Low-carbon steels are the easiest of their class to forge. They also have better transverse properties than the harder alloys. Fine-grained ingots produce better transverse properties than coarse grained; thus, high-quality forgings are made generally from killed, ladle-deoxidized steel showing a minimum of segregation. Typical low-carbon steels for small forgings are C1020 and C1030. C1035 and C1040 are used for medium-sized forgings. Forging temperatures for these steels range from 1500 to 2500F. As carbon and alloy contents increase, the strength of the metal at any temperature increases, as do the forging load requirements and the wear on dies. Forging temperatures range from 1700 to 2200F for those medium carbon, high carbon and alloy grades. Typical forging compositions are 2315, 2330, 2345, 3130, 3250, E4130, E4340, 5140, 6150; for tool steels, C1080; high-speed steel (18W, 4C, 1Va), and alloy tool steel (0.5C, 0.1Si, 0.6Mo, 0.35Mn); for stainless alloys, types 410, 420, 430, 440, 302, and 316.
The selection of forging temperatures for carbon and alloy steels is based on
- the carbon content
- the alloy composition
- the temperature range for optimum plasticity
- the amount of reduction.
The maximum temperature allowable by these factors ensures the best forgability, lowest forging pressure and so the lowest die wear. However, if a steel that has been heated to its maximum safe temperature is forged rapidly and with large reduction, the energy transferred to the steel during forging can substantially increase its temperature, thus causing overheating. Based on those factors, the upper limiting forging temperatures for steels are approximately determined and indicated in Table 1. The table shows the upper limiting forging temperatures are influenced most noticeably by carbon content; for both carbon and alloy steels, forging temperature decreases as carbon content increases.
Table 1: Maximum safe forging temperatures for carbon steels of various carbon contents,
in comparisn with alloy steels