Method and control system for producing cold-rolled dual-phase steels

Abstract

The invention relates to a method for producing cold-rolled dual-phase steels DP with a tensile strength in a target range, wherein at least one sample is taken from a melt of the last primary metallurgical unit of a production route and the content of accompanying and alloying elements is determined by analyzing the sample; actual analysis values of the accompanying and alloying element content are transmitted to a control system; a distinction is made between influencing and compensating elements, influencing elements and compensating elements being elements which have an influence or effect on the tensile strength Rm; the difference between the actual analysis values and limit values relating to the influencing elements is detected; the magnitude of the influence of the deviation of the actual analysis values from the limit values of all of the influencing elements on the tensile strength Rm is detected; and at least one compensating element is determined which is alloyed into the melt in such a way that the tensile strength is brought into a target range and the influence of the at least one influencing element is thereby compensated for.

Description

[0001] European patent application

[0002] Voestalpine Stahl GmbH

[0003] 250048WO

[0004] Process and control system for the production of cold-rolled dual-phase steels

[0005] The invention relates to a method for producing cold-rolled dual-phase steels (DP), cold-rolled dual-phase steels with improved formability (DP-HD), and / or cold-rolled dual-phase steels with high formability (DP-FH). The invention further relates to a control system for producing such steels.

[0006] For the primary metallurgical production of steel, iron is first obtained from iron ore by melting it together with coke and additives in a blast furnace. The molten iron is then further processed into crude steel in a converter process with oxygen or in an electric arc furnace with pig iron, sponge iron, or scrap as feedstock (individually or in combination).

[0007] The crude steel is then further processed in secondary metallurgy to improve its composition and purity. This involves treating the steel in special ladle furnaces and / or vacuum treatment plants, where additives such as alloying elements are added to achieve the desired chemical composition and specific properties of the steel.

[0008] Scrap metal is not normally used in blast furnaces, as the process is primarily based on the reduction of iron ore to produce liquid pig iron. However, scrap metal is used in other process steps in steel production, especially in electric arc furnaces or converters.

[0009] The pig iron produced in the blast furnace is then further processed in an oxygen converter. In such converters, for example in an LD converter (Linz-Donawitz process), liquid pig iron is decarburized by blowing in oxygen and converted into crude steel. Scrap metal is added as a coolant and additional material. The addition of scrap in the converter process helps to control the temperature, as exothermic reactions with oxygen heat the molten metal considerably.

[0010] Another important production method in the steel industry is the electric arc furnace (EAF). This uses scrap metal heated by electrical energy. European patent application

[0011] Voestalpine Stahl GmbH

[0012] 250048WO

[0013] It is melted down to produce liquid steel. This process is particularly environmentally friendly, as it mainly uses recycled material and causes fewer CO₂ emissions than the blast furnace process.

[0014] In the electric arc furnace process, steel is melted using electrical energy. An electric arc is generated between graphite electrodes and the scrap material in the furnace, creating high temperatures (up to 3500 °C at the focal point of the arc) that melt the scrap and process it into liquid steel.

[0015] Using scrap metal as a raw material for steel offers several advantages. Melting down scrap requires less energy than producing primary steel from iron ore. Furthermore, scrap recycling reduces CO₂ emissions and the need for new raw materials, thus lowering the environmental impact. Since steel can be recycled again and again, using scrap metal makes a significant contribution to the circular economy in the steel industry.

[0016] Although the use of scrap in the electric arc furnace (EAF) offers many advantages, there are also some disadvantages and challenges that need to be considered.

[0017] The first challenge in using scrap metal is its fluctuating quality. The scrap used in EAF (Energy Efficiency Forming) is often inhomogeneous and can contain impurities that negatively affect the steel's quality. For example, unwanted elements such as copper (Cu), nickel (Ni), molybdenum (Mo), and nitrogen (N) may be present in the scrap. These are difficult to remove from the steel, can alter its application properties (including strength), and can make it brittle or unsuitable for certain applications. Impurities can make the EAF process more complex and expensive, as additional processing or sorting steps may be required.

[0018] The second major challenge concerns controlling the chemical alloy composition. Because scrap can contain different alloys and metal compositions, it can be difficult to precisely control the chemical composition of the final product. Adding alloying elements to the melt therefore becomes more complicated, and additional adjustments are often necessary to achieve the desired steel specification. European patent application

[0019] Voestalpine Stahl GmbH

[0020] 250048WO

[0021] Due to potential impurities and the fluctuating quality of scrap metal, it is difficult to guarantee the lowest levels of elements such as Cu, Ni, Mo, and N using the EAF process, which are required for certain specialized applications (e.g., safety-relevant components in the automotive industry). In such cases, the use of primary materials or very high-quality, sorted scrap is necessary, which increases costs.

[0022] In addition to the chemical composition, which is difficult to precisely adjust in an electric arc furnace process and is therefore often kept within predetermined tolerance limits defined by minimum and maximum levels, the effects of individual elements on the properties of the final product must also be taken into account.

[0023] The mechanical properties of the steel are further controlled, particularly during subsequent heat treatment or mechanical processing, such as rolling or forging.

[0024] Several solutions are already known that take into account the undesirable elements in the alloy composition or provide for additional adjustments to the alloying elements.

[0025] It is common practice to define specific target ranges for the alloying elements of a given steel grade, specifying the minimum and maximum values ​​for each element. For accompanying elements that are not intentionally added but are present in the raw materials in unknown concentrations, threshold values ​​exist to guarantee that, even if these levels are not exceeded, the material properties remain within the desired range. However, the actual concentration of these accompanying elements is not taken into account in the liquid phase.

[0026] A disadvantage of this approach is that low threshold values ​​for accompanying elements necessitate the use of feedstocks with low concentrations of these elements. This is primarily achieved through a high proportion of feedstocks produced from primary materials (iron ore).

[0027] To reduce CO₂ emissions, a high proportion of secondary raw materials (e.g., scrap metal) in the feed mix is ​​advantageous. This increases both the content of European patent application

[0028] Voestalpine Stahl GmbH

[0029] 250048WO

[0030] as well as the dispersion of accompanying elements and thus also the dispersion in material properties.

[0031] From EP 3 956 481 Bl, a computer-aided method for monitoring the steelmaking process in a converter is known. In this method, various materials with specific properties are introduced into the converter to produce liquid steel and slag. The method first defines the desired properties of the liquid steel and slag to be produced. Then, the required quantities of each material that must be introduced into the converter to achieve the defined target characteristics of the steel and slag are calculated. The calculated material quantities are transmitted to the automatically controlled operator or to automatic loading systems, and the converter is loaded accordingly.

[0032] This section describes the loading of the converter with various feedstocks. A disadvantage is that only the composition of the melt produced in the converter is controlled. Subsequent manipulation of the alloy composition is not specified.

[0033] German patent DE 10 2021 211 320 A discloses a method for controlling and regulating a production plant for rolled products made of metallic alloys such as steel, iron, or aluminum. The aim of the method is to optimize the use of raw materials and reduce production costs. Initially, specific target values ​​for the material, surface, and geometric properties of the final product, as well as permissible chemical compositions with defined tolerance ranges, are established for each order. By applying process models, predictive actual values ​​of the product properties are calculated for each order and compared with the target values. Only compositions that fall within the specified tolerances are selected. For each selected chemical composition, cost parameters such as alloy, scrap, energy, iron, additive, and CO₂ costs are determined. These are quantified in the form of penalty points or a penalty function.Subsequently, the intersection of permissible chemical compositions is determined for various combinations of production orders that are to be melted in a common batch. European patent application.

[0034] Voestalpine Stahl GmbH

[0035] 250048WO

[0036] The disadvantage of this approach is that tolerance ranges are determined for each composition. Precise control of the composition is not possible with this model.

[0037] From EP 4 183 498 A1, an AI-based predictive model is known that can predict mechanical properties from previously measured input values, such as the composition of the melt. To influence the mechanical properties, an adjustment of the manufacturing parameters, such as the roughing ratio, finishing ratio, rolling start temperature, cooling start time, cooling rate, or line speed, is proposed as output.

[0038] A disadvantage of this approach is that combining a machine learning model with a metallurgical model requires significant computing power and extensive data acquisition. The models must be continuously trained and updated, which can be time-consuming and resource-intensive. Furthermore, the model is optimized for specific production lines and processes. If production conditions or requirements need to change rapidly, the system may struggle to adapt.

[0039] From EP 0 152 665 Al a process for the production of cold-rolled dual-phase steel with improved deep-drawing capability is known, which is achieved by a coordinated combination of niobium and boron and continuous annealing with a two-stage, strictly controlled cooling.

[0040] US Patent 5462613 A discloses a process for producing wire rod with a predefined tensile strength. An empirical model is used to first predict the tensile strength based on a sample analysis of the steel melt. The same model is then used to calculate a "moving setpoint" for one or more control elements, such as carbon, required to achieve the target tensile strength. The melt is then "trimmed" by adding these elements before being processed into wire rod.

[0041] The object of the invention is to provide a method for producing cold-rolled dual-phase steels (DP), cold-rolled dual-phase steels with improved formability (DP-HD) and / or cold-rolled dual-phase steels with high formability (DP-FH) for European patent application

[0042] Voestalpine Stahl GmbH

[0043] 250048WO

[0044] to provide a level of product quality that ensures consistent product characteristics even with larger fluctuations in the accompanying element load.

[0045] The problem is solved by a method having the features of claim 1.

[0046] Advantageous further training options are indicated in the sub-requirements.

[0047] Furthermore, the object of the invention is to provide a system for the production of cold-rolled dual-phase steels (DP), cold-rolled dual-phase steels with improved formability (DP-HD) and / or cold-rolled dual-phase steels with high formability (DP-FH), with which it is possible to ensure constant product properties even with larger fluctuations in the accompanying element load.

[0048] The problem is solved with a control system having the features of claim 17.

[0049] This involves the concept of dynamic alloying. The target values ​​for alloying elements in the liquid phase are adapted. Using a predictive model, the influence of the measured concentrations of accompanying elements on the material properties is mapped, and a correction model proposes a response in the form of adapted target values ​​for the elements to be alloyed.

[0050] The inventors recognized that a distinction should be made between two types of elements when dynamically correcting element levels: influencing elements and compensating elements.

[0051] Various raw materials are used in the steelmaking process. These include, for example, iron ore, coke, slag formers, sponge iron, and scrap metal. These raw materials naturally introduce not only pure iron, but also so-called accompanying elements and trace elements.

[0052] Trace elements are usually undesirable and are removed during a subsequent metallurgical process, if possible. If removal is not possible, the trace element and its influence on metallurgical processes must be taken into account. European patent application

[0053] Voestalpine Stahl GmbH

[0054] 250048WO

[0055] For every alloy, which is defined by its chemical composition, there exists a defined class of accompanying elements, meaning that certain threshold values ​​of the accompanying elements should not be exceeded.

[0056] The alloy is a basic requirement for achieving the desired or required properties of the final product.

[0057] Trace elements are explicitly disruptive accompanying elements (e.g., arsenic) that are present in very small quantities. These are not taken into account during the (dynamic) alloying process carried out here.

[0058] Alloying elements are elements that are deliberately added (alloyed) to steel to improve its material properties in a desired way. These material properties can include mechanical properties such as hardness, tensile strength, toughness, and others, as well as chemical properties such as resistance to corrosion or hydrogen embrittlement, and others.

[0059] The alloying elements must be part of the melt to produce a desired steel grade with a defined target alloy composition. This composition allows for certain tolerances regarding the individual alloying element contents; that is, within the steel grade, a minimum and a maximum content are specified for the alloying elements.

[0060] When using scrap metal, it must be taken into account that scrap metal, viewed in isolation, contains accompanying elements and trace elements from its raw material history and alloying elements from its metallurgical history.

[0061] If scrap metal is used as a raw material in steel production, its components, apart from iron, are accompanying elements, trace elements or alloying elements for the product to be produced using the scrap metal.

[0062] Their presence must therefore be taken into account if they (as former alloying elements) cannot be easily or economically removed from the product via metallurgical processes. However, their effect can be considered and compensated for according to the invention. European patent application

[0063] Voestalpine Stahl GmbH

[0064] 250048WO

[0065] In the traditional manufacturing process, the starting point is a product (steel) that, according to market requirements, possesses specific material properties, particularly mechanical and / or chemical characteristics. It is then chemically / metallurgically modified to meet these requirements. Such a product is therefore an alloy, where the alloying elements are defined by a minimum and maximum content. Thus, the properties of a given alloy are known.

[0066] If, due to changed conditions, the scrap metal input is significantly increased, the product will consequently be loaded with a higher quantity of former alloying elements, accompanying elements, and trace elements. These elements have an influence, for example, on the product's mechanical properties.

[0067] The invention addresses this by selecting alloying elements that can compensate for the influence of the influencing elements on a desired scope of influence (hereinafter referred to as compensation elements) in addition to the trace elements, accompanying elements and former alloying elements that have an influence on one or more desired properties (hereinafter referred to as influencing elements).

[0068] Influencing elements are trace elements, accompanying elements and former alloying elements, which are introduced from raw materials and whose content in the melt can exceed a defined threshold.

[0069] Compensation elements are elements that, ideally, are regular alloying elements, meaning they are present in the target alloy, and whose content introduced by feedstocks is below a target value defined by the target alloy. This does not preclude the selection of a non-regular alloying element as a compensation element in certain cases. For example, the undesirable effect of so-called red brittleness caused by copper could be compensated for by adding nickel. Even if nickel is not a regular alloying element in the target alloy, it could still be used as a compensation element.

[0070] Should a first compensation element selected to compensate for the influence of an influencing element on a first (mechanical) property additionally have a European patent application

[0071] Voestalpine Stahl GmbH

[0072] 250048WO

[0073] If a first element has an influence on a second (mechanical) property, it may be necessary to compensate for this influence with a second compensating element. In this case, the first compensating element would also be an influencing element.

[0074] In certain borderline cases, it may even become necessary to adjust (upwards) the target values ​​of certain alloying elements defined by the target alloy if an amount exceeding the maximum content has to be added to compensate.

[0075] A simple example will illustrate this. In addition to iron, a desired steel alloy contains the elements A, B, and C. A is an influencing element and is now present in an amount exceeding the threshold value due to the raw materials. If the compensating element C has a comparable influence on a desired property as A, but is present in small amounts or not at all in the alloy, only enough of it is added so that the combined effect of A and C brings the desired property within a target range. In this case, this means that the original target value of the compensating element C is adjusted by adding less C (adapted target value) to compensate for the excessively high A content.

[0076] Another example is that if the influencing element A is present in a quantity that exceeds the threshold, and C is a compensation element that reduces the influence of A on a desired property, C is added in a quantity that, in addition to its own effect, also compensates for the effect of A.

[0077] Compensation in the sense of the invention thus means that an adjustment of the alloy composition can take place upwards or downwards in order to compensate for the influence on mechanical properties or deviations of the mechanical properties caused by influencing elements.

[0078] In this case, B is, for example, an element that has no influence on the desired property, such as strength.

[0079] Overall, this approach allows for a coarser pre-selection of scrap, thereby increasing the efficiency of the entire process in terms of costs, time, and resources. European patent application

[0080] Voestalpine Stahl GmbH

[0081] 250048WO

[0082] Input parameters for the forecasting model are influencing elements whose concentrations in the liquid phase are no longer changed, such as Cu, Mo, Ni, N.

[0083] The input parameters of the correction model are adapted target values ​​of elements that are alloyed in the liquid phase. These are the so-called compensation elements, such as C, Si, Mn, Cr, and Nb. Compensation elements are therefore elements that are added in the liquid phase to counteract the influence of the other elements, so that the target properties of the target alloy (defined by the desired steel grade) are achieved.

[0084] As mentioned above, some elements can also act as compensating elements even if they are not alloying elements of the target alloy. Since these elements used as compensating elements can also exert a (further) influence in the target alloy, they are also influencing elements in this respect, whose influence may in turn need to be compensated for by another compensating element.

[0085] The forecasting model determines the effect or influence of deviations of the influencing elements that exceed their threshold values ​​from their respective threshold values ​​on the tensile strength R. m The input parameters for this are the deviations of the influencing element contents from the threshold values.

[0086] A simple implementation of the correction model uses the actual (based on sample analyses) deviations of the levels of the influencing elements from their respective threshold values, as well as variations of deviations of the levels of the compensation elements from their respective target values, as input variables.

[0087] In steel production, "scrap" refers to recycled, reusable metallic secondary material that serves as raw material for the production of new steel. Scrap consists mainly of iron and steel and is classified into different grades and varieties depending on its purity, shape, size, and chemical composition. Types of scrap include: old scrap, new scrap, shredded scrap, etc.

[0088] The present process, which uses scrap, relates to the production of cold-rolled dual-phase steels (DP), cold-rolled dual-phase steels with improved European patent application

[0089] Voestalpine Stahl GmbH

[0090] 250048WO

[0091] Formability (DP-HD) and / or cold-rolled dual-phase steels with high formability (DP-FH).

[0092] Dual-phase steels, also referred to as DP steels, belong to the AHSS (advanced high-strength steels) grades or the group of multiphase steels. Steels in this group exhibit a mixed microstructure with several different microstructural constituents. Depending on the proportions of the different microstructural phases, the strength-to-elongation ratio can be adjusted. DP steels have a low yield strength ratio, resulting in very good overall ductility. Therefore, DP steels are particularly suitable for deep-drawn components. The strength classes differ primarily in their chemical composition, as this significantly determines the strength of the individual microstructural constituents and the transformation behavior, as well as the proportions of the respective microstructural phases. Furthermore, microalloying elements are added, which influence the grain size and form precipitates, thus having a significant impact on the tensile strength.

[0093] Compared to classic DP steels, DP steels with improved formability (DP-HD steels) and DP steels with high formability (DP-FH steels) are characterized by even better global ductility and thus deep-drawing properties.

[0094] In general, such cold-rolled dual-phase steels offer the following advantages:

[0095] • High variety of strength variants with tensile strengths up to 1350 MPa;

[0096] • High elongation (DP < DP-HD < DP-FH) and excellent deep-drawing properties;

[0097] • Corrosion resistance through zinc-based coatings, for example ZE, Z, ZF or EG, Gl, GA or ZM coatings.

[0098] The concept is based on producing cold-rolled dual-phase steel of a predetermined grade, in which the tensile strength R is particularly important. mDespite increased levels of influencing elements introduced by the scrap in the electric arc furnace, the tensile strength remains unchanged or changes only minimally. In particular, the change in tensile strength is considered in comparison to the tensile strength achieved via the primary route with no or minimal scrap input (e.g., in the LD process). European patent application

[0099] Voestalpine Stahl GmbH

[0100] 250048WO

[0101] This is done by providing a forecast regarding the effect of the influencing elements on the tensile strength R. m by means of a forecasting model and subsequent adaptation of the target values ​​of one or more compensation elements by applying a correction model. This concept is subsequently referred to as dynamic alloying.

[0102] In the present procedure, the effect of the elements is described as the slope or factor of the change in strength with varying alloy content.

[0103] Starting with a target alloy composition defined by the specified steel grade, the deviations of the influencing elements from their respective threshold values ​​are determined. Using a predictive model, the effect of these deviations on the tensile strength R is then calculated. m The necessary reduction or adaptation of one or more compensation elements (adapted target values) is then calculated using a correction model. The correction model can also take into account further restrictions or specific customer requirements.

[0104] Accordingly, the dynamic alloying process comprises two interacting components. The first component is a predictive model, and the second component is a correction model.

[0105] The actual values ​​of the elements contained in the melt can be continuously determined through analysis, initially in the last primary metallurgical unit, the converter, the electric arc furnace, the ladle, or at any intermediate stage. These actual values ​​can be analyzed before any initial alloying step. Based on the analysis, a variable alloy addition, determined by the minimum concentrations of the alloying elements, is calculated and added after tapping. Subsequently, a purge gas treatment is performed to homogenize the melt, and a second analysis may be conducted. Dynamic alloying then begins based on the determined actual values.

[0106] Initially, the actual values ​​are deliberately kept below the target values ​​of the alloying elements. This is necessary to allow for the further addition of alloying elements. European patent application

[0107] Voestalpine Stahl GmbH

[0108] 250048WO

[0109] The deviations from the threshold values ​​are determined using the actual values ​​of the influencing elements analyzed. These deviations result from the unintentional exceedance of the threshold values ​​due to the use of input materials with an increased load of influencing elements. Subsequently, an influencing factor F is applied in the forecasting model. E calculated from the deviations of the influencing element contents from the threshold values, which is a measure of the influence of the influencing elements on the tensile strength R m represents.

[0110] The influencing factor F E MPa is calculated in the forecasting model using the following formula:

[0111] F E= 95 × Δ[at%]Cu + 118 × Δ[at%]Ni + 1802 × Δ[at%]Mo − 290 × Δ[at%]N,

[0112] where Δ[at%]X is the content of the influencing element X exceeding the threshold value and where the slope determined for the respective influencing element X, which represents its influence on the tensile strength R m The actual value may deviate by ±25% from the stated value.

[0113] The necessary dynamic correction is then determined using the correction model.

[0114] In the correction model, dynamically corrected target values ​​of the compensation elements for the desired alloy are calculated based on an optimization calculation, whereby these may be reduced by a maximum of 30%, preferably 25%, and most preferably 20% compared to their actual target values. Subsequently, a compensation factor F is determined. KThe values ​​are calculated from the deviations of the compensation element contents from the target values. These deviations arise from a deliberately altered chemical composition with respect to the compensation elements.

[0115] The compensation factor F K The MPa value for DP steels in the correction model is calculated using the following formula:

[0116] F K = 1052 × [at%]C Ziel × ΔC[at%] + 10435 × [at%]C Ziel × (2 × [at%]Nb Ziel × ΔC[at%] + ΔNb[at%] × [at%]C Ziel ) + 123 × ΔSi[at%] + 115 × ΔMn[at%] + 177 × ΔCr[at%],

[0117] where Δ[at%]Y is the deviation of the tensile strength R in the correction model to compensate for the tensile strength m calculated compensation element content from the target value of the compensation element Y and [at%]Y Ziel the target value of the compensation element Y is and where the slope determined for the respective compensation element Y, which determines its influence on the tensile strength R mThe actual value may deviate by ±25% from the stated value.

[0118] For DP-HD and / or DP-FH steels, a different formula is used to calculate the compensation factor F than the one above. K in MPa in the correction model:

[0119] F K = 1312 × [at%]C Ziel × ΔC[at%] + 6523 × [at%]C Ziel × (2 × [at%]Nb Ziel × ΔC[at%] + ΔNb[at%] × [at%]C Ziel ) + 57 × ΔSi[at%] + 180 × ΔMn[at%] + 177 × ΔCr[at%] − 2329 × [at%]Cr Ziel × (2 × [at%]C Ziel × ΔCr[at%] + ΔC[at%] × [at%]Cr Ziel ),

[0120] where Δ[at%]Y is the deviation of the tensile strength R in the correction model to compensate for the tensile strength m calculated compensation element content from the target value of the compensation element Y and [at%]Y Ziel the target value of the compensation element Y is and where the slope determined for the respective compensation element Y, which determines its influence on the tensile strength R mThe actual value may deviate by ±25% from the stated value.

[0121] Finally, the sum of the influencing factor F is calculated. E and the compensation factor is determined as follows:

[0122] ΔF = |F E + F K |

[0123] The aim is to minimize ΔF so that ΔF does not exceed a maximum value, in particular 20 MPa, preferably 10 MPa, most preferably 5 MPa.

[0124] The calculation of adapted compensation element contents or target values ​​and the compensation factor is iterated in the correction model until a solution is found which satisfies the above condition for ΔF.

[0125] Within the framework of the dynamic alloying process according to the invention, only the deviations from the target range defined for the target alloy, caused by influencing elements, in particular Cu, Mo, Ni, N, are relatively compensated. For this purpose, compensation elements, in particular C, Si, Mn, Cr, Nb, are adjusted only to the extent necessary to compensate for the deviation in tensile strength (ΔR) caused by the influencing elements. m ) to compensate. The base alloy remains unchanged; only the proportion of compensating elements is adjusted, which serves to relatively compensate for the differences described in the European patent application.

[0126] Voestalpine Stahl GmbH

[0127] 250048WO

[0128] The deviation caused by influencing elements is required. The model parameters used for this purpose are the influencing factor F. E (from threshold exceedances of the influencing elements) and compensation factor F K(from targeted deviations of the compensation elements from their target values) are determined such that the sum ΔF = |F E + F K | is minimized, thereby achieving the overall tensile strength that would be expected without increased levels of influencing elements and without compensation by adjusting the compensating elements. In this way, the adjustment of the tensile strength is largely decoupled from geometric product parameters, such as the sheet thickness, since the compensation addresses only the chemically induced deviation and does not require any dimension-dependent degrees of freedom; the method according to the invention is therefore dimension-independent.

[0129] The following criteria can be used when selecting compensation elements: possibility of element correction within the target range, accuracy of the respective compensation element, timing of alloy adjustment, strength of the dependence of the tensile strength Rm of the respective compensation element, difference from the tensile strength R used to compensate m calculated compensation element content and the target value of the compensation element, selection of further compensation elements, costs of the respective compensation element.

[0130] The possibility of element correction within the target range means that a compensating element is selected whose content, recalculated and adapted by the correction model, does not deviate from the original target range defined by the desired steel grade. This is considered particularly advantageous.

[0131] The accuracy of the respective compensating element means that a compensating element is selected whose content can be adjusted with a high degree of accuracy; that is, when implementing the alloying process within the framework of dynamic alloying, only a small deviation of ±5% from the target content is to be expected. Such compensating elements should be selected preferentially. European patent application

[0132] Voestalpine Stahl GmbH

[0133] 250048WO

[0134] The timing of alloy formulation can also be a selection criterion. For example, it may be advantageous to first add the compensating elements carbon and manganese, and then add boron and titanium at a later stage.

[0135] The strength of the dependence of the tensile strength R mThe specific compensation element may vary. It is advantageous to select a compensation element that has a strong effect on compensating for the influence of the influencing element on the tensile strength R. m In this case, it may be sufficient to use only one or a few compensating elements for dynamic alloying. For example, the following sequence should be chosen: 1) Mn, 2) C, 3) Nb

[0136] The difference from the tensile strength R used to compensate m The calculated compensation element content (adapted target value) and the target value of the compensation element should be as small as possible to avoid increased resource consumption and potential secondary effects caused by the changed compensation element content. Unintended secondary effects could, in turn, necessitate further compensation of the influence of the compensation element in question.

[0137] The selection of further compensatory elements may become necessary if a single compensatory element cannot be adjusted sufficiently to adequately offset the effects of the influencing elements. If the effect of one compensatory element is insufficient, a second compensatory element is used. If these, in combination, are still insufficient to offset the effects of the influencing elements, a third compensatory element is used, and so on.

[0138] The cost of each compensating element can also be considered when selecting or ranking them. It is economically advantageous to initially use more expensive compensating elements, as their contents are typically reduced during dynamic alloying. In this sense, the ranking of the compensating elements would be, for example, as follows: 1) Nb, 2) Mn, 3) Si, 4) Ti, 5) C. European patent application

[0139] Voestalpine Stahl GmbH

[0140] 250048WO

[0141] All these criteria can play a role, individually or in combination, in the selection of compensation elements.

[0142] The influence of the individual elements is as follows.

[0143] Copper increases strength but simultaneously reduces hot formability and elongation at break. Copper enrichment can also be observed on the surface. At low concentrations, the strength-enhancing effect of copper is due to solid solution strengthening. However, its low solubility in steel can lead to low-melting phases at the grain boundaries, thus significantly impairing hot formability. This can subsequently lead to cracking. Copper also affects the transformation behavior by increasing the austenite region and / or austenite stability. For multiphase steels (DP or CP), the altered transformation behavior also results in a change in the microstructure, which is adjusted during the final heat treatment or annealing after cold rolling. This also influences the mechanical properties (strength, yield strength, elongation).Furthermore, copper stabilizes retained austenite, which remains in the microstructure after heat treatment and has a significant effect on the ductility properties of HD / FH grades. Copper influences the transformation behavior and can lead to negative surface effects or red fracture, which is why a maximum copper content must not be exceeded. It is advantageous if the copper content does not exceed 0.343 at%. The threshold for copper, above which intervention by dynamic alloying is carried out, is 0.023 at%.

[0144] Nickel increases strength through solid solution strengthening and can improve toughness. Furthermore, nickel increases the solubility of copper. Nickel also influences the transformation behavior by expanding the austenite region and increasing austenite stability. For multiphase steels (DP or CP), the altered transformation behavior also results in a change in the microstructure, which is adjusted during the final heat treatment or annealing after cold rolling. This also affects the mechanical properties (strength, yield strength, elongation). In addition, nickel stabilizes retained austenite, which remains in the microstructure after heat treatment and has a significant impact on the European patent application.

[0145] Voestalpine Stahl GmbH

[0146] 250048WO

[0147] It possesses ductility properties of HD / FH grades. Nickel strongly influences the conversion process, therefore a maximum nickel content must not be exceeded. It is advantageous if the nickel content does not exceed 0.317 at%. The threshold for nickel, above which intervention by dynamic alloying is carried out, is 0.021 at%.

[0148] Molybdenum delays the austenite-ferrite transformation and recrystallization, thereby leading to grain refinement that increases strength. Consequently, the strength of the steel increases with a higher molybdenum content. It is advantageous if the molybdenum content does not exceed 0.259 at%. The threshold for molybdenum, above which dynamic alloying is considered, is 0.01 at%.

[0149] Carbon acts as an interstitial atom, bound in cementite or transformed into pearlite, and in carbides such as NbC and TiC, it increases strength. Carbon also has a significant influence on transformation behavior. In multiphase steels, carbon is essential for the formation of bainitic and martensite. The strength of martensite is strongly dependent on the carbon content. The temperature ranges in which bainitic transformation or the conversion of austenite to martensite occurs are also dependent on the carbon content. A carbon content of 0.008 to 0.056 at% is advantageous.

[0150] Silicon acts as a solid solution hardener and increases strength. It also has a strong effect on the transformation behavior and suppresses cementite formation, which is very important for HD / FH grades. A silicon content of 0.051 to 1.113 at% is advantageous.

[0151] Manganese is a solid solution strengthening element. It binds sulfur to form manganese sulfides and is a strong austenite stabilizer. Therefore, it lowers the Ac3 temperature. Too much manganese can stabilize the austenite and prevent it from transforming into ferrite and pearlite upon cooling. In HD / FH grades, retained austenite is intentionally added to adjust the ductility properties. Manganese tends to cause segregation. Manganese also has a strong effect on bainitic transformation and martensitic flip-over. Furthermore, martensite strength is strongly influenced by manganese, which is important in multiphase steels. A manganese content of 0.324 to 3.237 at% is advantageous. European patent application

[0152] Voestalpine Stahl GmbH

[0153] 250048WO

[0154] Chromium increases strength through solid solution hardening, but can also promote the formation of microstructural constituents that further enhance steel strength by delaying austenite transformation. Chromium carbides can form in combination with carbon. These can have a strength-enhancing effect because they inhibit grain growth and lead to precipitation hardening. However, the binding of carbon reduces the amount of interstitially dissolved carbon, which is important for the formation of bainite and martensite in multiphase steels. This can also negatively affect strength. A chromium content of 0.093 to 1.310 at% is advantageous.

[0155] Niobium is used to increase strength and toughness due to its influence on grain size. Niobium increases the strength of steel through the precipitation of NbC and / or Nb(C,N) in the ferrite matrix. Furthermore, it can inhibit recrystallization and phase transformations, thereby reducing grain size and increasing the strength and toughness of the steel. A niobium content of < 0.251 at% is advantageous.

[0156] Titanium is a strong deoxidizing agent and binds nitrogen. Titanium nitrides in austenite are stable up to and sometimes beyond their melting point. Therefore, titanium in combination with nitrogen is an ideal element for reducing the grain growth of austenite at high temperatures. Titanium carbides and titanium carbonitrides precipitate at lower temperatures and improve strength and toughness due to the precipitation hardening effect and its influence on a smaller grain size. Titanium is also important in combination with boron for binding nitrogen, which would otherwise bind boron through the formation of boron nitrides, leaving no boron available at the grain boundaries. A titanium content of < 0.129 at% is advantageous.

[0157] Boron improves hardenability and reduces the risk of red brittleness in copper-alloyed steels. Through segregation at the former austenitic grain boundaries, boron also increases resistance to hydrogen fracture. Boron acts synergistically with molybdenum and niobium, thus enhancing the effectiveness of these elements. However, higher boron contents should be avoided, as these lead to the formation of brittle iron-boron carbides. Boron also results in less susceptible grain boundaries when welding galvanized grades, thereby preventing embrittlement (liquid metal embrittlement susceptibility). Furthermore, boron also has an influence on [European patent application].

[0158] Voestalpine Stahl GmbH

[0159] 250048WO

[0160] This affects the transformation behavior and thus the formation / origin / quantity of bainite and martensite. It is advantageous to choose a boron content of < 0.1 at%.

[0161] Nitrogen, in the presence of titanium and aluminum, forms corresponding nitrides: titanium nitrides (TiN) and aluminum nitrides (AlN), which suppress excessive coarsening of the austenite grains during steel heat treatment. Nitrogen also enables the formation of carbonitride precipitates, which contribute to achieving the desired strength. Furthermore, nitrogen acts similarly to carbon as an austenite former. To prevent aging, nitrogen is bound in many steels by the addition of alloying elements, such as AlN, TiN, and BN. It is advantageous if the nitrogen content does not exceed 0.006 at%. The threshold for nitrogen, above which intervention through dynamic alloying is considered, is 0.002 at%.

[0162] The effects of phosphorus and sulfur are particularly detrimental, as these elements lead to segregation at grain boundaries, which increases the risk of grain boundary cracking. Furthermore, phosphorus and sulfur increase the risk of hot cracking. Therefore, the concentrations of phosphorus and sulfur must be kept very low (P: < 0.028 at%; S: < 0.006 at%).

[0163] Aluminum is an optional alloying element in multiphase steels, increasing the Ac3 temperature, promoting ferrite formation, and facilitating precipitation hardening. Aluminum is commonly used as a deoxidizing agent in steel. Aluminum can lead to the formation of aluminum nitrides, which can impede grain boundary movement and thus contribute to grain refinement. Aluminum can be used as a partial substitute for silicon to suppress cementite formation. An aluminum content of 0.007 to 0.0486 at% is advantageous.

[0164] It is also advantageous if the tensile strength R m for DP steels between 290 MPa and 1350 MPa, for DP-HD steels between 590 and 1350 MPa and for DP-FH steels between 980 and 1350 MPa.

[0165] In an exemplary embodiment, the tensile strength R m in MPa for DP steels can be calculated using the following formula: European patent application

[0166] Voestalpine Stahl GmbH

[0167] 250048WO

[0168] R m = 250 + 526 x [at%]C 2 + 10435 x [at%]Nb x [at%]C 2 + 123 x [at%]Si + 115 x [at%]Mn + 177 x [at%]Cr + 95 x [at%]Cu + 118 x [at%]Ni + 1802 x [at%]Mo — 290 x [at%]N,

[0169] where [at%]i is the content of the respective element i and where the slope determined for the respective element i (the factor before the element content), which influences its tensile strength R mThe actual value may deviate by ±25% from the stated value.

[0170] The slopes (i.e., the influence of the elements on the tensile strength R) m ) result from practical experiments, for example laboratory experiments, as well as from the statistical evaluation of process and test data from series production.

[0171] In another exemplary embodiment, the tensile strength R can be m in MPa for DP-HD and / or DP-FH steels can be calculated using the following formula:

[0172] R m = 250 + 656 x [at%]C 2 + 6523 x

[0173]

[0174] [at%]Nb x [at%]C 2 + 57 x [at%]Si + 180 x [at%]Mn + 177 x [at%]Cr — 2329 x [at%]C x [at%]Cr 2 + 95 x [at%]Cu + 118 x [at%]Ni + 1802 x [at%]Mo - 290 x [at%]N,

[0175] where [at%] i is the content of the respective element i and where the slope determined for the respective element i (the factor before the element content), which influences its tensile strength R m The actual value may deviate by ±25% from the stated value.

[0176] Furthermore, in an exemplary embodiment, the DP, DP-HD and / or DP-FH steels have a thickness of 0.30 to 3.0 mm and a corrosion protection coating based on zinc.

[0177] It should be noted that the detrimental effects of accompanying elements are particularly critical in combination with one another, their origin being due to corresponding scrap contamination (in the feed mix used to create the melt). When using melting technologies with increased scrap quantities, the inevitably higher load of accompanying elements can therefore lead to greater variations in performance-relevant material properties. European patent application

[0178] Voestalpine Stahl GmbH

[0179] 250048WO

[0180] The invention thus relates to a method for producing cold-rolled dual-phase steels DP, cold-rolled dual-phase steels with improved formability DP-HD and / or cold-rolled dual-phase steels with high formability DP-FH, which have a target range of tensile strength Rm and are adjusted by a target alloy comprising iron, as well as accompanying elements and alloying elements, wherein an electric arc furnace and / or LD converter is loaded with at least steel scrap and the contents of the electric arc furnace and / or the LD converter are melted, wherein at least one sample is taken from a melt of a final primary metallurgical unit of a production route and the contents of the accompanying and alloying elements are determined by its analysis, wherein actual analytical values ​​of the accompanying and alloying element contents are transmitted to a control system, wherein accompanying elements are elements,which are introduced into the melt by feedstocks and whose contents must not exceed a maximum content defined by the target alloy, and alloying elements are elements that are specifically added according to target values ​​defined by the target alloy, whereby a distinction is made between influencing and compensating elements, whereby influencing elements and compensating elements are elements that have an influence or effect on the tensile strength R, m have, whereby the difference between the actual analysis values ​​and threshold values ​​with respect to the influencing elements is recorded, whereby the magnitude of the influence of the deviation of the actual analysis values ​​from the threshold values ​​of all influencing elements on the tensile strength R m is recorded, whereby at least one compensation element is determined, which is adjusted, i.e. according to a corrected target value, and added to the melt in such a way that the tensile strength R mbrought into a target area and the influence of at least one influencing element is thereby compensated, whereby the influencing elements whose influence on the tensile strength R m to be compensated, comprising one, several or all from the group of Cu, Mo, Ni, N and wherein one, several or all from the group of C, Si, Mn, Cr, Nb are chosen as compensation elements.

[0181] An advantageous further development provides that the influencing elements, whose influence on the tensile strength R m to be compensated, include Cu, Mo, Ni and / or N.

[0182] An advantageous further development provides for the selection of C, Si, Mn, Cr and / or Nb as compensating elements. European patent application

[0183] Voestalpine Stahl GmbH

[0184] 250048WO

[0185] An advantageous further development approach involves using two components in the tax system: a forecasting model and a correction model, with the forecasting model representing an influencing factor F. E The magnitude of the influence of the deviation of the actual analysis values ​​from the threshold values ​​of all influencing elements on the tensile strength R is determined. m describes, and with the correction model for compensating the tensile strength R m The required compensation element contents are calculated, as well as a compensation factor F. K The magnitude of the influence of a deviation of the calculated compensation element contents from the target values ​​of all compensation elements on the tensile strength R is determined. m describes.

[0186] An advantageous further development approach stipulates that the tensile strength R is calculated using... m The following formula is used for the tensile strength in MPa of cold-rolled dual-phase steels DP:

[0187] Rm = 250 + 526 x [at%]C 2 + 10435 x [at%]Nb x [at%]C 2 + 123 x [at%]Si + 115 x [at%]Mn + 177 x [at%]Cr + 95 x [at%]Cu + 118 x [at%]Ni + 1802 x [at%]Mo — 290 x [at%]N,

[0188] where [at%]i is the content of the respective element i and where the slope determined for the respective element i, which influences its tensile strength R m The actual value may deviate by ±25% from the stated value.

[0189] An advantageous further development approach stipulates that the tensile strength R is calculated using... m The following formula is used in MPa for cold-rolled dual-phase steels with improved formability DP-HD and / or cold-rolled dual-phase steels with high formability DP-FH:

[0190] R m = 250 + 656 x [at%]C 2 + 6523 x

[0191]

[0192] [at%]Nb x [at%]C 2+ 57 x [at%]Si + 180 x [at%]Mn + 177 x [at%]Cr — 2329 x [at%]C x [at%]Cr 2 + 95 x [at%]Cu + 118 x [at%]Ni + 1802 x [at%]Mo - 290 x [at%]N,

[0193] where [at%] i is the content of the respective element i and where the slope determined for the respective element i, which influences its tensile strength R m depicts a value that may deviate by ±25% from the specified value. European patent application

[0194] Voestalpine Stahl GmbH

[0195] 250048WO

[0196] An advantageous further training approach stipulates that the influencing factor F is included in the forecasting model. E The influencing elements are calculated in MPa using the following formula:

[0197] F E = 95 × Δ[at%]Cu + 118 × Δ[at%]Ni + 1802 × Δ[at%]Mo − 290 × Δ[at%]N,

[0198] where Δ[at%]X is the content of the influencing element X exceeding the threshold value and where the slope determined for the respective influencing element X, which represents its influence on the tensile strength R m The actual value may deviate by ±25% from the stated value.

[0199] An advantageous further training provides that, in the compensation model for cold-rolled dual-phase steels DP, the compensation factor F K The compensation elements are calculated in MPa using the following formula:

[0200] F K = 1052 × [at%]C Ziel × ΔC[at%] + 10435 × [at%]C Ziel × (2 × [at%]Nb Ziel × ΔC[at%] + ΔNb[at%] × [at%]C Ziel ) + 123 × ΔSi[at%] + 115 × ΔMn[at%] + 177 × ΔCr[at%],

[0201] where Δ[at%]Y is the deviation of the tensile strength R in the correction model to compensate for the tensile strength m calculated compensation element content from the target value of the compensation element Y and [at%]Y Zielthe target value of the compensation element Y is and where the slope determined for the respective compensation element Y, which determines its influence on the tensile strength R m The actual value may deviate by ±25% from the stated value.

[0202] An advantageous further development provides that, in the compensation model for cold-rolled dual-phase steels with improved formability DP-HD and / or cold-rolled dual-phase steels with high formability DP-FH, the compensation factor F K The compensation elements are calculated in MPa using the following formula:

[0203] F K = 1312 × [at%]C Ziel × ΔC[at%] + 6523 × [at%]C Ziel × (2 × [at%]Nb Ziel × ΔC[at%] + ΔNb[at%] × [at%]C Ziel ) + 57 × ΔSi[at%] + 180 × ΔMn[at%] + 177 × ΔCr[at%] − 2329 × [at%]Cr Ziel × (2 × [at%]C Ziel × ΔCr[at%] + ΔC[at%] × [at%]Cr Ziel ),

[0204] where A[at%]Y is the deviation of the tensile strength R in the correction model to compensate for the tensile strength m calculated compensation element content from the target value of the compensation element Y and [at%]Y Z iei is the target value of the compensation element Y and where the value for the respective European patent application

[0205] Voestalpine Stahl GmbH

[0206] 250048WO

[0207] The calculated slope of the compensation element Y, which determines its influence on the tensile strength R, is determined. m The actual value may deviate by ±25% from the stated value.

[0208] An advantageous further training provides that the sum of the influence factor and the compensation factor ΔF = |F E + F K | is minimized so that AF does not exceed a maximum value, in particular 20 MPa, preferably 10 MPa, most preferably 5 MPa.

[0209] An advantageous further development provides that the method is independent of geometric product parameters, i.e., dimensionally independent, whereby preferably only the influence of the influencing elements on the tensile strength R is affected. m This is relatively compensated by adjusting the compensation elements only to the extent necessary to reduce the influence of the influencing elements on the tensile strength R. m , namely to compensate for a chemically induced deviation.

[0210] An advantageous further training provides that the compensation element levels are reduced by a maximum of 30%, preferably 25%, and most preferably 20% compared to the target value.

[0211] An advantageous further development approach provides for the selection of compensation elements according to one, several, or all of the following criteria: possibility of element correction within the target range, accuracy of the respective compensation element, timing of alloy adjustment, strength of the dependence of the tensile strength on the respective compensation element, difference between the compensation element content calculated to compensate for the tensile strength and the target value of the compensation element, selection of further compensation elements, cost of the respective compensation element.

[0212] An advantageous further development provides for the selection of compensation elements according to the following criteria: possibility of element correction within the target range, accuracy of the respective compensation element, timing of alloy adjustment, strength of the dependence of the tensile strength on the respective compensation element, difference between the compensation element content calculated to compensate for the tensile strength and the target value of the compensation element, selection of further compensation elements and / or the cost of the respective compensation element. European patent application

[0213] Voestalpine Stahl GmbH

[0214] 250048WO

[0215] An advantageous further development provides that influencing elements are elements which are trace elements, accompanying elements or alloying elements in the feedstock and whose content exceeds a defined threshold, and compensating elements are elements which are regular alloying elements of the target alloy or other elements.

[0216] An advantageous further development provides that sampling and analysis, especially after tapping of crude steel, are carried out at least in the melt of the last primary metallurgical aggregate of the production route and after each further addition of elements.

[0217] An advantageous further development provides that the cold-rolled dual-phase steels DP, the cold-rolled dual-phase steels with improved formability DP-HD and / or the cold-rolled dual-phase steels with high formability DP-FH have a thickness of 0.30 to 3.0 mm and a corrosion protection coating based on zinc.

[0218] An advantageous further development stipulates that the cold-rolled dual-phase steels DP have a tensile strength R m from 290 to 1350 MPa, the cold-rolled dual-phase steels with improved formability DP-HD have a tensile strength R m from 590 to 1350 MPa and the cold-rolled dual-phase steels with high formability DP-FH have a tensile strength R m have a power output of 980 to 1350 MPa.

[0219] An advantageous further development stipulates that the target alloy comprises the following target alloy composition in at%:

[0220] C 0.008-0.056

[0221] Si 0.051-1.113

[0222] Mn 0.324-3.237

[0223] P < 0.028

[0224] S < 0.006

[0225] AI 0.007-0.0486

[0226] Ti < 0.129

[0227] Nb < 0.251

[0228] Cu < 0.343

[0229] Cr 0.093-1.310 European patent application

[0230] Voestalpine Stahl GmbH

[0231] 250048WO

[0232] Mo < 0.259

[0233] Ni < 0.317

[0234] N < 0.006

[0235] Residual iron and impurities resulting from the smelting process.

[0236] An advantageous further training program stipulates that the threshold values ​​of the influencing elements in at% are as follows:

[0237] Cu 0.023;

[0238] Ni 0.021;

[0239] Mon 0.01;

[0240] N 0.002,

[0241] where, if at least one actual value of an analysis of at least one influencing element exceeds the respective threshold, a compensation of the effect of the at least one influencing element on the tensile strength R is applied. m This becomes necessary through adjusted compensation element contents.

[0242] The invention further relates to a control system for the production of cold-rolled dual-phase steels DP, cold-rolled dual-phase steels with improved formability DP-HD and / or cold-rolled dual-phase steels with high formability DP-FH, which achieve a desired range of tensile strength R m exhibit and are adjusted by a target alloy comprising iron, as well as accompanying elements and alloying elements, and for carrying out the method of the invention, wherein the control system comprises two components: a prediction model and a correction model, wherein the prediction model is designed to detect the influence of influencing elements on the tensile strength R mto calculate, and the correction model is designed to compensate for the tensile strength R m required compensation element contents and the influence of the compensation elements on the tensile strength R m to calculate.

[0243] The invention is illustrated by way of example in a drawing. The drawing shows: European patent application

[0244] Voestalpine Stahl GmbH

[0245] 250048WO

[0246] Figure 1 shows a graph illustrating the concept! I keiten threshold, analysis actual value,

[0247] Deviation of the actual analysis value from the threshold value of the influencing element X, A[at%]X, and maximum content with respect to the influencing elements illustrated;

[0248] Figure 2 shows a graph which defines the terms target value, adapted target value,

[0249] Deviation of the tensile strength R in the correction model to compensate for mThe calculated compensation element content (= adapted target value) is illustrated in relation to the target value of the compensation element Y, Δ[at%]Y, and the maximum content with respect to the compensation elements;

[0250] Figure 3 shows exemplary actual values ​​from analyses, target values / adapted target values ​​and calculated tensile strengths for three different DP grades, showing the initial state, effects of increased scrap use without countermeasures according to the invention and effects of correction by dynamic alloying;

[0251] Figure 4 shows exemplary actual values ​​from analysis, target values / adapted target values ​​and calculated tensile strengths for three different DP-HD grades, showing the initial state, effects of increased scrap use without countermeasures according to the invention and effects of correction by dynamic alloying.

[0252] In an exemplary embodiment of dynamic alloying according to the invention, the following steps are carried out:

[0253] 1) Record the actual values ​​of the analyses and compare them with threshold values. Based on this, a decision must be made as to whether dynamic alloying is necessary. If so, proceed to step 2;

[0254] 2) Calculation of the influencing factor F E in the prediction model (measure of the influence of the influencing elements on the tensile strength R) m );

[0255] 3) Calculation of adapted compensation element contents in the correction model (adapted target values), wherein these may be reduced by a maximum of 30%, preferably 25%, particularly preferably 20% compared to their actual target values; European patent application

[0256] Voestalpine Stahl GmbH

[0257] 250048WO

[0258] 4) Calculation of the compensation factor F K in the correction model (measure of the influence of the compensation elements on the tensile strength R) m );

[0259] 5) Calculation of the sum AF from the influencing factor and the compensation factor;

[0260] 6) Repeat steps 3) to 5) until AF is minimized to such an extent that it does not exceed a maximum value, in particular 20 MPa, preferably 10 MPa, most preferably 5 MPa;

[0261] 7) Adding the compensation element contents to the adapted target values ​​to increase the tensile strength R m to bring the final product into a target range.

[0262] After recording the actual values ​​of the analyses, if the levels of the influencing elements exceed their respective thresholds, the influencing factor F is first determined using the forecasting model. E calculated in MPa for the influencing elements using the following formula:

[0263] F E = 95 × Δ[at%]Cu + 118 × Δ[at%]Ni + 1802 × Δ[at%]Mo − 290 × Δ[at%]N,

[0264] where Δ[at%]X is the content of the influencing element X exceeding the threshold value and where the slope determined for the respective influencing element X, which represents its influence on the tensile strength R m The actual value may deviate by ±25% from the stated value.

[0265] Copper, nickel, molybdenum and nitrogen are the influencing elements here.

[0266] Subsequently, adapted compensation element contents (adapted target values) are determined using the correction model, whereby these may be reduced by a maximum of 30%, preferably 25%, particularly preferably 20% compared to their actual target values.

[0267] In the correction model, the compensation factor F is used for DP steels. K The following formula was used to calculate the MPa for the compensation elements:

[0268] F K = 1052 × [at%]C Ziel × ΔC[at%] + 10435 × [at%]C Ziel × (2 × [at%]Nb Ziel × ΔC[at%] + ΔNb[at%] × [at%]CZiel ) + 123 × ΔSi[at%] + 115 × ΔMn[at%] + 177 × ΔCr[at%],

[0269] where A[at%]Y is the deviation of the tensile strength R in the correction model to compensate for the tensile strength m calculated compensation element content from the target value of the compensation element Y and European patent application

[0270] Voestalpine Stahl GmbH

[0271] 250048WO

[0272] [at° / o]Yziei is the target value of the compensation element Y and where the slope determined for the respective compensation element Y, which determines its influence on the tensile strength R m The actual value may deviate by ±25% from the stated value.

[0273] For DP-HD and / or DP-FH steels, the compensation factor F is calculated K In MPa, however, the following formula is used:

[0274] F K = 1312 × [at%]C Ziel × ΔC[at%] + 6523 × [at%]C Ziel × (2 × [at%]Nb Ziel × ΔC[at%] + ΔNb[at%] × [at%]C Ziel) + 57 × ΔSi[at%] + 180 × ΔMn[at%] + 177 × ΔCr[at%] − 2329 × [at%]Cr Ziel × (2 × [at%]C Ziel × ΔCr[at%] + ΔC[at%] × [at%]Cr Ziel ),

[0275] where Δ[at%]Y is the deviation of the tensile strength R in the correction model to compensate for the tensile strength m calculated compensation element content from the target value of the compensation element Y and [at%]Y Ziel the target value of the compensation element Y is and where the slope determined for the respective compensation element Y, which determines its influence on the tensile strength R m The actual value may deviate by ±25% from the stated value.

[0276] Carbon, silicon, manganese, chromium and niobium are among the compensating elements.

[0277] The sum of the influencing factor F E and the compensation factor F K is determined as follows:

[0278] ΔF = |F E + F K |

[0279] The aim is to minimize ΔF so that ΔF does not exceed a maximum value, in particular 20 MPa, preferably 10 MPa, most preferably 5 MPa.

[0280] The calculation of adapted compensation element contents (adapted target values) is iterated in the correction model until a solution is found that satisfies the above condition for AF.

[0281] Figures 1 and 2 illustrate the terms threshold value, actual value of the analysis, deviation of the actual value of the analysis from the threshold value of the influencing element X, A[at%]X, and maximum content with respect to the influencing elements (Figure 1) and target value, adapted target value, deviation of the value in the correction model to compensate for the tensile strength R m calculated compensation element content (= adapted target value) from the target value of the European patent application

[0282] Voestalpine Stahl GmbH

[0283] 250048WO

[0284] Compensation element Y, Δ[at%]Y, and maximum content with respect to the compensation elements (Figure 2).

[0285] Δ[at%]X is calculated as the difference between the actual value of the analysis and the threshold value, i.e., Δ[at%]X = actual value of the analysis – threshold value. Accordingly, Δ[at%]X always has a positive sign if the threshold value is exceeded. Δ[at%]Y, on the other hand, is calculated as the difference between the adapted target value and the actual target value (without dynamic alloying), i.e., Δ[at%]Y = adapted target value – target value. Accordingly, Δ[at%]Y always has a negative sign.

[0286] The threshold value is the concentration at which intervention through dynamic alloying becomes necessary; that is, if the actual analytical value of an influencing element exceeds this value, its contribution to the FE (feature element) influence factor must be considered and its influence compensated by adjusting the concentrations of compensating elements. This concentration, at which intervention occurs, is usually significantly lower than the maximum concentration specified by the target alloy up to which intervention is permissible.

[0287] Threshold values ​​of the influencing elements in at% are:

[0288] Cu 0.023;

[0289] Ni 0.021;

[0290] Mon 0.01;

[0291] N 0.002.

[0292] If the actual analysis values ​​or actual analysis levels exceed their respective thresholds, this must be compensated for by adjusting the compensation element levels, i.e., dynamic alloying must take place.

[0293] The concept of dynamic alloying according to the invention will be illustrated below using examples.

[0294] Figure 3 shows exemplary data for three different DP steel grades.

[0295] For each of the three grades, an initial state is shown, which concerns steel production via the blast furnace / LD route. Here, the contents of the European patent application are shown.

[0296] Voestalpine Stahl GmbH

[0297] 250048WO

[0298] The influencing elements listed in the scrap metal (underlined element symbols) are generally low. These elements therefore do not make a significant contribution to the tensile strength R. m and do not need to be specifically compensated, so that the target values ​​of the compensation elements (element symbols highlighted in bold) do not need to be adjusted to bring the tensile strength into a desired target range (no dynamic alloying).

[0299] In addition to the initial state, a situation with increased scrap input is also shown. Here, the influencing element contents (actual values ​​from analysis) are correspondingly higher compared to the initial state. Without intervention in the sense of the dynamic alloying according to the invention, i.e., with the addition of the compensating elements according to their actual target values ​​(no dynamic alloying), a significantly higher tensile strength value is obtained compared to the initial state. Therefore, due to the increased influencing element contents, there is a risk of exceeding the permissible R m -interval or the target area is missed.

[0300] It is therefore desirable to consider the contribution of the varying chemical composition in the manufacturing process. This can be achieved by the method according to the invention, i.e., by dynamic alloying.

[0301] Finally, Figure 3 also shows data illustrating an exemplary dynamic alloying process that takes into account the increased influence element contents and the tensile strength R. m The process is designed to reliably control the process. Regarding a steel melt with increased levels of influencing elements (Mo, N, Cu, Ni) compared to the initial state, the effect of these increased levels is largely compensated for during dynamic alloying by adjusting the compensating elements (C, Si, Mn, Cr, Nb). The successful compensation is evident in the calculated tensile strength of the final product. This strength is identical for all three grades considered to the tensile strength obtained via the blast furnace / LD route with a very low influencing element load (initial state). This demonstrates the exceptional effectiveness of the process according to the invention.

[0302] Figure 4 shows analogous exemplary data for DP-HD quality. The same effect of the inventive method is shown as described for Figure 3. European patent application

[0303] Voestalpine Stahl GmbH

[0304] 250048WO

[0305] The slopes (i.e., the influence of the elements on the tensile strength R) m ) result from practical experiments, for example laboratory experiments, as well as from the statistical evaluation of process and test data from series production.

[0306] In a laboratory experiment, a small-scale cast ingot is heated in a test facility comprising all the essential components of a rolling mill for the production of flat products. Following a defined sequence of passes, determined by the individual pass thicknesses and one or more target temperatures to be maintained during or at the end of the rolling process, the ingot is rolled to the desired hot strip thickness. The resulting strip is then cooled in water or air. The hot-rolled, cooled strip is subsequently cold-rolled, and samples are heat-treated in an annealing simulator. One or more tensile specimens are taken from the annealed samples, and their mechanical properties, such as yield strength, tensile strength, and elongation at break, can be determined on conventional tensile testing machines.

[0307] The data obtained in the experiment serve as the basis for the development of a model for predicting the tensile strength R. m depending on the alloying elements, accompanying and trace elements, and the manufacturing route of the sheets. The predictive model is therefore based on fundamental principles sound from materials science and, in particular, from physics and metallurgy.

[0308] To calculate the slope of a specific element, experiments can be conducted on two samples that differ only in their elemental content. The slope for that one element is then calculated from the resulting delta.

[0309] The small-scale production of the cast blocks takes place in a specially designed melting furnace. This allows for variations in the alloying elements beyond the alloy range used in large-scale production. Furthermore, process parameters (such as heating temperatures, rolling temperatures, and cooling rates) can be set to values ​​that are not typical in large-scale processes or are even technically impossible to achieve with standard production equipment. European patent application

[0310] Voestalpine Stahl GmbH

[0311] 250048WO

[0312] This approach, which involves applying both alloying element contents and process parameters that exceed the usual limits of the produced sheets, yields well-established model parameters for the predictive and / or correction models. The influence of alloying and accompanying elements is essential for dynamic alloying.

[0313] Since a tensile test is taken from a large proportion of the sheet metal after production, these values ​​can be used to verify the prediction model, but also to fine-tune the parameters.

[0314] This fine-tuning of the parameters, specifically the slope values, is performed using computer-aided methods. Selected parameters of the model equations described above are determined using the method of least squares. The use of artificial intelligence methods (e.g., neural networks) is also conceivable for this fine-tuning. Since this fine-tuning is always based on measured data, a variation in the slope values ​​of ±25% is possible. Due to measurement errors in the process data, as well as in the measured mechanical properties themselves, a corresponding inaccuracy and thus a variation in the slope values ​​is unavoidable. The variation itself decreases the larger the datasets that can be used for fine-tuning.

[0315] Thus, with the present method, which enables dynamic, variable and flexible alloying, constant product properties can be guaranteed even with larger fluctuations in the influencing element load.

Claims

European patent application Voestalpine Stahl GmbH 250048WO Claims 1. A process for producing cold-rolled dual-phase steels DP, cold-rolled dual-phase steels with improved formability DP-HD and / or cold-rolled dual-phase steels with high formability DP-FH, which have a target range of tensile strength Rm and are adjusted by a target alloy comprising iron, as well as accompanying elements and alloying elements, wherein an electric arc furnace and / or LD converter is loaded with at least steel scrap and the contents of the electric arc furnace and / or the LD converter are melted, wherein at least one sample is taken from a melt of a final primary metallurgical aggregate of a production route and the contents of the accompanying and alloying elements are determined by analysis of this sample, wherein actual analytical values ​​of the accompanying and alloying element contents are transmitted to a control system, wherein accompanying elements are elements,which are introduced into the melt by feedstocks and whose contents must not exceed a maximum content defined by the target alloy, and alloying elements are elements that are specifically added according to target values ​​defined by the target alloy, characterized by the fact that A distinction is made between influencing and compensating elements, whereby Influencing elements and compensating elements are elements that have an influence or effect on the tensile strength R. m have, whereby The difference between the actual values ​​of the analysis and the threshold values ​​with respect to the influencing elements is recorded, whereby the magnitude of the influence of the deviation of the actual analysis values ​​from the threshold values ​​of all influencing elements on the tensile strength R m is recorded, whereby at least one compensation element is determined, which is adjusted, i.e., added to the melt according to a corrected target value, in such a way that the tensile strength R m brought into a target area and the influence of at least one influencing element is thereby compensated, wherein European patent application Voestalpine Stahl GmbH 250048WO the influencing elements whose influence on the tensile strength R m to be compensated, comprising one, several or all from the group of Cu, Mo, Ni, N and wherein One, several or all of the elements from the group of C, Si, Mn, Cr, Nb may be chosen as compensation elements.

2. The method according to claim 1, characterized in that two components are used in the control system: a forecasting model and a correction model, wherein the forecasting model represents an influencing factor F. EThe magnitude of the influence of the deviation of the actual analysis values ​​from the threshold values ​​of all influencing elements on the tensile strength R is determined. m describes, and with the correction model for compensating the tensile strength R m The required compensation element contents are calculated, as well as a compensation factor F. K The magnitude of the influence of a deviation of the calculated compensation element contents from the target values ​​of all compensation elements on the tensile strength R is determined. m describes.

3. Method according to claim 1 or 2, characterized in that the tensile strength R is calculated using... m The following formula is used for the tensile strength in MPa of cold-rolled dual-phase steels DP: R m = 250 + 526 x [at%]C 2 + 10435 x [at%]Nb x [at%]C 2 + 123 x [at%]Si + 115 x [at%]Mn + 177 x [at%]Cr + 95 x [at%]Cu + 118 x [at%]Ni + 1802 x [at%]Mo — 290 x [at%]N, where [at%]i is the content of the respective element i and where the slope determined for the respective element i, which influences its tensile strength R m The actual value may deviate by ±25% from the stated value.

4. Method according to one of the preceding claims, characterized in that the tensile strength R is calculated using... m in MPa of cold-rolled dual-phase steels with improved formability DP-HD and / or of cold-rolled dual-phase steels with high formability DP-FH, the following formula is used: European patent application Voestalpine Stahl GmbH 250048WO R m = 250 + 656 x [at%]C 2 + 6523 x [at%]Nb x [at%]C 2 + 57 x [at%]Si + 180 x [at%]Mn + 177 x [at%]Cr — 2329 x [at%]C x [at%]Cr 2 + 95 x [at%]Cu + 118 x [at%]Ni + 1802 x [at%]Mo - 290 x [at%]N, where [at%]i is the content of the respective element i and where the slope determined for the respective element i, which influences its tensile strength R m The actual value may deviate by ±25% from the stated value.

5. Method according to one of the preceding claims, characterized in that the influencing factor F is included in the forecasting model. E The influencing elements are calculated in MPa using the following formula: F E = 95 × Δ[at%]Cu + 118 × Δ[at%]Ni + 1802 × Δ[at%]Mo − 290 × Δ[at%]N, where Δ[at%]X is the content of the influencing element X exceeding the threshold value and where the slope determined for the respective influencing element X, which represents its influence on the tensile strength R m The actual value may deviate by ±25% from the stated value.

6. Method according to one of the preceding claims, characterized in that, in the case of the cold-rolled dual-phase steels DP, the compensation factor F in the compensation model K The compensation elements are calculated in MPa using the following formula: F K = 1052 x [at%]C Ziel x ΔC[at%] + 10435 x [at%]C Ziel x (2 x [at%]Nb Ziel x ΔC[at%] + ΔNb[at%] x [at%]C Ziel ) + 123 x ΔSi[at%] + 115 x ΔMn[at%] + 177 x ΔCr[at%], where Δ[at%]Y is the deviation of the tensile strength R in the correction model to compensate for the tensile strength m calculated compensation element content from the target value of the compensation element Y and [at%]Y Ziel the target value of the compensation element Y is and where the slope determined for the respective compensation element Y, which determines its influence on the tensile strength R m depicts a value that may deviate by ±25% from the specified value. European patent application Voestalpine Stahl GmbH 250048WO 7. Method according to one of the preceding claims, characterized in that, in the case of the cold-rolled dual-phase steels with improved formability DP-HD and / or the cold-rolled dual-phase steels with high formability DP-FH, the compensation factor F in the compensation model K The compensation elements are calculated in MPa using the following formula: F K = 1312 x [at%]C Ziel x ΔC[at%] + 6523 x [at%]C Ziel x (2 x [at%]Nb Ziel x ΔC[at%] + ΔNb[at%] x [at%]C Ziel ) + 57 x ΔSi[at%] + 180 x ΔMn[at%] + 177 x ΔCr[at%] — 2329 x [at%]Cr Ziel x (2 x [at%]C Ziel x ΔCr[at%] + ΔC[at%] x [at%]Cr Ziel ), where Δ[at%]Y is the deviation of the tensile strength R in the correction model to compensate for the tensile strength m calculated compensation element content from the target value of the compensation element Y and [at%]Y Zielthe target value of the compensation element Y is and where the slope determined for the respective compensation element Y, which determines its influence on the tensile strength R m The actual value may deviate by ±25% from the stated value.

8. Method according to one of the preceding claims, characterized in that the sum of the influence factor and the compensation factor ΔF = |F E + F K | is minimized so that AF does not exceed a maximum value, in particular 20 MPa, preferably 10 MPa, most preferably 5 MPa.

9. Method according to one of the preceding claims, characterized in that the compensation element contents are reduced by a maximum of 30%, preferably 25%, particularly preferably 20% compared to the target value.

10. Method according to one of the preceding claims, characterized in that the selection of the compensation elements is made according to one, several or all of the following criteria: possibility of element correction within the target range, accuracy of the respective compensation element, time of alloy adjustment, strength of the dependence of the tensile strength on the respective compensation element, difference between the compensation element content calculated to compensate for the tensile strength and the target value of the European patent application Voestalpine Stahl GmbH 250048WO Compensation element, choice of further compensation elements, cost of each compensation element.

11. Method according to one of the preceding claims, characterized in that influencing elements are elements which are trace elements or accompanying elements or alloying elements in the feedstock and whose content exceeds a defined threshold value, and compensating elements are elements which are regular alloying elements of the target alloy or other elements.

12. Method according to one of the preceding claims, characterized in that the sampling and analysis, in particular after tapping of crude steel, are carried out at least in the melt of the last primary metallurgical aggregate of the production route and after each further addition of elements.

13. Method according to one of the preceding claims, characterized in that the cold-rolled dual-phase steels DP, the cold-rolled dual-phase steels with improved formability DP-HD and / or the cold-rolled dual-phase steels with high formability DP-FH have a thickness of 0.30 to 3.0 mm and a corrosion protection coating based on zinc.

14. Method according to one of the preceding claims, characterized in that the cold-rolled dual-phase steels DP have a tensile strength R m from 290 to 1350 MPa, the cold-rolled dual-phase steels with improved formability DP-HD have a tensile strength R m from 590 to 1350 MPa and the cold-rolled dual-phase steels with high formability DP-FH have a tensile strength R m have a power output of 980 to 1350 MPa.

15. Method according to one of the preceding claims, characterized in that the target alloy comprises the following target alloy composition in at%: C 0.008-0.056 Si 0.051-1.113 Mn 0.324-3.237 P < 0.028 European patent application Voestalpine Stahl GmbH 250048WO S < 0.006 AI 0.007-0.0486 Ti < 0.129 Nb < 0.251 Cu < 0.343 Cr 0.093-1.310 Mo < 0.259 Ni < 0.317 N < 0.006 Residual iron and impurities resulting from the smelting process.

16. Method according to one of the preceding claims, characterized in that the threshold values ​​of the influencing elements in at% are as follows: Cu 0.023; Ni 0.021; Mon 0.01; N 0.002, where, if at least one actual value of an analysis of at least one influencing element exceeds the respective threshold, a compensation of the effect of the at least one influencing element on the tensile strength R is applied. m This becomes necessary through adjusted compensation element contents.

17. Control system for the production of cold-rolled dual-phase steels DP, cold-rolled dual-phase steels with improved formability DP-HD and / or cold-rolled dual-phase steels with high formability DP-FH, which achieve a desired range of tensile strength R m exhibit and are adjusted by a target alloy comprising iron, as well as accompanying elements and alloying elements, and for carrying out the method according to one of the preceding claims, characterized in that the control system comprises two components: a prediction model and a correction model, wherein the prediction model is designed to detect the influence of influencing elements on the tensile strength R m to calculate, and European patent application Voestalpine Stahl GmbH 250048WO the correction model is designed to compensate for the tensile strength R mrequired compensation element contents and the influence of the compensation elements on the tensile strength R m to calculate.

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