Optimization of Weld Parameters and Weld Bead Dimensions in Welding of 0.3%C-Cr-Mo-V Steel by Gas Tungsten Arc Welding Process

Abstract

ISRO space programs use Maraging Steel for its Solid rocket motor casings. Because of its higher cost and limitations in the availability,there is a need to develop alternate to this steel.ISRO has developed a unique material as a alternative to Maraging Steel namely 0.3%C-Cr-Mo-V steel (Electro Slag Refined modified 15CDV6 steel-ESR MOD 15CDV6). This material is being considered for making rocket motor casings and considered as substitute as well as replacement for Maraging Steel.Weldability is an important factor considered for fabrication of this material in the areas of rocketry.Since it is a new material, enough studies and welding details are not available to exploit this material for aero space applications.Among the various welding methods available in the welding of steels,GTAW (Gas Tunsten Arc Welding) process selected for undertaking this study because this process is clean,contamination free, easily adaptable and generally suitable for welding of high strength alloy steel.Literature survey indicates not much work has been reported in welding of such low alloy high strength steel with conventional welding methods.Similarly effect of heat treatment on weldments,quench characteristics,hardness response etc.also not available much. Hence, these factors are main reason to undertake this study.This paper is limited to studying , fixing of weld parameters and weld bead dimensions. In this expriment the welding parameters , its response for each set of experiments and influence on weld dimensions are studied.In this work a combination of weld parameters were selected using Design of Experiment (DOE) principle with three levels and four parameter (variables).Totally nine experiments with different combination of parameters conducted on the test coupons of size 8×200×150mm.The chemistry of parent metal and filler rod remains same. Three levels of current and voltage,and correspondingly other parameters like root gap,number of passes and welding speeds were employed.Details like the amount of shielding, purging gas used and quantity of flow are noted.Weld bead dimensions like bead width –B,reinforcement-R,penetration –r,penetration height-b are chosen as response.All the nine test coupons were subjected to Liquid Penetrant Test (LPT), X-ray radiography and found defect free.