An Approach to Assessing S960QL Steel Welded Joints Using EBW and GMAW

Abstract

In recent years, ultra-high-strength structural (UHSS) steel in quenched and tempered (Q+T) conditions, for example, S960QL has been found in wider application areas such as structures, cranes, and trucks due to its extraordinary material properties and acceptable weldability. The motivation of the study is to investigate the unique capabilities of electron beam welding (EBW) compared to conventional gas metal arc welding (GMAW) for a deep, narrow weld with a small heat-affected zone (HAZ) and minimum thermal distortion of the welded joint without significantly affecting the mechanical properties. In this study, S960QL base material (BM) specimens with a thickness of 15 mm were butt-welded without filler material at a welding speed of 10 mm/s using the high-vacuum (2 × 10−4 mbar) EBW process. Microstructural characteristics were analyzed using an optical microscope (OM), a scanning electron microscope (SEM), fractography, and an electron backscatter diffraction (EBSD) analysis. The macro hardness, tensile strength, and instrumented Charpy-V impact test were performed to evaluate the mechanical properties. Further, the results of these tests of the EBW joints were compared with the GMAW joints of the same steel grade and thickness. Higher hardness is observed in the fusion zone (FZ) and the HAZ compared to the BM but under the limit of qualifying the hardness value (450 HV10) of Q+T steels according to the ISO 15614-11 specifications. The tensile strength of the EBW-welded joint (1044 MPa) reached the level of the BM as the specimens fractured in the BM. The FZ microstructure consists of fine dendritic martensite and the HAZ predominantly consists of martensite. Instrumented impact testing was performed on Charpy-V specimens at −40 °C, which showed the brittle behavior of both the FZ and HAZ but to a significantly lower extent compared to GMAW. The measured average impact toughness of the BM is 162 J and the average impact toughness value of the HAZ and FZ are 45 ± 11 J and 44 ± 20 J, respectively.

Numerical Simulation and Experimental Measurement of Residual Stresses in a Thick-Walled Buried-Arc Welded Pipe Structure

“…For the welding of thick structures, processes such as submerged arc welding [24], electroslag welding [25] and electrogas arc welding [26] have been applied in industrial production. Nowadays, laser hybrid welding processes [27] are also well known and used along with plasma arc welding [28], especially with "keyhole" technology and in some special cases electron beam welding [29]. However, conventional MAG welding is more flexible and applicable in conventional metal transfer modes, but in areas of high currents, when unstable arc and intensive spattering can occur if the arc control is not at the highest level.…”

The effect of heat input in multi-pass GMAW of S960QL UHSS based on weaving and stringer bead procedure on microstructure and mechanical properties of HAZ

“…While some investigated weld metal properties and microstructures, others focused on the HAZ. Sisodia and Gáspár [4] investigated mechanical strength and microstructure of weld metal and HAZ of multi-pass gas metal arc welded S960QL. They observed microstructure of relatively coarse lath martensite in CGHAZ and mixture of tempered martensite and M/A constituents in ICHAZ.…”

Optimization of GMAW Process Parameters in Ultra-High-Strength Steel Based on Prediction

“…Thus, the welding parameters may need to be optimized to guarantee a reliable product. Along with optimization, it is fundamental to consider computational tools that can reduce the development time of a product [21][22][23][24]. However, while most simulation software available today performs different functions, only a few are designed specifically for welding simulations.…”