Chrome plated stainless steel for high temperature valves?

Hard chrome begins to soften at around 260-280 C and looses most of its hardness at the temperature you mention. There are other options worth investigating such as tungsten carbide coatings applied by ESD or HVOF. Perhaps PVD TiN would also work if its thickness is OK for the application. Nitriding, on the other hand, does not sound like a very good option for such SS grade.

Jaymin,

What are you trying to achieve with the hard chrome? Is it for wear? Or a repair? Or for some other reason?

Hard chrome does soften when operated at high temperatures for long periods. This may be a case for one of the flame spray type coatings.

Dear Sir,
the melting point of SS316 is above 1400 degree Centigrade, melting point of Chromium is 1930 degree centigrade, other wise this used it steam column, so hot Chromium plated SS316 will withstand this temperature of nearly 600 degree centigrade.

Mr R.Shanmugavel Thangappan,

Unfortunately you cannot compare the melting/boiling temperatures of metallic chromium with operational conditions. What happens is that the microstructure of the metal changes over time which softens the material. This does not have to be near the melting temperature of the metal.

It is well documented that hard chromium plating reduces significantly in hardness with exposure to high temperatures with respect to time.

In this case it may not be a problem, but we do not know what the chromium is there for, so the advice is that the chrome will soften with time and temperature.

Brian Terry
aerospace - Yeovil, Somerset, United Kingdom

Dear Jaymin Patel

I think plating the valve with hard chrome is worth to test.

It is true that hard chrome layers loose some hardness by heat. But in most cases the high hardness is not necessary.

We use hard chrome layers in a application with high erosion, extreme loads and pressures and temperatures of 700° C (and peaks >1250° C) with success.

best regards
Michael

Will heating a hard chromed stainless steel part cause crazing in the chrome due to the two materials' differing thermal expansion coefficients? Literature puts hard chrome at roughly 7.4e-6 in/in/C whereas our 2205 Duplex SS substrate is roughly 13.5e-6 in/in/C.
We plan on heating the part from ambient to roughly 250° C. I assume the thickness of the coating is 0.01" to 0.02".

Even considering the assumption is right about thickness, it is mathematically impossible to answer with the info provided. Besides temperature, the units for thermal expansion have two dimensions, total and deformation. Here total dimension is unknown.
G. Marrufo