Influence of welding procedure and PWHT on HSLA steel weld metals

TLDR

Welding high‑strength steels remains challenging due to diverse alloy systems, especially in offshore structures where SMAW is still preferred. The study compares the mechanical properties of HSLA weld metals produced by SMAW and GMAW to evaluate higher‑productivity processes. Multipass SMAW and GMAW welding was performed on 750 × 150 × 19 mm plates with 200 °C preheat, followed by 600 °C/1 h PWHT; mechanical tests, OM, SEM, EBSD, and Thermo‑Calc simulations were used to characterize microstructure and carbides. Both SMAW and GMAW welds showed comparable strength–toughness relationships, with GMAW delivering similar performance and improved productivity even after PWHT.

Abstract

The development of consumables for welding of high strength steels represents a continuous challenge taking into account the great variety of alloy systems. In this regard, there are many applications, such as offshore structures, where the welding is still preferably done by the SMAW process. In order to evaluate the properties of weld metals obtained by other processes with higher productivity, the present work presents a comparative analysis between the mechanical properties of high strength steel weld metals obtained by shielded metal arc (SMAW) and gas metal arc (GMAW) welding processes. Multipass welding by SMAW and GMAW processes was performed with preheating of 200 °C, in 750 × 150 × 19 mm plates. After welding, a post weld heat treatment (PWHT) at 600 °C for 1 h was performed and this condition was compared to the as welded one. Mechanical tests and metallographic examination by optical microscopy (OM), scanning electron microscopy (SEM) and electron backscattered diffraction (EBSD) were performed for mechanical and microstructural characterization. Thermodynamic calculations were also performed by using Thermo-Calc software, in order to evaluate the occurrence of carbides as a consequence of the PWHT. Although presenting impact toughness behavior slightly different due to the chemical composition and carbide precipitates, as predicted by computational simulation, both processes showed a good relationship between mechanical strength and impact toughness for all analyzed conditions, even after PWHT. Based on this scenario, it can be inferred that GMAW process can be applied as an interesting alternative for welding of high strength steels, once this process promotes a significant improvement in productivity with good quality.