In several reddit posts about German tanks and their ability to bounce enemy projectiles I see mentioned the fact that German steel was increasingly brittle due to missing alloys. I read the same in various blogs about real time tank warfare games (although not so realistic). Then, reading "Panther the German quest for combat dominance" I read the passage:
This damage should have excluded tank No. 3 from even being part of the testing process. Erickson makes the valid point that the Panther tank labeled No. 2 with the best plate reflected the true quality of Panther glacis plates for most of World War II and not the face-hardened armored Panther tank or the battle damaged example used at Isigny. Erickson is not the only one who believes that Panther armor remained free of serious defects for the duration of the war in Europe. Jentz and Doyle stated in their book Germany’s Tiger Tanks VK45.02 to Tiger II: Design, Production and Modifications that “There is no proof that substandard German armor plate was used during the last years of the war. All original documents confirm compliance with standard specifications throughout the war.” Evidence for the quality of late-war German armor plate can be found in a postwar U.S. Army Aberdeen Proving Ground firing test (Project number 5044: July 16, 1945), which consisted of American 90-mm M82 AP projectiles fired at an early production Panther Ausf. D tank and at a late-war produced Panther Ausf. G tank. (late-war being the time period of supposed inferior steel). The 90-mm M82 AP rounds punched two holes through the Panther Ausf. D tank’s glacis plate with significant break out due to FHA brittleness in the face of overmatching projectiles. The 90-mm M82 AP projectiles did not penetrate the glacis plate of the Panther Ausf. G tank but did achieve a penetration through the glacis plate machine gun mount. The end result being only “scoops” upon the late-war glacis plate, not an indicator of substandard late-war armored steel against an overmatching projectile.
Can someone clarify this point? Was the German steel as good as the allies for heavy protection or duty (tanks, ships, guns, etc..) after 1943?
In general the quality of German weaponry decreased as the war went on. The Nazis struggled in access to necessary resources in most logistical categories & most production of materiel in the latter years of the war, was performed by Holocaust prisoners & Russian POWs committed to slave labor by the Nazis in underground production facilities. As they were slaves of individuals trying to eliminate your people(s) from the face of the earth, you could imagine they didn't much morale for high efficiency in the work place. In fact, it seems sabotage was quite commonplace in these facilities.
I can't answer specifically to the changing rates in the quality of tank production or the metals used for that purpose (I hope someone with such specialized knowledge will be able to), but generally after Stalingrad the quality of all German equipment grew more & more outclassed by the equipment of the allies.
Once the Barbarossa offensive failed, Hitler's strategy for victory was to hold out for as long as possible & hope some miracle technology (or just a miracle) would allow the Reich to defeat hundreds of millions of Russians, Americans, Brits, & everybody else. Hitler green-lit a lot of experimental projects (all of which demanded the precious few resources the Germans had.) Many never managed to be built or advance beyond prototype because of resource availability. Simpler & cheaper equipment like a rocket propelled grenade (panzerfaust) or an assault rifle (Sturmgewehr 44) seemed to be produced more successfully than bigger more complicated equipment like jets. Much of this more complicated equipment produced later in the war that went beyond prototype stage, likely suffered failures because of being built by slaves (when they weren't poorly designed to begin with.) When you see a video of one of Von Braun's rockets spinning out of control, you could easily imagine it doing so because a miserable slave laborer poked a small hole in a hose.
I don't believe the Nazis did very rigorous quality testing either as the war drug on. When you're fighting millions of men from dozens of nations, you have to field more tanks than you can afford to let sit in a testing site. Nor could you really afford to take the time to scrap the ones found defective. The factory could be bombed tomorrow after all. There was likely wide variety in the production qualities between the different facilities at different times based simply on what & whom they were furnished with.
As for the ability to bounce projectiles, I think this was more of a property of the architectural design of the tank. If you want projectiles to bounce off your tank, designing it to where enemy projectiles meet the armor at a deflecting angle is what you'd want. When the Russians redesigned their tanks after the Winter War, they did a good job at designing it so enemy projectiles deflected off the armor. When Russian tanks outclassed German tanks, the Germans designed the Panther to match its quality in the field.
Additionally German tanks were notoriously heavy (& gas guzzling). A Sherman had two inches of plate but a Panther had over 5 inches of plate. Germans might even weld on shields to the sides of the tank for more armor (at least older models; I'm not sure about the Panther.) The general thickness of German tanks helped them additionally in protection against projectiles (unless the thickness made them run out of gas.) The best place to shoot most German tanks (if not the underbelly) was in the back. The back was generally thinner in plating, not angled to deflect, & held the tank's engine. Many would be lost however to breaking down & having to be abandoned or being obliterated by allied air support (which the Germans had little to fight against with in the end of the war.)
Also as much as American tank crews went on about how fearsome German tanks were, I've heard several accounts on how the Germans themselves had little faith in their tanks. They in particular complained about frequent engine failures & lack of access to fuel. They even seemed to have more respect for the Sherman than they did their own Tigers & Panthers.
I'm sorry I have no sources. Most of what I know is from seeing many documentaries & reading many reference books over the years. The book you are reading sounds like it may be a good read, especially as a companion to other sources on German equipment & production. I think in particular reading or watching something on El-Alamein, Kursk, & the Battle of the Bulge would the good places to start with in regards to German tank performance in the field. Armor was pivotal in these battles & accounts of soldiers of both sides that bore witness to German tank performance, as well as analysis by experts, is likely to better answer your inquiry into the subject than I ever could.
Tl;DR - The Reich decreased in general during the war.