Hard Chrome Plating needs more Salt Spray Test hours

A. Check your trivalent status in chrome bath that should be less than 6 gm./ltr. Second increase the no. of microcracks on the job more than 400 cracks/linear cm.

A. Hi Chandra. I think it's borderline possible -- but carefully re-engineering a plating process to attempt to pass a wrong and non-informative accelerated corrosion test doesn't seem like a very productive path to follow :-)

The thing is, real-world corrosion is a complex phenomena and we think that, for the case of nickel-chrome plating, the standard ASTM B117 salt spray test is rather non-informative because it poorly imitates real-life. CASS and Corrodkote tests seem to more accurately predict the life of nickel-chrome coatings.

I think what you might want to do is decide what life you need under what real-world conditions, and then try to design an accelerated corrosion test that will be helpful towards predicting whether the parts will pass the real-world needs. Good luck.

Regards,

A. ASTM B456 has the specification for nickel/chrome plating corrosion resistance. It lists the thickness needed and how many hours the plating will survive various tests.

A. Hard chrome is a poor corrosion protector. It only gives approx. 48 hours in NSST.

A. Hi Chandra,

500 hours of a CASS is quite a challenge for any coating! I guess if it was me I'd go with about 75 microns of nickel undercoat followed by chrome to the finish size, but would probably want somewhere around 100-150 microns as a minimum.

I'm not going to guarantee that it will work, but it is a starting point.

A. Hi,

The only way to receive 500 hours in a salt spray test for chromium is to pulse plate the chrome.

Regards

Hi Chandra. This is the 4th time you've asked your "simple" question on this page, and it was also asked asked & answered a 5th time on letter 54204.

Please try to PARTICIPATE in the discussion, phrasing your on-going questions in terms of the many answers that have already been offered to you, so we can keep moving forward. But rather than thanking any of the six people who helped you for their efforts on your behalf and engaging them, you simply ignore them and keep posting the same question again & again, insisting that it is "simple" :-(

It may have worn out their patience ... it wore out mine :-)

Regards,

A. Dear Sir,

500 hrs of CASS life for nickel plated MS pipe seems very difficult to achieve. Kindly favor with end application details. This can help us in understanding the need for such high performance from the coating.

Even for automotive tubular components such as Two wheeler handles, which are exposed to most severe (Grade 4) of outdoor atmospheric conditions under high intensity motion such high CASS life is not specified. It may be Neutral Salt spray test life. Please Confirm.

Regards,

A. Hi. I am not familiar with the pulse plating which Anders describes, but you could ask him for more info.

Have you considered nickel plating under the hard chrome?

Regards,

A. Hi, I would not expect any real corrosion resistance from hard chrome plating to that thickness. Hard chrome is micro-cracked, due to the stresses in the coating, this means the base material can be attacked with relatively thin coatings of chrome. You either need to look at different technologies (e.g. thin dense chrome, which is not micro-cracked) or you need an undercoat as Ted has suggested (nickel or copper will serve your purposes, although nickel is the usual standard)

A. Hi,
A combination with electroless nickel and hard chrome will give you more than 75 hour in salt spray test. But is a little difficult to activate the EN; to do the activation must be in an acid which contains sulfuric acid and hydrofluoric acid. The detail must be cathodic in activation.

Best regards

Hi,
If anyone who plates hard chrome is interested about pulse plating with hard chrome, I can help you serious about it. We tested the plating in a salt chamber, after 500 hours no corrosion. So I know pulse plating works great.

Regards,

A. Hi Rahul. I'm not aware offhand of any research paper which addresses that comparison, although some papers have been written about attempts to replace hard chrome with electroless nickel in specific applications. You can look for papers with the data and numbers you want at surfacequery.com, or possibly scholar.google.com.

As you probably know, parameters like salt spray hours cannot be used to predict the relative corrosion resistance of different finishes; and the wear resistance of an oil-retaining micro-cracked chrome plated hydraulic component is very different than the wear resistance of non-porous surfaces whether oiled or dry. Electroless nickel is available as nickel-boron, or low-, mid-, or high-phosphorous, heat treated or not (heat treatment increases hardness as the cost of reduced corrosion resistance). Electroless nickel composites can contain TFE, diamond dust, or other particles.

We've posted your inquiry hoping that another reader can point you to comparison papers. If no one refers you to them, you might look at https://www.finishing.com/consultants or the Indian Association of Metal Finishers Association of India to retain a consultant to help with the assignment. But I do feel obligated to offer the general warning that we can usually help you choose a finish for a specific application, but trying to generate charts which will tell you the best finish for arbitrary applications tends to be a fool's errand. Good luck.

Regards,

A. Hi Brian. Although the ASTM B456 reference caught your eye, your questions seem to be about hydrogen embrittlement and decorative nickel-chrome plating rather than hard chrome. I mention this because we have dozens of threads on your subject if you search the site with appropriate search terms.

I am not familiar with baking in between layers of copper-nickel-chrome plating, but baking before and after plating is common. You might need to check whether baking is sufficient though. There are grades of steel for which plating is unacceptable, and chrome plating is exceptionally prone to causing hydrogen embrittlement. General specs you might review include ASTM B849-02 and ASTM B850-98

Copper plating before the nickel plating is not the usual practice when plating on steel these days; thread 0713 is about that exact subject. Good luck.

Regards,

A. Hi Brian. A number of years ago there was serious interest in trying to replace the chrome plating on hydraulic cylinders with electroless nickel plating because of its far greater corrosion resistance. As you doubtless appreciate, the efforts weren't very successful because smooth electroless nickel is no substitute for the porous oil-holding nature of hard chrome plating. But I believe it did result in quite a bit of research into electroless nickel followed by hard chrome. This would seem to me to be the right approach for a marine environment. Please try surfacequery.com and scholar.google.com and see what you can find (maybe with the search term "rod AND electroless AND nickel AND hard AND chromium"). Good luck.

Regards,