It’s a light surface rust that appears to have come from a water table on the plasma when they cut the master sheets down. I have a laser cutter that is going to cut these into steel targets for me and I need to clean them up somehow so they’re at least presentable or potentially ready to paint if required. A local company will tumble blast them for me but that only works with the smaller parts and then I have to deal with a 1 week lead time. Are there any chemical options worth pursuing or any other mechanical abrasive methods that would work well without being incredibly time-consuming? (I’m a one-man shop with limited space)
That’s unacceptable in my opinion. I’ve never received steel in that condition in 25 years. Probably a cup wire wheel would be a good starting place. Good luck
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Have you ever ordered steel directly from a Mill? SSAB is claiming that this is the standard “light mill scale” finish and that any of the better finishes (like Pickling and oiling) are done downstream at a 3rd party processing center.
If you have space after cutting put in a vinegar bath overnight the wipe down or wire wheel the resadew that is left.
That’s a crazy amount of rust for plasma cut. I run a plasma and use an additive in the water to prevent any rust. Occasionally you will hear hobby guys try to get by with no additive or less expensive alternatives but for a professional shop that’s just being cheap on their part.
To your question, any chemical solution (vinegar/acid) will need to be immediately followed up with a stop rust solution or it will flash rust all over again.
In the end, my guess is, you’ll find that any savings from going through that particular shop will long be lost in labor by the time you get that cleaned up.
Do they have to be clean before laser cutting them? If not, you could coat them in Ospho rust treatment and then paint.
https://www.ospho.com/directions.htm
“OSPHO has the consistency of water and treats up to 600 square feet per gallon. When applied to rusted surfaces, OSPHO causes iron oxide (rust) to chemically change to iron phosphate - an inert, hard substance that turns the metal black. Where rust is exceedingly heavy, two coats of OSPHO may be necessary to thoroughly penetrate and blacken the surface to be painted.”
If you are going to be cutting with laser or plasma i would always buy pickled. You’ll get a better finish end of cut, and your starts will be butter.
I often use diluted pool acid (muratic) in a garden pump sprayer to take off rust. Works almost instantly for light rust, then hose off with hot water and blow dry or wipe down to prevent flash rust as was mentioned. If I have to store outside, I hit it with Boeshield T9.
Depending on what services are available try looking for someone with a Wheel-a-brator, or similar product. Shipyards use them to shot blast 10’x40’ plates on both sides. It removes rust and mill scale and can leave the surface in a near white (Sa2.5) condition. You can have them coat with a Nippe Ceramo coating. Nippe Ceramo, as I recall, is a zinc rich primer that prevents rust and is weldable.
You have seen this done at steel supplier?
There is only one place by me that I see rusty steel and that’s because some of it sets outside. I buy very little from them.
If it were me I would deal with them after they are cut to size and are much easier to handle.
I soak stuff in a vinegar bath, I buy 45% vinegar in gallons and cut one gal with 7-8 gallons of water. soak parts overnight. I then rinse and soak for 15 mins in a mix of baking soda and water. Dry when done and they will look great and they are ready for paint or powder. Plus they can sit around for weeks and wont rust.
There is lots of info online of different ways people do this, this is just how I do it.
I cant believe how much dross there is from having those sheets cut. You must have got a good deal on them.
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My experience is with steel delivered to shipyards in the US. In the mid-1970’s raw steel arrived primarily by rail. The shipyard owned Wheelabrators and they processed their own steel. In the late 1990’s to early 2000’s the shipyard sent raw steel through their Wheelabrators and they cleaned and applied Nippe Ceramo in the shipyard. If I remember correctly there were steel mills that were supplying steel that had been primed.
The ships we were building had about 20,000 MT of steel when completed. This was the finished product. I don’t remember how much total steel was purchased. For the small quantity of steel shown in the picture I would start my search with the paint supplier. In the late 1990’s our paint supplier was International Paint, an AkzoNobel subsidiary. Nippe Ceramo was developed by Nippon Paint. Nippon Paint now calls it Nippon Ceramo. International Paint/Akzo Nobel now calls it Interplate 937.
International Paint should be able to point you in the right direction as to who might supply coated plates.
I don’t think anyone here is buying steel from any place that supplies steel to a shipyard. 
Laser rust removal is an option.