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 280…388 НВ. 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:

The typical armor steels of this grade are MARS 190 (France), ARMOX 370S (Sweden).
ARMOX 300S and ARMOX 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°С and ballistic resistance (V₅₀).

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 about 1000…1400 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 477…534 НВ. 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 are Grade 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°С 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 534…601 НВ (for 4.7…25.4mm thicknesses) and 477…534 НВ (for 25.5…76.2mm thicknesses). The armor of Class 2 is supplied with 302…352 НВ.

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°С and ballistic resistance to 7.62mm, 12.7mm and 14.5mm AP bullets, as well as to 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

Table 2. Main Swedish Armor Steel Grades

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