The microstructural response of P7, a high-swelling, “pure” Type 316 stainless steel and the Magnetic Fusion Engineering (MFE) heat of Type 316 stainless steel were investigated after 14-Me V nickel-ion irradiation. Specimens of the P7 alloy were irradiated to fluences of 3.3 × 10¹⁶ 14-Me V nickel ions/cm². Irradiation temperatures ranged from 500°C to 650°C (0.45 to 0.6 Tm). In addition, a sample of Type 316 stainless steel was irradiated at 650°C (0.6 Tm) to a fluence of 3.3 × 10¹⁶ 14-Me V nickel ions/cm². The irradiated specimens were examined in cross section by electron microscopy. the 500°C irradiation of the P7 alloy produced a depth-dependent void distribution influenced by the excess interstitial effect of the bombarding ions. The 650°C irradiations of the P7 alloy produced a bimodal void distribution at the damage peak. The 650°C irradiation of Type 316 stainless steel produced needle-like precipitation in the entire damage region.