Gunnar Eriksson Symposium &

GTT-Technologies Annual Workshop and Users’ Meeting

Herzogenrath-Kohlscheid (Aachen, Germany)

12th July, 2012

Internal Oxidation and Nitridation of Hot Rolled

Steels - A Theoretical Study and its

Experimental Verification

Where we work…

Max-Planck-Institut

für Eisenforschung GmbH

Head: Prof. Dierk Raabe

Founded in 1917 from the “Kaiser Wilhelm Institute”

by Fritz Wüst.

3 Departments:

Computational Materials Design

Interface Chemistry and Surface Engineering

Microstructure Physics and Alloy Design

Outlook

– Motivation

– Theoretical Calculations

– Programme Algorithm and Possibilities

– Oxygen and Nitrogen Diffusion

– Some Examples

– HT-Corrosion in binary and ternary Alloys

– Important Modelling Effects

– Conclusion

Oxidation Processes in Steel Sheets

scale (mainly ‘FeO’)

Fisher’s Model of Diffusion

3

5

56

log3292.0

z

c

t

DDs GB

Whipple – Le Claire equation

3

5

56

log4704.0

z

c

t

DDs GB

Levine – MacCallum equation

I. Kaur “Fundamentals of … Boundary Diffusion” WILEY (1995)

Fine grained

C’ – regime B’ – regime A’ – regime

Coarse grained

C – regime B – regime A – regime

Grain Boundary Diffusion Regimes

Figure: Illustration of different diffusion regimes, depending on total diffusion time and ratio of DGB/D.

I. Kaur “Fundamentals of … Boundary Diffusion” WILEY (1995)

Some Published Works on HT-Corrosion

Programme Algorithm

0.00 0.25 0.50 0.75 1.00-40

-35

-30

-25

-20

-15

-10

Fe2O

3 (hematite) + Al

2O

3

Fe3O

4 + FeAl

2O

4

oxyg

en p

ress

ure

log(

p(O

2)

/ po)

mole fraction aluminium xAl

Fe + Al

Fe + Al2O

3

'FeO' + FeAl2O

4

Fe + FeAl2O

4

Fe3O

4 + Al

2O

3

Al2O

3 + FeAl

2O

4

700 °C

element migration chemical reaction

tx,iTx,i

tx,ic.D=

dt

dcdiv

ASTRID, published in Oxid. Met. 76 (2011) 247

Data Handling

Al - total

Al

Al-Oxide

Figure: Spatial phase distributions of Fe, 2 wt-% Al (4.05 mol-% Al) after oxidation

at p(O2) = 10-22 bar for 60 min at 700 °C.

Al

Al2O3

FeAl2O4

Oxide Stability

figures from FACTSage (left) and ww.doitpoms.ac.uk (right)

0 250 500 750 1000 1250 1500 1750 20001250

1000

750

500

250

0

3/2 Fe + O 2 = 1/2 Fe 3

O 4

2 Fe + O 2 = 2 FeO

4/3 Cr + O 2 = 2/3 Cr 2

O 3

2 Mn + O 2 = 2 MnO

Si + O 2 = SiO 2

Sta

nd

ard f

ree

ener

gy

of

form

atio

n o

f ox

ides

(-

Go =

-R

T l

n(p

O2

) /

kJ

mo

l-1

Temperature / °C

4/3 Al + O 2 = 2/3 Al 2

O 3

0 K

O2

-25

-20

-15

-10

-5

0

Ox

ygen

par

tial

pre

ssure

log

(pO

2

)

Figure: Calculated and experimentally determined Ellingham-Diagrams for the

Oxide Stability of Iron, Chromium, Manganese, Silicon and Aluminium.

Iron – Manganese – Chromium alloy

Figure: Spatial phase distribution in an Fe, 2 wt-% Mn, 0.8 wt-% Cr alloy after

oxidation at p(O2)= 3·10-22 bar and 700 °C for 120 min and ternary phase diagram.

published in Mater. Sci. Forum 969 (2011) p.76

Properties of Nitrogen

figures from Landoldt-Börnstein (right) and FACTSage (left)

Nitride Stability

0 250 500 750 1000 1250 1500 1750 2000750

500

250

0

-250

2 Cr2N + N2

= 4 CrN

8 Fe + N2 = 2 Fe4

N

4 Cr + N2 = 2 Cr2

N

8 Mn + N2 = 2 Mn4

N

3/2 Si + N 2 = 1/2 Si 3

N 4

Sta

ndar

d fr

ee e

nerg

y of

for

mat

ion

of n

itri

des

(-

Go =

-R

T ln

(pN

2

) / k

J m

ol-1

Temperature / °C

2 Al + N 2 = 2 AlN

0 K

N2

-15

-10

-5

0

5

Nit

roge

n pa

rtia

l pre

ssur

e lo

g(p

N2

)

Theoretical Principles

Figure: Lehrer-Diagram of iron nitrides according to literature (left) and calculated

with the programme FactSage (right).

http://www.ipsenusa.com (dl 12.10.2010)

Iron – Chromium – Carbon alloy

published in HTM J. Heat Treatm. Mat. 66 (2011) p.100

Figure: Spatial phase distribution in an Fe, 1 wt-% Cr, 0.1 wt-% C alloy after gas

nitriding at KN= 2.4 and 500 °C for 48 h and phase stability diagram.

-10

-5

0

5

0.00 0.25 0.50 0.75 1.0010

-9

10-7

10-5

10-3

10-1

101

CrN

Cr2N

Cr 3

C2

Cr 7

C3

K

N =

p0

.5

o p

NH

3

/p1

.5

H2

xCr

/ (xCr

+xC)

Cr 2

3C

6

Fe + C + Cr3C

2

Fe + Cr

+Cr23

C6

Fe + C + CrN

Fe4N + CrN + C

Fe2N + CrN + C

log

10(p

N2

) /

bar

Figure: Comparison of the carbide phase distribution in two SAE51xx type steels

after gaseous nitriding at KN = 1 000 (ptot= 1 atm) and 500 °C for 48 h.

Comparison of the SAE51xx steels

„Real“ Steels

Figure: Calculated phase distribution of an industrial steel alloy after oxidation at

p(O2) = 10-22 bar and a technical cooling programme.

Diffusion between different Phases

http://adsjapan.blogspot.com and http://www.gettyimages.com

Figures: Shibuya (渋谷) crossing in Tokyo with green and red pedestrian lights.

single phase

cDJ A LJ A

RTLc

c

RTL oc

cLLJ A

D

general description

Segregation

[1] Blavette et al. Microsc. Microanal. 13 (2007) 464

Figure: Numerical simulation of segregation (left) and 3D atom probe tomography

of segregated boron atoms along the grain boundary in a NiAl superalloy [1] (right).

t = 0

t

concentration

Binary Iron Alloys

Figure: SEM and EDX-images of four different binary iron alloys, oxidised at 700 °C

for 5 h in N2 / 2.5 % H2 / H2O (DP +8 °C). The red arrow marks the N signal position.

Fe, 1 wt-% Al Fe, 1 wt-% Cr

Fe, 1 wt-% Si Fe, 1 wt-% Mn

SEM measurements by E. Müller-Lorenz, MPIE

Cross Section

SEM measurement by E. Müller-Lorenz, MPIE

Al AlN Al2O3

FeAl2O4

Figure: Fe, 1wt-%Al, oxidised at 700 °C for 5 h in N2 / 2.5 vol-% H2 / H2O (DP +8 °C).

SEM-picture (left) and numerical simulation of the phase distribution (right).

Summary

• Reaction-Diffusion-Systems provide a powerful

method to describe High Temperature Processes

• FactSage and ChemApp proved to be a valuable

tool for making theoretical assumptions

• Good agreement with experimental values for

oxidation depth and oxide formation

• Deviations between theory and experiment can be

used to foster further research

Acknowledgements

Dirk and Alexandra Vogel,

Else-Marie Müller-Lorenz,

Monika Nellessen

Prof. H. Danninger

Vera G. Praig, Markus Holzweber,

Kurt Piplits

Dr. Paesold

Bernhard Linder, Klaus Rendl

Funding

www.free-desktop-backgrounds.net (dl 3.11.2011)