Cr-Mo steels are used in the petroleum industry in applications with crude oils rich in sulfur compounds. 2.5Cr1Mo or 9Cr1Mo do not resist to operating conditions when in contact with crude oils. The increasing of molybdenum content can improve the corrosion resistance of these alloys. This paper studied the effect of increased concentration of molybdenum in the microstructure of Fe-9Cr-xMo alloys, annealed and welded. Phase diagrams were built with the aid of commercial program to check the possible phases to be formed and to identify the problems of welding. Analyses were realized by optical microscopy, EBSD and hardness tests. Autogenous welds were carried out to verify the effect of heat input on microstructure and hardness of the alloys. The results indicated that the increase in molybdenum concentration resulted in increased hardness of the alloys. After welding the alloy with lower molybdenum content presented the formation of martensite. Alloys with molybdenum content above 5% presented a fully ferritic microstructure. The formation of martensite can be a problem in weld alloys with lower content of molybdenum, since it can cause loss in mechanical properties hindering their application.
Ferritic Stainless Steel; Welding; Phases Diagram; Molibdenum
