With an industry trend towards application of modern high strength steels for construction of large diameter, high pressure pipelines from remote northern regions there is a need to develop high-productivity welding processes to reduce costs and deal with short construction seasons. Achieving the required level of weld metal overmatching together with adequate ductility and good low temperature toughness is another major challenge for joining high strength X80/100 pipes. It is important to develop an improved understanding of weld metal systems that are required for the successful production of high strength pipeline girth welds that are needed for such demanding pipeline construction. In this investigation a range of weld metal (WM) compositions based on (i) C-Mn-Si-Mo, (ii) C-Mn-Si-Ni-Mo-Ti and (iii) C-Mn-Si-Ni-Cr-Mo-Ti was selected for more detailed evaluation of experimental plate welds complemented by specimens simulated by Gleeble® thermal cycling. Five specially-designed experimental plate welds were made with a robotic single torch pulsed gas metal arc welding (GMAW-P) procedures with wire electrodes applicable for joining X100 pipe. The procedures consisted of three initial fill passes deposited at 0.5 kJ/mm and a final deep-fill pass at 1.5 kJ/mm to just fill the narrow-gap joint. An important part of the research focused on development of WM Continuous Cooling Transformation (CCT) diagrams to establish the influence of composition and thermal cycle (cooling time) on formation of fine-scale, predominantly martensite, bainite and acicular ferrite (AF) microstructures. For the relatively wide range of cooling times investigated (Δt800−500 = 2 to 50 s), the lowest-alloyed WM (LA90) exhibited microstructures dominated by bainite with martensite to AF, whereas the highest-alloyed WM (PT02) formed large fractions of martensite with bainite to AF. Weld metal toughness was evaluated using both through-thickness notched 2/3 sub-size Charpy-V-notch (CVN) specimens as well as full-size surface-notched specimens. Post-test metallographic and fractographic examinations of selected fractured specimens were used to correlate WM microstructure and notch toughness.
Microstructure and Properties of High Strength Steel Weld Metals
- Views Icon Views
- Share Icon Share
- Search Site
Gianetto, JA, Goodall, GR, Tyson, WR, Fazeli, F, Quintana, MA, Rajan, VB, & Chen, Y. "Microstructure and Properties of High Strength Steel Weld Metals." Proceedings of the 2012 9th International Pipeline Conference. Volume 3: Materials and Joining. Calgary, Alberta, Canada. September 24–28, 2012. pp. 515-526. ASME. https://doi.org/10.1115/IPC2012-90526
Download citation file: