Transcript Current Activities at CSIR-NML on Steel

Current Activities
at CSIR-NML
on Steel
Steel Research
Silt Erosion Resistant Steel for Turbine Hydrogenerator
High Strength High Formable Steels for Automobiles
Technology Development for CRGO Steels
API X80 Steel Development
Steels for Ultra Supercritical Boilers
Cementite Dissolution in Cold Drawn Pearlitic Steel
Low Temperature Sensitization & Intergranular Corrosion
Silt Erosion Resistant Material
for Turbine Hydrogenerator
Francis Turbine
New CSIR for New India
Damaged RUNNER
due to Silt
Shark Bite
Developed material to have :
 Corrosion resistance similar to 13%Cr4%Ni
 Good Castability
 Good Weldability
 Improved Impact toughness property for
resistance to cavitation erosion by silts
 Improved abrasion and erosion resistance
Two Phase (Martensite + Austenite) Cr-Ni-Mn-Cu-Mo
alloyed Steels developed for this application
Process Flow Chart
New CSIR for New India
Alloy Melting
(Vacuum Arc Melting of 40Kg)
Casting
Check homogeneity by chemical analysis and NDT (UT)
Characterization
Microstructural,
Mechanical property
(Optical, SEM, TEM)
(Tensile, Impact)
Heat Treatment at air atmosphere
Microstructural, mechanical property
Wear Study
(Solid particle Impingement, Cavitation)
Making of set up
Characterization after Wear
Scaling up to make prototype components
Structureproperty
correlation
 (222)
 (311)
' (211)
 (220)
'(200)
' (220)
 (222)
 (311)
 (220)
'(200)
' (211)
S8-400C
6.5
5 hrs of impingement
10
15
20 hrs
6.0
Wear rate(microgm/sec)
 (222)
 (311)
' (211)
 (220)
'(200)
 (200)
 (200)
S8-450C
 (200)
 (111)
' (110)
' (110)
 (111)
 (111)
' (110)
Intensity (a.u)
S8-500C
5.5
5.0
13Cr-4Ni
4.5
4.0
3.5
150 micro Alumina, Discharge-9.8,
150 m/sec,N.dia.-2.8 mm
3.0
10
20
30
40
50
60
70
Erosion Angle/deg
40
50
60
70
80
90
100
2 (degree)
developed alloy-2 aged at 400C
developed alloy-2 aged at 300C
16/5(Check Plate from actual
turbine runner)
Developed alloy-2 Homogenised
at 1100C
Developed alloy-2 aged at 350C
Wt. loss in (gm.)
0.10
0.05
2.24
Developed Alloy-2
2.22
Wear Rate(g/sec)
0.15
5 hr of impingement
10
15
20
2.20
2.18
2.16
2.14 150 m alumina powder,150 m/s,
Nozzle dia-2.8mm )
*
0
H.T at 600 C for
1 hr Water Quenched
2.12
2.10
26
0.00
0
5
10
15
Time in (hr.)
20
25
28
30
Erosion Angle(deg)
32
34
80
Properties
New CSIR for New India
Variation of tensile strength with
tempering temperature
Variation of Impact toughness
values with tempering temperature
300
Developed alloy-2 at 0C
Developed alloy-2 at RT
Developed alloy-1
Developed alloy-2
1200
250
1100
Impact Energy / J
Ultimate Tensile Strength / MPa
1300
1000
900
800
700
200
150
600
500
200
300
400
500
600
700
Temperature / C
13Cr-4Ni has tensile strength
of 1000 MPa
100
200
300
400
500
600
700
Tempering Temp. / C
13Cr-4Ni has impact toughness of 6080J at room temperature
Material is now undergoing field trial; components have been
fabricated and will be put in the plant for the coming monsoon
High Strength High Formable Steels
New CSIR for New India
Design steel chemistry and processing parameters in order to get

Yield Stress:
650 - 700 MPa

Tensile Stress:
900-1000 MPa

Uniform Elongation:
50% (Min.)

Optimization of
strength and formability

Optimum balance between strength, fracture toughness and corrosion
Gaps Areas
TWIP
Gap details
Single phase TWIP was developed
(UTS:700MPa; eu: 80%)
No commercial production (POSCO
and ARCELOR have their own grades)
TWIP being high strength has high springback
during processing
NML Work
Two phase (ferrite +
austenite)TWIP being developed
takes care of Springback
Two phase TWIP cold rolled up
to 90% at NML
Process Flow Chart
New CSIR for New India
Two Phase (Austenite + Ferrite) Mn-Cr-Alalloyed Steels developed for this application
Alloy Melting
(Vacuum Arc Melting of 40Kg)
Hot forging followed by hot rolling (normal air cooling)
Characterization
Microstructural,
Mechanical property
(Optical, SEM, TEM)
(Tensile, Impact)
Cold rolling (11 passes) up to 90% reduction in thickness
Microstructural Characterization
Annealing at air atmosphere of 90% cold rolled sheet
Microstructural,
(Optical, SEM, TEM)
Mechanical property
(Tensile)
High strain rate testing for crash resistance
& corrosion testing
Structureproperty
correlation
Process Flow Chart
New CSIR for New India
{211}a
{311}g
{220}g
{200}a
{110}a
{200}g
Only observed after 90% cold rolling
{111}g
Hot forged and hot rolled microstructure
 Necklace type structure: generally observed for
dynamically recrystallized grains
 Dynamic recrystallization is unlikely at room
temperature
 Chances of back transformation from ferrite to
austenite is probable
Sample Details
(YS)
(MPa)
(UTS)
(MPa)
(n-value)
Uniform
Elongati
on
750 0C – 30 min.
624
852
0.288
28
800 0C – 30 min.
634
888
0.297
30
900
strain rate = 2.5*10-4 s-1
1200
800
True Stress, MPa
Engineering stress, MPa
1000
700
600
500
750oC-30min
800oC-30min
400
300
200
100
800
Strain rate 0.1
600
strain rate 0.01
400
strain rate 0.001
0
0
1000
0.05
0.1
0.15
0.2
0.25
0.3
0.35
0.4
Engineering strain
Unlike in the literature, shows no serration in
the stress-strain plot at different strain rates
200
strain rate 0.0001
0
0
0.1
0.2
True Strain
0.3
Forming limit diagram (FLD) has been determined from the annealed
specimens along the rolling direction.
The FLD presented in
the graph shows
better forming
properties compared
to DP600
Cementite Dissolution in Cold
Drawn Pearlitic Steel
Drawing strain:0.12
Drawing strain:1.4
Alternate ferrite and cementite
lamella in pearlite
New CSIR for New India
Drawing strain:1.4
Equilibrium weight fraction
of cementite in pearlite:
12wt%
Quantitative XRD shows <
5wt% cementite at strain
1.4;
Conclusion: more than
50% cementite got
dissolved
cementite lamella
Fragmented cementite
buckling
lamella and its
dissolution
SEM micrograph
SEM micrograph
TEM micrograph
80k
Intensity (counts)
Quantitative X-ray diffraction
60k
Intensity (counts)
14k
110 F
12k
cementite
110 Ferrite
Iobs
10k
Icalc
8k
Diff.
6k
110
ferrite
35
40
45
50
Two-theta (degree)
40k
211 F
Drawing strain:1.4
200 F
20k
220 F
0
-20k
55
310 F 222 F
< 5 wt% cementite
40
60
80
100
Two-theta (degree)
120
140
Cementite Dissolution in Cold
Drawn Pearlitic Steel
New CSIR for New India
Role of ferrite dislocations in the dissolution
Traditional Williamson-Hall plot
Modified Williamson-Hall plot
(Ungar-Borbley )
0.09
0.075
310
222
0.06
0.050
nm 
211


nm 
220
200
110
0.025
0.000
2.0
As drawn(strain:0.12)
o
Heat treated(strain:0.12) 300 C
As drawn(strain:1.4)
o
Heat treated(strain:1.4) 300 C
4.0
-1
110
2
As drawn; Strain: 0.12; R = 0.976
As drawn; Strain:1.4
0.00
2
R = 0.995
2
heat treated (strain:0.12); R = 0.995
2
heat treated (strain:1.4); R =0.978
6.0
Non-monotonic increase of
FWHM with angle of diffraction
310
0.03
0
K (nm )
Key results
222
220
200
211
2
4
1/2
-1
KC (nm )
6
Confirmation: Strain anisotropy due
to dislocations in the ferrite matrix
Strain 0.12: 44%screw + 56%edge
Total avearge dislocation density: 6 x 1014/m2
Strain: 1.4: 60%screw + 40%edge
Total avearge dislocation density: 8 x 1015/m2
Note: ferrite lattice parameter
remains unchanged even after the
dissolution. Hence, screw
dislocations perhaps predominantly
pull the carbon atoms from the
cementite causing its dissolution.
CSIR-NML Tata Steel collaboration
Sensitization & Intergranular
Corrosion (IGC) of Stainless Steel
New CSIR for New India
Role of deformation, GBE, and welding on susceptibility to LTS, classical
sensitization, IGC, and IGSCC
Prediction of LTS for 100 years at 300oC and Time-temperature-sensitization
diagram
Deformation effects
Observations and
outcome
40
RS
% DOS
30
Weld
M
C
TS
CTS
450C/1300h
20
10




0
0
10
20
% Cold Rolling
Heat affected zone and base (304LN) are safe against IGC at 300oC for 100 years
operation
Weld zones are susceptible to failure due to phase separation and LTS
Deformation e.g. >2.5% reduction in thickness causes IGC in 304LN
30
500
0.028
450
0.093
0.01
0.06
400
HAZ
BASE
0.004
Temperature, deg C
Temperature, deg C
500
0.098
0.046
0.050
0.015
350
300
450
0.11
0.29
0.50
0.17
0.21
400
0.44
0.36
0.32
0.06
350
300
100
1000
10000
100000
Time, h
100
1000
10000
100000
Time, h
Note: TTS Base and HAZ line
separates ‘step’ from ‘dual’
microstructure; assigned values
are %DOS
Temperature, deg C
500
Weld
450
Note: TTS weld line separates
fissured and non fissured regions
400
350
300
100
1000
Time, h
10000
100000
Designing of bulk nanostructure/ultrafine austenitic stainless steel
Solution Annealed
Matrix
Cold
Deformation
Thermal Cycle
Recrystallisation
Cold
Deformation
Solution Annealed
Matrix
Isothermal
1400
Tensile Properties
304L SS
1200
Engineering Stress, MPa
Recrystallisation
Ultrafine Grained Stainless Steel
A novel Cyclic Strain Anneal process
for Bulk nano structure / ultra fine grain
1000
800
600
400
200
Increase in YS 3 to 4 times
0
0
2
4
6
8
10
12
14
Engineering Strain, %
Present methods
 Severe Plastic Deformation
 Accumulative Roll Bonding
 Repetitive Corrugation
Limitations ?
Pub: Metall. Mater. Trans. A, 40, 2009, 3227
Mater Sci & Eng A 528, 2011, 2209
16
18
Ultra fine / nano structure Austenitic Stainless Steel -Deformation mechanism
Concerns
Considère Criterion
(
σ
)ε  σ
ε
• Plastic instability
• Poor strain hardenability &
• Strain rate sensitivity
Bimodal grain size
1400
UFG II
1200
Change in deformation mechanism
UFG-I: Grain size
Below 500nm
•Strain localization
UFG-I
True Stress, MPa
1000
UFG-II: Bimodal
maxima at ~650nm and
~1400nm
800
600
400
200
0
0.0
0.1
0.2
% True Strain
0.3
0.4
• Strain induced
transformation of
austenite to martensite
Pub:Scripta Mater, 66,2012, 634
API X80 Steel Development
New CSIR for New India
through Thin Slab Casting and Rolling (TSCR) – In collaboration with Tata Steel
Targeted properties
 Yield strength : 600-660 Mpa; YS/UTS ratio : 0.85-0.88;  Elongation : 20-25%
 Fracture Appearance Transition : -50 to -70 oC  Charpy Energy (-20 oC): 150-250 J
Challenges
Coarse austenite grain size
► Limitation in temperature, strain and strain rate
► Criticality of composition selection (issues with Ti and Nb carbonitrides)
►
For API grade steel
CΕ  C 
Si Μn Cu Ni Cr Μο V





  5Β
30 20 20 60 20 15 10
Ti  V  Nb  0.15
Typical Process for API Grade Steel
New CSIR for New India
T OT AL  f (Df , Xe , d , Dppt , f ppt...)  gb  M(ss  D  ppt )1/ 2
2
2
2
Technology Development for
CRGO Electrical Steel Sheets
New CSIR for New India
International Status : Very Few producers of HI-B CRGOs, no Indian producer
Partnership : CSIR-Tata Steel-Ministry of Steel
(one of the largest PPP programmes ever)
Indian Demand : ~ 1000 million USD worth
Justification/ Need :
 It is not just developing another steel grade, but recreation of a jealously guarded technology
 Creation of a pilot scale integrated Flat Products
development & processing facility – the only one of
its kind in the country
Scale of operation: 3 – 5 Tonne per batch
Areas for Collaboration
New CSIR for New India
 ICME:
Processing-Structure-Property
Correlation
Models,
Development
of
databases
on
composition-processingmicrostructure-property correlation for steels
 Design and development of high strength
high formable steels for automotive
applications
 Design and development of pipeline steels.
 Development of steels for application in USC
boilers (30 MPa, 700oC Steam Conditions)
 Fundamental understanding of deformation
characteristics in steels