A study of the microstructural basis for the strength and toughness properties of overaged HSLA-100 steel

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

Department dc:contributor.department

Mechanical Engineering

Grantor dc:publisher

Monterey, California. Naval Postgraduate School

Year dc:date.issued

1991

Author dc:creator

• Comerford, Lawrence Whitley

Advisor dc:contributor.advisor

• Fox, Alan G.

Statement dc: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.

Language dc:language.iso

en_US

Handle dc:identifier.uri

https://hdl.handle.net/10945/28574

OAI identifier oai:identifier

oai:calhoun.nps.edu:10945/28574