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Conventionally, the Ni-based superalloys NCF3015 (30Ni-15Cr) and the high nickel content NCF440 (70Ni-19Cr) (with its outstanding wear resistance and corrosion resistance), have been used as engine exhaust valve materials. In recent years, automobile exhaust gases have become hotter because of exhaust gas regulations and enhanced fuel consumption efficiency. Resource conservation and cost reductions also factor into global environmental challenges. To meet these requirements, NCF5015 (50Ni-15Cr), a new resource-conserving, low-cost Ni-based heat-resistant alloy with similar high-temperature strength and wear resistance as NCF440, has been developed. NCF5015's ability to simultaneously provide wear resistance, corrosion resistance and strength when NCF5015 is used with diesel engines was verified and the material was then used in exhaust valves.

Engine valve development trends are to first, reduce the costly metal content and secondly, increase strength or reduce weight. These developments can be used to reduce valve cost or fuel consumption or increase power. The authors developed a new strain age hardening type alloy, NCF2415C, which has both good cold forgeability and heat resistance. Its chemical composition is Fe-24Ni-15Cr-2.2Ti-1.5Al-0.5Nb-0.02C-.006B-2Cu. This new alloy and the establishment f cold forging technology made it possible to develop cold forged exhaust valves having durability equal or better than the conventional hot forged exhaust valves.