What "P&O" Means on Your Quote: Pickled & Oiled vs. Hot Rolled Steel

If you've looked at one of our quotes or used the material dropdowns on our quote form, you've seen designations like A1011 P&O, A36 PO, A36 HRS, and A1008 CSB. They're all plain carbon steel. The letters after the grade tell you how the mill finished it, and that affects how it cuts, how it forms, how it welds, and what it costs. Here's the plain-English version.

Hot rolled steel (HRS)

Hot rolled steel is rolled to thickness while it's glowing hot, then allowed to cool. It's the least processed and least expensive form of steel, and it's what most structural work is made from. The trade-off is mill scale: as the hot steel cools in the air, a bluish-gray layer of iron oxide forms on the surface. Scale is hard and brittle. It flakes under paint and powder coat, it contaminates welds, and it wears cutting tooling. If your parts are getting blasted or if surface finish doesn't matter — a machine base, a counterweight, a weldment that gets ground anyway — hot rolled is the right, economical choice.

Pickled and oiled (P&O or PO)

Pickled and oiled steel starts as the same hot rolled material. The mill then runs it through an acid bath — the "pickling" — which strips the scale off, and coats it with a light oil to keep it from rusting before you use it. What comes out is a clean, uniform gray surface with more consistent thickness than as-rolled material. For us that means:

• Better laser cuts. Mill scale varies in thickness across a sheet and absorbs the beam unevenly. P&O cuts more consistently with less spatter, especially on the CO₂ laser.
• Cleaner forming. No scale to crack and flake off in the press brake dies.
• Less prep before coating. Powder coaters and painters want a scale-free surface. P&O parts usually need only a solvent wipe to get the oil off.
• Better welds. No scale to grind back before you strike an arc.

It costs a little more per pound than hot rolled, and it saves a lot more than that in cleanup time on anything that's going to be finished.

Cold rolled steel (A1008 CSB)

Cold rolled steel is P&O that has been rolled again at room temperature. That extra step tightens the thickness tolerance, gives a smooth, bright surface, and increases strength slightly. It's the standard for thin sheet where flatness and appearance matter — enclosures, panels, brackets you can see. We stock it from 24 gauge up to 11 gauge (0.12").

Why A36 PO stops at 1/2"

This is the question that prompted this post. Pickling works on coil and on relatively thin plate; mills don't pickle plate over about 1/2" thick. So on our quotes, A36 PO covers 1/4" through 1/2", and anything thicker — 5/8", 3/4", 1" and up — is A36 HRS, hot rolled with the scale on it. If you need thick plate with a scale-free surface, we can run the cut parts through our wide-belt sander or send them out for blasting; just tell us on the quote.

How our steel grades line up

Which one should you pick?

• It's getting painted or powder coated → P&O for plate up to 1/2", cold rolled for thin sheet.
• It's structural and will be blasted or left raw → hot rolled. Don't pay for pickling you'll blast off.
• Flatness and appearance matter → cold rolled.
• It has to be strong for its weight → ask about A572-50.
• You're not sure → pick the material and thickness on the quote form, and tell us what the part is for in the notes. We'll pick the grade and explain why.