MECHANICAL-PROPERTIES AND MICROSTRUCTURAL CHARACTERISTICS OF LASER AND ELECTRON-BEAM WELDS IN V-4CR-4TI

Mechanical properties and microstructural characteristics of laser and electron-beam (EB) welds of a 500-kg heat of V-4Cr-4Ti were investiga ted in as-welded condition and after postwelding heat treatment (PWHT) by impact testing, microhardness measurement, optical microscopy, X-r ay diffraction, and transmission electron microscopy (TEM). Ductile-br ittle-transition temperatures (DBTTs) of the laser and electron-beam w elds were significantly higher than that of the base metal. However, e xcellent impact properties could be restored in both types of welds by postwelding annealing at 1000 degrees C for 1 h in vacuum. Analysis b y TEM revealed that annealed weld zones were characterized by extensiv e networks of fine V(C,O,N) precipitates, which clean away O, C, and N interstitials from the grain matrices. This process is accompanied by simultaneous annealing-out of the dense dislocations present in the w eld zone. This finding could be useful in identifying an optimal weldi ng procedure by controlling and adjusting the cooling rate of the weld zone by an innovative method to maximize the precipitation of V(C,O,N ). (C) 1998 Published by Elsevier Science B.V. All rights reserved.