Heterogeneous steel armor – a new direction or a well-forgotten old one

Authors:K.D. Ivanov, D.G. Kupryunin, E.N. Chistyakov

The protection of lightly armored vehicles and fighters has always needed strengthening. This is especially true today, when in numerous local conflicts it is these positions of the belligerents that bear the maximum losses.

It is no coincidence that in almost all countries there is an intensive development of so-called light armor designed to protect, first of all, from small arms bullets and small-caliber cannon shells [1-3]. But, if 5-7 years ago the main emphasis was on combined barriers using ceramics, today various spaced barriers using ultra-high-strength steels are being used more and more actively. There are many reasons for this, the main ones ; the high cost of ceramics, its low survivability and poor maintainability on the one hand, and the emergence of new grades of steels with high strength and protective characteristics on the other. Moreover, the development of such steels continues in many countries.

One of the possible and obvious solutions for improving the ballistic characteristics of armored steels is the creation of heterogeneous structures [1-5]. Developers of many countries, including Russia, are working on such materials today. Such studies are conducted by the Foundation for Advanced Research (FPI), which develops heterogeneous structures based on new technologies for the formation of a cemented layer. Fort Technology CJSC has been developing heterogeneous steel for armor elements of bulletproof vests for several years using explosion welding technology. The same technology was used in the early 2000s by the FSUE Gosniimashinostroeniya[5].FSUE RFNC-VNIIEF patented in 2013 a heterogeneous steel bulletproof armor obtained by gluing two grades of steel with a hardness of the front and back layers 62-67/46-51 [6].The SIC Kurchatov Institute and the Central Research Institute of KM Prometheus, within the framework of the Zaslon Research Institute, investigated possible technologies for obtaining bulletproof heterogeneous steel materials, and batch rolling, explosion welding and surfacing are considered as the main ones. In the article Promising steels for the protection of special equipment, published in the journal HERE, series 16 for 2018[1], their latest achievements are presented, which show that samples of heterogeneous material can give certain advantages over homogeneous ones. (see Table 1).

Table.1. Comparison of conventional and heterogeneous bulletproof steels when fired with a 7.62 mm B-32 armor-piercing incendiary bullet

Note: Data on domestic bulletproof steels are not given due to the closeness of this information, however, it is known that they are at the level of the foreign brands listed here.

At the same time, it is clearly seen from the table that with a significant complication and increase in the cost of technology for obtaining heterogeneous material, the gain in comparison with homogeneous is very small, especially when compared with foreign, in particular, Swedish steels.

And yet, can we expect any prospects from heterogeneous materials in the foreseeable future and how much progress have developers made today in comparison with past work that was carried out both in the USSR and in advanced Western countries?

Recall that back in 1933-1935, almost simultaneously with the development of the production of cemented armor, at the Zhdanov plant named afterExperiments were conducted on the creation of two-layer ingots for the manufacture of heterogeneous bulletproof armor, the front layer of which contained 0.48-0.52% C, and the rear; 0.27-0.30% C. The initial ingots-billets were cast by simultaneous pouring of steel of two compositions into a mold with a vertical dividing partition, melting as the mold was filled with metal. Due to technological difficulties, the method has not found application. Temperature fluctuations and the pouring speed strongly influenced the weldability of the separation partition with liquid metal and the mixing of metal of various compositions. In addition, this process required two melting units synchronized by the time of the end of melting.

Another method of obtaining a heterogeneous ingot, called the cast cladding method, was developed around the same period at the Gorky Metallurgical Plant and consisted of the following. Carefully cleaned (and sometimes chrome-plated) one or more plates of steel of one composition were inserted into the mold, and then steel of another composition was poured. The advantage of this method is that only one melting unit was required here. But this method did not provide reliable welding of the clad and cladding layers. True, with subsequent hot rolling, it was possible to achieve a more or less satisfactory connection of the layers, but still it was not used for the industrial production of heterogeneous armor. Although for the manufacture of multilayer tools, the production of plough dumps, this method was successfully used at the Gorky and Taganrog metallurgical plants.

In 1960, this method was again tested by the Research Institute of Steel to obtain heterogeneous armor. Together with the Gorky Metallurgical Plant, prototypes of double-layer armor with a thickness of 8-14 mm were made. 60KHNM, 60X2M and U8 steel grades were used as the front layer, as the rear; high hardness armor steel. The relative thickness of the front layer varied from 10 to 30% (in increments of 10%), i.e. for the first time an attempt was made to systematically assess the effect of this parameter on bullet resistance. The hardness of the front/back layers was 62-64/45-48HRC. The samples were tested with armor-piercing bullets of 7.62 mm caliber (more than 200 rounds) and 12.7 mm (about 100 rounds). The tests showed, firstly, a monotonous increase in bullet resistance with an increase in the relative thickness of the front layer, and, secondly, the possibility of obtaining a significant increase in the level of resistance when fired at normal armor-piercing bullets of 7.62 mm caliber. Two-layer armor with a thickness of 10 mm provided protection from this bullet at point-blank range. [7]. Thus, already in the 1960s, the fundamental possibility of reducing the thickness of steel bulletproof armor was shown. However, the same work has shown that the survivability of such armor is low and, in addition, with an increase in the angles of fire to 20-30 °, its advantages over homogeneous armor are lost. As a result of the search for the optimal composition of heterogeneous armor, which also meets the requirements for survivability, its protective thickness increased to 13 mm. [7].

In the 1948-1950s, another method of obtaining a heterogeneous billet was tested at the Krasnoe Sormovo plant - the method of layer-by-layer pouring of steels of different composition into a horizontally arranged mold. Rolling of blanks and testing of the obtained plates also gave positive results, but technological difficulties in ensuring the quality of the adhesion of layers stopped the continuation of work in this direction.

This method was further developed in the works of the E.O.Paton Institute of Electric Welding. The method was called ESHO (electroslag heating) and consisted in electroslag heating of successively filled layers of various compositions. A flux was first poured into a horizontally arranged sand mold, which was melted using graphite electrodes. Then the electrodes were pulled aside, the first layer of steel of a given composition was poured and the electrodes returned to their place, maintaining the required slag temperature, which allowed the liquid layer necessary for welding with a subsequent layer of steel of a different composition to be preserved on the surface of the crystallized metal. The disadvantage of this method is again the need for two or more melting units.

In 1969, the Paton Institute also proposed a method for layer-by-layer electroslag melting of composite electrodes. In fact, it was an ordinary ESP, only the consumable electrode consisted of several steels of different composition. The method made it possible to obtain high quality metal in the workpiece, good adhesion of layers with the presence of a smooth transition zone in chemical composition, but did not make it possible to ensure the same thickness of layers in length and width of the ingot, which ultimately did not guarantee the required ballistic resistance, which was confirmed by testing samples of heterogeneous 3-layer plates with a thickness of 16 mm, the front and back layer of which consisted of high-hardness armor steel, and the middle layer of high-strength steel SHX15 or 30X3G2S

In 1970, the Research Institute of Steel proposed and implemented a method that, in fact, combined ESP with ESHO.

Heterogeneous ingots consisting of 3 layers were created by this method (see Table 2).

Table.2. Characteristics of the heterogeneous structure obtained by the ESP+ESHO method

Heterogeneous ingots were first forged to a thickness of up to 30 mm, then some of them were pierced to a thickness of 18 mm and tested by firing an armor-piercing bullet of 12.7 mm caliber. The samples did not break through at a speed of 800 m/s (from 75 m). For comparison, the best foreign homogeneous steels provide such resistance in thicknesses of 20-25 mm.

During 1971-1975, the Research Institute of Steel actively researched this technology in relation to thin-sheet bulletproof and thick-sheet anti-discharge heterogeneous armor. During this period, more than a hundred sheets of thin armor with a thickness of 14-22 mm and more than forty sheets of thick armor with a thickness of 80 mm were manufactured and tested. Moreover, what is very important, the sheets were made in the size of 1600x6000mm, i.e. in real dimensions, real armored components were made of them, imitating the side of a tank. At the same time, the issue of welding was solved, welding modes were worked out, the compositions of layers of heterogeneous armor were adjusted, i.e. in fact, the serial technology of using heterogeneous material in the protection of tanks and LBM was being tested.

Thin-sheet heterogeneous armor was made in two and three-layer versions. The two-layer had 0.4% C in the front layer, 0.3% C in the back. In a thickness of 18.9 mm, it provided protection against 12.7 mm caliber bullets with a control panel = 6 °.

On a thick sheet with a front layer of medium hardness and a back layer of increased hardness, a gain of 100 mm and 115 mm sub-caliber projectile from 11 to 16% was obtained.

Fig.1. Hardness distribution over the thickness of a heterogeneous double-layer sheet with a thickness of 80 mm. (face ; left, rear; right)

At the same time, both thin-sheet and thick-sheet heterogeneous armor showed satisfactory survivability and weldability.

In 1975, these works were unexpectedly curtailed and heterogeneous steel obtained using ESP+ESHO technology never went into production.

Batch rolling was also in the field of attention of many developers [8]. In 1970, the Research Institute of Steel, together with TsNIIchermet, carried out a number of works to evaluate this technology for the possibility of obtaining a strong interlayer bond in a heterogeneous sheet. For this purpose, two different grades of steel were used, including 50KHN3MA with a content of C = 0.5%.

The 4-layer package was subjected to batch rolling with 30-fold compression to a thickness of 12 mm. The cards were tested with a 12.7 mm bullet in order to determine the control panel. However, it was not possible to obtain it, because the samples showed unsatisfactory survivability, cracked, stratified with the formation of splinters at the first hit. In this regard, it was concluded that heterogeneous steels obtained by this technology may have very limited use.

This conclusion was confirmed in 1973, when the Research Institute of Steel tried to adapt aviation heterogeneous armor based on KVK alloys in relation to the protection of LBM. Giving advantages in bullet resistance, it showed low survivability.

By the way, although many foreign brands of heterogeneous armor are obtained using this technology, there is no information on their use in the protection of serial LBM. There, ordinary homogeneous steels are used as part of complex barriers.

The Institute of Steel drew attention to the problems with the use of explosion welding technology to produce heterogeneous steels back in 1970, when work was carried out to evaluate multilayer samples with a thickness of 16-20 mm by bullet and shell fire. All samples had delaminations in the welding area and splinters in the affected areas, although many samples showed very high values in terms of resistance for the first hit. In fact, the same conclusion was made by the developers of the FSUE Gosniimashinostroeniya [5], trying to create a heterogeneous blast-proof steel based on C-85 grade steel by explosion welding. Having received a certain gain in durability, they significantly lost in the survivability of samples that split after the 2nd shot.


Does this mean that heterogeneous steel materials have no prospects?

Of course not. The physics of the interaction of the striker with the barrier requires its heterogeneity. Moreover, the developments of the Research Institute of Steel in the field of layered both steel and aluminum armor [3, 4, 7] convincingly show that heterogeneous materials have prospects. This is confirmed by the work of other organizations. Another thing is that research in this area should not be conducted in haste, but systematically, taking into account the study of many factors. Today, unfortunately, Russian materials science in this area is marking time.


Tsukanov V.V., Mileykovsky A.B., Nigmatulin O.E., Savichev S.A.Promising steels for the protection of special equipment/Issues of defense technology. Series 16: Technical means of countering terrorism. No.: 1-2, 2018.

Bespalov I.A., Alekseev M.O., Kupryunin D.G. Light protective structures. ; M., Radiosoft, 2017.


3.. Artsruni A.A., Kupryunin D.G. Aluminum armor for military equipment. Theory, technology, practice. ; M., Radiosoft, 2017.

Gladyshev S.A., Grigoryan V.A. Armored steels. — M., Intermet Engineering. 2010. 334c

V.A.Avenyan, V.K.Ashiev and others. Explosive methods of creating heterogeneous barriers of increased bullet resistance based on steel Ts-85./ Proceedings of the All-Russian Scientific and Practical Conference Actual problems of protection and safety, St. Petersburg, 2001

RF Patent No. 2472100 Bulletproof heterogeneous steel armor, FSUE RFNC VNII EF, 2013

Scientific analysis of the directions of development, technical level and stages of development of domestic and foreign materials for protection against dynamic impact. Selection of the most effective experimental materials based on own developments and development of criteria for assessing their properties, report of JSC Research Institute of Steel, 2009

Arkulis. G.E. Joint plastic deformation of dissimilar metals. ; M., Metallurgy, 1964.


The article was published in the scientific and technical journal "Issues of Defense Technology", series 16, issue 11-12, 2018, pp. 95-100

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