I would suggest looking at the "Combined Intelligence Objectives Sub-Committee Item No. 2, File No XXXI-40: Berlin-Lübecker Maschinenfabrik (BLM)". The British National Archives or the Imperial War Museum should be able to help you access it.
It is referenced in Appendix V of Backbone of the Wehrmacht by Richard D Law. Seeing as you appear to know what hammer-forging is I will not repeat it here, because sadly it does not contain any information about the materials, only the machine and the process. If this is because the report mentioned above did not contain this information or because the author didn't see it as important, I don't know, but at least it's a start.
The report should also contain some information about the BLM barrel straightening machine which I found to be quite interesting.