ريزساختار و رفتار شكست جوش هاي مقاومتي نقطه اي ناهمجنس فولاد دوفازي DP600 و فولاد ساده كم كربن St14

Microstructure and Failure Behavior of Dissimilar Resistance Spot Weld of DP600 Dual Phase Steel and Stl4 Low Carbon Steel

This paper aims at investigating the microstructure and failure behavior of dissimilar resistance spot welds between low carbon steel (st14) and ferrite-martensite dual phase steel (DP600). The effects of welding current in the range of 7.5 to 9.5 kA on the metallurgical and mechanical behavior of the weld were investigated. Microstructural characterization, microhardness tests and the tensile shear tests were conducted. Mechanical properties of spot welds were described in terms of failure mode, peak load and energy absorption. The fusion zone microstructure exhibited martensite, bainite, allotriomorphic ferrite and Widmanstatten ferrite, resulting in high hardness of fusion zone compared to base metals. Results showed that the mode of failure changed from interfacial fracture to pullout as the welding current was increased. Fusion zone size proved to be the most important controlling factor for peak load and energy absorption of dissimilar DP600/Stl4 resistance spot welds.