Quantitative Microstructural Analysis of Formability Enhancement in Dual Phase Steels Subject to Electrohydraulic Forming

• Published in: Journal of materials engineering and performance Vol. 22; no. 7; pp. 2080 - 2088
• Main Authors: Samei, Javad, Green, Daniel E., Golovashchenko, Sergey, Hassannejadasl, Amir
• Format: Journal Article
• Language: English
• Published: Boston Springer US 01.07.2013; Springer
• Subjects: Applied sciences; Characterization and Evaluation of Materials; Chemistry and Materials Science; Corrosion and Coatings; Engineering Design; Exact sciences and technology; Forming; Materials Science; Metals. Metallurgy; Production techniques; Quality Control; Reliability; Safety and Risk; Tribology; hyperplasticity; electrohydraulic forming; quantitative metallography; dual phase steel; high strain rate; microstructure strain; mixture rule; Deformation band; Metallography; Formability; Modeling; Electrohydraulic forming; High speed; Microstructure; Dual phase steel; Strain rate
• ISSN: 1059-9495; 1544-1024
• DOI: 10.1007/s11665-012-0438-2

Under certain conditions, strain rate sensitive materials such as dual phase steels, show formability improvement under high strain rate forming which is known as hyperplasticity. In this research, two commercial dual phase steel sheets, DP500 and DP780, were formed under quasi-static conditions using the Nakazima test and under high strain rate conditions by electrohydraulic forming (EHF) into a conical die. Macro-strains, measured from electro-etched circle grids with an FMTI analyzer, showed remarkable formability improvement in EHF specimens. Micro-strains, i.e., the strains in the ferrite and the martensite, were calculated by quantitative metallography of more than 7000 ferrite grains and 10,500 martensite islands. The goal was to investigate the deformation improvement of the constituents under EHF. Around 20 and 100% deformation improvements were observed in ferrite and martensite, respectively. Furthermore, as a micro-mechanical modeling technique, correlation of the micro-strains with the macro-strains was investigated by applying the mixture rule. Results showed a reasonable correlation between the macro and micro-scale strains; however in banded microstructures, the strain in the martensite should be determined precisely for more accuracy.