Conventionally cast IN738LC is widely used as turbine blade material. In this work, the alloy was cast in step wedge and plate geometries by varying casting temperature, shell insulation and mass of melt. The microstructural properties (size of columnar grains, the fraction of equiaxed grains, secondary dendrite arm spacing and porosity) were investigated by light microscopy. Mechanical properties were determined by Vickers hardness measurements. It was found that porosity increases by increasing temperature gradient at constant cooling rate. This leads to a decrease of hardness. In first-order approximation Vickers hardness shows a positive linear correlation to secondary dendrite arm spacing but with a high deviation of measured values in cast state. The deviation can be explained quantitatively by the influence of temperature gradient.