Quality Assessment of Mechanical and Metallurgical Properties of Modified 9Cr-1Mo Steel-Indigenously Developed Electrodes for PFBR Project

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IWA 040
Quality Assessment of Mechanical and Metallurgical
Properties of Modified 9Cr-1Mo Steel-Indigenously
Developed Electrodes for PFBR Project
K. Shanmugam*, Shaju K. Albert#
, V. Ramasubbu#
and A. K. Bhaduri#
*Quality Assurance Division #
Metallurgy & Materials Group
Indira Gandhi Centre for Atomic Research
Kalpakkam – 603 102, India
(E-mail: ksm@igcar.ernet.in)
Abstract
Modified 9Cr-1Mo steel is used in prototype fast breeder reactor (PFBR) Project
for the manufacture of once through steam generator (SG). Most of the welding in
SG is carried out by Shielded Metal Arc Welding (SMAW) process and hence
require matching Modified 9Cr-1Mo Steel basic coated (E 9016-B9) electrode with
modified requirements compared to AWS SFA 5.5. In order to manufacture of
these electrodes number of trials were carried out and developed modified 9Cr-
1Mo steel electrodes indigenously and tested to meet the PFBR specification. In
this paper details of various inspection and tests such as weld deposit chemical
analysis, all weld tensile test at ambient and high temperature 798K (525°C),
Charpy V notch impact test at 293K (20°C), drop weight test, hardness test, fillet
weld test etc and their results discussed. Also the requirements of SFA 5.5 and
PFBR specification are discussed in detail.
KEY WORDS
Modified 9Cr-1Mo Electrodes, Destruction tests, Nil ductility transition
temperature, Indigenous development, Test results
1.0 INTRODUCTION
PFBR is a sodium cooled pool type fast breeder reactor. The heat generated inside
the reactor core is removed by circulation of sodium called primary sodium through
the core. The primary sodium then transfers its heat to the secondary sodium in the
intermediate heat exchanger. Secondary sodium is non-radioactive and heating
water/steam in the once through steam generator (SG) to raise steam for running the
turbo generator. SG is a vertical shell and tube type heat exchanger and fabricated
from modified 9Cr-1Mo steel plate (P 91). The modified 9Cr-1Mo steel has good high
temperature mechanical properties, good weldability, good creep property, resistance
to loss of carbon to liquid sodium, resistance to stress corrosion cracking and
compatible with sodium, water and steam. The technical specification for both
structural material and welding consumable are arrived at to meet the demand of

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high quality with superior mechanical and metallurgical properties for high
temperature service condition. The existing products readily available to
ASME/ASTM specifications or other national standards could not be utilized in view
of the modified/supplementary requirements. Modified 9Cr-1Mo steel plate and its
welding consumable are developed indigenously to meet the special requirements
particularly to get controlled mechanical properties without wide scatter, to improve
weldability and higher degree of cleanliness of steel.
2.0 Necessity for Development of Electrode
To achieve specified requirements of AWS SFA 5.5 with modified requirements for
electrodes and non-availability of modified 9Cr-1Mo steel material of different shapes
and size in the current manufacturing practice of leading steel and electrode
manufacturers, necessitated development of raw material with steel manufacturer
and electrodes with electrode manufacturer. Two manufacturers were identified for
the supply of modified 9Cr-1Mo steel electrodes. Many number of trials were carried
out by the firm, finalized parameter to get the desired chemical and mechanical
properties and defect free weld. The comparison of test requirements of SFA 5.5 and
PFBR specifications of modified 9Cr-1Mo steel electrodes are given in Table 1.
Table 1. Comparison of tests for SFA 5.5 and PFBR modified 9Cr-1Mo
welding electrode
Sl.
No
Description of
Requirement
ASME Section II C SFA 5.5 PFBR Requirement
1.0 Core wire chemical
composition NS
core wire shall have matching
composition
2.0 Flux coating type Low hydrogen potassium Same as SFA 5.5
3.0 Moisture content limits
electrode covering
0.15% by weight max. Same as SFA 5.5
4.0 Dimensional
inspection of electrode Required Required
5.0 Weld test pad
requirements
Welded in flat (1G) position
for chemical & mechanical
test
Welded in flat (1G) & over head (4G)
position for Chemical & mechanical
and other test
6.0 Radio graphic
examination
Yes, as per SFA 5.5 Yes, as per class 1 requirements
7.0 Chemical analysis Yes as per Modified with restricted composition
as per PFBR requirement
8.0 Tension test at room
temperature
Yes, 1 No. Yes, 2 Nos.
9.0 Tension test at 525°C NS Yes, 2 Specimens
10.0 Impact test at 20°C NS Yes, 3 Specimens
11.0 TNDT NS As per ASTM E 208
12.0 RTNDT NS as per ASME section III class I
13.0 Fillet weld test Vertical & overhead Same as SFA 5.5
14.0 Hardness test NS Vickers hardness test after PWHT
NS - not specified, FI - for information

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Fig. 1 Edge preparation detail for 1G
and 4G position
All dimensions
are in mm
20°
20
276
500
Backing strip
Modi. 9Cr-1Mo
6
16
6
125
Modi.9Cr-1Mosteel
3.0 Qualification of Electrodes
Based on the results of successful initial
trials, modified 9Cr-1Mo steel basic
coated welding electrode of size (3.15
dia. x 350) mm long was developed and
manufactured by vendor and subjected
to all the tests as per PFBR
specification.
3.1 Preparation of Weld Test Pads
Modified 9Cr-1Mo steel plates of sizes
500 x 125 x 20mm and 500 x 125 x
13mm were edge prepared with 10°
taper on each plate. Test pads of size
(500 x 276 x 20)mm in 3 numbers for
1G (flat) position and test pads of size
(500 x 276 x 13)mm 2 numbers for 4G
(over head) position were assembled
with 20° included angle, 16mm root gap
and 6mm thick modified 9Cr-1Mo steel
backing strip as shown in Fig. 1.
Restraints were provided to the weld
pads to avoid distortion during welding.
In addition two numbers of weld pads
were prepared for chemical analysis as
per AWS SFA 5.5 specification.
3.2 Execution of Test Pads
Five pockets of electrode were
randomly taken out from the IGCAR
lot. Two electrodes from each
pocket were inspected for their core
wire size and coating and
adherence of coating. The same
pocket electrodes were used for
execution of test weld pads. All the
test pads were preheated to 250°
C
and welded by a qualified welder
using modified E 9016-B9
indigenously developed electrodes
by shielded metal arc welding
(SMAW) process. Inter-pass temperature was maintained at 200-250°
C. Immediately
after completion of the welding post heating was carried out at 300°C for 2h. LPE was
carried out after post heating. All the weld pads were welded with average heat input
Fig. 2 Schematic diagram of weld sequence

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of less than 1kJ/mm. The weld parameters including number of layer/bead, average
current, volt and heat input for each test pads are given in Table 2.
Table 2. Welding Parameter & Heat Input Detail
Sl N0. Layer/ bead Current
Amps
Voltage
V
Speed
mm/s
Heat input
J/mm
Weld pad No. 513036-1 1G Position
1 1/1-3 103.3 23.3 2.3 1046.5
2 2/4-6 105 23.3 1.94 1261
3 3/7-10 104.75 23.75 2.85 872.9
4 4/11-14 104.75 23.25 2.67 912.1
5 5/15-18 105 23.75 2.49 1001.5
6 6/19-22 104.75 23.25 2.63 946.2
7 7/23-26 105 23.25 2.58 956
8 8/27-31 105 23.4 2.57 990.275
1 1/1-3 95 24 2.24 1017.9
2 2/4-6 94.7 23.3 2.63 838.98
3 3/7-9 94.75 23.5 3.14 709.12
4 4/10-13 95 23.75 2.90 778
5 5/14-17 95 23.75 2.54 888.3
6 6/18-21 95 23.75 2.61 864.5
7 7/22-25 95 23.5 2.47 903.8
8 8/26-29 95 23.5 2.48 900.2
9 9/30-35 95.2 23.8 2.8 809.2
1 1/1-3 95 23.3 2.26 984.1
2 2/4-6 94.7 24 2.35 974.33
3 3/7-9 95 23.3 2.10 1060.33
4 4/10-13 94.25 23.75 2.9 788.25
5 5/14-17 94.75 23.75 2.8 806
6 6/18-21 95 25.25 2.74 878
7 7/22-25 95.25 24.5 2.51 930
8 8/26-29 94.5 23 2.53 860.95
9 9/30-34 94.8 24.4 2.24 1053.6
1 1/1-4 80 21.75 2.4 729.75
2 2/5-8 80 21.5 2.02 865
3 3/9-12 80 21.75 2.10 832.25
4 4/13-16 81.25 21.5 1.88 930.25
5 5/17-20 85 22 2.15 873.25
6 6/21-25 85 22.4 2.19 872.4
1 1/1-4 81.25 21.5 2.06 848.25
2 2//-8 81.75 22.25 2.10 864.75
3 3/9-12 80 22.25 2.18 824.5
4 4/13-16 81.5 22.25 2.52 735.5
5 5/17-20 81.75 22 2.09 860
6 6/21-24 82.5 21.25 2.34 785.25
Test pads of 1 to 3 were welded in 1G position with 20mm thick plates and the test
pad number 4 & 5 were welded in 4G position with 13mm thick plate. The schematic
diagram of weld bead sequence for weld pad No. 513036-3 in 1G position is given in

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Fig. 2. During deposition of weld pad, the detachability of slag was visually inspected
and found slags are easily removable.
3.3 Radiographic Examination
All the five weld pads after machining and removal of backing plate were subjected to
x-ray examination and evaluation as per PFBR class I component requirements and
were found meeting the acceptance criteria. Test pads were subsequently cut and
specimens were prepared for testing. The specimens required for various tests were
prepared and tested as per standard.
3.4 Chemical Analysis
The samples prepared for chemical analysis were subjected to analysis and the
achieved values are satisfactory to the PFBR specification. The details of elements,
specific range of values for AWS/SFA 5.5 electrodes of E 9016-B9, PFBR
specification requirements for electrodes and plates and actual values of chemical
composition of core wire and weld deposits of electrode are given in Table 3.
3.5 Testing and their Results
Two numbers of all weld tension test specimens for room temperature test, 2 Nos. for
high temperature tension test and all other test specimens from IG & 4G position
weld pads were prepared as per standard ANSI/AWS B4 (mechanical test for welds
and tested using calibrated testing equipments. The test results discussed in the
following.
Table 3. Percentage of chemical composition required and achieved
Elements
Wt %
Electrode Specification Actual value achieved
in
Modi. 9Cr-1Mo
Steel plate
specification
AWS SFA 5.5 PFBR Core wire weld metal
C 0.08 – 0.13 0.08 – 0.12 0.0135 0.086 0.08-0.12
Cr 8.0 – 10.5 8.0 – 9.5 8.56 8.69 8.0-9.5
Mo 0.85 – 1.20 0.85 – 1.05 1.0 0.99 0.85-1.05
Mn 1.25 (max) 0.5 – 1.20 0.45 0.65 0.3-0.6
Ni 1.0 (max) 0.4 – 1.0 0.74 0.73 0.04(max)
Mn + Ni NS ≤ 1.5 1.19 1.38 NS
Si 0.3 (max) 0.15 – 0.30 0.19 0.24 0.2-0.5
P 0.01 (max) 0.01 (max) 0.007 0.0076 0.02(max)
S 0.01 (max) 0.01 (max) 0.0052 0.0062 0.01(max)
Nb 0.02 – 0.10 0.04 – 0.07 0.095 0.066 0.06-0.01
V 0.05 – 0.30 0.15 – 0.22 0.22 0.16 0.18-0.25
N 0.02 – 0.07 0.03 – 0.07 0.0433 0.058 0.03-0.07
Cu 0.25 (max) 0.25 (max) -------- 0.03 NS
Al 0.04 (max) 0.04 (max) 0.0024 < 0.005 0.04(max)
Iron Balance Balance Balance Balance Balance
NS – not specified

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3.5.1. All Weld Tensile Test at Room Temperature
2 numbers of each all weld tensile test specimens were prepared from 1G and 4G
position test weld pads. The tensile specimens were tested at room temperature and
all the 4 results are much higher than PFBR minimum requirement. The details of the
test results and specified values are given in Table 4.
Table 4. Room temperature tensile test results and requirement as per AWS
SFA 5.5 and PFBR specification
Position
Description of Tests
Specification Result
AWS SFA 5.5 PFBR Test I Test II
1G
All weld
tensile test at
Room
Temperature
YS MPa 530 (min) 415 (min) 674.1 664.5
UTS MPa 620 (min) 585 (min) 774.4 766.8
L = 5D % EL 17 (min) 16 (min) 18.1 18.6
% RA NS FI 61 91.8
4G
All weld
tensile test at
Room
Temperature
YS MPa NR 415 676.6 670.0
UTS MPa NR 585 787.9 787.9
L = 5D % EL NR 16 18.3 16.1
% RA NR FI 61.6 61.6
NS - not specified, NR- not required, FI - for information
3.5.2 All weld tensile test at high temperature
2 Nos. of all weld tensile test specimen from 1G test pad and another 2 Nos. of all
weld tensile specimens prepared from 4G position was tested at 798K (525°C) as
per ASTM E21. The details of test results for 1G and 4G position are well above the
minimum specified value are given in Table 5.
Table 5. High temperature tensile test results and requirement as per AWS SFA
5.5 and PFBR specification
Position
AWS SFA 5.5 PFBR Test I Test II
1G
All weld
tensile test at
798K (525°C)
YS MPa NS 313 (min) 501.1 495.8
UTS MPa NS FI 543.1 534.0
L = 5D % EL NS FI 14.6 17.1
% RA NS FI 64.4 69.6
4G All weld
tensile test at
798K (525°C)
YS MPa NR 313 (min) 483.4 485.0
UTS MPa NR FI 525.4 525.0
L = 5D % EL NR FI 17.9 17.2
% RA NR FI 72.2 69.4
NS-not specified, NR-not required, FI-for information
3.5.3. Impact test
Charpy V-notch (CVN) of impact test specimens of size 10 x 10 x 55 mm as per
ASTM E 23 were prepared from in 1G and 4G position test pads. 5 numbers from 1G
and 5 numbers from 4G were tested at 293K (20°
C). Of the 5 specimen tested
values, the lowest and the highest values (under line values) were not considered as

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per the SFA 5.5 and the average of three values of other specimens are taken for
acceptance. The obtained average values of 59.7J in 1G position and 73.6J in 4G
position are satisfactory to the minimum requirement of 45J average on three
specimens. The actual tested values are given in Table 6.
Table 6. Impact test values obtained in 1G and 4G position
Position
AWS SFA
5.5
PFBR Test Average
of 3
1G Charpy ‘V’ notch impact
test at 293K (20°C)
NS Average
45J (min)
54.2, 59.7, 73.2,
59.7, 59.7
59.7
4G Charpy ‘V’ notch impact
test at 293K (20°C)
NR NR 75.9, 73.2, 58.3,
74.5, 73.2
73.6
NS – not specified, NR – not required
3.5.4 Nil Ductility Transition Temperature (TNDT) by Drop weight test
The nil ductility transition temperature (TNDT) is defined as the higher temperature at
which a test piece with a very small crack and loaded under stress close to yield
strength can exhibit a brittle fracture under an impact. Above this temperature, the
crack can’t extend but for a stress higher than the yield strength and this involves
plastic flaw, which increases with temperature rise. The TNDT is determined by drop
weight test.10 numbers of drop weight test specimens were prepared as per ASTM E
208-P2 type of 130 x 50 x 19mm from 1G position test pad. The single pass stinger
bead crack starter weld was made using BOR-C electrode. To avoid grain growth
due to high heat input specimens were provided under heat sink. Copper template
was provided during crack starter welding to eliminate spatter. The crack starter bead
was made in transverse direction to the welding direction as per the fig 3a and notch
was machined as per Fig. 3b & 3c. The tests were conducted at temperatures -20, -
15, -10, -5 and 0°
C and the test results are given in Table 7. The established nil
ductility transition temperature (TNDT) by drop weight test is °-5°
C.
Table 7. Drop weight test result
Test
Temp.
°
C
Specimen
No.
Observation of cracking
behavior
Break/
No break
TNDT
Remarks
0 513036-3-2 Crack entered base metal to
both sides then arrested No-break
-5
°
C
ASTM E 208 is
silent about
opening of an
internal crack
however, for a
conservative
estimation of TNDT,
these cases has
been considered
as break
conditions
* Two pass weld
0 513036-3-6 -Do- No-break
-5 513036-3-4 -Do- No-break
-5 513036-1-1 Crack opened internally one
side
Break
-10 513036-3-3 Crack entered inside base
metal to both sides, then
arrested
No-break
-10 513036-3-8 Crack opened to one side Break
-15 513036-3-5 Cracks opened to both sides Break
-20 513036-3-7 Crack opened internally to
one side*
Break

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Three number of standard size charpy V-notch impact test specimens were carried
out at 28°
C. All three obtained impact energy values are 76, 69 & 77.3J and the later
expansion are 0.95, 0.91 & 0.84mm. Though the impact energy values are higher
than the minimum requirement of 68J but one of the specimen’s lateral expansion is
lower than the requirement of 0.89mm, hence TNDT is not equal to RTNDT. To
establish exact RTNDT, further 4 more samples were tested at 30°
C. The obtained
energy values and lateral expansions are more than of the required. The average
values obtained are 78.25J and 1.0075 mm the lateral expansion, hence, the RTNDT
is -3°
C (30 - 33°
C). The impact test values at 28 and 30°
C are given in Table 8.
Table 8. Impact test values obtained at 30K in 1G and 4G position
Position Charpy ‘V’ notch
impact test
PFBR Specification Result
Impact
Energy J
Lateral
expansion mm
Impact Energy
J
Lateral expansion
mm
1G 303K (28°C) 68 (min) 0.9 (min) 76, 69, 77.3 0.95, 0.91, 0.84
303K (30°C) 68 (min) 0.9 (min) 75, 77, 76, 85 0.9, 1.2, 0.9, 1.03
4. 0. Fillet Weld Test
It is a usability test for electrodes, whether it is suitable for all position or not.
Therefore it is necessary to do fillet weld test. Test pad has been prepared as per
specification and fit-up was made as per Fig. 4. four numbers of fillet weld test pads
size of (300 × 50 × 6 mm) for two each test pad was welded using 3.15 electrodes in
3F and 4F position. Welding parameters employed to prepare weld pad is given in
Table 9.
The fillet weld test pads were visually
inspected and found to be defect free.
Two number of specimens were cut from
each weld pad, which were ground,
polished and etched using villela’s
reagent to examine whether any lack of
penetration. The fillet welds have
penetration beyond the junction of edges
of plates and the welds have no defects.
The measured fillet dimensions of the
fillet weld leg and size, actual throat, and
convexity are given in Table 10.
Table 9. Fillet welding parameters
Identification
of test pad
No. of
electrodes used
Current
Amps
Voltage
Volts
Travel Speed
mm/sec
Heat Input
J/mm
3F1 3 83 23 1.75 1090
3F2 3 83 23 1.75 1090
4F1 3 83 23 1.94 984
4F2 3 85 24 1.88 1039
Fig. 4. Schematic diagram of fillet weld test
Actual
Throat
Convexity
Leg & Size

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Table 10. Dimensional inspection of filler weld
Position
Measured leg and size (mm)
(Minimum requirement 6.4 mm)
Actual Throat
(mm)
Convexity (mm) (Minimum
requirement 1.2mm)
Side 1 Side 2
Leg 1 Leg 2 Leg 1 Leg 2 Side 1 Side 2 Side 1 Side 2
3F1 6.28 6.51 6.39 6.54 7.68 7.52 1.05 1.14
3F2 6.33 6.49 6.45 6.54 7.64 8.65 1.48 1.37
4F1 6.51 6.43 6.48 6.28 7.71 7.81 1.41 1.53
4F2 6.49 6.39 6.35 6.47 7.68 7.68 1.52 1.56
P1 – Phase 1, P2 – phase 2
5.0 Hardness Test
Hardness measurements were carried out on the weld metal after PWHT using
Vickers hardness testing machine at 10Kg load. The average hardness on the weld
metal was 214Hv.
6.0 Diffusible Hydrogen Measurement, HD
Cold crack is caused by diffusible hydrogen (HD). The source of hydrogen is welding
consumable, which contains moisture in the flux, therefore it is necessary to measure
hydrogen content in the weld metal. During welding hydrogen enters as atomic
hydrogen into the weld metal through welding arc. Solubility of hydrogen is more in
liquid metal but less in solid metal. The super saturated hydrogen in solid metal
diffuses into defects like porosity, inclusion, dislocation etc, when it gets sufficient
pressure, it cracks the weld metal and escape, the net result is hydrogen assisted
crack. Hence the following method was carried out to measure the HD content.
Using non-backed modified 9Cr-1Mo steel electrode, welding was carried out on a ‘U’
shape grooved copper plate, which was cooled by water circulation. The weld
parameters such as current 95 amps, Volts 24 and welding speed 0.75mm/s are
used for the collection of specimen for HD measurement. Immediately after
completion of weld, the weld metal was chipped out of the copper plate, quenched in
liquid nitrogen and the slag was removed thoroughly. The weld metal was then
flushed with alcohol and dried and kept an argon flushed chamber at 2bar
atmospheric pressure. The time gap between the completion of welding and insertion
of the sample in the chamber and flushing with in 60 seconds were maintained. The
chamber was kept in an oven at 45ºC for 72h. After 3 days the chamber was
connected with Gas chromatograph. The measured HD value was less than the
recommendation value 4ml/100g. The average value obtained was 3.7mm/100g of
weld metal.

11
7.0 Conclusion
1. It has been possible to indigenously develop and manufacture modified E 9016-
B9 (9Cr-1Mo steel) electrode meeting without any deviation and all the
requirements of PFBR specification.
2. Indigenous manufacturer M/s. MIDHANI, Hyderabad was successful in
manufacture of these electrodes.
3. This experience has shown that the identification of critical requirements and
problems in indigenous manufacture and their resolution through collective
efforts have contributed to the success of this effort in development of indigenous
electrodes.
8.0 Acknowledgement
The authors are thankful to Dr. Baldevraj, Director, Indira Gandhi Centre for Atomic
Research, Shri. Y.C. Manjunatha, Director, ESG and Dr. S.L.Mannan, Director,
MMG, IGCAR for their guidance and encouragement given for under taking the
development of electrodes and presentation of this paper in the International welding
Conference (IWC-2005).
9.0 References:
1. PFBR/33010/SP/1006 specification for modified 9Cr-1Mo welding electrodes for
shielded metal arc welding
2. PFBR/01950/SP/1001 – Specification for radiography examination.
3. AWS classification E 9016-B9 of ASME Section II-C SFA 5.5
4. ASME Section III subsection NB - Class I components
5. ASTM E208 specification for drop weight test
6. ANSI/AWS B4.0-85 - “mechanical test for welds”
7. ASTM E21 for high temperature tensile test
8. ASTM E23 for Charpy V-notch test
9. ANSI/AWS 4.3 for diffusible hydrogen content test

Quality Assessment of Mechanical and Metallurgical Properties of Modified 9Cr-1Mo Steel-Indigenously Developed Electrodes for PFBR Project

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