Two alternative composite welds were manufactured by GTAW technology according to standard technological procedures. The welds connected two base materials with different chromium content using high chromium intermediate layer and low alloyed main weld consumable material. Experimental analysis was carried out on weld samples after PWHT and on samples annealed up to 1000 hours at 650stC. Microhardness and chemical profiles of interstitial and substitutional elements across all weld interfaces in the samples were measured. Phase diagrams, activity values for diffusing elemnts for all materials used in the welds were calculated by ThermoCalc using Steel16 database. Phase and chemical profiles for all interfaces in the welds after heat treatment and annealing were also calculated using DICTRA and Steel16 and Dif databases. Non-linear starting chemical profiles were used for the kinetic simulations to modell the mixing during realistic welding. The results of the simulations agree well with all experimental results.