Performed numerous stress-strain elasticity tests along with impact test under controlled temperature and stress factors. then the corrosion properties were studied based on the microstructures and corrosion current graphs.

1. EFFECT​ ​OF
THERMO-MECHANICAL
PROCESSING​ ​ON​ ​CORROSION
IN​ ​STEEL
THIRD​ ​EVALUATION​ ​REPORT

2. Contents
INTRODUCTION:
CHARACTERIZATIONS:
EXPERIMENTS:
CHARACTERIZATIONS:
EXPERIMENTS
CHARACTERIZATIONS​ ​(CONTD.)
EXPERIMENTS​ ​(CONTD.)
WORK​ ​REMAINING:

3. INTRODUCTION:
Steels​ ​are​ ​the​ ​most​ ​widely​ ​used​ ​materials,​ ​possessing​ ​properties​ ​apt​ ​for​ ​their​ ​use​ ​as
structural​ ​materials,​ ​machine​ ​parts,​ ​automobile​ ​parts​ ​etc.​ ​What​ ​makes​ ​them​ ​even​ ​more
attractive​ ​is​ ​the​ ​fact​ ​that​ ​their​ ​properties​ ​can​ ​be​ ​manipulated​ ​by​ ​methods​ ​like​ ​alloying,
mechanical​ ​working​ ​and/or​ ​by​ ​providing​ ​appropriate​ ​heat​ ​treatments.​ ​One​ ​of​ ​the​ ​many
ways​ ​to​ ​fine​ ​tune​ ​steel’s​ ​mechanical​ ​properties​ ​is​ ​by​ ​Thermo-Mechanical​ ​Processing​ ​(TMP),
which​ ​is​ ​straining​ ​steel​ ​at​ ​elevated​ ​temperatures,​ ​usually​ ​above​ ​its​ ​recrystallization
temperature.
Most​ ​applications​ ​of​ ​steel​ ​expose​ ​it​ ​to​ ​the​ ​atmosphere​ ​or​ ​other​ ​severely​ ​corrosive
environments.​ ​Species​ ​like​ ​O​2​​ ​and​ ​CO​2​​ ​in​ ​air,​ ​Cl-​ ​ions​ ​in​ ​aqueous​ ​or​ ​acidic​ ​mediums,​ ​OH-​ ​ions
in​ ​basic​ ​mediums​ ​etc.​ ​damage​ ​steels​ ​physically,​ ​chemically​ ​and​ ​aesthetically.​ ​The​ ​situation
can​ ​become​ ​threatening​ ​if​ ​it​ ​leads​ ​to​ ​the​ ​compromise​ ​of​ ​their​ ​strength​ ​and​ ​ductility​ ​in
structural​ ​parts.​ ​Thus,​ ​it​ ​is​ ​required​ ​to​ ​study​ ​how​ ​processing​ ​of​ ​steels​ ​affects​ ​their
electrochemical​ ​behaviour​ ​which​ ​may​ ​enable​ ​us​ ​to​ ​tailor​ ​corrosion​ ​resistive​ ​steel
components.
This​ ​project​ ​deals​ ​with​ ​this​ ​very​ ​study​ ​of​ ​how​ ​electrochemical​ ​properties​ ​of​ ​the​ ​given​ ​steel
sample​ ​change​ ​with​ ​its​ ​TMP.​ ​Gleeble​ ​3800​ ​Thermo-Mechanical​ ​Simulator​ ​is​ ​used​ ​for​ ​the
purpose​ ​of​ ​physical​ ​simulation​ ​of​ ​steel,​ ​which​ ​in​ ​this​ ​case​ ​is​ ​hot​ ​compression.​ ​This​ ​is​ ​done​ ​at
two​ ​different​ ​regions,​ ​one​ ​above​ ​and​ ​one​ ​below​ ​the​ ​AC​3​​ ​temperature​ ​of​ ​the​ ​given​ ​steel
sample.​ ​This​ ​report​ ​is​ ​a​ ​compilation​ ​of​ ​results​ ​of​ ​all​ ​the​ ​characterizations​ ​and​ ​experiments
performed​ ​till​ ​date.
Following​ ​are​ ​the​ ​characterizations​ ​and​ ​experiments​ ​performed​ ​in​ ​this​ ​study:
CHARACTERIZATIONS:
a) Microstructural​ ​Analysis​ ​(Pre​ ​and​ ​Post​ ​TMP)
b) Optical​ ​Spectroscopy
c) Macro/Micro​ ​Vickers​ ​Hardness​ ​Measurement​ ​(Pre​ ​and​ ​Post​ ​TMP)
d) Dilatometry
EXPERIMENTS:
a) Thermo-Mechanical​ ​Processing
b) Tafel​ ​Extrapolation
c) Cyclic​ ​Polarization

4. CHARACTERIZATIONS:
a) Microstructural​ ​Analysis​ ​:​ ​As-given​ ​Sample
In​ ​accordance​ ​with​ ​the​ ​composition​ ​of​ ​the​ ​steel​ ​sample​ ​found​ ​using​ ​spectroscopy,​ ​the​ ​initial
micrograph​ ​can​ ​be​ ​concluded​ ​to​ ​contain​ ​Ferrite​ ​(bright​ ​region)​ ​and​ ​Pearlite​ ​(dark​ ​region).
b) Elemental​ ​Spectroscopy:
It​ ​can​ ​be​ ​concluded​ ​from​ ​the​ ​compositional​ ​analysis​ ​that​ ​the​ ​given​ ​steel​ ​sample​ ​is​ ​that​ ​of​ ​a
hypoeutectoid​ ​plain​ ​carbon​ ​steel​ ​​with​ ​negligible​ ​alloying​ ​elements.​ ​This​ ​composition​ ​makes
the​ ​sample​ ​fall​ ​in​ ​the​ ​category​ ​of​ ​commercial​ ​steel​ ​AISI-1035.
Note:​ ​The​ ​as-given​ ​sample​ ​micrograph​ ​does​ ​not​ ​conform​ ​very​ ​well​ ​with​ ​the​ ​microstructure
of​ ​hypoeutectoid​ ​steels​ ​as​ ​available​ ​in​ ​the​ ​literature.​ ​This​ ​may​ ​be​ ​because​ ​of​ ​any​ ​prior
unknown​ ​heat​ ​treatments​ ​given​ ​to​ ​the​ ​sample.​ ​Microstructure​ ​of​ ​annealed​ ​sample​ ​may
resemble​ ​more​ ​closely​ ​to​ ​that​ ​found​ ​in​ ​the​ ​literature.

5. c) Vickers​ ​Hardness​ ​Measurement:
The​ ​average​ ​hardness​ ​value​ ​was​ ​found​ ​to​ ​be​ ​​286​ ​±​ ​4​ ​HV​.
d) Dilatometry:
Dilatometry​ ​was​ ​performed​ ​using​ ​Gleeble​ ​3800​ ​from​ ​room​ ​temperature​ ​to​ ​950​ ​​o​
C.​ ​This
detects​ ​very​ ​minute​ ​changes​ ​in​ ​sample​ ​dimensions​ ​with​ ​the​ ​change​ ​in​ ​temperature.​ ​As​ ​steel
goes​ ​from​ ​room​ ​temperature​ ​to​ ​Ac​1​​ ​and​ ​beyond​ ​its​ ​Ac​3​,​ ​its​ ​crystal​ ​structure​ ​changes​ ​from
BCC​ ​to​ ​a​ ​mixture​ ​of​ ​BCC​ ​and​ ​FCC​ ​to​ ​completely​ ​FCC.​ ​This​ ​results​ ​in​ ​peaks​ ​in​ ​the​ ​curve​ ​which
can​ ​be​ ​identified​ ​as​ ​the​ ​appropriate​ ​critical​ ​temperatures.​ ​Peaks​ ​are​ ​also​ ​obtained​ ​while
cooling​ ​which​ ​can​ ​be​ ​identified​ ​as​ ​Ar​1​​ ​and​ ​Ar​3​,​ ​but​ ​are​ ​not​ ​relevant​ ​to​ ​this​ ​study.
EXPERIMENTS
a) Thermo-Mechanical​ ​Processing
This​ ​was​ ​performed​ ​using​ ​Gleeble​ ​3800​ ​Thermo-Mechanical​ ​Simulator​ ​at​ ​two​ ​different
regions​ ​of​ ​Fe-C​ ​phase​ ​diagram,​ ​namely​ ​Gamma​ ​and​ ​Alpha​ ​+​ ​Gamma​ ​for​ ​the​ ​given
hypoeutectoid​ ​steel​ ​sample.​ ​Using​ ​Dilatometry​ ​results,​ ​hot​ ​compression​ ​in​ ​Gamma​ ​region

6. was​ ​done​ ​at​ ​850​ ​​o​
C​ ​and​ ​in​ ​Alpha​ ​+​ ​Gamma​ ​Region​ ​at​ ​750​ ​​o​
C.​ ​Following​ ​parameters​ ​were
decided​ ​by​ ​appropriate​ ​literature​ ​survey:
● Deformation​ ​regions:​ ​1)​ ​Alpha​ ​+​ ​Gamma​ ​​ ​2)​ ​Gamma
● Strain​ ​Rate:​ ​1​ ​s​-1
● Strain:​ ​50%
● Holding​ ​times
● Heating/Cooling​ ​Rates
● Deformation​ ​followed​ ​by​ ​immediate​ ​quenching​ ​to​ ​RT.
1) Alpha​ ​+​ ​Gamma​ ​Region​ ​Sample:

7. 2) Gamma​ ​Region​ ​Sample:

9. CHARACTERIZATIONS​ ​(CONTD.)
Microstructures​ ​and​ ​Microhardness:​ ​Thermo-Mechanically​ ​Processed​ ​samples:
1) Alpha​ ​+​ ​Gamma​ ​Region​ ​Sample:
a)
b)
3​ ​different​ ​regions​ ​can​ ​be​ ​distinguished​ ​in​ ​the​ ​sample​ ​by​ ​Nital​ ​etching​ ​even​ ​at​ ​lower
magnifications.​ ​Martensitic​ ​lathes​ ​can​ ​be​ ​clearly​ ​seen​ ​covering​ ​majority​ ​of​ ​the​ ​area​ ​at

10. relatively​ ​higher​ ​magnification.​ ​The​ ​grain​ ​boundaries​ ​are​ ​contrasted​ ​by​ ​black​ ​regions,
with​ ​irregularly​ ​distributed​ ​white​ ​regions.​ ​Both​ ​these​ ​regions​ ​have​ ​average​ ​hardness
values​ ​significantly​ ​lower​ ​than​ ​that​ ​of​ ​the​ ​martensitic​ ​region​ ​but​ ​have​ ​comparable
hardness​ ​among​ ​themselves.​ ​Thus,​ ​phase​ ​composition​ ​of​ ​these​ ​two​ ​regions​ ​cannot​ ​be
established​ ​by​ ​optical​ ​micrographs​ ​and​ ​hardness​ ​values​ ​alone.​ ​They​ ​need​ ​to​ ​be​ ​studied
under​ ​a​ ​higher​ ​magnification​ ​using​ ​an​ ​SEM.
2) Gamma​ ​Region​ ​Sample:
a)

11. b)
The​ ​Gamma​ ​region​ ​sample​ ​microstructure​ ​was​ ​found​ ​to​ ​have​ ​2​ ​separate​ ​regions,​ ​one​ ​of
which​ ​could​ ​be​ ​easily​ ​identified​ ​as​ ​martensite​ ​due​ ​to​ ​the​ ​presence​ ​of​ ​characteristic
martensitic​ ​lathes.​ ​The​ ​other​ ​black​ ​region​ ​was​ ​found​ ​to​ ​have​ ​slightly​ ​lesser​ ​hardness​ ​than
the​ ​martensitic​ ​phase,​ ​yet​ ​nothing​ ​could​ ​be​ ​resolved​ ​visually​ ​by​ ​optical​ ​micrographs.
Observations​ ​from​ ​SEM​ ​micrographs​ ​are​ ​required.
EXPERIMENTS​ ​(CONTD.)
ELECTROCHEMICAL​ ​TESTS:
Two​ ​corrosion​ ​tests​ ​were​ ​performed​ ​on​ ​each​ ​sample,​ ​namely​ ​the​ ​Tafel​ ​Test​ ​and​ ​the​ ​Cyclic
Polarization​ ​test.​ ​A​ ​standard​ ​3​ ​electrode​ ​arrangement​ ​(figure​ ​below)​ ​was​ ​used​ ​in​ ​a​ ​glass
electrochemical​ ​cell​ ​for​ ​carrying​ ​out​ ​both​ ​type​ ​of​ ​tests.

12. Following​ ​are​ ​the​ ​specifications​ ​of​ ​the​ ​tests:
● Reference​ ​Electrode:​ ​Standard​ ​Calomel​ ​Electrode
● Counter​ ​Electrode:​ ​Platinum​ ​Mesh
● Electrolyte:​ ​3.5​ ​wt%​ ​NaCl
a) Tafel​ ​Extrapolation:

13. a)
b)

14. c)
Sample i​corr​​ ​(µA) E​corr​​ ​(millivolts) Corrosion​ ​Rate
(mpy)
As-Given 16.70 -495 27.33
Alpha​ ​+​ ​Gamma​ ​Region 8.49 -578 9.70
Gamma​ ​Region 29.00 -544 33.17
It​ ​was​ ​observed​ ​that​ ​the​ ​corrosion​ ​current​ ​density​ ​i​corr​​ ​increased​ ​as:​ ​Alpha​ ​+​ ​Gamma​ ​Region
sample​ ​<​ ​As-given​ ​sample​ ​<​ ​Gamma​ ​Region​ ​sample.​ ​Consequently,​ ​the​ ​corrosion​ ​rate​ ​also
increased​ ​in​ ​the​ ​same​ ​manner.

15. b) Cyclic​ ​Polarization:
a)

16. b)
c)
All​ ​three​ ​cyclic​ ​polarization​ ​curves​ ​indicate​ ​no​ ​passivation​ ​in​ ​any​ ​of​ ​the​ ​samples.​ ​This​ ​was
expected​ ​since​ ​the​ ​steel​ ​sample​ ​was​ ​plain-carbon​ ​and​ ​was​ ​devoid​ ​of​ ​any​ ​passive​ ​film
forming​ ​elements​ ​like​ ​Cr,​ ​Al​ ​etc.
WORK​ ​REMAINING:
The​ ​only​ ​characterization​ ​remaining​ ​to​ ​complete​ ​the​ ​scope​ ​of​ ​this​ ​study​ ​is​ ​SEM​ ​imaging​ ​of
processed​ ​samples​ ​in​ ​order​ ​to​ ​delineate​ ​the​ ​exact​ ​phases​ ​seen​ ​in​ ​the​ ​optical​ ​micrographs.
However,​ ​if​ ​time​ ​permits,​ ​XRD​ ​of​ ​the​ ​all​ ​samples​ ​will​ ​also​ ​be​ ​done​ ​in​ ​order​ ​to​ ​determine​ ​the
residual​ ​stresses​ ​present.​ ​This​ ​shall​ ​further​ ​provide​ ​a​ ​perspective​ ​on​ ​the​ ​obtained
electrochemical​ ​results.
Furthermore,​ ​what​ ​remains​ ​is​ ​to​ ​examine​ ​where​ ​the​ ​results​ ​of​ ​this​ ​study​ ​stand​ ​with​ ​respect
to​ ​the​ ​previous​ ​work​ ​done​ ​in​ ​this​ ​area.​ ​Also,​ ​conclusions​ ​are​ ​needed​ ​to​ ​be​ ​drawn​ ​about​ ​the
results​ ​obtained​ ​with​ ​appropriate​ ​explanation​ ​of​ ​each.​ ​Finally,​ ​all​ ​this​ ​is​ ​needed​ ​to​ ​be
compiled​ ​in​ ​the​ ​form​ ​of​ ​a​ ​Bachelor’s​ ​Thesis.