Effect of repair welds on the microstructure and mechanical properties of 9Cr1Mo welding joint

9Cr1Mo steel is widely used in the construction of power plant components. Since performing periodic repairs is one of the most important requirements for industrial use of 9Cr1Mo steel, in the present study, the repair welding of the steel and post-weld heat treatments was carried out and its effect on the mechanical properties and microstructural evolutions after several stages of repair welding was studied. Therefore, a detailed structure-property relationship of weld metal, base metal, and HAZ using optical microscopy, scanning electron microscopy techniques as well as room temperature tensile test, impact test, and microhardness examinations were found. The results showed that there was a direct relationship between the number of welding repairs and the increase in average hardness. Moreover, the hardness gradient in the several welded samples was significantly higher than the one-pass welded sample. On the other hand, post-weld heat treatment operations increased the number of precipitations in the weld metal and HAZ and the size of primary austenite grains in the weld metal and HAZ was more homogeneous.