Download MARTENSITE TRANSFORMATION ON MECHANICAL PROPERTIES OF METASTABLE ... PDF

TitleMARTENSITE TRANSFORMATION ON MECHANICAL PROPERTIES OF METASTABLE ...
LanguageEnglish
File Size13.9 MB
Total Pages127
Document Text Contents
Page 1

TKK Dissertations 71
Espoo 2007

EFFECT OF STRAIN-INDUCED α’-MARTENSITE
TRANSFORMATION ON MECHANICAL PROPERTIES
OF METASTABLE AUSTENITIC STAINLESS STEELS
Doctoral Dissertation

Helsinki University of Technology
Department of Mechanical Engineering
Laboratory of Engineering Materials

Juho Talonen

Page 2

TKK Dissertations 71
Espoo 2007

EFFECT OF STRAIN-INDUCED α’-MARTENSITE
TRANSFORMATION ON MECHANICAL PROPERTIES
OF METASTABLE AUSTENITIC STAINLESS STEELS
Doctoral Dissertation

Juho Talonen

Dissertation for the degree of Doctor of Science in Technology to be presented with due permission
of the Department of Mechanical Engineering for public examination and debate in Auditorium
K216 at Helsinki University of Technology (Espoo, Finland) on the 1st of June, 2007, at 12 noon.

Helsinki University of Technology
Department of Mechanical Engineering
Laboratory of Engineering Materials

Teknillinen korkeakoulu
Konetekniikan osasto
Koneenrakennuksen materiaalitekniikan laboratorio

Page 63

62

4.3 Results of X-ray diffraction line broadening analysis

Integral breadths of the austenite 111 and 222, α’-martensite 110 and 220 and ε-
martensite 1110ε reflections of the EN 1.4318-1 steel tensile strained at 3×10-4 s-1 at
room temperature are plotted as a function of true plastic strain in Figure 26. Other
studied steels exhibited essentially similar characteristics, and the integral breadths are
not given here, but the further analysis of these results is presented in the following
sections.

0.0 0.1 0.2 0.3 0.4
0.0

0.2

0.4

0.6

0.8

1.0

1.2

1.4

β E
(

°)

True plastic strain

γ111
α'110
ε1011

(a)

0.0 0.1 0.2 0.3 0.4
0.0
0.2
0.4
0.6
0.8
1.0
1.2
1.4
1.6
1.8

(b)

β E
(

°)

True plastic strain

γ222
α'220


Figure 26 Integral breadths βE of the measured (a) austenite 111, α’-martensite 110 and ε-

martensite 1110 reflections and (b) austenite 222 and α’-martensite 220 reflections
in EN 1.4318-1 steel tensile strained at 3×10-4 s-1 at room temperature

Comparison between the integral breadths of the reflections of various phases reveals
interesting features: integral breadths of the austenite reflections increased with
increasing plastic strain, whereas the α’-martensite reflections were initially much
broader, and with increasing plastic strain the integral breadths remained relatively
unchanged. This indicates that the plastic deformation took place mostly in the austenite
phase. The only detected ε-martensite reflection 1110ε exhibited high integral breadth
compared to the austenite and α’-martensite reflections. Due to the low intensities,
accurate determination of the integral breadth of the 1110ε reflections was difficult.
However, it seems that the integral breadth did not significantly change with increasing
plastic strain.

Two approaches, viz., the integral breadth and the Voigt methods, were used to estimate
the microstrains, domain sizes and dislocation densities from the XRD line broadening
data. The results on the austenite phase are summarised in the following two sections.
The comparison of the results obtained by IBM and VM is presented in section 4.3.3.
The analysis of the XRD line broadening results on the α’-martensite phase are
presented in section 4.3.4.

4.3.1 Analysis of austenite phase by integral breadth method

The root mean square microstrains <ε2>1/2 and domain sizes 〈D〉 of the austenite phase
in the EN 1.4318-1, EN 1.4301 and EN 1.4318-2 steels determined by the integral
breadth method (equation 21) are plotted as a function of true plastic strain in Figures
27, 28 and 29, respectively.

Page 64

63

0.0 0.1 0.2 0.3 0.4
0.0

0.5

1.0

1.5

2.0


2 >

1/
2

(x
10

3 )

True plastic strain

3 x 10-4 s-1

10-1 s-1

200 s-1

(a)

0.0 0.1 0.2 0.3 0.4
0

50

100

150
3 x 10-4 s-1

10-1 s-1

200 s-1

<D
>

(n
m

)

True plastic strain

(b)


Figure 27 (a) Root mean square microstrain <ε2>1/2 and (b) domain size 〈D〉 of austenite
phase calculated by IBM as a function of true plastic strain in EN 1.4318-1 steel
tensile strained at strain rates 3×10-4, 10-1 and 200 s-1 at room temperature

0.0 0.1 0.2 0.3 0.4 0.5
0.0

0.5

1.0

1.5

2.0

(a)

3 x 10-4 s-1

10-1 s-1

200 s-1


2 >

1/
2

(x
10

3 )

True plastic strain
0.0 0.1 0.2 0.3 0.4 0.5

0

50

100

150

200

(b)

<D
>

(n
m

)

True plastic strain

3 x 10-4 s-1

10-1 s-1

200 s-1




Figure 28 (a) Root mean square microstrain <ε2>1/2 and (b) domain size 〈D〉 of austenite
phase calculated by IBM as a function of true plastic strain in EN 1.4301 steel
tensile strained at strain rates 3×10-4, 10-1 and 200 s-1 at room temperature

0.0 0.1 0.2 0.3 0.4 0.5 0.6
0

1

2

3


2 >

1/
2

(x
10

3 )

True plastic strain

-40°C
+40°C
+80°C

(a)


0.0 0.1 0.2 0.3 0.4 0.5 0.6
0

50

100

150

(b)

<D
>

(n
m

)

True plastic strain

-40°C
+40°C
+80°C


Figure 29 (a) Root mean square microstrain <ε2>1/2 and (b) domain size 〈D〉 of austenite

phase calculated by IBM as a function of true plastic strain in EN 1.4318-2 steel
tensile strained at strain rate 3×10-4 s-1 at temperatures -40, +40 and +80°C

Page 126

125

Williamson G.K. and Smallman, R.E. 1956. Dislocation Densities in Some Annealed
and Cold-Worked Metals from Measurements on the X-Ray Debye-Scherrer Spectrum.
Philosophical Magazine, 1 (1), pp. 34-46.

Zackay, V.F., Parker, E.R., Fahr, D. and Busch, R. 1967. The Enhancement of Ductility
in High-Strength Steels. Transactions of the ASM, 60 (2), pp. 252-259.

Page 127

ISBN 978-951-22-8779-6
ISBN 978-951-22-8780-2 (PDF)
ISSN 1795-2239
ISSN 1795-4584 (PDF)

Similer Documents