Hot Ring Rolling and Cold Expanding Strengthening of Mn18Cr18N Thick-Wall Hollow Ingots

A short route manufacturing process of retaining rings was put forward, which was composed of hollow ingots manufacturing by Electro-Slag Re-melting (ESR), hot ring rolling and cold expanding strengthening. And microstructure mechanisms, deformation characteristics, and process parameters during both of hot ring rolling and cold hydraulic expanding strengthening were investigated. The results show that the multi-pass flow stresses decreased with increase of interval time. During multi-pass compression, grain refined at lower temperature of 1050 °C by static recrystallization, then grain refined at higher temperature of 1150 °C by both of dynamic and static recrystallization. Based on the influence of the contact arc length ratio on strain penetration in the wall deformation zone, the driving roller radius of 500 mm and the pressure roller radius of 130 mm were determined for the ring rolling process ofφ712 mm/308 mm × 902 mm thick-wall hollow ingot. The optimum rotate velocity of the driving roller should be 0.8 rad/s. And the feeding velocity of the pressure roller should to be 1 mm/s for matching. During cold deformation, planar slip and twinning predominated at small and large deformation, respectively, to increase strength. For the hydraulic expanding process of ϕ937/672 × 1034 mm hollow forging, the optimum matching of 60° punch angle and 5 mm contact seal height can be adopted for obtaining well-shaped strengthening forgings.