Evaluation of cold wire addition effect on heat input and productivity of tandem submerged arc welding for low-carbon microalloyed steels

Abstract

The addition of a cold wire in conventional tandem submerged arc welding (TSAW), i.e., the CWTSAW process, is proposed to improve the productivity of pipeline manufacturing by increasing welding travel speed and deposition rate, while retaining adequate joint geometry without increasing the welding heat input. In addition to increasing productivity, incorporating a cold wire in the TSAW process improves the fracture toughness by refining the microstructure of the weld heat-affected zone (HAZ). In the present work, the influence of cold-wire addition on the heat input, productivity and properties of an X70 microalloyed steel welded by CWTSAW is investigated. Charpy impact testing and microhardness testing were utilized to investigate the mechanical properties of the HAZ. Scanning electron microscopy (SEM) and tint etching optical microscopy (TEOM) were used to correlate the microstructure alterations with the properties. The low-temperature fracture toughness of the HAZ was improved by 38% when a cold wire was fed at 25.4 cm/min in the conventional TSAW process with a heat input of 22.1 kJ/cm. This improvement was attributed to a reduction in the prior austenite grain (PAG) size and martensite-austenite (M-A) constituent fraction as a result of the reduction in the effective heat input (7.5% reduction) by cold wire addition. The amount of heat input reduction is a function of the cold wire addition rate and the nominal welding heat input. The increase in travel speed and deposition rate of welding by addition of a cold wire at 58 cm/min in the TSAW process with a heat input of 23.2 kJ/cm was 26 and 12%, respectively.