Highly tempered, high-hardness – experimental armor for IS tanks
New type of tank armor – high-tempered armor with high hardness
The presented work was carried out by the Moscow branch (MB) of NII-48 in the period from September to December 1948 by a team consisting of senior engineers Vodisko A. M. (team leader), Pronina A. G. and laboratory assistant Shchegoleva A. M.
The study of weldability was carried out by senior engineer Mitris P.P. and Andreev V.P.
All work was carried out under the supervision of the Head of the MF Research Institute-48 Delle V.A., chief engineer Danilevsky O.F. and the chief engineer of the 3rd Main Directorate of the People's Commissariat tank industry of Kanevsky L.A.
This material presents the main results and conclusions of the work.
Detailed technological data are not included in the extensive experimental material in order to avoid cluttering the main conclusions in this report.
The purpose and method of obtaining a new type of armor
To protect light, medium and heavy tanks in modern tank construction, homogeneous armor is used in most cases.
Heterogeneous armor, which, under certain test conditions (with a ratio of plate thickness to projectile caliber equal to one or more), and especially when tested with the currently most common projectiles with a pointed warhead, has a higher resistance, has not been widely used until recently due to the complexity of its manufacture.
Only comparatively recently, the MF NII-48 established that heterogeneous armor is used by the Germans to protect individual sections of the hulls of Panther and Ferdinand tanks.
In domestic tank building, only two types of homogeneous armor are used: high-hardness armor and medium-hardness armor.
The first of these types, compared to the second, is characterized by higher projectile resistance when tested at angles of up to 45-50 degrees, especially when firing sharp-nosed projectiles.
Relative projectile resistance of 60 mm thick homogeneous armor
Along with its higher resistance, high-hardness homogeneous armor, compared to medium-hardness armor, exhibits increased brittleness, especially when tested with large-caliber projectiles. This is explained by the lower ductility properties of high-hardness armor.
The increased fragility of high-hardness armor makes it difficult to use it for protection against large-caliber projectiles. artillery.
The manufacturing process for high-hardness armor is more complex and less stable in production, which often leads to significant difficulties.
Particularly large difficulties arise in production, due to the formation of cracks in the hulls during welding and during the subsequent operation of the tanks.
In armor practice, for example, there have been cases where more than 30% of the hulls produced in certain periods had cracks of varying lengths.
During operation of the tanks, cracks in some cases increased to 500-700 mm.
It is therefore not surprising that exceptional attention has been and continues to be paid to the fight against the appearance of cracks, especially at present.
It can be said that the fight against cracks is the central core around which the main issues of the technology of manufacturing high-hardness armor and hulls made from it revolve.
As a result of a variety of measures, ranging from adjusting the chemical composition of the steel to tempering welded assemblies, the number and length of cracks in hulls at NKTP (People's Commissariat of Tank Industry) plants has been reduced to a minimum. However, the possibility of crack-related defects still exists, given the generally low quality of armor metal, minor, and sometimes even unnoticeable, flaws in hull manufacturing technology can cause crack-related defects.
Unlike high-hardness armor, the manufacturing process for medium-hardness armor is extremely simple.
However, the most valuable technological advantage of medium-hardness armor is its low sensitivity to weld cracking.
Suffice it to say, for example, that in the practice of armor production, not a single case of the formation of significant cracks on hulls made of armor of medium hardness has been recorded.
The latter circumstance is not accidental, but is the result of the peculiarities of the technological process of manufacturing medium-hard armor and its physical and mechanical properties.
The main and distinctive feature of the technology for producing medium-hardness armor, compared to high-hardness armor, is the tempering operation, after hardening, at temperatures sufficient to relieve a significant portion of the residual stresses.
In fact, immediately after hardening, armor parts receive large residual stresses, the magnitude of which reaches values of 100-120 kg/mm2.
When producing high-hardness armor, during the tempering process, carried out at relatively low temperatures of 200-270 degrees, residual stresses are reduced only partially.
The magnitude of residual stresses in high-hardness armor parts subjected to straightening after low tempering reaches values of at least 60-90 kg/mm2.
During the straightening process of hard armor, a further increase in residual stresses can be expected.
As a result, high-hardness armor parts are sent to the hull assembly plant with very high residual stresses.
Conversely, in the case of medium-hard armor, tempering at high temperatures of 580-650 degrees Celsius will almost completely relieve residual stresses. Only relatively small residual stresses may appear as a result of rapid cooling after high-temperature tempering. Subsequent straightening of ductile medium-hard armor will not significantly increase the magnitude of residual stresses.
Thus, parts made of medium-hardness armor arrive for assembly with significantly lower residual stresses compared to parts made of high-hardness armor.
During the assembly and subsequent welding process, additional residual stresses arise due to the high rigidity of the parts being fastened, as well as due to the special heating and cooling conditions during welding in the weld zone.
The total amount of residual stress in individual sections of the weld zone may be sufficient to cause brittle fractures.
The further development of brittle tears and long-term cracks is determined by the magnitude of residual stresses obtained as a result of heat treatment, straightening and the conditions of fastening of the welded parts.
Since these stresses are insignificant in medium-hardness armor components, it is for this reason that, in practice, there are no known cases of tears developing into large cracks in hull components (made from medium-hardness armor). Conversely, the appearance of large cracks in hull components made from high-hardness armor is primarily the result of significant stresses generated by heat treatment and straightening.
If we add to all of the above that medium-hardness armor, compared to high-hardness armor, has greater metal ductility, which facilitates the release of residual stresses due to local plastic deformation, then the main reason for the different behavior of these two types of armor with respect to the occurrence, and most importantly, the development of cracks becomes clear.
Thus, a seemingly insignificant fact – the final tempering temperature of the armor – is in fact a colossal factor that determines the sensitivity of the armor to cracks and their development over time.
From this, a radical method for eliminating cracks in high-hardness armor also becomes clear.
To completely eliminate the possibility of the formation of significant cracks on hulls made of high-hardness armor, it is necessary to radically change the method of heat treatment of the armor.
Instead of the usual method of heat treatment of high-hardness armor - quenching with low tempering, it is necessary to switch to quenching with high tempering.
It is quite obvious that the production of high-hardness armor using high-tempering as the final heat treatment operation will require the creation of fundamentally new armor steel grades.
The latter circumstance introduces many variables; for example, the question of the armor resistance of these new steel grades and their technological features remains completely open.
However, the idea of creating high-hardness armor that is not prone to cracking was so tempting that, despite the great difficulties facing researchers, in 1943-1944 the Moscow branch of NII-48 began developing a new type of armor – high-tempered armor with high hardness.
The creation of highly tempered, crack-resistant, high-hardness armor is especially important for heavy tanks protected by thicker armor than, for example, the T-34.
In fact, the use of high-hardness conventional armor for heavy tanks requires the production of steel grades that are heavily alloyed with nickel and are in short supply.
However, despite this, as in the production of the T-34, and perhaps even more acutely, the issue of combating cracks is always acute, since the thicker the low-tempered armor of high hardness, the more residual stresses it contains.
Finally, when developing a new type of armor, it was assumed that by radically changing the chemical composition of the steel, an attempt would be made to increase armor resistance or, in the worst case, eliminate brittle armor failures (cracks, splits), as a rule, observed in tests with large-caliber projectiles of low-tempered armor of high hardness.
Chemical composition of high-tempered high-hardness armor steel grades
Fig. 1 shows the effect of tempering temperature after quenching on the magnitude of residual stresses in cylindrical samples.
From the data in Fig. 1 it follows that in order to effectively relieve residual stress in hardened steel, the latter must be tempered at temperatures of approximately 550-600 degrees.
If we refer to the well-known diagrams of changes in the mechanical properties of samples of grades 8s and 49s steel quenched and tempered at different temperatures, it is easy to see that these grades of steel are unsuitable for high-tempered armor of high hardness.
In fact, steel grade 8s after starting at the specified temperatures has a hardness of 3,7-3,8, steel grade 49s – 3,4-3,5 mm according to Brinell.
Consequently, both the first and the second are unable to provide sufficient hardness for high-hardness armor (2,9-3,3 mm) after tempering at temperatures of 550-600 degrees.
Therefore, for high-tempered hardness armor, it is necessary to develop new steel grades whose primary feature should be high tempering stability. In other words, these steel grades should have a Brinell indentation after tempering at 550-600°C of no more than 3,2-3,3 mm.
Modern metal science provides comprehensive guidance on methods for solving the given problem.
High stability of steel during tempering can be achieved by alloying it with carbide-forming elements with a high temperature of carbide precipitation.
The influence of alloying elements on the stability of hardness during tempering
From the data in the table it follows that manganese does not have a noticeable effect on the stability of steel when tempered in the temperature range sufficient to relieve residual hardening stresses.
In this regard, chromium has a much more active effect than manganese, but chromium steels are still not sufficiently resistant even when they contain 0,30 percent molybdenum.
Only when chromium steel contains about 0,4 percent molybdenum can the tempering hardness required for high-hardness armor be achieved at approximately 600 degrees.
It is interesting to note that increasing the chromium content from 2 to 2,5 percent does not significantly affect the stability of the steel hardness during tempering.
Vanadium has an even more active effect in this direction than molybdenum, which is explained by the higher temperature of the release of its carbides during tempering.
The data in the table can be accepted as sent for the design of high-tempered high-hardness armor steel grades.
Obviously, the most rational in terms of composition should be recognized as steel grades based on chromium-molybdenum, containing about 0,4-0,45 percent molybdenum, or chromium-molybdenum-vanadium, having up to 0,15-0,20 percent vanadium in their composition.
The chromium content in them should obviously be set at no less than 1,5 percent. A higher chromium content, as noted above, does not fundamentally alter the stability of hardness after tempering, but it may be dictated by the need to improve hardenability when manufacturing armor of significant thickness.
As for the nickel content, since nickel belongs to the group of elements that do not form carbides and, therefore, do not have a significant effect on the stability of the hardness of steel during high tempering, its introduction into steel for high-tempered armor is not mandatory and can only be caused by the desire to improve technological properties and, in particular, to obtain the necessary hardenability in large sections of armor.
In conclusion, it should be noted that, obviously, in steel grades for high-tempered armor of high hardness, an increased carbon content should be adopted in accordance with the number of carbide-forming elements.
Calculations show that in order to effectively utilize the influence of these elements when they are present in quantities of 2,5-3,0 percent, the carbon content should be taken within the range of 0,37-0,47 percent.
A carbon content higher than 0,5 percent is not advisable due to the inevitable deterioration of the technological properties of the steel (difficulty in processing into fiber, excessive hardenability, etc.).
Based on the above considerations, in the works of the Moscow branch of Research Institute-48, three grades of steel were initially studied for high-tempered hardness armor, the chemical composition (of cast melts) of which is shown in the table below.
As can be seen from the table data, the experimental steels differ somewhat from each other in nickel content; the third grade of steel also has a lower chromium content.
All three grades were smelted in open-hearth furnaces and were intended primarily to study the properties of armor with a thickness of approximately 100 mm, but the properties of thinner armor made from these grades of steel were also studied at the same time.
Some physical and physicochemical properties of high-tempered high-hardness armor steel grades
When cooled in oil from a heating temperature of 850 degrees and above, the steel grades studied easily accept hardening, acquiring an enormous hardness of about 2,5 (Fig. 2).
However, stable mechanical properties after high tempering of hardened steel samples, as can be seen from the data in Fig. 3, are observed only if the heating temperature before hardening is above 890-900 degrees.
Increasing the pre-quenching heating temperature to 950°C does not significantly impair the mechanical properties of steel tempered at 340°C. However, as the first column of Fig. 4 shows, excessively raising the pre-quenching heating temperature leads to a deterioration in the fracture appearance of high-tempered steel. From this perspective, the optimal pre-quenching heating temperature for the steel grades studied should be considered to be 900–910°C.
The data in the second column of Fig. 4 show that air and water cannot be used as a cooling medium during quenching of the steel grades under study, since in the first case the cooling rate is insufficient, while in the second case, on the contrary, due to the increased cooling rate, cracks are observed to occur during quenching.
The only suitable cooling medium for hardening the steel grades under study should be considered oil, which, generally speaking, is their negative property.
However, from the data in the third and fourth columns of Fig. 4 it is clear that oil with a very wide range of cooling rates can be used for hardening.
The latter circumstance is favorable from a production point of view.
Changes in mechanical properties and hardness of experimental steel grades depending on temperature tempering
Fig. 5 shows the change in mechanical properties of the studied steel grades depending on the tempering temperature after hardening.
As can be seen from the data in Figure 5, the mechanical characteristics of steel, determined by tensile, impact and hardness testing, change linearly after tempering in the temperature range of 520-660.
Taking the ratio between tensile strength or hardness and impact toughness as an assessment of mechanical properties, it is easy to see that the most unfavorable combination of these properties is found in grade I-1, which, with equal hardness to other tested grades of steel, has lower plastic properties, especially in the region of low tempering temperatures.
As for the properties of steel grades I-2 and I-3, in this case it is difficult to give preference to any of them.
In fact, if the I-2 steel grade has, with equal hardness, a high viscosity after tempering in the region of temperatures around 650 degrees, then, on the contrary, it is somewhat inferior to the I-3 steel grade after tempering at around 520 degrees.
The absolute values of impact toughness of the steel grades tested with a hardness of about 3,2 are at the lower limit of those permitted for high-hardness armor of 5-3 kg/cm2.
However, the latter, as we shall see further, will not lead to brittle destruction of the armor during projectile tests, since, apparently, the regularities established during the study of fundamentally different steel grades used for the production of low-tempered armor of high hardness cannot be unconditionally extended to the properties of the steel grades under study.
Along with mechanical properties, a very important characteristic for armor steel grades is the ability to be easily processed into fiber.
Fig. 6 shows that in this respect, grades I-1 and I-2 are sharply inferior to grade I-3 steel.
Indeed, grade I-3 steel reliably produces a fibrous fracture when processing armor to a Brinell hardness of 3,1-3,2 mm. Grade I-1 and I-2 steel samples, which have the same hardness, exhibit a "crystalline rash" in the fracture.
In all likelihood, the difference in the behavior of the studied steel grades I-1 and I-2 compared to steel grade I-3 is due to the high chromium content in them.
The data in Fig. 6 also allow us to draw indirect conclusions about the hardenability of the steel grades studied. It is clear that grade I-1 steel does not have sufficient hardenability at a plate thickness of 120 mm, as in this case, even with a hardness of 3,35-3,4, a crystalline precipitate is formed in the fracture.
As for steel grades I-2 and I-3, they can be reliably annealed when processing 120 mm thick plates.
Thus, taking into account the entire set of data obtained, it must be acknowledged that of the steel grades studied, grade I-1 proved to be the least successful in terms of its physical and mechanical properties. Conversely, the best results were obtained with grade I-3. Grade I-2 occupies an intermediate position.
Bulletproof and projectile-proof resistance
Experimental firing shows that the high-tempered, high-hardness armor of I-3 steel is practically equivalent in bulletproofness to the low-tempered armor of 2P steel adopted for service.
The projectile resistance of 45 mm thick experimental steel grades tempered at 560-580 degrees is shown in the table, which shows that this new type of armor, in terms of its resistance, fully satisfies the current technical conditions for high-hardness armor and is almost as good as the latter in terms of actual projectile resistance.
Anti-projectile resistance of highly tempered experimental armor with a thickness of 45 mm
Note:
1) According to technical specifications, high-hardness armor (2,9-3,15 mm according to Brinell) must withstand a 45 mm projectile test at a normal velocity of 630 m/sec.
2) Armor 50 mm thick of medium hardness (3,4-3,6) must withstand a 45 mm caliber projectile test at a normal velocity of 620 m/sec.
All three steel grades tested demonstrated roughly equivalent armor resistance when tested on 45mm-thick plates. Regarding the nature of damage, grade I-1 was more prone to spalling.
However, of greatest interest in light of current tank-building challenges are the results of tests of 90 mm thick armor plates of a new type.
The table shows the average test results of high-tempered armor made of steel grades I-1, I-2, I-3, treated to a hardness of 3,1-3,3, in comparison with the test data of armor of medium and high hardness adopted for service.
Comparative results of testing 90mm thick armor at the Gorokhovets Artillery Scientific and Testing Range. Key: RTR – armor penetration limit; PSP – armor penetration limit.
As follows from the data in the table, the experimental high-tempered armor is superior to medium-hard armor in terms of its projectile resistance and is not inferior to high-hard armor.
The nature of damage to the experimental armor was quite satisfactory - no cracks or splits were observed in the plates treated to the specified hardness.
On the contrary, when testing high-hardness armor of similar thickness, cracks and even splits in the plates occurred in many cases.
Thus, high-tempered armor with high hardness combines the advantages of low-tempered armor with high hardness - high resistance to penetration, with the advantages of medium-hardness armor - good ductility, eliminating the possibility of cracks and splits in plates.
However, the most interesting results are the results of rigorous control tests of 90 mm thick plates of high-tempered, high-hardness armor made of I-3 steel grade, carried out in 1944 at the testing ground of Plant No. 9 of the National Design Bureau.
In this case, the tests were carried out with an 88-mm German armor-piercing sharp-nosed projectile of the 1943 model.
The test results, compared with the test data for medium and high hardness armor, are shown in the table.
Comparative testing of 90 mm thick armor with a German 88 mm armor-piercing pointed projectile with an armor-piercing tip, model 1943. Weight: 10,16 kg. Designations: PTP – armor penetration limit; PSP – armor penetration limit.
As the table shows, high-tempered, high-hardness armor occupies an intermediate position between high- and medium-hardness armor in normal testing, differing little from them, as the resistance characteristics of these two armor types are very similar. When tested at a 30-degree angle, it outperforms both medium-hardness and high-hardness armor.
Moreover, the obtained values of resistance at an angle of 30 degrees are generally higher than all previously known test results for 90 mm thick slabs.
Considering that the 30 degree angle is extremely important from a tactical point of view, the significance of the obtained data cannot be underestimated.
It should be noted that during testing of experimental 90 mm thick plates, despite the significant projectile load (up to 10 hits on a 1,2 x 1,2 m plate), no cases of splitting or cracking were observed, and the size of the spalls did not exceed the caliber.
Thus, possessing high projectile resistance, high-tempered armor of high hardness compares favorably with low-tempered armor of high hardness by the absence of splits and cracks during shell fire.
It should be noted, however, that an absolute requirement for high-tempered armor of high hardness is the presence of a fibrous structure in the fracture.
If this requirement is not met, the formation of cracks is inevitable, as with low-tempered armor.
However, as experience has shown, obtaining a fibrous fracture with a hardness of 3,1-3,25 mm on plates even with a thickness of 90, 120 mm made of grade I-3 steel does not present any difficulty.
In conclusion, it should be noted that the tests of low-tempered high-hardness armor given in the table were obtained on plates made of steel grade 51C, containing 3,0-3,5 percent of acutely deficient nickel.
While grade I-3 steel contains it in an amount not exceeding 1,5 percent, the significance of the latter circumstance in the conditions of wartime savings cannot be underestimated.
Technological features of high-tempered armor with high hardness.
During the experimental work on the type of armor under study, 4 melts were smelted, of which three melts (compositions I-1, I-2 and I-3) were smelted at the Kulebak plant in a 50-ton main open-hearth furnace, and one pilot bulk melt was smelted at the Nizhny Tagil Metallurgical Plant in a 150-ton main open-hearth furnace.
The metal from these smelts was used to make plates for field tests, two SU-76 hulls, and six sides of the new heavy tank.
Based on the experience of carrying out these four melts and observing their behavior in production at various stages of the technological process, the following remarks can be made about the technology of manufacturing high-tempered armor of high hardness.
At both the Kulebaki and Nizhny Tagil plants, smelting was carried out using the existing technology for armor steel grades; no special smelting requirements were imposed. Due to a number of production problems (lack of charge, unprepared pit), which led to artificially prolonged periods of smelting, we were unable to identify certain potential advantages resulting from the chosen chemical composition of the experimental steel grades in pilot smelts. The high carbon content with relatively low chromium alloying in I-3 steel in full production should result in an overall reduction in the smelting process, especially compared to smelting steel grades for high-hardness armor, where the established requirement for a lower carbon content in the final analysis requires carbon burnoff before deoxidation to extremely low limits. Furthermore, the use of low-carbon ferrochrome is eliminated, while maintaining the boiling period within normal limits.
Simple general alloying distinguishes the new grade of armor from existing Mn-Si-Cr-Ni steel grades used for high-hardness armor and makes it possible to obtain significantly higher-quality metal in open-hearth production.
An inspection of the metal quality by fractures showed that concerns regarding increased liquation of this steel were unfounded, and, despite a number of abnormalities in the smelting process itself, the resulting fractures were quite satisfactory in terms of slate and delamination.
No differences were observed in the rolling of the ingots compared to the rolling of existing armor steel grades. In all cases, rolling proceeded normally, without any defects.
Experience has shown that it is entirely possible to temper sheets after rolling using the same regime adopted for tempering sheets of 8C and 49C steel.
Heat treatment, other than the mandatory requirement of oil quenching, presents no production difficulties. With proper quenching (no underheating or severe overheating), achieving the specified hardness (3,2-3,3) and a fibrous fracture is easily achieved by a single tempering at 560-590 degrees Celsius.
Gas cutting, as shown by timing at Plant No. 176, during the production of SU-76 parts is somewhat complicated and requires lower cutting speeds than is allowed when cutting conventional grades of 2P armor steel.
Straightening the final heat-treated armor of the new steel grade is straightforward and, as the plant's experience has shown, is significantly easier than melting high-hardness armor. It should be assumed that, due to the high final tempering temperature and the resulting significant relief of quenching stresses, straightening this armor should not be significantly more difficult than straightening medium-hardness armor.
The most critical component of the new armor manufacturing technology is welding. Clearly, given the high carbon content of the steel grades used for this armor, a number of significant changes to the welding process must be made.
A characteristic feature of welding high-hardness armor with a high carbon content (up to 0,5 percent) is the fact that the hardening zone under the weld seam acquires particularly high hardness and brittleness, which is especially noticeable when applying seams in one layer.
The figure shows the hardness distribution curves across the heat-affected zones for single-layer welding and with an annealing bead. Curve (1) shows the hardness distribution for single-layer welding, and curve (2) for an annealing bead.
It is quite obvious that the main requirement when welding high-tempered armor of high hardness must be the execution of all joints with annealing beads, and at the same time it is necessary to take into account all the means for obtaining their maximum effect (multilayer welds, small electrode diameter, short length of individual sections of the weld).
The behavior of welded joints made of high-hardness steel during field testing was studied only on two experimental hulls of the SU-76 self-propelled gun. One of these hulls was subjected to shell tests, with particularly harsh conditions used to determine the weld strength: the hull, made of 15-25 mm thick armor, was fired at with a 45 mm shell.
If we look at the nature of the destruction of welded seams during field tests, it is easy to see that the destruction begins at the junction of the weld seam with the plane of the welded parts, and then the chipping line goes along the boundary of the hardening zone and the base metal, and the seam is chipped out together with the hardened zone of the base metal.
In the steels currently used in our bulk production, destruction occurs along the weld seam.
Finally, it should be particularly noted that, despite the high carbon content of the steel, welding of SU-76 hulls made of high-tempered, high-hardness armor produced no cracks, and no cracks appeared on the hulls after two months. These hulls were welded using conventional electrodes.
Thus, the experience of manufacturing the SU-76 hulls brilliantly confirmed the previously expressed theoretical considerations about the low tendency of high-tempered, high-hardness armor to form cracks.
As for the not entirely satisfactory strength of the welded joints obtained on the SU-76 hulls, in this case, due to the small cross-section of the seams, it was not possible to effectively carry out a multi-bead welding system.
It's possible that when welding thicker armor, the ductility of welded joints with large cross-sections can be improved by applying a system of annealing beads. Certainly, for this purpose, it would be necessary to manufacture and test a prototype heavy tank hull made of highly tempered, high-hardness armor.
CONCLUSION
A new type of tank armor for domestic production has been developed: highly tempered armor with high hardness, which has high projectile resistance, a low tendency to form brittle damage during projectile testing, and is insensitive to the development of cracks in tank hulls.
Based on the research, the following chemical composition of steel can be recommended for high-tempered, high-hardness armor with a thickness of 90 mm and above:
In terms of its projectile resistance, high-tempered, high-hardness armor is not inferior to the resistance of low-tempered, high-hardness armor adopted for the production of serial tanks, and in some cases even surpasses it.
In terms of the nature of brittle fractures during shell tests, the developed armor is better than the serial high-hardness armor.
For the production of high-tempered, high-hardness armor with a thickness of 90 mm or more, steel grades significantly less alloyed with scarce nickel can be used, compared to steel grades used for serial low-tempered, high-hardness armor (reducing the nickel content from 3,5 to 1,5 percent).
The technological process for manufacturing the developed armor does not differ fundamentally from the technological process for manufacturing medium-hard armor, with the exception of hardening and welding.
Hardening of high-tempered armor with high hardness must be carried out in oil, welding of the armor must be carried out especially carefully and with the obligatory application of a system of annealing rollers.
In this work, the strength of welded seams of high-tempered, high-hardness, large-thickness armor was not established, which is the subject of work currently being carried out.
If the decision is positive, the new type of armor will undoubtedly be adopted for new heavy tanks.
In conclusion, it should be noted that the developed type of armor has enormous potential, as it will allow for the easy transition in production to the manufacture of single-sided hardened heterogeneous armor.
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