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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 degrees 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.

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.

The deep drawing technology has a significant place in the contemporary industry. Intensive development of the automotive industry contributes a lot to that fact. With development of the new materials of the poorer machinability and with increase of the technological requirements to the higher level, the necessity for complete control of the forming process is increasing as well. There are significant difficulties in realizing any action during the process duration. In present conditions, only two possibilities are at hand: the blank holding force of the variable intensity and drawing beads of the variable height. Both actions require complex control systems. Contemporary technological problems in deep drawing of parts of the complex geometry can be successfully studied experimentally by means of the physical modeling. The physical model of the contact between the flat surfaces has the dominant space at the flange during the deep drawing process of thin sheets. The emphasis is on realizing the nonlinear dependencies of the contact pressure during the process, as one of the possibilities for the process control. The forming process is usually realized in such a way that all the process parameters and conditions (the blank holding force, deformation rate, etc.) are being set prior to the sliding path of the machine. The concrete investigation shows what effects are realized due to the variable intensities of the blank holding force during the deep drawing process. In addition, it is important to define the functional dependencies of the blank holding force. The basic idea is setting the variable pressure in the contact during the sliding process and monitoring the drawing force (the friction force), the friction coefficient, surface roughness of the thin sheet and the tool. Three different materials were applied, two types of lubricants and four versions of the tool's contact elements. The conducted investigations were of the theoretically-experimental chara, REZIME: Tehnologija dubokog izvlačenja zauzima značajno mesto u savremenoj industriji. Intenzivan razvoj automobilske industrije tome veoma doprinosi. Razvojem novih materijala lošije obradivosti i povećanjem tehnoloških zahteva na viši nivo, raste potreba za potpunim upravljanjem procesom oblikovanja. Postoje znatne teškoće u ostvarivanju bilo kakvih dejstava dok proces traje. U sadašnjim uslovima to su samo dve mogućnosti: sila držanja promenljivog intenziteta i zatezna rebra promenljive visine. Oba dejstva zahtevaju složene upravljačke sisteme. Savremena tehnološka problematika dubokog izvlačenja delova složene geometrije može se uspešno eksperimentalno izučavati putem fizičkog modeliranja. Fizički model kontakta između ravnih površina zauzima dominantan prostor na obodu komada pri dubokom izvlačenju tankih limova. Jedna od mogućnosti upravljanja procesom je zadavanje nelinearnih zavisnosti kontaktnog pritiska za vreme njegovog trajanja. Proces oblikovanja se najčešće realizuje tako što se svi parametri i uslovi procesa (sila držanja, brzina deformisanja, i dr.) podešavaju pre početka radnog hoda mašine. Konkretno istraživanje pokazuje kakve efekte ostvaruju promenljivi intenziteti sile držanja za vreme procesa dubokog izvlačenja. Takođe, od bitnog značaja je i definisanje funkcionalnih zavisnosti sile držanja. Osnovna ideja je zadavanje promenljivog pritiska u kontaktu za vreme procesa klizanja i praćenje promene vučne sile (sile trenja), koeficijenta trenja, površinske hrapavosti lima i alata. Primenjena su tri različita materijala, dve vrste maziva i četiri varijante kontaktnih elemenata alata. Sprovedena istraživanja su teorijsko-eksperimentalnog karaktera s težištem na eksperimentu. U prvom delu istraživanja izvodi se teorijska analiza i kritičko sagledavanje dosadašnjih rezultata. Zatim sledi formiranje nelinearnih i linearnih funkcionalnih zavisnosti simultane promene sile držanja (kontaktnog pritiska) tokom procesa, zavisno od hoda uzorka lima. Osobenost

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 550A degrees 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 450A degrees C.

In exploitation, the forging dies are exposed to heating up to very high temperatures, variable loads: compressive, impact and shear. In this paper, the reparatory hard facing of the damaged forging dies is considered. The objective was to establish the optimal reparatory technology based on cooling time t8/5. The verification of the adopted technology was done by investigation of the hard faced layers microstructure and measurements of hardness within the welded layers’ characteristic zones. Cooling time was determined theoretically, numerically and experimentally.

This paper presents the analysis of the influence of temperature on mechanic properties of the base material and welded joints made of high strength steel. The joints were welded on S690QL high strength steel plates using the Metal Active Gas (MAG) Welding and two filler materials of different properties. Since the steel S690QL belongs to a group of steels with high strength, the aim of this paper is to determine the temperature at which strength starts to decrease. Experimental tensile testings of the welded joints were performed at five different temperatures in the range from 20 to 550 °C.

This paper points out complex working conditions of forging dies, which are the most frequent causes of their damage, and proposes suitable hard-facing repair procedures. The shear strength between the hard-faced layer and base metal has been measured using specially developed tool, and correlation between output results and the applied hard-facing technology is established.

Predstavljena je nova metoda intenzivne plastične deformacije – višefazno sabijanje V-alatom. Koristeći ovu metodu, sabijanjem u osamnaest faza, unapređene su mehaničke osobine niskougljeničnog čelika Č.1221 – tvrdoća, čvrstoća i deformabilnost. Za ispitivanje mikrostrukture korišćeni su svetlosni, skening i transmisioni mikroskop. Prosečna veličina kristalnog zrna početnog materijala od 19 mikrometara je smanjena na 250 nanometara nakon dvanaest faza sabijanja. Nakon osamnaest faza sabijanja na čelu uzorka ostvarena je ukupna deformacija u iznosu od 3,38., A new severe plastic deformation method has been presented - multistage upsetting by V-shape dies. By using this method, in eighteen upsetting stages, mechanical propreties (hardness, strenght and formability) of C15E low carbon steel has been improved. For microstructure analysis light, scanning and transmission microscopes have been employed. Initial average grain size of 19 μm has been reduced to 250 nm after twelve upsetting stages. After eighteen upsetting stages, total effective deformation at the sample forehead of 3,38 has been obtained.

A possibility of extending the service life of the working parts of construction machinery with particular attention to hardfacing of loader bucket teeth was investigated. In the first part of this paper the tribological processes typical for this machinery is analysed. Worn excavator parts are made of conditionally weldable cast steel that requires a special hardfacing technology, so numerous investigations were performed to obtain the most appropriate technology. In the experimental part of the paper, the selection of the optimum hardfacing technology for bucket teeth and the procedure of the manual arc hardfacing are presented. The samples were first hardfaced using different techniques and technologies and then the microstructure and microhardness of characteristic hardfaced layers were studied. Specially prepared samples were used for tribological investigations. The results of experimental investigations enabled the selection of the most suitable hardfacing technology and its application to real parts. The bucket teeth, with their hardfaced layers applied vertically, horizontally or in a honeycomb pattern were mounted onto a loader bucket, alternated with the new non-hardfaced teeth and their performance during the operation was regularly monitored. After a certain period, the degrees of the wear for the non-hardfaced and differently hardfaced teeth were measured. Taking into account both technical and economic factors, the most suitable hardfacing technology was determined.

Complex working conditions of forging dies are the most frequent causes of their damage, requiring suitable hard facing repair procedures. The method of determining the bond strength between the hardfaced layer and the base material is explained in details, and the relation between hardfaced layer output results and the applied technology is established. Shear testing of materials has proven to be one of the most difficult areas of mechanical property testing. Shear modulus measurements are mainly accurate, but it is very difficult to measure shear strength. Edges, material coupling, non-pure shear loading, non-linear behaviour, imperfect stress distribution and coupling with normal stresses make shear strength determination difficult. None of the available test methods are without inaccuracies. Therefore, in structural applications, shear strength data should be used very carefully, on a case-by-case basis, appreciating the consequences of potential inaccuracies of the used values.

We have investigated the possibility of repairing damaged machine parts by hard facing with austenite-manganese steel electrodes. The subject is a Fe-C-Mn alloy with a microstructure of soft austenite which, after cold deformation, transforms by a shearing mechanism into a hard martensite microstructure. These steels are used mainly for parts exposed to high impact loads and intensive abrasive wear. Depending on the degree of wear, these parts can be replaced by new ones or repaired by hard facing. The selection of the optimal reparation technology for the rotational crusher's impact beams is the subject of this study. Investigations of model samples were conducted first, followed by layers hard faced onto samples with austenite manganese and special electrodes. After this the microstructure and hardness of the welds' characteristic zones were investigated. After reparatory hard facing the impact beams were mounted in the crusher and their behaviour was monitored periodically. Both the new and hard-faced beams' behaviours were monitored and compared under the same working conditions. In this way, the optimal technology for hard facing was established, taking into account not only the technical indicators, but also the economic effects.

High strength steels belong into a group of high quality steels, with exceptional mechanical properties, especially in regards to tensile strength. At the same time, as their deficiency is emphasized the limited and difficult weldability. In other words, some of those steels are weldable only with application of special measures related to controlled heat input. In that way, the favorable mechanical properties can be kept within the heat affected zone, with condition that the optimal welding technology is selected. Existing, very scarce and often unclear and insufficient recommendations for selection of the optimal welding technology are one of the causes of large number of flaws in welded joints. Mentioned problems, as well as others, can be successfully solved by proper selection of the procedure, filler metal and technology of welding, verified by experiments conducted in laboratory or in real operating conditions. Those experiments can not be performed in arbitrary conditions. Thus, partially due to results reported in this paper, technologists will obtain the possibility to predict in advance, in a very short time period, the mechanical and metallurgical properties of joints of this class of high strength steels. This will be possible without conducting the large number of practical tests or relying on personal experience of a designer.

This paper studies problems of hard facing of damaged and initially cracked mechanical engineering heavy parts of complex geometry such as large rams of air powered drop hammers. During long-term exploitation, these parts are subjected to thermal fatigue due to cyclic temperature changes and variable impact compression. Taking into consideration high ram costs and difficulties to purchase ram, the necessity of its reparation becomes obvious. The choices of the most suitable technologies of hard facing and welding of an initially cracked ram are also studied here. Besides the techno-economic analysis, an energetic analysis is performed as an additional criterion in assessment of the proposed technology.

This paper investigates the accuracy of analytical, empirical, and numerical expressions, i. e. the most favourable methods for calculating the cooling time from 800 to 500°C (t8/5). The degree of accuracy of time t8/5 is very significant, because it determines the cooling rate, and consequently the structural changes in heat affected zone for hard faced layers. Based on the presented results, one can conclude that the finite element method provides the best conformity with the experiment and among analytical and empirical formulas the same goes for the expression of Japanese authors, for the case of hard facing of plane and prismatic parts.

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 radu se navode osnovne karakteristike materijala i tehnologije toplog kovanje delova od Allegura. Za legure EN AW 2007 I EN AW 2024 ispitivana je mogućnost novog tehnološkog postupka livenja Al-legura pod dejstvom elektromagnetnog polja. Ovakav postupak omogućava modifikovanje mikrostrukture i poboljšanje mehaničkih osobinama odlivaka. Takođe, u radu se navodi i analiza kovanja u proizvodnim uslovima za leguru dobijenu istiskivanjem, uz pomoć odgovarajućeg SC.SuperForge softvera za 3D probleme. Kao primer, navode se rezultati distribucije ekvivalentnog napona u komadu koji se oblikuje u različitim fazama obrade., The paper presents the basic properties of materials and technology of hot forging of Al-alloy parts. For alloys EN AW 2007 and EN AW 2024 the possibility of new technological procedure for casting Al-alloys under the influence of electromagnetic field was investigated. Such a procedure enables modification of microstructure and improvement of mechanical properties of ingots. In addition to that, the paper presents analysis of forging in manufacturing conditions for alloy obtained by extrusion with the application of suitable SC.SuperForge software for 3D problems. The obtained results show the equivalent stress distribution in work-piece which is being formed.