1892 - Indira Gandhi Centre for Atomic Research

TRANS. INDIAN INST. MET., VOL. 57, NO. 3, JUNE 2004
of the hardface coating, while locked-in residual
stresses may increase the risk of micro cracking
during thermal cycling in low-ductility coatings.
Further, high compressive residual stresses parallel
to the surface improves the tribological behaviour of
the deposit, 6 and a compressive pre-stress to the
deposit beneficially balances the tensile thermal stress
during high temperature application. 3 Also, the
magnitude and distribution of residual stresses
depends on the maximum temperature, holding time,
and heating/ cooling rate during thermal cycling.
The GP sleeves of PFBR are to be hardfaced at two
locations where it comes in contact with the core
subassembly (Fig. 1) – one on the top chamfered
portion and the other on the inner diameter 470 mm
from top. As thinner coatings have better thermal
shock resistance due to reduced accumulated residual
stresses, the low-dilution PTAW process was chosen.
To eliminate the risk of micro cracking and
delamination of the deposit, and to minimize the
magnitude of residual stress, an optimised PTAW
deposition procedure has been qualified. In this work,
the effect of thermal cycling during service on the
residual stress distribution of hardfaced austenitic
SS sleeves has been studied.
2. EXPERIMENTAL PROCEDURE
Hardfacing on the inside of the GP sleeve was
simulated by hardfacing a 316 SS sleeve (106 mm
OD x 80 mm ID x 45 mm height) on its inside
surface with nickel base WT-50 hardfacing alloy
powder (composition given in Table 1) using the
PTAW process (Fig. 2). After hardfacing, the sleeve
was cooled slowly in vermiculite powder, machined
to the required thickness of 1.5 mm, and examined
by liquid penetrant test (LPT).
The hardfaced sleeve was cut into two halves along
AB (Fig. 2). One half (with location C at the middle)
was stress relieved at 1123 K for 35 minutes, using
a heating rate of 150 K h –1 and holding time of 2.5
Fig. 1 : Drawing of grid plate sleeve, showing the two
hardfacing locations
min per mm of thickness, as per the specification. 7
The other half of the sleeve (with location D at the
middle) was retained in the as-deposited condition,
for comparison. Both the sleeve-halves were then
subjected to thermal cycling between 473 and 823 K
Table 1
CHEMICAL COMPOSITION OF WT-50 HARDFACING ALLOY POWDER USED
Elements C Si Cr Fe B Others Ni
Wt.-% 0.46 3.88 10.59 3.00 2.34 < 0.5 Balance
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