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
  • C22C38/40—Ferrous alloys, e.g. steel alloys containing chromium with nickel
  • C22C38/58—Ferrous alloys, e.g. steel alloys containing chromium with nickel 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
• • 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
  • C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
• • 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
  • C22C38/40—Ferrous alloys, e.g. steel alloys containing chromium with nickel
  • C22C38/48—Ferrous alloys, e.g. steel alloys containing chromium with nickel with niobium or tantalum
• • 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
  • C22C38/40—Ferrous alloys, e.g. steel alloys containing chromium with nickel
  • C22C38/50—Ferrous alloys, e.g. steel alloys containing chromium with nickel with titanium or zirconium

Definitions

• the innovation relates to an austenitic stainless cast steel part, and a method for the production and use thereof.
• Austenitic stainless cast steel alloys are not alloyed with aluminium, and usually contain silicon levels of about 1%. Aluminium and high levels of silicon impair the purity of the cast steel part if contact between the molten steel and oxygen is not suppressed during the metallurgical production process. For this reason, the aluminium and silicon content in austenitic stainless cast steel alloys is minimised or restricted.
• Typical commercial austenitic stainless cast steel parts usually have ⁇ -ferrite levels of 5 to 10%.
• the ⁇ -ferrite level fractions lead to an increase in yield strength at 0.2% offset and in tensile strength and a decrease in elongation at break compared with the purely austenitic microstructure state.
• a balanced nickel and chromium equivalent is adjusted via the chemical composition of the cast steel.
• the low 6-ferrite content changes the solidification structure. Undesirable liquation products, which accumulate at the grain boundaries, are reduced, a fact which positively affects the susceptibility to hot cracking.
• the chromium content of austenitic stainless cast steel is around 19%. Moreover, it is often alloyed with 2 to 3% molybdenum. The chromium and molybdenum content creates a passivating protective layer that increases the resistance to corrosion, especially by halides. It also supports ferrite formation.
• the nickel content of rustproof austenitic cast steel is about 10% and the carbon content is about 0.03% [1-3, 6].
• patent application [7] discloses a stainless cast steel that has a high corrosion fatigue strength and high pitting corrosion resistance.
• the TRIP effect (transformation induced plasticity) has yet to be studied in austenitic cast steel alloys. Nor have technical applications materialized that exploit the TRIP effect in austenitic cast steel. The reason for this is apparently the fact that austenitic cast steel parts are not cold formed and the manufactured parts are used in the cast state. Thus, it is not technically possible to use the TRIP effect in cast alloy parts, as opposed to wrought alloy parts, to improve cold formability. As yet, there are no references in the literature to the occurrence of a TRIP effect in austenitic cast steel alloy parts. This is due primarily to the fact that the TRIP effect in the form of a plastic yield contribution has not yet been quantified.
• High-manganese austenitic steels usually have a chromium content of less than 12%, which is why they are non-rusting. In these steels, iron oxide layers are formed on the surface and the material rusts. If aluminium and silicon oxides are occluded in these rust layers, the corrosion resistance grows.
• Patent DE 199 00 199 describes such a high-strength lightweight construction steel that contains manganese. The concentrations of the alloying elements aluminium, silicon, nickel, manganese and nitrogen are similar to the concentrations of the inventive cast steel. Unlike the inventive steel, this steel has a chromium content of less than 10% and is therefore not a stainless steel. Moreover, this steel is not used in the cast state, but rather is worked to produce vehicle bodies and semifinished prestressed concrete goods.
• Warm- or cold-rolled semifinished goods serve as starting material for cold-formed parts.
• the TRIP effect in austenitic alloys is regulated via the chemical composition of the austenite and the forming conditions [5].
• Ni equiv. % Ni+30% C+18% N+0.5% Mn+0.3% Co+0.2% Cu ⁇ 0.2% Al (2)
• inventive austenitic cast steel alloy parts are to be found in the increase in tensile strength and elongation at break. That means that the TRIP effect renders the cast steel part stronger and tougher simultaneously. It can therefore accommodate greater forces and deform more extensively, without breaking. As a result, the application range of the inventive TRIP cast steel alloy parts is expanded. Above all, the resultant lightweight construction leads to savings on costs for energy and material.
• the inventive cast steel yields tensile strength greater than 550 MPa and elongation at break of more than 30%. Consequently, the cast steel can be used to make cast parts with a kind of crash reserve. This means that the steel is cast and integrated into an application, without exposure to a tensile load. If, however, a crash or a heavy load occurs, the part, thanks to the potential to exhibit the TRIP effect, can accommodate/absorb high tensile strength and elongation at break.
• the TRIP effect can be influenced via the chemical composition of the austenite. Moreover, it requires that the austenite- and ferrite-stabilising elements be coordinated.
• the microstructure of austenitic cast steel and the microstructure of formed austenitic wrought alloys of the same chemical composition differ, however.
• the microstructure of austenitic cast steel parts contains solidification-induced liquation, the vast bulk of which is retained during technical cooling.
• dendritic solidification influences the defect structure of the austenite.
• austenite and ferrite are simultaneously present in a stainless cast steel, internal stresses are formed during cooling.
• separation of the alloying elements occurs. When this happens, the austenite-stabilising elements accumulate chiefly in the austenite. At the same time, the austenite becomes depleted in ferrite-stabilising elements. The influence of these factors on the TRIP effect in cast steel alloy parts is not yet known.
• the microstructure of the inventive cast material must consist of metastable austenite. Consequently, austenite has a corresponding tendency to form deformation-induced martensite at room temperature and at low temperatures.
• a corresponding chromium and nickel equivalent is adjusted in the austenitic cast steel.
• the chemical composition of the steels must be coordinated with regard to the ferrite-stabilising and austenite-stabilising elements, as specified in the patent claim.
• the chromium and nickel equivalent to be adjusted for producing an austenitic cast steel part which has a TRIP effect differs from the chromium and nickel equivalent for austenitic wrought alloys which have a TRIP effect.
• Nickel and/or manganese are added to cast austenitic steel in order that austenite may be formed at high temperatures.
• Manganese serves in this regard as an inexpensive substitute for nickel. This is usually accompanied by a deterioration in corrosion resistance. Adding nitrogen can compensate this negative effect in certain circumstances. The nitrogen improves the strength and corrosion properties [8] and simultaneously effects austenite stabilisation.
• the chromium content of the inventive cast steel ranges from 12 to 20%, but is never less than 10%. Steel with a chromium content higher than 12% acts as guarantor for passivation of the material.
• chromium is added to stabilise ferrite. It simultaneously influences the austenite stability as well because it hampers martensite formation as the chromium content rises.
• the contents of the elements for stabilising austenite and ferrite have to be coordinated with each other.
• the elements aluminium and silicon are used first to adjust the necessary chromium or nickel equivalent.
• the influence which the aluminium and silicon dissolved in the austenite exert on the corresponding equivalents is thereby described with the aid of effective factors.
• the TRIP effect can be adjusted selectively via the solution or segregation state of nitrides, such as AlN.
• both grain refinement and consolidation of the austenite are achieved.
• the profile of a cast steel part as regards its strength and toughness properties are additionally improved by highly disperse AlN segregations in the fine-grained austenite.
• the ready availability of the elements silicon and aluminium means that more costly steel alloying elements in steel, such as nickel and chromium, can be replaced.
• the inventive austenitic stainless cast steel part has a manganese content of 0 to 25%, a chromium content of 12 to 20%, but never less than 10%, a nickel content of 0 to 12%, a niobium content of 0 to 1.2%, a tantalum content of 0 to 1.2%, a carbon content of 0.01 to 0.15%, a nitrogen content of 0.005 to 0.5%, a copper content of 0 to 4%, a cobalt content of 0 to 1%, a molybdenum content of 0 to 4%, a tungsten content of 0 to 3%, a titanium content of 0 to 1% and a vanadium content of 0 to 0.15%.
• the mechanical properties improve.
• the tensile strength increases to more than 550 MPa and the elongation at break to more than 30%.
• cast steel material is particularly tough despite the increased strength values.
• the inventive cast steel part has a high energy absorption capacity at room temperature and low temperatures.
• the energy absorption capacity for these alloy parts is approximately between 0.30 and 0.40 J/mm 3 at room temperature. This means that in the event of a sudden stress, such as a crash, the cast steel part consolidates and simultaneously deforms, without breaking. Therefore, the cast steel part is particularly suitable for crash-stressed parts used in automotive construction.
• the manganese content is 0 to 25%
• the chromium content is 12 to 20%
• the nickel content is 0 to 12%
• the niobium content is 0 to 1.2%
• the tantalum content is 0 to 0.2%
• the carbon content is 0.01 to 0.15%
• the nitrogen content is 0.005 to 0.5%
• the copper content is 0 to 4%
• the cobalt content is 0 to 1%
• the molybdenum content is 0 to 4%
• the tungsten content is 0 to 3%
• the titanium content is 0 to 1%
• the vanadium content is 0 to 0.15%.
• the inventive austenitic stainless cast steel part has a chromium content of 16.5%, a nickel content of 6.5%, a silicon content of 1.1%, a manganese content of 7% and an aluminium content of 0.05%.
• the carbon content is 0.04% and the nitrogen content is 0.1%.
• the cast steel part can undergo heat treatment in a further step.
• the alloy used in the method has, especially, a manganese content of 0 to 25%, a chromium content of 12 to 20%, a nickel content of 0 to 12%, a niobium content of 0 to 1.2%, a tantalum content of 0 to 0.2%, a carbon content of 0.01 to 0.15%, a nitrogen content of 0.005 to 0.5%, a copper content of 0 to 4%, a cobalt content of 0 to 1%, a molybdenum content of to 4%, a tungsten content of 0 to 3%, a titanium content of 0 to 1%, and a vanadium content of 0 to 0.15%.
• the alloy employed in the method has a manganese content of 5 to 12%, a nickel content of 2 to 8%, a copper content of 0 to 2%, a cobalt content of 0 to 0.5%, a molybdenum content of 0 to 2.5%, and/or a tungsten content of 0 to 0.5%.
• the object is also achieved by a cast steel part (steel casting or steel casting part), produced by a method as previously described, characterised in that the cast steel part has a tensile strength greater than 550 MPa and an elongation at break of more than 30%.
• the cast steel part exhibits a TRIP effect under load.
• An inventive method for using a cast steel part in a technical application comprises the steps: performing the steps of one of the methods described above for the production of the cast steel part; and use of the cast steel part in a technical application, wherein use after casting proceeds without the performance of a chipless forming process.
• chipless or non-cutting forming processes are all forming processes which, due to mechanical action, would trigger the TRIP process in the cast steel part.
• These forming processes, such as rolling, forging, pressing, etc. are not performed, with result that the cast steel part, after being integrated in the application, still has the potential to exhibit the TRIP effect and thus, in the event of a stress situation, has a reserve with regard to tensile strength and elongation at break. It should, however, be possible to perform cutting processes on the cast steel part which do not trigger the TRIP effect, without departing from the framework of the invention.
• the cast steel part is used as casting material for plant and refrigeration technology, for equipment and components for the production of gases and for liquefying and fractionating gases, for use in automotive and aircraft construction, for crash-stressed parts, such as crash boxes in motor vehicles, for components for transporting liquid gases and as a component which is exposed to low temperatures, and/or as casting steel foam.
• An inventive component for automotive or aircraft construction especially, crash box, A, B or C pillar of a motor vehicle, is formed as a cast steel part as described above.
• the austenitic cast steel part has an austenitic microstructure at room temperature with a 5% ⁇ -ferrite content. On account of the TRIP effect triggered in the tensile test, tensile strength greater than 550 MPa and elongation at break greater than 30% are obtained. At temperatures below room temperature, the cast steel material is tough despite increased strength values.
• the inventive cast steel has an energy absorption capacity at room temperature of approximately 0.37 J/mm 3 .

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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)
• Heat Treatment Of Steel (AREA)
• Heat Treatment Of Articles (AREA)

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• 2006
  • 2006-07-20 DE DE102006033973A patent/DE102006033973A1/de not_active Ceased
• 2007
  • 2007-07-19 RU RU2009105693/02A patent/RU2451763C2/ru not_active IP Right Cessation
  • 2007-07-19 WO PCT/EP2007/057473 patent/WO2008009722A1/de not_active Ceased
  • 2007-07-19 CA CA002657747A patent/CA2657747A1/en not_active Abandoned
  • 2007-07-19 JP JP2009519986A patent/JP5340148B2/ja not_active Expired - Fee Related
  • 2007-07-19 CN CN2007800274368A patent/CN101490297B/zh not_active Expired - Fee Related
  • 2007-07-19 KR KR1020097003429A patent/KR20090035710A/ko not_active Withdrawn
  • 2007-07-19 EP EP07787731A patent/EP2059623A1/de not_active Ceased
  • 2007-07-19 US US12/374,482 patent/US20090324441A1/en not_active Abandoned

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