Rolling: the metal blank through a pair of rotating roll gap (various shapes), due to the compression of the roll to reduce the material section, the length of the pressure processing method, which is the most commonly used production of steel production, mainly used to produce profiles, plates, pipes.

Rolling methods are divided into longitudinal rolling, transverse rolling and skew rolling according to the movement of rolled pieces.

The longitudinal rolling process is the process in which the metal passes between two rolls with opposite rotation directions and produces plastic deformation between them.

Cross rolling: The direction of movement of the rolled piece after deformation is consistent with the direction of the roll axis.

Slant rolling: the rolling piece is in spiral motion, and the rolling piece has a non-specific angle with the roll axis.

Advantages

It can destroy the cast structure of steel ingot, refine the grain of steel, and eliminate the defects of 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 pouring can also be welded under high temperature and pressure.

Disadvantages

1. After rolling, the non-metallic inclusions (mainly sulfides and oxides, as well as silicates) inside the steel are pressed into sheets, resulting in delamination (interlayer). Delamination greatly deteriorates the tensile properties of the steel along the thickness direction, and there is a possibility of interlayer tearing 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 load.

2. Residual stress caused by uneven cooling. Residual stress is the stress of internal self-equilibrium under the action of no external force. Hot-rolled steel of various cross-sections have such residual stress. The larger the cross-sectional size of steel, the greater the residual stress. Although the residual stress is self-balanced, it still has some influence on the performance of steel members under the action of external force. Such as deformation, stability, fatigue resistance and other aspects may have adverse effects.

3. Hot rolled steel products, for the thickness and side width of this aspect is not good control. We are familiar with thermal expansion and contraction, because at the beginning of hot rolling out even if the length and thickness are up to standard, there will still be a certain negative difference after final cooling, the wider the side width of this negative difference, the thicker the thickness, the more obvious the performance. Therefore, for large steel, the width, thickness, length, angle and edge of the steel cannot be too accurate.

Forging: It is a processing method that uses forging machinery to apply pressure to metal blanks to produce plastic deformation to obtain forgings with certain mechanical properties, certain shapes and sizes. Forging (forging and stamping) is one of the two major components. Forging can eliminate the defects such as loose casting in the smelting process and optimize the microstructure. At the same time, due to the preservation of the complete metal flow line, the mechanical properties of forgings are generally better than castings of the same material. For important parts with high load and severe working conditions in related machinery, forgings are mostly used except for rolled plates, profiles or weldments with simple shapes.

Forging can be divided into free forging, die forging, closed die forging

1, free forging. The use of impact or pressure to make the metal in the upper and lower two (anvil) between the deformation to obtain the required forgings, mainly manual forging and mechanical forging two.

2, die forging. Die forging is divided into open die forging and closed die forging. Metal blanks are deformed under pressure in a forging die bore with a certain shape to obtain forgings, which can be divided into cold heading, roll forging, radial forging and extrusion, etc.

3, closed die forging and closed upsetting because there is no flash, the material utilization rate is high. It is possible to complete the finishing of complex forgings with one process or several processes. Since there is no flash, the force area of the forging is reduced, and the required load is also reduced. However, it should be noted that the blank cannot be completely restricted. For this reason, the volume of the blank should be strictly controlled, the relative position of the forging die should be controlled and the forging should be measured, and efforts should be made to reduce the wear of the forging die.

Features:

Compared with castings, forging can improve the microstructure and mechanical properties of metal after forging. After hot working and deformation by forging method, the original coarse dendrites and columnar grains become equiaxed recrystallization structure with fine grains and uniform size due to the deformation and recrystallization of the metal, which makes the original segregation, looseness, porosity, slag inclusion and other compaction and welding in the ingot, and its organization becomes more compact, improving the plasticity and mechanical properties of the metal.

The mechanical properties of castings are lower than those of forgings of the same material. In addition, the forging process can ensure the continuity of the metal fiber structure, so that the fiber structure of the forging is consistent with the shape of the forging, and the metal flow line is complete, which can ensure that the parts have good mechanical properties and long service life. Forgings produced by precision die forging, cold extrusion, warm extrusion and other processes are incomparable to castings.

comparison of forging and rolling:

(1) The difference between the axial and radial mechanical properties of forgings is smaller than that of rolling pieces, that is to say, the isotropy of forgings is much higher than that of rolling pieces, so the life of forgings is much higher than that of rolling pieces. The following figure is a metallographic diagram Cr12MoV the morphology of eutectic carbides in different directions of the rolled plate.

(2) From the degree of change, the degree of deformation of forgings is much greater than the degree of deformation of rolling, that is to say, the effect of crushing eutectic carbide through forging is better than that of rolling.

(3) From the processing cost, the cost of forging is much higher than the cost of rolling. For some key parts, workpieces that bear large loads or impacts, and workpieces with complex shapes or very strict requirements, forging must be used. The process is processed.

(4) The forging has a complete metal flow line. After rolling, the mechanic destroys the integrity of the metal flow line, which greatly shortens the life of the workpiece. The following figure shows the metal flow line of casting, machining and forging workpieces.