C. Bos

Tata Steel · Materials Design

A mixed-mode model for the interface velocity during partitioning phase transformations [J. Sietsma, S. van der Zwaag, Acta Mater. 52 (2004) 4143–4152] is reformulated and rigorously validated. Comparison with a numerical treatment shows that the model gives a near-exact description of the growth kinetics. In addition, the model provides informatio...

A three-dimensional cellular automata model is developed for the description of the relevant metallurgical mechanisms occurring in the annealing stage of dual-phase steels: ferrite recrystallisation, pearlite-to-austenite and ferrite-to-austenite transformation on heating and austenite-to-ferrite transformation on cooling. Based on the local grain-...

During the production of dual-phase (DP) steels, many transformation phenomena occur, each of which may significantly influence the final properties of the product. In the continuous annealing line, recovery, recrystallization, carbide dissolution, austenite formation, ferrite formation, and martensite formation may all occur. These processes can s...

A multi-lattice kinetic Monte Carlo atomistic simulation method has been used to simulate the austenite to ferrite interface-controlled transformation in pure iron. By performing simulations with different amounts of “free volume” at the interface, quantitative relations between the activation energies for interface mobility, boundary self diffusio...

A kinetic Monte Carlo method has been developed for the simulation of interface controlled solid-state transformations to overcome timescale limitations associated with other atomistic simulation methods. In the simulation method the atoms can take place on sites from (at least) two intertwining crystal lattices. To enable the atoms to also take po...

In the present study, the nucleation of static recrystallization (SRX) in austenite after hot deformation is experimentally analyzed using a Ni-30 pct Fe model alloy. In agreement with the predictions by current models, nucleation rate exhibits a strong peak, early during SRX. Whereas such an early peak is explained by current models by the saturat...

Modelling dislocation glide over the initial part of a stress–strain curve of metals received little attention up to now. However, dislocation glide is essential to ones understanding of the fundamental relationship between inelastic deformation and the evolution of the dislocation network structure. Therefore, we present a model of dislocation-dri...

A Reference-Free Modified Embedded Atom Method (RF-MEAM) potential for iron has been constructed. The new potential is made to predict both bcc and fcc (α-Fe and γ-Fe) lattice properties, with a special interest in modelling in the 800-1300 K temperature range. This is the range in which transformations and key processes in steel occur. RF-MEAM pot...

Predicting microstructure and (micro-)texture evolution during thermo-mechanical processing requires the combined simulation of plastic deformation and recrystallization. Here, a simulation approach based on the coupling of a full-field dislocation density based crystal plasticity model and a cellular automaton model is presented. A regridding/reme...

The volume increase and shape change during austenite to martensite transformation in dual-phase (DP) steels are largely accommodated in the microstructure by the deformation of the surrounding ferrite matrix. Accurate estimation of transformation-induced deformation of ferrite via experiments and modeling is essential for predicting the subsequent...

A cellular automaton algorithm for curvature-driven coarsening is applied to a cold-rolled interstitial-free steel’s microstructure - obtained through electron backscatter diffraction (EBSD). Recrystallization nucleation occurs naturally during the simulation, due to the highly heterogeneous and hence competitive growth among pre-existing (sub) gra...

During the production of DP steels, the volume expansion and shape change accompanying the austenite to martensite transformation is accommodated by the deformation of surrounding ferrite grains. The extent of the deformation in ferrite grains ultimately affects the mechanical properties of DP steels. Using electron backscatter diffraction measurem...

A new approximation to the equations describing Classical Nucleation and Growth Theories, is proposed providing quick, and intuitive insight. It gives a prediction of the mean precipitate radius and number density development under quasi-isothermal conditions. Current “mean-radius”, and “multi-class” approaches to modelling classical nucleation and...

The mechanical properties of ferrite-martensite dual phase (DP) steels are influenced by the internal stresses induced during austenite to martensite transformation. The volumetric expansion during this transformation causes plastic deformation of surrounding ferrite grains and creates regions with higher density of geometrically necessary dislocat...

In a hot strip mill (HSM), the evolution of phase transformation in steel during the dynamic cooling process on a run-out table has a significant effect on the microstructure and mechanical properties of hot-rolled materials and further processing in the subsequent processing steps. An electromagnetic (EM) sensor array system, EMSpec® (ElectroMagne...

In this work, we show how the presence of microstructural banding and segregation affects the work-hardening behaviour of a dual phase steel with improved formability. This steel contains chemical segregation inherited from the casting process. Our previously developed 3D cellular automaton model allowed us to design thermo-mechanical processes to...

In order to achieve the customer-required microstructure and mechanical properties of hot-rolled steel strip, the cooling process on the run-out table in a hot strip mill is dynamically controlled to optimize the temperature and phase transformation trajectories. The current practice is to feed a run-out table temperature control model with strip t...

A concise semi-analytical mixed-mode model is proposed to describe the ferrite-to-austenite transformation kinetics. The initial microstructure for the model consists of a ferrite matrix with supersaturated austenite grains. The carbon supersaturation of austenite grains resulted from the rapid dissolution of pearlite colonies present in the initia...

The potential to utilize controlled thermal processing to minimize banding in a DP780 steel with 2 wt pct Mn was evaluated on samples processed on a Gleeble® 3500 thermomechanical processing simulator. All processing histories were selected to result in final dual-phase steel microstructures simulating microstructures achievable during annealing of...

In this work the formation of microstructural banding in a dual-phase steel is investigated by using a three-dimensional cellular automata model for phase transformations. Originally developed for describing the metallurgical processes occurring during the annealing stage of cold-rolled strips, this model is presently applied to investigate microst...

A three-dimensional mixed-mode (MM) transformation model accounting for both soft impingement and hard impingement was developed that calculates the growth kinetics of ferrite grains in an austenite matrix. The simulations are compared to the kinetics of ferrite formation in high-purity Fe-C alloys for which phase-transformation kinetics were meas...

A three-dimensional cellular automata (CA) model is developed for the kinetic and microstructural modelling of the relevant metallurgical mechanisms occurring in the annealing stage of low–alloy steels: recrystallisation, pearlite–to–austenite transformation and ferrite–to–austenite transformation on heating and austenite–to–ferrite transformation...

A mixed-mode model is defined for solid-state phase transformation in multi-component systems. In contrast to diffusion-controlled phase transformation models, the mixed-mode nature of the presented transformation model takes the effect of a finite interface mobility into account over the entire temperature range of the transformation. In the model...

A fast three-dimensional phase transformation model is formulated for the transformation from ferrite to austenite in low-carbon steel. The model addresses the parent microstructure, the nucleation behaviour of the new phase and the growth of the new phase. During the growth, the interface velocity of the ferrite grains is calculated using a mixed-...

The progress of solid-state phase transformations can generally be subdivided into three overlapping mechanisms: nucleation, growth and impingement. These can be modelled separately if hard impingement prevails. On that basis, an overview has been given of recent numerical and analytical methods for determination of the kinetic parameters of a tran...

The structural and dynamic properties of the interface during the fcc-bcc transformation in pure iron have been investigated by molecular dynamics simulations. An embedded atom method potential was used for the atomic interactions. Two interfaces, close to the Bain and Kurdjumov-Sachs orientation relations, have been examined during the fcc-to-bcc...

Using an embedded atom method potential for iron, the kinetics of (lateral) growth in the massive austenite (γ) to ferrite (α) transformation was analysed applying a newly developed multi-lattice kinetic Monte Carlo simulation approach. On this basis, for the first time the variable, individual activation energy for each single atomic jump could be...

A typical example of an interface controlled phase transformation is the massive transformation. The rate of transformation in a massive transformation is determined by processes at the interface. In many iron-based alloys the austenite to ferrite transformation is of massive nature. Most experimental data is collected after the transformation was...

A new multi-lattice kinetic Monte Carlo method has been used for an atomistic study on the interpretation of the interface mobility parameter for a massive face-centred cubic (fcc) to body-centred cubic (bcc) transformation in a single element system. For lateral growth of bcc in a system with an fcc(111)//bcc(110) and fcc[112¯]//bcc[001¯] interfac...

A multi-lattice kinetic Monte Carlo method has been used for an atomistic study on moving interfaces in interface-controlled phase transformations. Depending on the driving force of the transformation a continuous or a plane-by-plane lateral growth mode occurs. In case of plane-by-plane growth 2-dimensional nucleation is required to accomplish the...

A multi-lattice kinetic Monte Carlo method has been developed for the atomistic simulation of massive phase transformations. Beside sites on the crystal lattices of the parent and product phase, randomly placed sites are incorporated as possible positions. These random sites allow the atoms to take favourable intermediate positions, essential for a...