Allied tank armor, quality control

[critical mass]

For whats worth, German data in general attribute 15% loss of resistence to CHA if compared to similar thickness RHA. Generally, the difference was attributed to lack of cross rolling, which helps orienting the crystal structure of the metal matrix. This lead to considerable differences in reference nominal resistence of plate (=G(s) in german parlance, with only a smooth bulge allowed on the back side but no cracks or spall emitted form the backside of the plate) when attacked obliquiely by APC.

As a further notice, mastering thick RHA or CHA armor was not a trivial achievement. It was extremely difficult to translate lab knowledge into applicable mass production techniques. Large section thoicknesses don´t cool quickly internally and this can cause temper brittleness. In order to retain ductility, all manufacturers added relatively high% of Nickel, which was an effective toughening agent in thick sections. However, large amounts of Ni also increase the chance of temper embrittlement from secondary and tertiary reheating exposure such as welding. That was even moreso if the heat had elevated impurities (sulpur and phosphorus) or other hardening but also embrittling agents (like manganese and silicium, among others).
The Germans largely resorted back to Krupps expensive Ni/Cr steel for the thickest section plates to adress these issues and developed very clean electrosteel (low impurities) with very complex multi stage thermo-mechanical treatment to create weldable medium section thickness plate. Even then, the welding had to be done interlocked to provide constructive resistence if the weld seam broke.