Classifications

• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B22—CASTING; POWDER METALLURGY
  • B22D—CASTING OF METALS; CASTING OF OTHER SUBSTANCES BY THE SAME PROCESSES OR DEVICES
  • B22D11/00—Continuous casting of metals, i.e. casting in indefinite lengths
  • B22D11/06—Continuous casting of metals, i.e. casting in indefinite lengths into moulds with travelling walls, e.g. with rolls, plates, belts, caterpillars
  • B22D11/0622—Continuous casting of metals, i.e. casting in indefinite lengths into moulds with travelling walls, e.g. with rolls, plates, belts, caterpillars formed by two casting wheels
• • 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
  • C21D8/021—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips involving a particular fabrication or treatment of ingot or slab
  • C21D8/0215—Rapid solidification; Thin strip casting
• • 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
  • C22C38/001—Ferrous alloys, e.g. steel alloys containing N
• • 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
  • C22C38/06—Ferrous alloys, e.g. steel alloys containing aluminium
• • 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
  • C22C38/38—Ferrous alloys, e.g. steel alloys containing chromium with more than 1.5% by weight of manganese
• • 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

Definitions

• the invention relates to a method for producing a steel strip or sheet consisting predominantly of Mn austenite.
• Steels that are suitable for the manufacture of such products are assigned to the AISI 200 and have the designation S20100 to S24000.
• Steel materials of this type are characterized by high strength, which is retained even after welding in the area of the weld.
• a further increase in the strength of steels of the conventionally castable steels explained above can be achieved by alloying aluminum and / or silicon. These two elements support mixed crystal hardening and thus lead to a further increase in strength.
• the addition of aluminum and silicon can influence the stacking error energy, which in turn has an influence on the deformation processes.
• the addition of aluminum leads to an increase in the stack error energy and favors the deformation due to the formation of twins.
• silicon lowers the stack fault energy, but favors the deformation about martensite formation.
• the combined addition of silicon and aluminum can thus have a targeted influence on the hardening of the material during deformation.
• the formation of martensite leads to a firm consolidation, while the formation of twins reduces the consolidation.
• the object of the invention is to provide a method for producing a steel consisting predominantly of Mn austenite, which can be produced cost-effectively and at the same time has increased strength compared to the prior art.
• This object is achieved by a method for producing a steel strip or sheet consisting predominantly of Mn austenite, in which a steel is melted which contains (in% by weight) the following alloy components: 15.00 - 24.00 Cr,
• the steel in a casting gap formed between two rotating rolls or rollers to form a thin strip with a thickness of max. 10 mm is poured, the rollers or rollers being cooled so strongly that the thin strip cools in the casting gap at a cooling rate of at least 200 K / s.
• the thickness of the thin strip is preferably between 1 and 5 mm.
• the specification of the steel composition used according to the invention also includes those alloys in which the content of those alloy elements is zero, for which only a maximum permissible upper limit of the content is specified.
• the chromium content of the steel can be 17.00-21.00% by weight of Cr, the manganese content can be 8.00-12.00% by weight of Mn and / or the nitrogen content limited to 0.40-0.60 wt% N his.
• levels of Ni, Mo and / or Cu may be present in the steel.
• the contents of the alloy elements contained in the steel composition used according to the invention are each optimized with regard to the effect of these elements.
• Cr, Mn, Mo, V, Nb and Al increase the nitrogen solubility in the melt, while Ni, Cu as austenite formers and Si reduce the nitrogen solubility.
• Si also acts as a mixed crystal hardener. It is also used for grain refinement and lowers the stacking error energy.
• AI increases the stack fault energy.
• Mo also acts as a mixed crystal hardener and improves the corrosion behavior.
• V also has a grain-refining effect and increases strength.
• the addition of Nb leads to an increase in strength through precipitation hardening.
• the invention makes use of the basically known technology of a strip caster by casting the steel in the casting gap formed between the rolls or rolls, for example a double-roll casting apparatus ("double roller"), and thereby cooling it so much that it causes a displacement of primarily ferritic solidification comes towards primary austenitic solidification.
• double roller double-roll casting apparatus
• This makes it possible to transfer the nitrogen dissolved in the melt into the steel, because the austenite has a high solubility for nitrogen.
• the possibility of such intensive cooling is only opened by casting a thin strip in a casting nip, the walls of which are formed by the casting rolls or rollers moving at essentially the same speed as the cast strip, so that a constant, intensive heat exchange between the walls (casting rollers / rollers) and the cast steel in the casting gap is guaranteed.
• the intensive cooling which takes place at a high cooling rate, ensures that nitrogen gas bubbles which may form in the solidifying melt remain small and the pressure directed against them is high. This prevents outgassing of the nitrogen during the solidification.
• such leakage of nitrogen is suppressed by the high ferrostatic pressure which occurs due to the large height of the melt pool in the casting gap. In this way it is ensured that the pressure P N in the nitrogen gas bubbles which may arise is always lower than the sum of the ambient pressure P A , the ferrostatic pressure P F and twice the surface tension ⁇ of the gas bubbles in relation to the bubble radius r (ie P N ⁇ P A + P F + 2 ⁇ / r).
• Hot strip made of continuously cast alloy can currently only be produced on a conventional hot strip mill with a thickness of at least 3.5 mm.
• the production of cold strip in the typical target thicknesses of 0.8 - 1.2 mm can only be achieved by intermediate annealing.
• intermediate annealing is no longer necessary due to the smaller thickness of the hot strip obtained.
• the procedure according to the invention makes it possible to produce steel strips and sheets which have particularly high nitrogen contents of 0.4 to 0.6% by weight and to which up to 3% of aluminum and / or silicon are alloyed at the same time, without the steel production having to do so must be carried out under excess pressure or particularly high levels of manganese are required.
• the steel products produced in this way have a fine-grained, isotropic structure with a small macro-segregation or a small number of coarse inclusions. Due to its Al and / or Si content, they also have increased strength and ductility compared to the prior art.
• the hardening and thus the energy absorption in the event of deformation can also be set in a targeted manner by the choice of alloy.
• the thin strip is preferably cast under a protective gas atmosphere.
• a thin strip with a modified surface can be produced in a simple manner, the degree of oxidation of which can be influenced in a targeted manner. In this way, scaling can be avoided.
• the strip obtained in this way can then be hot-rolled "inline" in a roll stand without the risk of the rollers sticking together.
• it is particularly advantageous if the thin strip is heated to an initial rolling temperature before hot rolling. This increase in temperature enables higher degrees of forming to be achieved during hot rolling.
• the hot strip By subjecting the hot strip to a heat treatment after hot rolling, its structure can be specifically optimized.
• the heat treatment can include annealing and subsequent controlled cooling.
• steel sheets produced according to the invention are particularly suitable for the production of body sheet metal parts, of stiffening structural components used in particular in general vehicle construction and especially in automobile construction, of chassis parts, of vehicle wheels and of fuel tanks.
• the particularly good strength properties of steel sheets produced by the method according to the invention have an advantageous effect.
• the good corrosion resistance of steel sheets and strips according to the invention proves to be advantageous in those applications in which they come into contact with aggressive media, such as fuels. The invention is explained in more detail below on the basis of a drawing illustrating an exemplary embodiment.
• the single figure shows schematically a strip casting installation 1.
• a steel is processed which, in addition to the usual unavoidable impurities (in% by weight), contains 0.08% C, 0.5% Si, 10% Mn, 19% Cr, 0.5% N , 0.3% AI and the rest contains iron.
• the strip caster 1 comprises a “double roller” two-roll casting apparatus, of which the rolls 2, 3, which rotate in opposite directions about an axis of rotation, are shown in the figure.
• a casting gap 4 is formed between the rollers 2, 3 and is continuously filled with melt, so that a melt pool S is formed above the casting gap 4.
• the rollers 2, 3 are intensively cooled during the casting process, so that the melt entering the casting gap 4 primarily solidifies austenitically at cooling rates of more than 200 K / s and the casting gap 4 as thin strip D with a thickness of 1 to 5 mm leaves.
• the thin strip D produced in this way then passes through a furnace 5, in which it is heated to an initial rolling temperature.
• Both the two-roll casting device with the rolls 2, 3 and the furnace 5 are accommodated in a housing 6 in which a protective gas atmosphere is contained.
• a protective gas atmosphere is contained.
• the thin strip D heated to the initial rolling temperature enters a rolling mill 7, in which it is hot-rolled to a final dimension. Due to the high initial rolling temperature, large degrees of forming are possible.
• the hot strip W rolled out of the thin strip D, which reaches the rolling mill essentially without scale, has a particularly high-quality surface after hot rolling.
• the hot strip W is annealed in a continuous annealing furnace 8 and then cooled in a controlled manner under a cooling device 9 in order to specifically improve its structure.
• the hot strip W heat-treated in this way is finally wound into a reel 10.
• Steel strip produced in the manner explained above has particularly high strength compared to conventionally assembled and produced steel strips due to its high nitrogen content achieved by the rapid cooling between the rolls 2, 3 of the two-roll casting apparatus, and at the same time good deformability and good energy absorption capacity.
• the table below compares the superior strength values of the hot strip W produced according to the invention in the casting and rolling mill 1 with the strength values of Mn austenite steels conventionally produced by continuous casting.

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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)
• Continuous Casting (AREA)
• Heat Treatment Of Sheet Steel (AREA)
• Metal Rolling (AREA)
• Heat Treatment Of Articles (AREA)
• Heat Treatment Of Strip Materials And Filament Materials (AREA)

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• 2000
  • 2000-09-19 DE DE10046181A patent/DE10046181C2/de not_active Expired - Fee Related
• 2001
  • 2001-09-14 WO PCT/EP2001/010645 patent/WO2002024969A1/de active IP Right Grant
  • 2001-09-14 US US10/380,792 patent/US20040025979A1/en not_active Abandoned
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  • 2001-09-14 AT AT01978372T patent/ATE350504T1/de not_active IP Right Cessation
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  • 2001-09-14 JP JP2002529559A patent/JP2004509762A/ja active Pending
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