The Difference between Hot Rolled Steel and Cold Rolled SteelAuthor : hani Time : 2018/09/05
A general process of steel production is as follows: iron making → steel making → continuous casting (or die casting) → hot rolling (out of hot rolling products) → cold rolling (out of cold rolling products). First, let’s take a look at what kind of cold rolled and hot rolled products are available in various products:
Wire rod: The diameter is 5.5-40 mm, coiled, all hot rolled. After being cold drawn, it is a cold drawn material.
Round steel: Except the bright material with precise size, it is usually hot rolled, and there are also forged materials (the surface has forged traces).
Strip steel: Both hot-rolled and cold-rolled, cold-rolled materials are thinner.
Steel plate: Cold-rolled plate is thinner, such as automotive sheets; more medium-thick plates are hot rolled.
Angle steel: All hot rolled.
Steel pipes: Welded, hot rolled and cold drawn.
Channel steel and H-beam: Hot rolled.
Rebar: Hot rolled material.
Hot rolled products are basically rough, such as hot rolled sheets, and the thickness is generally above 3 mm. Hot rolling is processed at high temperature and does not change the structural properties of the metal.
Cold rolling is cold processing, including cold drawing to remove rust and straighten the steel products, and most importantly, the performance of steel is changed by cold drawing. In terms of composition, cold-rolled steel is low-carbon steel. Because of its low carbon content and good plasticity, it can be cold-rolled. In terms of surface quality, the surface quality of cold-rolled sheet is better than that of hot-rolled sheet because scale will appear on the steel surface if being hot rolled.
The advantage of hot rolling is that it can destroy the cast structure of the ingot, refine the grain of the steel, and eliminate the defects of the microstructure, so as to make the steel structure compact and improve the mechanical properties. This improvement is mainly reflected in the rolling direction, so that the steel is no longer an isotropic body to some extent; bubbles, cracks and looseness formed during casting can also be welded under high temperature and pressure.
Cold rolling refers to the processing of steel sheets or steel strips into various types of steel at room temperature by cold drawing, cold bending, and other cold treatment. The advantages are fast forming speed, high output, and no damage to the coating, and can be made into various cross-section forms to meet different needs; cold rolling can achieve plastic deformation of the steel to raise the yield point of the steel. The disadvantage is that there is no thermal plastic compression during the forming process, but residual stress still exists in the cross section, which affects the overall and local buckling characteristics of the steel.
The heat-treated steel has better tensile strength, yield strength, ductility and toughness. In addition, it is important that heat treatment can eliminate residual stress. Cold rolled steel products may be deformed unevenly due to the yield of steel, and the residual stress will affect the stability. Both hot rolling and cold rolling are processes of forming steel or steel sheets, which have a great influence on the microstructure and properties of steel. The rolling of steel is mainly hot rolling, and the cold rolling is only used for producing small steel and thin steel.
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