Bonding Process of Steel-Steel Interface Under Low Temperature and Low Reduction Conditions

Joining steels under relatively low temperatures and low reduction conditions has been desired to avoid the degradation of properties of the steels to be bonded. In this study, the evolution of bonding strength between steel and steel or between steel and nickel during heat treatment was investigated using a model interface bonded by a surface activation bonding method. Furthermore, we also tried to bond steels under low-temperatures (500-600 ˚C) and low-reduction conditions (a few %) using an insert metal which can be melted at bonding temperature.

Using the model interface consisting of type 304 stainless steel (SS304), interstitial free (IF) steel and pure Ni sheets, the bonding strength was evaluated by the interfacial toughness obtained from peel test after heat treatment. The results of peel test demonstrated that interfacial toughness increased with increasing heat treatment time, and the evolution of interfacial toughness was clearly divided into two stages. In the first stage, interfacial toughness increases rapidly from zero to a certain level, above of which it increases gradually in the second stage. The rate of the increase in interfacial toughness was varied by heat treatment temperature. The activation energy of the rate of the increase in interfacial toughness was evaluated at each stage, and microstructure development at the interface during each stage was also clarified. Furthermore, two IF steels were also stacked with an insert metal, Zn or Sn, with 1 micron thicknesses, and then heat treated at 500 to 600 ˚C for various holding time. In the case of Sn insertion, steels was not bonded, while good bonding strength above the yield strength of IF steel was obtained in the case of Zn insertion.