Analysis of the Welding Type and Filler Metal Influence on Performance of a Regenerated Gear

This paper presents the results of voluminous experimental investigations conducted to analyze the influence of the welding procedure on the performance of regenerated gears. Cylindrical spur gears were tested, both newly manufactured and regenerated, in two fundamentally different ways: by hard facing (surfacing) with the “hard” filler metal (DUR 600-IG) and with the “soft” filler metal (EVB2CrMo) with subsequent cementation and quenching. The regeneration procedures were defined and executed, while, subsequently, the microstructure and microhardness of the hard-faced layers were established and measured, followed by checking the durability of the hard-faced teeth flanks. Finally, techno-economic analysis was performed to establish the rationality of the conducted regenerations, i.e., the costs of regenerated and newly manufactured teeth were compared. Based on the results of the conducted investigations, it was possible to establish the influence of the welding type on the performance characteristics (primarily the service life) of the regenerated gears. For individual reparatory hard facing, the procedure with the “hard” filler metal exhibited better characteristics, while for batch reparation of numerous damaged gears, the reparation with the “soft” filler metal, followed by cementation and heat treatment, might be more convenient.


Introduction
The gears transfer the load through the teeth, i.e., the active parts of their flanks. The load transfer is accompanied by the relative movement of the gear and pinion teeth with mutual sliding and rolling. In this way, the stress of the surface layers, caused by the contact (Hertz) pressures, appears on the teeth flanks, while the flanks of the teeth slide at the same time. The bending stress occurs at the teeth base.
Statistical data show that in the gear transmission elements, newly manufactured, most damages appear on gears, followed by failures of bearings, while failures of other parts of the power transmitters are significantly less common. That is the primary reason why many researchers paid special attention to the phenomena of the damage and destruction of gear teeth, their character, the causes for their appearance and the possibility of eliminating those causes [1][2][3][4][5]. A much smaller number of researchers have studied the possibility of repairing those damages, namely, extending the service life of gears and increasing their safety and reliability in operation. By analyzing the causes for loss of the gears' operational capacity and techno-economic indicators of restoration, one can conclude that it is most expedient to regenerate gears to prolong their service life. cored arc welding) process [10]. They evaluated the effect of the number of layers on the microstructure and wear resistance of a nanostructured iron-based alloy deposited by the FCAW process. The wear resistance was higher for the specimen welded with two layers which could be associated with the increased presence of ultra-hard carbides.
Suraj discussed different methods to evaluate the wear and corrosion resistance properties of mild steels, such as EN-8, EN-9 and EN-24, by calculating their corrosion rate [11]. He used the pin on disc apparatus for analysis of ferrous welded materials, hard-faced by the tungsten inert gas (TIG) welding process, and the Vickers microhardness tester for measuring the microhardness. He found that EN-24 exhibited the least wear when compared to EN-8 and EN-9, since its microhardness was higher than that of the other two materials. The hard-faced materials were more corrosion-resistant than the parent metal. The hardness of the three materials varied in accordance with their chemical composition.
Czuprynski studied the metal-mineral-type abrasive wear of a wear-resistant plate, made by a tubular electrode with a metallic core and an innovative chemical composition, using the manual metal arc hard facing process [12]. The properties of the new layer were compared to the results of eleven wear plates manufactured by global suppliers. Based on the wear resistance tests in laboratory conditions and surface layer hardness tests, the wear plates most suitable for use in the metal-mineral conditions were chosen. The results demonstrated the high metal-mineral abrasive wear resistance of the deposited weld metal produced by the new covered tubular electrode. Results also suggested the high linear relationship between an increase in the surface hardness and an increase in the mineral abrasive resistance of the wear-resistant plate's hard-faced layers.
Josifović and Marković laid down some theoretical considerations on gears' regeneration in general, emphasizing advantages of hard facing as the reparation procedure, especially from the aspect of economic effectiveness [13,14]. Lazić et al. conducted an educated selection of hard facing technology, related to the complex procedure of checking the quality of the hard-faced layer [15]. They concluded that the reparatory hard facing operations of various machine parts could be performed only in specialized regeneration workshops. Those should be furnished with adequate equipment and employ the corresponding expert and skilled staff. The estimated financial net benefits of regeneration vs. purchasing the new parts were exceptionally high. They include several items: the regeneration procedure is much cheaper than purchasing the new part; the working life of properly regenerated parts far exceeds the working life of the new parts; the machine downtimes are reduced (the hard facing lasts much shorter than the period of ordering and procuring the new part); assortment and quantity of necessary spare parts are reduced. Similar effects can be expected in other areas such as regeneration of damaged pipes, [16] or other working parts [17].
Marković, on the other hand, also considered the tribological characteristics of gears regenerated by hard facing [18]. His research was focused on the difference in those characteristics when the regeneration hard facing was conducted with the so-called "soft" and "hard" filler metals.
Popovic et al. executed the surface welding of rail steel with self-shielded wire, with different heat inputs, and investigated the influence of the welding heat input on the total impact energy and its components, crack growth rate and fracture mechanisms [19]. They showed that toughness decreased as the heat input increased, but with a temperature decrease, those differences were not so marked. An increase in the heat input led to an increase in the share of trans-granular brittle fracture. They also established that the fatigue life increased with welding heat input increase, while the crack growth resistance decreased in the final deposited layer up to the HAZ, at all heat inputs.
Arsić et al. performed an investigation to show which filler metal is the best for hard facing of parts of the construction mechanization and parts subjected to intensive abrasive wear at stone mines [20]. Since the quality of the surface layer imposes a great influence on the working life of parts, the purpose was to find which filler metal would contribute to extending the working life of parts exposed to intensive wear. The tested hard-faced models were made of the low-carbon steel. Samples were prepared from plates hard-faced with various filler metals and subjected to experimental testing of tribological properties, hardness and microstructure. Research was conducted by using a combination of experimental and theoretical approaches. Results showed that the CrWC 600 alloy was the optimal filler metal for hard facing of the analyzed parts. However, the filler metal E DUR 600 also exhibited good results during the experiments.
Ulewicz and Novy [21] studied the influence of surface fatigue properties of steel S355JR2 in the area of ultra-high cycle numbers (in the range from 6 × 10 10 to 10 × 10 10 cycles). Their samples were coated by electrolytic coatings and the effect of those coatings on the fatigue properties of the material under an ultra-high cycle was determined.
Vicen et al. [22] investigated the tribological properties of a nitride layer applied to a low-alloyed steel. The authors reported the results of the experimental work, which included determination of the chemical composition and wear resistance, and Rockwell, Vickers and nano-indentation tests, both of the substrate material-the low-alloyed steeland the deposited nitride layer. They concluded that applying the nitride layer does not significantly improve the tribological properties of the tested low-alloyed steel samples, and thus they do not recommend it for achieving that purpose.
Trsko et al. [23] tested the influence of the welding process on the creation of tensile residual stresses in the heat-affected zone of high-strength low-alloy (HSLA) steels. Results showed that the welding process caused significant grain coarsening in the heat-affected zone. The microstructural changes were also accompanied by the creation of a tensile residual stress field in the weld metal and heat-affected zone, reaching up to a depth of 4 mm. Tensile residual stresses are well known for acceleration of fatigue crack initiation and, together with coarse grains, can lead to a significant decrease in the fatigue properties of the welded structure.
Vicen, Bronček and Novy [24] presented an investigation dealing with a reduction in the friction coefficient of bearing steel 100Cr6. The reduction in friction was realized by the CarbonX DLC (Diamond Like Carbon) coating, which exhibited excellent friction and mechanical properties. Reducing the friction of 100Cr6 bearing steel resulted in reduced wear and an increased lifetime.

Technological Procedure of Gear Regeneration
Basically, the technological procedure of a gear's regeneration consists of the following operations [25]

Preparation of Samples for Experimental Testing
Previous research in the field of gear regeneration has shown that reparatory hard facing of the damaged working surfaces is the most reliable method for the renewal of the shapes, dimensions and working performances of the teeth. For the proper selection of an adequate method for reparatory hard facing, it is necessary to know the mechanisms of the contact surfaces' wear. The regeneration itself is a complex process consisting of numerous technological operations, whose order of execution is particularly important and precisely defined.
The cylindrical spur gears, of the following characteristics, were used as samples for testing [26]: The base material, used for samples in these experiments, was steel for cementation 20MnCr5, whose marks according to different standards and chemical composition are given in Table 1, [26]. The gear regeneration through hard facing by the TIG procedure, with DUR 600-IG, consists of the following processes:

•
Removal of the cemented layer from the active working surfaces by grinding to the depths of 1.2 + 0.2 and 12 mm along the tooth height; • Preheating of the gears to a temperature of 230 • C and holding at that temperature for 2 h; • The TIG hard facing of the prepared surfaces in the argon-protected atmosphere with the DUR 600-IG wire of diameter Ø1.2 mm; • Returning of the hard-faced gear into the furnace and slow cooling with it; • Grinding of the hard-faced teeth on the gear-grinding machine "Niles".
In the case of regeneration by the "soft" filler metal EVB2CrMo, the technological procedure of regeneration is significantly different from the previously described one. It consists of the following operations: • Soft annealing-this operation is necessary to reduce the surface hardness of the teeth working surfaces and to enable preparation by milling. Annealing was conducted in vacuum, heating up to a temperature of 680 • C, at a rate of 10 • C/min. The gears were then held at that temperature for 4 h and then cooled at a rate of 2 • C/min. During the hard facing, the thickness of the hard-faced layer had to be increased for the size of addition predicted for subsequent surface machining.

Investigation of Microstructure
The metallographic investigations were conducted on the quantitative optical metallographic microscope POLYVAR-MET (Leica Reichart-Jung, Wien, Austria) with magnifications of 20 to 2000 times [26]. Figure 1 presents the microstructure of the cemented layer and of the transient zone of the hard-faced tooth.

•
Removal of the cemented layer from the teeth active working surfaces by milling on the universal milling machine, to the depths of 1.2 + 0.2 and 12 mm along the tooth height.

•
Preheating of the gears to a temperature of 230 °C and holding at that temperature for 2 h.

•
Drying of electrodes at a temperature of 350 °C for 4 h.

•
The Manual Metal Arc (MMA) hard facing of the prepared surfaces by the cored electrodes, EVB2CrMo.

•
High annealing in the furnace.

•
Milling to the over-dimension (with addition for grinding) on the gear milling machine Pfauter. • Soft annealing. • Cementation in the CO2 + CO mixture to the depth 1.0 + 0.1 mm with cooling in the pit.

•
Grinding of the hard-faced teeth to nominal size.
During the hard facing, the thickness of the hard-faced layer had to be increased for the size of addition predicted for subsequent surface machining.

Investigation of Microstructure
The metallographic investigations were conducted on the quantitative optical metallographic microscope POLYVAR-MET (Leica Reichart-Jung, Wien, Austria) with magnifications of 20 to 2000 times [26]. Figure 1 presents the microstructure of the cemented layer and of the transient zone of the hard-faced tooth. The microstructure of the surface and subsurface layers (cemented layer and the core of the newly manufactured tooth) is presented in Figure 1a. The basic micro-constituent of the tooth cemented layer is the tempered martensite (dark areas in the figure). The smaller share of the retained austenite can also be noticed. In the surface zone, up to the depth of 0.2 to 0.3 mm, individual coarser carbides of the alloying elements are also present. Based on the appearance of the martensite needles, one can conclude that the material possesses a fine-grained structure, which points to the fact that the heat treatment process was properly conducted. Based on Figure 1b  The microstructure of the surface and subsurface layers (cemented layer and the core of the newly manufactured tooth) is presented in Figure 1a. The basic micro-constituent of the tooth cemented layer is the tempered martensite (dark areas in the figure). The smaller share of the retained austenite can also be noticed. In the surface zone, up to the depth of 0.2 to 0.3 mm, individual coarser carbides of the alloying elements are also present. Based on the appearance of the martensite needles, one can conclude that the material possesses a fine-grained structure, which points to the fact that the heat treatment process was properly conducted. Based on Figure 1b  The microstructure of the tooth hard-faced by the TIG procedure and the filler metal DUR 600-IG in the argon protective atmosphere is shown in Figure 2a, while in Figure  2b, one can see the transition from the surfaced layer and the heat-affected zone. In the first figure, one can clearly notice the cast dendritic (stick-like) structure of the welded metal. The more prominent dendritic branches are present in the second surfaced layer, unlike the first layer where, due to the heat input during the second layer deposition, a smaller homogenization of the microstructure occurred. The dendrites' growth direction, with respect to the base metal (BM) and the first deposited layer, is perpendicular to the tooth surface.

of 16
The microstructure of the tooth hard-faced by the TIG procedure and the filler metal DUR 600-IG in the argon protective atmosphere is shown in Figure 2a, while in Figure 2b, one can see the transition from the surfaced layer and the heat-affected zone. In the first figure, one can clearly notice the cast dendritic (stick-like) structure of the welded metal. The more prominent dendritic branches are present in the second surfaced layer, unlike the first layer where, due to the heat input during the second layer deposition, a smaller homogenization of the microstructure occurred. The dendrites' growth direction, with respect to the base metal (BM) and the first deposited layer, is perpendicular to the tooth surface. The microstructure of the cemented layer hard-faced with the filler metal EVB2CrMo is shown in Figure 3. The basic micro-constituent in the hard-faced layer zone is the tempered martensite. Based on the degree of etched material, one can conclude that there is a significant difference in the chemical composition between the FM and BM. Since the exploitation characteristics of the hard-faced layer depend, to a great extent, on the size of dendrites within it, the dendritic crystals' width was measured on the optical microscope [26]. Those measurements were performed at a distance of 0.2 mm from the joint line, as shown in Figure 4. A total of 217 dendritic crystals were measured over the The microstructure of the cemented layer hard-faced with the filler metal EVB2CrMo is shown in Figure 3. The basic micro-constituent in the hard-faced layer zone is the tempered martensite. Based on the degree of etched material, one can conclude that there is a significant difference in the chemical composition between the FM and BM.
The microstructure of the tooth hard-faced by the TIG procedure and DUR 600-IG in the argon protective atmosphere is shown in Figure 2a, whi one can see the transition from the surfaced layer and the heat-affected zo figure, one can clearly notice the cast dendritic (stick-like) structure of the The more prominent dendritic branches are present in the second surface the first layer where, due to the heat input during the second layer deposi homogenization of the microstructure occurred. The dendrites' growth d respect to the base metal (BM) and the first deposited layer, is perpendicu surface. The microstructure of the cemented layer hard-faced with the filler me is shown in Figure 3. The basic micro-constituent in the hard-faced lay tempered martensite. Based on the degree of etched material, one can conc is a significant difference in the chemical composition between the FM and Since the exploitation characteristics of the hard-faced layer depend, to on the size of dendrites within it, the dendritic crystals' width was measured microscope [26]. Those measurements were performed at a distance of 0.2 joint line, as shown in Figure 4. A total of 217 dendritic crystals were mea measurement width of 6.615 mm. The measurement results are presented in Figure 5 [29]. Since the exploitation characteristics of the hard-faced layer depend, to a great extent, on the size of dendrites within it, the dendritic crystals' width was measured on the optical microscope [26]. Those measurements were performed at a distance of 0.2 mm from the joint line, as shown in Figure 4. A total of 217 dendritic crystals were measured over the      Based on the results presented in Table 2 and the diagrams in Fi that the average width of the dendritic crystals is 30.48 μm. From the h also notice that about 30% of dendrites have an average width of up to of dendrites have an average width of up to 30 μm, while about 80% width of up to 40 μm. A width of over 60 μm is only achieved in abo The largest number of dendrites, i.e., 15.66% of them, have a width of 73.7% of dendrites have a width within the range of 10 to 40 μm. Consid one can conclude that the liquid bath during the hard facing had a relat and that the hard-faced layer possesses a fine-grained dendritic structu Based on the results presented in Table 2 and the diagrams in Figure 5, one can see that the average width of the dendritic crystals is 30.48 µm. From the histograms, one can also notice that about 30% of dendrites have an average width of up to 20 µm. About 45% of dendrites have an average width of up to 30 µm, while about 80% have an average width of up to 40 µm. A width of over 60 µm is only achieved in about 3% of dendrites. The largest number of dendrites, i.e., 15.66% of them, have a width of 20 to 25 µm, while 73.7% of dendrites have a width within the range of 10 to 40 µm. Considering these results, one can conclude that the liquid bath during the hard facing had a relatively small volume and that the hard-faced layer possesses a fine-grained dendritic structure [26].

Investigation of Microhardness
The microhardness of the teeth, hard-faced by the TIG procedure with the filler metal DUR 600-IG, was measured in two directions, close to the top of the tooth and in the zone of the pitch circle, Figure 6a. Results are presented in Tables 3 and 4, as well as in diagrams in Figure 7 [18]. For the tooth hard-faced with the filler metal EVB2CrMo, hardness was also measured in two directions, but in the zones of the pitch circle and the lowest area of the hard-faced layer, Figure 6b. Measurement results are presented in Tables 5 and 6, as well as in Figure 8. of the pitch circle, Figure 6a. Results are presented in Tables 3 and 4, as well as in diag in Figure 7 [18]. For the tooth hard-faced with the filler metal EVB2CrMo, hardness also measured in two directions, but in the zones of the pitch circle and the lowest ar the hard-faced layer, Figure 6b. Measurement results are presented in Tables 5 and well as in Figure 8.   Besides the conducted investigations, the microhardness of the inactive tooth flanks of the regenerated teeth was measured, as well. For the sample hard-faced with the DUR 600-IG filler metal, hardness was measured in three directions, close to the tooth top (I-I), in the pitch circle zone (II-II) and at the tooth base (III-III), Figure 9a, while for the tooth hard-faced with the EVB2CrMo filler metal, hardness was measured only in the middle of the tooth, Figure 9b. Measurements' results are presented in Tables 7-10, as well as in Figure 10.      Besides the conducted investigations, the microhardness of the inactive tooth flanks of the regenerated teeth was measured, as well. For the sample hard-faced with the DUR 600-IG filler metal, hardness was measured in three directions, close to the tooth top (I-I), in the pitch circle zone (II-II) and at the tooth base (III-III), Figure 9a, while for the tooth hard-faced with the EVB2CrMo filler metal, hardness was measured only in the middle of the tooth, Figure 9b. Measurements' results are presented in Tables 7-10, as well as in Figure 10.    From the diagram in Figure 10, it is obvious that a hardness reduction occu non-hard-faced surfaces of the teeth. From the presented results, one can easily no the largest hardness reduction occurs for the tooth hard-faced by the TIG proced the DUR 600-IG filler metal at the tooth head, while the tooth base (where there more material and which is further from the heat source during the hard facing) lowest hardness reduction. Such results were expected and are quite logical [26].  From the diagram in Figure 10, it is obvious that a hardness reduction occurs on the non-hard-faced surfaces of the teeth. From the presented results, one can easily notice that the largest hardness reduction occurs for the tooth hard-faced by the TIG procedure with the DUR 600-IG filler metal at the tooth head, while the tooth base (where there is much more material and which is further from the heat source during the hard facing) had the lowest hardness reduction. Such results were expected and are quite logical [26].

Investigation of the Tooth Flanks' Durability
Investigation of the regenerated and newly manufactured teeth flanks' durability was performed on a closed-circuit device shown in Figure 11 [27]. The workload of 3000 Nm was introduced to gears gradually. In that way, failures were avoided.

Investigation of the Tooth Flanks' Durability
Investigation of the regenerated and newly manufactured teeth flanks' du was performed on a closed-circuit device shown in Figure 11 [27]. The workload Nm was introduced to gears gradually. In that way, failures were avoided. The appearance of the destructive wear, namely, the first pitting pits, was after 69 × 10 6 loading cycles for the newly manufactured teeth and for the teeth ha with the EVB2CrMo filler metal after 70 × 10 6 cycles. The longest operation prio appearance of the first pits was exhibited by teeth hard-faced by the TIG proced the DUR 600-IG filler metal, where the destructive pitting started after 74 × 10 6 cycles. After 98 × 10 6 loading cycles, the full duration of tests, for newly manu teeth, 18% of the most endangered tooth surface was covered with pitting; for t hard-faced with the EVB2CrMo filler metal, the attacked area was about 50 %; an tooth hard-faced by the TIG procedure, this was only about 12 %. Analyzing the o time until the first appearance of the destructive pitting of the regenerated an manufactured teeth produced the diagram shown in Figure 12. The size of the pitted surface of the tooth was determined by the visual meth template was made of opaque foil, the opening of which was as long as the tooth (about 17.5 [mm]) and 10 [mm] wide. Then, the teeth portions were examined magnifying glass (magnification 5×). The assessment was made according to t worn teeth and their parts with the most pits. Those tests were performed in the destructive pitting, namely, after noticing the initial pits with the naked eye. The appearance of the destructive wear, namely, the first pitting pits, was noticed after 69 × 10 6 loading cycles for the newly manufactured teeth and for the teeth hard-faced with the EVB2CrMo filler metal after 70 × 10 6 cycles. The longest operation prior to the appearance of the first pits was exhibited by teeth hard-faced by the TIG procedure and the DUR 600-IG filler metal, where the destructive pitting started after 74 × 10 6 loading cycles. After 98 × 10 6 loading cycles, the full duration of tests, for newly manufactured teeth, 18% of the most endangered tooth surface was covered with pitting; for the tooth hard-faced with the EVB2CrMo filler metal, the attacked area was about 50 %; and for the tooth hard-faced by the TIG procedure, this was only about 12 %. Analyzing the operation time until the first appearance of the destructive pitting of the regenerated and newly manufactured teeth produced the diagram shown in Figure 12.

Investigation of the Tooth Flanks' Durability
Investigation of the regenerated and newly manufactured teeth flanks' durabilit was performed on a closed-circuit device shown in Figure 11 [27]. The workload of 300 Nm was introduced to gears gradually. In that way, failures were avoided. Figure 11. Gears' testing device with closed circuit and reactive loader.
The appearance of the destructive wear, namely, the first pitting pits, was notice after 69 × 10 6 loading cycles for the newly manufactured teeth and for the teeth hard-face with the EVB2CrMo filler metal after 70 × 10 6 cycles. The longest operation prior to th appearance of the first pits was exhibited by teeth hard-faced by the TIG procedure an the DUR 600-IG filler metal, where the destructive pitting started after 74 × 10 6 loadin cycles. After 98 × 10 6 loading cycles, the full duration of tests, for newly manufacture teeth, 18% of the most endangered tooth surface was covered with pitting; for the toot hard-faced with the EVB2CrMo filler metal, the attacked area was about 50 %; and for th tooth hard-faced by the TIG procedure, this was only about 12 %. Analyzing the operatio time until the first appearance of the destructive pitting of the regenerated and newl manufactured teeth produced the diagram shown in Figure 12. The size of the pitted surface of the tooth was determined by the visual method. Th template was made of opaque foil, the opening of which was as long as the tooth's heigh (about 17.5 [mm]) and 10 [mm] wide. Then, the teeth portions were examined with th magnifying glass (magnification 5×). The assessment was made according to the mos worn teeth and their parts with the most pits. Those tests were performed in the phase o destructive pitting, namely, after noticing the initial pits with the naked eye. The size of the pitted surface of the tooth was determined by the visual method. The template was made of opaque foil, the opening of which was as long as the tooth's height (about 17.5 [mm]) and 10 [mm] wide. Then, the teeth portions were examined with the magnifying glass (magnification 5×). The assessment was made according to the most worn teeth and their parts with the most pits. Those tests were performed in the phase of destructive pitting, namely, after noticing the initial pits with the naked eye.

Techno-Economic Analysis of Applied Regeneration Procedures
Economic analysis of the applied regeneration procedures assumes a comparison of costs of the regenerated and newly manufactured gears. The regeneration price includes material and labor costs, as well as overheads. The comparison results are presented in Table 11. Analysis is performed through the following parameters [27]: Indicator of economic justification of regeneration (k e )-represents the relative price of the regenerated gear (C r ) with respect to price of the new gear (C n ) and is determined according to expression: Assuming that 5% of the teeth working surfaces being affected by pitting are a criterion for interruption of the gears' working capacity (i.e., the wear limit), the operating time of the gears regenerated by the appropriate welding method (t r ) was determined from the diagram shown in Figure 12. The operation time (service life) of the new gear, until reaching the limit wear, is t n = 1510 h.
Coefficient of the exploitational reliability (k ep )-represents the ratio of the regenerated and new gear service lives: Condition for economic rationality of regeneration (β)-takes into account both the regeneration price and the service life of regenerated teeth until the limit wear appearance. It is calculated according to β = C n · t r C r · t n .
Regeneration is justified when the coefficient β is greater than 1. Individual values of all the factors mentioned above, for both regeneration procedures are given in Table 11, [26].

Conclusions
Improvement of all the mechanical properties of regenerated gears can be achieved through the careful and well-organized preparation of hard facing, selection of the adequate filler metals and the welding method, strict obedience to the prescribed working regimes and by precisely defined and carefully executed heat treatment processes of the regenerated gears' working surfaces. Standard equipment, available in any metal working shop, can be used for regeneration, which makes the investment costs minimal.
From the aspect of the teeth flanks' durability, namely, resistance to fatigue wear, the best characteristics possess teeth regenerated by the TIG procedure with the DUR 600-IG filler metal. Somewhat worse properties were obtained for teeth regenerated by the EVB2CrMo filler metal, which were subsequently cemented and heat treated. However, their service life was also longer than expected. Considering the calculated coefficients of economic justification/rationality of the regeneration procedures, one can conclude that the best reparatory hard facing is by the TIG procedure and DUR 600-IG filler metal.
In individual regeneration of gears, somewhat more convenient is hard facing with "hard" filler metals. However, if batch regeneration of the damaged gears would be required (as well as other machine parts), it would be more convenient to apply the "soft" filler metals with subsequent cementation and heat treatment. Funding: This research was partially financially supported through the project "Innovative Solutions for Propulsion, Power and Safety Components of Transport Vehicles" ITMS 313011V334 of the Operational Program Integrated Infrastructure 2014-2020 and co-funded by the European Regional Development Fund and projects TR35006 and TR35024 financed by the Ministry of Education, Science and Technological Development of the Republic of Serbia. Publication was also partially financed by statutory research of the Department of Mechanics and Machine Design Fundamentals of Czestochowa University of Technology BS/PB-1-100/3010/2021/P.