Military grade steel is an important component in defense and security, and is used in anything from tanks to armored vehicles. Military and ballistic grades of steel – unlike structural or non-structural low-carbon steel – are manufactured, formed, and tested to different standards, in order to ensure high quality and integrity.
This article looks more closely at the properties, standard grades, and most common uses of military and ballistic steel.
What is Military and Ballistic Steel?
There are many grades of low-carbon steel that meet specific chemical standards.
While military grades of steel come with some chemical guidelines – such as a maximum carbon weight percentage of 0.32% – the focus of military grade standards is primarily on two criteria: hardness and ballistic limit.
Represented by the Brinell Hardness Number (BHN), hardness is calculated by comparing the amount of applied force on a piece of material to the size of the indentation of the force.
Common low-carbon steel – such as A36 – has a BHN that is two to three times lower than military grades of steel. Indeed, BHN is a critical characteristic of military steel, since a higher BHN indicates more abrasion-resistant material.
The below chart compares the BHN of standard low-carbon steel, military grade steels, as well as abrasion resistant steels.
In fact, grades of steel that are abrasion-resistant (AR) have similar or higher BHNs than military grades of steel. However, the difference between AR and military grade steel lies in the fact that military grades undergo a special testing called ballistic limit testing.
Using a controlled projectile, firing pattern, and velocity, ballistic testing identifies the velocity at which a target would both completely as well as partially penetrate a target.
Moreover, once the material has been certified as military grade standard-appropriate, the certification completely guarantees the material’s ballistic limit and integrity.
In fact, it is this certification which is the important differentiating factor between abrasion resistant steel and military grades of steel. Naturally, this comes at a cost – military grade steel is approximately twice as expensive as abrasion resistant material. Nevertheless, this high cost guarantees the material’s integrity during combat.
Commercial Grade Armor
Commercial grade armor lies in between abrasion resistant grades and military certified grades. In fact, commercial grade armor is certified to meet the National Institute of Justice (NIJ) standards 0101.06, which classify ballistic “threat levels” against which the armor will protect.
Engineers may opt for commercial grade armor – which is slightly more expensive than abrasion resistant grades, but less expensive than military certified grades – for projects that require some ballistic protection. However, commercial grade armor cannot protect to the level of military combat. Common examples of such projects include bank vaults, armored cars for transportation of currency, and body armor.
Overview of Common Military Grades
There are many types of military grades of metal materials, but the most common steel grades are MIL-A-46100, MIL-A-12560 and MIL-A-46177.
Typically used to stop hyper-velocity projectiles (HVPs), the MIL-A-46100 steel plate is also used to shield against sniper fire. Depending on the size and speed of the projectile as well as the distance the projectile is traveling, this grade is available up to 2 inches in thickness.
A common military-specified armor, MIL-12560 is used in a variety of defense applications, including:
- The manufacture of combat vehicles
- The testing of ammunition
- The protection of landmines and explosives
In comparison to other military grades, MIL-12560 absorbs shock extremely well. Before being certified, MIL-12560 must meet Fragment Simulated Projectile standards, and is available in four classes:
Class 1: Resists penetration
Class 2: Resists shock
Class 3: Testing and evaluation
Class 4: Maximum resistance to penetration
MIL-A 46177 is a less commonly used grade, with a maximum thickness of 0.249 inches. This grade is primarily used for armor, liners, or small vehicle applications.
This information has been sourced, reviewed and adapted from materials provided by Leeco Steel, LLC.
For more information on this source, please visit Leeco Steel, LLC.