Cooling Specifications for Forgings of Various Materials

Forging in the forging process, the die groove surface and high temperature billet continuous contact, will lead to die heating, local temperature will exceed the temperature of the die tempering temperature, so that the die wear and tear accelerated or even failure, so it must be cooled to the die, cooling die commonly used methods of compressed air direct spray or spray cooling, cooling with salt water, cooling on the die using circulating water cooling and so on. With compressed air or spray cooling, spray plus into the lubricant effect is better, brine cooling is stronger, in a large number of children’s production can effectively cool the mould, the use of circulating water cooling effect is better, but the mould manufacturing complexity, generally used in static deformation mould.

Usually, the cooling specification after forging is based on the chemical composition of the bad material, organisational characteristics, raw material state and section size and other factors, with reference to the relevant information to determine.

Generally speaking, the simpler the chemical composition of the billet, the faster the cooling rate after forging, and vice versa. Carbon steel and low alloy steel forgings, forging can be taken after air cooling. Complex alloy composition of medium and high alloy steel forgings or high hardenability forgings, should be taken after forging pit cooling or furnace cooling.

Carbon tool steel, alloy tool steel and bearing steel and other high carbon steel, if forging after taking slow cooling, in the grain boundaries will precipitate reticulated carbide, will seriously affect the performance of forgings. Therefore, such forgings after forging first air-cooled, blast or spray rapid cooling to 700 ℃, and then put the forgings in the pit or furnace slow cooling.

Austenitic steel, ferritic steel and other steel grades without phase change, due to the cooling process after forging without phase change, can take rapid cooling. In addition, in order to obtain single-phase organisation, to prevent ferrite steel 475 ℃ occurs slow cooling embrittlement, also requires rapid cooling. Therefore, such forgings can be used after forging air cooling.

For air-cooled quenched steel, such as bainitic steel, martensitic stainless steel, high-speed steel, high-alloy tool steel, etc.. Because of the air cooling can occur bainite, martensite phase transition, will cause greater organisational stress, and easy to produce cooling cracks. Therefore, this kind of forging should be level after forging slow cooling.

For the white point sensitive steel, such as chromium-nickel steel, in order to prevent the cooling process to produce white point, should be in accordance with certain cooling specifications for furnace cooling.

The use of steel forging forgings, forging after the cooling rate can be faster, while the ingot forging forgings, forging after the cooling rate should be slow. In addition, for the section size of large forgings, due to cooling temperature stress, after forging should be slow cooling, while the section size of small forgings, after forging can be quickly cooled.