THE EFFECT OF OPERATING TEMPERATURE EXPOSURE ON NON-POST-WELD HEAT-TREATED 2.25CR-1MO STEEL WELDMENTS

Usually a post-weld heat treatment is performed on weld repairs for heavy section low alloy 2.25Cr-1 Mo steel power plant components. This procedure relieves the stresses in the weldment and results in improvements in both the room and high temperature properties. A significant saving, in both time and cost, could be realized if the post-weld heat treatment could be safely eliminated by an in situ heat treatment or non-post-weld heat treatment. In the present work, two different multi-pass and multi-layer welding procedures were employed and the resulting welds were subjected to a simulated in situ heat treatment of 538-degrees-C for up to 4000 h. The first procedure followed the relatively standard weaving method of pressure pipe welding, while the second involved a low heat input ratio temper-bead technique. A refined grain structure, within the HAZ was observed for both welding procedures. After exposure, at the simulated operating temperature of 538-degrees-C, there was an initial rapid reduction in hardness and an increase in toughness. Carbide development had a major influence on the mechanical properties. The conventional welding procedure resulted in a higher degree of tempering than the temper-bead weld procedure.