Classifications

• • 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
  • C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
• • 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
  • C21D8/00—Modifying the physical properties by deformation combined with, or followed by, heat treatment
  • C21D8/02—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips
  • C21D8/0205—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips of ferrous alloys
• • 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
  • C21D8/00—Modifying the physical properties by deformation combined with, or followed by, heat treatment
  • C21D8/02—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips
  • C21D8/04—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips to produce plates or strips for deep-drawing
  • C21D8/0405—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips to produce plates or strips for deep-drawing of ferrous alloys

Definitions

• This invention relates to the deep drawing of stainless steels containing 1420% chromium, and has as its object to provide a steel amenable to deep drawing without the occurrence of stretch strains, and to provide a procedure for production of deep drawn products free of stretch strains, as well as a procedure for providing a steel suitable for deep drawing without the occurrence of stretch strains.
• the sharp yield point can be eliminated by a slight cold deformation of less than 3%, and at the same time the point at which flow begins can be shifted to the lower strain figures, since the release of the dislocations from the carbon atoms or nitrogen atoms has already taken place.
• a slight cold working therefore, results in a lower yield point and hence in an easier flow, and makes it possible to avoid the occurrence of the great elongation at the yield point and hence to avoid the undesired stretch strains.
• This knowledge has led to the widespread practice of subjecting deep drawing sheets and strips after annealing to cold rolling with a slight reduction of thickness (temper rolling), in order to eliminate the sharp yield point and reduce the tendency toward the formation of stretch strains.
• the amount of temper rolling required is determined by the length of the yield point elongation, which in turn depends on the amount of cold deformation before the final annealing.
• ferritic chromium steels such as x 8 Cr 17 steels after German Standard DIN 17006, corresponding to AISI 430, are not stable ferritic steels; as a result of brief annealing at temperatures in the range of 850 to 930 C., small amounts of austenite occur along with the ferrite, which during the subsequent cooling are transformed to the pearlite phase, bainite phase or martensite phase, depending on the rate of cooling.
• the temperature at which the first austenite is formed depends on the ratio of ferrite formers (Cr, Si, Mo, etc.) to austenite formers (C, Mn, Ni, N etc.). In the case of longer annealing times, small amounts of austenite can occur even at temperatures under 850 C. Now, if the annealing temperature and time are adapted to the chemical composition in such a manner that, in. addition to the ferrite, some austenite occurs or, after cooling, some martensite or bainite structures occur, stretcher strains no longer occur in the material thus treated, even if it is not temper rolled.
• the invention is based on a process which results in the prevention of stretch strains by matching the annealing temperature and annealing time to the chemical composition of the sheets or strips being treated, some amounts of martensite or bainite structures being produced in addition to the ferritic basic structure. It is expedient to keep the percentage of martensite or bainite structures low so as to avoid affecting the mechanical values.
• the invention provides a method for production of steel amenable to deep drawing without the occurrence of stretch strains.
• the method comprises annealing the steel at a temperature and for a time sufficient to provide it in such condition.
• the annealing temperature can be above 830 C., and is preferably in the range of 850 to 930 C.
• the annealing time is in the range of /2 to 5, preferably of 1 to 3 minutes depending on the thickness of the sheet or strip, ranging from .5 to 3 millimetres.
• After annealing-the sheet or strip is air-cooled.
• the steel subjected to the treatment of the invention can be, and preferably is, a cold rolled steel, for example a cold rolled steel which has been cold rolled to the drawing thickness, i.e. to the thickness of steel utilized in the deep drawing step.
• the deep drawing employed to produce products from the steel of the invention can be any of the conventional deep drawing procedures.
• For the annealing preferably a continuous annealing
• Example Two chromium steel strips of the following chemical composition were cold rolled from a hot rolled strip thickness of 3 mm. to 1 mm. After the customary annealing of about 11 /2 minutes at 850 C., a temper rolling of 1% (strip 1) and 1.2% (strip 2) had to be performed to prevent stretcher strains. Without temper rolling, the same effect could be achieved by annealing strip 1 at 860 C., while the annealing of strip 2 was performed at 910 C. (Annealing time 11 /2 minutes).
• the invention is applicable to any deep draw product, it is especially applied in the production of hub or wheel caps and of scouring basins.
• Method for production of ferritic steel containing about 14-20% chromium and amenable to deep drawing without the occurrence of Liiders lines which comprises annealing the steel at a temperature and for a time sufficient to impart thereto, upon cooling, a structure comprising a minor proportion of martensite or bainite phase and a major proportion of ferrite phase, the steel following said annealing being amenable to deep drawing without the occurrence of Liiders lines.

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• Chemical & Material Sciences (AREA)
• Engineering & Computer Science (AREA)
• Materials Engineering (AREA)
• Mechanical Engineering (AREA)
• Metallurgy (AREA)
• Organic Chemistry (AREA)
• Physics & Mathematics (AREA)
• Thermal Sciences (AREA)
• Crystallography & Structural Chemistry (AREA)
• Heat Treatment Of Sheet Steel (AREA)

Applications Claiming Priority (1)

Publications (1)

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ID=7458146

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Country Status (6)

Cited By (5)

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Citations (7)

• 1962
  • 1962-05-16 DE DEST19249A patent/DE1188109B/de active Pending
• 1963
  • 1963-03-20 CH CH353063A patent/CH441408A/de unknown
  • 1963-05-06 LU LU43686D patent/LU43686A1/xx unknown
  • 1963-05-14 US US280438A patent/US3309238A/en not_active Expired - Lifetime
  • 1963-05-15 GB GB19283/63A patent/GB1041636A/en not_active Expired
  • 1963-05-15 AT AT395163A patent/AT245602B/de active

Patent Citations (7)

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