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the late war electro smaleted E19 material for 35-55mm thick plating (in red) has increased non metallous alloying (silicon and manganese, both of which were not critically short ressources) but reduced chromium content (a critical ressource), compared to mid war E22SM (cast by Siemens Martin open hearth in a special duplex process, which achieved almost the same clean steel as electro resmelted). Because chromium is an effective hardening agent, the loss in hardenability caused by the lower allowance of Cr in E19 was counteracted by a slight increase in carbon and silicium content. Both armors were virtually free of any Nickel (reserved only for thicker section thicknesses, where it was needed to provide toughness).
This is a low alloy armor steel. It posesses enough hardnebaility from its chemical analysis. However, because of the increased carbon and silcium, it also requires careful controll of heat treatment times to prevent embrittlement of the hardened product.
The proof of plate minimum acceptance curves show that E22 (blue curve) offers more resistence at low impact obliquity, while the E19 (red) offers increased resistence at high impact obliquities. This is shown by the lower thickness of plating required to prevent holing or crack through against this projectile (german angular definition, 90° = perpendicular to the plate):
- 55mm plating
E22: -not tested E19: safe at 85°
- 50mm plating
E22: safe at 85° E19: safe at 75°
- 45mm plating
E22: safe at 70° E19: safe at 65°
- 40mm plating
E22: safe at 59° E19: safe at 57°
- 35mm plating
E22: safe at 49° E19: safe at 49°
- 30mm plating
E22: safe at 40° E19: safe at 42°
- 25mm plating
E22: safe at 30° E19: -not tested
Context is important in judging this product. If only tested for at normal impact, E22 would be rated superior and the lower resistence of E19 would be mistaken as an indicator of reduced late ww2 armor resistence, particularely with the lower Cr content. However,because late in ww2, most armor applications in this thickness range specified the need for increased oblique impact resistence (think of Hetzer and JP plates, or general tank and turret side plates in this thickness), E19 was naturally the better option to go with. It offered a higher degree of ballistic resistence under more acute obliquities and also safed critical ressources. A testiment for a good application of metallurgical knowledge.