| Abstract Scope |
For decades, multi-pass butt joints have been welded using conventional arc welding processes such as SMAW, GMAW, and GTAW, playing a crucial role in the manufacturing of pressure retaining equipment. To date, handheld laser welding (HLBW) applications have been primarily focused on single pass welding of thin components. However, contrary to prevalent belief, welding thick components is possible with HLBW. Experimental HLBW joints were made with ASTM A516 Gr 70 (low-carbon steel) plates and ER70S-6 filler wire. The welds showed significantly higher strength than the base metal, excellent bending properties and remarkable low-temperature impact toughness without PWHT. The impact toughness measured was 127 J (94 ft-lbs) at -45°C (-49°F), surpassing the ASME Sec. VIII requirement by a substantial 370%. The cause of this outstanding performance is the focus of current studies, and seems to be due to a very fine microstructure and extremely narrow HAZ, both associated with the low heat input of HLBW (<0.5 kJ cm^(-1)), a shallow bead-tempering effect, and grain refinement from rapid solidification. This work also discusses feasibility of multi-pass welds with root gaps from 0 mm (no gap) to 5 mm (3/16”), which is extremely difficult with other welding processes. |