Description
Different advantages and disadvantages
Advantages: fast forming speed, high output, no damage to the coating, and can be made into a variety of cross-section forms to meet the needs of service conditions; Cold rolling can produce great plastic deformation of steel, so as to improve the yield point of steel. Disadvantages: 1. Although there is no hot plastic compression in the forming process, there is still residual stress in the section, which will inevitably affect the overall and local buckling characteristics of steel; 2. The style of cold rolled section steel is generally open section, so that the free torsional stiffness of the section is low. Torsion is easy to occur in bending, bending and torsional buckling is easy to occur in compression, and the torsional performance is poor; 3. The wall thickness of cold-rolled formed steel is small, and there is no thickening at the corner of plate connection, so the ability to bear local concentrated load is weak. Compared with cold-rolled seamless pipe, hot-rolled seamless pipe is rolled below the recrystallization temperature, and hot-rolled seamless pipe is rolled above the recrystallization temperature. Advantages: it can destroy the casting structure of ingot, refine the grain of steel and eliminate the defects of microstructure, so as to make the steel compact and improve the mechanical properties. 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 pouring can also be welded under the action of high temperature and pressure. Disadvantages: 1. After hot rolling, the non-metallic inclusions (mainly sulfide, oxide and silicate) in the steel are pressed into thin sheets, resulting in delamination (interlayer) phenomenon. 2. Delamination greatly deteriorates the tensile properties of steel along the thickness direction, and interlayer tear may occur when the weld shrinks. The local strain induced by weld shrinkage often reaches several times of the yield point strain, which is much larger than that caused by load; 2. Residual stress caused by uneven cooling. Residual stress is the internal self-equilibrium stress without external force. Hot rolled sections of various sections have this kind of residual stress. Generally, the larger the section size of section steel, the greater the residual stress. Although the residual stress is self balanced, it still has a certain impact on the performance of steel members under external force. For example, it may have adverse effects on deformation, stability and fatigue resistance. 3. The thickness and side width of hot rolled steel products are not easy to control. We are familiar with thermal expansion and cold contraction. Even if the length and thickness meet the standard at the beginning of hot rolling, there will be a certain negative difference after cooling. The wider the edge width of this negative difference is, the thicker the thickness is, the more obvious it is. Therefore, for large steel, the side width, thickness, length, angle and edge line of steel can not be required to be too accurate. (1) General structure Seamless pipe for mechanical structure (GB / t8162-87) (2) seamless pipe for low and medium pressure boiler (GB / t3087-1999) (3) seamless pipe for high pressure boiler st45.8/111 (GB / t5310-85) (4) seamless pipe for fluid transmission (GB / t8163-1999) (5) cold drawn or cold rolled precision seamless pipe (GB / t3639-83) (6) steel pipe for geological drilling (yb235-70) (7) petroleum drilling steel pipe (yb528-65) (8) ）Seamless pipe for precision inner diameter of hydraulic cylinder barrel (GB8713-88) (9) seamless pipe for chemical fertilizer (gb6479-86) (10) marine pipe (gb5312-85) (11) petroleum cracking pipe (gb9948-88) (12) various alloy pipes 16Mn 27SiMn 15CrMo, 35CrMo 12CrMoV 20g 40Cr1. Cold rolled steel allows local buckling of the section, which can make full use of the bearing capacity of the member after buckling; The hot-rolled section steel does not allow local buckling.2. The causes of residual stress in hot rolled section steel and cold rolled section steel are different, so the distribution on the section is also very different. The residual stress distribution on the section of cold-formed thin-walled section steel is bending type, while the residual stress distribution on the section of hot-rolled section steel or welded section steel is thin-film type.
3. The free torsion stiffness of hot-rolled section steel is higher than that of cold-rolled section steel, so the torsion resistance of hot-rolled section steel is better than that of cold-rolled section steel. Cold rolling refers to the processing of steel plate or strip into various types of steel at room temperature through cold drawing, cold bending, cold drawing and other cold processing.