Microstructural changes during welding and subsequent heat treatment of 18Ni (250-grade) maraging steel

Sheet material specimens from 18Ni (250-grade) maraging steel were gas tung sten-arc welded using two different filler wires: one matching the base mat erial in composition and the other with higher cobalt but lower molybdenum and titanium contents. Welding was carried out both in constant-current and pulsed modes. Post-weld aging was performed at three different temperature s, viz., 425, 480 and 520 degrees C. Metallographic characterization reveal ed pronounced segregation, presumably of Ti and Mo, along interdendritic an d intercellular boundaries in the weld metal produced with filler of matchi ng composition. This led, during subsequent aging. to austenite reversion a t temperatures much lower than in wrought (unwelded) material. Segregation and austenite reversion were not noticed when Ti and Mo contents were reduc ed in the filler wire, except at the highest aging temperature used. The us e of pulsed welding resulted in some grain refinement, but the effect was n ot considerable. (C) 2000 Elsevier Science S.A. All rights reserved.