Method and control system for producing hot-rolled, low-alloy or microalloyed steels

Abstract

The invention relates to a method for producing hot-rolled, microalloyed steels with a tensile strength Rm in a target range, the tensile strength being adjusted by a target alloy comprising iron as well as impurity elements and alloying elements, wherein an arc furnace and / or LD converter is loaded by adding at least steel scrap, and the contents of the arc furnace and / or of the LD converter are melted; at least one sample is taken from a melt of the last primary metallurgical unit of a production route, and the content of impurity and alloying elements is determined by analyzing the sample; actual analysis values for the content of impurity and alloying elements are transmitted to a control system, impurity elements being elements which are introduced into the melt via feedstock and the content of which must not exceed a maximum content defined by the target alloy, and alloying elements being elements which are controlledly added in accordance with target values defined by the target alloy; 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, and the magnitude of the influence of the deviation of the actual analysis values from the limit values for all of the influencing elements on the tensile strength Rm is detected; and at least one compensating element is determined which is adjustedly alloyed into the melt, i.e. the compensating element is alloyed into the melt according to a corrected target value, in such a way that the tensile strength Rm is brought into a target range and the influence of the influencing element is compensated for as a result, wherein the influencing elements with an influence on the tensile strength Rm which is to be compensated for comprise one, a plurality, or all of the elements of the group consisting of Cr, Cu, Mo, and Ni, and one, a plurality, or all of the elements of the group consisting of C, Mn, Nb, V, Ti, N are selected as compensating elements. The invention also relates to a control system for carrying out the method according to the invention.

Description

[0001] International patent application

[0002] Voestalpine Stahl GmbH

[0003] 250043WO

[0004] Process and control system for the production of hot-rolled, low-alloy or micro-alloy steels

[0005] The invention relates to a method for producing hot-rolled, low-alloy or micro-alloy steels. The invention further relates to a control system for producing hot-rolled, low-alloy or micro-alloy 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). Here, scrap metal is melted using electrical energy to produce liquid steel. This process is particularly environmentally friendly, as it primarily uses recycled material and produces fewer CO2 emissions than the blast furnace process. International patent application

[0011] Voestalpine Stahl GmbH

[0012] 250043WO

[0013] 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.

[0014] 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.

[0015] 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.

[0016] The first challenge in using scrap metal is its fluctuating quality. The scrap used in EAF (Energy Efficiency Forming) is often heterogeneous and can contain impurities that negatively affect the steel's quality. For example, unwanted elements such as copper (Cu), chromium (Cr), nickel (Ni), and molybdenum (Mo) 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.

[0017] The second major challenge concerns controlling the chemical alloy composition. Because scrap metal can contain a variety of alloys and metal compositions, precisely controlling the chemical composition of the final product can be difficult. Adding alloying elements to the melt therefore becomes more complex, and additional adjustments are often necessary to achieve the desired steel specification.

[0018] Due to potential impurities and the fluctuating quality of scrap metal, it is difficult to guarantee the lowest levels of elements such as Cu, Cr, Ni, and Mo using the EAF process, which are required for certain specialized applications (e.g., in mechanical engineering and the automotive industry). In such cases, the use of primary materials or very high-quality, sorted scrap is necessary, which increases costs. International patent application

[0019] Voestalpine Stahl GmbH

[0020] 250043WO

[0021] 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.

[0022] The mechanical properties of the steel are further controlled, particularly during subsequent heat treatment or mechanical processing, such as rolling or forging.

[0023] 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.

[0024] 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.

[0025] A disadvantage of this 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).

[0026] To reduce CO2 emissions, a high proportion of secondary raw materials (e.g., scrap metal) in the feedstock mix is ​​advantageous. This increases both the concentration and the variability of accompanying elements, and thus also the variability in material properties.

[0027] 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. International patent application

[0028] Voestalpine Stahl GmbH

[0029] 250043WO

[0030] The calculated material quantities are transmitted to the automatically controlled operator or to automatic loading systems, and the converter is loaded accordingly.

[0031] 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.

[0032] 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.

[0033] 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.

[0034] 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.

[0035] A disadvantage is that combining a machine learning model with a metallurgical model requires high computing power and extensive data acquisition. International patent application

[0036] Voestalpine Stahl GmbH

[0037] 250043WO

[0038] The models require continuous training and updates, 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] 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.

[0040] A process for producing titanium micro-alloyed steel is known from CN 107 287 489 A. For this process, titanium-containing raw materials are melted successively in a converter and subsequently in a low-temperature furnace. The molten steel is then passed through a continuous thin-slab casting and rolling line to produce hot-rolled strip steel.

[0041] The object of the invention is to provide a method for the production of hot-rolled, low-alloy or micro-alloyed steels, with which constant product properties are ensured even with larger fluctuations in the accompanying element load.

[0042] The problem is solved by a method having the features of claim 1.

[0043] Advantageous further training options are indicated in the sub-requirements.

[0044] Furthermore, the object of the invention is to provide a system for the production of hot-rolled, low-grade micro-alloyed steels, with which it is possible to guarantee constant product properties even with larger fluctuations in the accompanying element load.

[0045] The problem is solved with a control system having the features of claim 15.

[0046] This involves the concept of dynamic alloying. The target values ​​for alloying elements are adapted in the liquid phase. A predictive model is used to map the influence of the measured concentrations of accompanying elements on the material properties, and a correction model proposes a response in the form of adapted target values ​​for the elements to be alloyed. International patent application

[0047] Voestalpine Stahl GmbH

[0048] 250043WO

[0049] The inventors recognized that a distinction should be made between two types of elements when dynamically correcting element levels: influencing elements and compensating elements.

[0050] 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.

[0051] 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.

[0052] 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.

[0053] The alloy is a basic requirement for achieving the desired or required properties of the final product.

[0054] 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.

[0055] 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.

[0056] The alloying elements must be part of the melt to produce a desired steel grade with a defined target alloy composition. The latter 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. International patent application

[0057] Voestalpine Stahl GmbH

[0058] 250043WO

[0059] 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.

[0060] 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.

[0061] 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.

[0062] 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.

[0063] 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 mechanical properties of the product.

[0064] 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).

[0065] Influencing elements are trace elements, accompanying elements, and former alloying elements that are introduced from raw materials and whose content in the melt can exceed a defined threshold. International patent application

[0066] Voestalpine Stahl GmbH

[0067] 250043WO

[0068] 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.

[0069] If a first compensation element, selected to compensate for the influence of an influencing element on a first (mechanical) property, also has an influence on a second (mechanical) property, it may become necessary to compensate for this influence with a second compensation element. In this case, the first compensation element would simultaneously be an influencing element.

[0070] 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.

[0071] 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.

[0072] 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.

[0073] Compensation in the sense of the invention thus means that an adjustment of the alloy composition upwards or downwards can take place in order to influence the International Patent Application

[0074] Voestalpine Stahl GmbH

[0075] 250043WO

[0076] To compensate for mechanical properties or deviations in mechanical properties caused by influencing elements.

[0077] In this case, B is, for example, an element that has no influence on the desired property, such as strength.

[0078] Overall, this approach allows for a coarser pre-selection of scrap, thereby increasing the efficiency of the overall process in terms of costs, time and resources.

[0079] Input parameters for the forecasting model are influencing elements whose concentrations in the liquid phase are no longer changed, such as Cr, Cu, Mo, Ni.

[0080] 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, Mn, Nb, Ti, V, and N. 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.

[0081] 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.

[0082] 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.

[0083] 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.

[0084] In steel production, "scrap" refers to recycled, reusable secondary metallic material that serves as raw material for the production of new steel. Scrap consists mainly of iron and steel and is available in various grades and varieties. International patent application

[0085] Voestalpine Stahl GmbH

[0086] 250043WO

[0087] Scrap is classified according to purity, shape, size, and chemical composition. Types of scrap include: old scrap, new scrap, shredded scrap, etc.

[0088] The present process, which uses scrap metal, relates to the production of hot-rolled, low-alloy or micro-alloyed steels.

[0089] Hot-rolled, micro-alloyed steels achieve their strength through alloying with niobium, titanium, and / or vanadium. These alloying elements can be added individually or in combination. The steels are available in various strength classes and, due to their homogeneous microstructure, are ideally suited for cold forming operations. The characteristically low carbon content results in excellent weldability. Furthermore, the fine-grained microstructure of these steels provides high resistance to the formation and propagation of brittle cracks.

[0090] In general, such hot-rolled, low-alloy or micro-alloyed steels offer the following advantages:

[0091] • High variety of strength variants with minimum yield strengths up to 750 MPa;

[0092] • High yield strength ratio;

[0093] • Very good cold formability;

[0094] • Good weldability

[0095] • High toughness

[0096] The concept is based on producing hot-rolled, low- or micro-alloyed steel of a specified grade, in which the tensile strength Rm, in particular, remains unchanged or changes only minimally despite increased levels of influencing elements introduced by the scrap in the electric arc furnace. Specifically, 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).

[0097] This is done by providing a forecast regarding the effect of the influencing elements on the tensile strength R. mby 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 hereinafter referred to as dynamic alloying. International patent application

[0098] Voestalpine Stahl GmbH

[0099] 250043WO

[0100] 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.

[0101] 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. mThe 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.

[0102] Accordingly, the dynamic alloying process comprises two interacting components. The first component is a predictive model, and the second component is a correction model.

[0103] 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.

[0104] 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.

[0105] The deviations from the threshold values ​​are determined using the analysis-I st values ​​of the influencing elements. These deviations result from the unintended exceedance of the threshold values ​​due to the use of raw materials with an increased influencing element load. Subsequently, an influence factor FE is calculated in the prediction model from the deviations of the influencing element contents from the threshold values, which represents a measure of the influence of the influencing elements on the tensile strength Rm. International patent application

[0106] Voestalpine Stahl GmbH

[0107] 250043WO

[0108] The influence factor FE in MPa is calculated in the forecasting model using the following formula:

[0109] F E = 109 x A[at%]Cr + 44.7 x A[at%]JVj + 164 x A[at%]Mo + 63.3 x A[at%]Cu,

[0110] where A[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.

[0111] The necessary dynamic correction is then determined using the correction model.

[0112] In the correction model, dynamically corrected target values ​​for the compensating elements in the desired alloy are calculated based on an optimization calculation. These values ​​may be reduced by a maximum of 30%, preferably 25%, and most preferably 20% compared to their actual target values. Subsequently, a compensation factor FK is calculated from the deviations of the compensating element contents from the target values. These deviations arise from a deliberately altered chemical composition with respect to the compensating elements.

[0113] The compensation factor FK in MPa is calculated for Nb and / or V-alloyed steels in the correction model using the following formula:

[0114] F K = (392 x [at%]C ziel - 22) x A[at%]C + 26 x [at%]Mn + 1015 x [at%]V + (7840 -165540 x [at%]Nb ziel - 50450 x [at%]N ziel ) x [at%]Nb + (1310 - 50450 x [at%]Nb Ziel ) x [at%]N,

[0115] where [at%]Yziei is the target value of the compensation element Y and A[at%]Y is the deviation of the compensation element content calculated in the correction model to compensate the tensile strength Rm from the target value of the compensation element Y, and where the slope determined for the respective compensation element Y, which represents its influence on the tensile strength Rm, may deviate by ±25% from the specified value.

[0116] In the case of titanium-alloyed steels, it is necessary to adjust the compensation factor FK to account for the effect of the added titanium and the altered influence of other alloying elements. Therefore, for titanium-alloyed steels, the formula for calculating the compensation factor FK, -ieg in MPa in the correction model differs from the formula above:

[0117] F Ki Ti-ieg = 26.0 x A[at%]Mn + 619 x A[at%]Ti, International patent application

[0118] Voestalpine Stahl GmbH

[0119] 250043WO

[0120] 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 where the slope determined for the respective compensation element Y, which reflects its influence on the tensile strength Rm, may deviate by ±25% from the specified value.

[0121] Finally, the sum of the influence factor FE and the compensation factor is determined as follows:

[0122] AF = \F E + F K \ or AF = \F E + F KiTi -i eg \.

[0123] AF should be minimized so that AF 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 that fulfills the above condition for AF.

[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 Cr, Cu, Mo, Ni, are relatively compensated. For this purpose, compensation elements, in particular C, Mn, Nb, V, Ti, N, are adjusted only to the extent necessary to compensate for the deviation in tensile strength (ARm) caused by the influencing elements. The base alloy remains unchanged; only the proportion of the compensation elements required for the relative compensation of the deviation caused by the influencing elements is adjusted. The model parameters used for this purpose, the influencing factor FE (from threshold exceedances of the influencing elements) and the compensation factor FK (from targeted deviations of the compensation elements from their target values), are determined such that the sum AF = \F E + F KThe effect 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 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. International patent application

[0126] Voestalpine Stahl GmbH

[0127] 250043WO

[0128] 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 R mof the respective compensation element, difference between the compensation element content calculated to compensate for the tensile strength Rm and the target value of the compensation element, selection of further compensation elements, cost of the respective compensation element.

[0129] 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.

[0130] The accuracy of the respective compensation element means that a compensation 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 compensation elements should be selected preferentially.

[0131] 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.

[0132] The degree of dependence of the tensile strength Rm on the respective compensating element may vary. It is advantageous to select a compensating element that has a strong effect on compensating for the influence of the influencing element on the tensile strength Rm. 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) Nb, 2) Mn, 3) C.

[0133] The difference between the compensation element content calculated to compensate for the tensile strength Rm (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. International patent application

[0134] Voestalpine Stahl GmbH

[0135] 250043WO

[0136] 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.

[0137] 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.

[0138] All these criteria can play a role, individually or in combination, in the selection of compensation elements.

[0139] The influence of the individual elements is as follows.

[0140] 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. It is advantageous if the copper content does not exceed 0.35 at%. The threshold for copper, above which intervention by dynamic alloying is carried out, is 0.015 at%.

[0141] Nickel increases strength through solid solution strengthening and can improve toughness. Furthermore, nickel increases the solubility of copper. It is advantageous if the nickel content does not exceed 0.39 at%. The threshold for adding nickel, above which dynamic alloying is considered, is 0.03 at%.

[0142] Molybdenum delays the austenite-ferrite transformation and recrystallization. Consequently, the strength of the steel increases with a higher molybdenum content. It is advantageous if the molybdenum content does not exceed 0.12 at%. The threshold of the international patent application

[0143] Voestalpine Stahl GmbH

[0144] 250043WO

[0145] Molybdenum, at which intervention by dynamic alloying is carried out, is at 0.005 at%.

[0146] Carbon acts as an interstitial atom, bound in cementite or transformed into pearlite, and in carbides such as NbC and TiC, it increases strength. A carbon content of 0.1 to 0.55 at% is advantageous.

[0147] Silicon acts as a solid solution hardener and increases strength. It is advantageous to choose a silicon content of less than 1 at%.

[0148] 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. Manganese is prone to segregation. A manganese content of 0.2 to 2.1 at% is advantageous.

[0149] Chromium increases strength through solid solution hardening, but can also promote the formation of microstructural constituents that further increase steel strength by delaying austenite transformation. It is advantageous if the chromium content does not exceed 0.43 at%. The threshold for dynamic alloying is 0.04 at%.

[0150] 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 < 0.055 at% is advantageous.

[0151] Titanium is a strong deoxidizing agent and binds nitrogen. Titanium nitrides in austenite are stable up to and partially 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. A titanium content of < 0.26 at% is advantageous. International patent application

[0152] Voestalpine Stahl GmbH

[0153] 250043WO

[0154] Vanadium can delay recrystallization and thus contribute to grain refinement. Furthermore, vanadium carbides and nitrides can form, which increase strength due to precipitation hardening. A vanadium content of < 0.22 at% is advantageous.

[0155] It is advantageous if the sum of Ti + Nb + V in the alloy is 0.003 to 0.26 at%.

[0156] 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 to choose a nitrogen content of less than 0.08 at%.

[0157] 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: < 0.045 at%; S: < 0.035 at%).

[0158] Aluminum is an optional alloying element that increases the Ac3 temperature, promotes ferrite formation, and can facilitate precipitation hardening. In microalloyed steels, the addition of aluminum as an alloying element is not strictly necessary. However, aluminum is commonly used as a deoxidizing agent for the steel and is therefore present in smaller quantities. Aluminum can lead to the formation of aluminum nitrides, which can impede grain boundary movement and thus result in grain refinement. An aluminum content of 0.03 to 0.2 at% is advantageous.

[0159] It is also advantageous if the tensile strength R m between 390 MPa and 950 MPa.

[0160] In an exemplary embodiment, the tensile strength R can be determined for an Nb and / or V-alloyed steel. m MPa can be calculated using the following formula:

[0161] R m = 329 + 196 x [at%]C 2 — 22.0 x [at%]C + 99.3

[0162]

[0163] x + 26.0 x [at%]Mn + 243 x [at%]P - 104 x [at%]S + 18.6 x [at%]Al + 109 x [at%]Cr + 44.7 x [at%]Ni + 164 xInternational patent application

[0164] Voestalpine Stahl GmbH

[0165] 250043WO

[0166] [at%]Mo + 63.3 x [at%]Cu + 1015 x [at%]V - 1530 x [at%]Ti - 82770 x [at%]Nb 2 + 7840 x [at%]Nb + 1310 x [at%]N - 50450 x [at%]N x [at%]Nb,

[0167] 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.

[0168] The slopes (i.e., the influence of the elements on the tensile strength Rm) result from practical tests, for example laboratory tests, as well as from the statistical evaluation of process and test data from series production.

[0169] In the case of differing alloy compositions, for example in Ti-alloyed steels, it may be necessary to adjust the above formula accordingly.

[0170] Furthermore, in an exemplary embodiment, the hot-rolled, low- or micro-alloyed steel has a thickness of 1.5 to 20 mm.

[0171] It should be noted that the detrimental effects of trace elements are particularly critical when combined with one another, and their origin lies in corresponding scrap contamination (during the feed mix used to create the melt). When using melting technologies with increased scrap quantities, the inevitably higher trace element load can therefore lead to greater variations in performance-relevant material properties.

[0172] The invention thus relates to a process for producing hot-rolled, micro-alloyed steels with a target tensile strength Rm, which is set 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 feed materials and whose contents must not exceed a maximum content defined by the target alloy, and alloying elements are elements whichwhich are added in a targeted manner according to target values ​​defined by the target alloy, whereby a distinction is made between influence and international patent application,

[0173] Voestalpine Stahl GmbH

[0174] 250043WO

[0175] A distinction is made between compensation elements, whereby influencing elements and compensation elements are elements that have an influence or effect on the tensile strength R. mhave, wherein the difference of the actual analysis values ​​from threshold values ​​with respect to the influencing elements is recorded, wherein 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 m is recorded, wherein 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 is brought into a target range and the influence of the influencing element is thereby compensated, wherein the influencing elements whose influence on the tensile strength Rm is to be compensated include one, several or all from the group of Cr, Cu, Mo, Ni and wherein one, several or all from the group of C, Mn, Nb, V, Ti, N are chosen as compensation elements.

[0176] An advantageous further development provides that the influencing elements whose influence on the tensile strength Rm is to be compensated include Cr, Cu, Mo and / or Ni.

[0177] An advantageous further training approach involves choosing C, Mn, Nb, V, Ti and / or N as compensatory elements.

[0178] An advantageous further development provides for the use of two components in the control system: a forecasting model and a correction model, whereby the forecasting model determines an influence factor that describes the magnitude of the influence of the deviation of the actual values ​​of the analyses from the threshold values ​​of all influence elements on the tensile strength Rm, and the correction model calculates the compensation element contents required to compensate for the tensile strength Rm, as well as determining a compensation factor that describes 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 Rm.

[0179] An advantageous further development provides that the following formula is used to calculate the tensile strength Rm in MPa for Nb and / or V-alloyed steels:

[0180] R m = 329 + 196 x [at%]C 2 — 22.0 x [at%]C + 99.3

[0181]

[0182] x + 26.0 x [at%]Mn + 243 x [at%]P - 104 x [at%]S + 18.6 x [at%]Al + 109 x [at%]Cr + 44.7 x [at%]Ni + 164 x [at%]Mo + 63.3 x [at%]Cu + 1015 x [at%]V - 1530 x [at%]Ti - 82770 x [at%]Nb 2 + 7840 x [at%]Nb + 1310 x [at%]N - 50450 x [at%]N x [at%]Nb, International patent application

[0183] Voestalpine Stahl GmbH

[0184] 250043WO

[0185] 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.

[0186] An advantageous further training provides that the influence factor FE in MPa for the influencing elements is calculated in the forecasting model using the following formula:

[0187] F E = 109 x A[at%]Cr + 44.7 x A[at%]JVj + 164 x A[at%]Mo + 63.3 x A[at%]Cu,

[0188] where A[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 m, may deviate by ±25% from the specified value.

[0189] An advantageous further development provides that for Nb and / or V-alloyed steels in the correction model, the compensation factor FK in MPa for the compensation elements is calculated using the following formula:

[0190] F K = (392 x [at%]C ziel - 22) x A[at%]C + 26 x [at%]Mn + 1015 x [at%]V + (7840 -165540 x [at%]Nb ziel - 50450 x [at%]N ziel ) x [at%]Nb + (1310 - 50450 x [at%]Nb Ziel ) x A[at%]N,

[0191] where [at%]Yziei is the target value of the compensation element Y and A[at%]Y is the deviation of the compensation element content calculated in the correction model to compensate the tensile strength R from the target value of the compensation element Y, and where the slope determined for the respective compensation element Y, which represents its influence on the tensile strength Rm, may deviate by ±25% from the specified value.

[0192] An advantageous further development provides that for Ti-alloyed steels in the correction model, the compensation factor Fic / n-ieg in MPa for the compensation elements is calculated using the following formula:

[0193] F Ki Ti-ieg = 26.0 x A[at%]Mn + 619 x A[at%]Ti,

[0194] where A[at%]Y is the deviation of the compensation element content calculated in the correction model to compensate for the tensile strength Rm from the target value of the compensation element Y, and where the slope determined for the respective compensation element Y, which represents its influence on the tensile strength Rm, may deviate by ±25% from the specified value. International patent application

[0195] Voestalpine Stahl GmbH

[0196] 250043WO

[0197] An advantageous further training program stipulates that the sum of the influencing factor and the compensation factor AF = |F £ + F K | or AF = |F £ + F KiTi _i eg \ is minimized so that AF does not exceed a maximum value, in particular 20 MPa, preferably 10 MPa, most preferably 5 MPa.

[0198] An advantageous further development provides that the method is independent of geometric product parameters, i.e., dimensionally independent, wherein preferably only the influence of the influencing elements on the tensile strength Rm is relatively compensated by adjusting the compensation elements only to the extent necessary to compensate for the influence of the influencing elements on the tensile strength m, namely a chemically induced deviation.

[0199] 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.

[0200] 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.

[0201] An advantageous further training 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 cost of the respective compensation element.

[0202] 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. International patent application

[0203] Voestalpine Stahl GmbH

[0204] 250043WO

[0205] 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.

[0206] An advantageous further development provides that the hot-rolled, micro-alloyed steels have a thickness of 1.5 to 20 mm and a tensile strength Rm of 390 to 950 MPa.

[0207] An advantageous further development stipulates that the target alloy comprises the following target alloy composition in at%:

[0208] C 0.1-0.55

[0209] Si <1

[0210] Mn 0.2-2.1

[0211] P <0.045

[0212] S <0.035

[0213] AI 0.03-0.2

[0214] Ti <0.26

[0215] Nb <0.055

[0216] Cu <0.35

[0217] Cr <0.43

[0218] Mo <0.12

[0219] Ni <0.39

[0220] N <0.08

[0221] V <0.22

[0222] Ti+Nb+V 0.003-0.26

[0223] Residual iron and impurities resulting from the smelting process.

[0224] An advantageous further training program stipulates that the threshold values ​​of the influencing elements in at% are as follows:

[0225] Cu 0.015;

[0226] Ni 0.03;

[0227] Mo 0.005;

[0228] Cr 0.04, International patent application

[0229] Voestalpine Stahl GmbH

[0230] 250043WO

[0231] 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. mThis becomes necessary through adjusted compensation element contents.

[0232] The invention further relates to a control system for the production of hot-rolled, micro-alloyed steels of a desired range of tensile strength m, which is set by a target alloy comprising iron, as well as accompanying elements and alloying elements, and for carrying out the method according to the invention, wherein the control system comprises two components: a prediction model and a correction model, wherein the prediction model is designed to calculate the influence of influencing elements on the tensile strength R, and the correction model is designed to calculate the compensation element contents required to compensate for the tensile strength Rm as well as the influence of the compensation elements on the tensile strength Rm.

[0233] The invention is illustrated by way of example with a drawing. The drawing shows:

[0234] Figure 1 shows a graph which defines the terms threshold, analysis actual value,

[0235] Deviation of the analysis I st value from the threshold value of the influencing element X, A[at%]X, and maximum content with respect to the influencing elements illustrated;

[0236] Figure 2 shows a graph which defines the terms target value, adapted target value,

[0237] Deviation of the compensation element content calculated in the correction model to compensate for the tensile strength Rm (= adapted target value) from the target value of the compensation element Y, A[at%]Y, and maximum content with respect to the compensation elements illustrated;

[0238] Figure 3 shows exemplary data for an S355MC steel melt with low influencing element load and without dynamic alloying;

[0239] Figure 4 shows exemplary data from an S355MC steel melt with increased influencing element load and without dynamic alloying;

[0240] Figure 5 shows exemplary data from an S355MC steel melt with increased influencing element load and dynamic alloying.

[0241] In an exemplary embodiment of dynamic alloying according to the invention, the following steps are carried out: International patent application

[0242] Voestalpine Stahl GmbH

[0243] 250043WO

[0244] 1) Record the actual values ​​of the analysis and compare them with the threshold values. Based on this, a decision must be made as to whether dynamic alloying is necessary. If so, proceed to step 2;

[0245] 2) Calculation of the influence factor FE in the prediction model (measure of the influence of the influencing elements on the tensile strength R) m );

[0246] 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;

[0247] 4) Calculation of the compensation factor FK or FK, n-ieg in the correction model (measure of the influence of the compensation elements on the tensile strength Rm);

[0248] 5) Calculation of the sum AF from the influencing factor and the compensation factor;

[0249] 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;

[0250] 7) Adding the compensation element contents to the adapted target values ​​in order to bring the tensile strength Rm of the final product into a target range.

[0251] After recording the actual values ​​of the analyses, if the levels of the influencing elements exceed their respective thresholds, the influence factor FE in MPa for the influencing elements is first calculated using the forecasting model and the following formula:

[0252] F E = 109 x A[at%]Cr + 44.7 x [at%]Ni + 164 x A[at%]Mo + 63.3 x A[at%]Cu,

[0253] where A[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 Rm, may deviate by ±25% from the specified value.

[0254] Chromium, copper, molybdenum and nickel are influencing elements in this process.

[0255] 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. International patent application

[0256] Voestalpine Stahl GmbH

[0257] 250043WO

[0258] In the correction model, the compensation factor FK in MPa for the compensation elements of Nb- and / or V-alloyed steels is calculated using the following formula:

[0259] F K = (392 x [at%]C ziel - 22) x A[at%]C + 26 x [at%]Mn + 1015 x [at%]V + (7840 -165540 x [at%]Nb ziel - 50450 x [at%]N ziel ) x [at%]Nb + (1310 - 50450 x [at%]Nb Ziel ) x A[at%]N,

[0260] where [at%]Yziei is the target value of the compensation element Y and A[at%]Y is the deviation of the compensation element content calculated in the correction model to compensate for the tensile strength Rm from the target value of the compensation element Y, and where the slope determined for the respective compensation element Y, which represents its influence on the tensile strength R m The actual value may deviate by ±25% from the stated value.

[0261] For Ti-alloyed steels, the following formula is used to calculate the compensation factor FK, -ieg in MPa:

[0262] F Ki Ti-ieg = 26.0 x A[at%]Mn + 619 x A[at%]Ti,

[0263] where A[at%]Y is the deviation of the compensation element content calculated in the correction model to compensate for the tensile strength Rm from the target value of the compensation element Y, and where the slope determined for the respective compensation element Y, which represents its influence on the tensile strength Rm, may deviate by ±25% from the specified value.

[0264] Carbon, manganese, niobium, titanium, vanadium and nitrogen are among the compensating elements.

[0265] The sum of the influence factor FE and the compensation factor FK is determined as follows:

[0266] AF = \F E + F K \ or AF = \F E + F KiTi -i eg \.

[0267] AF should be minimized so that AF does not exceed a maximum value, in particular 20 MPa, preferably 10 MPa, most preferably 5 MPa.

[0268] 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. International patent application

[0269] Voestalpine Stahl GmbH

[0270] 250043WO

[0271] Figures 1 and 2 illustrate the concepts: 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 compensation element Y, A[at%]Y, and maximum content with respect to the compensation elements (Figure 2).

[0272] A[at%]X is calculated as the difference between the actual value of the analysis and the threshold value, i.e., A[at%]X = actual value of the analysis - threshold value. Accordingly, A[at%]X always has a positive sign if the threshold value is exceeded. A[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., A[at%]Y = adapted target value - target value. Accordingly, A[at%]Y typically has a negative sign.

[0273] 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.

[0274] Threshold values ​​of the influencing elements in at% are:

[0275] Cu 0.015;

[0276] Cr 0.04;

[0277] Mo 0.005;

[0278] Ni 0.03.

[0279] If the actual values ​​or actual content of the analyses exceed their respective threshold values, this must be compensated for by adjusting the levels of the compensating elements, i.e., dynamic alloying must take place.

[0280] The concept of dynamic alloying according to the invention will be illustrated below using three examples. International patent application

[0281] Voestalpine Stahl GmbH

[0282] 250043WO

[0283] The first example (Figure 3) concerns steel production via the blast furnace / LD route. Here, the concentrations of the influencing elements iA introduced by scrap are low (e.g., Cr < 0.04 wt.%, Ni < 0.03 wt.%, Cu < 0.02 wt.%, Mo < 0.01 wt.%). These elements therefore do not make a significant contribution to the tensile strength R. mTherefore, it is expedient to specify fixed target values ​​for the alloying element contents, regardless of the fluctuating levels of the influencing elements, which remain at a low level. Figure 3 shows data for an Nb microalloyed structural steel S355MC. Based on the actual values ​​obtained through analysis, the threshold values ​​of the influencing elements are not exceeded. Thus, no intervention through dynamic alloying is warranted, i.e., no changes to the target values ​​for the compensating elements are necessary. The calculated tensile strength of 493.2 MPa lies in the middle of the standard-compliant target range of 430 to 550 MPa for this steel grade. The analysis, which is carried out immediately before casting, largely corresponds to the target values. The measured tensile strength of the final product is 512 MPa.

[0284] In the second example (Figure 4), higher concentrations of influencing elements are introduced into the melt through the input materials, such as scrap metal. These cannot be removed—at least not the elements Cr, Ni, Mo, and Cu. Figure 4 shows data from an S355MC steel melt with increased concentrations of Cr, Ni, Mo, and Cu compared to the first example. Based on the actual analytical values, the sum of the influencing factor and the compensation factor AF is 15.2 MPa. This is significantly higher than a defined maximum value of, for example, 5 MPa. Nevertheless, in this case as well, the alloying elements are adjusted in secondary metallurgy without dynamic alloying, i.e., without considering the high concentrations of influencing elements. The calculated tensile strength Rm of the final product is 513.9 MPa, approximately 20 MPa higher than that in Example 1. The measured tensile strength of the final product is even higher, at 527 MPa.Therefore, due to the increased levels of influencing elements, there is a risk of missing the permissible Rm interval or the target range.

[0285] 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.

[0286] In the third example (Figure 5), dynamic alloying is carried out to account for the increased influencing element contents and to reliably control the tensile strength Rm. This is possible with regard to the elements Cr, Ni, Mo, and Cu because their contents are known before the final adjustment of the alloying elements in the secondary metallurgy. Figure 5 shows the International Patent Application.

[0287] Voestalpine Stahl GmbH

[0288] 250043WO

[0289] Data from an S355MC steel melt with increased levels of influencing elements (Cr, Ni, Mo, and Cu) compared to the first example are shown. Within the framework of dynamic alloying, the effect of the increased influencing element levels is largely compensated for by adjusting the compensating elements (C, Mn, and Nb). This results in a sum of 3.8 MPa for the influencing factor and the compensation factor (AF). This is below a defined maximum value of, for example, 5 MPa, indicating a suitable correction. The calculated tensile strength is now 496.8 MPa. The measured tensile strength of the final product is 510 MPa and is thus almost identical to the tensile strength obtained via the blast furnace / LD route with a very low influencing element load. This demonstrates the exceptional effectiveness of the process according to the invention.

[0290] 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.

[0291] 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 and at the end of the rolling process, the hot-rolled strip is rolled to the desired thickness. The resulting strip is then cooled in water, air, and / or in a furnace at a defined cooling rate. One or more tensile specimens are taken from the hot-rolled samples, and their mechanical properties, such as yield strength, tensile strength, and elongation at break, can be determined on conventional tensile testing machines.

[0292] The data obtained in the experiment serve as the basis for developing a model to predict the tensile strength m as a function of the alloying elements, accompanying and trace elements, and the manufacturing process of the sheets. The predictive model is thus based on sound material science principles, particularly those from the fields of physics and metallurgy.

[0293] 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 single element is then calculated from the resulting delta. International patent application

[0294] Voestalpine Stahl GmbH

[0295] 250043WO

[0296] 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.

[0297] 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.

[0298] 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.

[0299] 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.

[0300] 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

International patent application Voestalpine Stahl GmbH 250043WO Claims 1. Method for producing hot-rolled, micro-alloyed steels with a target tensile strength R range m, which is set 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 the addition of 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 which 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 compensation elements are elements that have an influence or effect on the tensile strength Rm, 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 Rm 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 Rm is brought into a target range and the influence of the influencing element is thereby compensated, whereby the influencing elements whose influence on the tensile strength Rm is to be compensated comprise one, several or all from the group of Cr, Cu, Mo, Ni and wherein International patent application Voestalpine Stahl GmbH 250043WO One, several or all of the elements from the group of C, Mn, Nb, V, Ti, N 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 determines an influencing factor which determines the magnitude of the influence of the deviation of the actual values ​​of the analysis from the threshold values ​​of all influencing elements on the tensile strength R m describes, and with the correction model for compensating the tensile strength m, the required compensation element contents are calculated, and a compensation factor is determined, which describes the magnitude of an influence of a deviation of the calculated compensation element contents from the target values ​​of all compensation elements on the tensile strength Rm.

3. Method according to claim 1 or 2, characterized in that the following formula is used for calculating the tensile strength Rm in MPa for Nb and / or V-alloyed steels: R m = 329 + 196 x [at%]C 2 — 22.0 x [at%]C + 99.3 x + 26.0 x [at%]Mn + 243 x [at%]P - 104 x [at%]S + 18.6 x [at%]Al + 109 x [at%]Cr + 44.7 x [at%]Ni + 164 x [at%]Mo + 63.3 x [at%]Cu + 1015 x [at%]V - 1530 x [at%]Ti - 82770 x [at%]Nb 2 + 7840 x [at%]Nb + 1310 x [at%]N - 50450 x [at%]N x [at%]Nb, where [at%]i is the content of the respective element i and where the slope determined for the respective element i, which represents its influence on the tensile strength Rm, may deviate by ±25% from the specified value.

4. Method according to one of the preceding claims, characterized in that the influence factor FE in MPa for the influence elements is calculated in the forecasting model using the following formula: F E = 109 x A[at%]Cr + 44.7 x A[at%]JVj + 164 x A[at%]Mo + 63.3 x A[at%]Cu, where A[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 Rm, may deviate by ±25% from the specified value. International patent application Voestalpine Stahl GmbH 250043WO 5. Method according to one of the preceding claims, characterized in that for Nb- and / or V-alloyed steels in the correction model the compensation factor FK in MPa for the compensation elements is calculated using the following formula: F K = (392 x [at%]C ziei— 22) x A[at%]C + 26 x A[at%]Mn + 1015 x A[at%]V + (7840 - 165540 x [at%]Nb ziel - 50450 x [at%]N ziel ) x [at%]Nb + (1310 - 50450 x [at%]Nb Ziel ) x [at%]N, where [at%]Yziei is the target value of the compensation element Y and A[at%]Y is the deviation of the tensile strength R in the correction model. m calculated compensation element content from the target value of the compensation element Y, and where the slope determined for the respective compensation element Y, which reflects its influence on the tensile strength m, may deviate by ±25% from the specified value.

6. Method according to one of the preceding claims, characterized in that for Ti-alloyed steels in the correction model the compensation factor Ficm-ieg in MPa for the compensation elements is calculated using the following formula: F Ki Ti-ieg = 26.0 x A[at%]Mn + 619 x A[at%]Ti, where A[at%]Y is the deviation of the compensation element content calculated in the correction model to compensate for the tensile strength Rm from the target value of the compensation element Y, and where the slope determined for the respective compensation element Y, which represents its influence on the tensile strength Rm, may deviate by ±25% from the specified value.

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

8. A method according to any 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. International patent application Voestalpine Stahl GmbH 250043WO 9. 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 compensation element, selection of further compensation elements, cost of the respective compensation element.

10. 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.

11. 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.

12. Method according to one of the preceding claims, characterized in that the hot-rolled, micro-alloyed steels have a thickness of 1.5 to 20 mm and a tensile strength R m exhibit values ​​from 390 to 950 MPa.

13. Method according to one of the preceding claims, characterized in that the target alloy comprises the following target alloy composition in at%: C 0.1-0.55 Si <1 Mn 0.2-2.1 P <0.045 S <0.035 AI 0.03-0.2 Ti <0.26 Nb <0.055 International patent application Voestalpine Stahl GmbH 250043WO Cu <0.35 Cr <0.43 Mo <0.12 Ni <0.39 N <0.08 V <0.22 Ti+Nb+V 0.003-0.26 Residual iron and impurities resulting from the smelting process.

14. Method according to one of the preceding claims, characterized in that the threshold values ​​of the influencing elements in at% are as follows: Cu 0.015; Ni 0.03; Mo 0.005; Cr 0.04, 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.

15. Control system for the production of hot-rolled, micro-alloyed steels of a desired range of tensile strength m, which is set 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 calculate the influence of influencing elements on the tensile strength Rm, and the correction model is designed to calculate the compensation element contents required to compensate for the tensile strength Rm as well as the influence of the compensation elements on the tensile strength Rm.

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