The cast-versus-forged debate is real for shafts and pinions — but at girth gear scale, physics and economics push strongly toward cast construction, which is why the overwhelming majority of mill and kiln ring gears worldwide are cast steel.
The forging size ceiling
Forging a seamless ring beyond ~6 meters requires press and ring-mill capacity that very few plants possess, at extreme cost. Cast segments sidestep the limit entirely: pour quarter rings, machine the joints, bolt and finish-hob as an assembly. For 8–10m gears, casting is frequently the only practical route.
Strength in practice
A properly refined and heat-treated cast gear (LF refining, normalize + temper, 100% UT of rim and teeth) meets the same AGMA/ISO tooth ratings specified for mill duty. Service life is decided far more by alignment, lubrication and tooth-contact maintenance than by the cast/forged distinction.
Cost and lead time
Cast girth gears typically come in at a fraction of the forged price with shorter, more predictable lead times — and integral casting of features like bolting flanges removes machining and welding operations entirely. Spend the savings on better condition monitoring; your gear will thank you.