Structure-property correlation of submerged-arc and gas-metal-arc weldments in HY-100 steel |
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Authors: | P Deb K D Challenger and A E Therrien |
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Affiliation: | (1) APTECH Engineering Services Inc., 94303 Palo Alto, CA;(2) Materials Engineering Group, Mechanical Engineering Department, Naval Postgraduate School, 93943 Monterey, CA;(3) U. S. Navy, USA |
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Abstract: | Structure-property relationships of two HY-100 steel weldments prepared by submerged arc (SAW) and gas metal arc (GMAW) welding
processes using identical heat input (2.2 kJ mm-1) have been studied. It has been found that submerged arc welded (SAW) HY-100 steel weldments have a lower weld toughness
than welds produced by the gas metal arc welding (GMAW) process. Optical, scanning, and transmission electron microscopy were
used in conjunction with microhardness traverses to characterize and compare the various microconstituents that are present
in the last weld pass of both weldments. TEM examination revealed the presence of coarse upper bainite, B-II bainite, and
carbides in a highly dislocated ferrite matrix as well as in ferrite laths in the SAW weldment, while the GMAW weldment exhibited
a typical fine low carbon lath martensite, autotempered martensite, and mixed B-II and B-III bainites which occasionally contained
small regions of twinned martensite. The measured cooling rate in the SAW was found to be about 40 pct slower than that in
GMAW. It was also found in the SAW that the weld metal inclusion number density was about 25 pct greater than that in GMAW.
Micro-hardness traverses exhibited significantly lower hardness (about 50 HV) in the SAW weldment compared with GMAW, but
the tempered weld metal microhardness in both the weldments was measured about the same, at 250 HV. The ductile-to-brittle
transition temperature (DBTT) of both weldments was determined by Charpy impact test. Based on an average energy criterion,
the DBTT of the SAW weldment was 323 K (50 °C) higher than that of the GMAW weldment. This difference in fracture resistance
is due to the different weld metal microstructures. The different microstructures most probably result from differences in
cooling rate subsequent to welding; however, the SAW weld also has a higher inclusion number density which could promote a
higher transformation temperature for the austenite.
Formerly Adjunct Research Professor with the Materials Engineering Group, Naval Postgraduate School
Formerly Graduate Student at NPS |
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