Metal additive manufacturing methods were classified as feed systems based on powder or wire and bed systems with powder by Frazier. Wire-Arc Additive Manufacturing investigations have been conducted to obtain stronger weldments with rapid production times and microstructure investigations gained importance. Early investigations of crystal phase stability were reported by Leon Guillet at the beginning of the 19. Century. According to the literature “Equivalence Coefficient” term was first used to define included chemical elements. In 1920, StrauB and Maurer illustrated their diagrams and Scherer, Riedrich and Hoch redeveloped them. Field, Bloom and Linnert added “equivalence coefficients to emphasize the roles of ferrite and austenite stabilizers. After many investigations, Anton Schaeffler illustrated his well-known diagram to predict solidification mode and also the ferrite content. DeLong added extra element to the vertical axis as an austenite former and brought the “N number” usage as a welding term. Welding Research Council redeveloped them in 1992 and in 1998. These diagrams have been still used to estimate microstructures of the weldments for additive manufacturing with wire arc (WAAM) investigations. This paper aims to emphasize the beneficial role of constitution diagrams and to understand their usage for promising additive manufacturing investigations.