DESCRIPTION

Technical field

The present invention relates to an apparatus for continuous monitoring of a metallic material, in particular a steel, in a rolling process.

The present invention also relates to a method for continuous monitoring of a metallic material, in particular a steel, in a rolling process.

The invention has a preferred application in the metalworking industry, for example in relation to the production of rolled steel, and the following description is made with reference to this field of application for the sole purpose of simplifying the exposure thereof.

Prior art

A hot and cold rolling process is fully described by the rolling schedule which consists in specifying the number of passes, the strain of each rolling pass, the temperature that the strip or metal sheet must have during strain and finally the time between one pass and the next (“interpass time”).

Currently, rolling schedules are calculated by means of mathematical models based on empirical equations from the literature that estimate the evolution of the microstructure of the metallic material as a function of time, by calculating the precipitation state and the recrystallisation fraction of the metal sheet. Alternatively, rolling schedules are calculated using statistical models, for example based on machine learning methodologies, which require a high amount of process data and high temperature mechanical and microstructural properties or alternatively data on finished products. It is clear that these metallurgical data, necessary for the model training step, can only be obtained on a laboratory scale, which notoriously cannot reproduce the actual conditions of the industrial rolling process with sufficient reliability and precision.

A problem that afflicts current empirical models and machine learning models is that the instantaneous boundary conditions used in the metallurgical model consisting of the thermal profile in the metal sheet, recrystallization and precipitation kinetics and metal sheet-rolling roll interaction conditions are not known with precision or are not known at all. The forecasts of the metallurgical models currently in use in hot rolling mills are characterised by still very high errors and are therefore mostly used for off-line simulation and qualitative definition of rolling schedules.

The current state of the art therefore lacks a device and relative methodology for continuously and in real time measuring the evolution of the microstructure during the various steps of the hot or cold rolling process. This device would offer the opportunity to provide experimental data for the calibration of empirical models and / or machine learning that can be obtained directly from the industrial process.

Summary of the invention

An object of the present invention is to overcome drawbacks of the prior art.

A particular object of the present invention is to present a methodology and an apparatus suitable for evaluating the micro structure of a metallic material during the hot or cold rolling process.

A further particular object of the present invention is to carry out a continuous monitoring of a metallic material in a rolling process which is more precise. A further particular object of the present invention is to effectively exploit the knowledge of instantaneous boundary conditions of the rolling process, for example constituted by the thermal profile in the metal sheet, and/or by the metal sheet-rolling roll interaction conditions.

These and other objects are achieved by an apparatus for continuous monitoring of a metallic material in a rolling process and a relative method, according to the features of the appended claims which form an integral part of this description.

An idea underlying the present invention is to provide an apparatus for continuous monitoring of a metallic material in a rolling process. The apparatus comprises at least one roll- separating force sensor configured for measuring over time a roll- separating force applied by at least one pair of rolls on a strip of metallic material during the rolling process. The apparatus comprises at least one strain sensor configured for measuring over time a strain to which the metallic material is subjected during the rolling process. The apparatus comprises at least one temperature sensor configured for measuring over time a temperature of the metallic material during the rolling process. The apparatus comprises at least one work hardening calculation module comprising at least one processor configured for calculating over time a work hardening of the metallic material, the work hardening being defined as a derivative of a stress over strain curve and depending on the temperature of the metallic material and on a strain rate to which the metallic material is subjected. The work hardening calculation module receives as input at least: the roll- separating force measured by the at least one roll- separating force sensor, the strain measured by the at least one strain sensor, an equivalent radius size associated to a radius of a working roll of the pair of rolls, a thickness of the metallic material, a contact angle between the working roll and the metallic material, an effective friction coefficient between the metallic material and the pair of rolls.

A further idea underlying the present invention is to provide a method for continuous monitoring of a metallic material in a rolling process. The method comprises measuring over time a roll- separating force applied by at least one pair of rolls on a strip of metallic material during the rolling process. The method comprises measuring over time a strain to which the metallic material is subjected during the rolling process. The method comprises measuring over time a temperature of the metallic material during the rolling process. The method comprises calculating over time a work hardening of the metallic material, the work hardening depending on the temperature of the metallic material and a strain rate to which the metallic material is subjected. The work hardening is calculated as a function of at least: the roll- separating force measured, the strain measured, an equivalent radius size associated to a radius of a working roll of the pair of rolls, a thickness of the metallic material, a contact angle between the working roll and the metallic material, an effective friction coefficient between the metallic material and the pair of rolls.

In general, the present invention advantageously provides for a calculation of work hardening, starting from measured process parameters (such as roll- separating force, strain, temperature), and further as a function of quantities linked to the rolled material or to the rolling mill (such as an equivalent radius size, thickness of the metallic material, contact angle, effective friction coefficient) which can be measured or estimated much more readily than the work hardening itself.

In other words, the inputs provided to a work-hardening calculation module, either directly or by means of sensors, which can operate in real time and continuously, thus being more effective in describing work hardening in an industrial rolling process.

Advantageously, the continuous monitoring of the metallic material according to the present invention allows to provide a cold or hot rolling plant equipped with advanced metallurgical “smart sensors”, by means of which the evolution of the microstructure of the metallic material can be monitored during the entire rolling process. In particular, advantageously, the continuous monitoring of the metallic material according to the present invention can be used for the purpose of operating a dynamic feedback of the rolling process, and / or to make real-time corrections to the rolling process.

Advantageously, the continuous monitoring of the metallic material according to the present invention enables online adjustments to be introduced to the rolling schedule of the metallic material in order to optimise productivity and improve final quality of the strip/ plate and mechanical performance.

Advantageously, the continuous monitoring of metallic material according to the present invention enables a significant competitive advantage to be achieved due to lower production costs and a better ability to meet the most stringent expectations and specifications of end users.

Preferably, a main feature of the continuous monitoring of the metallic material according to the present invention is the development of a virtual sensor consisting of physical models, implemented in the rolling process, which provide for each rolling cage and at each pass the evolution of the mechanisms of recrystallization (formation of new grains), recovery (redistribution of dislocations) or work hardening (multiplication of dislocations) of the metallic material, which occur in the strip/ metal sheet rolling process.

Preferably, a key enabling factor of the continuous monitoring of the metallic material according to the present invention is the on-line measurement of the instantaneous work hardening of the metal sheet/ strip by means of specific equations.

Advantageously, the calculation of the model parameters takes place automatically and without the need for laboratory tests, thanks to a self training algorithm. Further features and advantages will become more apparent from the detailed description below of preferred, non-limiting embodiments of the present invention, and from the depending claims outlining preferred, particularly advantageous embodiments of the invention.

Brief description of the drawings

The invention is illustrated with reference to the following figures, provided by way of non-limiting example, wherein:

- Figure 1 exemplifies a rolling mill comprising an apparatus for continuous monitoring of a metallic material according to the present invention.

- Figure 2 exemplifies a strip of metallic material during a rolling process according to the present invention.

- Figure 3 exemplifies a temperature-dependent work hardening of the metallic material calculated by the method for continuous monitoring of a metallic material according to the present invention.

In the different figures, analogous elements will be identified by analogous reference numbers.

Detailed description

Figure 1 exemplifies a rolling mill 10 comprising an apparatus 100 for continuous monitoring of a metallic material according to the present invention. The metallic material is a strip (not depicted in Figure 1) which is subject to rolling by at least one pair of rolls 11 and 12, which are configured opposing each other so as to act on the strip of metallic material.

The apparatus 100 for continuous monitoring comprises at least one roll- separating force sensor 101 configured for measuring over time a roll- separating force applied by the at least one pair of rolls 11, 12 on the strip of metallic material, during the rolling process. The rolls 11, 12 of the rolling mill 10 may have the same or different diameters.

Preferably, the roll- separating force sensor 101 comprises at least one load cell applied to at least one roll of the pair of rolls 11, 12.

The apparatus 100 for continuous monitoring further comprises at least one strain sensor 102 configured for measuring over time a strain to which the metallic material is subjected during the rolling process.

Preferably, in embodiments for hot rolling, the strain sensor 102 comprises at least one thickness meter of the strip of metallic material by measuring a separation distance of the rolls 11, 12 or by ultrasonic, X- ray or radioactive isotopes devices.

Preferably, in embodiments for cold rolling, the strain sensor 102 comprises at least one thickness meter of the strip of metallic material by an X-ray device, or at least one velocimeter or at least one encoder applied to one or more of the rolls 11, 12.

The apparatus 100 for continuous monitoring further comprises at least one temperature sensor 103 configured for measuring over time a temperature of the metallic material during the rolling process.

The apparatus 100 for continuous monitoring further comprises at least one work hardening calculation module 104 comprising at least one processor 105 configured for calculating over time a work hardening of the metallic material.

In general, the work hardening of metallic material depends on the temperature of the metallic material and on a strain rate to which the metallic material is subjected. The work hardening of metallic material is defined as a derivative of a stress over strain curve.

The work hardening calculation module 104 is configured for calculating the work hardening. The work hardening calculation module 104 receives as input the at least one roll- separating force applied by the at least one pair of rolls 11, 12 on the metallic material, measured by the at least one roll- separating force sensor 101.

The work hardening calculation module 104 further receives as input the strain to which the metallic material is subjected, measured by the at least one strain sensor 102.

Preferably, the processor 105 is further configured for calculating over time a strain rate to which the metallic material is subjected during the rolling process, starting from the strain measured by said at least one strain sensor 102. Preferably, the work hardening calculation module 104 receives as further input the strain and the strain rate, and further a strain gradient over the metallic material.

The work hardening calculation module 104 further receives as input at least one equivalent radius size associated to a radius of the working roll 11 of the pair of rolls 11, 12.

In a first preferred embodiment, the apparatus 100 further comprises a radius measuring device 106, configured for measuring the actual radius size of the working roll 11, while the processor 105 is further configured for receiving the measured actual radius size of the working roll 11. The equivalent radius size in this case is the actual measured radius size of the working roll 11. It is reminded that the rolls 11, 12 including the working roll 11 are deformable under the loads encountered during the rolling process, so that the actual radius size will be less than a nominal radius size.

In a second preferred embodiment, the processor 105 is further configured for calculating an estimate of deformed radius, expected to be provided during the specific rolling conditions. The estimate of deformed radius R' will be further described in the following. The nominal radius of the working roll 11 can be predefined or set by means of a user interface of the apparatus 100. In this case, the equivalent radius size is the estimate of deformed radius.

In a third embodiment, a less-preferred alternative, the equivalent radius size is simply a nominal radius of the working roll 11 which can be predefined or set by means of a user interface of the apparatus 100.

The work hardening calculation module 104 further receives as input at least one thickness of the metallic material.

The work hardening calculation module 104 further receives as input at least one contact angle between the working roll 11 and the metallic material.

The work hardening calculation module 104 further receives as input at least an effective friction coefficient between the metallic material and the pair of rolls 11, 12.

Preferably, the apparatus 100 further comprises at least one velocity sensor (not depicted) configured for measuring a velocity of the metallic material entering and/or exiting the at least one pair of rolls 11, 12, and further comprises at least one rotation sensor (not depicted) configured for measuring a rotational velocity of the working roll 11. In this case, the processor 105 is further configured for calculating the effective friction coefficient as a function of a forward slip depending on the velocity of the metallic material 20 and on the rotational velocity of the working roll 11.

In a first embodiment, the apparatus 100 is used for continuous monitoring of a metallic material in a hot rolling process.

In the context of the present invention, by way of example, a hot rolling process is considered to be a process for deforming a metallic material by means of counter-rotating metallic rolls, wherein the temperature of the metallic material during the strain phase is equal to or higher than 30% of the melting temperature of the metallic material (i.e., Temp/Temp _m > 0.3). In such embodiment in a hot rolling process, the at least one temperature sensor 103 is configured for measuring over time at least one temperature profile of the metallic material subjected to the hot rolling process. Preferably, the work hardening calculation module 104 receives as input at least one temperature derived from the temperature profile.

More preferably, the at least one temperature sensor 103 is further configured for measuring over time at least one first temperature profile, along a width of the metallic material in proximity of the at least one pair of rolls 11, 12, and even more preferably the at least one temperature sensor 103 is further configured for measuring over time at least one second temperature profile, along a rolling axial length of the metallic material subjected to the hot rolling process.

Preferably, in further embodiments, the processor 105 is further configured for a self-learning calculation of at least one yield stress or tensile strength of the metallic material, as a function of temperature and strain rate, using Artificial Intelligence.

In a second embodiment, the apparatus 100 is used for continuous monitoring of a metallic material in a cold rolling process.

In the context of the present invention, by way of example, a cold rolling process is considered to be a process for deforming a metallic material by means of counter-rotating metallic rolls, wherein the temperature of the metallic material during the strain step is less than 30% of the melting temperature of the metallic material (i.e., Temp/Temp _m < 0.3).

In such embodiment in a cold rolling process, the apparatus 100 further comprises at least one tension force sensor (not depicted) configured for measuring over time a longitudinal tension force applied by the at least one bridle-roll (not depicted) on the strip of the metallic material, during the cold rolling process.

In this embodiment, the work hardening calculation module 104 receives as input the longitudinal tension force applied by the at least one bridle- roll on the metallic material.

A further embodiment of the apparatus 100 for continuous monitoring according to the present invention may advantageously include additional calculation modules (not shown in Figure 1) configured for calculating additional microstructural properties of the metallic material subjected to the rolling process. These additional microstructural properties may include, but are not limited to: recrystallisation, recovery, grain size evolution, yield stress, tensile strength, uniform elongation, retained strain, stored dislocations.

Figure 2 exemplifies a strip of metallic material 20 during a rolling process according to the present invention.

In a preferred embodiment, the at least one processor 105 of the work hardening calculation module 104 is configured for calculating the work hardening according to the following equation:

(tantf ± p _slip ) wherein a _c is a yield stress of the metallic material 20, wherein e is a strain of the metallic material 20, wherein is the work hardening, being a function of strain rate έ and temperature Temp, wherein 5 is a pressure acting on the metallic material 20 due to the roll- separating force measured by the at least one roll-separating force sensor 101, wherein d is a contact angular coordinate between the working roll 11 and the metallic material 20, wherein T is a longitudinal tension of the metallic material 20 (of significant magnitude in the case of cold rolling, as explained, and of minor magnitude in the case of hot rolling), wherein R' is an equivalent radius associated to a radius of the working roll 11, wherein h is an average thickness of the metallic material 20 along a contact arc 21 between the working roll 11 and the metallic material 20, wherein p _stip is an effective friction coefficient between the metallic material 20 and the pair of rolls 11, 12.

In particular, the effective friction coefficient p _sUp has a minus (-) sign in a rolling entry zone 22 and has a plus (+) sign in a rolling exit zone 23. In particular, the rolling entry zone 22 and the rolling exit zone 23 are divided by a neutral plane 24 of the metallic material, the neutral plane 24 being defined as a plane in which a local speed of the metallic material is equal to a local speed of the working roll.

In one embodiment, the at least one processor 105 is configured for approximating the work hardening according to the following formula: (tan Dΰ - p _slip ) wherein is a finite difference approximation of said work hardening, being a function of strain rate έ and temperature Temp, wherein D5 is a variation of stress in a direction normal to a plane of the strip of the metallic material 20 between an entry plane of said rolling entry zone 2 and an exit plane of said rolling exit zone 23, wherein De is an overall strain of the metallic material after a rolling pass, wherein Dϋ is an overall contact angle between the working roll 11 and the metallic material 20, wherein S is an average pressure acting on the metallic material 20 due to the roll- separating force.

In one embodiment, the at least one processor 105 is configured for calculating (rather than measuring, as described above) the equivalent radius size associated to the working roll 11 as a deformed radius R' according to the following equation: wherein R is an undeformed radius of the working roll 11, wherein / is a force per unit width acting on the metallic material 20 due to the roll- separating force, wherein C is a stiffness constant of the working roll 11, wherein Ah is a variation in thickness of the metallic material before and after the pair of rolls 11, 12.

Preferably, the at least one processor 105 is further configured for calculating the effective friction coefficient m _ear between the metallic material 20 and the pair of rolls 11, 12, according to the following equation: wherein T _q is a rolling torque per width unit acting on the metallic material 20, wherein / is a force per width unit acting on the metallic material 20 due to the roll- separating force, wherein R' is the deformed radius of the working roll, wherein v is the forward slip, wherein r is a thickness reduction ratio of the metallic material 20 in the rolling process.

Preferably, the at least one processor 105 is further configured for calculating the forward slip v according to the following equation: wherein V _s is an exit velocity of the metallic material 20 exiting the at least one pair of rolls 11, 12, and wherein V _c is a tangential velocity of the working roll 11.

In an alternative embodiment, the at least one processor 105 of the work hardening calculation module 104 is configured for calculating the work hardening by looking up a predetermined data table, instead of calculating the work hardening according to a specific equation.

The data table can be determined by a specific equation or model, or it can be determined based on experimental data.

In general, the predetermined data table for work hardening presents its data as a function of: roll-separating force, strain, an equivalent radius size, thickness, contact angle, effective friction coefficient.

A further embodiment of the apparatus 100 for continuous monitoring according to the present invention can advantageously calculate additional microstructural properties of the metallic material subjected to a cold rolling process. These additional microstructural properties include a determination of the volumetric fraction of the martensite phase F _MA and of average size of martensite particles d _MA , these two metallurgical characteristics being proportional to the instantaneous work hardening, calculated as illustrated above.

In particular, a preferred formulation of this volumetric fraction of the martensite phase F _MA and of average size of martensite particles d _MA is expressed in the following equation: wherein K, n and m are constant parameters that can be determined by means of laboratory tests for a specific composition of the metallic material. Figure 3 exemplifies a temperature-dependent work hardening of the metallic material calculated by the method for continuous monitoring of a metallic material according to the present invention.

In particular, the method for continuous monitoring of a metallic material in a rolling process according to the present invention comprises the steps of:

- measuring over time a roll- separating force applied by at least one pair of rolls 11, 12 on a strip of metallic material 20 during the rolling process;

- measuring over time a strain e to which the metallic material 20 is subjected during the rolling process;

- measuring over time a temperature Temp of the metallic material 20 during the rolling process;

- calculating over time a work hardening of the metallic material 20, the work hardening being defined as a derivative of a stress over strain curve and depending on the temperature Temp of the metallic material 20 and on a strain rate έ to which the metallic material 20 is subjected.

The work hardening is calculated as a function of at least the roll- separating force measured, the strain e measured, an equivalent radius size R' associated to a radius size of a working roll 11 of the at least one pair of rolls 11, 12, a thickness of the metallic material 20, a contact angular coordinate d between the working roll 11 and the metallic material 20, an effective friction coefficient p _sUp between the metallic material 20 and the pair of rolls 11, 12.

As described, in a preferred embodiment, the at least one processor 105 of the work hardening calculation module 104 is configured for calculating the work hardening according to the following equation: Such equation can be re-written in a more compact fashion, by defining: wherein W is a “stability function”. The equation can be integrated within the roll bite to arrive to: wherein s ₀ is the yield stress of the workpiece at the entry of the roll bite, before the rolling deformation occurs. The stability function W is calculated numerically by integrating the equation along the contact arc, with suitable boundary conditions.

In particular for cold rolling applications, the stability function W is e defined:

In particular for hot rolling applications or in general for high-friction rolling processes (dry-rolling), the stability function W is defined:

In the above expressions of the stability function W: m is an effective friction coefficient between the metallic material 20 and the pair of rolls 11, 12, i.e. the same as m _ear above; h _exit is a thickness of the metallic material 20 at an exit plane of the rolling exit zone 23;

R' is an equivalent radius associated to a radius of the working roll 11; ϋ is a contact angular coordinate between the working roll 11 and the metallic material 20; a _c is a yield stress of the metallic material 20;

5 is a pressure acting on the metallic material 20 due to the roll- separating force;

T is a longitudinal entry tension of the metallic material 20;

In practical rolling applications, for both cold rolling and hot rolling it has been determined that the value of W is substantially close to 1 , typically comprised between 0.9 and 1.2.

In general, the method for continuous monitoring according to the present invention is implemented in an apparatus for continuous monitoring according to the present invention, such as the apparatus 100 described above. Therefore, it is understood that the method for continuous monitoring according to the present invention comprises functional technical features corresponding to the structural technical features of the relevant apparatus for continuous monitoring described herein.

By way of example, a steel is considered as a metallic material, having a Carbon content [C wt%] 0.18, a Manganese content [Mn wt%] 1.49, a Niobium content [Nb wt%] 0.026 and a non-recrystallisation temperature [Temp_no-rx] 1075 °C. In this example, the rolling mill has a roll radius of 330 mm, a maximum roll- separating force of 35000 KN, a maximum strip width of 3000 mm and a strip thickness of 230 to 300 mm. In this example, the process parameters include 19 passes, a strain rate between 0.1 and 10 [1/s], a strip width of 2450 mm, an entry strip thickness of 250 mm, an exit strip thickness of 70 mm, an initial temperature of 1060°C and a final temperature of 960°C.

By calculating the work hardening (presented in Mpa on the y-axis of Fig. 3) of the steel characterized above, as a function of the 19 passes in the rolling mill (presented on the x-axis of Fig. 3, which also gives an indication of the associated temperature expressed in °C), it can be noted that the work hardening shows a strong dependence on temperature and on accumulated strains, with a slope of the curve being more significant in the final rolling passes, around 900-950°C.

Industrial applicability

Advantageously, the continuous monitoring of the metallic material according to the present invention can be used for the purpose of operating a dynamic feedback of the rolling process, and / or to make real time corrections to the rolling process.

Advantageously, the continuous monitoring of the metallic material according to the present invention enables a refined fine-tuning of the rolling schedule and to reduce the time for the development of new high- strength products.

Advantageously, the continuous monitoring of the metallic material according to the present invention makes it possible to detect the evolution of the stored strain and the evolution of the microstructure during the various rolling passes.

Advantageously, the continuous monitoring of the metallic material according to the present invention makes it possible to detect and recognise in real time the phenomena of tempering and / or hardening of the metallic material, and at what temperature they occur.

Advantageously, the continuous monitoring of the metallic material according to the present invention makes it possible to study, directly in an industrial context, the kinetics of static (SRX), dynamic (DRX) and metadynamic (MDRX) recrystallisation of the microstructure as a function of the chemical composition of the metallic material, the strain path and the temperature.

In view of the description given herein, the person skilled in the art will be able to devise further modifications and variations, in order to satisfy contingent and specific needs.

For example, continuous monitoring could be optimised for different metallic materials or alloys, and for hot and/or cold rolling processes.

The embodiments described herein are therefore intended to be illustrative and non-limiting examples of the invention.