IGCAR : Annual Report - Indira Gandhi Centre for Atomic Research
IGCAR : Annual Report - Indira Gandhi Centre for Atomic Research
IGCAR : Annual Report - Indira Gandhi Centre for Atomic Research
You also want an ePaper? Increase the reach of your titles
YUMPU automatically turns print PDFs into web optimized ePapers that Google loves.
IGC<br />
<strong>Annual</strong> <strong>Report</strong> 2007<br />
the nitrided layer is confined to<br />
the surface. Cross-section TEM<br />
(XTEM) has been undertaken to<br />
characterize the nitride phase.<br />
Fig. 1 represents the results on<br />
a specimen that was nitrided at<br />
773K <strong>for</strong> 24hrs, (a) TEM<br />
micrograph taken close to<br />
surface, and (b) SADP intensity<br />
plots against the reciprocal<br />
lattice vector, IgI, taken<br />
from various depths<br />
from the surface.<br />
Fig. 1(a) shows that the EP-Cr is<br />
columnar in nature. Fig. 1(b)<br />
shows that a Cr 2 N phase is<br />
found only on the surface while<br />
all other peaks are from Cr. The<br />
results show that nitride <strong>for</strong>ms<br />
only on the surface as a mixture<br />
of Cr and Cr 2 N, under the<br />
given conditions of plasma<br />
nitriding.<br />
III.C.12. In - house Development of Test Facilities to<br />
Study Hydrogen Assisted Cracking in Steel Weldments<br />
Hydrogen Assisted Cracking<br />
(HAC) is one of the major <strong>for</strong>ms<br />
of cracking that occur in steel<br />
welds. Four different tests,<br />
namely UT-Modified Hydrogen<br />
Sensitivity Test (UT-modified<br />
HST), Implant test, Gap Beadon-Plate<br />
(G-BOP) test and Y-<br />
groove test, were set up<br />
indigenously to study this <strong>for</strong>m<br />
of cracking in steel weld joints.<br />
Susceptibility of modified 9Cr-<br />
1Mo steel and its weld metal<br />
produced from indigenously<br />
developed welding electrodes<br />
has been studied using these<br />
tests. Results from various tests<br />
(except from Y-groove tests)<br />
indicated that a preheat of the<br />
order of 473-523 K is<br />
necessary to prevent HAC in<br />
these steel welds. In the case of<br />
Y-groove test, restraint was low<br />
because of the lower thickness<br />
of the plate used <strong>for</strong> testing (12<br />
mm and 30 mm) and it was<br />
found that with increase in plate<br />
thickness, the preheat<br />
temperature to prevent cracking<br />
increased. Fig.1 and 2 show the<br />
various of preheat temperature<br />
with volume % hydrogen in the<br />
shielding gas <strong>for</strong> UT-modified<br />
HST and with lower critical<br />
stress <strong>for</strong> implant test<br />
respectively. No cracking was<br />
observed at higher<br />
temperatures <strong>for</strong> the given<br />
testing parameters.<br />
Results from different tests<br />
indicated that both weld metal<br />
and base metal are susceptible<br />
to HAC with weld metal more<br />
susceptible than the base<br />
Fig.1 Variation in critical preheat temperature as<br />
function of hydrogen in the shielding gas and strain<br />
applied on the specimen in UT-modified HST<br />
Fig.2 Variation of lower critical stress above which<br />
the specimens cracked as a function of preheat<br />
temperature. No cracking was observed in<br />
specimens prepared at preheat temperature >573 K.<br />
R&D FOR FBRs 61
Change language