A study of the microstructural basis for the strength and toughness properties of as-quenched and quenched and tempered high copper HSLA-100 steel

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Author
Winters, Harvey Allen
Date
1991-12Advisor
Fox, Alan G.
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Show full item recordAbstract
A program for the use of high copper HSLA-100 steel as
a replacement for HY-130 in ship construction is in progress
at the David Taylor Naval Research Center in Annapolis,
Maryland. The characterization of the microstructure of this
highly weldable high copper HSLA-100 steel is extremely
important to this program. In the present work, optical,
scanning electron and transmission electron microscopy were
employed to analyze and characterize the microstructural basis
for the mechanical properties off as-quenched and quenched and
tempered high copper HSLA-100 steel in the form of 19.05 mm
plate. The as-quenched and samples aged at 538 CC and 621°C were
examined in great detail. In the as-quenched condition the
microstructure consisted of small packets of highly dislocated
lath martensite containing autotempered Fe 3C carbides with
small amounts of retained austenite present as thin films
(200-300 A in width) at lath boundaries. The basis for the
high strength and toughness of this as-quenched sample is the
small transformation product packet size and the highly
dislocated structure. The best combination of strength and
toughness occurred in the sample aged at 538°C. Contributing
to these desirable characteristics was the recovery of the
dislocation substructures, the precipitation of coherent BCC
copper precipitates (12-20 A in size) further precipitation
(FeM) 3 C carbides and the small transformation product packet
size. In the overaged (621°C) condition, the toughness was
increased and the strength decreased due to the absence of coherent BCC copper precipitates and the presence of FCC Ecopper
incoherent precipitates. Further recovery of the
dislocation substructures was also evident. All of the samples
(lot GLB) studied met the MILSPEC for HY-130 and would be
suitable replacements. As a result of this investigation it is
suggested that the optimum aging temperature for the 19.05 mm
as-quenched high copper HSLA-100 plate is around 550°C.
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This publication is a work of the U.S. Government as defined in Title 17, United States Code, Section 101. Copyright protection is not available for this work in the United States.Collections
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