Microstructure and Properties of Press-Bonded Dissimilar Stainless Steel and Mild Carbon Steel Ingots

Dissimilar steel welds between stainless and mild steels are necessary for the efficient utilization of stainless steels in construction. In the present work, a dissimilar large-sized steel ingot was fabricated by press bonding a Q235 steel to a SUS 304 steel at 1100–500 °C. The microstructure of bonded interfaces has been characterized by scanning electron microscopy, electron probe microanalysis, and transmission electron microscopy, together with tensile tests to evaluate the bonding strength. It has been demonstrated that a strong-bonded, high-quality, dissimilar steel ingot could be fabricated by press bonding. The (Fe, Cr)3C carbide is present in the narrow zone of diffusion-bonded stainless steel and mild steel. Interestingly, the maximum hardness is not too high to make the transition zone brittle but enough to constrain the narrow soft ferrite during tensile and fatigue tests, causing the final fracture to occur in the mild steel region rather than the bonding interface.