METHOD FOR PRODUCING A FORMED COMPONENT FROM A MEDIUM MANGANESE-CONTAINING FLAT STEEL PRODUCT

Description

[0001] The invention relates to a method for producing a component from a medium-manganese-containing flat steel product with 4 to 12 wt.% Mn, preferably more than 5 to less than 10 wt.% Mn, and with TRIP / TWIP effect.

[0002] European patent application EP 2 383 353 A2 discloses a flat steel product made of manganese-containing steel with a tensile strength of 900 to 1500 MPa and consisting of the following elements (contents in weight percent 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, with the remainder being iron and unavoidable impurities. Optionally, one or more elements from the group "V, Nb, Ti" are provided, with the sum of the contents of these elements being at most 0.5. 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 thus significantly improved formability.

[0003] High-strength steels with a medium manganese content are also known from the published patent applications US 2012 / 0070330 A1 and DE 10 2008 005 158 A1. US 2012 / 0070330 A1 relates to a process for producing a steel strip from a high-strength steel with an average manganese content of 4 to 14 wt.% Mn. During production, the steel strip is rolled at a rolling temperature of 60°C to 500°C with a rolling reduction R of 20% to 70%.

[0004] The German patent application DE 10 2012 013 113 A1 also describes so-called TRIP steels, which have a predominantly ferritic microstructure with embedded residual austenite, which can transform into martensite during forming (TRIP effect). Due to its strong work hardening, TRIP steel achieves high values ​​of uniform elongation and tensile strength. TRIP steels are suitable for use in structural, chassis, and crash-relevant vehicle components, as sheet metal blanks, and as welded blanks. Further steels with TRIP and / or TWIP properties are mentioned in the published patent applications US 2007 / 0289717 A1, DE 10 2012 111 959 A1, WO 2013 / 064698, WO 2005 / 061152 A1, and US 2006 / 0179638. The patent applications DE 10 2004 054 444 B3 and US 6,387,192 B1 also disclose steels with TRIP / TWIP properties.

[0005] Furthermore, German patent DE 10 2013 104 298 B4 describes roll forming, also known as roll forming, as a forming process for medium- or high-manganese-content steel strips. Roll forming, or roll forming, is a continuous bending process in which the steel strips are gradually formed by a plurality of pairs of rollers until they reach a desired final shape. Roll forming is often combined with other manufacturing processes such as punching, longitudinal welding, or embossing to produce virtually any profile shape, even with cross-sections that vary along the length of the component.

[0006] Another well-known forming process, so-called internal high-pressure forming, is described in the published patent application DE 10 2008 014 213 A1, for example, using the internal high-pressure forming of pipes. In this process, tubular workpieces are inserted into at least two-part tools and subjected to a high-pressure active medium on the inside. This expands the workpiece, shapes it into a groove or geometry of the tool, and partially pushes it forward, thus taking on the shape of the tool. The material must be designed in such a way that it can absorb even localized high deformation without material failure.

[0007] Furthermore, European Patent Application EP 2 778 247 A1 discloses a method for producing a hot-pressed motor vehicle component from a medium-manganese-containing flat steel product with a manganese content of 3 to 15 wt.%, preferably 5 to 11 wt.%. This manufacturing method comprises a heat treatment in which the flat steel product or the motor vehicle component is heated before or after hot forming to a temperature in the range of Ac1 to Ac3 with a heating rate of 1°C / s to 1000°C / s and a holding time of 1 to 10,000 s. The hot pressing or hot forming comprises a cooling step with

[0008] Cooling rates range from 1°C / s to 1000°C / s. The corresponding examples specify heat treatment temperatures in the range from 500 to 850°C, holding times of 300s, and cooling rates of 5 to 45°C / s.

[0009] Also known from published patent application WO 2014 / 180456 A1 is a method for producing a formed component, in particular a body or chassis component, from an austenitic lightweight steel that is metastable in its initial state and exhibits a temperature-dependent TRIP and / or TWIP effect during forming. Forming the component above room temperature at 40 to 160°C is intended to avoid the temperature-dependent TRIP / TWIP effect and achieve high toughness of the component.

[0010] Based on this, the present invention is based on the object of creating a method for producing a component from a medium-manganese-containing flat steel product, which is characterized by an improvement in the degree of deformation of the formed component while simultaneously reducing the forming forces.

[0011] This object is achieved by a method for producing a component from a medium-manganese-containing flat steel product with the features of claim 1. Advantageous embodiments of the invention are specified in the subclaims. According to the invention, a method for producing a component from a medium-manganese-containing flat steel product which is produced with the following chemical composition (in wt. %): C: 0.0005 to 0.9, preferably 0.05 to 0.35; Mn: 4 to 12, preferably greater than 5 to less than 10; remainder iron including unavoidable steel-accompanying elements, with optional alloying of: Al: 0 to 10, preferably 0.05 to 5, particularly preferably greater than 0.5 to 3; Si: 0 to 6, preferably 0.05 to 3, particularly preferably 0.1 to 1.5; Cr: 0 to 6, preferably 0.1 to 4, particularly preferably greater than 0.5 to 2.5; Nb: 0 to 1, preferably 0.005 to 0.4, particularly preferably 0.01 to 0.1;V: 0 to 1.5, preferably 0.005 to 0.6, particularly preferably 0.01 to 0.3; Ti: 0 to 1.5, preferably 0.005 to 0.6, particularly preferably 0.01 to 0.3; Mo: 0 to 3, preferably 0.005 to 1.5, particularly preferably 0.01 to 0.6; Sn: 0 to 0.5, preferably less than 0.2, particularly preferably less than 0.05; Cu: 0 to 3, preferably less than 0.5, particularly preferably less than 0.1; W: 0 to 5, preferably 0.01 to 3, particularly preferably 0.2 to 1.5; Co: 0 to 8, preferably 0.01 to 5, particularly preferably 0.3 to 2; Zr: 0 to 0.5, preferably 0.005 to 0.3, particularly preferably 0.01 to 0.2; Ta: 0 to 0.5, preferably 0.005 to 0.3, particularly preferably 0.01 to 0.1; Te: 0 to 0.5, preferably 0.005 to 0.3, particularly preferably 0.01 to 0.1; B: 0 to 0.15, preferably 0.001 to 0.08, particularly preferably 0.002 to 0.01; P: less than 0.1, preferably less than 0.04; S: less than 0.1, preferably less than 0.02; N: less than 0.1, preferably less than 0.05;the flat steel product is produced with a structure which has an austenite content of 10 to 80%, 20 to 90% martensite, ferrite and bainite, with at least 30% of the martensite being present as tempered martensite, preferably 40 to 80% austenite, less than 20% ferrite / bainite and the remainder martensite, and with TRIP / TWIP effect, comprising the steps of: - preheating the flat steel product to a desired temperature in the range from 60 °C to Ac3 and - forming the flat steel product into a component with a first forming step at a temperature of the flat steel product of 60 °C to 450 °C, wherein the temperature desired for forming is already reached by the preheating before the first forming step, i.e. does not arise only through the forming itself, achieved that when forming the flat steel product into a component the maximum degree of forming of the formed flat steel product is increased by reducing the work hardening during forming.;

[0012] The aforementioned feature—with a first forming step at a temperature—means that the desired temperature is already reached before the first forming step and does not arise during the forming process itself. Increasing the temperature before the first forming step also reduces the required forming forces. This also results in an increase in the residual formability of the formed components, with tensile strengths of greater than 800 MPa to 2000 MPa and elongations at break of greater than 3% in the most severely formed areas. Preheating of the flat steel product can be performed for the coil or the unwound strip or sheet material.By forming with the inventive preheating of the flat steel product before the first forming step, a transformation of metastable austenite into martensite (TRIP effect) is completely or partially suppressed during the forming process, whereby deformation twins (TWIP effect) can form in the austenite. This achieves the inventive and advantageous prevention of hardening and a reduction of the forming forces, thereby increasing the overall formability.

[0013] In a further process variant, the flat steel product is formed into a component with further forming steps at a temperature of the flat steel product from room temperature to below Ac3, preferably from room temperature to 450 °C. This allows for the targeted introduction of deformation twins, which further convert into martensite at room temperature, thereby increasing the energy absorption capacity and allowing a higher degree of deformation.

[0014] In the context of the present invention, room temperature is defined as being in the range between 15 to 25 °C.

[0015] In another process variant, the flat steel product is formed into a component with additional forming steps at a temperature of -100 °C to 60 °C. This specifically converts metastable austenite into martensite, significantly increasing the strength in the affected area of ​​the flat steel product.

[0016] The flat steel product can be particularly advantageously formed into a component with further forming steps at temperatures ranging from -100 °C to below Ac3. Forming at low temperatures is used in the final forming steps.

[0017] It is particularly advantageous that the flat steel product is formed into a component with the subsequent individual forming steps at different temperatures, each of which can be locally limited. This optionally allows for a targeted and local adjustment of the component's strength and elongation properties by varying the forming temperature. Thus, a targeted adjustment of properties is achieved locally through local cooling or heating. Targeted cooling primarily results in higher strengths, while local heating results in higher residual elongations or greater formability.

[0018] In one variant, the flat steel product is preheated from one side. Alternatively, it can be preheated from both sides.

[0019] In order to maintain the temperature window for forming according to the invention, the flat steel product can be intermediately heated or cooled between the forming steps to temperatures between -100 °C and below Ac3 - depending on the desired process.

[0020] The process is particularly advantageous for forming the flat steel product by means of roll forming.

[0021] During roll forming, the flat steel product undergoes at least one bending, upsetting, partial thickness reduction, embossing, punching, or grooving, or combinations thereof, in a variety of successive deformation or processing steps. Components in the form of closed profiles can also be produced, which can optionally be welded, preferably longitudinally welded, after roll forming.

[0022] The process is also particularly advantageous for forming the flat steel product by means of internal high-pressure forming. Internal high-pressure forming is preferably carried out using solid, liquid, or gaseous active media. In a known manner, during internal high-pressure forming, the flat steel product, in particular a rolled hot or cold strip, is formed into a can and then longitudinally welded to form a tubular component, in particular a pipe, or alternatively, is spirally formed and spirally welded to form a tubular component, in particular a pipe. Preferably, but optionally, the tubular component, in particular the pipe, is then annealed (500 to 850 °C, 30 seconds to 12 hours) immediately after longitudinal seam welding or spiral seam welding, for example inductively or in a continuous furnace or in stationary furnace units, such as a hearth furnace or muffle furnace.Alternatively, if the degree of deformation is low and residual ductility is sufficient for subsequent hydroforming, annealing can be omitted, allowing further processing to take place in the solidified state. The hydroforming according to the invention then takes place at a preferred temperature of 60 to 450 °C. Heating is preferably carried out via the active medium. The forming can be carried out in several steps. After semi-hot hydroforming, the component preferably still has at least 50% of the initial austenite content. An advantageous temperature range for hydroforming is between 60 and 450 °C.

[0023] With regard to the component obtained by roll forming or internal high-pressure forming, the following dependencies of tensile strength Rm in MPa and elongation at break A80 in % result: Rm from 700 to 800 MPa: Rm x A80 ≥ 15400 up to 50000 MPa% Rm of over 800 to 900 MPa: Rm x A80 ≥ 14400 up to 50000 MPa% Rm of over 900 to 1100 MPa: Rm x A80 ≥ 13500 up to 45000 MPa% Rm of over 1100 to 1200 MPa: Rm x A80 ≥ 13200 up to 45000 MPa% Rm of over 1200 to 1350 MPa: Rm x A80 ≥ 11200 up to 45000 MPa% Rm from over 1350 to 1800 MPa: Rm x A80 ≥ 8000 up to 45000 MPa% Rm of over 1800 MPa: Rm x A80 ≥ 4000 up to 30000 MPa%

[0024] This flat steel product made from medium-manganese TRIP (TRansformation Induced Plasticity) and / or TWIP (TWinning Induced Plasticity) steel exhibits excellent cold and warm formability, increased resistance to hydrogen-induced delayed fracture, hydrogen embrittlement after forming, and liquid metal embrittlement (LME) during welding.

[0025] The flat steel product described above is usually manufactured using the following production route: Melting a steel melt with the chemical composition described above in a blast furnace steelworks or electric arc furnace steelworks with optional vacuum treatment of the melt; casting the steel melt into a pre-strip by means of a near-net-shape horizontal or vertical strip casting process or casting the steel melt into a slab or thin slab by means of a horizontal or vertical slab or thin slab casting process, Heating the preliminary strip to a rolling temperature of 1050 to 1250°C or inline rolling from the casting heat (first heat), hot rolling of the preliminary strip or slab or thin slab to a hot strip with a thickness of 20 to 0.8 mm with a final rolling temperature of 1050 to 800°C, coiling the hot strip at a temperature of more than 100 to 800°C, pickling the hot strip, annealing the hot strip in a continuous or batch annealing plant or in a continuous or discontinuous annealing plant with an annealing time of 1 minute.up to 24 hours and temperatures from 500 to 840°C, optional cold rolling of the hot strip at room temperature, preferably with preheating to 60 to below Ac3 temperature, preferably 60 to 450°C before the first rolling pass to reduce the rolling forces and form deformation twins in the austenite and, if required, cooling or heating between the rolling passes to 60°C to below the Ac3 temperature, preferably 60 to 450°C, optional annealing at 500 to 840°C for 1 minute to 24 hours in a continuous annealing plant or batch annealing plant, optional electrolytic galvanizing or hot-dip galvanizing of the steel strip or application of another organic or inorganic coating.

[0026] Subsequently, the forming according to the invention, in particular roll forming or internal high pressure forming, of the flat steel product into a component takes place.

[0027] Typical thickness ranges for transfer strip are 1 mm to 35 mm, and for slabs and thin slabs, 35 mm to 450 mm. Preferably, the slab or thin slab is hot-rolled into a hot strip with a thickness of 20 mm to 0.8 mm, or the near-net-shape cast transfer strip is hot-rolled into a hot strip with a thickness of 8 mm to 0.8 mm. The cold-rolled strip typically has a thickness of less than 3 mm, preferably 0.1 to 1.4 mm.

[0028] In the context of the above-described method according to the invention, a near-net-shape pre-strip produced 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 considered a hot-rolled strip. Due to the deformation introduced by the two counter-rotating rolls, the pre-strip produced in this way as a hot-rolled strip has no cast structure. Hot rolling thus takes place inline during the two-roll casting process, so that separate heating and hot rolling can optionally be omitted.

[0029] Cold rolling of the hot strip can take place at room temperature or, advantageously, at elevated temperature with heating before the first rolling pass and / or heating in a subsequent or between several rolling passes. Cold rolling at elevated temperature is advantageous for reducing rolling forces and promoting the formation of deformation twins (TWIP effect). Advantageous temperatures of the rolled stock before the first rolling pass are 60°C to below the Ac3 temperature, preferably 60 to 450°C.

[0030] If cold rolling is performed in multiple passes, it is advantageous to heat or cool the steel strip between passes to a temperature of 60°C to below the Ac3 temperature, preferably between 60°C and 450°C, as the TWIP effect is particularly beneficial in this range. Depending on the rolling speed and degree of deformation, both intermediate heating, for example, at very low deformation degrees and rolling speeds, and additional cooling, due to the heating of the material during rapid rolling and high deformation degrees, can be performed.

[0031] After cold rolling the hot strip at room temperature, the steel strip should be annealed in a continuous annealing plant (conveyor or batch annealing plant) or in a continuous or discontinuous annealing plant to restore sufficient forming properties, preferably with an annealing time of 1 minute to 24 hours, preferably less than 10 minutes, and at temperatures of 500 to 840°C. If necessary to achieve certain material properties, this annealing process can also be carried out on steel strip rolled at elevated temperatures.

[0032] After annealing, the steel strip is preferably cooled to a temperature of 250°C to room temperature. If necessary, it is then reheated to a temperature of 300 to 450°C during an aging treatment to achieve the required mechanical properties. It is held at this temperature for up to 5 minutes and then cooled to room temperature. The aging treatment can be advantageously carried out in a continuous annealing plant.

[0033] The flat steel product produced in this way can optionally be electrogalvanized or hot-dip galvanized. In an advantageous further development, the steel strip produced in this way receives an organic or inorganic coating instead of or after electrogalvanizing or hot-dip galvanizing. These can be, for example, organic coatings, plastic coatings, paints, or other inorganic coatings such as iron oxide layers.

[0034] A formed component can be produced using the process described above. The component, preferably formed at elevated temperature, exhibits at least the same or higher strength properties (yield / proof strength and / or tensile strength) compared to a component formed at room temperature, with the same degree of deformation, and elongation at break being at least 10% higher than when forming at room temperature. Similarly, it is possible to set comparable elongation at break values, with the strength value (yield / proof strength and / or tensile strength) being 10% higher than when forming at room temperature. The warm-formed component exhibits increased resistance to hydrogen-induced embrittlement and delayed cracking, as the TRIP effect is at least partially suppressed. Furthermore, no liquid metal embrittlement occurs during welding.

[0035] The invention makes it possible to produce a high-strength component which has significantly improved residual elongation and / or residual toughness compared to low-alloyed steels of the same strength class and is significantly more cost-effective than high-manganese and / or high-Cr alloyed and / or Cr-Ni or other high-alloyed steels with alloy content > 12 wt.% currently used for such applications.

[0036] The use of a component manufactured according to the above-described process is advantageous in automotive engineering, rail vehicle construction, shipbuilding, plant engineering, infrastructure construction, aerospace, household appliance technology and in tailored welded blanks.

[0037] A steel strip produced by the process according to the invention advantageously has a yield strength Rp0.2 of 300 to 1350 MPa, a tensile strength Rm of 1100 to 2200 MPa and an elongation at break A80 of more than 4 to 41%, with high strengths tending to be associated with lower elongations at break and vice versa: Rm from 700 to 800 MPa: Rm x A80 ≥ 15400 up to 50000 MPa% Rm of over 800 to 900 MPa: Rm x A80 ≥ 14400 up to 50000 MPa% Rm of over 900 to 1100 MPa: Rm x A80 ≥ 13500 up to 45000 MPa% Rm of over 1100 to 1200 MPa: Rm x A80 ≥ 13200 up to 45000 MPa% Rm of over 1200 to 1350 MPa: Rm x A80 ≥ 11200 up to 45000 MPa% Rm from over 1350 to 1800 MPa: Rm x A80 ≥ 8000 up to 45000 MPa% Rm of over 1800 MPa: Rm x A80 ≥ 7200 up to 30000 MPa%

[0038] For the elongation at break tests, specimen shape 2 with an initial gauge length of A80 was used in accordance with DIN 50 125.

[0039] The use of the term "up to" in the definitions of the content ranges, such as 0.01 to 1 wt.%, means that the key values ​​- in the example 0.01 and 1 - are included.

[0040] Alloying elements are generally added to steel to specifically influence certain properties. An alloying element can influence different properties in different steels. The effect and interaction generally depend heavily on the quantity, the presence of other alloying elements, and the solution state in the material. The relationships are diverse 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.

[0041] Carbon C: Carbon is required for the formation of carbides, stabilizes the austenite, and increases strength. Higher C contents impair welding properties and lead to a deterioration in elongation and toughness properties, which is why a maximum content of 0.9 wt.%, preferably 0.35 wt.%, is specified. To achieve the desired combination of strength and elongation properties of the material, a minimum addition of 0.0005 wt.%, preferably 0.05 wt.%, is required.

[0042] Manganese Mn: Mn stabilizes the austenite, increases strength and toughness, and enables deformation-induced martensite and / or twinning in the alloy according to the invention. Contents below 4 wt.% are insufficient to stabilize the austenite and thus impair the elongation properties, while contents of 12 wt.% and above over-stabilize the austenite, thereby reducing the strength properties, particularly the 0.2% yield strength. For the manganese steel according to the invention with medium manganese contents, a range of greater than 5 to less than 10 wt.% is preferred.

[0043] Aluminum Al: Al improves the strength and elongation properties, lowers the specific density, and influences the transformation behavior of the alloy according to the invention. Excessively high Al contents impair the elongation properties. Higher Al contents also significantly impair the casting behavior in continuous casting. This results in increased casting costs. High Al contents delay the precipitation of carbides in the alloy according to the invention. Therefore, an Al content of 0 to 10 wt. %, preferably 0.05 to 5 wt. %, particularly preferably greater than 0.5 to 3 wt. % is specified.

[0044] Silicon Si: The optional addition of Si in higher amounts inhibits carbon diffusion, reduces specific density, and increases strength, elongation, and toughness properties. Furthermore, an improvement in cold rollability has been observed through the alloying of Si. Higher Si contents lead to embrittlement of the material and negatively impact hot and cold rollability, as well as coatability, for example, by galvanizing. Therefore, a Si content of 0 to 6 wt.%, preferably 0.05 to 3 wt.%, and particularly preferably 0.1 to 1.5 wt.%, is specified.

[0045] Chromium Cr: The optional addition of Cr improves strength and reduces the corrosion rate, delays ferrite and pearlite formation, and promotes the formation of carbides. Higher contents lead to a deterioration in elongation properties. Therefore, a Cr content of 0 to 6 wt.%, preferably 0.1 to 4 wt.%, and particularly preferably greater than 0.5 to 2.5 wt.%, is specified.

[0046] Microalloying elements are generally added only in very small quantities. Unlike alloying elements, they act primarily through precipitation, but can also influence properties in a dissolved state. Even small additions of microalloying elements significantly influence processing and final properties. Especially during hot forming, microalloying elements have a beneficial effect on recrystallization behavior and cause grain refinement.

[0047] Typical microalloying elements are vanadium, niobium, and titanium. These elements can dissolve in the iron lattice and form carbides, nitrides, and carbonitrides with carbon and nitrogen.

[0048] Vanadium V and niobium Nb: These have a grain-refining effect, particularly through the formation of carbides, which simultaneously improves strength, toughness, and elongation properties. Concentrations above 1.5 wt.% and 1 wt.%, respectively, offer no additional benefits. For vanadium and niobium, a minimum content of 0.005 wt.% and a maximum content of 0.6 wt.% and 0.4 wt.%, respectively, is optionally preferred, with a minimum content of 0.01 wt.% and a maximum content of 0.3 wt.% and 0.1 wt.%, respectively, particularly preferred.

[0049] Titanium Ti: Ti acts as a carbide former to refine grains, thereby simultaneously improving strength, toughness, and elongation properties, and reducing intergranular corrosion. Ti contents above 1.5 wt.% impair elongation properties, which is why a maximum content of 1.5 wt.%, preferably 0.6 wt.%, and particularly preferably 0.3 wt.%, is optionally specified. Minimum contents of 0.005 wt.%, preferably 0.01 wt.%, can be provided to bind nitrogen and advantageously precipitate Ti.

[0050] Molybdenum Mo: Mo acts as a carbide former, increasing strength and resistance to delayed cracking and hydrogen embrittlement. High Mo contents impair elongation properties. Therefore, a Mo content of 0.005 to 1.5 wt.%, particularly preferably greater than 0.01 to 0.6 wt.%, is optionally specified.

[0051] Tin Sn: Sn increases strength, but similar to copper, it accumulates at higher temperatures beneath the scale layer and at the grain boundaries. By penetrating the grain boundaries, it leads to the formation of low-melting phases and, consequently, to cracks in the structure and brittleness of the solder. Therefore, a maximum content of 0.5 wt.%, preferably less than 0.2 wt.%, and particularly preferably less than 0.05 wt.%, is optionally provided.

[0052] Copper Cu: Cu reduces the corrosion rate and increases strength. Concentrations above 3 wt.% impair manufacturability due to the formation of low-melting phases during casting and hot rolling, which is why a maximum content of 3 wt.%, preferably less than 0.5 wt.%, and particularly preferably less than 0.1 wt.%, is optionally specified.

[0053] Tungsten W: W acts as a carbide former and increases strength and heat resistance. W contents above 5 wt.% impair the elongation properties, which is why a maximum content of 5 wt.% is optionally specified. A content of 0.01 wt.% to 3 wt.% is preferred, and 0.2 to 1.5 wt.% is particularly preferred.

[0054] Cobalt Co: Co increases the strength of the steel, stabilizes the austenite, and improves high-temperature strength. Concentrations above 8 wt.% impair the tensile properties. The Co content is therefore set at a maximum of 8 wt.%, preferably from 0.01 to 5 wt.%, and particularly preferably from 0.3 to 2 wt.%.

[0055] Zirconium Zr: Zr acts as a carbide former and improves strength. Zr contents above 0.5 wt.% impair elongation properties. Therefore, a Zr content of 0 to 0.5 wt.%, preferably 0.005 to 0.3 wt.%, and particularly preferably 0.01 to 0.2 wt.%, is specified.

[0056] Tantalum Ta: Similar to niobium, Ta acts as a carbide former for grain refining, thereby simultaneously improving strength, toughness, and elongation properties. Concentrations above 0.5 wt.% do not result in any further improvement in properties. Therefore, a maximum content of 0.5 wt.% is optionally specified. A minimum content of 0.005 and a maximum content of 0.3 wt.% are preferred, at which grain refinement can be advantageously achieved. To improve cost-effectiveness and optimize grain refinement, a content of 0.01 wt.% to 0.1 wt.% is particularly preferred.

[0057] Tellurium Te: Te improves corrosion resistance and mechanical properties, as well as machinability. Furthermore, Te increases the strength of manganese sulfides (MnS), which are therefore less elongated in the rolling direction during hot and cold rolling. Contents above 0.5 wt.% impair elongation and toughness properties, which is why a maximum content of 0.5 wt.% is specified. Optionally, a minimum content of 0.005 wt.% and a maximum content of 0.3 wt.% are specified, which advantageously improve the mechanical properties and increase the strength of existing MnS. Furthermore, a minimum content of 0.01 wt.% and a maximum content of 0.1 wt.% are preferred, which enable optimization of the mechanical properties while simultaneously reducing alloy costs.

[0058] Boron B: Boron B delays austenite transformation, improves the hot-forming properties of steels, and increases strength at room temperature. It is effective even at very low alloying contents. Contents above 0.15 wt.% severely impair elongation and toughness properties, which is why the maximum content is set at 0.15 wt.%. Optionally, a minimum content of 0.001 wt.% and a maximum content of 0.08 wt.% are specified, and preferably a minimum content of 0.002 wt.% and a maximum content of 0.01 wt.% are specified to take advantage of the strength-enhancing effect of boron.

[0059] Phosphorus P: P is a trace element, originating primarily from iron ore and dissolved in the iron lattice as a substitution atom. Phosphorus increases hardness through solid solution strengthening and improves hardenability. However, the aim is generally to reduce the phosphorus content as much as possible because, among other things, its low diffusion rate makes it highly susceptible to segregation and significantly reduces toughness. The accumulation of phosphorus at grain boundaries can cause cracks to occur along them during hot rolling. In addition, phosphorus increases the transition temperature from tough to brittle behavior by up to 300°C. For the reasons stated above, the phosphorus content is limited to values ​​below 0.1 wt.%, preferably below 0.04 wt.%.

[0060] Sulfur S: Like phosphorus, S is a trace element in iron ore, but especially in the coke produced via the blast furnace process. It is generally undesirable in steel because it tends to segregate strongly and has a strong embrittling effect, which impairs elongation and toughness properties. Therefore, efforts are made to minimize the amount of sulfur in the melt (for example, through deep desulfurization). For the reasons stated above, the sulfur content is limited to values ​​below 0.1 wt.%, preferably below 0.02 wt.%.

[0061] Nitrogen N: N is also an impurity element from steel production. In its dissolved state, it improves the strength and toughness properties of steels with higher manganese contents, with greater than or equal to 4 wt.% Mn. Steels alloyed with lower Mn content than 4 wt.% tend to experience severe aging in the presence of free nitrogen. The nitrogen diffuses onto dislocations even at low temperatures and blocks them. It thus causes an increase in strength combined with a rapid loss of toughness. Binding of the nitrogen in the form of nitrides is possible, for example, by alloying with titanium or aluminum, 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 0.1 wt.%, preferably less than 0.05 wt.%.

Claims

1. Method for manufacturing a component from a medium manganese-containing sheet steel product produced so as to have the following chemical composition in wt.%: C: 0.0005 to 0.9, preferably 0.05 to 0.35 Mn: 4 to 12, preferably greater than 5 to less than 10 the remainder being iron, including unavoidable steel-accompanying elements, with the optional addition by alloying of: Al: 0 to 10, preferably 0.05 to 5, particularly preferably greater than 0.5 to 3 Si: 0 to 6, preferably 0.05 to 3, particularly preferably 0.1 to 1.5 Cr: 0 to 6, preferably 0.1 to 4, particularly preferably greater than 0.5 to 2.5 Nb: 0 to 1, preferably 0.005 to 0.4, particularly preferably 0.01 to 0.1 V: 0 to 1.5, preferably 0.005 to 0.6, particularly preferably 0.01 to 0.3 Ti: 0 to 1.5, preferably 0.005 to 0.6, particularly preferably 0.01 to 0.3 Mo: 0 to 3, preferably 0.005 to 1.5, particularly preferably 0.01 to 0.6 Sn: 0 to 0.5, preferably less than 0.2, particularly preferably less than 0.05 Cu: 0 to 3, preferably less than 0.5, particularly preferably less than 0.1 W: 0 to 5, preferably 0.01 to 3, particularly preferably 0.2 to 1.5 Co: 0 to 8, preferably 0.01 to 5, particularly preferably 0.3 to 2 Zr: 0 to 0.5, preferably 0.005 to 0.3, particularly preferably 0.01 to 0.2 Ta: 0 to 0.5, preferably 0.005 to 0.3, particularly preferably 0.01 to 0.1 Te: 0 to 0.5, preferably 0.005 to 0.3, particularly preferably 0.01 to 0.1 B: 0 to 0.15, preferably 0.001 to 0.08, particularly preferably 0.002 to 0.01 P: less than 0.1, preferably less than 0.04 S: less than 0.1, preferably less than 0.02 N: less than 0.1, preferably less than 0.05, the sheet steel product is manufactured so as to have a structure comprising an austenite content of 10 to 80%, 20 to 90% martensite, ferrite and bainite, wherein at least 30% of the martensite is tempered martensite, preferably comprising 40 to 80% austenite, less than 20% ferrite / bainite and the remainder martensite, and having a TRIP / TWIP effect, the method comprising the steps of: - preheating the sheet steel product to a desired temperature in the range of 60°C to Ac3 and - shaping the sheet steel product to form a component in a first shaping step at a sheet steel product temperature of 60°C to 450°C, wherein the desired sheet steel product temperature is already reached by preheating before the first shaping step, and does not arise only as a result of the shaping itself.

2. Method according to claim 1, characterised in that the sheet steel product is shaped to form a component in further shaping steps at a sheet steel product temperature of - 100°C to below Ac3.

3. Method according to claim 1 or claim 2, characterised in that the sheet steel product is shaped to form a component in further shaping steps at a sheet steel product temperature in a temperature range from 15 - 25°C to below Ac3, preferably in a temperature range from 15 - 25°C to 450°C.

4. Method according to at least one of claims 1 to 3, characterised in that the sheet steel product is shaped to form a component in further shaping steps at a sheet steel product temperature of -100°C to 60°C.

5. Method according to at least one of claims 1 to 4, characterised in that the sheet steel product is shaped to form a component in the further individual shaping steps at different temperatures, each of which is locally limited.

6. Method according to at least one of claims 1 to 5, characterised in that the sheet steel product is preheated from one or both sides.

7. Method according to at least one of claims 1 to 6, characterised in that during shaping, the sheet steel product is temporarily heated or temporarily cooled between the shaping steps to temperatures between -100°C to below Ac3.

8. Method according to at least one of claims 1 to 7, characterised in that the sheet steel product is shaped by means of a roll-forming process.

9. Method according to any of claims 1 to 8, characterised in that the sheet steel product is shaped into a tubular component, in particular into a tube, longitudinally or spirally seam welded and shaped by internal high pressure, and optionally annealed.

10. Method according to any of claims 1 to 9, characterised in that the sheet steel product or the component is coated using a metal, inorganic or organic coating.