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

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

Nagyszilárdságú acélok elektronsugaras hegesztett kötéseinek fáradásos repedésterjedéssel szembeni ellenállása

A kutatómunka az S960QL nemesített és az S960M termomechanikusan kezelt nagyszilárdságú szerkezeti acélok elektronsugaras hegesztett kötéseinek fáradásos repedésterjedéssel szembeni ellenállására irányult. A hegesztési kísérletek során 15 mm vastag alapanyagokat alkalmaztunk hozaganyag nélküli (autogén), I-varratos, hegesztett kötések létrehozásához. A repedésterjedési vizsgálatokhoz alkalmazott hárompontos hajlító (TPB) próbatesteket úgy munkáltuk ki, hogy azok a jellemző irányokra merőlegesek, illetve párhuzamosak legyenek, valamint a bemetszések helyzetét a hegesztett kötések jellemző részeinek (varrat, beolvadási vonal, hőhatásövezet) elemzése céljából is változtattuk. Ennek megfelelően a vizsgálataink során terjedő repedések a valós szerkezetekben előforduló, különböző repedés megjelenési helyeknek felelnek meg. A vizsgált S960M acél elektronsugaras hegesztett kötésének fáradásos repedésterjedéssel szembeni ellenállása a vizsgált irányokban szignifikánsan különbözőnek bizonyult, az S960QL acél esetében ilyen különbség nem mutatkozott. A vizsgált S960QL acél elektronsugaras hegesztett kötései, mindkét vizsgált irányban lényegesen érzékenyebbeknek bizonyultak a fáradással terjedő repedések elhelyezkedésére, mint a vizsgált S960M acél kötései

Challenges and opportunities in the arc welding of offshore steels

Offshore steels are required not only good strength properties but also outstanding toughness at low temperatures to ensure the safety of the structures in an extremely cold environment. The new generations of offshore steels, in the range of S420-S500 range, exhibit remarkable toughness characteristics which must be preserved as much as possible during welding. However, welding processes, can significantly reduce the toughness properties due to the welding heat input. Furthermore, it is a challenge to guarantee the impact energy level in the dendritic, mostly multi-pass weld, is the same as that in the fine-grained and micro-alloyed steel plate, which is rolled through specific rolling processes, including thermomechanical controlled process (TMCP). The welding process and its’ parameters, as well as the filler material selection, play a significant role in the formation of an ideal weld and heat-affected zone (HAZ) microstructure with appropriate strength and toughness properties. The effect of microalloying elements on the formation of acicular ferrite (AF) in weld and HAZ has a determining role in terms of the toughness properties. This paper provides a detailed literature review of the characteristics, processing routes and weldability of advanced offshore steels. Gas Metal Arc Welding (GMAW) and Submerged Arc Welding (SAW) are the most frequently used technologies for offshore steels. The research results demonstrate that special attention is needed during the welding process, parameter and filler material selection to ensure the high impact safety of the welded joints under low temperatures