Desenvolvimento de fio máquina para a fabricação de arames para soldagem MIG, com carepa adequada ao processo de descarepação mecânica

Abstract

AWS ER70S 6 steel is used in MIG welding electrodes and presents a very adherent scale due to its high Si level. Another point to be noted refers to P level. Its control allows the production of a steel with less Mn and Si segregation that, with appropriate cooling control gives to the wirerod the characteristics needed to the end use. Besides segregation, P raises the hardness of the steel, what may cause breakages during the drawing process, specially to sizes under 1mm. Other important factors that affect the thickness and constituents of each scale oxide are wire rod temperature in the laying head and its cooling rate. In this work were tested different cooling rates looking for the best scale condition formechanical descaling, without damages to the required microstructure or to mechanical properties. For the analyzed parameters, there were no significant changes in the microstructure, especially in the MA constituent volumetric faction or in mechanical properties of the wire rod.Higher laying head temperatures allow the formation of a thicker scale layer and with more FeO that, associated to a slow cooling rate, giving the relation 1:1 among FeO and Fe3O4 constituents. For the test using different cooling rates, the slower cooling (27 covers closed) showeda 20% thicker scale layer, and a bigger scale removal (+ 0,5%, in average). Considering all involved parameters, the best association was a laying head temperature of 870°C and closed covers until the 27 ª cover. They produced a thicker scale layer due to the longer time at high temperatures, what allowed the growing of FeO layer and the more effective scale removal.