.008% by carbon, the balance being substantially iron.
  • This steel preferably has a carbon content of less than 0.005 weight percent.
  • the steel can contain the usual, generally unavoidable impurities, such as manganese, sulfur and phosphorus.
  • the strip or sheet is one which is a scale-free sheet and cold-rolled to a final thickness.
  • the final annealing consists of a single final heat treatment at a temperature above 1,000 C. which serves both for decarbonization and for the development of the magnetic properties.
  • the atmospheric moisture content lies within a quite specific range depending on the temperature.
  • the partial pressures of water vapor and hydrogen are, in accordance with the invention, in a ratio of 2X 10* to 3 X 10*, and at a temperature of 1,300 C., they are in a ratio of 2X 10* to 10- At temperatures within this temperature range, the partial pressures are in a correspondingly interpolated ratio to one another.
  • the upper limit of the heat treating temperature is determined solely by the technical possibilities, especially by the mechanical strength of the sheet which diminishes with increasing temperature.
  • the heat treatment atmosphere is only very slightly in motion, this movement being brought about only by the fact that an inflow of hydrogen is required to sustain the regeneration and to compensate leakage losses.
  • the heat treatment in accordance with the invention is performed preferably in a continuous manner. Batch heat treatment of coils or packs is also possible, however, although free access of the atmosphere to the surface must, of course, be assured. It is furthermore recommended in accordance with the invention that the heat treatment be performed in an atmosphere consisting exclusively of hydrogen and water vapor. If other gases, such as nitrogen or argon, are present, the water vapor content is determined solely on the basis of the hydrogen content in accordance with the ratios specified above.
  • FIG. 1 shows the effect of the water vapor content of the furnace atmosphere and of the heat treatment temperature on the carbon content that can be removed from the specimen material
  • FIG. 2 shows the range of temperature and water vapor content within which the heat treatment of the invention is to be performed
  • FIG. 3 shows the relationship between the carbon content that is removed by 5 minutes of heat treatment and the water vapor content of the furnace atmosphere, with the annealing temperature as a parameter
  • FIG. 4 shows a comparison of the coercive field strength in oersteds of a specimen subjected to final heat treatment by the prior art, two-step method and of the specimen treated according to the present invention.
  • the broken line in FIG. 1 indicates the usual relationship between the carbon content of the experimental material which has been removed by the heat treatment, and the moisture of the hydrogen atmosphere.
  • the decarbonization is completely successful. If the moisture falls below about 10%, the decarbonizationability of the material diminishes rapidly, becoming virtually zero when hydrogen with a moisture content of 0.03% is used.
  • the decarbonization of high-alloy electric sheet steel is performed technically today on the basis of this knowledge. Thus, a relatively high gas moisture is required. The formation of a thick oxide coating on the sheet surface is then inevitable.
  • the decarbonization reaction vanishes again.
  • the water vapor content can by no means be made as small as one pleases or equal to zero.
  • the water vapor content lies within a quite specific range with definite upper and lower limits. This range is identified by single hatch lines.
  • a boundary line marks off the crosshatched area or range in which it is possible to diminish the carbon content to less than half of the original content within a few minutes.
  • the dots 1, 2, 3, 4, 5 mark the optimum moisture values at the corresponding temperature. They correspond to the maximums illustrated in FIG. 3.
  • the heat treatment will attempt to achieve a state that is as close as possible to the broken line joining points 1, 2, 3, 4 and 5 of FIG. 2.
  • the temperature range in which the decarbonization takes place coincides with the range within which there is an optimum development of the magnetic properties of the material. Consequently, the high annealing which follows the decarbonization treatment in the prior art processes is unnecessary.
  • FIG. 4 shows curves representing the relationship between the coercive field strength in oersteds and the annealing time in minutes in the high-annealing process used in the prior art method (broken line) and in the method of the invention (solid line) for the experimental material. Apparently, the less scale producing heat treatment results in lower magnetic hardness in the electric sheet.
  • the new method is primarily suited for the manufacture of non-oriented cold-rolled sheets of the initially stated composition and makes possible the economical manufacture of an electric strip or sheet steel that is improved as regards surface quality and magnetic characteristics. Even in the decarbonization of oriented sheet steel, it can be applied in regard to the heat treatment that is required in this case, especially in the case of stringent surface quality requirements.
  • a process for the simultaneous decarbonization and development of magnetic properties of cold-rolled nonoriented electrical strip or sheet steel having a silicon content between 2 and 6% by weight which comprises continuously annealing a strip or sheet of said steel in an atmosphere contacting the entire surface of the steel and comprising water vapor and hydrogen, wherein the am nealing is at a temperature between 1,100 C. and 1,300 C. and the ratio of the partial pressure of water vapor to the partial pressure of hydrogen is in the range of 5 x10- to 2 10- at 1,100 C. and in the range of 5Xl0 to 2 1(lat 1,300 C. an in correspondingly interpolated ratios at temperatures between 1,100 C. and 1,300 C.

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  • Chemical & Material Sciences (AREA)
  • Engineering & Computer Science (AREA)
  • Mechanical Engineering (AREA)
  • Materials Engineering (AREA)
  • Metallurgy (AREA)
  • Organic Chemistry (AREA)
  • Physics & Mathematics (AREA)
  • Thermal Sciences (AREA)
  • Crystallography & Structural Chemistry (AREA)
  • Manufacturing Of Steel Electrode Plates (AREA)
  • Soft Magnetic Materials (AREA)
US00227921A 1971-02-20 1972-02-22 Process for the decarbonization of steel Expired - Lifetime US3823042A (en)

Applications Claiming Priority (1)

Application Number Priority Date Filing Date Title
DE19712108242 DE2108242C (de) 1971-02-20 Verfahren zur Herstellung von Elektroband

Publications (1)

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US3823042A true US3823042A (en) 1974-07-09

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US00227921A Expired - Lifetime US3823042A (en) 1971-02-20 1972-02-22 Process for the decarbonization of steel

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US (1) US3823042A (it)
JP (1) JPS5413845B1 (it)
BE (1) BE779481A (it)
BR (1) BR7200914D0 (it)
CS (1) CS166652B2 (it)
FR (1) FR2126015A5 (it)
IT (1) IT947633B (it)
RO (1) RO64233A (it)

Cited By (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4127429A (en) * 1976-07-05 1978-11-28 Kawasaki Steel Corporation Forsterite insulating films formed on surface of a grain-oriented silicon steel sheet having a high magnetic induction and a method of forming the same
EP0147659A2 (en) * 1983-12-02 1985-07-10 Kawasaki Steel Corporation Method for manufacturing grain-oriented silicon steel sheet
US5203928A (en) * 1986-03-25 1993-04-20 Kawasaki Steel Corporation Method of producing low iron loss grain oriented silicon steel thin sheets having excellent surface properties

Cited By (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4127429A (en) * 1976-07-05 1978-11-28 Kawasaki Steel Corporation Forsterite insulating films formed on surface of a grain-oriented silicon steel sheet having a high magnetic induction and a method of forming the same
EP0147659A2 (en) * 1983-12-02 1985-07-10 Kawasaki Steel Corporation Method for manufacturing grain-oriented silicon steel sheet
US4576658A (en) * 1983-12-02 1986-03-18 Yukio Inokuti Method for manufacturing grain-oriented silicon steel sheet
EP0147659A3 (en) * 1983-12-02 1987-04-22 Kawasaki Steel Corporation Method for manufacturing grain-oriented silicon steel sheet
US5203928A (en) * 1986-03-25 1993-04-20 Kawasaki Steel Corporation Method of producing low iron loss grain oriented silicon steel thin sheets having excellent surface properties

Also Published As

Publication number Publication date
DE2108242A1 (it) 1972-08-31
CS166652B2 (it) 1976-03-29
IT947633B (it) 1973-05-30
RO64233A (fr) 1979-02-15
JPS5413845B1 (it) 1979-06-02
DE2108242B2 (de) 1972-08-31
BE779481A (fr) 1972-08-17
BR7200914D0 (pt) 1973-05-03
FR2126015A5 (it) 1972-09-29

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