Chrome Removal

If you are equipped safety wise to handle dilute hydrochloric acid which is corrosive, gasses, etc., then commercially available Muriatic Acid is the dilute form of hydrochloric acid which will work just fine. Leave it in the acid until it stops bubbling. However, since the surface of the raw steel will be activated it will immediately start to flash rust upon removal from the acid and will require some sort of rust preventative treatment such as oil, replate etc. Also, you will have to dispose of the chrome containing acid which will require pH adjustment, removal of the dissolved chrome and a wastewater permit! As you can tell this is not as easy as one might think at first blush. Your best bet is to find your nearest friendly plating shop which routinely does this sort of thing, and pay them to strip it. They can also replate with chrome, electroless nickel or some such and you'll be good to go for a few more years.

There are a couple of ways you can go here. First, I would not recommend HCl. Considering you have areas which are plated and others are not, chances are you are going to etch or damage the areas which are not plated.

The alternative I would recommend is to strip the plating with reverse current at about 1 amp/sq in in a chromic acid solution at 130 °FF. You can strip approximately 2 mils/hour and you will not damage the part as long as you check it periodically. Do keep a close eye on it though because if you let it continue to strip after the plating has been removed you will damage the steel.

The safest but slowest method would be to use 6 oz/gal of NaOH at 90 °F. You can strip at 4-6 volts and the part will not etch. Expect this technique to strip approximately .5 mil/hour but it is by far the safest method.

I have stripped literally thousands of hydraulic cylinders and piston rods with all types of steel and hardened steel using the chromic acid method with absolutely no problems. Good luck!