Hastelloy C-4 is a nickel-chromium-molybdenum alloy with improved thermal stability: tungsten is fully omitted, iron reduced to about 1%, and about 0.3% titanium added. Excellent high-temperature stability with good ductility and corrosion resistance after long-term aging at 650-1040 C; resists grain-boundary precipitates in the weld heat-affected zone, making it ideal for as-welded chemical process equipment.