Studies on microstructure and mechanical properties of modified 9Cr–1Mo (P91) steel in submerged arc welding with TiO-enriched fluxes

In the present work is studied the influence of titanium dioxide on the microstructure and mechanical properties of submerged arc weld P91 steel weldment. To manipulate the chemical composition of the weldment, the titanium dioxide (TiO) powder was added with fresh welding flux in various proportions (2.5–12.5%). The results of optical emission spectroscopy test showed that Ti wt% is systematically increased from 0.00 to 0.021, whereas, other alloying elements were fairly uniform. The micrographs of the scanning electron microscope reveal the presence of finely dispersed precipitates in the weld metals, and the percentage of precipitation increases with respect to the enrichment of titanium dioxide. The hardness profile of weld metal increases significantly with respect to the TiO addition. Formation of TiC and TiN could be the possible reason for the enhancement of hardness, which has a positive impact on the creep property of steel weldment. Enrichment of TiO reveals the appreciable improvement in the tensile strength properties. However, the highest percentage of TiO addition provides the adverse effect on the yield strength and ultimate tensile strength values. The presence of surplus quantity of oxide content into the weld metal could be the possible reason behind this. Toughness value of the weld samples showed the negative trend with the addition of TiO which can be increased by increasing the post-weld heating time.