A study of the microstructural basis for the strength and toughness properties of overaged HSLA-100 steel
By:  Lawrence Whitley Comerford
Publisher: Naval Postgraduate School; Available from the National Technical Information Service
Published: 1991
Place of publication: Monterey, Calif; Springfield, Va
Language: eng
Number of pages: 104
Description: A certification program for the use of HSLA steel in ship construction is currently being funded by the U.S. Navy. Integral to this program is the characterization of the microstructure of the highly weldable HSLA-100 steel. In the present work, optical, scanning electron and transmission electron microscopy were employed to analyze the microstructural basis for the mechanical properties of as-quenched and tempered HSLA 100 steel in the form of 31.75 mm plate. The as-quenched microstructure contained bainite/martensite laths and a small amount of retained austenite. The strength and toughness in this specimen was based on the small transformation product packets with their fine laths and highly dislocated substructures. The best combination of strength and toughness occurred for the sample tempered at 621 degC; the recovery of the dislocation substructures, the precipitation of overaged copper and carbides, and the small transformation product packet size accounted for the high toughness at this tempering temperature. The size, distribution, and composition of non-metallic inclusions were also determined; the inclusion population generally consisted of small, globular, homogeneously dispersed particles. However, exogenous oxides on the order of 50 um were occasionally found as well as slightly brittle oxides which had broken up in the rolling direction. As a result of this investigation, it is suggested that the optimum aging temperature for 31.75 mm as-quenched HSLA-100 plate is around 600 degC and that improved secondary steelmaking procedures are adopted to eliminate the large, deleterious non-metallic inclusions. HSLA, non-metallic inclusions
Notes: Thesis advisor(s): Alan G. Fox.

"June 1991."

Thesis (M.S. in Mechanical Engineering) Naval Postgraduate School, June 1991.

Includes bibliographical references.

Approved for public release; distribution unlimited.

United States Navy (USN) author.