Issue 48

H. S. Patil et alii, Frattura ed Integrità Strutturale, 48 (2019) 377-384; DOI: 10.3221/IGF-ESIS.48.36 383 H ARDNESS PROPERTIES ANALYSIS ig. 7 shows the hardness variations (across the weld) from the center of fusion zone to the base metal for various sample welded at different parameters for 3 mm thickness joints. These hardness values have some fluctuations along the fusion zone to base metal. This is due to the irregular grain growth and inherent variations of the alpha - beta phases in the microstructure of the weldment of C.P titanium material. This behaviour is also due to the slow cooling rate of TIG weld process. The maximum value of hardness at the fusion zone has found 235HV (for sample 5) and minimum value of 175 HV (for sample 9). As expected, the hardness value increased with increasing cooling rate i.e. low heat input due to the formation of an increasingly finer transformed structure. In addition, the hardness of the fusion zone increases with decrease in heat inputs. Based on the micro-hardness test, it is evident that the weld provides good strength than the base metal due to the hardness in the fusion zone which is relatively higher than the hardness of the base metal. Figure 7: Hardness profile showing hardness in the BM, HAZ and FZ C ONCLUSION ased on available literature and the results drawn from this investigation in TIG welding of C.P titanium materials, the conclusions are: Welding parameters like welding current, weld gap and gas flow rate are optimized and established from bead-on plate trials for full penetration V welds. In the fusion zone, a significant grain coarsening size is noticed consisting of alpha phase in different direction bounded by beta phase. In HAZ, equiaxed grains had grown larger in size compared to grains in base metal. As a result, the degree of grain coarsening decreases as one move from the fusion zone to the base metal. Tensile test illustrates that the yield and ultimate strengths of the joints rises above the base metal and in actual fact all failures occurred in the base metal area. Furthermore, percentage of elongation decreases in the order of fine grain microstructure due to the decreased heat input. It also seen that, hardness values are having some fluctuation because of variation in grain structures. The optimized weld sample 5 with weld parameters- Current-95A, Gas flow-25lit/min, wed gap-1mm has good mechanical properties with respect to other weld samples. R EFERENCES [1] Szymlek, K. (2008). Review of titanium and steel welding methods, Advances in Materials Science, 8(1), pp. 186-194. [2] Pal, S., Pal, S.K., Samantaray, A.K. (2010). Determination of optimal pulse metal inert gas welding parameters with a neuro-GA technique, Materials and Manufacturing Processes, 25, pp. 606- 615. F B