Hot Cracking in Laser Braze Joint of High Strength Stainless Steel using Gold Brazing Filler Metal
Kazuyoshi SAIDA, Takehiro SAKATANI, Woohyun SONG, Kazutoshi NISHIMOTO
Hot cracking behavior in laser braze joint of 13Cr-4Ni stainless steel has been investigated using BAu-4 (Au-18%Ni) filler metal. The diode laser brazing was carried out for the T-fillet joint as well as the L-fillet joint which simulates the second bead in the T-fillet joint. The tandem beam brazing with a post-heating beam was also carried out in order to prevent the hot cracking. The laser powers of main and trailing beams were varied. The center line crack occurred in the second braze bead of the T-fillet joint, and was characterized as ductility-dip crack. Hot cracking susceptibility in Au-Ni braze metal was evaluated by spot-Varestraint test. The ductility-dip cracking temperature range (DTR) was about 1000-1250K. The FEM analysis of thermal stress/strain revealed that the rise curve of plastic strain intersected the DTR in the single beam brazing, however, it would not intersect the DTR by post-heating during laser brazing. The tandem beam brazing confirmed that no cracks occurred in the L-fillet braze bead made with trailing beam at the laser power of 200-300W.