Trembach B. Increase of the wear resistance of machine parts for processing of solid minerals resources by self shielded flux-cored wire

The dissertation on competition of a scientific degree of the doctor of philosophy on a specialty 132 "Materials science" (13 - Mechanical engineering). - DSEA of Ukraine, Kramatorsk, 2021. The object of the study is the process of hardening and renovation of parts of solid mineral processing machines by hardfacing with self-shielded flux-cored wire with an exothermic addition. The subject of the study is the hardfacing alloy and hardfacing technological properties of self-shielded flux-cored wire with an exothermic addition, which increase the operational resistance of the deposited metal to abrasive and corrosion wear. Hardfacing is the most widely-used technology for such parts renovation. At present, the requirements to welded parts operating in these conditions are increasing. The dissertation aim is to solve the actual scientific and technical problem, as follows: development of the self-shielded flux-cored wire electrode (FCAW-S) with an exothermic addition CuO–Al in the core filler for hardening and renovation of working surfaces of machines parts for processing of solid minerals. There is a lack of data and studies in literature sources concerning influence CuO–Al exothermic addition to the core filler and alloying of deposited metal by copper and tribological properties of deposited metal. This is expected to be a significant margin to increase the service life of the parts subject to wear. The first section represented an analytical review of the issue and grounding of the research line choice. Modern view at the requirements to be met were analized, as well as the deposited metal characteristics. A review of modern literature on metal alloying systems is presented. It is substantiated that further improvement of welding and technological properties of FCAW-S and tribological properties of deposited metal is possible due to exothermic addition CuO-Al, which is included in the composition of the core filler. The second section "Choice of lines, methods and equipment of the researches" described the study of standard and original test methods which canprovide avalidity of the received results and reproducibility of the results by other researchers. New research methods are proposed to estimate the of exothermic addition addition in to the core filler during melting of self-shielded flux-cored wire and to determine the temperature of a possible exothermic reaction in the core filler. The third section "Main directions of the self-shielded flux-cored wire composition optimization" described the thermodynamic studies of evaluation of reactions behaviour in the flux-cored wire core filler, and thermodynamic calculations of phase composition using the software Thermo.For the first time, multi-method researches of influence of some hardfacing mode parameters and the amount of exothermic addition (CuO-Al) in the core filler during FCAW-S on melting parameters, geometry of the weld bead and heat input were conducted. The optimal values of the hardfacing parameters were selected. The limits for exothermic addition CuO–Al addition were grounded. The fourth section "Investigation of exothermic addition influence on the thermal state of self shielded flux-cored wire electrode" presented the study of the influence of the self shielded flux-cored wire filler composition on melting indicators and recovery rate of alloying element. An influence of the core filler composition on the melting indicators, alloy recovery efficiency and alloy transfer efficiency of alloying elements was investigated. An alloying of deposited metal by copper was confirmed experimentally and based on calculations. Mathematical relationships of specified factors influence were built and their optimal values were chosenbased on the received experimental data, as follows: ЕД=33..39%, CuO/Al=3,75…4, CuO/C= 5…5,25. The fifth section "Investigation of mechanical and tribological properties of advanced self shielded flux-cored wire electrode" presented the study and comparison of FCAW S 200Cr15Si1MnBTi used during revamping of machine parts for processing of solid minerals with experimental flux-cored wire electrode with the introduction of exothermic addition CuO-Al in the core filler. Experimental studies have shown the following: the introduction of exothermic addition CuO Al to the core filler reduced the grain size of deposited metal and had a positive effect on the size and morphology of non-metallic inclusions in the deposited metal. Comparative tribological tests showed an increase in resistance to abrasive wear by two-body and three-body abrasive wear test in 1.52 and 1.63 times correspondingly. The dissertation presented new scientifically grounded developments in the field of technology, materials and restorative hardfacing of teeth of walking and mine draglines, providing increased resistance to abrasive wear and improvement of deposited metal quality due to the introduction of exothermic additions in the core filler at FCAW-S.