Evaluation of Hot Wire GTAW Process for 18Ni M250 Maraging Steel

Abstract

Maraging steels possesses ultrahigh strength and excellent fracture toughness which newlinemakes it suitable for rocket motor casing and other defence applications. In Indian newlineoperational launchers, 18Ni 250 maraging steel is extensively used in fabrication of newlinerocket motor casings. Fabrication of motor casings involve joining of shells and end newlinerings, which is performed through gas tungsten arc (GTA) welding, as the technique is newlinenot only simple but also provides the desired mechanical properties. Though the alloy newlinehas good weldability and effectively welded by conventional or cold wire Gas Tungsten newlineArc Welding (CW-GTAW), reverted austenite present in weld and dark band of heat newlineaffected zone (HAZ) is detrimental. In CW-GTAW of maraging steel, defect like newlineentrapped adherent slag, lack of fusion, porosity are observed. The weld pool in newlinemaraging steel is sluggish and does not flow freely as with a carbon steel or stainless newlinesteel. In addition, the CW-GTAW process has limitation of low speed and hence lower newlinedeposition rates. To overcome these issues hot wire Gas Tungsten Arc Welding (HWGTAW) newlineprocess is studied to weld maraging steel. The HW-GTAW process is a variant newlineof the CW-GTAW process, in that filler metal is preheated prior to its entry in the weld newlinepool. As preheated wire enters the weld pool, nearly all the energy of the welding arc newlineis available for penetration or to generate the weld pool and hence chances of lack of newlinefusion (LOF) are reduces drastically. The HW-GTAW process is ideally suited for newlineincreasing the weld fluidity which helps the slag to afloat easily. This process provides newlinethe benefit of virtual elimination of porosity from the weld deposit along with increased newlineweld speed and deposition. Additionally, the advantage of using HW-GTAW is reduced newlineheat input. These benefits enhance the quality and productivity of maraging steel newlinewelding. newline