Factors influencing the microstructural and mechanical properties of ULCB steel weldments.
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Authors
McHale, Paul F.
Subjects
ultra low carbon bainitic steel
nonmetallic inclusions
constitutional supercooling
nonmetallic inclusions
constitutional supercooling
Advisors
Fox, Alan G.
Date of Issue
1991-12
Date
December 1991
Publisher
Monterey, California. Naval Postgraduate School
Language
en_US
Abstract
The U.S. Navy has maintained a continuous research, development and
certification program in HSLA and ULCB steels as a replacement for the HY steels used
in ship construction. The major benefit of the HSLA and ULCB steels stems from the
relative ease of weldability as compared with the HY steels which require large amounts
of preheating to prevent weld metal crack formation. This study focused on ULCB steel
weldment mechanical properties which were shown to be largely dependent on the heat
input and to a lesser extent the base plate composition, cover gas and nonmetallic
inclusion composition and content. The heat input rate and subsequent cooling rate for
the ULCB/ULCB steel weldments determined the degree of constitutional supercooling
indicating a high heat input (large constitutional supercooling) resulted in a tough, finely
grained macrostructure while the lower heat input (small constitutional supercooling)
generated a weak, columnar/dendritic macrostructure. The utilization of HY-130 base
metal resulted in increased carbon pickup in the fusion zone and consequently poorer
mechanical properties. The use of a reactive cover gas markedly increased the inclusion
density and promoted the formation of carbides producing the poorest overall mechanical
properties. The majority of the nonmetallic inclusions identified were spherical, complex
aluminum-silicates or manganese-aluminum-silicates. The presence of inclusions did not
appear to be dominant in the nucleation of acicular ferrite or in controlling the
microstructural development.
Type
Thesis
Description
Series/Report No
Department
Mechanical Engineering
Organization
Naval Postgraduate School (U.S.)
Identifiers
NPS Report Number
Sponsors
David Taylor Research Center, Code 2814
Funder
David Taylor Research Center, Code 2814
Format
93 p.;28 cm.
Citation
Distribution Statement
Approved for public release; distribution is unlimited.
Rights
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.