Effects of some of the shielding gas performances on the characterization of super martensitic stainless steel 12cr5ni2mo welds

Abstract

The effects of using different shielding gases and shielding gas mixtures at three different heat inputs on the mechanical and metallurgical properties of AISI 410 S Super Martensitic Stainless Steels (SMSSs) welds by Gas Metal Arc Welding (GMAW) process are investigated. 1.2 mm diameter of solid wire made of AISI 410 S Super martensitic stainless steel with a filler wire was used in this study. First, the beads on plate welding trails were carried out. The welding was carried out at different heat inputs (3.00, 3.65 and 4.33 KJ/mm) with different shielding gas mixures like 100% CO2, 100% Ar, 80% Ar + 20% CO2, 100% He and 50% He + 50% Ar. The input process variables considered in this study included Current (I), Voltage (V) and Travel Speed (S). All these parameters were having 3 levels and the process output characteristics were weld bead width (W), reinforcement (R) and Depth of Penetration (DOP). All welded samples were evaluated by radiographic testing according to ANSI B31.3 standard. As per the AWS D1.2 standard for preparation of metallurgical testing, the welded samples were extracted after welding. The samples were prepared as per the ASTM: E8 standards. The test was carried out in a Universal Testing Machine (UTM) 40 tones capacity FIE make. The Charpy V-notch (CVN) tests were conducted at room temperature (300C) for all conditions analyzed. The long axis of the sample is machined perpendicular to the notch on the impact specimen. The prepared specimens were tested for their hardness in ZWICK 3212 hardness testing machine. A comprehensive and comparative microstructural analysis of the weld region was performed by Optical Microscopy (OM) and the phases were identified through X-ray diffraction method. Impact test, microhardness and tensile tests (room temperature and 8000C) were performed in this experiment. The tensile and impact tested samples also were further carried out for fractography analysis by using Scanning Electron Microscope (SEM). The corrosion study was carried out for different gases at different heat input. From this analysis, it is concluded that the 100% He gives better performance results than other gases based on bead profile, tensile test, toughness test, lower spatter, porosities, inclusions and fine dimple. Due to this reason, 100% He was considered for further detailed analysis on SMSS. As per the statistical design of experiments by taking Taguchi L27 orthogonal array, the experiments were carried out and the bead width, the reinforcement and the depth of penetration were measured. The optimization was carried out for best gas by using grey on based Taguchi s approach and grey based on fuzzy logic method. The objectives considered were the maximization of the depth of penetration, minimization of bead width, reinforcement. The mathematical models were developed by the grey fuzzy logic approach. The developed grey-fuzzy models have been found newline