Classifications

• • 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
  • C21D9/00—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor
  • C21D9/46—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor for sheet metals
• • 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
  • C21D1/00—General methods or devices for heat treatment, e.g. annealing, hardening, quenching or tempering
  • C21D1/62—Quenching devices
  • C21D1/673—Quenching devices for die quenching
• • 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
  • C21D9/00—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor
  • C21D9/0068—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor for particular articles not mentioned below
• • 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
• • 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
  • C22C38/04—Ferrous alloys, e.g. steel alloys containing manganese
• • 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
  • C22C38/14—Ferrous alloys, e.g. steel alloys containing titanium or zirconium
• • 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
  • C21D2211/00—Microstructure comprising significant phases
  • C21D2211/001—Austenite
• • 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
  • C21D2211/00—Microstructure comprising significant phases
  • C21D2211/008—Martensite

Definitions

• the invention describes the use of a steel alloy.
• thermoforming and press hardening It has been proven to produce high strength, relatively thin components with complex shape and high dimensional accuracy for structural and safety parts such as A and B pillars or bumpers in the automotive industry.
• sheets with thicknesses of 3 mm or less are typically formed and steels with a low carbon content are used.
• the cited document describes a steel alloy with C ⁇ 0.4%; Silicon in a steel-making method dependent, but otherwise insignificant Salary; 0.5 to 2.0% Mn; Max. 0.05% P; Max. 0.05% S; 0.1 to 0.5% Cr and / or 0.05 to 0.5% Mo; up to 0.1% Ti; 0.0005 to 0.01% B, up to a total of 0.1% Al and, where appropriate, levels of copper and nickel up to 0.2% each.
• a typical boron-alloyed steel for thermoforming and hardening is, for example, In DE 197 43 802 C2 disclosed.
• the DE 197 43 802 C2 describes a method of making a metallic mold component for automotive components having regions of higher ductility.
• a board is provided of a steel alloy, which is in weight percent of carbon (C) from 0.18% to 0.3%; Silicon (Si) 0.1% to 0.7%; Manganese (Mn) 1.0% to 2.5%; Phosphorus (P) maximum 0.025%; Chromium (Cr) 0.1% to 0.8%; Molybdenum (Mo) 0.1% to 0.5%; Sulfur (S) maximum 0.01%; Titanium (Ti) 0.02% to 0.05%: boron (B) 0.002% to 0.005%; Aluminum (Al) 0.01% to 0.06% and the balance iron including melting impurities.
• the named alloy is outstandingly suitable for thermoforming and press hardening. However, the alloy structure in the hardened state consists predominantly of martensite. Thus, there is not always enough ductility in the material for the particular load case.
• the DE 10 2005 054 847 B3 therefore proposes to use a thermoformed and press-hardened structural member which has been heat treated at 320 to 400 degrees Celsius after the thermoforming and press hardening process.
• This heat treatment specifically influences the high-strength properties of the component.
• the yield strength R p0.2 and the elongation A 5 remain almost unchanged. Only the tensile strength values Rm are reduced by 100 to 200 N / mm 2 .
• the material still has the necessary high-strength mechanical properties, but due to the slightly lower tensile strength Rm, the material is so ductile that it wrinkles when it is loaded instead of breaking or tearing.
• Rm slightly lower tensile strength
• the prior art is also the US 6,544,354 B1 to name, which relates to the production of a high-strength steel alloy.
• the steel alloy has a structure that is composed of ferrite and / or bainite and retained austenite. This steel alloy is particularly suitable for absorbing high forces under dynamic load.
• the thermoformed structure is suitable for compression molding.
• the prior art are the EP 2 003 221 A1 as well as the EP 2 039 791 A1 to be mentioned, each of which relates to high-strength steel alloys and corresponding manufacturing processes.
• TRIP steels (TRANSformation Induced Plasticity) are well known. These are particularly high-strength steel alloys that have a multi-phase structure. TRIP steels are stronger and, at the same time, more ductile than conventional steel grades. They thereby enable the production of lighter components with a given required strength and ductility.
• the TRIP effect is the special martensite formation during forming. This causes a simultaneous increase in hardness and formability in mechanical forming in product manufacture or use.
• the manifestation of the effect is mainly influenced by the cost-effective alloying elements aluminum and silicon. In addition, much more expensive alloying elements such as nickel can be saved. The inherent yield strength is higher than that of comparable steels, since the silicon enables the form of solid solution hardening.
• the metastable carbon-rich begins Austenite transforming into martensite induced by deformation.
• the TRIP steel is purposefully solidified after the plastic deformation.
• TRIP steel is cold formed.
• cold-formed components with high yield strength and tensile strength are limited in the complexity of the geometry.
• the springback of the steel must already be considered when designing the tool.
• the residual strain is lower than in the un-formed area. The component consequently has uneven component properties.
• the WO 2004/022794 A1 shows a method of producing a steel having a retained austenite content in the steel structure by heating a corresponding steel to produce austenite and then quenching it to at least partially convert the austenite to martensite. Then carbon is redistributed from martensite into the remaining austenite. This redistribution takes place in the area of the martensite start temperature. Therefore, the steel is kept in this temperature range correspondingly long or heated again and then selectively cooled.
• the WO 2004/022794 A1 does not disclose boron-alloyed steel.
• the DE 10 2008 010 168 A1 describes the use of a type of steel for tanking a vehicle, expressed as a percentage by weight, of 0.35 to 0.55% carbon; 0.1 to 2.5% silicon; 0.3 to 2.5% manganese; Max. 0.05% phosphorus, max. 0.01% sulfur; Max. 0.08% aluminum; Max. 0.5% copper; 0.1 to 2.0% chromium; max 3.0% nickel; max 1.0% molybdenum; max 2.0% cobalt; From 0.001 to 0.005% boron; 0.01 to 0.08 niobium; Max. 0.4% vanadium; Max. 0.02% nitrogen; Max. 0.2% titanium, remainder iron and impurities caused by melting.
• This steel grade is also thermoformed. In addition to being used for armor purposes, this alloy has a relatively high carbon content which reduces weldability.
• the invention is therefore the object of a hot-formed and press-hardened component with a high yield strength and a high tensile strength, but at the same time to provide improved over the prior art ductility.
• thermoforming and press hardening process Remaining iron and unavoidable impurities dissolved in a thermoforming and press hardening process.
• a board separated from a strip material or an already preformed component is heated to a temperature above the Ac 3 point of the alloy, so that a transformation of the microstructure into austenite takes place.
• the blank or preformed component is placed in a forced-cooled mold, reshaped and simultaneously cured by cooling to a temperature below about 200 ° C. Pressing in the closed tool prevents a delay.
• the finished thermoformed and press-hardened component is removed from the tool. Due to the special composition of the steel, in particular the relatively large addition of silicon, hardening does not only produce martensite.
• austenite remains as retained austenite, which remains stable up to temperatures of minus 100 ° C.
• the microstructure may also contain portions of bainite.
• the silicon in the steel prevents carbide formation, which makes carbon available to stabilize retained austenite.
• the retained austenite gives the steel according to the invention a higher Elongation at break as the classical boron-alloyed pure martensitic hot-forming steel.
• the crash case of structural and safety components are typically used for the thermoformed and press-hardened components, formed from the remaining austenite martensite again, which additionally hardens the steel in the event of a crash.
• tensile strengths are achieved, which are comparable to conventional thermoforming steel with a comparable carbon content.
• the desired structure is not achieved in the hot rolling process, but in the thermoforming process (press hardening). If the structure already exists after hot rolling, the steel is suitable for cold forming. During the forming of the steel, the metastable retained austenite present in the hot strip can be transformed into martensite. On the other hand, in hot working / press hardening, the hot strip, which in the initial state may have any structure, is austenitized, thermoformed and press hardened, so that in combination with a subsequent tempering, the desired microstructure of mainly martensite with proportions of bainite and retained austenite is achieved.
• the steel according to the invention has the following composition expressed in weight percent: C 0.22 - 0; 25% Mn 1.5-1.7% Si 1,95-2,1% Cr Max. 0.15% al 0.03 - 0.05% Ni Max. 0.2% B 0.002 - 0.0035% P Max. 0.015% S max: 0.01% Ti 0.005 - 0.1% Nb Max. 0.1% N Max. 0.01%
• this alloy composition After being heated above Ac 3 and thermoformed and press-hardened in a water-cooled indirect thermoforming tool, this alloy composition reaches a yield strength Rm> 1600 MPa, a tensile strength R p0 . 2 > 1050 MPa and an elongation at break A 5 > 10.5%.
• the hardened structure consists of martensite and retained austenite.
• the fraction of retained austenite in the finished component increases the elongation at break of the component.
• a typical for press hardening as fast and direct cooling process for the achievement of the desired structure sufficient.
• a separate carbon redistribution need not be performed. Due to the thermoforming and press hardening, no springback of the material is to be expected.
• the surface of the component is less scaled when heated than with conventional thermoforming steels. This makes it possible to produce a thermoformed and press-hardened component having a surface that can be directly coated without previous blasting. In addition, the hardened steel is more durable due to the high silicon content.
• the formation of carbides during tempering is suppressed, so that the material can be galvanized even at 400 to 450 ° C, while maintaining the tensile strength Rm still> 1450 MPa. Since the Ac 3 temperature of the alloy is increased by the high silicon content, the heating temperature must be set correspondingly higher. It must be at least 960 ° C with a silicon content of 2%.
• the inventive use of the alloy composition according to the invention in a thermoforming and Press hardening process good for producing a dimensionally accurate high strength component with increased ductility.

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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 Articles (AREA)
• Shaping Metal By Deep-Drawing, Or The Like (AREA)

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• 2010
  • 2010-01-04 DE DE102010003997A patent/DE102010003997A1/de not_active Withdrawn
  • 2010-12-29 US US12/980,805 patent/US20110182765A1/en not_active Abandoned
  • 2010-12-29 EP EP10016155.3A patent/EP2341156B1/fr not_active Not-in-force

Patent Citations (13)

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