

	S ss Valve seat : Stellite No.6 or No.32 (F) st Tip : Stellite No.1 T Wafer welded valves Small wafer ( normally in our A material ) is welded at the valve tip. C Chromium plated valve stems N Soft nitrided valves Soft nitrided finish, in other words "Tufftride" , or so called "Black Finish" in gneral. The significance of these inprovements resulting from soft nitriding is of course an extended valve life. Na Sodium cooled valves Demands are increasing for racing car engines, for severe operating purposes and for long run under high speeds. Sodium affects lowering temperature at valve haed. Bi These are required for some types of engines, to economically provide a valve with the head resistent to heat, crrosion and mechanical stresses and the stem with good wear resistance. The bi-metallic Valve has the head made from a high temparature and corrosion resistant steel, and the stem made from a steel ( usually martensitic ) with good mechaninal properties at medium temperatures. This combination is highly recommended for Exhaust Valves.



	The tufftride compound layer is composed of tough carbon-bearing epsilon iron nitride which provides extreme hardness and superior wear and seizure resistance. The diffusion layer im-proves the fatigue endurance and pitting resistance of treated materials. 1.ENHANCEMENT OF ABRAISON RESISTANCE The figure below illustrates the results of adrasion test comparing tufftride treated steels with steels using other heat treatment method. Carbon steel with heat treatment Tuffride treated steel Tuffride treated steel Crome and Molibdenium steel with carburinzing and quenching When the speed of sliding is 2.0m/sec, non-tufftride steel show 8.0-9.0mg. abraision loss. On the contrary tufftride treated steel shows only 0.3mg 2.HARDNESS DISTRIBUTION CHARISTARISTICS OF TUFFTRIDE TREATED STEEL The figure below illustrates the hardness distribution of tufftride treated steel. The hardness of non-treated SUH-3 steel is 320 Hmv. And that of 21-4N is 360 Hmv. As a result, the hardness is DOUBLED with tufftreide treatment. 3.INPROVED HEAT RESISTANCE The hardness of carburized or induction hardened steels steels start to drop at about 400F. Tufftride treated steel retain stablility in the compound layer till about 930F. Beneficiaries of the tufftride process are wear resistanct parts used under high temparature conditions like: casting die, engine valves etc.