Softening effect in the heat-affected zone of laser-welded joints of high-strength low-alloyed steels

The softening effect, which occurs as an undesirable consequence of microstructural changes in the heat-affected zone as a result of the welding process, is an inherent aspect of welding high-strength low-alloyed steels. One of the recommended ways to minimize these changes is the application of laser beam welding as a lower heat input technology. Hence, this work compares and investigates the effects of laser beam welding on the weld joint properties of S690QL, S960QL, S1100QL, S700MC, S960MC, and S1100MC steels. This research operates on the assumption that the mechanical properties of the zones surrounding the soft zone—base metal and weld metal—affect the mechanical properties of weld joints as well. The work shows that the total value of yield strength, tensile strength, and elongation of welded joints increases when the value of the strength of the weld metal and the soft zone increases and when the width of the soft zone narrows, and vice versa. Furthermore, the study demonstrates that the amount of C, Cr, Mn, Mo, Cu, and Ni in steel as well as the thermal cycle is directly associated to strength in these zones. The findings indicate that although the welded joints’ yield strength and tensile strength values remained over 96% of the base metal’s value, in certain cases the elongation values decreased to a mere 21% of the base metal’s value.