This article is a very interesting!
Most tanks at the beginning of World War II had cast turrets. These are T-28, T-34, KV-1, T-III and T-V tanks, "Cromwell", "Matilda", "Churchill" and others. Only France at that time produced "Samua-19" tank with a cast turret. The advantage of rolled steel armor is that with the same thickness as cast armor, it has a higher (by 10-20%) anti-bullet and anti-shell resistance. During the Second World War, most countries switched to the manufacture of cast turrets, and only Germany produced tanks with turrets made of rolled armor.
read more: http://btvt.info/3attackdefensemobility/turret_welded.htm
BM “Oplot” turret on Malyshev Plant, 2015