Formation
Hot-rolled steel: slabs are used as raw materials, and after heating, they are made into strip steel by rough rolling units and finishing rolling units.
Cold-rolled steel: hot-rolled steel coils are used as raw materials, and after pickling to remove the oxide scale, cold rolling is carried out, and the finished product is hard rolled coils.
Performance
Hot-rolled steel:
Strength: Although not very high, it is enough to meet general use needs.
Plasticity and weldability: Good, so hot-rolled steel is more commonly used.
Appearance color: Not bright, the surface may have an oxide layer or a black layer of ferroferric oxide.
Cold-rolled steel:
Strength: High.
Toughness and weldability: Relatively poor, the material is hard and brittle.
Surface quality: Since surface finishing is performed during the cold rolling process, the surface quality of cold-rolled steel is usually better than that of hot-rolled steel, and the surface is bright.
Process
Hot-rolled steel: ironmaking → steelmaking → continuous casting (or die casting) → hot rolling (hot-rolled products). During the hot rolling process, the material needs to be heated to a high temperature, and generally it needs to be heated above the recrystallization temperature before rolling to allow the steel to recrystallize inside and have better material properties.
Cold-rolled steel: On the basis of hot-rolled steel, further cold rolling is performed, that is, ironmaking → steelmaking → continuous casting (or die casting) → hot rolling (hot-rolled products) → cold rolling (cold-rolled products). The cold rolling process requires a large rolling mill power, and the rolling efficiency is low. Intermediate annealing is usually required to eliminate work hardening.
Appearance and surface quality
Hot-rolled steel: The appearance color is usually black or dark gray, and the surface may have an oxide layer or a black layer of ferroferric oxide.
Cold-rolled steel: The surface quality is good, usually metallic, smooth and bright.
In summary, Hot-rolled steel has good plasticity and weldability, but relatively poor surface quality; while cold-rolled steel has higher strength and better surface quality, but relatively poor toughness and weldability. Therefore, in practical applications, it is necessary to select the appropriate type of steel according to specific needs.
Read more post:
Advantages and disadvantages of hot rolling and cold rolling
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