A study of the microstructural basis for the strength and toughness properties of water-quenched and air-cooled HSLA-100, HSLA-100 with increased copper, and a ULCB steel.

Abstract

The microstructural basis for strength of the water-quenched and aircooled HSLA-100, HSLA-100 with increased copper, and a ULCB steel was investigated by conducting an inclusion study and characterizing the microstructure of each of the steels. For the inclusion study, the SEM was used to examine a large number of fields and determine inclusion morphology while the EDX was used to determine inclusion composition. The microstructure of both the water-quenched and air-cooled steels was characterized using the optical microscope, SEM, and TEM. The HSLA-100 with increased copper steel was adequately calcium treated and aluminum deoxidized as evidenced by the low sulfur content, few MnS stringers, and lack of large oxide arrays. The ULCB steel was not calcium treated or Al-killed; nor was it thermo-mechanically processed as shown by the lack of lipped, broken, or elongated stringers. Both MnS and oxide inclusions were present, and consequently, ladle metallurgy would have to be used before the ULCB steel was hot-worked.