Abstract
In this study, a mechanical and microstructural constituent of welded joints of dissimilar high-strength and ultra-high-strength steels (S700MC/S960QC) using overmatched filler wire was evaluated. Three different heat inputs (18 kJ/cm, 8 kJ/cm, and 10 kJ/cm) and overmatched filler wire were applied using the GMAW process. Micro-hardness measurement was conducted using Vickers hardness test, tensile test, and microstructural constituents by scanning electron microscopy (SEM) and energy-dispersive X-ray spectroscopy (EDS) were performed in this analysis. A dissimilar welded sample with a cooling time of 51s (18 kJ/cm) showed a substantial hardness reduction in the fine grain heat-affected zone (HAZ) of the S700MC steel side, which was between 220-240 HV5. The cause could be the increase of heat input but also the use of overmatched filler wire, which can be the result of an increase of ferrite to austenite formation in the HAZ. SEM/EDS results confirmed the increase of carbide clusters, and tempered Martensite in the CGHAZ of the S960QC side, and ferrite-bainite on the S700MC side. An increase in the presence of high carbide content and the formation of Ni, Mo, and Mn were observed on the S960QC side. The increase of carbide formation in the CGHAZ of both sides reduced the hardness and strength of the welded joints. The tensile test confirms the softening observed in the FGHAZ of the S700MC side, which caused the joint fracture on this side during the test. Â
Highlights
Manufacturing companies nowadays need some materials that are light in weight and strong in their functions
In the S960QC side, the lowest hardness value was observed in the fine grain heat-affected zone (FGHAZ) of the welded joint and had a value of 290 HV5 a difference of 30 HV5 compared to the BM in the S700MC side, which was the most impacted during the welding process, has the lowest hardness value of 192 HV5 in the FGHAZ
We show the hardness profile, which has developed softening on the FGHAZ due to an increase of heat input and the use of overmatched filler wire
Summary
Manufacturing companies nowadays need some materials that are light in weight and strong in their functions. The issues of welding dissimilar high and ultra-high-strength steel with overmatched filler wire will resume defining optimum mechanical properties and microstructural characterization especially in the FGHAZ, which is always the most affected by softening in the HAZ [33]. The welding process using the GMAW process of dissimilar S700MC/S960QC using an overmatched filler wire was applied followed by different mechanical tests such as tensile and hardness tests. The results of this research allowed us to synchronize the effect of heat input and overmatched filler wire on the mechanical properties and microstructural constituents on the HAZ of dissimilar welded joints. The best combination of heat input and overmatched filler wire can be defined in other to obtain optimum mechanical properties and microstructural constituents of these particular dissimilar welded joints
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