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Journal of KWJS 2011;29(1):65-73.
Published online March 4, 2011.
800 ㎫급 고강도강 용접금속의 미세조직 특성 비교 연구
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Microstructural Characteristics of 800 ㎫ Grade High Strength Steel Weld Metals
Jaehee Lee, Sanghoon Kim, Byunghyun Yoon, Hwantae Kim, Sangcheol Kil, Changhee Lee
Abstract
  Microstructural characteristics of two high strength (600 ㎫ & 800 ㎫) weld metals produced by flux-cored arc welding process (FCAW) were evaluated. The 600 MPa grade weld metal was consisted of 75% acicular ferrite and 25% ferrite which was formed at relatively high temperature (grain boundary ferrite, widmanstatten ferrite, polygonal ferrite). However, the 800 ㎫ grade weld metal was composed of about 85% acicular ferrite and 15% low temperature forming phases (bainite, martensite). The prior austenite grain size of 800 ㎫ grade weld metal was decreased by solute drag force. The compositions and sizes of inclusions which are the dominant factors for the formation of acicular ferrite were analyzed by a transmission electron microscopy (TEM). In both 600 ㎫ and 800 ㎫ grade weld metals, the inclusions were mainly consisted of Ti-oxide and Mn-oxide, and the average size of inclusions was 0.7 ㎛. The 800 ㎫ grade weld metal exhibited higher tensile strength and similar toughness compared with the 600 ㎫ grade weld metal. This result is mainly due to a higher fraction of low temperature products and a lower fraction of grain boundary ferrite in the 800 ㎫ grade weld metal.
Key Words: High strength weld metal, Acicular ferrite, Lath size, Inclusions


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