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
  • 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
  • C21D8/0221—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips characterised by the working steps
  • C21D8/0226—Hot rolling
• • C—CHEMISTRY; METALLURGY
  • C21—METALLURGY OF IRON
  • C21C—PROCESSING OF PIG-IRON, e.g. REFINING, MANUFACTURE OF WROUGHT-IRON OR STEEL; TREATMENT IN MOLTEN STATE OF FERROUS ALLOYS
  • C21C1/00—Refining of pig-iron; Cast iron
• • 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
• • 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
  • C21D8/0221—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips characterised by the working steps
  • C21D8/0236—Cold rolling
• • 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
  • C21D8/0247—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips characterised by the heat treatment
  • C21D8/0263—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips characterised by the heat treatment following hot rolling
• • 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
• • 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
  • C22C38/12—Ferrous alloys, e.g. steel alloys containing tungsten, tantalum, molybdenum, vanadium, or niobium
• • 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
  • 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
  • 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

Definitions

• the invention relates to a method for producing a high-strength steel strip with improved properties during further processing and a corresponding steel strip.
• the invention relates to the production of a steel strip from a manganese-containing TRIP (TRansformation Induced Plasticity) and/or TWIP (TWinning Induced Plasticity) steel with excellent cold and warm formability, increased resistance to hydrogen-induced delayed fracture, to hydrogen embrittlement and to liquid metal embrittlement during welding.
• TRIP Traansformation Induced Plasticity
• TWIP TWinning Induced Plasticity
• the steel consists of the elements (contents in percent by weight and based on the steel melt): C: up to 0.5; Mn: 4 to 12.0; Si: up to 1.0; Al: up to 3.0; Cr: 0.1 to 4.0; Cu: up to 4.0; Ni: up to 2.0; N: up to 0.05; P: up to 0.05; S: up to 0.01; as well as residual iron and unavoidable impurities.
• one or more elements from the group “V, Nb, Ti” are provided, the sum of the contents of these elements being at most equal to 0.5. For an Mn content of 5 and an Al content of 2, the total is 7.
• This flat steel product consists of 30 to 100% martensite, tempered martensite or bainite, the balance austenite.
• This steel is said to be characterized by the fact that it is more cost-effective to produce than high-manganese steels and at the same time has high elongation at break values and, as a result, significantly improved formability.
• a method for producing a flat steel product from the above-described higher-strength manganese-containing steel comprises the following work steps: - Melting the above-described molten steel, - Producing a starting product for subsequent hot rolling by forming the molten steel into a strand, of which at least one slab or thin slab is used as the starting product for the Hot rolling is divided, or is cast into a cast strip, which is fed to hot rolling as the starting product, - heat treating the starting product in order to bring the starting product to a hot rolling start temperature of 1150 to 1000 ° C, - hot rolling the starting product into a hot strip with a thickness of a maximum of 2.5 mm, with the hot rolling being completed at a hot rolling end temperature of 1050 to 800 ° C, - coiling the hot strip into a coil at a coiling temperature of ⁇ 700 ° C.
• the hot strip can be annealed at 250 to 950°C, then cold rolled and annealed again at 450 to 950°C. After the cold or hot rolling of the flat steel product, it is also provided with a metallic corrosion protection coating or an organic coating.
• TRIP steels have already been described, which have a predominantly ferritic basic structure with retained austenite, which can convert to martensite during forming (TRIP effect).
• the manganese content of the steel strip is 1.00 to 2.25 percent by weight.
• the steel strip is coated and tempered in a melt bath. Because of its strong work hardening, TRIP steel achieves high values of uniform elongation and tensile strength.
• TRIP steels are used, among other things, in structural, chassis and crash-relevant components of vehicles, as sheet metal blanks and as welded blanks.
• the European patent EP 1 067 203 B1 discloses a method for producing a steel strip.
• a thin strip with a thickness of 1.5 mm to 10 mm is cast from a steel melt that consists of at least the elements (contents in percent by weight) C: 0.001 to 1.6; Mn: 6 to 30; Al: up to 6; P: up to 0.2; S: up to 0.5; N: up to 0.3 and the remainder iron and unavoidable impurities.
• the thin strip is hot rolled with a degree of reduction between 10% and 60%, acid pickled, cold rolled with a degree of reduction between 10% and 90% and recrystallization annealed for 1 to 2 minutes at 800 to 850°C.
• a high-strength steel strip which has the following composition in percent by weight: C: 0.05 - 0.3; Si: ⁇ 0.2; Mn: 0.5 - 4.0: P: ⁇ 0.1; S: ⁇ 0.1; Ni: 0 - 5.0; Al: 0.1 - 2.0 and N ⁇ 0.01.
• the structure contains ⁇ 5% volume retained austenite.
• a melt of the steel described above is melted in a vacuum laboratory furnace.
• a test block with a thickness of 25 mm is produced using hot forging. This is then heated to 1250°C in an electric oven for one hour. Hot rolling is then carried out at 930 to 1150 ° C to achieve a steel strip thickness of 5 mm.
• the steel strip is immediately cooled to 500°C and annealed in an electric furnace at this temperature for one hour.
• a spot weld connection of at least two steel sheets is already known, with at least one sheet being made of an aluminum alloy steel.
• This aluminum alloy steel comprising in weight percentages: 0.05 ⁇ C ⁇ 0.21%; 4.0 ⁇ Mn ⁇ 7.0%; 0.5 ⁇ Al ⁇ 3.5%; Si ⁇ 2.0%; Ti ⁇ 0.2%; V ⁇ 0.2%; Nb ⁇ 0.2%; P ⁇ 0.025%; B ⁇ 0.0035%; S ⁇ 0.004%, the balance being iron and unavoidable impurities.
• the aluminum alloy steel sheet has a yield point above or equal to 600 MPa, a breaking strength above or equal to 1000 MPa and a uniform elongation above or equal to 15%.
• the microstructure of the aluminum-alloyed steel sheet contains 20% to 50% austenite, 40% to 80% annealed ferrite and less than 25% martensite.
• the Korean disclosure document KR 2016 0003744 A and the parallel international disclosure document WO 2014/180456 A1 disclose a further method for producing components from lightweight steel with TRIP/TWIP properties by forming a sheet, a circuit board or a pipe in one or more stages.
• the forming is carried out at a temperature above room temperature at 40 to 160 °C to avoid the TRIP/TWIP effect.
• a particularly high strength of the component is achieved by forming at a temperature below room temperature at -65 to 0 °C, which enhances the TRIP/TWIP effect.
• the present invention is based on the object of specifying a method for producing a high-strength steel strip from a manganese-containing TRIP and/or TWIP steel with strengths between 1100 and 2200 MPa, which is cost-effective and improves the steel strip Properties during further processing, in particular a good combination of strength and forming properties, increased resistance to hydrogen-induced delayed cracking, to hydrogen embrittlement and to liquid metal embrittlement. Furthermore, a high-strength and cost-effective steel strip with improved properties during further processing should be provided.
• a method for producing an ultra-high-strength steel strip comprising the steps of: - melting a steel melt containing (in weight %): C: 0.1 to ⁇ 0.3; Mn: 4 to ⁇ 8; Al: > 1 to 2.9; P: ⁇ 0.05; S: ⁇ 0.05; N: ⁇ 0.02; remainder iron including unavoidable steel-accompanying elements, with optional alloying of one or more of the following elements (in weight %): Si: 0.05 to 0.7; Cr: 0.1 to 3; Mo: 0.01 to 0.9; Ti: 0.005 to 0.3; B: 0.0005 to 0.01 via the blast furnace steelworks process route or the arc furnace process, in each case with optional vacuum treatment of the melt; - Casting the steel melt to form a preliminary strip using a near-net-shape horizontal or vertical strip casting process or casting the steel melt to form a slab or thin slab using a horizontal or vertical slab or thin slab casting process, - Heating to a rolling temperature of 1050
• pre-strip are 1 mm to 35 mm and for slabs and thin slabs 35 mm to 450 mm. It is preferably provided that the slab or thin slab is hot-rolled into a hot strip with a thickness of 12 mm to 0.8 mm or that the pre-strip cast close to the final dimension is hot-rolled into a hot strip with a thickness of 8 mm to 0.8 mm.
• the cold strip according to the invention has a thickness of at most 3 mm, preferably 0.1 to 1.4 mm.
• a pre-strip produced close to the final dimension using the two-roll casting process with a thickness of less than or equal to 3 mm, preferably 1 mm to 3 mm, is already understood to be a hot strip.
• the pre-strip produced in this way as hot strip does not have a 100% cast structure due to the forming of the two opposing rollers. Hot rolling therefore already takes place inline during the two-roll casting process, so that separate heating and hot rolling can optionally be omitted.
• the cold rolling of the hot strip can take place at room temperature or advantageously at elevated temperature before the first rolling pass in one or more rolling passes.
• Cold rolling at elevated temperature is beneficial to reduce rolling forces and promote the formation of deformation twins (TWIP effect).
• Advantageous temperatures of the rolling stock before the first rolling pass are 60 to 450°C.
• the steel strip between the rolling passes it is advantageous to use the steel strip between the rolling passes to a temperature of 60 to 450 ° C between heating or cooling down, as the TWIP effect is particularly advantageous in this area.
• both intermediate heating for example at very low degrees of deformation and rolling speeds, as well as additional cooling, due to the heating of the material during fast rolling and high degrees of deformation, can be carried out.
• the steel strip is to be annealed in accordance with the invention in a continuous annealing plant, in particular a continuous annealing plant, with an annealing time of 1 to 15 minutes and temperatures of 720 °C to 840 °C in order to restore sufficient forming properties.
• annealing can be carried out using a discontinuous annealing plant at a temperature of 550 °C to 820 °C and an annealing time of 30 minutes to 48 hours. If necessary to achieve certain material properties, this annealing process can also be carried out on the steel strip rolled at an elevated temperature.
• the steel strip is advantageously cooled to a temperature of 250 °C to room temperature and then, if necessary, to set the required mechanical properties, heated again to a temperature of 300 to 450 °C in the course of an aging treatment, held at this temperature for up to 5 minutes and then cooled to room temperature.
• the ageing treatment can advantageously be carried out in a continuous annealing plant.
• the steel strip can be skin-passed after cold rolling, which creates the surface structure required for the final application.
• Skin-passing can be carried out using the Pretex ® process, for example.
• the steel strip produced in this way receives a further coating on an organic or inorganic basis instead of or after electrolytic galvanizing or hot-dip galvanizing.
• a further coating on an organic or inorganic basis instead of or after electrolytic galvanizing or hot-dip galvanizing.
• organic coatings plastic coatings or paints or other inorganic coatings such as iron oxide layers.
• the steel strip produced according to the invention can be used as a sheet, sheet section or blank or can be further processed into a longitudinally or spirally welded tube.
• the steel sheet or steel strip is particularly advantageous for further processing into a component using cold or warm forming, for example in the automotive industry, in infrastructure construction and mechanical engineering.
• the steel strip with improved properties during further processing has a TRIP/TWIP effect, with a structure (in volume %) of 10 to 80% austenite, 10 to 90% martensite, the remainder ferrite and bainite with a total proportion of less than 20%. At least 20% of the martensite is present as tempered martensite and optionally > 10% of the austenite is in the form of annealing or deformation twins.
• the austenite Due to the final annealing of the cold strip produced at room temperature or at elevated temperatures, the austenite is in a metastable state and optionally with deformation twins, whereby it partially converts into martensite via the TRIP effect when subjected to mechanical force (e.g. forming).
• the austenite portion of the steel according to the invention can partially or completely convert into martensite when mechanical stresses are present (TRIP effect).
• the alloy according to the invention When subjected to appropriate mechanical stress, the alloy according to the invention also exhibits twinning during plastic deformation (TWIP effect). Because of the strong work hardening induced by the TRIP and/or TWIP effect, the steel achieves high values of elongation at break, especially uniform elongation, and tensile strength.
• the steel according to the invention can then be particularly advantageously Warm forming can be carried out at 60 to 450°C, as the austenite stability at these temperatures at least partially suppresses the transformation of austenite into martensite (TRIP effect), whereby 50 to 100% of the initial austenite is retained and optionally partially converted into deformation twins (TWIP effect).
• the deformation twins can convert into martensite at room temperature with the expenditure of additional energy (TRIP effect, increased energy absorption capacity, e.g. in the event of a crash).
• TRIP effect increased energy absorption capacity, e.g. in the event of a crash.
• the remaining residual elongation until component failure is significantly increased in warm forming compared to cold forming.
• preventing the TRIP effect in warm forming results in a significant improvement compared to undesirable hydrogen-induced influences (delayed crack formation, hydrogen embrittlement).
• Warm forming also advantageously increases the 0.2% yield strength of the formed material, which could, for example, advantageously reduce the sheet thickness.
• the method according to the invention can be used to produce a very cost-effective steel strip with an alloy concept that requires only the elements carbon, manganese and aluminum in addition to iron.
• the required annealing treatment can advantageously be carried out by means of continuous annealing, which is significantly more economical than batch annealing.
• a steel strip produced according to the method according to the invention has a yield strength Rp0.2 of 300 to 1550 MPa, a tensile strength Rm of 1100 to 2200 MPa and an elongation at break A80 of more than 4 to 41%, whereby high strengths tend to be associated with lower elongations at break and vice versa: - Rm of over 1100 to 1200 MPa: Rm x A80 ⁇ 25000 up to 45000 MPa% - Rm from over 1200 to 1400 MPa: Rm x A80 ⁇ 20000 up to 42000 MPa% - Rm from over 1400 to 1800 MPa: Rm x A80 ⁇ 10000 up to 40000 MPa% - Rm of over 1800 MPa: Rm x A80 ⁇ 7200 up to 20000 MPa%
• test specimen A80 was used for the elongation at break tests in accordance with DIN 50 125.
• the elongation and toughness properties are advantageously improved by the TRIP and/or TWIP effect of the alloy according to the invention.
• the steel strip produced according to the invention offers a good combination of strength, elongation and forming properties.
• the production of this manganese steel according to the invention with a medium manganese content (medium manganese steel) based on the alloying elements C, Mn, Al is very cost-effective.
• the manganese steel according to the invention is also characterized by increased resistance to delayed fracture and to hydrogen embrittlement and liquid metal embrittlement during welding.
• Alloying elements are usually added to steel to specifically influence certain properties.
• An alloying element can influence different properties in different steels. The effect and interaction generally depends heavily on the amount, the presence of other alloying elements and the state of solution in the material. The relationships are varied and complex. The effect of the alloying elements in the alloy according to the invention will be discussed in more detail below. The positive effects of the alloying elements used according to the invention are described below.
• Carbon C Is required for the formation of carbides, stabilizes the austenite and increases the strength. Higher contents of C impair the welding properties and lead to a deterioration of the elongation and toughness properties, which is why a maximum content of less than 0.3 wt.% is specified. In order to achieve a To achieve sufficient strength of the material, a minimum addition of 0.1 wt.% is required.
• Manganese Mn Stabilizes the austenite, increases the strength and toughness and enables deformation-induced martensite and/or twinning in the alloy according to the invention. Contents of less than 4 wt.% are not sufficient to stabilize the austenite and thus impair the elongation properties, while contents of 8 wt.% and more stabilize the austenite too much and thus reduce the strength properties, in particular the 0.2% yield strength. For the manganese steel according to the invention with medium manganese contents, a range of 4 to ⁇ 8 wt.% is preferred.
• Aluminum AI An Al content of greater than 1% by weight improves the strength and elongation properties, reduces the specific density and influences the conversion behavior of the alloy according to the invention. Al contents of more than 2.9% by weight impair the elongation properties. Higher Al contents also significantly worsen the casting behavior in continuous casting. This results in greater effort when casting. Al contents of more than 1% by weight delay the precipitation of carbides in the alloy according to the invention. Therefore, a maximum content of 2.9% by weight and a minimum content of more than 1% by weight are set.
• a minimum content (in% by weight) of more than 6.5 and less than 10 should be maintained for the sum of Mn and Al in order to ensure the desired conversion behavior.
• a Mn + Al content of 10% by weight or more impairs castability, thereby reducing output and thus increasing costs.
• Mn + Al contents of 6.5% by weight or less sufficient austenite stability for the desired transformation behavior cannot be ensured.
• Silicon Si The optional addition of Si in levels greater than 0.05% by weight hinders carbon diffusion, reduces specific gravity and increases strength and elongation and toughness properties. Furthermore, an improvement in cold rolling ability could be observed by alloying Si. Contents of more than 0.7% by weight lead to embrittlement of the material and have a negative impact on hot and cold rolling as well as coatability, for example through galvanizing. Therefore, a maximum content of 0.7% by weight and a minimum content of 0.05% by weight are set.
• Chromium Cr The optional addition of Cr improves strength and reduces the corrosion rate, delays ferrite and pearlite formation and forms carbides.
• the maximum content is set at 3 wt.%, as higher contents result in a deterioration in elongation properties.
• a minimum Cr content for effectiveness is set at 0.1 wt.%.
• Molybdenum Mo acts as a carbide former, increasing strength and increasing resistance to delayed cracking and hydrogen embrittlement. Mo contents of over 0.9% by weight impair the elongation properties, which is why a maximum content of 0.9% by weight and a minimum content of 0.01% by weight required for sufficient effectiveness are set.
• Phosphorus P Is a trace element from iron ore and is dissolved in the iron lattice as a substitution atom. Phosphorus increases hardness through solid solution strengthening and improves hardenability. However, attempts are generally made to reduce the phosphorus content as much as possible because, among other things, its low diffusion rate makes it highly susceptible to segregation and greatly reduces toughness. The accumulation of phosphorus at the grain boundaries can cause cracks to appear along the grain boundaries during hot rolling. In addition, phosphorus increases the transition temperature from tough to brittle behavior by up to 300 °C. For the reasons mentioned above, the phosphorus content is limited to values of less than 0.05 wt.%.
• Sulfur S Like phosphorus, it is bound as a trace element in iron ore. It is generally undesirable in steel because it tends to segregate and has a highly brittle effect, which reduces the elongation and toughness properties. An attempt is therefore made to achieve the lowest possible amounts of sulfur in the melt (e.g. through deep desulfurization). For the reasons mentioned above, the sulfur content is limited to values of less than 0.05% by weight.
• Nitrogen N Is also an accompanying element from steel production. In its dissolved state, it improves the strength and toughness properties of steels with a high manganese content and greater than or equal to 4% by weight Mn. Steels alloyed with low Mn and less than 4% by weight with free nitrogen tend to have a strong aging effect. The nitrogen diffuses to dislocations even at low temperatures and blocks them. It thus causes an increase in strength combined with a rapid loss of toughness. Binding the nitrogen in the form of nitrides is possible, for example, by alloying with aluminum or titanium, although aluminum nitrides in particular have a negative effect on the forming properties of the alloy according to the invention. For the reasons stated above, the nitrogen content is limited to less than 0.02% by weight.
• Titan Ti As a carbide former, it has a grain-refining effect, which simultaneously improves the strength, toughness and elongation properties and reduces intergranular corrosion. Ti contents of over 0.3% by weight impair the elongation properties, which is why a maximum Ti content of 0.3% by weight is set. Optionally, a minimum content of 0.005 is set in order to bind nitrogen and advantageously eliminate Ti.
• Boron B Delays austenite transformation, improves the hot forming properties of steels and increases strength at room temperature. It develops its effect even with very low alloy contents. Contents above 0.01% by weight severely deteriorate the elongation and toughness properties, which is why the maximum content is set at 0.01% by weight. Optionally, a minimum content of 0.0005% by weight is set in order to take advantage of the strength-increasing effect of boron.
• alloy 1 contains extracts of the following elements in the listed contents in% by weight: alloy C Mn Al Si Leg. 1 0.2 7.0 1.1 0.5
• alloy Rolling force [kN] cumulative - cold rolling Rolling force [kN] cumulative - at 250 °C Degree of deformation (e ⁇ d/d0) [%] Rolling force reduction [%] Leg. 1 147000 52500 45 approx. 64
• Cumulative rolling force means adding up the rolling forces of the individual passes in order to obtain a comparable measure of the effort required.
• the rolling force was standardized to a band width of 1000 mm.
• the degree of deformation e is defined as the quotient of the change in thickness ⁇ d of the examined steel strip by the initial thickness d0 of the examined steel strip.
• the rolling force reduction is the calculated reduction in rolling force at 250 °C compared to the rolling force during cold rolling.
• the elongation values represent the elongation in the rolling direction. A clear increase in the yield strength can be seen with the same elongation at break.

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• 2017
  • 2017-08-18 US US16/323,222 patent/US20190185951A1/en not_active Abandoned
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• 2021
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