Friction stir welding: An alternative to fusion welding for better stress corrosion cracking resistance of maraging steel

Abstract

Friction stir welding (FSW), a solid state welding process, is generally used for welding soft materials like aluminium and magnesium alloys. In this work, maraging steel, an ultra high strength steel, is welded using FSW process. Major problems associated with fusion welded maraging steel, i.e segregation of alloying elements and formation of reverted austenite pool, were suppressed by FSW. Slow strain rate stress corrosion characteristic of 18%Ni maraging steel (grade-250) and its weldments, by gas tungsten arc welding (GTAW) and FSW, has been investigated in air and 3.5% NaCl solution. It was observed that FSW joints demonstrated higher resistance to stress corrosion cracking (SCC) compared to both, base metal and gas tungsten arc weldments. Improved stress corrosion resistance of friction stir weldments was correlated to microstructural differences and residual stress. Fine grain structure, absence of segregation of alloying elements and high compressive residual stress in friction stir weld resulted in better SCC resistance compared to that of fusion weldment. It is brought out from the present study that FSW process can be used as an alternative to fusion welding process for better SCC resistance.