Here is a great site dealing with Finnish armor. http://www.andreaslarka.net/ Andreas is someone that I have not met in person but have had email contact with in the past. He is a nice guy and has a site that is full of great information. It is not only the best site on Finnish armor but is hands down one of the most informative sites on the subject of armor that can be found on the Net. Well worth checking out.
"Certainly the US had the expertise and facilities to produce
cast AFV hulls and turrets. As another poster detailed, most of the
many M4s we produced had cast turrets, and a majority had cast
hulls. Castings, though, have certain inherent disadvantages. No
matter how metallurgically sophisticated a nation is, the physics
dictates that grain orientation cannot be controlled, and grain growth
is mostly uncontrollable, in large castings. Thus even the most
elegant tool steel alloys are not particularly strong as raw castings,
without work hardening to make a fine grain structure. Casting's main
advantages, once the tooling is built, are production rate and lower
(not higher!) technological requirements. A casting
facility--especially one that works with simple alloys--can be not
much more than a big building, an overhead crane and a furnace.
Rolled plate, on the other hand, may not be perfect, but it can offer
fairly good and consistent grain size, work hardening, and especially
grain orientation. Welding of fabricated plate sections, if done
properly, does not compromise these advantages. The gains from plate's
metallurgical advantages more than offset the small trigonometric
differences in effective thickness from small angles of incidence of
shell impact against angled sections of cast hulls and
turrets. Sophisticated heat treating can be combined with rolling to
make very strong steel. But good rolled plate requires a very, very
expensive and complicated mill. There are not many in the world. I
believe the reason the Russians did not make tanks of plate is that
they simply did not have the mill capability.
The ideal tank structure is a forging. Forged steels can be
roughly twice as strong as cast, pound for pound, and much more so
around curves, unlike fabricated plate. If you want me to admire a
nation's military metallurgical capability, show me a tank with a
forged hull. Not very easy to do. To the best of my knowledge, no one
forged tank structures in WWII."