Current Activities at CSIR-NML

on Steel

Silt Erosion Resistant Steel for Turbine Hydrogenerator

High Strength High Formable Steels for Automobiles

Steels for Ultra Supercritical Boilers

API X80 Steel Development

Stee

l Res

earc

h

Technology Development for CRGO Steels

Cementite Dissolution in Cold Drawn Pearlitic Steel

Low Temperature Sensitization & Intergranular Corrosion

Francis TurbineDamaged 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

for Turbine HydrogeneratorNew CSIR for New India Silt Erosion Resistant Material

New CSIR for New India Process Flow ChartAlloy Melting

(Vacuum Arc Melting of 40Kg)

CastingCheck homogeneity by chemical analysis and NDT (UT)

CharacterizationMicrostructural, Mechanical property

(Optical, SEM, TEM) (Tensile, Impact)

Heat Treatment at air atmosphereMicrostructural, mechanical property

Wear Study (Solid particle Impingement, Cavitation)

Making of set up

Characterization after Wear

Scaling up to make prototype components

Structure-property

correlation

Two

Pha

se (M

arte

nsite

+ A

uste

nite

) Cr-

Ni-M

n-C

u-M

o al

loye

d S

teel

s de

velo

ped

for t

his

appl

icat

ion

40 50 60 70 80 90 100

S8-400C

(1

11)

' (11

0)

' (2

11)

'(2

00)

(2

20)

(3

11)

(2

22)

(200

)

' (2

20)

S8-450C

(1

11)

' (11

0)

' (2

11)

'(2

00)

(2

20)

(3

11)

(2

22)

(2

00)

Inte

nsity

(a.u

)

2 (degree)

S8-500C

(11

1)'

(11

0)

' (2

11)

'(2

00)

(22

0)

(3

11)

(2

22)

(2

00)

10 20 30 40 50 60 70 80

3.0

3.5

4.0

4.5

5.0

5.5

6.0

6.5

150 micro Alumina, Discharge-9.8, 150 m/sec,N.dia.-2.8 mm

13Cr-4Ni

Wea

r rat

e(m

icro

gm/s

ec)

Erosion Angle/deg

5 hrs of impingement 10 15 20 hrs

0 5 10 15 20 25

0.00

0.05

0.10

0.15

Wt.

loss

in (g

m.)

Time in (hr.)

developed alloy-2 aged at 400C developed alloy-2 aged at 300C 16/5(Check Plate from actual

turbine runner) Developed alloy-2 Homogenised

at 1100C Developed alloy-2 aged at 350C

26 28 30 32 342.10

2.12

2.14

2.16

2.18

2.20

2.22

2.24

*H.T at 6000C for 1 hr Water Quenched

150 m alumina powder,150 m/s, Nozzle dia-2.8mm )

Developed Alloy-2

Wea

r Rat

e(

g/se

c)

Erosion Angle(deg)

5 hr of impingement 10 15 20

Variation of tensile strength with tempering temperature

13Cr-4Ni has tensile strength of 1000 MPa

200 300 400 500 600 700500

600

700

800

900

1000

1100

1200

1300

Ulti

mat

e Te

nsile

Str

engt

h /

MPa

Temperature / C

Developed alloy-1Developed alloy-2

200 300 400 500 600 700100

150

200

250

300

Impa

ct E

nerg

y / J

Tempering Temp. / C

Developed alloy-2 at 0C Developed alloy-2 at RT

13Cr-4Ni has impact toughness of 60-80J at room temperature

Variation of Impact toughness values with tempering temperature

Material is now undergoing field trial; components have been fabricated and will be put in the plant for the coming monsoon

New CSIR for New India Properties

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

Single phase TWIP was developed (UTS:700MPa; eu: 80%)

Two phase (ferrite + austenite)TWIP being developed takes care of Springback

Two phase TWIP cold rolled up to 90% at NML

Gap details NML Work

No commercial production (POSCO and ARCELOR have their own grades)

TWIP being high strength has high springback during processing

TWIP

New CSIR for New India High Strength High Formable Steels

New CSIR for New India Process Flow ChartTw

o P

hase

(Aus

teni

te +

Fer

rite)

Mn-

Cr-

Al-

allo

yed

Ste

els

deve

lope

d fo

r thi

s ap

plic

atio

n Alloy Melting

(Vacuum Arc Melting of 40Kg)

Hot forging followed by hot rolling (normal air cooling)

CharacterizationMicrostructural, 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, Mechanical property(Optical, SEM, TEM) (Tensile)

High strain rate testing for crash resistance & corrosion testing

Structure-property

correlation

Hot forged and hot rolled microstructure

{111

} g

{110

} a

{200

} g

{200

} a

{220

} g

{311

} g

{211

} aOnly observed after 90% cold rolling

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

New CSIR for New India Process Flow Chart

Sample Details (YS)(MPa)

(UTS)(MPa)

(n-value) Uniform Elongati

on750 0C – 30 min. 624 852 0.288 28800 0C – 30 min. 634 888 0.297 30

Unlike in the literature, shows no serration in the stress-strain plot at different strain rates

0 0.05 0.1 0.15 0.2 0.250

100200300400500600700800900

1000

Strain rate 0.1

strain rate 0.01

strain rate 0.001

strain rate 0.0001

True Strain

True

Stre

ss, M

Pa

0

100

200

300

400

500

600

700

800

900

1000

0 0.05 0.1 0.15 0.2 0.25 0.3 0.35 0.4

Engineering strain

Engi

neer

ing

stre

ss, M

Pa strain rate = 2.5*10-4 s-1

750oC-30min800oC-30min

The FLD presented in the graph shows better forming properties compared to DP600

Forming limit diagram (FLD) has been determined from the annealed specimens along the rolling direction.

40 60 80 100 120 140-20k

0

20k

40k

60k

80k

222 F220 F

310 F

211 F

200 F

110 F In

tens

ity (c

ount

s)

Two-theta (degree)

Iobs

Icalc

Diff.35 40 45 50 55

6k

8k

10k

12k

14k

110 ferrite

Inte

nsity

(cou

nts)

Two-theta (degree)

cementite 110 Ferrite

Drawing strain:1.4

< 5 wt% cementite

Quantitative X-ray diffraction

Equilibrium weight fraction of cementite in pearlite: 12wt%Quantitative XRD shows < 5wt% cementite at strain 1.4;Conclusion: more than 50% cementite got dissolved

Drawing strain:0.12 Drawing strain:1.4 Drawing strain:1.4

Fragmented cementite lamella and its dissolution

Alternate ferrite and cementite lamella in pearlite

cementite lamella buckling

SEM micrograph TEM micrographSEM micrograph

Drawn Pearlitic SteelNew CSIR for New India Cementite Dissolution in Cold

2.0 4.0 6.00.000

0.025

0.050

0.075

K (nm-1)

nm

As drawn(strain:0.12) Heat treated(strain:0.12) 300oC As drawn(strain:1.4) Heat treated(strain:1.4) 300oC

222

310

220

211200

110

0 2 4 6

0.00

0.03

0.06

0.09

As drawn; Strain: 0.12; R2 = 0.976As drawn; Strain:1.4 R2 = 0.995heat treated (strain:0.12); R2 = 0.995 heat treated (strain:1.4); R2 =0.978

222310

220

211200

110

KC1/2 (nm-1)

n

m

Role of ferrite dislocations in the dissolutionTraditional Williamson-Hall plot Modified Williamson-Hall plot

(Ungar-Borbley )

Confirmation: Strain anisotropy due to dislocations in the ferrite matrix

Non-monotonic increase of FWHM with angle of diffraction

Strain 0.12: 44%screw + 56%edge

Strain: 1.4: 60%screw + 40%edge

Total avearge dislocation density: 6 x 1014/m2

Total avearge dislocation density: 8 x 1015/m2

Key results 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

Drawn Pearlitic SteelNew CSIR for New India Cementite Dissolution in Cold

Role of deformation, GBE, and welding on susceptibility to LTS, classical sensitization, IGC, and IGSCCPrediction of LTS for 100 years at 300oC and Time-temperature-sensitization diagram

0

10

20

30

40

0 10 20 30% Cold Rolling

% D

OS

RS TS CTS

450C/1300h

MC

Deformation effectsObservations and outcome

Weld

Corrosion (IGC) of Stainless SteelNew CSIR for New India Sensitization & Intergranular

Heat affected zone and base (304LN) are safe against IGC at 300oC for 100 years operationWeld zones are susceptible to failure due to phase separation and LTSDeformation e.g. >2.5% reduction in thickness causes IGC in 304LN

300

350

400

450

500

100 1000 10000 100000

0.028

0.0930.01

0.004

0.06 0.098

0.050

0.046

0.015

Tem

pera

ture

, deg

C

Time, h

BASE

300

350

400

450

500

100 1000 10000 100000

0.290.500.17

0.11

0.21 0.36

0.32

0.44

0.06

Tem

pera

ture

, deg

C

Time, h

HAZ

300

350

400

450

500

100 1000 10000 100000

Tem

pera

ture

, deg

C

Time, h

Weld

Note: TTS weld line separates fissured and non fissured regions

Note: TTS Base and HAZ line separates ‘step’ from ‘dual’ microstructure; assigned values are %DOS

Designing of bulk nanostructure/ultrafine austenitic stainless steel

A novel Cyclic Strain Anneal processfor Bulk nano structure / ultra fine grain

Solution Annealed Matrix

Cold Deformation

Solution Annealed Matrix

Cold Deformation

Ultr

afine

Gra

ined

Sta

inle

ss S

teelRecrystallisation

Recrystallisation

Isothermal

Thermal Cycle

gs< 200 nm

Present methods Severe Plastic Deformation Accumulative Roll Bonding Repetitive Corrugation

Limitations ?

0 2 4 6 8 10 12 14 16 180

200

400

600

800

1000

1200

1400

Engi

neer

ing

Stre

ss, M

Pa

Engineering Strain, %

Tensile Properties 304L SS

Increase in YS 3 to 4 times

Pub: Metall. Mater. Trans. A, 40, 2009, 3227Mater Sci & Eng A 528, 2011, 2209

Considère Criterion

σε)εσ(

• Plastic instability• Poor strain hardenability &• Strain rate sensitivity

Ultra fine / nano structure Austenitic Stainless Steel -Deformation mechanism

UFG-I: Grain size Below 500nm

•Strain localization

UFG-II: Bimodal maxima at ~650nm and ~1400nm

• Strain induced transformation of austenite to martensite

Bimodal grain size Change in deformation mechanism

Concerns

0.0 0.1 0.2 0.3 0.40

200

400

600

800

1000

1200

1400

UFG-I

True

Stre

ss, M

Pa

% True Strain

UFG II

Pub:Scripta Mater, 66,2012, 634

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)

through Thin Slab Casting and Rolling (TSCR) – In collaboration with Tata Steel

5Β10V

15Μο

20Cr

60Ni

20Cu

20Μn

30SiCCΕ 15.0NbVTi

For API grade steel

New CSIR for New India API X80 Steel Development

2/12ppt

2D

2ssgbpptpptdefTOTAL )(M...)f,D,,X,D(f

New CSIR for New India Typical Process for API Grade Steel

International Status : Very Few producers of HI-B CRGOs, no Indian producer

Indian Demand : ~ 1000 million USD worth

Justification/ Need : It is not just developing another steel grade, but re-

creation 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

CRGO Electrical Steel SheetsNew CSIR for New India Technology Development for

Partnership : CSIR-Tata Steel-Ministry of Steel(one of the largest PPP programmes ever)

ICME: Processing-Structure-Property Correlation Models, Development of databases on composition-processing-microstructure-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

New CSIR for New India Areas for Collaboration