Stainless vs. Chrome Plated

[leecoop]

Our company is considering using stainless steel for the exposed parts of our machine. Currently, we use .001 in. thick chrome plated carbon steel. We are trying to slow down the rust process. Is there a major advantage to stainless steel over the chrome plate? The dimensions of the part are 3" diameter rod, 10" long, exposed to sea air.

Thanks

 

[Ashereng]

If a portion of the chrome plating chips off, you can get localised oxidation/corrosion of the underlying CS.

With stainless steel, the corrosion is over the entire surface, so it is more distributed.

Sorry, I am not much more help.

"Do not worry about your problems with mathematics, I assure you mine are far greater."
Albert Einstein
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[mcguire]

Chromium has microcracks in such thick layers and corrosion of the underlying metal isn't prevented. Stainless is quite expensive these days, but you can cost out a suitable grade. 2205 will resist corrosion by seawater very well. 2003 is cheaper and should be adequate.
Don't bother with austenitics like 316, 317. Too expensive for not enough corrosion resistance.

Michael McGuire

http://stainlesssteelforengineers.blogspot.com/

 

[TVP]

Hard chromium plating will not render the carbon steel immune from corrosion in a sea air environment. If your application is currently limited by corrosion resistance, then it is quite possible to improve this by using a suitable stainless steel alloy. As mcguire suggested, grade 2205 is probably the best grade to begin investigating.

 

[yates]

Hard (or 'engineering') chrome plate is applied to carbon steels mainly for increased wear resistance to movement and does not afford any increase in corrosion resistance. This type of chrome plate is porous due to the numerous microcracks down to base metal. Decorative chrome plate on the other hand is not porous and does improve corrosion resistance.

 

[ornerynorsk]

Have you checked into a nitride process. I hear the corrosion resistance is very good, plus the added benefit of surface hardness.

 

[TVP]

yates

FYI, newer hard chrome plating processes have been developed that change the deposit characteristics such that some corrosion resistance is provided. Depending on the plating thickness and post processing performed, corrosion resistance in standard salt spray tests can be greater than 150 hours with no red rust. Still a long away from immunity though...

 

[EdStainless]

I like the idea of a lean duplex, like AL2003, or the regular 2205. The duplex grades will give you strength, cracking resistance and toughness.
Your next concern should be the end connections. If this part fits into a steel part you will increase the corrosion on the steel part.

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[swall]

For what its worth, "crack-free" engineering chrome has been around for a while. We used to use it for strut rods on landing gear in the '70's. The lack of cracks makes for greatly enhanced corrosion resistance at the cost of some loss of hardness.

 

[Flesh]

Also consider electroless-nickel plating. A high-phosphorus grade would offer much higher resistance than standard hard chrome. I've used 0.001-inch to provide complete protection on cylinder rods.

Another idea is to modify your current plating by adding a thin nickel layer underneath the chrome such that the base material is "sealed" from the exposure given by the micro-cracks in the chrome layer.

 

[leecoop]

Thank you all. We are getting prices for 2205. It looks favorable.

ornerynorsk:
Sometimes we see "nitride procesed" in the spec. Isnt this expensive?

 

[TVP]

Ferritic nitrocarburizing (liquid nitriding) is usually competitive with chrome plated parts. The process is known by many tradenames such as Kolene or Durferrit. The temperature is usually a little higher than with conventional gas nitriding, with cycles times of the former usually around 2 hours instead of 24+ with gas nitriding.