HETEROGENEOUS LASER WELDS OF DUCTILE IRON AND Cr-Mo LOW ALLOYED STEEL

For some powertrain components deep penetration laser welding is considered very advantageous and prospective joining technology. Presented article focuses on heterogeneous laser welds of two widely used materials, ductile iron with pearlitic matrix (e.g. differential carrier) and Cr-Mo low alloy steel (e.g. gears). When homogeneous welds without filler wire are done, both materials show poor laser weldability, because unacceptable welding defects, mainly cracks, are created in the weld. In ductile iron, almost under all welding conditions, cracks in WM and HAZ due to brittle phases (cementite and martensite) are created. Low alloy Cr-Mo steel creates under all welding conditions solidification cracks and microcracks, caused by solidification. Even though homogenous welds of both materials are unacceptable, for heterogeneous welds possibility to create sound welds was found. By mixing of materials approximately 1:1 substantial amount of retained austenite is present in the WM, helping to suppress creation of brittle cracks and also partially suppress solidification cracks. To supress solidification cracks completely, full penetration welds and welds with V shape were used. Also use of Ni filler wire proved successful to create sound welds. The weld joint strength for heterogeneous welds for both used solutions was about 450 N/mm2, which is less than BM strength, yet acceptable. Occurring phenomena connected with ration of materials mixing and its influence on WM properties, structure and behaviour is explained.