Techniques characterization and quantification of microconstituent MA in HSLA steels

The HSLA (high strength low alloy) steel API 5L steel grade have complex microstructure which consists mainly for austenite decomposition products such as acicular ferrite or bainite, perlite, and a complex microconstituent Martensite/Austenite (MA). The determination of the amount of MA is important because there is a strong relationship with toughness of these steels grade. The objective of this study is to develop a methodology for characterization and quantification of these microconstituent MA. Two steels HSLA (API 5L X70 and X80) were subjected to different cooling rates to promote changes in the type and amount of microconstituents. The samples were characterized by MO, with differential chemical etching, SEM, AFM and XRD reveal the presence of MA. The results show an increase in the amount of MA levels with increasing cooling rate, the Rietveld refinement was feasible to measure the austenite phase, and are therefore a useful tool for future applications. (author)