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Posted

Surface hardening adds hardness, often at the expense of toughness, thus producing somewhat brittle armor.

I think I read on Carius' Tigers in the Mud, that at the beginning of the Russian campaign, the German-manufactured tanks were preferred to the Czech ones because the later had too hard armor that tended to crack instead of deform like the former ones.

Posted

When properly done, surface hardening should not induce excess brittleness, because the bulk of the material remains at a moderate hardness. The hardened surface will crack but the cracks won't propagate into the ductile core.

In the case of WW2 era tanks, issues with brittle plate or casting are due to homogeneous armor of excess hardness, or to impurities or poor production. If the alloy is a simple carbon steel then there is a quite sharp tradeoff between hardness and toughness. I suspect in many cases high hardness was sought, and engineers tried to push it as high as possible whilst still having acceptable toughness, but wartime expediency then led to slacker standards and batches ending up with excess hardness.

Posted

Lack of alloyants, too. Especially manganese, molybdenum, nickel or vanadium.

America has lot of molybdenum, for instance, in Colorado. Germany was not so fortunate.

Posted
8 hours ago, sunday said:

Lack of alloyants, too. Especially manganese, molybdenum, nickel or vanadium.

America has lot of molybdenum, for instance, in Colorado. Germany was not so fortunate.

Yes, I was discussing this obliquely above, i.e. 'If the alloy is a simple carbon steel'. In compositions with significant quantities of alloying metals, the tradeoff can be severely attenuated.

In the extreme case you can get expensive but also very strong and tough alloys like AerMet.

Posted

Isn't it tougher (I mean more difficult) to make high-quality "thin" or "thick" plates?    I think I have read that the "sweet spot" for ship armor is somewhere in the 6-8" range with progressively higher thicknesses, while being overall more resistant than thinner ones, having lower figures of merit--and with armors BELOW a certain thickness (I'm not recalling off the top of my head) also being very difficult to make except in simple homogeneous form.  

Posted (edited)
4 hours ago, Poopstain said:

Isn't it tougher (I mean more difficult) to make high-quality "thin" or "thick" plates?    I think I have read that the "sweet spot" for ship armor is somewhere in the 6-8" range with progressively higher thicknesses, while being overall more resistant than thinner ones, having lower figures of merit--and with armors BELOW a certain thickness (I'm not recalling off the top of my head) also being very difficult to make except in simple homogeneous form.  

It is hard to make a categorical statement because of changing technology.

In the case of homogeneous plates, the optimal hardness falls with thickness.

For face hardened armour, thinner plates tends to run the risk of proportionally too deep a hardened layer, and for very thick plates it is hard to get a sufficiently deep penetration. In the case of large calibre APC, the hardened layer tends to be too thin in comparison to the penetration, and so that the advantage of hardening dissipates. According to Krupp engineers there was no advantage at all to cemented armour vs battleship main gun APC.

 

Edited by KV7
Posted
On 3/27/2022 at 10:46 PM, KV7 said:

It is hard to make a categorical statement because of changing technology.

In the case of homogeneous plates, the optimal hardness falls with thickness.

For face hardened armour, thinner plates tends to run the risk of proportionally too deep a hardened layer, and for very thick plates it is hard to get a sufficiently deep penetration. In the case of large calibre APC, the hardened layer tends to be too thin in comparison to the penetration, and so that the advantage of hardening dissipates. According to Krupp engineers there was no advantage at all to cemented armour vs battleship main gun APC.

 

Yeah the whole "cemented" thing was seen as revolutionary but as soon as someone came up with the "cap" idea it was pretty much back to square one.....

Posted
3 hours ago, Poopstain said:

Yeah the whole "cemented" thing was seen as revolutionary but as soon as someone came up with the "cap" idea it was pretty much back to square one.....

It took some time for shells to be resistant to the best face hardened armours though, and U.S. class A with a deep hardened layer (up to 55 % of the plate including the transition zone) was used till quite late and showed very good performance against many projectiles. Only the best shells with hardened caps could resist shatter at some obliquity.

  • 2 weeks later...
Posted
On 3/25/2022 at 6:41 PM, sunday said:

Lack of alloyants, too. Especially manganese, molybdenum, nickel or vanadium.

America has lot of molybdenum, for instance, in Colorado. Germany was not so fortunate.

Other stuff from Canada too. The Canadian Shield and Sudbury complexes for example. 

https://opentextbc.ca/geology/chapter/20-1-metal-deposits/

Posted
On 3/27/2022 at 7:51 PM, Poopstain said:

Isn't it tougher (I mean more difficult) to make high-quality "thin" or "thick" plates?    I think I have read that the "sweet spot" for ship armor is somewhere in the 6-8" range with progressively higher thicknesses, while being overall more resistant than thinner ones, having lower figures of merit--and with armors BELOW a certain thickness (I'm not recalling off the top of my head) also being very difficult to make except in simple homogeneous form.  

I think the thinner the piece the easier it is for it to get to the point of brittleness FASTER. Heat treating being the key thing. One thing I recall from reading on the Manufacture of British WWII Armored cars was that that the thinner plates of rolled armor, ,while hard was brittle. It could shatter if dropped, say like a sheet was standing up and fell over. 

The hardness/softness toughness/brittleness factors are tricky in metallurgy. Getting the right admixtures too is added complexity. 

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