ELIMINATION OF FISSURES IN THICK SECTION INCONEL ALLOY 740 WELDS

摘要

INCONEL® alloy 740* has been identified as a prime candidate for the severe operating conditions of Ultrasupererifical boilers. Compared to other asndidate alloys it exhibils the highest stress rupture strength and corrosion resistance at projected operating steam temperatures approaching 1400℉ (760°C). Alloy 740 is a prccipitation-hardcnablc nickcl-chromium-cobalt alloy with a niobium addition. Ft is a new alloy that was derived from INCONEL® alloy 263~*. Extensive studies were executed to characterize it's weldability using typical boiler shop welding equipment and practices. The alloy was originally found to be susceptible to heal affected zone microtissuring in sections greater than one inch in thickness. This paper describes successful recent efforts to eliminate this microfissuring through modification of the base and weld filler metal chemistries. Tomorrow's USC boiler will require the use of thiek section supenralloys previously used in aerospace applieations. Lessons learned from that industry ore being applied and expanded to boiler applications up to three inches in thickness,Acceptable welding processes ami techniques are being developed which will result in sound thick section, crack free welds, Severnl weld processes were evaluated for welding the INCONEl alloy 740, Gas, tungsten arc welding and pulsed gas metai arc welding have emerged as the two most favorable processes