Hot Rolled vs Cold Rolled

Hot-rolled steel refers to steel being rolled under heating. After rolling, the surface of the material has an oxide scale, which needs to be pickled to remove the oxide scale, and the surface is rough.

Cold-rolled steel refers to the steel rolled at room temperature. Generally, hot-rolled and pickled steel is used as the raw material. The surface finish of the cold-rolled steel is improved, and the reprocessing performance of stamping and drawing is better than that of hot-rolled steel. Improved.

Difference

1. Generally, hot rolling is the previous process of cold rolling.

2. The raw material for hot rolling is steel billets from steel mills; the raw material for cold rolling is hot rolled coils.

3. The hot rolling process is heating furnace -> rough rolling -> 7-stand finishing rolling; the cold rolling process is pickling cold continuous rolling -> heating furnace or continuous annealing furnace -> cleaning unit -> smoothing unit- >Rewinding unit.

4. There is no uncoiler for hot rolling, and the incoming material is steel billet; for cold rolling, there is an uncoiler because the incoming material is a hot-rolled coil.

Process flow

Cold-rolled

Raw material preparation → pickling → rolling → degreasing → annealing (heat treatment) → trimming, oiling, sub-coiling → finishing → packaging

Cold rolling uses hot rolled products as raw materials. The raw materials must be dephosphorized before cold rolling to ensure that the surface of the cold-rolled products is clean.

The purpose of degreasing is to remove the lubricating grease attached to the rolled material during rolling, so as not to pollute the surface of the steel during annealing, and to prevent carbon increase in stainless steel.

Annealing includes intermediate annealing and finished product heat treatment. Intermediate annealing is to eliminate work hardening caused by cold deformation through recrystallization, to restore the plasticity of the material and reduce the deformation resistance of the metal.

Hot-rolled

The slab is first raised to the required rolling temperature in the heating furnace, and then enters the rough rolling descaling machine through the roller table to process the scale produced by the slab, and then enters the rough rolling mill to determine the width of the strip.

And the thickness is rolled, and then transported from the roller table to the finishing descaler to treat the scale produced on the surface of the strip, and then enter the finishing rolling mill to perform a more precise rolling of the thickness and width of the strip.

After the strip is subjected to strict control of the surface temperature before coiling by the roller table through the layer cooling, it enters the coiler to become the steel coil and is finally bundled, sprayed, and sent to the coil stock for packaging.

Features

The hot-rolled sheet has low hardness, easy processing, good ductility, and hot-rolling can improve the process performance and processing performance of the metal.

The cold-rolled sheet has high hardness and is not easy to process, but it has high strength and is not easy to deform. The thickness of the cold-rolled plate is more accurate, and the thickness difference of the cold-rolled steel strip does not exceed 0.01~0.03mm. And it shows that it is smooth and has excellent mechanical properties at the same time.

Surface

1. The surface of the cold-rolled sheet has a certain degree of gloss and the surface is relatively smooth.

2. The surface of the hot-rolled plate is similar to that of many ordinary steel plates on the market. The rusted surface is red, and the unrusted surface is purple-black.

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