A pressureless sintering method was utilized to fabricate metal/ceramic joints out of yttria‐stabilized zirconia (3Y‐TZP) and stainless steels (SS). Ultrafine (150 nm) and nanoscale (75 nm) 3Y‐TZP particles and micrometric 17‐4PH, 316L, and 420 SS (<31 μm) powders were tested. Isothermal and nonisothermal sintering behaviors of the powders and composite layers in hydrogen, argon, and vacuum atmospheres were examined. It was found that the mismatch strain between the zirconia ceramic and SS during cosintering is significant, which leads to bond cracking and joint failure. Nevertheless, interlayer diffusion of Zr, Fe, and Cr and the formation of a reaction zone, particularly during vacuum sintering, enables an accommodation of the residual stresses caused by the mismatch shrinkage upon cooling. The formation of a porous region close to the metal layer was observed. Sinter joining of zirconia to 420 SS is more successful compared with austenitic steel because of a lower difference in the coefficient of thermal expansion.