A nickel-base casting superalloy consisting essentially (by weight of the alloy) of 7% to 25% chromium, 02.% to 7% aluminum, 0.2% to 6% titanium, 0.01% to 0.25% carbon, up to 0.2% zirconium, up to 0.15% boron, up to 3% hafnium, at least 5% of a matrix-strengthening element selected from the group consisting of 0 to 25% cobalt, 0 to 10% molybdenum, 0 to 13% tungsten to 6% tantalum, 0 to 5% columbium, and 0 to 1.5% vanadium, a carbide shape controller selected from 0.022% to 0.15% magnesium, 0.005% to 0.1% calcium, or mixtures thereof, and the balance nickel except for impurties, said alloy in the as-cast condition having a fine grain macrostructure in thick as well as thin sections, exhibiting a microstructure having precipitated carbide particles which are substantially equi-axed in shape and well-distributed through the alloy with a substantial portion of the magnesium and/or calcium content of the alloy concentrated in such particles and at grain boundaries, and displaying in its thick sections a tensile strength and elongation substantially higher than a corresponding thick-section alloy having a microstructure exhibiting script-like carbide particles substantially free internally and at grain boundaries of said carbide shape controller.