Welding filler metals tested in service for the high temperature resistant 9% chromium steel P91

In order to improve the efficiency of conventional power stations, header systems and steam piping constructed from the martensitic steel commonly known as Grade P91 have been used in several plants recently. We expect a large application of this steel in new power stations. In comparison to P22 or the super 12% Chromium steels, higher steam temperatures are possible where higher creep rupture properties can be expected. For many years, BOHLER Thyssen SCHWEISSTECHNIK GmbH has accompanied this development in close cooperation with engineering and construction companies in order to create suitable welding filler metals. Thyssen BRAND CHROMO 9 V - SMAW electrode (AWS E9015-B9) THERMANIT MTS 3 - TIG and MIG wires (AWS ER90S-B9) THERMANIT MTS 3 - SAW wire (AWS EB9 proposed) MARATHON 543 - SAW flux are TÜV approved filler metals already used in a number of plants world-wide. The major problem during the intense development of these consumables was the criteria to ensure sufficiently high toughness of the weld metal (min. values of the base material) with the shortest possible stress relieving time. Filler metals developed by BOHLER Thyssen SCHWEISSTECHNIK GmbH show toughness properties of greater than 50 J (37 ft-lbs.) at room temperature after heat treatment at 760°C (1400°F) for two hours and thus are on a higher toughness level than the commonly used filler metals for the super 12% Chromium steels. Contrary to the super 12% Chromium steels prescribing a post heat for wall thicknesses of greater than 10mm (0.375 inch), P91 weldments can be cooled to room temperature without the risk of cold cracks. In fact, P91 weldments should be cooled to 90°C (200°F) after welding and prior to post weld heat treatment to allow for complete transformation of the microstructure. Further development of the martensitic steel grades have lead to new grades of steel for even better high temperature properties. These new grades are known commercially as Nf616 (P92) and E911. Matching consumables MTS 616 and MTS 911 are available. In addition, Union I Cr 2 WV has been developed as a matching consumable for the welding of grade T23 ferritic – bainitic steel. We have presented the development and applications of these welding alloys in numerous papers and publications around the world. More detailed information is available on request.