Development of Nickel-Base Superalloy for Exhaust Valves

These days, nickel-base superalloy has been applied to reduce the valve weight of motorcycles. Inconel 751 is excellent in performance but expensive in cost. Therefore, we verified the constituents of nickel-base superalloys corresponding to the requirements of valves and we succeeded in developing a new superalloy and applying it to motorcycle exhaust valves.

The characteristics are summarized as follows:

1. 1.
   The basic composition is Fe-46Ni-18Cr-4Ti-1Al-0.3C-0.004B. It is a precipitation-hardened nickel alloy characterized by precipitation of Ni3 (Al,Ti) and, crystallization and dispersion of fine TiC.
2. 2.
   It has the following distinctive features.
   1. (1)
      Superior to Inconel 751 in wear and heat resistance.
   2. (2)
      Superior to 20-11P steel in resistance to lead oxide corrosion.
   3. (3)
      Applicable to both unleaded and low-lead gasoline.
3. 3.
   The exhaust valves using this new superalloy are lighter in weight by 18% and lower in cost by 13% as compared to the conventional type using 20-11P hard-faced with Stellite. They have been mass-produced from 1990.