Effect of various factors on toughness in P92 SAW weld metal

In order to increase efficiency in thermal power plants, new grades of 9 %Cr steels have been developed and are now being used. Even though these steels are used at high temperature, where toughness is not a matter of concern, it is important that the welded joints show a good toughness at room temperature, for fabrication and construction steps and for start up / shut down considerations. As a consequence the best toughness / creep compromise has to be obtained to guarantee all the requirements. The present work aims at evaluating the effect of various chemical elements on weld metal toughness in P92 steels. All-weld metal characterizations using submerged arc process were done. Chemical elements which were varied are carbon, chromium, nitrogen and tungsten. Variations of W, C and Cr within the base material range did not significantly affect toughness of the weld metal. However nitrogen content has a great influence on toughness level, decreasing N content resulting in a toughness improvement. The detrimental effect of B and Ti on toughness of weld metal for P92 steels has also been confirmed. An optimised chemical composition has been defined on the basis of this work. This solution features a promising toughness/creep compromise, as very good toughness at room temperature and satisfactory creep behaviour have been obtained.