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
  • C21D1/00—General methods or devices for heat treatment, e.g. annealing, hardening, quenching or tempering
  • C21D1/18—Hardening; Quenching with or without subsequent tempering
  • C21D1/185—Hardening; Quenching with or without subsequent tempering from an intercritical temperature
• • 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
  • C22C1/00—Making non-ferrous alloys
  • C22C1/02—Making non-ferrous alloys by melting
• • 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
  • C22C38/002—Ferrous alloys, e.g. steel alloys containing In, Mg, or other elements not provided for in one single group C22C38/001 - C22C38/60
• • 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
  • C22C38/06—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
  • C22C38/26—Ferrous alloys, e.g. steel alloys containing chromium 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
  • C22C38/28—Ferrous alloys, e.g. steel alloys containing chromium with titanium or zirconium
• • 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
  • C22C38/32—Ferrous alloys, e.g. steel alloys containing chromium with boron
• • 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
  • 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
  • C22C38/44—Ferrous alloys, e.g. steel alloys containing chromium with nickel with molybdenum or tungsten
• • 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
  • C22C38/46—Ferrous alloys, e.g. steel alloys containing chromium with nickel with vanadium
• • 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
  • C22C38/54—Ferrous alloys, e.g. steel alloys containing chromium with nickel with boron
• • 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
  • C21D2211/00—Microstructure comprising significant phases
  • C21D2211/002—Bainite
• • 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
  • C21D2211/005—Ferrite
• • 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 relates to a steel for the production of a steel component, a flat steel product consisting at least in sections of such a steel, a steel component produced from such a steel flat product by hot forming and quenching and a method for producing such a steel component.
• the present invention relates to the use of steels having a ferritic / pearlitic / bainitic structure in the delivery state with precipitation hardening, for the production of press-hardened components in the strength range of about 700 to 1150 MPa.
• alloy contents are stated here only in “%”, this always means “% by weight”, unless expressly stated otherwise.
• components which are produced by hot forming and subsequently hardening of flat steel products which consist of a manganese-boron steel have prevailed here for crash-relevant automotive components.
• hot press hardening manufacturing components can be produced, which can be used with optimally thin wall thickness and concomitantly minimized weight, for example, as B-pillars, B-pillar reinforcement and bumpers.
• a typical example of a manganese-boron steel of the type mentioned above is the steel known in the art as 22MnB5, which has been given the material number 1.5528.
• Hot forming with subsequent press hardening makes it possible to produce components with complex geometries with optimum properties from steels of this type Create dimensional accuracy. Due to their predominantly martensitic structure, the components obtained by hot-pressing hardening have the highest strengths (Rm approx. 1500 MPa, R P0 , 2 approx. 1100 MPa) and thus have an optimized lightweight construction potential.
• Rm approx. 1500 MPa, R P0 , 2 approx. 1100 MPa Due to their predominantly martensitic structure, the components obtained by hot-pressing hardening have the highest strengths (Rm approx. 1500 MPa, R P0 , 2 approx. 1100 MPa) and thus have an optimized lightweight construction potential.
• Rm approx. 1500 MPa, R P0 , 2 approx. 1100 MPa Due to their predominantly martensi
• Tailored blanks are blanks composed of at least two sheets. The sheets in question differ in at least one property.
• a particularly high strength and at the same time comparatively low toughness can be provided, while in another section a reduced strength but increased toughness is available.
• a Tailored Blank for a B-pillar may be designed so that, for example, the upper area associated with the roof of the vehicle to which high strength requirements apply is 22MnB5, while the area associated with the B-pillar foot is a steel grade exists, which has an increased ductility after curing.
• An example of a suitable steel for this purpose is steel H340LAD, to which the material number 1.0933 has been assigned. This steel reaches a Tensile strength of about 500 to 650 MPa at an elongation of about 15% after hot working.
• WO 2008/132303 Al Another development towards partner material for tailored blanks is in the WO 2008/132303 Al described.
• This is a steel plate made of a microalloyed steel with an Al or Zn-based corrosion protection coating. After full austenitization and subsequent press hardening, it has a predominantly ferritic structure (> 75%) with lower levels of martensite (5-20%). and bainite ( ⁇ 10%). Restaustenitanteile in the structure are expressly undesirable.
• Components made from 0.5 - 4 mm thick steel blanks produced by this hot forming process have tensile strengths in the range of 500-600 MPa at elevated elongation values (> 15%). The improved ductility ensures a higher energy absorption capacity in the event of a crash.
• an apparatus and a method for press hardening of blanks of higher and ultrahigh - strength steels are known.
• the known device allows the control of the tool temperature during the forming process, whereby tailored tempering and hot forging can be performed.
• tailored tempering and hot forging only partially heats the dies during hot forming.
• the targeted temperature control produces locally a mixed structure with reduced strengths but improved ductility.
• the workpiece In warm forging, the workpiece is heated to a temperature below the recrystallization temperature.
• the warming temperature for warm forging is typically in the range of 400-650 ° C.
• An example of a steel which is particularly suitable for hot forging is the steel known as "CP-W 800", which according to DIN EN 10336 is assigned the designation HDT780C.
• Conventional practice for the 22MnB5 steel subjected to phase transformation during press-hardening requires mold temperatures below 200 ° C to produce a martensitic structure after press-hardening.
• the object of the invention was to provide a steel which is optimally suitable for the production of components by hot-press hardening, a steel flat product also optimally suitable for hot-press hardening, a steel component in which high strength and high ductility are optimally achieved combined, and to provide a method for producing such a component.
• the solution according to the invention of the abovementioned object is that such a flat steel product consists of a steel according to the invention.
• a flat steel product according to the invention accordingly consists, at least in one section, of a steel according to the invention.
• the flat steel product according to the invention consists of at least one section of a steel according to the invention includes, of course, the possibility that the flat steel product as a whole is made of a steel according to the invention.
• the at least one section of the flat steel product consisting of the steel according to the invention may be formed from a hot-rolled sheet or a sheet produced by conventional cold-rolling.
• the flat steel product according to the invention can be a tailored blank, which is composed of at least two sheet metal parts which are themselves in addition to possibly existing differences in their areal extent in at least one property, such as thickness, strength, toughness, elongation properties, etc., distinguish.
• the steel component according to the invention is produced by hot forming and subsequent quenching of a flat steel product according to the invention.
• the steel component has a tensile strength of at least 700 MPa in the region in which the steel obtained according to one of claims 1 to 5 has a structure consisting of a combination of finely divided hard phases (martensite / bainite ) and ductile phases (globular ferrite and dislocation-rich bainitic ferrite) and a residual austenite content of at most 5 area% in a fine-grained microstructure with additional precipitation hardening of titanium carbonitrides.
• the average grain diameter of the globular ferrite or of the bainitic ferrite is 1.5-4.0 ⁇ m and the proportion of ductile phases is at least 5 area%.
• the structure consists of a combination of finely divided hard phases (martensite / bainite) and more ductile phases (bainitic ferrite and globular ferrite) and retained austenite with additional precipitation hardening by titanium carbonitrides.
• the proportion of ductile phases depends thereby directly from the C content and amounts to at least 5 area%.
• the ferrite structure of the steel component according to the invention is extremely fine.
• the average grain diameter of the ferrite or bainitic ferrite here is 1.5-4.0 microns, which according to DIN EN 643 with a particle diameter of 4.0 microns a particle size index of at least 13 and with a particle diameter of 1.5 microns a grain size number> 15 corresponds.
• the fine-grained microstructure means not only small grains but also a high number of phase boundaries in the steel component produced from the steel according to the invention by hot press hardening. These have a stronger effect on the tensile strength than the ferritic grain boundaries alone.
• the bainitic ferrite also has a high dislocation density. The fine structure and the high dislocation density contribute to the special mechanical and technological properties of the steel according to the invention, of a steel flat product consisting thereof and of a steel component produced therefrom.
• the transfer from the oven to the tool can be completed within 5 to 12 seconds.
• the invention provides a steel and a flat steel product made therefrom which, after hot-pressing hardening, have a tensile strength which, at breaking elongation values A 80 of 6 to 15%, are typically in the range from 700 to 1200 MPa, in particular 700 to 1150 MPa. In this way, the invention closes the gap between the materials with relatively low tensile strength and higher elongation at break (eg H340LAD) and materials with high tensile strength values and low elongation at break (eg 22MnB5).
• C is present in a steel according to the invention with a content of at least 0.05% by weight and at most 0.150% by weight, in particular 0.06-0.11% by weight, in order, on the one hand, to ensure that the final one Deterrence, the minimum tensile strength of 700 MPa required for steel components according to the invention forms necessary Martensithärte and on the other hand to avoid an excessive increase in hardness.
• the C content is limited to a maximum of 0.150 wt .-%, so as not to affect the weldability of the steel component according to the invention.
• the range of tensile strength prescribed for the steel components according to the invention can be achieved particularly reliably if the C content of the steel is at least 0.08% by weight.
• Mn in contents of 0.50-2.0% by weight serves as austenite former in the steel according to the invention by reducing the A C3 temperature by its presence.
• the result is a high austenite content even at relatively low heating temperatures.
• To optimize the weldability of the Mn content can be lowered to a maximum of 1.20 wt .-%.
• Si acts as an oxidizing agent in the steel according to the invention on the one hand on the other hand, it has a positive effect on the mechanical properties. This is the case in particular if at least 0.20% by weight of Si are present in the steel according to the invention.
• the presence of Si in the limits specified by the invention increases the yield strength and stabilizes the ferrite and the austenite at room temperature.
• Si prevents unwanted carbide precipitation in austenite during cooling. Excessive Si content causes surface defects.
• the size of the grains forming in the microstructure of the steel according to the invention can be controlled via the Al content. Accordingly, the formation of a particularly fine-grained microstructure contributes when the Al content of the steel according to the invention is at least 0.020% by weight.
• Ti increases the yield strength and causes the formation of precipitates, which are present, for example, as titanium carbonitrides in a steel according to the invention.
• precipitation formation increases tempering resistance and improves toughness by inhibiting grain growth during furnace heating during hot working.
• a steel according to the invention contains relatively high Ti contents of 0.08-0.14% by weight, in particular at least 0.09% by weight.
• Cr is contained in the steel according to the invention in amounts of 0.15-0.5% by weight in order to promote through-hardenability and thereby minimize the dependence on the cooling rate. In this way, steel according to the invention becomes less sensitive to possible fluctuations of the hot working parameters. However, in order to avoid surface defects on the finished steel component according to the invention, the Cr content must not exceed 0.5% by weight. The positive effects of the presence of Cr in a steel according to the invention can be used particularly reliably if the Cr content is 0.3-0.4% by weight.
• the S-content of the steel according to the invention must not exceed 0.010% by weight, because otherwise problems in welding, in surface finishing and in the formation of harmful, elongated MnS precipitates are to be expected.
• the S content of the steel according to the invention is as low as possible.
• a steel according to the invention may optionally contain one or more of the elements selected in the group "P, N, Cu, Ni, Mo, V, B, Nb, Ca "are summarized. Each of these elements can have a positive benefit, but is not a compulsory component and can be dispensed with as such in order to be able to produce a steel component with the properties prescribed according to the invention by hot forming and subsequent hardening.
• P may be present in amounts of up to 0.1 wt .-%.
• P increases the stability of austenite. Too high a P content, however, damages the ductility and toughness of the steel.
• N stabilizes the austenite in the steel according to the invention and increases the yield strength.
• the presence of N enables the desired formation of titanium carbonitrides according to the invention. If N is not completely bound by Ti and the steel according to the invention additionally contains B, N reacts in combination with boron to boron nitrides, which cause grain refining of the starting structure and thus a refining of the martensitic structure present in the finished steel component after hot working and hardening.
• the N content of the steel according to the invention may be set to at least 0.0025% by weight.
• Cu can be used in the steel according to the invention to increase the yield strength. However, at levels above 0.1% by weight, the presence of Cu may affect the hot workability of the steel.
• Ni can improve the yield strength and elongation at break of the steel of the present invention. In addition, contents are avoided for cost reasons.
• Mo is optionally present in the steel of the present invention at levels of up to 0.1% by weight. Mo promotes martensite formation and improves toughness. Over 0.1% by weight However, exceeding Mo content may cause cold cracking in the steel according to the invention.
• V increases the yield strength of the steel of the invention by grain refining and improves weldability.
• B By adding up to 0.001% by weight of B, the hardenability of the steel according to the invention can be improved.
• B prolongs the transformation times and stabilizes the mechanical properties for a wide temperature range of the hot working process in terms of early, homogeneous martensite formation.
• amounts of B exceeding 0.0010% by weight markedly reduce the formability of the steel according to the invention.
• Nb in amounts of up to 0.25% by weight increases the yield strength of the steel according to the invention by carbide precipitation and, by austenitic grain refining, produces a fine martensite structure which has a high resistance to crack propagation.
• These positive properties can be used in particular when the Nb content is at least 0.001% by weight, in particular at least 0.005% by weight.
• Ca is optionally alloyed to a steel of the invention at levels of 0.001-0.004 wt%, especially 0.001-0.003 wt%, to allow sulfide form control through the formation of spherical CaS over MnS. In this way, the isotropy of the mechanical properties is improved.
• a Ca-treatment of the melt of the Steel according to the invention can also reduce the S content of the steel according to the invention.
• the flat steel product according to the invention may have a surface finish for protection against scaling or corrosion.
• the protective coating concerned can be applied by conventional methods.
• the protective coating is applied in the hot dipping process and can contain zinc or aluminum in a conventional manner as a basic element.
• the basic elements Zn and Al may optionally be alloyed with each other or additionally each with one or more oxygen-affine elements such as Mg, Si, Ti, Ca, boron, Mn.
• Typical layer thicknesses of the protective coating are in the range 3-30 ⁇ m, preferably between 5-20 ⁇ m.
• the hot dip coating can be preceded by a preoxidation in which a 10 to 1000 nm, preferably 70 to 500 nm, thick oxide layer is produced on the flat steel product to be coated.
• the generation and adjustment of the oxide layer can take place in an oxidation chamber, as in the WO 2007/124781 A1 is described, the contents of which is included in the present application in this respect.
• the complete reduction of the iron oxide layer thus formed takes place under a hydrogen-containing atmosphere and is carried out before immersion in the melt or before surface refinement.
• Oxides of the alloying elements of the steel according to the invention can be present on the steel strip surface.
• PVD / CVD processes processes with electrolytic or electroless or chemical deposition of metallic coatings, in particular coatings based on Zn, Zn-Ni, Zn-Fe and their combinations, as well as processes in which organic, organometallic, inorganic Coatings are applied in coil coating systems in the coil coating, spraying or dipping process can be used.
• Steel flat products according to the invention can be produced by casting a molten steel composite according to the invention into slabs or thin slabs, which are subsequently brought to a temperature of 1050.degree.-1260.degree. C., at a hot rolling end temperature of 800.degree.-1000.degree. C. to form a hot strip having a hot strip thickness of to be hot rolled less than 4.5 mm.
• the resulting hot strip is then coiled at a reel temperature of 450 - 700 ° C to form a coil.
• Steel flat products according to the invention which are present as hot strip or sheet metal can produce steel components according to the invention in the same way as steel flat products according to the invention which are present as cold strip or sheet metal.
• this can be done following the hot strip production explained above hot rolled strip obtained is cold rolled to a cold strip having a thickness of typically 0.5 to 2.85 mm.
• blanks are separated from the flat steel product then present as a strip.
• these boards can be welded to at least one other board.
• the boards split off from the flat steel products produced according to the invention can also be processed as one piece into a steel component according to the invention.
• the flat steel product which is now in the form of a single-piece blank or blanked blank, is heated to a heating temperature of 750-950 ° C.
• a heating temperature 750-950 ° C.
• the heating in accordance with the invention predetermined range of heating temperatures leads to a hot working and a press hardening to a microstructure, which consists of a combination of finely divided martensite and bainite phases, dislocation rich bainitic ferrite, globular ferrite and retained austenite.
• an additional precipitation hardening by titanium carbonitrides is also used for the production of the steel component.
• the result is a fine and homogeneous phase distribution, which causes an improvement in the elongation values and an increase in energy absorption at relatively high tensile strength values.
• a small residual austenite content of up to 5% is achieved, which also contributes to the improvement in elongation values.
• the proportion of ductile phases ferrite and bainitic ferrite is at least 5 area%.
• the respective flat steel product is heated in the hot forming and curing preceding heating to heating temperatures of up to 900 ° C, in which there is only a partial Austenitmaschine.
• the resulting component has further improved strengths, as is the case with a full austenitization, which with a heating in the temperature range> 900 ° C, in particular> 925 ° C. is reached.
• This effect is due to the high Ti content of the steel according to the invention, which can be supported by the optionally additionally present contents of Nb and V. The presence of a larger amount of these micro-alloying elements, the grain size remains fine even during the heat treatment and hot working.
• a particle size index of at least 13 determined according to DIN EN 643 is guaranteed here.
• the holding time required for the heating on the heating temperature is typically 2 to 10 minutes, depending on the dimension of the flat steel product to be processed.
• the heated steel flat product is transferred from the oven used for the heating to the tool in which the flat steel product is hot worked.
• the thermoforming tool can be designed in such a way that the steel component thermoformed from the flat steel product is still quenched in the tool (single-stage process). Alternatively it is also possible to quench the resulting steel component outside the thermoforming tool in a separate workstation to produce the desired hardness structure (two-stage process). To avoid excessive cooling of the steel flat product between the heating furnace and the thermoforming tool, the transfer time should be limited to 5 - 12 seconds.
• the cooling of the steel component formed from the respective flat steel product preferably takes place in the hot forming tool so rapidly that the component structure after cooling consists of a fine-grained structure of martensite, bainite, dislocation-rich bainitic ferrite, globular ferrite and retained austenite.
• the required cooling rate is at least 25 ° C / s.
• the molten steels E1 - E3 and V1 - V4 were cast into slabs, which were then hot rolled with a hot rolling end temperature WET to hot strip with a hot strip thickness WBD.
• the hot strip obtained was then coiled at a reel temperature HAT to a coil.
• the hot strips obtained after the coiling or optional annealing and coating, which consisted of the steels E2, E3 and V1 - V4, were then cold rolled with a cold rolling grade KG to cold strip with a cold strip thickness KBD.
• annealing took place at an annealing temperature GT.
• the annealed cold strips E2 and V4 were then covered with an aluminum-silicon protective layer ("AS coating"), which protects the respective strip against corrosion.
• AS coating aluminum-silicon protective layer
• Table 2 shows the hot rolling end temperature WET, the hot strip thickness WBD, the reel temperature HAT, the cold rolling degree KWG, the cold strip thickness KBD and the annealing temperature GT, among the hot and cold strips produced from the steels E1-E3 and V1-V4.
• the respective flat steel products were heated in an oven to a heating temperature EWT within a heating time EZ and then placed within a transfer time TZ in a thermoforming mold having a tool temperature WZT. Within the thermoforming tool, the flat steel products are each formed into a steel component and cooled at a cooling rate AKR.
• Tables 3 to 8 indicate the heating temperature EWT, the heating time EZ, the transfer time TZ, the cooling rate AKR of the quenching in the thermoforming mold and the tool temperature WZT for the steel components produced in the above-described manner. In addition, it is indicated in Table 3a whether the respective component has been subjected to a cathodic dip coating.
• the average mechanical-technological values yield strength R p0.2 , tensile strength R m , uniform elongation Ag, elongation A 80 , the content of the structure F / BF to ferrite and bainitic ferrite, the content of the structure RA of retained austenite, the content M of the microstructure of martensite, the content B of the microstructure of bainite and the ferrite grain size KG determined in accordance with DIN EN 643.
• the respective grain size has not been determined or could not be determined due to the extremely fine structure, this is indicated by the entry "---".
• Tables 3 and 4 relate to steel components produced from the steels E1 (Table 3), E2 and E3 (Table 4) according to the invention, while Tables 5 to 8 consist of the comparative steels V1 (Table 5), V2 (Table 6), V3 (FIG. Table 7) and V4 (Table 8) relate to steel components produced.

Priority Applications (1)

Applications Claiming Priority (1)

Publications (1)

Family

ID=46318839

Family Applications (1)

Country Status (1)

Cited By (7)

Citations (6)

• 2012
  • 2012-05-16 EP EP12168384.1A patent/EP2664682A1/fr not_active Withdrawn

Patent Citations (6)

Similar Documents

Legal Events