Investigation of the mechanical properties martensitic steel sheet in cold metal transfer welding method

SUMMARY Keywords: CMT- Brazing, 1200M Martensitic Steel, Tensile Strength The vehicles use high strength steels developed to increase driver and passenger safety and reduce fuel consumption. Very high strength martensitic steels have application areas such as automobile safety components, door beams and bumpers. Since martensitic steels contain completely martensitic structure, cold metal transfer (CMT) method with less heat input has been preferred instead of traditional gas welding methods such as Metal Inert Gas (MIG) and Metal Active Gas (MAG). At the same time, CuAl8 solder wire with low melting point (1030-1035ºC) was used as solder wire. In this study, DOCOL 1200M martensitic steel plates having 1 mm thickness were joined by copper-based CuAl8 wire in gas metal arc brazing technique. Specimens were prepared in two different joining forms as butt joint and overlap joint. Brazing operations were done with five different parameters, current intensities, travel speeds, shielding gas, brazing gaps and torch angles. Tensile strength, bending force, microstructure of brazed materials, and their micro hardness distribution throughout joining were determined. In macro and microstructure examinations, stereo optical microscope, scanning electron microscope (SEM), SEM/energy dispersive spectroscopy was used. This study investigated effects of current intensities, travel speeds, shielding gas at flow rates, brazing gaps and torch on microstructure and microhardness distribution of transition zone between 1200M martensitic steel and brazed metal of joined material.