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The paper presents experimental testing of wear resistance of steel samples from the same groups of steel. Test results were recorded and presented in the form of diagrams showing the wear resistance of the tested materials in different sliding conditions. The tested steels have high carbon content; the addition of chromium and molybdenum results in the high hardness and low impact toughness of the steels. The addition of vanadium changes the microstructure when the metal grain becomes smaller and the whole structure is martensitic, with chromium and vanadium carbides in the metal matrix. A change in the microstructure causes a change in mechanical properties. The obtained results showed that the addition of vanadium increases impact toughness. However, it is not known how it affects wear resistance and hardness. This type of steel belongs to a new group of steels resistant to wear. A change in the vanadium content causes a decrease in the hardness and wear resistance of the steel and an increase in its impact toughness.

During the process of regeneration of machine parts, certain phenomena occur that have a significant impact on the loss of their working ability. Hereditary properties are expressed by the interdependence of geometric and physical-mechanical-metallurgical parameters of gear teeth created during the technological operations of regeneration of worn teeth by hard-facing. The influence of the type of additional material (electrodes and their combinations) on the tribological characteristics of welded gear teeth was considered, whereby the so-called hard additional materials were applied. Those are the additional materials that give the required surface hardness of the teeth without subsequent thermal or thermochemical treatment. This research did not involve the regeneration of specific worn gears removed from machine systems, but the new gears were made, which were then damaged and then regenerated by hard-facing using the shielded metal arc welding (SMAW) procedure. Thus, all the tested gears were made of the same material, belonged to one batch and were machined on the same machines with the same machining regimes. The tests were performed on samples made of 20MnCr5 steel for cementation, on a tribometer by the “block on disc” method, which was designed to simulate the operating conditions of coupled teeth of concrete gears in the exploitation conditions. Based on the conducted tribological tests, the average coefficients of friction and topography of the surfaces were determined by measuring the wear trace and it was defined which additional materials give the best tribological characteristics of the surfaces of gears regenerated by hard-facing.

Hard-facing as a type of the coating depositing is increasingly used today. Physical-chemical-metallurgical characteristics of contact layers in tribo-mechanical systems depend on the operating conditions and the conditions under which the work surfaces were created. That is the reason the influence of the processing procedures and regime, used in the contact surfaces formation, on development of the wear process of contact elements, is being considered ever more. To determine the influence of the hard-facing technology on characteristics of the gears’ working surfaces, the experimental investigations were performed on samples hard-faced on the steel for cementation, by varying the filler metals (FM) and the hard-facing regimes. The samples tested were hard-faced by five “hard” and three “soft” filler metals. Experimental investigations included measuring the hard-faced layers’ hardness and determination of their microstructure, as well as the wear resistance in the laboratory conditions, on tribometer and on a specially designed device for tests in the real operating conditions of gears. The wear intensity was monitored by the wear trace’s width in the laboratory conditions and by the share of the teeth surfaces affected by the destructive pitting in the operating conditions. The results obtained were compared to results of the base metal (BM) tests, which provided the certain conclusions on which filler metal and which welding procedure are the optimal ones for regeneration of the worn teeth surfaces.

The problem considered in this paper is the welding technology of the steel assembly of a firefighter truck rear bridge semi-housing. Since in this procedure the welding is done of the two dissimilar steels, it is necessary to analyze effects of welding on mechanical properties and microstructure of individual joint’s zones. The weldability of the base metal was considered first (semi-housing tube and flange), then the welding method and the filler metal were selected and, finally, the technological parameters of welding were calculated. The computational and experimental methods were used for the base metal weldability estimate, based on the hardness measurements in the joint’s critical zones and analysis of their structures. Experimental investigations performed were aimed for verification and/or eventual correction of the proposed welding technology.

Two aspects of various steels’ weldability are considered in this article. The theoretical part presents general concepts related to steel’s weldability and the application of the most important methods for its determination. In the experimental section, results of the hard-facing application to several samples are presented, and consist of hardness measurements in the different zones of the welded samples, with the evaluation of those zones’ microstructures. The tested materials included two carbon steels and two alloyed steels, with hard-facing layers deposited by various filler metals. Experimental results were compared to results obtained by calculations; using both, authors were able to conclude which combination of filler metal, welding procedure and, if necessary, heat treatment, would achieve the optimal improvement of weldability in welding/hard-facing of each of the tested base metals.

This paper presents new methodology for determining the actual stress–strain diagram based on analytical equations, in combination with numerical and experimental data. The first step was to use the 3D digital image correlation (DIC) to estimate true stress–strain diagram by replacing common analytical expression for contraction with measured values. Next step was to estimate the stress concentration by using a new methodology, based on recently introduced analytical expressions and numerical verification by the finite element method (FEM), to obtain actual stress–strain diagrams, as named in this paper. The essence of new methodology is to introduce stress concentration factor into the procedure of actual stress evaluation. New methodology is then applied to determine actual stress–strain diagrams for two undermatched welded joints with different rectangular cross-section and groove shapes, made of martensitic steels X10 CrMoVNb 9-1 and Armox 500T. Results indicated that new methodology is a general one, since it is not dependent on welded joint material and geometry.

The aim of this paper is to show wear properties of different types of filler metals aimed for hard facing and exploitation in dry condition. Testing of wear resistance is done in laboratory on prepared samples/models in order to simulate real exploitation conditions. Samples were made by hard facing of carbon steel using 4 different filler metals. Hard facing was done by using MMA welding method in three layers with enough height so samples could be made. After samples were made, the hardness and microstructure of all zones of hard facing were determined. Testing of wear resistance is done using block on disc contact on samples made from pure weld metal. As a parameter for estimates of the wear resistance of models it was used volume of worn material in mm3. Metallographic investigations and hardness measurements were used as additional parameter for drawing the conclusions.

Determination of corrected main process parameters procedure in the strip ironing process with double side thinning, as well as appropriate experimental results are presented in this paper. Given is modified analysis for friction coefficient and contact pressure determination. Classical common so called “Schlosser model” is not suitable in many cases, and give unreal values for both of main process parameters. Formulas obtained here were verified in suitable examples which are, also, presented in the paper. Verification was performed on the base of experimental results. Realised was the single and four phase process of mild steel DC04 sheet stripes drawing. Stripes were 20 mm wide and 2.5 mm thick. Lateral force intensities were 5, 10 and 15 kN. Maximal obtained thinning deformation in one phase was about 17%. Appropriate lubrication with mineral oil and grease was used in conditions of lower speed of 20 mm/min. Results shows that proposed corrected parameters enables more precise process monitoring and precise quantification of lateral force, contact pressure and thinning strain influence on friction.

Steels of the ARMOX class belong into a group of the fine-grained, increased strength steels, which are manufactured by the quenching and low-tempering procedure, with intensive thermo-mechanical treatment at high temperatures. Combination of the heat and mechanical treatments provides for the fine grains and exceptionally good properties of these steels, while the low-tempering enables relatively high hardness and good ballistic properties. This is why the welding of these steels can negatively affect the material properties in individual zones of the welded joint, what could lead to worsening of the material's ballistic properties, as well. The model plates were welded with the specially prescribed technology; the joints were the but-joint, corner joint and the joint with the shielding plate. In this paper are presented results obtained from the ballistic tests of the plates welded by the prescribed technology; tests consisted of shooting with three types of live ammunition at different types of the welded joints.

Numerous phenomena that occur during the process of machine parts’ regeneration have a significant impact on the loss of their working ability. Therefore, the properties of the working surfaces of the teeth flanks of repaired gears were analyzed in this research. The hereditary properties of the gear teeth are expressed by the interdependence of their geometric and physical-mechanical-metallurgical parameters created during the technological operations of regeneration of worn teeth by welding/hard-facing. The hard-facing was executed with three filler metal types, namely: combination Inox 18/8/6 + EDur 600, Castolin 2 and UTP 670. The tested properties included geometrical accuracy, microstructure and microhardness. Evaluation of the executed regeneration procedures was done by comparing the mentioned parameters of the regenerated gears and the new ones. The tested gears were not withdrawn from production due to damage, but they were newly manufactured and intentionally damaged gears, made of the same materials, subjected to the same manufacturing process. In this way, all influences except for the considered filler metal type were eliminated. Based on results of the conducted experiments, it was possible to establish the influence of the filler metal type on the surface characteristics of the regenerated gears’ teeth flanks.

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.

Influence of the contact pressure in the deep drawing processes is a very actual research topic in the metal forming technology. Within this research the tribological model of the strip sliding in the flat die was developed. The original experimental computerized apparatus for testing of the strip sliding in the variable contact pressure conditions was developed, as well. The complex, multi-factor experiment was performed by application of the Al thin sheet, with the contact elements of various roughnesses, with different lubricants application and with the variable contact pressure. Besides the description of the developed apparatus, the theoretical way for determination of the pressure dependences was also presented. Based on the theoretical changes of pressure, set in advance, the real influence of the contact pressure was obtained, for each of the given conditions. That makes possible to determine the influence of the tribological factors on the actual pressure. The obtained real contact pressure has verified the reliability of the experimental apparatus, namely the degree of the theoretical pressure dependences deviation from the real ones.

This paper deals with the problem of defining the optimal procedure for reparation of the machine parts of large dimensions and complex shapes. The procedure consists of establishing the causes of the part's damages, definition of the reparation technology, with selection of its parameters and ways of execution. The reparation is done by hard-facing, with heat treatment that consists of preheating, additional heating and the post hard-facing tempering. The process parameters' selection includes choosing the right filler metal(s), ways and order of depositing the hard-faced layers, ways of reaching and maintaining the preheating temperatures, checking of the base metal's chemical composition and mechanical properties and deciding on the post-process heat and mechanical processing of the executed hard-facing. The executed reparation of the forging hammer's mallet, presented in details, serves as an example how the reparation can successfully serve as a substitute for procuring the new part and thus producing the savings both directly in lower costs and indirectly in shortening the down-time of the damaged part operation.

This research was focused on characterization of the influence of laser cutting on the material made from the PMMA. The comparison of mechanical properties of samples cut by the laser beam to the properties, obtained after the conventional method of cutting by milling, are presented in this paper, as well. The 4 mm thick samples were prepared from the PMMA and subjected to tensile test to establish their material strength after the two different types of cutting. Samples that were cut by the laser beam were also subjected to tempering to improve their mechanical properties. It was concluded that the way of cutting has a strong influence on the PMMA samples mechanical properties. The outcome of the experiment is a direct assessment of roughness of the cut samples. It is shown that the laser cutting produces lower values of the surface roughness. However, for manufacturing the structural elements, the more suitable would be application of the milling technology since it results in better mechanical properties of the cut sample.

Experimental investigation of the integrity of casing pipes, used in the oil drilling rigs, withdrawn after about 70,000 h of service, has been conducted, together with numerical simulation. Pipes were manufactured by the high frequency contact welding (HF) of API J55 steel. The influence of corrosion damage is investigated by means of pressure test of a pipe with different damage levels made by machining the circular holes. The finite element analysis of the damaged pipe subjected to internal pressure is conducted to simulate the stress state in the pipe and to establish the criteria for the maximum pressure that a damaged pipe can withstand. Several analytical expressions were used to estimate the maximum pressure in a damaged pipeline, and the solutions were compared to predictions of finite element models and experimental results.

This paper presents an experimental and numerical study into the influence of elevated temperatures on mechanical properties of the heat treated high quality hot work tool steel H11. This steel belongs to a group of alloyed steels with extraordinary mechanical properties. The aim of this study was to determine the highest temperature at which these properties are still maintained. The experimental investigation focused on the tensile testing of specimens at seven different temperatures, including the room temperature. The highest testing temperature was 700 °C. The heat treatment of plates (specimens) consisted of quenching and tempering. Although the strain hardening of this type of materials is small, the strain hardening curves were calculated to show if there was a possibility for the material to increase its strength due to exploitation loads. Also, a numerical analysis of the tensile test by using the finite element method was done in order to define an appropriate model for numerical testing. The obtained results are then compared with the experimental results.

The presented article deals with the technology and principals of laser cutting. The article describes the properties of CO2 laser beam, input parameters of laser cutting process, assist gases, the interaction of the cut material and the stability of laser cutting. The chemical compositions of cut materials and their influence on the cutting properties focusing on the roughness of the surface, are described as well. In the experimental part the roughness of the surface was measured by using the 3D scanning and evaluation of the microstructure in the HAZ area was provided.

The objective of the research, presented in this paper, was to demonstrate the superiority of the hard facing as the revitalization technology of various damaged machine parts. The analysis of the two different revitalization methods of the damaged machine parts is presented – the replacement of the damaged part by the new – spare part and reparation by hard facing. The comparison is done on the example of hard facing and replacing of damaged loader's teeth. The paper presents a method for calculating costs of the two revitalization technologies based on their profitability and their comparison. That method could be applied for similar calculations for any machine part, with smallest or no adjustments. The paper presents a verification of advantage of applying the hard facing as the machine parts reparatory technology with respect to the other revitalization technology. The savings realized by application of hard facing reparation of the loader's teeth reach 73.5 % for one set of teeth and 82.40per annum of the costs for purchasing the new spare parts. The analysis was conducted under an assumption that organization of the maintenance function is at the exceptionally high level so that the purchasing of the new part/repairing of the damaged one is always done in time. This idealized approach was adopted since in that way one obtains the least economic effects of the reparatory technology application with respect to replacing the part with the spare one. In any other case the economic effects would be significantly higher, namely even more positive in favor of the hard facing revitalization technology.

We present the experimental-numerical analysis of the influence of temperature on mechanical properties of structural high-strength steel class S690QL. Since the steel S690QL belongs to a group of steels with good mechanical properties, the aim of this paper is to determine the highest temperatures at which these good characteristics are kept. Experimental tensile testings of the specimens were performed at five different temperatures in the range from 20 to 550°C. Beside experimental testing, strengthening curves were calculated and numerical analysis using finite element method was performed. Both the experimental and numerical results have shown that decrease of mecahanical properties occurs at approximately 450°C. Представлены результаты расчетно-экспериментального анализа влияния температуры на механические свойства высокопрочной конструкционной стали S690QL. Определена максимальная температура при статических испытаниях на растяжение, при которой данная сталь сохраняет высокие механические характеристики. Статические испытания на растяжение проводились при пяти различных температурах в диапазоне 20 550°С. Полученные экспериментальные данные сравнивались с результатами конечноэлементных расчетов путем построения соответствующих кривых упрочнения стали. Представлено результати розрахунково-експериментального аналізу впливу температури на механічні властивості високоміцної конструкційної сталі S690QL. Визнаaчено максимальну температуру при статичних випробуваннях на розтяг, за якої ця сталь зберігає високі механічні характеристики. Статичні випробування на розтяг проводились за п'яти різних температур у діапазоні 20 550°С. Отримані експериментальні дані порівнювались з результатами скінченноелементних розрахунків шляхом побудови відповідних кривих зміцнення сталі.

The theoretical and experimental analyses of the friction welding pressure influence on the plastic deformation level and the quality of the friction welded joint are presented in this paper. The joint of the tempering and the High-Speed steel was realized by the friction welding. The objective was to relate the two basic process parameters - the friction and compacting pressures - to plastic deformation parameters during the friction welding of two the steels. The fact that materials are dissimilar additionally complicates the welding procedure and its analysis. The friction welding is a specific and complex process, since in the joint zone material is heated and plasticized with necessary action of the multi-step pressure to realize the joint. The total deformations in the axial and radial directions are directly dependent on the applied welding pressure. Considering that geometry and shape of the friction welded joint directly depend on the friction pressure, some welded joints' basic shapes obtained with various pressures are presented. The experimental investigation was conducted on cylindrical samples made of the two steels and the analysis of results served for establishing the influences of the friction and compacting pressures on changes of the steel samples dimensions and shapes.

The spot welded thin steel sheets specimens are experimentally and numerically examined in this paper. The two specimens are joined using Resistance Spot Welding (RSW) method. The spot-welded joints consist of three zones with different material properties. Change of material properties during the welding process is caused by mechanical and thermal loading. The mechanical properties of thin steel sheets are determined by several tension tests. The specimens are cut in three different directions regarding a rolling direction of the basic material plate. Shear resistance of the spot welded joints is experimentally examined on the universal testing machine by displacement-controlled tensile loading tests. The numerical analysis is performed by large-strain plasticity theory implemented into a Finite Element Method based software. Comparison of the Finite Element (FE) modeling and experimental results verifies the proposed stress integration algorithm and modeling technique as powerful tools for prediction of the spot-welded joint behavior.

Premature damages and fractures of components and structures of bucket-wheel excavators at open-pit mine often occur in exploitation, caused either by inadequate design or insufficient knowledge of the material properties, welded joints and flaws in component production technology. The bucket-wheel excavator, TAKRAF SRs 2000 × 32/5.0 was employed on the excavation of barren soil for 5.000 h (a few weeks more than a year after the assembly) when the fracture of the tooth of the girth gear, which enables the circular motion of the upper structure of the bucket-wheel excavator, occurred. The gear was, according to the manufacturer’s certificate, made of the cast steel GS 40 MnCrSi3 V. The paper presents calculations of the stress variations cycles’ number for one tooth, as well as of the fracture mechanics parameters – the critical stress intensity factor and critical crack length. It was established that the fracture of the tooth occurred due to an initial crack existing in its base, which originated during the gear’s manufacturing, i.e. due to the so-called "manufacturing-in defect".

The procedure for experimental determination of the longitudinal and lateral residual stresses in the multi-layer hard-faced plates, made of the hot work tool steel used for forging dies manufacturing, is presented in this paper. The objective of this research was to establish the influence of the multi-layer hard-facing on residual stresses in the thin and thick plates, which could later, in exploitation, cause the appearance of cracks and fracture. The influence of tempering on decreasing the residual stresses was monitored, as well. The plates were hard-faced in three layers, while the stresses were measured by the magnetic method. The obtained results have shown, among others, that the residual stresses are higher in the thick plates, as well as that the proper regime of the heat treatment can significantly reduce the level of residual stresses.

In the friction welding of dissimilar base metals occurs an uneven heating in the outside and inside zones of materials what causes appearance of various structures in the joint zone. Considering that the objective is achieving of the homogeneous welded joint, an imperative is to analyze the microstructure of the realized welded joint. By the microstructure analysis, one can establish the relationship between the friction welding parameters and the structure that appears in each of the joint's characteristic zones. In addition, it is possible to analyze the potential appearance of flaws during the welding process and to discover the causes for their appearance in order to prevent those in the future. This paper presents a review and analysis of microstructures of the characteristic joint zones in the friction plane of the two different steels, the high-speed steel and carbon steel for tempering. The experiment consisted of varying the friction welding parameters (friction pressure and friction time) and monitoring of micro structure in the joint zone and its immediate vicinity, both from the side of the tempering steel and the HS steel, as well as defining the present phases and compounds. The emphasis was set on analysis of the melting and the mixing zones and carbides created during the welding.

An experimental procedure for determination of the lateral and longitudinal deformations of the multi-layer hard faced samples made of steel for operating at elevated temperatures is presented in this paper. Two plates, which were hard faced in three passes, were used to determine the level of residual stresses. The cored electrodes UTOP 38 and UTOP 55 were used. Deformations were measured in two phases: before and after the hard facing. The objective of deformations measurements was to establish the correlation between deformations, namely the applied technology (the input energy/heat) and the level of residual stresses, for different plate thicknesses.

Results of experimental and numerical investigations of the three types of lubricants influence on the ironing process are pr esented in this paper. The tribological model was based on the strip sliding between the two lateral contact elements. The strip w as made of the low carbon steel. Variations of the friction coefficient and the contact pressure in the single-stage ironing were reco rded at the constant sliding speed for each of the tested lubricants. The effective normal stress distribution within the material w as simulated by the finite element method (FEM). The objective was to compare the applied lubricants from the aspect of their applicability in the ironing process. © 2015 The Authors. Published by Elsevier B.V. Peer-review under responsibility of organizing committee of the XXIV R-S-P seminar, Theoretical Foundation of Civil En gineering (24RSP)

In the study of wave propagation, bulk waves exist in infinite homogeneous bodies and propagate indefinitely without being interrupted by boundaries or interfaces. Such waves may be decomposed into finite plane waves propagating along arbitrary directions of the solid. The properties of these waves are determined by the dependence between the propagation direction and the constitutive properties of media. Three types of such waves may be distinguished in connection to the three displacement vectors which determine an acoustic polarization. These three polarization vectors are mutually orthogonal, but in most cases they are neither perpendicular nor parallel to the propagation direction. There are a number of papers and books describing wave front surfaces as a consequence of the study of the acoustic tensor, which, in fact, represents the propagation condition of such waves. The surfaces associated with wave front surfaces are slowness surfaces, with slowness defined by the inverse of the wave front speeds, and energy flow surfaces, also known as group velocity surfaces. Here slowness surfaces are studied analytically and numerically to obtain information about wave propagation in arbitrary directions. The degree of wave surface deviation depends upon degrees of anisotropy, and may give valuable information about dynamic deformations. The materials, used in the present analysis, are fibre-reinforced materials with two families of continuous elastic fibres. Since fibres are much stronger than a matrix, anisotropic properties are emphasized. Coordinate-free constitutive relations give the possibility of considering fibres embedded in such materials as extensible or inextensible. Such an approach gives the opportunity to follow behaviour directly considering both the geometry and the stiffness of the fibres. The material considered here is reinforced by two families of mechanically equivalent fibres and, therefore, behaves like orthotropic, having axes of symmetry along bisectors of the fibre directions and along the normal to the plane tangent to the fibres. Such a material has nine independent material constants. When constraints of inextensibility are imposed on the fibres, it leads to the so-called ideal fibre-reinforced material, which may be obtained from materials with extensible fibres in a limiting process. In order to follow the influence of fibre direction on the mechanical properties, constitutive relations are modelled as a function of the fibre directions in each point of the continuous media. An often-used representation of such materials is an epoxy resin–carbon fibre composite whose material constants, for materials reinforced by one family of fibres, are determined using ultrasound methods. Here we consider the dynamical behaviour of the material reinforced by two families of strong mechanically equivalent elastic fibres by comparing the behaviour of extensible fibres to the behaviour of inextensible fibres. Solids made of the above-described materials show some interesting dynamic properties in the propagation of elastic waves. Some recent results of the dynamic behaviour when the material has strong anisotropy shall be presented.

In this paper the analysis of welding technology to mechanical properties of welded joints at high strength low alloyed steel S690QL is presented. Experimental testing was done at models with V-groove butt joints that are done by MMA or MIG for root pass and MAG for other passes of multipass welded joints with related parameters and consumables. Yield and tensile strength, so as answer to load of models are determined experimentally in order to analyses the effect of welding technology to resulted mechanical properties. On the basis of the obtained results it can be concluded that welding parameters have significant influence to mechanical properties of welded joints at high-strength low-alloyed steel. Furthermore, it can be concluded that welded joints with root pass done by MIG and other passes by MAG provide better mechanical properties. Presented research point out that welding parameters at high strength low alloyed steels must be selected and controlled precisely to obtain welding joints with adequate mechanical properties. Welding, as dominant method of joining, is primary factor that provide beneficial application of high-strength low-alloyed steels. The paper highlight the influence of material degradation due to welding. This paper point out the importance of analysing the welded joints at different levels of dimensions, while further, more detailed, research can be continued through development of a numerical model of the welded joints which will complete the experimentally obtained results. As experimentally obtained results correlate to material degradation due to welding it is implicated that future development of high-strength low-alloyed steels must be followed with development and modification of welding processes.

The three-dimensional transient nonlinear thermal analysis of the hard facing process is performed by using the finite element method. The simulations were executed on the open source Salome platform using the open source finite element solver Code_Aster. The Gaussian double ellipsoid was selected in order to enable greater possibilities for the calculation of the moving heat source. The numerical results were compared with available experimental results.

Here is analyzed selection of the optimal technology for heat treatment during the reparation of the damaged forging dies. Those tools are manufactured from alloyed tool steels for operation at elevated temperatures. Those steels are prone to self-hardening, so in reparatory hard-facing they must be preheated, additionally heated and tempered. During the tempering, in temperature interval 500-600°C, a secondary increase of hardness and decrease of impact toughness occurs, the so-called reversible tempering brittleness. Here is shown that it can be avoided by application of metallurgical and technological measures. Metallurgical measures assume adequate selection of steels. Since the considered steels are per se prone to tempering brittleness, we conducted experimental investigations to define the technological measures to avoid it. Tests on models were conducted: tempering from different temperatures, slow heating and cooling in still air. Hardness measurements showed that at 520°C, the secondary increase of hardness occurs, with drop of the impact toughness. Additional hard-facing tests included samples tempered at various regimes. Samples were prepared for mechanical and metallographic investigations. Results presented illustrate influence of additional heat treatment on structure, hardness and mechanical properties of the hard-faced layers. This enabled establishing the possibility of avoiding the tempering brittleness through technological measures.

In this paper, a steel structure of a motor vehicle hydrodynamic clutch (HDC) is analyzed in order to obtain the optimal design parameters. Realization of such a steel structure with those parameters enables achieving of the optimal efficiency coefficient. The paper presents large number of data, originated from the past research, which may be used in determination of the meridian cross-section shapes and the position of blade circuits within the operating space of the hydraulic turbo converter. The experimental results concerning the influence of the geometric, kinematic and hydrodynamic parameters on characteristics of the hydraulic turbo converter are presented also. The knowledge about all those relations may be very useful to all dealing with hydraulic torque converters. For conducting experimental investigations an indirect measuring method was used, based on defining the pressure distribution over the speed probes’ walls. The original experimental equipment was developed for that purpose.

Analysis of output quality of power transmitters is possible in position when characteristics are determined earlier. This is the reason why we focused on determination of these characteristics for a concrete power hydro-transmitter. This means that the investigation task primarily consisted of determination of functional characteristics, defining of the sliding curves and temperature regimes of a concrete hydrodynamic clutch. Results of velocity and pressure field investigations in the working space of this clutch, obtained by use of the same test setup, are the basis for determination and analysis of the functional characteristics, sliding curves and temperature regimes. In this work we also analyzed function of the hydrodynamic transmitter in assembly with an internal combustion engine, as well as a process of acceleration and deceleration of a vehicle with this assembly in it.

Kovački alati su dijelovi, koji rade na povišenim temperaturama, dok su istodobno izloženi promjenljivim opterećenjima, koja mogu biti tlačna - čak i udarna i smična. Utjecaj tehnologije navarivanja je vrlo jak, pošto se variranjem njegovih parametara direktno utječe na izlazne karakteristike navarenih slojeva. Kriterij za procjenu tog utjecaja bio je utemeljen na rezultatima obavljenih triboloških ispitivanja. Praćeni tribološki parametri bili su faktor trenja, širina traga (brazgotine) habanja kao i površina habanja navarenih slojeva, uz uporabu dva tipa maziva. Tehnologija navarivanja je podrazumijevala selekciju procesa zavarivanja, dodatnih materijala, temperature predgrijavanja i ostalih parametara procesa navarivanja. Utjecaj predložene tehnologije navarivanja je određivan praćenjem tvrdoće, mikrostrukture i otpornosti na habanje izvedenih spojeva, nakon navarivanja i nakon otpuštanja. Cilj ovog rada bio je uspostavljanje korelacija izabrane tehnologije navarivanja, dodatnih materijala i primijenjene toplinske obrade s mehaničkim i tribološkim karakteristikama izvedenih navarenih slojeva., The forging dies are parts, which are operating at elevated temperatures, while simultaneously subjected to variable loads that can be compressive - even impact and shear. Impact of the hard facing technology is very strong since varying of the hard facing parameters directly affects the output characteristics of the hard faced layers. The criterion for estimating that impact was based on results of performed tribological investigations. The tribological parameters that were monitored were the friction coefficient, the wear scar/trace width and the wear area of the hard faced layers, with the two different types of lubricants. Hard facing technology implied selection of the welding process, filler metals, preheating temperatures and other parameters of the hard facing process. The influence of the proposed hard facing technology was determined by monitoring hardness, microstructure and wear resistance of the executed joints after the hard facing and after tempering. The objective of this work was to establish the correlation between the selected hard facing technology, filler metals and applied heat treatment on mechanical and tribological characteristics of the executed hard faced layers.

In this paper the problems related to the maintenance of large forging mallets of pneumatic hammers including hard facing of cracked or worn working surfaces are considered. Actually, the choice of optimum technology for the reparation of hard facing of the broken forging press frame and cracked mallet of the forging pneumatic hammer are taken into consideration., U ovom radu se razmatra problematika održavanja velikih batova kovačkih pneumatskih čekića, uključujući tu i navarivanje napuklih i pohabanih radnih površina. Konkretno, ovdje je riječ o izboru optimalne tehnologije reparaturnog zavarivanja napuklog bata. Pored tehno-ekonomske analize, u radu se navodi i energetska analiza, kao dodatni kriteriji za ocjenu primijenjene tehnologije.