Recent Developments in Steel Friction Stir Welding: Project HILDA

Abstract

Friction stir welding of steel presents an array of advantages across many industrial sectors compared to conventional fusion welding techniques. Preliminary studies have identified many positive effects on the properties of welded steel components. However, the fundamental knowledge of the process in relation to structural steel remains relatively limited, hence industrial uptake has been essentially non-existent to this date. The European-funded project HILDA, the first of its kind in terms of breadth and depth, is concerned with enhancing the understanding of the process on low alloy steel, establishing its limits in terms of the two more significant parameters which can be directly controlled, tool traverse and rotational speed, thus improving its techno-economic competitiveness to fusion welding. A detailed study investigated the effect of process parameters on the evolved microstructure. In parallel, a full programme of mechanical testing was undertaken to generate data on hardness, impact toughness and fatigue. From this, it has been established that friction stir welding of steel produces high integrity joints that exhibit excellent fatigue properties. From a simulation perspective, a local microstructural numerical model has been developed to predict the microstructural evolution within the weld zone during friction stir welding of low alloy steel. This model concentrates on predicting grain size evolution due to dynamic recrystallization with respect to tool traverse and rotational speed. Furthermore, a computational efficient local-global numerical model capable of predicting the thermal transients, stir and heat affected zone, residual stresses and distortion produced by friction stir welding of DH36 plates is presented.

Properties and microstructure of double-sided friction stir-welded microalloyed steel

“…In single-sided FSW, temperatures >773 K have been recorded in the machine bed. 31 These temperature effects could explain the distinct differences in observed microstructures of TMAZ and IZ. However, if the highest temperature of IZ remains below Ar 1 , a problem arises in explaining the observation in Figs.…”

Microstructure and fatigue properties of friction stir welded high-strength steel plates

“…Thomas et al [10] demonstrated the feasibility of FSW of steels in 1999 on a 12% chromium alloy and a low carbon steel. Since then, several authors addressed this subject, including studies in numerical modelling [11,12] and economic analysis [13]. FSW was considered superior to conventional fusion welding in many categories, although tooling costs and limited service life are viewed as obstacles to a faster uptake by industry.…”

Thermomechanical Modeling of Material Flow and Weld Quality in the Friction Stir Welding of High-Density Polyethylene

“…Although friction stir welding (FSW) has been extensively researched for joining steel alloys [1][2][3] and aluminum alloys [4][5][6][7], the industrial application of polymer FSW is still under consideration due to several limitations [8,9]. These mainly include the weld strength, potential defects and optimal process parameters to obtain a good-quality weld [10,11].…”