Forgings for the reactor pressure vessel (RPV) of the pressurized heavy water reactor (PHWR) 700 MWe, which is composed of seven major parts and nozzles totaling about 965 tons, were successfully developed. These forgings are: 1. Flanges: an outside diameter of 8440 mm and a weight of 238 tons max, requiring an ingot of 570 tons. 2. Shells and torus: an outside diameter of about 8000 mm with large height. 3. Cover dome: a diameter of 6800 mm and a thickness of 460 mm, requiring a blank forging before forming of 8000 mm in diameter and 550 mm thick.

The material designation is 20Mn-Mo-Ni 5 5 (equivalent to SA508, Class 3).

Even with greater dimensions and weight than the current largest forgings, the manufacture and the qualities achieved were satisfactory. These successful results were obtained by recent developments in the manufacturing technology of steels, such as steel making, metal-working processes, and heat treatment, which are vital to the quality of large-sized and heavy-walled steel forgings.

In this paper, the manufacturing of and the properties of such large and integral forgings are discussed, including an overview of manufacturing processes for ultralarge-sized forgings over the last two decades.