Abstract: This article analyzes and summarizes the development process of a forging for the mechanical penetration of a nuclear island containment vessel in a certain company. This forging has a slender thin-walled stepped structure. In order to prepare high-quality steel ingots for nuclear power forgings, a control scheme for the number of ladle cycles was independently designed, and the Ca line addition was adjusted based on the ladle age, achieving the effect of Ds type inclusions ≤ 1.0 level. A specialized insulation device for forging design has achieved multi-stage temperature control forging method, reducing the temperature drop at both ends, minimizing the number of fires, and avoiding high-temperature small forging ratio forging. Calculate the phase transition point based on the composition, determine the two normalizing temperatures, and obtain 7.5 grade fine grains; Tempering increases the hydrogen expansion time, effectively avoiding hydrogen induced defects. The development of through piece forgings was optimized through three processes: smelting, forging, and heat treatment, and the rationality of the plan was verified through demonstration and testing. This provides a reference for ensuring the design and research of the safety shell pipeline system.