"On the Causes of Crack Formation in Cast Turrets Produced by Plant No. 112." 1943 Report
The T-34 leaves the gates of Krasnoye Sormovo.
The Fight for Steel
"Sormovo freak"—that's what tank crews called the T-34 tanks produced at the Krasnoye Sormovo plant (plant no. 112) near Gorky. Interestingly, it was at this plant that the first tank in the USSR was built in 1920. танк, but later they distinguished themselves by the less-than-stellar quality of T-34 production. Initially, the tank from the Gorky region was not well-respected due to cracks in its armor, which significantly reduced its survivability in combat. The epic story of how critical production defects in turret production at Krasnoye Sormovo were eliminated is recounted in a voluminous document stored in the Russian State Archive of Economics.
Necessary clarifications.
Tempering is a technological process involving heat treatment of an alloy or metal hardened to martensite. The main processes involved are the decomposition of martensite, as well as polygonization and recrystallization. High tempering is performed at temperatures of 500–680°C. This maintains high strength and ductility, as well as maximum toughness. High tempering is used on parts subject to impact loads (armor, gears, shafts).
A riser (in foundry) is the top, bottom, or side portion of a steel ingot (casting) whose dimensions extend beyond the required limits. Its purpose is to supply the casting with liquid molten metal during its solidification.
The Brinell test is a standardized method for determining hardness in materials science, based on pressing a hard alloy ball with a diameter of 1 to 10 mm into the metal being tested.
Liquation process is segregation, heterogeneity of the chemical composition of steel that occurs during its crystallization.
Introduction
This work is a continuation of the work previously conducted by the TsNII-48 team in conjunction with Plant No. 112, which determined the nature and number of defects in armor castings and the causes of their formation. Among other defects, cracks were considered in this work.
While the study reached fairly definitive conclusions regarding cavities, film clogging, and other defects, it was unable to achieve such definitiveness regarding cracks. The insufficient completeness and reliability of the source data (data sheets) prevented this. Only hypotheses were made regarding the causes of crack formation, and the production areas where these cracks occur were identified.
Nevertheless, some proposals were made to combat cracks, based on the resulting understanding of the causes of this defect.
The work presented below concerns only the issue of crack formation in towers. This work, like the previous one, was conducted on products of mass production. However, the data used to draw conclusions in this case were obtained through direct observation by the individuals conducting the work.
Due to the limited time and number of people allocated to this work, the assignment included a minimum of questions. At a meeting with the plant's chief metallurgist, Comrade A.A. Borovikov, it was decided to clarify the matter.
a) is it advisable to pass the towers through high tempering before the profit section;
b) what is the hardness of the towers before and after preliminary high tempering;
c) is it advisable to strive to minimize the interval between the end of the profit segment and the moment of setting the towers for the subsequent high release;
d) whether new cracks appear after hardening and low tempering or whether there is an increase in the size of cracks that formed earlier, before heat treatment, were not confirmed.
d) whether the number of cracks on towers cast with a reduced allowance (15 mm) for machining on the side surface of the tower ring and an increased allowance (up to 35 mm) on its end surface is reduced.
All these questions were planned to be clarified by observing the behavior of 4-6 business melts, from the metal of which at least 4 towers from each would be cast.
During the course of the work, it became possible to conduct similar observations on both the 44L and 8S turrets. Therefore, the work also resulted in comparative characteristics of both types in terms of their potential for cracking in the turret ring.
The work described below was actually carried out on a significantly larger number of melts than anticipated in the planned work. This is evident even from the number of melts used in the report. These data indicate that a total of 29 towers (8 melts) of grade 8S steel and 58 towers (30 melts) of grade 44L steel were used, although the team members actually observed more towers and melts.
It should be noted that the cracks discussed in this work are found exclusively on the ring section of the tower after it has been turned. The size of these cracks can be characterized as follows: they are too wide to allow the tip of a penknife to penetrate them; they are usually located radially relative to the ring, often intersecting the entire thickness of the ring, or less commonly only part of it. The length (or depth) of the overwhelming majority of cracks does not exceed 30–35 mm, rarely reaching 50–60 mm. Cracks of this type are characterized by a sinuous shape.
All of these cracks are repairable. Like cavities, they can be welded shut. Their greatest inconvenience to the plant is the need to perform the associated repairs and delay the towers during production for this purpose. The degree of danger these unwelded cracks pose to the towers' survivability during operational use has yet to be determined.
In addition to repairable cracks, this paper examines large quenching cracks in both the ring and the tower recess. In most cases, these cracks are irreparable, but they are significantly less common than the repairable cracks discussed above, which form the main focus of this paper.
The work was carried out by a team of employees of TsNII-48 consisting of: engineers KAPTYUG I.S., KHMELEVSKY R.G. and OLKHOVA and the team leader, engineer FEDOSEENKO G.I.
Laboratory assistants from the laboratory of plant No. 112, RYVANOVA T.A., SHAMSHINA N.A. and KUDAVKINA A.E., took part in monitoring the towers at various production sites.
Particularly noteworthy is the participation in this work of the plant's chief metallurgist, Comrade A.A. BOROVIKOV, who provided valuable assistance to the team both through personal advice and instructions, as well as through administrative and organizational measures.
The report was compiled by KAPTYUG I.S.
The effect of high tempering on the formation of cracks in the tower ring
When systematizing the materials characterizing the state of production of armor castings at Plant No. 112, it was possible to notice the high tempering and the extent to which it prevents the formation of cracks in subsequent operations.
For this purpose, in two heats of the brand, but also in four heats of the 44L brand, not all towers were subjected to high tempering before cutting off the profits.
From a comparison of data on cracks in pre-tempered and non-tempered towers of the same heat, it follows that for grade 8C steel it is completely unacceptable to cut off risers without passing the towers that cooled in the ground through preliminary high tempering.
While on the towers that have undergone preliminary high tempering, cracks are either not observed or are counted in the amount of 1-2 pieces, on the towers of the same melts that have not undergone preliminary high tempering, 20-25 cracks are counted.
Steel grade 44L behaves differently in this regard. Despite the lack of preliminary high-temperature tempering, cracks in the tempered towers are not only smaller, but in some cases, there are no cracks at all. Meanwhile, cracks are observed in other towers from the same heats.
Among the 44L grade melts, only melt 80373 stands out somewhat. In this melt, tower 1564, which underwent a preliminary high-temperature tempering, has more cracks than the other towers in this melt that also underwent a preliminary high-temperature tempering. However, even in this case, the number of cracks (5) is within the limits typically observed in towers of other melts of this grade that undergo preliminary high-temperature tempering, such as towers 1570 and 1638.
The analyses of both 8C grade heats do not cover the entire range (within the current grade range) of the main elements that influence crack formation (carbon, manganese, chromium, and phosphorus). Nevertheless, it can be stated that for all analyses of 8C steel within the grade range, avoiding the preliminary high-temperature tempering before riser cutting is not recommended. The increase in cracking in this grade is too dramatic to expect a similar phenomenon to be avoided in heats containing carbon and chromium near the lower limits.
Analyses of four 44L grade melts also do not cover the full range of elemental contents as specified in the grade specification. Therefore, for this grade, it is recommended to waive pre-tempering for melts with the following chemical compositions: carbon content no higher than 0,26 percent, chromium 1,50 percent, phosphorus 0,035 percent, and manganese content of any grade specification.
The chromium content in the melts of gross production remains virtually constant at no more than 1,4 percent. Therefore, to avoid complicating the implementation of this assumption in standard production, the chromium content limit should be raised to 1,4%. Therefore, there is no reason to expect any negative consequences if the preliminary tempering is cancelled.
As for melts with a carbon content of 0,27–0,28 and chromium of 1,41–1,70 percent, the issue of canceling the preliminary high tempering must be verified by additional observations.
In drawing these conclusions, it's important to consider the following circumstance. How does the time interval between the end of riser cutting and the subsequent high-temperature tempering of the towers affect crack formation? For this purpose, the specified interval was determined for towers whose risers were cut before high-temperature tempering.
For towers made of grade 8s steel, this interval was 11 hours 30 minutes for tower 1486 and 37 hours 30 minutes for tower 1366. Despite the large difference in time, the crack results are virtually identical. Consequently, for grade 8s steel, no correlation was observed between the number of cracks and the interval size starting from 11 hours 30 minutes and above.
For towers made of 44L steel, the tested interval varies considerably. The minimum interval is 10–12 hours (towers 1688 and 1883) and the maximum is 80 hours 40 minutes.
If we compare the number of cracks on the towers with the corresponding interval between the end of the profit segment and the beginning of the high season, but in this case the absence of any relationship became even more clear.
The most compelling example is heat 70370. In this heat, towers 1688 and 1883 were simultaneously subjected to high tempering in the same furnace and in the same arrangement. However, one tower showed no cracks afterward, while the other showed five. The third tower from this heat (1514) was subjected to riser cutting simultaneously with the first two, but was subjected to high tempering separately after 40 hours. No cracks were found. Towers 1824 and 1444 from heat 60336, which were tempered no less than 48 hours apart, also passed riser cutting without cracks.
Thus, for grade 44L steel, the interval between the end of the riser cutting and the start of high tempering, at least within 48 hours, does not affect the formation of cracks after the riser cutting.
These conclusions apply to the case of a profit segment in an untempered state for both 44L and 8S steel towers. There are strong grounds to believe that this relationship will not differ if the profit segment is measured after preliminary high-tempering, but this cannot be confirmed without appropriate verification.
Likewise, it cannot be stated without appropriate verification that if the interval between the end of the riser section from towers on 8C steel in an untempered condition and the start of high tempering is less than 11 hours 30 minutes, then there will be very few cracks.
Firstly, it is difficult to count on this, because even a difference of 26 hours = 37 hours 30 minutes – 11 hours 20 minutes had almost no effect on reducing the number of cracks.
Secondly, it's unwise to expect this interval to be significantly reduced compared to the proven 11 hours and 30 minutes. A shorter interval would hinder the work of the trimming shop and would still be frequently violated.
A comparison of the tower hardness before and after tempering reveals no difference. In both cases, the Brinell indentation size ranged from 4,2 to 4,4 (hardness was determined directly on the tower ring using a caliper).
Thus, it must be noted that brittleness, which in this case leads to cracks, is not associated with hardness.
Having established the influence of preliminary high-temperature tempering on the formation of cracks during riser cutting, one can expect that the quality of this production operation should also have some impact. This quality is primarily determined by the temperature regime.
Unfortunately, during this work, the plant faced severe limitations not only in terms of measuring equipment but also in terms of the availability of sufficiently qualified observers. In this shop, where the majority of the towers were monitored, the tempering furnaces do not have thermocouples.
Therefore, we had to limit ourselves to recording the towers' positions in the furnace as an indirect indicator of how well a given tower was heated during the heating and holding process. Depending on the furnace size, two to six towers were tempered simultaneously, with the latter case being arranged in two rows.
Based on the towers' location, four positions could be discerned:
A) The tower is located at the bottom and faces downwards, i.e. towards the furnace bottom /location conventionally designated by the letter “b”/.
B) The tower is located at the bottom, but its tops are facing upwards /symbol “c”/.
B) The tower is located in the top row, but its tops are facing downwards /symbol “st”/.
D) The tower is located at the top, but its ends are facing upwards /“v”/.
To simplify the comparison of conclusions, it was agreed to distinguish only two positions of the towers during high tempering:
- Unfavorable, in which the tower is at the bottom and turned with the risers facing downwards; in other words, the risers are on the lower horizon of the furnace /conventionally designated as "n"/.
- It is more favorable when the tower occupies any of the other three positions, in which the risers are either on the middle /s and sv/, or on the upper horizons of the furnace.
Based on the data, it follows that for grade 8C steel, the unfavorable position of the tower in the furnace during tempering somewhat increases the number of cracks on the end of the ring.
For 44L steel towers with favorable placement, the ratio between the number of towers with and without cracks is no different from that for 8S steel. However, it is impossible to say how this ratio would change with unfavorable tower placement in the furnace, as there is no similar data for 44L steel.
The heating and holding times for high-temperature tempering are characterized by slight variations that do not distort the conclusions reached. According to current instructions, the heating time should be 5-6 hours and the holding time (at a temperature of 670-690 degrees) 6-7 hours. Only in cases of increased holding time (due to small armor castings) is it recommended to increase the holding time, which was done in some cases.
The influence of the fire section of the risers on the formation of cracks on the tower ring
Cracks are closely related to the flame cutting process. Flame cutting is used to cut off risers, fillets, and to trim off thickenings, burrs, and other burrs. In this case, we are primarily referring to the cracks found on the machined surface of the tower ring.
The overwhelming majority of cracks are located in those sections of the ring where the risers were located before they were cut off.
This suggests that crack formation is closely related to the cutting of metal by fire. However, the existence of such a fact alone does not exhaust the issue.
If flame cutting were the only solution, then after machining the end portion of the ring and subsequent hardening, new cracks should be distributed relatively evenly around the entire perimeter of the tower ring. But in reality, most newly formed cracks are located in sections of the ring corresponding to the locations of the cut risers.
This indicates that both fire cutting and quenching undoubtedly cause cracking (see below for the effect of quenching). However, these cracks form primarily in areas where the metal is least able to resist the stresses caused by fire cutting of risers and quenching of machined towers.
Such places undoubtedly include the sections of the tower ring where risers were located during casting. In these areas, liquation processes undoubtedly occurred to a greater extent.
This is associated with the acquisition of a more developed physical and chemical heterogeneity of the metal, which apparently leads to a weakening of the strength of the metal in this place.
However, along with the establishment in this work of the fact of the predominant location of cracks under the risers, both after fire cutting of the risers and after hardening of the towers, two more facts have been established for which it is necessary to give an explanation, but one that contradicts the provisions just expressed.
1. There are towers with cracks, but the cracks are not visible under all the risers.
2. There are melts where cracks form on some towers and not on others.
In the first case, the explanation must be sought in the realistic size of the allowance for mechanical processing of the end part of the tower ring, remaining in the riser sections after the last cut.
With careful riser trimming, the cutting line does not extend beyond the overall allowance provided for the entire ring. In this case, cracks formed during riser trimming do not extend beyond the allowance into the ring body, if the allowance is large enough. This ensures that the cracks are completely removed with the chips during subsequent machining.
If the cutting is done carelessly, the cutting line may extend deeper into the specified allowance in places. This may cause some cracks to extend beyond the allowance into the ring body and remain untreated with the chips during subsequent machining.
Observations of the machining of several tower rings confirmed the role of the machining allowance: after the first cut, which removed a 15-mm layer of metal along the ring's end face, several cracks were visible. After the second cut, which removed a second 15-mm layer, the cracks were no longer present. Thus, a 30-mm allowance in this case ensured that the cracks formed would be removed with the chips.
How, then, can we explain the formation of new cracks after hardening under the risers? In this case, "new" refers to cracks found at the weld site or not at the site of an old, unwelded crack, but rather cracks in a completely different location, where none were present before hardening.
The formation of these cracks can be associated with cases where the remaining allowance is of some intermediate value. In this case, obvious cracks will be removed with the chips. However, a portion of the metal zone affected by the fire-cutting action will remain. This zone does not exhibit visible (macroscopic) cracks, but microscopic cracks are very likely to form along the crystallite boundaries. During subsequent hardening, these cracks transform from microscopic to macroscopic, requiring the use of steaming to eliminate them.
When explaining the second fact—the formation of cracks in some towers and their absence in others from the same heat—the influence of other factors must be added to the aforementioned influence of the amount of allowance left. These include:
a) different conditions of tower hardening;
b) different thickness of the ring in the cast state;
c) different quality of high release carried out before cutting off profits after their cutting off /this point relates mainly to the 8c brand/.
The influence of the tower ring mass on crack formation
Above, an explanation was given for the fact that the overwhelming majority of cracks found on tower rings after their mechanical processing are formed in those sections of the ring where the risers are located.
This explanation is also supported by another fact. According to old technology No. 112, the machining allowance for the inner side surface of the turret ring was 50 mm, measured at the ring's largest cross-section (at the base of the risers). Therefore, the ring's thickness at this cross-section reaches 120 mm. This same thickness was also the minimum for the risers where they were cut off by fire.
Considering the undesirability of having excessive massiveness of the casting in this place, when carrying out work to establish the state of production of armor casting at Plant No. 112, it was proposed to leave a uniform allowance along the entire height of the ring of 15 mm.
Excessive bulk is undesirable both from the standpoint of excessive metal consumption and from the unnecessary consumption of oxygen for cutting the risers, tooling, and energy for machining the ring. Switching to a uniform 15 mm allowance reduced the ring thickness at the base of the risers to 80 mm, which, in turn, reduced the overall bulk of the ring in its as-cast state.
In connection with the above explanations of the reasons for the predominant location of cracks in the areas under the risers, one could expect a reduction in the number of cracks after such a reduction in the massiveness of the casting.
Special observations of towers with varying ring thicknesses allowed us to collect relevant data. The results clearly demonstrate a correlation between the number of cracks on the machined casting surface and the mass in that area.
It seemed that it could be argued that the indicated connection was entirely due to the fact that cutting off the profits with fire, which have thinner bases, reduces the degree of heating of the metal in the zones adjacent to the cut, and thereby reduces the stresses and the cracks they cause.
In the group of towers with a thicker ring wall (the machining allowance is 50 mm), the percentage of towers with cracks detected after machining was 60 percent. When switching to a smaller allowance (15 mm), the percentage of towers with cracks decreased to 15-20 percent, which is understandable if we attribute this to lower ring heating at the riser cutting points.
In the group of towers with a large machining allowance (wall thickness 120 mm), the percentage of towers with cracks detected after hardening is 55 percent. When switching to a small machining allowance, this percentage also decreases to 23-41 percent.
However, this reduction cannot be explained by a decrease in stresses associated with the heating mode for hardening; it remains practically constant, independent of the amount of allowance for mechanical processing.
Since the quenching stresses remain the same and the average number of cracks has decreased, it can be assumed that the average strength of the metal has increased. This increase in strength can be explained by the increased physical and chemical heterogeneity of the metal, resulting from the reduced development of the liquation process during the solidification of the tower ring due to its reduced mass.
The effect of quenching on crack formation in towers
A significant number of turrets made of grade 8S and 44L steel, which, after mechanical treatment of the turret ring, showed no cracks during a thorough inspection, developed cracks after final heat treatment. These cracks appeared either at the end of the turret ring or at the bottom of the niche, and sometimes in both places simultaneously.
The appearance of these cracks undoubtedly indicates that quenching stresses were the immediate cause of their formation in this case. Of the total number of processing towers (before quenching), 43 percent (23 units) had cracks after final heat treatment.
Towers made of grade 8s and 44l steel were grouped separately, on which cracks were discovered and welded after mechanical treatment, but on which they reappeared after the final heat treatment at the place where the cracks were welded.
The formation of large cracks in turret 1493 is entirely explained by the abnormal analysis of heat 80375. This heat, in addition to carbon and chromium contents at the upper limits, has an excessively high manganese content, exceeding the grade limit. Therefore, not only this turret, but also other turrets in this heat developed cracks during quenching. One turret in this heat did not even reach quenching, as it developed a through crack along the side while being clamped on a machine tool in the machine shop and was also rejected.
It should be noted that this tower had undergone two high-temperature temperings (before and after cutting off the risers). Nevertheless, it retained very high stresses, which, combined with the stresses generated during the tower's clamping on the machine, led to the formation of a large primary crack.
In the remaining melts, the content of carbon, manganese and chromium does not exceed the grade limits and cannot be the cause of the formation of extremely large cracks, since other towers of the same melts did not produce cracks of a similar nature.
What aspects of heat treatment could influence, and do influence, crack formation? Comparing data from turrets without cracks after quenching with turrets from the same heats but with cracks, we can see a correlation between crack formation and the temperature of the quenching medium (water) at the moment the turret is immersed.
For grade 8s steel, this dependence was quite clear. Cracks form at very low water temperatures, especially when the carbon, chromium (and manganese) content is close to the upper limit. The minimum permissible water temperature for quenching towers made of grade 8s steel should be considered 30 degrees Celsius (heats 90199, 100131, and 80367).
For 44L steel this dependence was not clearly revealed.
In some heats (60623, 80336), the towers where cracks were detected were quenched in colder water, while in other heats (70354, 50507), on the contrary, they were quenched in hotter water than the towers where cracks were not detected. Clearly, further observations are needed to clarify this issue for this grade of steel.
Further monitoring is also required to determine the effect of the temperature at which the towers are held in the furnace and the duration of that holding. In some melts (80373, 60623, 50507, 80336), cracks were observed in towers held in the furnace at a higher temperature and for a longer period.
It's in no way correct that for tower 1371 (melt 80372), with carbon, manganese, and chromium contents at the upper limits, the furnace was held at a temperature of 360 degrees. Furthermore, the temperature was maintained at 1000 degrees for 30 minutes (due to the heater operator's fault).
In the same way, for tower 2956 /melt 50476/ with the content of carbon, manganese and chromium at the upper limit, it was not possible to allow water with a temperature of 25 degrees at the time of quenching.
It is worth noting two more circumstances that are not reflected in the hardening process charts, but which can have a significant impact on the creation of excess stress in hardened towers and, consequently, on the formation of cracks, since they occur in the practice of the heat treatment shop.
First, uniform heating of all parts of the turret and maintenance of this uniformity until immersion in the quenching medium are essential. The turret is a complex combination of thin and thick components, and therefore, uneven heating should not significantly increase the stress state of the quenched turret.
This unevenness cannot be achieved in the case of incorrect placement of the tower in the furnace, when its thinner parts /niche/ are closer to the combustion zone than the thicker parts /tower/.
The same thing happens when the tower is not kept in the oven for long enough, when the thin parts have time to heat up, but the thick ones, of course, do not.
Finally, when feeding the tower to the quenching tank, if this feeding is too delayed, thin parts may lose temperature faster than thick ones.
This creates stresses in addition to those stresses that inevitably arise even with normally conducted hardening of the tower as a part of a complex shape.
Secondly, the temperature of the turret when it leaves the quenching tank. In some cases, the turret cools completely during quenching (the turret dries slowly after being removed from the tank). In other cases, the turret reaches a temperature above 100 degrees Celsius (the water on the surface of the turret after being removed from the tank boils).
In the latter case, the remaining heat will cause partial tempering of the tower, relieving some of the stress before the tower is placed in the low-temperature tempering stage. In the former case, the tower cannot self-temper. The cracking results may differ for both cases, even if the towers belong to the same heat.
The influence of variations in the chemical composition of melts on the formation of cracks in towers
Along with the content of the main elements influencing crack formation, data were recorded on the number of cracks found on each tower before and after hardening, the amount of allowance for mechanical processing, and the position of the towers in the furnace during high tempering.
Based on the number of cracks found in the towers, all 44L grade melts can be divided into four groups:
Group 1 – melts in which all towers do not have cracks either during or after quenching.
Group 2 – melts in which only part of the towers have cracks.
Group 3 – melts whose towers have cracks only after hardening.
Group 4 – melts whose towers have a large number of cracks or which are not suitable for inclusion in the first three groups.
Within each melt group, a specific analysis can be identified that encompasses the content of the main elements found in most melts in that group. This analysis is called typical, as opposed to the average analysis of the group.
A comparison of typical and average analyses shows that there is a significant difference in the content of carbon, manganese and chromium between the group of melts with and without cracks.
Heats that are not prone to cracking contain carbon in the range of 0,22-0,25 percent, manganese in the range of 0,9-1,06 percent, and chromium in the range of 1,22-1,40 percent. Heats that are highly prone to cracking contain carbon in the range of 0,25-0,28 percent, manganese in the range of 1,05-1,10 percent, and chromium in the range of 1,30-1,40 percent.
The analysis of Group 2 and 3 melts is within the analysis limits of the melts in the cracked group, but with some deviations. While there is no difference in chromium content, Group 2 melts have slightly higher carbon and manganese contents.
Thus, from the point of view of the content of the main elements that can influence the formation of cracks, the melts of groups 2, 3 and 1 can be combined into one group of melts in which cracks on the towers are observed, in contrast to the other group, where cracks on the towers are completely absent.
Consequently, for grade 44L, the upper limit of the content of the main elements limiting the area of analysis unfavorable for the formation of cracks on the end part of the tower ring is characterized by the following: carbon content no higher than 0,23 percent, manganese no higher than 1,05 percent, chromium no higher than 1,40 percent.
The exception to this rule are melts 50444 and 50445 with chromium content at the upper limit, 50438 and 50436 with carbon content at the upper limit.
The towers of these melts under observation showed no cracks. The lack of data on cracks in other towers of these melts does not allow us to consider this exception significant.
It's quite possible that the remaining towers of these heats, processed without crew supervision, had cracks. The absence of cracks in towers 2868, 2857, and 2241 of heats 50444, 50445, and 50433 can be attributed, in part, to the lack of excessive casting bulk due to the small machining allowance (15 mm).
It's also noteworthy that heat 50439, like heat 50438, has the highest silicon content compared to the other heats. This distinguishes these heats from the other 44L grade heats under consideration, but it still doesn't allow us to draw any conclusions about the relationship between silicon content and crack incidence.
In melt 80340, the absence of cracks can be explained by the fact that the unfavorable effect of the increased manganese content /1,10 percent/ is compensated by the reduced chromium content /1,24 percent/ and nickel content /1,09 percent/.
As for exceptions of the opposite order, i.e. when the melts have cracks on the towers, although according to chemical analysis there should not be any cracks, then in this regard the following remarks can be made:
In heat 80336 (Group 2), cracks after riser cutting were detected only on the tower (1633) with the more massive ring. The other three towers of the same heats, each with a less massive ring, showed no cracks before quenching, which is consistent with the low carbon and chromium content typical of heats without cracks. Only a slightly elevated manganese content under favorable conditions (the casting's excessive mass) could have contributed to crack formation in one of the four towers of this heat.
Heats 80333 and 50427 have carbon contents typical of crack-free heats. However, the high manganese and chromium contents in this case counteracted the beneficial effects of the lower carbon content, causing cracks to form in the towers. The excessive bulk of the ring also contributed to this.
From all of the above regarding the influence of fluctuations in the chemical composition of melts on the formation of cracks in tower rings, it follows that for grade 44L, such an influence occurs for carbon, manganese, and chromium. The formation of such cracks is unlikely (under normal process conditions) if the carbon content does not exceed 0,25 percent, the manganese content does not exceed 1,05 percent, and the chromium content does not exceed 1,40 percent. However, increasing the content of one of these elements to the upper limit of the grade specification while simultaneously reducing the content of the other two elements to the lower limit is permissible.
More dangerous in terms of crack formation in grade 44L steel is approaching the upper limit of carbon and manganese content than chromium.
A reduced chromium content, while desirable for crack prevention, is undesirable for the formation of fibrous fractures. To achieve the latter, cast armor parts made of grade 44L steel must have a chromium content of at least 1,30 percent.
Otherwise, especially when the carbon and manganese content is at the lower limit, repeated thermal processing of the parts is inevitable.
Based on this observation, the optimal chromium content in 44L steel, which takes into account these opposing requirements, can be determined as 1,3-1,6 percent.
The insufficient number of 8s steel melts, which were observed by the team members in parallel with 44l steel melts, does not allow any conclusions to be drawn about the relationship between the carbon, manganese and chromium content in 8s steel and the number of cracks in the tower ring.
The influence of phosphorus deserves special attention. This element is considered the most dangerous in terms of its impact on crack formation. However, the cited data show that, at levels up to 0,035 percent, the negative impact of phosphorus is practically negligible.
Examples show that, despite a phosphorus content of 0,032-0,35 percent, only a few towers exhibit cracks, while the remaining towers of the heats are crack-free. Clearly, such a phosphorus content does not determine crack formation, as otherwise cracks would have formed in all towers of these heats.
Even more definitively, it was established that phosphorus has no effect on the formation of cracks in cast armor parts of the 8s brand.
Heat 100128 contains 0,037 percent phosphorus, while heats 100130 and 100131 contain as much as 0,039 percent. It would seem that with such a phosphorus content, the number of cracks should increase sharply, if one accepts the notion that phosphorus plays a significant role in the formation of cracks in armor castings. Heat 100130 should have been particularly unfavorable in terms of crack incidence, with its high manganese content (1,30 percent), particularly carbon (0,26 percent), and chromium (1,06 percent). In reality, the turrets of this heat are completely free of cracks. As for the other melts, three towers out of four from melt 100126 and three towers out of six from melt 100131 are also completely free of cracks. The remaining towers of the two melts have 1–2 cracks each, and only one of the six towers from melt 100131 developed 4 cracks.
If we compare these results with the results for cracks for melts 90199, 80367 and 80332, which contain 0,031–0,032 percent phosphorus, then we must once again acknowledge the correctness of the conclusion made above that there is practically no negative effect of phosphorus on the formation of cracks in armor castings with its content up to 0,039 percent.
Comparison of steel grades 8s and 44l in their application for the production of armor castings
If we compare both grades by the total number of cracks that are found on the towers before and after laying, then towers made of 8S steel are somewhat less likely to develop cracks at the end of the tower ring (48 percent) than towers made of 44L steel (52 percent).
If this comparison is conducted separately before and after quenching, the opposite relationship is observed. Before quenching, grade 8S steel is slightly more prone to cracking than grade 44L steel (32 percent versus 46 percent). In the latter case, the difference is more significant than before quenching, which ultimately explains some of the advantages of grade 8S steel.
The aforementioned negative properties of grade 44L steel are confirmed by its greater susceptibility to cracking at the bottom of the niche after tower hardening. While the percentage of towers made of grade 8S steel with niche cracks is 8 percent, the percentage of towers made of grade 44L steel with such cracks is 18 percent.
A more significant difference in favor of the 8c grade emerges when comparing the grades not by the number of towers of each grade with cracks, but by the number of cracks in the towers themselves. Four groups of towers were identified for comparison. The first group includes towers with 1-2 cracks, the second with 3-6 cracks, the third with 7-9 cracks, and the last group includes towers with more than 9 cracks.
A comparison of this characteristic shows that towers made of grade 8s steel most frequently exhibit 1–2 cracks (32 percent of the total number of towers examined), while those with 3–6 cracks are comparatively rare (12 percent), and those with 7–9 cracks are very rare (2 percent). As for towers made of grade 44l steel, the percentages for the first three groups are 20, 18, and 10 percent, respectively. Additionally, although rare (4 percent), towers of the fourth group—that is, with more than 9 cracks—are also encountered, which is absent in grade 8s.
If we compare towers of both grades, which have an excessively massive ring in the casting (wall thickness of 120 mm), then the towers made of grade 8s steel produce slightly more cracks (73 percent) than the tower made of grade 44l steel (65 percent).
However, when comparing the results obtained before heat treatment of the towers (the results characterize the quenching analysis), the difference between the grades in this case, i.e. with a massive ring, is not detected.
Switching to a less massive ring (80 mm wall thickness) significantly changes these ratios. For both grades, a decrease in the percentage of towers with cracks is observed.
However, for grade 8s, this decrease occurs by a factor of 2,4 (from 73 percent to 31 percent), while for grade 44l, the decrease is only 1,6 (from 65 percent to 41 percent). As a result, grade 44l retains a higher tendency to crack.
A T-34 at the Krasnoye Sormovo plant before restoration.
The reason why the marks changed places when switching to a less massive ring can be seen from a comparison of the inspection data of the towers before and after hardening.
For grade 8s, a different reduction in crack formation is observed both during riser trimming (before hardening) and during hardening. For grade 44l, a sharp reduction in crack formation is observed only during riser trimming. The reduction in crack formation during hardening in this case is not as dramatic as for grade 8s.
As a result, with a less massive ring, only 23 percent of 8s grade turrets develop cracks during hardening, while for 44l grade steel turrets the same figure is 41 percent.
It should be kept in mind that Plant No. 112 will be casting all turrets with a less massive ring. Therefore, when considering the difference between grades 8S and 44L, only the difference established for turrets with a less massive ring should be considered. As stated above, in this case, grade 44L is significantly inferior to grade 8S than with a more massive ring. This difference is entirely due to the less favorable behavior of 44L steel compared to 8S steel with respect to crack formation during hardening.
After hardening, 13 percent of turrets made of grade 8S steel, 32 percent of turrets made of grade 8S steel, and 32 percent of turrets made of grade 44L steel developed cracks in the ring. If cracks in the niche bottom are also included, these figures rise to 25 percent and 31 percent, respectively.
This is also confirmed by the formation of large cracks of quenching origin. Of the five towers rejected for this reason in October and November, all were grade 44L, even though towers made of grade 8S steel were being processed alongside these towers during the same period.
At the beginning of the report, it was stated that the main focus of this work is repairable cracks. These cracks are repaired by cutting and then welding them back together. This repair delays the towers' passage through the production areas and requires additional labor and materials. At the same time, the size of these cracks and their location on the tower ring raise doubts about their threat to the tower's survivability.
Based on this, it would be advisable to address the issue of checking the degree of danger they pose to the survivability of the tower and the possibility of leaving them unwelded.
If the results of such testing confirmed that there was no need to repair such cracks, then the main drawback of grade 44L compared to grade 8S, which had been revealed during Plant No. 112's annual production of this grade, would be eliminated. In this case, the decision to retain grade 44L in full production would be made without regard for the virtually insignificant drawback of grade 44L (cracks) and with consideration for the significant and currently relevant advantage of reducing nickel and ferromolybdenum consumption.
Another, purely technical, drawback of grade 44L is its higher casting viscosity compared to grade 8S. This only becomes apparent when open-hearth furnaces are operating at cool temperatures and the casting process takes a long time. Therefore, at Plant No. 112, this drawback of grade 44L manifests itself in Shop No. 20, where the furnaces operate at cool temperatures and casting takes about an hour, as small armor castings are also cast here in addition to turrets. In Shop No. 21, where only turrets are cast and casting takes 20-25 minutes, this characteristic of grade 44L is not noticeable.
In addition, the possibility of canceling the preliminary high tempering of towers before cutting off the profits, which has become apparent for the 44L brand, is a very valuable advantage of this brand in the conditions of Plant No. 112, which does not have a sufficient number of furnaces in which high tempering of towers can be carried out.
SUMMARY
Small, repairable cracks, up to 30 mm deep, which very often appear on the machined surface of the tower ring made of 44L and 8S steel, and in the overwhelming majority (at least 80 percent) are formed in those sections of the ring where risers were located in the casting.
A similar pattern of crack distribution is observed not only after cutting off the risers with fire, but is also repeated after hardening the towers.
The predominant distribution of cracks under the risers and the repetition of a similar distribution after hardening – both of these facts allow us to consider that the reasons for the formation of these cracks are:
1) the presence of weakened areas on the tower ring /under the risers/.
2) internal stresses of casting origin, largely retained after high tempering of the towers.
3) stresses arising during the fire cutting of profits.
4) stresses arising during hardening.
The last two reasons are caused by the influence of external factors and can be called external, in contrast to the first two, which are embedded in the casting from the very beginning of its existence, are caused by the natural properties of the metal and can be called internal characteristics.
The predominant formation of cracks under the risers is explained by the reduced strength of the metal, due to the physical and chemical inhomogeneity of the casting in these areas. This inhomogeneity is due to the more intense development of the liquation process in the riser zone due to the slower solidification of the steel there.
As the tower cools after casting, internal stresses arise due to its shrinkage. The tower's complex shape contributes to uneven shrinkage and, consequently, the development of high internal stresses within the tower.
High-temperature tempering at temperatures of 670-690 degrees Celsius relieves only part of these stresses. This is confirmed by the formation of a large crack on the ring and below the turret, which had previously undergone high-temperature tempering, during riser cutting. Another incident that occurred in the machine shop was when the turret, after being highly tempered twice, with a hardness of 4,3-4,4, cracked through the entire flange and ring when mounted on a machine under a relatively minor additional load.
One external cause of the formation of cracks found on the ring before hardening is sharp local stresses that arise under the influence of local heating during the fire cutting of the risers.
These stresses are superimposed on the casting stresses that remained in the tower after high-tempering. If the resulting stresses ultimately exceed the metal's strength in the weakest areas, they discharge, forming cracks. As noted above, these areas are the sections of the tower ring where the risers were located.
These considerations are confirmed by the fact that very often on the same tower cracks are observed only under part of the risers.
Another external cause of crack formation in the same areas of the ring is stresses that arise during the hardening of the tower. These stresses are not local in nature. The internal prerequisite for crack formation—the presence of weak points—remains and even increases in this case. The increase in stresses occurs due to the removal of the healthy metal crust during machining of the inner surface of the tower ring.
Thus, in this case, the stresses that arise have the opportunity to discharge in places of weakness with the formation of new cracks, which is what happens if the magnitude of the stresses reaches the ultimate strength of the metal.
This confirms the fact that cracks predominantly form during hardening in the same areas of the ring where the risers were located before they were cut off.
The sharpness of quenching, which determines the magnitude of quenching stresses, depends not only on the quenching mode, but also on the chemical analysis of the tower.
For grade 44L, it has been established that, from the point of view of reducing the possibility of cracks forming on the tower ring both from hardening and from fire cutting, it is desirable to have a carbon content of no more than 0,25 percent, a manganese content of no more than 1,05 percent, and a chromium content of no more than 1,4 percent.
However, from the standpoint of fibrous fracture formation, it is desirable for the chromium content in this steel grade to be no lower than 1,3 percent. Therefore, the optimal chromium content range for 44L steel, which takes these opposing requirements into account, can be roughly determined as 1,3–4,6 percent.
It was not possible to establish the desired limits for the content of carbon, manganese and chromium for grade 8s steel due to the insufficient number of heats of this grade that were observed.
No hazardous upper limit for phosphorus content has been established for either grade. In any case, it is above 0,035 percent for grade 44L steel and above 0,039 percent for grade 8S steel.
Previously, in another study, it was established that at a content of up to 0,044 percent, phosphorus does not worsen the fracture after final heat treatment and does not reduce the armor resistance required by technical specifications.
Therefore, the current phosphorus content limit of 0,030 percent for armor castings is an unjustified restriction. The need for this limitation has not been confirmed in castings, with regard to phosphorus's effect on each of the three main armor properties (fracture, armor resistance, and crack formation).
Taking this into account and the difficulties that are currently observed in the metallurgical industry, in particular at Plant No. 112, with the production of low-phosphorus charge materials, it is intolerable to continue to maintain this limitation on armor casting from steel of these grades.
The positive results achieved during the transition to casting a turret with a less massive ring due to a reduction in the allowance for machining the side surface of the latter from 50 mm to 15 mm, as well as a reduction in the quantity from 9 to 7 pieces, confirmed the presented ideas about the main causes of crack formation on the turret ring.
These reasons, as indicated above, come down, on the one hand, to the presence of weakened areas on the ring under the risers of internal stresses of casting origin, and on the other hand, to the appearance of stresses from the fire section of the risers, acting in combination with casting stresses, and to the appearance of stresses from hardening.
Reducing the ring's mass naturally slowed the development of liquation within the ring as a whole, and under the risers in particular. This reduced the metal's heterogeneity and reduced the likelihood of cracking.
On the other hand, reducing the ring thickness from 120 mm to 80 mm also reduced the thickness of the risers at their base, where they are cut off by flame. Consequently, the cutting process was accelerated and the local heating of the ring in the riser area was reduced. This reduced the stresses generated during flame cutting of the risers.
Furthermore, replacing the 50 mm allowance with a 15 mm allowance eliminated the exposure of the most unhealthy inner (by cross-section) area of the ring, which inevitably occurred when turning the inside side surface of a more massive ring. This less healthy surface created favorable conditions for crack formation during subsequent hardening.
The following figures can serve as an illustration of the correctness of these explanations.
The total number of towers with cracks /for the 8s and 44l grades together/ with a massive ring is 68 percent, with a lightweight ring – only 38 percent.
The total number of towers with cracks detected before hardening is 50 percent for a massive ring and 37 percent for a lightweight ring.
The total number of towers with cracks after hardening with a massive ring is 55 percent, with a lightweight ring – 35 percent.
The preservation of some of the cracks caused by fire cutting on the end surface of the machined tower ring also depends on the amount of allowance for machining that remains in the areas under the risers after cutting.
When carefully cutting off the risers, the cutting line should not go down into the total allowance provided for the entire ring.
In this case, cracks formed during riser cutting do not extend beyond the allowance in the ring body, provided that the allowance is large enough. Then, during subsequent machining, the cracks are completely removed with the chips.
If the cutting is done carelessly, the cutting line may extend deeper into the specified allowance in places. This may cause some cracks to extend beyond the allowance into the ring body and remain untreated with the chips during subsequent machining.
Observations of the processing of several towers confirmed the indicated role of the size of this allowance.
There is a difference in crack resistance between 8s and 44l steel.
The ability of 8s steel to form small, repairable cracks on the end of the ring is generally less than that of 44l steel /48 percent of towers with cracks versus 52 percent/.
This difference is due to the greater ability of 44L steel to form cracks after hardening compared to 8S steel /46 percent of 44L grade towers have cracks versus 32 percent of 8S grade/.
Before hardening /cracks from flame cutting/ an inverse relationship is observed, but the difference is less significant /36 percent versus 26 percent in favor of grade 44l/.
When comparing turrets cast with a less massive ring separately, the difference in cracks after hardening increases sharply (41 percent of turrets with cracks for grade 44L versus 23 percent for grade 8S).
In this regard, in general, in terms of cracks /before and after hardening/, grade 44L is inferior to grade 8S (41 percent of towers with cracks versus 31 percent).
A more significant difference is observed when comparing not the number of towers of one brand and another that have cracks, but the number of cracks on the towers.
Among towers made of 8s steel, the most common are towers with 1-2 cracks (32 percent), less often with 3-6 cracks (12 percent), and very rarely with 7-9 cracks (4 percent).
Among towers made of grade 44L steel, the corresponding figures are 20, 18, and 10 percent. Furthermore, towers with more than nine cracks (4 percent) are rare, although not observed at all in grade 8S steel.
The ability to form large hardening cracks both on the niche (require major repairs) and on the tower ring (lead to the rejection of towers) is also higher for the 44L brand than for the 8s (for the niche we have 18 percent of towers with cracks versus 8 percent).
Turret crack repair data for April-July shows that 44L turrets undergo repairs in greater numbers than 8S turrets. Ring repairs are 30 percent versus 8 percent, niche repairs are 6 percent versus 2 percent, and side repairs are 1 percent versus zero.
During the same period, 2 percent and zero 8c towers were rejected due to cracks.
Steel grade 44L exhibits higher viscosity during casting compared to steel grade 8S. This increased viscosity is felt in cooler furnaces and during long-term castings (for small castings).
The towers, before and after preliminary high-temperature tempering, have identical hardness, ranging from 4,0 to 4,4 (Brinell dimple diameter). Therefore, the brittleness that leads to cracks during riser cutting is not related to the metal's hardness. This brittleness is due to casting stresses that are not relieved by the high-temperature tempering performed at Plant No. 112.
High-temperature tempering to prevent cracking during riser cutting is mandatory only for grade 8C steel. This tempering regime must ensure uniform and sufficient heating of the towers. For this reason, towers made of grade 8C steel must be placed on the furnace hearth with the riser facing upward.
When arranging the towers in the furnace in two tiers, the upper towers can be positioned /if necessary/ with their risers facing downwards.
For grade 44L steel, cutting risers in an untempered condition does not increase the incidence of cracks during flame cutting, unlike grade 8S steel. Therefore, preliminary high-temperature tempering is not necessary for grade 44L steel.
A delay in placing towers for subsequent high tempering within 80 hours from the end of the riser section in the untempered state also does not increase the number of cracks in towers made of grade 44L steel.
Low quenching temperatures promote the formation of new cracks in the tower's 8C steel ring. The minimum permissible water temperature in this case is 30 degrees Celsius.
For 44L steel, this work failed to reveal a similar dependence.
CONCLUSIONS
A. Based on the results of the work carried out, the following was established:
1. The reason for the formation of small, repairable cracks up to 30 mm deep, which very often open up on the mechanically processed surface of the tower ring made of grade 44L and 8S steel, is the effect of internal stresses of casting origin in combination with stresses from the fire cutting of risers and subsequent hardening on weakened areas of the metal, which are the sections of the ring where the risers were located before they were cut.
2. The brittleness that leads to cracks during riser trimming is not related to the metal's hardness. This brittleness is due to casting stresses that are not completely relieved by the high-temperature tempering performed at Plant No. 112.
3. The ability of castings to form cracks increases with increasing ring mass (due to an excessively large allowance for mechanical processing of the side surface of the ring).
4. The ability of castings to form cracks depends on the content of carbon, manganese and chromium in the steel.
To reduce the risk of cracking in the tower ring of grade 44L steel, while maintaining the steel's normal ability to form fibrous fractures, it is recommended that the carbon content be no higher than 0,25 percent, the manganese content no higher than 1,05 percent, and the chromium content be within 1,3-1,0 percent. Due to insufficient data, a similar relationship has not been established for towers made of grade 8S steel.
5. The upper limit of phosphorus content in armor casting that is dangerous from the point of view of crack formation is above 0,035 percent for grade 44L steel and above 0,039 percent for grade 8S steel.
6. Steel grade 8S has a lower tendency to form cracks on the tower ring than steel grade 44L. This difference is observed in the number of cracks present and, in particular, in the number of cracks found on towers of both grades.
7. For grade 44L steel, the absence of high tempering before cutting the risers does not result in an increase in the number of cracks, unlike grade 8C steel, for which the absence of preliminary high tempering sharply increases the number of cracks formed during cutting the risers.
8. A delay in placing towers for subsequent high tempering within 80 hours from the end of the riser section in the untempered state also does not increase the number of cracks in towers made of grade 44L steel.
9. Low quenching temperatures contribute to crack formation in the tower ring made of grade 8C steel. The minimum permissible water temperature in this case is 30 degrees.
ПРЕДЛОЖЕНИЯ
A. To reduce the number of cracks found on the tower ring, the following measures must be taken:
1. In the near future, completely switch to casting towers with a small allowance for mechanical processing of the side surface of the ring (15 mm) and an allowance of 35 mm on its end surface.
2. Keeping the number of risers unchanged (5 pcs.), reduce their length from 450-500 mm to 350-400 mm, confirming the optimality of the selected riser sizes through enhanced control of the first batch of 25 towers.
3. Chamfering during mechanical processing eliminates sharp edges that currently occur on the machined portion of the tower ring and facilitate the formation of cracks during hardening.
4. Prohibit placing towers made of grade 8s steel in the high-tempering furnace /before cutting off the risers/ with the risers down, if they are placed in the bottom row, i.e. directly on the furnace hearth.
5. Prohibit hardening of towers made of grade 8C steel in water with a temperature below 30 degrees.
6. For 44L steel, it is recommended to maintain carbon content no higher than 0,25 percent, manganese 1,1 percent, and chromium within 1,3–1,6 percent. If the content of one of these elements is at the upper limit, the content of the other two elements should preferably be at the lower limit.
7. When the content of these elements exceeds the specified limits, adjustments must be made to the quenching regimes to reduce the severity of the quenching (reducing the holding temperature, increasing the water temperature, etc.). This is especially necessary when the content of all three elements is close to the upper limit.
B. To eliminate the waste of fuel oil, unnecessary inter-shop transportation, and to increase the throughput of high-tempering furnaces, the following measures must be taken:
8. Schedule a one-month preliminary high-temperature tempering for turrets and small armor castings made of grade 44L steel before the riser cutoff. Keep a special record of the datasheets for these turrets. At the end of the trial period, check the datasheets for the number of cracks on the turrets. Based on the data obtained, summarize the impact of canceling the preliminary tempering and draw a final conclusion on this matter. Involve TsNNI-48 to summarize the results and draw up a final conclusion.
9. The cancellation of the high monthly release shall be extended to all melts with a carbon content of no more than 0,26 percent, manganese no more than 1,30 percent, chromium no more than 1,40 percent, and phosphorus no more than 0,035 percent, not excluding the case of a combination of all these elements at the specified upper limits.
10. There is no reason to expect that, with a chromium content of 1,41–1,70 percent and a carbon content of 0,27–0,28 percent, eliminating the preliminary high-temperature tempering will result in increased crack growth. However, without appropriate testing, which should be performed simultaneously with the work described in point 8, it is impossible to make a categorical statement.
B. To eliminate unnecessary field testing of towers with phosphorus content in the range of 0,036–0,040 percent and the associated delays in production melts, increase the permissible limit of phosphorus content to 0,040% for armor castings made from grades 8s and 44l steel.
G. To check the influence of small cracks observed on the treated surface of the turret ring in an unfinished state on the survivability of the latter under shell fire.
The purpose of the test should be to determine the extent to which welding of such cracks is necessary, as this requires additional labor, time, and materials. The size and location of these cracks, in our opinion, raise doubts about their potential for jeopardizing the survivability of the towers under operational conditions.
This inspection must be carried out with the utmost urgency. If its results confirm that there is no need to repair such cracks, then Plant No. 112, regardless of the steel grade, will be relieved of a large amount of unnecessary work and will be able to increase vehicle production as a result.
At the same time, the main argument against grade 44L, used for armor casting, as being more prone to cracking compared to grade 8S, would disappear.
If we do not take into account another disadvantage of 44L - increased viscosity during pouring, which, however, manifests itself only during the cool running of open-hearth furnaces and long pouring, then, having eliminated the main argument, fifteen months of work at Plant No. 112 on this grade of steel confirms the possibility of using its main advantage - the absence of the need for nickel and ferromolybdenum, the economical use of which continues to be a very urgent task at the present time, regardless of the operating conditions of various plants.
Head of the Moscow group of TsNII-48 Larin
Head of the metallurgical sector of the Central Research Institute-48 Kaptyug.
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