Forging and Hot rolling

Forging and rolling are two different processes, which are widely used in daily life. Today we will briefly talk about the difference between the two.

Hot rolling: pass the blank metal through the gap of a pair of rotating rollers forged round bar (various shapes), due to the compression of the roller to reduce the section of the material, increase the length of the pressure processing method, this is the most common way to produce steel production, mainly used for the production of profile, plate, pipe.

The advantage is that it can destroy the cast structure of ingot, refine the grain of steel and eliminate the defect of microstructure, so that the microstructure of steel is compacting and the mechanical properties are improved.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) in the steel are pressed into thin sheets, resulting in lamination. 2. Residual stress caused by uneven cooling.Residual stress is the internal self-phase equilibrium stress without external force, hot rolled section steel of various sections have this kind of residual stress, the larger the section size of general section steel, the greater the residual stress. 3. It is difficult to control the thickness and edge width of hot rolled steel products.We are familiar with thermal expansion and cold contraction. At the beginning, even if the length and thickness reach the standard after hot rolling, there will still be a certain negative difference after cooling. The wider the edge width is, the thicker the thickness is, the more obvious the negative difference will be.

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

1. Free forging.Use impact force or pressure to make the metal in the upper and lower two impact iron (anvil block) deformation to obtain the required forgings, mainly manual forging and mechanical forging.

2. Die forging.Die forging can be divided into open die forging and closed die forging. The metal blank can be formed by compression deformation in the bore of a forging die with a certain shape, and can be divided into cold heading, roll forging, radial forging and extrusion, etc.

3. Closed die forging and closed upsetting have high utilization rates of materials due to the absence of flash.It is possible to finish a complex forging with one or more steps.With no flash, the forgings have less stressed area and less load.

Forgings usually have denser microstructure than rolled round steel, and through heat treatment, the fatigue strength is mainly higher.Therefore, the high requirements of shaft parts, should be repeatedly upset and pull long, in order to obtain better anti-fatigue performance.

In general, than in the same deformation under the condition of the forging method round steel quality is better than the method of rolling production, because the forging repeatedly required to achieve the same deformation of rolling forging to pull long, so the same billet production the same product round steel forging is equivalent to rolling deformation ratio increased by more than 50%, the other is in general forging steel from the surface to the internal overall deformation and rolling surface deformation, so the internal organization of both production of round steel, the degree of segregation, such as metal flow is completely different,The quality of forged round steel is generally superior to that of rolled round steel.So the key parts of crane hook must be forged.

Comparison between forgings and rolled pieces:

(1) the difference in axial and radial mechanical properties of forgings is smaller than that of rolled pieces, that is to say, the isotropy of forgings is much higher than that of rolled pieces, so the life of forgings is much higher than that of rolled pieces.(2) in terms of the degree of transformation, the deformation degree of the forging is much higher than that of the rolled piece, that is to say, the crushing effect of eutectic carbide through forging is better than that of rolling.

(3) in terms of processing cost, the cost of forging is much higher than that of rolling. For some critical parts, workpiece bearing large load or impact, workpiece with complex shape or very strict requirements, the forging process must be adopted for processing.

(4) forgings have complete metal streamline, which is destroyed by mechanical workers after rolling, greatly shortening the service life of the workpiece.