Most components, for instance this engine Intake and Exhaust valves have few surfaces exposed to extreme wear. During this case the tip and seat.
The most popular materials for exhaust valves, however, are Austenitic Chrome Steel alloys like 21-2N and 21-4N. Though austenitic chrome steel can handle high temperatures very well, the steel is softer than martensitic steel at lower temperatures and can't be hardened by heat treatment. To enhance wear, a tough material could also be welded to the tip and therefore the valve stem.
So you would like to overlay the tip and seat with a hard material for an extended life. Cobalt based alloys give a hardness upto 38 HRC and more but is costly. If you create the entire part out of this material it'll be very costly for the end customer.
21-2N alloy has been around since the 1950s and is an austenitic chrome steel with 21 percent chromium and a couple of percent nickel. It holds up well for general available valve applications and costs less then 21-4N because it contains less nickel.
21-4N is additionally an austenitic chrome steel with an equivalent chromium content but contains almost twice the maximum amount nickel (3.75 percent), making it a costlier alloy. 21-4N is typically considered to be the premium material for performance exhaust valves. 21-4N steel also meets the “EV8” Society of Automotive Engineers (SAE) specification for exhaust valves.
SAE classifies valve alloys with a code system: “NV” is that the prefix code for a low-alloy valve, “HNV” may be a high alloy valve material, “EV” is an austenitic valve alloy, and “HEV” may be a high-strength valve alloy.
So the part is formed of 21-2N alloy at 28 HRC less expensive than cobalt based alloys. But the end performance as far as tip and seat wear resistance is concerned is the equivalent of cobalt based alloys of 38 HRC.
Cost of cobalt based alloys and 21-2N / 21-4N will differ across countries so we'll not specify it here.
So you can first calculate the saving when this part is made in millions all over the world. There are hundreds of components across the engineering spectrum requiring hard facing only on mating parts and not the whole surface both internal and external surfaces.
We supply options for both Internal and Surface hard facing,surfacing, reclamation applications with equipment using the latest technology.
For more details write to us at [email protected]
visit our Web Site : www.arcraftplasma.com
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