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

Metallurgical Investigations on Hyperplasticity in Dual Phase Steel Sheets

“…Furthermore, using the results of the quantitative metallography of DP500 and DP780 which were presented in a previous paper [19], it is shown that a notable enhancement of plastic compatibility between ferrite and martensite occurred in EHF, which contributes to the hyperplas ticity of dual phase steels in EHF. Observation of disloca tions and deformation twinning were carried out to understand the mechanisms that lead to the significant deformation improvements of ferrite grains and martensite islands in EHF.…”

“…The present paper is a develop ment on the previous research by Golovashchenko et al [18] and Samei et al [19] where dual phase steels were formed by an EHF process into a 34 deg conical die. Hyperplasticity was observed in these specimens deformed by EHF.…”

“…Samei et al [19] analyzed the microstructure of DP500 and DP780 steel specimens formed in quasi-static and high strain rate conditions using the Nakazima test [20] and EHF into a 34 deg conical die, respectively. Statistical quantitative metallography of DP500 and DP780 specimens showed relative deformation improvements of approximately 20% in ferrite grains and 100% in martensite islands that were formed by EHF compared to the specimens formed under quasi-static conditions.…”

Simulation of electrohydraulic free forming of DP600 sheets using a modified Rousselier damage model

“…Different materials exhibit different forming and damage behaviour when they are deformed in freeforming (EHFF), as shown in figure 1, or die-forming (EHDF) conditions [8][9][10]. Samei et al [11,12] showed significant improvement in the formability of DP600 steel sheets subjected to EHF through the activation of different plastic deformation mechanisms in both ferrite and martensite. Jenab et al [3,13] investigated the deformation and damage mechanisms in AA5182 and showed that ductile damage mechanisms were suppressed as a result of die impact during electrohydraulic die forming.…”

Comparison of quasi-static and electrohydraulic free forming limits for DP600 and AA5182 sheets

“…More recently, Samei et al (2013) observed that high-velocity impact of the sheet against the die in EHF leads to suppression of void nucleation and growth in dual phase steels and significantly delays the onset of failure. However, analysis of stresses in the die for pulsed pressure forming, performed by Ibrahim et al (2013) indicated that the high-velocity of the blank required to achieve significant formability improvement causes significant plastic deformation that leads to fracture and accordingly shortens the lifespan of the forming dies.…”