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What are the specifications when forging forgings?

Update:18-02-2021
Summary:

The key to formulating cooling specifications for hot f […]

The key to formulating cooling specifications for hot forging steel  is cooling rate. The appropriate cooling rate should be determined according to the chemical composition of the forging material, the characteristics of the structure, the cross-sectional size of the forging, and the forging deformation. Generally speaking, forgings with a low degree of alloying, a small cross-section and a simpler shape can allow a fast cooling rate and can be cooled in air after forging; otherwise, they must be cooled slowly (ash cooling or furnace cooling) or separated Stage cooling.

For steels with high carbon content, in order to avoid precipitation of network carbides in the rock grain boundaries at the initial cooling stage after forging, air cooling or blasting should be carried out first, and spray cooling should be carried out to 700℃, and then the forgings should be put into ash and sand. Cool down slowly in the furnace or in the furnace.

For steel without phase change, it should be cooled quickly in the temperature range of 800-550℃ to avoid the precipitation of network carbide. For steel that is prone to martensitic transformation during air cooling, in order to avoid cracks, it must be cooled slowly after forging. For steel that is sensitive to white spots, in order to prevent white spots during cooling, furnace cooling should be carried out in accordance with certain cooling specifications.

For high-temperature alloys, due to the slow recrystallization rate, recrystallization can be completed at the same time as the deformation only at a higher temperature and appropriate degree of deformation. Therefore, the residual heat after forging is often used to slowly cool it. For some small and medium-sized forgings, the stacking air cooling method is often used. Nickel-based superalloys have higher recrystallization temperature and slower recrystallization speed. In order to obtain forgings with a completely recrystallized structure, the forgings can be put into higher alloys in time. Keep it in the furnace at the recrystallization temperature for 5-7 minutes, and then take it out for air cooling. In the forging process, if intermediate cooling is required due to a breakdown, the final cooling specification shall also be handled according to the time.

The tools for measuring the geometric shape and size of forgings are mainly steel rulers, calipers, vernier calipers, depth gauges, squares, etc.; forgings with special or more complex shapes can be tested with templates or special instruments. The general forging inspection has the following contents.

Inspection of length, width, height and diameter of forgings. Calipers and calipers are mainly used. Inspection of the inner hole of the forging. Calipers and calipers without inclination, plug gauges with inclination. Inspection of special surface of forging. For example, the blade profile size can be checked with profile model, inductance meter, and optical projector.

 

Check the amount of misalignment of forgings. For forgings with complex shapes, the center lines of the upper and lower dies of the forging can be drawn separately by the scribing method. If the two center lines coincide, the forging has no misalignment; if not, the staggered distance between the two center lines is the amount of misalignment of the forging . For forgings with simple shapes, you can observe whether the misalignment amount is within the allowable range with your experience or with the help of simple tools, or you can use a template to check.

Inspection of forging curvature. Usually the forging is placed on the platform to roll or the forging is supported by two fulcrums to rotate the forging, and the value of the bending is measured with a dial indicator or a scoring disc. The inspection of forging warpage is to check whether the two planes of the forging are on the same plane or keep parallel. Usually the forging is placed on the platform, and a certain part of the forging is pressed by hand. When there is a gap between the other flat part of the forging and the platform plane, use a feeler gauge to measure the gap caused by warping, or use a dial indicator to place it Check the amount of warping swing on the forging.

 

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