Effects of precipitates on mechanical properties of P91 submerged arc welds

Modified 9Cr–1Mo, or P91, is a creep resistance steel grade for high temperature applications. Creep strength and ambient temperature impact toughness are required for welded joints, the latter of which is often a challenge especially for high deposition process such as submerged arc welding. In this study, three P91 welds with substantial differences in impact toughness and tensile properties are investigated. An extensive characterisation of precipitates in post-weld heat treated P91 welds was performed with electron microscopy (STEM), transmission kinetic diffraction, energy dispersive spectroscopy and an electrolytic precipitate extraction technique. Among the three welds, significant difference is observed in the amount of fine MX precipitates, which is correlated to yield strength, tensile strength and impact toughness.