Advantage:
a. Hot rolling can significantly reduce energy consumption and reduce costs. During hot rolling, the metal has high plasticity and low deformation resistance, which greatly reduces the energy consumption of metal deformation.
b. Hot rolling can improve the processing performance of metals and alloys, that is, the coarse grains in the as-cast state are broken, the cracks are healed significantly, the casting defects are reduced or eliminated, the as-cast structure is transformed into the deformed structure, and the processing performance of the alloy is improved.
c. Hot rolling usually uses large ingots and large reduction rolling, which not only improves production efficiency but also creates conditions for increasing the rolling speed and realizing the continuity and automation of the rolling process.
Disadvantages:
a. After hot rolling, the non-metallic inclusions (mainly sulfides and oxides, as well as silicates) inside the steel are pressed into thin sheets, and delamination (interlayer) occurs. Delamination greatly deteriorates the tensile properties of the steel in the thickness direction, and interlayer tearing may occur when the weld shrinks. The local strain induced by weld shrinkage often reaches several times the yield point strain, which is much larger than the strain caused by the load.
b. Residual stress caused by uneven cooling. Residual stress is the internal self-balanced stress without external force. Hot-rolled steel sections of various cross-sections have such residual stresses. Generally, the larger the section size of the steel section, the larger the residual stress. Although the residual stress is self-balanced, it still has a certain influence on the performance of the steel member under the action of external force. For example, it may have adverse effects on deformation, stability, fatigue resistance, etc.
c. Hot rolling cannot control the required mechanical properties of products very accurately, and the structure and properties of hot rolled products cannot be uniform. Its strength index is lower than that of cold-work-hardened products but higher than that of fully annealed products; its plasticity index is higher than that of cold-work-hardened products but lower than that of fully annealed products.
d. The thickness of hot-rolled products is difficult to control, and the control accuracy is relatively poor; the surface of hot-rolled products is rougher than that of cold-rolled products, and the Ra value is generally 0.5~1.5um. Therefore, hot-rolled products are generally used as cold-rolled billets.
The process of producing coiled hot-rolled steel strips with a thickness of 1.2~8mm on a hot strip rolling mill. Strip steel with a width of 600mm or less is called narrow strip steel; those with a width of more than 600mm are called wide strip steel. The first hot strip rolling mill was put into operation in the United States in 1905, producing strip steel with a width of 200 mm.
The hot strip rolling mill has superior technical and economic indicators and is developing rapidly. In industrially developed countries, the output of hot-rolled wide strip steel accounted for about 25% of the total steel output before 1950 and reached about 50% in the 1970s. The raw material of hot-rolled strip steel is a continuous casting slab or blooming slab with a thickness of 130~300mm.
After the slab is heated in the heating furnace, it is sent to the rolling mill to be rolled into strip steel with a thickness of 1.00~25.4mm and coiled into steel coils.
The rolled steel grades include ordinary carbon steel, low alloy steel, stainless steel, and silicon steel. Its main purpose is to make cold-rolled strip steel, welded pipe, cold-formed, and welded section steel; or used to make various structural parts, containers, etc.
Post time: Jun-02-2021