Development of computa/onal microstructure model

Transcription

1 Development of computa/onal microstructure model Aarne Pohjonen, PhD, Computa/onal materials science, Postdoctoral researcher, University of Oulu,

2 Prior work: Cooling model by Juha Pyykkönen I have implemented input files reading and interaction with user interface for Juha Pyykkönen s code, currently in use at SSAB User interface developed at VTT (Vesa Kyllönen)

3 Computa/onal model for microstructure evolu/on in hot rolling and subsequent cooling developed by A. Pohjonen

4 Coupled plas9city/heat concuc9on/microstructure model (Pohjonen) Simulate plas%c deforma%on in rolling process and subsequent cooling, which both will be coupled with microstructure model Simula/ons and literature knowledge to obtain parameters to model Differen8al equa8on solver (FEM): Plas8city, heat conduc8on. Solve the equa8ons for 8me t Output local stress, strain, strain gradient, temperature, etc. needed by microstructure model Microstructure model Calculate, for example: - Local grain size change - Local disloca/on density - Phase changes in cooling Increase /me, t = t + Δt Correc/on: Change parameters of the differen/al equa/ons according to microstructure model for next /mestep

5 Cooling model (Pohjonen) Set up ini/al values for physical quan//es ρ(x,t 0 ) c p (x,t 0 ) T(x,t 0 ) h(x,t 0 ) k(x,t 0 ) Increase /me t = t + Δt Differen/al equa/on solver Solve temperature distribu/on, T(x,t), from the non-linear heat conduc/on equa/on ρ(x,t)c p (x,t) T(x,t) [ k(x,t) T(x,t) ] = ρ(x,t)h(x,t) t Finite element solver implemented in FORTRAN 90 language Calculate physical quan//es for the next /mestep ρ(x,t + Δt) c p (x,t + Δt) h(x,t + Δt) k(x,t + Δt) Phase transforma/on model Calculate frac/ons of phases transformed during /mestep (ferrite, pearlite, bainite, martensite) Implemented in FORTRAN 90 language

6 Ready: Heat equa9on solver Model comparison to analy9cal result Time-dependent linear heat equa9on: ( Conduc/on of Heat in Solids, Carslaw, Jaeger, Oxford University Press) X: simula/on result, Lines: analy/cal solu/ons

7 Ready: Heat equa9on solver Solu/on: Model comparisons to analy9cal results Steady state case 1. Dirichlet boundary condi8ons 2. Heat transfer boundary condi8ons X: simula/on result, Lines: analy/cal solu/ons f(x)=1+x, k(x)=1+x/2 1. Dirichlet boundary condi8ons: T(0)=0, T(2)= Heat transfer boundary condi8ons: 2. Heat transfer 1. Dirichlet a=0, b = 2.0, T ext1 =0.0, T ext2 =3.0 h 1 = 10 = h 2

8 Ready: Phase transforma9on model Based on regression modelling, source: Computer assisted modelling of metallurgical aspects of hot deforma9on and transforma9on of steels (J. Herman, B. Thomas, U.Loaer ) Gives an es/mate, which can be further adjusted according to frac/onal CCT diagram The model can be adjusted exactly for given steels, provided experimental data is available (frac/onal CCT + Final frac/ons of phases transformed)

9 Phase transforma9on simula9on: TH25 simula/on vs. experimental Experimental values from EU report: Computer assisted modelling of metallurgical aspects of hot deforma9on and transforma9on of steels (Phase 2) ISBN (J-C. Herman, B. Donnay, A. Schmitz, U. Loaer, R. Grossterlinden)

10 Phase transforma9on simula9on:crm39 simula/on vs. experimental Experimental values from EU report: Computer assisted modelling of metallurgical aspects of hot deforma9on and transforma9on of steels (Phase 2) ISBN (J-C. Herman, B. Donnay, A. Schmitz, U. Loaer, R. Grossterlinden)

11 Phase transforma9on simula9on:th25 final phase frac/ons, simula/on vs. experimental Experimental values from EU report: Computer assisted modelling of metallurgical aspects of hot deforma9on and transforma9on of steels (Phase 2) ISBN (J-C. Herman, B. Donnay, A. Schmitz, U. Loaer, R. Grossterlinden)

12 Phase transforma9on simula9on:crm39 final phase frac/ons, simula/on vs experimental Experimental values from EU report: Computer assisted modelling of metallurgical aspects of hot deforma9on and transforma9on of steels (Phase 2) ISBN (J-C. Herman, B. Donnay, A. Schmitz, U. Loaer, R. Grossterlinden)

13 Heat conduc9on and phase transforma9on simula9on: - Simula/on seing Pulsed water flows W = 10 10sin 2πt l 1.5s m 2 s Calculate: 1. Time dependent temperature distribu/on 2. Phases transformed as func/on of /me - on surface - on ¼ thickness

14 Heat conduc9on and phase transforma9on simula9on: - Time dependent temperature distribu/on Pulsed water flows

15 Heat conduc9on and phase transforma9on simula9on: - Temperature at surface - Temperature at ¼ thickness - Frac/ons of ferrite and bainite formed on surface and on ¼ thickness

16 Experimental data required for the model A Experimental data required to run the model as fiqed to the original data: 1. Steel composi/on and austenite grain size 2. Final rolling temperature B Experimental data required to fit the model: 1. Frac/onal CCT diagram for linear cooling rates 2. Transforma/on kine/cs (transformed austenite as func/on of temperature//me) 3. Final phase frac/ons aler cooling to room temperature

17 Effec/ve ac/va/on energy of transforma/on start Nuclea/on and growth described by avrami eq.

18 Effect of altering composi/on to the effec/ve ac/va/on energy of transforma/on start Ferrite

19 Effect of altering composi/on to the effec/ve ac/va/on energy of transforma/on start Bainite

20 Effect of austenite deforma/on To the transforma/on start

21 Plas9city simula9ons FEM numerical simula/on with Abaqus CAE (A. Pohjonen, J. Ilmola, O. Leinonen) Gleeble physical simula/on (J. Uusitalo)

22 Effect of hot forming to phase transforma9on Microstructure evolu/on during and aler plas/c deforma/on - Anisotropic plas/city - Recrystalliza/on - Disloca/on substructures Effect on phase transforma/on during cooling

23 Addi9onal tools developed Graphical user interface for defining cooling path and calcula/ng phases formed Graphical user interface for es/ma/ng required water to cool steel strip to desired temperatures in cooling system (Joni Paananen Bachelor Thesis, supervised by A. Pohjonen)

24 Addi9onal tools developed: Graphical user interface for defining cooling path and calcula/ng phases formed T e m p e r a t u r e C Time (s)

25 Addi9onal tools developed: Graphical user interface for es/ma/ng required water to cool steel strip to desired temperatures in cooling system (Joni Paananen Bachelor Thesis, supervisesd by A. Pohjonen) T e m p e r a t u r e Distance (m) C

26 Phase transforma/on model Transforma9on start Scheil s addi/vity rule Kine9cs Avrami type func/on Frac/on transformed t i τ (T ) =1 i χ =1 exp( K(T)tn) n, a, b, c are parameters determined from Experimental CCT (inversion of CCT to TTT) τ (T ) determined from experimental CCT (inversion of CCT to TTT) K(T ) = exp a(t b) 2 c Umemoto 1983

27 Model fiaed to 960QC / deformed at 850 C simula/on vs. experiment

28 2d/3d coupled heat conduc/on / phase transforma/on simula/ons for any geometry (preliminary results) PT model coupled with Elmer FEM

29 Coupled plas9city/heat concuc9on/microstructure model (Pohjonen) Simulate plas%c deforma%on in rolling process and subsequent cooling, which both will be coupled with microstructure model Simula/ons and literature knowledge to obtain parameters to model Differen8al equa8on solver (FEM): Plas8city, heat conduc8on. Solve the equa8ons for 8me t Output local stress, strain, strain gradient, temperature, etc. needed by microstructure model Microstructure model Calculate, for example: - Local grain size change - Local disloca/on density - Phase changes in cooling Increase /me, t = t + Δt Correc/on: Change parameters of the differen/al equa/ons according to microstructure model for next /mestep