Srbislav Aleksandrović

IMPACT OF THE HARD FACING TECHNOLOGY AND THE FILLER METAL ON TRIBOLOGICAL CHARACTERISTICS OF THE HARD FACED FORGING DIES

Subject review 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.

Experimental-Numerical Study of Tensile Strength of the High-Strength Steel S690QL at Elevated Temperatures

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.

Tribological behavior of four types of filler metals for hard facing under dry conditions

Purpose The purpose of this study is to show which filler metal is the best for hard facing. Because the quality of the surface layer has a great influence on the working life of parts, the purpose was to extend the working life of parts exposed to intensive wear. The tested hard-faced models were made of low carbon steel to save the expensive base metal and to analyze the possibilities of extending the service life of existing structural parts. Design/methodology/approach Samples were prepared from plates hard faced with various filler metals. Samples were then subjected to experimental testing – testing of tribological properties and hardness and microstructure. Testing was done in conditions similar to real ones – with a sliding speed of 0.25, 0.5 and 1 m/s and with a load of 50, 75 and 100 N and in most rigorous dry conditions. Research was done by using a combination of experimental and theoretical approaches. Findings The paper shows the results of the experimental testing of four different filler metals aimed for hard facing of parts exposed to highly intensive wear. Results shown that CrWC 600 alloy is the most favorable filler metal for hard facing of parts such as those of construction mechanization and those subjected to intensive abrasive wear at stone mines. Practical implications All obtained results are real and fully applicable, as there is a huge industrial need for these types of technologies. With the application of these technologies, beside money savings, the working life of parts can be significantly extended. Originality/value The research presented in this paper was conducted because of the lack of results from this area in Serbia and because of the necessity for application of obtained results in companies for road maintenance and stone excavation in the region of Sumadija, Serbia.

Experimental measuring of residual stresses in hard faced layers of the hot work tool steel

Rad je u izvornom obliku objavljen u Zborniku sa savetovanja „ZAVARIVANJE 2016“ održanog na Srebrnom jezeru 14-17. Septembra 2016 Adresa autora / Authors address: 1 ) Profesor, Fakultet inženjerskih nauka u Kragujevcu, Sestre Janjić 6, Srbija, vlazic@kg.ac.rs 2 ) Istraživač-saradnik, Fakultet inženjerskih nauka u Kragujevcu, Sestre Janjić 6, Srbija, dusan.arsic@fink.rs 3 ) Profesor, Tehnološko-metalurški fakultet u Beogradu, Karnegijeva 4, Srbija

Experimental-numerical analysis of contact conditions influence on the ironing strip drawing process

Purpose The purpose of this paper is comparison of experimental values of the drawing forces to numerical values in different contact conditions, taking into account the appearance of galling which occurs due to of difficult drawing process conditions. Design/methodology/approach The following two research approaches are used in this paper – the physical modeling, realized by the laboratory experiment, and the numerical simulation of the ironing drawing process. By analyzing the obtained results, the technique of physical modeling, with help of the laboratory equipment and numerical simulation by application of the finite element method, can be successfully used in studying the thin sheet ironing – strip drawing process. Findings It is significant to compare values of the deformation forces obtained by physical experiment to values obtained by the numerical simulation. In that way, it is possible to compare applied contact conditions (four lubricants in that case) and estimate matching of experimentally and numerically obtained results of the deformation forces. Presented results point out very good technological characteristics of ecologically friendly lubricant (single-bath) and grease based on MoS2. Significant decrease of the deformation force was achieved by its application, as well as maintaining of the lubricant’s layer during the forming process and almost complete elimination of galling on the contact. Practical implications Numerical analysis of stresses in the working piece wall, during the thin sheet strip drawing, requires precise values of the friction coefficient. It is an important indicator because one can define the contact conditions as the input data for the numerical simulation, based on its values for each type of lubricants and each value of the compressive lateral force. Originality/value The environmentally friendly lubricant tested exhibits a more favorable distribution of the drawing force during the process, mainly in experimental case. Grease based on MoS2 has good lubricating properties but that lubricant is conventional and environmentally unacceptable. Ecologically friendly lubricant can be successfully used in real ironing strip drawing process especially for high values of holding force achieving an increased tool life.