The USSR received a lot of American armour, both as a part of finished tanks and armour plates. Soviet representatives had some access to the American steel industry as a result, and specialists toured the American Car & Foundry Company in April of 1943 where they picked up some information on American steel manufacturing.
"This factory is the largest supplier of cemented armour in the USA. It began to supply cemented armour about 3 years ago and in these 3 years it improved and developed its process.
Armour up to 2 inches in thickness is cemented.
Armour up to 2 inches in thickness is cemented.
Today the factory makes about 5000 tons of armour per month, about 60% of it is cemented (out of accepted plates). About 18-20% of the production is discarded as byproducts, about 2-3% due to production defects.
There used to be a lot of cracks, but a lot of work was spent on this issue and now cracks are rare. Work was done to make welding more precise, maintaining gap tolerances, training welders (they have schools for this), protection of the places from carbonization by schoop-plating them with copper, changing the design (sharp angles were removed), etc.
This factory (unlike many others) has very strict military QA with well educated workers and managers.
Armour now comes from the Republic Steel Co., Jones and Laughlin, thin armour is now purchased from Armco. Earlier the armour came from Carnegie-Illinois but it is no longer ordered due to low quality (impure and heterogeneous steel)"