e3 ligases The M Shape profile for

The M-Shape profile for measured RS may be attributed to the phase transformation occurring during solid state transformation of equiaxial ferrite in e3 ligases material to grain boundary ferrite, accicular ferrite, Widmanstatten ferrite, bainite and micro alloying phases, which causes volume changes in weld metal. The volume expansion due to phase transformation counters the volume contraction due to shrinkage, releasing the tensile RS. The RS induced by shrinkage of the molten region are usually tensile. The compressive residual stresses are formed in the transformed areas where the effect of phase transformations is dominant. The area fractions of various ferritic morphologies seen in optical images were ascertained with systematic manual point counting as per ASTM E 562. The SMAW exhibited higher percentage of microphases and polygonal ferrite and A-GTAW associated with high heat input was observed to contain about more of Widmanstatten ferrite. The volume fractions of grain boundary ferrite, Widmanstatten ferrite, polygonal ferrite and microphases for the SMAW and A-GTAW weld metals are given in Table 6. The transformation of austenite to these ferritic morphologies are distinguished by the atomic mechanism of transformation as reconstructive (grain boundary/polygonal ferrite) and displacive (Widmanstatten, acicular and bainitic ferrites). While reconstructive transformation is associated with volume change, the displacive transformation is accompanied by invariant plane strain (IPS) [28–31]. The M-Shape profile for measured RS is attributed to the volume fraction changes due to transformation of equiaxial ferrite in base material to Grain Boundary Ferrite, Accicular Ferrite, Widmanstatten Ferrite, bainite and micro alloying phases in weld metal [32,33]. The marginally higher residual stresses in A-GTAW as compared to SMAW is attributed to higher percentage of displacively transformed Widmanstatten ferrite and microphases (combination of acicular ferrite and bainite) in A-GTAW weld metal and also expected formation of higher percentage of bainite in HAZ due to higher heat input and slower cooling rates [34]. The presence of higher percentage of reconstructively transformed grain boundary and polygonal ferrite in SMAW as compared to A-GTAW resulted in volume change in weld metal, leading to reduction in tensile residual stresses at weld center. A-GTAW being an automated process, the variations in experimentally measured residual stresses and derived from FEM were observed to be minimal (Fig. 11(a)). Minor variation in residual stress values of experimental measurements and FEM for SMAW (Fig. 11(b)) is due to manual process being used. For SMAW, there is minor variation in the location of passes in experiment and FEM. Also, the energy absorbed during SMAW not being uniform might have impacted the field under stress. The impact toughness, with notch in weld metal, was carried out at room temperature for SMAW and A-GTAW joints. The impact toughness was found to be 150 J and 200 J for SMAW and A-GTAW joints respectively. The tensile test performed on cross weld specimen of both joints has shown comparable yield strength of about 480 MPa and percentage elongation of 20% but the ultimate tensile strength of 640 MPa in G-TAW specimen was higher as compared to about 600 MPa of SMAW specimen (Fig. 12). The tensile fracture of the cross weld specimen of SMAW and A-GTAW occurred in the base metal region away from weld metal which confirmed the existence of adequate strength in weld metal of both processes. The comparison of mechanical tests of SMAW and A-GTAW joints are given in Table 7. The fractography studies of tensile specimen and V-notch Chapry impact specimen for both the arc weld joints revealed ductile fracture with characteristic cup and cone dimples structure. The fractography studies confirmed and corroborated the high values measured for UTS and impact tests as given in Table 7 above. The fractured tensile and impact specimens with scanning electron microscope images are shown in Figs. 13 and 14 respectively.