The aim of the present study is to derive optimized post heat treatment temperatures to get a proper formability for Ti/STS409L/Ti clad materials. These clad materials were fabricated by cold rolling followed by a post heat treatment process for 10 minutes at temperatures ranging from $500^{circ}C$ to $850^{circ}C$. The microstructure of the interface was observed using a Scanning Electron Microscope(SEM) and an Energy Dispersive X-ray Analyser(EDX) in order to investigate the effects of post heat treatment on the bonding properties of the Ti/STS409L/Ti clad materials. Diffusion bonding was observed at the interfaces with a diffusion layer thickness increasing with the post heat treatment temperature. The diffusion layer was composed of a type of(${varepsilon}+{zeta}$) intermetallic compound containing additional elements, namely, Fe, Ti and Ni. The micro Knoop hardness of the Ti/STS409L interfaces was found to increase with heat treatment up to $800^{circ}C$ and then decrease for temperatures rising up to $850^{circ}C$. The tensile strength was shown to decrease for heat treatment temperature increasing to $750^{circ}C$ and then increase rapidly for temperature rising up to $850^{circ}C$. A post heat treatment temperature range of $700{sim}750^{circ}C$ was found to optimize the formability of Ti/STS409L/Ti clad materials.