Hot rolled or cold rolled sheet metal - Langmuir Systems Forum

If you use hot rolled, a half hour bath in muriatic acid solution is enough to get rid of it (50:50 mix with water - you can add propylene glycol or isopropyl alcohol to keep it from freezing if that’s an issue). Then just rinse with water (you can also do a dip in a sodium carbonate - baking soda solution to counteract the acid but a good water wash is enough).

Goto Steelhighsen to know more.

You can get a plastic tub from a farm store like Tractor Supply or a small water “pond” from Home Depot that will hold the 2x2 stock we can fit on the Crossfire. You only need a few inches of solution - just lay the steel in the tray and have the solution cover it.

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The scale dissolves and you’ll have nice clean steel.

One thing though - keep your tray & solution covered. The fumes will attack any unprotected metal nearby. You should also use a respirator if you’re spending much time doing this. Always wear nitrile gloves.

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They have stated the reason why they are called "hot" and "cold" rolled but not why you would choose one over the other. There can be other differences and reasons for selection so some of the multiple answers you got are likely right; partial, but right.

The first thing you should understand is that neither is a definite alloy. The exact alloy can vary from one supplier to another or even different items from the same supplier. This means that when you ask for hot or cold rolled, you are just saying "cheap, generic steel".

Hot rolled is generally thought to be better for welding. Cold rolled is not. I don't weld much so I can't say much more about that.

Most, but not necessairly all, cold rolled can be galvanized. Hot rolled never is.

If you need a steel with some definite property then neither hot rolled not cold rolled is likely to fit the bill. Look in catalogs like McMaster-Carr's (or their web site) for a quick discussion of the properties of a variety of steels (and other metals as well). Many of the specific alloys will be rolled at a lower temperature: some at a higher one. But they will not be specified that way.

Oh, and if you need a specific alloy steel that may have been cold rolled and you need to avoid distortion after machinning, then look for "stress relieved". That means it's been heat treated to relieve the internal stresses after rolling.

Paul A. Are we up to 10 different answers yet?

First as Paul pointed out, hot rolled or cold rolled just describes the process- it says nothing about the alloy.
Out here on the west coast, I have never seen hot rolled that was anything but A36, which is generic cheap steel. But I understand in the industrial heartland, there are actually places that stock hot rolled steels in higher carbon alloys.
And as Wille pointed out, Cold Rolled isnt really rolled cold- just cooler.
Hot rolled is cheaper. At least for A36. That is the reason most people use it. It is also the most widely available, and is made in the most wide range of sections and shapes. You can get hot rolled sheet, plate, angle, round, square, flat bar, I beam, and Channel.

Cold rolled is often available in round, less so in square and flat bar, and much harder to find in angle or channel or I beam. Cold rolled is available in sheet, up to about 1/8", but much beyond that in thickness it gets a lot harder to find. There may be 1" cold rolled sheet somewhere, but I have never seen any of it.

Many times when you buy Cold Rolled, you are automatically getting a slightly higher carbon, slightly better made product- A36, used for hot rolled, has a very wide range of acceptable chemical compositions- kind of a moving target. If you buy , or , in cold rolled, you get something that has a much tighter tolerance on the composition and carbon content.

To confuse things even more, most all higher carbon, tool steels, and exotic alloys are cold rolled, but usually not what the steelyard guy will think of as "cold rolled". When you ask for "cold rolled" you usually will be sold or , which both have relatively low carbon contents, and are as close to hot rolled in chemical composition as is available these days.

I disagree with Paul about welding and galvanizing.
I weld a lot, and cold rolled is often easier to weld- with some processes, you have the possibility of crummy welds because the electrode has a hard time penetrating the hard mill scale. With enough heat, cold rolled welds very nicely, especially tig welding. The reason most welding shops use hot rolled is just cost- they buy the cheapest steel they can, unless the specs call for something stronger.
As far as galvanizing, its true that if you buy pregalvanized sheet, it will have been cold rolled. But I have had literally tons of hot rolled fabrications galvanized, and I am an itty bitty customer at my galvanizer. When galvanizing, the parts are often sandblasted, and always acid pickled first, and most of the mill scale comes off before galvanizing.

For small parts, where great strength, or special heat treating is not a consideration, hot rolled is the cheapest. Sometimes you will find inclusions or cracks or cold shuts in today's hot rolled, but it works fine for non critical machining.
Cold rolled does often have more stress in the material from the rolling, and depending on what you do to it, it can sometimes move when you machine it. It can be annealled first to relieve this stress, by heating it then allowing it to cool slowly, such as in a pile of vermiculite.
So it really depends on the part, and the budget, and the customer, and what you have lying around.