FCAW에서 용접변수에 따른 용접금속 강도 및 와이어 합금원소 회수율 변화

Abstract

용접입열을 결정하는 용접변수인 용접전류, 전압, 속도를 독립적으로 변화시켜 각 변수가 와이어 합금원소 회수율 및 인장강도에 미치는 영향을 조사하여 다음과 같은 결론을 얻었다. (1) 용접전류와 속도의 증가는 탄소, 실리콘, 망간 등의 산화손실을 억제하여 용접금속의 Pcm을 증가시켜 강도를 증가시키는 반면, 전압의 증가는 산화손실을 촉진시켜 강도를 저하시킨다. (2) Pcm에 영향을 미치는 용접금속 중 탄소, 실리콘, 망간, 보론 등의 회수율은 용접조건에 영향을 받아 용접전류와 속도가 증가할수록, 그리고 전압이 감소할수록 증가하였다. 다중회귀분석 결과 각 성분의 회수율은 다음 식으로 나타내어진다. Recovery of C (%) = 92.9 - 2.5V + 0.16I + 0.31S Recovery of Si (%) = 91.8 - 2.5V + 0.14I + 0.84S Recovery of Mn (%) = 96.5 - 2.1V + 0.06I + 0.61S Recovery of B (%) = 84.9 - 2.5V + 0.11I + 0.35S (3) 탄소, 실리콘, 망간이 각각 0.037, 0.14, 1.5%인 모재를 사용하여 470A-45V-25cm/min으로 용접하는 경우, 용접금속 인장강도와 Pcm은 다음과 같은 관계를 가지며 인장강도 규격치인 590MPa 이상을 나타내기 위해서는 Pcm이 0.167 이상이어야 한다. TS (MPa) = 127.3 + 2,770Pcm

600MPa grade weldable steels were gas metal arc welded with flux cored wires to study the effects of welding parameters such as welding current, voltage and travel speed on the tensile properties of weld metal. The results were interpreted in terms of chemical composition and microstructural change in the weld metal. When heat input was increased to 21kJ/cm by increasing welding current, the tensile strength of the weld metal increased. However, the tensile strength of the weld metal decreased when heat input was increased from 21 to 45kJ/cm by reducing travel speed or by increasing voltage. It showed that the decrease of tensile strength in higher than 21kJ/cm was related with the microstructural change. However, the increase of tensile strength in lower than 21kJ/cm was not related with the microstructural change, but caused by the increase of alloying elements such as carbon and manganese in the weld metal. It showed that the variation of the welding parameter resulted in different recoveries of the alloying elements in the wire. The recoveries increased with an increase of welding current and/or travel speed, but they decreased with an increase of voltage. The effects of welding parameters on the recoveries were rationalized with the time available for the reaction with oxygen during welding.