9Cr steels are widely used for high temperature service, principally in applications related to energy generation. Lately several variants of these materials have been developed through the addition of B, W and Co, among others. Due to the fact that information on influence of welding procedure on the welded joint is scarce, the objective of this work was to study the behavior of both the base metal and the weld metal of circumferential weldments performed using semiautomatic welding process under gas mixture protection. Two FCAW rutilic slag wires, alloyed with 9Cr1Mo and 9Cr0.5Mo1W1Co respectively, were used under Ar/20%CO2 gas shielding. Post weld heat treatments of 4 and 2 hours have been carried out. The microstructure was analyzed in the different zones: weld metal, heat affected (coarse and fine grain, intercritical and subcritical) and not affected base metal. Chemical composition of the weld metal, transversal tensile properties of the joint and microhardness along the weld transversal section were determined. In all cases it was obtained maximum hardness values in the weld metal and a decrease in this property in the heat affected zone from the coarse grain zone to the base metal one. The minimal hardness values were achieved in the intercritical zone, lower than those of the metal base. Hardness and tensile strength increased when the weldment was performed with the 9Cr0,5Mo1W wire. The shorter heat treatment allowed obtaining higher values of tensile strength, in all the cases. Toughness and creep resistance determinations will be the next step.
9Cr steel; Post welding heat treatment; Microstructure; Welded joint; Tubular wire
