The main characteristics of forgings

1. Large weight range. Forgings can be as small as a few grams to as large as several hundred tons

2, higher than casting quality. The mechanical properties of forgings are better than castings, can withstand large impact force and other heavy loads, so, all of the important, stressed parts are used forgings.

Forgings are of better quality than rolls for high - carbide steels. For example, only after the high speed steel rolling can meet the requirements of use. In particular, high speed steel mills must be forged.

3, light weight. Under the premise of ensuring the design strength, the weight of the forgings is lighter than that of the castings, which reduces the weight of the machine itself, and is of great significance for vehicles, aircraft, vehicles and robots.

4. Save raw materials. For example, the static weight of the crankshaft used in the car is 17kg. When the rolling cutting and forging is used, the chip will account for 189% of the crankshaft weight, while when the die forging is used, the chip will only account for 30%, and the machining time will be shortened by 1/6.

Precision forging forgings can not only save more raw materials, but also save more machining hours.

5. High productivity. For example, using two hot die forging presses to forge radial thrust bearings can replace 30 automatic cutting machines. When the top forging automaton is used to produce M24 nuts, the productivity of the six-axis automatic lathe is 17.5 times.

6, free forging flexibility, therefore, some repair factories are widely used in the production of forging methods of various accessories.

Main features of large forgings:

1, the main and fundamental characteristics of large size and weight of large forgings are its large size and weight. For example, the size of 600MW turbogenerator rotor forgings made successfully in recent years is F1280mm x 16310mm, single weight 11.5 T21; The dimensions of 2200~2400MW turbogenerator rotor forgings produced abroad are $1808mm x 16880mm, single weight 247.

Due to their large size and weight, large forgings must be forged directly from large ingot. It is well known that segregation, loose, shrinkage, non-metallic sundries and various tissue inhomogeneity in large ingot are very serious, and the gas content is relatively high, and these defects are difficult to remove in the subsequent forging process. Therefore, in large forgings, there are often significant chemical composition inhomogeneity: a variety of tissue defects and excessive harmful gas. As a result, the heat treatment process of heavy forgings is often complicated, time-consuming and expensive. Therefore, it must be done with care.

Secondly, because of the large size and weight, the heat capacity of the workpiece is bound to be large, which makes it impossible to get a relatively large heating rate and cooling rate in the execution of the heat treatment process of large forgings. Therefore, for high performance, quality requirements, must be tempered or quenched to make the internal structure of the steel has a significant change of large forgings. Must use supercooled austenite very stable, high hardenability of steel, such as; Ni-cr-mo. Ni-mo-v, Ni-CR-MO-V steel, etc. However, the supercooled austenitic steels with high stability are prone to microstructure inheritance and lead to coarse grain size and uneven size in large alloy steel forgings.