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The formation of Laves phase and its effect in aged G-911 steel for ultra super critical steam cycle boilers.

This microstructure posted 31 March, 2010 - 12:09 by Samirbose

Occurances of Laves phase in aged G-X 12 CrMoVWNbN 1011 (G-911)

Highlighting of the Laves phase through image processing in optical microscope.

Presence of Laves phase and its effect to create embrittlement in the martensitic matrix.

EDS tracing confirming the presence of Laves phase.
Material (Name/Designation/Grade): 
G-X 12 CrMoVWNbN 1011 (G-911)
Material Condition (Heat treatment/Service history/Source): 
Normalised at 1053 K for 8 h, hardening by forced air cooling after soaking at 1363 K for 8 h, further, tempering at 1003 K for 8 h followed by air cooling. Stress relieving at 1003 K for 8 h by furnace cooling to 523 K . Ageing heat treatment: at 923 K for 1200 h and then upgraded to 973 K for 300 h.( this ageing treatment simulates to the service ageing at 873 K for 100,000 h)
Chemical Composition: 
C
0.13
Si
0.3
Mn
0.88
P
0.016
S
0.004
Cr
9.10
Mo
1.01
V
0.25
W
0.8
N
0.05
Nb
0.05
Ni
0.64
Fe
bal
Chemical Composition (Phases/Compounds): 
Laves phase: Fe - 49%, Cr - 9%, W - 26% and Mo - 16%
Metallographic Preparation
Etchant: 
1) light etching in 5%picral added with 2% ferric chloride and 2) deep etching in 20% NaOH + 10% hydrogen peroxide solution
Special Techniques: 
swabing process
Imaging Details
Device: 
SEM / Light optical Microscope
Mode: 
secondary electrons for SEM.
Magnification: 
Special Techniques: 
using CLEMEX image analyzing software
Image Uploaded By
Name: 
Samir Bose
Email Id: 
benu79@rediffmail.com
Morphological Features
fig 1:Delineation of Laves phase via etching technique . fig 2:Quantification of the Laves phase(4%)using image processing software. fig 3:The creation of brittle crack at martensitic lath boundaries due to the presence of massive Laves phase. fig 4:EDS analysis confirming the presence of Laves phase.
References
MSEA vol 476, issue,1-2, 2008, p.257
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