The development of cooling specifications for
forgings, the key is to choose the appropriate cooling rate. Usually according to the chemical composition of the billet, organizational characteristics, the original state and section size and other factors, refer to the relevant information to determine the appropriate cooling rate. Usually forged with steel forging
forgings in the forging cooling rate than forging ingots forging cooling rate, section size of small forgings in the forging cooling rate than the section size of large forgings cooling rate.
After the
forging and forming of forgings must choose the most appropriate cooling rate, determine the cooling rate needs to take into account the size of the forgings and the chemical composition of the material. According to the cooling rate of the forging is different, the commonly used cooling force method of air-cooled, pile cold, pit (box) cold, gray sand cold and furnace cold.
Cooling in the air, faster. Forgings forging single or heap directly on the workshop floor cooling, but can not be placed on the wetlands or metal plate, and do not put on the place where there is a penetrating wind, so as to avoid uneven cooling of forgings or localized cold cracks caused by rapid cooling.
Forging pile in the box in the air cooling. Medium and small carbon steel and low alloy steel forgings are often used.
Forging after forging in the pit or steel fire layer containing insulation asbestos steel plate box closed cooling.
Forging buried in the pit fine sand, lime or asbestos material, slag cooling. General forging sand temperature should not be less than 500 ℃, around the thickness of sand storage can not be less than 80 mm. forging cooling speed in the pit, can be adjusted by different insulation materials and insulation medium. In order to effectively prevent the fine forging parts in the cooling process oxidation, can be cooled in the device with a protective atmosphere.
forging directly into the furnace after forging according to certain cooling specifications for slow cooling. As the furnace cooling can be accurately controlled by controlling the furnace temperature to control the cooling rate, so it is suitable for high alloy steel, special steel forgings and a variety of large forgings after forging cooling. Generally, the temperature of the forging is not less than 600℃~650℃, and the temperature of the furnace should be raised to the same temperature as that of the forging beforehand, so that the cooling rate can be controlled after all the forging parts are loaded into the furnace. Generally, the discharge temperature should not be higher than 100℃~150℃. Commonly used cooling specifications are isothermal cooling and undulating isothermal cooling.
For some forgings, the cooling must be controlled, for example, T12, GCrlS, 9CrSi and other steel forgings, after the final forging, spray cooling to 600℃~650℃, and then put into the pit to cool slowly, to avoid the production of coarse reticulation carbide, and to prevent cracks.
White point sensitive steel ingots after forging cooling is very important, stop forging directly after the expansion of hydrogen isothermal annealing to prevent white point.
Generally speaking, the simpler the chemical composition of the billet, the faster the cooling rate after forging: the opposite is slow. So for small and medium-sized carbon steel and low alloy steel forgings, forging are used after air cooling.
Alloy steel forgings with complex alloy composition should be pit-cooled or furnace-cooled after forging. Cooling specifications for tool steel and bearing steel: For steel containing higher carbon content (such as carbon steel, alloy tool steel and bearing steel, etc.), in order to prevent the precipitation of reticulated carbides at the grain boundary, the forging is first cooled by air-cooling, air-blasted or sprayed to 700°C, and then the forging is put into a pit or slowly cooled by a furnace.
For steel with phase change (such as austenitic steel, ferritic steel, etc.), due to the cooling process of the forging without phase change, fast cooling can be used. At the same time, in order to obtain a single-phase organization after forging, to prevent ferrite brittleness at 475 ℃ or so, also requires rapid cooling, so the forging is usually used after forging air cooling.
For such steels, furnace cooling should be carried out according to certain cooling specifications in order to prevent white spots from arising during the cooling process. Forging not only in the final forging should be cooled in accordance with the specifications, sometimes in the forging process should also be cooled, called intermediate cooling, intermediate cooling is used for forging after heating is not forged (for example, multi-fire forging large dump crankshaft), the need for local heating of the forging as well as in the process of forging to be carried out in blanks to detect or clean up the defects of the forging. Forging intermediate cooling specification determination and waste end cooling specification is the same.
The cooling process of forgings is a complex and delicate process that needs to be carefully designed according to the material properties, dimensions and expected mechanical properties of the forgings. By choosing the appropriate cooling rate and method, not only can the mechanical properties of the forging be optimized, but also improve the reliability of its processing and use. The correct implementation of cooling specifications is the key to ensuring the quality of forgings and is an important part of the success of the forging process.
