Re: OFCC University - Metallurgy 102 (External Coatings)
Posted: Fri May 22, 2009 6:38 pm
I agree that a gun maker like S&W has no purpose in using stainless for their slide if they know they want to harden and blacken the surface with a nitrocarburized treatment. They could have used 4140 (by the way, anyone know the type of steel Glock uses?)Morne wrote:NOTE - Stainless steel parts that get EITHER carburized OR nitrocarburized are, metallurgically speaking, no longer stainless. The reason is because the carbon combines with the chromium to form chromium carbides. This decreases from the available "free" chromium content needed to form the tightly adherent chromium oxide film. Lacking that, the steel becomes just a very expensive low-alloy steel. Why firearms makers bother to make parts from stainless steel and then nitrocarburize them is completely beyond me. They'd get virtually identical performance from a low-alloy steel like 4140 that got nitrocarburized and it would cost a LOT less. For you welders out there - this same phenomenon can happen when welding certain grades of stainless steel. That's why there are "L" grades of the 300-series stainless steels, the "L" indicates low carbon content so as to avoid making the weld-zone non-stainless.
So certainly there is no upside to stainless except maybe marketing purposes. And it seems true that 'it is no longer stainless' on the surface. But there is another claim out there that stainless loses its corrosion resistance once nitrocarburized. From what I can gather, that actually depends on the type of stainless.
Austenitic stainless (304) corrodes more easily after being nitrocarburized in nearly all cases.
http://www.google.com/patents?id=3d4PAA ... es&cad=1_1" onclick="window.open(this.href);return false;
However, Martensitic (416, 17-4) stainless DOES NOT lose corrosion resistance from being nitrocarburized . In fact, it is the same as before treatment, and sometimes gains it.
http://www.google.com/patents?id=3d4PAA ... es&cad=1_1" onclick="window.open(this.href);return false;
That said, 4140 which has been nitrocarburized will do about 400 hours of salt spray while 416 stainless will be about 80 with or without some type of nitrocarburization or up to 150 with other types. So once again, why not use 4140 to begin with?