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Digitalization is becoming increasingly common in the steel industry. Formerly developed models of individual phenomenon or separate sub-processes are being further developed into wider complexes where multiple models are coupled together. Virtual rolling automation, which can be used to control a finite-element rolling model, is a new element in these complexes. The automation enables to model the variations caused by the process adjustment. It must be taken in the account that neither the model nor the industrial process are ideal, but there are limitations in the attainable accuracy in both cases. Inclusion of the new automation control in the FE-model introduces new requirements: the setup calculations for all six rolling stands and the automation logic adjustments must perform within the model. The focus of the current article is prediction of the roll force and the virtual rolling automation of six stand finishing mill.

A combination of experimental and numerical approaches was applied for constructing a dynamic model for thermomechanical processing, which was used for simulating laboratory rolling and cooling, and for designing a cooling path to enable phase transformation from austenite to ultrafine (~ 50–100 nm) bainitic laths. Physical thermomechanical simulation experiments were used for calibrating the numerical models. Hot rolling and water cooling experiments were conducted and they were numerically simulated. The calibrated numerical models were used for simulating the main processing stages affecting the final microstructure evolution during a laboratory scale processing, i.e. the low temperature (500 °C) ausforming and subsequent cooling schedules leading to the decomposition of austenite into bainite and martensite. The fitted model parameters and simulation results are presented for the laboratory rolling and two different cooling paths: (i) air cooling to 350 °C temperature with subsequent holding for 1–1.5 h, and (ii) water cooling close to martensite start temperature, and furnace holding for 1–1.5 h. Microstructural analysis was carried out using scanning electron microscopy combined with electron backscatter diffraction as well as X-ray diffraction and the structures were corroborated with mechanical properties evaluated in respect of hardness, tensile and impact toughness properties. The achieved mechanical properties and microstructures were further interpreted with the numerical simulation results. The results show that the calibrated numerical simulations provide an effective tool for designing suitable thermomechanical processing paths leading to desired microstructure.

Dual-phase steels are generally used in the car industry due to high tensile strength and good formability, which are obtained by a mixture of bainite and ferrite phases. This microstructure is achieved through slow rate coil cooling. However, the manufacturing of dual-phase steels introduces various challenges such as the instability of the cold rolling process. An important factor affecting this is the non-uniform coil cooling of a hot rolled strip. In coil cooling the cooling rates are not controlled and there are different thermal contacts during coil conveyance causing unequal cooling of the steel coil. Unequal cooling rates lead to non-uniform coil cooling, producing irregular phase transformations on different sides of the coil, which causes periodical variations of the phase fractions in the steel strip. Varying phase fractions cause thickness deviations in the strip during the cold rolling process. A three-dimensional transient heat transfer finite element model was developed and used for modeling the complete coil conveyance chain and coil field cooling of the coil on an industrial scale. A coupled phase transformation model is implemented as a subroutine into the finite element model for calculating the resulting phase fractions. It was found that the different thermal contacts during the coil conveyance produce uneven cooling rates causing length- and widthwise variations in the phase fractions. The heat transfer model is validated by comparing temperature profiles between the simulated and measured coil edges. The phase transformation model is fitted into experimental data and verification is carried out in industrial conditions by comparing the modeled phase fractions and test samples from a cooled and unwound steel coil.

Coil cooling process is an important step in production of certain steel grades. Phase transformations for dual phase steels and precipitations for precipitation hardened steels occur mainly during the coil cooling. Generally, a coil goes through a coil conveyance chain before arriving at the final cooling storage at a steel plant. This conveyance chain contains various thermal contacts with different types of conveyors. Ambient temperatures and weather conditions may also change considerably. Those variables are relatively easy to measure and define in a simulation model whereas internal stresses and contact pressure inside the coil are very challenging to measure in industrial scale process. Thermal conductance between adjacent strip revolutions is dependent of contact pressure. In addition, thermal conductance is influenced by the combined thermal conductivity of steel and oxide layer of contact interfaces as well as thickness profile. In this paper the internal contact pressure between strip revolutions due to strip coiling and gravity are solved and considered when defining thermal conductance. Heat transfer is computed using FE-model, and GAPCON subroutine in Abaqus is utilized to calculate thermal contact conductance, taking into consideration the contact pressure between the strip revolutions. Also, the whole coil conveyance chain commencing from downcoiler mandrel to coil field cooling is implemented..

Accurate control of the temperature of the workpiece is crucial when carrying out thermal processing of steel. Effective heat transfer coefficient for water cooling of hot rolled steel was calibrated using spray nozzles with different amounts of water flux. Austenitic stainless steel was chosen for the studies in order to avoid the release of latent heat, which would affect the result in the case of carbon steels. Three different measurement sites acquired with thermocouples were used, namely in the middle and at the quarter distance from both top and bottom surfaces. The heat transfer coefficient was fitted to the experimental data using a computational model, which calculated the time-dependent temperature distribution within the steel slab. The model was validated by altering the experimental exposure time to the water spray and compared the model prediction to the observed result. The calibrated model provides the capability to design and carry out cooling routes in thermomechanical processing of steel in practice.

In order to study the coupled effect of rolling deformation, heat transfer and water cooling on microstructure formation of a steel strip, a multiscale and multiphysical FE-model is developed. The deformation state and temperature distribution of the steel strip after the last rolling pass are required to calculate the final microstructure. The sub-model predicting final microstructure on the steel strip after accelerated water cooling is implemented numerically. Final phase fractions are calculated with the Johnson-Mehl-Avrami-Kolmogorov equation for different parts of the object, taking into account non-uniform temperature distribution.