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Ask the Expert Question-and-Answer Archive
(Hard Chrome Plating)

by Randy Taylor, Advanced Tooling Corporation.
August, 2011

Plating of A2 Tool Steel

Q. I have an application where I would like to introduce some corrosion resistance to 6"x"6"x1/2" A2 tooling plate. The plate already has been heat treated but it is showning some signs of rust in factory. Rather than applying light machine oil is it possible to "flash" chromium plate the A2 steel to give it the required protection? Must I be concerned about hydrogen embrittlement? The tooling plate is used in conjunction with some locating pins as a test fixture. It is exposed to repeated loading and unloading of parts into the fixture by an operator.

Thanks for your insight!

A. Hard chromium can do a decent job and if it's just a cosmetic issue, you can achieve what you want using a flash of standard hard chromium. Some prefer a single coating of electroless nickel which is corrosion resistant, wear resistant and plates evenly on all surfaces with no build up on corners.

A flash thickness of hard chrome is generally 0.0002 to 0.0005 and one can expect a slight "build up" of thickness on corners. If the plate must be truly accurate, it may need lapping or grinding after plating.

If the tooling plate is to be kept in a dry stable environment, say a laboratory or inspection room, chromium could be expected to last. If kept in a more hostile environment, a shop area or out doors, the coating is likely to be affected by the elements over time.

If chromium is still preferred, I'd recommend a procedure referred to as "thin dense" hard chrome which can impart a greater degree of high wear and corrosion resistance.

If the heat treated condition of the plate is greater than RC 36, a bake after plating is recommended to relieve hydrogen embrittlement. Temperatures are generally in the 375-400 degree range. Bake cycle times are from 3 hours to 24 hours depending on hardness (tensile strength) Refer to your engineering department for the appropriate bake time and temperature.

Good Luck,

Randy Taylor

 



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