T-34 Nose Girder Casting Armor

Let's take a real close look at the armor basis of the T-34 bow/nose girder.  This is the cast piece that joins the two armor plates at the front of the T-34. 
1.  There are two styles of this piece.  There is the early style - a rounded piece that is described (Preliminary Report) as having a radius of about 4½".  There is the late style that is more angled but not as thick. It is the type in the T-34/85 and some T-34 model 1943 tanks.  Cross-section photos and armor specifications can be found in Review of Soviet Ordnance Metallurgy 1953 [PDF].  The Brinell hardness number for this armor casting is given as 192 BHN.  This is below the scale of anything I found in AP vs BHN testing documents (page 36) and is below the 200 minimum scale of my BHN calculator. As a thick rounded casting it should resist a little better than rolled armor of the same BHN as was noticed of the US 90mm cast turrets of 230 BHN resisting like 260 BHN in the Yugoslav Ballistics tests*.  Just splitting the difference the casting should resist like ~204 BHN. The standard that armor is compared to in our game is 270 BHN.   This gives it a 0.8955 comparative quality vs. an average of all types of projectiles.  (Solid shot penetrates softer armor comparatively better than large cavity AP.§)  The photos are scaled to one pixel per 1 mm. The cross-section thickness of each type nose girder is then measured at approximately 10mm intervals of height. 

2.  The thickness of the armor basis is rounded as per our game's values to the nearest centimeter.  It then is found that the early style nose girder has a height of 122nn for the 10cm armor basis coverage.   The new style has a height of 66mm coverage for the 10cm armor basis. The early nose style even has a 11cm armor basis that extends for

68mm coverage in the vertical.
3.  Now to find what percentage of the area this covers.  First we look at the T-34/76 turret.  This is 1.0156 m².
4.  The turret of the T-34/85 including cupola is 1.63 m².
5.  The hull silhouette area of both is the same and is 2.23 m².
6.  Putting these together gives the area of the T-34/76 = 3.25m² and that of the T-34/85 = 3.86m².
7. The lower hull is 1.78m wide thus the old style casting which has a 10 cm or better basis is 0.122m high = 0.217m².  0.217/3.25 =.0667 or 6.67%.  The new style casting which is 10cm or better basis is 0.066m high = 0.1176m².  0.1176/3.86 = .0305 or

Click to enlarge

Early style nose casting on the left.  New style on the right.  Numbers in red are actual thickness.  Numbers in green are normalized basis per quality.  The numbers in blue are the vertical heights that contribute 10cm and 11cm of protection. 

Welds are considered to be of 0.89 relative quality while 45-46mm rolled homogenous plates are 1.0 quality.   Values are prorated where they overlap.

Above - the area of the T-34/76 turret is about 1.02 m².  Right - the area of the T-34/85 turret is about 1.63 m².  The total area of the T-34/76 = 3.25m² and the T-34/85 = 3.86m². The percentage that is covered 10cm or better for the old style bow is 6.67%  For the T-34/85 the surface area of the bow that is covered by 10cm or more is 3.05%.

3.05%.
8. PW does not just go by percentages but by locations and there are only 8 hull and turret locations so the percentage must be multiplied by 8 to find the number of locations attributed to this value.   For the T-34/76 this gives 0.53 locations or slightly over one half location.  For the new style casting times 8 gives 0.244 locations.   It is less than half of a half location which just means it doesn't even round to a single half location.  It then does not rate a mention as a half location.  The old style casting has 0.373% chance of having 11cm armor basis.  When multiplied by 8 does produce 0.298 locations with this armor basis. So either a half location of 10cm or 11cm.  I'll probably make this a 10cm as 11cm might be too optimistic. The Armor Defense calculator program shows the difference between 10 and 11 results in a 1% overall change in penetration chance for PW.

9.  While the bow-nose girder had particularly poor quality armor it was thick enough to do its job.  As is shown its armor basis is even superior to the two plates it binds.  One exception might be the T-34 model 1940 which bolted the girder to the plates instead of welding them.  That may have produced a weaker area near the joint.

Comparison of armor values

* The relative quality increase in curved 90mm cast armor of the Sherman turret could also be attributed to a deflection angle of 11.5°.  There's no way to know.
§ In full size tests the US 76.2mm M62 shell assumes 204 BHN armor to have 0.944 quality while the US M79 shot assumes it to have 0.886 relative quality compared to 270 BHN homogeneous armor.

85mm gun penetration.
Firing table data sets from various countries are normalized to the US standard V50 criteria.   However the sets are also adjusted to an armor hardness of 270 BHN.  Which is close to the German test armor quality of 80-105 kg/mm² of 244-303 BHN or avg. of 267 BHN. Unlike others I don't use DeMarre* nor some other formula to come up with my own values. 
   An example: the Soviet 85mm S-53 tank cannon. The colored lines represent a data set, the black line represents the average of 5 sets.  The final values are rounded to the nearest centimeter and ranges given depending on what game they are for.
*Note - Each country may individually be applying DeMarre's formula to their test results to fill out their firing table data. Thus the average may be an average of how well this was accomplished.  I have no control of that.