Microstructure embrittlement of hard metal–steel joint obtained under induction heating diffusion bonding

The aim of this work was to investigate the effect of the distance between the workpiece and the coil on the properties of a hard metal–steel joint obtained under induction heating diffusion bonding. Also it was aimed at understanding the microstructure evolution and embrittlement.It was found that at a distance of 2–2.5 mm the joint's tensile strength was close to zero and the hard metal plate became extremely brittle. The normal texture of the Ni-interlayer was partially replaced by solidification structure due to overheating and melting. The formation of a brittle eutectics and complex carbides, as well as reduction of the Co binder phase of the hard metal were identified as the reason causing embrittlement and cracking of the joint material.In order to prevent the overheating and embrittlement of the hard metal–steel joint it is recommended that heating should be carried out with a lower heating efficiency and low heating rate, especially when approaching the holding temperature set for bonding.

► Overheating of the hard metal plate was due to a low distance to the induction coil.
► Solidification of eutectics and carbides was demonstrated.
► Loose WC-grains due to partial reduction of the Co binder phase were established.
► The joint microstructure was found to be crack sensitive providing a low tensile strength and ductility
► In order to get a quality joint heating efficiency and heating rate should be low.