Metal Parts are Nickel Plated but are still RUSTING

A. Increasing your EN to 0.0015 minimum should take care of most of your problems.

Also shifting to a higher phosphorous content will help greatly. You probably are using a mid P of 5-7 %. Try increasing to a minimum of 9 with 10 or 11 being even better if you can get it for a reasonable cost including shipping.

Finally, try to find out what metal it is in contact with and what the environment is. If it is in contact with steel that is rusting, it will also rust. If it is in a marine atmosphere, hot and slightly acid it will also rust faster.

A. Hi Glenn,

your problem might be as simple as using the correct specification...

For the 8630 steel , the proper specification would call for Wood's Nickel Strike before electroless Nickel. The Electroless Nickel should have a minimum thickness of 1.5 thousands of an inch, but it MUST be Hi Phosphorous Nickel (approx. 12 % Phosphorous); for some extra protection you could coat the Electroless Nickel with a minimum of 50 Millionths of an inch of Hard Chromium Deposit .

For the 17-4PH S/S the simple answer may be to electropolish the S/S , there by enriching the surface in Nickel & Chrome by selectively removing the Iron and at the same time "Passivating" the enriched Nickel / Chrome surface .

Best regards

A. There are many ways to prevent corrosion, but nickel plating will probably look the best. Electroless nickel specifically can be made very hard and durable. I suggest you take the hilt over to a local electroless nickel plater and have them give you a quote. The cost will be high, but you should get it professionally done.

A. Hi David. Take a moment and think of a steel ship which is equipped with zinc anodes to keep the hull from corroding. The zinc is more "active" than the steel, so when corrosive forces threaten to attack the steel, electrons flow from the zinc to the steel; thus the steel is preserved while the zinc atoms lose electrons and corrode away as zinc ions.

Caveat emptor! Big box stores are selling you Chinese nickel-chrome plated hotel shelves & toilet frames that are rusting & pitting before you even buy them.

Now picture your steel parts with a thin and porous or pinholed nickel plating on them. Steel is more active than the nickel, so when corrosive forces threaten to attack the nickel, electrons flow from the steel to the nickel; thus the nickel is preserved while the areas of steel exposed through the pinholes lose electrons and corrode away into pitted rust. Poor nickel plating is far worse than no plating at all as it greatly accelerates rusting.

It would only be a guess as to exactly why the steel parts from which the nickel has been stripped are now gray with a white haze -- something to do with the stripping process and/or a smut from acid cleaning -- but it's unimportant, and you probably did nothing wrong. A plating shop may or may not be able to replate these parts satisfactorily, but that has to be their call whether they are salvageable or over-etched. Good luck.

Regards,

A. Unless there is something missing in your post, If you have certs for the 1018 steel and the customer accepted them and they had them plated, then the problem is theirs and not yours.
1018 steel is a "low" grade steel that has many uses. If rust is a problem, then the customer should shift his spec to one of the stainless steels.

If he sticks with the 1018, then he should have over 0.0015 electroless nickel put on it. 0.002 would be much better. At this point 316 SS rather than 1018 becomes a better choice in my mind.

A. Hi Alok. Parts must be properly cleaned & activated before nickel plating. Unless I have misunderstood you, you are attempting to go directly from mechanical deburring and a long rinse/hold station to nickel plating without activation. At the least, you need a dip in HCl followed by a rinse after this holding period.

Regards,

A. Hi again Alok. As you have noted, the process used to work until you changed the pretreatment, so the first assumption has to be that the new pretreatment process is not satisfactory. Of course it is not ideal to "store" parts between cleaning and plating, either in or out of water, but ...

As mentioned, my first guess is that the main problem is that the surface is not active when the parts enter the plating tank, so let me emphasize the word that I think you may have glossed over: "At the least you need a dip in HCl followed by a rinse *after* this holding period". Good luck.

Regards,

A. Hi again, Alok. If you answered my question of whether you do the HCl dip immediately before plating or 2-3 hours before plating I'm not seeing the answer, but I'll restate it: you can only electroplate onto active surfaces, and a surface will not remain active for 2-3 hours after an HCl dip; the dip should almost immediately precede plating.

We don't compare brands here (why?), but a scattergun approach does tend to introduce problems. You've changed many different things, and are encountering problems, and asking what caused it. I think maybe you should carefully examine the parts by eye, with a low magnification loupe, and by cross-sectioning and microscopic examination and try to determine exactly what is wrong with the parts that is leading to the rusting. For example, simply describing the steps you go through, like 5 minutes in chrome dip, while it is certainly useful information, doesn't really guarantee anything -- are you even sure that any chrome at all is deposited? Try to send the best photos you can to finishing.com@earthlink.net for posting here, and hopefully it will be apparent what is wrong. Best of luck!

Regards,

? Hello Gaspar,
Could you provide us with the substrate (which I assume is steel) and all processes before EN? Thanks.

A. Hello again Gaspar,
I have to say that I've never heard of an EN process that did not have a pre clean sequence, as you list the only processes before EN are machining/milling. Aside from that, a deposit thickness of .0015 to .002 should offer ample corrosion resistance unless storage conditions are unsatisfactory. I am not familiar with "boronated" water and don't know what the concentration is. I would request pictures of the surface to verify that it is actual rust your customer is seeing. It could be a film that can be cleaned off and the part saved and be able to be used again. Have you had good results over the years with other parts using the same process? It would also be beneficial to contact your EN supplier to see if they have ever encountered this problem. Good Luck.