Phase Field Modelling of Microstructure Evolution in the HAZ of X80 Linepipe Steel

2012 ◽  
Author(s):  
Morteza Toloui ◽  
Matthias Militzer
Keyword(s):  
Grain Boundaries ◽  
Grain Growth ◽  
Microstructure Evolution ◽  
Phase Field ◽  
Phase Field Model ◽  
Carbon Diffusion ◽  
Austenite Decomposition ◽  
Austenite Grain ◽  
Austenite Grain Growth ◽  
Linepipe Steel

The heat affected zone (HAZ) during welding experiences a very steep temperature gradient which results in significant microstructure gradients. Thus, model approaches on the length scale of the microstructure, i.e. the so-called mesoscale, are useful to accurately simulate microstructure evolution in the HAZ. In this study, a phase field model (PFM) is employed to simulate austenite grain growth and austenite decomposition in the HAZ of an X80 linepipe steel microalloyed with Nb and Ti. The interfacial mobilities and nucleation conditions are obtained by benchmarking the PFM with experimental data from austenite grain growth and continuous cooling transformation tests. An effective grain boundary mobility is introduced for austenite grain growth to implicitly account for dissolution of NbC. Subsequently, austenite decomposition into polygonal ferrite and bainite is considered. For this purpose the PFM is coupled with a carbon diffusion model. Ferrite nuclei are introduced at austenite grain boundaries and suitable interfacial mobilities are selected to reproduce experimental ferrite formation kinetics. Bainite nucleation occurs for a sufficiently high undercooling at available interface sites (i.e. austenite grain boundaries and/or austenite-ferrite interfaces). For simplicity, the formation of carbide-free bainite is considered and a suitable anisotropy approach is proposed for the austenite-bainite interface mobility. The model is then used to predict austenite grain growth and phase transformation in the HAZ.

3D Phase Field Simulation of Austenite Grain Growth in Microalloyed Linepipe Steel

2012 ◽  
Vol 715-716 ◽  
pp. 800-805
Author(s):  
Morteza Toloui ◽  
Matthias Militzer
Keyword(s):  
Grain Growth ◽  
Phase Field ◽  
Rapid Heating ◽  
Three Dimensional ◽  
Heating And Cooling ◽  
Austenite Grain ◽  
Cooling Conditions ◽  
Strong Pinning ◽  
Austenite Grain Growth ◽  
Linepipe Steel

Three dimensional (3D) phase field modelling is used to simulate austenite grain growth in X80 linepipe steel for thermal paths that are typical in the heat affected zone (HAZ). In the HAZ austenite grain growth is affected by pinning due to precipitates and their potential dissolution. Effective grain boundary mobilities are introduced that are consistent with strong pinning at lower temperatures and weak pinning at higher temperatures separated by the estimated dissolution temperature range of fine NbC precipitates. These mobility relationships are then used to describe austenite grain growth in bulk samples subjected to rapid heating and cooling conditions to replicate thermal cycles at various positions in the HAZ.

Microstructure Evolution in Belt-Casted Strip of Grain Oriented Electrical Steel

2019 ◽  
Vol 810 ◽  
pp. 82-88 ◽  
Author(s):  
Vlastimil Vodárek ◽  
Carl Peter Reip ◽  
Anastasia Volodarskaja
Keyword(s):  
Grain Boundary ◽  
Grain Boundaries ◽  
Microstructure Evolution ◽  
Phase Field ◽  
Liquid Steel ◽  
Electrical Steel ◽  
Low Energy ◽  
Austenite Decomposition ◽  
Plate Martensite ◽  
Displacive Transformation

This paper deals with the formation and decomposition of Widmanstätten austenite during solidification of the thin belt-casted strip made of a grain oriented electrical steel (GOES). Solidification of liquid steel starts with the formation of d-ferrite. Cooling in the delta + gama phase field results in the formation of a small fraction of Widmanstätten austenite by displacive transformation accompanied by carbon partition. Widmanstätten austenite laths have an orientation relationship with the ferrite grain into which they grow. Furthermore, they form a flat low energy interface along the ferrite grain boundary. In order to minimize the interfacial energy, ferrite grain boundaries in the vicinity of flat austenite/ferrite interface facets are forced to migrate which results in straightening of these grain boundaries. If parallel Widmanstätten austenite laths form in two adjacent ferrite grains, zig–zag ferrite grain boundaries arise. Precipitation of sulphides along ferrite/austenite interfaces make it possible to study the early stages of austenite decomposition under the delta + gama phase field. It starts with the formation of epitaxial ferrite accompanied by further partitioning of carbon into remaining austenite. The growth of epitaxial ferrite into the flat ferrite/austenite interface facets along ferrite grain boundaries results in a wavy shape of these ferrite grain boundaries. Finally austenite transforms either to pearlite or to plate martensite.

Nonisothermal Austenite Grain Growth Kinetics in a Microalloyed X80 Linepipe Steel

2010 ◽  
Vol 41 (12) ◽  
pp. 3161-3172 ◽  
Author(s):  
Kumkum Banerjee ◽  
Matthias Militzer ◽  
Michel Perez ◽  
Xiang Wang
Keyword(s):  
Grain Growth ◽  
Growth Kinetics ◽  
Austenite Grain ◽  
Grain Growth Kinetics ◽  
Austenite Grain Growth ◽  
Linepipe Steel

Non-Isothermal Austenite Grain Growth Kinetics in the HAZ of a Microalloyed X-80 Linepipe Steel

2011 ◽  
Vol 172-174 ◽  
pp. 809-814 ◽  
Author(s):  
Kumkum Banerjee ◽  
Michel Perez ◽  
Matthias Militzer
Keyword(s):  
Grain Size ◽  
Heating Rate ◽  
Grain Growth ◽  
Growth Kinetics ◽  
Electron Microscopic ◽  
Austenite Grain Size ◽  
Austenite Grain ◽  
Grain Growth Kinetics ◽  
Austenite Grain Growth ◽  
Linepipe Steel

Non-isothermal austenite grain growth kinetics under the influence of several combinations of Nb, Ti and Mo containing complex precipitates has been studied in a microalloyed linepipe steel. The goal of these studies is the development of a grain growth model to predict the austenite grain size in the weld heat affected zone (HAZ). A detailed electron microscopic investigations of the as-received steel proved the presence of Ti-rich, Nb-rich and Mo-rich precipitates. Inter and intragranular precipitates of ~5-150 nm have been observed. The steel has been subjected to austenitizing heat treatments to selected peak temperatures of 950, 1150 and 1350°C at various heating rates of 10, 100 and 1000°C/s. Thermal cycles have been found to have a strong effect on the final austenite grain size. The increase in heating rate from 100 to 1000°C/s has a negligible difference in the austenite grain size irrespective of the austenitizing temperature. However, the increase in grain size has been noticed at 10°C/s heating rate for all the austenitizing temperatures. The austenite grain growth kinetics have been explained taking into account the austenite growth in the presence of precipitates.

Modeling austenite–ferrite transformation in low carbon steel using the cellular automaton method

2004 ◽  
Vol 19 (10) ◽  
pp. 2877-2886 ◽  
Author(s):  
Y.J. Lan ◽  
D.Z. Li ◽  
Y.Y. Li
Keyword(s):  
Carbon Steel ◽  
Cellular Automaton ◽  
Grain Boundaries ◽  
Grain Growth ◽  
Low Carbon Steel ◽  
Carbon Diffusion ◽  
Cellular Automaton Model ◽  
Low Carbon ◽  
Austenite Grain ◽  
Ferrite Transformation

Austenite–ferrite transformation at different isothermal temperatures in low carbon steel was investigated by a two-dimensional cellular automaton approach, which provides a simple solution for the difficult moving boundary problem that governs the ferrite grain growth. In this paper, a classical model for ferrite nucleation at austenite grain boundaries is adopted, and the kinetics of ferrite grain growth is numerically resolved by coupling carbon diffusion process in austenite and austenite–ferrite (γ–α) interface dynamics. The simulated morphology of ferrite grains shows that the γ–α interface is stable. In this cellular automaton model, the γ–α interface mobility and carbon diffusion rate at austenite grain boundaries are assumed to be higher than those in austenite grain interiors. This has influence on the morphology of ferrite grains. Finally, the modeled ferrite transformation kinetics at different isothermal temperatures is compared with the experiments in the literature and the grid size effects of simulated results are investigated by changing the cell length of cellular automaton model in a set of calculations.

Physical and Mathematical Modeling of Austenite Microstructure Evolution Processes Developing in Line-Pipe Steels under Hot Rolling

2012 ◽  
Vol 706-709 ◽  
pp. 2836-2841 ◽  
Author(s):  
Alexander A. Vasilyev ◽  
Andrey Rudskoy ◽  
Nicolay G. Kolbasnikov ◽  
Semen Sokolov ◽  
Dmitry F. Sokolov
Keyword(s):  
Experimental Data ◽  
Flow Stress ◽  
Grain Growth ◽  
Microstructure Evolution ◽  
Hot Rolling ◽  
Pipe Steels ◽  
Line Pipe ◽  
Austenite Grain ◽  
Austenite Grain Growth ◽  
Flow Stress Model

An experimental study (physical modeling) of the processes of austenite microstructure evolution occurring under hot rolling was performed for line-pipe steels with different chemical composition. All investigations were conducted with the help of the Gleeble 3800 system. Empirical quantitative models of austenite grain growth, static and dynamic recrystallization, as well as a flow stress model were developed. The effect of complex alloying by such elements as C; Mn; Si; Ni; Mo; Nb; Ti; and V on grain growth and recrystallization is accounted for under the condition that all elements are in a solid solution. The set of the models empirical parameters is determined utilizing corresponding experimental data available from literature. Modeling results for static recrystallization and flow stress in the investigated steels are compared with experimental data.

Austenite Grain Growth Kinetics during Continuous Heating of a Microalloyed X-80 Linepipe Steel

2012 ◽  
Vol 715-716 ◽  
pp. 292-296
Author(s):  
Kumkum Banerjee ◽  
Michel Perez ◽  
Matthias Militzer
Keyword(s):  
Grain Size ◽  
Heating Rate ◽  
Grain Growth ◽  
Growth Kinetics ◽  
Continuous Heating ◽  
Austenite Grain Size ◽  
Austenite Grain ◽  
Grain Growth Kinetics ◽  
Austenite Grain Growth ◽  
Linepipe Steel

Non-isothermal austenite grain growth kinetics has been studied in a microalloyed linepipe steel with complex precipitates containing Ti, Nb and/or Mo. The goal of these experimental studies is to provide the basis for the development of a grain growth model to predict the austenite grain size evolution in the weld heat affected zone (HAZ). Detailed electron microscopic investigations of the as received steel proved the presence of Ti-rich, Nb-rich and Mo-rich precipitates. The steel was subjected to austenitizing heat treatments to selected peak temperatures of 950, 1150 and 1350 °C at heating rates of 10, 100 and 1000 °C/s, respectively. Thermal cycles have been found to have a strong effect on the austenite grain size. Austenite grain sizes increase with peak temperature and decreasing heating rate. However, the increase in heating rate from 100 to 1000 °C/s has a negligible effect on the austenite grain size. The observed austenite grain growth kinetics can be explained taking into account the potential dissolution of Nb-rich precipitates.

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