Papers by Author: D. Sivakumar

Abstract: This paper discusses the modeling of gas-tungsten arc welding (GTAW) process being adopted for maraging steel plates used in aerospace applications. Primary objective of this work is to predict the temperature profile of heat affected zone in a maraging steel weld. Finite element modeling was done utilizing a gaussian heat flux distribution on a weldment. Model also incorporated a moving heat source along with provision for heat sinks in the form of copper backup plates. For validating the model, welding experiments were conducted on 2 mm and 8 mm thick 250 grade maraging steel plates. Thermal profiles were acquired at different locations of heat affected zone using thermocouples and compared with the predictions from the model.

Abstract: 0.3C-CrMoV(ESR) steel is an ultra-high strength low alloy steel indigenously developed by ISRO for space applications. The steel is used in the form of rings of 2.8 m diameter also. In this paper, the effect of tempering temperature on ring rolled steel for the best combination of fracture toughness and strength properties is studied. The tensile properties and fracture toughness of the steel were evaluated in the as quenched and tempered conditions through the specimens drawn in radial direction of the ring segment. Five tempering temperatures were used in the study: 200, 450, 475, 500 and 510°C. Tensile strength of the steel showed continuous decrease with increasing tempering temperature, but yield strength increased reaching maximum when tempered at 450°C and further decreased with increasing tempering temperature. The elongation was higher for higher tempering temperature. The strain hardening exponent decreased with increasing tempering temperature. The fracture toughness test results showed that tempering between 475 and 510°C exhibited better combination of fracture toughness and strength.

Abstract: The detrimental laves formation in fusion zone during welding of Inconel 718 is controlled with compound current pulsing technique along with helium shielding gas. Also solid solution filler wire is used to minimize the niobium segregation. Welds were produced in 2mm thick sheets by GTA welding process and subjected to the characterization techniques. The results show, refined fusion zone microstructure, reduced amount of laves phase, minimum niobium segregation and softer fusion zone in the as welded condition.