tions of the base metal and austenitic 308L, 1.2-mm-diameter filler metal used are given in Table 1. Welding Procedure The experiments were conducted using a water-cooled universal GMAW machine (Make: KEMPPI, Finland; Model: EVOLUTION PRO 4200) using DC electrode positive (DCEP). The welding conditions and process parameters used to fabricate the joints are given in Table 2. The initial joint configuration was obtained by securing the plates in the flat position using tack welding. Square butt joints with a root opening of 1.5 mm were fabricated with the GMAW process using the selected welding parameters for the spray mode of metal transfer. To ascertain the operating mode, current and voltage waveforms were recorded by an oscilloscope during each welding run. The welding operations were performed using pure Ar, Ar + 5% CO2, Ar + 10%CO2 and Ar + 20%CO2 shielding Fig. 5 — Optical emission spectroscopy reveals the variation of carbon content in different weld metals. gas mixtures at constant heat input. All necessary care was taken to avoid joint distortion by applying proper clamping devices. The soundness of all the welded plates was examined using radiography. Metallographic Study The specimens for metallography study comprised of weld metal, heataffected zone (HAZ), and base metal were polished using different grades of emery papers followed by a final polishing with a disc using diamond compound (2-μm particle size). The specimens were then etched with 10 mL hydrochloric acid, 0.5 g cupric chloride, and 10 mL ethanol for 10 –15 s. Microstructural examination was carried out using a light optical microscope (Make: Carl ZEISS India Pvt. Ltd.; Model: Imager.A1m). The welded specimens were also examined under transmission electron microscope (TEM) (Make: Philips Ltd., Netherlands; Model: CM-70). The specimens from the weld metal and HAZ were prepared using a diamond cutting tool WELDING RESEARCH and fine grades of emery papers up to 0.1 mm followed by a chemical etching/ thinning process up to 10 μm. Dilution Calculation The percentage dilution (DL%) of base metal was calculated from the geometrical characteristics of weld joints such as total area of weld deposit (AWD), area of top (ATR) and root (ARR) reinforcement, area of base metal fusion (ABF), and area of root opening (ARG), as schematically shown in Fig. 2. The estimation of AWD , ABF , and DL% was found out as follows (Refs. 1, 2): AWD = ARG + ATR + ABF + ARR (1) ABF = AWD – ARG – ATR – ARR (2) DL% = ABF/AWD × 100% (3) Calculation of CrNi Equivalents and Martensite Transformation Temperatures Weld metal compositions obtained APRIL 2015 / WELDING JOURNAL 103-s Fig. 4 — Schematic representation shows the effect of turbulent fluid flow induced in the weld pool by the combined result of different driving forces on the weld pool dimensions and shape. Table 2 — Welding Conditions and Process Parameters Sample Current Voltage WFS WS HI Gas Mixture GFR Specification (A) (V) (m/min) (mm/min) (kJ/mm) (L/min) J1 100% Ar J2 240 ±10 28.0 ±0.7 7.0 ±0.1 500 ±5 0.72 ±0.5 Ar + 5% CO2 15 J3 Ar + 10% CO2 J4 Ar + 20% CO2 Note: WFS = wire feed speed; WS = welding speed; HI = heat input (I × v × η × 60)/(WS × 1000); GFR = gas flow rate.
Welding Journal | April 2015
To see the actual publication please follow the link above