Influence of cold-wire tandem submerged arc welding parameters on weld geometry and microhardness of microalloyed pipeline steels

Abstract

Tandem submerged arc welding with an additional cold-wire (CWTSAW) is being developed for pipeline manufacturing to improve productivity in terms of deposition rate and travel speed of welding. An appropriate understanding of the welding conditions to guarantee requisite weld geometry, appearance, and mechanical properties is always essential in the development of a welding process. Currently, the effect of the cold-wire addition parameters on dilution and the geometry and properties of the weld metal (WM) and the heat-affected zone (HAZ) is not well understood. In this work, heat input, voltage, and travel speed of both electrodes along with three main cold-wire parameters are investigated and correlated with the geometry of the weld and HAZ, i.e., aspect ratio (AR), semi-penetration ratio (SPR), reinforcement area (RA), and coarse-grained heat-affected zone (CGHAZ) area, dilution, and the microhardness of the WM and CGHAZ. The results showed that varying the cold-wire parameters significantly affects the dilution, AR, SPR, and microhardness. The addition of a cold-wire at a lagging position with a feed speed of 8.5 mm/s at 63° resulted in an overall improvement in the weld geometry, dilution, and microhardness. Cold-wire addition led to a reduction in the CGHAZ area, the amount of dilution, and the microhardness of the CGHAZ. Microstructural analysis, using both optical microscopy and scanning electron microscopy (SEM), indicated the formation of finer prior austenite grains (PAGs) and less martensite-austenite (M-A) constituent within the CGHAZ of the CWTSAW samples. The appropriate process parameters are defined to control the weld and HAZ geometry, dilution, and mechanical properties.