셀프실드 아크용접에서 용접금속 수소량에 미치는 용접변수 및 플럭스 조성의 영향

Abstract

Effects of welding parameters, contact tip-to-workpiece distance (CTWD), current, and voltage, on the diffusible hydrogen content in weld metal deposited by self-shielded flux cored arc welding were investigated and rationalized by comparing the amount of heat generated in the extension length of the wire. It showed that as CTWD increased from 15mm to 25mm, the amount of heat generated was increased from 60.5J to 148.7J, and thus hydrogen content was decreased from 11.3mL/100g to 5.9mL/100g. Even if little difference was observed in the amount of heat generated, hydrogen content was increased with an increase of voltage because of longer arc length. However, it showed that hydrogen content was not influenced by the current. Various fluorides, CaF2, K2SiF6, LiF, and NaF, were added to the wire and their effects on the hydrogen contents in weld metals were also studied. Wires with K2SiF6, LiF, and NaF showed less hydrogen contents than the wire with CaF2. The hydrogen content in the weld metals was not influenced by the slag basicity but by the fluorine gas formed in the arc. Thermodynamic analysis showed that K2SiF6, LiF, and NaF are easily dissociated and vaporized to form fluorine gas and thus reduce hydrogen partial pressure in the arc. However, because of vigorous fluorine gas formation in the arc, wires containing K2SiF6, LiF, and NaF showed unstable arc, resulting in much more spatter than the wire containing CaF2..