A new constitution diagram for dissimilar metal welds of high-manganese steels

When dissimilar metal welding of high-manganese (Fe-Mn) steels with low-alloyed steels, martensite may form in the weld metal. Current constitution diagrams for weld metal microstructure prediction cannot be used for Fe-Mn steels since the influence of the high manganese content in those steels is not sufficiently considered in the Ni equivalent. This paper concentrates on the development of a new constitution diagram for reliable weld metal microstructure prediction when dissimilar metal welding of Fe-Mn steels with low-alloyed ferritic and martensitic steel grades. For developing the constitution diagram a specially designed arc melting technique was used to experimentally simulate dissimilar weld metals in different dilutions and compositions. The resulting samples were evaluated regarding the type and quantity of the microstructural phases by means of hardness and ferrite number measurements as well as light-optical microscopy. Using this dataset it was possible to determine functional correlations between the chemical composition and the weld metal microstructures. By means of statistical analysis, a new constitution diagram was developed. Actual GMAW welds of different material combinations were performed to validate the applicability of the diagram. The new constitution diagram has a very high prediction accuracy and also distinguishes between the different types of martensite (epsilon and ').