What is the difference between cold rolled steel and hot rolled steel?

Answer 1

Rolling metal is basically like rolling pizza dough. The idea behind the process is to make the material (metal or dough) cover a larger area by making it thinner.

Hot rolled steel, is obviously done while heated. The metal is hot enough to glow red (at minimum), orange, or yellow-white (at its hottest) and is typically a large slab or thing beam of solid metal. The rolling process involves pushing the metal piece between two massive rollers that squeezes the metal into a thinner and longer piece that it originally was. Large scale rolling is typically done at the foundry where the hot slab was just recently poured from the furnaces and allowd to cool just enough to solidify before it is fed through the rollers to work the large piece into several thin plates or strips. The large metal plates used to make the hulls of ships are a prime example of pieces made from hot rolled steel.

Cold rolled steel is basically the same process of thinning the metal by passing it through rollers, but because the metal is not softened though heating, the process requires higher pressure on the rollers to work the cold metal into shape. Ironically, the metal piece becomes warmer as the physical energies of friction and pressure are transformed into heat energy as the metal molecules move to assume the new thinner shape. Large scale cold rolling is done at various manufacturing plants as initial processes turning thicker pieces of metal into thin strips and sheets that are later stamped, cut, and welded into things like mail boxes, storage cases, housing units (for ACs, winch motors, etc.), or other structures. A prime example of cold rolling on a small scale can be found in auto body shops where metal pieces shaped for motorcycles and older cars.

The cold rolling process is also used by the U.S. mint to create the new gold dollar coin. The gold ingot is passed through many sets of rollers that work it into a thin strip seveal feet long before it is fed into another machine that punches out the circular blanks.

Answer 2

Cold Rolled steel does not go through the level of abuse that Hot Forged steel does.
You can also Heat Roll Steel, but it has the same damaging effect.
The effects are on an atomic scale, but can and are measured and known to exist.
A Fine Japanese Technique of Cold Rolling Steel and Irons has been used for centuries. It is this technique that gave the Samurai Sword its fame and popularity, and Ginsu Knives, but I don't think Ginsus were cold rolled.
Heat Forged Steel, well that's kinda the only way to actually extract the Iron Elements that make Steel, is sometimes called Tempered Steel. There are many different techniques used to temper steel, some of them are still very closely guarded secrets.
The Cold Rolling method usually does no damage to the steel that is noticeable to any commercially sold gauge or device.
To Cold Roll takes either years of craftsmanship, some very expensive machines, and or both.
I can manufacture a knife with a Hot Forge and it will function for a life.
I can cold roll the steel for the knife and depending on the ore,my skill,time and patience, it will last 1000 years.
Its basically Heat Destroys the Atomic Binding of the Ore that is Steel, whereas Cold Forging, or Rolling does far less damage to the same atomic structure.
It is worth doing research on though, cause I only know what I know from 10 years of welding, and that was 20 years ago. But the elements do not change that fast.

Answer 3

The only real difference between the two types of rolled steel is that hot rolled is milled to its final dimensions while hot (over 1700 degrees F) while cold rolled steel is milled to its final dimensions at a temperature well below that.
There are a few differences in the finished product, cold rolled is slightly harder, has less pits and rust. It is also processed to higher tolerences (it's squarer and more to scale). However it is more expensive due to the higher processing cost.
For almost all purposes though, they are both the same product.

Disclaimer: there might be different types of steel used, but you also get the same difference within the separate processes.

Answer 4

The term hot rolled means the final thickness is achieved by passing it under pressure between rolls while it is still red hot. The surface of the plate will have a thin tight scale of carbon which provides a temporary protection from rusting. Cold rolling is the same process but at ambient temperature. The rolling process removes the scale from previous hot thickness reduction and is usually oiled to provide protection from flash rusting. Galvanized steel is the same material as above but it is passed through a molten zinc bath to provide superior rust protection. To the best of my knowledge, tor steel is a trade name for deformed concrete reinforcing bar.