화학공학소재연구정보센터
Materials Science Forum, Vol.426-4, 1451-1456, 2003
Development of an ultra-low carbon high strength welding wire
Through the combination of TMCP with RPC (Relaxation-Precipitation Control) heat treatment, a high strength steel plate of 800 MPa was produced. This steel possesses not only high strength but also good toughness and excellent weldability due to its low carbon equivalent and very fine microstructure. The development of a welding filler metal is required to weld the steel. It is designed that the weld metal should have equivalent mechanical properties to the base metal and neither preheating nor post weld heat treatment is allowed. The principle of designing the chemical composition of the filling wire is based on generating ultra low carbon bainite microstructure in the weld metal that is strong, tough and resistant to cracking. After testing of 9 heats of welding wires of variant chemical compositions, a filling wire is determined. This filling wire generates a weld metal of good strength and toughness. The tensile strength of the weld metal is higher than 800 MPa. At such a strength level, the Charpy-V impact energy at -50degreesC maintains a high level over 100 J. Microstructure analysis reveals that the weld metal is mainly composed of bainite, without grain boundary ferrite at the primary austenite grain boundaries and martensitic transformation.