Brief descripion of what causes strain induced martensite in austenitic stainless steels.

1. Effect Of Cyclic Deformation Damage On
The Corrosion Rate Of Metastable
Austenitic Stainless Steels
Chayon Mondal
Roll no.: 16142006
M.Tech I (Alloy Technology)
Metallurgical Engineering
Indian Institute of Technology (Banaras Hindu University), Varanasi

2. Acknowledgement
Dr. Pravash C. Chakraborti
Professor, Dept. of Metallurgical and Material Engineering,
Jadavpur University, Kolkata
Dr. Amrita Kundu
Asst. Professor, Dept. of Metallurgical and Material Engineering,
Jadavpur University, Kolkata
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3. Overview
Introduction : AISI 304
Applications and complications
Metastability and martensite formation
Objectives of the Experiments
Experiments performed
Results and Conclusion
References
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4. Introduction : AISI 304
18/8 Cr/Ni Stainless Steel
Excellent corrosion resistance and weldability
Good mechanical properties
High work-hardening
Automotive body parts, pressure vessels, nuclear vessels,
cryogenic vessels, kitchen utensils, etc.
Table 1. Chemical Composition
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Cr% Ni% C% Fe%
18.15 7.88 0.08 74.27

5. Stress- and Strain-induced
martensite
• At Ms, pre-existing nucleation
sites without application of
stress
• Between Ms and Ms
σ, nucleation
with aid of stress
• Above Ms
σ, plastic straining
required
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Figure 1. Schematic representation of inter-relationships between stress-assisted
(below Ms
σ) and strain-induced (above Ms
σ) nucleation of α’ martensite in Fe-Ni-C
alloys. After results of Boiling and Richman (1953).

6. Metastable behaviour
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where, U’ is the mechanical
driving force for transformation
Figure 2. Schematic illustration of chemical free energies of
austenite and martensite phases as a function of temperature
(Wayman and Bhadeshia, 1996)
Metastable austenite (fcc) Strain-induced martensite (bcc)

7. Objective of the Experiments
 Effect of low cycle fatigue on metastable austenitic stainless steel
 Stored energy variation with increase in cyclic deformation
 Effect of deformation-induced martensite on the corrosion rate
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8. Experimental Procedure
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• Solution anneal
• Tensile test
• Sample design
• Fatigue test
• Martensite
quantification
• Corrosion tests
Table 2. Flowchart showing the various experimental steps

9. Low Cycle Fatigue
Specimen:
Total strain controlled fatigue
 εt =0.375%,0.50%
 Strain rate=5*10e-2
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Figure 4. Instron 8082 for performing low cycle fatigue
L/d=2.57
Figure 5. The fatigue test specimens used (before and after LCF)

10. Calculation of stored energy
-0.3 -0.2 -0.1 0.0 0.1 0.2 0.3 0.4 0.5
-200
0
200
400
Stress(MPa)
Total Strain
Stress
0.375 strain amplitude(1/4th life)
HYSTERESIS LOOP
Plastic Strain
Energy
Elastic Strain
Energy
Elastic
Strain energy
Total
Strain energy
Plastic
Strain energy
Figure 6. Schematic of a hysteresis loop during strain controlled cyclic deformation

11. Microstructural Evolution
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Martensite
Figure 7. Solution annealed at 1150ºC
Figure 8a. Half-life at 0.5% Strain amplitude Figure 8b. Full-life at 0.5% Strain amplitude
Figure 9a. Half-life at 0.375% Strain amplitude Figure 9b. Full-life at 0.375% Strain amplitude

12. Potentiodynamic Polarization
Test
Involve changing the
potential of the working
electrode
monitoring the current
produced as a function of
time or potential
Tests performed in 1N
H2SO4, 3.5% NaCl solution,
NACE solution
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Figure 10. Schematic of polarization curves

13. Results Of The Corrosion Tests
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0 5 10 15 20 25 30 35 40 45 50 55 60 650
100
200
300
400
CorrosionRate(mpy)
Martensite %
1N H2
SO4
0.375% Strain Amplitude
3.5% NaCl Solution
NACE Solution
0 5 10 15 20 25 30 35 40 45 50 55 60 65
0
50
100
150
200
250
300
350
400
450
500
550
600
650
700
750
CorrosionRate(mpy)
Martensite %
NACE Solution
3.5% NaCl Solution
1N H2
SO4
0.5% Strain Amplitude
(a) (b)

14. Conclusion
 With cyclic deformation induced, there is an increase in martensite
formation as we vary the life until fracture
 Increase in strain energy density with variation of life cycles which can be
associated with DIM formation
 Increase in martensite formation renders more corrosion susceptibility of
the steel which is confirmed by potentiodynamic testing
 Effect of strain amplitude on DIM formation is limited
 Work needs to carried out in future with other quantification methods like
X-ray diffraction, ferritoscope etc. to study its effect
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15. References
J. Talonen (2007) Effect of strain induced α’-martensite on mechanical
properties of metastable austenitic stainless steels. Doctoral dissertation,
Helsinki University of Technology
J. Talonen, H. Hanninen (2007) Formation of shear bands and strain-
induced martensite during plastic deformation of metastable austenitic
stainless steels. Acta Materialia 55 (2007) 6108–6118
P. Hedstrom (2007) Deformation and Martensitic Phase Transformation in
Stainless Steels. Doctoral Thesis, Lulea University of Technology
Olson, G.B., Cohen, M. (1972) A mechanism for the strain-induced
nucleation of martensitic transformations. Journal of the Less-Common
Metals, 28, 107-118
A. Das et al (2007) Analysis of deformation induced martensitic
transformation in stainless steels. Mat. Sci. Tech. Vol 27, 1, 366-370
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16. Thank You
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