Development of welded turrets for post-WW2 tanks in USSR ,

Russia and Ukraine

Andrei Tarasenko

Most tanks at the beginning of World War II had cast turrets. These are T-28, T-34, KV-1, T-III and T-V tanks, "Cromwell", "Matilda", "Churchill" and others. Only France at that time produced "Samua-19" tank with a cast turret. The advantage of rolled steel armor is that with the same thickness as cast armor, it has a higher (by 10-20%) anti-bullet and anti-shell resistance. During the Second World War, most countries switched to the manufacture of cast turrets, and only Germany produced tanks with turrets made of rolled armor.

Switching to cast turrets production was associated with the need for a significant increase in the tanks production output with the same production capabilities. Cast turrets did not require limited in quantity and expensive rolling and pressing equipment, the need for assembly and welding equipment was significantly reduced. Casting turrets could be mastered in any steel foundries equipped with melting units of the necessary capacity and with appropriate lifting and transport equipment. The labor effort of making cast turrets was lower, since the production of cast armor excludes a large amount of manual gas cutting and welding operations.

Automatic cutting of details, automatic and semi-automatic welding at that time were not yet sufficiently developed in armor production. In addition, the use of casting made it possible to obtain a number of advantages in the design of towers. For example, weakened welds were excluded. Casting was easier than the shape of the armor required for the layout conditions and an optimal combination of thicknesses and design angles of shape, inclination and thickness distribution, providing low probability of penetration by a caliber armor-piercing projectiles.

The Soviet designers created the turrets of IS-3, T-10, T-55, T-62 tanks, in which the spherical shape of the turret was used, contributing to the ricochet of by a caliber and APDS (Armour-piercing discarding sabot) projectiles.

Such turrets were adequate design decision for it’s time. Western countries also used casting for production of tanks turrets and also hulls. The comparison of western and soviet armor design approach of 1960-1970-s is described in the material - Armor protection of the tanks of the second postwar generation T-64 (T-64A), Chieftain Mk5P and M60.

In the postwar years, simple and technological grades of medium-hard cast armor MBL-1 and SBL-2 were developed, which at a thickness of up to 200 mm and a high level of armor protection.

The scheme of the turret casting of "Object 432" – a. roof down b. roof up

Scheme of the assembled mold for casting T-64 "Object 432" turret

1 - paired box form; 2 - profits; 3 - the core of emptying; 4 - power supply system of the casting; 5 - a fixing bolt; 6 - refrigerator; 7-plates forming the bevel 9 ° and the bore 53 mm ;

8 - plate of the base of the mold

However, despite the advances made in the development of new brands of cast armor, the anti-ballistic protection of new rolled armor types remained higher. The accuracy of the execution of geometric dimensions in the manufacture of turrets by casting remained much lower than in the manufacture of them from rolled steel plates.

Up to a certain point, the level of protective properties of cast turrets ensured the fulfillment of requirements for the protection of soviet tanks, and the sufficiently high processability of casting in the mass production of turrets made it possible to tolerate a number of serious technological disadvantages inherent to armor casting.

First of all, this is the instability of qualitative characteriistics of casting, leading to a differentiating characteristics of armor resistance and requiring a constant and large scale tests, including costly firing tests.

Particular mention should be made of a significant number of different types of foundry defects (cracks, shells, metal stratifications etc.), large variations in the geometry and thickness of the castings, and associated with the elimination of these defects in labor-intensive operations.

In the beginning of 60-s cast turrets with composite armor were introduced for T-64, T-64A (later for T-72A and T-80B) which had a significant protection against shaped-charge projectiles and APDS rounds. Such protection provided Soviet tanks with protection superiority over western designed tanks of that time like M60A and “Chieftain”. In the 1-st half of 70-s a new design of turret which can be called a 2-nd generation of Soviet turret with combined armor was designed for “Object 476” . This turret with reduced weakened zone was later used in the production of T-80U, T-80UD tanks. The turret included cavities for “special armor”. This type of armor implements so-called "semi-active" defense systems, in which the energy of the shaped charge jet itself is used for destabilizing itself. The method was proposed by the Institute of Hydrodynamics of the Siberian department of the USSR Academy of Sciences. Described in - Бронирование современных отечественных танков.

But in same period of time in the 1-st half of 70-s it became evident, that future development of tank cast turrets has no long term perspectives comparing to welded design. An experimental turret was tested with results published in 1977 special literature. The development was headed by I. I. Terekhin, M. I. Maresev, O.I. Alekseev, A. N. Popov from research institute of steel (NII Stali). In serial production, the welded turret (NII Stali, UKBTM) based on the solutions of the above mentioned authors will only be realized after more than 20 years on the T-90A tank.

Vertical section of the frontal armor of the turret from the rolled steel:

1 - front plate of medium hardness armor; 2 - turret base; 3 - rear plate of increased hardness steel(shaded by a grid of anti shaped charge filler)

View of the welded rolled steel turret after the tests

Tests showed high resistance of the main armor and satisfactory survivability of welded seams

Calculations show, that the weight of a welded turret of a hardened rolled steel in comparison with a similar cast turret of armor of medium hardness with an equal protection level can be reduced by 6-8% with a turret weight of 6000- 7000 kg . This is achieved by reducing by 10-20% the thickness of the walls of the turret, as well as reducing the positive tolerance for parts from rolled products in comparison with casting.

With the same thickness rolled armor provides more then 10% increase of armor protection against sub caliber and ~4...5% against shaped charge projectiles.

Experimental types of rolled armor showed up to 30% increase of armor protection comparing to cast steel.

Continuous improvement in the destruction means (projectiles such as ATGM, APFSDS etc.), aimed primarily at increasing armor penetration, led to the fact that the cast armored structures almost exhausted their capabilities as protective systems.

With the use of composite “steel + special armor+ steel” armor, there is no need for a spherical shape more suitable for casting, since the turret design, construction and “special armor” technology can be greatly simplified with flat and simple conical shapes typical for rolled armor. The increase in the angles of impact with armor up to 45-60, useful on spherical cast turrets, will not lead to a significant decrease in weight, since modern armor piercing-subcaliber and especially cumulative projectiles do not reduce their armor-piercing ability at such angles of impact. This also concerns APFSDS (Armour-piercing fin-stabilized discarding-sabot) rounds with a large elongation of the core.

But it was hard to replace cast turrets in an established Soviet mass production process. Works continued in 80-s with anticipated implementation for both improved T-72B and T-80U and T-80UD main battle tanks.

In the design of new turrets, it was planned to use new electroslag remelting high-strength armor steels (SK-2Sh, SK-3Sh) superior to the armored steel of increased hardness of the existing brands (BTK-1 and BTK-1SH). These steels (BTK-1 and BTK-1SH) were much superior to medium-hardened serial steels 42SM and 49S grades, but tend to crack during welding, because in the composition of these steels, copper was used as the alloying element.

Improved T-72B "Object 186" with the welded turret, 1986

The variant of the turret of the improved T-72B (overall LOS 620 mm at ±35), T-80U (D) ( 570 mm overall at ±35) with welded base of SK-2Sh and SK-3Sh steel and ceramic filler (SiC)

But welded turrets failed to enter in mass production during Soviet era. Only in 90-s when tank production in ex-soviet countries – Russia and Ukraine was at it’s decline with forging equipment reoriented on other tasks a possibility for welded turret production appeared.

First welded turrets entered mass production in Ukraine Malyshev Plant in Kharkov , when the contract for delivery of 320 T-80UD tanks to Pakistan was signed.

For the new post USSR tank production a new grades of steels were implemented into production. The production of increased hardness steel was concentrated in Ukraine ’s “Azovsteel” foundry. A set of research and experimental works on the development and industrial implementation of high-strength armored steel with use of electroslag remelting of SK-2Sh and SK-3Sh brands started. This works were carried by Mariupol “GSKTI” design and technology institute headed by A. Chepurnoy.

Hulls from the new grades of steel SK-2Sh and SK-3Sh were manufactured on the "Malyshev Plant". Turrets on "Azovmash" plant.

First 6 experimental samples of welded turrets were produced basing the design documentation developed by the KMDB named after A. A. Morozov, taking into account the use of high-strength armored steel armor.

After testing in industrial conditions, these technologies are proposed for introduction into mass production. Welded connections of the turrets are made with mutual support of the sheets, using U-shaped locks, ensuring the survivability of welded joints during firing and high accuracy of interfacing of the plates during assembly.

Two turrets were intended for construction and assembly works, and four - for extended tests by shelling, in order to determine the levels of armor protection of new design in comparison with the same type cast turrets.

BM “Oplot” turret

In the front parts of the turret, the face plates are made of medium hardness steel, and the rear plates are made of hardened steel of the SK-3Sh grade, which provides good manufacturability of these parts, their satisfactory weldability and meeting the requirements for the protection and survivability.

Welded turret designed by KMDB before firing trials, early 2000-s

The side zones of the turret from the rolled armor is made equivalent in protection, but smaller in thickness by 30% (comparing to cast steel turret). So increased hardness steel of the SK-3Sh brand made it possible to reduce the weight of the turret sides. Similarly, for the rear and roof of the turret, steel of increased hardness was used, but smaller than that of the cast tower thickness.

The reduction in the mass of the parts of the side zone, rear and the roof made it possible to increase the equivalent weight of the frontal zone of the turret, and, consequently, its overall level of protection.

The turrets are assembled without the use of stands and accessories, directly by mounting the parts on the bottom sheet with tack welds. The assembly time of one turret takes 1 working shift, and welding - 5 shifts.

BM “Oplot” turret on Malyshev Plant, 2015

Firing trials were carried out at the range of "Azovmash", according to a program developed from the conditions for determining the level of protection of the rolled armor turret and determining its survivability in the case of shelling with armor-piercing, armor-piercing subcaliber, cumulative and high-explosive rounds.

The tests showed the increased levels of anti-ballistic protection of welded-turret structures from armor-piercing subcaliber projectiles by at least 15% and from the shaped charge projectiles - not less than 13% with respect to the cast turret of T-80UD. An effective cellular type “special armor” installed in turret cavities.

Due to “special armor” functioning peculiarities there is an intermediate

plate dividing “special armor” cavity into two pats.

Into each of them plates with cells filled with polymer resin are installed

As a response to Pakistan acquirement of T-80UD tanks, which greatly surpassed Indian T- 72 a contract for T-90S was signed with Russian Uralvagonzavod. T-90S and T-90A turret uses medium hardness steel. It’s main features are based on 1970-1980-s Research institute of Steel design described above. The “special armor” consists of an improved “reflecting plates” and a high hardness steel plate placed after them before turret rear plate. The design is generally similar to a well known design T-72B turret which was studied in USA . This type of armor is Soviet analogue of western “special armor” called “ Burlington ” and “Chobbham”. 

T-90S turret.

Patents WO9922196A1 (pdf) describe the turret features

Conclusions

Soviet tanks of 2-nd post WW2 generation significantly outclass western (USA, NATO) opponents in armor protection because of use of the composite armor.

In the beginning of 80-s the introduction of new generation of western tanks –"Leopard-2", "Abrams", and "Leclerc" with welded turrets and effective “special armor” zeroed out this advantages.

Throughout the 80s and early 90s, the feature of the new generation Western tanks "Leopard-2", "Abrams", and "Leclerc" was the use of towers made of rolled welded armor. Such towers possessed a number of advantages - a simple form of a convenient filler package, called "special armor" for Western countries, as well as increased anti-ballistic resistance provided by rolled armor in comparison with the cast.

The exceptions of this rule are British “Challenger” tank which uses cast turret base and experimental Russian “Object 640” Black eagle,  which uses the same design.

Curious is that the welded rolled armor turret was developed and tested in the USSR back in the mid-70's.

The use of welded-rolled armored steel turret of the battle tank made it possible to increase its anti-ballistic and anti-shaped charge protection in comparison with the cast turret, which significantly improved the tactical and technical characteristics of tanks. Especially good results are provided by new brands of high hardness steel made with electroslag remelting used for T-80UD and BM “Oplot” turret armor.

Sources

O.I. ALEXEEV, M.I. MARESEV, A.N. POPOV, I.I. Terekhin. To the question of the use of rolled armor for manufacturing of turrets of main battle tanks. Questions of the defense industry, 1977, No 75-76.

A.D. Chepurnoy. Development and industrial development of the production of the welded-rolled turret of the battle tank // News of Priazov state power university, 2000. - Issue 10