Duplex stainless steels (DSS) are characterized by their high corrosion resistance coupled with good mechanical properties. Their physical properties are based on the microstructure, which consists of a balanced phase ratio of ferrite (α) and austenite (γ). For many industrial applications DSS must be welded. This can lead to an unbalanced γ/α-ratio due to the high cooling rates with changes of the chemical composition of both phases. Subsequently, mechanical properties and corrosion resistance of the joint can degrade. In situ measurements of the chemical composition of the weld pool and during cooling of the solidified weld seam were realized by using LIBS, with a high time and spatial resolution. With help of Certified Reference Materials and a customized Partial Least Squares regression (PLS), the measurements were calibrated. Previous research has shown that the LIBS method is suitable to detect chemical elements during welding and to show their distribution by LIBS mapping.