The loss of the Nikopol mines has a HUGE effect on German Steel production.
Starting shortly, Speer orders that Manganese content, as well as nickel, in steel be cut back severely, making armor more brittle, and prone to penetration.
By June, Germany will have less than 30 days supply of some critical minerals like Chromium, Manganese, and Nickel.
Speer stated after the war that the loss of Nickel deliveries from the Petsamo, Finland mines is when he realized Germany had no hope of winning the war, no matter what he did.
It was also about this time the Allies will convince Portugal to stop exporting tungsten ore to Germany. Just as the loss of the ferro-alloys is affecting German armor plate, the loss of tungsten will result in less effective armor-piercing shells for tanks and anti-tank guns. One of the reasons you will see so many German soldiers carrying panzerfausts from now on is that they don’t have any other alternatives.