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Honda has developed, in collaboration with Hitachi Metals and Daido Steel, two types of low-nickel heat-resistant alloys for exhaust valves which are more cost effective than the conventional nickel alloys. They are NCF4015 that contains approximately 40% nickel and NCF3015 with approximately 30% nickel content. The two types of new alloys were developed based on our unique alloy design concept. Both alloys feature superb high-temperature strength and are capable of maintaining favorable material properties, even after an high-temperature exposure. The NCF4015 is compatible with the conventional Inconel 751 and 60Ni alloys in terms of high-temperature strength. The NCF3015 falls slightly behind the two metals, but overwhelms the 21-4N (SUH35) in high-temperature strength. The exhaust valves made of the two alloys developed have been used for mass production engines.

In order to save molybdenum (Mo) in chromium - molybdenum steels for automobile components, medium carbon - boron steels were investigated. Boron is not a new alloying element for structural steels, however, to date boron steels have not been widely used because of their unstable hardenability and poor machinability. Therefore, in this paper, the optimum content of boron was reexamined, and also the appropriate addition of titanium as a stabilizer of boron was investigated from the view point of hardenability. Furthermore the upper limit of manganese (Mn) content was studied to keep good machinability. The new steel grades, established on the basis of the above fundamental research, have been used on vital components of passenger cars.

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.