Taming the Armor
One of the main problems in the production of hulls and turrets of T-34 medium tanks was cracking in the welded parts. It’s all about the high hardness of the 8C armor, when small tears or microcracks form next to the welded seam. The presence of residual stresses after welding in the first time after the production of the armored vehicle did not make itself felt, but over time it came out with cracks up to 500 mm long. All this, of course, reduced the impact resistance of tank armor. To solve this problem, immediately after the organization of production of the evacuated enterprises, in the second half of 1942, specialists from the Armored Institute (TsNII-48) and the Electric Welding Institute of the USSR Academy of Sciences were involved. The research was carried out at two enterprises: the Ural Tank Plant No. 183 in Nizhny Tagil and the Ural Heavy Engineering Plant in Sverdlovsk. In total, from July to October, metallurgists and materials scientists investigated the formation of cracks during welding of about 9,500 armored parts. The purpose of the study was to find the most optimal chemical composition of the 8C armor. It turned out that the most important component in the armor in this situation was carbon. If its content in the armor was more than 0.25%, the hardness of the hardened zone in the area of the welded seam increased sharply, which inevitably led to cracking.
Installation for automatic submerged-arc welding of the T-34-85 tank hull. Factory number 183, 1944. Source: Russian State Archives of Economics
But it was not easy to ensure such a low carbon content in armor steel in peacetime, and in wartime it seemed impossible at all. Small “cosmetic” changes in the welding cycle through the use of austenitic electrodes, a multi-roll system for applying weld seams and a low tempering of the assemblies after welding made it possible to raise the upper limit of the carbon content only to 0.28%. By the way, the German tank industry did not even hear about such serious requirements for tank armor – on average, the share of carbon was in the range of 0.4-0.5%. The solution to the problem of the appearance of cracks in the welding area was preheating the parts to 150-200 degrees Celsius, followed by slow cooling of the parts after welding to 100 degrees for 30 minutes. For this purpose, the Armored Institute developed special inductors that provide local heating of armored parts in the zone of gas cutting or welding. At the Ural Heavy Machine Building Plant, inductors were used to weld the joint of the frontal part with the sides and roof, as well as when cutting out the balancing holes in the hardened side parts of tanks. Thus, the problem of cracking during welding of medium-carbon armor steels was solved. Over time, the practice of the Sverdlovsk plant was extended to other tank plants.
In July 1941, by order of the Council of People’s Commissars, the Electric Welding Institute of the USSR Academy of Sciences was evacuated to Nizhny Tagil. That is why automatic submerged arc welding of tank hulls was introduced at Uralvagonzavod for the first time. Of course, this technology was known earlier, but the group of Academician Yevgeny Oskarovich Paton with employees of TsNII-48 were able to adapt it for welding armored steels. One of the outstanding scientists who contributed to the development of armored welding was Vladimir Ivanovich Dyatlov. Together with the employees of the Kharkov Comintern Plant, he solved the problem of cracking in the armor during welding by introducing a low-carbon wire into the weld pool (more on this below). In 1942, a scientist, the first in the world, discovered the phenomenon of self-regulation of arc processes with a consumable electrode, which made it possible to significantly simplify the design of the feeding mechanisms of welding machines. Also, due to this, it was possible to create relatively simple single-motor welding heads, more reliable and cheaper. Without Dyatlov, it would not have been possible to create effective fluxes based on slags of blast-furnace charcoal furnaces of the Ashinskiy metallurgical plant, which were named “slag fluxes ША”. Since October 1943, the scientist headed the laboratory of the welding Uralvagonzavod and stayed in this position until 1944, until he was transferred to the Central Research Institute of Shipbuilding Technologies.
But back to the legendary T-34, which would never have become such a massive tank, if not for the automatic welding of its armored hulls (towers) at factories No. 183 and UZTM. The use of automatic welding machines made it possible to reduce the welding time by 3-6.5 times. At the same time, at least 40 linear meters of welding seams were used for each tank corps.
Academician Evgeny Oskarovich Paton. Source: patom.kiev.ua
In addition to the T-34, the welding of Academician Paton was used at the armored hull plant No. 200 in Chelyabinsk. With its help, the bottom of the KV tank hull was cooked, which in total amounted to about 15 running meters of the seam per vehicle. It is important that the automation of the welding of armor made it possible to attract low-skilled workers to the production – foremen-welders throughout the war there was a chronic shortage. Since July 1942, a unique tank conveyor has been operating in Nizhny Tagil, on which 19 automatic submerged-arc welding units operated. Estimate the scale of the innovation – this freed up 280 high-quality welders for other work, replacing them with 57 low-skilled workers. Academician Yevgeny Oskarovich Paton himself in a memo addressed to the secretary of the tank industry department of the Sverdlovsk regional committee of the All-Union Communist Party of Bolsheviks in March 1942 spoke about the effectiveness of the introduction of automatic welding (quote from N. Melnikov’s book “Tank industry of the USSR during the Great Patriotic War”):
“Due to the high productivity of high-speed automatic welding under flux layers, the time for welding the bodies will be significantly reduced, and the consumption of labor, electricity and electrode wire will decrease.”
A comparison of the time spent on manual and automated welding can be found in the archives of the exhibition complex of OAO NPK Uralvagonzavod. In accordance with them, welding, for example, of the T-34 turret ring sector, takes a welder a little more than five hours, and automatic welding does it in just 40 minutes. Bottom joints are welded manually in three hours, and in automatic mode – in one hour.
Fight for the seam
It cannot be said that automatic welding machines suddenly appeared at the assembly plants of the Soviet tank industry. Firstly, the share of manual welding was still very large in the production of armored products, and secondly, at first, not everything was smooth with the technology itself. It was not possible to give the weld the required level of ductility – after cooling, it became hard and brittle. This, of course, had the most negative effect on the armor’s projectile resistance. After analyzing the reasons, it turned out that it was all about exceeding the penetration depth of the welded metal, mixing the wire metal with the base metal and significant alloying of the weld metal. Groups from TsNII-48 under the leadership of I. F. Sribny and from the Institute of Welding, headed by the aforementioned V. I. Dyatlov, proposed and tested the following methods of welding “recalcitrant” armor 8C and 2P. First of all, this is multi-pass welding, when the machine connects the parts to be welded in several steps. This ensures low penetration of the joints and the formation of a strong and flexible seam. It is clear that such a technique is not the most effective in wartime conditions: after all, multi-pass welding requires a lot of time in comparison with single-pass.
Installation for automatic submerged arc welding of the roof of the tower of the T-34-85 tank. Plant No. 112 “Krasnoe Sormovo”, 1945. Source: Russian State Archives of Economics
The second technique from TsNII-48 and the Institute of Welding was the laying of a low-carbon steel wire in the groove of the seams to reduce the “fading” of the armor metal. As a result, the seam after cooling became more plastic, the wire seriously reduced the temperature inside the groove of the seam, and also doubled the productivity of the welding machines. This turned out to be the most effective technique, which was even further improved. A new method of welding “in two wires”, in which a second (filler) wire, not connected to the current source, was fed into the weld pool at an angle to the electrode wire. The feed and diameter of the second wire were calculated so that the amount of metal deposited from it was equal to the amount of metal from the deposited electrode wire, that is, the diameter of the second wire should be equal to the diameter of the electrode wire and their feed rates should be the same. However, due to the need to re-equip the automatic heads from feeding one wire to feeding two wires, the introduction of this method was postponed and it was replaced by the method with bar insertion. Nevertheless, already in June-July 1942, this method was applied at plant No. 183 when welding a batch of the lower plates of the tank hull nose with bow beams.
Installation for automatic submerged-arc welding of the roof of the tower of the T-34-85 tank at the Nizhny Tagil plant No. 183. 1944 year. Source: Russian State Archives of Economics
Difficulties with the automation of welding of tank corps (turrets) were also organizational. It is worth remembering that welding machines had never been assembled in series before and were, in fact, products of the pilot production of the Institute of Welding. This explains some of the slowness in the development of new technologies in the tank industry. So, by the end of 1942, the tank factories had only 30 to 35 welding machines, which, of course, were not enough. Therefore, the People’s Commissar I.M. Zaltsman, by order No. 200s of March 28, 1943, ordered at plant No. 183 to additionally install 7 auto-welding units by mid-May, at the Ural Heavy Machine Building Plant by June 1, 8 automatic machines and by June 15, 5 units demanded to be delivered to the Chelyabinsk plant. No. 200. This step was one of many that allowed the domestic tank industry to reach the planned production targets for the much-needed tracked armored vehicles for the front.
To be continued…