A new method to make hollow ingots was developed to produce cylindertype forgings economically. The key-point of this method is the structure of the core which, consisting mainly of outer and inner steel pipes and intermediate special refractory, can readily be constructed, set in the mold and pulled out from the ingot, and which enables to control the cooling from inner surface of the ingot, without such defects as inner-side cracks.
Large hollow ingots up to 140 ton can be made by this method with less segregation than that of conventional ingots and with such small porosities that close and diminish at forging ratio of about 2. Thus, hollow ingots are utilized as materials for high grade forgings, as pressure vessels, resulting in effective saving of production cost.
Compared with conventional ingots, hollow ingots have following characteristics of solidification;
(1) Total solidification time is short (2) Minimum solidification rate is high (3) Final solidification is not so rapid (4) Solidification from inner surface is slow.
Every feature in the internal quality of hollow ingot can be explained from these characteristics of so-lidification.
