The difference between cold rolled ribbed steel bar and hot rolled ribbed steel bar, steel technology
The hot-rolled steel bars are processed directly on the steel mold in the steel furnace in the steel processing plant, that is, the finished product that comes out of the furnace is hot (hence the name “hot rolled”), and can be used after cooling. Cold-rolled steel bars are obtained by cold-working hot-rolled steel bars, such as cold-drawn and drawn steel bars at room temperature.
Keyword：Hot rolled steel bars; cold rolled steel bars; advantages; differences
Realed product：rolling mill roll
Hot-rolled steel bars have low yield strength and good plastic properties. Cold-rolled steel bars have higher yield strength and poor plastic properties. Both have the same ultimate tensile and compressive strength.
Generally 5-11MM, mainly used for all kinds of cast-in-place slabs, the strength is much higher than that of first-grade steel. It is a process of quasi-rolling and ribbing of wire or round steel. Its strength is nearly doubled, and its binding force is increased by 4-5 times. It is used in prestressed dangerous components and can save cement 50- 70kg/m3; used in non-stress risk components, can save 20-40% of steel.
The grades of hot-rolled ribbed steel bars consist of HRB and the minimum yield point of the grades. H, R, and B are the first letters of the three words: Hotrolled, Ribbed, and Bars respectively.
Its advantages are:
- Economy: Due to the high strength, the use of new grade III threaded steel bars can save 10-15% of steel compared to grade II threaded steel bars, so it can reduce the construction cost of construction projects.
- High strength and good toughness: using microalloying treatment, the yield point is above 400Mpa, and the tensile strength is above 570Mpa, which are 20% higher than grade II threaded steel bars.
- Seismic resistance: Vanadium-containing steel bars have higher bending resistance, aging performance, higher low-cycle fatigue performance, and their seismic performance is significantly better than Grade II threaded steel bars.
- Easy welding: Because the carbon content is less than or equal to 0.54%, the welding performance is good, suitable for various welding methods, and the process is simple and convenient.
- Convenient construction: The use of new grade III threaded steel bars increases the construction gap and provides a guarantee for construction convenience and construction quality.
Cold rolled steel bar: It is a steel bar with a regular cross section that is rolled on a rolling mill to improve its strength and adhesion to concrete.
Hot-rolled steel bar: a pressure processing method that allows the processed steel billet to pass through the gap between a pair of rotating rolls (various shapes) at high temperatures, and the cross-section of the material is reduced due to the compression of the rolls, and the length is increased.
Reinforcing steel bars widely used in construction projects by cold working have obvious economic benefits. However, the yield strength of the steel bars after cold processing is relatively large, and the safety reserve is small, especially for cold drawn steel wires. Therefore, it is increasingly difficult to see the cold processing workshops of steel bars in the construction sites of important buildings that emphasize safety.
- The steel bars of reinforced concrete are hot rolled.
- For HRB500, hot rolling should be used.
- The price of cold-rolled steel of the same grade is lower.
The difference between hot rolled steel and cold rolled steel
“CRS (Cold Roll Steel)” or “HRS (Hot Roll Steel)” This refers to cold-rolled steel and hot-rolled steel. I would like to ask you to compare cold-rolled and hot-rolled. This is a classification based on the difference in steel production process. .
Excuse me: The steel rolling process is different, and the composition can be the same. For the same steel grade, hot rolling is generally softer. High-precision sheets are generally produced by cold rolling. The automotive industry and household appliances use a lot of cold-rolled steel.
The material manual should indicate the standard state corresponding to its mechanical properties. If it is not for the various standard profiles of the steel plant (no size data), it may be the standard data of the quenched and tempered or annealed state. If it is the material from the steel plant, it should be marked as cold-rolled or hot-rolled, most of which are hot-rolled, and usually precision-sized steels are cold-worked. If the manual does not indicate it, then the manual is not good enough and can only be judged by experience.
Wire: 5.5-40mm in diameter, coiled, all hot-rolled. After being cold drawn, it is a cold drawn material.
Round steel: In addition to the precise size of the bright material, it is generally hot-rolled, and there are also forged materials (with forging marks on the surface).
Strip steel: both hot-rolled and cold-rolled, cold-rolled products are generally thin.
Steel plates: Cold rolled plates are generally thinner, such as automotive plates; there are more hot rolled medium and thick plates, with similar thicknesses as cold rolled plates, and their appearance is obviously different.
Angle Steel: All are hot rolled.
Steel tube: Welded/hot rolled and cold drawn.
Channel steel and H-section steel: hot rolled.
Rebar: Hot rolled steel.
Cold rolled steel is generally divided into ordinary grade (C<0.12%), low carbon grade (C<0.10%) and ultra-low carbon grade (C<0.08%). The lower the carbon content, the better the cold plasticity. It is used in the electronics industry. It is more extensive, and the plate thickness is generally less than 3mm, and cold-rolled steel plates greater than 3mm are more difficult to cold work.
Due to different production and processing processes, hot-rolled steel sheets have better cold plasticity, good stamping formability, and small wear to the mold.Therefore, in industrial applications, hot-rolled steel sheets can generally be thicker than cold-rolled steel sheets.
SAPH in JIS is a kind of hot-rolled steel plate, which is mostly used in automobile door locks.
<?20 is generally cold-rolled (cold drawn, cold drawn), <?70 is generally rolled (hot rolled), >?100 is generally forged.
Generally cold-rolled steel such as galvanized steel and color steel plate must be annealed, so the plasticity and elongation are also better. It is widely used in automobiles, home appliances, hardware and other industries! Generally, the surface finish of hot-rolled plates cannot meet the requirements, so hot-rolled steel strips need to be cold-rolled, and the thinnest thickness of hot-rolled steel strips is generally 1.0mm, and cold-rolled can reach 0.1mm.
Professionally speaking, hot rolling is rolling above the crystallization temperature point, and cold rolling is rolling below the crystallization temperature point.
A general process of steel production is as follows:
Ironmaking→Steelmaking→Continuous casting (or die casting)→Hot rolling (out of hot-rolled products)→Cold rolling (out of cold-rolled products)
The general structural steel, angle, channel steel, H-beam steel is all hot-rolled steel, medium and heavy plates are also hot-rolled steel, that is, the finished product is produced after hot rolling. Some products need to be cold rolled after hot rolling, such as hot rolled coils to cold rolled coils.
In some applications, such as automotive panels and home appliance panels, cold-rolled sheets are required to ensure dimensional accuracy and surface quality, while hot-rolled materials are generally sufficient for building structures.
Hot-rolled and cold-rolled are optional, and more commonly seen in steel pipes. Seamless steel pipes of the same specification are either hot-rolled, cold-rolled or cold-drawn. Hot-rolled is basically continuous production on the production line, and cold-rolled Rolling and cold drawing are non-continuous production. The surface quality and dimensional accuracy of cold-rolled steel pipes are better than those of hot-rolled steel pipes.
In terms of composition, cold-rolled steels are low-carbon steels. Because of their low carbon content and good plasticity, they can be cold-rolled. In terms of surface quality, the surface quality of cold-rolled plates is better than that of hot-rolled plates, because when hot-rolled Oxide scale will be formed on the surface of steel.
Hot rolling is rolling above the recrystallization temperature of metal materials.Cold rolling refers to rolling below the recrystallization temperature of metal materials.Each metal material has its own recrystallization temperature.
Hot rolling refers to the need to heat the material during the steel rolling process or before the steel rolling. Generally, it must be heated to a temperature above the recrystallization temperature, such as 1000 degrees or more;
Cold rolling means that the steel rolling process does not require heating of the material, or heating to below the recrystallization temperature of the material.
Hot-rolled material products are basically rough, such as hot-rolled plates, whose thickness is generally above 3mm
Hot rolling and cold drawing are the difference between the production process. Hot rolling is processed at high temperatures and does not change the structural properties of the metal. Without tempering, such processing will affect the crystal structure of the metal
Hot rolling is hot processing, which allows steel to recrystallize internally and make it better in material properties. The blacksmith’s sword is the process of hot rolling (you always see it in the movie).
Cold rolling is cold processing, including cold drawing and cold drawing, which can remove rust and straighten. The most important thing is to change the properties of steel through cold drawing strengthening and steel aging! Hot-rolled steel bars are usually grade 1, 2, 3, and 4, except for grade 1 low carbon steel, the others are ordinary low alloy steel.
The advantage of hot rolling is that it can destroy the casting structure of the steel ingot, refine the grain of the steel, and eliminate the defects of the microstructure, so that the steel structure is dense and the mechanical properties are improved. This improvement is mainly reflected in the rolling direction, so that the steel is no longer isotropic to a certain extent; bubbles, cracks and looseness formed during casting can also be welded under high temperature and pressure.
- The cold-rolled formed steel allows local buckling of the section, so that the bearing capacity of the bar after buckling can be fully utilized; while the hot-rolled steel does not allow local buckling of the section.
In general, hot rolling has better mechanical properties than cold rolling. After heat treatment, the tensile strength, yield strength, plasticity, and toughness of steel will be improved. In addition, I feel that it is very important that heat treatment can eliminate residuals. However, cold rolling may produce residual stress due to the uneven deformation of the steel yield during the processing process. This residual stress has a great influence on the stability.
Simply put, it is continuous casting. Generally speaking, it is relative to die casting.
The efficiency of cold-rolled ribbed steel bars and the quality of cast slabs are greatly improved.
Both hot rolling and cold rolling are processes for forming section steel or steel plate, and they have a great influence on the structure and properties of steel. The rolling of steel is mainly hot rolling, and cold rolling is only used to produce small sections and thin plates.
Generally speaking, the billet will be cut or chopped after it exits the straightening machine, and then sent to the rolling mill after cooling. But there are also continuous casting and rolling (that is, the straightened billet directly enters the rolling mill and exits the profile without cooling).
The refined molten steel is poured into the tundish (can hold dozens of tons of molten steel), and the liquid molten steel (about 1500 degrees) flows vertically through the small holes under the tundish to the constantly vibrating mold (usually arc-shaped). , More than 1 meter long) in. The outside of the mold is continuously cooled with high-pressure water, and the molten steel in the mold forms a solid state on the outside and a liquid state on the inside. Outside the crystallizer is an arc-shaped cooling roller table. After cooling, the billet is completely solid (about 800 degrees). Then there is a billet straightening machine, which straightens the arc-shaped billet and provides traction to continuously pull the billet out of the mold.
Cold drawing and cold drawing are the treatment of hot-rolled steel bars. Cold drawing is drawing to exceed the yield point at room temperature, and cold drawing is passing through a wire drawing die at room temperature.
Heat treatment is made by quenching and tempering some specific varieties whose strength is roughly equivalent to level 4.
Continuous casting process of steel ingot:
The first disadvantage is that although there is no thermal plastic compression during the forming process, there are still residual stresses in the section, which will inevitably affect the overall and local buckling characteristics of the steel.
Continuous casting has very high technical requirements and also very high equipment requirements.
According to “Cold-Rolled Ribbed Steel Bars” (GBl3788-92), cold-rolled ribbed steel bars are divided into three levels according to their tensile strength. The codes are LI550, ll650 and LL800. Two Ls represent “cold” and “rib The Chinese Pinyin of the word “Yutou”, the number behind it indicates the value of the tensile strength of the steel bar.
The second is the 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.