A novel approach to suppression of reverted austenite in aerospace grade thick maraging steel weldments using the turbo-TIG welding process

Abstract

This research examines aerospace grade-maraging steel weldments produced by the novel Turbo-TIG welding technique. The vital challenge in welding maraging steel is the development of reverted austenite in the weld region and HAZ. This reverted austenite degrades the mechanical characteristics of weldments. MDN 250 maraging steel with a 12 mm thick plate was welded at a high speed of 300 mm/min with consistent quality using the Turbo-TIG welding technique. The objective of the present work is to suppress the reverted austenite in the 12 mm thick plate of MDN 250 using the Turbo-TIG welding technique. Three different postweld heat treatments were applied, namely, (i) aging heat treatment (AT), (ii) solutionizing + aging (ST), and (iii) homogenization + solutionizing + aging (HT). The microstructure and X-ray diffraction analysis of the weld zone under AT and ST conditions demonstrate the existence of reverted austenite in the grain boundary regions. The SEM/EDS analysis of the weld zone of welded, AT, and ST conditions indicated Ni, Mo, and Ti microsegregation from the center matrix to the grain boundary regions. In contrast, neither microsegregation nor austenite reversion occurred in the HT condition. The tensile test demonstrates a maximum strength of 1797 MPa (UTS) under HT conditions. Likewise, the microhardness of the HT conditions exhibits a higher hardness of 552 HV in the fusion zone. In light of the metallurgical and mechanical characteristics of the weld, the HT heat treatments provide better weld performance in the case of Turbo-TIG welding of maraging steel grade MDN 250.