Solid state transition joints made, by cold extrusion, between steel and Cu powder metallurgical (P/M) preform tubes were heat treated at various temperatures and time, with and without interlayer, to evaluate the weld strength and microstructural characteristics. Post-joining heat treatments lead to different recrystallized structures near the interface due to strain localization and solute drag effect. The strain localization and residual porosity in the joints enhanced void formation in the diffusion zone when the interlayer was absent. Coarse Ni powder as an interlayer reduced the weld strength due to physical discontinuities and residual particles at the interface, after heat treatment. On the other hand, finer Ni powder improved the weld strength. Use of 1 μm Ni interlayer in combination with optimal heat treatment conditions (950°C for 2 h) resulted in about 45% increase in weld strength. © 2006 Springer Science + Business Media, Inc.