One of the most frequent specification errors we see is buying hot rolled where cold rolled is needed — or paying for cold rolled where hot rolled would do. The difference is not the steel; it is what happens after the last rolling pass.
Hot rolled sheet is rolled above recrystallisation temperature: cheaper, available thick, with a mill-scale surface, looser tolerances and less predictable flatness. Cold rolled sheet is hot rolled material that has been pickled and re-rolled at room temperature: smoother, thinner (down to about 0.15 mm), tighter tolerance, harder temper, and ready for painting.
Structural plates, machinery frames, trailer bodies, anything welded in thickness above 3 mm where surface appearance is irrelevant. Painting over mill scale requires blast cleaning, so if the part will be painted, either budget for blasting or buy pickled-and-oiled material.
Anything thinner than 3 mm with a visible surface or a forming operation: appliance panels, lighting fixtures, drums, furniture. Cold rolled also bends more predictably because the temper and the surface are uniform through the coil.
The price gap is typically 15–30 %, but the true comparison is landed cost per finished part. A hot rolled part that needs blasting and filling costs more in total than a cold rolled part that paints straight away. A cold rolled part specified where hot rolled would do is simply money donated to the mill.
If your part is deep drawn or bends across the grain, specify drawing quality (DC03/DC04 or SPCD) rather than commercial quality. The surcharge is small; the scrap-rate difference is not.
Send the grade, the size and the quantity — you get a costed quotation within two working days.