Effects of Mo, V, and Nb on κ-Carbide and Mechanical Properties in Heat Affected Zone of Austenitic Fe-Mn-Al-C Lightweight Steels

This study examines the effects of Mo, V, and Nb additions on the metallurgical and mechanical behavior of austenitic Fe-Mn-Al-C lightweight steels and their heat-affected zone (HAZ), with a particular focus on κ-carbide precipitation behavior. Microstructural characteristics and mechanical properties, including tensile behavior and Charpy V-notched impact toughness, were evaluated for both the base metal and simulated HAZ specimens, produced using a Gleeble thermal simulator. Metallurgical analyses revealed that the addition of Mo, V, and Nb effectively suppresses κ-carbide precipitation during welding thermal cycles by increasing the thermodynamic barrier to κ-carbide formation and/or by consuming carbon through competitive carbide precipitation, thereby mitigating the degradation of impact toughness in the HAZ compared to the base metal. However, since a small amount of κ-carbide still formed during the welding thermal cycle, tensile fracture occurred in the base metal rather than in the HAZ, indicating localized strengthening of the HAZ as each HAZ was locally strengthened by κ-carbide precipitation. These findings demonstrate that controlled alloying and steelmaking strategies can enhance the weldability and mechanical reliability of austenitic lightweight steels, while highlighting the importance of balanced alloy design to achieve optimal performance under welding conditions.