Desenvolvimento de método para quantificação de fases em aços dual phase via EBSD

Abstract

The dual Phase steels are advanced high strength steels widely used for automotive body manufacturing in the automotive industry. Its microstructure is consisting by martensite-austenite (MA) microconstituents islands, dispersed in a polygonal ferrite matrix, they induce high mechanical strength and good conformability. The phases quantification is really relevant in these steels, after all the mechanical properties are highly dependent on this parameter. This study analyzed a Dual Phase steel annealed at different isotherms (720 ° C, 740 ° C and 760 ° C) and quenched by oil. Phase quantifications (MA and ferrite fractions) were obtained by OM images and application the IQ (image quality) method using EBSD. The OM quantification was did by the binarization method in samples attacked by LePera. For EBSD, three different methods were tested through IQ histogram analysis, reported as arbitrary threshold method, deconvolution assigned threshold method and deconvolved histogram area method. It was observed the quantification of MA by deconvolution assigned threshold method was the most accurate. The OM and EBSD methods were compared, the last one always presented more accurate results, providing greater repeatability.