Autogenous laser welding of stainless steel to free-cutting steel for the manufacture of hydraulic valves

The hydraulic valves referred to in this study are made of AISI304L non-magnetic stainless steel and AISI12L13 free-cutting steel tubular parts, which make up the main valve cylinder. The valves must have mechanical properties of a high level in order to be able to stand up to the demanding operating pressure cycles. In the final assembly, the valve cylinder, with its internal slider piece. is sealed by means of two butt welds. A laser-welding technique for the fabrication of the hydraulic valves is presented, in which the butt welds joining the AISI304L to the AISI12L13 were performed in such a way as to control solidification cracking and micro-fissuring. Metallurgical analyses revealed that both solidification cracking in the fusion zone and micro-fissuring in the heat-affected zone result from S, Pb and P contained in the AISI12L13. The relationships between the redistribution of elements in the fusion zone, the welding parameters, and the microstructures were investigated. A 0.12 mm off-set of the laser beam towards the AISI304L and an impingement angle of 15 degrees with respect to the fit-up face of the butt joints can produce sound welds on the hydraulic valves made of 0.9 mm thick AISI304L and AISI12L13. Tests of the mechanical properties of the hydraulic valves revealed good-strength welds, high repeatability? and reliability of the welding parameters adopted. The results may provide a contribution to overcoming problems of dissimilar fusion joints, where one of two materials is unweldable, by the application of the laser welding technique del eloped in this study. (C) 1998 Elsevier Science S.A.