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Title: Characterization of the interpass microstructure in low alloy steel/Alloy 625 HW-GTAW narrow groove welds
A dissimilar weld between a low alloy steel (LAS) butter weld joined to a F65 steel pipe using a narrow groove hot wire gas tungsten arc welding (HW-GTAW) procedure with Alloy 625 filler metal was investigated. The weld interpass microstructure is comprised of large swirls formed by a macrosegregation mechanism involving partial, non-uniform mixing of liquid base metal with the lower melting temperature weld pool, followed by fast solidification. This mechanism produces steep gradients in composition and solidification behavior. The resulting swirls are composed of alternating iron-rich peninsulas and partially mixed zones (PMXZ) that are surrounded by planar and cellular zones exhibiting multiple solidification directions. Large austenitic grains, encompassing planar, cellular, and dendritic morphologies, nucleate off peninsulas in direct contact with the weld pool. The highest hardness was found in nickel and chromium rich PMXZs that exhibited a lath martensite microstructure. In the event of exposure to hydrogen containing environments, the PMXZs could serve as nucleation sites for hydrogen assisted cracking.  more » « less
Award ID(s):
2052747
PAR ID:
10506625
Author(s) / Creator(s):
; ;
Publisher / Repository:
ScienceDirect
Date Published:
Journal Name:
Materials Characterization
Volume:
170
Issue:
C
ISSN:
1044-5803
Page Range / eLocation ID:
110638
Format(s):
Medium: X
Sponsoring Org:
National Science Foundation
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