Laser beam welding of 2205 duplex stainless steel with metal powder additions

Abstract

Laser beam welding with the aid of metal powder additions to the weld pool was carried out to modify the ferrite/austenite (α/γ) ratio of the weld metal of 2205 duplex stainless steel (DSS). The α content in the weld metal of DSS welds could be controlled by the proper flow rate of nickel powder through a coaxial nozzle. This process had the advantage of using only a small amount of filler metal, i.e. a few grams per minute of nickel powder, in the welding process. Imapct and notched tensile tests were utilized to evaluate mechanical properties of laser welds. The notched tensile test was also carried out in hydrogen under a slow displacement rate. The susceptibility to hydrogen embrittlement (HE) was estimated from the loss in notched tensile strength and correlated with the microstructure of a given laser weld. On the whole, the susceptibility to HE decreased with increasing the γ content of DSS welds. Autogeneous laser welds containing the highest α content of all welds tested were most susceptible to HE. The base material with banded α+γ structures was susceptible to HE and exhibited severe secondary cracks mainly along α/γ phase boundaries. Although laser welds produced at a flow rate of 3 g/min nickel powder had similar α content to the base material, they were more resistant to HE owing to randomly distributed α and γ phases in the weld metal. The impact energy of laser welds at low temperatures (−75 to −100°C) along with the hardness test could also be used to check if the proper amount of nickel powder was added in laser welding of DSSs.