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The flux-cored wires and technologies of arc surfacing of steel hot mill rolls were developed. The results of investigations and practical experience allows recommending the developed flux-cored wires for surfacing of steel rolls of the following mills: for roughing (blooming and slab) -PP-Np-25Kh5MSGF; for continuous billet -PP-AN147, PP-Np-35V9Kh3GSF; for heavy-section and rail-beam -PP-Np-25Kh5MSGF; for medium-and light-section -PP-Np-25Kh5MSGF, PP-AN147, PP-AN204; for wire -PP-Np35V9Kh3GSF, PP-AN132; for sheet -PP-AN132, PP-Np-25Kh5MSGF; for pipe ones -PP-AN147, PP-Np-35V9Kh3GSF. Nowadays the surfacing of mill rolls for their restoration and increase in life is applied almost at all the metallurgical enterprises in Ukraine. Using modern methods of mechanized surfacing a roll can be created with a very ductile and strong core, which is well resistant to mechanical loads and also has a wear-and heat-resistant surface. Surfacing allows significantly increasing of life of rolls, decreasing their consumption, increasing yield of efficient rolled metal due to improvement of accuracy of rolling, decreasing expenses for processing and cost of rolled metal [1].The efficiency of application of surfacing of mill rolls depends significantly on right selection of composition of deposited metal. Therefore, it is necessary to perform a thorough analysis of conditions of rolls operation, character and intensity of their wear. At different metallurgical enterprises the rolls of mills even of the same type are worn out to different extent and should be surfaced using different consumables.For wear-resistant surfacing of steel hot rolls of different mills most often, though not always reasonably, the flux-cored wire of grade PP-Np35V9Kh3GSF is applied. The deposited metal of Cr-W type of steel possesses a high resistance to abrasion at higher temperatures but its thermal life is comparatively low, and the rolls, deposited using this wire, often come out of order due to formation of fire net and spallings. Therefore, to deposit the rolls using this wire, to which the requirements of maximum cleanness of surface of body or grooves of a roll are specified, is not rational.The experience in development of steels for dies of hot deformation of metals, conditions of work of which are largely close to those for work of hot mill rolls, indicates the challenge in use of Cr-W-Mo (partial replacement of tungsten with molybdenum) and Cr-Mo steels for these purposes. As to heat resistance, these steels are almost not inferior to Cr-W ones and, as to resistance to thermal fatigue, are significantly superior to them. It is connected with the fact that molybdenum facilitates formation of fine-grain

Effect of electric parameters of arc surfacing using self-shielding flux-cored wires on process stability and base metal penetration was investigated. The experiments were carried out with computer registration of electric parameters of surfacing. The results of oscillogram processing were used for plotting of Iw and Uw diagrams with outlined areas of stable process of surfacing, short circuits and arc extinctions. Coefficient of process instability γ was derived from received real parameters of arc surfacing using flux-cored wire. It is determined that voltage has the largest effect on stability indices and its rise improves process stability. Effect of modes of surfacing on penetration and portion of base metal in the deposited metal was investigated. 3D chart was plotted on estimation results. An area of optimum modes, providing sufficient stability of the process at minimum penetration and good formation of deposited beads, is outlined. K e y w o r d s : arc surfacing, flux-cored wire, stability of surfacing process, instability coefficient, base metal penetration, portion of base metalNecessary composition of the deposited metal in multilayer arc surfacing can be obtained only in the third or fourth layer [1] due to its mixing with the base metal. Five layers as minimum should be surfaced, if machining of part is necessary after surfacing. The problem becomes more complicated due to the fact that rise of thickness of the deposited layer promotes for growth of residual shearing stresses and, simultaneously, increases the possibility of appearance in the deposited layer of different type defects, which reduce its service properties, including fatigue life under cyclic loading [2,3]. Thus, one of the most important characteristics for surfacing is a portion of base metal (PBM) in the deposited metal proportional to base metal penetration other things equal. Reduction of the base metal penetration not only decreases consumption of expensive consumables, but improves quality and service properties of the parts to be surfaced.Aim of the present work is a study of effect of electric parameters of flux-cored arc surfacing, in particular, stability of these indices on characteristics of the base metal penetration.Consumables and equipment. Self-shielding flux-cored wire PP-AN130 was used for investigations. It provides for production of surfaced metal of tool steel 25Kh5FMS type. Gas-slagforming system of the flux-cored wire, which would provide the best welding-technological properties, was preliminary selected. Four selfshielding flux-cored wires PP-AN130 of 2 mm diameter having different systems of gas-slagforming components, namely СаO + TiO 2 + MgO + CaF 2 + Al 2 O 3 (wire with reference designation PP-AN130-1); СаO + MgO + CaF 2 + Al 2 O 3 (PP-AN130-2); СаO + CaF 2 + Al 2 O 3 (PP-AN130-3); СаO + CaF 2 + Al 2 O 3 + starch (PP-AN130-4), were manufactured for this purpose.Expert estimation (5 examiners) of the welding-technological properties of all four wire types (nature of metal transfer, slag coating of the ...