What is Armour Steel?
As the name implies, armour steel, protection steel, or “ballistic protection” steel is used to defend against an external danger like incoming bullets.
There are several steels used for armour applications, including stainless steels, manganese steels, Hadfield steels, and others, although martensitic-hardened steels are the most popular armour steels. Iron (Fe) and carbon are the primary chemical elements that harden steels (C). The qualities are often produced by varying the carbon content, additional alloying elements including chromium, nickel, and molybdenum, as well as specialized heat treatment methods.
Hardening and, occasionally, tempering are the main steps in the heat treatment process. This depends on the grade. In order to harden steel, it must be heated to a point at which the cubic iron crystals transform from their low-temperature ferritic (body-centered) structure to their high-temperature austenitic (face-centered) structure. Depending on the alloying content and the equipment being utilized, this temperature typically ranges from 700 to 900 degrees.
When the steel reaches the austenitic stage, it is quenched, which means it is quickly cooled to practically room temperature. The solid state solution of carbon atoms in the iron matrix is “frozen in” by the fast cooling, creating twisted ferritic cubical crystals. A very high strength is provided by the twisted crystals. The term “martensitic armour steels” refers to the twisted cubical form of iron crystals known as martensite.
To increase the steel’s ductility, formability in the cold state, and resistance to fatigue cracking, a second heat treatment procedure termed tempering can be used. It has become able to produce steels with less impurities during the past 20 years as steel production technology has advanced; this has eliminated the need to constantly temper steel to achieve essential mechanical qualities.
Armour steels are often classified according to their hardness, which is typically measured and designated in Brinell Hardness (HB).
Different armour steels – classes and use
Blast protection steel
Steels between 370 and 460 Brinell are referred to be blast protection steels. They are especially made to withstand high intensity strikes and waves from grenades, IEDs, and even mines. The majority of blast protection steels used today are 440 Brinell, which provides an excellent balance of hardness and toughness.
Typically, blast protection steels are utilized for armoured vehicles’ hull and floor. The hull or floor part of a vehicle is made from a single piece of extremely broad plate to ensure the maximum level of protection and integrity. Strong, lengthy presses that may be up to six meters long and 800 tonnes in weight are used to bend these plates. The “V-shape,” which is the most typical design for the hull, may channel blast forces under a vehicle.
Steels used for blast protection must be extremely robust in order to absorb a significant quantity of blast energy. The most popular method of evaluating and comparing blast protection steels is impact toughness testing at minus 40 degrees Celsius since actual blast tests are difficult to conduct. These steels are typically referred to by the NATO standard STANAG 4569’s blast classes. The range of carbon content is 0.12 to 24%.
Ballistic protection steels
A construction steel is often utilized for the load-bearing portion of a vehicle since it must not only be bendable and weldable but also have the maximum resistance to cyclical loading and fatigue. All “blast steels,” together with steel grades 500 and 550 Brinell, ought to be appropriate for use as “building steel.” Based on workshop features and usability, vehicle makers may quickly identify subpar brands and varieties of steel. Cracking, an inability to bend or shape, and restricted weldability are all indications of subpar steels that should be avoided.
High Hardness Armour (HHA) – 500 Brinell steel (HB477-540)
The most prevalent armour steels worldwide are high hardness (HHA or HH) steels, whose characteristics were first described by the US military standard MIL-DTL-46100.
The HHA steels must be weldable, fatigue-resistant, and flexible. They are typically employed in construction as load-bearing steels. HHA steel typically has a carbon content of 0.27 percent. Steel SS109, which is typically 6.5 mm thick, is required to stop NATO standard 5.56 mm calibre bullets.
Very High Hardness Armour (VHH) – 550 Brinell steel (HB530-590)
In essence, these steels are steels of the 500 type but with slightly more carbon—about 0.31%. The HHA steels must be fatigue-resistant, weldable, and capable of being bent.
NATO standard 5.56 mm calibre bullets require SS109, which is typically 5.5 mm thick steel.
“Add on steel”
As the name implies, add-on steel is steel that is added to an existing body or building. In many situations, add-on steels are bolted on as a “spaced armour” option.
Ultra High Hardness Armour steel (UHH) – 600 Brinell (HB580-640)
Even though many customers nowadays actually produce load bearing bodies/constructions out of these sorts of steel, 600 Brinell type armour steel is still regarded as somewhat exotic by certain users, and no steel supplier promotes 600 type steels as construction material.
The ability to produce steel has recently improved, and chemical compositions have been refined via research and development. As a result, 600 Brinell steels should be flexible and typically useful without instantly splitting during usage.
When compared to the HHA and VHH grades, UHH has a wider range of chemical compositions since various producers use different approaches and aim for distinct mechanical qualities.
NATO standard 5.56 mm calibre bullets require SS109, which is typically 5.0 mm thick steel, to stop.
Extreme High Hardness Armour steel (XHH) – 650 Brinell (HB630-700)
These days, XHH armour steels are regarded as uncommon and unusual. Not all steel firms produce XHH armour steels, which are now used mostly as add-ons. Although welding and bending are somewhat conceivable, they are often not advised. The fracture behavior of XHH steels begins to resemble that of ceramic materials.
Spaced armour and perforated armour are similar in certain ways, however the front layer of perforated armour has one or more plates with holes in them (perforations). Regularly spaced holes that are often smaller than the calibre of the bullet they were intended to stop are present.
Perforated armour functions by causing the bullet to be disturbed and twist, which lessens the projectile’s ability to penetrate armour. Making the holes may be expensive since it must be done either before the armour is hardened or, if done later, must be done carefully to avoid heating up the material and destroying its hardness.
Perforations can be made before to hardening via punching or laser cutting, although few manufacturers are able to do so and properly harden the steel afterwards. It is possible to drill and cut using a laser, but due to the large number of holes, this can be a time-consuming and expensive operation.
Drilling and water jet cutting are alternatives after hardening. Due to the quantity of holes needed, both procedures take a lot of time and money.
Protection against 7.62 x 54 mm AP is a common application of perforated armour (Dragunov). A 6.5mm 500 Brinell type armour steel with a 4.0 mm perforated 600 Brinell type armour steel may be utilized in place of a 16 mm solid 500 Brinell armour type steel. This approach has the potential to reduce weight by more than 40%.
How to buy armour steel – a simple guide
There are several producers of blast or ballistic grade steel plate across the world, with the bulk of them being in Europe. The following questions must be addressed in order to make an educated selection about the sort of armour steel you will employ:
- What kind of defense do I need? What kind of ammunition (calibre, geometry, armour-piercing, etc.)? What hit velocity and angle must the armour protect?
- What maximum weight is permitted for steel? Is the vehicle or application being safeguarded subject to any weight restrictions?
- How much can I afford? Can I choose a 500 Brinell type armour steel over a more costly 550 Brinell or 600 Brinell type?
- How is the steel supposed to be made? Here, you need to think about cutting, welding, and material bending.
- Should I purchase steel straight from the producer or through a distributor or stockholder? You may purchase directly from the majority of reputable armour steel manufacturers to save money, get complete certification and warranties, and receive product support.
- Direct order or from stock? Do I have time and a large enough number to purchase a manufacturing order in order to save money, or do I have to purchase from stock?
- How do I receive support? A reputable armour steel supplier will have staff on hand to assist you with both purchasing and using the steel.