Optimización del proceso RSW para acero DP 1000

ABSTRACT In recent times new materials have been introduced in automobiles construction in order to reduce their weight and consequently fuel consumption and emissions level. Among them are Dual Phase (DP) steels, constituted by a ferritic matrix with martensite islands. Resistance Spot Welding (RSW) is the most commonly used welding process in the automotive industry. However, the welding of these materials presents greater challenges, since the parameters used for RSW welding of conventional steels are not applicable on these advanced steels. Also, the welding thermal cycle degraded its properties, with the minimum hardness being found in the sub and/or inter critical zone. In turn, due to the high cooling rates imposed by the strong cooling of the electrodes, structures of high hardness can be generated in the nugget region. In this sense, the optimization of welding procedures is of particular interest. In other way, productivity is an great relevance aspect in these applications, thus reducing welding times is a requirement. The objective of this work is to evaluate the effect of RSW welding parameters on DP1000 steels in order to optimize them. To this end, 1.2 mm thick DP1000 steel probes were welded by RSW, varying the current and the welding time. On the welded joints, macro and microstructural characterization was performed by optical and scanning electron microscopy, Vickers microhardness profiles and peel-test and shear-test stripping tests. The fracture surfaces were analyzed by light microscopy. A set of parameters that optimizes the welding process of DP1000 steels by RSW was obtained. It was found that from 10 welding cycles and with current levels of 7 KA the points achieves the dimensional requirements and mechanical properties adopted by the automotive industry.