Stainless steel Engine
Made as a single piece forged device for higher energy and reliability.
We make use of mostly EV8 (21-4N) for consumption and EV16 (23-8N) for Exhaust valves but there are more alloys that people utilize alongside various temperature treatments to make valves for different programs. (See Inconel)
Other difficult metal alloys can be welded to solidify certain areas like the ideas or seating.
We use mainly two different form of coatings:
Popular in high end valves.
This will be a hardening treatment that although it just isn't widely used given that chrome coating, this has several advantages and it is becoming highly popular, primarily for European and Japanese applications.
The microhardness is higher than the metal base material, maintaining good ductility under the hard nitrided layer (microhardness is 800HV minimal).
Exterior finish is smoother than with chromed stems, having less rubbing between stem and guide.
Valve seat area is harder aided by the nitrided level, lasting longer with lead free fuels, alcohols, nitro or any other "explosive" mixes. Matches any kind of chairs (nodular iron seating, metallic powder metal seats, tough aluminum-copper seating or beryllium copper chairs).
Greater rpm's engines make the most of all previous features. The larger the motor speed the larger the power reduction due to interior engine rubbing! The black colored nitride level decreases this energy loss considering less valve-guide rubbing.
The nitrided level is adhered to the bottom material at a microscopic amount, so doesn't "flake" or break if the valves flex because effects aided by the pistons.