Effect of welding parameters of plasma transferred arc welding method on abrasive wear resistance of 12V tool steel deposit

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Aalto-yliopiston teknillinen korkeakoulu | Doctoral thesis (monograph)
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TKK dissertations, 220
In the plasma transferred arc, PTA, welding method the powder consumable makes it possible to weld wide variety of alloys. The dilution of the deposit is typically 3-10 % and, thus, the properties of the deposit can be achieved with one-layer deposit. The studied alloy was an iron-based 12V tool steel reinforced with primarily precipitating vanadium carbides. Wide deposits are welded by oscillating the plasma arc and overlapping the weld beads. The mobility of the molten pool of 12V tool steel is good. The location of the plasma arc in relation with the molten pool during perpendicular movement and the shape of the plasma arc had strong effects on both the dilution control and the microstructure of the 12V tool steel deposit. The location of the plasma arc can be in the edge or on top of the molten pool. Depending on the parameter window the mean sizes and the volume fractions of vanadium carbides were 0,5-1,8 micrometers and 12,2-17,5 vol.-%, respectively. When the plasma arc was precisely in the edge of the molten pool, the size, the distance between vanadium carbides, and the shape of vanadium carbides were optimal. With the studied welding parameters, the 12V tool steel deposit is extremely sensitive to small variations in the welding parameters. If the molten pool is stirred slightly when oscillating the plasma arc, vanadium carbides cannot grow and the shapes of the carbides are mainly more needle-shaped instead of round-shape. Wear tests were made by the rubber wheel abrasion test according to standard ASTM G 65-94. Round-shaped, 1,2-1,4 micrometer-sized vanadium carbides were the most beneficial according to the wear surface examinations. The optimized PTA welded 12V tool steel deposit had better abrasive wear resistance when compared to the 12V tool steel deposit manufactured by the hot isostatic pressing, HIP.
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Hänninen, Hannu, Prof.
Thesis advisor
Hänninen, Hannu, Prof.
PTA, tool steel, powder consumable, dilution, vanadium carbide, abrasive wear resistance
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