Effect of solution treatment on deep drawability of IN718 sheets: Experimental analysis and metallurgical characterization

A promising approach to decrease deformation load and improve ductility during forming of Inconel-718 (IN718) is through the use of solution treated blanks. In the present work, IN718 sheets were separately solution treated to different temperatures in the domain of 970-1070 degrees C at an interval of 50 degrees C to dissolve the strengthening precipitates (gamma' and gamma ''), and subsequently, were oil quenched to retain the microstructure. Due to significant difference in average grain size, the solution treated samples of 970 degrees C (HT970) and 1070 degrees C (HT1070) were selected for tensile characterization, deep drawing analysis, and micro-texture evolution. The tensile test response showed approximately 30% improvement in ductility and 27% reduction in load in case of HT1070 material with respect to that of HT970 material. The deep drawing process window was evaluated using flat bottom and hemispherical dome punch geometries, and it was found that the limiting draw ratio (LDR) improved marginally by 4.5% in case of HT1070 material. This improvement was due to the dominating presence of cube component in initial texture of HT1070 material. The high presence of cube and goss components in initial texture and the large difference in Taylor factor of individual grains at critical regions of deep drawn cups led to higher unsatisfactory surface roughness in the case of HT1070 material. Hence, it is suggested that the deep drawn components of HT970 material has better part performance in terms of surface roughness. Further, an attempt was made to correlate the fractographs with the fracture and formability behavior of sheet metal.