Hot rolled steel vs Cold rolled steel which is better?

Hey buddies,

I was at a lost when I got to the metal supplier asking myself which is better for my 2 projects. One for the back plate to raise my mill z axis higher (small miller cowells type) and second a mounting plate on to mill bed to extend the table width for clamping jobs.

Hot rolled plate may not be as flat but it's stress free, warping is minimum.

While cold rolled plate being more expensive, flat and free of oxide, it contains compressed stresses during production. Will it warp over time when under heavy loads? After I googled, many machine manufactures prefer using hot rolled plates than cold rolled....any comments?

Steve Wan

Hi John

Yes! No capacity to mill flat but getting sq possible for smaller piece.
I could not get cast iron billet here in Singapore but in rod type.

Just wondering those rolled steels between both any advantage and disadvantage?

Steve Wan

Provided you dont cut anything off the width or thockness cold rolled steel should not distort. At least it will be better than hot rolled as far as surface fiish is concerned. Drilling holes shouldn't pose a problem as long as you keep things symetrical.

Russell.

P.S. Might you be able to get cast iron blocks in Malaysia?

Hi Russell

Yes again! cold rolled steel have a better finish. Guess I made a wrong move getting the hot rolled plates, may have to mill a bit/sand it flat for better clamping on the mill bed.

Have not tried getting stuffs from Malaysia yet. I usually mail-order from College Engineering Supply from UK, Hemingway kits do have some nice castings.

Only cast iron is hard to comeby locally, other metals are relatively easy to get though.

Thanks for the reply

Steve Wan

Steve,

The problem with cold rolled steel only really becomes major if you machine it asymmetrically - it has compressive stress on the surface, so if you remove one side it will bend. It will be fine if you anneal it first - heat up to a certain temperature and allow to cool as slowly as you can. Can't recall the exact temperature - you can look it up as well as I can - but it's around dull red heat. It's possible that ageing will achieve the same result, but I can't say how long, and life's too short unless you happen to have had some in stock for 20 years.

Up to you whether the better dimensional accuracy and surface finish outweighs the need to anneal.

David

Hot rolled steel is fine to work, but you need to machine it all over, so it can be slower.

So, parts which require minimal machining - cold rolled/drawn steel. Strange shaped parts or those requiring a lot of machining - hot rolled.

Neil

Steve,

Cold rolled steel is far better quality, and will machine better, hot rolled can be a bit woolly sometimes when milling or turning it,

However as David says, if you anneal it first cold rolled should be stress free, nicer to machine, and will have a better finish.

If you can't find anyone with a forge or gas furnace, try a propane torch, or even a bonfire would do, get it to dull red and let it soak for a while, then let it cool down slowly, at this point it should be stress free.

It will probably have some scale on the surface, which is easily cleaned off with a sander of some sort, all this effort will be well worthwhile, as you will end up with a far better job than using hot rolled.

Richard.

Hi Richard, Neil and David

Thanks for the tips! Wonder a normal kitchen toaster oven is able to carry out the annealling process? If i could recall, temp around 250 deg. and duration of 30 mins?

Open to more suggestions

Steve Wan

Hi Steve

Annealing temperature is around 700 deg C, dull cherry red as stated previously and will need to be held for a period to soak depending upon size/volume.

So domestic appliances are not suitable. Maybe a gas ring will do for very small pieces?

Chunky pieces will require a good size propane torch or a furnace.

Nigel