SSAW 용접기법이 강재의 용접부 미세조직에 미치는 영향
Effects of SSAW Techniques on the Microstructures of Welded Parts in Steel
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본 연구는 SSAW 용접공정이 LC-TMCP, TiN, B급강 용접부의 미세구조에 미치는 영향을 조사하기 위해 수행되었다. 융합영역의 미세구조는 페라이트(GBF+AF+FSP) 상과 펄라이트 상으로 구성된 세 시료 모두 동일하며, LC-TMCP와 TiN강은 B급강에 비해 페라이트의 부피분율이 높고 입도가 작았다. 세 시료 모두 융착선 부근의미세구조는 페라이트와 펄라이트 상으로 바이나이트가 소량이었고, LC-TMCP와 TiN강의 입도는 B급강보다 작았다. 또한 TiN강은 TMCP강보다 작았으며, 페라이트(GBF 등)의 부피분율은 B급강이 가장 높았고 TiN강이 가장낮았다. 열영향부의 미세구조는 세 시료 모두 융착선(1mm) 부근의 페라이트 및 펄라이트 상에서 소량의 바이나이트 구조가 존재하는 상이었으나, 모재와는 형태가 달랐으며, 결정립 크기는 B급강이 가장 크고 TiN강이 가장 작았다. 또한 페라이트의 부피분율(GBF 등)은 B급강에서 가장 높았고 TiN강에서 가장 낮았으며, 3개의 시료 모두 융착선으로부터 5mm 떨어진 곳에서 모재상과 동일한 형상을 보였으나, 그레인은 성장하였다.
Abstract
This study investigated the effects of self-shielded arc welding on the microstructures of welded parts in laminar-cooled-thermo-mechanical-controlled-process (LC-TMCP), titanium nitride (TiN), and B grade steels. The microstructure of the fusion zone was the same in all three samples, consisting of ferrite (grain boundary ferrite (GBF)+acicular ferrite+ferrite side plate) and pearlite phases, and the LC-TMCP and TiN steels had a higher volume fraction of ferrite and smaller grain sizes than those of the B grade steel. In all three samples, the microstructure near the fusion line consisted of ferrite and pearlite phases with a small amount of bainite, and the grain sizes of the LC-TMCP and TiN steels were smaller than those of the B grade steel. In addition, the TiN steel was smaller than the TMCP steel, and the volume fraction of ferrite (GBF, etc.) was the highest in the B grade steel and lowest in the TiN steel. The microstructure of the heat-affected zone included a phase in which a small amount of bainite was present in the ferrite and pearlite phases near the fusion line (1 mm) in all three samples. However, the shape was different from that of the base material, and the grain size was the largest in the B grade steel and smallest in the TiN steel. The volume fraction of ferrite (GBF, etc.) was the highest in the B grade steel and lowest in the TiN steel. All three samples had the same shape as the base metal phase at 5 mm from the fusion line. However, grain was growth.
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