Non-homogeneous armor(NHA) in WW2

[Peasant]

First, I have a question: exactly to what extent NHA was used in WW2 armored vehicles? Most sources seems to indicate that it's been widely applied at least to front armour plates of German Panzers and Stugs before 1943, but the exact model and dates of introduction remain elusive. I've been able to find a single reference on historyofwar.org about it(see attached screenshot)
Any data on tests against unambiguously identified NHA on captured vehicles would also be appreciated.

[Peasant]

Examination by soviet specialists in June 1940 of Pz.Kpfw.III Ausf.G reveals that its hull and turret side were made with homogeneous armor, while the frontal parts with non-h.
Source: https://warspot.ru/10340-svoevremennaya-pokupka

[Jan-Hendrik]

Wrong subforum....

Jan-Hendrik

[Peasant]

Wrong subforum....

Jan-Hendrik

Is it? "Discussions on all (non-biographical) aspects of the Freikorps, Reichswehr, Austrian Bundesheer, Heer, Waffen-SS, Volkssturm and Fallschirmjäger and the other Luftwaffe ground forces"
I see no other subforum here that matches better the purpose of this thread.

Anyway: British "Technical Report No.7", dated 7 June 1942, Appendix "B" places the penetration of the 50mm driver's plate of the new PzIII tank at 200yrd for 2600fps 2pdr gun. Terminal velocity: 728m/s. Application of reverse DeMarre formula yields the K=2400, same as for soviet AP shells.
30mm side armour is penetrated at expected range and striking speed (K=1880). Cemented armour or just bad quality shells, I wonder?

[Jan-Hendrik]

There is a 'Panzer& other vehicles'-Forum....

Here is more the issue of units, KStN's, employments and so on...

Jan-Hendrik

[Peasant]

I see, you've got a point. I will ask the moderators team to move this thread there. Thanks for advice.
Edit: It looks like it's been done. My gratitude to the administration.

[Mobius]

Speaking of Russians and the 2 pdr.

[Mobius]

Maybe whelm can post British '43 curve CV 1 or one other early one on the 2 pdr to compare.

[critical mass]

German FH armor in AFV is either induction- or flame-hardned, thus a kind of surface hardned armor. It´s not a KC type naval face hardened sort of non-hemogenious armor! Chemically, all face hardned AFV plates were "homogenious", they just differed in hardness (much like monobloc AP-shell bodies could have variable hardness from front to back). That´s a significant difference to naval armor, which was indeed non-homogenious due to carburization of the face.

The depth of the hard face in flame hardened plates (20-50mm thick) is 6mm backed by a deep and soft backing. Flame hardning is best employed in relatively thin plating (20-30mm)due to the constant depth of face of 6mm. Thinner plates (6-18mm) typically were homogenious hard plates (sort of high hardness homogenious rolled plate).
With electric induction hardened armor, different thicknesses could be employed, and the depth of hardening was more easily manipulated due to the dependency on the speed of adcance. Electric induction hardening was preferred for manufacturing the thicker plating ranges (35-80mm). The chill is relatively hard with an abrupt drop in hardness to the soft back. Sort of dual hardness plating.

FH armor was rarely ever used for side plating or for sloped areas, where resistence to oblique impact was paramount. A primary function was vertical plating in areas, where protection against perpendicular impacts and direct line of fire was considered (f.e. turret faces, mantlets, spaced shields of the vertical driver or nose plates).

[Peasant]

Maybe whelm can post British '43 curve CV 1 or one other early one on the 2 pdr to compare.

Yeah, that would be great. I was about to post the one I had but its the CV.28, from 2/2/1944 that's explicitly noted to superseded the CV.1 from 17/3/1943.

FH armor was rarely ever used for side plating or for sloped areas, where resistence to oblique impact was paramount. A primary function was vertical plating in areas, where protection against perpendicular impacts and direct line of fire was considered (f.e. turret faces, mantlets, spaced shields of the vertical driver or nose plates).

Yes, I've already realized that it might under-perform at obliquity, compared to a softer material, but It's good to have someone confirming it.

German FH armor in AFV is either induction- or flame-hardned, thus a kind of surface hardned armor. It´s not a KC type naval face hardened sort of non-hemogenious armor! Chemically, all face hardned AFV plates were "homogenious", they just differed in hardness (much like monobloc AP-shell bodies could have variable hardness from front to back). That´s a significant difference to naval armor, which was indeed non-homogenious due to carburization of the face.

The depth of the hard face in flame hardened plates (20-50mm thick) is 6mm backed by a deep and soft backing. Flame hardning is best employed in relatively thin plating (20-30mm)due to the constant depth of face of 6mm. Thinner plates (6-18mm) typically were homogenious hard plates (sort of high hardness homogenious rolled plate).
With electric induction hardened armor, different thicknesses could be employed, and the depth of hardening was more easily manipulated due to the dependency on the speed of adcance. Electric induction hardening was preferred for manufacturing the thicker plating ranges (35-80mm). The chill is relatively hard with an abrupt drop in hardness to the soft back. Sort of dual hardness plating.

Well, I've used therm "Non-homogeneous" because I wanted to encompass all types of face hardened armour, both flame- and induction-hardened and the types employed by other nations in WW1/2 as well. I had no idea that it could refer to "chemically non uniform" armour. I'm not very knowledgeable in naval tech.
One thing I'd like to get a clearer view of is this part here ". The chill is relatively hard with an abrupt drop in hardness to the soft back. Sort of dual hardness plating.". Now I've read somewhere(could be even on this forum) that there are few sub-variants of surface hardened armours, and the so called "cemented"? one is superiour to the simple "dual hardness" plating, because its hardness gradient smoothly decreases along its thickness, with the hardest layer on top, sort of like in PzGr.39 post-1942 design, you've posted in the other thread.

Some pertinent data from 1942 "Report on the shooting of German tanks with AP and HE shells from tank guns" (CAMD RF 38-11355-832):

The 45mm gun in T-70 penetrates Pz.IV front hull part(the transmission housing) 2/2 shots at 50m entrance diameter 55mm, exit 50mm, while failing and leaving dents 30,28,25mm deep from 3 shots at 100m. Obliquity is: 14°+ 20° side angle(25° effective). Btw, it is explicitly stated the V0 of this gun is 760m/s.

Stug.III: 4 shots from 50 and 100m leave only 20mm dents in the 50mm frontal armour. Obliquity is 15°.

But most surprising are these results: Pz.III with 30+30mm armour bolted on front hull. Both shots fail at 50m leaving only 15mm dents in the first plate. Afterwards the bolts holding the plate are torn off and it fell. Angle 15°+ 20°.
It's almost certain that the 30mm add-on plate is FHA. The performance is remarkable. I wonder if it would've stopped it alone.

The results with 2pdr AP are similar to those from Cairo tests: cannot penetrate even from 50m. Dents 12,17,18mm deep, 60-65mm wide. V0 stated as 807m/s.

[Mobius]

Maybe whelm can post British '43 curve CV 1 or one other early one on the 2 pdr to compare.

Yeah, that would be great. I was about to post the one I had but its the CV.28, from 2/2/1944 that's explicitly noted to superseded the CV.1 from 17/3/1943.

That might be better as it would be more accurate.
(Someone posted a Canadian firing table awhile back and there might be an error in the 2 pdr 2800 f/s column. It's source is OB 43 CV/1)

[critical mass]

One thing I'd like to get a clearer view of is this part here ". The chill is relatively hard with an abrupt drop in hardness to the soft back. Sort of dual hardness plating.". Now I've read somewhere(could be even on this forum) that there are few sub-variants of surface hardened armours, and the so called "cemented"? one is superiour to the simple "dual hardness" plating, because its hardness gradient smoothly decreases along its thickness, with the hardest layer on top, sort of like in PzGr.39 post-1942 design, you've posted in the other thread.

The question what form of face hardening is better depends on the alloy condition, the heat treatment and the section thickness employed.
Assming one does not mess up either hardenability (via alloying) nor heat treatment, an answer can be provided in reference to section thickness.

However, one word of warning. The use of the word "cementated" has ramifications people may not be aware of. Each nation defines slightly different, with the UK using the term "non-cementated armor" for RHA, while both, Germany and the US refer to face hardened armor under the same term (class A deep chilled plate made by Betlehem and Midvale and Krupp KCN, both without the thin, cementation surface layer).

The gradual hardness contour in FH armor was first developed by Krupp 1892/3 for experimental Nickel-only steel armor plate No.49 (Harvey one year before used sort of dual hardness setup for Harveyized FH armor but unlike ww2 dual hardness armor it was truly heterogenious, due to a carburization of the face, and used either plain mild carbon or Nickel-steels but always without Chromium / Mo/ Va). Armor in this period was for naval applications and fortresses, only. This type was successful but very difficult to manufacture due to limited manipulation of heat treatment times (too narrow ranges), particularely in section thicknesses >260mm.
Krupp in 1894 tests with Plate No.420 Chromium-Nickel steel as a base (which it was using some years earlier for gun barrel production). This was the grandfather of all full strength homogenious and face hardened armor steels of the 20th century. When Krupp applied thecementation process and decremental face hardening to this plate, Krupp Cementiert was created, and had the benefit of beeing more easily manipulated in heat treatment times.
Both KC and Q-420 quickly replaced all previous grades of armor in production in all major powers. US ww2 AFV armor was chrome-nickel sort of Q-420 chemically and in view of the heat treatment. In germany, however, they moved on to Chrome-molly and later, chrome-vanadium steels due to the higher capacity of work hardening of the latter.

KC had a shortcoming in small section thicknesses. Because the superhard cementated layer (640-700BHN, depending on manufacturer) was almost always (1935 period KC/n.A. beeing the exception) the same depth, and ~1/3 of the plate also beeing chilled, the drop of hardness becomes quickly too rapid in small section thicknesses, creating a weakpoint, which upset the whole back-supporting-the-rigid-front principle. KC was not made -by any manufacturer- in thicknesses smaller than 100mm during ww2 anymore. A step in hardness becomes a more logical solution here, because the weakspot in hardness contour is still there but You maximize both, the superhard front to break up incoming shell, and the tough back to allow plastic deformation of the plate against an -ideally- broken up penetrator.

In ballistic tests, KC armor of 100mm thickness was rated "330" in relative ballistic resistence against calibre attack and induction hardned beeing "325", or 98.5% the resistence of KC against calibre attack. In 200mm thickness gauge, the difference was more dramatic: "350" vs "320" (91.4%). In thicknesses smaller than 100mm induction hardening ("dual hardness plate" was therefore preferred to KC "decrementally hardened plate". KC was preferred in thicknesses larger 120mm and larger but KC was a very expansive process and I know of no >100mm AFV armor plate beeing made of this process.
From time to time, WaPrüf and the HWA tested real KC plates but even for MAUS, the rather soft, homogenious Navy Wh/n.A. plates, and not KC was employed.

[Peasant]

snip

Again, great info from CM. although this was more of a historical excursion. I am more interested in practical stuff, like how FHA of DualHardness(DH?) type would perform compared to good RHA of the same thickness in a range of conditions. Would it be as superior against overmatching attack(probably not)? What if the projectile would've be already broken by normal RHA, would it still provide relatively better protection? I have found a US research paper on how the plate resistance changes with its hardness, but it gives info only on homogeneus armour.
Edit: Recently, when I was consulting the BIOS Report, and found a some info(see attachment).

[critical mass]

That quetion cannot be answered in general terms. The relative ballistic performance of FH armor depends primarely on the projectile quality. As a tendency, FH armor was superior, if it succeeded to break up the attacking shot and inferior or, at best, equal to good quality RHA, if it failed to break up the attacking shot. That, of course, holds only true, if the RHA in comparison always fails to break up the attacking shot, which is a presumption, from which we already know, that it is incorrect for certain obliquity and T/D ratio´s and projectile qualities.

[Peasant]

From "Hunnicutt - Stuart" p.134