| | | | |

Armor steels

Both in Russia and abroad homogeneous low-alloy armor steels are mostly used for combat equipment protection.

 

1.     Steels for Heavy Combat Vehicles (Tank Armor)

 

Such steels shall not crack under impact of large-caliber shells (survivability requirement); they also shall meet the welding requirements (no tempering of welds is allowed).

For the most part Cr-Ni-Mo alloy steels are used with the upper allowable limit of carbon content (no more than 0.30% for thicknesses up to 100mm).

Such steels are supplied after hardening and high-temperature tempering to 280388 . The main specifications and acceptance requirements abroad are stated in MIL-A-12560 Armor plate, steel, wrought, homogeneous. For use in combat-vehicles and for ammunition testing.

The hardness requirements depend on the plate thickness, namely:

for6.212.6mm: 341388
for 12.719.0mm: 331375
for 19.131.7mm: 321375
for 31.850.5mm: 293331
for 50.5101.3mm: 269311

The typical armor steels of this grade are MARS 190 (France), ARMOX 370S(Sweden).
ARMOX 300S andARMOX 400S also belong to the above strength class, but because of lower carbon content the required strength (hardness) is achieved by hardening and low-temperature tempering.
Domestic steels usually feature higher carbon content which imposes heavier requirements on the choice of welding materials and armored structure welding methods.

Acceptance Requirements

According to MIL-A-12560 armor plates shall be checked for their hardness, Charpy impact energy at -40° and ballistic resistance (V50).

Plate thickness range, mm

Ammunition caliber and type

Impact angle, deg.

6.3 14.3

7.62mm , 2

0

14.4 28.6

12.7mm , 2

0

28.7 69.8

20mm -, 602

0

70.0 100

57mm , 70

0

90mm , 82

45

In Russia the acceptance requirements are different. In the ballistic resistance tests by small arms instead of V50 the non-perforation angle is defined; 20mm ammunition is not used; 100mm ammunition is used instead of 90mm ammunition etc. Besides, instead of impact energy the specimen fracture mode is checked.

These differences are only conditional and there is no problem to agree on the acceptance requirements acceptable for both parties.

Typical foreign steels belonging to this class are given below in Tables 1 and 2. The strength of domestic hardened and tempered cannonproof armor steels is about10001400 MPa.

 

2.Armor Steels for Light Armored Vehicles (APC, IFV)

 

Such steels shall resist without cracking hits of large-caliber small arms bullets (survivability requirement) and meet the welding requirements (in case of welds tempering).

For such applications steels with the upper allowable limit of carbon content (no more than 0.32%) are used.

Such steels are supplied after hardening and low-temperature tempering to 477534 . The main specifications and acceptance requirements abroad are regulated by MIL-A-46100 Armor plate, steel, wrought, high-hardness.

The most typical armor steels of this grade are MARS 240 (France), ARMOX 500S (Sweden).

Domestic steels of this grade areGrade 2P and Grade 7. Besides, steel Grade 7 does not require welds tempering.

According to MIL-A-46100 armor plates shall be checked for their hardness, Charpy impact energy at -40° and ballistic resistance to 7.62mm, 12.7mm and 14.5mm AP bullets. The differences in foreign and Russian acceptance tests have been mentioned before.

Typical Russian and foreign steels of this grade are given in Tables 1, 2 and 3.

 

3.Steels of Wide Application Range

 

Such steels shall not crack under impact of 20mm ammunition.

Such steels are supplied after hardening and low-temperature tempering to 534601 (for 4.725.4mm thicknesses) and477534 (for 25.576.2mm thicknesses). The armor of Class 2 is supplied with 302352 .

The main specifications and acceptance requirements abroad are regulated by MIL-A-46173 Armor steel, plate, wrought, (ESR). (3/16 through 3 inches, inclusive).

The most typical armor steels of this grade are MARS 270 (France), ARMOX 560S (Sweden).

The most typical armor steels of this grade are Grade 77 and Grade 88. Steel Grade 77 does not require welds tempering.

According to MIL-A-46173 armor plates shall be checked for their hardness, Charpy impact energy at -40° and ballistic resistance to 7.62mm, 12.7mm and 14.5mm AP bullets, as well asto 20mm ammunition (only for 25-50mm thick plates). The differences in foreign and Russian acceptance tests have been mentioned before.

Table 1. Main French Armor Steel Grades

Steel Grade

Nominal Chemical Composition

Thickness, mm

Carbon, % by weight

σ,MPaaverage

Hardness,HB

Production method features

Standard

MARS 190

0.30C-1.10Cr-2.0Ni-0.45Mo

2 - 50

≤ 0.30

1100

≤ 388

out-of-furnace treatment

S ≤ 0.005%

MIL 12560

51 - 500

≤ 0.33

900

MARS 240

0.285C-1.50Cr-1.50Ni-0.30Mo

≤ 38

≤ 0.32

1700

477 - 534

same S ≤ 0.004%

MIL 46100

38 - 50

1650

450 - 534

MARS 270

0.35C-0.75Cr-3.10Ni-0.40Mo

< 25

≤ 0.37

2000

534 - 601

same S ≤ 0.002%

MIL 46173

25 - 75

1700

477 - 534

MARS 300

0.50C-0.80Si-4.0Ni-0.40Mo

≤ 8

≤ 0.54

2180

578 - 655

 

Table 2. Main Swedish Armor Steel Grades

Steel Grade

Nominal Chemical Composition

Thickness, mm

Carbon,% by weight

σ,Mpaaverage

Hardness,HB

Production method features

Standard

ARMOX 300 S

0.18-1.5Mn-0.4Cr-0.65Mo-0.003B

5 - 60

≤ 0.20

900

280 - 340

Out-of-furnace treatment

S ≤ 0.010%

Thermo-mechanical treatment

MIL 12560

ARMOX 400 S

1150

360 - 420

ARMOX 370 S

0.28-1Mn-0.8Cr-1.1Ni-0.65Mo-0.002B

5 12.9

≤ 0.30

1300

390 - 440

MIL 46100

MIL 12560

13 22

350 400

22.1 34.9

330 380

35 59.9

300 350

60 - 80

265 - 315

ARMOX 500 S

6 13

≤ 0.30

1600

480 - 540

MIL 46100

13.1 - 50

450 - 520

ARMOX 560 S

0.35-1Mn-1.2Cr-3Ni-0.65Mo-0.002B

6 20

≤ 0.38

1850

534 - 601

MIL 46173

ARMOX 600 S

0.45-0.8Mn-0.8Cr-2.5Ni-0.65Mo-.002B

4 10

≤ 0.50

2150

570 - 640

   

Table 3. Armor Steels with Low-Temperature-Tempered Martensite Structure (Russia)

Steel Grade

Alloy System

Thickness, mm

Carbon,% by weight

σ,MPaaverage

Hardness,HB

Production method features

Similar standard

2P

Si-Mn-Mo

4 7

≤ 0.29

1550

444 514

Out-of-furnace treatment S ≤ 0.010%

(MIL 46100)

8 14

1450

388 495

15 22

1400

363 495

7

Si-Cr-Ni-Mo

4

≤ 0.24

1550

444 - 514

Same

Same

5 6

1500

429 514

8 13

1450

388 495

15 22

1400

375 495

77

 

8 - 20

≤ 0.37

1900

477 - 532

electroslag remelting

(MIL 46173)

88

 

8 - 20

≤ 0.42

2000

495 - 540

electroslag remelting

(MIL 46173)

44

Cr-Ni-Mo-V

2 - 15

≤ 0.47

2100

511 - 555

Electric arc remelting, electroslag remelting

-

 


| | | | |