Diffusion Bonding of Steeles at Temperatures Below A<SUB>1</SUB> Transformation Point

Diffusion bonding of S35C and SCM 435 steel was performed at temperatures (973 K and 925 K) below A1 point under various loads in vacuum (5×10−3 Pa) . The effects of post-bonding heat treatment and application of fine grained insert-metal prepared by a thermomechanical processing of SUJ 4 steel on the joint properties were evaluated from the results of tensile tests of bonded specimens and optical microscopy of bonded interfaces.A post-bonding heat treatment consisting of heating the bonded specimens of S35C up to just above the A3 point followed by air cooling markedly improved the joint strength by introducing the transformation aided migration of bonded interface and offered a successful bonding with low bonding strain. The application of fine grained superplastic insert-metal to the diffusion bonding of SCM 435 steel was effective to improve the joint strength. In this case, however, it was necessary to performe the post-bonding heat treatment consisting of heating at 1133 K for 1.8 ks followed by quenching and heating at 873 K for 1 .8 ks followed by air cooling, in order to produce a successful bonding with low bonding strain.