Journal of Metals, Materials and Minerals

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Dual Phase (DP) steels have been gradually used in the automotive industries because of their distinguished strength and ductility properties. Principally, microstructure of the DP steels contains defined amount of hard martensite islands dispersed in soft ferrite matrix. This microstructure characteristic and corresponding mechanical properties of the DP steels can be adjusted by heat treatment. In this work, effects of tempering temperature and time on tensile properties of DP steels were investigated. Continuous yielding behavior of tempered DP steels was observed up to around a temperature of 300C. At higher tempering temperature, DP steels showed distinct increased yield point. Furthermore, ultimate tensile strength decreased and elongation increased, when the tempering temperature and time were elevated. The investigated DP steel, which was tempered at 200C for 60 min, exhibited optimal combination of strength and ductility. Additionally, stretch-flangeability of the DP steels was examined. Three types of hole manufacturing process, namely, drilling, blanking and wire cut, were taken into account. It was found that formability of the DP steel sheets was significantly affected by quality of the hole edge. The samples prepared by wire cutting resulted in highest hole expansion ratio, since it caused the least prior damage.

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