Publication: Influence of thermomechanical treatments on the microstructure and mechanical properties of HSLA-100 steel plates
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Date
2003
Authors
Journal Title
Metallurgical and Materials Transactions A: Physical Metallurgy and Materials Science
Journal ISSN
Volume Title
Publisher
Minerals, Metals and Materials Society
Abstract
The influence of thermomechanical treatment (TMT), i.e., controlled rolling and direct quenching, as a function of rolling temperature and deformation on the microstructure and mechanical properties of HSLA-100 steel have been studied. The optical microstructure of the direct quenched (DQ) and tempered steel rolled at lower temperatures (800°C and 900°C) showed elongated and deformed grains, whereas complete equiaxed grains were visible after rolling at 1000°C. The transmission electron microscope (TEM) microstructure of the 800°C rolled DQ steel showed shorter, irregular and closer martensite laths with extremely fine Cu and Nb(C,N) precipitates after tempering at 450°C. The precipitates coarsened somewhat after tempering at 650°C; the degree of coarsening was, however, less compared to that of the reheat-quenched (RQ) and tempered steel, indicating that the DQ steel was slightly more resistant to tempering. Similar to the RQ steel, at a 450°C tempering condition, the DQ steel exhibited peak strength with extremely poor impact toughness. After tempering at 650°C, the toughness of the DQ steel improved significantly, but at the expense of its strength. In general, the strength of the DQ and tempered steel was good and comparable to that of the RQ and tempered steel, although, its impact toughness was marginally less than the latter. The optimum combination of strength and toughness in the DQ steels was achieved after 900°C rolling with 50 pct deformation, followed by direct quenching and tempering at 650°C (yield strength (YS) = 903 MPa, ultimate tensile strength (UTS) = 928 MPa, and Charpy V-notch (CVN) strength = 143 J at -85°C).