Method and control system for producing heavy plate

Abstract

The invention relates to a method for producing flat steel products, in particular heavy plate having in particular mechanical properties, which are set by a target alloy comprising iron, and accompanying elements and alloying elements, wherein an arc furnace and / or LD converter is loaded by adding at least steel scrap and the content of the arc furnace and / or of the LD converter is melted, wherein at least one sample is taken from the melt of the last primary metallurgical unit of the production route and contents of the accompanying and alloying elements are determined, wherein actual 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 the contents of which must not exceed a threshold value defined by the target alloy, and alloying elements are elements which are added in a targeted manner in accordance with the target alloy, wherein a distinction is made between the influencing elements and compensating elements, wherein influencing elements are elements which have an influence or an effect on one or more mechanical properties, and compensating elements are elements which compensate for the influence or the effect of the influencing element on at least one mechanical property of the end product, wherein the difference between the actual values from threshold values of the target alloy is detected with respect to those influencing elements which have an influence on at least this one mechanical property, wherein the magnitude of the influence of the deviation of the actual values from the threshold values of all influencing elements on the at least one mechanical property is detected, wherein at least one compensating element is determined for the respective mechanical property, which compensating element compensates in a targeted manner for the effect of the influencing element on the mechanical property, and wherein one or more compensating elements are alloyed into the melt at an amount which brings the corresponding mechanical property to the target value and compensates for the influence of the influencing element, and wherein two components are used in the control system for this purpose: a forecast model and a correction algorithm, wherein the influence of the influencing elements on mechanical properties of the end product is calculated using the forecast model and target contents of the compensating elements are calculated using the correction algorithm. The invention also relates to a control system for carrying out the method according to the invention.

Description

[0001] European patent application

[0002] Voestalpine Grobblech GmbH

[0003] P380702WO

[0004] Process and control system for the production of heavy plate

[0005] The invention relates to a method for producing heavy plates. Furthermore, the invention relates to a control system for producing heavy plates.

[0006] Conventionally, hot-rolled flat steel products, such as heavy steel plates, are manufactured from steel. For the primary metallurgical production of steel, iron is first extracted 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 (e.g., with oxygen) or in an electric arc furnace (using scrap as raw material).

[0007] The raw steel is then further processed in secondary metallurgy to improve its composition and purity. This involves treating the steel in special ladle furnaces 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 during smelting in converters.

[0009] Although the blast furnace itself does not use scrap, the pig iron produced in the blast furnace can subsequently be 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 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 generates fewer CO2 emissions than the blast furnace process. European patent application

[0011] Voestalpine Grobblech GmbH

[0012] P380702WO

[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 when using scrap metal is its fluctuating quality. The scrap used in EAF is often inhomogeneous and can contain impurities that negatively affect the steel's quality. For example, unwanted elements such as copper (Cu), tin (Sn), antimony (Sb), and arsenic (As) may be present in the scrap, which are difficult to remove from the steel 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 possible levels of elements such as Cu, Sn, and As using the EAF process. These levels are required for certain specialized applications (e.g., in the linepipe and offshore industries, the chemical industry, and equipment and machinery manufacturing). In such cases, the use of primary materials or very high-quality, sorted scrap is necessary, which increases costs. The lowest possible levels are defined as values ​​< 0.005 wt.%. European patent application

[0019] Voestalpine Grobblech GmbH

[0020] P380702WO

[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 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).

[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 maximum concentrations 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. European patent application

[0028] Voestalpine Grobblech GmbH

[0029] P380702WO

[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 application 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. European patent application

[0036] Voestalpine Grobblech GmbH

[0037] P380702WO

[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] From EP 1 310 573 Bl, a process for producing steel or stainless steel using the AOD process is known. This process aims to implement predictive control: First, current actual values ​​of process variables, such as temperature and / or chemical composition of the melt, are measured. Based on this data, a process model then simulates the values ​​of the corresponding process variables at a later time. If the predicted value deviates from a target value, the process model calculates necessary corrective measures, for example, the addition of cooling scrap if a predicted excessively high temperature is expected. This cycle of measurement, simulation, and correction can then be repeated to optimize the process control.

[0040] The object of the invention is to provide a method for the production of heavy plates which ensures constant product properties even with larger fluctuations in the accompanying elements.

[0041] The problem is solved by the method with the features of claim 1.

[0042] Advantageous further training options are indicated in the sub-requirements.

[0043] Furthermore, the object of the invention is to provide a control system for the production of heavy plates, with which it is possible to ensure constant product properties even with larger fluctuations in the accompanying elements.

[0044] The problem is solved with the system having the features of claim 16.

[0045] This involves the concept of dynamic alloying. The minimum and maximum concentrations of 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 algorithm proposes a response in the form of adapted minimum and maximum concentrations, or adapted target concentrations, of the elements to be alloyed.

[0046] Elemental content is given below in weight percent (abbreviated wt.% or m%). European patent application

[0047] Voestalpine Grobblech GmbH

[0048] P380702WO

[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 must be adhered to.

[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 (> 0 wt.%) and a maximum content are specified for the alloying elements. European patent application

[0057] Voestalpine Grobblech GmbH

[0058] P380702WO

[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, since 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 classic manufacturing process, the starting point is a product (steel) that, according to market requirements, exhibits specific material properties, particularly mechanical and / or chemical characteristics. It is then chemically / metallurgically adjusted to meet these requirements. Such a product is therefore an alloy, where the alloying elements are defined by a minimum content (> 0 wt%) and a 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] Therefore, this must be taken into account when adding alloys. The following scenarios can occur:

[0065] A) For example, the proportion of chromium introduced by the scrap metal is below the desired level. In this case, less chromium needs to be added.

[0066] B) The chromium content introduced via scrap metal is already within the target range. No further alloying is necessary.

[0067] C) More chromium than desired is introduced. The chromium content cannot be reduced chemically or metallurgically. Therefore, the effect of the chromium must be compensated for. European patent application

[0068] Voestalpine Grobblech GmbH

[0069] P380702WO

[0070] The above example becomes more complex when several trace elements, accompanying elements, or former alloying elements interact to produce specific properties.

[0071] The invention addresses this by selecting alloying elements that can compensate for the influence of the influencing element 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).

[0072] Influencing elements are trace elements, accompanying elements and / or former alloying elements that are introduced from raw materials and whose content in the target alloy should not exceed a defined threshold.

[0073] 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 minimum content 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.

[0074] 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.

[0075] In certain borderline cases, it may even become necessary to adjust (upwards) the maximum levels of certain alloying elements defined by the target alloy if an amount exceeding the maximum level has to be added to compensate.

[0076] A simple example will illustrate this. In addition to iron, a desired steel alloy contains elements A, B, and C as alloying elements. A is present in an amount exceeding the maximum permitted level due to the raw materials. If element C has a comparable effect on a desired property as A, but is present in the alloy in small quantities or not at all, only such a small amount is added as required. (European patent application)

[0077] Voestalpine Grobblech GmbH

[0078] P380702WO

[0079] that the combined effect of A and C results in the desired property's target value. In this case, that means less C is added than would normally be added to compensate for the excessively high A content.

[0080] Another example is that if element A is present in an amount that exceeds the maximum content, and C is an element that reduces the influence of A on a defined size of a property, C is added in an amount that, in addition to its own effect, also compensates for the effect of A.

[0081] 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.

[0082] In this case, B is, for example, an element that has no influence on the defined target parameter, such as strength.

[0083] Overall, this approach allows for a rougher pre-selection of scrap metal.

[0084] Preferably, no compensating elements are used in the production of heavy plates that significantly alter their effect on the final product through subsequent treatment steps, and in particular thermal treatment steps carried out after continuous casting (i.e., on the heavy plate), such as annealing or tempering processes or thermomechanical processes, for example, increasing the hardness. Otherwise, the properties of the final product would be unpredictable.

[0085] On the other hand, the result, i.e. the intermediate product or pre-material (the slab after continuous casting), is also more versatile in its applications, since the subsequent treatment steps mentioned above do not have to be taken into account as a condition for the guaranteed property.

[0086] Input parameters for the forecasting model are influencing and compensating elements whose concentrations in the liquid phase are no longer changed, such as Cu, Ni, Mo, Cr, Sn.

[0087] The input parameters of the correction algorithm are adapted minimum and maximum concentrations (adapted target concentrations) of elements alloyed in the liquid phase. These are the so-called compensation elements, such as Si, Mn, Cr, and Ni. European patent application

[0088] Voestalpine Grobblech GmbH

[0089] P380702WO

[0090] Compensation elements are therefore elements that are added in the liquid phase to balance the influence of the influencing elements, so that the target properties of the target alloy (defined by the desired steel grade) are achieved.

[0091] As mentioned above, some elements, such as chromium and nickel, can act as compensating elements even if they are not alloying elements in the target alloy. Since these elements used as compensating elements can also exert a (further) influence in the target alloy, they are also considered influencing elements in this respect, whose influence may, in turn, need to be compensated for by another compensating element.

[0092] The predictive model calculates a deviation from the target value of the respective mechanical property. Input parameters for this are the deviations in the levels of the influencing and compensating elements.

[0093] A simple implementation of the correction algorithm uses the forecasting model with the actual (based on sample analyses) deviations in the levels of the influencing elements as well as variations in deviations in the levels of the compensation elements as input variables.

[0094] The possible deviations of the compensating elements are determined based on the interval within which the corresponding alloying element is allowed to vary due to manufacturing processes. This interval is extended downwards and subdivided into ranges of 5-25% of the manufacturing-related interval.

[0095] Example: If the manufacturing-related interval of a compensating element is, for example, 0.7–0.9 wt.% with a target content of 0.8 wt.%, the interval is extended to 0.5–0.9 wt.% and subdivided into 25% increments. Another extension to multiples of the interval width is also conceivable. Possible values ​​for the 0.5–0.9 wt.% interval would then be 0.5 wt.%, 0.55 wt.%, 0.6 wt.%, 0.65 wt.%, 0.7 wt.%, 0.75 wt.%, and 0.8 wt.%. This results in the following compensating element deviations: 0.3 wt.%, 0.25 wt.%, 0.2 wt.%, 0.15 wt.%, 0.1 wt.%, 0.05 wt.%, and 0 wt.% for the specific compensating element.

[0096] This is performed for all compensation elements. Using the predictive model, the correction algorithm calculates the property deviation for all possible combinations of compensation element deviations for all European patent applications under consideration.

[0097] Voestalpine Grobblech GmbH

[0098] P380702WO

[0099] Properties. For each combination, the weighted residual is calculated, and the combination with the lowest residual is selected. Further restrictions may apply, such as only allowing positive deviations for strength properties.

[0100] 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.

[0101] The present process, which uses scrap metal, relates to the production of hot-rolled heavy plates.

[0102] Heavy plate is a flat steel product with a thickness of more than 3 mm, produced by hot rolling. It is characterized by the fact that it is not wound into coils and is processed as a sheet. Furthermore, it is distinguished by its greater thickness and a coarser surface compared to thin plates. Heavy plates are typically produced in widths of up to 5 m and lengths of up to 20 m, with thicknesses of up to 350 mm, and in particular up to 200 mm.

[0103] Hot-rolled steel flat products, especially heavy plates, can be further processed after production, e.g. by cutting, bending or welding, to manufacture specific components and structures.

[0104] The concept is based on producing semi-finished materials (e.g., slabs) of a specific steel grade in which the strength properties (yield strength and tensile strength), as well as other parameters such as the carbon equivalent (CAE), remain unchanged or change only minimally despite increased trace element content introduced by the scrap in the electric arc furnace. In particular, the changes are compared to the strength properties and other parameters that occur when smaller scrap proportions are used in the melt production process, resulting in lower levels of undesirable trace elements (e.g., in the LD process).

[0105] This is achieved by adapting one or more alloying elements and is subsequently referred to as dynamic alloying. The adaptation is carried out by applying a predictive model for mechanical properties combined with a correction algorithm. European patent application

[0106] Voestalpine Grobblech GmbH

[0107] P380702WO

[0108] The approach of producing the pre-material with properties that are as constant as possible is valid as long as the influence of those alloying elements that play a role in the concept of dynamic alloying does not have a significantly different effect through the subsequent manufacturing process (rolling, rapid cooling, heat treatment) than they do during the manufacturing process of the pre-material (continuous casting and slow cooling).

[0109] However, if the effect of one of the elements, or the effect of an element's deviation from the target content considered in dynamic alloying, depends significantly on the subsequent manufacturing process, the present approach has limited applicability. Instead, the effect of this element must be considered based on the subsequent process. A typical example is carbon content. The influence of carbon content is highly dependent on the cooling rate and sheet thickness. Therefore, carbon content is not directly considered in the present model. With vacuum degassing, for example, using an RH system (Ruhrstahl-Heraeus system) as a component in secondary metallurgy, it is possible to control the carbon content in the alloy very reliably.

[0110] This also applies to other elements, especially Nb, V, and Ti, whose effect on the material properties depends on the subsequent treatment. The microalloying elements Nb, V, and Ti have a particularly significant impact following thermomechanical rolling.

[0111] 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.

[0112] Starting with a target alloy composition and based on threshold values ​​for undesirable influencing elements that should not be exceeded, the changes in mechanical properties, and in particular the strength values ​​(yield strength and tensile strength), as well as, if necessary, the change in carbon equivalent (CAE) caused by these influencing elements, are calculated. Based on these results, which are obtained by a model for calculating the change in mechanical properties when the chemical composition changes, the necessary reduction or adaptation of one or more alloying elements is calculated using a correction algorithm. The correction algorithm can also apply further restrictions (e.g., limiting the change in chemical composition). European patent application

[0113] Voestalpine Grobblech GmbH

[0114] P380702WO

[0115] due to limitations in toughness requirements) or specific customer requirements.

[0116] The target values ​​for the mechanical properties apply to the slab as a precursor material for the heavy plate.

[0117] Accordingly, the dynamic alloying process comprises two components. The first component is a predictive model, and the second component is a correction algorithm.

[0118] From the predictive model for mechanical properties, e.g., for strength, the part that represents the change in mechanical properties, such as changes in strength (yield strength change AR), is extracted. P o.2 and tensile strength change AR m ) calculated for all influencing or compensating elements. The following equation is used:

[0119] AR = ax AEi + bx AE2+ ••• + n* x A£„,

[0120] where

[0121] AR is a deviation from the target value of the desired mechanical property, where

[0122] a, b to n* factors are which correspond to the effects of the individual elements on at least one mechanical property, are largely independent of any subsequent thermal or thermomechanical post-treatment and are determined using the predictive model and through experiments and material science equations, and wherein

[0123] AE1, AE2 to AE n on the one hand, the individual deviations in wt.% from the respective target content of the corresponding alloying element or from the threshold value of the corresponding influencing element and on the other hand, possible correction steps of the compensation elements.

[0124] Additionally, the carbon equivalent can be taken into account, whereby the change in the carbon equivalent in an advantageous embodiment is calculated according to the following formula:

[0125] A

[0126]

[0127] CAE = AC + — + — + 5AB

[0128] 30 20 20 60 20 15 10 European patent application

[0129] Voestalpine Grobblech GmbH

[0130] P380702WO

[0131] where

[0132] Ai is the deviation of the respective element i from its target content in wt.%.

[0133] In other exemplary embodiments, the carbon equivalent can alternatively be calculated using the following formulas:

[0134] CET (Carbon Equivalent Thyssen) = C+ Mn+Mo + Cr+Cu DLL unc |

[0135]

[0136] K J ' 10 20 40

[0137] ... , , , , , , “ , Si , Mn+Cu+Cr , Ni , Mo , V , “

[0138] PCM (Critical Metal Parameter) = CH - 1 - 1 - 1 - 1 - 1- 5 x ß,

[0139] 30 20 60 15 10 '

[0140] where the concentrations of the respective elements are to be entered in wt.%.

[0141] The influence of the individual elements is as follows.

[0142] Copper has a work-hardening and hardening effect in heavy plates, but simultaneously reduces hot formability and elongation at break. Copper enrichment can also be observed on the surface. Copper can increase the strength of steel through precipitation at concentrations > 0.8 wt.% Cu. Accordingly, 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 and thus significantly impair hot formability. This subsequently leads to cracks in the final product. Therefore, it is advantageous to select a copper content of 0.0001–0.50 wt.%, preferably 0.01–0.50 wt.%, particularly preferably 0.02–0.40 wt.%, and even more preferably 0.03–0.30 wt.%.

[0143] Nickel increases the toughness of steel and enhances its hardness and strength. Furthermore, nickel increases the solubility of copper in heavy plates. Therefore, a nickel content of 0.0001–10.0 wt.%, preferably 0.001–3.0 wt.%, more preferably 0.01–3.0 wt.%, and particularly preferably 0.01–1.0 wt.% is advantageous.

[0144] Even small amounts of molybdenum significantly increase the hardenability of steel. However, excessive fluctuations in analysis lead to increasing instability of the microstructure. Besides the formation of fracture-inducing martensite phases in the segregation zone, undesirable foreign microstructure constituents can develop, potentially resulting in accelerated surface fatigue. Furthermore, the weldability of the steel decreases with increasing molybdenum content. The influence of molybdenum on the transformation behavior also increases the risk associated with larger fluctuations in analysis.

[0145] Voestalpine Grobblech GmbH

[0146] P380702WO

[0147] Process uncertainty exists in the heat treatment plant downstream of the rolling process, as the accelerated cooling can lead to the formation of undesirable mixed phases in the heavy plate. Corresponding operational experience clearly shows that exceeding critical values ​​increasingly results in mixed phase content. Therefore, it is advantageous to select a molybdenum content of 0.0001–1.0 wt.%, preferably 0.01–1.0 wt.%, more preferably 0.02–1.0 wt.%, and particularly preferably 0.03–1.0 wt.%.

[0148] Tin has a work-hardening and hardening effect. At the same time, it reduces elongation at break and tends to segregate more readily, thus affecting microstructure stability. Furthermore, tin is surface-active and impairs hot formability. Therefore, it is advantageous to select a tin content of 0.0001–0.20 wt.%, preferably 0.01–0.20 wt.%, more preferably 0.02–0.18 wt.%, particularly preferably 0.03–0.16 wt.%, and even more preferably 0.04–0.15 wt.%.

[0149] Silicon acts as a solid solution hardener and increases strength. Therefore, it is advantageous to select a silicon content of 0.0001–1.0 wt.%, preferably 0.01–1.0 wt.%, preferably 0.02–0.90 wt.%, particularly preferably 0.03–0.80 wt.%, and more preferably 0.04–0.60 wt.%.

[0150] Manganese binds sulfur to form manganese sulfides. Manganese increases hardenability, thus lowering the critical cooling rate. This allows for higher hardness values ​​to be achieved at lower cooling rates. Manganese also tends to segregate more readily. Therefore, it is advantageous to select a manganese content of 0.0001–3.0 wt.%, preferably 0.01–3.0 wt.%, more preferably 0.02–2.0 wt.%, particularly preferably 0.03–2.0 wt.%, and even more preferably 0.04–1.7 wt.%.

[0151] Chromium increases hardenability, thus lowering the critical cooling rate. The hardening effect of chromium is significantly stronger than that of manganese. Furthermore, chromium has a negative impact on weldability. The formation of chromium carbides is also possible. Therefore, it is advantageous to select a chromium content of 0.0001–2.6 wt.%, preferably 0.01–2.6 wt.%, more preferably 0.02–2.0 wt.%, particularly preferably 0.03–2.0 wt.%, and even more preferably 0.04–2.0 wt.%.

[0152] Vanadium generally has a grain-refining and strength-enhancing effect. Limitations are primarily economic in nature, based on the volatility of the ferrovanadium used. Therefore, a vanadium content of 0.0001–0.5 wt.% is advantageous. European patent application

[0153] Voestalpine Grobblech GmbH

[0154] P380702WO

[0155] It is advantageous if Nb + V + Ti are present in the alloy in a content of 0.0001-0.45 wt.%, preferably 0.01-0.45 wt.%, preferably 0.02-0.40 wt.%, particularly preferably 0.03-0.40 wt.%, and further particularly preferably 0.04-0.40 wt.%.

[0156] Tungsten is a very strong carbide former, narrowing the austenite region (ferrite former). It increases high-temperature strength, tempering resistance, and wear resistance at high temperatures up to red heat. Therefore, it is advantageous to select a tungsten content of 0.0001–0.20 wt.%, preferably 0.01–0.19 wt.%, more preferably 0.02–0.18 wt.%, particularly preferably 0.03–0.17 wt.%, and even more preferably 0.04–0.16 wt.%.

[0157] Nitrogen contributes to the improvement of mechanical and other properties by precipitating as fine nitrides (for example, titanium nitride (TiN) or aluminum nitrides (AlN)) and by preventing excessive coarsening of the austenite grain during the heat treatment of the steel. Therefore, a nitrogen content of 0.0001–0.020 wt.%, preferably 0.001–0.02 wt.%, is advantageous.

[0158] 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 levels of phosphorus and sulfur must be kept very low (0.0001–0.02 wt%).

[0159] It is advantageous if the yield strength R P o.2 between 250 MPa and 1450 MPa, in particular between 350 MPa and 1200 MPa, preferably between 450 MPa and 1100 MPa.

[0160] It is further advantageous if the tensile strength Rm is between 300 MPa and 1500 MPa, in particular between 400 MPa and 1300 MPa, preferably between 500 MPa and 1200 MPa.

[0161] 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

[0162] Voestalpine Grobblech GmbH

[0163] P380702WO

[0164] The actual values ​​of the accompanying and alloying elements can be continuously determined by analysis, initially in the last primary metallurgical unit, the converter, the electric arc furnace, the ladle, or at intermediate stages. The initial state can be analyzed before any alloying step. Based on this analysis, a variable alloy addition, guided by the minimum content of the alloying elements, is calculated and added after tapping. Subsequently, purging gas treatment is performed to homogenize the melt, and a second analysis may be conducted. Dynamic alloying then begins based on the determined values.

[0165] Initially, the actual values ​​are deliberately kept below the target levels of the alloying elements. This is necessary to allow for the further addition of alloying elements.

[0166] The deviations in mechanical properties are calculated using the actual values ​​of the influencing elements. The necessary dynamic correction is determined using the correction algorithm.

[0167] The correction algorithm dynamically calculates target levels of the compensating elements for the desired alloy based on an optimization calculation. Residuals are calculated from the deviations in yield strength, tensile strength, and carbon equivalent. These deviations arise from an unintended exceedance of the threshold values ​​of the influencing elements as well as an intentionally altered chemical composition with respect to the compensating elements.

[0168] The residuals of the individual contributions from yield strength, tensile strength, and carbon equivalent are multiplied by weighting factors and then added together. In discrete steps, all residuals of all possible combinations of the compensation elements are calculated. For dynamic alloying, the composition of compensation elements that yields the smallest residual is then selected. The algorithm also takes into account restrictions that may be imposed by further product requirements (e.g., toughness properties) or customer requirements.

[0169] In general, the equation used to calculate the residual can be represented as follows:

[0170] Res = Abs[weightR pQ 2 x AR p02 + weightR m x AR m + weightCAE x CAE ,European patent application

[0171] Voestalpine Grobblech GmbH

[0172] P380702WO

[0173] the prerequisite being that AR P o.2 and AR m are positive, so that the contributions to the residual resulting from AR are positive,

[0174] where the consideration of the carbon equivalent is optional,

[0175] Res is the residual that is minimized during the correction algorithm.

[0176] Abs is the absolute value function, which provides the absolute value.

[0177] weightRpo.2 is the weighting of the yield strength,

[0178] ARpo.2 the deviation of the yield strength is,

[0179] weightRm is the weighting of the tensile strength,

[0180] ARm the deviation of the tensile strength is,

[0181] weightCAE is the weighting of the carbon equivalent,

[0182] ACAE is the deviation of the carbon equivalent and

[0183] where weightCAE = 0 if the carbon equivalent is not taken into account.

[0184] The invention thus relates to a process for the production of flat steel products, in particular heavy plates with specific mechanical properties, which are determined 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 the melt of the last primary metallurgical unit of the production route and the contents of the accompanying and alloying elements are determined, wherein actual 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 threshold value defined by the target alloy, and alloying elements are elements whichwhich are added specifically according to the target alloy, whereby a distinction is made between influencing and compensating elements, wherein influencing elements are elements which have an influence or effect on one or more mechanical properties, and compensating elements are elements which reduce the influence or effect of the influencing element on at least one mechanical property. European patent application,

[0185] Voestalpine Grobblech GmbH

[0186] P380702WO

[0187] Compensate for a property of the final product, whereby the difference between the actual values ​​and the threshold values ​​of the target alloy with respect to those influencing elements that have an influence on at least this one mechanical property is recorded, wherein the magnitude of the influence of the deviation of the actual values ​​from the threshold values ​​of all influencing elements on the at least one mechanical property is recorded, wherein at least one compensation element is determined for the respective mechanical property, which specifically compensates for the effect of the influencing element on the mechanical property, and wherein one or more compensation elements are added to the melt in an amount that brings the corresponding mechanical property to the target value and compensates for the influence of the influencing element, and wherein two components are used for this purpose in the control system: a forecasting model and a correction algorithm.where the forecasting model calculates the influence of the influencing elements on the mechanical properties of the final product, and the correction algorithm calculates target values ​​of the compensation elements.

[0188] Sampling and analysis are carried out particularly from the tapping of crude steel, at least in the melt of the last primary metallurgical aggregate of the production route, and after each further addition of elements.

[0189] 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 in the melt exceeds a threshold value defined by the target alloy, and compensating elements are elements which are regular alloying elements of the target alloy or other elements.

[0190] An advantageous further development provides that elements are used as compensation elements whose effect on the mechanical properties, in particular the tensile strength Rm, of the final product is not altered, or not significantly altered (i.e., by no more than ±10%), by a thermal or thermomechanical treatment following the casting process. For example, the change in tensile strength caused by the element in a sample taken from the pre-product (i.e., after the casting process) is compared with the change in tensile strength caused by the element in a sample taken from the final product (i.e., after thermal or thermomechanical treatment). European patent application

[0191] Voestalpine Grobblech GmbH

[0192] P380702WO

[0193] Therefore, the elements manganese (Mn) and silicon (Si) are particularly suitable as compensating elements, as they influence the tensile strength of steel through solid solution strengthening. In theory, this relationship is described by a square root function. However, for certain alloy ranges, for example, in the case of Mn in a range of approximately 1 wt.% to 3 wt.% and in the case of Si in a range of approximately 0.2 wt.% to 0.8 wt.%, these relationships can be approximated by linear functions, allowing the effect of the individual elements to be expressed as slopes: 150 MPa / wt.% for Mn and 25 MPa / wt.% for Si. The strength-enhancing mechanism of solid solution strengthening thus acts in the same way regardless of any thermal or thermomechanical treatment.

[0194] Another important strength-enhancing mechanism is transformation hardening, where the beginning and end of the phase transformation are determined by both the time-temperature forming history and by specific elements. For the time-temperature forming history, the cooling rate at which the rolled material is cooled after the hot rolling process or after heating in a heat treatment furnace is particularly important; the relationships between cooling rate, alloy, and phase transformation are known from time-temperature transformation diagrams. Generally, low cooling rates result in a microstructure with low strength, while high cooling rates result in a microstructure with high strength. Furthermore, the element carbon plays a crucial role here, as it significantly determines the microstructure.The effect of carbon on tensile strength varies considerably depending on the microstructure: For low-strength microstructures (typically ferrite-pearlite), slope values ​​for tensile strength of approximately 1000 MPa / wt% are obtained, while for high-strength microstructures (typically martensite), slope values ​​exceeding 3000 MPa / wt% apply. Consequently, the effect of the carbon content is highly dependent on the thermal or thermomechanical treatment following the casting process. Therefore, carbon would only be suitable as a compensating element if the subsequent thermal or thermomechanical treatment were predetermined. Since this is not the case in practice, carbon is not used as a compensating element.

[0195] Cr, Ni, Mo, Mn, and Si also influence the phase transformation of steel—and thus its tensile strength. However, their effect depends significantly less on the thermal or thermomechanical treatment following the casting process, particularly the cooling rate, than is the case with carbon. Furthermore, these elements are also... (European patent application)

[0196] Voestalpine Grobblech GmbH

[0197] P380702WO

[0198] The variations are so small that no change in the microstructure is to be expected. Therefore, the effect of these alloying elements unfolds to a comparable extent regardless of thermal or thermomechanical treatment, for example, at both low and high cooling rates, making these elements fundamentally suitable as compensating elements.

[0199] For the elements titanium (Ti), nitrocellulose (Nb), and viscoelasticity (V), two different strength-enhancing mechanisms must be considered: precipitation hardening and grain refinement, both of which are significantly influenced by these elements. However, both mechanisms are also determined by thermal or thermomechanical treatments following the casting process, particularly by the time-temperature forming history during thermomechanical rolling and by the heating temperature and cooling rate during any heat treatment. Therefore, the effect of Ti, Nb, and V on the mechanical properties, especially tensile strength, is again highly dependent on the process sequence, meaning these elements cannot be used as compensating elements.

[0200] An advantageous further development provides that certain mechanical properties of the final product, such as the hardness, yield strength, tensile strength, elongation at break, impact strength in the high position, and the toughness transition temperature in Kelvin, do not differ significantly from the corresponding mechanical properties of conventionally manufactured flat steel products, i.e., that after applying the same thermal or thermomechanical treatment, the mean value of a series of flat steel products manufactured according to the invention differs from the mean value of a series of conventionally manufactured sheets by no more than ±5%.

[0201] An advantageous further development provides that if an alloying element of the target alloy is already introduced by a feedstock in a proportion below a desired target content defined by the target alloy, this element is added to the extent necessary to achieve the target content; or if the alloying element of the target alloy is already introduced by a feedstock in a proportion that already corresponds to the target content, nothing is added; or if the alloying element of the target alloy or the influencing element is already introduced by a feedstock in a proportion that exceeds the target content or threshold, it is compensated by a reduced alloying proportion of at least one other second element with similar mechanical properties and / or an increased alloying proportion of at least one opposing third element.European patent application.

[0202] Voestalpine Grobblech GmbH

[0203] P380702WO

[0204] An advantageous further development provides that the influencing elements, whose influence on the mechanical properties of the final product is to be compensated, comprise one, several or all from the group of Cu, Mo, Ni, Cr.

[0205] An advantageous further development provides that the influencing elements, whose influence on the mechanical properties of the final product is to be compensated, include Cu, Mo, Ni and / or Cr.

[0206] An advantageous further development method proposes that one, several or all of the elements from the group Si, Mn, Cr, Mo, Ni be chosen as compensation elements.

[0207] An advantageous further development involves choosing Si, Mn, Cr, Mo and / or Ni as compensation elements.

[0208] An advantageous further development provides that the predictive model is used to calculate mechanical properties with the actual values ​​of the element contents, or mechanical properties with the actual values ​​of the element contents and the carbon equivalent with the actual values ​​of the element contents, whereby a deviation of the respective mechanical property or the carbon equivalent from the target value is determined, whereby the same elements have different effects on different mechanical properties.

[0209] An advantageous further training method stipulates that the following formula is used in the forecasting model:

[0210] AR = ax RL + bx AE2+ — I- n* x AR,,,

[0211] where

[0212] AR is a deviation from the target value of the desired mechanical property, where

[0213] a, b to n* factors are which correspond to the effects of the individual elements on at least one mechanical property, are largely independent of any subsequent thermal or thermomechanical post-treatment and are determined using the predictive model and through experiments and material science equations, and wherein

[0214] AEi, E2 to AE n on the one hand, the individual deviations in wt.% from the respective target content of the corresponding alloying element or from the threshold value of the corresponding European patent application

[0215] Voestalpine Grobblech GmbH

[0216] P380702WO

[0217] Represent the influencing elements and, on the other hand, possible correction steps of the compensation elements.

[0218] An advantageous further development provides that the mechanical properties include the tensile strength Rm and / or the yield strength. Po.2 are, where AR is the yield strength change ARpo.2 and / or the tensile strength change ARm, so that in the prediction model either the yield strength change or the tensile strength change is calculated, or the yield strength change and the tensile strength change are calculated.

[0219] It is advantageous if the tensile strength Rm is between 300 MPa and 1500 MPa and the yield strength R P o.2 lies between 250 MPa and 1450 MPa.

[0220] Other properties that can be used as AR include impact strength, hardness, tendency to hydrogen embrittlement, conductivity and corrosion resistance, so that either one or more of the aforementioned property changes are calculated in the prediction model.

[0221] An advantageous further development provides that the method is independent of geometric product parameters, i.e., dimensionally independent, wherein preferably only the influence on the mechanical property caused by the influencing elements is relatively compensated by adjusting the compensation elements only to the extent necessary to compensate for the influence of the influencing elements on the mechanical property, namely a chemically induced deviation.

[0222] An advantageous further development involves using additional restrictions in the correction algorithm through minimum or maximum element contents in the target alloy composition and / or a desired ratio of individual elements to each other.

[0223] An advantageous further training method stipulates that the following formula is used in the correction algorithm:

[0224] Res = Abs\weightR x R + weightR2x AR2+ weightCAE x ACAE],

[0225] where the consideration of the carbon equivalent is optional,

[0226] Res is the residual that is minimized during the correction algorithm.

[0227] Abs is the absolute value function, which provides the absolute value, European patent application

[0228] Voestalpine Grobblech GmbH

[0229] P380702WO

[0230] weightRi is the weighting of the first mechanical property,

[0231] ARi is the deviation of the first mechanical property,

[0232] weightR2 is the weighting of the second mechanical property,

[0233] AR2 is the deviation of the second mechanical property,

[0234] weightCAE is the weighting of the carbon equivalent,

[0235] ACAE is the deviation of the carbon equivalent and

[0236] where weightCAE = 0 if the carbon equivalent is not taken into account.

[0237] An advantageous further training method stipulates that the following formula is used in the correction algorithm:

[0238] Res = Abs[weightR pQ 2 x AR p02 + weightR m x AR m + weightCAE x CAE ,

[0239] the prerequisite being that AR P o.2 and AR m are positive, so that the contributions to the residual resulting from AR are positive,

[0240] where the consideration of the carbon equivalent is optional,

[0241] Res is the residual that is minimized during the correction algorithm.

[0242] Abs is the absolute value function, which provides the absolute value.

[0243] weightRpo.2 is the weighting of the yield strength,

[0244] ARpo.2 the deviation of the yield strength is,

[0245] weightRm is the weighting of the tensile strength,

[0246] ARm the deviation of the tensile strength is,

[0247] weightCAE is the weighting of the carbon equivalent,

[0248] ACAE is the deviation of the carbon equivalent and

[0249] where weightCAE = 0 if the carbon equivalent is not taken into account. European patent application

[0250] Voestalpine Grobblech GmbH

[0251] P380702WO

[0252] It is important that, when considering strength properties, the correction algorithm only allows solutions for AR that yield positive AR values, so that the contributions to the residual originating from AR are positive.

[0253] A beneficial further training program stipulates that the following formulas are used in the forecasting model:

[0254] AR p02= 120 x AMn + 40 x ACr + 170 x ACu + 200 x AMo + 16 x A57 + 17 x Ni,

[0255] m = 140 x AMn + 50 x ACr + 170 x ACu + 240 x AMo + 25 x A57 + 16 x Ni,

[0256] ACr + AMo +

[0257] ACAE = AC + —+ —+ —+ — + AV + 5AB

[0258]

[0259] 30 20 20 60 20 15 10

[0260] where the slope values ​​can vary by a maximum of ±20% and where

[0261] Ai is the deviation of the respective element i from its target content in wt.%.

[0262] An advantageous further development provides that the variation of the compensation elements in the correction algorithm is carried out in step sizes, wherein the step sizes 5-25%, preferably 10-25%, particularly preferably 20-25% correspond to the interval in which the corresponding alloying element may vary due to manufacturing.

[0263] For example, the step sizes for the corrections can be 0.01 wt.% for Mn and 0.005 wt.% for Cr.

[0264] An advantageous further development provides that the target alloy comprises the following target alloy composition in wt.%:

[0265] C 0.020-0.30

[0266] Si 0.0001-1.0

[0267] Mn 0.0001-3.0

[0268] P 0.0001-0.02

[0269] S 0.0001-0.02

[0270] Cr 0.0001-2.6

[0271] Cu 0.0001-0.50

[0272] Mon 0.0001-1.0

[0273] Ni 0.0001-10.0

[0274] Nb + V + Ti 0.0001-0.45 European patent application

[0275] Voestalpine Grobblech GmbH

[0276] P380702WO

[0277] W 0.0001-0.20

[0278] N 0.0001-0.020

[0279] Sn 0.0001-0.20

[0280] Residual iron and impurities resulting from the smelting process.

[0281] The invention further relates to a control system for the production of heavy plate and for carrying out the method according to the invention, wherein the control system comprises two components: a forecasting model and a correction algorithm, wherein the forecasting model is designed to calculate the effect of influencing elements and compensation elements on the mechanical properties of the heavy plate, and the correction algorithm is designed to calculate target contents of compensation elements.

[0282] The invention is illustrated by way of example with a drawing. The drawing shows:

[0283] Figure 1 shows a calculation for dynamic alloying for an embodiment without relevance of the CAE;

[0284] Figure 2 shows a calculation for dynamic alloying with extended analysis for an embodiment without relevance of the CAE;

[0285] Figure 3 shows an example area for dynamic alloying taking R into account.P o.2 and R m ;

[0286] Figure 4 shows a calculation for dynamic alloying for an embodiment relevant to CAE;

[0287] Figure 5 Slopes for equations 1 and 2.

[0288] In an advantageous embodiment, the changes in strength values ​​can be calculated using the following equations:

[0289] AR p 0.2 = 12° x AMn + 40 x ACr + 170 x ACu + 200 x AMo + 16 x A57 + 17 x ANi (Eq. 1)

[0290] AR m = 140 x AMn + 50 x ACr + 170 x ACu + 240 x AMo + 25 x ASi + 16 x ANi (Eq. 2)

[0291] When the carbon equivalent is taken into account, the following equation can be used to calculate the change in the carbon equivalent: European patent application

[0292] Voestalpine Grobblech GmbH

[0293] P380702WO

[0294] ACAE = AC + —+ —+ —+ —+ —+ — + —+ 5AB (Eq. 3)

[0295] 30 20 20 60 20 15 10

[0296] Ai is the deviation of the respective element i from its target content in wt.%.

[0297] The residue is calculated using equation 4:

[0298] Res = Abs[weightR p02 x AR p02 + weightR m x AR m + weightCAE x ACAE] (Eq. 4)

[0299] If the carbon equivalent (CAE) is not to be taken into account, weightCAE = 0.

[0300] The results of equations 1 and 2 are exemplary calculated changes in the strength of the pre-material (for example, a slab) when the specified influencing and compensating elements are changed.

[0301] Here, the elements Mo and Cu are used as influencing elements and the elements Mn and Cr as compensating elements.

[0302] In one embodiment (Figures 1 and 2), the target values ​​of the correction, i.e., the change in the content of the compensation elements, are calculated only for the yield strength and the tensile strength and without relevance of the CAE.

[0303] The changes in the strength values ​​Rpo.2 and AR™ must always be positive. This is necessary to prevent a decrease in strength values ​​when applying dynamic correction of compensation elements, thus ensuring that the mechanical properties of the heavy plate are reliably achieved.

[0304] In the first embodiment (Figures 1 and 2), the weighting is weightR P o.2 for AR P 0.2 equals 1 (weightR P o.2 = 1) and for ARm the weighting weightRm is equal to 2 (weightRm = 2).

[0305] The weighting is individually selected according to predefined requirements. In the example shown, tensile strength is given a higher weighting. This higher weighting can be derived, for example, from a customer requirement to guarantee the lowest possible variation in the measured tensile strength of a produced sheet metal series.

[0306] Since the CAE value is not taken into account in the calculation, weightCAE = 0.

[0307] In the first embodiment, no restrictions regarding toughness are specified. European patent application

[0308] Voestalpine Grobblech GmbH

[0309] P380702WO

[0310] In Figures 1 and 2, AO is a target alloy with a precise, predetermined alloy composition. The target values ​​for the mechanical properties apply to a finished hot-rolled flat product, in particular to steel strips or heavy plates; that is, the target values ​​do not apply to slabs.

[0311] Regarding the influencing element molybdenum (Mo), a threshold of 0.005 wt.% is specified by the target alloy. For copper (Cu), a threshold of 0.01 wt.% applies. These limits apply when all other alloying elements are added within the limits originally defined by the target alloy.

[0312] Al represents the first measured analysis, which corresponds to the actual alloy contents after the smelting process in the ladle furnace. It is evident that the actual values ​​of Mo and Cu are higher than the originally defined threshold values. This deviation results from the use of scrap metal.

[0313] With increased actual Mo and Cu values, the deviations AMo and ACu are calculated. This results in higher strength values, assuming Mn and Cr values ​​remain unchanged.

[0314] The residues are calculated according to equation 4.

[0315] Subsequently, the dynamic deviations for the compensation elements Mn and Cr are calculated (AMn and ACr), which are added to the melt during dynamic alloying to minimum levels.

[0316] The step sizes for the corrections of Mn are preferably 0.025 wt.% and for Cr 0.01 wt.%. These step sizes correspond to approximately 25% of the interval within which the alloying element may vary due to manufacturing processes.

[0317] In sample A2, the content of the compensating element Mn is reduced by 0.2 wt.% compared to the original target alloy. This results in a difference in tensile strength of less than 0. Therefore, this is an impermissible correction.

[0318] In sample A3, the manganese content is reduced by 0.125 wt.%. Both strength values ​​are now higher than the reference values ​​and thus represent a possible correction.

[0319] In sample A4, the manganese content is reduced by 0.125 wt.% and the chromium content by 0.01 wt.%. Both strength values ​​are again higher than the reference values ​​and thus represent a further possible correction. European patent application

[0320] Voestalpine Grobblech GmbH

[0321] P380702WO

[0322] For the first embodiment (Figures 1 and 2), variant A4 is the optimal correction because the residual (without relevance of the CAE value) is lowest here.

[0323] In summary, the procedure can be carried out as follows:

[0324] 1) Minimum levels or ranges for compensation elements are defined;

[0325] 2) These areas are divided into step sizes;

[0326] 3) The forecasting model determines the properties R for all combinations of possible compensation element contents (steps) and influencing elements (actual value). m or R P 0.2 calculated;

[0327] 4) For positive Rm or Rpo.z values, the weighted residuals are calculated;

[0328] 5) The combination with the lowest residual is chosen.

[0329] Figure 3 shows an example range for dynamic alloying for the strength values ​​R. PThe original target alloy (represented by AO) has no strength deviations. Accordingly, the value for AO lies at the origin. The increased Mo and Cu content causes the deviations in tensile strength and yield strength, which are represented by Al. Since the correction algorithm only allows solutions in the upper right quadrant (positive change in both yield strength and tensile strength), variant A2 is not possible. Variants A3 and A4 lie in the upper right quadrant and thus represent possible solutions. A4 shows the smallest deviation in both yield strength and tensile strength compared to the target alloy and is therefore defined as the optimal solution.

[0330] Figure 4 shows a second embodiment. Here, the target parameters of the correction, i.e., the change in the compensation elements, are calculated only for the yield strength and the tensile strength, and with the relevance of the CAE.

[0331] Here, the elements Mo and Cu are again used as influencing elements, and the elements Mn and Cr as compensating elements.

[0332] The changes in the strength values ​​ARp0.2 and ARm must always be positive, so that a calculated decrease in the strength values ​​is prevented when applying a dynamic correction of compensation elements. European patent application

[0333] Voestalpine Grobblech GmbH

[0334] P380702WO

[0335] In this embodiment, the weighting is weightR P 0.2 for ARpo.2 equals 1 (weightR P o.2 = 1) and for ARm the weighting weightRm is equal to 2 (weightRm = 2).

[0336] In this case, the calculation is performed taking into account the relevance of the CAE value. The weighting for CAE is 3000, i.e., weightCAE = 3000.

[0337] In the second embodiment, no restrictions regarding toughness are specified.

[0338] B0 is a target alloy with a precise, predetermined alloy composition. The target property values ​​apply to a finished hot-rolled steel flat product, particularly steel strip or heavy plates; that is, the target values ​​do not apply to slabs as feedstock.

[0339] Bl stands for the first measured analysis, which determines the actual alloy contents after the smelting process in the ladle furnace. It is evident that the actual values ​​of Mo and Cu are elevated. This deviation results from the use of scrap metal.

[0340] With increased actual Mo and Cu values, the deviations AMo and ACu are calculated. This results in higher strength values ​​and a higher carbon equivalent CAE, assuming otherwise unchanged values ​​for Mn and Cr.

[0341] The residues are calculated according to equation 4.

[0342] Subsequently, the dynamic deviations for the compensation elements Mn and Cr are calculated (AMn and ACr), which are added to minimum levels during dynamic alloying.

[0343] The correction steps for Mn are 0.025 wt.% and for Cr 0.01 wt.%. These steps correspond to approximately 25% of the range within which the alloying element may vary due to manufacturing processes.

[0344] In sample B2, the content of the compensating element Mn is reduced by 0.2 wt.%. This results in a difference in tensile strength of less than 0. Therefore, this is an impermissible correction.

[0345] In sample B3, the manganese content is reduced by 0.125 wt.%. Both strength values ​​are now higher than the reference values ​​and thus represent a possible correction. European patent application

[0346] Voestalpine Grobblech GmbH

[0347] P380702WO

[0348] In sample B4, the manganese content is reduced by 0.125 wt.% and the chromium content by 0.01 wt.%. Both strength values ​​are again higher than the reference values ​​and thus represent a further possible correction.

[0349] For the second embodiment (Figure 4), variant B3 is the optimal correction because the residual (with relevance to the CAE value) is lowest here.

[0350] In contrast to the restriction on strength values, namely that when the compensation elements are corrected they must not decrease, a decrease in CAE when the compensation elements are corrected may well be desirable.

[0351] The exemplary embodiments have shown that, with the same influencing element load, different variants for the dynamic alloying of the respective melts can be achieved under different conditions and restrictions for the correction.

[0352] Thus, the present method enables dynamic, variable and flexible alloying while taking into account different conditions and restrictions.

[0353] Figure 5 shows the gradients (i.e., the influence of the elements on the mechanical properties, such as yield strength and tensile strength) as well as the maximum permissible levels of the elements (column 4).

[0354] The strength values ​​are determined using the following methods:

[0355] 1) Determination of hardness values ​​using dilatometer tests;

[0356] 2) Determination of strength values ​​based on laboratory rolling tests;

[0357] 3) Determination of strength values ​​based on produced sheet metal.

[0358] For a dilatometer test, a cylindrical sample (typically with a diameter of 5 mm and a length of 10 mm) is used, which is subjected to a defined time-temperature forming history in a forming dilatometer. The sample is heated to a predetermined temperature at a specific heating rate and then held at that temperature for a defined time. Subsequently, the sample can be formed (upset) and then cooled again at a specific cooling rate. This test serves to simulate the manufacturing process, starting with the heating of a slab in the furnace and continuing to the European patent application.

[0359] Voestalpine Grobblech GmbH

[0360] P380702WO

[0361] The process involves rolling and subsequent cooling or heat treatment. Following this sequence of tests, a hardness measurement is performed on the sample's end face. The resulting hardness value indicates the expected tensile strength. The sample is obtained from a small-scale cast block, but can also be taken from a large-scale sheet.

[0362] In a laboratory rolling test, a small-scale cast ingot is heated in a test facility that includes 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 final thickness. The resulting rolled strip is then cooled in water or air. One or more tensile specimens are taken from the cooled strip (typical dimensions are a width of 150 mm, a length of 500 mm, and a thickness of 20 mm). Their mechanical properties, such as yield strength, tensile strength, and elongation at break, can be determined on conventional tensile testing machines. Alternatively, the rolled strip can be subjected to subsequent heat treatment before samples are taken for tensile testing.

[0363] The data obtained using both experimental methods serve as the basis for developing a model to predict the mechanical properties (yield strength, tensile strength, and elongation at break) as a function of the alloying elements, accompanying and trace elements, and the manufacturing process of the sheets. The predictive model is based on mathematical equations grounded in sound material science principles, particularly those relating to physics and metallurgy.

[0364] 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.

[0365] The small-scale production of the cast blocks takes place in a specially designed melting furnace. The alloying elements can be varied beyond the alloy range used in the large-scale production process. This also applies to the specification of process parameters (such as heating temperatures, rolling temperatures, and cooling rates). European patent application

[0366] Voestalpine Grobblech GmbH

[0367] P380702WO

[0368] Values ​​can be achieved that are not common in large-scale industrial processes, or that are not technically feasible at the production facilities.

[0369] 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 model. The influence of alloying and accompanying elements is essential for dynamic alloying.

[0370] By using two different experiments, the advantage arises that, in the case of dilatometer tests, process parameters can be specified that cannot be achieved in the laboratory process. This applies particularly to the cooling rate. In the dilatometer test, a cooling rate spectrum can be realized that can simulate both air cooling and water cooling across the entire thickness range produced, but especially for very thick sheets (e.g., > 150 mm sheet thickness). This is not possible with sheets rolled in a laboratory rolling mill because the rollable sheet thickness is limited.

[0371] On the other hand, total deformation values ​​(calculated from the original casting thickness and the final thickness of the rolled sheet) can be applied in laboratory rolling tests, which are not achievable in dilatometer tests. Furthermore, combining results from dilatometer tests and laboratory rolling tests allows the theoretical yield strengths to be determined from the hardness values ​​obtained in dilatometer tests. This is done using the yield strength ratios (yield strength divided by tensile strength) obtained from the tensile tests of the rolled strips from the laboratory rolling tests.

[0372] 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.

[0373] This fine-tuning of the parameters, specifically the slope values, is carried out using computer-aided methods by determining selected parameters of the model equations described above 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 ±20% is possible. (European patent application)

[0374] Voestalpine Grobblech GmbH

[0375] P380702WO

[0376] 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.

Claims

European patent application Voestalpine Grobblech GmbH P380702WO Claims 1. A process for producing flat steel products, in particular heavy plates with specific mechanical properties, which are determined 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 the melt of the last primary metallurgical unit of the production route and the contents of the accompanying and alloying elements are determined, wherein actual 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 threshold value defined by the target alloy, and alloying elements are elements which are added specifically according to the target alloy. characterized by the fact that A distinction is made between influencing and compensating elements, whereby Influencing elements are elements that have an influence or effect on one or more mechanical properties, and compensating elements are elements that compensate for the influence or effect of the influencing element on at least one mechanical property of the final product, wherein the influencing elements whose influence on the mechanical properties of the final product is to be compensated comprise one, several or all from the group of Cu, Mo, Ni, Cr, wherein as compensation elements one, several or all from the group of Si, Mn, Cr, Mo, Ni are chosen, wherein the difference between the actual values ​​of the threshold values ​​of the target alloy with respect to those influencing elements that have an influence on at least this one mechanical property is recorded, wherein the magnitude of the influence of the deviation of the actual values ​​from the threshold values ​​of all influencing elements on at least one mechanical property is recorded, wherein 35 European patent application Voestalpine Grobblech GmbH P380702WO for the respective mechanical property at least one compensation element is determined which specifically compensates for the effect of the influencing element on the mechanical property, and wherein one or more compensation elements are added to the melt in an amount which brings the corresponding mechanical property to the target value and compensates for the influence of the influencing element, and wherein Two components are used in the control system for this purpose: a forecasting model and a correction algorithm, whereby the forecasting model is used to calculate the influence of the influencing elements on the mechanical properties of the final product and the correction algorithm is used to calculate target values ​​of the compensation elements.

2. Method according to claim 1, characterized in that influencing elements are elements which are trace elements or accompanying elements or alloying elements in the feedstock and whose content in the melt exceeds a threshold value defined by the target alloy, and compensating elements are elements which are regular alloying elements of the target alloy or other elements.

3. Method according to claim 1 or 2, characterized in that the compensating elements used are elements whose effect on the mechanical properties of the final product is not changed or not significantly changed, i.e. by no more than ±10%, by a thermal or thermomechanical treatment following the casting process.

4. A method according to one of the preceding claims, characterized in that, if an alloying element of the target alloy is already introduced by a feedstock in a proportion below a desired target content defined by the target alloy, this element is added to the extent necessary to achieve the target content; or, if the alloying element of the target alloy is already introduced by a feedstock in a proportion corresponding to the target content, nothing further is added; or, if the alloying element of the target alloy or the influencing element is already introduced by a feedstock in a proportion above the target content or threshold, by a reduced alloying proportion of at least one further second element with similar mechanical properties. 36 European patent application Voestalpine Grobblech GmbH P380702WO and / or compensates for an increased alloy content of at least one opposing third element.

5. Method according to one of the preceding claims, characterized in that the predictive model is used to calculate mechanical properties with the actual values ​​of the element contents or mechanical properties with the actual values ​​of the element contents and the carbon equivalent with the actual values ​​of the element contents, wherein a deviation of the respective mechanical property or the carbon equivalent from the target value is determined, wherein identical elements have different effects on different mechanical properties.

6. Method according to one of the preceding claims, characterized in that the following formula is used in the forecasting model: AR = ax AEi + bx AE2+ ••• + n* x AR,,, where AR is a deviation from the target value of the desired mechanical property, where a, b to n* factors are which correspond to the effects of the individual elements on at least one mechanical property, are largely independent of any subsequent thermal or thermomechanical post-treatment and are determined using the predictive model and through experiments and material science equations, and wherein AEi, E2 to AE n on the one hand, the individual deviations in wt.% from the respective target content of the corresponding alloying element or from the threshold value of the corresponding influencing element and on the other hand, possible correction steps of the compensation elements.

7. Method according to one of the preceding claims, characterized in that the mechanical properties include the tensile strength R m and / or the yield strength P o.2 are, where AR is the yield strength change AR Po.2 and / or the tensile strength change ARm, so that in the prediction model either the yield strength change or the tensile strength change is calculated, or the yield strength change and the tensile strength change are calculated. European patent application Voestalpine Grobblech GmbH P380702WO 8. Method according to one of the preceding claims, characterized in that the correction algorithm takes into account additional restrictions by minimum or maximum element contents in the target alloy composition and / or a desired ratio of individual elements to each other.

9. Method according to one of the preceding claims, characterized in that the following formula is used in the correction algorithm: Res = Abs\weightR x AR + weightR2x AR2+ weightCAE x ACAE], where the consideration of the carbon equivalent is optional, Res is the residual that is minimized during the correction algorithm. Abs is the absolute value function, which provides the absolute value. weightRi is the weighting of the first mechanical property, ARi is the deviation of the first mechanical property, weightR? The weighting of the second mechanical property is, AR? The deviation of the second mechanical property is, weightCAE is the weighting of the carbon equivalent, ACAE is the deviation of the carbon equivalent and where weightCAE = 0 if the carbon equivalent is not taken into account.

10. Method according to one of the preceding claims, characterized in that the following formula is used in the correction algorithm: Res = Abs[weightR pQ 2 x AR pQ 2 + weightR m x AR m + weightCAE x ACAE , provided that ARpo.2 and AR m are positive, so that the contributions to the residual resulting from AR are positive, where the consideration of the carbon equivalent is optional, European patent application Voestalpine Grobblech GmbH P380702WO Res is the residual that is minimized during the correction algorithm. Abs is the absolute value function, which provides the absolute value. weightRpo.2 is the weighting of the yield strength, Rpo.2 the deviation of the yield strength is, weightRm is the weighting of the tensile strength, Rm is the deviation of the tensile strength. weightCAE is the weighting of the carbon equivalent, ACAE is the deviation of the carbon equivalent and where weightCAE = 0 if the carbon equivalent is not taken into account.

11. Method according to one of the preceding claims, characterized in that the following formulas are used in the forecasting model: Rp0.2 = 12° x ^ Mn + 40 x ACr + 170 x ACu + 200 x AMo + 16 x ASi + 17 x ANi, = 140 x AMn + 50 x ACr + 170 x ACu + 240 x AMo + 25 x ASi + 16 x ANi, ACr + AMo ACAE = AC + —+ —+ —+ — + + AV + 5AB 30 20 20 60 20 15 10 where the slope values ​​can vary by a maximum of ±20% and where Ai is the deviation of the respective element i from its target content in wt.%.

12. Method according to one of the preceding claims, characterized in that the variation of the compensation elements in the correction algorithm is carried out in step sizes, wherein the step sizes 5-25%, preferably 10-25%, particularly preferably 20-25% correspond to that interval in which the corresponding alloying element may vary due to manufacturing.

13. Method according to one of the preceding claims, characterized in that the target alloy comprises the following target alloy composition in wt.%: 39 European patent application Voestalpine Grobblech GmbH P380702WO c 0.020-0.30 Si 0.0001-1.0 Mn 0.0001-3.0 P 0.0001-0.02 S 0.0001-0.02 Cr 0.0001-2.6 Cu 0.0001-0.50 Mon 0.0001-1.0 Ni 0.0001-10.0 Nb + V + Ti 0.0001-0.45 W 0.0001-0.20 N 0.0001-0.020 Sn 0.0001-0.20 Residual iron and impurities resulting from the smelting process.

14. Control system for the production of heavy plate and for carrying out the method according to one of the preceding claims, characterized in that the control system comprises two components: a forecasting model and a correction algorithm, wherein the forecasting model is designed to calculate the effect of influencing elements and compensation elements on the mechanical properties of the heavy plate, and the correction algorithm is designed to calculate target contents of compensation elements. 40

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