enginehistory.org

[jjuutinen]

Which method produces:
-higher hardness
-lesser friction (smoother surface)
-better resistance to wear

I have tried to check several sources but none of them really offer comparison info.

[jrussell]

In general, a chrome crank offers a harder, lower friction surface. The biggest advantage is that it can be used as a repair technique on a single journal without re-chroming the entire crank, with a depth of 5mm not uncommon. You can not use a Nitriding process as a repair technique, you just buy a new part.Also, the nitriding process requires a higher quality base material to start with. For instance, the typical forged crank for an American V-8 of the 60"s ( which had a tufttrided surface ) would use a 1020 base material. A nitrided crank would reqiure a 5140 series material. It was common to chrome a tuftrided crank. So a lower cost crank could receive the chroming process. However, the chroming process would have a negative effect on the metallurgy of the crank, so it was used only in limited circumstances. One such use, was in Drag Racing vehicles which burned Nitromethane ( I am very aware of your views of such activity ). In such an application, in spite of all of it"s drawbacks, it was the only journal treatment which would survive for any length of time ( due to the dilution of the oil with Nitro). On other engine components, the metallurgy probllem was less severe ( for example cam followers or rocker arm pads )
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It runs best just before it blows!

[jjuutinen]

To be honest, I was looking the info to compare these treatments for gun barrels, including artillery pieces. In this applications the base material is not a problem as it has to be of high quality anyway.

[jrussell]

For that application chrome would usually be seen as superior due to its resistence to corrosion and high temperture erosion . One of the fixes to the early M-16 problems was to chrome plate the chamber, and thats pretty widely done. Chroming the land area of the barrels is not common, although I have heard of it being done when cost is not a primary concern. Most cannon seem to got to a high Nickel alloy for the barrel, but the higher the Nickel content. the more difficult it becomes to machine the lands.
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It runs best just before it blows!

[jjuutinen]

But that chroming can flake off, while nitriding can´t. And I am especially talking about the barrel itself, not chamber. It would be most interesting to know how you quarantee an even result when chroming tight spots like the area between lands.

[jrussell]

I assume we are talking about hard chroming, not ornamental chroming. I've never seen hard chrome flake, even in pretty severe environments. The biggest problem would be in developing land profile. With a nitriding process, the land profile is machined before Nitriding, and then you could lap for surface finish if desired.With chrome, you would have to grind or lap to desired profile. The smaller the barrel size, the harder this would be. But this is also one of the advantages of chroming, it can be used to build up dimensionally, where Nitriding can't.In the final analysis, chroming is probably a superior finish for a gun barrel, but it would cost a whole lot more. Nitriding is a lot more practical - you only have to deal with one company, and it can be done without dimensional change. I've never seen a chrome barrel for a small bore rifle, but I have seen a large naval cannon which had a chrome bore.
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It runs best just before it blows!

[jjuutinen]

Weren´t Merlin cam followers hard chromed? They did flake off, according to A. Rubbra. QED.