Complete Calculation of Steel Microstructure for Strong Alloys

J. Chen, H. K. D. H. Bhadeshia, University of Cambridge

S. Hasler, H. Roelofs, U. Ulrau, Swiss Steel AG

Outline of presentation

• Introduction

• Mechanism of the program

• Predictions

• Conclusions

Introduction

Metallographic microstructuresMetallurgical analysis

Chemical compositionHeat treatment

Initial design Modelling

Alloy Design Cycle

Modelling

Mechanism of the program

C, Si, Mn, Ni, Mo, Cr, VAustenite grain size

Heat treatment method

Calculate various driving forces

Calculate nucleation rates and growth rates of individual phases

Call subroutine that calculatestransformation kinetics

Print out microstructures

INPUTS

OUTPUTS

PROGRAM

INPUT

Avrami Method

€

ΔOi = 1−Oii

∑Ototal

⎛

⎝ ⎜ ⎜

⎞

⎠ ⎟ ⎟ΔOi

e

€

ΔOe

Time = t Time = t + Δt

parallel plane

grain boundary€

Oi, j

€

Δd

€

Vi = Oi, j × Δd∑

I+1

I

Time

I+2

Growth Mechanism: Allotrimorphic ferrite, Widmanstätten ferrite, Pearlite

sub-unit

sheaf

t1

t2

t3

t4

time

The physical metallurgy of bainite kinetics (Bhadeshia, Proc. R. Soc. Lond. A, 2004, 460, 1707-1722)

• Bainite

Growth Mechanism

time

€

−

€

=Nucleation interval Δti+n

i

Incubation time Δ = f(T,ΔGm)

function of temperature and maximum Gibbs energy of forming nucleus

€

TIME LOOP {

IF Δt ≥ Δτ( ) THEN

α B GROW

ENDIF

}

I+1 Grain boundaryNucleation time

I

time

I

I+11

1

uS

ul

Grain boundaryNucleation time

Predictions

Bhadeshia, H. K. D. H. 1982 Bainite: overall transformation kinetics.J. Phys. Paris C 43 (Colloq. C4), 443-448.

C Si Mn Ni Mo Cr V GS

0.44 1.74 0.67 1.85 0.83 0.39 0.09 86 µm

Carbon Steel 1566 - C 0.64, Mn 1.13

Atlas of isothermal transformation and cooling transformation diagrams.American society for metals. 1977

620 oC

600 oC

570 oC

390 oC

380 oC

Conclusions

• Complete information of microstructure

• Diverse calculations (cc,iso,TTT,CCT..)

• Reasonable accuracy

• Transferable to other applications

Gracias !