Transient liquid phase bonding of carbon steel components using Ni-based foils – A comprehensive joint characterization

Abstract

The transient liquid phase bonding (TLPB) process is one of the selected joining technologies to replace threaded connections in solid expandable tubulars. In particular, for expandable hot-rolled seamless carbon steel tubular products using Ni-based amorphous metallic foils as filler material. In this work, a comprehensive mechanical properties and microstructural characterization was carried out in TLP-bonded bars for this base metal/filler material combination. Both the joint and the heat affected zone exhibited a strength which compares well with the base metal, and a ductility in accordance with that which is typically specified for steel arc-welded joints. A coalesced lath-like bainitic microstructure was found at the joint. In addition, and by means of orientation imaging, a parent austenite grain - which is shared by the joint and an adjacent ferrite grain from the base metal - was found, which demonstrates the epitaxial nature of the TLPB solidification process. Also, a cell-block-like structure at ferrite grains next to the joint was detected, due to the plastic deformation developed in tensile-tested samples at room temperature.